Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Impact of juvenile wood on the drying characteristics of Pacific Coast Hemlock structural timber Bradic, Slobodan 2005

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_2006-0013.pdf [ 20.72MB ]
Metadata
JSON: 831-1.0074974.json
JSON-LD: 831-1.0074974-ld.json
RDF/XML (Pretty): 831-1.0074974-rdf.xml
RDF/JSON: 831-1.0074974-rdf.json
Turtle: 831-1.0074974-turtle.txt
N-Triples: 831-1.0074974-rdf-ntriples.txt
Original Record: 831-1.0074974-source.json
Full Text
831-1.0074974-fulltext.txt
Citation
831-1.0074974.ris

Full Text

Impact of Juvenile Wood on the Drying Characteristics of Pacific Coast Hemlock Structural Timber by SLOBODAN BRADIC B.Sc, The University of Belgrade, 1997 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE F A C U L T Y OF G R A D U A T E STUDIES (Forestry) THE UNIVERSITY OF BRITISH C O L U M B I A December, 2005 © SLOBODAN BRADIC, 2005 ABSTRACT Large volumes o f relatively small-diameter logs are generated from sustainable sources such as the Pacific Coast Hemlock second-growth forests. The percentage of juvenile wood in this kind of material is higher compared to limited old growth wood supplies. The present scientific knowledge is often limited to individual properties of juvenile wood without including interactions with other drying factors. For that reason, this investigation evaluates the drying quality of the mix of 105 mm square timbers from second-growth western hemlock (Tsuga heterophylla) and amabilis fir (Abies amabilis), commercially known as Pacific Coast Hemlock baby-squares, using two different concepts o f interactions. First, the evaluation is based on the influence of juvenile wood presence shown with a pith location at their end-surface and drying target moisture content, while in the second concept the cutting season is added as the third controlled factor. Timber specimens were classified into four groups depending on the presence and location of the tree pith. A total of 640 specimens were dried in a laboratory conventional (heat-and-vent) k i ln in four drying runs to 15% and 20% target moisture contents, with one charge o f specimens from the summer and other of the fall cutting season. The results showed that timbers with the pith shown in the centre should be avoided in the production of baby-squares because of its high propensity for bow, twist and surface checks, due to the problems with variable shrinkage coupling of juvenile and mature wood within specimens. Specimens with the pith shown close to one of the sides in the cross-section had a lower, but acceptable, quality according to the E l 20 C F L A grading rules. Because of the higher shrinkage, the lower target moisture content shows a greater risk for twist and surface checks, compared with the higher moisture content. The importance of the cutting season is reflected through its significant interactions with the target moisture content in the case of volumetric shrinkage, and with the pith location in the case of twist. These are consequences of lower initial moisture content i n summer-cut specimens that could occasionally reach moisture content below the fiber saturation point, and start to shrink before ki ln drying. n TABLE OF CONTENTS Abstract 1 1 Table of Contents i i i Lis t o f Tables vi Table of Figures v i i i Table of Figures v i i i List of Abbreviations and Acronyms x Acknowledgements x i 1 Introduction 1 1.1 Pacific Coast Hemlock 2 1.1.1 Distribution 3 1.1.2 Properties and usage 5 1.2 Juvenile wood 10 1.3 Wood drying 19 1.3.1 Wood moisture relations 20 1.3.2 K i l n drying 22 1.4 Drying defects 29 1.4.1 Shrinkage 30 1.4.2 Surface and end checks 31 1.4.3 Shape distortions 32 1.4.3.1 B o w 32 1.4.3.2 Twist 34 1.4.3.3 Diamonding 35 1.5 K i l n drying of P C H 36 1.6 Wood grading 41 1.7 Research Objectives 42 2 Materials and methods 44 2.1 Materials 44 2.2 Experimental Design 46 2.3 Methods of timber evaluation 49 2.3.1 Green timber evaluation 49 2.3.1.1 Density and initial moisture content 49 2.3.1.2 Green shape distortions 53 2.3.1.3 Measuring of green surface checks 55 2.3.2 K i l n and ki ln data collection and drying schedule used 56 2.3.3 K i l n dried timber evaluation 58 2.3.3.1 K i l n dried moi sture content 58 2.3.3.2 Shrinkage 59 2.3.3.3 Shape distortions 60 2.3.3.4 Surface checks 60 i i i 2.3.4 Evaluation of planed timber 60 2.3.4.1 Planed moisture content 61 2.3.4.2 Shape distortions 62 2.3.4.3 Surface checks 62 2.3.5 Other wood attributes 62 2.3.5.1 Slope of grain 62 2.3.5.2 Compression wood 63 2.3.6 Grading of baby-squares 65 2.4 Statistical analysis 66 2.4.1 Factorial design 67 2.4.1.1 Concept A - 2x4 design 67 ' 2.4.1.2 Concept B - 2x2x4 design 69 2.4.2 Contingency table 72 2.4.3 Other tests 73 3 Results and Discussion 7 4 3.1 Basic density 74 3.2 Initial moisture content 77 3.2.1 Concept A 77 3.2.2 Concept B 78 3.3 Drying time and rate 80 3.4 K i l n dried rough moisture content 84 3.4.1 Concept A 85 3.4.2 Concept B 86 3.4.3 Core and shell moisture content 87 3.5 Planed moisture content 89 3.6 Volumetric shrinkage 91 3.6.1 Concept A 93 3.6.2 Concept B 94 3.7 K i l n dried rough shape distortions 96 3.7.1 B o w 96 3.7.1.1 Concept A 99 3.7.1.2 Concept B 101 3.7.2 Twist 102 3.7.2.1 Concept A 105 3.7.2.2 Concept B 107 3.7.3 Diamonding 109 3.7.3.1 Concept A 112 3.7.3.2 Concept B 112 3.8 K i l n dried rough surface checks 113 3.8.1 Concept A 116 3.8.2 Concept B 117 3.9 K i l n dried shape distortions after planing 119 3.9.1 Planed bow 119 3.9.2 Planed twist 120 3.9.3 Planed diamonding 121 3.10 K i l n dried planed surface checks 123 3.11 Effects o f the slope of grain and compression wood 124 iv 3.11.1 Slope of grain 124 3.11.2 Compression wood 129 3.12 Grading 133 4 Conclusion and future work 135 4.1 Conclusions 135 4.1.1 Concept A 136 4.1.2 Concept B 137 4.1.3 General conclusions 139 4.2 Future Work , 140 5 References 142 v LIST OF TABLES T A B L E 1.1: A P P R O X I M A T E P E R C E N T A G E A N D SPECIFICATIONS FOR S T R U C T U R A L L U M B E R U S A G E IN A T Y P I C A L J A P A N E S E POST A N D B E A M H O U S E 8 T A B L E 1.2: F I N A L MOISTURE C O N T E N T R A N G E FOR VARIOUS W O O D PRODUCTS 20 T A B L E 2.1: D E T A I L S OF T H E DRYING RUNS 44 T A B L E 2.2: D R Y I N G S C H E D U L E USED IN T H E FOUR RUNS 58 T A B L E 2.3: A N A L Y S I S O F V A R I A N C E T A B L E - C O N C E P T A 68 T A B L E 2.4: A N A L Y S I S O F V A R I A N C E T A B L E - C O N C E P T B 71 T A B L E 3.1: B A S I C DENSITY STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 74 T A B L E 3.2: A N A L Y S I S OF V A R I A N C E FOR BASIC DENSITY 75 T A B L E 3.3: INITIAL MOISTURE C O N T E N T STATISTICS FOR DIFFERENT PITH CLASSES A N D DRYING RUNS 77 T A B L E 3.4: A N A L Y S I S O F V A R I A N C E FOR INITIAL MOISTURE C O N T E N T - C O N C E P T A 77 T A B L E 3.5: A N A L Y S I S O F V A R I A N C E FOR INITIAL MOISTURE C O N T E N T - C O N C E P T B 78 T A B L E 3.6: A C T U A L A N D A D J U S T E D DRYING TIMES FOR T H E F O U R DRYING RUNS 81 T A B L E 3.7: F I N A L MOISTURE C O N T E N T STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS B A S E D O N T H E WEIGHT DIFFERENCE 84 T A B L E 3.8: A N A L Y S I S O F V A R I A N C E FOR T H E FINAL MOISTURE C O N T E N T B A S E D O N T H E WEIGHT DIFFERENCE-C O N C E P T A 85 T A B L E 3.9: A N A L Y S I S O F V A R I A N C E FOR T H E FINAL MOISTURE C O N T E N T B A S E D O N T H E WEIGHT DIFFERENCE -C O N C E P T B : 86 T A B L E 3.10: A V E R A G E FINAL MOISTURE C O N T E N T STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS B A S E D O N PIN M E A S U R E M E N T S 88 T A B L E 3.11: P L A N E D W O O D MOISTURE C O N T E N T STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS B A S E D O N PIN-METER M E A S U R E M E N T S 90 T A B L E 3.12: P A I R E D T - T E S T FOR DIFFERENCES OF KILN DRIED MOISTURE C O N T E N T A N D 9 0 T A B L E 3.13: A V E R A G E DIRECTIONAL S H R I N K A G E P E R C E N T A G E S F R O M G R E E N T O KILN DRIED SPECIMENS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 91 T A B L E 3.14: A N A L Y S I S O F V A R I A N C E FOR V O L U M E T R I C S H R I N K A G E - C O N C E P T A 93 T A B L E 3.15: A N A L Y S I S O F V A R I A N C E FOR V O L U M E T R I C S H R I N K A G E - C O N C E P T B 94 T A B L E 3.16: G R E E N B O W STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 96 T A B L E 3.17: K I L N DRIED B O W STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 98 T A B L E 3.18: A N A L Y S I S O F V A R I A N C E OF B O W DIFFERENCES C R E A T E D DURING KILN DRYING - C O N C E P T A 99 T A B L E 3.19: A N A L Y S I S O F V A R I A N C E OF B O W DIFFERENCES C R E A T E D DURING KILN D R Y I N G - C O N C E P T B 101 T A B L E 3.20: G R E E N TWIST STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 103 T A B L E 3.21: K I L N DRIED TWIST STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 104 T A B L E 3.22: A N A L Y S I S O F V A R I A N C E FOR TWIST DIFFERENCES C R E A T E D DURING KILN DRYING - C O N C E P T A . . . . 105 T A B L E 3.23: A N A L Y S I S OF V A R I A N C E FOR TWIST DIFFERENCES C R E A T E D DURING KILN DRYING - C O N C E P T B . . . . 107 T A B L E 3.24: G R E E N DIAMONDING STATISTICS F O R DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS 110 T A B L E 3.25: K I L N DRIED DIAMONDING STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 111 T A B L E 3.26: A N A L Y S I S O F V A R I A N C E FOR DIAMONDING DIFFERENCES C R E A T E D DURING KILN DRYING - C O N C E P T A 112 T A B L E 3.27: A N A L Y S I S O F V A R I A N C E FOR DIAMONDING DIFFERENCES C R E A T E D DURING KILN DRYING - C O N C E P T B 113 T A B L E 3.28: G R E E N S U R F A C E C H E C K STATISTICS F O R DIFFERENT PITH C L A S S E S A N D DRYING RUNS 114 T A B L E 3.29: K I L N DRIED S U R F A C E C H E C K S STATISTICS FOR DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS 114 T A B L E 3.30: A N A L Y S I S OF V A R I A N C E FOR S U R F A C E C H E C K DIFFERENCES C R E A T E D DURING KILN D R Y I N G -C O N C E P T A 117 T A B L E 3.31: A N A L Y S I S OF V A R I A N C E FOR S U R F A C E C H E C K DIFFERENCES C R E A T E D DURING KILN DRYING -C O N C E P T B : 118 T A B L E 3.32: P L A N E D B O W STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 119 T A B L E 3.33: P L A N E D TWIST STATISTICS FOR DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS 120 T A B L E 3.34: P L A N E D DIAMONDING STATISTICS F O R DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS 121 v i T A B L E 3.35: P L A N E D S U R F A C E C H E C K S STATISTICS FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 123 T A B L E 3.36: S L O P E OF GRAIN STATISTICS FOR DIFFERENT PITH CLASSES A N D DRYING RUNS 125 T A B L E 3.37: A N A L Y S I S OF V A R I A N C E FOR SLOPE OF GRAIN 126 T A B L E 3.38: COMPRESSION W O O D STATISTICS FOR DIFFERENT PITH CLASSES A N D DRYING RUNS 129 T A B L E 3.39: A N A L Y S I S OF V A R I A N C E FOR COMPRESSION WOOD 131 T A B L E 3.40: C O N T I N G E N C Y T A B L E OF PITH LOCATION C L A S S E S A N D A C C E P T A B L Y FOR EXPORT PRODUCTS 133 v i i TABLE OF FIGURES F I G U R E l . l : PACIFIC C O A S T H E M L O C K SPECIES 3 F I G U R E 1.2: O C C U R R E N C E OF WESTERN H E M L O C K A N D AMABILIS FIR 4 F I G U R E 1.3: T Y P I C A L USES OF PACIFIC C O A S T H E M L O C K IN W O O D E N TRADITIONAL HOUSING IN J A P A N 7 F I G U R E 1.4: D I A G R A M M A T I C REPRESENTATION OF JUVENILE A N D M A T U R E W O O D DISTRIBUTION 10 F I G U R E 1.5: S C H E M A T I C REPRESENTATION OF T H E G R A D U A L I M P R O V E M E N T IN PROPERTIES WITH A G E 11 F I G U R E 1.6: ANISOTROPIC CHARACTERISTICS OF W O O D A N D FIBRIL ORIENTATION IN N O R M A L , JUVENILE A N D COMPRESSION W O O D 12 F I G U R E 1.7: A V E R A G E RING DENSITY T R E N D F R O M PITH TO B A R K IN S O M E S E C O N D - G R O W T H WOODS 12 F I G U R E 1.8: P A C K A G E - L O A D E D KILN WITH FANS C O N N E C T E D DIRECTLY T O MOTORS 23 F I G U R E 1.9: INSIDE VIEW OF T H E U B C 8-FOOT L A B O R A T O R Y DRY KILN 25 F I G U R E 1.10: T H E O R E T I C A L DRYING C U R V E 27 F I G U R E 1.11: RELATIONSHIP B E T W E E N A V E R A G E MOISTURE C O N T E N T A N D S C H E D U L E SETTINGS 28 F I G U R E 1.12: ANISOTROPIC S H R I N K A G E A N D SHAPE DISTORTIONS 29 F I G U R E 1.13: M O I S T U R E C O N T E N T OF W O O D A T VARIOUS R E L A T I V E HUMIDITY 31 F I G U R E 1.14: E X A M P L E OF B O W IN A S Q U A R E TIMBER 33 F I G U R E 1.15: E X A M P L E O F TWIST IN A S Q U A R E TIMBER 34 F I G U R E 1.16: E X A M P L E O F DIAMONDING IN A SQUARE T I M B E R 35 F I G U R E 1.17: T A N G E N T I A L A N D R A D I A L S H R I N K A G E DIRECTIONS IN RELATION T O T H E 36 F I G U R E 1.18: T H E D S R D S T R A T E G Y 40 F I G U R E 2.1: T H E A L B E R N I PACIFIC DIVISION S A W M I L L 44 F I G U R E 2.2: L O C A T I O N O F T H E T R E E PITH ON G R E E N SPECIMENS 45 F I G U R E 2.3: L A B O R A T O R Y W O O D DRYING KILN A T U B C 47 F I G U R E 2.4: C U T T I N G O F SPECIMENS A T F O R I N T E K 47 F I G U R E 2.5: C U T T I N G P R O T O C O L OF G R E E N WOOD FOR T H E PREPARATION O F DRYING SPECIMENS 48 F I G U R E 2.6: M E A S U R I N G O F V O L U M E USING T H E W A T E R IMMERSION M E T H O D 50 F I G U R E 2.7: W O O D D R Y I N G O V E N WITH W O O D SLABS AT U B C 50 F I G U R E 2.8: D I G I T A L L Y S C A N N E D COOKIES F R O M T H E S A M E T I M B E R 51 F I G U R E 2.9: E L E C T R O N I C S C A L E F O R M E A S U R I N G O F T I M B E R W E I G H T E D 52 F I G U R E 2.10: D I G I T A L CALIPERS FOR M E A S U R I N G DIMENSIONS 52 F I G U R E 2.11: T A B L E F O R M E A S U R I N G O F SHAPE DEFORMATIONS 53 F I G U R E 2.12: D I G I T A L DIAL G A U G E 54 F I G U R E 2.13: M E A S U R I N G OF B O W A N D TWIST 54 F I G U R E 2.14: M E A S U R I N G OF DIAMONDING 55 F I G U R E 2.15: M E A S U R I N G OF S U R F A C E C H E C K S 56 F I G U R E 2.16: C O M P U T E R I Z E D C O N T R O L P A N E L O F T H E KILN 57 F I G U R E 2.17: R E S I S T A N C E PIN-TYPE MOISTURE M E T E R : 59 F I G U R E 2.18: S T O R A G E O F SPECIMENS B E T W E E N T H E E V A L U A T I O N S 61 F I G U R E 2.19: M E A S U R I N G OF SLOPE OF GRAIN 63 F I G U R E 2.20: M E A S U R I N G OF P E R C E N T A G E OF COMPRESSION W O O D 64 F I G U R E 3.1: D R Y I N G C U R V E S OF T H E F O U R RUNS A N D DRYING S C H E D U L E 81 F I G U R E 3.2: A D J U S T E D D R Y I N G C U R V E S FOR T H E F O U R RUNS 82 F I G U R E 3.3: D R Y I N G R A T E S O F T H E F O U R RUNS VS. MOISTURE C O N T E N T 83 F I G U R E 3.4: F I N A L MOISTURE C O N T E N T DISTRIBUTIONS OF T H E FOUR DRYING RUNS 89 F I G U R E 3.5: V O L U M E T R I C SHRINKAGES FOR DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS 93 F I G U R E 3.6: Bow DIFFERENCES C R E A T E D DURING KILN DRYING FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 99 F I G U R E 3.7: T W I S T DIFFERENCES C R E A T E D DURING KILN DRYING FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 105 F I G U R E 3.8: D I A M O N D I N G DIFFERENCES FOR DIFFERENT PITH C L A S S E S A N D D R Y I N G RUNS I l l F I G U R E 3.9: S U R F A C E C H E C K DIFFERENCES C R E A T E D DURING KILN D R Y I N G FOR DIFFERENT PITH C L A S S E S A N D DRYING RUNS 116 F I G U R E 3.10: F R E Q U E N C Y OF B O W D E V E L O P E D DURING DRYING VS. S O G 126 F I G U R E 3.11: Bow D E V E L O P E D DURING DRYING VS. S O G 128 v m F I G U R E 3.12: TWIST D E V E L O P E D DURING DRYING vs. S O G 128 F I G U R E 3.13: D I A M O N D I N G D E V E L O P E D DURING DRYING vs. S O G 128 F I G U R E 3.14: S U R F A C E C H E C K S D E V E L O P E D DURING DRYING vs. S O G 128 F I G U R E 3.15: FREQUENCIES OF T H E PRESENCE OF COMPRESSION WOOD 130 F I G U R E 3.16: Bow D E V E L O P E D DURING DRYING vs. COMPRESSION W O O D 132 F I G U R E 3.17: TWIST D E V E L O P E D DURING DRYING vs. COMPRESSION W O O D 132 F I G U R E 3.18: D I A M O N D I N G D E V E L O P E D DURING DRYING VS. COMPRESSION W O O D 132 F I G U R E 3.19: S U R F A C E C H E C K S D E V E L O P E D DURING DRYING VS. COMPRESSION W O O D 132 ix LIST OF ABBREVIATIONS AND ACRONYMS % percent o degree ° c degree Celsius 1 liter A S T M American Society for Testing and Materials Coast Forest and Lumber Association C F L A FSP fiber saturation point Ft g foot, feet gram H relative humidity hr hour J Joule K Kelvin kg kilogram kJ kiloJoules M moisture content m meter m 2 square meter m 3 cubic meter M c moisture content of core M s moisture content of shell M e equilibrium moisture content M f final moisture content M F B M thousand board feet measure (1 M F B M = 2.36 m3) M i initial moisture content M J megaJoule mm millimeter M O E modulus of elasticity M O R modulus of rupture MPa megaPascal M , target moisture content N Newton Pa Pascal P C H Pacific Coast hemlock PL pith location R F V radio frequency vacuum SOG slope of grain Tdb dry-bulb temperature Twb wet-bulb temperature Twbd wet-bulb depression w Watt PL pith location CS cutting season X I ACKNOWLEDGEMENTS I would like to take this opportunity to express my heartfelt appreciation to all those people who stand out most notably in my mind, as significantly contributing not only to my research, but also to the indispensable knowledge and experience that I have gained from this Master's degree. I would like to sincerely thank my supervisor, Dr. Stavros Avramidis, for his support, assistance and advice through the completion of my thesis. M y sincere gratitude is also extended to my committee members for their input. A special thanks to Dr. Tony Kozak for his assistance and expertise in statistical analysis. Furthermore, my sincere thanks go to Dr. Bingye Hao and Dr. Diego Elustondo for their help and constructive discussions. I would also like to express a special thanks to Weyerhaeuser Company (Alberni Pacific Division) and Forintek Canada Corporation (Western Laboratory) for their unconditional assistance. Finally, I am truly grateful to my family and friends for their overwhelming encouragement, support and belief in all my exertions. x i 1 INTRODUCTION In the era of increased degradation of the natural environment, the old growth forested areas as a natural source of wood, are obtaining protected status. A t the same time, growth in total wood consumption closely follows population growth (Hammett and Youngs 2002). For that reason, in recent years, wood manufacturers as well as their customers, have become more concerned about the protection of limited old growth forests; as a result, they have been trying to find rational solutions for the problems of processing small-diameter wood from second-growth and ecologically suitable plantation forests (LeVan-Green 2001). This type of tree grows fast, rapidly reaches saw-timber size and is harvested at a younger age, and because the growth is generally greatest during the formation of juvenile wood, the juvenile wood core may represent a larger proportion compared with old-growth trees (Kretschmann et al. 1993). Therefore, this larger proportion in one log, together with a smaller diameter of modern log supplies (Green et al. 2005), makes juvenile wood a significant part of today's harvest. It has been reported that the percentage of juvenile wood in plantation trees ranges from 7% in a 53-year rotation to 47% in an 18-year rotation (Zobel and McElwee 1958). A decrease in the rotation age wi l l increase the proportion of juvenile wood (Gartner 2005). Juvenile wood typically has characteristics that negatively impact a number of wood properties. The greatest concerns regarding the presence of juvenile wood in solid products are focused on its behavior under changing moisture content. Because of its cost, long production times, and influence on the final quality of products, wood drying is a very important component of the solid wood products industry. The modern wood drying concept should be a 1 strong component in current issues regarding the rational use of natural resources and the reduction of material losses. Unfortunately, the current k i ln drying approach to new wood supplies is basically the same as the optimized technology/strategy for old growth wood. The constant shift towards the use of smaller diameter logs does not allow for such past luxurious thinking, or lack of knowledge/forethought, as was acceptable during the era o f old growth supplies with large tree diameters (Smith and Briggs 1985). Consequently, it is obvious that wood processing technologies and ki ln drying, as one of the crucial components, need to be the subject of reorganization; also, new strategies should be analyzed in terms of technological, economical and ecological consideration. Canada accounts for approximately 48% of all international trade in softwood lumber products (Council of Forest Industries 2000), and British Columbia is the source of more than 50% of Canadian lumber production (Morton and Greenwood 2004). In British Columbia (BC) more than 250,000 ha of forest land are logged each year (Natural Resources Canada 2000), and such a large area causes related issues to the B C forest industry to have global importance. In this context, the following study of k i ln drying techniques of juvenile wood, involving Pacific Coast hemlock baby-squares as one of B C ' s most profitable wood products, is an important contribution to globally required knowledge towards a step forward in the evolution of the utilization of natural resources. 1.1 Pacific Coast Hemlock The combination of western hemlock and amabilis fir is a common softwood species mixture from the Pacific Coast region of Canada. Commercially, it is known as Pacific Coast Hemlock (PCH) or Western hem-fir or simply "Hem-Fir". This section provides an overview of its geographical distribution, properties and usage. 2 1.1.1 Distribution The two species comprising the P C H commercial group are western hemlock (Tsuga heterophylla (Raf.) Sarg.) and amabilis fir (Abies amabilis (Dougl.) Forbes). According to Pojar et al. (1991), the P C H zone occurs at low to middle elevations mostly west of the coastal mountains, along the entire B C coast, and on into both Alaska and Washington/Oregon. The zone covers much of Vancouver Island, the Queen Charlotte Islands, and the Coast Mountains. It sometimes occurs within the coastal mountain barrier in major river valleys, especially along the Fraser and Skeena rivers (Figures 1.2). Because of their close physical and visual similarities, these species are usually harvested, processed, and marketed together. Both are strong, straight trees which have grown to mature heights of 60 meters, and have diameters exceeding two meters (Isenberg 1980). They prune their branches as they grow, leaving clear symmetrical trunks up to three-quarters of their height, which is a natural characteristic that produces large volumes of clear timber from the log (Burns and Honkala 1990). Figure 1.1: Pacific Coast Hemlock species (western hemlock-left, amabilis fir-right) 3 The rain forests of BC's coast provide ideal growing conditions for these quickly regenerating species (Pojar et al. 1991). Conifers in general do well in the wet Pacific Northwest, because their evergreen habit allows them to maintain positive net rates of photosynthesis during the long and wet winters. Many of them are very shade-tolerant, so they are able to survive in a relatively dark under-story until the death of over-story trees allows them to continue their growth. The infrequency o f stand-destroying disturbance is readily exploited by these long-lived trees (Waring and Franklin 1979). Hemlock does particularly well because the most common disturbance in this ecosystem is wind throw that may destroy single trees or, more rarely, even wipe out forests across a landscape. Hemlock seedlings establish preferentially on organic substrates, especially downed wood. This gives hemlock a significant competitive advantage over most other conifers in the area. ' CANA • • V^ancouver <3 AN ^ P o r t l a n d Figure 1.2: Occurrence of western hemlock (right) and amabilis fir (left) P C H forests are precious resources, and are one o f the world's last abundant sources o f a stable supply of clear timber. In the future, the relative importance of P C H is likely to increase because of the shade tolerance and amenability to a wide range of silvicultural systems (DeBell et al. 2004). 1.1.2 Properties and usage On the market, P C H is often considered to be a combination of strength and beauty. The products are described as bright in colour, and vary from a light honey to a rich golden tan (Alden 1995). The sapwood is sometimes lighter in colour than the rest, but usually is not distinct from the heartwood (Isenberg 1980). Generally, the sapwood is less than 1 inch thick. The annual rings are distinct, but the transition from earlywood to latewood is gradual (Panshin and deZeeuw 1980). Occasionally, western hemlock may have a slight lavender cast in the transition area around the knots (Somers 1997). According to Alden (1995), the wood may contain small sound black knots which are usually tight and stay in place. The species have a straight, even grain with a medium to fine texture. The physical properties of western hemlock and amabilis fir are similar. Using previously published information about density and specific gravity by Jessome (1977), Kennedy and Swan (1969), Gonzales (1987), Smith (1970), Lavers (1983), Standish (1983) and Farr (1973), Gonzales (1990) reported average basic densities from 409 to 439 kg/m 3 for western hemlock from British Columbia, and 360 to 386 k/m for Amabilis fir from British Columbia. Similar values are reported from Zhang et al. (1996). The initial moisture content o f freshly cut P C H timbers is previously reported to range from 26% to 60% (Oliveira and Wallace 2001) and 5 8 % to 7 2 % (Hao and Avramidis 2004). Zhang et al. (1996) reported that Amabilis fir has a lower initial moisture content compared with western hemlock. P C H species are moderate in strength, hardness, stiffness, and shock resistance (Alden 1995). They have moderately large shrinkage of 13% as the total volumetric shrinkage from green to oven-dried for amabilis fir, and 12% for western hemlock (Forest Products Laboratory 1999). Western hemlock may contain ring shake or wet-wood, a specialty type of wood formed in the heartwood zone associated with bacterial activity that has a high moisture content and density, and it is difficult to dry (Schneider and Zhou 1989, Schroeder and Koz l ik 1972). P C H from B C has long been used for general construction as dimension lumber, and in industrial remanufacturing of products in woodworking shops and factories. When a high quality of millwork and joinery is needed, P C H is very suitable to substitute light coloured and strong hardwood species. P C H also machines satisfactorily, sands smoothly, glues easily, and has high nail and screw holding abilities (Alden 1995). Western hemlock has superior planing, mortising and boring properties from amabilis fir, whereas amabilis fir has superior turning and shaping properties (Williams and Morris 1998). Painting and staining characteristics are very good and this wood nicely accepts finishes. P C H ' s close texture and freedom from pitch eliminates bleeding through the surface finish. The grain pattern smoothly and evenly accepts wide range of solid, semi-transparent or clear finishes in either paint or stain. This multi-finish versatility makes P H C excellent for matching existing millwork. Both species are equally amenable to fire-retardant or preservative treatments when required; therefore, beside its safety matters, it is a good choice for outdoor construction. Timber from P C H is produced in a wide variety of metric and imperial sizes to meet the structural specifications of the international marketplace. The Ministry of Finance and Corporate Relations (2001), reported that approximately 95% of B C coastal sawmills' remanufacturing production is exported to Japan, where lumber market wood from B C consistently and widely used (Daniels 2005). Their products are mainly used in traditional post and beam wood-frame housing (Figure 1.3). Using the commercial name "baby square", 6 Canadian mills manufacture P C H to the standard 105 x 105 mm (4") cross-section and 3 m (10 ft), 4 m (13 ft) or 6 m (20 ft) lengths. m w n a g a i Figure 1.3: Typical uses of Pacific coast hemlock in wooden traditional housing in Japan (from Eastin, 2004) Since 1998, Japanese Government Housing Loan Corporation ( G H L C ) authorities have inserted design values of P C H into the G H L C manual, where a special recognition has been obtained for Canadian P C H . Design values for P C H from Canada are considerably higher than that of US Hem-fir. Similarly, the Platform Frame Construction Structural Design manual has made similar references to P C H . The U S D A Forest Products Laboratory rates P C H in the top group of softwoods for ease of gluing under varying conditions and with different types of adhesives (Western Wood Products Association 1997). 7 According to Eastin (2004), the total volume of structural lumber used in Japanese post and beam houses in 2002 was approximately 7.1 mil l ion cubic meters. According to the same source, the end-use application that consumed the greatest volume of structural lumber was a structural beam (hirakaku) representing 32% of structural lumber usage. Other important end-uses included posts (kudabashira: 11%), non-structural studs (mabashira: 11%), floor joists (neda: 9%), balloon posts (toshibashira: 9%) and purlins (moya: 9%). Table 1.1: Approximate percentage and specifications for structural lumber usage in a typical Japanese post and beam house (from Eastin, 2004) Structural member English term Cross-section size (mm) / presence (%) Length (m) Dodai Ground sill 105 x 105/(80-90%) 120 x 120/(10-20%) 4.0, 3.65, 3.0 Tsuka Floor post 90x90 Short Obiki Girder 105 x 105/(80-90%) 90x90/(10-20%) 4.0, 3.65, 3.0 Neda Joist 45 x 45, 45 x 60, 60 x 60, 45 x 105 4.0, 3.65, 3.0 Toshibashira Balloon post 120x 120, 105 x 105 6.0 Kudabashira Post 105 x 105/(75%) 120 x 120/(25%) 3.0, 2.8 Mabashira Non-structural stud 27 x 105/(70%) 30 x 120/(25%) 45x105/(5%) 3.0,2.8 Sujikai Diagonal wall brace 45 x90 3.0 Hirakaku Structural beam 120x240, 105x210, 105 x 180 4.0, 3.0 Keta Top plate 105 x105 4.0 Koyazuka Roof support post 105 x 105,90x90 Short various Moya Purlin 90x90 4.0 Tarouki Rafter 45 x 45, 30 x 40 4.0, 3.8, 3.65, 3.0 Munagai Ridge beam 105 x 105, 90x90 4.0 Japanese builders have to provide a warranty for all new homes, for a period of at least 10 years. This leads to the demand for high dimensional stability o f k i ln dried construction material. Japanese house construction is switching to a pre-cutting concept rather than using traditional carpenters (Matsumura and Murata 2004). Virtually all pre-cut housing 8 manufacturers use ki ln dried lumber to manufacture housing components (Daniels 2005). The pre-cutting is usually a C A D / C A M machining system that w i l l notch, dri l l , shape, and cut to length lumber that is fed into a pre-cutter. The pre-cutter has a very tight tolerances request because lumber should be still and have secure precise notching. Lumber should also be very straight to allow accurate passing through, so bows and twists are highly undesirable. The B C forest industry has lost a considerable percentage of Japanese housing market because P C H is consistently rejected for precutting (Gaston et al. 2000). The reasons for this are shape deformations, which together with moisture variations continue to develop after drying P C H baby-squares. Some B C mills are supplying P C H baby-squares to Japan with mean moisture contents of between 18 and 25%, and are having their product readily accepted by Japanese consumers (Hao and Avramidis 2004). These products are usually dried in conventional kilns in approximately 5-day cycles. In addition, market diversification and reduction in drying costs, as well as the drying time of P C H timbers have become paramount under current market pressures. Drying difficulties and tight markets could make the drying o f P C H baby-squares with variable target moisture content (Mt) levels suitable to decreases in degradation, making drying times shorter, avoiding over-drying and better serving different market demands (Avramidis and Hao 2004). A s a result, these types of studies are necessary to comprehensively evaluate the k i ln drying quality of P C H baby squares dried to different Mt, and relate them to various wood attributes such as slope of grain, juvenile and compression wood, and initial moisture content (Mi). These sorts of studies could assist B C coastal mi l l managers in setting up goals and strategies in order to increase the share in Japanese post-and-beam market with maximum revenue. 9 1.2 Juvenile wood Based on fundamental structure and the properties of wood, the tree stem can be classified as two distinct regions, namely juvenile (core) and mature (outer) wood (Panshin and Zeeuw 1980). A tree produces juvenile wood as a zone of wood extending outward from the pith. This zone should be flexible and adept at surviving high winds, rains, snowfalls, ice, birds, and so on. During this early growth period, characteristics of the wood produced from year to year in each successive growth ring change markedly; this change occurs as a result o f the cambial meristem ageing (Thomas 1985). From pith to bark, wood gradually changes in its - a 1 m t I | 1 ( I j I ; ' 1 m l | • juveniie wood 14- ; mature wood ~r\ \ -JHHI Figure 1.4: Diagrammatic representation of juvenile and mature wood distribution (from Jozsa and Middleton 1994). properties until it turns out to be constant (Bendtsen 1978, Bendtsen and Senft 1986, Zobel and Sprague 1998). This type of wood with relatively constant properties is mature wood. The formation of juvenile wood varies between species, but often occurs during the first 5 to 20 annual rings (Thomas 1985). A s shown in Figure 1.4, typically the lower portion of stem, 1 0 below the live crown and around the juvenile core, is a shell of mature wood, whereas in the crown, the wood is mainly juvenile (Jozsa and Middleton 1994). Juvenile wood usually displays significantly different wood attributes when compared with mature wood (Figure 1.5), and thus plays an important role in wood quality characteristics (Bendtsen 1978). For most wood species, it negatively affects the material's quality. Juvenile wood has shorter cells, which in softwoods could be even ten times shorter than those of mature wood (Dadswell 1958, Krahmer 1985). SPECIFIC GRAVITY 'CELL LENGTH • STRENGTH 'CEU. - ^U- t . . THICKNESS TRANSVERSE SHRINKAGE PERCENT LATE WOOD MATURE WOOD FIBRIL ANGLE LONGITUDINAL SHRINKAGE ^JUVENILE MATURE--. WOOD' PITM:- 5^20 Rllfes; BARK PITH 5-20 RING^ M « K Figure 1.5: Schematic representation of the gradual improvement in properties with age (from Bendtsen, 1978) Its greater fibril angle in the S2 layer of cell wall (Figure 1.6) is responsible for much of the decreases in properties (Cave 1976, Cave and Walker 1994) required for high quality k i ln dried wood products. In conifers, this fibril angle could be 50°, when in mature wood it is around 20°, and in hardwood, the same comparison is 28° against 10°, respectively (Dadswell 1958). The cell wall is thinner, with lower cellulose and often 9% greater lignin content compared with mature wood (Zobel and Sprague 1998). Because of higher growth rates, juvenile wood has wider annual rings with a lower percentage of latewood (Larson et al. 2001). 11 c o m p r e s s i o n w o o d Figure 1.6: Anisotropic characteristics of wood and fibril orientation in normal, juvenile and compression wood (from Jozsa and Middleton 1994). Its greater fibril angle in the S2 layer of the cell wall (Figure 1.6) is responsible for many of the decreases in properties (Cave 1976, Cave and Walker 1994) required for high quality k i ln dried wood products. In conifers, this fibril angle could be 50°, when in mature Relative density at breast height Douglas-fir W. larch W. hemlock \ . - »•••••* • ^ 7 • • Yellow cedar Lodgepole pine Sitka spruce ' " \N.> . . . . • • — • — _ Interior spruce Subalpine fir W. redcedar Juvenile wood Mature wood Age (years) Figure 1.7: Average ring density trend from pith to bark in some second-growth woods (from Jozsa et al. 1998) wood it is around 20°, and in hardwood, the same comparison is 28° against 10°, respectively (Dadswell 1958). The cell wall is thinner, with lower cellulose and often 9% greater lignin 12 content compared with mature wood (Zobel and Sprague 1998). Because of higher growth rates, juvenile wood has wider annual rings with a lower percentage of latewood (Larson et al. 2001). The properties of juvenile wood are inconsistent through the entire juvenile area (Jozsa et al, 1998). Although lodgepole pine (Pinus contorta) has a longer period of juvenility than western hemlock, the difference between low-density inner wood and high-density outer, wood is about one half of that in western hemlock or Douglas-fir (Pseudotsuga menziesii). Jozsa et al (1998) explained that western hemlock, because of its crown persistence, has a relatively long low-density juvenile wood period. This inconsistency of properties represents an additional problem related to the drying of wood products with juvenile wood. The above properties are not variable just among different wood species (Burdon et al. 2004), but also within them as a result of different growing conditions (Zobel and Sprague 1989). In spite of all o f these differences, in practice it is almost impossible to separate juvenile from mature wood by visual inspection. The only significant visual indicator of the presence of juvenile wood in a piece of wood is the pith at the center of the log. This is why juvenile wood is often referred to as pith wood. Juvenile wood has been a focus of wood science investigations for a long time. Probably, the first conclusions about the potential problem of lower mechanical properties of juvenile wood come from the observations of Dadswell (1958), Hallock (1965) and K o c h (1966; 1971). The latter concluded that most properties of southern yellow pine (Pinus spp) veneer cores from the center of logs had a lower bending strength and stiffness than expected from mature wood. Additional evidence of properties reduction of lumber as a result of juvenile wood was suggested by Moody (1970). He noted that during his evaluation of finger 13 joints in southern pine lumber, strength and stiffness of control specimens with pith-associated materials were 30% and 10% less than that of material without pith, respectively. Works by Boone and Chudnoff (1972) and Bower et al. (1976) on plantation Caribbean pine (Pinus caribaea) drew attention to the lower properties of plantation wood. They reported that clear wood plantation material had less than 50% of the expected specific gravity, bending strength, and stiffness than virgin timber of the same species; but, at the same time, Pearson and Gilmore (1971) in their research on loblolly pine clearly demonstrated that the problem was juvenile wood, not plantation wood. They concluded that juvenile wood has substantially lower values of most mechanical properties compared to mature wood. This accounts for the subordinate properties of plantation wood when compared with that of old-growth timber. The work by Bendtsen and Senft (1986) demonstrated that juvenile properties for loblolly pine (Pinus taeda) and Eastern cottonwood (Populus deltoides) are important for solid wood processing. These woods improve dramatically each year in the early juvenile wood zone, and more gradually during the latter years. Early juvenile wood that is closest to the pith is distinctly o f poorer quality than later juvenile wood. Bendtsen (1978, 1986) confirmed previous conclusions on several studies which evaluated the influence of juvenile wood on the mechanical properties of Douglas-fir and southern pine dimension lumber, and Zobel et al. (1998) have also thoroughly documented the properties of juvenile wood and its effects on solid wood products. In B C , juvenile wood was investigated by Barrett and Kel logg (1989), through studies conducted on second growth Douglas-fir. They concluded that the reduction in specific gravity related with juvenile wood, could have a significant impact on lumber strength and stiffness properties. Second growth and young western hemlock were both comprehensively investigated (Jozsa et al. 1998, DeBel l 2004), with the obvious evidence of changes in properties concerning the presence of juvenile wood. In a study about the 14 mechanical properties of second growth western hemlock, El l is (1995) reported that both M O R and M O E values showed a general increase from pith to bark. Several studies often indicated that lumber from the juvenile tree zone has a propensity for poorer strength and dimensional stabilities compared with lumber from the tree's mature zone (Zobel and Sprague 1998). When water molecules are removed from the wood cell wall structure, as during the drying process, micro-fibrils in the most dominant S2 layer of the cell wall , move closer together, and this causes the cell to shrink. On the other hand, when the cell wall moisture increases, water molecules move into the cell wall , causing the S2 layer micro-fibrils to increase their distance between each other, resulting in swelling. In mature wood, the micro-fibrils in the S2 layer of the cell wall are oriented in lower degrees from the cell axis, usually around 10° (sometimes even less from 7°), so longitudinal shrinkage is often insignificant (0.1 to 0.2%). On a contrary, in juvenile wood they could be oriented up to 50° from the cell axis, so longitudinal shrinkage could be higher (Ying et al. 1994), even up to 9% (Meylan 1968). These changes are not of the same level in all species, and they can also vary within the same species (Zobel and Sprague 1998). In practice, one part of a wood product could be juvenile wood with its different properties and the rest could be mature wood. The part with juvenile wood w i l l mostly tend to shrink in length, but the mature wood wi l l mainly force tangential and radial shrinkage, and these conflicts w i l l result in warp, checks and other defects ( M c M i l l a n 1973). Gorman (1985) reported that juvenile wood is a major effect for bow development in southern pine. Shelly et al. (1979) found that the presence of pith in young-growth ponderosa pine (Pinus ponderosa) studs had the greatest effect of all the variables they studied when looking at bow, crook, and twist. Voorhies and Blake (1981) developed their idea and found that juvenile and compression wood in young-growth ponderosa pine were the main causes for warp, because of 15 the greater longitudinal shrinkage than that of mature or normal wood. Voorhies and Groman (1982) found a strong relationship between longitudinal shrinkage in juvenile wood and fibril angle. They concluded that the greater the fibril angle, the greater the longitudinal shrinkage. Milota (1992) dried Douglas-fir 2 x 6 lumber from both large- and small-diameter trees by slow and fast k i ln schedules at conventional and elevated temperatures. Boards from the small-diameter logs twisted more than those from the large-diameter logs. After high-temperature drying of 25 year old radiata pine, Haslett, Simpson and Kimberley (1991) found that twist was the major reason for degradation and that it was strongly related to log diameter. Danborg (1994) concluded that in k i ln drying of Norway spruce (Picea abies) and Sitka spruce (Picea sitchensis), bow and spring are only problems for part o f the board, namely the very small dimensions from near the pith. He concluded that the twist is caused by spiral grain in combination with anisotropic shrinkage. In Sandberg's (1996) research, after cycles of drying and wetting of Scots pine (Pinus sylvestris) and Norway spruce, he demonstrated that the proportion of cracks is clearly related to the distance of the pith in sawn timber. Dumail and Castera (1997) studied eleven year old and twenty year old maritime pine (Pinus pinaster), and reported that, over time, the tangential shrinkage and the anisotropic ratio between radial and tangential dimensional variations are increasing from the top to the base of the stems, and that this effect is independent o f the tree. The variations from the pith outward are significant, but the amplitude of problems related with these variations may depend on other effects. According to Simpson and Tschernitz (1997), it seems that the extreme thickness variation generated in their study of the high-temperature drying of plantation-grown loblolly pine aggravates warp, especially twist. It is also clear that thin boards warped more than the thick boards that made good sticker contact. Lenth and Kamke (2001) observed that the high temperature water sorption behavior of 16 juvenile wood of radiata pine is unique from that of mature wood, and demonstrated that the common predictive relationships for equilibrium moisture content used at low to moderate temperatures are ineffective at high temperatures. Widlak (2002) concludes that both the rate of increase and the absolute values of stress and strain are different in juvenile and mature ki ln dried birch (Betula verrucosa) and aspen (Populus tremula). Compression wood, the presence of which is often in correlation with juvenile wood (Zobel and Sprague 1998), has attracted the attention of numerous scientists. Compression wood is found in the area surrounding the pith and appears in most conifer trees (Zobel and Haught 1962, D u Toit 1963, L o w 1964, Timell 1986). During juvenile growth, small trees are especially susceptible to environmental forces that cause the formation of compression wood (Zobel and Sprague 1998). In young and small trees, mechanical instability may result in leaning stem and the development of basal sweep when they strive to regain a vertical position by forming compression wood (Larson 1965, Archer and Wilson 1973, Yoshizawa et al. 1986, Timel l 1986). Compression wood has larger micro-fibril angles than normal wood (Figure 1.6). To a large extent, it is the micro-fibril angle that governs the longitudinal shrinkage in wood and Koch et al. (1990) reported this angle to be more than 45° in severe compression wood. Compression wood is also characterized by thick cell walls (Figure 1.6) and the rounded outline of its tracheids, the profuse occurrence of spaces and the absence of the inner part of the secondary wall , which is called the S3-layer (Boyd 1973). The inner part of the secondary cell wall in severe compression wood is often highly lignified and is referred to as the S2 (L)-layer. In longitudinal sections, the secondary cell walls show abundant radial striations. Compression wood is often distinguished by its characteristic darker color (Timell 1986). In western hemlock, compression wood was studied by Lewis (1950) who reported a 17 lignin content of 28.8%. Siripatanadilok and Leney (1985) reported that in western hemlock the fibril angle of compression wood was significantly larger than in the normal wood; the angle decreased from compression wood to side wood and increased again in opposite wood, and the tracheid length was distinctly shorter in compression wood. They reported considerable variability of these properties between trees. A s a result of all these properties, compression woj^d affects longitudinal stresses and dimensional stability (Archer and Wilson 1973). The presence of compression wood was often related with deformations such as bow or crook. (Timell 1986, Beard et al. 1993, Warensjo et al. 1998, Perstorper et al. 1995). Another wood attribute, the slope of grain (SOG), is often connected with juvenile wood (Cown et al. 1991). Sometimes, it can also come as a consequence of the sawing procession, so in its natural occurrence it is called the spiral grain. When trees are subjected to wind forces, bending deformation occurs when there is symmetry in the plane (Skatter and Kucera 1997). If the tree has a crook in this plane, i f the crown is unevenly distributed in this plane, or even i f the roots are asymmetric in this plane, the tree wi l l also be twisted by the wind. This twisting movement is also caused by the inclination of tracheids in the tangential direction, thus forming a helix around the stem axis, a phenomenon called spiral grain (Skatter and Kucera 1997). S O G is defined as the angle between the direction of wood grain and the main axis of lumber. It could reduce strength and promote twist as the moisture content varies (Kliger 2001). According to Balodis (1972), twist increases with S O G and decreases with the distance from the board to the pith. Haslett et al. (1991) pointed out that the juvenile properties contributing to warp in the processing of young radiata pine are mainly spiral grain and longitudinal shrinkage. Warensjo (2001), in a study on Norway spruce, concluded that S O G on a log surface accounted for a larger part of twist than S O G on lumber. S O G influence on k i ln 18 dried P C H was studied by Hao and Avramidis (2004), who found that its occurrence in 800 baby squares was insignificant (average 1.2°). A t that level, SOG' s reflects on shape distortions were inconclusive. Zobel (1998) lists comprehensive literature with the conclusion that S O G is not necessarily related to shape distortions. 1.3 Wood drying The fundamentals of wood-moisture relationships, the reasons for wood drying, and the drying practices used by the industry have been well documented in the literature (Kollmann 1951, M c M i l l e n 1958, Kol lman and Cote 1968, Rietz and Page 1971, Skaar 1972, Siau 1984, Simpson 1991). Wood in its natural state contains a large amount of water. In practice, the maximum moisture content (M) o f a standing tree is usually below 200%, but sometimes could even be more than 500%, i f degraded. A part of that water should be removed in order for wood products to have M i n a mid-range of the expected M o f their surroundings. This is termed as lumber drying or seasoning. The term seasoning is mostly used to refer to air-drying (Bachrich 1980). The aim of industrial drying is to take advantage of dried wood and increase its value by improving the usefulness, while minimizing losses and drying time. The advantages are that it provides dimensional stability in the end-use environment, protects wood from biological degradations (Highley et al. 1994) and make it able to be treated with preservatives (Winandy 1995) and glued. Further operations in the wood process such as machining, planing, sanding, turning, shaping operations and assembly are also influenced by drying quality. The cost of transportation of green lumber by rail or truck could be approximately twice as transport of dry lumber. Most strength properties of lumber dried below the fiber saturation point are typically higher compared to wet lumber, what allows dried structural components to have smaller 19 dimensions and lighter weight. Various end-uses require wood to be dried to specific M (Table 1.2). Hoadley (1979) indicates that the relative humidity (H) is the "cause" and the equilibrium moisture content (Me) is the "effect". Lumber must be dried to target moisture content (Mt) within a specified range and allowance, known as the final moisture content (MJ) distribution. Table 1.2: Final moisture content range for various wood products L u m b e r products M f (%) Softwood Plywood 3-4 Furniture and millwork 7-9 Framing for construction 15-19 Glued laminated timbers 11 Other uses 10-12 Hardwood Furniture and millwork 6-8 Framing for construction 15-19 Bending stock 25-28 Preservative treated stock 20-30 European export 10-12 Tropical export 12-16 1.3.1 Wood moisture relations The moisture content (Equation 1.1) is expressed as "mass of the wood before drying minus mass of the oven dried wood divided by the oven dried wood multiplied by 100" (Esping 2001). Usually it is named "the oven dry based" (Kollmann 1951, Kol lman and Cote 1968, Skaar 1972, Siau 1984). W - W M = ^ ^ x l 0 0 [ % ] W, (1.1) od where M- moisture content [%] W0d - oven dried weight o f wood [g] Wi— initial or green weight [g]. 20 Moisture exists in wood as bound water within the cell wall , liquid form in the cell lumens (free water), and water vapor in gas form in the voids of wood (Simpson 1999). The free water is held by weak capillary forces and requires less energy to be removed. Bound water is the water molecules dissolved or adsorbed through hydroxyl groups to the cellulose, hemicellulose and to a lesser extent lignin (Berthold et al. 1994). It is limited by the available number of sorption sites and by the number of water molecules a sorption site can hold. They are held into the wood by hydrogen bonds and van der Waals ' forces and need more energy for diffusion and evaporation (Siau 1995). Water vapor exists in the cell lumens and intercellular spaces, which are without liquid water (Blass et al. 1994, Panshin and de Zeeuw 1970, Siau 1984). It is assumed that the bound water is not removed until all free water has been evaporated, what is termed by Tiemann (1906) as the fiber saturation point (FSP). Below FSP, more energy is required to remove moisture from the cell wall than the cell cavity (5% more at 15% moisture content and 15% more at 6% moisture content), shrinkage starts to occur and significant physical and mechanical changes begin to take place (Haygreen and Bowyer 1996, Simpson 1997). FSP varies from 25 to 35%, and in practice is usually assumed to be 30%. Water usually moves from higher to lower moisture content zone (Siau 1984). The wood drying process involves the movement of moisture from the core to surface, and from the surface into the environment (Vansteenkiste et al. 1997). The first process is about 100 to 1000 times slower than the second (Pagnozzi 1991). The level of balance of these two movements during the drying w i l l determine the level of internal stresses, checks and moisture gradient between the interior (core) and surface (shell) layers. Moisture w i l l migrate to the surface and evaporates into environment until Me is established. Me is a dynamic steady moisture balance between wood and environment. It w i l l be established i f wood is exposed to the same temperature and H for sufficiently long time. H is the ratio of partial vapor pressure 21 of the air to the saturated vapor pressure at a prevailing temperature, expressed in percentage (Siau 1984). A n increase in the temperature of wood wi l l reduce the viscosity of water, what wi l l increase its mass movement, so that drying could be faster. 1.3.2 Kiln drying There are various techniques that can be used for drying of wood, as they are air drying, conventional drying, radio frequency vacuum drying etc. Before the ki ln drying, lumber was dried with the air-drying technique using the solar energy. A i r drying, which needs low initial investments, can produce a good quality, but has slow drying speed and can cause significant defects of the lumber as stains, discoloration, warping and checking (Reitz et al. 1971). This leads to higher insurance premiums emanating from high inventories (Bachrich 1980). It takes approximately one year to air dry P C H baby-square to reach about 15% of Mr. Drying a 25mm thick lumber from green to 20% using air-drying as compared with ki ln drying the same thickness from green to 6% moisture content, 75% to 90% drying time was saved and about 90% to 99%> was saved by ki ln drying from 20% to 6% (Kollmann and Cote 1968). Demands for speedy flow of capital in the wood industry led to the development of different drying options. Drying wood in an insulated chamber and circulating air over it is called ki ln drying. The more acceptable techniques are conventional (heat and vent) and non-conventional which includes dehumidification, conductive vacuum, superheated steam vacuum, radio frequency vacuum ( R F V ) and solar kilns. The most widely used is the conventional k i ln (Rosen 1995). The conventional k i ln (Figure 1.8) is made mostly of aluminum or stainless steel. It is designed to specifically control the principal lumber drying parameters (temperature, H and air 22 velocity). They could be compartment or progressive based. The compartment kilns are most common. They are loaded in one operation and wood remains stationary during drying. This offers the advantage of flexibility in varying the ki ln climate to a specified condition and has reasonably uniform instantaneous conditions within the ki ln. The kiln parameters can be controlled by a predetermined schedule that is in turn controlled with heat, humidification, ventilation and air circulation. Automat ic w - s a t s r e Figure 1.8: Package-loaded ki ln with fans connected directly to motors (from Simpson, 1999). Owing to the high heat of evaporation of water (2326 kJ/kg), large quantities of heat energy is needed to dry lumber. According to Hansom (1988), the total energy required to remove a kilogram o f water from lumber consists of 2.4 M J heat of vaporization (the dry bulb temperature of 50°C), energy used to raise ventilation air to k i ln conditions, energy needed to heat k i ln and wood to maximum operating temperatures and energy lost through ki ln fabric and excess air interchange. It is estimated that a commercial softwood ki ln requires about 1.1 23 kJ per 0.24 m per second (Simpson 1991, Bramhall and Wellwood 1976). Energy is transferred to the wood through the air either directly or indirectly. If indirect, heat is conducted in with a hot fluid (steam, hot water and thermal oil systems) through pipes into a radiator, which gives off its heat to the ki ln atmosphere. The heating fluid could also be combined with electric heat energy. On the control panel, the dry bulb temperature (7^) depicts the heat supply in the ki ln . A i r circulation is needed in the ki ln as a medium of transporting heat to the lumber and removing moisture from wood. H is especially important at the beginning of drying, equalization and conditioning stages. Moisture is added to a ki ln atmosphere when H is lower than required. In steam heated kilns the moisture is supplied as steam spray, which mixes with the circulating air before reaching the wood. Removal of wood moisture causes a rise in ki ln air moisture level with time. Excess moisture is vented either by static or pressure venting system. The number of vents and their sizes are dependent on the amount of water to be removed from lumber (species and size of lumber). In order to distribute air of controlled temperature and humidity uniformly over lumber throughout a dry ki ln , fans are installed to circulate kiln-air. They could be in the line or cross-shaft system. For the fan to effectively function, the size, speed, location, and the reversibility must be appropriate. The volume of air to be moved is directly proportional to the fan speed with static pressure varying with the square of fan speed, whilst the horsepower varies as the cube of fan speed and directly proportional to air density. The speed of modern ki ln fans is adjustable. Typical air velocity is between 1 and 1.5 m/s. The higher air velocities can increase drying rates, but w i l l increase degrade too. 24 Figure 1.9: Inside view of the U B C 8-foot laboratory dry ki ln Baffles, usually made of steel (Figure 1.9) or plastic, are installed with hinges on the ki ln ceiling and floor, for the effective direction of the airflow through lumber. Facilitation of airflow across each piece of lumber is achieved by placing stickers of equal size and species and at equal intervals on the layers of lumber. The interrelationship between temperature, humidity and air velocity is carefully controlled during the drying cycle using specific schedules. It is designed for the species, size, and end use. Drying schedule is a series or progressive sequence of air temperature and H used to direct the whole lumber drying process. Usually, the Tdb gradually increases and H decreases. This implies a gradual increase in the wet-bulb depression (Twbd)-High H is usually maintained at early stages, especially with thick timbers. A s long as external convection controls the process the lumber surface remains saturated. When internal moisture-transfer rate lags behind external vapor-transfer rate, the surface temperature rises and decreases the surface M to establish a moisture balance (Keey et al. 2000). TWM depression 25 of a typical normal temperature convectional schedule lies within 5 to 10°C, whilst at high temperature it may increase above 50°C (Keey et al. 2000). Using the rate of moisture removal (moisture gradient) and Me, Keylwerth (1950) introduced a term called "drying gradient" used to control the drying process. Drying gradient is defined as the ratio of the momentary average M to the average Me to which timber wi l l adjust, i f the k i ln climate at that moment were to remain constant until hygroscopic equilibrium. Increasing of drying gradient w i l l increase drying rate, but it w i l l also increase the internal stresses. A good schedule wi l l maintain the drying tension stresses at low levels at any given temperature and M, otherwise, degradation wi l l be developed. The three types of k i ln schedules as far as the x-axis is concerned are: 1) moisture-based; 2) time-based; and 3) mixed (time-moisture based). In the moisture based schedule, the k i ln temperature and H are changed according to the changing of lumber M. Usually hardwood species use moisture based schedules. The time based schedule is a list o f temperatures as a function of time. Normally it is used for softwoods. The mixed drying schedules usually have the same principle of drying stages as moisture-based or time-based. The drying parameters are time-based at the beginning, but at a certain level, approximately when the load has reached an average moisture of 30%, they start to be constant until the Mt is reached. A n additional schedule type is the cyclical or oscillating, which can be moisture content- or time based, and the principle is to oscillate the climate within the ki ln . The drying process is a function of average M of wood, and the k i ln atmosphere where moisture content decreases with time (Hansom 1988). Figure 1.10 illustrates a theoretical drying curve, which assumes only a single set of dry and wet bulb temperatures making up the drying schedule and over given M-range, so that there is no change of temperatures as drying proceeds. 26 That (fc«ui<$)< Figure 1.10: Theoretical drying curve (after Hansom 1988) where M o -moisture content at time zero [%] D R - drying rate [% / hr] The k i ln drying can be divided into stages (Figure 1.11) which overlap. The stages could be: 1. warm-up period (low temperature and high H) - heating up the ki ln and lumber 2. main drying a. phase 1 (temperature increases and H decrease) - drying to FSP b. phase 2 (temperature increases and H decrease or constant) — remove bound water while moving M towards M h 3. conditioning (temperature high and H high) - stress relief 4. cooling - no heating, vents closed, fans turned on 27 Figure 1.11: Relationship between average moisture content and schedule settings The temperature of the ki ln atmosphere is set to rise to a certain point (usually 24 hours) whilst maintaining a high H to protect the lumber from defects. After the heating up temperature is reached, it is allowed to stay until the temperature gradient in the timber approximately equalizes. It is followed by the main drying phase in which, H is gradually reduced to create a moisture gradient in the profile of the timber. The drying phases are greatly influenced by the species, thickness, desired quality and air velocity. The main drying phase could be subdivided into drying above and below FSP. During drying above FSP the drying rate is high and constant which is commonly known as constant rate period. A t the period below FSP the timber is more resistance to drying, so higher drying gradient is applied to remove water from small capillaries and bound water and the lumber begins to shrink. This period is commonly called falling rate period. The followed, conditioning is applied to relief stress, minimize drying degrade and evening M differences within boards. This phase is sometimes ignored especially in high temperature drying .The final cooling stage is applied to cool down the load to almost ambient conditions within the 28 still closed ki ln to avoid surface checks and accompanying quality decrease (Brunner-Hildebrand 1987, Henderson 1951, Kollmann 1955, Pratt 1974). 1.4 Drying defects Drying losses in the wood mass include timber pieces that drop one or more grades after drying and pieces that require remanufacturing to maintain their grade. The first group is termed as drying degrades (Bramhall and Wellwood 1976). Wengert and Lamb (1993) classified their causes into six major categories: 1) dried too fast; 2) drying too slow; 3) poor stacking; 4) operator or management error; 5) equipment problems; 6) natural effects. According to their appearance, Ward and Simpson (1997) categorized them into the following groups: 1) discolorations; 2) shape deformations; 3) uneven moisture content; and 4) rupture of wood tissue. The majority of drying degradation attributes is associated with the anisotropic shrinkage of wood (Figure 1.12). Figure 1.12: Anisotropic shrinkage and shape distortions (from Simpson et al. 1991) 29 1.4.1 Shrinkage Shrinkage (or swelling) is the characteristic of wood to change dimensions when changing its moisture content below FSP (Noack et al. 1973). It could be calculated as: Shrinkage = — x 100[%] (1.2) d where Ad — decrease in dimension (or volume) d - original dimension (or volume) Shrinkage occurs when bound-water molecules escape from spaces between cellulose molecules, what allows them to move closer together. These dimensional changes vary with the amount of water that is removed from the wood, the species and the orientation of the wood fibrils. The dominant S2 layer of the cell wal l (Figure 1.6), contributes the most to the overall shrinkage. Its molecular orientation determines how shrinking occurs, and therefore cause different shrinkages of normal, juvenile and compression wood. The micro-fibrils are in the S2 layer nearly parallel to the cell axis and swell mainly in the transverse direction as moisture increases. Longitudinal shrinkage is about 0.1 to 0.3% (Deresse et al. 2002), and it is reported to be greater in juvenile and compression wood (McAlister and Clark 1992, Y i n g et al. 1994). Lateral shrinkage (radial and tangential) is much greater (Harris and Meylan 1968), and varies greatly between species and densities. In common U.S . woods, over the range from FSP to oven-dry, the tangential shrinkage ranges from 4.7% to 12.7%, and the radial from 2.1%) to 7.9%). Generally, tangential shrinkage is two times greater than radial shrinkage and the ratio varies from 1.2 to 3.3 depending on species (Simpson 1991). The reasons are the presence of rays in the radial direction, (Kollmann et al. 1968), and the presence of early-wood 30 and late wood in the annual growth rings, where the early-wood has a lower tendency to shrink compared with the latewood. Shrinking produces stresses that can rupture wood. Stresses develop because the dimensional changes are anisotropic. The wood w i l l be free from these stresses when it reaches the equilibrium with the surrounding air. This equilibrium moisture level depends principally on H of the air (Figure 1.13). A i r temperature has little effect on the equilibrium moisture level over its normal indoor range. Wood with low tangential and radial shrinkage coefficients is more stable and less likely to warp or crack, when moisture content changes. Figure 1.13: Moisture content of wood at various relative humidity 1.4.2 Surface and end checks Surface checking is the occurrence of separation of wood cells, along the length of a lumber in the longitudinal direction. These are caused when the aforementioned shell tension stresses exceeds the tensile strength of the wood perpendicular to the grain (Bramhall and Wellwood 1976). They can occur i f Me is low during the early stages of drying, and could be minimized by maintaining high H, what w i l l maintain higher surface moisture content to 31 prevent shrinkage and increase the plasticity of the wood to accommodate the stresses (Keey et al. 2000). These checks may penetrate to the inner parts of the wood as the dry zone spreads into the interior and cause at this point an internal check. After the stress reversal, the surface checks may close up, but the internal check wi l l remain and causes rupture type defect called honeycomb (McMi l l en 1958). The end check develops as a result o f the more intensive diffusion of moisture along the grain than across. The permeability of wood in the longitudinal direction is about 50 to 100 times greater than in transverse direction (Stamm 1964). Exposure of the end boards leads to rapid drying along the wood grain. Using moisture resistant end coats may prevent or reduce longitudinal moisture movement (Milota et al. 1991). The use of stickers flush with end boards and slower air velocity may also minimize them. 1.4.3 Shape distortions Shape distortions (warp) is any diversion of the face or edge of a lumber from the flatness or any edge that is perpendicular to the adjacent face or edge (Simpson et al. 1991). It is a result of the anisotropic shrinkage and presence of irregularity in wood structure as high S O G , juvenile wood or compression wood. It can occur in one or more forms which are cup and diamonding, bow, crook, and twist. Use o f proper k i ln schedule can help to reduce them. 1.4.3.1 Bow B o w is warp along the length of the face of lumber. It occurs when one face of lumber shrinks more in length than the other. B o w causes the lengthwise curvature of a piece of lumber, such that it resembles a bow used in archery (Figure 1.14). Crook, or side bend, is 32 warp along the length of the edge of lumber, and in squared wood products, baby-squares for example, bow is a general term. Bow can be developed in the green timber immediately after sawing as a result of growth stress release (Sandberg 2005). Usually, wood closer to the center of tree shrinks longitudinally more along the grain than mature wood (Bendtsen 1978). For that reason, the part of a lumber with juvenile wood, which is in disagreement with the mature part, w i l l cause the lumber to try to bow excessively during drying. If bow is significant, that type of pieces wi l l be classified as degraded after drying. The critical lumber could also be sawn from a crooked log or in wood around large branches (Larson et al 2001, Burdon et al. 2003). The wood cells in the resulting lumber are oriented at an angle, causing longitudinal shrinkage and a tendency to bow. Figure 1.14: Example of bow in a square timber Uniformity of thickness in a drying charge can also produce bow problems. Improper saw feed speeds or lapses in saw maintenance can result in lumber that is thinner on the ends than in the middle. This leads to a type of bow, called "pile bend," which appears in the upper layers of a pack. Proper and timely handling can help to reduce or eliminate bow. Wood that is 33 wet and warm can bend quite easily. The shrinkage that causes bow usually occurs at high moisture content, above 40% (Simpson et al. 1991). The incorrect stacking procedure can be a contribution to bow. Both lumber and stickers must have a uniform thickness. Careful stickering practices, such as maintaining good vertical alignment and assuring no stickers are up on edge, are a contribution for decreases of bow. Foundations for green lumber piles, whether in the ki ln, pre-dryer or air-drying yard, must be flat. Drying wood too slowly w i l l exacerbate bow. Fast drying, especially at high moisture content, can reduce the amount of bow, but fast drying results in checks. 1.4.3.2 Twist Many authors (Woxblom 1993, Danbourg 1994, Perstorper et al. 1995) reported twist as the most sever problem in the construction industry. Twist is the turning of the four corners of timber ends, so that they are no longer in the same plane (Figure 1.15). Figure 1.15: Example of twist in a square timber 34 In the wood science literature (Boladis 1972, Forsberg and Warensjo 2001) it is often related with the fibril orientation and distance from the center of a log, but some authors (Shelly et al. 1979, Beard et al. 1993) showed no or little correlation between twist and grain angle. Twist does not occur directly after sawing, but arise during seasoning of the wood (Sandberg 2005). Lumber containing these grain characteristics can sometimes be dried better with the proper stacking procedures (Simpson et al. 1991). 1.4.3.3 Diamonding Diamonding occurs when one face shrinks more in width than the opposite face. It is a form of warp found in timber (Figure 1.16). For true quarter-sawn lumber, where the ring pattern is symmetrical, both faces w i l l shrink evenly, and diamonding wi l l not occur. For any other grain pattern, the outer face, which faced away from the center of the tree, w i l l shrink more than the other face, what w i l l cause diamonding. 1^ Figure 1.16: Example of diamonding in a square timber Figure 1.17 shows the location of the lumber with respect to its location in the tree. The heavy, longer arrows represent shrinkage in the tangential direction, while the lighter, shorter 35 arrows are the direction of radial shrinkage. Shrinkage along surface A is more in the tangential direction, and along surface B it is mostly radial. Because wood shrinks nearly twice in the tangential direction, surface A wi l l shrink more than surface B , causing the diamonding on the square pieces. The variation of diamonding within a dry charge is caused by differences in individual tangential and radial shrinkage rates of pieces. Figure 1.17: Tangential (bold) and radial shrinkage directions in relation to the lumber's original position in the tree (from Simpson, 1991) Diamonding can be minimized, with careful handling (Simpson et al. 1991). When lumber is in a ki ln , diamonding w i l l be smaller i f lumber is not dried very slowly. This w i l l avoid over-drying and not allow partially dried lumber to inadvertently regain moisture quickly. The planing of dried lumber wi l l also reduce diamonding. 1.5 Kiln drying of PCH The most common type of P C H drying in B C is the conventional, using heat-and-vent kilns (Wallace et al. 2003). K i l n drying related problems are often seen as having a limitation to retrieving a maximum profit in the production of P C H structural products. The root o f major 36 problems are a wide range of M , (Dedman and Van Dusen 1965, K o z l i k 1963, K o z l i k 1970, Koz l ik and Halman 1972, Avramidis and Mackay 1988, Oliveira and Mackay 1991, L i et al. 1997), the presence of wet pockets in heartwood (Kozl ik 1970, Koz l ik and Halman 1972, Ward 1986), and the different basic densities of the species (Avramidis and Oliveira 1993). A s a consequence, a wide range of Mt (over-drying or under-drying) is present. The over-drying increases the development of drying defects (Kozl ik and Hamlin 1972, Oliveira and Mackay 1991) and requirements for extended drying times (Kozl ik 1970, Koz l ik et al. 1972). The under-dried pieces increase higher shape instability of dried P C H squares (Avramidis 2002). Jessome (1997) reported an average M , of 69% and 85% for amabilis fir and western hemlock, respectively, with a standard deviation of 15%>. According to K o z l i k (1970), an average M , of normal western hemlock heartwood is 66% and 153% for wet-wood. A s ranges, he reported 33% to 152% and 108% to 186%,, respectively. K o z l i k and Halman (1972) reported that, out of the 54 specimens, only five from normal heartwood were found to have Mi above 100%, dry basis. Chafe (1996) found a high variability in M , and a relatively dry sapwood zone surrounding the wet-wood. Furthermore, in the green wood, density and M , increased towards the pith with no significant relationship between these properties. Because of the negative relationship between density and moisture content, this abnormality also indicated the presence of wet-wood. A n important wood characteristic concerning drying is permeability or the ease o f fluid flow under the influence of a pressure gradient through the interconnected void-volume of wood (Ward 1986, Siau 1971). L i n et al. (1973) reported three classes of the initial average water permeability of western hemlock: wet-wood that was 6.64 x 10"6 m 2 , sapwood 9.6 x 10"6 m 2 and normal heartwood 4.4 x 10"8 m 2 . In addition, they reported that both in sapwood and wet-wood the permeability becomes lower with time. The permeability o f sapwood was 37 influenced by time-dependent pit aspirations because of hydrostatic pressure differentials during testing. For wetwood, the results were attributed to the extractives which were transported by water and deposited on pit membranes, and it probably created almost impermeable pit membranes. Schroeder and Koz l ik (1972) confirmed this by reporting a higher extractive content in wetwood than in sapwood and normal heartwood. Regardless of using steady or unsteady state techniques, the longitudinal permeability of western hemlock to water was the highest in sapwood, and was slightly higher in wet-wood than normal heartwood (Lin and Lancaster 1973). The aspiration of the wet-wood pits is also one of its characteristics (Kozl ik and Halman 1972, L i n et al. 1973). According to Simpson (1991), a typical k i ln drying time for drying P C H dimension lumber to 19% Mt for instance, is approximately 78 hours for normal heartwood (M, o f 65%), 115 hours for sapwood (M, of 170%), and for wet-wood, 160 hours (M, of 145%). In a study performed by Koz l ik and Halman (1972), in which the evaporable water o f sinker and normal heartwood were compared, the normal heartwood reached a lower moisture content in the shortest time. The total drying rate of wet-wood was about 60% slower than the normal heartwood (Kozl ik and Ward 1981). Hao and Avramidis (2004) reported that the annual ring orientation has a significant effect on the drying time of P C H baby-squares. When dried to 15% Mt, the horizontal annual ring orientation pile arrangement shortened the drying time by 11%, compared with the random pile, whereas the vertical annual ring orientation pile arranged lengthened the drying time by 28%). Milo ta et al. (1993) reported that presorted P C H by Mi w i l l reduce drying time for 10%. The P C H presorting idea has existed for a long time in the studies concerning P C H ki ln drying problems. Dobie et al., (1966), suggested that presorting balsam fir from western hemlock may be worthwhile because their results showed that fir suffers less degradation and 38 is dried faster. Avramidis and Oliveira (1993) also presorted P C H timbers into high and low density groups, and concluded that the low density wood is dried faster, the difference in core and shell moisture content was significantly improved, and the total shrinkage was reduced. This approach was also tested by Milota et al, (1993), but their results were insignificant for improvement of Mf variability. Zhang et al. (1996) presorted lumber into six groups based on species and basic density. Species separation was unrelated to Mf. The lower density groups showed reduction of drying times, volumetric shrinkage, core and shell moisture content difference and variability of Mf. The softwood presorting concept was analyzed by Nielson and Mackay (1985). Their study on lodgepole pine with the sorting of lumber before drying into green and dry, demonstrates an extra cost incurred by drying the already dry wood, and extensive degrade and planer breakage as a result of over-drying in the dry sort. In general, it seems that the quality of conventional k i ln drying of supplies as P C H is a factor with many variables that require a better understanding of them and their interaction, i f a reliable presorting system is supposed to be developed. Some other techniques were also tested to improve the k i ln drying o f P C H . Presteaming o f wetwood before drying (Kozl ik 1970, K o z l i k and Hamlin 1972) indicated an increase in the drying rate, but later work from Avramidis and Oliveira (1993) did not deliver the same conclusions. Koz l ik and Hamlin (1972) in a different study concluded that the drying with a temperature above 100°C is able to reduce the drying time by 50%, without the increased degradation and with smaller variation o f Mf. L i et al. (1997) reported that vertical air gaps in a k i ln stack and changing the air velocity could reduce drying time, but a disadvantage is the decreased drying capacity. Sackey et al. (2004) investigated the effect of oscillated schedules. They concluded that while oscillated increases drying rate by 12%, 39 oscillated TWD decreased core and shell variation. L o w oscillation of Tdb increased drying stress and reduced shrinkage, and oscillated drying schedules were found to reduce Mf variability. A n interesting approach for drying P C H baby-squares is presented by Elustondo and Avramidis (2002). They investigated the dry/sort/re-dry (DSRD) concept by using combined conventional and radio frequency vacuum (RFV) technologies (Figure 1.18) to obtain an optimum drying strategy. Results of the simulations showed that the on-grade percentage has a maximum when the conventional Mt is between 20% and 24%, and the R F V ' s Mt is between 15% and 17%, approximately. This provided a good estimation of the range of Mt which should be used to obtain an efficient D S R D combination. It was observed that for the conventional stage, M, over 20% provided a decrease in the over-drying and increase in the under-drying, together with the increment of the R F V ' s Mt. Under a conventional Mt o f 20%, the over-dried timber percentage becomes independent of the R F V ' s Mt. A t this point, it should be clear why despite the fact that the P C H baby-squares are recommended to be dried to the maximum of 19% Mt (Wallace et al. 2003), in the current study 20% was chosen instead of a higher Mt. f G r e e n • A V T i m b e r j t n l l U M l l l ' -IV11 Figure 1.18: The D S R D strategy If using a re-drying with only conventional kilns, Ward (1984) reported that the re-drying operations can increase kiln-drying costs to about 40%, and the Forest Products 40 Laboratory (1999) gave an approximation of about 25%. Updated estimations, as well as an estimation for conventional/RFV drying concept, w i l l l ikely show better results. 1.6 Wood grading Grading rules provide lumber users with a dependable measure for determining the quality and uniformity of lumber, as well as its performance capabilities. Regardless of species, lumber has characteristics, such as knots, S O G , shape distortions and others, which define its strength and appearance. Grades are assigned to lumber according to these characteristics. The grades usually follow national rules which define the properties of each grade and procedure for inspections. Grading rules are part of a quality-control system, extending from the mi l l through the supply channel to the job site. Knowing the properties associated with each grade is critical to being able to design, specify and build with structural lumber according to local building regulations. Depending on species, target market, usage and other criteria, wood products could be graded using an international grading standard or on the basis o f some other specific standard. Within the geographic bounds of Canada's British Columbia Coastal region, the Coast Forest & Lumber Association ( C F L A ) have developed specific C F L A Japanese Product Standard JPS1, which defines Canadian P C H lumber grades that have known engineering properties derived by in-grade testing methods. These grades have been developed specifically for a range of lumber products intended for structural use in traditional Japanese post and beam building construction. The Standard specifies the maximum grade characteristics and the evaluation criteria for assessing an E l 2 0 module of elasticity rating to the lumber. In order to ensure consistency in the lumber products, the standard also stipulates that all lumber manufactured to this standard is to be grade stamped or certified under the authority and 41 supervision of a recognized grading agency accredited and audited by the Canadian Lumber Standards Accreditation Board ( C L S A B ) . The style and content of this Standard is similar to those found in a number of Japanese standards as well as those involving the International Organization for Standardization (ISO) standards for the visual grading of structural lumber. Hence, except the visual criteria for defining the resource origin, it contains control of the grade sorting process, the initial evaluation and ongoing monitoring of structural properties of the modulus of elasticity ( M O E ) and the modulus of rupture ( M O R ) , re-inspection, the grade stamping requirements, and the contents required in each manufacturer's quality manual. This Standard provides visual grading criteria for both the structural and utility requirements of E l 2 0 Canadian P C H lumber. In addition, it also specifies methods for measuring grade characteristics, procedures to evaluate and monitor the structural properties, the quality control and grade stamping requirements, and the requirements for each manufacturer's quality control manual. The Standard applies to both seasoned and unseasoned sawn lumber, and rectangular or squared cross-sections. 1.7 Research Objectives Apart from timber size the trends of transition, from harvesting old growth to second-growth and ultimately to silvicultural stands, results in changes to timber characteristics. The most important change is an increased proportion of juvenile wood relative to mature wood. This has implications to previously established standards for wood processing, based on the essentially old growth reference values, which are becoming increasingly less applicable. The forest industry of British Columbia w i l l be incessantly faced with inescapable changes, particularly the production of P C H baby squares. 42 The primary objective of this thesis is to undertake a fundamental evaluation on how the pith location (PL), as the only visible indicator of juvenile wood, effects the k i ln drying characteristics of P C H baby-squares. Together with the pith location, cutting season and Mt w i l l be also controlled variables in this project. The thesis w i l l address these effects, on the following outcomes: 1. final moisture content 2. shrinkage 3. shape distortions a. bow b. twist c. diamond 4. surface checking 5. grade classification. The relationship of obtained results with S O G and compression wood w i l l be also considered. 43 2 MATERIALS AND METHODS The detailed sampling procedure, evaluation of properties, ki ln drying process, measuring tools and techniques, and statistical models used in this investigation are explained in the subsequent sections of this chapter. 2.1 Materials Green P C H square timbers were used as specimens in the four test runs. They were all purchased from Weyerhaeuser's Alberni Pacific Divis ion (Figure 2.1) mi l l , located on Vancouver Island. Figure 2.1: The Alberni Pacific Division sawmill A s seen in Table 2.1, the timbers for the first two runs were purchased during the hot and dry summer period (the mi l l summer cutting season) and for the second two runs during the Vancouver Island's rainy fall period (the mi l l fall cutting season) of 2004. The first and 44 fourth runs were randomly selected and were dried to Mt o f 15 % and the other two to Mt o f 20%. Table 2.1: Details of the drying runs Run Cut M t (%) 15-S July, 2004 15 20-S August, 2004 20 20-F November, 2004 20 15-F November, 2004 15 The total sample size was 640 pieces, and for each run 160 specimens were randomly selected. In every run four different pith locations classes (PL) were determined to visually represent the presence of juvenile wood. The classification of specimens regarding the presence and location of the tree pith within the square area of the end cross-section can be seen in Figure 2.2. The dark squares represent a cross-section of green specimens, and the pith (dark dot) is located on the hatched area. 30 mm 30 nn Class 1 Class 2 Class 3 Class 4 Figure 2.2: Location of the tree pith on green specimens If the ends of a specimen were from different P L classes, that kind of specimen was classified based on the end from the class which represent higher amount of juvenile wood. 45 In the class 1 the pith is centrally located. Its distance from each side of a green specimen is more than 30 mm toward the centre of cross section. In this class the largest amount of juvenile wood is present on the cross section. The pith in the class 2 is located less than 30 mm from one of the sides of cross section, and represents juvenile wood predominantly located on the one side of the cross section. Class 3 is without the pith shown on its cross-section, but growth rings with their shape clearly indicate that the pith is located less than 30 mm from one of the sides. The presence of juvenile wood in this class is also asymmetric. Class 4 is also without the pith on its cross section, but in contrary to class 3, the growth rings on this type of specimens indicate that they come from mature wood locations. Each pith location class is represented with 40 randomly selected specimens in each drying run. The specimens were all 3048 mm long (10 ft), namely 114 x 114 mm (4 Vi by 4 Vz in) in cross-section and of rough surfaces. Actual measure was mostly equal or more than 115mm by 115mm, for rough and freshly cut specimens. The mil l ' s best estimated percentage of amabilis fir in the population of the four runs was 25 to 30%. A l l runs used the same log source of North Vancouver Island and Port Alberni. 2.2 Experimental Design The four drying runs, listed in Table 2.1, were carried out with 160 specimens (8 ft long), each in an 8-foot steam/electricity heated laboratory k i ln located at the U B C Wood Drying Laboratory (Figure 2.3). 46 Figure 2.3: Laboratory wood drying ki ln at U B C For each test run, the following procedure in specimen preparation was used. Once the green wood was shipped to Forintek Canada Corp., it was cut to 2.44 m (8 feet) long ki ln specimens by one-foot trimming from each end with a radial arm saw (Figure 2.4). Figure 2.4: Cutting of specimens at Forintek One 25.4 mm thick slab (cookie) was cut from each end, next to the trimmed end, for calculation of basic density and Mj measurement (Figure 2.5). These cookies were immediately labeled [Run # (1 to 4) - Specimen # (1 to 160) - End # (A or B)] and placed into 47 a plastic container with a tight cover. The label on the cookies was mapped to show the timber orientation in the ki ln . reject Cookie A 25.4mm (1 inch) k i l n s p e c i m e n •4 • reject Cookie B 25.4mm (1 inch) 2.44m (8 ft) Figure 2.5: Cutting protocol of green wood for the preparation of drying specimens In order to evaluate the possible effects of cross-sectional characteristics on drying quality, each pair of cookies from each timber was scanned with a digital scanner together into one image file with the front end above (close to the ki ln door), the back end below (close to the ki ln back), and oriented up as the timber specimen was stacked in the ki ln. The timbers were loaded into the laboratory k i ln that could accommodate specimens up to 2.44 m long and is typical of an industrial type heat-and-vent ki ln. The green timber package was comprised of 8 rows high and 20 pieces wide and 20 mm stickers. The locations of specimens in the each ki ln load were completely randomized by random number generator. To be able to determine timber location effects in the ki ln , digital pictures of the front end of the wood stack close to the ki ln door (Figure 2.3) were taken before and after drying, so that the ki ln stack could be digitally rebuilt. For each ki ln specimen, the same green timber evaluation procedure was implemented. Upon completion of each drying run, the wood was left to cool down in the ki ln for 12 hours with the doors closed. After unloading the wood from the ki ln , post-drying evaluation for each timber specimen was carried-out. 4 8 Upon completion of all the after-drying measurements, the wood was wrapped and shipped to a local custom planer mi l l . Planing was done to dimensions of 105 by 105mm, by planing of 5 mm from one side, and then the rest from the opposite side. Thereafter, the specimens were sent back to the U B C Wood Drying Lab where a B C professional lumber grader did the grading o f each timber according to the C F L A E l 2 0 visual grading procedure stated in Section 1.6. Upon completion of grading, the final, post-planing, evaluation was performed for each piece of timber. 2.3 Methods of timber evaluation 2.3.1 Green timber evaluation For each green specimen, its density, M , , shape deformations (bow, twist and diamonding) and length of surface checks were measured. 2.3.1.1 Density and initial moisture content The A S T M oven-dry method was used with the 25.4 mm thick cookies that were cut from each end of timber, as shown in Figure 2.5. The weight o f each cookie was immediately measured with a digital balance to 0 .0 lg and recorded. Their green volume was obtained by the water immersion method, by dipping the cookie entirely and quickly into water and recording the volume from the electronic balance (Figure 2.6). 49 Figure 2.6: Measuring o f volume using the water immersion method The cookies were then oven-dried at 103±2°C for 24 hours in the Model Blue M B -2730-Q wood drying oven (Figure 2.7). Oven-dry weights were immediately measured with the same electronic balance (Figure 2.6) and M , was calculated as dry-basis, as described in Section 1.2.1. A n average moisture content of two cookies from each timber was used as the Mi o f that particular k i ln specimen. Figure 2.7: Wood drying oven with wood slabs at U B C Basic density of each timber was calculated from the same two cookies used in Mt determination. The basic density of each cookie was calculated by the ratio of the oven-dry 50 weight to the green volume. The average basic density of these two cookies was considered as the basic density of the particular timber piece. The digital scanning of each cookie followed the volume measurement for each timber piece in each run. The two cookies from each timber were scanned into a [x-xxx.jpg] image file, as shown in Figure 2.8. Figure 2.8: Digitally scanned cookies from the same timber The first number on the scanned cookies indicates the number of drying runs (1 to 4), and the second represents the number of specimens in the run (1 to 160). The cookie with the " A " mark was always from the front end of the timber (kiln door side) and the " B " marked from the back end. Each green and k i ln dried timber was weighted with an Accu-Weight Pak-150 electronic scale (Figure 2.9). The range of the scale is 150 kg measurable to ±0.1 kg. 51 Figure 2.9: Electronic scale for measuring of timber weighted The width and thickness o f each timber was measured by using a pair of Model 500-196 digital calipers, made by Mitutoyo (Figure 2.10), at the mid-length point before and after drying. The resolution was 0.01 mm and the measurement accuracy was better then 0.25 mm. Before measurement, a line was drawn to ensure that the same point before and after drying was always used. If there was a knot at the mid-point, the measuring point yielded to its neighboring sound point. Figure 2.10: Digital calipers for measuring dimensions 52 2.3.1.2 Green shape distortions Shape distortions (twist, bow, and diamonding) were measured on a shop-built aluminum table calibrated for straightness and flatness (Figure 2.11). It consisted of a " U " shape aluminum base that is clamped, in an upside down position, onto two support stands with leveling feet. The flatness of the surface of the base was ground to 0.25 mm. A n aluminum fence was lapped, shimmed, and mechanically clamped at 90° to the base. Its straightness was adjusted to 0.25 mm with a piece of 19 mm M D F sawn on a very accurate sliding table saw and a feeler gauge. The straightness of the M D F edge was checked against a ground case steel machine surface to be within 0.05 mm. The measuring table was fixed to the same location in the lab where the table was adjusted for straightness and flatness. The angle between the fence and the base was adjusted to 90° ±0.5°. Figure 2.11: Table for measuring of shape deformations In conjunction with the measuring table, two special shop-built digital dial gauges were used for bow, twist, and diamonding measurement. Bow and twist deformations were measured with a Mitutoyo Model ID-C1012EB Digital Dial Gauge attached at 90° to a flat 53 aluminum reference plate (Figure 2.12). The resolution was 0.01 mm and the measurement accuracy was better than ±0.5 mm i f measured skillfully. Figure 2.12: Digital dial gauge The bow measurement was done by finding the surface with the biggest bow on a specimen, and measuring the biggest gap between the timber and the fence, as shown left in Figure 2.13, while pushing its two ends against the table fence. Figure 2.13: Measuring of bow (left) and twist (right) The twist assessment was done by touching one end of the piece against the fence and checking how far the other end was off the fence at the top corner, with the bottom corner 54 touching the fence as shown right in Figure 2.13. The largest over the four faces of the timber piece was assigned as the twist of that particular timber piece. Evaluation of diamonding was carried out with a shop-built instrument consisting of a Mitutoyo Model ID-SI012EB Digital Gauge attached to a precision steel machine square (Figure 2.14). The resolution is 0.01mm and the measurement accuracy was better than 0.25 mm. The diamonding measurement was done by pressing the vertical steel bar against one surface of the timber and checking how far the right top corner was away from the horizontal bar that is welded to the vertical bar in 90 degrees. Figure 2.14: Measuring of diamonding 2.3.1.3 Measuring of green surface checks The total length of checks on each side of a specimen was measured using the Starrett C1-8M8 measuring tape. During the stacking of drying loads (Figure 2.15). The data was entered separately for each side of every specimen, as well as a summary for the whole pieces. A l l surface checks that were present on green specimens were marked with a permanent marker prior to k i ln drying, to allow the later untruthful detection of checks that w i l l develop during the ki ln drying. 55 Figure 2.15: Measuring of surface checks 2.3.2 Kiln and kiln data collection and drying schedule used The U B C ' s laboratory ki ln with a wood capacity of 3000 board feet (about 7 m 3 ) is a typical track-loaded, heat-and-vent ki ln. It can easily hold the 160 pieces of 116 mm squares, 2.44 m long specimens used in each of the runs of this study. The fan area is relatively high to accommodate three larger diameter fans which easily maintain the uniformly ki ln climate. The k i ln cart is sitting on a scale, which allows continuous monitoring of the weight o f the charge and thus its mean moisture content. Both electric heating elements and steam heating coils are located in the center part above the fan deck. The top and bottom baffles (Figure 1.9) are needed on both sides to guide the flow of air through the area between stickers (air channels). The air flow is even more uniform compared with the commercial industrial kilns of this type. H is controlled by low pressure steam sprayers and two roof vents. The ki ln has dry-bulb and wet-bulb sets on the left and right walls (Figure 2.16). The drying process is controlled by a specially written computer program in conjunction with a 56 data acquisition system that traces the ambient conditions in the ki ln and adjusts according to the pre-inserted drying schedule. At the same time, based on the weight difference between the start and current weight, the program monitors the average moisture content of the wood pile and stops the drying process when it reaches the Mt. A l l collected process data is saved every five minutes during each drying run and real-time plots are generated. The real-time drying curve which shows trend variables can be used at any time to monitor and control drying stages, conditions in the ki ln and overall proper working of the ki ln. Figure 2.16: Computerized control panel of the ki ln The drying schedule used for this study is shown in Table 2.3. It is a mixed time-moisture based schedule, developed at U B C . The drying schedule is terminated by the moisture content monitored by an in-kiln load cell based on M , estimated and provided to the program. The initial drying stages had a very low wet-bulb depression to minimize surface checking and other drying defects early in the cycle on thick P C H timbers. Thereafter, wet-bulb depression and dry-bulb temperature increased in a step-wide mode until reaching the highest temperature level at the beginning of the ninth day (Step 9). The drying was maintained at this level until the designated average timber load moisture content, as 57 calculated by its weight, was reached. The drying then entered into the conditioning step (Step 10) during which the dry-bulb and wet-bulb depression were reduced. A i r velocity was set to 3 m/s (600 feet/minute) through the timber stack in all runs, and was kept constant though the study with a flow direction reversal every 12 hours. Table 2.2: Drying schedule used in the four runs Step Time (hour) T d b (°C) T w b (°C) M E (%) Fan reversal (h) 1 6 49 49 25.0 3 2 24 52 51 21.5 12 - 3 24 55 53 17.5 12 4 24 58 55 15.6 12 5 24 62 57 12.6 12 6 24 66 59 10.6 12 7 24 70 61 8.6 12 8 24 74 63 7.8 12 9 last until M = 15% 78 65 7.0 12 10 12 72 69 15.1 6 2.3.3 Kiln dried timber evaluation After the cooling time, the timber was pulled out from the chamber and the weight base Mf, shell (Ms) and core (Mc) moisture content, length of surface checks and drying distortions were immediately measured. 2.3.3.1 Kiln dried moisture content Each green ki ln dried timber was weighted with the same Accu-Weight Pak-150 electronic scale (Figure 2.9) used for the pre-drying measurements. Based on the weight difference between green and k i ln dried weight, the final weight-based MF was calculated. 58 Figure 2.17: Resistance pin-type moisture meter The measurement of Mc and Ms of the rough ki ln dried timbers was done with the Delmhorst resistance pin-type moisture meter, (Model R D M - 2 of 0.1 % resolution) shown in Figure 2.17. For this study, we chose 14 mm as the shell depth, and 56 mm as the core depth. After each Ms measurement, the original shell pin holes were drilled down to a depth of 50 mm to assist the intrusion of the long thicker pins, so that they can readily reach the core and measure Mc. 2.3.3.2 Shrinkage At the same position as described in Section 2.3.1.1, the width and thickness of each dried timber were measured. It was performed using the same pair of Model 500-196 digital calipers, made by Mitutoyo. The calculation of the shrinkage of each specimen was described in Section 2.3.1.2. It was calculated separately for width and thickness. The volumetric shrinkage was calculated based on width and thick shrinkage. 59 2.3.3.3 Shape distortions Shape distortions (twist, bow, and diamonding) of the k i ln dried specimens were measured using the same procedure and the same equipment as was in used on green specimens. The distortions were measured at the same side of specimens as was done before drying. Later, these measurements were recorded, and the differences between the green and k i ln dried values were calculated. These differences represent the ki ln drying distortions. 2.3.3.4 Surface checks Using the same Starrett C1-8M8 measuring tape, as was used for green checks, the total lengths of checks were measured on each side of the k i ln dried specimen. In order to prevent bias, as a result of the eventual development of checks caused by different uncontrolled after-drying factors, this measurement was performed immediately after the cooling period, during the unloading of the ki ln . 2.3.4 Evaluation of planed timber Upon finishing the ki ln drying evaluation, the specimens were transported to a local planing mi l l . The planing was done by removing the surface layers from all four sides of a rough specimen, in order to form the final planed baby square cross-section with dimensions of 105 by 105 mm. To be able to detect the original sides of specimens, previously marked on the frontal cross-section, the usually performed end-trimming operation was canceled for this study. The planed moisture content, length o f surface checks, shape distortions and slope o f grain were measured on each specimen of this type. To secure the highest possible comparability of the rough and planed shape distortions and surface checks, the same methods, 60 equipment, locations on specimens and personnel were used in these evaluations. For the same reason, before and after planing, high importance was dedicated to proper storage of specimens. The piles were wrapped in a waterproof covering immediately after post-drying evaluations, and again after planing. Between operations they were stored in a covered, closed, and water and wind-free space (Figure 2.18). Figure 2.18: Storage of specimens between the evaluations 2.3.4.1 Planed moisture content The measurement of moisture content of planed specimens is done with the Delmhorst resistance pin-type moisture meter, Model R D M - 2 of 0.1 % resolution, shown in Figure 2.17. For each specimen, their planed moisture content is measured in three locations. One location was 500 mm from the right end, the second in the middle of a specimen, and the third was 500 mm from the left end. For these measurements, we chose 26 mm as a representative depth. This depth is in the mid-distance between a side and the center of a cross-section, so the core/shell effect is expected to be minimized. The after-planing moisture content of each specimen was calculated as the mean value of these three measurements. 6 1 2.3.4.2 Shape distortions A s in the pervious evaluation, the measured shape distortions of planed specimens were bow, twist and diamonding. Wi th keeping the original cross-sections, the previously measuring positions were easily detected. 2.3.4.3 Surface checks During the planing, the surface layers of specimens were removed together with an amount of surface checks, which were present after the ki ln drying. Using the same Starrett C1-8M8 measuring tape, the lengths of surface checks, still present on a planed specimen, were measured. This date were collected for each side, summarized, and later compared with the after-drying data sets. 2.3.5 Other wood attributes In order to produce sufficient information for the explanation of drying behavior and quality, and in addition to the controlled factors and previously listed measurements, the slope of grain and percentage of compression wood were also identified for each k i ln specimen in the study. 2.3.5.1 Slope of grain S O G was measured with a shop-built scratch gauge with a pivoting handle for scribing a light groove parallel to the grain (Figure 2.19 left). A M I T E - R - G A G E adjustable Lexan protractor was used to measure the angle, with respect to timber edge (Figure 2.19 right), measurable to 0.5°. To increase the accuracy o f measurement, S O G was instead measured on the planed surfaces, instead of initially on the rough specimens. 62 Figure 2.19: Measuring of slope of grain S O G measurement with this method is called apparent or surface, instead of machine-measured internal S O G . For each piece of timber, the S O G was measured at three points, namely, the front-quarter-end, middle-point, and rear-quarter-end. The surface groove made by the scratch gage had a minimum length of 300 mm, so that an average S O G , instead of a local one, could be measured. 2.3.5.2 Compression wood The presence of compression wood is detected with a picture analyzing method. Digitally scanned images of cookies are imported into A u t o C A D software. With the selection tools, a complete image of a cookie is marked and its area is calculated (Figure 2.20 up). The same was done with compression wood area (Figure 2.20 down). The criterion for distinction of a compression wood area is its characteristic dark color compared with the surrounding non-compression wood area (Timell 1986). 63 Polyline AutoCAD 2004 - [Drawingl .dwg] 1 3 File Edit View Insert Format Tools Draw Dimension Modify Express Window Help & • 0 i >^ • BVLI Color Layer Line type Linetype scale Plot style Lineweight Hyperlink Thickness • ByLayer 0 1.0000 ByColor - ByLayer - ByLayer Vertex 1 Vertex X 31.1168 : Vertex Y 4.1678 Start segment width 0.0000 End segment width 0.0000 Global width 0 0000 Elevation 0.0000 [Area 306.7966 Length 70.1572 Command. Command: _ p r o p e r t i e s Count and 32 7854.2 0983 . 0 0000 SMAP GRID ORTHU POLAR foSNAP OTRACK LWT |MC0EL - i . -S! AutoCAD 2004 - [Drawingl .dwg] C File Edit jja g jj View Insert Format Tools Draw Dimension Modify Express Window Help id o ». 411 Iii •Bvu l Polyline m % Color • ByLayer jLayer 0 Linetype ByLayer Linetype scale 1.0000 Plot style ByColor | Lineweight ByLayer ; Hyperlink ! Thickness 0.0000 : Vertex l : Vertex X 13,6261 Vertex Y 5.7774 i Start segment width 0.0000 End segment width 0.0000 Global width 0.0000 : Elevation 0.0000 Area 9.9509 Length 32.1541 > X Model -.IBBIICTi Command Command _ p r o p e r t l e s V Command < 32.8429.12 4459.0 0000 SNAP GRID 0RTH0 POLAR |0SNAP OTRACK LWT jMODEL Figure 2.20: Measuring of percentage o f compression wood 64 Based on a difference of these two areas, the presence of compression wood on each specimen is calculated and expressed through the percentage of compression wood per total cross-section: C w = ^ * 1 0 0 [ % ] (2.1) A where C w - percentage of compression wood [%] A c w - area of compression wood [mm 2] A t - total area of scanned specimen [mm 2] The large variation in its appearance was sometimes a problem for the determination of its percentage. 2.3.6 Grading of baby-squares A s the final stage of the study, all specimens were graded by a professionally accredited B C lumber grader. The grading was performed according to the Coast Forest and Lumber Association ( C F L A ) grading procedure. A s the grading standard, the C F L A E l 2 0 standard for visual grading of structural P C H was selected. A l l specimens were graded in five grading classes: 1. E120 (the lumber of best quality) 2. Industry 3. Standard 4. Uti l i ty 5. Reject The lumber quality in this list is in descending order. The first three classes are acceptable for export to Japan as a post-and-beam construction lumber, while utility and reject 65 classes do not meet the minimal requirements. Therefore, to get a clearer picture, the grading results could be also classifieds as the accepted for export (including E l 2 0 , Industry and Standard classes) and rejected (including Uti l i ty and Reject classes). Furthermore, keeping in mind the objective of this study or the ki ln drying influence on the final quality, the grader was asked to provide the reasons for degradation of all specimens which are under the highest E l 20 quality. According to this type of information, all specimens where a reason for degradation was not the drying process, were classified as the accepted specimens. This was done to prevent eventual misleading information about k i ln drying. 2.4 Statistical analysis B C coastal sawmills export P C H baby-squares in the planed form. For that reason, all specimens in this study are planed as described in Section 2.3.4. The conclusions which in a very clear way explain the drying quality of these products are about the development of shape deformations and checking. The planed specimens still contain an amount of shape deformations and checks, but it is incorrect to compare them directly with green values, because except for the k i ln drying process, there is also the planing process, which by itself has an influence on these comparisons. For that reason, the most robust and complex tests are performed on the data which represents the differences between green and k i ln dried rough values. Because of the nature of the results, which show significant differences between replications, this thesis offers two different concepts of statistical analysis of results. One concept is termed as Concept A and it is analyzed as a 2x4 factorial design, while in Concept B different M , between summer and fall supplies are detected as a reason for differences between replications, therefore, the cutting season is treated as the third factor with a possible 66 influence on results. For that reason, in the case of Concept B , a 2x2x4 factorial design is applied. In both concepts, in order to provide a linkage between initial form (green) and final form (planed) of specimens, as the one that should be delivered to customers, a paired t-test is applied to test differences between the rough after-drying and planed specimens. If the paired test shows no difference, the conclusions from the green/dried relation are fully applicable; but in contrast, eventual changes on the planed specimens could be the results of the planing process, after-drying stresses, or other uncontrolled factors like variable H or temperature of environment. In addition to the aforementioned tests, some other ones were used. They wi l l be explained in the following sections. For all tests the level o f significance (type I error) is set to be 0.05. 2.4.1 Factorial design 2.4.1.1 Concept A - 2x4 design To test the main effects of two main factors: target moisture content (Mi) with two levels and the pith location (PL) with four levels, as well as their interaction on shape deformation, surface checking, shrinkage and Mf, an appropriate 2x4 factorial design was applied. The tested hypotheses for each 2x4 factorial design are stated as: H o i : Interaction between Mt and PL is N O T significant H 0 2 : Ma in effect o f factor Mt is N O T significant H 0 3 : Ma in effect o f factor P L is N O T significant The linear model is: y i l f = ! i + ai + pf+(aP)lf+ s i ( l f ) (2.5) 67 where y - an observation [i - the allover mean a - the effect of factor A (Mt) p - the effect of factor B (PL) aP - interaction between factors A and B s - sampling error Subscripts: 1 - levels of factor A l = l , . . . ,m f - levels o f factor B f = l,...,p i - number of observations within the highest level o f interaction i = l , . . . , n The partition of total variation for sum of squares is: n m p XXE(^/-7"02=^Z(7-'--7---)2+^E(r--/-r---)2 + ,:=i 1=1 f=\ /=] ' y=i m p n m p nXE(r.//-F.,-7.. / +7...) 2 +2;iE(^-^) 2 /=! f=\ m = 2 p = 4 n = 80 (2.6) ;=1 1=1 f=\ or SSt — S S A "t" S S B S S A X B ± S S E Table 2.3: Analysis of variance table - Concept A (2.7) Source of variation Degrees of freedom Sum of squares Mean square Proper F test Factor A m - 1 S S A M S A M S A / M S E Factor B p-1 S S B M S B M S B / M S E Interaction A x B (m-l )*(p- l ) S S A X B M S A X B M S A X B / M S E Experimental error mp(n-l) S S E M S E M S E Total mpn-1 S S T 68 2.4.1.2 Concept B - 2x2x4 design To test the main effects of three main factors: the cutting season (CS) with two levels, target moisture content (Mt) with two levels, and the pith location (PL) with four levels, as well as their interaction on shape deformation, surface checking, shrinkage and Mf, an appropriate 2x2x4 factorial design was applied. The tested hypotheses for each 2x2x4 factorial design are stated as: H o i : Interaction between CS, Mt and PL is N O T significant H02: Interaction between CS and Mt is N O T significant H03: Interaction between CS and PL is N O T significant H04: Interaction between M, and PL is N O T significant H05: Ma in effect of factor CS is N O T significant H06: M a i n effect of factor Mt is N O T significant H07: Ma in effect of factor PL is N O T significant Linear model is: yiifk = \i + a, + pf + y k + (ap)lf + ( a y ) l k + ( f i y ^ + (a[3y) l f k + e i ( l f k ) (2.2) where y - an observation p - the allover mean a - the effect of factor A (CS) (3 - the effect of factor B (Mt) y - the effect of factor C (PL) a(3 - interaction between factors A and B ay - interaction between factors A and C py - interaction between factors B and C a(3y - interaction between factors A , B and C e - sampling error 69 Subscripts: 1 - levels of factor A l = l , . . . , m m = 2 f - l e v e l s of factor B f = l,...,p p = 2 k - levels of factor C k = l , . . . , q q = 4 i - number of observations within the highest level of interaction i = l , . . . , n n = 40 The partition of total variation for sum of squares is: /) in p g m p EZSZ(^- F --) 2 =npq2(Y.,..-Y....)2 + nmq ^ (7. . / . - 7 . . . . ) 2 + ,-=i /=i /=i k=] i=\ /= i < 7 _ _ m p _ _ _ _ nmp^(Y...k.-Y...y +nq^^(Y.,f.-Yj..-Y..j. + Y....)2 + k=\ l=\ f=\ _ P I — _ _ _ ^ES(7-"'- Yj- -Y...k + Y....)2 +nmYJYj(Y..Jk- 7. . / . - Y...k + 7 . . . . ) 2 + /=1 k=\ f=\ k=\ "i P 1 — — — — — — _ _ n H Z Z (7-«* ~ Yjf- - Yj-k -Y- +Y-'-+Y- •/•+Y...k+Y...y + /=1 /=1 A = l ,=1 /=l /=1 t=l or (2.3) S S T — S S A + S S B + SSe + S S A X B + S S A X C + S S B X C + S S A X B X C + S S E (2-4) In both concepts, the calculated F-value is compared with a critical F-value, and i f the former is higher the related null hypothesis is rejected. First, the highest level of interaction is interpreted, and i f it is insignificant, the lower level of interaction is compared. 70 Table 2.4: Analysis of variance table - Concept B Source of variation Degrees of freedom Sum of squares Mean square Proper F test Factor A m - 1 ssA M S A M S A / M S E Factor B p - 1 S S B M S B M S B / M S E Factor C q - 1 S S C M S C M S C / M S E Interaction A x B (m-l )*(p- l ) S S A X B M S A X B M S A X B / M S E Interaction A x C (m- l )* (q - l ) S S A X C M S A X C M S A X C / M S E Interaction B x C (P-D*(q-1) S S B X C M S B X C M S B X C / M S E Interaction A x B x C (m-l)*(p-l)*(q-l) S S A X B X C M S A X B X C M S A X B X C / M S E Experimental error mpq(n-l) S S E M S E M S E Total mpqn-1 S S T The conclusions about the main effect of factors A , B and C are interpreted only i f a specific factor does not participate in any interaction that shows significant influence on results. If an interaction or PL has a significant influence, the Bonferroni's test is selected as the multiple comparisons test. It is chosen because it is the least liberal multiple comparison test (less type I error). The critical difference for the Bonferroni's test is: CD = t^y[2S^ (2.8) 2m where a - level of significance (0.05) m - number of comparisons Sy - standard error of the mean Taking into consideration that the effects of Mr and CS are on two levels, i f a null hypothesis is rejected there is no need for a multiple comparison test. 71 2.4.2 Contingency table To analyze the grading results, a 4x2 contingency table was used to deliver conclusions of influence of PL on drying quality. The hypotheses are stated as: H 0 : The effect of PL on grading quality is N O T present. H A : The effect of PL on grading quality is present. Effects in a contingency table are defined as relationships between the row and column variables based on a Chi-square statistic. Contingency tables are constructed by listing all the levels of PL as columns in a table and the levels of the grading classes ("accepted" and "not accepted") as rows, then finding the joint or cell frequency for each cell. The cell frequencies are then summed across both rows and columns. The sums are placed in the margins, as the marginal frequencies. The lower right hand corner value contains the sum of either the row or column marginal frequencies. The expected cell frequency for each cell is calculated as: E= ( R T * Column Total) / F, (2.9) where E - expected cell frequency Rt - row total frequencies Ct - column total frequencies Ft - allover total frequencies This value is subtracted from the observed cell frequency for each cell. The chi-square statistic is computed by summing each of these differences, squared and divided by the expected cell frequency for each cell. 72 The obtained chi-square statistic is compared with the critical value found using the chi-square table. If the observed value is greater than the expected value, the null hypotheses (no effect) are rejected. 2.4.3 Other tests To test the data collected before drying (M„ basic density, green shape deformations and checking) it is incorrect to apply factorial designs as explained in details in Section 2.4.1. On the values of these recordings, Mt did not have any influence. For that reason, a 4x4 factorial design is used instead, to provide a decision tool for questions about eventual pre-drying differences between the drying runs and P L . One factor is Run, with four levels (each drying run representing one level), and second is P L , also with four levels. To test the slope of grain and compression wood percentage on differences between the pith location classes, a standard One-way analysis of variance and the Boneferroni multiple compression test is applied. For conclusions about their shape distortions, the relationships were examined by using the linear regressions model, by fitting a straight regression line. In the scatter plots, the S O G or compression wood percentage was used as the repressor, and the difference between green and k i ln dried rough distortion was used as the criterion. In addition, as was previously explained, the paired t-test is also one of the tests used in this study. This was performed to test whether paired sets of k i ln dried rough and planed specimens differ from each other in a significant way. 73 3 RESULTS AND DISCUSSION 3.1 Basic density Basic density is an important wood property which directly influences many drying characteristics. The full range of basic density for the four drying runs in this study was from 281 to 556 kg/m 3 , with a mean value of 402 kg/m 3 and a standard deviation o f 48 kg/m 3 . The basic density statistics for each pith location class per drying run are presented in Table 3.1. Table 3.1: Basic density statistics for different pith classes and drying runs Mean (kg/m3) St. Dev. (kg/m3) Minimum (kg/m3) Maximum (kg/m3) 15-S Class 1 404 44 295 510 Class 2 411 39 325 485 Class 3 405 43 320 495 Class 4 405 46 330 490 total run 406 43 295 510 15-F Class 1 399 59 303 556 Class 2 387 52 282 477 Class 3 401 43 281 488 Class 4 398 49 307 509 total run 396 51 281 556 20-S Class 1 401 47 290 490 Class 2 408 46 295 525 Class 3 399 49 290 525 Class 4 404 58 300 530 total run 403 50 290 530 20-F Class 1 406 36 319 484 Class 2 395 53 303 513 Class 3 399 46 291 480 Class 4 404 52 313 525 total run 401 47 291 526 74 These results are compared with results obtained by other researchers. Avramidis and Hao (2004) reported that an average basic density in five drying runs (total 800 P C H 3 3 specimens) varied from 380 to 410 kg/m with a standard deviation of 40 to 50 kg/m . The basic density of western hemlock from the technical literature is in the range of 294 to 524 3 3 kg/m (Zhang et al. 1996), whilst for amabilis fir it is often in the range of 245 to 475 kg/m (Isenberg 1980). The presence of amabilis fir in P C H is usually below 35% (Avramidis 2001, Avramidis et al. 2004), and because of its lower density is expected to dry faster than western hemlock (Avramidis and Oliveira 1993). The analysis of variance test performed for Table 3.2 indicated that the pith classes with juvenile wood and the mature wood class did not demonstrate significant differences in basic densities. It should be noted that this conclusion regards differences between average basic densities of specimens, but it does not mean that basic density is uniform within each timber. It is concluded that this variability is l ikely higher in the juvenile wood classes compared with the mature wood class, despite the overall lack of difference; this probability is based on the fact that wood has a variable density in juvenile tissue, while the density is relatively constant in mature wood. According to Josza et al. (1998), the high-density wood of western hemlock is associated with the pith, the lowest density values are found approximately 30 to 70 mm from the pith and after that, density is fairly constant toward the bark. Weldwood and Smith (1962) noted that the greatest density is in rings 1 to 5 with a steep decline to rings 16 to 20 and recovery from 26 ring; El l is (1995) reported a similar trend. A n additional factor for variation around the pith of most conifer trees is the frequent presence of compression wood, with its characteristically higher density (Du Toit 1963, Low 1964, Timell 1986). Due to all of these reasons and regardless of the overall uniform density between the pith location 75 classes, the uneven drying behavior of specimens from the juvenile wood classes compared with mature wood specimens should not be excluded. Table 3.2: Analysis of variance for basic density Source of Variation DF Sum of Mean F F Squares Square calculated Critical Run 3 8,294 2765 1.20 2.63 Pith 3 608 203 0.09 2.63 Run x Pith interaction 9 10,454 1162 0.50 1.91 Experimental error 624 1,440,167 2308 Total (Adjusted) 639 1,459,523 *Term significant at a = 0.05 This analysis also shows that there is no evidence for differences in basic densities between any of the four runs dried in this experiment. This could be seen as a conformation for the assumption that with the exception of M„ there were no additional significant differences in basic densities of specimens, but for the sake of better understanding the further drying characteristics investigated in this thesis, it should be listed that for: a) Concept A Specimens dried to Mt o f 15% have an overall mean basic density of 401 kg/m 3 , with a standard deviation of 47 kg/m 3 , while timbers dried to Mt o f 20%> are 402 kg/m 3 and 47 kg/m 3 respectively. b) Concept B The overall mean basic density o f specimens from the summer cutting season is 404 kg/m , with a standard deviation of 46 kg/m , while for the fall cutting season they are 399 kg/m 3 and 49 kg/m 3 respectively. 76 3.2 Initial moisture content The Mi o f freshly cut P C H timbers, calculated with the same method as in our experiment, was previously reported to range from 26 % to 60 % (Oliveira and Wallace 2001) and 58 % to 72 % (Hao and Avramidis 2004). M , statistics calculated from the cookies of our experiment are indicated in Table 3.3. Table 3.3: Initial moisture content statistics for different pith classes and drying runs Mean (%) Sta. Dev. (%) Minimum (%) Maximum (%) S15 Class 1 41.62 18.17 25.16 118.54 Class 2 42.38 17.64 19.83 113.24 Class 3 41.86 16.66 16.78 88.21 Class 4 53.25 22.88 20.41 102.55 total run 44.78 19.44 16.78 118.54 F15 Class 1 69.43 16.69 Aim 104.47 Class 2 75.54 19.17 44.18 111.64 Class 3 73.20 16.56 47.29 105.33 Class 4 79.19 20.27 44.14 127.18 total run 74.34 18.42 42.02 127.18 S20 Class 1 54.11 19.77 31.48 102.87 Class 2 50.57 17.25 34.83 120.95 Class 3 54.83 23.32 30.00 113.66 Class 4 58.26 25.90 27.80 130.77 total run 54.44 21.18 27.8 130.77 F20 Class 1 64.45 17.80 41.22 119.57 Class 2 64.73 22.24 41.71 133.45 Class 3 69.51 23.96 45.34 147.65 Class 4 77.41 28.18 43.98 166.81 total run 69.02 23.71 41.22 166.81 3.2.1 Concept A The results in Table 3.4 show a significant difference in M,- within the pith location classes. Specimens from the pith location class 1 had an average M , of 57.19% with a standard 77 deviation of 20.83%. Respectively, they are 58.22% and 23.04% for the class 2, 59.82% and 23.92% for the class 3, and 66.75% and 26.88% for the pith location class 4. Table 3.4: Analysis of variance for initial moisture content - Concept A Source of Variation DF Sum of Squares Mean Square F calculated F Critical Pith 3 9,170 3,057 5.44* 2.63 Experimental error 636 357,358 561 Total 639 366,528 *Term significant at a = 0.05 Nicholls et al (2003) reported that M , of western hemlock tends to increase as the distance from the pith increases. A Bonferroni's multiple comparison test of the results from this study shows a similar conclusion. The mature wood class 4 had a significantly higher M,-compared with the other three classes. A possible explanation could be that because of their location (close to the center of a log), the first three classes of specimens are sapwood free. In the class 4, there is a probability for the occurrence of sapwood, which is expected to have a considerably higher moisture content than heartwood. Nielson et al. (1985) reported that an average M , of western hemlock heartwood could be three times lower compared with sapwood. The high M , of P C H and its large variation may also be a result o f characteristic P C H wet pockets (Kozl ik 1970). Many authors suggest that reducing this variability could lead to a reduction o f problems related to uneven Mf (under-drying or over-drying). 3.2.2 Concept B The timbers dried from the first two runs (the summer cutting season) had an average Mi o f 49.61%), with a standard deviation of 21.17%), while for the second two runs (the fall cutting season) they are 71.68 % and 21.36%, respectively. The timbers used in this study 78 were stored for about two weeks at the sawmill yard upon sawing and prior to sampling, therefore, summer supplies show statistically lower M , (Table 3.5). It is interesting to note that some specimens from the summer cutting season have M , below the FSP. Likely, these specimens come from the outside layers of the green timber piles that were directly exposed to the summer sun in the mi l l . Table 3.5: Analysis of variance for initial moisture content - Concept B Source of Variation D F Sum of Squares Mean Square F calculated F Critical CS 1 77,943 77,943 176.62* 3.87 Pith 3 9,170 3,057 6.93* 2.63 CS x Pith interaction 3 503 168 0.38 2.63 Experimental error 632 278,912 441 Total 639 366,528 *Term significant at a = 0.05 During warm summer days, unprotected timbers, under the influence of sunlight and wind, easily start to air dry. This drying process is especially fast for green timbers because their cell 's lumens contain free water that easily evaporates under warm conditions. Contrarily, during rainy seasons, a constant presence of high humidity could easily maintain a high Mi o f green timber. Timbers with the pith shown on their end cross-sections are often considered to be low quality timbers, so they are stored in an open area where they are not protected from environmental conditions. However, with proper storage procedures, this variability could be lower. The results in Table 3.5 show a significant difference in M , within the pith location classes. Specimens from the pith location class 1 had an average Mt o f 57.19% with a standard deviation of 20.83%. Respectively, they are 58.22% and 23.04% for the pith class 2, 59.82% and 23.92% for the class 3, and 66.75% and 26.88% for the pith location class 4. Nicholls et al 79 (2003) reported that the M , of western hemlock tends to increase as the distance from the pith increases. The Bonferroni multiple comparison test of the results from our study shows a similar conclusion. The mature wood class 4 had a significantly higher M , compared with the other three classes. A possible explanation could be that because of their location (close to the center of a log), the first three classes of specimens are sapwood free. In the mature class, there is a probability for the occurrence of sapwood, which is expected to have a considerably higher moisture content than heartwood. Nielson et al. (1985) reported that an average M / of western hemlock heartwood could be three times lower compared with sapwood. The high M , of P C H and its large variation may also be a result of characteristic P C H wet pockets (Kozl ik 1970). Many authors suggest that reducing this variability could lead to a reduction of problems related with uneven A / f (under-drying or over-drying). 3.3 Drying time and rate The drying curves of the four runs are plotted in Figure 3.1. The fact that the runs with close Mt dried with almost an identical drying curve under the same drying schedule, indicates that the k i ln was functioning consistently well throughout the project and thus ensured the drying data quality of the project. In order to understand how the drying curve changed with the drying schedule, the schedule is plotted as a secondary Y-axis into Figure 3.1 as well . 80 Time (hour) Figure 3.1: Drying curves of the four runs and drying schedule Since the drying runs started with different M , levels, for comparison purposes, their estimated drying times were adjusted to start from the same level as for the run with the lowest Mt. The actual drying times of runs 2, 3 and 4 are reduced to include the time that was required for each o f them to reach approximately 47.8 % moisture content, which is the equivalent to the Mt o f the first run. These times are listed in Table 3.6. This procedure is a fairly accurate approximation, even with a warm-up effect in force. The warm-up effect could be seen when comparing the shape of the unadjusted curve of first run and other curves, but for practical purposes, the procedure can be accepted as proper, based on experience from similar past project results (Avramidis and Hao 2004). Table 3.6: Actual and adjusted drying times for the four drying runs 15-S (hours) 15-F (hours) 20-S (hours) 20-F (hours) Actual drying time 324 450 330 368 Adjusted drying time 324 334 226 209 81 The adjusted times were similar to previously reported values for P C H baby-squares. After drying P C H baby-squares using the same ki ln and schedule as in this study, Avramidis and Hao (2004) reported that drying times for M , of 53.4 % to be dried to a Mt o f 15%, took 391 hours, and to reach Mt of 20%, for 293 hours. Avramidis et al. (2004), reported similar drying times in a P C H dry/re-dry sorting project, where one drying run was dried from an M , of 55% to a Mt o f 15% taking 367 hours, and the second run was dried from an M,- o f 51% to a Mf o f 20% taking 276 hours. The drying rates in both studies on average were about 0.2 %/hour, which makes them similar to the drying rate of this study. The adjusted drying curves in (Figure 3.2) show similar drying times for runs one and four (dried to a Mt o f 15%), as well as for runs two and three (dried to a Mt o f 20%). In both cases the difference is less than 24 hours. 0 48 96 144 192 240 288 336 Time (hour) Figure 3.2: Adjusted drying curves for the four runs 82 From the drying rate curves plotted against moisture content in Figure 3.3, it can be seen that the drying rate was high until FSP (beginning of Step 9) for all five runs. During this period, the moisture content for Run 15-S was in the range of 40% down to 25%; for Run 20-S between 52 and 35%; and for Runs 15-F and 20-F from 65% down to 30%. During the previous steps, most of the free water was dried; therefore most of the drying in Step 9 occurred below FSP. The bound water removal is the main reason for the decrease of drying rates toward Mt and it is commonly known as the falling rate period. — a — Run 15% summer cut — a — R u n 20% summer cut —e— Run 20% fall cut i—Run 15% fall cut o T3 Moisture content (%) Figure 3.3: Drying rates of the four runs vs. moisture content A n average drying rate o f about 0.2 % per hour, could seem too high for the drying of thick P C H timbers, but the subsequent grading results and k i ln dried timber evaluation proved that this was not the case, so it could be concluded that the schedule was successful with different M,- and Mt. 83 3.4 Kiln dried rough moisture content Due to its influence on the further shape stability, Mf is important information about thick timber. When Mf is lower than Mt it could lead to unaccepted degradations (Hart 1986), and specimens with higher Mf being dimensionally unstable, could have negative effects on the commercial value of final products (Avramidis 2002). Mf statistics of rough timbers, calculated by using the timber weight before and after drying, and M„ are listed in Table 3.7. Mf for all runs was similar to Mt. A n average Mf for the runs dried to an Mt o f 15% was 15.43%), with a standard deviation of 4.18%). The runs dried to Mt of 20% had an average Mf o f 20.36%), with a standard deviation of 5.51%. These values are strong conformation for the quality of drying process of U B C s laboratory ki ln and the accomplished drying schedule. Table 3.7: Final moisture content statistics for different pith classes and drying runs based on the weight difference M e a n (%) Sta. Dev. (%) M i n i m u m (%) M a x i m u m (%) 15-S Class 1 14.87 3.78 9.33 23.81 Class 2 15.10 3.59 9.97 22.80 Class 3 14.79 3.77 9.48 22.81 Class 4 15.81 4.40 9.07 25.34 total run 15.14 3.88 9.07 25.34 15-F Class 1 15.46 4.12 6.24 25.31 Class 2 15.81 5.14 8.48 31.54 Class 3 15.28 4.04 8.73 26.32 Class 4 16.32 4.53 10.12 33.12 total run 15.72 4.45 6.24 33.12 20-S Class 1 19.85 6.00 10.55 35.53 Class 2 18.87 4.37 11.81 28.67 Class 3 21.37 7.44 11.73 40.40 Class 4 20.21 6.88 10.16 43.46 total run 20.08 6.29 10.16 43.46 20-F Class 1 20.30 5.23 11.80 35.58 Class 2 20.33 3.82 13.72 29.58 Class 3 20.71 4.92 10.92 29.73 Class 4 21.27 4.49 15.29 35.73 total run 20.65 4.62 10.92 35.73 84 3.4.1 Concept A The analysis of variance listed in Table 3.8 shows significant differences between different Mt, and what is expected. In this study, the drying schedule included a combination of time and moisture-based schedules, and the drying was finished when the scale showed a weight equivalent to Mt. A s a result, drying runs were not limited by time. Unfortunately, this is not acceptable in an industrial environment, where a short drying time is an important factor, so time-based drying schedules are dominant. Table 3.8: Analysis of variance for the final moisture content based on the weight difference-Concept A Source of Var ia t ion DF Sum of Squares Mean Square F Calculated F Cr i t ica l M t 1 3,895.30 3895.29 162.78* 3.87 P L 3 77.87 25.95 1.08 2.63 M t x P L 3 73.39 24.46 1.02 2.63 Exp. Error 632 15,123.25 23.93 Total 639 19,169.81 *Term significant at a = 0.05 Focusing on individual runs, the well known lack of uniformity in moisture content of P C H timber (Kozl ik 1972) could be seen through the standard deviations shown in Table 3.6. A n average variation of Mf for runs dried to 20% was higher compared with an Mt o f 15%. K o z l i k and Hamlin (1972) indicated that this variability is attributed directly to wet pockets or streaks in the heartwood. Some other researchers (Zhang et al. 1996, L i et al. 1997, Hao and Avramidis 2003) also reported wide Mf variations as a characteristic problem in the ki ln drying of P C H . It is usually the result of a wide variation of M„ wet pockets, and the mixing of the species with different basic densities. 85 Table 3.8 indicates that, in this study, the pith location was a factor without any influence on Mf measured on the basis of weight difference. A l l together though, it is interesting to note that the pith class with mature wood specimens is often the class with the highest average Mf. A possible reason for this is a higher Mt o f this class compared with other classes (Table 3.3). 3.4.2 Concept B The analysis of variance listed in Table 3.9 shows significant differences only between different Mh and what is expected. The season when specimens were cut does not show a significant influence on the average Mf. Again, the drying schedule included a combination of time and moisture-based schedules, and was finished when the weight was equivalent to Mty and not according to time constraints. A s time is an important factor in an industrial environment, this schedule would not be appropriate there, where a short drying time is a factor that affects profit margins. Table 3.9: Analysis of variance for the final moisture content based on the weight difference -Concept B Source of Variation DF Sum of Squares Mean Square F Calculated F Critical CS 1 53.29 53.29 2.21 3.87 M t 1 3,895.30 3895.29 161.85* 3.87 P L 3 77.87 25.95 1.08 2.63 C S x M t 1 0.00 0.00 5.54E-07 3.87 C S x P L 3 30.09 10.03 0.42 2.63 M t x P L 3 73.39 24.46 1.02 2.63 C S x M t x P L 3 22.21 7.40 0.31 2.63 Exp. Error 624 15,017.66 24.07 Total 639 19,169.81 *Term significant at a = 0.05 86 Focusing on individual runs, the well known lack of uniformity in the moisture content of P C H timber (Kozl ik 1972) could be seen through the standard deviations shown in Table 3.7. A n average variation of Mf for runs dried to 20% was higher compared with a n M ( of 15%. Koz l ik and Hamlin (1972) indicated that this variability is attributed directly to wet pockets or streaks in the heartwood. Some other researchers (Zhang et al. 1996, L i et al. 1997, Hao and Avramidis 2003) also reported wide Mf variations as a characteristic problem in the ki ln drying of P C H . It is usually the result of a wide variation of M„ wet pockets, and the mixing of the species with different basic densities. Table 3.9 indicates that in this study, the pith location was a factor without any influence on M F measured on the basis of weight difference. However, at the same time,- it is interesting to note that the pith class with mature wood specimens is often the class with the highest average Mf. Probably a reason for this is a higher M i of this class compared with other classes (Table 3.3). 3.4.3 Core and shell moisture content The ki ln dried Ms and Mc had average values listed in Table 3.10. A n average Ms for runs dried to an Mt o f 15% was 13.10%, with a standard deviation of 3.90%, and 19.48%) and 6.26%o for an Mt o f 20%, respectively. For the core, both averages and variations were higher. The average Mc calculated for the runs with an Mt o f 15% was 20.37%, with a standard deviation of 6.15%; and for a M, o f 20% they were 28.92% and 6.69%, respectively. These values are considerably higher when compared with the previous method. 87 Table 3.10: Average final moisture content statistics for different pith classes and drying runs based on pin measurements Core . (%) Shell (%) Core - Shell (%) 15-S Class 1 21.29 14.66 6.63 Class 2 21.41 15.42 5.99 Class 3 20.87 15.06 5.8 Class 4 21.38 14.89 6.49 total run 21.24 15.01 6.23 15-F Class 1 18.89 11.13 7.77 Class 2 19.03 10.69 8.34 Class 3 19.5 10.33 9.16 Class 4 20.59 12.61 7.98 total run 19.50 11.19 8.31 20-S Class 1 27.11 17.68 9.44 Class 2 28.24 18.45 9.79 Class 3 30.58 19.69 10.89 Class 4 28.72 19.76 8.97 total run 28.66 18.89 9.77 20-F Class 1 28.84 19.63 9.21 Class 2 26.77 19.73 7.05 Class 3 29.2 20.49 8.71 Class 4 31.91 20.41 11.5 total run 29.18 20.06 9.11 The high variability of Ms and Mc could be explained by the fact that drying takes place starting with the surface layers, so that in the case of thick timber, the moisture content distribution is usually not uniform among specimens. This could be partially corrected with a longer conditioning phase. Avramidis and Oliveira (1993) showed that the presorting of thick green P C H timber into high and low basic densities is able to improve the variability of Ms and Mc. In this study, it was sometimes noticed that, for individual specimens, the difference between the shell and the core had negative values. This is not unusual for P C H timbers (Hao and Avramidis 2004) and often indicates the existence of wet pockets. 88 In addition, it was noted that for both methods of moisture content measurements, the higher moisture content has a wider variation. This could be a reason why in Figure 3.4 the final moisture distributions curves have wider tail on the side of higher moisture contents. 40 8 12 16 20 24 28 32 More Final moisture content (%) Figure 3.4: Final moisture content distributions of the four drying runs The shape of Mf distributions (weight based) indicates that under-drying appeared more often than over-drying. Some authors suggested (Nielson et al. 1966) that presorting of the P C H species may improve Mf uniformity, but some authors (Zhang et al. 1996) reported that instead of sorting species, density sorting is what shows better results for this variability. This could be explained by the fact that a lower density wood dries faster when compared with a higher density. 3.5 Planed moisture content After k i ln drying, wood w i l l continue to change its moisture content in order to establish equilibrium with its environment. A s a result, it w i l l continue with anisotropic 89 shrinkage and the changing of its shape. To secure the highest possible comparability of the rough and planed shape distortions and surface checks, extra efforts were dedicated to its storage between the ki ln dried and planed evaluations. The moisture content of planed specimens was measured with the pin-meter before the final evaluation, and statistics of the four runs are listed in Table 3.11. A n average Mf for the runs dried to an M t o f 15% was 15.44%, with a standard deviation of 3.70%, and for the runs dried to an M , o f 20% it was 20.22%, and 5.30%, respectively. • Table 3.11: Planed wood moisture content statistics for different pith classes and drying runs based on pin-meter measurements M e a n (%) S t D e v . (%) M i n i m u m (%) M a x i m u m (%) S15 Class 1 15.07 2.49 10.47 20.53 Class 2 15.25 2.98 9.93 21.43 Class 3 14.69 3.06 9.70 21.17 Class 4 15.83 3.97 9.27 23.70 total run 15.21 3.17 9.27 23.70 S20 Class 1 15.41 3.89 7.87 25.23 Class 2 15.82 4.76 9.57 29.93 Class 3 15.20 3.83 8.93 25.60 Class 4 16.28 4.17 10.60 28.57 total run 15.68 4.16 7.87 29.93 F15 Class 1 19.80 6.03 10.50 35.30 Class 2 18.82 4.31 11.60 28.57 Class 3 21.30 7.43 11.53 40.67 Class 4 20.12 6.81 10.43 43.30 total run 20.01 6.26 10.43 42.30 F20 Class 1 20.14 4.01 11.70 28.57 Class 2 19.96 3.48 14.47 29.80 Class 3 20.29 4.76 9.90 29.20 Class 4 21.31 4.18 14.77 34.07 total run 20.42 4.13 9.90 34.07 These measurements show some dissimilarity compared with the Mf sets of data based on weight differences, but a paired t-test performed in Table 3.12 demonstrates that there are no significant differences between them. For this reason, it could be concluded that there was not any change in the moisture content after the drying. This maintenance of moisture content was accomplished by using the proper storage procedure of k i ln dried timber; wrapping each pile immediately after the post-drying measurements and keeping it in a covered space protected from rain, sun and wind until planing. This procedure was repeated with the planed specimens. Table 3.12: Paired t-test for differences of k i ln dried moisture content and planed wood moisture content for the four drying runs Hypothesis t - value Probability level Conclusion Power (a=0.05) H 0 , : Run 1 K D - Run 1 Planed = 0 -0.7163 0.474836 Accept Ho 0.109795 H o 2 : Run 2 K D - Run 2 Planed = 0 1.0320 0.151829 Accept Ho 0.268524 H o 3 : Run 3 K D - Run 3 Planed = 0 1.4095 0.160630 Accept Ho 0.288490 H o 4 : Run 4 K D - Run 4 Planed = 0 0.7816 0.435599 Accept Ho 0.121495 The aforementioned minor dissimilarities are possibly a consequence of different measuring techniques, including the variability of the properties within each timber. Also , because the planing operation only took away a small amount of wood mass, it could not be a reason for a significant changing of average moisture content. The lack of significant difference between the moisture contents of rough and planed specimens reduces the number of factors that should be taken into consideration for the evaluation of differences between rough and planed shape distortions and surface checks. 3.6 Volumetric shrinkage Shrinkage is a clear indicator of the hydro-mechanical behavior of wood below FSP. Average percentages of width and thickness shrinkages, which were calculated from the caliper readings, are listed in Table 3.13. They have similar average values and standard 91 deviations, and a paired t-test confirmed that estimate. This type of shrinkage was on average 2.56% with a standard deviation of 1.28% for runs with an Mt o f 15%, and 2.02% and 1.01% for an Mt of 20% respectively. Table 3.13: Average directional shrinkage percentages from green to k i ln dried specimens for different pith classes and drying runs W i d t h shrinkage (%) Thickness shrinkage (%) S15 Class 1 2.28 2.49 Class 2 2.47 2.45 Class 3 1.89 2.25 Class 4 1.92 2.07 total run 2.14 2.31 S20 Class 1 2.23 2.05 Class 2 1.93 2.29 Class 3 2.11 1.90 Class 4 1.87 2.17 total run 2.04 2.10 F15 Class 1 1.93 2.01 Class 2 2,04 1.88 Class 3 2.02 1.86 Class 4 2.01 2.00 total run 2.00 1.94 F20 Class 1 2.88 2.82 Class 2 3.00 2.81 Class 3 3.17 2.97 Class 4 2.61 2.95 total run 2.92 2.89 The average volumetric shrinkages for each pith class per drying run is plotted in Figure 3.5. In drying runs with an Mt o f 15%, the average volumetric shrinkage was 5.06%. with a standard deviation of 1.91%, and for drying runs with an Mt o f 20% it was 4.00%> and 1.58%), respectively. These shrinkages are similar to values previously reported by Avramidis and Hao (2004) and Zhang et al. (1996). 92 9 8 15% Summer cut 15% Fall cut 20% Summer cut 20% Fall cut Pith location Figure 3.5: Volumetric shrinkages for different pith classes and drying runs 3.6.1 Concept A The analysis of variance listed in Table 3.14 shows significant differences between different Mh and just as expected a lower Mt can cause greater volumetric shrinkage. This could be explained by the fact that shrinkage increases with the removal of bound water, and more bound water is removed with a lower Mt. Table 3.14: Analysis of variance for volumetric shrinkage - Concept A Source of Var ia t ion D F Sum of Squares M e a n Square F Calculated F Cr i t i c a l M t 1 180.933 180.933 57.783* 3.874 P L 3 8.927 2.976 0.950 2.634 M t x P L 3 6.643 2.214 0.707 2.634 Exp. Error 624 1,953.919 3.131 Total 639 2,150.421 *Term significant at a = 0.05 93 According to some researchers (Yao 1970, Bendtsen 1978), a decrease in the transverse shrinkage is more pronounced closer to the center of a log as a result of lower density, but Dumail and Castera (1997) showed in their study on maritime pine trees that the amplitude of transverse shrinkage effect is dependant on other tree properties. This study is closer to the latter point of view because its test failed to reject the null hypothesis that volumetric shrinkages are different between the pith location classes. Specimens from the first tree classes have certain amounts of juvenile wood, but contain mature wood as well . The mature wood of P C H baby-squares, according to these results, could reduce an eventual abnormal shrinkage of juvenile wood. Products with a smaller size of cross-section could show different results, because they could have a higher percentage of juvenile wood. For that reason, the results of this study could not be generalized to all P C H products. 3.6.2 Concept B The analysis o f variance listed in Table 3.15 shows a significant interaction between the cutting season and M T on the volumetric shrinkage. Table 3.15: Analysis of variance for volumetric shrinkage - Concept B Source of Variation DF Sum of Mean F F Squares Square Calculated Critical CS 1 91.917 91.917 31.964* 3.874 M T 1 180.933 180.933 62.919* 3.874 P L 3 8.927 2.976 1.035 2.634 C S x M , 1 50.037 50.037 17.400* 3.874 C S x P L 3 5.203 1.734 0.603 2.634 MF x P L 3 6.643 2.214 0.770 2.634 CS x M t x P L 3 12.365 4.122 1.433 2.634 Exp. Error 624 1,794.397 2.876 Total 639 2,150.421 *Term significant at a = 0.05 94 The Bonferroni's multiple comparison test shows significant differences between the following runs: • Run 15-S had significantly greater volumetric shrinkage from the run 20-S; • Run 15-F had significantly greater shrinkage from all other runs. The characteristics of this result indicate that i f differences are significant within Mt and within Mh the moisture range between M , and Mt is the factor to be considered in the development of volumetric shrinkage. The behavior of M , in the interaction could be unexpected because of the fact that shrinkage starts under FSP, and in this study both cutting seasons had an average Mt above FSP. Nevertheless, it should be kept in mind that in green timbers, because of the surface air drying, a certain volume is under FSP and shrinkage could begin before ki ln drying, even in a timber with an average moisture content above FSP (Simpson and TenWolde 1999). Wi th a lower A/,-, this drier wood volume is larger. Therefore, this pre-kiln-drying shrinkage does not appear in the ki ln drying evaluation of timbers. A s a result, the last run, as in the run with the widest range between M , and Mt, showed a significantly greater volumetric shrinkage compared to all other runs. The test also shows that i f a significant difference is only within Mt, a lower Mt can cause greater volumetric shrinkage. This could be explained by the fact that shrinkage increases with the removal of bound water that increases in volume as Mt becomes lower. This is confirmed in the drying runs from the summer cutting season (15-S vs. 20-S), as well as in the drying runs from the fall cutting season (15-F vs. 20-F). According to Yao (1969) and Bendtsen (1978), a decrease in the transverse shrinkage is present toward the center of a log as a result of lower density. Dumail and Castera (1997) showed in their study on maritime pine trees that the amplitude of transverse shrinkage effect is dependant on other tree properties. The results of this study support the latter point o f view, 95 because the test (Table 3.15) failed to reject the null hypothesis that volumetric shrinkages are different between the pith location classes. Specimens from the first tree classes have certain amounts of juvenile wood, but contain mature wood as well . The mature wood of P C H baby-squares, according to these results, could reduce an eventual abnormal shrinkage of juvenile wood. Products with a smaller size of cross-section could show different results, because they could have a higher percentage of juvenile wood. For that reason, the results of this study could not be generalized to all P C H products. 3.7 Kiln dried rough shape distortions 3.7.1 Bow Green bow (Table 3.16) exhibited the widest range of all green shape distortions, and it is almost three times wider compared with other tested distortions. The overall mean value was 2.69 mm, with a standard deviation of 1.53 mm. Avramidis and Hao (2004) reported similar results, using the specimens from the same sawmill; according to their study, these values are close to the maximum of 3 mm allowed by Japanese carpenters (called "bu"). There are two main reasons for the formation of green bow, namely growth stresses and drying of the surface layers. Growing stresses in the tree are released in the sawing process (Sandberg 2005). The second reason is longitudinal shrinkage of the surface layers that could reach moisture contents below FSP even before ki ln drying, while the moisture content of internal layers is still unchanged. This type of partial shrinkage could result in bow toward the drier side of a timber. For this reason, more efforts should be made to protect green timber before the k i ln drying with proper storage procedures. 96 Table 3.16: Green bow statistics for different pith classes and drying runs Mean (mm) St. Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 2.60 1.21 0.47 6.12 Class 2 3.08 1.36 1.32 6.11 Class 3 2.86 2.04 0.33 11.50 Class 4 2.64 1.70 0.21 8.15 total run 2.80 1.61 0.00 4.04 15-F Class 1 2.73 1.67 0.09 8.02 Class 2 2.50 1.43 0.28 7.95 Class 3 2.39 1.13 0.29 6.01 Class 4 2.62 1.03 0.40 6.82 total run 2.56 1.33 0.09 8.02 20-S Class 1 2.49 1.89 0.00 11.06 Class 2 3.28 1.86 0.52 8.65 Class 3 2.18 1.76 0.12 10.41 Class 4 2.54 2.13 0.49 12.64 total run 2.62 1.94 0.00 12.64 20-F Class 1 2.82 1.17 1.19 7.90 Class 2 2.70 0.83 1.25 4.90 Class 3 3.13 1.48 1.34 11.20 Class 4 2.49 0.91 1.28 4.62 total run 2.79 1.14 1.19 11.20 K i l n dried bow is an extremely important shape distortion for structural wood products, as they are P C H baby-squares. The statistics concerning this defect are listed in Table 3.17. The overall average was 3.34 mm, with a standard deviation 2.60 mm. Its increase during drying was smaller compared to twist, but still had the widest absolute range. Avramidis and Hao (2004), reported similar values after drying P C H baby-squares with the same k i ln and with the identical drying schedule. 97 Table 3.17: K i l n dried bow statistics for different pith classes and drying runs Mean (mm) St.Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 4,35 2.57 0.80 10.34 Class 2 3.68 2.44 0.13 10.12 Class 3 2.92 2.08 0.34 8.70 Class 4 2.65 1.66 0.63 8.15 total run 3.40 2.29 0.13 10.34 15-F Class 1 4.28 3.75 0.00 11.15 Class 2 3.35 2.79 0.00 10.85 Class 3 3.12 2.51 0.05 10.85 Class 4 3.19 2.32 0.00 10.85 total run 3.48 2.90 0.00 11.15 20-S Class 1 3.29 2.74 0.00 13.00 Class 2 3.88 3.04 0.35 13.00 Class 3 2.83 2.46 0.00 12.70 Class 4 2.54 2.15 0.15 12.60 total run 3.13 2.64 0.00 13.00 20-F Class 1 3.85 2.67 0.00 10.82 Class 2 3.72 2.67 0.21 9.88 Class 3 3.51 2.71 0.19 10.82 Class 4 2.33 1.80 0.00 6.64 total run 3.35 2.54 0.00 10.82 The influence of controlled factors was tested on bow that developed during ki ln drying. These values represent the differences between before and after drying values, and are plotted in Figure 3.6. The full range of these differences is from -3.28 to 9.24 mm. Every pith location and drying run shows positive and negative changes in shape distortions. Negative distortions come from specimens deformed in the opposite direction to their original one. They are recovered distortions and their appearance seems to be random. The overall average bow difference was 0.65 mm, with a standard deviation of 2.21mm. 98 6 T3 0 5 H 4 3 2 1 0 -1 I .L= I 15% Summer 15% Fall 20% Summer 20% Fall Drying run • C l a s s I B C l a s s 2 H C l a s s 3 • C l a s s 4 Figure 3.6: Bow differences created during k i ln drying for different pith classes and drying runs 3.7.1.1 Concept A In Table 3.18, the analysis of variance reveals a significant influence of the pith location on an average bow developed during the ki ln drying. Table 3.18: Analysis of variance of bow differences created during ki ln drying - Concept A Source of Var ia t ion D F Sum of M e a n F F Squares Square Calculated Cr i t i ca l M t 1 8.27 8.27 1.73 3.87 P L 3 119.37 39.79 8.34* 2.63 M t x P L 3 19.53 6.51 1.36 2.634 Exp. Error 624 2,977.66 4.77 Total 639 3,124.83 *Term significant at a = 0.05 The Boneferroni multiple comparison test shows significant difference between following pith location classes: • The pith location class 1 has a significantly larger bow difference from: The pith location classes 4 and 3; 99 • The pith location class 2 has a significantly larger bow difference from: The pith location class 4. Our results confirmed the fact that juvenile wood has a higher propensity for bow. Danborg (1994) reported that a consequence of increased presence of juvenile wood in a timber, was an increased bow. One reason this kind of behavior is the nature of gradual change in properties within juvenile wood. These changes include normalization of the fibril angle in the S2 layer of wood cells from the pith toward mature wood. This angle is the main reason for the higher longitudinal shrinkages of juvenile wood, which w i l l in conflict with different shrinkages of mature wood cells resulting in a bow in the specimen. Consequently, juvenile wood in the pith location class 3 w i l l have less power to bow a specimen when compared with juvenile wood in the pith class 1. The second reason is that, because of its origin within a log, each pith location class has a lower percentage of juvenile wood than previously, and decreasing the amount of juvenile wood wi l l result in the reduction of internal stresses which try to bow a timber. Contrary to juvenile wood specimens, the drying process was almost insignificant for the development of bow in the mature wood class. Our study did not show significant difference between Mt> which could be an indication that bow is a more important problem before the final stages of drying process. This could be explained by the fact that in these stages all four sides o f a specimen are under FSP, so it shrinks similarly on all sides. B y contrast, in previous drying stages, usually one side reaches FSP prior to others and starts to shrink prior to others, and for that reason bow is easily formed as a result o f asymmetric stresses in a specimen. 100 3.7.1.2 Concept B A s seen in the analysis o f variance listed in Table 3.19, the study reveals a significant influence of the pith location on an average bow developed during the ki ln drying. Table 3.19: Analysis of variance of bow differences created during k i ln drying - Concept B Source of Variation DF Sum of Squares Mean Square F Calculated F Critical CS 1 5.66 5.66 1.20 3.87 M t 1 8.27 8.27 1.75 3.87 P L 3 119.37 39.79 8.41* 2.63 C S x M t 1 2.91 2.91 0.61 3.87 C S x P L 3 2.09 0.70 0.15 2.63 M t x P L 3 19.53 6.51 1.38 2.63 CS x M t x P L 3 13.62 4.54 0.96 2.63 Exp. Error 624 2,953.39 4.73 Total 639 3,124.83 *Term significant at a = 0.05 The Boneferroni multiple comparison test shows significant difference. between following pith location classes: • The pith location class 1 has a significantly larger bow difference from classes 4 and 3; • The pith location class 2 has a significantly larger bow difference from the class 4; These results confirmed the fact that juvenile wood has a higher propensity for bow (Danborg 1994). He reported that a consequence of increased presence of juvenile wood in a timber, was an increased bow. There are two main reasons for this kind of behavior. One reason is the nature of gradual change in properties within juvenile wood. These changes include normalization of the fibril angle in the S2 layer of wood cells from the pith toward mature wood. This angle is the main reason for the higher longitudinal shrinkages of juvenile wood, which w i l l in conflict with different shrinkages of mature wood cells resulting in a bow in the specimen. Consequently, juvenile wood in the pith location class 3 w i l l have less power 101 to bow a specimen when compared with juvenile wood in the pith class 1. The second reason is that, because of its origin within a log, each pith location class has a lower percentage of juvenile wood than previously, and decreasing the amount of juvenile wood w i l l result in the reduction of internal stresses which try to bow a timber. Contrary to juvenile wood specimens, the drying process was almost insignificant for the development of bow in the mature wood class. 1 The analysis did not show significant difference between Mu which could be an indication that bow is a more serious problem before the final stages of drying process. This could be explained by the fact that in these stages all four sides of a specimen are under FSP, so it shrinks similarly on all sides. B y contrast, in previous drying stages, usually one side reaches FSP prior to others and starts to shrink prior to others, and for that reason bow is easily formed as a result of asymmetric stresses in a specimen. 3.7.2 Twist In the literature, twist is often related to the existence o f higher S O G and large annual ring curvature. The twist statistic measured in specimens prior to drying is shown in Table 3.20. The average values are higher when compared with diamond and lower when compared with bow. The same is true for its full range. Values in Table 3.20 are similar within the pith location classes, as well as within drying runs. The overall average green twist was 1.42 mm, with a standard deviation of 0.74 mm. Avramidis and Hao (2004) reported an average green twist to be from 1.43 to 1.91 mm. 102 Table 3.20: Green twist statistics for different pith classes and drying runs Mean (mm) StDev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 1.33 0.67 0.09 2.92 Class 2 1.50 0.67 0.00 2.97 Class 3 1.47 0.78 0.00 4.04 Class 4 1.28 0.54 0.26 2.51 total run 1.40 0.67 0.00 4.04 15-F Class 1 1.41 0.81 0.10 2.94 Class 2 1.33 0.88 0.00 3.02 Class 3 1.24 0.71 0.00 2.80 Class 4 1.29 0.76 0.11 3.06 total run 1.32 0.79 0.00 3.06 20-S Class 1 1.35 0.53 0.08 2.48 Class 2 1.73 0.91 0.14 4.18 Class 3 1.56 0.86 0.26 4.72 Class 4 1.40 0.59 0.00 2.77 total run 1.51 0.75 0.00 4.72 20-F Class 1 1.54 0.68 0.37 2.82 Class 2 1.56 0.78 0.35 4.31 Class 3 1.43 0.85 0.18 4.31 Class 4 1.27 0.68 0.12 3.10 total run 1.45 0.75 0.12 4.31 During k i ln drying, twist is usually increased. The statistics of twist, measured on the rough k i ln dried specimens and sorted per pith location classes, is listed in Table 3.21. It has the highest average value from all shape distortions. The overall mean value is 2.45 mm, with a standard deviation of 1.95 mm. 103 Table 3.21: K i l n dried twist statistics for different pith classes and drying runs Mean (mm) StDev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 3.27 2.35 0.00 8.60 Class 2 2.31 1.54 0.00 7.35 Class 3 2.98 2.24 0.07 11.60 Class 4 2.15 1.34 0.38 6.32 total run 2.68 1.96 0.00 11.6 15-F Class 1 3.31 2.84 0.00 10.05 Class 2 3.90 3.18 0.20 11.20 Class 3 2.26 1.62 0.50 9.95 Class 4 2.49 1.69 0.53 7.51 total run 2.99 2.50 0.00 11.20 20-S Class 1 2.45 2.18 0.00 9.45 Class 2 1.85 1.46 0.12 6.20 Class 3 1.91 2.03 0.24 11.30 Class 4 2.48 1.63 0.54 7.15 total run 2.17 1.85 0.00 11.30 20-F Class 1 1.87 1.33 0.30 6.96 .Class 2 2.11 1.15 0.31 6.96 Class 3 1.93 1.06 0.26 6.96 Class 4 1.92 0.68 1.10 4.56 total run 1.96 1.08 0.26 6.69 Sorted to the drying runs and pith locations, differences between green and dried rough twist are plotted in Figure 3.7. Some specimens randomly show recovering changes, the same as with bow, The full range o f twist difference is from -3.39 to 10.75 mm. The overall average was 1.03 mm, with a standard deviation of 1.91 mm. 104 7 • C l a s s 1 • C l a s s 2 • C l a s s 3 • C l a s s 4 15% Summer 15% Fall 20% Summer 20% Fall Drying run Figure 3.7: Twist differences created during ki ln drying for different pith classes and drying runs 3.7.2.1 Concept A The analysis of variance test in Table 3.22 shows a significant evidence for the interaction between Mt and the pith location. Table 3.22: Analysis of variance for twist differences created during kiln drying - Concept A Source of Var ia t ion D F Sum of M e a n F F Squares Square Calculated Cr i t i ca l M t 1 126.80 126.80 36.82* 3.87 PL 3 19.69 6.56 1.90 2.63 M . x P L 3 33.59 11.20 3.25* 2.63 Exp. Error 624 2,148.92 3.44 Total 639 2,328.99 *Term significant at a = 0.05 The Boneferroni multiple comparison test shows significant differences between: • The pith location class 1 dried to 15% has a significantly larger twist difference from: The pith location class 4 dried to 15%, and all pith location classes dried to 20%; • The pith location class 2 dried to 15% has a significantly larger twist difference from: A l l pith location classes dried to 20%; H 4 -I l l k}[\ mC^l 105 • The pith location class 3 dried to 15% has a significantly larger twist difference from: The pith location class 2 dried to 20% and pith location class 3 dried to 20%; These results indicate that the pith location class 1, with the largest percentage of juvenile wood, has a higher propensity for k i ln dried twist compared with that of class 4, which is the juvenile wood free class. One reason for this could be its propensity for a higher S O G , what is in the literature so often reported as the major reason for the twist of lumber. The effect o f S O G is tested and discussed in details in Section 3.9.1. Another reason could be the fact that specimens near the pith have a larger annual ring curvature when compared with mature wood, and because of the high tangential shrinkage, this curvature could be a factor for the higher twist. There is also a possibility that an asymmetric appearance of juvenile wood inside a specimen, with its larger longitudinal shrinkage, could result in twist. Its symmetric position wi l l more l ikely result in bow rather than twist, but its diagonal position could also deform a thick specimen in an asymmetric form like in a twist. The presence of Mt in the interaction is probably related with its influences on the shrinkage of juvenile wood. A lower Mt w i l l result in a larger longitudinal shrinkage o f juvenile wood and a larger twist w i l l be developed when compared with a higher Mt. This is also influenced by the amount of juvenile wood on the cross-section, or the pith location as its indicator. A l l this can be seen in Figure 1.7 by observing the pith class 1, which is the class with the maximum amount of juvenile wood. Classes 2 and 3 are not so representative because they have juvenile wood located near one of the timber's sides, and this position would more l ikely develop bow than twist; still it could be noticed that these classes w i l l easily develop higher twist with lower Mt which is not the case for class 4 which is obviously less sensitive to the interaction. 106 3.7.2.2 Concept B The analysis of variance test in Table 3.23 shows complex interactions with a significant evidence for the interaction between the cutting season and pith location, as well as the interaction between M, and the pith location. The Boneferroni multiple comparison test shows significant differences between the following interactions: • The pith location class 1 from the summer cutting season has a significantly larger twist difference from: The pith location class 2 from the summer cutting season; • The pith location class 2 from the fall cutting season has a significantly larger twist difference from: The pith location class 2 from the summer cutting season and the pith location class 3 from the fall cutting season; • The pith location class 1 dried to 15% has a significantly larger twist difference from: The pith location class 4 dried to 15%, and all pith location classes dried to 20%; • The pith location class 2 dried to 15% has a significantly larger twist difference from: A l l pith location classes dried to 20%; • The pith location class 3 dried to 15% has a significantly larger twist difference from: The pith location class 2 dried to 20% and pith location class 3 dried to 20%. Table 3.23: Analysis of variance for twist differences created during k i ln drying - Concept B Source of Variation DF Sum of Mean F F Squares Square Calculated Critical CS 1 2.24 2.24 0.68 3.87 M t 1 126.80 126.80 38.42* 3.87 P L 3 19.69 6.56 1.99 2.63 C S x M , 1 11.89 11.89 3.60 3.87 C S x P L 3 54.18 18.06 5.47* 2.63 M t x P L 3 33.59 11.20 3.39* 2.63 CS x M t x P L 3 21.04 7.01 2.12 2.63 Exp. Error 624 2,059.56 3.30 Total 639 2,328.99 *Term significant at a = 0.05 107 Appearance of the pith location as a factor in two significant interactions could indicate that specimens with juvenile wood have a higher propensity for twist. One reason could be their higher propensity for S O G compared with class 4, which in the literature is often reported as the major reason for twist. The effect of S O G is tested and discussed in details in Section 3.9.1. Another reason is the fact that specimens near the pith have larger annual ring curvature when compared with mature wood, and because of the high tangential shrinkage, this curvature could be a factor for the higher twist. There is also a possibility that an asymmetric appearance of juvenile wood inside of a specimen, with its larger longitudinal shrinkage, could be one of the reasons for twist. Its symmetrical position w i l l more likely have a result in bow rather than twist, but its diagonal position could also deform a thick specimen into an asymmetric form such as a twist. Nevertheless, the presence of the pith location as one of the factors in two significant interactions indicates that it is incorrect to treat it as a separate main effect. The interaction of the pith location and cutting season, as well as the interaction between the pith location and Mt, are probably related with influences of these factors on the shrinkage of juvenile wood. Significances o f these interactions are synchronized with conclusions about shrinkage obtained in this study. Summer cutting season w i l l have a lower M / compared with the fall cutting season, so that smaller shrinkage w i l l occur during the k i ln drying period, i f dried to the same Mt, because of the fact that a certain amount of wood mass could shrink even before the k i ln drying, and therefore w i l l not be reported in a k i ln drying evaluation. For that reason, specimens from summer cutting season w i l l result in a smaller k i ln drying twist compared with the fall cutting season. In the same manner, a higher Mt w i l l result in a smaller longitudinal shrinkage of juvenile wood, and again a smaller twist w i l l be developed when compared with a lower Mt. Both cases are influenced by the amount of juvenile wood on the cross-section, or 108 the pith location as its indicator. A l l this could be seen in Figure 1.7 by observing the pith class 1, which is the class with the maximum amount of juvenile wood. Classes 2 and 3 are not so representative because they have juvenile wood located on one of the timber's sides, and this position w i l l more l ikely develop bow instead of twist. This study indicates that twist is obviously a complex issue and many variables should be controlled in order to provide a clear picture about its behavior during the k i ln drying of P C H post-and-beam construction timbers. A n option for scanning the internal configuration o f specimens prior to k i ln drying could improve chances for research results. 3.7.3 Diamonding Diamonding is usually the shape distortion with the smallest amplitude of all k i ln drying distortions. It occurs when one face shrinks more in width than the opposite face. Thanks to its geometry, it is easily corrected during the planing process, so in general only higher diamonding values represent an important reason for drying degradations. Green diamonding statistics are shown in Table 3.24. The overall mean value is 0.55 mm, with a standard variation of 0.37 mm. It shows the lowest average value and variation from all distortions measured in the present study, and is fairly uniform within the pith location classes. For development of a significant diamonding, except shell, the core should also be dried under FSP, which is rare in green P C H timbers, so these results are not surprising. Avramidis and Hao (2004) reported similar values of green diamonding with an average value of 0.60 mm and a standard deviation o f 0.44 mm. 109 Table 3.24: Green diamonding statistics for different pith classes and drying runs Mean (mm) StDev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 0.63 0.39 0.05 1.86 Class 2 0.52 0.40 0.03 1.58 Class 3 0.61 0.46 0.10 2.57 Class 4 0.59 0.35 0.06 1.56 total run 0.59 0.40 0.03 2.57 15-F Class 1 0.43 0.35 0.03 1.67 Class 2 0.57 0.28 0.10 1.34 Class 3 0.60 0.27 0.25 1.35 Class 4 0.40 0.27 0.06 1.08 total run 0.50 0.30 0.03 1.67 20-S Class 1 0.58 0.48 0.00 1.99 Class 2 0.63 0.52 0.00 2.05 Class 3 0.57 0.39 0.00 1.50 Class 4 0.55 0.42 0.00 2.00 total run 0.58 0.45 0.00 2.05 20-F Class 1 0.56 0.25 0.10 1.11 Class 2 0.52 0.33 0.00 1.89 Class 3 0.50 0.25 0.04 0.86 Class 4 0.57 0.33 0.09 1.61 total run 0.54 0.29 0.00 1.89 K i l n dried diamonding (Table 3.25) had a similar range as green had, but average values and standard deviations are approximately two times higher than on green specimens. The overall average k i ln dried diamond is 0.94 mm, with a standard deviation of 0.77 mm. K i l n dried diamonding was relatively low attributable to the appropriate drying schedule, which did not cause significant over-drying. 110 Table 3.25: K i l n dried diamonding statistics for different pith classes and drying runs Mean (mm) St. Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 0.81 0.87 0.00 2.SI Class 2 1.15 1.10 0.02 4.27 Class 3 0.81 0.66 0.02 2.69 Class 4 1.20 0.79 0.03 3.19 total run 0.99 0.88 0.00 4.27 15-F Class 1 0.83 0.70 0.07 2.92 Class 2 0.92 0.92 0.07 4.37 Class 3 0.94 0.83 0.01 3.82 Class 4 0.82 0.63 0.05 2.74 total run 0.88 0.77 0.01 4.37 20-S Class 1 1.02 0.76 0.00 3.04 Class 2 0.95 0.62 0.04 2.36 Class 3 1.01 0.86 0.00 4.36 Class 4 0.98 0.70 0.00 2.73 total run 0.99 0.73 0.00 4.36 20-F Class 1 0.75 0.47 0.13 1.95 Class 2 1.03 0.63 0.15 2.82 Class 3 0.89 0.80 0.21 3.18 Class 4 1.00 0.83 0.17 3.07 total run 0.92 0.70 0.13 3.18 Average differences between green and ki ln dried rough diamonding are plotted gure 3.8. • Clas s 1 • Class 2 • Class 3 • Class 4 15% Summer 15% Fall 20% Summer 20% Fall Drying run Figure 3.8: Diamonding differences for different pith classes and drying runs created during ki ln drying 111 The full range of diamonding differences that are produced during the ki ln drying is from -1.60 mm to 3.61 mm. The overall average diamond difference is 0.39 mm, with a standard deviation of 0.81 mm. If compared with bow and twist, these values do not represent an imperative k i ln drying problem for P C H post-and-beam construction timbers, but represent a strong conformation for the quality of this drying schedule. Also , a fairly symmetrical ring pattern on specimens had an influence in the reduction of this shape distortion. 3.7.3.1 Concept A Despite the fact that transversal shrinkage is lower in juvenile wood (Bendtsen 1978) and that there is different growth ring orientation variation between P L classes, the analysis of variance in Table 3.26 indicates a lack of evidence to claim a significant influence on any of the factors on the development of diamonding during the ki ln drying process. Table 3.26: Analysis of variance for diamonding differences created during k i ln drying -Concept A Source of Variation DF Sum of Squares Mean Square F Calculated F Critical M t 1 0.0004 0.0004 0.0005 3.8741 P L 3 3.1870 1.0623 1.5899 2.6341 M t x P L 3 1.3409 0.4470 0.6690 2.6341 Exp. Error 624 416.9137 0.6681 Total 639 421.4420 *Term significant at a = 0.05 3.7.3.2 Concept B Despite the fact that transversal shrinkage is lower in juvenile wood (Bendtsen 1978) and that there is different growth ring orientation variation between P L classes, the analysis of variance in Table 3.27 indicates a lack of evidence to claim a significant influence on any of the controlled factors on the development of diamonding during the k i ln drying process. 112 Table 3.27: Analysis of variance for diamonding differences created during k i ln drying -Concept B Source of Variation DF Sum of Squares Mean Square F Calculated F Critical CS 1 0.1238 0.1238 0.18796 3.87413 M t 1 0.0004 0.0004 0.00055 3.87413 P L 3 3.1870 1.0623 1.61229 2.63413 C S x M t 1 0.0000 0.0000 1.48E-08 3.87413 C S x P L 3 0.4489 0.1496 0.22711 2.63413 M t x P L 3 1.3409 0.4470 0.67839 2.63413 C S x M t x P L 3 5.1965 1.7322 2.62893 2.63413 Exp. Error 624 411.1445 0.6589 Total 639 421.4420 *Term significant at a = 0.05 3.8 Kiln dried rough surface checks During the drying of surface layers of timbers, surface checks start to develop on all four sides of timbers. The following analysis is based on the sum of check lengths from all four sides of a specimen. The green surface checks statistics are listed in Table 3.28. The larger surface checking is noticed in the runs from the summer cutting season. It is a consequence of the drying of surface layers caused by the higher air temperature when timber is stored after the sawing. A n average green surface check from the summer cutting season was 97.45 mm, with a standard deviation of 134.79 mm. For the fall cutting season the average was 71.76 mm, with a standard deviation of 122.97 mm. A s seen, timbers containing juvenile wood developed more green checks compared with the pith class 4. A reason for this could be found in the fact that specimens near the pith have a larger annual ring curvature when compared with mature wood and due to its high tangential shrinkage, checks could be easily form in the surface layers. A n additional problem is the low density of juvenile wood, which has two negative effects. One is that it makes juvenile wood weak enough to fail 113 internal stresses, and second is that it could have a higher drying rate compared with mature wood and therefore produce more shrinkages and stresses. For these reasons, a recommendation for sawmills is that P C H timbers with juvenile wood should be carefully stored before the ki ln drying and protected from the sun or wetting before drying. Failure to do this could increase length, width and deep of surface checks, and therefore decrease profit. Table 3.28: Green surface check statistics for different pith classes and drying runs Mean (mm) St.Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 139.63 163.54 0.00 606.00 Class 2 92.40 119.94 0.00 486.00 Class 3 101.93 132.24 0.00 516.00 Class 4 23.83 56.85 0.00 243.00 total run 89.44 130.11 0.00 606.00 15-F Class 1 36.38 87.06 0.00 370.00 Class 2 85.00 137.45 0.00 503.00 Class 3 77.73 159.09 0.00 643.00 Class 4 38.50 83.01 0.00 343.00 total run 59.40 122.00 0.00 643.00 20-S Class 1 162.93 0.00 487.00 Class 2 118.98 134.95 0.00 483.00 Class 3 103.33 149.58 0.00 553.00 Class 4 51.83 83.41 0.00 339.00 total run 105.46 139.26 0.00 553.00 20-F Class 1 89.15 126.39 0.00 486.00 Class 2 99.30 127.16 0.00 396.00 Class 3 91.50 112.52 0.00 353.00 Class 4 56.53 108.93 0.00 450.00 total run 84.12 119.04 0.00 486.00 The k i ln dried surface check statistics are listed in Table 3.29, where it can be seen that conventional k i ln drying obviously increases surface checking. Similar to green specimens, k i ln dried specimens from the pith location class 1 have the highest tendency for surface checking. A timber with higher surface checking during drying w i l l also be more sensitive after the process, because of the same reasons as explained for the green checking. For that 114 reason, specimens near the center require more attention after k i ln drying when compared with mature wood specimens. Table 3.29: K i l n dried surface checks statistics for different pith classes and drying runs Mean (mm) StDev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 328.15 172.67 0.00 774.00 Class 2 186.13 144.00 0.00 511.00 Class 3 147.08 149.16 0.00 516.00 Class 4 73.53 108.96 0.00 425.00 total run 183.72 171.50 0.00 774.00 15-F Class 1 266.25 170.25 0.00 676.00 Class 2 245.25 142.62 0.00 540.00 Class 3 126.53 173.27 0.00 643.00 Class 4 88.90 132.14 0.00 399.00 total run 181.73 171.73 0.00 676.00 20-S Class 1 320.70 203.93 0.00 801.00 Class 2 201.25 183.07 0.00 700.00 Class 3 137.23 167.64 0.00 553.00 Class 4 87.13 109.54 0.00 370.00 total run 186.58 189.57 0.00 801.00 20-F Class 1 259.23 160.20 0.00 523.00 Class 2 184.43 170.69 0.00 729.00 Class 3 130.15 137.03 0.00 403.00 Class 4 93.43 130.84 0.00 453.00 total run 166.81 161.76 0.00 729.00 The influences of the controlled factors were tested on the surface checks that developed during k i ln drying. These values represent the differences between green surface checks and after k i ln drying values, and are plotted in Figure 3.9. The full range of surface check differences is from -92 to 672 mm. Negative values of surface check differences come from specimens where the drying shrinkage was able to closed some shallow green checks, but this was an uncharacteristic behavior, Also , from a technical point o f view, there is still a weakness in the wood although these checks are not visible anymore to the naked eye, because the chemical bonds should not be re-established in the check area during the k i ln drying. 115 500 400 05 -1 — S 200 100 15% Summer 15% Fall 20% Summer 20% Fall Drying run • Class 1 • Class 2 O Class 3 • Class 4 Figure 3.9: Surface check differences created during ki ln drying for different pith classes and drying runs 3.8.1 Concept A The statistical analysis in Table 3.30 shows a significant influence of M, on checking developments. A larger amount of checks are developed in the drying runs dried to an Mt of 15%, compared with runs with a Mt o f 20%. This is l ikely because the tangential shrinkage of growth rings is higher in the lower Mt. The test also detects a significant individual main effect of the pith location. The Bonferroni's multiple comparison test shows significant differences between following pith location classes: • The pith location class 1 has significantly larger checking differences from the pith location classes 2, 3 and 4; • The pith location class 2 has significantly larger checking differences from the pith location classes 3 and 4. 116 Table 3.30: Analysis of variance for surface check differences created during k i ln drying -Concept A Source of Variation DF Sum of Squares Mean Square F Calculated F Critical M t 1 111,540.00 111,540.00 8.93* 3.87 P L 3 2,359,368.73 786,456.24 62.99* 2.63 M t x P L 3 32,552.23 10,850.74 0.87 2.63 Exp. Error 624 7,790,657.44 111,540.00 Total 639 10,294,118.40 *Term significant at a = 0.05 The study reveals that the surface checks clearly increased when a timber was located more centrally in the log. Similar to green surface checks, the reasons could be the fact that specimens near the pith have larger annual ring curvatures and a higher tangential shrinkage when comparing it to mature wood. Additional problems include faster drying and the weaker structure of juvenile wood, because of its lower density. Moreover, it is expected that the initial stages of the drying process are the most critical period since shrinkage of the surface layers of the timber is restrained by the wetter core material. High superficial tension stresses may then lead to surface checking, i f the strength of the timber perpendicular to the grain is exceeded. For that reason, less aggressive drying in the initial stages could lead to a reduction of surface checking. 3.8.2 Concept B The statistical analysis in Table 3.31 did not detect significant influence of the cutting season on checking developments, but it shows a significantly larger development of checks in the drying runs dried to a Mt o f 15%, compared with runs with a Mt o f 20%. This is l ikely because the tangential shrinkage of growth rings is higher in the lower Mt. The test also detects a significant individual main effect of the pith location. 117 Table 3.31: Analysis of variance for surface check differences created during ki ln drying -Concept B Source of Variation DF Sum of Mean F F Squares Square Calculated Critical C S 1 35,120.44 35,120.44 2.858 3.874 M , 1 111,540.00 111,540.00 9.078* 3.874 P L 3 2,359,368.73 786,456.24 64.009* 2.634 C S x M t 1 28,050.26 28,050.26 2.283 3.874 C S x P L 3 28,550.99 9,517.00 0.775 2.634 M t x P L 3 32,552.23 10,850.74 0.883 2.634 C S x M t x P L 3 32,095.62 10,698.54 0.871 2.634 Exp. Error 624 7,666,840.13 12,286.60 Total 639 10,294,118.40 *Term significant at a = 0.05 The Bonferroni's multiple comparison test shows significant differences between following pith location classes: • The pith location class 1 has significantly larger checking differences from the pith location classes 2,3 and 4; • The pith location class 2 has significantly larger checking differences from the pith location classes 3 and 4. The study reveals that the surface checks clearly increased when a timber was located more centrally in the log. Similar to green surface checks, the reasons could be the fact that specimens near the pith have larger annual ring curvatures and a higher tangential shrinkage when comparing it to mature wood. Additional problems include faster drying and the weaker structure of juvenile wood, because of its lower density. Moreover, it is expected that the initial stages of the drying process are the most critical period since shrinkage of the surface layers of the timber is restrained by the wetter core material. High superficial tension stresses may then lead to surface checking, i f the strength of the timber perpendicular to the grain is exceeded. For that reason, less aggressive drying in the initial stages could lead to a reduction of surface checking. 118 3.9 Kiln dried shape distortions after planing 3.9.1 Planed bow The planed bow statistics are shown in Table 3.32. The full range is almost the same as before the planing. A n average bow after planing was 2.98 mm, with a standard deviation of 2.12 mm. Therefore, it could be calculated that an average rough bow value is reduced by 11% on average. Table 3.32: Planed bow statistics for different pith classes and drying runs Mean (mm) St.Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 3.64 2.07 0.70 8.99 Class 2 3.77 2.49 0.16 13.18 Class 3 2.81 1.70 0.39 8.06 Class 4 2.67 1.79 0.28 9.61 total run 3.22 2.07 0.16 13.18 15-F Class 1 2.56 2.47 0.00 9.00 Class 2 2.25 1.94 0.00 8.52 Class 3 2.36 1.79 0.20 7.32 Class 4 2.35 1.45 0.00 7.35 total run 3.69 3.00 0.00 13.95 20-S Class 1 2.76 1.61 0.00 6.76 Class 2 3.82 2.69 0.31 11.59 Class 3 2.68 2.47 0.00 12.87 Class 4 . 2.48 1.31 0.03 5.66 total run 2.93 2.14 0.00 12.87 20-F Class 1 3.73 2.09 0.00 9.67 Class 2 3.74 2.52 0.00 10.57 Class 3 3.37 2.33 0.17 10.03 Class 4 2.76 1.78 0.00 6.57 total run 3.40 2.21 0.00 10.57 A paired t-test is used to estimate the significance of these changes and it accepts the null hypothesis, so it could be concluded that based on available data, there is no significant change of bow distortions after the planing. For this reason, planing could not be considered as an option for a reduction of this distortion. Keeping in mind the importance of this deformation for construction use, and urgent solutions in pre-drying and drying operations are required to lessen problems related with juvenile wood dominancy in foreseeing P C H supplies. 3.9.2 Planed twist The statistics of planed twist are shown in Table 3.33. It has the same full range as in planed bow, but smaller average values. The overall mean value of this shape distortion is 2.33 mm with a standard deviation of 1.79 mm. Table 3.33: Planed twist statistics for different pith classes and drying runs Mean (mm) St.Dev. (mm) Minimum (mm) Maximum (mm) S15 Class 1 3.18 1.59 0.70 6.67 Class 2 2.48 1.65 0.14 6.82 Class 3 2.67 1.58 0.39 8.00 Class 4 2.08 1.49 0.21 6.67 total run 2.60 1.61 0.14 8.00 S20 Class 1 2.18 1.53 0.02 6.44 Class 2 1.73 1.46 0.05 7.14 Class 3 1.91 2.20 0.03 13.12 Class 4 1.75 1.09 0.07 4.08 total run 1.89 1.62 0.02 13.12 F15 Class 1 3.14 2.58 0.00 9.47 Class 2 3.40 2.72 0.34 10.59 Class 3 1.98 1.48 0.07 9.13 Class 4 2.23 1.49 0.51 6.23 total run 2.69 2.21 0.00 10.59 F20 Class 1 1.68 1.27 0.10 5.81 Class 2 2.15 1.16 0.00 4.42 Class 3 1.80 1.02 0.02 4.08 Class 4 1.68 0.92 0.19 3.86 total run 1.83 1.11 0.00 5.81 It could be calculated that an average rough twist is reduced by 8% on average. The paired t-test rejected the null hypothesis, so it could be concluded that these data indicates a significant difference between the k i ln dried rough and planed specimens. Taking into consideration that the previous results showed no changes in moisture content of the rough and 120 planed specimens, and that the same methods, equipment, personnel and locations on timber were used for data collection, an acceptable explanation could be that the differences are seen because of the planing process which has a considerable influence on the geometry of specimens. Nevertheless, it should be pointed out that compared with diamonding (shown in the following section), planed twist shows a small dissimilarity with the ki ln dried rough data (approximately 0.08%). For that reason, this operation is an ineffective solution for the reduction of twist. 3.9.3 Planed diamonding Planed diamonding has the narrowest data range and is almost three times smaller than other planed shape distortions. The average value was 0.49 mm, with a standard deviation of 0.41 mm. Thus, it could be calculated that an average rough diamond is reduced by 48% on average. The detailed statistics are listed in Table 3.34. A paired t-test was used for testing the change of k i ln dried rough diamonding after planing the rough specimens to the final baby-square cross-section. The null hypothesis was rejected, so there is enough evidence to conclude that data sets with rough and planed diamonding are significantly different. A s it was for the planed twist, considering that there were no changes in moisture content, and that the same methods, equipment, personal and measurement locations on specimens were used for data collection, an acceptable explanation could be that the difference is shown because of the planing process, which has a significant influence on the geometry of specimens. Knowing the planing process, which is focused on the standardization of the cross section, and the fact that the diamonding is a deformation reflected on the cross-section as well , this explanation is highly logical. 121 Table 3.34: Planed diamonding statistics for different pith classes and drying runs Mean (mm) StDev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 0.43 0.37 0.03 1.90 Class 2 0.49 0.36 0.04 1.56 Class 3 0.47 0.34 0.10 1.40 Class 4 0.52 0.55 0.08 3.09 total run 0.48 0.45 0.03 3.09 15-F Class 1 0.44 0.42 0.00 1.76 Class 2 0.47 0.47 0.00 2.55 Class 3 0.51 0.52 0.01 2.00 Class 4 0.49 0.44 0.00 1.80 total run 0.48 0.46 0.00 2.55 20-S Class 1 0.43 0.31 0.00 1.18 Class 2 0.54 0.39 0.00 1.80 Class 3 0.55 0.37 0.00 1.70 Class 4 0.48 0.45 0.00 2.00 total run 0.50 0.38 0.00 2.00 21-F Class 1 0.48 0.43 0.00 2.20 Class 2 0.58 0.41 0.15 2.60 Class 3 0.46 0.37 0.03 1.60 Class 4 0.49 0.43 0.02 1.86 total run 0.50 0.41 0.00 2.60 In addition, it should be pointed out that this decrease o f diamonding is relatively high, compared with other shape distortions. For total data sets, the diamonding of planed specimens is almost twice as small as the rough ki ln dried values. Furthermore, it could be noted that the range of diamonding is also smaller, which could lead to the conclusion that the most critical highest values are reduced. In summary, this makes drying problems concerning diamonding less important than previous distortions. 122 3.10 Kiln dried planed surface checks During the planing process and forming of the standardized baby-square cross-section, together with the removing of surface layers from all four sides of specimens, a part of surface checks is removed as well . Some shallow checks are removed in total, but a certain amount of deeper checks are still present. Planed surface checks statistics are listed in Table 3.35. The average value was 139.81 mm, with a standard deviation of 153.83 mm. Therefore, it could be calculated that an average surface check of rough specimens was reduced with planing by 22.04%. Table 3.35: Planed surface checks statistics for different pith classes and drying runs Mean (mm) St. Dev. (mm) Minimum (mm) Maximum (mm) 15-S Class 1 282.33 144.54 0.00 533.00 Class 2 144.30 140.12 0.00 516.00 Class 3 130.73 131.64 0.00 486.00 Class 4 64.10 102.39 0.00 378.00 total run 155.36 151.97 0.00 533.00 15-F Class 1 257.78 171.98 0.00 685.00 Class 2 214.38 148.04 0.00 543.00 Class 3 105.35 155.01 0.00 648.00 Class 4 66.85 109.76 0.00 427.00 total run 161.09 166.01 0.00 685.00 20-S Class 1 204.33 156.28 0.00 550.00 Class 2 115.43 166.79 0.00 626.00 Class 3 96.58 140.98 0.00 486.00 Class 4 70.13 92.24 0.00 328.00 total run 121.61 149.44 0.00 626.00 20-F Class 1 212.93 152.14 0.00 490.00 Class 2 146.50 153.96 0.00 720.00 Class 3 70.98 108.73 0.00 362.00 Class 4 54.25 96.94 0.00 383.00 total run 121.16 144.00 0.00 720.00 Similar to the rough ki ln dried evaluation, the longest average checks on planed specimens were present in the class 1 (239.4 mm) and were gradually reduced as the distance 123 from pith increased. Class 4 had an average value of 63.85 mm. The planed surface checks still showed a high variation, just as the rough ki ln dried did. The performed paired t-test rejected the null hypothesis. The conclusion that there is enough evidence to claim that planing significantly decreases surface checks could be explained with the removing of surface layers of specimens. For this reason, it should be concluded that the planing process significantly helps in the removing of unwanted surface checks from final products, but their existence in specimens with juvenile wood is still a very important problem. A n improvement of the drying procedure is required to reduce their appearance in high quality products as P C H baby squares should be. 3.11 Effects of the slope of grain and compression wood 3.11.1 Slope of grain Statistical calculations performed on S O G measurements on the planed specimens are listed in Table 3.36. It is clear that the S O G had similar average values and standard deviations for all drying runs. The full range was between 0.00 to 6.65°. The overall mean value is 1.66°, with a standard deviation of 1.50°. These values are similar to previous results; for example, Hao and Avramidis (2004), using the same measuring technique and the same source for purchasing timbers, reported a mean value of 1.2° S O G . Jozsa et al. (1998), who measured S O G on second growth western hemlock from five locations, using a different custom made measuring device from the one used in this study, obtained a mean value of 2°. 124 Table 3.36: Slope of grain statistics for different pith classes and drying runs M e a n (°) St.Dev. o M i n i m u m o M a x i m u m (°) S15 Class 1 1.93 1.55 0.00 5.00 Class 2 1.79 1.42 0.00 5.50 Class 3 1.74 1.51 0.00 5.00 Class 4 1.00 1.12 0.00 4.00 total run 1.61 1.44 0.00 5.50 S20 Class 1 2.13 1.61 0.00 5.00 Class 2 1.69 1.55 0.00 5.00 Class 3 1.86 1.60 0.00 6.50 Class 4 1.35 1.07 0.00 4.00 total run 7.76 1.49 0.00 6.50 F15 Class 1 1.89 1.90 0.00 6.00 Class 2 1.70 1.76 0.00 5.50 Class 3 1.54 1.53 0.00" 6.00 Class 4 1.09 1.24 0.00 5.00 total run 1.55 1.64 0.00 6.00 F20 Class 1 1.70 1.35 0.00 6.00 Class 2 2.03 1.48 0.00 6.00 Class 3 1.76 1.20 0.00 6.50 Class 4 1.31 0.73 0.00 3.00 total run 1.70 1.24 0.00 6.50 The fact that this study (please see Figure 3.10), as well as previous studies on P C H , shows relative low values of S O G , could be explained with the shape and nature of the growth of these species. Both species have a relatively symmetrical bole and crow; consequently, this symmetrical shape does not twist under an external force (i.e. wind, snow) such as in the case of asymmetrical species. Furthermore, in Chapter 1, it is explained that these species are very shade tolerant and occur in dense forests. Thanks to this fact, in juvenile stages, these trees are often protected from external forces by the surrounding stronger plants. Studies, such as Harris (1989) and Pape (1999) performed, also reported that S O G seems to depend on factors that affect growth conditions, as well as genetic factors. 125 250 » 2 0 0 c a> 8 1 5 0 a g 100 a> 3 l l 50 230 Frequency Cumulative % 132 T 100% 80% 60% 40% 17 0% 0 1 2 4 5 6 More Slope of grain (degree) Figure 3.10: Frequency of bow developed during drying vs. S O G Table 3.37 displays the one-way analysis of variances for differences in S O G between the pith locations. This test demonstrates that there is a significant difference in S O G between the pith classes. The Bonferroni's multiple comparison test detected that there is an absence of differences between the first three classes, but they are all different from the mature wood class. Class 4 shows a lower S O G from the other classes. The lack of differences between classes 1, 2 and 3 could be explained by the fact that all these classes, concerning the size of its cross-section, come from almost the same area of log and all o f them contain juvenile wood with its propensity for a higher S O G in contrary to the mature wood class 4. Table 3.37: Analysis of variance for slope of grain Source of Variation DF Sum of Squares Mean Square F calculated F Critical Run 3 3.9137 1.3046 0.63 2.63 P L 3 49.4700 16.4900 7.93* 2.63 Run x P L 9 8.3785 0.9309 0.45 1.91 Experimental error 624 1297.0190 2.0786 Total (Adjusted) 639 1358.781 *Term significant at a = 0.05 126 Figures 3.11 and 3.12 show bow and diamond shape distortions formed on specimens during k i ln drying, plotted against the S O G . It can be seen that the coefficients of determination were very low in both cases. The geometry of these shape distortions and knowledge about the reasons for their development confirms these results. The coefficient of determination is higher for twist (r 2 = 0.4983) compared with other shape distortions. This could indicate an influence of S O G on this shape distortion (Boladis 1972, Forsberg and Warensjo 2001), but it was surprising to see these obviously large variations. These variations could indicate that in addition to S O G , there could be other important factors for the development of twist during the ki ln drying. This could be confirmed by the fact that sometimes even specimens with a S O G of 0° developed twist. Some of these additional factors are previously reported interactions of the pith location and cutting season; along with the pith location and Mt. In addition to these interactions, there is a possibility that an asymmetric appearance of juvenile wood along with a specimen could also result in twisting. Some authors, like Forsberg and Warensjo (2001), reported that S O G of the timber surface sometimes does not accurately represent the S O G of its entire volume; so, the S O G of a log could be strongly correlated with twist. This could be particularly true for thick specimens, as was the case in this study. For this reason, an additional control of wood and drying factors is required for the development of the multi-factorial prediction equation of behavior of this deformation during ki ln drying. Also , as it was previously explained, the S O G of a log could be more useful information than the S O G of the surface of timber, since it w i l l more accurately represent the entire volume of specimens. In Figure 3.13, the individual surface check differences between green and k i ln dried rough specimens were plotted against S O G and as shown, they form a weak r 2 (0.0095) of the fitted strength line. Therefore, it could be concluded that this study did not provide enough 127 evidence that S O G could be an important variable for the significant losses in tensile strength perpendicular to the grain. This strength is required in a timber in order to survive tension stresses in the shell during ki ln drying. 10 S. 4 -a 2 S A Bow = 0.0817*SOG + 0.516 * R2 = 0.0029 0 -2 .4 x. 2 4 Slope of grain (degree) Figure 3.11: B o w developed during drying vs. S O G 10 A Twist = 0.9242*SOG - 0.4987 R2 = 0.4983 2 . 4 6 Slope of grain (degree) Figure 3.12: Twist developed during drying vs. S O G 10 E 8 + E 6 + 4 2 i 0 -2 -4 A Diamnod = 0.0027*SOG + 0.4055 R 2 = 2E-05 2 4 6 Slope of grain (degree) 600 500 400 300 200 100 o -S -100 A Surface checks = 8.5013*SOG + 81.028 R 2 = 0.0095 2 4 6 Slope of grain (degree) Figure 3.13: Diamonding developed during drying vs. S O G Figure 3.14: Surface checks developed during drying vs. S O G 128 In addition, it should be taken into consideration, that the overall average S O G of 1.66° is relatively low from the solid wood products perspectives (Zpbel et al. 1968). Cown et al. (1991) reported 5° as a critical level of S O G , above which significant twist is very likely. However, we should be careful with these S O G conclusions because of the lack of sawing pattern adjustments. The sawing pattern adjustment was not able to be done because of the nature of the sampling procedure. Information required for the pattern adjustments w i l l be available only with more in-depth studies and a detailed control of the sawing process. 3.11.2Compression wood Statistical calculations in regards to the presence of compression wood on the cross-sections are displayed in Table 3.38. Table 3.38: Compression wood statistics for different pith classes and drying runs Mean (%) St. Dev. (%) Minimum (%) Maximum (%) S15 Class 1 2.94 7.51 0.00 44.60 Class 2 1.14 2.09 0.00 7.80 Class 3 0.79 2.40 0.00 10.90 Class 4 0.30 1.14 0.00 5.43 total run 1.29 4.20 0.00 44.60 S20 Class 1 2.77 4.86 0.00 20.30 Class 2 1.72 3.54 0.00 14.38 Class 3 1.41 4.73 0.00 28.70 Class 4 0.14 0.63 0.00 3.35 total run 1.51 3.92 0.00 28.70 F15 Class 1 2.61 7.27 0.00 44.87 Class 2 1.06 2.39 0.00 11.23 Class 3 0.41 1.70 0.00 9.24 Class 4 0.20 0.70 0.00 2.94 total mn 1.07 4.01 0.00 44.87 F20 Class 1 1.68 4.42 0.00 26.25 Class 2 1.58 5.08 0.00 31.40 Class 3 0.96 3.18 0.00 18.31 Class 4 0.74 3.03 0.00 18.38 total run 1.24 4.00 0.00 31.40 129 The average percentage was 1.28%, with a standard deviation of 4.03%. The maximum amount of compression wood was 44.87% and was recorded at the cross section of one sample from the class 1. Compression wood does not show significant differences between drying runs, which could indicate that the logs used for production of specimens were growing in the same environmental conditions. The majority of specimens (75%) do not contain compression wood (Figure 3.15). The main reason for the formation of compression wood is a reaction of wood to external forces like wind or snow (Larson 1965). Small trees are especially susceptible to environmental forces that cause formation of compression wood during juvenile growth; however, P C H species during this stage are often protected from these forces by the surrounding stronger plants. In later stages, they prune their branches as they grow, leaving a clear symmetrical trunk, thus, they are usually strong enough to support them with normal xylem. For these reasons, they do not need to form compression wood to protect the static stability at the level as it is expected from other species. ZZ3 Frequency •a—Cumulative % + 60% - 70% C L - 50% o -o 200 --E - 40% - 30% Z 100 -84 + 20% 0 3 6 9 12 15 18 21 More Percentage of compression wood (%) Figure 3.15: Frequencies of the presence of compression wood 130 The fact that in conifers the compression wood is mostly present in areas surrounding the pith (Du Toit 1963, Timell 1986) is confirmed in the one-way A N O V A in Table 3.39. The Bonferroni's multiple comparison test shows that the centrally located pith class has a significantly higher percentage of compression wood than other classes. The average percentage in Class 1 was 2.50%, and in other classes it is between 0.34 and 1.38%. Even though, the Bonferroni's test estimates that the differences among other classes were not important, it was obvious that the percentage of compression wood decreased with the distance from pith and a decreased amount of juvenile wood. This could be explained by the fact that a tree becomes gradually stronger, so in later stages it reduces its need to form compression wood as a reaction to external forces and to protect its shape. It seems that the trend of a decreasing percentage of compression wood was less steep among the pith classes 2, 3 and 4 than it was between classes 1 and 2, thereby making it a reason for the lack of statistical significance shown here. Table 3.39: Analysis of variance for compression wood Source of Variation DF Sum of Squares Mean Square F calculated F Critical Run 3 15.84 5.28 0.33 2.63 P L 3 403.50 134.50 8.49* 2.63 Run x P L 9 64.17 7.13 0.45 1.91 Experimental error 624 9,881.74 15.84 Total (Adjusted) 639 10,365.25 *Term significant at a = 0.05 Many studies have reported that because of its thick cell wall , higher fibril angle and shorter tracheid length, compression wood with its higher longitudinal shrinkage, negatively influences drying behavior of sawn timber. But, many studies have offered counter-augments showing that shape distortions are not necessary correlated to compression wood content (Johansson and Kliger 2002, Forsberg and Warensjo 2001). Figures 3.16, 3.17 and 3.18 131 graphically show our values of shape distortions developed during ki ln drying, plotted against the percentage of compression wood on the cross-section. 10 1 6 § 4 o -2 A Bow = 0.0617*CW + 0.5724 R 2 = 0.0126 2 4 6 8 Compression wood (%) 10 Figure 3.16: B o w developed during drying vs. compression wood 10 6-I 5 l -ATwist = -0.006*CW + 1.0389 R 2 = 0.0002 2 4 6 Compression wood (%) 10 Figure 3.17: Twist developed during drying vs. compression wood 10 4-E ' E, S 6 + T3 O E 2 b A Diamond = -0.0103*CW + 0.4232 R 2 = 0.0024 2 4 6 Compression wood (%) 10 600 500 400 + £ 300 o 200 S 100 0 4 -100 ASurface check = 1.9793*CW + 92.571 R 2 = 0.0039 2 4 6 8 10 Compression wood (%) Figure 3.18: Diamonding developed during drying vs. compression wood Figure 3.19: Surface checks developed during drying vs. compression wood This study shows that regardless of the unquestionable different properties of compression wood, it is incorrect to use it as a single predicting factor for shape distortions of 132 ki ln dried P C H baby-squares. It is expected, according with the wide spread scatters in all distortions and low coefficients of determinations, that the wide variation is influenced by other factors. The same could be said for values of surface checks developed during ki ln drying (Figure 3.19). The reason for the lack of evidence for the influences that compression wood has is probably its relatively small presence in specimens and the large number of specimens without it. The first could be particularly important for thick timbers like P C H baby-squares, where normal wood, as the majority, could easily minimize the negative effects of compression wood. Finally, it should be stated that the large variation in the appearance of compression wood was sometimes a problem for the determination of its percentage in specimens. For that reason, in some further, more detailed, studies there is a necessity for its classification into two (Pillow 1941, Nicholls 1982) or more (Low 1964, Harris 1977) color grades. 3.12 Grading The C F L A ' s E l 2 0 grading classification is a very important indicator that shows the market value of P C H structural products. Based on the procedure explained in Section 2.3.6, Table 3.40 shows the contingency table of the pith location classes, with the number of specimens which fit, or do not fit the level of drying quality for the E l 20 standard. Table 3.40: Contingency table of pith location classes and acceptably for export products Count, Total % Accepted Not accepted Total Pith Class 1 114 71 % 46 29% 160 100% Pith Class 2 138 86% 22 14% 160 100% Pith Class 3 137 83 % 23 17% 160 100% Pith Class 4 137 83 %, 23 17%> 160 100% Total 526 82% 114 18% 640 133 As seen, the class with the centrally located pith had the most problems in terms of meeting the export requirements. Chi-square test confirms the conclusion that this class significantly decreases grading results. In this class, 28.75% of specimens are not acceptable for the E l 2 0 standard. This percentage is twice as large when compared with other classes, where it went from 13.75 to 14.38%. This conclusion about Class 1 is synchronized with the previous results in this study regarding shape distortions and surface checks. It was evident that for the down-grading of specimens, bow was the most prevalent attribute of the drying quality; however, many specimens were down-graded from the combined effect of two or more forms of shape distortions or surface checks. Although the level of degradation may be higher for a lower Mt, there is very little difference (1.87%) in the level of degradation of the runs dried to Mt o f 15% and the runs dried to Mt o f 20%>. 134 4 CONCLUSION AND FUTURE W O R K K i l n drying of Pacific Coast Hemlock baby-squares is a very important operation that affects production costs and time effectiveness, and is obviously under the influence of many variables. Many of those variables are unpredictable and make ki ln drying a hard-to-control process, that in practice is often based on the individual experience and skills of k i ln operators. For this reason, there is a need for the extension of knowledge in this field. In addition, with the current trends in harvesting and the unavoidable increase o f juvenile wood proportion in sawmills, the requirement for this knowledge and the evolution of the drying process is staggering. This study should be one of many more contributions to this field. The overall summary of conclusions which are obtained through this study and recommendations for future research activities are presented in this chapter. 4.1 Conclusions After drying 640 specimens in the laboratory ki ln , planing them, collecting data, performing statistical analyses, and using the comprehensive literature, here are the recapitulated conclusions about the drying behavior of Pacific Coast Hemlock baby squares influenced by the pith location and target moisture content (Concept A ) and the pith location, cutting season and target moisture content (Concept B) . 135 4.1.1 Concept A 1. The results indicate that the pith presence and location on a cross-section of Pacific Coast Hemlock baby-square does not affect its average basic density. 2. A comprehensive analysis of the moisture content indicated that the average initial moisture content is affected by pith location. Specimens which are located less than 30 mm from the tree pith had a lower average initial moisture content than the others. 3. Final moisture content was affected by target moisture content, but it was not affected by the pith location. 4. The volumetric shrinkage is associated with the level of the target moisture content. The lower target moisture content developed greater volumetric shrinkages. The pith location did not necessarily have an influence on the volumetric shrinkage. 5. The pith location demonstrated influences on the k i ln dried bow. Specimens with the pith shown centrally on a cross-section, demonstrated a significantly higher propensity to bow, compared with specimens without the pith. Specimens with the pith shown on the cross-section near one of the sides' demonstrated a higher bow from the mature wood specimens. 6. K i l n dried twist was attributed to an interaction between the target moisture content and pith location. Attempts to interpret any of the controlled factors separately are not considered to be fully appropriate, but this study sees it as a valuable approach to the exploration of this subject. A n especially sensitive situation was when a baby-square with the pith shown in the center was dried to the lower target moisture content. In this case, the twist was larger not only from the higher target moisture content, but also from the juvenile wood free specimens dried to the same target moisture content. 136 7. There is a lack of evidence to claim an effect of the pith location or target moisture content on ki ln dried diamonding. 8. Analysis of surface checking developed during the ki ln drying demonstrates that the target moisture content and pith location are significant main effects. The lower target moisture content increased surface checks. This study provides the evidence that a baby-square with the pith in the center of the cross-section develops the longest surface checks. Moreover, it shows that the surface checks are shorter i f the pith is shown on a cross-section near one of its sides. The checks are even shorter i f the pith is about 30 mm outside of the square. The analysis demonstrates that the mature wood specimens wi l l have shorter surface checks when compared with others. 4.1.2 Concept B 1. The results indicate that the pith presence and location on a cross-section of Pacific Coast Hemlock baby-square does not affect its average basic density. 2. A comprehensive analysis of the moisture content indicated that an average initial moisture content was affected by the cutting season and pith location. Timbers from the summer cutting season showed lower initial moisture content when compared with the fall cutting season. Specimens located less than 30 mm from the tree pith had a lower average initial moisture content than other specimens. 3. Final moisture content was affected by the target moisture content, but it was not affected by the cutting season or pith location. 4. If a difference was present within both the initial moisture content and target moisture content, the volumetric shrinkage was attributed to the interaction of the cutting season and 137 target moisture content. Their wider range resulted in a higher shrinkage. The pith location did not necessarily have an influence on the volumetric shrinkage. 5. The pith location demonstrated influences on the ki ln dried bow. Specimens with the pith shown centrally on a cross-section, demonstrated a significantly higher propensity to bow, compared with specimens without the pith. Specimens with the pith shown on the cross-section near one of the sides' demonstrated a higher bow from the mature wood specimens. 6. K i l n dried twist could be attributed to two interactions: the interaction between the cutting season and pith location, and the target moisture content and pith location. A n y attempt to interpret any of the controlled factors separately is not usually statistically valid; however, upon researching this topic, this study shows that this method can be an invaluable way to interpret the data. 7. There is a lack of evidence to claim an effect of the pith location, cutting season or target moisture content on ki ln dried diamonding. 8. Analysis of surface checking developed during the ki ln drying demonstrates that the target moisture content and pith location are significant main effects. The lower target moisture content increased surface checks. This study provides the evidence that a baby-square with the pith in the center of the cross-section develops the longest surface checks. Moreover, it shows that the surface checks are shorter i f the pith is shown on a cross-section near one of its sides. The checks are even shorter i f the pith is about 30 mm outside of the square. The analysis demonstrates that the mature wood specimens wi l l have shorter surface checks when compared with others. 138 4.1.3 General conclusions Based on available data, there is a solid indication that the pith presence and location in the cross-section of a green Pacific Coast Hemlock timber is useful information for predicting the drying quality. If all is taken into consideration, the following general conclusions could be drawn: 1. Pacific Coast Hemlock timbers with the pith shown in the centre should be avoided in the production of baby squares to be k i ln dried, because of a high propensity to drying defect formation. Pith presence in a k i ln timber load wi l l result in an unnecessary waste of energy and a decrease in drying capacity. 2. Pacific Coast Hemlock timbers with the pith shown close to one of the sides of the cross-section w i l l have a lower, but generally acceptable quality after k i ln drying. When they are stored, these types of timbers are more sensitive to the environmental conditions compared with pure mature wood specimens; therefore, in both warm and dry (summer) or high humidity environmental conditions (fall), extra care is required to protect them prior to and after drying. Treating them in the same manner as previous types of timbers and sorting them as "out-of-class timber" before k i ln drying results in a loss of profit. 3. Significant evidence is provided to claim that the planing of rough specimens reduces twist, diamonding and surface checks, but does not decrease bow. 4. There is lack of clear evidence that the slope of grain or compression wood had an influence on results. Only the slope of grain and the ki ln dried twist could have a relationship, albeit weak. 139 5. The central pith location demonstrates a risk for the level of drying quality required from baby-squares to meet the C F L A E l 2 0 grading criterions for the Japanese post-and-beam construction market. 4.2 Future Work The presented study, together with the comprehensive previous investigations on individual issues in this area, represents a solid basis for future ideas and suggestions about the evolution of Pacific Coast Hemlock baby-square ki ln drying. However, much more work is necessary to expand our understanding. If we intend to effectively use the currently available smaller diameter wood of the Pacific Coast Hemlock, and be ready for future changes in the log market, we must understand the interrelationships between all possible factors and try to control them before, during, and after drying. Besides anatomical and technological issues, further research should also include both the economic consequences of juvenile wood, and the effects o f the development and implementation of new drying concepts. A s an extension to the existing knowledge base, further analyses with an increased number o f influences and advanced diagnostic models, which detect the characteristics of their interactions, are necessary. Furthermore, this work should not be limited to laboratory kilns, but tested in the industrial environment, as well . A t this point, the essential questions and tasks relative to the utilization of juvenile wood in Pacific Coast Hemlock baby-squares include: (1) Are forest practices able to decrease the presence of juvenile wood, slope of grain and compression wood of Pacific Coast Hemlock in the future? 140 (2) What consequences wi l l an increased presence of juvenile wood have on an industry that is already struggling, as the forest industry of British Columbia is? Is there a need for adjustments to current standards? (3) How can we improve measuring techniques for juvenile and compression wood which include the development of methods and scanning techniques applicable in a dynamic industrial environment? (4) Which are the characteristics of the interaction between the basic density, slope of grain, compression wood, and juvenile wood on k i ln dried shape distortions and checking? Are the interactions the same for western hemlock and Amabilis fir? (Including the development o f a model for the sorting of the species in an industrial environment.) (5) Is the interaction the same for other wood drying methods, or with the application of different k i ln drying techniques, for the reduction of degradations? (6) What are the conclusions of an economic analysis of the development and implementation of the pre-drying sorting system for Pacific Coast Hemlock baby-squares, based on the current technology level? (7) If the timbers with the pith shown centrally in a cross-section are de-selected from further baby-square production, what kind of options, technologically and marketing-wise, does the industry have? Answers to the preceding key questions relative to the Pacific Coast Hemlock baby-squares can significantly impact the future of the Western Canadian forest industry. 141 5 REFERENCES Alden, H . 1995. Softwoods of North America. FPL-GTR-102 . Madison, WI. U .S . Dept. of Agriculture, Forest Service, Forest Products Laboratory. 151 pp. Archer, R .R. and B .F . Wilson. 1973. Mechanics of the compression wood response. Plant Physiology 51:777-782. Avramidis, S. 2001. Evaluation of conventional and radio frequency vacuum drying and re-drying of pacific coast hemlock hashira and hirakaku timbers. ( C A R P - 2 U B C - W o o d Science report to the Coastal Forest and Lumber Association and the Z A I R A I Lumber Partnership, Vancouver, B C . 42 pp. Avramidis, S. 2002. Stability response of square timbers: a laboratory simulation of shipping and storage. J. Inst. Wood. Sci. 16(1): 36-43 Avramidis, S. and B . Hao 2004. Pacific coast hemlock stability and moisture class assessment U B C - W o o d Science report to the Coastal Forest and Lumber Association and the Z A I R A I Lumber Partnership, Vancouver, B C . 41 pp. Avramidis, S. and J .F .G. Mackay. 1988. Development of k i ln schedules for 4-inch by 4-inch pacific coast hemlock. For Prod. J: 38(9):45-48. Avramidis, S. and L . Oliveira. 1993. Influence of presteaming on ki ln drying o f thick hem-fir lumber. For. Prod. J. 43 (11/12):7-12. Bachrich, J .L. 1980. Dry K i l n Handbook, Vancouver: H A . Simons (International) Ltd. 374 pp. Balodis, V . 1972. Influence of grain angle on twist in seasoned boards. Wood Sci . 5:44-50 Barrett, D.J . and R . M . Kellogg. 1985. Lumber quality from second growth managed forests. Juvenile wood - What does it means to forest management and forest products: A technical workshop proceedings 47309. The Forest Product Research Society and The Society of American Foresters. Oregon: 57-71 Beard, J.S., F . G . Wagner, F .W. Taylor and R . D . Seale. 1993. The influence of growth characteristics on warp in two structural grades of southern pine lumber. For. Prod. J. 43(6): 51-56. Bendtsen, B . A . 1978). Properties of wood from improved and intensively managed trees. For. Prod. J. 28(10): 61-72. 142 Bendtsen, B . A . and J. Senft. 1986. Mechanical and anatomical properties in individual growth rings of plantation-grown eastern cottonwood and loblolly pine. Wood Fiber Sci. 181: 23-38. Berthold, J., J. Desbrieres, M . Rinaudo and L . Salmen. 1994. Types of adsorbed water in relation to the ionic groups and their counter-ions for some cellulose derivatives. Polymer. 35(26): 5729-5736. Blass, H.J . , P. Aune, B .S . Choo, R. Gorlacher, D.R. Griffiths, B . O . Hilson, P. Racher and G . Steck. 1994. Timber Engineering STEP 1, Basis of design, material properties, structural components and joints. I Edition. The Netherlands. Centrum Hout: 400 pp. Boone, R.S. and M . Chudnoff. 1972. Compression wood formation and other characteristics of plantationgrown Pinus caribaea. Res. Pap. ITF-13. Rio Piedras, Puerto Rico: U . S . Department of Agriculture, Forest Service, Institute of Tropical Forestry. Bower, R . W . , A . DeSouze and S.F. Senft. 1976. Physical and mechanical properties of fast grown, plantation Caribbean pine (Pinus caribaea) Trom Brazi l , South America. Res. B u l l . 936. Lafayette, IN: Purdue University. Boyd, J.D. 1973. Helical fissures in compression wood cells: Causative factors and mechanics of development. Wood Sci Technol. 7: 92-111. Bramhall, G . and R . W . Wellwood. 1976. K i l n drying of western Canadian lumber. Information Report V P - X - 159. Western Forest Prod. Lab., Vancouver. 112 pp. Burdon R .D . , R.P. Kibblewhite, J .C.F. Walker, R . A . Megraw, R. Evans and D.J . Cown. 2004. Juvenile Versus Mature Wood: A New Concept, Orthogonal to Corewood Versus Outerwood, with Special Reference to Pinus radiata and P. taeda. For Sci . 50(4): 399-415 Burdon, R., J. Walker, B . Megraw, R. Evans and D . Cown. 2003. Juvenile wood (sensu novo) in pine: Conflicts and possible opportunities for growing, processing and utilisation. N Z J F o r . 49(3):24-31 Burns, R . M . and B . H . Honkala, (Eds). 1990. Silvics of North America: 1. Conifers. Agriculture Handbook 654. U .S . Department of Agriculture, Forest Service, Washington. 2: 877 pp. Castera, P. and J.F. Dumail . 1997. Transferse shrikage in maritime pine juvenile wood. Wood Sci Technol. 31(4): 251-264. Cave, I.D. 1976. Modell ing the structure of the softwood cell wall for computation of mechanical properties. Wood Sci Technol. 10:19-28. Cave, I.D. and J .C.F. Walker. 1994. Stiffness of wood in fastgrown plantation softwoods: the influence of microfibril angle. For. Prod. J. 44(5):43-48. 143 Council of Forest Industries. 2000. British Columbia Forest Industry Fact Book-2000. Vancouver, B . C . , Council of Forest Industries: 1-39, 60-72. Cown D.J . , G .D . Young and M . O . Kinmerley. 1991. Spiral grain patterns in plantation-grown pinus radiata. N Z . J. For. Sci. 21 (2/3): 206-216 Cown, D.J . , D . L . McConechie and G.D. Young. 1991. Radiata pine wood properties survey. FRI Bulletin. (50) Dadswell, H . E . 1958. Wood structure variations occurring during tree growth and their influence on propeties. J Inst Wood Sci 1:1-2 Danborg, F. 1994. Drying properties and visual grading of juvenile wood from fast grown Picea abies and Picea sitchensis, Scand. J. For. Res. (9) 91-98. Danborg, F. 1994. Spiral grain in plantation trees of Picea abies, Can. J. For. Res. 24:1662-1671. Daniels, J . M . 2005. The rise and fall o f the Pacific Northwest log export market. Gen. Tech. Rep. PNW-GTR-624 . Portland, OR: U .S . Department of Agriculture, Forest Service, Pacific Northwest Research Station. 80 pp. DeBel l , D.S. , R. Singleton, B.L.Gartner and D . D . Marshall. 2004. Wood density o f young-growth western hemlock: relation to ring age, radial growth, stand density and site quality. Can J For Res 34:2433-2442 Dedman, J. and E . Vandusen. 1965. K i l n drying western hemlock and Douglas fir dimension lumber. Proc. 17th Annual meeting, Western Dry K i l n Clubs, West Coast Dry K i l n Assoc., Portland, Oregon: 20-25. D u Toit, A . J . 1963. A study of the influence of compression wood on the warping of Pinus radiata D . Don timber. S. Afr . For. J. 44:11-15. Dumail , J.F. and P. Castera. 1997. Transverse shrinkage in maritime pine juvenile wood. Wood Sci. Technol. 31:251-264 Eastin, I. 2004. Structural analysis of post and beam homes in Japan. Center for international trade in forest products. C I N T R A F O R News. 4 pp. Retrieved January 20, 2005, from (http://www.cintrafor.org/OUTREACH_TAB/links/WrNTER2004.pdf) El l is , S. 1995. Mechanical Properties of Second-growth Western Hemlock. Basic Wood Properties of Second-growth Western Hemlock. Forintek Canada Corp., Vancouver, B C Spec. Publ Sp-3 8:44-49 Elustondo, D . and S. Avramidis 2004. The demonstration of increased lumber value using combined lumber sorting and R F V drying In proceedings of the C O S T E l 5 European Wood Drying Conference, A p r i l 2004, Athens, Greece:! 11-120. 144 Farr, W . A . 1973. Specific gravity of western hemlock and Sitka spruce in southeast Alaska. Wood Sci. 6(1):9-13 Forest Products Laboratory. 1999. The wood handbook: wood as an engineering material. Gen. Tech. Rep. FPL-GTR-113 . Madison, WI : U .S . Department of Agriculture, Forest Service. 463 pp. Forsberg, D . and M . Warensjo. 2001. Grain Angle Variation: A Major Determinant of Twist in sawn Picea abies (L.) Karst. Scand. J. For. Res. 16: 269-277 Gartner, B . L . 2005. Assessing wood characteristics and wood quality in intensivly managed plantations. J. For. 103(2):75-77 Gonzalez, J. 1987. Wood Density of Canadian tree species in British Coulmbia. Report prepared for the Canadian Forestry Service, Ottawa, Ontario. Gonzalez, J. 1990. Wood Density of Canadian Tree Species. Forintek., Edmonton, A B . Inf. Rep. N O R - X - 3 1 5 . Gorman, T . M . 1985. Juvenile wood as a cause of seasonal arching in tissues. For. Prod. J. 35(11-12): 35-40 Hallock, P. 1968. Observations on form of juvenile core in loblolly pin. Res. Pap. FPL-0188 . Madison, WI : U .S . Department of Agriculture, Forest Service, Forest Products Laboratory. 4 pp. Hammett, A . L . and R . L . Youngs. 2002. Innovative Forest Products and Processes: Meeting Growing Demand. J. For. 100(4):6-11 Hansom, O.P. 1988. Contemporary Timber Drying. T B L 60, Timber Research and Development Association - T R A D A . Buckinghamshire. U K . 84 pp. Hao B . and S. Avramidis. 2004. Annual ring orientation effect and slope of grain in hemlock timber drying. For. Prod. J. 54(11):41-49 Harris, J . M . and B . A . Meylan. 1965. The influence of micro-fibril angle on longitudinal and tangential shrinkage in Pinus radiata. Holzforschung. 19:144-153. Haslett A . N . , I.G. Simpson and M . O . Kimberley. 1991. Utilisation of 25-year-old Pinus radiata. Part 2: Warp of structural timber in drying, N . Z . J. For. Sci. 21:228-234. Haygreen, J .G. and J. L.Bowyer. 1996. Forest Products and Wood Science: A n Introduction. Iowa State University Press, Iowa. 484 pp. Highley, T .L . , C A . Clausen and S.C. Croan. (Eds.). 1994. Research on biodeterioration of wood, 1987-1992. I. Decay mechanisms and biocontrol. Res. Pap. F P L - R P - 5 2 9 . Madison, WI : U . S . Department of Agriculture, Forest Service, Forest Products Laboratory. 20 pp. 145 Hoadley, H . V . 1979. Effect of temperature, humidity and moisture content on solid wood products and end use. In: Symposium wood moisture content-temperature and humidity relationships V D I & S U Blacksburg Virginia, U S D A F R L North Central For. Exp. Stat: 92-96 Isenberg, I.H. 1980. Pulpwoods of the United States and Canada. V o l . I - Conifers. 3rd ed. Inst, of Paper Chem. Appleton, WI . Jessome, A . P . 1977. Strength and Related Properties of Woods Grown in Canada. Eastern Forest Products Laboratory Technical report 21: Ottawa. Johansson, M . , and R. Kliger. 2002. Influence of material characteristics on warp in Norway spruce timber. Wood Fiber Sci. 342: 325-336. Jozsa, L . A . and G.R. Middleton. 1994. A Discussion of Wood Quality Attributes and their Practical Implications. Forintek Canada Corp., Vancouver, B C Spec. Publ SP-38. Jozsa, L . A . , B . D . Munro and J.R. Gordon. 1998 Basic wood properties of second-growth western, hemlock. Forintek Canada Corp., Vancouver, B C Spec. Publ Sp-38 Keey, R . B . , T . A . G . Langrish and J .C.F. Walker. 2000. Ki ln-Drying of Lumber, Berlin Heidelberg: Springer-Verlag, Berlin. 326 pp. Kennedy, R . W . and G .W. Swan. 1969. Comparative specific gravity o f amabilis fir and western hemlock grown in British Columbia. Can. Dep. Fish. For., West. For. Prod. Lab. Vancouver, B C . Inf. Rep. V P - X - 5 0 Keylwerth, R. 1950. Drying gradients and the control of timber kilns. Holz-Zent.bl.. 76:375 Koch , P., W . A , Cote, J. Schlieter and A . C . Day. 1990. Incidence of compression wood and stem eccentricity in lodgepole pine of North America. U S D A Forest Service. Intermountain Research Station, Research paper INT-420, Ogden, U S A , 42 pp. Kollmann, F. 1951. Technologie des Holzes und der Holzwerkstoffe. Erster Band, Berl in Heidelberg. Springer-Verlag, Berlin. 1050 pp. Kollmann, F.P. and W.A.Cote . 1967. Principles of Wood Science and Technology. Volume I: Solid Wood. Springer-Verlag, Berlin. I S B N 82-13-00284-9. Koz l ik , C.J. 1970. Problems of drying western hemlock heartwood to a uniform final moisture content. Proc. 21st Annual Meeting, Western Dry K i l n Clubs, Washington- Idaho-Montana Seasoning Club, Missoula, Montana: 55-61. Koz l ik , C.J. and J.C. Ward. 1981. Properties and kiln-drying characteristics of young-growth western hemlock dimension lumber. For. Prod. J. 31(6): 45-53. Koz l ik , C.J . and L . W . Hamlin. 1972. Reducing variability in final moisture content of k i ln-dried western hemlock lumber. For. Prod. J. 22(7):24-31 146 Kozl ik , C.J. , R . L . Kramer and R. T. L i n . 1972. Drying and other related properties of western hemlock sinker heartwood. Wood and Fiber 42: 99-111 Krahmer, R . L . 1985. Fundamental anatomy of juvenile and mature wood. Juvenile wood -What does it means to forest management and forest products: A technical workshop proceedings 47309. The Forest Product Research Society and The Society of American Foresters. Oregon: 12-16 Kretschmann, D .E . , R . C . Moody, R.F. Pellerin, A . B . Bendtsen, J . M . Cahil l , R . H . McAlis ter and D . W . Sharp. 1993. Effect of various proportions of juvenile wood on laminated veneer lumber. Res. Pap. F P L - R P - 5 2 1 . Madison, WI : U .S . Department of Agriculture, Forest Service, Forest Products Laboratory. 31 pp. Larson P.R. 1965. Stem form of young Larix as influenced by wind and pruning. For. Sci. 11: 413-424. Larson, P.R., D . E . Kretschmann, A.III. Clark and J .G. Isebrands. 2001. Formation and properties of juvenile wood in southern pines: a synopsis. Madison, WI: U .S . Department of Agriculture, Forest Service, Forest Products Laboratory. 42 pp. Lavers, G . 1983. The strength properties of timber. Dep. Environ., Princes Risborough Lab., Princes Risborough, Aylesbury, U K Bui ld . Res. Establ. Rep. Lenth, C A . and F . A . Kamke. 2001. Equilibrium moisture content of wood in high-temperature pressurized environments. Wood Fiber Sci. 331:104-118. LeVan-Green, S. L . and J. Livingston. 2001. Exploring the uses for small-diameter trees. For. Prod. J. 51(9): 10-2 Lewis, H.F . 1950. The significant chemical components of western hemlock, Douglas fir, western red cedar, loblolly pine, and black spruce. Tappi J. 33(6):299-301. L i , M . , S. Avramidis, L . C. Oliveira and I. Hartley. 1997. The Effect of Vertical A i r Gaps, A i r Velocities and Fan Revolutions on the Drying Characteristics of Thick Pacific Coast Hemlock Lumber. Holzforshung 51(4):381-387. L i n , R.T. and E.P. Lancaster. 1972. Longitudinal water permeability of western hemlock. II. Unsteady-Steady Permeability. Wood Fiber Sci. 40(4): 290-297. L i n , R.T. , E . K . Lancaster and R . L . Kramer. 1973. Longitudinal water permeability of western Hemlock. I. Steady State Permeability. Wood Fiber Sci. 4(4): 278-289. Low, A . 1964. A study of compression wood in Scots pine (Pinus sylvestris L. ) . For. 37: 179-201. Mackay, J .F.G. and L . C Oliveira. 1989. K i l n Operator's handbook for Western Canada Forintek Canada Corp. Special Publication No . SP-5. 147 Matsumura, Y . and K . Murata. 2004. Analysis of precut industry in Japan. Holz Roh Werkst 63:68-72 McAlister , R . H . and A.III. Clark. 1992. Shrinkage of juvenile and mature wood of loblolly pine from three locations. For. Prod. J. 42(7/8): 25-28. M c M i l l a n , C W . 1973. Fibri l angle of loblolly pine as related to specific gravity, growth rate and distance from the pith. Wood Sci 2: 26-30 M c M i l l e n , J . M . 1958. Stresses in wood during drying. Madison, WI : U .S . Department of Agriculture, Forest Service, Forest Products Laboratory. 1652. 174 pp. Meylan, B . 1968. Cause of high longitudinal shrinkage in wood. For. Prod. J. 18(4):75-78 Milota , M . 1992. Effect of k i ln schedule on warp in Douglas-fir lumber. For. Prod. J. 422:57-60 Milota, M . R . , J.J. Morrel l and S.T. Lebow. 1993. Reducing Moisture Content Variability in Kiln-dried Hem-Fir Lumber through Sorting: A Simulation. For. Prod. J. 43(6):6-12 Milota, M . R . , R. Boone, D . Sidney, J.D. Danielson and D . W . Huber. 1991. Quality Drying of Softwood Lumber: Guidebook and Checklist. Madison, WI : U . S . Department of Agriculture, Forest Service, Forest Products Laboratory. 50 pp. Ministry of Finance and Corporate Relations. 2001. Exports (B.C. Origin) B C Stat. Retrieved March 15, 2005, from (http://www.bcstats.gov.bc.ca/pubs/exp/exp0103.pdf) Morton, P. and J. Greenwood. 2004. National Post. Don M i l l s , Ont.: Dec 15, 2004. pg. F P . l . F r Nicholls, D . L . , A . M . Brackley and T. Al len . 2003. Moisture distribution in Western hemlock lumber from trees harvested near Sitka, Alaska. U . S . Department of Agriculture, Forest Service, Pacific Northwest research station. 8 pp. Nicholls, J .W.P. 1982. Wind action, leaning trees and compression wood in Pinus radiata D . Don. Australian Forest Research 12: 75-91. Nielson, R . W . , J. Dobie and D . M . Wright. 1985. Conversion factors for Forest Products Industry in Western Canada. Special Publication No . SP-24R. Forintek, Canada Corp.: 91pp. Noack, D . , E . Schwab and A . Bartz. 1973. Characteristics for a judgement of the sorption and swelling behavior of wood. Wood Sci . Technol. 7(3):218-236. Oliveira, L . C . and J .F .G. Mackay. 1991. Improving efficiency of hem-fir k i ln drying. Forintek, Canada Corp., Unpublished report. # 02-12-12-k-002. Vancouver. 63 pp. 148 Oliveira, L . C . and J.W. Wallace. 2001. Examining some Drying/Re-Drying options for 105mm x 105mm green hem fir lumber. Forintek, Canada Corp., Report prepared for C F L A . 17pp. Pagnozzi, E . 1991. Physique du sechage sous vide. In: 5 ieme Seminaire International E D G : Des procedes performants de sechage du bois pour accroitre la rentabilite et ameliorer la qualite des produits CTBA/Par i s , E D G . 9 pp. Panshin, A . J . and C. deZeeuw. 1980. Textbook of wood technology: structure, identification, properties, and usage of the commercial woods of the United states and Canada. 4 t h ed. M c G r a w - H i l l , New York. 722 pp. Pape, R. 1999. Influence of thinning on spiral grain in Norway spruce grown on highly productive sites in southern Sweden. Suva Fenn. 33: 3-12. Pearson, R . G . and R . C . Gilmore. 1971. Characterization of the strength of juvenile wood of loblolly pine (Pinus taeda L.) . For. Prod. J. 21(1): 23-31. Perstorper, M . , I.R. Pellicane, R. Kliger, R. and G . Johansson. 1995. Quality of timber products from Norway spruce part 2. Influence of spatial position and growth characteristics on warp. Wood Sci Technol. 29: 339-352. Pi l low, M . Y . 1941. A new method of detecting compression wood. J. For. (39): 358-387. Pojar, J., K . Kl inka and D . A . Demarchi. 1991. Ecosystems of British Columbia Province of British Columbia. (Meidingerl D . and Pojar (Eds) J. Research Branch Ministry o f Forests. I S B N 0-7718-8997-6. 9 5 - 111 Reitz, R . C . and R . H . Page. 1971. A i r drying of lumber: A guide to industry practice. Agric . Handb. 402. Washington, D C : U . S . Department o f Agriculture. 110 pp. Rosen H.N..1995. Drying of Wood and Wood Products. In,. Handbook of Industrial Drying; 2nd Ed. New York, Marcel Dekker. 899-921 Sackey, E . K . , Avramidis, S. and L . C. Oliveira 2004. Exploratory Evaluation of Oscillation Drying for Thick Hemlock Timbers. Holzforschung, 58: 428-433. Schneider, M . H . and L.Zhou. 1989. Characterization of wetwood from four balsam fir trees. Wood Fiber Sci. 211:1-16. Schroeder, H . A . and C. J. Koz l ik . 1972. The Characterization of Wetwood in Western Hemlock. Wood Sci . Technol. 62: 85-94. Sendberg D . 1996. Influence of pith and juvenile wood on proportions of cracks in saw timber when ki ln dried and exposed to wetting cycles. Holz Roh Werkst. (54): 152 Shelly, J.R. and W.T.Simpson 1999. Analysis of warp in lumber manufactured from suppressed growth Douglas-fir. Issues related to handling the influx of small-diameter 149 timber in North America.. Madison. U .S . Department of Agriculture, Forest Service, Forest Products Laboratory. Siau, J.F. 1984. Transport processes in wood. New York, Springer-Verlag, Berlin. 245 pp. Siau, J.F. 1995. Wood: influence of moisture on physical properties. Department of Wood Science and Forest Products, Blacksburg, Virginia Polytechnic Institute and State University. 227 pp. Simpson, W . 1982. Warp reduction in kiln-drying hardwood dimension. For. Prod. J. 32(5): 29-32. Simpson, W . and A . TenWolde. 1999. Physical properties and moisture relations of wood. Wood handbook - Wood as an engineering material. Gen. Tech. Rep. F P L - G T R - 1 1 3 . Madison, WI : U . S . Department of Agriculture, Forest Service, Forest Products Laboratory. 463 pp. Simpson, W.T . (Eds). 1991. Dry k i ln operator's manual. Rev. Agric . Handbook. 188. Madison, WI : U . S . Department of Agriculture, Forest Service, Forest Products Laboratory. 174 pp. Simpson,W.T. and J .L. Tschernitz. 1998. Effect of thickness variation on warp in high-temperature drying plantation- grown loblolly pine 2 by 4's. Wood Fiber Sci . 30: 165-174 Siripatanadilok,S. and L . Lawrence. 1985. Compression wood in western hemlock. Wood Fiber Sci. 17(2): 254-265. Skaar, C. 1972. Water in wood. New York, Syracuse University Press. 218 pp. Skatter, S. and B . Kucera. 1997. Spiral grain - A n adaptation of trees to withstand stem breakage caused by wind-induced torsion. Holz Roh Werkst. 55: 207-213. Smith, W . 1970. Wood density survey in western Canada. Can. Dep. Fish. For., West. For. Prod. L A b . , Vancouver, B C . Inf. Rep. V P - X - 6 6 Smith, W . and D . Briggs. 1985. Juvenile wood: Has it come of age? Juvenile wood - What does it means to forest management and forest products: A technical workshop proceedings 47309. The Forest Product Research Society and The Society of American Foresters. Oregon: 5-12 Softwood Export Council - S E C . 2001. Western hemlock. Retrieved March 05, 2005, from (wttp://www.softwood.org/Hem%20Fir%20Web/eHemFir/EN/HemFir.htm) Somers, D (Eds.). 1997. Southeast Timber Task Force Report. Appendix I. Retrieved January 30, 2004, from: (http://www.dced.state.ak.us/oed/forest_products/forest_productslO.htm) 150 Stamm, A . J . 1964. Wood and Cellulose Science, New York: The Ronald Press Company. 549 pp. Standish, J.T. 1983. Development of a system to estimate quantity of biomass following logging in British Columbia forests to specified recovery criteria. Report prepared for the Canadian Forestry Service, Ottawa, Ontario. Thomas, R.J . 1985. The characteristics of juvenile wood. Symp Ut i l Chang Wood Res South U S North Carolina State University. North Carolina. 18 pp. Tiemann, H . D . 1906. Effect of moisture upon the strength and stiffness of wood. U . S . Dep. Agric . For. Serv. B u l l . 70. 144 pp. Timell , T .E . 1986. Compression wood in gymnosperms. V o l 1-3. Springer-Verlag, Berlin. 2150 pp. Vansteenkiste, M . , M . Stevens, and J. van Acker. 1997. High temperature drying of fresh sawn poplar wood in an experimental convective dryer. Holz . Roh. Werkst. 55:307-314. Voohries G . and W . A . Groman 1982. Longitudinal shrinkage and occurrences of various fibril angles in juvenile wood of young growth ponderosa pine. Arizona Forestry notes. Northern Arizona University, Arizona. 15:8 pp. Wallace, J.W., I.D.Hartley, S. Avramidis and L . Oliveira. 2003. Conventional k i ln drying and equalization of Western hemlock (Tsuga heterophylla (Raf.)[Sarg]) to Japanese equilibrium moisture content. Holz Roh Werkst. 61: 257-263 Ward, J. C. 1984. Influence of Wetwood on pulsed-current resistances in lumber before and during drying. Wood and Fibre Sci. 16(4): 598-617. Ward, J. C. 1986. The effect of Wetwood on Lumber Drying Times and Rates: A n exploratory valuation with longitudinal gas permeability. Wood and Fibre Sci. 182: 288-307. Warensjo, M . and C. Lundgren. 1998. Impact of compression wood on deformations o f sawn wood of spruce (Picea abies (L.) Karst.). Department of Forest Products. Swedish University of Agricultural Sci. Report 255. 38 pp. Waring R . H . and F.J. Franklin. 1979. Evergreen Coniferous Forests of the Pacific Northwest Science, New Series. 204(4400): 1380-1386 Wellwood, R . W . and J .H.G. Smith. 1962. Variation in some important qualities of wood from young Douglas-fir and hemlock trees. The University of British Columbia, Faculty of Forestry, Vancouver, B . C . Res. Pap. 50. Wengert E . M . and F. M . Lamb. 1993. End coating of lumber to prevent end checking. Proc. 2nd I U F R O Int. Wood Drying Conf. Seattle. W A : 164-168. Western Wood Products Assosiation. 1997. Hem-Fir Species Facts. Retrieved March 15, 2005, from (http://www.wwpa.org/hemfir.htm) 151 Widlak, H . 2002. The effect of age desorption stress and strain rate in birch and aspen. Electronic Journal of Polish Agricultural Universities. 52 Retrieved March 15, 2004, from (http://www.ejpau.media.pl/series/volume5/issue2/wood/art-03.pdf) Will iams D . and R. Morris. 1998. Machining and related properties of 15 B C wood species. Forintek Canada Corp., Vancouver, B C Spec. Publ Sp-39 Winandy, J.E. 1995. The effects of waterborne preservative treatment on mechanical properties: A review. In: Proceedings, American Wood Preservers' Association; Woodstock, M D : 91:17-33. Woxblom, L . 1993. Quality variations in wall studs - a study conducted at five sawmills in southern Sweden. Dept o f Forest-Industry-Market Studies, Swed. Univ. of Agric . Sci . , Uppsala. Report 28:50 pp. Yao, J. 1970. Influence of growth rate on specific gravity and other selected properties of loblolly pine. Wood Sci Technol. 4: 163-175. Y i n g , L . , D . E . Kretschmann and B A . Bendtsen. 1994. Longitudinal shrinkage in fast-grown loblolly pine plantation wood. For. Prod. J. 44 1:58-62. Yoshizawa, N . , Okamoto and T. Idei. 1986. Righting movement and xylem development in tilted young conifer trees. Wood Fiber Sci . 18: 579-589. Zhang, Y . , L . Oliveira and S. Avramidis. 1996. Drying characteristics o f hem-fir squares as affected by species and basic density presorting. For. Prod. J. 46(2):44-50. Zobel, B . J. and A.E.Jr . Ffaught. 1962. Effect of bole straightness on compression wood o f Loblol ly Pine. Technical Report Sch, Forest North Carolina State College N o 15. 12 pp. Zobel, B . J . 1976. Wood properties as affected by changes in the wood supply o f southern pines. T A P P I J. 59:126-128. Zobel, B . J . and J.P. van Buijtenen. 1989. Wood Variation: Its Causes and Control Springer-Verlag, Berlin. 363 pp. Zobel, B . J . and J.R. Sprague 1998. Juvenile Wood in Forest Trees. Springer-Verlag, Berlin. 315 pp. Zobel, B . J . and R . L . McElwee. 1958. Natural variation in wood specific gravity of loblolly pine, and an analysis of contributing factors. T A P P I J. 41:158-161. 152 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0074974/manifest

Comment

Related Items