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Peeling, gluing and bonding characteristics of Nigerian plantation-grown Gmelina arborea (Roxb.) Badejo, Solomon Olufunmilayo Olubunmi 1977-02-16

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PEELING, GLUING AND BONDING CHARACTERISTICS OF NIGERIAN PLANTATION-GROWN GMELINA ARBOREA (ROXB.) by SOLOMON OLUFUNMILAYO OLUBUNMI BADEJO B.Sc. (Hons.) Forestry, University of Ibadan, 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY in the Department of Forestry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1977 Solomon Olufunmilayo Olubunmi Badejo, 1977 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 ABSTRACT The gluing properties of plantation-grown gmelina wood (Gmelina arborea Roxb.) from Nigeria were investigated. Three wood peeling temperatures - 20°C, 50°C and 85°C; two glue types -urea-formaldehyde (UF) and phenol-formaldehyde (PF); two glue spreads -25 kg/MDGL (55 lb) and 32 kg/MDGL (70 lb); and two closed assembly times - 10 minutes and 20 minutes were used. Veneers from the sample logs were peeled tight and were 1.27 mm (0.05 in) thick. The specific gravity for the logs was determined and its influence on the probable end uses of gmelina plywood discussed. Three 5-ply plywood panels were made, for each treatment combination for 72 in all. A total of 1438 shear test specimens were used. The UF specimens were tested dry and after vacuum-pressure treatment whereas the PF specimens received vacuum-pressure and boil-dry-boil tests. Bond quality was evaluated on the basis of wood shear strength and percentage wood failure. Results were compared to the U.S., British and German Plywood Standards. Wood peeling temperature was highly significant regardless of glue type and bond quality testing method. Heating of gmelina logs prior to peeling did not improve veneer peel-quality. Veneers were of the highest peel-quality (basis: Thickness variation and surface roughness) when logs were peeled at 20°C. The highest peeling temperature -ii--iii-yielded the lowest peel-quality. Bond quality, (percentage wood failure), was consistently reduced by increasing peeling temperature and was lowest at 85°C in all the UF and PF treatments, regardless of bond quality testing method. Ignoring glue spreads, panels made from veneers cut at temperatures of 50°C and 85°C gave the highest shear strength values among the UF treatments. On the other hand, panels from veneers cut at temperatures of 20°C and 85°C gave the highest shear strength values among the PF treatments. All factors considered, treatment combination of Spread 55 -Time 20, arising from veneers cut at the control temperature of 20°C, gave an impressive bond quality in all the UF and PF treatments used. Five of the 12 PF treatments used, regardless of type of bond quality testing method, pass the U.S. Plywood Standard; one passes the British Standard; while all pass the German Standard. On the other hand, five of the 12 UF treatments from vacuum-pressure test j pass the U.S. Standard; two pass the British Standard; while all pass the German Standard. Furthermore, all the 12 UF treatments from dry test pass the U.S. Standard; six pass the British Standard; while all pass the German Standard. -iv-From the results obtained, plantation-grown Gmelina arborea wood from Nigeria, with a specific gravity of 0.41 + 0.027 (as determined), was found suitable for use as construction plywood, core and crossband veneer for decorative panel as well as container veneer and plywood. The dominant factor accounting for the general trend of low percentage wood failure was attributed to veneer surface inactivation, resulting from surface aging of veneers. TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT ii TABLE OF CONTENTS \y LIST OF TABLES x LIST OF FIGURES \. xii ACKNOWLEDGEMENT . . xiv 1.0 INTRODUCTION 1 1.1 Objective and scope of study .... 1 1.2 Background information on the Nigerian wood-based panel industry ...... 3 1.2.1 Log supply situation ...... 3 1.2.2 Growth and yield of gmelina in Nigerian plantations ....... 4 1.2.3 An overview of the industry .... 6 1.2.3.1 Employment ....... 6 1.2.3122.3.2 Value-added 7 1.2.3.3 Development ....... 7 1.2.3.4 Export trade ....... 8 1.2.4 Prospects of development ..... 8 1.2.4.1 Domestic consumption of plywood ... 8 1.2.4.2 Utilization of wood-based panels ... 9 2.0 LITERATURE REVIEW 11 2.1 General wood properties of gmelina ... 11 2.2 Log heating ........ 12 2.3 Log peeling ........ 15 2.4 Veneer drying ....... 19 2.5 Adhesion and adhesives ...... 21 2.5.1 Adhesion: Wood bonding theories ... 21 2.5.1.1 Mechanical theory ...... 21 2.5.1.2 Adsorption theory ...... 22 -v--vi-Page 2.5.2 Adhesives: UF and PF resin adhesives 2.5.2.1 UF glue 2.5.2.2 PF glue 2.6 Factors affecting plywood bond quality 2.6.1 Glue spread .... 2.6.2 Assembly time .... 2.6.3 Glueline thickness 2.6.4 Pressing ..... 2.6.5 Degree of cure .... 2. 7 Wp:SbmeP.Nat±onalt;P/lywo6d :S.t_nrd;ards- andf Specif icat 2.7.1 British Standard . 2.7.2 Japanese Standard 2.7.3 German Standard 2.7.4 United States Standard 2.8 Gluability of Hardwoods 3.0 EXPERIMENTAL PROCEDURES 3.1 Experimental design . . , 3.2 Materials and preparation 3.2.1 Wood species characterization 3.2.1.1 Specific gravity determination 3.2.1.2 Moisture content determination 3.2.1.3 Determination of the optimum lathe settings for peeling 3.2.2 Logoheating 3.2.3 Log peeling 3.2.4 Peel-quality evaluation 3.2.4.1 Veneer roughness 3.2.4.2 Veneer thickness measurement 3.2.5 Veneer drying 3.2.6 Glues and glue mixing 3.2.6.1 IB-334 Plyophen 3.2.6.2 Monsanto UF 109 resin with EK Hardener 3.2.7 Glue spread ..... ions 24 25 26 27 27 28 29 30 30 31 32 32 33 33 34 40 40 41 41 42 42 42 43 45 45 46 46 46 47 47 48 49 -vii-Page 3.2.8 Plywood panel pressing . . . . . .50 3.2.8.1 Press Pressure ...... 50 3.2.8.2 Pressing Temperature and Time ... 50 3.2.9 Test specimen preparation .... 51 3.2.10 Bond quality testing procedures ... 51 3.2.10.1 Dry test 53.2.10.2 Vacuum-pressure test ..... 52 3.2.10.3 Boil-dry-boil-cool test .... 53 3.2.11 Statistical analysis ..... 53 4.0 RESULTS 54 4.1 Moisture content and specific gravity of gmelina v logs used ........ 54 4.2. Log heating and peeling ..... 54 4.3 Veneer peel-quality ...... 55 4.4 Veneer moisture content prior to gluing . . 55 4.5 UF resin adhesive ....... 56 4.5.1 Dry test: Shear strength and wood failure percent ....... , 56 4.5.2 Vacuum-pressure test: Shear strength and wood failure percent ....... 56 4.6 PF resin adhesives' ...... 57 4.6.1 Vacuum-pressure test: Shear strength and wood failure percent ....... 57 4.6.2 Boil-dry-boil test: Shear strength and wood failure percent ....... 57 4.7 Analysis of variance ....... 58 4.7.1 Factorial analysis ...... 58 4.7.2 Duncan's multiple range test .... 59 5.0 DISCUSSION 60 5.1 Sample, specific gravity ..... 60 5.2 Log heating ........ 60 5.3 Veneer peel-quality ...... 61 5.3.1 Thickness . 6-viii-6.0 5. 3.2 Roughness ; . 5.4 Plywood bond quality ..... 5.4.1 Treatment panels bonded with UF glue 5.4.1.1 Dry test: Shear strength and wood failure percent ....... 5.4.1.2 Vacuum-pressure test: Shear strength and woo< failure percent ..... 5.4.2 Treatment panels bonded with PF glue 5.4.2.1 Vacuum-pressure test: Shear strength and woo failure percent ..... 5.4.2.2 Boil-dry-boil test: Shear strength and wood failure percent ..... 5.4.3 Probable factors accounting for low percentage wood percentage wood failures in the treatment 5.4.4 Comparison of study results with some National Plywood Standards .... 5.4.4.1 U.S. Hardwood Plywood Standard 5.4.4.2 British Hard Plywood Standards 5.4.4.3 German Hardwood Plywood Standard 5.5 Probable end uses of Gmelina arborea Veneer and Plywood ...... 5.5.1 Construction plywood .... 5.5.2 Core and Crossband veneer for decorative plywood . . . . . 5.5.3 Container veneer and plywood SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION 6.1 Summary ......... 6.2 Suggestions for further studies .... 7 ft 7.4T-8.0 9/0 10..0 6;. 3T TConclusion BIBLIOGRAPHY TABLES FIGURES APPENDICES Page 61 62 62 62 64 65 65 67 69 73 73 77 78 78 78 79 80 82 82 85 85 86 100 123' 13 9 LIST OF TABLES Table Page 1 De'scrriptive 'features of Gmelina arborea logs used for study ......... 100 2 Initial and peeling moisture content (%) of the Gmelina arborea logs used for study . . . . 101 3 Specific gravity of the Gmelina arborea logs used for study .......... 102 4 Water bath and log temperature changes against time of peeling - 50°C ........ 103 5 Water bath and log temperature changes against time of peeling - 85°C 104 6 Lathe specifications for peeling ..... 105 7 Peel-quality attributes: Veneer roughness measurement. 106 8 Veneer peel-quality statistics - 1.27mm (0.05 in) Gmelina arborea green veneer ..... 107 9 Veneer moisture content prior to gluing . . . 108 10 Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Urea - For maldehyde (UF) glue 109 11 Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Phenol-Formaldehyde (PF) glue ....... 110 -ix--x-Table Page 12 Within- and between-panel variation in bond quality of 5-ply:Gmelina arborea Plywood bonded with UF glue: Dry test, wood failure ....... Ill 13 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with UF glue: Vacuum pressure test, wood failure . . . . 112 14 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: Vacuum pressure test, wood failure . . . . 113 15 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: Boil-dry-boil test, wood failure . . . . . 114 16 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality in 5-ply Gmelina arborea Plywood: Dry test ......... 115 17 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality in 5-ply Gmelina arborea Plywood: Vacuum pressure test . . . . . . . 116 18 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on PF glue bond quality in 5-ply Gmelina arborea Plywood: Vacuum pressure test . . . . . . . 117 19 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and. Closed Assembly Time on PF glue bond quality in 5-ply Gmelina arborea Plywood: Boil-dry-boil test ........ 118 -xi-Table Page 20 Duncan's multiple range test for shear strength of Gmelina arborea Plywood bonded with UF glue . . 119 21 Duncan's multiple range test for wood failure of Gmelina arborea Plywood bonded with UF glue . . 120 22 Duncan's multiple range test for shear strength of Gmelina arborea Plywood bonded with PF glue. . . 121 23 Duncan's multiple.range test for wood failure of Gmelina arborea. Plywood bonded with PF glue. 122 LIST OF FIGURES Figure Page 1 Pattern of cut of test samples from logs for specific gravity and moisture content determination tests .......... 123 2 Temperature changes within a log, 8 ft long and 7.7 in diameter: 50°C heating ....... 124 3 Temperature changes within a log, 8 ft long and 8.0 in diameter: 85°C heating ...... 125 4 Frequency distribution of visual veneer roughness . 126 5 Dependence of bond quality on peeling temperature and assembly time interaction: UF Dry test (shear strength) ......... 127 -6 Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Dry test (wood failure) ...... 128 7 Dependence of bond quality on peeling temperature and glue spread interaction: UF Vacuum pressure test (shear strength) ........ 129 8 Dependence of bond quality on peeling temperature and glue spread interaction: UF Vacuum pressure test (wood failure) ........ 130 9 Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Vacuum pressure test (wood failure) . . . . 131 -xii--xiii-Figure Page 10 Dependence of bond quality on peeling temperature and glue spread interaction: PF Vacuum pressure test (shear strength) . . . . . . . . .. 132 11 Dependence of bond quality on peeling temperature and closed assembly time interaction: PF Vacuum pressure test (shear strength). 233 12 Dependence of bond quality on peeling temperature and"" assembly time interaction: PF Vacuum pressure test (wood failure) . . . ... . .- . 134 13 Dependence of bond quality on peeling temperature, glue spread and closed assembly time interaction: PF Vacuum pressure test (wood failure). 135 14 Dependence of bond quality on peeling temperature and closed assembly time interaction: PF Boil-dry-boil test (shear strength) . . . . . . . 136 15 Dependence of bond quality on peeling temperature and glue spread interaction: PF Boil-dry-boil test (wood failure) . . . . . . . . . 137 16 Dependence of bond quality on peeling temperature and closed assembly time interaction: PF Boil-dry-boil test (wood failure) ....... 138 ACKNOWLEDGEMENT The author wishes to express his gratitude to Dr. R. W. Wellwood of the Faculty of Forestry, who kindly arranged for the supply of the gmelina logs used. His understanding, constant advice and critical review of the draft made the study possible. Thanks are also due to SNC-Rust Company Limited, Montreal, Canada for its cooperation in providing the logs. I am greatly indebted to the Western Forest Products Laboratory, Vancouver, Canada, for being allowed to use the Laboratory's facilities. Special thanks are due to Dr. W. V. Hancock, Dr. S. Z. Chow and Mr. J. R. T. Hailey (WFPL) for their constant assistance, constructive criticism, and numerous helpful suggestions throughout the experimental work. Dr. Hancock and Mr. Hailey read the thesis draft and made many valuable comments. Jack Williams and Les Rozon (Plywood Section, WFPL) deserve my appreciation for their help during veneer cutting and gluing. Appreciations are also due to Mr. L. Valg, Dr. L. Paszner, and Dr. D. Haley, of the Faculty of Forestry for their help and assistance. Mr. Valg and Dr. Paszner read the thesis and offered valuable advice. I thank Dr. A. Kozak for his advice during the analysis of results; and Mr. Richard Yang (graduate student) who wrote the programme used. The financial backing of my employer, the Federal Department of Forestry, Ibadan, Nigeria, has also made the study possible. Finally, special thanks are due to my wife, Remi, who has patiently endured my absence from Nigeria for two years. -xiv-- 1 -INTRODUCTION 1.1 Objective and Scope of Study This study proposes an hypothesis that the wood of the Nigerian plantation-grown Gmelina arborea Roxb. (referred to hereafter by its trade name, gmelina) can be peeled into high quality veneer and glued into commercially acceptable plywood. This investigation has been prompted by the publication of the International Union of Forestry Research Organizations (IUERO 1973) in which the Forest Products Research Laboratory (FPRL), Princes Risborough, England indicated that gmelina wood was an unsuitable plywood species. The research centre obtained its sample logs from Thailand, Sarawak and an unspecified African country. In the same publication, the Centre Technique du Bois, Paris, France reported that gmelina wood is moderately suited for construction plywood, container veneer and plywood, and inner plies for decorative panels. The sample logs used by the French research centre were obtained from the Ivory Coast, in West Africa. No published reports have been found on the gluability of this wood in Nigeria. The findings of the FPRL, Princes Risborough, England, are considered of significant importance to the wood-based panels industry in Nigeria for two reasons: 1. The United Kingdom is the most important single market for all wood products export from Nigeria, accounting for about 90% of the veneer and plywood export in 1972. 2. The current objective of management of gmelina plantations, in - 2 -at least two of the States in Nigeria, has incorporated future supply of sawlogs and veneer logs (Alade 1970, Enemuoh 1970). In the Western State\ for example, it is intended that about 30 trees per acre from the existing and future plantations will be allowed to grow into sawlog and veneerlog sizes concurrent with pulpwood harvesting. To test the proposed-hypothesis, therefore, plywood panels 2 from plantation-grown 'gmelina wood from Nigeria, will be prepared, and standard glueline tests will be conducted. The following plywood production variables will be used: 1. Three levels of wood peeling temperature 2. Two adhesive types 3. Two levels of glue spread 4. Two closed assembly times Results from this study could serve to indicate whether to accept or reject the suitability of gmelina wood for use as plywood. If results are encouraging, the study could, -have*. arapLmpact?'on . p._§Lntat -onpmanage—entinand gen-the awdo de.ba sedwpariel aindus t ry.linn <•; • •• Nigeria^ -• t Now comprising three New States - Oyo, Ogun and Ondo after February 1976. The logs used for study were part of consignment of logs shipped to SNC-Rus'^ Lilted of Montreal, Canada, from Nigeria, for pulping studies. - 3 -1.2 Background Information on the Nigerian Wood-based Panel Industry 1.2.1 Log supply situation Log supply is one of the major current problems confronting the Nigerian wood industries. Various studies (Okigbo 1964, Eklund et. al. 1966, Wellwood 1966, Huuhtanen 1975) have indicated the serious ness of this situation in the forseeable future. The problem of log supply is not peculiar to Nigeria. Grudzinski (1975) has indicated that this factor has posed a problem.in all areas of the world where the plywood mills are fairly concentrated. Nevertheless, the Nigerian case has not resulted from industrial concentration as such but from a limited wood-resource base. The total land area in Nigeria is about 93 million ha of which the productive high forest reserves (the only source of industrial wood supply) accounts for only 1.9 million ha or about 2%. The growth rate and rate of forest regeneration after logging is quite low. Natural regeneration.has been inadequate, even where attempts were made to induce it (Lowe 1966). Bamgbala and.Oguntala (1970) put the timber 3 3 yield from the natural moist forest in Nigeria at about 35jmp_per ha. With a rotation of about 50.years in.the high forests, this seemed a low \ figure. Increasing efforts have been made to improve and restock the forests. The two methods used to encourage the regeneration and growth of the economically desirable tree species, are the Tropical Shelterwood System (T.S.S.) and the Enrichment. Planting. Anakwenze (1966) and Oseni and Abayomi (1970) have pointed.out that T.S.S. has proved a failure in. Nigeria while Igugu and Bamgbala (1970) indicated that - 4 -Enrichment Planting has had little success. In view of the foregoing, the long term prospect of wood supply situation in Nigeria seems to depend on.the development of planta tions of fast-growing species for sawlogs, veneerlogs and pulpwoods. As indicated by Fox (1972), the fast growth of planted trees is perhaps the most important advantage of the developing countries. The Federal and States governments in Nigeria seem committed to this concept as evidenced by their forest policy statements. Nigeria.has.a vast forest land, as distinct from productive high.forests, that accounts for about 35% of the total land area. With better land use planning, enough land could still easily be allocated to Forestry for afforestation purposes. Afforestation schemes were started in Nigeria before 1950. By 1950 and 1969, the country had a total of 7,468 ha and 51,560 ha of planted areas respectively (Oseni and Abayomi 1970). The planted area was estimated to increase, to a total of 61,548 ha by 1970 (Enabor 1973). Plantings are being stepped up in the poorly stocked, highly degraded and the savannah areas of the country with fast growing exotic and indigenouss. species. Gmelina. arborea is one of the major exotic species established in the plantations. In order to.safeguard the future supply of timber, Nigeria proposes to establish a minimum of 12,140 ha of plantation, annually. 1.2.2 Growth and yield of gmelina in Nigeria. LT Gmelina has.become a popular plantation species in Nigeria for six major reasons: 1. The seeds are readily available. - 5 -2. . It is easy to propagate from seeds and cuttings_. 3. It coppices well. 4. It shows adaptability to a wide range of soil and climatic conditions. 5. It is fast growing and has ability to coppice for about 50 years (Scherpe 1968). 6. It suppresses the growth of weeds at an early age, thus reducing cleaning and weeding costs. Gmelina grows very well in Nigeria. In a 2-year old plantation, the average g.b.h. (girth at breast height) recorded is 38.1 cm with a height of 12.2 m(Alade 1970). In another 7-year old plantation, the mean g.b.h. of 298 trees thinned per acre is 35.5 cm with a mean height of 8.5 m (Enemuoh 1970). Aladejana (1971) also reported a mean g.b.h. of 88.g cm with a corresponding height of 19p2cm>for 30 randomly selected trees in another 7-year old plantation. 3 Chittenden et_r-.>al. (1964) quoted a yield of about 84 m per ha in a 12-year old plantation on poor sandy soils.of the Derived 3 Savannah Zone of Nigeria. They also reported a yield of about 252 m per ha on the most favourable Savanna sites and in the Rain Forest Zone, 10 and 8 years respectively, after planting. From studies conducted by 3 the Federal Department of Forestry, Ibadan, a yield of about 184 m per 3 ha, with a Mean Annual Increment of about 23-27 m was reported for an 8-year old gmelina plantation at Omo Forest Reserve (Modugu 1977). - 6 -1.2.3 An overview of the industry. Nigeria is a major African producer of wood-based panels. The 3 actual wood-based panels production for 1973 was 55,000 m (FAO 1975a) in the following product categories: 3 i) Hardwood Plywood ...... 45 ,100' m 3 ii) Veneer Sheets ...... 1,200 m 3 iii) Blockboard, Laminboard, Battenboard . . 8,700 m Total 55,000-m3. Wood-based industries have played a major role in the economy of Nigeria, contributing substantially to employment and value - added in manufacturing. Since the industrial survey publications in Nigeria have always treated all the wood-based industries as a single sector, it is difficult to appraise the percentage contribution being made by the wood-based panel industry. Nevertheless, within the many wood-based industries of the country, the sawmilling, wood-based panel and the furniture are the most important. I. 2.3.1 Employment The wood-based industries have been the largest employment sector for labor in Nigeria, apart from agriculture and fisheries (Adeyoju 1968). With a total employment of 11,910 workers in 1963, the wood-based industries accounted for 17.5% of the total employment in manufacturing. The total number of workers employed decreased to 11,240 and 11,540 in 1967 and 1969 resulting in a decreased share of 14.6% and II. 3% respectively, of the total manufacturing employment. In "spite of these decreases, Enabor (1976), however, indicated that the wood-based industries still ranked second to the textile industries in the country's - 7 -manufacturing employment. 1.2.3.2 Value-added The value-added in the wood-based industries in 1963 was $13.1 million, representing 8.5% of the national total. Although by 1967, the value-added.in these industries had increased to $14.5 million, it represented id a,reduced share of 5.9% of the value-added in all the manufacturing industries.-. Again an increase to.^$23.4 million by 1970 , accounted for only 4.2% of the national, total (Enabor 1976). Rate of expansion and.level of efficiency have been indicated as some of the factors controlling ',,to value-added . in manufacturing within the wood-based industries. Thus, the. small*»scale of operations and inefficiency within the sawmilling .industry could.have significantly accounted for the decreased share of value-added in manufacturing from the wood-based industries. 1.2.3.3. Development Nigeria's production of wood-based panels began in 1946 when the first veneer mill was established as part of African Timber and 3 Plywood (A.T.& P) Company in Sapele. For-almost two decades, this was the only operating mill in the country, producing veneer and plywood for export and domestic consumption. Now, there are four operating wood-based panel mills in the country located at Sapele, Calabar, Ologbo and Epe. Another wood processing complex, having facilities for veneer and plywood production is planned for Ondo at an investment of about 3 A.T.& P. accounts for about.40% of Nigeria's production of plywood and as indicated by Wellwood (1966), it was the largest of its kind in the World, though no longer the most modern. $20 million. This proposed mill is expected to start production under the 1976-1980 Development Plan. 1.2.3.4 Export trade There is no co-operative selling and shipping of the wood-based panels among the four operating mills in the country. Each mill undertakes the shipment of its products. Export trade has accounted for an increasing share of the total wood-based panels production over the years. This averaged 69% (FAO 1975b) during the fe.y^en year period of 1962 to 1968. Export trade was highest in 1970 when it accounted for about 91% of the total production. Due to increased domestic consumption, the share exported has decreased dramatically since then. It was about 45% in 1971 and from FAO estimates for 1972 and 1973 (FAO 1975b), export trade was expected to account for only about 42% and 38% respectively. The main markets for veneer and plywood are the United Kingdom, Germany, Holland, Denmark, Italy and the United States of America. However, the bulk of the plywood exported goes to the United Kingdom. Veneer and plywood have contributed an average of $2.7 million, annually, to the Nigerian foreign exchange earnings since 1964. Export earnings from these commodities account for about 27%, 24% and 14% of the total export earnings of about $10.1 million (1971), $10.6 million (1972), and $19.4 million (1973) respectively from all wood products (Nigeria 1972, FAO 1974). 1.2.4 Prospects of development 1.2.4.1 Domestic consumption of plywood A major prospect for development of the wood-based panel - 9 -industry in Nigeria lies internally. There is currently a booming trade for plywood. Apparent plywood consumption increased substantially from 3 3 9,000 m in 1962 to 26,000 m in 1971, giving an increase of about 289% or an annual growth rate of 12.5% (FAO 1975b). Consumption was 3 3 estimated to increase to 30,000 m and 34,000 m in 1972 and 1973 respectively. Of the total wood-based panel consumption in 1967 and 1971, plywood accounted for a share of about 64.3% and 66.7% respectively. This was expected to increase, to 71.4% and 72.3% by 1972 and 1973 respectively. 1.2.4.2 Utilization of wood-based panels The major use of wood-based panels in Nigeria is in manufactur ing, accounting for about 50% of the total annual domestic consumption of veneer and plywood. Paneling, boat building and wood-based components jointly account for about 40%; while the remaining 10% goes into packag ing and other forms of uses (Enabor 1972). The furniture industry has contributed a great deal to increased use of wood-based panels in Nigeria and more furniture mills are proposed for the country. For the 1970-74 Development Plan Period, the Federal and States governments in Nigeria proposed anrinViestmentmof.Labdutu — $2 million.on two wooden furniture factories. This is considered an incentive for further development within the wood-based panel industry. Development may not .necessa-r-i_yatake" .a form of increased number of operating mills, but rather that of increased production capacity of the existing ones via higher output. - 10 -Enabor (1976) projected a consumption of 102,000 to 132,000 3 m (r) of wood-based panels in Nigeria by 1985. Similarly, he forecasted 3 a consumption of 231,000 to 363,000 m (r) by 2000 A.D. Even though forecasts are sometimes erroneous, future consumption of wood-based panels, in Nigeria, is indeed anticipated to increase with growth in 4 population and higher per capita income. The country's population increased from 56 million in 1963, to an estimated 80 million in 1973. - 11 -2.0 LITERATURE REVIEW This literature review initially covers some of the most important process steps in plywood production including: 1. Log heating 2. Log peeling 3. Veneer drying A further section of the review focuses on adhesion of wood and factors affecting plywood bond quality as well as some characteristics of the two adhesives - phenol—formaldehyde (PF) and urea—formaldehyde (UF) used to make experimental plywood. Some of the different national plywood standards and specifications used to evaluate study results, are surveyed. As only limited information is available on the gluability of gmelina wood, the chapter concludes by giving a general review of the gluability of hardwoods. 2.1 General Wood Properties of Gmelina Gmelina wood is diffuse porous and, as indicated by Esan (1966), fast growth does not change the density of the wood. Growth rings are visible and from studies done on the wood grown in Thailand (Lamb 1968) and Nigeria (Esan 1966), they appeared to be annual. The wood in appearance is straw yellow to creamy white (Lamb 1968). He (Lamb) further reported that selected samples of the wood show fiddle back mottling and a fine sheen on quarter sawn boards. Gmelina wood is indicated to contain a high resin content. Sample logs from Nigerian plantations were peeled, in the country, into 2.25 mm thick veneers for match splints. Veneers were found to be smooth, straight grained and of medium texture. 'J. 2.2 Log Heating Heating of logs before veneering is a conditioning process (TRADA 1967) commonly practised in the hardwood plywood industry. It decreases the ratio of compressive to tensile strength of wood thereby giving a more uniform material (Hancock 1977a). Several heating systems have so far been developed. These include circulating hot water, steam heating, electrical heating, water/ air heating and high pressure heating (Seidel 1952; Fleischer and Downs 19535, Lickess 1957; Kubinsky and Sochor 1968). Of/these, hot water systems of heating are the most commonly practiced in the plywood industry (Feihl 1972). Hot water systems give better uniformity compared to steam ing, and also ensure freedom from block end splits (Fleischer 1959; Anon 1968). Heating of logs helps to plasticize the wood for best veneer cutting. With most woods, the fibers and hard knots present in the wood are softened and cutting becomes easier. Fleischer (1948), Lutz (1960), Anon (1968) and Palka (1974) reported that log peeling as a result of prior heating becomes easier and smoother veneers are produced without excessive lathe checks. Lathe checks, as ascertained by Chow (1974), contribute in large measure to reduced shear strength of plywood. Considerable reduction in damage to lathe knives has been reported, when Original not seen. Cited from reference of 0. Feihl 1972. - 13 -peeling heated logs (Lickess 1957; Feihl and Godin 1975). Ellwood and Erickson (1962) reported that there is loss of moisture by vaporization when logs are steamed prior to peeling. There is, generally, loss of moisture through evaporation, as the heated logs begin to cool after removal from the heating mediums. These must have facilitated the shorter veneer drying time resulting from heated logs indicated by Anon (1968) and Kollman et. al. (1975). Batey (1955) showed that tight veneers produced from heated bolts reduce plywood face checking. Generally, Nakamichii.:and Konno (1965) pointed out that heating is essential for hardwoods from which lumber cores are to be cut. The optimum cutting temperature for any wood is a function of its specific gravity, presence of hard knots, tendencies for end splitting and color changes (Fleischer 1959). The heating period required to obtain such optimum temperature, as well as the rate of temperature changes within the wood to give it, are functions of the green specific gravity of the wood, the type of vat used for heating and its temperature and warm-up period, the initial log temperature and diameter, the temperature required within the log as well as the outside air temperature (MacLean 1946, Fleischer 1959, Seidel 1952, Nakamichi• and Konno 1965, Altukhov 1965, Garrison 1967, Anon 1968, Feihl 1972, Feihl and Godin 1975). As cutting from too cold or too hot logs results in lower veneer peel-quality, (Feihl and Godin 1975),each wood species therefore cuts best within a certain temperature range. With too low a peeling temperature, loose or rough veneers are produced (Fleischer 1959; Feihl and Godin 1970) while too high temperature tends to soften the - 14 -wood excessively thereby resulting In woolly-surfaced veneers. Palka (1974) reported that for most species, with the exception of low density ones (e.g. poplar and western red cedar), peel-quality improves when veneers are cut from logs heated, usually to a temperature range of 49-71°C. Optimum cutting temperatures vary between hardwoods and soft woods . Fleischer (1959) stated that best cutting temperatures in hard wood species are roughly related to the wood density. Hardwoods of low specific gravity (^=0.40) are reported to cut well at room temperature (the specific gravity of Gmelina. arborea used for this study falls within this group of hardwoods). Medium density hardwoods are reported to cut well at a temperature of 60°C; while yellow birch is indicated to cut best at aet!emperaturefof.babouE171^C.Furthermore, Feihl and Godin (1975) pointed out that soft species such as poplar and basswood cut best at a temperature of about 32°F (0°C). Cutting temperatures have also been correlated to the veneer nominal thickness intended to be peeled irrespective of wood-type. Fleischer (1959) indicated that thin veneers of 0.16 cm (1/16 inch) or thinner cut at lower temperatures without serious degrade (the veneer nominal thickness peeled for this study also falls within this group -0.127 cm [1/20 inch]). Many investigators (Fleischer 1948, Grantham and Atherton 1959, Corder and Atherton 1963, Hailey et al. 1968) have reported on the various effects of heating on veneer cutting. These studies were, however, conducted on softwood species. In their study on hardwood species, Wangaard and Saraos (1959) showed that there was an impressive degree of - 15 -improvement in the tightness of veneers obtained from white and red lauan bolts heated in water at about 71°C compared to unheated bolts. All the foregoing emphasizes the existence of an optimum cutting temperature for each wood. 2.3. Log Peeling One of the aims of rotary cutting of logs is the production of veneers in uniform thickness, reasonable tightness and smoothness for gluing into plywood. These properties serve to achieve good bonding during gluing. As indicated by Bryant et. al. (1965), poor glue bonds in core veneers, as well as excessive panel-thickness variation, are largely accounted for by the extent of veneer-thickness variation. They also pointed out that gluing of such veneers requires greater pressures in panel pressing so as to promote intimate contact between all the glued laminates. Lutz et. al. (1969) also reported that variation in veneer thickness can cause problems of show-through of the core veneer in decorative panels. Various studies have revealed that efficient rotary-cutting of logs hinges on many variables. These include the log diameter, the moisture content of the wood, the knife pitch angle, the nose-bar openings of the lathe, the lathe conditions and to a certain extent the lathe cutting speed. Log diameter has been found to influence, significantly, the peel-quality obtained during rotary-cutting of logs (Fleischer 1949). For example, Kovanen (1963) demonstrated that tensile strength of Finnish birch veneers decreases with decreasing initial log diameter. A similar - 16 -trend was reported by Cade and Choong (1969) in their study with Southern pine. From their study, veneer tensile strength perpendicular to the grain improves with increasing;log diameters. Sivananda et, al. (1973) also ascertained that thickness variation of Vellapine (Vateria, indica) veneers increased at reduced diameters of the logs. For production of veneer of high peel-quality, the lathe has to be accurately adjusted for proper knife angle and adequate nose-bar openings. Panshin e_t. al. (1962) and Feihl and Godin (1963) identified lathe adjustment as a key to proper cutting of thin veneers of uniform thickness. This adjustment has also been recognised essential (Fleischer 1956, Hancock and Hailey 1975) for cutting smooth veneers of uniform thickness. rToo. large a knife angle and insufficient nose-bar pressure were reported to influence veneer thickness variation (Barefoot and Salehuddin 1962) as well as resulting in loose and rough veneer (Feihl and Godin 1970). The pitch angle (the knife cutting angle) is the angle the plane of the knife tip and centre of rotation of /the.'rlathe spindles makes with the knife face (Hancock and Hailey 1975). Fleischer (1949), Wangaard and Saraos (1959), Kovanen (1963), Knospe (1964), Barefoot and Salehuddin (1962) and Feihl and Godin (1967) all refered to the pitch angle as a major factor responsible for veneer thickness uniformity. The knife angle used at any particular cutting period has been related to the veneer nominal thickness peeled. Available studies indicated that the angle should decrease as the veneer thickness decreases. Hancock and Feihl (1976) for example, recommended jaUpixtcfojangle of. 90 30' when peeling veneers thinner than 0.84 mm (1/30 in.) for all diameters. To - 17 -maintain a constant bearing on the knife, it has also been pointed out that the knife angle should decrease as the diameter of the log being v peeled decreases (Fleischer 1949 and 1956, Kovanen 1963, Palka and Holmes 1973). This has been reinforced by Hancock and Hailey (1977). Their research study indicates that a modified pitch rail with a gradual increase in rub length gives superior results at small log diameters. For any particular wood, there is an optimum range of pitch angle in cutting within which veneer peel-quality can be maximised. -Madison (1951) and (1957) found an optimum pitch angle of 89°50' and 90°-93° adequate for peeling 0.32 cm (1/8 inch) thick Western larch veneer and 0.13 cm (1/20 inch) thick/aspen veneer respectively. A knife angle of 90° was indicated adequate (Wangaard and Saraos 1959) for cutting veneers of uniform thickness from Philippiah'- white and red lauan. For most species, they, and Feihl and Godin (1970) reported an optimum level of knife angle varying between 89°31' and 90°30' when peeling 0.32 cm (1/8 inch) thick veneers. Another lathe variable considered to play a dominant role in determining veneer peel-quality is the pressure bar compression / (Fleischer 1949, Leney 1960, Koch 1964, Palka. 1970, Cumming and Collett 1970, Lutz 1974). Fleischer (1949) pointed out that within the range of nose-bar settings, up to the point where over-compression of veneer occurs, increased pressure seemed to result in greater veneer tightness and smoothness. Barefoot and Salehuddin (1962) demonstrated that insufficient nose-bar pressure could influence variation in veneer thick ness when peeling small diameter bolts from woods of Albizzia procera. The horizontal opening (gap) is the horizontal distance between - 18 -knife tip and bar tip and it is the main control on veneer roughness while the vertical opening (lead), which controls the veneer thickness variability, is the vertical distance between knife tip and bar tip (Hancock and Feihl 1976). Fleisher (1949), Collins (1960), Feihl et. al. (1963), Feihl (1964), Lutz and Patzer (1966) all recognised the size of the horizontal roller-bar openings as an important variable influencing veneer thickness, roughness and lathe check formation. Lutz and Patzer (1966) reported that the veneer nominal thickness decreased with a decreased roller-bar gap when cutting Southern pine and yellow-poplar veneers. Also from their study, use of smaller gap improved the smoothness of veneers cut from yellow-poplar. Feihl (1964) reported that the use of smaller gaps result in smoother but too thin veneers when peeling curly birch logs. The nose-bar lead is not as important as the gap in determining veneer peel-quality. Fleischer (1949),however pointed out that suitable veneer cutting is obtained when the lead is varied approximately according to the nominal thickness of the veneer. Various studies (Madison 1951 and 1957, Feihl et- al. 1963, Cumming and Collett 1970) have shown, however, that there is an optimum range of gap and lead within which satisfactory veneer can be obtained. This optimum varies with species as well as veneer nominal thickness. Hancock and Feihl (1976) indicated that,generally, the gap is 5 to 15% narrower than the thickness of the veneer being peeled. They further indicated that,irrespective of type of bar used during peeling, the gap for a given species and given thickness is the same as long as the lathe is in good working condition. From the literature reviewed above, it is quite obvious that a - 19 -judicious selection of knife angle, horizontal and vertical pressure bar openings will serve to optimize veneer peel-quality during cutting with respect to species, veneer nominal thickness and log size. "4j Veneer Drying Drying^of freshly cut veneers, when properly controlled, reduces their moisture content to a level suitable for gluing into plywood. The rate of veneer drying is a function of the veneer initial moisture content, its thickness, species, dryer temperature, its air velocity and relative humidity (Bethel and Carter 1950, Bethel and Hader 1952, Fleischer 1953, Holden Jr. 1956, Milligan and.Davies 1963, Lutz 1974). The condition of peel-quality, especially the tightness of the veneer, was indicated by Bethel and Hader (1952) to affect veneer drying. Loose peeled veneers, as they pointed out, dry at a faster rate than tight peeled veneers. The moisture present in veneer prior to drying affects the total drying time. As sapwood and heartwood veneer pieces differ in moisture content, effective veneer segregation prior to drying helps to improve the drying control (Carroll and.Dokken 1970). In hardwoods where distinction between sapwood and heartwood may be difficult, Carroll and Dokken (1970) suggested the use of moisture meters to effectively achieve green sorting. Variability in moisture content of the dried veneer sheets has been reported as one of the causes of under-cured and washed out glue-lines and panel blow-ups during pressing (Fleischer 1958, Carroll'and~Dokken 1970). Comstock (1971) and Walters (1971) pointed out that the - 20 -density of the veneer may be a factor in the total drying time because : denser woods have slower drying time. ~ Bethel and Hader (1952) reported differences in the drying time of different species. Fleischer (1953) also reported that redwood and sweetgum heartwood veneers dried at a s%ower^rateiithaney.el'lw^popl"arerie"artwood. The rate of heat transfer to veneer surfaces during drying was identified as an important factor (Comstock 1971, Lutz 1974) in controlling rate of veneer drying. This rate is a function of the veneer thickness (Bethel and Hader 1952, Fleisher 1953). They also reported that veneer drying time is a function of the dryer temperature. The higher the temperature, the more accelerated the drying becomes and the shorter the total drying time. Drying should, however, be cautiously carried out as excessive drying with too high temperature results in veneer surface inactivation. As defined by Chow (1969a), "surface inactivation is due to the properties of veneer surfaces after thermal treatment whereby their reception of glue is made difficult". Northcott (1957) and Northcott et, al. (1959) pointed out that too high veneer drying temperatures and too long drying time are some of the factors inducing low wood failures in plywood. The inferior joints caused by increased drying temperature and time are pointed out by Currier (1958) to be results of reduced wettability of the veneers by the adhesives. Sisterhenm (1961) also showed that plywood made from Douglas-fir veneers dried to 232°C (450°F) developed a significantly lower bond quality compared to those made from veneers dried to a temperature of 191°C (375°F). Chow et. al. (1973) further indicated that overdrying or underdrying of veneers seriously affect the - 21 -bond quality obtained. 'I Carroll and Dokken (1970) nevertheless reported that surface inactivation occurs not as a result of the use of too high veneer drying temperature but that of overdrying at too high temperature. According to them, the.weaker bond quality obtained from such veneers is due to loss in strength of wood and not necessarily that of an adhesion. They further indicated that veneer surface inactivation can be avoided by the use of lower temperature at the dry end of the dryer. 2._5 Adhesion and Adhesives 2.5.1 Adhesion: Wood bonding theories Adhesion in wood is a complicated phenomenon. There are many factors that influence bonding in wood,and as stated by Allen (1967), it is often difficult to distinguish which factor is dominant. Apart from the type of adhesive used, joint quality in an adhesive bond depends on the nature of the substrate and the conditions existing during the bonding process (Collett 1972). The forces.that cause an adhesive to wet, spread and attach to the surface of a solid have been ascribed (DeLollis 1968) to chemical bonds, mechanical entanglement, physical and chemical adsorption due to polar groups, electrostatic forces of attraction inherent in all matter and to combinations thereof. From DeLollis viewpoint,therefore, it is quite obvious that mechanical and specific adhesion are essential to bonding in wood. 2.5.1.1 . Mechanical theory Mechanical adhesion in wood is effected by anchorage due to penetration into and hardening within capillaries in adherend surfaces - 22 -(Bikerman 1961, Heitler. 1966) . Marian and Stumbo (1962a) have indicated that mechanical adhesion certainly exerts an influence in wood, depending on joint type and condition of surfaces of the adherend members. They stated further that rough or damaged surfaces will influence mechanical adhesion but for smooth and undamaged surfaces, the influence is minimized. According to Parker and-Taylor (1966), highly polished surfaces contain small peaks and. troughs.and.so will give little adhesion. Patton''. (1970) further stated that surface roughness is essential for good bonding. Experimenting with planed, sanded, sawn and combed maple wood.samples, Maxwell (1945), however, reported that the planed samples yielded stronger bonds and highest shear strength. This tends to disprove the mechanical adhesion theory, advanced by Bikerman (1947), which was based.on the inherent roughness of surfaces. In view of these findings, it is evident that mechanical i adhesion alone is insufficient.for bonding strength in wood. Total adhesion inwood is dependent upon mechanical and.specific adhesions (Kollman et- al. 1975). Marian.and Stumbo (1962a), in a particularly elegant experiment,, indicated.that the physico-chemical forces are mainly responsible for adhesion in wood. According to them, mechanical adhesion.only contributes about 10-20% of the total, adhesion strength. 2-.<5_. 1 ..'2 Adsorption theory The basis of this theory is specific adhesion which results from forces of adhesion-acting-between the molecules of the wood and the adhesive. As indicated by Marian and Stumbo (1962a), specific adhesion .is caused by primary valence forces or secondary valence (Van der Waals) forces. Baier et. al. (1968) and Zisman (1963) - 23 -reported that the three requirements necessary for developing a strong adhesive joint are: 1. Good wetting by the adhesive liquid. 2. Solidification. 3. Sufficient deformability necessary to reduce the effect of elastic stresses in the formation of the joint. According to Marian and Stumbo (1962b), the wetting helps to assist spreading and penetration.of.the adhesive into the wood. DeBruyne and Houwink (1951) remarked in their discussion of adhesion theory that wetting of the surface by the adhesive is a necessary pre requisite for good gluing. The mutual attraction between the wood surface and the adhesive (resulting from the adhesive wetting power) has been attributed to different physical and chemical phenomena (DeBruyne 1947). Collett (1972) ascertained.that the covalent bond plays a very important role in specific adhesion, while the ionic bond was identified as of lesser importance. In this connection,therefore, the forces of molecular attraction were stated by Kollman etfj al_. (1975) to play an important role in the adhesion between wood and glue. Zisman (1965) also remarked that adhesion is caused-by forces between molecules in or near the surface of the two contacting materials and that these are primarily of van der Waals and hydrogen bonding type. All the foregoing emphasizes, the fact that an adhesive must spread and wet well the wood substrate to ensure good bonding since the forces that are causing the attraction between the wood and the glue act only over short distances (Zisman 1965). As it is, not all liquids that wet wood well can form strong joints with it. In this regard, the - 24 -internal cohesive strength of the adhesive itself on solidification must be high in order to obtain strong joints. _ . 2,. 5.2>. Adhesives: UF and PF resin adhesives Choice and performance of any resin adhesive for satisfactory bonds in wood varies with species. As indicated by Northcott and Hancock (1966), the service life of any bond is dependent on such factors as: 1. Conditions of service 2. Type of glue 3. Type of glue joint 4. Properties of the substrate Investigating the gluing characteristics of Determa (Ocotea  rubra Mez) Thomas (1959) reported that satisfactory bonds of maximum wood strength were easily obtained with the use of UF, RF and MF glues as well as casein glue. On the other hand, gluing was difficult with ,-" PF glue. This, as he explained,was due to the wax-like substances present in the wood. Thus, the incompatibility of the PF glue with Determa could be due to difference in polarity, which, as Thomas indicated, could result in the failure of the glue to wet the wood or penetrate adequately. However, the concept of adhesive and adherent having similar polarity which was postulated by DeBruyne, was no longer considered a precondition for the formation of adhesive bond (DeBruyne 1962) . ThusiS; the difficulty encountered when gluing Determa wood with PF glue could have been duesmes0m&e&t$e£tfJS@t6r§^Gerieially, PF resin adhesives require a certain amount of water to react or polymerize - 25 -(Hancock 1977b). Furthermore, Laidlaw (1976) remarked that apart from choice of timber species in plywood, manufacture, proper choice of adhesives serve to determine plywood strength as well as its ability to withstand environmental degrading effects. UF and PF glues came into commercial use in the plywood industries at about 1930 (Parker and Taylor 1966, Kollman et. al. 1975). These two synthetic glues have been widely used since then. A lot of modifications have also been done, especially with the UF glue to improve upon durability and ability to withstand exposures to adverse weather conditions. 2.5.2.1 UF glue UF glue produces a nearly colorless gluelirieo. The glue also has the ability.to cure at ambient temperatures. It is, however, unsuitable for service conditions of high humidity and temperatures above 60°C (SIRA 1970). Blomquist and Olson (1957) indicated that plywood made with this glue suffers an appreciable losses in joint strength when exposed to temperatures from about 27°C (80°F) to 70°C (158°F). Bergin - (1958) also stated that at a temperature of about 70°C and higher, deterioration of the glue becomes more rapid. For these reasons,therefore, UF glue is restricted to interior uses. Compared to PF glue, UF is deficient in long-term durability. The viscosity of the glue, its degree of cure and its adhesive formulation have been reported to influence the wood bond durability obtained with the use.of the UF glue. Rice (1965) investigated the effect of resin viscosity on plywood bond durability. He reported that resin viscosity (a measure of molecular weights and dispersion) results in a more durable glue-wood bond. Steiner (1973) further showed that molar ratio ranges of Formaldehyde/Urea (F/U) = 2.0 to 1.8 yielded slower bond deterioration under accelerated aging conditions than resins with F/U ratio in the range of 1.6 to 1.4. 2.5.2.2 - PF glue PF glue is more durable.than UF glue. It is quite suitable for service conditions of extreme temperature and humidity. Laidlaw (1976) experimented on the bond durability of plywood bonded with PF and UF glues, following a period of over 18 years of exposure. He found that the PF glues used without fillers or extenders or with only small addition of fillers maintained an efficient bond.over the prolonged test periods while the UF glues gave satisfactory service for shorter periods. Muller (1953)^ reported that the durability of phenolic wood glue joints is correlated with the wood species used as well as the glue-line thickness. In the plywood industries, fillers, extenders and hardeners are often used with the UF and PF glues. A filler is used to control the flow of the resin while the sole function of the extenders is to reduce the amount of adhesives to be used to maintain.an effective glueline. Hardeners are a blend of materials designed to give optimum working properties and bond quality (Hill 1952) and are essential in most cases in glue mixes. All the foregoing emphasizes the fact that proper selection of glue and its formulation are important factors in gluing (Bryant and ^ Original not seen. Cited from reference of Kollman et , al. 1975. - 27 -iStensrud •! 1954) in order to achieve the desired glue joint quality and durability (Blomquist 1954). 2.6 Factors Affecting Plywood Bond Quality 2.6.1 Glue spreading Proper glue spreading is essential as it ensures uniform distribution of the liquid glue. In order to obtain good wood-glue bond, Brown et. al. (1952) have emphasized that the glue must flow, transfer from spread to unspread surfaces, wet all surfaces, penetrate into the wood capillaries, and solidify into a strong substance. The flow of the glue is retarded if the glue rapidly hardens before pressure is applied. Thus, the rapidity with which the glue begins to set is of primary importance. Penetration is necessary to produce a strong mechanical bond but it should not be excessive, to avoid a starved glueline. Depending on the adhesive, solidification is achieved by curing or chemical polymerization, hardening by physical cooling, loss of solvent by evaporation, and gelling of a dispersed polymeric solid (Collett 1972). Furthermore, the amount of glue spread and the nature of resin formulation varies with respect to the type of glue and wood species. Jarvi (1967) indicated that heavier glue spreads usually require more press time. He also pointed out that the glue mixes for Southern pine require more phenolic resin content than normally used for Douglas-fir. This is probably due to differences in the degree of absorptivity of the two species. - 28 -2.6.2 Assembly time In plywood manufacturing, assembly time is the time elapsing between glue spreading and press closing. As indicated by Chow et al. —c<,.—- -(1973) the assembly time allows for some moisture absorption by the veneer and some reduction in viscosity of glue due to moisture loss. This serves to ensure that there is just the right amount of water in the panel glueline during bond curing. There seems to be a correlation between the maximum assembly time allowed during gluing and the moisture content of the veneer. At low veneer moisture content, prolonged assembly time results in (a starved, glueline condition. This leads to a situation whereby it becomes impossible for the glue to cure as most of the water in the glue is being readily absorbed into the wood while some is lost through evapora tion. There is thus a lack of cohesive strength in the glueline and this results in low wood failure. On the other hand, at higher veneer moisture content, prolonged assembly time is essential to facilitate high wood failure results. More so, as it provides enough time for the excess water in the glueline to be evaporated. For example, Northcott et"•aX. (1959) reported that short assembly time can induce undercure of phenolic resins thereby producing low wood failure. With long open assembly time, the PF resin has been noted to lose much of its moisture and shows a darkening in color as a result (Troughton and Chow 1972). Martin (1956) attributed this discoloration to quinone methide formation caused by oxidation. As indicated by Chow (1969b), this quinone methide.formation reduces, the number of - 29 -methylol groups present in the PF resin. This makes covalent bonding with wood ineffective and therefore fails to produce durable glue-wood bonds. However, with the addition of" polyethylene glycol 200 to the PF resin, Troughton and Chow (1972) were able to induce an increased wetting capacity of the glue on the treated wood thereby improving the bond quality obtained under prolonged open assembly time. It has to be indicated that PF glues, generally, require a certain amount of water to ensure favourable curing or polymerization. 2.6.3 Glueline thickness Specific adhesion in wood requires a strong continuous glueline in order to form a strong joint. Using 36 phenolic resins, Hse (1971) correlated the glueline thickness to the bond quality produced in Southern pine plywood. He reported that surface tension, contact angle and curing time were related to the glueline thickness within the panels. According to him, wet shear strength and percentage wood failure increased with increased glueline'thickness. Rice (1965) indicated that too thin glue-lines may bring about locational starved spots all over the glueline. These spots may act as weak points as. well as stress concentration areas, thereby causing bond deterioration. Contrary to these findings, however, Brown et^ al. (1952) stated that moderate over penetration.of glue, while maintaining a thin, uninter rupted and uniform glueline is a requirement for mechanical and specific adhesion. Thin glueline was also reported best for bond quality in wood (Poletika 1943)7. Bergin (1969) showed that adhesive strength generally decreases with an increase glueline thickness. 7 Original not seen. Cited from reference of J.T. Rice 1965. - 30 -The theory of cracks /seems to come into play with regards to these conflicting findings. Thick gluelines are viewed to have a greater potential for crack development. than do thin gluelines". this tends to account for the decreased strength associated with thick gluelines. 2.6.4 Pressing Application of pressure to the panel assembly after gluing promotes good contact between the glued veneer surfaces. It also aids penetration as well as ensuring good glue transfer to the unspread veneer surfaces (Chow et. al. 1973). Depending on the compressive strength of the wood, Kennedy (1965) reported a pressing pressure in the range of 2 2 10.5 kg/cm to 14.1 kg/cm (150-200 p.s.i.) for Canadian grown woods. 2 Freeman (1970) also reported a pressure in the range of 13.0 kg/cm to 2 14.1 gk/cm 185-200 p.s.i.) for most plywood mills. Thus the amount of pressure used at any time, seems to be a function of the wood strength as well as the physical condition of the wood surface. Freeman (1970) investigated the influence of production variables on bond quality of Southern pine plywood. He reported that coarse grain effect and surface roughness induced by it might require higher pressures during the pressing time. Bond quality (in terms of percentage wood failure), as he indicated, increased with increased press pressure. 2.6.5 Degree of cure The curing temperature of a glueline depends on type of resin adhesive used. Chow et.: al. (1973) pointed out that inadequate curing temperature results in undercured bonds. As they indicated, this defect - 31 -can be accentuated by insufficient pressing time. They further reported that a minimum glueline temperature of about 139°C (250°F) is necessary to pass the CSA 80% wood failure standard with the use of the vacuum-pressure-soak test. In his investigation of under-cure of phenolic glue bonds, Northcott (1955) showed that percent wood failure was proportional to the degree of cure of the glue used. Chow and Hancock (1969) revealed from their simple?sject-rophotometriq method that the degree of cure of phenolic resins is related to the wood failure and shear strength of the tested plywood panels. Bergin (1965) reported that the rate of cure of casein glues varies with the curing temperature in the range of about -7°C to 21°C (20°F to 70°F). Rate of cure decreased as the temperature, decreased. Rudriicki"' (1976) found that the strength and durability of PF glue bonds are determined by the curing temperature, the curing time and the amount of hardener used. Generally, the curing process of the plywood panel glueline is a complex one. As stated by Koch (1972), it involves properties of the resin and the wood, assembly times, prepressing procedures and hot pressing techniques. 2.7> Some National Plywood.Standards and Specifications. Plywood bond quality evaluation and. specification standards • vary from one country to another. While some countries assess plywood bond by percentage wood failure, some.favour shear strength as the major criterion of assessment. A combination of these two criteria is being used by the United States Department of Commerce for ^hardwood - 32 -and decorative plywood. Wood failure has for long been indicated as an impracticable means of judging joint strengths in plywood. Truax (1929) stated that under good gluing conditions, joint strengths are not seriously affected by the percentage wood failure developed. Northcott (1955) remarked that;, in order to use percentage wood failure to estimate bond strength, there must be a correlation between it and the shear strength. However, from his cleavage test (Northcott 1952) this correlation seemed not to exist. He therefore concluded at that time that the wood failure is of no value in judging plywood bond quality. The following analysis covers some of the world plywood standards and specifications related to bond quality. Details are included in Appendices 1-4. 2.7.1 British Standard The British Standard for hardwood plywood does not take into consideration plywood shear strength. Wood failure is the sole criterion of assessment. The BS 1455-1963 specifically applies to plywood manufactured from Tropical hardwoods (Appendix 1). Delamination test is required for the glue bond between individual panels. On the other hand, the adhesion test for the four kinds of bonding - WPB, BR, MR and INT (See Appendix 1) in volves wood failure reading. Wood failure is read off on a Master Scale of 0 to-10 corresponding to 0 to. 100% wood failure. The British Standard considers an average wood failure reading of 5 (50%) as adequate. 2.7.2 Japanese Standard The Japanese use the Export Standard specification for Japanese plywood. Shear strength is the sole criterion used to assess the - 33 -plywood bond quality... Depending on the type of species used to make the plywood, minimum shear strength required for Japanese woods ranges between 2 2 7 kg per cm (100 psi) to about 10 kg per cm (142 psi). For tropical 2 woods, the Japanese require only about 8 kg per cm (110 > psi) minimum shear strength (Appendix 2). 2.7.3 German Standard Just as with the Japanese standard, the German standard uses the shear strength as the sole criterion of assessment of plywood bond quality. The standard consists of. a lot of requirements. Some of these are related to cold-soaking and boiling cycles... The exterior, grade plywood is 2 designated AW100. A minimum shear strength of 10 kg/cm (142 „ psi) is required for non-coniferous woods (Appendix 3). 2.7.4 United States Standard The U.S. Department of Commerce voluntary product standard PS51-71 for hardwood and decorative plywood makes use of both the percentage wood failure.and shear strength to assess bond quality of plywood. The average wood failure for a particular panel under, test is qualified by the average shear strength for such a panel. Specimens are subjected to dry, cyclic-soak and .cyclic-boil tests. There is also a specified minimum per centage wood failure, for individual specimen tested. For example, for an 2 average failing load of between 18 to 25 kg per cm (250 to 350 psi) the minimum wood failure of test piece required is an.average of 30% with each individual specimen not having less than 10%.wood failure (Appendix 4). Of the four plywood standards reviewed above, it is the U.S., - 34 -British and German standards that will be used to evaluate results from this study. The U.S. standard is favored because it qualifies the percentage wood failure developed at testing with the shear strength obtained. Furthermore, U.S.A. has been an important importer of veneer from Nigeria since 1970. The British standards will be used because Britain is the largest market for Nigerian hardwood plywood. The Federal Republic of Germany is another major European, market for Nigerian wood products exports. 2.8]. Gluability of Hardwoods Various studies have been undertaken on the gluability of Tropical and secondary hardwoods in Europe, North America and Japan. Some of these studies, as shown below, are related to the effects of wetting phenomenon on wood gluability. Troop and Wangaard (1950) investigated the gluing characteris tics of 29 tropical American woods using RF and PRF glues. Assessing bond quality in terms of joint shear strength and percentage wood failure developed in the standard block shear test, they reported that many of the woods are suitable for structural uses. Results of their study also showed.that shear strengths, and wood failure values were, in general, strongly correlated with specific gravity. Defective surfacing of the glued materials and nature of their chemical constituents are some of the reasons they suggested for some.abnormal results obtained with some of the species. Freeman (1959) conducted an experiment relating the wettability of wood to its.glue bond quality. Using 22 hardwoods, he found that wettability, pH and specific gravity are closely related to glue bond quality. Glue bond quality improved with increasing wettability in the high density wood ( 0.80) glued with UF resin adhesive. With specific gravity below 0.80, Freeman discovered that wood specific gravity has more influence on bond quality than wettability. He further indicated that wood specific gravity, acidity and wettability seem to have potential significance in wood adhesion. Experimenting with 6 tropical hardwoods, Freeman and Wangaard (1960) investigated the effect of wettability of wood on glue-line behavior of two cold-setting urea resins. They reported that during the closed assembly period, glue-line solids content and viscosity increase more rapidly in woods of ..high wettability than in those of low wettability. These factors are essential in achieving optimum conditions for specific gluing operations. Carstensen '(1961) studied the gluing characteristics of secondary hardwoods, including red alder (Alnus rubra Bong.), cottonwood (Populus trichocarpa Torr. and Gray) and aspen (Populus tremuloides Michx.) as well as some softwood veneers. He reported that within any one species, gluability will vary accordingly because of the wide variations that exist in density, grain configuration, moisture content and veneer surface conditions. He attributed the gluing problems encountered to accumulation of resinous materials.on the veneer surfaces. Bodig (1962) studies wettability of 5 Philippine mahoganies as related to.their gluability. He reported that there is a high degree of correlation between the indices of gluability and wettability. This, according to him, reinforces the validity of the specific adhesion thesis. - 36 -As he stated further, surface condition of wood has an important effect on its wettability. He also indicated that it is possible to predict relative gluability values of an unknown species by simply measuring its wettability. Reporting on the gluability of Tectona grandis L. (Teak) and Acacia catechu Willd. , Narayamurti et,. al. (1962) showed that extractives present in these species affected the gelation time of the animal glue and UF glue used to glue the woods. The gluability of some California hardwoods including black oak (Quercus kelloggii Newb.), chinkapin (Quercus muehlenbergii Englem.), madrone (Arbutus menziesii Pursh) and tanoak (Lithocarpus densiflora Rehd.) was investigated by Dost and Maxey (1964). They reported that all four woods glue well with PF resin adhesive and with exterior PVA resin emulsion. Lee (1964) studied the gluability of Gmelina arborea Roxb. from Malaya. Even though he worked with a limited number of test samples, he reported that the wood showed good gluing properties. The FPRL, Princes Risborough, England (1966) indicated from a con-signmentaof logs from Gambia" that good corestock veneers-suitable for gluing int6i.p,lywood~can -be produced - from-gmelina^woodiwithoutwany prior heating. " ~J~SGoto et al. (1967) investigated the effects of specific gravity, wettability, pH and percentage of extractives on the gluing properties of 18 tropical woods. UF glue, PF glue and PVA emulsion adhesives were used to glue the woods. The following findings were reported: i) Glue-joint strength increased with increase of specific gravity, ii) There is a high degree of correlation between wettability and - 37 -specific gravity, iii) There was no significant relationship between glue-joint strength and pH. iv) The relationship between glue-joint strength and the percentage of extract either by cold or hot water is not significant. Chen. (1970) studied the effect of extractive removal on adhesion and wettability of 8 tropical woods. Ten percent solutions of sodium hydroxide, acetone and alcohol benzene solvents were used. Gluing was achieved with UF and RF resin adhesives. He reported that extractive removal improved.wettability.and increased the.pH of the wood surface thereby giving a more favorable bond quality. Using Philippines .red lauan (Shorea. negrosensis Foxworthy ), Moriya et;. al. (1971) investigated the gluing characteristics of laminated wood from this species. RF, PF, UF, PVA emulsion and casein adhesives were used to.glue the wood. From the block shear and delamination tests performed, glue joint strength was reported to increase with increase in wood specific gravity. Yamagishi and Honma.(1972) reported on mixed use of two different species in bonding?/ some tropical woods using UF and RF resin adhesives. Bond quality was evaluated dry and after cyclic treatments as well as by delamination tests. They indicated that difference of specific gravity between two species considerably influence.the glue bond durability. The higher the difference, the greater the bond quality degradation. They concluded that difference in specific gravity in the mix use should be maintained within +0.12. ..The ,gluing' ;prope_rties of 6 hardwoods from Burma were investi-" Crjoai (17 ' - 38 -gated by Chunsi (1973) using PRF, UF and Casein glues..Among the many conclusions reached, he reported that influence of specific gravity on the gluability of the woods varied with type of glue. While the lighter woods glued easily with the three glues, the medium density woods glued well with the UF and PRF glues but poorly with casein glue. With all three glues, the high density woods glued poorly. He concluded further that glue joint strength increased with increase in the pH of the wood, if the influence of specific gravity was excluded. Three of the six woods he used met the requirements for exterior structural lamination with PRF glue. The FPRL,- Princes Risborough, England, and Centre Technique du Bois, Paris, France (IUFRO 1973) investigated some aspects of peeling, drying and gluing of Gmelina arborea Roxb. The former concluded that the wood is not suitable for use as plywood because of wild grain and poor gluability. The sample logs used were heated to 85°C prior to peeling. On the other hand, the Research Centre at Paris concluded from its study that gmelina wood glues moderately .well.- There was no. indication as to whether the sample logs were heated prior to peeling or not. Tan (1974), studied the suitability of 9 Malayan hardwoods for plywood manufacture. Gluing was achieved with PF resin adhesives. He arrived at the following conclusions: i) That wood bulk density is a dominant factor influencing the bonding ability of the woods. Higher density woods (densities 3 3 3 3 of 0.64 g/cm , 0.66 g/cm , 0.80 g/cm and 0.88 g/cm respectively)' were found unsuitable for plywood manufacture because of low percentage wood failures developed. - 39 -ii) That thermal-degradation, due.to increasing veneer drying duration, was significant in reducing bonding ability of the woods. iii) That an adhesive formulation of higher viscosity than those used for softwoods was found necessary to prevent over-penetration of glue. All the foregoing emphasizes the fact that bond quality and durability of plywood bonded with different glues are strongly influenced by the wood species involved. - 40 -3.0 EXPERIMENTAL PROCEDURES 3.1 Experimental Design The design of the experiment included four variables. These were two glue types, three peeling temperatures, two glue spreads and two closed assembly times. The experimental steps were as indicated below: Two glue types - phenol—formaldehyde (PF) and urea-formaldehyde (UF) resin adhesives. Three veneer peeling temperatures - 20°C (control), 50°C and 85°C. Two levels of glue spread -approximately 25 kg/MDGL (55 lb// MDGL) and 32 kg/MDGL (70 lb.^/ MDGL). Two closed assembly times- 10 and 20 minutes. All combinations of the above variables gave 24 treatments. Three panels were made under each treatment, thus giving a total of 72 panels for the study. The veneer nominal thickness peeled was 1.27 mm (0.050 in) while the plywood assembly construction was 5-ply. Furthermore, two types of bond quality tests were used to evaluate bond performance for each type of glue. The Dry and Vacuum-Pressure-Soak tests were used for all the treatments bonded with UF resin adhesive while the Boil-Dry-Boil-Cool and Vacuum-Pressure-Soak tests were used for all the treatments bonded with PF resin adhesive. J I Mat "d pri. - 41 -3.2 Materials and preparation The logs used for this study were part of the consignment of logs shipped from Nigeria to.SNC-Rust Limited of Montreal, Canada, for pulping studies. They were kept in cold, storage while in Montreal for about a year prior to their use for this study. The ends and surfaces of the logs had considerably dried out by the time they arrived at the Western Forest Products Laboratory (WFPL), Vancouver (note the lower moisture content value of the sapwood compared to the heartwood in Table 23). The logs were examined visually on arrival at WFPL and 10 logs deemed of reasonable diameters.for peeling were selected. One of these 10 logs (Log No. 10) was used for preliminary determination of optimum lathe settings for peeling while the remaining 9 logs (Nos. 1-9) were used for veneer production. Their diameters ranged between 15.4cm to 22.9cm (6-9 in); lengths were about 2.7m (9 ft). They were subjected to water spray for 7 days before any test was performed. Six out of the 9 logs used for veneer production contained tension wood. The sapwood thickness was quite small and averaged ,20 mm (0.8 in). The logs were from a young plantation because growth ring count put their ages at 8 to 12 years. Bark thickness averaged 5.1mm (0.2 in). Furthermore, presence of knots ranged between 4 and 8 for the 9 logs. 3.2.1 Wood characterization Before the logs were peeled, preliminary investigation into the specific gravity arid moisture content of the samples were conducted for each of the logs -Nos- 1-9 from which veneers were obtained. The - 42 -sample's specific gravity was taken as an average of the nine results obtained. It was also essential, as part of the preliminary study, to determine the optimum lathe setting for peeling of the species. Log No. 10 was used for this investigation. 3.2.1.1 Specific gravity determination Specific gravity of each of the nine logs was determined by the -vblumelmeasur.ement...me.thod_in<.accofdancdawithwthe ASTMAStandards (ASTM 1975 No?^143^5;2)v,Fq.ur samples per log yielded a. total of 36 samples for the' specific gravity.determination. Figure 1 shows pattern of cut of test samples from a log. Both the air and oven.dried length, width and thickness of each specimen were taken.at three different places — the ends and center of the specimen. A log specific gravity is taken as the average of its four samples. 3.2.1.2 Moisture content determination The procedure for the determination of the moisture content of each of the nine logs also followed that of the specific gravity. It was in accordance with ASTM standards (A;STM 1975;:) .No. D143-52) . It must be indicated, however, that the moisture content of the logs were determined prior to peeling and, except for the control logs peeled at 20°C (ambient temperature) moisture contents of the logs heated to 50°C and 85°C were also determined following heating operations. 3.2.1.3 Determination of the optimum.lathe settings for peeling All peeling was done at"the Western Forest Products Laboratory, Vancouver, on their experimental.lathe equipped with a solid nose bar. Log No. 10 which was used for this study was cut into two bolts of 1.1m long each. Based on past peeling experiences of hardwoods of similar - 43 -veneer thickness (1.27mm), Hailey (1977a), recommended lathe settings of pressure bar horizontal and vertical openings of 1.112mm (0.044 in) and 0.254mm (0.010 in) respectively for rotary peeling of the first bolt from log No. 10. A pitch angle of 89°30' at 25.4cm (10 in) was used. The second bolt was peeled with the same settings but with a change in the pitch to 89°30' at 26.7cm (10-1/2 in). This latter trial was % found to improve the quality of the veneer obtained. In summary, therefore, the optimum.lathe settings determined for peeling 1.27mm veneer from Gmelina arborea logs (16.1 - 22.2cm diameter ranges) were presented in Table 6.' 3.2.2 Log heating Prior to the heating operations a disk about 30.5cm (1 ft) long was cut from one end of each log. Logs were grouped by diameter to give more uniform heating. For this reason, therefore, log numbers 5, 8 6 and 7, with diameters of 19.1cm (7.4 in), 19.7cm (7.7 in) and 18.4cm (7.3: in) were used for the 50°C heating. Similarly, for the 85°C heating, log numbers 1, 3 and 9, with diameters of 22.2cm (8.8 in), 21.0cm (8.2 in) and 20.3cm (8.0 in) were used. The diameters of the logs in.each of these two groups were.assumed close enough to ensure the use of the same heating time. The remaining logs, with diameters of 19.8cm (7.8.in), 16.5cm (6.5 in) and 18.4cm (7.2 in) were peeled at ambient temperature of about 20°C. Following the MacLean (1946).procedures on rate of temperature changes in short-length .round timbers, the initial heating time for the 8 ... oSAverageifordrbothiLends;. *-%ra - 44 -50°C heating was calculated at about 8 hours. Similarly, the heating time was calculated at about 11 hours for the 85°C heating with the use of his suggested formulae. However, due to certain factors discussed below the ultimate heating time for the 85°C heating exceeded the calculated time by about 8 hours. Logs were heated immersed in circulating hot water with over head spray. The temperature changes at the centre of the logs were determined by means of control logs in which thermo-couples were inserted. The drilled holes, through which the thermo-couples passed, were tightly sealed with corks to prevent flow of hot water into the logs. Due to procedural error, however, the temperature changes, 25.4mm (1 in) from the surfaces of the control logs, were not measured with similar uses of thermo-couples. This was not regarded as serious since a relationship exists (MacLean 1946) whereby such temperature changes could be obtained. The initial temperatures of the control logs were taken one minute after inserting, the thermo-couples while the subsequent temperature changes within.the logs were observed at every one-hour interval. The vat temperature was maintained at a level slightly higher than that required for peeling. For the 50°C peeling temperature, the vat was maintained at about 55°C (122°F) while it was about 86°C (190°F) for the 85°Cpeeling temperature. Because of possible technical problems with the heating, a temperature difference of + 2°C in the required peeling temperature was viewed as acceptable. - 45 -3.2.3 Log peeling As required for veneer cutting on the lathe, both the heated and unheated logs were bucked into 1.3 to 1.4m (51 to 53 in) bolts. All nine bolts were rotary cut with the same lathe settings (already determined). Throughout the cutting process, the speed of the lathe was maintained at about 36.6 metresper minute (120 feet per minute). All the veneers were tightly cut. After peeling, the veneer sheets were clipped into pieces about 30cm wide (12 in). To ensure adequate yield of veneer for use, pieces as narrow as 15 to 18cm wide (6 to 7 in) were also preserved. During the peeling, gmelina wood was noted to produce no disagreeable odor. In appearance, the peeled veneers (from heartwood) were light to medium yellow in color. Veneers were also noted to be straight grained. All veneer pieces were coded and stored in moisture proof plastic bags. 3.2.4 Peel-quality evaluation According to Hailey et. al. (1968),.peel-quality is a technical term used in describing or evaluating the effect of the peeling process on certain'^physical properties - namely; thickness, roughness and loose ness - of green veneer sheets. Since the veneers were peeled thin and tight, only two measures of veneer peel-quality were selected to evaluate the lathe settings used in this study with the different peeling tempera tures. These were veneer surface roughness and thickness variation; and all evaluations were made with green veneer sheets. - 46 -3.2.4.1 Veneer roughnes s Veneer surface roughness was estimated in terms of the reference standard maintained at the Western Forest Products Laboratory (Northcott and Walser 1965) in accordance with Hailey and Hancock (1973) description. All the clipped veneer sheets, irrespective of width, were used for roughness test. 3.2.4.2 Veneer thickness measurement Veneer thickness variation was measured in accordance with Hailey and Hancock (1973) description. From each set of veneers obtained from a particular peeling temperature, 10 approximately 30 cm wide (12 in) veneer sheets were randomly selectee for veneer thickness measurements. 3.2.5 Veneer drying The choice of the drying procedures used in this study were based on: 1. The need to avoid, as much as possible, over- or under-drying / - _.' '^r-of-tjie.-.yeneer sheetse (Theoef f ects~on_the; resultingl.plywood bond " J were, reviewed in'" Chapter two). 2. Since thirty days had elapsed between the peeling and drying of the veneer sheets, veneers were regarded to have lost a considerable amount of moisture. This was due to frequent removal of the sheets from the plastic bags in which they were kept for roughness and thickness measurements. 3. The likelihood of much moisture content variability among the sheets. Furthermore, no past veneer drying studies of this wood were available V- to work with. 4. There was difficulty in sorting the veneer sheets into moisture content grades with the use of the moisture meter. This was . ^ due to the thinness of the veneer. - 47 -For these reasons, therefore, the conventional high temperature drying method was avoided. Veneer was dried in a forced-air oven, operating at about 152m/ minute (500 ft/minute) air speed, while the dryer heating system was-completely turned off. For every batch-load of veneer in the oven, 5 wetter and 5 drier pieces were randomly selected and loaded along with the remaihingg sheets at different locations in the oven. These 10 pieces were continuously weighed until, they reached constant weights. All the batch-loads of the three sets of veneer reached constant weights between 5 to 7 hours. The veneer sheets at this stage were regarded 9 to contain a moisture content in the range required for gluing. Veneer moisture content checking prior to gluing indicated that the veneer pieces attained an equilibrium moisture content of between 5.5% and 7.5% regardless of peeling temperature level. 3.2.6 Glues and-glue mixing The two glue types used in this study - UF and PF - are the basic resin adhesives used in the Nigerian veneer and plywood mills. 3.2.6.1 IB-334 Plyophen On the advice of Dr. Chow and Mr. Hailey (Chow 1977, Hailey 1977b) of the Western Forest Products Laboratory, the PF glue chosen was IB-334 Plyophen (PF IB-334 hereafter). Afolayan (1974) used this glue successfully to produce laminated veneer lumber using Canadian hardwood species. Veneers were stacked in a controlled temperature-humidity (CTH) room operating at a dry-bulb temperature of about 26.7°C (80°F), a dew-point temperature of about 6.1°C (43°F) and a relative humidity of 26%. - 48 -The PF IB-334 glue was supplied ready-mixed by Reichhold Chemi cals Limited, Port Moody, B.C. It is a liquid water soluble phenolic resin, which produces high quality exterior adhesives bonds for the plywood industry. The glue was also claimed to provide excellent bonds at competitive press times, as well as being tolerant to conditions of long assembly times and high ambient and stock temperatures. The percentage of PF solids in the final mix of PF IB-334 glue is 26% as opposed to about 23%.for standard PF glue for softwoods. Furthermore, there is twice the concentration of wheat flour in this mix compared to the average plywood mix (See Appendix 5). This has thus necessitated a reduced use of extender in order to accommodate the additional wheat flour. The viscosity of the resin is about 370-470 cps (Gardner-Holdt) while.the viscosity of the glue mix was 1350 cps at 25°C measured by the manufacturer with.No. 3 spindle 60 rpm LVF Brookfield viscometer. The recommended glue spread was 27-30 kg/MDGL while higher spreads of about 34 kg/MDGL and 38 kg/MDGL can be used depending on how porous the wood is (Ainsley 1977)"^. The mixing sequence of the PF IB-334 is shown in Appendix 5. 3.2.6.2 Monsanto UF 109 resin with EK Hardener. Unlike the PF IB-334 glue, the Monsanto UF 109 glue, using EK Hardener, was prepared at the Western Forest Products Laboratory. The mix is"a suitable glue for interior softwood.and hardwood plywood. The components of the EK Hardener are urea, ammonium chloride (NH^Cl), sodium metabisulfite, and walnut shell flour. The urea constitutes the Personal communication. Ainsley is on the staff of the Reichhold Chemicals Limited that supplied the glue. - 49 -bulk of the hardener while the main function of the sodium metabisulfite is to disperse the wheat flour. Similar mix formulation of this glue at the Western Forest Products Laboratory (Rozon 1977) contains, about 29.8% of urea formaldehyde solids with a viscosity of about 2944 cps measured by No. 3 spindle at 30 rpm LVF brookfield viscometer 1/2 hour after mixing. The mixing sequence is.shown in Appendix 6 (supplied by Hart-z 11977-) . i 3.2.7 Glue Spread The glue was spread at about 25 kg/MDGL and 32 kg/MDGL ./as Iftiied fo>- =" v. In all cases, five veneers were assembled to make a panel. A mechanical glue spreader with rubber rolls was used to apply glue to veneers. Since the veneers were peeled tight, it was quite difficult to identify the side with the lathe checks (the loose side). The veneers were therefore assembled without consideration for which side to turn inside or outside. For the 50°C peeled veneers, enough materials were not available for use in all the 24 treatments used in fehe^study?. The veneers from gmelina.wood were therefore used as cores and crossbands while yellow birch veneers of the same thickness were used for the panel faces and backs. For each of the 24 treatments, 3 plywood panels were assembled. After gluingeach panel was coded and marked with respect to Its glue-type, peeling temperature, glue-spread and closed assembly time. - 50 -3.2.8 Plywood Panel pressing 3.2.8.1 Press Pressure Trial panels were assembled using three levels of platen 2 2 pressures of about 11 kg/cm (150 p.s.i.), 14 kg/cm (200 p.s.i.) and 2 18 kg/cm (250 p.s.i.). The three panels obtained were assessed on the 2 basis of the plywood knife-test. The platen pressure of 14 kg/cm (200 p.s.i.) gave the most favourable result. All the assembled panels, therefore, irrespective of glue-type, were pressed with this platen pressure. 3.2.8.2 Pressing Temperature and Time Following industrial practice, a platen temperature of 127°C was used for pressing.the panels glued with UF resin adhesive and 149°C for those panels .glued with PF resin adhesive. The assembled panels were pressed with two panels per press opening for 5 minutes with the Monsanto UF 109 glue and 4.5 minutes with the PF IB-334 glue. In summary, the following specifications and pressing schedule were used when making a typical, panel assembly: 1. Five-ply, with a glue spread of 25kg/MDGL or 32 kg/MDGL depending on treatment combination. 2. Ten minutes or 20 minutes closed assembly time depending on treatment combination. 3. Platen temperature of about 127°C (260°F) or 149°C (300°F) depending on glue type. 2 4. Press pressure of 14 kg/cm (200 p.s.i.) 5. Pressing time of 5 minutes or 4.5 minutes depending on glue type and platen temperature. 6. Hotstacking of the panels glued with PF for 10 minutes. - 51 -3.2.9 Test Specimen Preparation Tension-shear specimens from the plywood panels produced were prepared in accordance with the requirements of the CSA and NBS standards. Because of the small thickness of the panel's however, difficulties were encountered when making grooves on the 7.6cm (3 in) wide strips cut from the panels. The circular saw in some cases cut through the entire thickness of the core-ply instead of the two-thirds of it specified. Test specimens- obtained from such strips were regarded as "rejects" and were screened out of the lots after cutting. Specimens were coded by panel of origin to facilitate between and within panel comparison for shear strength and percentage wood failure. Specimens were randomized for the two types of test. :Testospecimens vary between 22 and 36 in all the 24 treatments used in this study. In all, a total of 1438 test specimens were stressed to failure.. Specimens were coded and marked according to type of bond quality test, panel number, glue-type, peeling temperature, glue spread and assembly time. For example, a sample designated UF-20-55-10 indicates that.the sample was from a panel glued with UF resin adhesive; veneers were peeled at 20°C; panel was glued at a spread of 551b /MDGL (25 kg/MDGL) and panel assembly was pressed after a closed assembly time of 10 minutes. 3.2.10. Bond Quality"^"*" Testing Procedures 3.2.10.1 Dry Test The UF test specimens were stressed to failure in a Globe Wood failure readings, regardless ofnbond-quality testing method, were based both on gross and fine fibre wood failures. - 52 -tension-shear machine in accordance with the NBS/CSA standards. Load was applied at the rate of about 272 kg to 454 kg per minute (600 to 1000 lb. per minute). The ultimate shear strength and wood failure were recorded for each specimen. 3.2.10.2 Vacuum-Pressure Test This test was usedhto assess bond :qual>i>t-yl performance in all the treatments used in this study, irrespective of glue-type. As investigated by Chow and Warren (1972), the vacuum-pressure test was -found to be.on a par with the cyclic cold-soak test. The vacuum applied was about 63.5cm (25 in) of mercury while the air pressure applied was 2 in the. range>of about 4.6-4.9 kg/cm (65-70 p.s.i.). The efficiency of water penetration into the test specimens was not investigated insofder to justify the use of a cycle greater than 30 minutes as was the case with Tan's study (Tan 1974). This was because his study involved the use of denser Malayan hardwoods whereas gmelina is a low to medium density hardwood.(specific gravity = 0.41). The 30-minute cycle was therefore viewed adequate. Evidence of adequate water penetration seemed to be provided by the wide differences shown by the wood.failure results between the dry and vacuum pressure tests of the treatments bonded with UF glue ((Table.; lOO}.. Specimens were sheared while wet on the same Globe testing machine used for the dry test. The shear strength was recorded while the wood failure was evaluated after oven-drying the sheared specimens overnight. This served to prevent reading errors due to the darkening by the water. - 53 -3.2.10.3. Boil-dry-boil Test The test specimens glued with PF resin adhesive, were subjected to boil-dry-boil test in accordance with DIN68705 and CSA standards. The specimens were sheared wet after having been cooled to room temperature in water. Shear strength was recorded for each specimen and,as before, wood failure was read after drying the sheared specimens overnight in an oven. 3.2.11 Statistical Analysis Factorial.analysis, was performed to facilitate the interpreta tion of the main and interacting effects that could evolve. Treatments were analysed with respect to glue-type as well as type of bond quality test used. Shear strength and wood failure were analysed separately. Also based on the advice of Dr. Kozak, Faculty.of Forestry, an analysis of variance was performed, for both the shear strength and wood failure according to type of test. It was hoped that this would show the comparative performance of a treatment with the others. Where significant differences were found, Duncan's New Multiple Range test was applied. In order to facilitate easier factorial analysis of results (Kozak 1977), the same number, of test specimens was used in all the treatments. Therefore, the treatment with the smallest number of specimens was used as a standard while the same.number of specimens were randomly selected, from the other treatments with the use of a Table of random numbers. Thus, 22 specimens, per treatment were used for the factorial analysis of variance. - 54 -4.0 RESULTS 4.1 Moisture content and specific gravity of gmelina logs used The initial and.peeling moisture contents (MCs) of the log samples used are presented in Table 2. Values are shown separately for sapwood, heartwood and corewood. The sapwood initial.-MCsv are consistently lower than those of the heartwood in all the 9 logs. MC values are in the ranges of 41% to 107% and 67%.to 147% for the sapwood and heartwood respectively. The MC of the sapwood increased for three of the six heated logs while the heartwood MC decreased for four of the six heated logs. Nevertheless, the sapwood MCs? at peeling are still consistently lower than those of the heartwoods in all the logs. The average log specific gravity (sp.gr.) as well as mean and standard deviation of gmelina sample logs.used, is given in Table 3. The sp.gr. values for the 9 logs are based on ovendry weight and green volume and are in the range of 0.37 to 0.44. This gives a sample mean of 0.41 with a standard deviation of 0.027. 4.2 Log heating and peeling The water bath temperature changes as well as temperature changes within.the log at positions.2.5cm (1 in) and 10.2cm (4 in) from the log surface are shown in Tables4 and 5 for the 50°C and 85°C (+2°C) heating, respectively. These changes are shown graphically in Figures (Fig.) 2 and 3. The logs heated to 50°C (+2°C) attained that temperature at the calculated heating time of 8 hours (hr) while those heated to 85°C (+2°C) attained that temperature at a heating time of 19 hrs - 55 -instead of the calculated time of 11 hrs. The lathe specifications.used for veneer cuttingare presented in Table 6. 4.3 Veneer peel-quality The frequency distribution.of visual roughness measurements is given in Table 7 for the.veneers peeled from the control bolts (20°C) and bolts heated to 50°C and to 85°C, and is.graphically presented in Fig. 4. The mean, maximum, minimum, standard deviation and range are presented.in Table 8 for each of the veneer peel-quality attributes measured; namely veneer thickness and veneer roughness. Veneer thick nesses were derived.from 10.specimens .each for the veneers peeled from the control bolts (20°C) and bolts.heated to 50°C and 85°C. On the other hand, the veneer roughness values, were derived, from 175, 194 and 173 specimens for the veneers peeled from the control bolts (20°C), bolts heated to.50°C and bolts heated.to.85°C respectively. Results show that peel-quality was best for the veneers peeled from the control bolts (20°C) while bolts heated to 85°C produced the roughest veneers. 4.4 Veneer moisture.content prior to gluing Table 9 shows the MC of the 10.pieces of veneer checked prior to gluing as well as the average MC for the 10 pieces. These averages are 6.6%, 6.4% and 6.4% for the veneers .peeled from the control bolts (20°C) and bolts heated to 50°C and 85°C respectively. These values give no indication of overdrying of veneers with.the use of the forced-air drying technique. - 56 -4.5 UF resin adhesive 4.5.1 Dry test: Shear strength and wood failure percent Table 10 summarizes the average.shear strength and percentage wood failure for the 12 treatment combinations of: peeling temperature (PT) , glue spread (GS) and-closed assembly time (AT). Individual specimen minimum wood failure in. each treatment combination is also shown, as well as treatment codes used in the study. This was done to facilitate comparison of bond, quality results with the U.S. Plywood Standard. Plywood panels made .from veneers peeled at 85°C (using a GS of 70 lb/MDGL and an AT of 20 minr) produced the highest shear strength of 389 psi; while those made from veneers peeled at 20°C (using a GS of 55 lb/MDGL and an AT 20-min;:) produced the. highest percentage wood failure of 70%. Generally, bond quality is best, at the PT of 20°C. The mean, maximum, minimum and.range.of percentage wood failure for each of the three panels produced for testing in each of the 12 treatments are presented in Table.12. Large variabilities in bond quality, within and between the panels, are noted. 4.5.2 Vacuum-pressure test: Shear strength and wood failure percent The average shear strength and percentage wood failure for the 12 treatment combinations of PT,.GS. and AT.subjected to this test are also shown in Table 10. Similar, to the dry test, plywood panels made from veneers peeled at 85°C(using a GS.of 70 lb/MDGL and an AT of 20 min: ) produced the highest shear strength of 307. psi; while those made from veneers - 57 -peeled at 20°C (using a GS of 55 lb/MDGL and an AT of 20 min ) produced the highest percentage wood failure of 59%. Generally, bond quality is best at the PT of 20°C. There is also a large variability in bond quality within and between panels as shown in Table 13. 4.6 PF resin adhesives 4.6.1 Vacuum-pressure test: Shear strength and wood failure percent Table 11 shows the average shear strength and percentage wood failure for the 12 treatment combinations of PT, GS and.AT. The minimum wood failure percent for each test specimen is also shown as well as treatment codes used. Plywood panels made from.veneers peeled at 85°C (using a GS of 70 lb/MDGL and an AT of 20 min. ) produced the highest wet shear strength of 405 psi; while those made from veneers peeled at 50°C (using a GS of 70 lb/MDGL and an. AT of 20 min.) produced the highest percentage wood failure of 64%. Generally, panels.made from veneers peeled at 20°C give ah impressive bond quality. The mean, maximum, minimum and range of percentage wood failure for each of the three panels produced for testing are presented in Table 14. Values are shown separately for each of the 12 treatments used. Large variabilities in bond quality, within and between panels, are noted. 4.6.2 Boil-dry-boil test: Shear strength and wood failure percent The average shear strength and percentage wood failure for the 12 treatment combinations of PT, GS and AT are also summarized in - 58 -Table 11. The minimum wood failure percent for each test specimen is also shown in order to facilitate comparison of bond quality results with the U.S. Plywood Standard. In this test, plywood-panels.made from.veneers peeled at 85°C '• (using a GS of 70 lb/MDGL and an AT of 20 min„) produced the highest shear strength of 334 psi; while those made from veneers peeled at 50°C (using a GS of 70.1b/MDGL and an AT of. 20 min .) produced the highest percentage wood failure of 66%. The mean, maximum, minimum and .range of percentage wood failure for each of the three panels produced.for testing are presented in Table 15. Values are shown separately for each.of the 12 treatments used. Large variabilities in bond quality., within and between panels, are also noted. 4.7 Analysis of variance 4.7.1 Factorial analysis The results of the dry test shear.strength and percentage wood failure for the.treatment panels, bonded with UF glue (factorial analysis) are summarized in Table 16; showing the significant main and interacting effects at the 0.01 and 0.05 levels. All. the significant interacting effects are graphically depicted in Fig. 5 and 6. Similarly, Table 17 summarizes the factorial analysis results of the vacuum-pressure test shear.strength and percentage wood failure for the treatment.panels bonded.with UF glue. The.significant inter acting effects at 0.01 and 0.05 levels.are graphically depicted in Fig. 7 to 9. - 59 -The results of the vacuum-pressure test shear strength and percentage wood failure for the panels bonded with PF glue are presented in Table loy' showing the significant main and interacting effects at the 0.01 and 0.05 levels. All.the significant interacting effects are graphically depicted in Fig. 10 to 13. Table 19 shows the factorial analysis results of the Boil-dry-boil test shear strength, and percentage wood failure for the treatment panels bonded with PF glue. All the significant interacting effects in this result are graphically depicted in.Fig. 14 to 16. 4.7.2 Duncan's multiple range test The results of the. Duncan's multiple range test for direct comparison of the average shear strength and percentage wood failure are presented in Tables 20 and 21 for the treatment panels bonded with UF glue (Dry test and Vacuum-pressure test respectively). Similarly, results are shown in Tables 22 and 23 for the treatment panels bonded with PF glue (Vacuum-pressure test and boil-dry-boil test respectively). - 60 -5.0 DISCUSSION 5.1 Sample specific gravity The mean sp. gr. of 0.41 + 0.027 found for the Nigerian plantation-grown gmelina logs used in this study compares favourably to a value of 0.41 + 0.060 reported by Nokoe-Sagary (1972) for Nigerian plantation-grown gmelina samples. Lamb (1968) also reported a nominal sp. gr. of 0.407 - 0.427 and 0.42 for work done on Gmelina arborea samples from Gambia and Malaysia respectively. Furthermore, IUFRO (1973) reported a sp. gr. value of 0.40 for Gmelina arborea samples from Thailand and Sarawak. The mean sp. gr. value of 0.41 +0.027 of this study, makes veneer and plywood produced.from.Gmelina arborea wood suitable for various end uses (elaborated further in_the discussion). 5.2 Log heating Because of technical problems with the heating, logs numbered 1, 3 and 9 did not attain a temperature of 85°C (+ 2°C) required for their peeling at the calculated time of 11 hr, but rather at an extended time of 19 hr. The temperature regulator of the vat. had to be adjusted several times before it was able to give the required temperature. The question of overheating the log for the 19-hour period did not arise for two reasons: 1. The water bath temperature did not at any time attain a tempera-. ture of 85°C (+ 2°C) until 18-19 hr. heating period. 2. The temperature within the log cannot exceed that of the - 61 -heating medium. The logs can therefore not attain a tempera ture of 85°C (+ 2°C) required for their peeling without the vat maintaining that temperature. 5.3 Veneer peel-quality 5.3.1 Thickness As shown in Table 8.9, the average veneer thicknesses were 1.25 mm, 1.22 mm and 1.19 mm; with standard deviations of 0.08 mm, 0.10 mm and 0.05 mm for the control bolts (20°C), bolts heated 8 hr, (to 50°C) and bolts heated 19 hr., (to.85°C) respectively. These averages are slightly below the objective veneer nominal thickness of 1.27 mm (0.05 in) by about 2%, 4% and 6% respectively. Even though the average veneer thickness is lowest at 85°C PT, thickness variation is under best control because of its smallest.range compared to the other PTs. Generally, results show that veneer thickness variation is under good control as the three means are equal at the 0.05 level. 5.3.2 Roughness As similarly shown in. Table 28, the average veneer roughnesses were 0.15 mm, 0.21 mm and 0.24 mm for the control bolts (20°C), bolts' heated 8 hr, (to 50°C)and bolts heated.19 hr. (to 85°C) with standard deviations of 0.05 mm, 0.07 mm and 0.06 mm respectively. The correspond ing veneer, roughness ranges are 0.12 mm,..0.38 mm and 0.38 mm for the three veneer PTs.of 20°C, 50°C and 85°C. On the basis of these average and range values, the logs peeled at 20°C give the best veneer smoothness results. Generally, veneer roughness is very good and well within the - 62 -limits for high quality veneer. In view of the above, therefore, it can be stated that variation in thickness and roughness of veneer were not improved by heating the gmelina bolts to temperatures of 50°C and 85°C prior to peeling. Measure ments by the visual roughness method indicated increased roughness at high PTs. Kinoshita. and Ohira. (1971), McMillin (1958) and Feihl (1964) reported from.their studies on certain hardwoods (Philippine red lauan and yellow birch) that.improved veneer peel-quality was obtained when these woods were heated prior to peeling. Madison (1957), however, indicated that heating of quaking aspen (Populus tremuloides) and big tooth aspen (Populus grandidentata) bolts above room temperature increased the fuzziness of the veneer surfaces. 5.4 Plywood bond quality 5.4.1 Treatment panels bonded with UF glue 5.4.1.1 Dry-test: Shear strength and wood failure percent The dry test shear strength results of the factorial analysis shown in Table 16 indicate that the PT and the GS are highly significant factors (i.e. significant at the 0.01 level). The interaction between PT and AT is significant, at the 0.05 level. The presence of this inter action obscures any interpretation that could have been made on the main effects. This interaction may be more clearly understood by referring to Fig. 5. At the PT of 20°C, AT of 10 and 20 min. have negligible influence on the shear strength of. the treatment panels bonded with UF glue. At the PT. of 50°C, however, prolonged AT of 20 min results in lower shear strength. A mild effect is produced at the highest PT of - 63 -85°C with the AT of 20 min. producing a higher shear strength. Generally, plywood panels made from veneers cut at the PT of 85°C produce^the highest shear strength at both levels of AT thus giving the most favourable bond quality on the basis of shear strength. At 2 this PT, the shear strength of about 28 kg/cm (398 psi) given by the treatment combination of Spread 70 - Time 20 is not statistically significant at the 0.05 level from the dry shear strength of about 2 2 26.8 kg/cm (381 psi) and 25.5 kg/cm (362 psi) given by the treatment combinations of Spread 70 - Time-10 and.Spread 55 - Time 10 respectively. 2 The lowest dry shear strength of about 21.5 kg/cm (306 psi) is given by the treatment combination of Spread 55 - Time 10 at the PT of 20°C. From the factorial analysis for wood failure shown in Table 16, the PT and the interaction of PT with GS and AT are highly significant. This interaction is better depicted in Fig. 6. Except for the treatment combination of Spread 70 - Time 20, bond quality, in terms of percentage wood failure, is consistently reduced at the higher PT for the remaining treatment combinations of Spread 55- Time 10, Spread 55 - Time 20 and Spread 70 - Time 10 respectively. Generally, bond quality (in terms of percentage wood failure) is best for the plywood panels made from veneers cut at the PT of 20°C. As shown in Table 21,. treatment UF-20-55-20 produced the highest percentage wood failure of 70%, which is not significantly different at the 0.05 level from the percentage wood failures of 62% and 61% produced by treatments UF-20-70-10 and UF-50-70-20 respectively. The lowest percentage wood failure is produced.by treatment UF-85-70-10. - 64 -5.4.1.2 Vacuum-pressure test: Shear strength and wood failure percent The factorial analysis results for the shear strength samples of the UF glued panels, subjected to vacuum-pressure test, follow the same pattern as the dry test. As.shown in Table 17, the PT is highly significant (0.01 level) whereas the GS is significant at the 0.05 level. The interaction between the PT and GS is highly significant. As depicted in Fig. 7, bond quality, in terms of wet shear strength, is slightly affected at both spread levels of 55 lb/MDGL and 70 lb/MDGL at the PT of 20°C and 85°C respectively. While wet shear strength is slightly higher with the higher spread at the PT of 20°C, the lower spread, on the other hand, gives a slightly higher shear strength at the PT of 85°C. The lower spread also gives higher shear strength at the PT of 50°C. Generally, plywood panels made from veneers cut at the PT of 85.°C, produce the highest shear strength values at the two spread levels. As shown in Table 20, the highest shear strength of about 22.4 2 -kg/cm (319 psi) given by treatment UF-85-55-20 is not•significantly diffefentnt at the 0.05 level from those given by treatments UF-50-55-10 (20.7 kg/cm2 i.e. 295 psi), UF-50-55-20 (21.0 kg/cm2 i.e. 299 psi), UF-85-70-20 (21.6 kg/cm2 i.e. 307 psi) and UF-85-55-10 (20.7 kg/cm2 i.e. 295 psi). In this test, the lowest shear strength of about 17.5 2 kg/cm (249 psi) is given by treatment UF-50-70-20. As further shown in Table 17, the vacuum-pressure test wood failure results for the UF glued panels indicate that the PT and the GS v are highly significant factors, as well as the interaction between the PT, GS and the AT. The interaction between the PT and the GS is significant at the 0.05 level. As depicted for the interactions in - 65 -Fig. 8 and 9, bond quality, in terms of percentage wood failure, is consistently reduced at the PT of 50°C and 85°C. The lowest percentage wood failure is obtained at the PT of 85°C for each of the treatment combinations. of Spread 55--^*Time£10*fSpread'^SS - Time 20, Spread 70 -Time 10 and Spread 70 - Time 20. As noted in Fig. 9, the influence of treatment combinations of Spread 55 - Time 20 and Spread 70 - Time 10 on percentage wood failure is not significant. These two treatments, at the PT of 20°C, give the highest percentage wood failure. At the PT of 50°C, there is no significant influence of treatment combinations of Spread 55 - Time 20 and Spread 70 - Time 20 on percentage wood failure. Bond quality at this PT is best with the treatment combination of Spread 55 - Time 20. Each of the four treatment combinations exerts a distinct influence on percentage wood failure at the PT of 85°C with treatment UF-85-55-20 giving the most.favourable result. The wood failure ranking in.Table 21 shows that the highest percentage wood failure of 59% given by treatment UF-20-55-20 is not r significantly .differentJ;: at the 0.05 level from the value of 56% given by<..treaemgS4 UF-20-70-10. The lowest percentage wood failure of 11% is given by the treatment combination of Spread 70 - Time 10 at the PT of 85°C. 5.4.2 Treatment panels bonded.with PF glue 5.4.2.1 Vacuum-pressure test: Shear strength and wood failure percent More interactions of the main effects are noted with the shear strength of the PF glued test samples subjected to vacuum-pressure test - 66 -than for the UF glued test samples. As noted in Table 18, PT, GS and AT are highly significant (at the 0.01 level). Similarly, the interaction between PT and AT is highly significant. The interaction between PT and GS is significant at the 0.05 level. Fig. 10 and 11 depict these inter actions. As shown in Fig. 10, higher wet shear strength is produced at each of the PT with the higher spread of 70 lb/MDGL. The spread of 55 lb/MDGL gives the highest shear strength at the PT of 20°C, whereas the spread of 70 lb/MDG gives the highest shear strength at the PT of 85°C (Fig. 10). As shown in Fig. 11, wet shear strength is slightly higher with the AT of 10 mim at the PT of 50°C whereas the AT of 20 min produces a slightly higher shear strength at the PT of 85°C. Generally, plywood panels made from veneers.cut at the PT of.20°C and 85°C produce the highest wet shear strength values. From the shear strength ranking presented in Table 22, the highest shear strength value of about 28.5 2 kg/cm (405 psi) is given by the treatment combination of Spread 70 -Time 20 at the PT of 85°C. This is, however, not statistically signifi-2 cant at the 0.05 level from the values of about 27.9 kg/cm (397 psi) 2 and about 26.9 kg/cm (382 psi) given by the treatment combinations of Spread 70 - Time 10 (at PT of 20°C) and Spread 70 - Time 10 (at PT of 2 85°C). The lowest shear strength of about 21.7 kg/cm (308 psi) is given by the treatment combination of Spread 55 - Time 10 at the PT of 50°C. The factorial analysis (Table 18) for the wood failure of the PF treatments subjected to vacuum-pressure test shows that the PT, AT, PT-AT interaction and PT-GS-AT interaction are all highly significant. The significant interactions are shown in Fig. 12 and 13. Fig. 12 shows that bond quality, in terms of percentage wood failure, is lowest at the PT of 85°C. Higher percentage wood failure is produced by the prolonged AT of 20 min.' at each level of PT as against the AT of 10 min The AT of 10 min. produces the highest percentage wood failure at the PT of 20°C; while the AT of 20 min. produces the highest percentage wood failure at the PT of 50°C. As shown in.Fig. 13, percentage wood failure decreased consistently between 20°C and 85°C PT for each of the treatment combina tions of Spread 55 - Time 20, Spread 70 - Time 10, Spread 70 - Time 20 and Spread 55 - Time 10. At the PT of 85°C, the highest percentage wood failure is produced by.the treatment combination of Spread 55 -Time 20. For the three.treatment combinations of Spread 55 - Time 10, Spread 55 - Time 20 and Spread 70 - Time 10, the highest percentage wood failures are produced at the PT of 20°C. For this particular test, however, the highest and most favourable bond quality is given by the treatment combination of Spread 70 - Time 20 at the PT of 50°C. From the wood failure ranking presented in Table 23, the percentage wood failure^ of 64% given by the treatment is significantly' different at the 0.5 level to the value shown by any other treatment. The lowest percentage wood failure of 7% is given by the treatment combination of Spread 55 - Time 10 at the PT of 85°C. 5.4.2.2 Boil-dry-boil test: Shear strength and wood failure percent Shear strength results for this test (Table 19) indicate that the PT, GS and AT are highly significant. Similarly, the interaction of the PT with the AT is highly significant. From Fig. 14., the lower AT - 68 -of 10 min. produces higher wet shear strength than the prolonged AT of 20 min. at the PT of 20°C and 50°C. At the PT of 85°C, however, the pro longed AT of 20min. gives a higher wet shear strength. Furthermore, with the AT of 10 min. the highest wet shear strength is produced at the PT of 20°C; whereas with the AT of 20 min. the highest wet shear strength is given at the PT of 85°C. Generally, plywood panels made from veneers cut at temperatures 20°C and 85°C.give the most favourable bond, quality. From the shear strength ranking presented in Table 22, the highest wet shear strength 2 of about 23.5 kg/cm (334 psi) is given.by the treatment combination of Spread 70 - Time 20 at the PT of 85°C. This, however, is not significant 2 at the 0.05.level from the values of about 22.6 kg/cm (322 psi) and 2 22.1 kg/cm (315 psi) given by the treatment combinations of Spread 70 -Time 10 (at the PT of 20°C) and.Spread 70 - Time 10 (at the PT of 85°C). 2 The lowest shear strength of 16.8.kg/cm (239 psi) is given by the treatment combination of Spread 55 - Time 20 at the PT of 50°C. Wood failure results.for same test (Table 19) indicate that the PT, GS and AT are highly significant. Similarly, the interactions between the PT and GS as well as PT and AT are highly significant. From the interaction shown graphically in Fig. 15, the PT of 85°C gives the lowest bond quality (in terms of percentage wood failure) at each of the spread levels of 70 lb/MDGL and 50 lb/MDGL. With the lower spread, percentage wood failure is highest at the PT of 20°C, while the higher spread gives the highest percentage wood failure at the PT of 50°C. Fig. 716 shows a.similar trend in bond performance to Fig. 15. The prolonged AT of 20 min. results in higher percentage wood failure - 69 -than the lower AT of 10 min- at all three levels of PT. For the AT of 10 min., percentage wood failure is highest at the PT of 20°C and lowest at the PT of 85°C. For the'AT of 20 min,, percentage wood failure is highest at the PT of 50°C and lowest at the PT of 85°C. Generally, plywood.panels made from veneers cut at 50°C gave the highest percentage wood failure for this particular test. From the wood failure ranking presented in Table 23, the highest percentage wood failure of 66% given by the treatment combination of Spread 70 - Time 20 at the PT of 50°C is sig-nificantlycS_ffereht. Vt"the 0.05 ievei^to'the value shown by any other treatment. Thellowest percentage wood failure of 12% is given by treatment combina tions of Spread 55 - Time 10 (at the PT of 50°C) and Spread 55 - Time 10 (at the PT of 85°C). 5.4.3 Probable factors accounting for low percentage wood failures in the treatments. The following explanations are presented as the possible causes of low bond quality performance (in terms of percentage wood failure) shown by the treatments, especially with the use of PF glue: 1. The veneers used for the study wereinbt obtained, from fresh logs. The logs peeled were from the consignment shipped from Nigeria to SNC-Rust Company Limited, of Montreal. They had been kept in cold storage by the company for at least a year prior to their use. The sapwood zone had dried out considerably and veneers from this wood zone were also used when constructing certain of the panels. Discoloration of such veneers to a dark brown or blackish color had already occurred, as noticed at - 70 -peeling. Further veneer discoloration occurred between the 30 days that expired between the peeling and drying of the veneers. 2. There is also the problem of influence of surface aging of veneer prior to gluing. Eighty days expired between the peeling and gluing of the veneers. Surface aging of wood has been reported to drastically reduce its wettability and, in turn, the quality of the glue bond (Gray 1962, Marian 1962, Marian and Stumbo 1962b, Stumbo 1964, Herczeg 1965 and Collett 1972). The relationship between wood wettability and its gluability has also been noted in Section 2.8. It was noticed that where the discolored veneers were used as cores, low or zero percentage wood failures were developed. No attempt was made to give the veneers light surface sanding prior to gluing. The introduction of such a variable would have doubled the number of treatments used. Due to the limited amount of veneer available, it was impossible to include this variable. Walters (1973), for example, reported that poor gluing resulted from decreased surface wettability and surface inactivation but could be improved upon by giving the veneers a light surface sanding prior to gluing. He obtained higher percentage wood failure for the sanded veneers compared to the unsanded veneers. Comparing the results of the PF treatments, vacuum-pressure test, with the UF treatments, vacuum-pressure test (Tables 10 and 11), the PF IB-334 glue used seems to be more - 71 -sensitive to surface inactivation, resulting from surface aging of veneers, than the Monsanto UF 109 glue used, thus accounting for its lower percentage wood failure. 3. Variability in bond quality between and within panels is a usual phenomenon. This is illustrated by Tables 12 to 15. Regardless of type of bond quality test, large variability in percentage wood failure was observed with both the UF and PF treatments alike. This is indicated by '£helwid§ ranges shown in columns 11-13 of Tables zl*2 tto 315 respectively. In addition, and more likely, this variability is the result of such factors as: i) differences in veneer moisture content at gluing, ii) - spanel edge effect, iii) differences in degree of cure of glueline. iv) numanrf-aetor introduced during veneer gluing especially with regards to the, open assembly time (Not introduced as a variable in the study), v) stress concentrations inherent in the test specimens during shear testing. It was noticed, for example, that longer open assembly time was used when gluing with the PF glue than the UF glue. This was due to the difficulty encountered while spreading the glue on the veneers. Because it was less viscous than the UF glue, it was leaking out of the roller spreader. The glue was therefore spread on one face of the veneer then the piece was flipped over for the spreading of the other face. The effect of long open - 72 -assembly time on phenolic glue has been reviewed in Section 2/6.2. 4. The PF.resin used was more caustic (pH 12.5 - 13.5) than the UF resin (pH 8.4). The buffering capacity of the UF resin, theref ore^would be low at high panel pressing. temperature of 127°C (260°F). Due to moisture and natural acids in wood (uronic acids of hemicelluloses), hydrolysis condition may be created. This weakens the wood structure in the vicinity of the glueline, thereby causing failure at lower shear loads with higher percentage wood failures as evidenced by vacuum-pressure results of both glues in Tables 10 and 11. 5. As reviewed in Section 2.1, the resin content of gmelina wood is high. The low percentage wood failures exihibitedvby the PF and UF treatments could, therefore, be due to interference of the wood extractives with the glues. The PF resin has a pH of 12.5 to 13.5, which should be enough to saponify the extractives on the veneer surfaces (Chow 1977b). However, the PF treatments showed lower percentage wood failure values compared to the UF treatments (UF has a pH of 8.5). This, seems to contradict the interference concept. The definite influence of the extractives of the wood on bond quality is therefore difficult to make. It is the view of the writer that with fresh veneers, better bond quality could be obtained with gmelina wood. - 73 -5.4.4 Comparison of study results with some National Plywood Standards As indicated in Section 2.7, the U.S., British and German; Plywood Standards will be used to assess bond quality results obtained in this study. 5.4.4.1 U.S. Hardwood plywood standard Voluntary Product Standard PS 51-71 for Technical and Type I (both Exterior Grades) Hardwood plywood are: The specifications of the U.S. Department of Commerce Average failing load (psi) Average Wood failure (%) Under 250 50 25 250 - 350 30 10 Above 350 15 10 PF treatments from this study that meet the above Exterior Grade Plywood requirements are as follows: - 74 -Average failing Average Wood Individual Specimen Treatments Load (pgi) failure (%) minimum wood failure (%) PF-Vacuum-Pressure 1. PF-20-55-20 318 45 15 2. PF-20-70-10 397 31 10 3. PF-20-70-20 337 34 10 4. PF-50-55-20 313 45 10 5. PF-50-70-20 317 64 30 PF-Boil-dry-boil 1. PF-20-55-20 255 43 10 2. PF-20-70-10 322 38 10 3. PF-20-70-20 276 34 10 4. PF-50-55-20 239 46 10 5. PF-50-70-20 258 66 10 As noted in the above comparison, three of the five treatments, from each of the bond.quality testing methods, passing the U.S. standard are treatment .combinations arising from the PT of 20°C. The remaining two treatments come from the PT of 50°C. No treatment combination arising from the PT of 85°C meets this standard. It can therefore be concluded that a PT of 85°C produces roughest veneers (compared to the PT of 20°C and 50°C) (Table 8) which, when glued into plywood, result in low bond quality - in terms of percentage wood failure. Among the five treatments that meet the U.S. standard, the 2 shear strength of about 22.3 kg/cm (317 psi) obtained from treatment PF-50-70-20 is not statistically different at the 0.05 level to the value - 75 -2 of about 22.4 kg/cm (318 psi).obtained from treatment PF-20-55-20 (Vacuum-pressure test). On the basis of the U.S. standard, therefore, treatment PF-20-55-20 may be of greater industrial importance than treatment PF-50-70-20. It facilitates lower production costs because higher energy consumption is required to heat logs to 50°C as well as higher adhesive cost at a spread of 70 lb/MDGL as against 55 lb/MDGL. However, where the industry hopes to maximise bond quality with respect to shear strength and percentage wood failure, treatment PF-50-70-20 is most suitable. Also comparing treatments PF-20-55-20 and: PF-20-70-10, the 2 shear strength of about 27.9 kg/cm (397 psi) obtained for the latter is statistically different at the 0.05 level from the shear strength of 2 about 22.4 kg/cm (318 psi) obtained for the former. Treatment PF-20-55-20 may, however,be of industrial importance because of<it-s.-lower glue cost (both treatments are from the same P^TdaMgpWdta'cfefctihe.'-highest ; percenfeageKwood-failure va'l-u'es):be Nevertheless,- wft'ereiath^ui-ndustry hopes •: to.jmaximiseibond quality inieterms.xoft^wood ' she'ariestrerTgtlSr^reatment PF^2a-r7i(D^10 is most favourable. This same analysis applies exactly to the five PF-Boil-dry-boil treatments that meet the U.S. standard. Treatment PF-20-55-20 is preferred because.of advantage of lower production cost in heating and adhesive cost; treatment PF-50-70-20 is preferred where both high shear strength and percentage wood failure are of prime importance and treatment PF-20-70-10 is most favoured where very high shear strength is most desirable. - 76 -UF treatments that, also meet the U.S. standard are as follows: Average failing Average Wood Individual Specimen Treatments Load (psi) failure (%) minimum wood failure (%) UF-Dry Test All the Twelve Treatments used. UF-20-55-10 through UF-85-70-20 306-389 35-70 10-35 UF-Vacuum Pressure 1. UF-20-55-10 264 38 10 2. UF-20-55-20 274 59 15 3. UF-20-70-10 260 56 15 4. UF-20-70-20 277 44 10 5. UF-50-55-10 295 33 10 Since vacuum-pressure results give better information on bond quality performance than the dry test, the five treatments listed above will only be viewed as the UF treatments meeting the U.S. standard. Of these five treatments, four arise from the PT of 20°C and none from the 85°C. This also suggests that even with the UF glue, the PT of 85°C fails to produce plywood of adequate bond quality regardless treatment combination. Among the five treatments listed, treatment UF-20-55-20 is most favoured to a plywood industry. It facilitates lower production cost because higher energy cost is required to heat logs to 85°C and lower glue cost is ensured at a spread' of 55 lb/MDGL as against 70 lb/ MDGL. High shear strength and percentage wood failure are both maximised - 77 -in the treatment. All five treatments are considered adequate for producing Interior grade plywood. 5.4.4.2 British Hardwood Plywood Standard The British Standard B.S. 1455:1963 for Tropical Hardwood Plywood specifies an average percentage wood failure of 50%. The study PF and UF treatments that meet this standard are as follows. Treatments Average Wood failure (%) PF-Vacuum Pressure PF-50-70-20 64 PF-Boil-dry-boil PF-50-70-20 66 UF-Dry Test UF-20-55-10 57 UF-20-55-20 70 UF-20-70-10 62 UF-20-70-20 52 UF-50-55-10 53 UF-50-70-20 61 UF-Vacuum Pressure UF-20-55-20 59 UF-20-70-10 56 On the basis of the British Standard, the only PF treatment that meets the standard (PF-20-70-20) is considered adequate for use as Weather and boil-proof, Boil-resistant and Moisture resistant Exterior grade plywood. On the other hand, the two UF treatments under Vacuum-pressure test that meet the standard are considered adequate for use as - 78 -Interior grade plywood. Out of these two treatments, however, UF-20-55-20 is of greater industrial importance than treatment UF-20-70-10 since its spread of 55 lb/MDGL ensures lower cost of adhesive consumption than the spread of 70 lb/MDGL for the other treatment. Its higher percentage wood failure of 59% is not statistically different at the 0.01 level from the average of 56% for the other treatment. 12 5.4.4.3 German . 'iHardwood. Plywoods Standard The German standard, Deutshe Industrie Normen DIN .68705-1968 2 specifies an average shear strength of 10 kp/cm (142 psi). All the 24 treatments used in this study, regardless of glue type and bond.quality testing methods, meet the German Hardwood Plywood Standard. Shear 2 strength values are in the range of about 16.8 to 28.5 kg/cm (239 to 405 psi). Cost consideration may justify the use of.treatment PF-20-55-20 2 and UF-20-55-20 with.average shear strengths of about 22.4 kg/cm 2 (318 psi) and about 19.3 kg/cm (274 psi) respectively under vacuum-pressure test. 5.5 Probable end uses of Gmelina arborea Veneer and Plywood From the findings of this study, Gmelina.arborea plywood is suited for the following uses: 5.5.1 Construction plywood Specific gravity in the range of 0.41 to 0.55, is one of the physical properties of. wood considered of.major importance for construc tion plywood (Lutz 1971). With a specific gravity of 0.41 + 0.027 as 12 1 Same as Japanese Standard •• hi:, s found for Gmelina.arborea in this study, the wood is marginally suitable for construction plywood. Shear strength is another mechanical property of major importance. From the glueline shear strength obtained in this study, therefore (Table 11), the wood is quite suitable for construction 2 plywood. This ranges between 239 - 405 psi (about 16.8 kg/cm - 28.5 2 kg/cm ) for the PF treatments that pass the various World plywood Standards already discussed. These shear strength values compare favour^ ably and in some cases more favourably (Hancock 1977c, Chow and Warren 1972, Walters 1973, Hse 1971) to the plywood shear strengths found from diverse studies for some woods used for construction plywood. Other essential considerations are moderate weight and ease of gluing. Lamb (1968) reported a density range of 30 to 31 lb,/cu-<,ft%> for Gmelina  arborea grown in Nigeria, India, Gambia and Malaysia. This, as he indicated, puts the wood in the right weight category for many uses. This study ;-has also demonstrated that the wood, glues easily depending on treatment combinations of peeling temperature, glue spread and closed assembly time. Therefore, Gmelina, arborea plywood may be considered suitable for building construction as subfloor, wall sheathing, roof sheathing and siding panels; overlaid panels; and concrete forms. 5.5.2 Core and Crossband veneer for decorative plywood Specific gravity is also one of the physical properties considered of major importance for core and crossband veneers for decora tive plywood (Lutz 1971). For such a use, a typical specific gravity range of 0.32 to 0.45 is required. The specific gravity of g'melina wood - 80 -(0.41 + 0.027) satisfies this requirement. On this basis, therefore, veneers from gmelina are quite suitable for use as core and crossbands for decorative plywood. As indicated by Lutz (1971), uniformity of wood structure is particularly desirable for crossband veneers meant to be used as decorative panels in order to minimize "telegraphing" of the grain to the face. Thus, diffuse-porous hardwoods like yellow birch and yellow-poplar have been reported as good veneer species. As a diffuse-porous hardwood, gmelina has been found from this study to yield relatively smooth veneers. Ease of gluing, straight and fine, uniform grain are other desirable veneer qualities when considering veneers for use as cores and crossbands for decorative plywood. As discussed in Section 2.1 and Section 3.2.3, gmelina wood satisfies these requirements. This seems to strengthen the suitability of gmelina wood for use as core and crossband veneers for decorative plywood for products like furniture, flush doors and case goods. 5.5.3 Container veneer and plywood Woods meant to be cut into veneers for use as container veneer and plywood are expected to possess the following physical and mechanical properties: specific gravity in the range of 0.36 to 0.65, light color, freedom.from odor, high stiffness (MOE), high shock resistance (MOR) and high strength in tension perpendicular to the grain. Since the only mechanical property measured in this study is the shear strength, it becomes difficult to access the gmelina veneers on the basis of MOE and MOR. However, on the basis of the shear strength and the physical pro perty involving specific gravity, color and odor (See Section 3.2.3), - 81 -gmelina wood is suitable.for use as container veneer and plywood. Since the veneers used for this study were not obtained from fresh-cut gmelina logs, it is difficult to assess the suitability of the wood for use as decorative veneer and plywood on the basis of attractive ness and figure. - 82 -6.0 SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION 6.1 Summary The data listed below contribute to the knowledge of the bonding characteristics of Gmelina arborea wood: 1. Even though the presence of a significant interacting effect may obscure interpretation of a significant main effect in a statistical analysis, the effects of the peeling temperatures used are nevertheless found highly significant regardless of glue type and bond quality testing method. 2. Similarly, the effects of the glue spreads used (a major factor in total cost of plywood manufacture) are found highly significant in 3 of the 4 ANOVA's for shear strength results. 3. Veneers of the highest peel-quality are produced with the 20°C (control) peeling temperature whereas the temperature of 85°C yields veneers of the lowest peel-quality. 4. Thus, the study has demonstrated that gmelina wood can be satisfactorily rotary-cut into good veneers without any prior heating. 5. Bond quality, in terms of percentage wood failure, is consistently reduced by increasing peeling temperature and is lowest at the peeling temperature of 85°C in all the UF and PF treatments used, reagrdless of bond quality testing method. 6. The peeling temperature of 20°C (control) gives the best bond quality results in terms of percentage wood failure in all the UF treatments used, regardless of type of bond quality - 83 -testing method. 7. In spite of the distinctive performance of the treatment combination of Spread 70 - Time 20 at the peeling temperature of 50°C, the treatments arising from the 20°C (control) peeling temperature also give the most impressive bond quality results in terms of percentage wood failure in all the PF treatments regardless of bond quality testing method. 8. Among the UF treatments used, ignoring glue spreads, those arising from the peeling temperatures of 50°C and 85°C give the highest shear strength values regardless of type of bond quality testing methods. In most cases, shear strength differences are marginal between these two peeling temperatures. 9. Among the PF treatments used, ignoring glue spreads, those arising from the peeling temperatures of 20°C and 85°C both give the highest shear strength values regardless of type of bond quality testing methods. 10. At the peeling temperature of 20°C (control), treatment combination of Spread 70 - Time 10 gives the most favourable bond quality among the UF treatments, regardless of type of bond quality testing method. However, the shear strength and percentage wood failure values developed are not significant at the 0.05 level from those given by treatment combination of Spread 55 - Time 20. Among the PF treatments, however, the treatment combination of Spread 70 - Time 10 develops a significantly higher shear strength than treatment combination of Spread 55 - Time 20, while the latter has a significantly - 84 -higher percentage wood failure in one of the bond quality testing methods used. 11. At the peeling temperature of 50°C, the highest percentage wood vfaiiureiisdeveloped with the treatment combination of Spread 70 -Time 20 regardless of glue type and bond quality testing method. 12. At the peeling temperature of 85°C, the highest shear strength is developed with the treatment combination of Spread 70 - Time 20 regardless of glue type and bond quality testing method. 13. All factors considered, the treatment combination of Spread 55 - Time 20, at the peeling temperature of 20°C (control), gives an impressive bond quality in all the UF and PF treatments used. 14. Five of the 12 PF.treatments used, regardless of type of bond quality testing method, pass the U.S. Plywood Standard; one passes the British Standard; while all pass the German Standard. On the other hand, five of the 12 UF treatments from vacuum-pressure test pass the U.S. Standard; two pass the British Standard; while all pass the German Standard. Furthermore, all the 12 UF treatments from dry test pass the U.S. Standard; six pass the British Standard; while all pass the German Standard. 15. From the results of this study, plantation-grown Gmelina  arborea wood, with a specific gravity of 0.41 + 0.027 (as determined), is suitable for use as construction plywood, core and crossband veneer for decorative panel as well as container veneer and plywood. - 85 -6.2 Suggestions for further studies Conclusive evidence has been presented for the suitability of Gmelina arborea wood for veneer and plywood production depending on the treatment combinations of wood peeling temperature, glue spread and 'closed assembly time. However, further work would be necessary to improve upon the bond quality achieved with the wood, especially using PF resin adhesive. Suggested areas of study are as follows: 1. Determination of the optimum peeling temperature. 2. Effects of veneer drying schedules on bonding characteristics of the wood. 3. Effects of assembly time (open and close), pressing time, temperature and pressure trials on bond quality. 4. Glue formulation and optimum glue spread trials. 5. 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Effect of degree of cure on the acid hydrolysis rates of formaldehyde glue-wood samples. Jour. Inst. Wood Sci. 4(5): 51-56. . , S^.ZijChow. 1972. A study on the cause for variation in plywood bond quality with open assembly time. For. Prod. Jour. 22(3): 55-58. Truax, T.R. 1929. The gluing of wood. U.S. Dept. of Agric, Tech. Bui. 1500. 23 pp. Walters, E.D. 1971. Sorting Southern pine green veneer to improve drying control. For. Prod. Jour. 21(11): 52-59. Walters, E.O. 1973. The effects of green veneer water content, dryer schedules, and wettability on gluing results for Southern pine veneer. For. Prod. Jour. 23(6): 46-53. Wangaard, F.F. and R.P. Saraos. 1959. Effect of several variables on quality of rotary-cut veneer. For. Prod. Jour. 9(6): 179-187. Wellwood, R.W. 1966. Forest Industries. Report to the govt, of Nigeria. FAO/UNDP, Rome. 64 pp. ±'.~j< Xhs 1975 Wcrid Wocd evjew- VJoi„d -99.-Yamagishi, Y., and Y. Honma. 1972. Study on the gluability of tropical woods.. I. Mixed use of.two different species in bonding some-, tropical woods. Japan Wood Ind., Wood Tech. Assoc. 27-11: 542-546. Zisman, W.A. 1963. Influence of constitution on adhesion. Ind. Eng. Chem. 55(10): 19-38. . 1965. Improving the performance of reinforced plastics. Ind. Eng. Chem. 57(1): 26-34. -100-Table 1. Descriptive features of logs used for study. the Gmelina arborea. Log Number Estimated' age from Growth Ring Count Noiotiknots present in 1 og Log d iameter* (cm) Bark th i ckness cm) Sapwood thickness (cm) Presence of Tension wood 1 8 5 22.2 4.1 2.8 Yes 2 !0 8 18.4 1.7 No 3 12 3 21.0 5.8 1.5 Yes 4 9 4 16.5 3.0 1 .8 Yes 5 10 6 19.1 4.6 2.0 No 6 8 5 19-7 4.3 2.7 Yes 7 9 5 18.4 5.3 1.7 Yes 8 10 7 19.7 5.8 1.5 No 9 12 20.3 3.6 1.8 Yes * Average for both ends of the log. 1 It was found convenient to use growth rings to estimate age of the logs since, as reported by Lamb (1968), growth rings are noted to be visible and usually annual for Gmelina arborea grown in Thailand. -101-Table 2. Initial and peeling moisture content {%) of the Gmelina arborea logs used for study. Log Peeli ng Initial MC Peeli ng MC Number temp( C) Sapwood Heartwood Corewood Sapwood Heartwood Corewood 2 20 90 124 132 124 132* 4 20 82 107 90 82 107 90* 8 20 96 114 104 96 - 114 104* 5 50 45 67 76 61 65 78 6 50 41 79 67 88 104 73 7 50 107 147 118 105 149 139 1 85 53 123 103 45 76 111 3 85 59 128 101 67 120 81 9 85 91 115 107 78 85 79 Since these logs were not heated, peeling MCs were not determined. They were assumed to be same as the initial MC previously determined. -102-Table 3. Specific gravity of the Gmelina arborea logs used for study. = Log Number 2 Log Average Specific Gravity Sample Mean Specific Gravity 1* 0.42 2 0.44 3* 0.37 Mean =0.41 SD3 = 0.027 0.43 5 0.38 6* 0.44 7* 0.41 8 0.41 g* 0.37 1 Determined by Volume Measurement Method. 2 Average for four test samples. 3 SD = Standard Deviation. * Logs with Tension wood (Identified by visual examination of Pith displacement). ) -103-Table 4. Water bath and log temperature changes against time of heating - 50 C. Nominal heating temperature: 50°cJ + 2°C Wood Temperature at core, 4 in from Wood Temperature Heating Water Bath Log Surface, at 1 in from the Period Temperature recorded by Log Surface, (hours) (°C) Thermocouples ( C) Est i ma ted 2 ( c) 0 21.5 17.8 18.8 1 46.6 20.1 27.9 2 46.4 25.3 30.7 3 45.6 30.1 36.0 4 45.0 33.9 37.7 5 48.8 36.9 42.2 6 52.9 38.0 47.9 7 53.0 39.8 50.0 8 54.4 41.6 51.8 1 A wood temperature of 50 C + 2 C was considered acceptable for the 50°C heating since it was difficult to control the temperature within the vat. 2 Using MacLean (1946) formulae -10^-Table 5. Water bath and log temperature changes against time of heating - 85 C. Nominal heating temperature: 85°C + 2°C Wood Temperature at core, 4 in from Wood Temperature Heat i ng Water Bath Log Surface, at 1 in from the Per iod Temperature recorded by Log Surface, (hours) (°0 Thermocouples ( C) Estimated^ ( C) 0 20.1 17.7 18.4 1 50.5 19.2 29.3 2 70.4 25.1 41 .4 3 81.6 45.0 60.0 4 81.4 60.1 64.3 5 81.5 64.9 68.0 6 81.5 67.4 72.5 7 81.6 68.9 76.2 8 81.5 69.9 77.5 9 81.4 70.8 78.8 10 ' 81.5 71.4 79.7 11 81.3 71.8 79.5 12 81.3 72.1 80.4 13 81.1 72.3 80.7 " 14 80.9 72.4 80.4 15 82.1 72.3 81.7 16 82.3 72.3 81.8 17 82.9 72.6 82.4 18 87.O 73.7 86.5 19 86.9 75.6 86.4 1 A Wood temperature of 85°C + 2°C was considered acceptable for the 85°C heating. 2 Using MacLean (1946) formulae. -105-Table 6. Lathe specifications for peeling: 1.27 mm (0.05 in) Gmelina arborea green veneer. 9 bolts sampled* Horizontal Gap 1.11 mm (O.Okk in) Vertical Gap 0.25 mm (0.010 in) Veneer Thickness 1.27 mm (0.05 in) Nosebar Type Solid nosebar Nosebar Face Angle 14° Knife Thickness 15-88 mm (5/8) in Knife Length 167-64 cm (66 in) Rockwel1 Hardness 56 Main Bevel 23° Cutting Angle (at 10-1/2 in) 89° 30' Speed of Cut 120 fpm Diameters of the bolts ranged between 16.5 cm (6.5 in) to 22.2 cm (8.8 in). -106-Table 1. Peel-quality attributes: Veneer roughness measurement. Total No.of Veneer sheets sampled Roughness in mm Frequency Scale Equivalent Equivalent Frequency % 20 C Peeling 175 0.000 0.005 0.010 0.00 0.13 0.25 0 143 32 0.0 81.7 18.3 50 C Peeling 194 0 1 2 3 0.000 0.005 0.010 0.015 0.00 0.13 0.25 0.38 2 65 120 7 1.0 33.5 61.9 3.6 85 C Peeling 173 0 1 2 3 4 0.000 0.005 0.010 0.015 0.020 0.00 0.13 0.25 0.38 0.51 0 26 132 13 2 0.0 15.0 76.3 7.5 1.2 -107-Table 8. Veneer peel-quality statistics. 1.27 mm (0.05~in) Gmelina arborea green veneer Veneer Attributes Peel ing temperature Mean SD* Max Min Range (mm) (mm) (mm) (mm) (mm) 1. Thickness 20°C (Control) 1.25 0.08 1.37 1.17 0.20 50°C (Heated 8 hr..) 1.22 0.10 1.32 1.04 0.28 85°C (Heated 19 hr.-,) 1.19 0.05 1.27 1.14 c0.13 2. Roughness 20°C (Control) 0.15 0.05 0.25 0.13 0.12 50°C (Heated 8 hr..) 0.21 0.07 0.38 0.00 0.38 85°C (Heated 19 hr. ) 0.24 0.06 0.51 0.13 0.38 N.B. Standard Deviation. -108-Table 9- Veneer moisture content prior to gluing. VENEER MOISTURE CONTENT {%) Sample VENEER PEELING TEMPERATURE CO Number 20 50 §5 1 6.6 6.8 7.4 2 7.3 5-9 6.2 3 6.5 6.1 5.5 4 6.4 7.3 6.3 5 7.3 6.4 . 6.6 6 5.7 6.4 6.4 7 6.7 6.0 7.2 8 7.2 6.9 6.4 9 6.0 6.0 6.0 10 5.8 6.5 5.8 Average 6.6 6.4 6.4 N.B. 1. CTH Room Conditions: Temperature = Dry bulb 80°F; Dew. Point 43°F Relative Humidity = 26%. 2. Time of conditioning in the CTH Room = 15 days. Table 10. Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Urea-Formaldehyde (UF) glue. DRY ' TEST VACUUM-PRESSURE TEST M i n imum Mini mum Mean Mean Spec imen No. of Mean Mean Spec imen No. of Treatments Shear Wood Wood Test Shear Wood Wood Test Strength Fa i1ure Fa i1ure Specimens Strength Fa i1ure Fa i1ure Specimens (psi) (*) (%) (psi) {%) (%) UF-20-55-10 306 57 20 34 264 38 10 34 UF-20-55-20 312 70 35 35 274 59 15 36 UF-20-70-10 332 62 30 28 260 56 15 36 UF-20-70-20 326 52 . 10 28 277 44 10 36 UF-50-55-10 312 53 10 22 295 33 10 25 UF-50-55-20 353 38 10 27 299 24 0 30 UF-50-70-10 334 40 10 24 253 18 5 23 UF-50-70-20 353 61 15 26 249 31 5 26 UF-85-55-10 362 39 15 30 295 24 0 36 UF-85-55-20 342 38 15 30 319 24 10 30 UF-85-70-10 381 35 10 23 281 11 0 29 UF-85-70-20 389 47 10 27 307 14 0 30 N.B. 1. Figures rounded to the nearest unit. 2. Treatment codes are as follows: e.g. UF-20-55-10 II -> Closed assembly time (min) » Glue spread (lb. IMDGL) ' > Peeling temperature (°C) • >Glue used (Urea-forma 1 dehyde) Table 11. Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Phenol-Formaldehyde (PF). VACUUM PRESSURE TEST BOIL-•DRY-BOIL TEST Minimum Minimum No. of Mean Mean Specimen No. of Mean Mean Specimen Shear Wood Wood Test Shear Wood Wood Test Treatments Strength Fa i 1 u re Failure Specimens Strength Failure Fa i1ure Specimens (psi) (%) (S) (psi) (*) {%) PF-20-55-10 346 20 0 36 288 21 5 35 PF-20-55-20 318 45 15 30 255 43 10 34 PF-20-70-10 397 31 10 31 322 38 10 33 PF-20-70-20 337 3*» 10 30 276 31* 10 28 PF-50-55-10 309 16 0 25 247 12 0 26 PF-50-55-20 313 45 10 22 239 46 10 23 PF-50-70-10 354 20 0 35 304 30 5 35 PF-50-70-20 317 64 30 30 258 66 10 30 PF-85-55-10 321 7 0 36 259 12 0 33 PF-85-55-20 330 19 5 28 286 16 5 35 PF-85-70-10 382 15 0 29 315 16 0 22 PF-85-70-20 405 10 0 36 334 16 0 31 o I N.B. 1. Figures rounded to the nearest unit, 2. Treatment codes are as follows: e.g. PF-20-55-10 L -> Closed assembly time (min) •> Glue spread (lb/MDGL) "> Peeling temperature (°C) Glue used (Phenol-formaldehyde) Table 12. Within - and between - panel variation in bond quality of 5~ply Gmelina arborea. Plywood bonded with UF glue: Dry test wood failure. Mean Wood Failure {%) Max.Wood Failure {%) Min.Wood Fa i1ure Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 UF-20-55-10 38 72 62 55 100 95 20 50 35 35 50 60 UF-20-55-20 77 69 63 95 95 85 55 55 35 40 40 50 UF-20-70-10 60 51 76 90 90 95 35 40 50 55 50 45 UF-20-70-20 43 57 51 85 90 90 10 25 20 75 65 70 UF-50-55-10 56* 46* 57 70 95 95 40 10 20 30 85 75 UF-50-55-20 .29* 47, 35* 45 80 90 15 15 10 30 65 ' 80 UF-50-70-10 52* 23* 36 95 40 75 10 10 10 85 30 65 UF-50-70-20 65* 49* 71 95 90 95 30 15 45 65 75 50 UF-85-55-10 37 43 36 55 60 60 20 15 20 35 45 40 UF-85-55-20 25 48 47 45 90 100 15 15 15 30 75 85 UF-85-70-10 19 34 46 40 85 70 10 10 15 30 75 55 UF-85-70-20 47 48 46 90 75 75 20 10 15 70 65 60 N.B. * Panels with yellow birch veneers as faces and backs. 1. Figures rounded to the nearest unit. 2. The Grand Mean Wood Failure of the Means of the above 3 panels for a particular treatment may not be same as in Table 10 due to rounding. 3. Panels 1, 2 and 3 above are same as those in Table 13, respectively. Half of the test samples from each panel was used for the above.test while the other half was used for the test in Table 13. Table 13- Within - and between - panel variation in bond quality of 5~ply Gmelina arborea Plywood bonded with UF glue: Vacuum-pressure test, wood failure. Mean Wood Failure ft) Max. Wood Failure ft) Min.Wood Failure ft) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 UF-20-55-10 44 42 32 70 70 55 10 10 15 60 60 40 UF-20-55-20 60 67 51 95 95 90 25 20 15 70 75 75 UF-20-70-1.0 81 70 37 100 90 65 50 30 15 50 60 50 UF-20-70-20 42 31 58 90 60 95 10 10 20 80 50 75 UF-50-55-10 24* 38* 35 35 55 75 '5 20 10 20 35 65 UF-50-55-20 12* 47 14* 40 60 55 5 30 0 35 30 55 UF-50-70-10 23* 17* 11 85 55 15 10 5 5 75 50 10 UF-50-70-20 16* 6* 68 40 10 85 5 5 35 35 5 50 UF-85-55-10 11 39 21 30 65 50 0 0 0 30 65 50 UF-85-55-20 15 38 20 35 75 45 10 10 10 25 65 35 UF-85-70-10 7 7 18 20 20 60 0 0 0 20 20 60 UF-85-70-20 • •-10 19 9 35 75 40 0 0 0 .75 40 N.B. * Panels with yellow birch veneers as faces and backs. 1. Figures rounded to the nearest unit. 2. Because of rounding, the Grand Mean Wood Failure of the means of the above 3 panels for a particular treatment may not be same as in Table 10. Table 14. Within - and between - panel variation in bond quality of 5~ply Gmelina arborea. Plywood bonded with PF glue: Vacuum-pressure test, wood failure. Mean Wood Failure (%) Max.Wood Failure (%] ) Min.Wood Fa i1ure (*) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 PF-20-55-10 28 13 13 75 30 35 5 0 0 70 30 35 PF-20-55-20 . 39 51* 49* 80 80 80 15 25 30 65 55 50 PF-20-70-10 37 32 25 80 60 85 10 10 10 70 50 75 PF-20-70-20 18 45 37 45 80 75 10 15 10 35 65 65 PF-50-55-10 3 6 35 10 ' 15 80 0 0 0 10 15 80 PF-50-55-20 38 31 52 90 75 95 10 10 10 80 65 85 PF-50-70-10 21 8* 29* 50 25 70 0 0 0 50 25 70 PF-50-70-20 64 68* . . 52* 95 95 80 35 30 35 60 65 50 PF-85-55-10 6 8 7 .10 30 45 0 0 0 10 30 45 PF-85-55-20 24 24 * 13 50 75 40 5 5 5 45 70 35 PF-&5-70-10 15 28 8 30 65 30 5 5 0 25 60 30 PF-85-70-20 4 3 18 15 10 55 0 0 0 15 10 55 N.B. * Panels with yellow birch veneers as faces and backs 1. Figures rounded to the nearest unit. 2. The Grand Mean Wood Fa i 1 ure of the means of the above 3 panels for a particular treatment may not be the same as in Table due to rounding. 3. Panels 1, 2 and 3 above are same as those in Table 15 respectively. Half of the test samples of each of the panel was used for the above test while the other half was used for the test in Table 11. Table 15. Within - and between - panel variation in bond quality of 5~ply Gmelina arborea Plywood bonded with PF glue: Boi1-dry-boi1 test, wood failure. Mean Wood Failure {%) Max.Wood Failure {%) Min.Wood Fa i1 lure (%) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 PF-20-55-10 31 12 12 90 35 20 5 5 5 85 30 15 PF-20-55-20 35 . 42* . 53* 90 . 75 90 10 15 10 80 .60 80 PF-20-70-10 39 "49 32 90 75 80 10 15 10 80 65 70 PF-20-70-20 27 44 32 80 95 80 10 10 10 70 85 70 PF-50-55-10 5 13 14 20 55 40 0 0 0 20 55 40 PF-50-55-20 23 19 69 90 45 95 10 10 25 80 35 70 PF-50-70-10 29 24* 34* 40 55 90 5 10 5 35 45 80 PF-50-70-20 18 85* 82* 55 100 95 10 50 70 45 50 25 PF-85-55-10 20 12 7 55 45 25 0 0 0 55 45 25 PF-85-55-20 11 22 13 15 55 40 5 5 5 10 50 35 PF-85-70-10 14 6 22 45 10 55 0 0 0 45 10 55 PF-85-70-20 1 21 . ' 18 45 35 60 0 0 0 45 35 60 N.B. * Panels with yellow birch veneers as faces and backs. 1. Figures rounded to the nearest unit. 2. The Grand Means of the three means above may not be same as in Table 11 due to rounding. -115-Table 16. Analysis of variance for testing the effects of peeling temperature, Glue Spread and Closed Assembly Time on UF Glue bond quality in 5~ply Gmelina arborea Plywood: Dry test. Shear Strength r . . Degrees q^ Mean F • Source or variation or j _ ~i n . . _ , Square Square Ratios ... Freedom • Peeling temperature (PT) 2 Glue Spread (GS) 1 Closed Assembly Time (AT) 1 PTxGS 2 PTxAT 2 GSxAT 1 PTxGSxAT 2 Error 252 Total 263 0.l6784Exl06 83920. 31 .26** 35887. 35887. 13 .37** 2920.0 2920.0 1. 22 6532.1 3266.1 1. 09 19442. 9721.1 3. 62* 541.23 541.23 0. 20 13396. , 6698.O 2. 50 0.67649x10° 2684.5 0.92304x1.0 Wood Fa i1ure Degrees _ c u c £ . ^. r Sum of Mean F Source of variation or _c D . Square Square Ratios Freedom Peeling temperature (PT) 2 18612 9306.2 18.12** Glue Spread (GS) 1 8.0152 8.0152 0.02 Closed Assembly Time (AT) 1 558.55 558.55 2.71 PTxGS 2 2782.4 1391.2 1.09 PTxAT 2 1183.9 591.95 1.15 GSxAT 1 1256.7 1256.7 2.45 PTxGSxAT 2 9459.4 , 4729.7 9.21** Error _ 252 0.12941x10? 513.54 Total 263 0.16327x10 Significant at the 0.01 level. Significant at the 0.05 level. -116-Table 17. Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF Glue bond quality in 5_ply Gmelina arborea. Plywood: Vacuum-pressure test. Shear Strength Degrees _ c u r r . . ..j. Sum or Mean F Source of variation '.or _ . D . Square Square Ratios Freedom Peeling Temperature (PT) 2 44448.0 22224.0 5.7269** Glue Spread (GS) 1 19605.0 19605.0 5.0518* Closed Assembly Time (AT) 1 9636.5 9636.5 2.4832 PTxGS 2 34173.0 17087. ~ 4.4030** PTxAT 2 IOO69.O 5034.5 1.2973 GSxAT 1 352.37 352.37 0.90800E-01 PTxGSxAT 2 1778.0 , 889.O 0.22909 Error 252 0.97794x10° 3880.7 Total 263 0.10980x10 Wood Fa i1u re Source of variation Degrees .of Freedom Sum of Square Mean Square F Rat ios Peeling Temperature (PT) 2 44537.0 22269.0 49.693** Glue Spread (GS) 1 3000.4 3000.4 6.6954** Closed Assembly Time (AT) 1 606.06 606.06 1.3524 PTxGS 2 3114.4 1557.2 3.4749* PTxAT 2 196.21 98.106 0.21893 GSxAT 1 836.74 836.74 1.8672 PTxGSxAT 2 6993.9 , 3497.0 7.8036** Error 252 0.11283x10° 448.12 Total 263 0.17221x10° Significant Significant at the 0.01 level. at the 0.05 level. -117-Table 18. Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on PF Glue bond quality in 5-ply Gmelina arborea Plywood: Vacuum-pressure test. Shear Strength Source of variation Degrees of Freedom Sum of Square Mean Squa re F Rat ios Peeling Temperature (PT) 2 55543.0 27772.0 9-5261** Glue Spread (GS) 1 84209.0 84209.0 28.885** Closed Assembly Time (AT) 1 19605.0 19605.0 6.7247** PTxGS 2 19768.0 9884.2 3.3904* PTxAT 2 36216.0 18108. 6.2113** GSxAT 1 1675.1 1675.1 0.57458 PTxGSxAT 2 6295.6 , 3147.8 1.0797 Error 252 0.73466x10? 2915.3 Total 263 0.95797xlOb Wood Fa i1 u rs \ Source of variation Degrees of Freedom Sum of Square Mean Square F Ratios Peeling Temperature (PT) 2 28089. 14044. 31.326** Glue Spread (GS) 1 1209.2 1209.2 2.6971 Closed Assembly Time (AT) 1 22644. 22644. 50.507** PTxGS. 2 1630.9 815.44 1.8188 PTxAT 2 14796. 7398.0 16.501** GSxAT 1 329.64 329.64 0.73525 PTxGSxAT 2 5041.1 , 2520.5 5.6220** Error 252 0.11298x10; 448.34 Total 263 0.18672x10 Significant at the 0.01 level. Significant at the 0.05 level. -118-Table 19- Analysis of variance for testing the effect of Peeling Temperature,' Glue Spread and Closed Assembly Time on PF Glue bond quality in 5-ply Gmelina arborea Plywood: Boi1-dry-boi1 test. Shear Strength Degrees _ ^ u r r r Sum of Mean F Source of variation of _ _ D .. , Square Square Ratios Freedom Peeling Temperature (PT) 2 49995. 24997. 9.16** Glue Spread (GS) 1 99103. 99103. 36.31** Closed Assembly Time (AT) 1 35352. 35352. 12.95** PTxGS 2 7302.8 3651.4 1.34 PTxAT 2 47467. 23734. 8.69** GSxAT 1 2578.1 2578.1 0.94 PTxGSxAT 2 20499. , 10250. 3.76 Error 252 0.68786x10^ 2729.6 Total 263 0.95015x10° Wood Failure Degrees _ c u „ r Sum of Mean Source of variation ot _c D-.4--~,-^ , Square Square Ratios Freedom Peeling Temperature (PT) 2 30012. 15006. 27.581** Glue Spread (GS) 1 3864.0 3864.0 7.1021** Closed Assembly Time (AT) 1 17837. 17837. 32.784** PTxGS 2 6021.2 3010.6 5.5335** PTxAT 2 9821.2 ; 4910.6 9.0258** GSxAT 1 985.23 985.23 1.8109 PTxGSxAT 2 2354.5 6 1177.3 c 2.1638 Error 252 0.13710x10? 544.07 Total 263 0.20800x10 Significant at the 0.01 level. Significant at the 0.05 level. -119-Table 20. Duncan's Multiple Range test for Shear Strength of Gmeli na arborea. Plywood bonded with UF Glue. TREATMENT RANKING Dry Test 1 2 5 4 3 7 10 6 8 9 11 12 Treatment Mean2 306 312 312 326 332 334 342 353 353 362 381 398 Vacuum Pressure Test 8 7 3 1 2 4 11 5 9 6 12 10 Treatment Mean2 249 253 260 264 274 277 281 295 295 299 307 319 N.B. 1. Means underscored by the sam the 5% level of significance 2. Numbers above means refer to 1 UF-20-55-10 2 UF-20-55-20 3 UF-20-70-10 4 UF-20-70-20 5 UF-50-55-10 , 6 UF-50-55-20 line are not significantly different at treatments as follows: 7 UF-50-70-10 8 UF-50-70-20 9 UF-85-55-10 10 UF-85-55-20 11 UF-85-70-10 12 UF-85-70-20 -120-Table 21. Duncan's Multiple Range test for Wood Failure of Gmelina arborea. Plywood bonded with UF Glue. Dry Test TREATMENT RANKING 11 10 6 9 7 12 Treatment Mean2 35 38 38 39 40 47 ' 52 53 57 61 62 70 Vacuum Pressure Test 11 12 7 6 9 10 8 5 1 4 3 2 Treatment Mean2 11 14 18 24 24 24 31 33 38 44 56 59 N.B. 1. Means underscored by the same line are not significantly different at the 5% level of significance. 2. Numbers above means refer to treatments as follows: 1 UF-20-55-10 7 UF-50-70-10 2 UF-20-55-20 8 UF-50-70-20 3 UF-20-70-10 9 UF-85-55-10 4 UF-20-70-20 10 UF-85-55-20 5 UF-50-55-10 1 11 UF-85-70-10 6 UF-50-55-20' 12 UF-85-70-20 -121-Table 22. Duncan's Multiple Range Test for Shear Strength df Gmelina arborea. Plywood bonded with PF Glue. T R E A T M E N T R A N K I N G Vacuum Pressure Test 5 6 8 2 9 10 4 1 7 113 12 Treatment Mean2 308 313 317 318 321 330 337 346 354 382 397 405 Boi1-dry-boi1 Test 6 5 2 8 9 4 10 1 7 11 3 12 Treatment Mean2 239 247 255 258 259 276 286 288 304 315 322 334 N.B. 1. Means underscored by the same line are not significantly different at the 5% level of significance. 2. Numbers above means refer to treatments as follows: 2 3 4 5 6 PF-20-55-10 PF-20-55-20 PF-20-70-10 PF-20-70-20 PF-50-55-10 PF-50-55-20 7 8 9 10 11 12 PF-50-70-10 PF-50-70-20 PF-85-55-10 PF-85-55-20 PF-85-70-10 PF-85-70-20 -122-Table 23. Duncan's Multiple Range test for Wood Failure of Gmelina arborea. Plywood bonded with PF Glue. TREATMENT RANKING Vacuum Pressure Test 9 12 11 5 10 1 7 3 4 2 6 8 Treatment Mean2 7 10 15 16 19 20 20 31 34 45 45 64 Boi1-dry-boi1 Test 5 9 10 11 12 1 7 4 3 2 6 8 Treatment Mean2 12 12 16 16 16 21 30 34 38 43 46 66 N.B. 1. Means underscored by the same line are-not significantly different at the 5% level of significance. 2. Numbers above means refer to treatments as follows: 1 PF-20-55-10 2 PF-20-55-20 3 PF-20-70-10 4 PF-20-70-20 5 PF-50-55-10 6 PF-50-55-20 7 PF-50-70-10 8 PF-50-70-20 9 PF-85-55-10 10 PF-85-55-20 11 PF-85-70-10 12 PF-85-70-20 -123-Sapwood Test Sample Heartwood Test Sample Heartwood Test Sample Corewood H„ Test Sample Thus, there are four test samples per log. The centre Sample is used for moisture content determination Used for Specific gravity. Figure 1. Pattern of cut of Test Samples from Logs for Specific Gravity and Moisture Content Determination Tests. -124-Figure 2. "Temperature Changes within a log 8ft long and 7.7 in diameter (50°C Heating). -125-4 ^ ' ' -n r-i 10 12 14 16 18 19 Heating Time (hr) Figure 3. 100 -, 80 -\ 60 -J ko-20-\ '20° CC Pee 1ed Venee r s 0 5 10 Visual roughness (.001 inch) 50°C Peeled Veneers T T 20 0 5 10 15 Visual roughness (.001 inch) Figure k. Frequency distribution of visual veneer roughness. 85°C Peeled Veneers 5 10 15 20 25 Visual roughness (.001 Inch) -127-Figure 5. Dependence of bond quality on Peeling Temperature - a nd C'i osed A; s:s emb 1 y T i meI h t-e ra c t i 6n -U F ~ D ryr Te s t (Shear Strength). -128-<u u 3 o o 70 60 50 40 i 30 0 0 20 40 60 Reeling Temperature. ..(.°'C) . Spread 70-Time 20 ^Spread 55-Time 20 Spread 55-Time 10 Spread 70-Time 10 80 100 Figure 6. •Dependence' of bon'd quality on Peeling Temperature, Glue spread and Closed "Assembly Time Interactions -UF Dry Test (Wood Failure). -129-~1 ' -r r- ,' V SO ,00 Peeling Temperature (°C ) Dependence of bond quality on Peeling Temperature ancl"G1 ue Spread "I ntferacV\Ion-OF5-Vaeuum-pressurre^Test (Shear Strength). -130-Spread 55 lb/MDGL Spread 70/lb/MDGL 0 20 40 60 80 Peeling Temperature Figure 8? Dependedceuof bbn'd qual i'ty'on»Peel ing' Temperature V'.nreerf aaaanduS'lue;Spread _ I htecaction-UFtJ/aGUum-pressure Test , ft (Wood Fai lure) . -131-0 ' - 1 , , , -, 0 20 40 60 80 100 Peeling Temperature (?C) Figure '9. Dependence of bond quality on Peeling Temperature, Glue Spread and Closed Assembly Time Interactions -UF vacuum-pressure Test (Wood failure). -132-500 -, ~ 1+00 in Q. c 1_ Z 300 H ro > I 20 40 60 Peeling Temperature Spread 70 lb/MDGL Spread 55 lb/MDGL 80 100 Figure 10. Dependence of bond quality on Peeling Temperature and Glue Spread Interaction-PF Vacuum-pressure Test (Shear Strength). •133-in o. cn c 500-1 4ooH 300 H Time 20 min. Time 10 min. 20 40 60 Peeling Temperature S(°.G') 80 100 Figure 11. Dependence of bond quality on Peeling Temperature and Closed Assembly Time Interaction-PF Vacuum-pressure Test (Shear Strength). -13**-Figure 12. Dependence of bond quality on Peeling Temperature 'and .'Oiro's'e'd' Assembly .;T:ime;tl"nteraiction-rPF Vacuum-pressure Test (Wood Failure). -135-70 60 i 50 3 -a O o 30 J 20 _J 10 -4 Spread 55" Time 20 Spread 70-Time 10 Spread 70-Time 20 Spread 55"Time 10 T 20 kO 60 Peeling Temperature (°(C)), 80 100 Figure 13- Dependence of bond quality on Peeling Temperature, Glue Spread and Closed Assembly Time Interaction -PF Vacuum-pressure Test (Wood Failure). -136-D-c 400-1 300 H 200 H 20 r 40 Time 20 min. -©T i me 10 min. T 60 80 Peeling Temperature (°6)v 100 Figure 14. Dependence of bond quality on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Shear Strength). -137-Figure 15. Dependence of bond quality on Peeling Temperature and Glue Spread Interaction-PF Boi1-dry-boi1 Test (Wood Fa i1ure). -138-60 -i 20 40 60 80 100 Peeling Temperature (°'C,) Figure 16. Dependence of bond quajity on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Wood Failure). -139-APPENDIX 1 B. S. 1455:1963 Specification for Plywood manufactured from Tropical Hardwoods. -140-SPECIFICATION FOR PLYWOOD MANUFACTURED FROM TROPICAL HARDWOODS B.S. 1455 : 1963 Price 10/6 net BRITISH STANDARDS INSTITUTION INCORPORATED BY ROYAL CHARTER BRITISH STANDARDS HOUSE, TELEGRAMS: STANDARDS AUDLEY LONDON TELEPHONE: MAYFAIR 9000 -141-B.S. 1455 CONTENTS _o-operating organizations Foreword . . . . ' . Page . 2 . 5 SPECIFICATION 1. Scope . . 2. Definitions 3. Grade . 4. Cores . . .......... 6 .......... 6 .......... 6 . 6 5. Assembly of veneers 6 6. Bonding . . . .6 7. Delamination 7 8. Removal of metal clips 7 9. Scarf joints in boards . 1 10. Testing the quality of the adhesion and the kind of bonding in the plywood 7 11. Moisture content. . . ... . . . . . ^ 12. Dimensions of plywood boards 7 13. Finishing . . . . . ... . . . . 8 14. Re-testing. . . . . . ...... 8 15. Marking ............ 8 Page . APPENDICES A. Selection of samples from a consignment for testing B. Method of making the tests and assessing the results C Method of applying the knifc-test.... . D. Method of determining moisture content. . . TABLES 1. Schedule of tests for proving compliance of the plywood with the requirement of its declared bonding . . . . . 2. Wet tests in hot water or steam. . . ... . . . 16. Manufacturer's warranty 8 IV. Bond quality No. V. Bond quality No. VI. Bond quality No. VII. Bond quality No. VIII. Bond quality No. 9 10 10 7 9 PLATES I. Tool for the knife-testing of plywood . . . 11 II. Knife-testing plywood. ...... 11 HI. Bond quality No. 10' 8 in the Master Scale for 6 ^ assessing bond quality At in plywood by the knife . test . . . . . 14-19 -142- B.S. 1455 BRITISH STANDARD SPECIFICATION FOR PLYWOOD • ' MANUFACTURED FROM TROPICAL HARDWOODS FOREWORD This British Standard prepared under the authority of the Timber Industry Standards Committee specifies requirements for plywood manufactured from tropical hardwoods and suitable for all general purposes. Although the scope of the previous issue was not restricted to tropical hardwoods, in practice these were the only species used for plywood manufacture in the U.K. This standard does not specify requirements for blockboards or plywood faced with decorative veneer nor certain specialitymateriais, some of which are covered by the following British Standards: B.S. 6V3. High strength plywood for aircraft. B.S. V35. Medium and low strength plywood for aircraft purposes. B.S. 10S3. British-made plywood for marine craft. ( B.S. 3444. Blockboard and laminboard. B.S (in course of preparation) Plywood treated with preservatives or flame retardants or both. SPECIAL NOTE In this revision the restriction of applicability of this British Standard to British-made material has been removed. While this allows oversea producers, who supply by far the greater part of the plywood used in the United Kingdom, to comply with the standard if they so wish, it should be borne in mind that the traditional suppliers to this country work to gradings, sluing standards and tests of their own which are well known in the U.K. market. The conditions of these are dictated by the woods available and internal requirements of the particular producing country. If users in the United Kingdom require plywood from overseas producers'whose manufacture does not comply with this standard, they should consult their suppliers as to the material most nearly equivalent to the requirements of this standard. Information as to the species, producing countries, sizes, grading and bonding of plywood commonly available in the United Kingdom is given in B.S. ?493,' Information about plywood '. The requirements have been modified in the light of experience, and the descriptions of adhesives in Clause 6 have been orought into conformity with those in B.S. 1203*. The dry test has been deleted as experience shows that the wet tests, and the mycological tests when appropriate provide sufficient control of bond quality. The term4 Grade ' used in this specification refers to the quality of the veneers forming the face and back of the plywood. According to the defects they contain, er.cli of the veneers classified by a number or symbol and the combination of these (e.g. 1 - 2, 2 - 2, or i) defines the grade of the plywood. The standard neither specifies nor gives advice upon the species of the timbers for plywood manufacture. Sources of supply and supplies themselves vary considerably over short periods, and any list of' approved * umbers would not only have to be long to bo comprehensive, but might well, by the omission of their names, piejudice the introduction of additional kinds. Purchasers and manufacturers should agree between themselves on the species that are to be used, having regard to the purpose for which the plywood is intended, particularly where immunity to insect attack is essential. The term ' Bonding * in this standard refers solely to the type of adhesive used in the manufacture of the plywood. It should be understood that although some types of adhesive have, over a period of years, proved themselves adequate to resist full exposure to weather, they do not impart this quality to the plywood as a material. It follows that when plywood is to be exposed to weather or to other severe conditions, not only must the appropriate type of adhesive be employed in its manufacture, but also the wood component must be of a suitable species or be treated with fungicidal or insecticidal preservatives, paints or other surface coatings according to circumstances. This standard does not cover such treatment or coating, which should be the subject of special arrangement between the parties concerned. Some of the te>ts for the compliance of the plywood with the bonding requirements (Clause 6 and the Appendices) arc of necessity somewhat lengthy and troublesome to make. The warranty (Clause 16) does not necessarily mean that the manufacturer has carried but all tlie tests set out in the Appendices, but, in cases of doubt or dispute, these Appendices enable the purchaser or an arbitrator to satisfy himself that the warranty is substantiated or otherwise. NOTE I. Where metric equivalents are given, the British units arc to be regarded as the standard. The metric equivalents arc approximate. More accurate conversions should be based on the tables in U.S. 330, * Conversion factors and tables *. NOTE 2. In place ofthc customary, but incorrect, use of the pound and kilopramm'e as units of force, the units called pound-force (abbreviation Ibf) and kilogramme-force (abbreviation kgf) have been used in this standard. These are forces which when acting on a body of mass one pound, or kilogramme respectively, give it an acceleration equal to that of standard gravity. ° B.S. 1203, * Synthetic resin adhesives (phenolic and aminoplastic) for plywood. * . 1455 : 1963 -143-SPECIFICATION SCOPE 1. This British Standard covers plywood for general purposes manufactured from, tropical hardwoods with rotary-cut or sliced veneers bonded together with an adhesive. The term 'plywood' is intended to include ' multi-ply'. DEFINITIONS 2. For .the purposes of this standard the definitions in B.S. 565, * Glossary of terms relating to timber and wood work', apply with the following modifications: Bonding. See Gluing. Discoloration. Areas, occurring in either streaks or patches, of colour different from that of the surrounding wood and differing from that normally associated with the species. Cluing. The process of uniting, by means of an adhesive, two or more pieces of wood. When used without qualification the t?nn implies a process characterized by continuity of the union over the whole of the areas of contact Rotary Cut {Peeled). (Veneer) produced in a continuous sheet by feeding a knife mounted parallel to the axis into ' a log rotating in a lathe. Cf. Sliced. Sliced {Flat cut). (Veneer) cut sheet by sheet from a stationary block of wood by a knife mounted approx imately parallel with and moving to and fro across the longitudinal axis of the block. In some machines the knife is fixed and the block moves. Cf. Rotary cut. GRADE 3. Plywood shall be graded according to the appearance of the face and back, each being assessed separately after the board has been made and not when in the form of veneer as defined in Clause 2. Grades of veneer are defined as follows: Grade 1 veneer. Grade 1 veneer shall be of one or two pieces of firm smoothly cut veneer. When of two pieces the joint shall be approximately at the centre of the board. The veneers shall be reasonably matched for colour. The veneer shall be free from knots, worm and beetle holes, splits, dote, glue stains, filling or inlaying of any kind or other defects. No end joints are permissible. Grade 2 veneer. Grade 2 veneer shall present a solid surface free from open defects. When jointed, veneers need not necessarily be matched for colour or be of equal width. A few sound knots are permissible, with occasional minor discoloration and slight glue stains and isolated pinholes not along the plane of veneer. Occasional splits not wider than Yit in (0.8 mm) at any point and not longer than one tenth of the length of the panel or slightly ojvned joints mi™ b« filled with a suitable filler. This grade shall admit neatly made repairs consisting of inserts of the same species as the veneer, which present solid, level, hard surfaces and are bonded with an adhesive equivalent to that used for bonding the veneers. No end joints are permissible. NOTR. Grade 2 venyer excluding pinhole* can be supplied l»y agreement between purchaser and 'supplier. Grade 3 veneer. Grade 3 veneer may include wood defects, including worm-holes, which are excluded from Grades I and 2 in number and si/.o which do not impair the serviceability of the plywood. It may also include manu facturing defects, such as rough cutting, overlaps, gaps or splits, provided these do not affect the use of the plywood. No end joints are permissible. Other grades. Other grades, appropriate to the end use, may be agreed between purchaser and supplier. CORES 4. Core veneers may contain knots, open defects, gaps, overlaps or pleats, provided such defects will not cause undulations or impair the smooth finish of the surfaces required for painting or staining. No end joints are permissible. In the cores of plywood faced on at least one side with Grade 1 or Grade 2 vcr.cer, open defects and gaps in the ply adjacent to the. Grade 1 or Grade 2 vcr.cer shali not exceed Mo in (2.5 mm). It shall be at the purchaser's option to accept .the manufacturer's warranty of compli ance (Clause 16) or to inspect the veneers before the plywood is assembled. ASSEMBLY OF VENEERS '5. Unless otherwise specified by the purchaser, the direction of the grain of the veneer shall be at right angles in adjacent plies, except in the case of boards compiling an even number of plies, when the grain of the centre pair shall follow the same direction. The veneers forming any one ply and the corresponding ply on the opposite side of the central plane of the board shall be of the same thickness and species or of species known to be similar to one another in physical character istics, and shall be cut by the same method, i.e. either all. totaiy-cut o." sliced. The tight side of the veneer should be turned outwards in faces and backs. Tapes shall not be used internally. When used for making edge joints or repairing splits in face veneers they shall be removed subsequently. This paragraph shall'apply unless otherwise agreed between purchaser and supplier. Ail plywood thicker than % in (10 mm) shall be made of not less than 5 plies. The core in 3 ply shall be not more than 60 per cent of the total thickness: for panels with more than three plies, the laces, and all plies running in the same direction as the faces, shall have a total or combined thickness of not less than 40 per cent and not more than 65 per cent'of the total thickness of the panel. In the dry state, no face ply shali be thicker than \s in (3 mm) and no inner ply shall exceed ?ie in (5 mm). BONDING 6. Bonding between veneers shall be WBP, BR, MR or INT defined* as follows, and these designatory letters siiiiil be toed in uiaiking iiic ply wOvu. •These designations are those used in D.S. 1203, 'Synthetic resin adhesives (phenolic and aminbplastic) for plywood". 6 -144- B.S. 1455 : Tvpr t!/?/'.- V'fdihci und hoil-pioof. Adhesives of the type'- which by systematic tests and by their records in bcrviic oxer ni;inv vr.irs h;ivi» heen nrovrd to n-iakr. joints '•:«*.hly resistant to weather, micro-organisms, cold and .ling water,steam and dry lieat. Type BR: Boil, resistant. Joints made with these adhesives have good resistance to weather and to the boiling water test, but fail under the very prolonged exposure to weather that Type WBP adhesives will survive. The joints will withstand cold water for many years and are highly resistant to attack by micro-organisms. Type MR: Moisture-resistant and moderately weather-resistant. Joints made with these adhesives will survive full exposure to weather for only a few years. They will withstand cold water for a long period and hot water for a limited time, but fail under the boiling water test. They arc. resistant to attack by micro-organisms. Type INT: Interior. Joints made with these adhesives arc resistant to coid water but are not required to with stand attack by micro-organisms. 0ELAMTNATION 7. The glue bond between individual plies shall be adequate"}- and continuous over the entire area. Any board showing delaminatibn or blistering does not comply with the requirements of this standard. REMOVAL OF METAL CLIPS 8. All metal clips used for assembly during the manufacture of board shall be extracted or cut away in trimming before delivery. SCARF JOINTS (N BOARDS 9. When sizes larger than available press sizes are required, scarf joints through the thickness of the board shall be permitted by agreement with the purchaser. All scarf joints shall be bonded with the equivalent type of adhesive used for the manufacture of the boards themselves, and shall be made with the following inclina tions: a. Board under Vi. in (13 mm) thick: Tin 10. b. Board Vi in (13 mm) thick and over: 1 in 8. NOTE. It should be noted thrst the glue line of any scarf joint is visible on the surface of the board. TESTING THE QUALTTY OK THE ADHF.SION AND THE KIND OF BONDING LN THH rj.YV.OOD 10. The appropriate tests for adhesion in the four kinds of bonding arc set out in Table 1, which gives the requirements for the particular appendices concerned. . present only certain phenolic adhesives have been shown to inert this requirement. t I'or interpretation of * adequate * see Clause 10 and appendices referred to therein. TABU' 1. SCHEDULE OF TESTS FOR PROVING COMPLIANCE OF THE PLYWOOD WITH THE RFOniRF.MF-NT OF ITS DECLARED BONDING The letters show the appendices giving details of the tests. A dash indicates thatthe test named in the column is not applicable. 1 Tests Donding ! Wet test in hot water or I fleam 1 Wet test in cold water Mycolo;;ical test WBP 1 j A, Bl, C A, B2o, C A. B3 BR j A, Bl, C • A, B&j, C A, B3 MR i A, Bl. C j A, B2o, C A, B3 INT ! - A, B26 — • When the adhesion of the plywood is tested by the methods described in Appendices A, B and C the results of the tests shall be as follows: Bonding WBP, BR and MR. The wet test in hot water or steam. (Appendix Bl) and the wet test in cold water (Appendix B2o). No glue line shall have a bond quality®  of less than two, and the average value for all those tested  shall be not less than five. Bonding INT. The wet test in cold water (Appendix B2b). At the conclusion of the test, none of the test pieces shall show any delamination, blistering on the surfaces or separation of the joints between veneers at the edges. Bonding WBP,. BR and MR. The mycological test (Appendix B3). At the conclusion of the test none of the test pieces shall show any delamination, blistering on the surfaces or separation of the joints between veneers at the . edges. MOIST'uRE CONTENT 11. At the time of leaving the factory, finished boards shall have a moisture content determined by the method described in Appendix D of 8 to 12 per cent. DIMENSIONS OF PLYWOOD BOARDS 12. The dimensions along the grain of the face veneer shall be quoted first. NOTE. It is not practicable to standardize the sizes of boards at present. Information on the sizes most commonly available are given in B.S. 3493, * Information about plywood ', a. Length ant! width. The length or width of a. board shall not be less than the specified size nor more than y6 in (3 mm) greater than the specified size. b. Thickness. Unless otherwise agreed between pur chaser and supplier, the nominal thickness shall be that of the board before sanding or scraping. The thickness of the board shall not differ from the nominal thickness by more than ± 5 per cent for boards up to and including V* in (6 mm) thick or ± 3 per cent for boards in excess of V* in (6 mm) thick. An additional allowance of 0 008 in (0-2 mm) per side shall be made for " scraping or sanding. 7 1963 Squareness. The lengths of the diagonals of a board shall not differ by more than in per foot (0-25 per cent) of the length of the diagonal. FINISHING 13. Boards shall be sanded or scraped both sides unless otherwise agreed between purchaser and supplier. RE-TESTING 14. In the event of failure to comply with any one of the test requirements given in Clauses 10 and 11, the plywood concerned need be re-tcsted only in respect of that require ment. If the rc-test fails, the batch shall be deemed not to comply with this British Standard. MARKING 15. Each board shall be marked with the following particulars and unless otherwise agreed the mark shall be near an edge on the back. a. Manufacturer's name or mark. b. Country of manufacture. e. The number of this British Standard, i.e. B.S. 1455. d. Grade for face and back (e.g. 2-3). For grades oilier than 1, 2 or 3 (see Clause 3) the grade mark shall be that agreed between purchaser and supplier. t. Bonding (i.e. WBP, BR, MR or INT). f. Nominal thickness of board. NOT!:. The mark U.S. 1455 on ilic product is a claim by ti;C manufacturer that it complies with the requirements pi this Uritish Standard. The Hrilish Standards Institution is the owner of the registered certification trade mark shown below. This mark can be used only by manufacturers licensed under the certification mark scheme operated by the B.S.I. The presence of this mark on a product is an assurance that the goods have been produced to comply v.ith the requirements of the British Standard under a ssstem of supervision, control and testing operated durinp manufacture and inclv.din'j! periodical inspection at the manufacturer's works in accordance with the certification mark scheme of the B.S.I. Further particulars of the terms of licence may be obtained from the Director, British Standards Institution. 2 Park Street, London. W.I. MANUFACTURER'S WARRANTY 16. The marking of the boards by the manufacturer as set out in Clause 15 itself constitutes a warranty that the plywood complies with the appropriate rcquircmctits of this standard. In cases of dispute or doubt, Clause 10 indicates the procedure for testing the plywood for compliance with the requirements for bonding (Clause 6): the grade (Clause 3) can be decided by inspection. -146-APPENDIX 2 Export Standard Specifications of Japanese Plywood, Excerpts. (Japan). 1968. -147- ~ ^" may -«o /sea r EXPORT STANDARD SPECIFICATION OF JAPANESE PLYWOOD Excerpted and Arranged for. Commercial Purposes Effective January 1, 1968 The Japan Plywood Manufacturers' Association The Japan Specialty Plywood Manufacturers' Association The Japan Plywood Inspection Corporation Japan Plywood Exporters' Association -148-foreword • This publication has been excerpted and arranged from Basic Rules of Inspection for Common Plywood and Specialty Plywood as set forth jointly by Ministry of Agriculture and Forestry, and Ministry of International Trade and Industry by joint Ordinance No. I. November 10, 1967. . History: The First standards were promulgated in June, 1950. The First Revision was announced in August, 1951. The Second Revision was announced in February, 1954. The Third Revision was announced in June, 1957. The Fourth Revision was announced in January, 1958. The Fifth Revision was announced in May, 1963. The Sixth Revision was announced in November, 1967. Interpretation: Any dispute as to interpretation of this unofficial translation for commercial purposes shall be finally decided on the basis of the original text in the Japanese language. -149-1. EXPORT STANDARD OF COMMON PLYWOOD Page (I) DOOR SKIN PLYWOOD 3 1. Plywood with a face veneer .of domestic species 3 2. Plywood with a face veneer of lauan species 10 (n) WALL. PANEL, PLYWOOD 18 1. Plywood with a face veneer of domestic species ." 18 <1) Regular 1(2) Rustic 25 2. Plywood with a face veneer of lauan species 31 (HI) PLYWOOD FOR GENERAL USES . 38 1. Plywood with a face veneer of domestic species 38 f. • ' 2. Plywood with a face veneer of lauan species 47 SEPARATE PARAGRAPH - Physical Inspection ;.. 57 1. Cyelic-boilTest -52. Hot and cold soaking Test 59 3. Pn bonding Test 60 4. Tyne I =oak delamination Test • 60 5. Type II soak delamination Test.. '. 60 6. Type III soak delamination Test 61 7. Moisture content Test 6-150-SEPARATE PARAGRAPH Physical Inspection 1. Cyclic-boil test (1) Preparation of Specimen Specimens shall be prepared in accordance with the following methods from the part of sample which is free from any defect to affect bonding strength of the said specimen. a. P'or 3 ply-plywood having face i-.nd back veneers in 1/16 in. or more of thickness, four specimens shall be prepared in . conformity to drawing A; and for the said plywood having face or back veneer in less than 1/16 in. of thickness or a veneer sheared easily, four specimens shall be prepared in conformity to drawing B. • In this case, one half of total specimens shall be prepared to comprise regular direction of core's reverse check and another half shall be prepared to involve contrary direction of core's reverse check. Tl 5— j H f— i HI— i H •'••>•»> "i i i,-^——| b. (Unit : inch) For 5 ply-plywood. 3 ply-plywood which comprises any two bonded layers respectively in a specimen shall be obtained by means of stripping surplus veneers and specimens shall be prepared from the said 3 ply-plywood in conformity to drawing A. 57 --151-(2) Testing method 'A specimen shall be submerged in boiling water for four hours and then dried at a temperature of GO°C + 3°C during 20 hours. Furthermore, it shall be submerged again in boiling water for four hours and then, shall be continuously kept in the* said water until its temperature goes down to a room temperature. Bonding test shall be performed on this specimen under wet conditions. (Bonding test: Both ends of specimen are clamped by grips and are tensioned by a load velocity of 1, 320 Lb., maximum per minute and maximum load is measured at the time of rupture.) (3) Successful standard of test Bonding strength of specimen shall be equal to or more than the standard figures of bonding strength stipulated in the following Table. Species of Wood Standard Figures of bonding strength Birch 145 (Lbs. /sq. in. ) Beech, Oak, Japanese Itaya Kaede (Maple), Japanese Akadamo (Elm), Japanese Shioji (Ash) and Japanese Yachidamo (Ash) 135 Japanese Sen (Caster Arabia), Japanese Hohnoki (Magnolia), Japanese Katsura (Judaf. Tree) and Japanese Tabu (Lourel) 115 Japanese Shiba (Bass wood) 100 Lauan and Others 110 Note- 1. When a specimen comprises veneers of different wood species, the species having lowest standard figure, out of various standard figures of bonding strength for those species shall be specified for the standard figure of this specimen. - 58 --152-2. Bonding strength of specimen shall be calculated by the *. following formula. But, provided that a thickness ratio of core sheet in proportion to face sheet is 1. 5 or more for this specimen, the above calculated figure shall be multiplied by a coefficient in column of the following table which is classified in conformity to thickness ratio in the said table and the multiplied figure shall be specified as this bonding strength. Bonding strength Lb. /sq. in. = P ^ , wherein p is maximum load (Lb.) in the test of bonding strength and b is width of bonded surface (surface between both grooves) and h is length of bonded surface (surface between both grooves): This formula is applicable for a specimen in the form of drawing A, and another specimen in the form of drawing B which is used for cyclic boil test and hot and cold soaking test. , p Bonding strength Lb. /sq. in. = b ^ x 0. 9, wherein p, b and h have the same significances with the above formula: This formula is applicable for a specimen in the form of drawing B which is used dry bonding strength test. Thickness Ratio Coefficient 1. 50 to less than 2. 00 1.1 2. 00 to less than 2. 50 1.2 2. 50 to less than 3. 00 1.3 3. 00 to less than 3. 50 1.4 3. 50 to less than 4. 00 1.5 4. 00 to less than 4. 50 1-7 4. 50 or more 2.0 Hot and cold soaking test (1) Preparation of Specimen To conform to the paragraph I-(l). (2) Testing method A specimen shall be submerged in hot water at a temperature of 60°C + 3°C for three hours and then shall be continuously kept in the said water until the temperature goes down to a room temperature. - 50 --153-Bonding test shall be performed for this specimen under wet conditions. (3) Successful standard of test. To conform to the paragraph I-(3). 3. Dry bonding test (1) Preparation of specimen To conform to the paragraph I-(l). (2) Testing method Test of bonding strength shall be performed for a specimen under common conditions. (3) Successful standard of test. To conform to the paragraph I-(3). 4. . Type I soak delamination test (1) Preparation of specimen Four specimens in size of 3 in. square shall be prepared from the part of sample which is free from any* defect to affect bonding strength of the said specimen. (2) Testing method A specimen shall be submerged in boiling water for four hours and then dried at a temperature of 60°C + 3°C during 20 hours. Furthermore, it shall be again submerged in boiling water for four hours and dried at temperature of 60"C + 3"C during three hours. (3) Successful standard of test. The part which does not delaminate in the same bonded layer of a specimen shall have 2 in. or more of length at the side surface. 5. Type 11 soak delamination test (1) Preparation of specimen To conform to the paragraph 4-(l). (2) Testing method A specimen shall be submerged in hot water at a temperature of 70°C + 3°C for two hours and then dried at temperature of 60°C + 3°C during three hours. - 60 --154-(3) Successful standard of test To conform to the paragraph, 4-{3). 6. Type Hi soak delamination test (1) Preparaiion of specimen To conform to the paragraph 4-(l). (2) ' Testing method A specimen shall be submerged in warm water at a temperature of 35°C'+3CC for two hours and then dried at temperature of 60"C +3°C during three hours. (3) Successful standard of test. To conform to the paragraph, 4-(3). 7. Moisture content test (1) Preparation of specimen Two specimens sized appropriately shall be prepared from the part of sample which is free from any defect to affect moisture content of the said specimen. (2) Testing method After weight of specimen is balanced, the specimen shall be dried at a temperature of 100°C to 105°C until it reaches to constant weight. This weight will be balanced and a moisture content shall be measured by the following formula. But, when moisture content is measured by another process besides the above mentioned method with equal or more degree of accuracy, the measurement may be accorded with this latter process. Wl - W2 Moisture content (per cent) ° — x 100 W2 wherein Wj is a weight in gram before drying and W*2 is a bone dry weight in gram. (3) • Successful Standard of Test • 13 per cont or less of moisture content for specimen. - 61 --155-APPENDIX 3 DIN 68705 Plywood Standards (translated) (Germany). 1968 : C01.4 January .190ft lilt Definitions Plywood General Recuirenents I HAR22 F i«7n^ Sheet a 2 E Sperrholr-; Becriffe, Allgemeine Anforderungen, Priifung ! 2ais Standard applies to veneer boards and blockboards. It specifies definitions, requirenents r and t-jmnrs which are applicable to all types of plywood regardless of its use. .rlyvoca BZ-J.1 be ta>:en as meaning all sheets consisting of at least three superimposed layers of £ voca Dondea together with the grain running crosswise. Plywood (syabol SP according to DIN 4076 h st y-sse-z -under revision) is therefore a generic definition for various typeB of sheets. A * t distinction is nade between: pa: a : '. Di to Dir; ^o?s) Veneer board consis the directions cf 2.2. 31ockoos.rds ailel to tne o a a 1 1 y 2^. Veneer board (synbol HJ according to DIN 4076) . Plyvocd in which all plies consist of veneers and are bonded one on top of the other crosswise -' " the sheet. Y'ith an even nuaber of veneers the two innerraost plies grain. laminated veneer board (symbol Stf according sting cf at least five plies of veneer bonded to each other, in such a way that the £~~ -1 of adjacent layers cross at angles of 45° or less. (symbol 71 according to Dili 4076) Plyvood consisting of at least two covering; veneers and a core of adjacent strips of* wood. In"blockboards consisting of three plies the direction of the grain of the .core runs crosswise, in blockboards consisting of i'ive plies parallel to the bonded covering veneers. All layers are bonded together crossvise. Slockboards consisting of five plies are mainly produced to neet higher standards of surface condition and diuensional stability. . . A distinction is nade b 8 2.2.1. L a n i n b o ;ween various blockboards, according to the type of core", a r d core (symbol SIAE according to DIH 4076) These are: - u ——. ' — I — • Karr.ov:, lemnated strips of wood consisting of rotary cut veneers up to 8on thick, bonded together and arranged edgewise to the plane of the board. 2.2.2. Bonded blockboard core (s.yiabol ST according to DIN 4076) Xaainated strips of wood bonded together side by side and usually about 24 on hut not nore than 50 cr: wide. 2.2.3- Unbonded blockboard core (synbol SH according to DUf 4076) Larjinated strips of wood arranged close together but not bonded and usually about 24 in but not core than 50 nc wide. Keouirenents 2i1i_3ondin2 Choice of plywood bondings shall be governed by the climatic conditions and hunidity to which tne^boards or sheets are subjected in use. A distinction is aade between the following types of 3.1.1. X? 20 (interior plywood) "5 resistant whan used in rooas with generally low atnospheric huaidity (not weather-. con resistant). (exterior plywood) to the effects of the weather and humidity (weather-resistant).^ la additi== tc ties? boadinga the following types can. also be produced! . AV 100 2.5 resistan 5.1.2 36ndi. Not IS i7z 3s:ii;j resistant «isi =s«d ia v&'-rr -p to about c" c-(set »eati-r-resist2r:t} A ICC: £ ia 7O0E9 with high atmospheric huaidity and resistant to occasional contact with s-r-.iti tie sheets or boards are protected against direct effects of the weather SzzzL^s ^tsis'.es: to tie actios of cold and hot water (limited weather resistance). • Fartiiu.ars r<!*uti=c to r*s tsr.ee refer only to bonding. -in- strength) industrially it te iiRS cec-a^ents, other sr usually bonded with hardening synthetic resin glues whos .,.„-«. - ^.es^0f1=^cd b7 long-ouration and outdoor tests. As a result; it is oocsible = short testings vmch are adjusted to the chemical basis of the resins. When uslnr other — short tests suitable for the appropriate bonding aCentsmust be £ofvS. ' itr.air.r strer tic.-.. It is Lr.er.s soai '£-4%*°"-^ j? IE ffill ff lhe "»i«*«c. of .glue joints to mechanical destruc-^;rinbwat:; and still weJ? *"* <a*/°r thC SheaP tCSt accorfi*S to MS 53255, usinG 1.1.1. n i f c S=:tplir.r; test riv* cpecir.e:.s neasurir.R 200 u x 100 un shall be taken for the knife test fron ever* sheet to *1 SVtfJill?'***1?™* T°a Ere?£8 °f b0?dinE AW 100>- ^ dimension 200 Z shafl"JplJ tno cirection of the r;ram of the coverintr veneern On» of th. r^,r« • ""UJ-1- °PP-LJ fro* the cd,:e of the sheet, the others froa fhe inllle S the shlet" ( ^ SI>eClnsnB ttust C0Oc Continued on panes 2 to 4 - Explanations on p'i£« 4 Allelnvukuut d.r Normblorlei durch Brulh-Veririeb OmbH, Berlin 30 und Kolo T1TU gniM. ^. Fac* 2 Dili 66705 Sheet 1 -157- J 4.1.1.2. Pretreatment of s p e c i m e n s The following short testa are sufficient for testing bonding provided the stated glues were used." Bondine; I? 20 (urea resins) Specimens immersed in voter for 24 hours at a water temperature of 20 °C + 2 dec-Bonding AV 100 (phenolic, phenolic-resorcin or reoorcin resins) a) Cold water test: r Specimens'immersed in water for 24 hours at a water temperature of 20 °C + 2 deg. b) Boiling test with alternate heating and. cooling as follows: Boiling for 4 hours (100 °C) Eeeoing for 16 to 20 hours in hot air at 60 °C + 2 deg in a hot cabinet acco-cVi r- to DIN 50011 ~ • . " Boiling for 4 hours Cooling for 2 to 3 hours under water at a water temperature of 20 °C + 5 defj. Motet Bonding IV* 67 (unextended or nelajaine-reinforced urea resins) . Specimens immersed in water for 3 hours at a water tesperature of 67 °C + 0.5 deg. Cooling under water for 2 hours at a rater temperature of 20 °C + 5 deg. Bonding A ICO (nelamine resins or mixtures of urea and melaaine resins) Boiling for 6 hours (100 °C) Coolins under water for 2 hours at a water temperature of 20 °C + 5 deg. 4.1.1.3- Test procedure Knife tests according to DIU 53255 shall be carried out on all plies of the five (ten) speciaens taken according to Section 4.1.1.1 and pretreated according to Section 4.1.1.2. 4.1.1.4. Assessment of test results Test results for all glue joints examined shall be designated according to DIN 53255 by the following grading numbers: 1 excellent. bord?ng 3 adequate bonding 2 good bonding 4 inadequate bonding 4.1.2. Shear test 4.1.2.1 Sampling and production of specimens At least ten simple tension/shear specimens shall be prepared according to Din 53255 frcn every sheet to be tested (20 simple tension/shear specimens from sheets of bonding tyje A'W 1C0). In the case of sheets with five and more layers bf veneer the.outer veneers shall" be removed (e.g. by planing down) to three plies. 4.1.2.2. Pretreatment of specimens according to Section 4.1.1.2. 4.1.2.3. Testing and evaluation Shear tests according to PITT 53255|irshall be carried out on the ten (20) specimens taken according to Section 4.1.2.1 and pretreated. according to Section 4.1.1.2, and the" results evaluated. 4.2 . _Bendir^_strenrjth -The bending strength shall be determined accordins to. DIK 52371 (at present still circulating as draft). 4.3. Moisture content The moisture content shall be determined according to DT.il 52183. 5. Quality safeguard Depeadins on the field of application of veneer boards and blockboards, they can or must be subjected to regular supervision of their quality in the form of a statistical quality control (own supervision) and/or a supervision testing (outside supervision). " . ft.1. Statistical quality control (own supervision) 5.1.1. Sampling ?or ova supervision the number of sheets to be selected will depend on the relevant production ' progrsrcse. At least one sheet must be taken at random from every lot (consignment) ahi, in the case of continuous production, at least one sheet daily, and must be tested for the specified rvrcperties. 5.1.2. Control cards The results of own supervision shall be recorded and entered on control card3. Statistic evaluation covers r.ean values for sheets and a fluctuation measure. The fluctuation measure .chosen caa either be the variable s2, the standard variation s or span R. Supervision of -the span does not require any calculations but it ia not suitable for systematic evaluations. For subsequent evaluations, for deciding whether several sheet or board thicknesses .-:r.d/or constructional combinations should be summarized under a basic lot and for calculating varniar; and control linit3 it is necessary to calculate and determine the sua total of individual values Zxi and their squares Ex^ for each sheet tested. Warning and control limits for the control cards can be calculated the first time after testing ebout 25 sheets per lot. They should be fixed annually and entered on new control cards. CY.TJ supervision records must be kept for at least five years. 5.1.3* Testing non-conditioned sp ec i n e n s Veneer boards and blockboards leaving the press frequently have a lower moisture content than in their state of equilibrium in a standard, climate 20/65 Dili 50014. As a rule adjustment of the noisturc content of sheets or boards to the standard climate takes about 7 days, even loader in -158- DIH 68705 Sheet 1 Page 3 aec The teeting of non-conditioned bending specimens can produce systematic variations from measurements undertaken on conditioned specimens. Systematic variations in bending properties cf non-conditioned specimens must therefore be taken into account by correction factors for the mean values and for the warning and control limits. Correction factors determined by experiment should be re-examined from time to time. 5.2._Superyision testing (outside supervision) Outride supervision testings must be carried out every .six months by an officially recognized material testing institute on the basis of a supervision agreement, provided regular supervision in accordance with regulations of building authorities does not take piece under the direction of a recognised quality control body. A condition for carrying out outside supervision is proof of properly conducted own supervision according to " Section 5-1. 5-2.1. Sampling • ~~ In outside supervision three sheets or boards shall always be selected at random from a lonrest possible production period by a representative of or person appointed by the super visor;.' department and shall be marked immediately so as to prevent confusion. A report cn selection of a random specimen shall be drawn up by the person choosing the specimen and countersigned by the v.-orks manager or his representative. This report must contain the following particulars: . e) Date and place of sampling; bJ Possible size of stocks from, which the sheets or boards are taken; c) Number and date of production of the boards or sheets belonging to the specimens taken at random; d) Particulars of how the sample sheets or boards were marked by the person selecting them; e; A statement to the effect that the specimen vas selected at random; f) Fames'of persons present during selection of the specimen; g) Ko'ces on t-sstiag and evaluation of records from own supervision. The report shall be submitted to the competent material testing institute together with the specimen taken at random. Note: The following material testing institutes (shown in alphabetical order) are et present available for supervision testing: Bayerische landesgewerbeanstalt, Niirnberg 2, Gewerbemuseuraplatz 2 Bundesforeehungsanstolt fiir Forst- und Holzwirtschaft, Heinbek bei Hamburg, Schlofl Bundesanstalt fi:r Kate rial priif ung (BAM), Berlin ^5 (Dahlem), Unter den Eichen 87 Forsehungsinstitut fur Holz'erkstoffe und Holzleime, Karlsruhe-Durlach, Dieselstrafle 6 Forschungs- uod Materialprufungsamt fur das Bauwesen - Otto-Graf-In&titut - , Stuttgart-Vaihiagen, Robert-ieieht-StraBe 209 Institut fur Baustoffkunde und Stahlbeton der Technischen Hochschule Braunschweig, Antliche Katerialpru'funr;sanstalt fiir das Bauwesen, Braunschweig, BeethovenstraBe „, Institut fiir Flugzeugbau und Leichtbau, Technische Hochschule Braunschweig, Braunschweig, Langer Kamp I9t> Institut fiir Eolzforschung und Holzteehnik der Universitat Kiinchen, Kiinchen 13, Winterers trade *»5 Institut fiir Katerialprufung und Foroehung des Bauwe6ens der Technischen Hochschule Hannover -.Antliche Katerialpriifungsanstalt fur das Bauwesen, Hannover, iiienburger StraBe 3 Staatlicbe Katerialpriifungsanstalt Darmstadt an der Technischen Hochschule Darmstadt Staatlicbes Katerialprufungsant Nordi-hein-tfestf alen, Dortmund-Aplerbeck, MarsbruchstraBe 186 Versuehsanatalt fur Stahl, Holz und Steine - Katerialpriifungsanstalt der Technischen Hochschule Karlsruhe, Karlsruhe, XaiserstraQe 12 ttllhelm-Klauditz-Institut fiir Eolzforschuag as der Technischen Hochschule Braunschweig, Braunschwelg-Kralenriede, Bienroder weg 51* * State testing institutes abroad can undertake quality supervision testings in cooperation with one of the above-mentioned German institutes. 5.2.2. Testing of own supervision Vhen sanplir.-- according to S«ction 5.2.1 records of own supervision mentioned in Section 5.1.2 shall be tested. Designation rlywood'"eheeus or boards in storage dimensions shall be marked by the manufacturer vith a sz?-~ on the rccrcr side. C rher s.tnndr'rd.-» *-C, o Weed, v.ood tutorials and laminated boards; definitions and symbols Sri: *07£ Tiyvco.-!; dir.cncions DIK 5001^ Tec^iri-;, of cart-rials, structural • components and equipment; standard climates Dili 51220 f.aterial testing machines; definition , general directions, classification DI« 51221 Sheet 1 Tensile testing machines; general requirements Sheet 5 Tensile testing machines; small tensile testing machines (at present still circulating as draft) Dili 52153 Testin.-r of v.ocd; determination of moisture content DIN 53251 Testing of wood glues and wood bondings, determination of bonding strenjth; general directions DIH 53255 Testing of wood glues and wood bondings, determination of bonding strength of plywood bondings (veneer boards and blockboards) in the tensile teBt and knife test BIN 66330 Veneers; definitions - - • DIN 68705 Sheet 2 Plywood for general purposes; quality conditions Sheet 3 Plywood; veneer boards for building, quality conditions Sheet 4 Plywood; building blockboarda, quality conditions (at present still circulating as draft). Pace 4 DIN 60705 Sheet 1 -159-Explanations Standard DIN 68705 has been separated into several standard sheets and extended because a single standard oheet con be adapted note easily to the latest state of technical developments in view of the considerably wider fields of application. DIN 68705 Sheet 1 contains the general bases for plywood ouch as definitions, requireoenta, testing specifications and instructions for safeguarding quality. DIN 63705 Sheet 2 contains the quality conditions for plywood UBed for general purposes, i.e. mainly with regard to plywood used for furniture, interior decoration of rooms and for panelling in all fields of application not subject to static stress. The qunlity requirements for these sheets or boards chiefly cover bonding of the sheets and grading of the covering veneers. DIN 68705 Sheet 3 contains the quality conditions for veneer boards and DIN 68705 Sheet k (at present still circulating as draft) the quality conditions for building blackboards. This Standard applies to plywood specially suitable for use in building by reason of its construction, veneer thicknesses and types of wood. CJ o o-1: _> •j c '5> _o o CJ VI 5 u ' c c t, Q a c o ,, 1 o IA '•"JE o ~j £ (!)•*. _-' *it u » k 5 — T 1. o b a t> o -U CD "5 O e z unc 67^-419. DEUTSCHE NORMEN Plywood Veneer Boards for Building Quality Condition Sperrholz; Bau-Furnierplatten, Giitebedingungen o n Scooe This Standard applies to veneer boarda used for building; in general they shall he unsanded. Dili 68705 Sheet 2 applies to building plywood used for panellings. 2. Definitions d Veneer board used for bui particularly suitable for building applications. For further definitions, see DIN 68705 Sheet 1. 1 d i n g (synbol BFU), veneer board 3. Requirenents ^.1.^Covering veneers.and_under_veneers 3.1.1. Types o'f wood The covering and under veneers of veneer boards used in building should be of the following types of woods Birch, beech, spruce, pine, linba, macore, mahogany species, gaboon, fir or woods with similar or better weather resistance. In view of their lower weather resistance, veneers made of Obeche, Ilonba, Samba and Wawa shall be inadmissible. o Z E o 1 a a -5 3 O •6 o Z I 3.1.2. Quality requirements n The following are permissible: 3 Wood discolourations and colour faults provided they do not impair the stability of the veneers, jj Joints with slight faults only in the case of boards consisting of five and raore plies of veneer s Cracks, isolated, up to 3 ma wide in boards consisting of three plies of the veneer, up to 5. ma 4 wide in boards consisting of five and^more plies of veneer 3 isolated, completely intergrown knots and knot places up to 25 ma diameter in boards consisting of three plies of veneer, up to 60 mm diameter in board? consisting of five and more plies of veneer isolated bore holes caused by insects of their larvae Covering veneers should not be more than 2.5 mm, under veneers not more than 3«7 mm thick. . Covering and under veneers should be composed of strips of any width. Repairs to covering veneers shall be carried out by a method of bonding suitable for the veneer board. Adhesive tapes which impair bonding stability shall be inadmissible. 2-2i_Cores 3.2.1. Types of wood All the types of wood mentioned in Section 3.1.1 can be used for cores (inner layers of veneer) regardless of the types of wood used for covering and under veneers, with the exception of Obeche, Ilomba, Samba and Wawa, provided quality specifications with regard to stability are satisfied. 3.2.2. Quality requirement Board thickness No. of plies up to 8 3 over 8 to 15 5 OTer 15 to 22 ' 7 over 22 to 29 9 5 • mi The inner plies of veneer must satisfy requirements for covering veneer3 although a rather higher proportion of sound knots and bore holes caused by insects can be penaitted, provided these do not occur frequently or spread over the entire sheet of veneer. * The inner plies of veneer should not be thicker than 3^7 mm. They may be composed of strips of any required width. Adhesive tapes which impair bond stability are inadmissible. 3-3- Board structure Boards must be built up symmetrical to the middle plane with regard to veneer thicknesses and types of wood and must have the following minimum, nuaber of veneer plies for the board thick nesses listed below: The bonding of the veneer boards specified in this Standard must conform to the types of bonding IF 20 or AW 100 according to DIN 53705 Sheet 1. Ii o t e 1 In addition to these bondings veneer boards Bay also be produced by the IW 67 oethod of bonding. 3.5i_Bond_strength (quality limits) Bond strength must be at Toast 10 V-^/Cn2. at least.8 kp/cm2 in the case of inside veneers I consisting of coniferous woods. Those limiting values referto the average values for three boards' In this connection none of the three average values for the boards should be more than 10 ?i belo* the limit. ^.. Hhndinff o^T^nerfrVj ^"v.?.lity limits) Longitudinal bending strength must be at least 400 kp/cmc and cross bending strength at least 150 kp/cm^. These limiting values refer to average values from three boards. In this connection none of th« three average values for the boards may be more than 10 % below the limit. Continued on pages 2 and 3 Vpce 2 DIN 68705 Sheet 3 -161-2-7. niricnsi2Qs_S-I^_2£IEi55i^l£_Y2EiS*i2!12 Dili 4073 applies to length and width. 2.8i_Hoisture_content_ • The moisture content of veneer boards for building according to this Standard should be at least 6 c/i related to the kiln-dried weight. Woods having good natural resistance should be used for plywood subjected for long periods to elevated ter.peratures and high humidity. Less resistant types or wood must be protected by a preservative. Note: Resistance of veneer boards for building to animal and plant pests is no greater than that of the types of wood employed. When using plywood in building necessary steps must therefore be taken by constructive measures to ensure the necessary protection against moisture, regardless of the type of bonding (see also DIN 68800). When using wood preservatives care should be taken to see that they are compatible with the binders used. a. Testing ^.i^^ondin^ (bond strength) Bor.d strength shall be tested by the shear test according to DIN 53255- Saraoling, production and pretreatment of specimens shall be carried out according to DIN 68705 Sheet 1. . <i-.2. Bending; strength Testing according to Dili 52371 (at present still circulating a3 draft) 4. ^. f-'oisture content . Testing according to.DIN.52183 5. Quality safeguard Veneer boards for building according to this Standard must be subjected to regular quality supervision. Such quality supervision consists of a statistic quality control (own supervision) and a supervisory test (outside supervision). Attention is drawn, in connection with implementa tion of the quality safeguard, to the instructions of the Giiteschutzgemeinschaft Sperrholz o.V. (address: 63 Gie3en 1, Bahnhofstrafie 52-56) on quality supervision of veneer boards for.building. 5.1 i._2,fB_§H225Zi5i22 Own supervision shall be carried out according to DIN 68705 Sheet 1. 5.1.1. Quality properties Own supervision of veneer boards for building shall cover bonding (determining bond strength in the shear test) and bending strength. ' When testing the bonding strength of bonding type AW 100 the only pretreatment given to the specimens shall be the cold water treatment according to DIN 68705 Sheet 1. 5.1.2. Sampling see DIN 6S705 Sheet 1. 5.1.3. Quaiity limits The limiting values stated in Section 3-6 shall be chosen as the lower warning boundary with a orcbable failing-short value of not more than 5 °,'«, where necessary taking into account the correction factor mentioned in Section 5.1-3 ot DIN 68705 Sheet 1, January" 1968 edition. 5.2. Outside supervision Outside supervision shall be carried out according to DIN 68705 Sheet 1; 5.2.1. Quality properties Outside supervision covers bonding (determining bonding strength in the shear test) and the • bending strength. Wher. testing bonding strength in bonding type AW 100 pretreatment of the specimens shall include the cold water treatment and the alternate boiling, heating and cooling treatment according to DIIT 65705 Sheet 1. 5.2.2. Sampling see DIN 63705 Sheet 1. 5.2.5. Quaiitylimits The requirements stated in Sections 3-5 and 3-6 with regard to various properties must be satisfied. 5.2.4. Testing own supervision Vhr;a sampling eccording to DIN 63705 Sheet 1 records of own supervision (according to DIN 68705 Sheet 1)*shall be tested. " 6. D«tsirrhntion Vvneer uoard3 for building according to this Standard shall be marked by the manufacturer on the poorer side with a stamp showing the symbol BHJ for veneer board for building, the manufacturer's mark, board thickness, type of bonding and DIN number. Example: Veneer board for building, manufacturer , hoard thlolrn-es 15 Ba, bondins AW 100 BHJ .... 15 AW 100 Dili 68705 Particulars used for designation (except for the manufacturer'a nark) may also be used for orders. -162- DIU 687C5 Sheet 3 Pace 3 Reference to further standards: DIN 1052 Wooden structures; calculation and construction DIN 4073 Plywood; dimensions DIN 5216J Testing of wood; deteraination of moisture content Dili 52371 Testing of plywood; bending test (at present still circulating as draft) DIN 53255 Testing of wood glues and wood bondings; determination of bond strength of plywood bondings (veneer boards and blockboards) in the tensile test and in the knife test DIN 68330 Veneers; definitions DIN 68705 Sheet 1 Plywood; definitions, general requirements, testing ' • Sheet 2 Plywood for general purposes, quality conditions Sheet 4 Plywood; blockboards for building, quality conditions (at present still circulating as draft) DIN 63800 Protection of wood used in buildings *; Explanations The specifications given in DIN 68705 Sheet 3 should be followed for veneer boards which are to be used chiefly for wooden houses constructed in panels and for light-weight roofs. This Standard is adapted to the relevant supplementary regulations for DIM 1052. It includes particulars of approved veneers, bonding and quality safeguards by own and outside supervision required by the building authorities. In defining strength requirenents the Advisory Committee proceeded on the basin that plywood is mainly subjected to bending stresses in wooden houses and light-weight roofs and reotricted the quality safeguard, apart froa bonding strength, to one charactci j t.trc, beDding strength. Is this connection is was assuaed that bending-elastic modulus is shown by experience to be linked correlatively with bending strength. The bending Btrength therefore serves chiefly as a control characteristic which can be subsequently checked in a very simple manner. However, decigDero and structural analysts need further information which is listed in the following Table. Manufacturers of veneer boards can vary their elastoaechanical properties within certain limits by their choice of woods and by the structure of the boards. This latitude could not be fully taken into account ln the Table (approximate values). In arriving at calculations for wooden constructions the least favourable table values are applicable in each case if more advantageous values cay not be used on the basis of a test certificate of a recognized material institute in an individual case or according to other German standards and specifications. Property Symbol Unit Numerical value • Bulk density u » 12 Si e . kg/m3 500 to800 Beading-elastic modolus along the grain £bll kp/cm* 70000 to 120000 across the grain (3 plies) (5 aod more plies) Dyaanic modulus of shear *b-L * G kp/cm» kp/cn* kp/cm* 7000 to 12000 30000 to 70000 5000 *» 6000' Lengthwise or crosswise swelling par percent change in wood moisture Coefficient of thermal conductivity (calculated value) Vapour diffusion resistance factor 9L % kcol/(mhdeg) 0.01 to 0.02 0,12 300 to 700 -163-APPENDIX A NBS Voluntary Product Standard PS 51-71 Hardwood and Decorative Plywood. U. S. Department of Commerce, National Bureau of Standards. UNITcO STATES ' PARtMfcM OF .: '• HiViMERCE I.. (LIGATION : i m U.S. DEPARTMENT OF ' COMMERCE Hational Bureau cf Standards _ i " -164-t.' -•>> if "> ., «»-Vl. J' produa X .... PS 51-71 ,'.S>" iC I I c Iv .... jftSgg&j^^ * • -165-UNITED STATES DEPARTMENT OF COMMERCE . Maurice 11. Stans, Secretary NATIONAL BUREAU OF STANDARDS • Lewis M. Rratiscomb, Director Voluntary Product Standard PS 51-71 Hardwood and Decorative Plywood Technical Slondsrds Coordinator: P. R. Sutula.'' Abstract Thla Voluntary Product Standard for hardwood and decorative plywood establishes the nationally rev.-oguiz'xJ marketing classifications, quality criteria, test methods, definitions, and giade-innrking and certification practices for plywood produced primarily from hardwoods. It is intended for voluntary use by refeit-nte in trade literature, catalogs, sales contracts, building codes, and procurement specifications t» describe the quality aspects of tin-product and the means to determine conformance. Requirements are given for wood species, veneer grading* lumber-core, partieleboanl-core, hartlboard-core, shic bond, panel constructions, dimensions, moisture content, sanding, and finishing. Sampling and testing provisions cover dry shear, cyclic-boil, three cycle wet and dry, and cold soak test methods for plywood delamination determination:;, and field and laboratory moisture content measuring methods. A glossary of trade terms is provided for better communication and understanding, and provisions are made for panel grade-marking and certification to indicate -compliance. Key words: Decorative plywood; hardwood plywood; plywood, hardwood and decorative; softwood plywood, decorative; veneer grades, decorative softwood and hardwood. Nat. Bnr. Stand. (U.S.), Prod. Stand, r.1-71. 18 pages (January 1!>72) CODKX:XXPSAX For rale by tbe Superintendent of Documents. D.S. Government Printing Office. Washlnirton D C 204O'» (Order by SD Catalog No. 03.20/2:51-71). Price 30 cent*. -166-Contents 1. Purpose " —•. 1 I. 1. Purpose : '- '— * 1lbtended use • * 2. Scope ami Classification . : . 1 2.1. Scope . 1 •2.2. Classification , : : 1 2:2.3. Species - • '. :2.2.2. Grades «f vt-neers  1 '2:2.3. Tyi-es of plywood  1 2.2.4. C»nsim»-ii"r;.5 > 1 II. 1'..". Sizes jui'l '.hhl<n"«^'>« . • — 1 3. Ueo.uirvtncnt* •- =— • 1 1. r»en«*rnl 1 3 2. Spn i<• « for ftw, liMcks. ami inner plies .— 2 3.2.1. Slnties W:i-?pi>ries  2 3.3. Veneer crade descriptions — 2 3.3.3. Premium erode (A) - 2 3.3.2. <5"'Ml sTaclr U) • 4 :;.:'..3. Sound prude (2) : : -_- . 4 3.3.-1. Utility ;:rnde (3)  4 3.3..1. Biu-kinc crane <4) 4 3.3. C. Specialty grade (SP) -3.3.7. Softwood reneers •3.4. Thickness of veneers _ .—__— 4 o.">. Lumber cores3..1.1. Clear grade . . . 4 3..1.2. Sound crade — . 4 3.0.3. Regular grade ; 6 3.."..4. Clear edge • 6 3."i."i. Banded core 6 3.C.. Parriclebonrd ond/hnrdboarri cores ' , G 3.7. Special cores -3.5. Construction : • 6 3.5.1. Special construction 7 3.0. Glue bond requirements3.0.1. Technical Typo plywood3.0.2. Type I plywood3.0. 3. Type IT piywood . 7 3!'. t. Type II r plywood3.10. Dimensions and tolerances •- 7 3.10.1. Squareness — 1 3.10.2. Straichtness  7 3.11. Snmlin? : 7 3.12. Moisture content '. 8 3.13. Factory finished panels 8 3.14. Marking ;— _4. Inspection and Test Procedures .4.1. General4.2. Specimens for clue bond test ; - 1 8 4.2.1. Technical and Type I plywood4.2.2. Type 11 plywood - 8 -1.2.3. Typo III plywood4.3. Dry shear test4.4. Cyclic-boil shenr test 9 4..". Three-cycle s=nak test . — '. —. 4.C Twtwycle son): trst - - - - - — 9 1.7. Moislnrc roriif.it test  .— 9 9 IVfuiitionsi — iV Tiicntlfi'-ati"" 7. Ms:.ilifiotl lnspii-ti'ia ami T-.'stinj: Acency S. I'.tTociiTc 11nr». 0. Tlisf.-ry of l'roifvr 10 Ptanuiiis Cmiiiiiif'-e , — 1. Acceptors . — —— Appendix — : III 10 11 11 12 12 12 12 15 -167-VOLUNTARY PRODUCT STANDARDS Voluntary Product Standards are standards developed under procedures established by the Department of Commerce (15 CFTl Part 10, as amended. May -28. H'TO). The standards may include (1) dimensional requirements for standard sizes and types of various products, (2) technical requirements, and (3) methods of testing, grading, and marking 'Hie objective of a Voluntary Product Standard is to establish requirements which • are in accordance with the principal demands of the industry and, at the same time, are not contrary to the public interest. Development of a VOLUNTARY PRODUCT STANDARD The Office of Engineering Standards Services of the National Bureau of Standards has been assigned by the Department of Commerce the responsibility to work closely with scientific and trade associations and organizations, business firms, testing laboratories, and other ap propriate groups to develop Voluntary Product Standard?. The Bureau has the following role in the development process: It (1) provides editorial assistance in the preparation of the standard; (2) supplies such assistance and review as is required to assure the technical soundness of the standard; (3) acts as an unbiased coordinator in the development of the standard; (4) sees that the standard is representative of the views of producers, distribu-tors, and users or consumers; (5) seeks satisfactory adjustment of valid points of disagree ment; (6) determines the compliance with the criteria established in the Department's pro-, cedures cited above; and (7) publishes the standard. Industry customarily (1) initiates and participates in the development of a standard; (2) provides technical counsel on a standard; and (3) promotes the use of. and support for, the standard. (A group interested in developing a Voluntary Product Standard may submit a written request to the Office of Engineering Standards Services. National Bureau of Stand ards, "Washington, D.C. 20234.) A draft of a proposed standard is developed in consultation with interested trade groups. Subsequently, a Standard Review Committee is established to review the proposed standard. The committee, appropriately balanced, includes qualified representatives of producers, dis tributors, and users or consumers of the product being standardized. When the committee approves a proposal, copies are distributed for industry consideration and acceptance. When the acceptances show general industry agreement, and when there is no substantive objec tion deemed valid by the Bureau, the Bureau announces approval of the Voluntary Product Standard and proceeds with its publication. Use of a VOLUNTARY PRODUCT STANDARD The adoption and use of a Voluntary Product Standard is completely voluntary. Voluntary Product Standards have been used most effectively in conjunction with legal documents such as sales contracts, purchase orders, and building codes. When a standard is made part of such a document, compliance with the standard is enforceable by the purchaser or the seller along with other provisions of the document. Voluntary Product Standards are useful and helpful to purchasers, manufacturers, and dis tributors. Purchasers may order products that comply with Voluntary Product Standards and determine for themselves that their requirements are met. Manufacturers and distribu tors may refer to the standards in sales catalogs, advertising, invoices, and labels on their product. Commercial inspection and testing programs may also be employed, together with grade labels and certificates assuring compliance, to promote even greater public confidence. Such assurance of compliance promotes better understanding between purchasers and sellers. rv — 168-Voluntary Product Standard PS 51-71 (Supersedes CS- 35-61) Hardwood and Decorative Plywood Effective August 15, 1971 (See section S.) (This Standard, initiated by the Hardwood Plywood Manufacturers Association, has been de veloped under the Procedure* for the Development of Voluntary Product Standards, published by the U.S. Department of Commerce, as a revision of Commercial Standard CS 35-61, Hardwood Plytrood.-See Section 9, History of Project, for futher information.) . 1. PURPOSE 1.1. Purpose—The purpose of this Voluntary Product Standard is to establish nationally rec ognized quality criteria for the principal types, grades, and sizes of hardwood and decorative plywood. The principal wood species used for hardwood and decorative plywood are hard woods: however, certain softwood species are also used.1 The Standard is intended to provide producers, distributors, architects, contractors, builders, and users with a basis for common understanding of the characteristics of this product. 1.2. Intended use—The plywood covered by is Voluntary Product Standard is intended for use as decorative wall panels where esthetic characteristics are important; for cut-to-size and stock panels used for furniture, cabinets, con tainers, and specialty products; and for marine applications.2 2. SCOPE AND CLASSIFICATION ?..L Scope—This Voluntary Product Stand ard covers the principal types, grades, and con structions of plywood made primarily with hard wood faces. Included are requirements for wood species and veneer grading: for lumber, particle-board, and hardboard cores; and for glue bond, panel construction, moisture content, and panel dimensions and tolerances. Test procedures are provided for determining conformance with the. requirements. Definitions of trade terms, methods of ordering, and methods for identifying prod ucts that conform to this Standard are included. 22. Classification—Plywood covered by this Standard is rln=sifWi ns follows: 2.2.1. Species- -The most commonly marketed spories for plywood faces are listed in table 1. 2.2.2. Grades of veneers—The grades of ve-1 This VnlnrtnrT rrn-iuct Stnndar.1 «l*o Includes oertnln •orotif* *ofnv«ort sp-rir.; for nnnconsfrnction Constrmr-..011 crnrt**? of «oftiv.M*il nntl hnrdwr.otl pl.vtv.wnl nrc covered In the l.i|i"-t rrtltlon i-f V«.Iuntnr.v Prodm-t Sinmlnril PS 1-Cfi. Po/ffoO'/ Pfyiro.x/. Construction nnil /fiVhi.'rci/. 1 Aririltlnnnl product Information in IITIIII.IMP from th# Hnrd-wood Plywood Miiiiiif;icnir.'ri Atxnrlntlon, 2310 S. Walter Reed Dr\rt. Arlington. Ylrclnln 22200. neers are listed below with the identification symbol for each grade: Premium grade (A) (1) Good grade Sound grade Utility grade Backing grade Specialty grade (2) (3) (4) (SP) 2.2.3. Typos of plyv/ood—The types of ply wood are listed below in descending order of water-resistance, capability. (See table 5.) Technical — (Exterior) Type I • — (Exterior) Type II -— (Interior) Type III — (Interior)-2.2.4. Constructions — The constructions, based on the kind of core, are listed below: 1." Hardwood veneer core (3-ply, 5-ply, etc. in odd numbers of plies) 2. Softwood veneer core (3-ply, 5-ply, etc. in odd numbers of plies) Hardwood lumber core (3-ply, 5-ply, and 7-ply) Softwood lumber core (3-ply, 5-ply, and 7-ply) Particleboard core (3-ply and 5-ply) Hardboard core (3-ply) Special core (3-ply or more) 3. 5. 6. 7. 22.5. Sizes and thicknesses—Most combina tions of length, width, and thickness are avail able. The common panel sizes are 48 by 84 inches, 48 by 06 inches, and 48 by 120 inches (1 inch equals 25.4 millimeters) with thicknesses rang ing from % to % inch. 3. REQUIREMENTS . 3.1. General—Products represented as com plying with this Voluntary Product Standard shall meet all of the requirements specified here in. Terms used in this Standard shall be as de fined in section 5. 3.2. Species for faces, backs, and inner plies —The species for the face shall be any hardwood species, and if used for decorative faces, anv softwood species listed in table 1 may be used. The panels shall be identified by the species of 1 -169-the fare (sec The, species of the. buck und tlie inner plies msiy be any hardwood or soft wood species. TABLE 1. Cat.itjories of commonly uird specie.) bused on specific gravity rmujei* as a face and when it consists of morn than one piece, it shall lie edge-matched aj outlined in Category-C Cate^.iry A species Category B specie* 1 species (0.5'J »r more (O.-ia Ihroush 0.55 10.1-- or less speoifie gravity) specific gravity) | speeilie gravity Ash. Commercial 1 Asb, Black ] Alder, Red White ' .Wo-lire lAspcu P.eevb, American Bay Basswood, Birch, Yellow, Ce<lar, Eastern American Sweet Redb Box MUler Buhinca Cherry, Black Cntivo Elm. Rock Chestnut, Cedar, Western Madrone, Pacific American Reel" Maple, Blnck Cypress" Ceiba (hard) Elm. American Cottonwood, Maple, Sugar (white, red,or Black (hard) pray) Cottonwood, Oak, Commercial Fir, Douglas" Eastern Red Gum, Black Pine, White and Oak, Commercial Gum, Sweet Ponderosa" White Hackberry Poplar, Yellow C"k, Oregon Lauan, (Philippine Redwood5 PaUlao Mahogany) Willow, Block • Pecan, Commercial Limba Rosewood Magnolia Sa.-le Mahogany, African Teak Mahogany, Honduras Maple, Red (soft) Maple, Silver (soft) Prima Vera Sycamore Tupelo, Water Walnut, American » Based on orendry ireljht and volume at 12 percent moisture content, b Softwood. 3.2.1. Species categories—Species of wood commonly used for veneers are listed in table 1 ai-.d are categorized by specific gravity for the purpose of establishing maximum veneer thick nesses (see table 5). The specific gravity ranges given in the three category headings shall also be used in determining the proper category for unlisted species. The Forest Products Laboratory in Madison, "Wisconsin, shall be considered as final JB valuator "of specific gravity data. 3~3. Veneer grade descriptions — The grade requirements and identification symbols for hard wood veneers are given in 3.3.1 through 3.3.6. Softwood veneer requirements are given" in 3.3.7. "When unsanded veneers are graded, such charac teristics as patches, rough areas of grain, shallow depressions, open splits, and machine marks which may be corrected by sanding are not con sidered. Panels shall lie identified by the veneer grade of the face (see 3.14). A grading tolerance of n percent of the shipment or order will be permitted (see appendix). 3.3.1. Premium grade (A)—The veneer shall bo smooth, tight-cut, and full-length. "When used BOOK MATCHING SUP MATCHING FIOUBE 1. Face matching. table 2, and as illustrated in figure I. Edge joints shall be tight. The natural and other character istics, the types of matching which will be per mitted for each species, and the defects which will, not be permitted shall be as specified in table 2. Hardwood veneers of species not covered in table ii may contain small burls, occasional pin knots, color streaks or spots, inconspicuous small patches, and usual characteristics inherent iu the given species; however, knots (other than pin knots), wormholes, rough-cut veneer, splits, shake, and doze and other forms of decay will not be permitted. 2 -170-• | U*i iUii ii iiij „ I, t^f££ i£ **** ~ |, ^55 »S|5*« « : j ]| #55 ffjj* 55 -j ];•!&**! |*«* « -11 ««j « *1« I 55 5§555 ii 5553 -55 ijiSi a ml -I laf f|5i5 a ml -555 5fll5 it mt *a| m&i ii ml Hia U mU £ |3i55 *|£5s 55 5555 -RS| 5555| £2 55|- •= *5f 5|5l5 55 ii&l ; |5f5555J « «*5 -|5§ Spl£ 55 555| -553 ££5£| 55 HiS -555 Ifia a. ml -=55 5§355 55 £^*5 * £51 fills 55 ml * 555 5|555 -55§§fll5 Si aq -|i|555 5555s 55 iUz * 551 5|lll Si ml * ii\\\lii-n ml «£§§§{£*«£ ml 5 £55 5|55^ M 555£ » 535 5|lli &i mi |55§ff555 ss 5535 J 5511|||5 55 ssfg 551 ff 555 55 5555 J 55| ||||5 55- ail i'4 ||ll5 55 55|| -55| ||555 55 5555 551 §§||5 55 55|| ,?yiiii!ifi!iij a •a 3 a "3 ** v . 0 -1 e 4 £ * s 3 M 3 i t a o II I S5s 56a iltiilli - J7/ 3.3.2. Good grade (1)—The veneer shall be smooth, tight-cut, and full-length. When used as a face and when it consists of more than one piece, the edge joints shall be tight. The pieces need not be matched for color or grain, but sharp contrasts between adjacent pieces of veneer with respect to grain, figure, and natural character markings will not be permitted. The natural and other characteristics which will be permitted for each species and the defects which will not be permitted shall be as listed in table 2. Veneers of species not covered in table 2 may contain small burls, pin knots, color streaks or spots, in conspicuous patches, and usual characteristics in herent in. the given species; however, knots (other than pin knots), wonnholes, rough-cut veneer, splits, shake, and doze and other forms of decay will Jiot be permitted. 3.3.3. Sound grade (2)—The veneer shall be free from open defects. Matching for grain or color is not required. The natural and other char acteristics which will be permitted and the de fects which will not be permitted shall be as listed in table 3. 3.3.4. Utility grade (3)—The natural and other characteristics which will be permitted and the defects which will not be permitted shall be as listed in table 3. TABLE 3. Summary of veneer characteristics and allowable defect* of Sound, Utility, and Backing Grades Defects Sapwood Discoloration & Stain Mineral Streaks Sound Tight Burls Sound Tight Knots Knotholes Wonnholes Open Splits or Jolnta Doze & Decay Rough Cut Patches Crossbreaks and Shake Bark Pockets B rashness Gum Spots Laps  Sound Grade (2)' Yes Yes Yes Max. diam. 1" Max. diam. %" No Filled or Patched" No Finn areas of dare Small area Ye3 No No No Yes No Utility Grade (3)' Yes Yes Ye3 Yes Yes Max. di&r.i. 1" Yes Yes; 3/10" for one-half length of panel Firm areas of doze in face. Areas of doze and decay in inner plies and backs provided serviceability of-panel is not impaired. Small area Ye? Max. 1" in length Yes No Yes Yes j Backing Grade (4) » JYes Yes Yes Yes Yes Max. dlaia. 3" Yes 1" for one-fourth length of panel; for one half length of panel; " for full length of panel. Areas of doze and decay provided serviceability of panel is not impaired. Yes Yes Yes Yes Yes Yes Yes » T»efects permitted In Premium and Oood Grades will be allowed 1 b CnHlled, Inconspicuous, vertical wonnholes not larger than 1/18 3.3.5. Backing grade (4)—The natural and other characteristics which will be permitted and thv defects which will not be permitted shall be aj listed in table 3. 3.3.6. Specialty grade (SP) — This grade shall include veneer possessing characteristics un like any of those described for the above-men tioned grades. Characteristics shall be as agreed tipon between buyer and seller. Species such as wormy chestnut, birdseye maple, and English brown oak which have unusual decorative fea tures are considered as Specialty Grade. (Wall panel veneer face grades generally fall in this category.) 3.3.7. Softwood veneers—The face grade re quirements for certain decorative softwoods shall be as listed in table 4. All other softwoods for faces, backs, or inner plies shall meet the same grading requirements as specified for hardwoods in 3.3.1 through 3.3.6. 3.4. Thickness of veneers— The maximum veneer thicknesses shall be as provided in table n thla grade (see tables 2 and 4). " ln diameter will be permitted in tropical nardwood9. 5. The minimum thicknesses of veneers shall be as agreed upon between buyer and seller. 3.5. Lumber cores—Lumber cores shall be of any species, except that mixing of species in a single core will not be permitted. The maximum permissible, widths of core strips shall lie 2V£> .inches for Category A species (see 3.2.1), 3 inches for Category B species, and 4 inches for Category C species. Core grades and core band ing requirements shall be as described in 3.5.1 through 3.5.5. Cores shall be conditioned after gluing to equalize moisture content before sand ing. . 3.5.1. Clear grade—The wood strips shall be full length or finger-jointed and shall be free of knots or other defects which would not properly shape or mold, except that discolorations will be permitted. Wood patches or plugs shall not be used, but wood filler will be permitted. 3-5^. Sound grade—The wood strips shall be full length or finger-jointed and shall be free 4 TAULK 4. Bvmmery of veneer characterise* and allcxal. JecU for Premium grade and Ooad Prod; decorative ioftwood tpeclcs Characteristics Discoloration Hurls Knots I'ln knots KlMlllll kllols Hplke knots Filled knot holes' Worm holes Open splits or jolntu 1)117.0 Rough cut Inconspicuous patches Pitch streaks Pitch pockets Crow's foot JIatcliing Rotary — Sliced — Knotty Ve.. Western Premium (A) No Yes Yes Yes Slight 94 m. No No No No Small Email No Slight a or c Goor. (1) White pine Premium (A) Slight Yes Yes Yes . Yes* Iv4 in. No No No Inconspicuous Yes Small Snail Occasional a ore No Yes Yes Yes Slight % in. No No No . No Small Small No No a ore Gcou (1) Slight Yes Yes Yes Yes" 1V4 in. No No No Inconspicuous Yes Small Small No a ore Sliced — Vertical grain Characteristics S&i>WGG<! Heartwood Coicr streaks Color variation Mineral streaks Sacurls Pin iric.is Knots Worm holes Open splits or Joints Shake or doze Rough cut Crossbars Inconspicuous patches Pitch streaks Pitch pockets Matching • Randomly spaced for pleasing appearance, b Mnilminu 2 Inches. t Slip watched. Must be matched ln scouenco wits tigi: B'.dt out i llripbl sapwood not permitted. • Six tir more nnnual rings per Inch. f Book matched. Matched for color and pain at the joints. Douglas Mr Premium < A) Limited * Yes' No Slight No Yes No No No No No No No Yes Small No corf Redwood Premium (A) No Yes* No Slight Slight Yes Yes No ' No No No No No Yes No No cor f TABLE 5. Limiting criteria for plywood Limiting factors Glue horn! (3.0) Adhesive performance (3.0) Species or specific gravity category of veneer (3.2) Veneer edge joints (3.3) Grade of faces or face and back (3.3) Grade of hard wood inner plies adjacent to faces (3.3) M Grade of softwood inner plies adjacent to faces (3.3.7)11 Grade of other inner plies (3.3.1 through 3.3.7) Grade of lumber core (3.5) Parllclelioard or hardboard core (3.0) Maximum veneer thickness in inches by specific gravity category (3.2.1): Category A Category II Category C Percentage of wood in face direction Sanding (3.11) . . Technical (Exterior) Fully waterproof Dry and cyclic boll shear Specify N:» tape Specify 2 under A or 1 3 under 2 2 3 or 4 Not suitable Not suitable 1/12 1/10 1/8 40 to CO Specify Type I* (Exterior) Fully waterproof Dry and cyclic boll shear Specify No tape Specify 2 or 3 . 2 or 3 3 Or 4 Specify Specify . • 1/8 3/10 1/4 No limitation Specify Type II (Interior) Water resistant 3-eycle soak Specify Tape Specify 2 or 3" 2 or 3« (4 under 3 or 4) 3 or 4 Specify Specify 3/10 1/4 1/4 No limitation Specify • Type HI (Interior) Moisture resistant 2-cycIe soak Specify Tape Specify 2or3c 2or3e 3 or 4 Specify Specify 3/10 1/4 1/1 No limitation Specify .. • Not recommended for continuous exposure to moisture. ip Specify Grade 2 lor solid inner piles. ... .. „. , t Whore 1/10 Inch or thicker faces are used, Grade 4 or better Inner piles are permitted. 173 of defects, except that discolorations, sound knots, and small open defects, if securely patched or plugged with wood or wood filler will he per mitted. 3.5.3. Regular grade—The wood strips shall be the same as sound grade, except that tightly butted end joints will be permitted. 3.5;4. Clear edge—The wood strips shall be "regular grade," except that the edge strips shall be iy2 incites or wider "clear grade" to permit shaping or molding. 3.5.5. Banded core — The bands shall be "clear grade." The species, width, number of bands, and grade between bands shall be as agreed upon between buyer and seller. The types of banding shall be as follows: 1. Banded one end (BlE) 2. Banded two ends (B2E) 3. Banded one side (BIS) • 4. Banded two sides (B2S) 5. Banded two ends and one side (B2E1S) 6. Banded two sides and one end (B2S1E) FACE » , •I THREE-PLY VENEER CORE CONSTRUCTION 7. Banded two sides and two ends (B4) 3.6. Particleboard and hardboard cores •— Particleboard cores shall be in accordance with Commercial Standard CS 23R-06, Mat-formed Wood Particlchoiird? JTardboard cores shall be in accordance with Commercial Standard CS 251-63, Hardbonrd* 3.7. Special cores—Cores made of other ma terial may be used providing all other applicable requirements of this Standard are met. 3.8. Construction—Plywood panels shall be constructed with an odd number of plies. All plies shall be combinations of species, thickness, and moisture content to produce a balanced panel. All inner plies, except the core or center ply, shall occur in pairs. P'.ach pair of inner plies shall be of the same thickness and direction of grain. Each, ply of each pair shall be placed on * Later Issues of this publication may be used providing the requirements are applicable and consistent with the Issue desig nated. Copies are available from the Superintendent of Docu ments, U.S. Government Printing Office. Washington, D.C. J0402. FIVE-PLY VENEER CORE CONSTRUCTION 6 FACE BACK CR0SS8ANDS CORE PIVSPLY LUMBER COHE CONSTRUCTION FACE CROSSBANOS (—.BACK BANDS OR RAILS CORE (LUMBER. PARTICLEBOARO. OR HARDBOARD) FIVE-PLY CONSTRUCTION WITH BANDING OR RAILING FIOURB i. Typical plywood constructions—continued. opposite sides of the core. The grain of all plies shall be at right angles to the grain of the ad jacent plies and to the ends or edges of the panel. Some typical constructions are illustrated in figure 2. The limiting criteria for plywood panels shall be as provided in table 5 except for con-incr plywood which shall utilize grade 4 or A.ev inner plies adjacent to the faces for each type. (See 3.14 for marking.) 3.8.1. Special construction—Because of spe cial panel constructions and because of special face treatments, certain panels may deviate from a Hat surface prior to their application. Such devintion shall not prevent their taking the shape of the surface to which they are applied without the development of defects attributable to this deviation. 3.9. Glue bond requirements— 3.9.1. Technical Type plywood — The glue bond of Technical Type plywood panels shall meet the wood failure requirements given in table 6 when tested in accordance with 4.2, 4.3, and 4.4. Technical Type plywood constructed with TABLE 6. Wood failure requirement* for Technical and Type I plywood glue bonds Avera.ce falling- load Minimum wood failure Indiv. specimen Test piece averace In/sq in. I'nder 230 2.-0 to .330 Above 3.->0 Percent* 25 10 10 Percent* CO 30 . 15 • Thev Talues are the percentage of wood area remaining ailhTfd to the fractured inrfacc In tbc test area. hnrdwood face veneers on softwood inner plies '•all also comply with the Exterior Type bond piirements specified in Voluntary Product otandard PS l-Gfi. Softwood Plytoood, Construc tion and Industrial.* « 8«e footnote 3, page 6. 3.9.2. Type I plywood — The glue bond of Type I plywood shall meet the same require ments as Technical Type. 3.9.3. Type II plywood—The glue bond of Type II plywood shall be of such quality that specimens shall withstand the 3-cycle soak test described in 4.2 and 4.5. 3.9.4. Type III plywood — The glue bond of Type, III plywood shall be of such quality that specimens shall withstand the 2-cycle soak test described in 4.2 and 4.6. 3.10. Dimensions and tolerances—The nom inal dimensions of the plywood panels shall be as agreed upon between buyer and seller. The for the nominal dimensions shall be tolerances as follows Width: Length: Thickness: Unsanded Sanded: plus or minus 1/32 in plus or minus 1/32 in plus or minus 1/32 in plus 0, minus 1/32 in except that a sanded tolerance of plus 0, minus 3/64 in will be permitted for panels having a nominal thickness of 14 in or more. .Vote: One inch equals 2.54 centimeters. 3.10.1. Squareness—Panels 4 feet by 4 feet or larger shall be square, within 3/32 inch.-Panels less than 4 feet in length or width shall be square within 1/1G inch. Squareness shall be de-length of the two termined by measuring the diagonals of the panel. 3.10.2. StraiRhtness—The edges of panels less than 8 feet long shall be such that a straight line from one corner to the adjacent corner shall fall within 1/10 inch of the panel edge. A de parture of 3/32 inch will be permitted for panels 8 feet long and longer. 3.11. Sanding—-The. types of sanding shall be os described below. The type of sanding and the 7 175 number of surfaces of the. panels to he sanded shall he. as agreed upon between buyer and seller, except that, in no case shall the plywood be con-' sidered as ready for finishing because raised grain due to moisture absorption and marks made • in handling the plywood during shipment or storage may require further sanding. No sanding—Surfaces need not be sanded nor tape removed. Ttough sanding—Sanding hit-or-miss. Tape re moval is not required. Regular sanding—Surfaces shall be clean and free of tape. Sander streaks are not consid ered defects. Polish sanding—Surfaces shall be clean and smoothly sanded. 3.12. Moisture content—The moisture con tent of plywood panels at the time of shipment from the producing mill shall not exceed 12 per cent of the ovendry weight, as determined an ac cordance with 4.7. 3.13. Factory finished panels—The finish of factory finished panels shall be as agreed upon between buyer and seller. 3.14. Marking—All plywood represented as conforming to this Voluntary Product Standard shall be identified by either of the following methods: (a) Each panel shall be marked with the sym bol of this Sandarcl, PS 51-71, the name or rec ognized identification of the producer; the'species and grade of the face veneer; the type of ply wood; the symbol "CP," if container plywood; and the identity of the qualified inspection and testing agency, if applicable (see section 7), or (b) The shipment or order shall be accom panied by a written certification which states that the panels conform to all of the require ments of Voluntary Product Standard PS 51-71, and identifies the producer; the species and grade of the face veneer: the type of plywood; the qualified inspection and testing agency, if ap plicable (see section 7); and the specific intended use if container plywood. 4. INSPECTION AND TEST PROCEDURES 4.1. General—The inspection and test pro cedures contained in this section are to be used to determine the conformance of products to the requirements of this Voluntary Product Stand ard. Each producer or distributor who represents his products as conforming to this Standard may utilize statistically based sampling plans which are appropriate for each particular manufactur ing process but shall keep such essential records as are necessary to document with a high degree of assurance his claim that all of the require ments of this Standard have been met. Addition al sampling and testing of the product, as may be agreed upon between purchaser and seller, is not precluded by this section. 4.2. Specimens for glue bond test— 4.2.1. Technical and Type I plywood — Three test pieces shall be cut from each panel selected: one piece from each end of the-panel and one piece near the center of the punel. l/ich test piece shall be of sufficient size to provide at least six specimens for the dry shear test and six specimens for the cyclic-boil shear test (see table 7). 4.2.2. Type II plywood—A total of 10 t<-st. specimens shall be cut from each panel selected: two specimens from each end approximately at mid-width of the panel; two specimens from each edge approximately at mid-length of the panel; and two specimens near the center of the panel. Test, specimens shall not have common edges (see table 7). 4.2.3. Type III plywood—-Three test speci mens shall be cut from each panel selected: one from each end of the panel and one near the cen ter of the panel (see table 7). TABLE 7. Test specimen sizes Type of plywood Specimen size Technical & Type I 3'A inch* by 1-inch specimens Type II (3-cycle) 5-inchb by 2-incb spccivuei;.-Type III (2-cyclc) G-inch by 6-inch specimens' a Parallel to the pniln of the outside venders In 7-. and ll-p!y construction. Perpendicular to the grain of the outside veneers In 0- nnd !>-piy construction. The precedtii.it nppllr.-. to specimens for testing Ihe Innermost piles. Specimens for tesilrisr the outer plies shall always be parallel to the- (train of the face veneer lu the 3Vi Inch dimension. "J Parallel to the grain of the face veneers. 4.3. Dry shear test—Shear tests shall be conducted on specimens prepared as shown in figure 3. The ends of each specimen shall be gripped in test machine retaining jaws, and the load shall be applied at the rate of 600 to 1.000 pounds per minute. Specimen notching shall be accomplished in. such a way as to assure that when the specimens are subjected to loading, the lathe checks in the center ply of half of the. specimens will be in tension, while in the other half the lathe checks will be in compression. An explanation of one method of notching speci mens to insure that half of the lathe checks are "pulled in tension and half are pulled in compres sion, is described in American Society for Test ing and Materials (ASTM) f) f>06-64, Stond.'rd Method of Test for Strength Properties of Ad hesives in Plywood Type Constructio-n in Shtor by Tension Looding.* If the number of plies ex ceeds three, the outer pairs of glue lines and in nermost glue lines shall be tested with separate sets of test specimens. In plywood with face plies thicker than 1/16 inch, the shear area shall b° 1 square inch, as shown in figure 3. specimen A. Specimens of plywood with face plies 1/1R inch •Later Issues of this publication may be u»ed providing the requirements ure applicable and ronalstent with the Issue de-dt--nnted. Copies of ASTM publication* are obtalnuble from the American Society for Test Inn and Materials. 191B Kace Street, Philadelphia, Pennsylvania 10103. 8 CUT 2/3 THROUGH CORE SPECIMEN A CUT 2/3 THROUGH CORE SPECIMEN 8 FIOUBE 3. Plywood bond shear test specimens. or less in thickness shall be of the form shown in figure 3. speci.ntn B. in which the shear area shall be reduced to ty square inch without chang ing the width of the specimen. Test machine loads obtained from specimens of ty square inch shear area shall be multiplied by 2 to convert to pounds per square inch and then reduced by 10 percent before comparing with the required -nhies set forth in table 6. For shear tests of lum-r core plywood, particleboard core plywood, «nd hardboard cove plywood, the core shall be cut away to 1/10 inch in thickness. •1.1. tyclic-boil uhear test —The specimens prepared as shown in figure 3 shall be boiled in water for 4 honi-s and then dried for 20 hours at a temperature of 145±5 °F (63±3 °C). They shall be boiled again for 4 hours, cooled in water, and then subjected while wet to the test described in 4.3. The values obtained from the six speci mens shall meet the applicable requirements given in table G. If the number of plies exceeds three, the outer pairs of glue lines and innermost glue lines shall be tested with separate sets of test pieces. 4.5. Three-cycle soak test—The 5-inch by 2-inch specimens from eacli test panel shall be submerged in water at 75 = 5 °F (24±3 °C) for 4 hours and then dried at a temperature between 120 and 125 rF f4f' to 52 CC) for 10 hours with SufiioK-nt air circulation to lower the moisture content (based on .ovendry weight) of specimens to a maximum of ^ percent. This cycle shall be repeated until all ^'ciim-ns fail or until three rvclfS have been completed, whichever occurs first. A specimen shall be considered as failing when any single delnmination between two plies is greater than 2 inches in continuous length, over 14 i,lcM m drpth at any point, and 0.003 ich in width, as determined by a feeler gage ,003-inch thick and V^-inch wide. Delamination duo to tape at-joint's of inner plies or defects per mitted by the grade shall be disregarded. Nine of the 10 specimens shall pass the first cycle and eight of the 10 specimens shall pass the third cycle. 4.6. Two-cycle soak test—The 6-inch by 6-inch specimens shall be submerged in water at 75 ± 5 °F (24 ±3 °C) for 4. hours, and then dried at 75 ±5 °F in an open room for 20 hours. . The cycle shall be repeated until all specimens fail or until two cycles have been completed, whichever occurs first. A specimen shall be con sidered as failing when any single delamination between two plies is greater than 2 inches in con tinuous length, over Vi m depth at any point and 0.003 inch in width. Separation is de termined with a 0.003-inch feeler gage. When this test is applied to lumber core or particle-boar;! core, plywood, the core should be cut away to a depth of 1 inch on all four edges, leaving only enough core in this stress-relieved section to produce an approximate balance with the lace ply. Delamination due. to tape at joints of inner plies or defects permitted by the grade shall be disregarded. If there is a failure of more than one test specimen, the panel shall be classified as defective. 4.7. Moisture content test — The. moisture content of the plywood shall be determined as follows: A small test specimen shall be cut from the sample panel; the test specimen shall meas-.ure hot less than 0 square inches in area and shall weigh not less than 20 grams. All loose splinters shall be removed from the 'specimen. The specimen shall be immediately weighed to the nearest 0.1 of a gram, and the weight shall be recorded as the original weight. The specimen shall then be dried in an oven at 212 to 221 °F (100 to 105 °C) until constant weight is attained. After drying, the specimen shall be reweighed immediately, and this weight shall be recorded as the ovendry weight. The moisture content shall be calculated as follows: Orlclnnl weight — oTmdrr weight x 100 = MoUture content Ovendry weight . {percent) 9 177 APPENDIX 5 The mixing sequence of the PF IB-334yGlue. 179 c.c. VJ.B. Smith Mr. F. Alan Tayelor, Industrial Development Officer, August 9, 1974 VANCOUVER, B.C. Dear Nr. Tayelor: Bill Hancock has requested that I forward details on the glue aix we prepared for use in bonding veneer for ladder stock at our lab. The mixes r/.ade August 8th vjere formulated a3 follows: IB-334 Plyophen Water K'orprof il Wheat Flour Soda Ash 5,872 gxas 1,781 gxas 93D RTP.S 900 gms *»00 gns Mix 30 minutes on Bower Mixer at 4000 rpn IB-334 Plyophen Jater 8,985 gas 1,13? gras 20,000 gms Total piv. solids: 4 3.8% Phenol Formaldehyde solids: 26.0% Viscosity 3 25°C £3 spindle 60 rpsi LVF Brookfield - 1350 cps This nix differs fron a standard plywood mix on two points. First, the PF solids are higher by approximately 3% - 26% as oppos-sd to 23%. Secondly, there is twice the concentration of wheat flour in this nix as in the average plywood mix. This formulation and resin has previously been successfully used in veneer laminating and appears to display the assembly tine tolerance required by the process. Should further assistance be required, please contact me. Yours very truly, REICIIHOLD CHEMICALS LIMITED W. C. Ainslie, Wood Lab. Manager • V/CA/jia c.c. Dr. y. V. Hancock [to APPENDIX 6 The mixing sequence of the Monsanto UF 109 Glue. (8.1 MONSANTO UF109 RESIN WITH EK HARDENER Mixing Directions 100 lbs. £5.43 15 lbs. o-<*'AZ \ lb. 100 lbs. 40 lbs. 6-S "f739 Sff S7/4 90 lbs. _ji£L— 345^ lbs.-i-6'S WATER at 65° - 70° F. MONSANTO EK CATALYST Mix 1 Minute STEROX CD WHEAT FLOUR Mix 5 Minutes or Until Lump Free MONSANTO UF109 RESIN Mix 3 Minutes or Until Lump Free MONSANTO UF109 RESIN Mix 5 Minutes with Cooling Water in Jacket Total Weight of Mix The mixed glue will have a working life of 24 hours at 70° F. Mixed glue left overnight should be mixed with a fresh batch before using. * The length of the mixing time prior to the addition of the resin will affect the final viscosity - increasing the mixing time will reduce the viscosity. ) HARDWOOD HOT PRESSING SCHEDULE* 0 UF-109 RESIN WITH EK HARDENER Si \ \) I } ) —r— Panels Max. Dist. p'SS No. ot per «o!»ex Construction Center Time Settings For Press Time - Mins. 240° F. 260° F. 3/16 1/4 1/4 1/4* 3/S 1/2 1/2 3/4 3/4 3/4 O 3/4 3/4 183 , 208 . 207 .063 . 138 .181 . 136 .326 .329 .352 . 138 163 1/7H 1/6M 1/7H 1/6 or 1/7 1/10M 2xl/7H 1/10M 3xl/7H lxl/7H 1x1/ 10M 1/10 1/8 1/7H 1/7H . 262B Plywood 2xl/7H 2x3/16H 2xl/7H 1/2 Plywood 1/2 Plywood 5-1/4 5-1/2 5-3/4 3- 3/4 4- 3/4 6 5- 1/4 8-1/4 8-1/4 8-3/4 5-1/4 5-1/2 4- 3/4 5 5- 1/4 3- 1/4 4- 1/4 5- 1/2 4-i,'4 7-3/4 7- 3/4 8- 1/4 4-3/4 5 »>' plus 1/2 min. for each additional 1/16 over the 3/4 . S OVERLAYS 1/4 with. 1/6 chipboard center - 2 panels per opening 6 1/4 with 1/6 chipboard center and 1/30 - 1/16 face and back 3-3/4. 1/2 with 7/16 chipboard center and 1/30 - 1/16 face and back 3-3/4 3/4 with 11/16 lumber or chipboard center 3-3/ABOVE TIME INCLUDE 15 SECS. CLOSING TIME AND 15 SECS. FOR CAULS. SPREADS Hemlock 62 , 1/10 \ ) 1/7 65 1/6 67 ^ Rough core add 3 to D lbs. Mahogany " 57 60 62 Maximum recommended time assembly. Minimum recommended time assembly 8 hours 5 mins. • Note: Pressure 175 lbs. per square inch. Pressure with chipboard 150-160 lbs. per sq. xn. reduce the press temperature to 220°F. add 

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