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The influence of conditioning on internal checking of high-temperature dried Pacific Coast hemlock Dubois, Joël 1991

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THE INFLUENCE OF CONDITIONING ON INTERNAL CHECKING OF HIGH-TEMPERATURE DRIED PACIFIC COAST HEMLOCK By JOEL DUBOIS B.A.Sc., Laval U n i v e r s i t y , 1988 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY in THE FACULTY OF GRADUATE STUDIES Department of Forestry Ve accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1991 © Joel Dubois, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. The University of British Columbia Vancouver, Canada Department DE-6 (2/88) ABSTRACT The purpose of t h i s study was t o e v a l u a t e the e f f e c t i v e n e s s of steam c o n d i t i o n i n g immediately a f t e r d r y i n g t o reduce i n t e r n a l c h e c k i ng r e s u l t i n g from high-temperature d r y i n g of P a c i f i c Coast hemlock lumber. Three d i f f e r e n t l e v e l s of c o n d i t i o n i n g time, 2, 4 and 6 hours, were c a r r i e d out on 2 inches wide by 4 inches t h i c k by 3 f e e t l o n g (51 mm by 102 mm by 0.91 m) , and on 4 inches wide by 4 inches t h i c k by 3 f e e t l o n g (105 mm by 105 mm by:0.91'm), specimens. For comparison purposes, c o n t r o l s of both s i z e s of specimens were a l s o h i g h -temperature d r i e d without c o n d i t i o n i n g . A n a l y s i s of the r e s u l t s i n d i c a t e d t h a t i n t e r n a l c hecking was not s i g n i f i c a n t l y reduced by steam c o n d i t i o n i n g and was more l i k e l y t o develop afterwards d u r i n g storage at room temperature, and t h a t t o t a l degrade observed i n the "4x4" specimens was more e x c e s s i v e than t h a t i n the "2x4" ones. The d e f e c t i v e "4x4" specimens were found o v e r - d r i e d (below the t a r g e t e d 12% moisture content) w i t h h i g h c o r e - s h e l l moisture content d i f f e r e n c e s . More i n t e r n a l checking was found when the specimens' f i n a l moisture content ranged from 7 to 8%. TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i i i LIST OF FIGURES v LIST OF TABLES v i i i ACKNOWLEDGEMENTS x ABBREVIATIONS USED x i 1 . INTRODUCTION 1 2 . LITERATURE REVIEW 4 2.1 High-temperature d r y i n g of P a c i f i c Coast hemlock 4 2.2 I n t e r n a l checking 9 2 . 3 C o n d i t i o n i n g 14 3. MATERIALS AND METHODS 18 3.1 Phase I 18 3.2 Phase I I 27 4. RESULTS AND DISCUSSION 34 4.1 Phase I 34 4.2 Phase I I 53 5 . CONCLUSION. . ' 90 6. LITERATURE CITED 93 7 . APPENDICES . 98 1. Load weight at 12% moisture content 99 2. T e s t i n g s e v e r a l p r o p o r t i o n s 99 2.1 "2x4" specimens..- 99 i i i 2.2 "4x4" specimens 102 3. Summary of d r y i n g q u a l i t y of "2x4" PCH lumber 103 4. Tests concerning means 103 5. Average i n i t i a l moisture contents i n a l l 4 loads of "4x4" PCH specimens 107 6. T e s t i n g the d i f f e r e n c e between two p r o p o r t i o n s 109 6.1 "4x4" specimens found d e f e c t i v e immediately and one week a f t e r d r y i n g and c o n d i t i o n i n g 109 6.2 "2x4" and "4x4" specimens found d e f e c t i v e one week a f t e r d r y i n g and c o n d i t i o n i n g 110 7. Summary of d r y i n g q u a l i t y of "4x4" PCH lumber. . . 110 i v L I S T OF FIGURES F i g u r e 1. Transverse r e s i d u a l s t r e s s e s i n lumber at v a r i o u s stages of c o n v e n t i o n a l d r y i n g 11 F i g u r e 2. Sawing p a t t e r n of "2x4" PCH lumber 19 F i g u r e 3. K i l n schedule of the "2x4" specimens 22 F i g u r e 4. Sawing p a t t e r n of the "2x4" specimens f o r i n t e r n a l checking e v a l u a t i o n 23 F i g u r e 5. Width gage 25 F i g u r e 6. P o i n t s at which the core moisture content of each c o n d i t i o n i n g sample were taken 2 6 F i g u r e 7. Sawing p a t t e r n of "4x4" PCH lumber 28 F i g u r e 8. K i l n schedule of the "4x4" specimens 2 9 F i g u r e 9. Sawing p a t t e r n of the "4x4" specimens f o r i n t e r n a l checking e v a l u a t i o n 31 F i g u r e 10. Core and s h e l l p a r t s of a "4x4" moisture content s e c t i o n 32 F i g u r e 11. I n i t i a l moisture content frequency d i s t r i b u t i o n of "2x4" PCH lumber 35 F i g u r e 12. Green s p e c i f i c g r a v i t y frequency d i s t r i b u t i o n of "2x4" PCH lumber 36 F i g u r e 13. P l o t of average moisture content a g a i n s t time f o r run #1 (no c o n d i t i o n i n g ) 39 F i g u r e 14. Plot" of average moisture content a g a i n s t time f o r run #2 (2 hours of c o n d i t i o n i n g ) 40 F i g u r e 15. P l o t of average moisture content a g a i n s t time f o r run #3 (4 hours of c o n d i t i o n i n g ) 41 F i g u r e 16. P l o t of average moisture content a g a i n s t time f o r run #4 (6 hours of c o n d i t i o n i n g ) 42 F i g u r e 17. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #1 (no c o n d i t i o n i n g ) 43 v F i g u r e 18. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #2 (2 hours of c o n d i t i o n i n g ) ....44 F i g u r e 19. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #3 (4 hours of c o n d i t i o n i n g ) ....45 F i g u r e 20. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #4 (6 hours of c o n d i t i o n i n g ) ....46 F i g u r e 21. P l o t of green s p e c i f i c g r a v i t y a g a i n s t i n i t i a l moisture content f o r "2x4" PCH lumber...52 F i g u r e 22. I n i t i a l moisture content frequency d i s t r i b u t i o n of "4x4" PCH lumber 54 F i g u r e 23. Green s p e c i f i c g r a v i t y frequency d i s t r i b u t i o n of "4x4" PCH lumber. . . 56 F i g u r e 24. P l o t of average moisture content a g a i n s t time f o r run #5 (no c o n d i t i o n i n g ) 60 F i g u r e 25. P l o t of average moisture content a g a i n s t time f o r run #6 (2 hours of c o n d i t i o n i n g ) .61 F i g u r e 26. P l o t of average moisture content a g a i n s t time f o r run #7 (4 hours of c o n d i t i o n i n g ) 62 F i g u r e 27. P l o t of average moisture content a g a i n s t time f o r run #8 (6 hours of c o n d i t i o n i n g ) 63 F i g u r e 28. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #5 (no c o n d i t i o n i n g ) 64 F i g u r e 29. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #6 (2 hours of c o n d i t i o n i n g ) ....65 F i g u r e 30. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #7 (4 hours of c o n d i t i o n i n g ) ....66 F i g u r e 31. P l o t of d r y i n g r a t e a g a i n s t average moisture content f o r run #8 (6 hours of c o n d i t i o n i n g ) ....67 F i g u r e 32. F i n a l moisture content frequency d i s t r i b u t i o n of "4x4" d e f e c t i v e specimens immediately a f t e r d r y i n g and c o n d i t i o n i n g 73 F i g u r e 33. F i n a l moisture content frequency d i s t r i b u t i o n of "4x4" d e f e c t i v e specimens one week a f t e r d r y i n g and c o n d i t i o n i n g 74 v i F i g u r e 34. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of n o n - d e f e c t i v e specimens cut immediately a f t e r d r y i n g and c o n d i t i o n i n g 77 F i g u r e 35. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of d e f e c t i v e specimens cut immediately a f t e r d r y i n g and c o n d i t i o n i n g 78 F i g u r e 36. F i n a l core and s h e l l moisture contents of no n - d e f e c t i v e specimens cut immediately a f t e r d r y i n g and c o n d i t i o n i n g 81 F i g u r e 37. F i n a l core and s h e l l moisture contents of d e f e c t i v e specimens cut immediately a f t e r d r y i n g and c o n d i t i o n i n g 82 F i g u r e 38. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of n o n - d e f e c t i v e specimens cut one week a f t e r d r y i n g and c o n d i t i o n i n g 83 F i g u r e 39. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of d e f e c t i v e specimens cut one week a f t e r d r y i n g and c o n d i t i o n i n g 84 F i g u r e 40. F i n a l core and s h e l l moisture contents of no n - d e f e c t i v e specimens cut one week a f t e r d r y i n g and c o n d i t i o n i n g 85 F i g u r e 41. F i n a l core and s h e l l moisture contents of d e f e c t i v e specimens cut one week a f t e r d r y i n g and c o n d i t i o n i n g 86 F i g u r e 42. Examples of d e f e c t i v e and n o n - d e f e c t i v e specimens of "4x4" PCH lumber 89 F i g u r e A - l . D e f e c t i v e and n o n - d e f e c t i v e specimens of "2x4" PCH.lumber 104 F i g u r e A-2. D e f e c t i v e and n o n - d e f e c t i v e specimens of "4x4 , r PCH lumber I l l v i i L I S T OF TABLES Table 1. K i l n schedule of the "2x4" specimens 24 Table 2. K i l n schedule of the "4x4" specimens 30 Table 3. I n i t i a l moisture content and green s p e c i f i c g r a v i t y of "2x4" PCH lumber 34 Table 4. K i l n - d r y i n g time of "2x4" PCH specimens 38 Table 5. Average moisture contents i n a l l 4 loads of "2x4" PCH specimens 38 Table 6. Dr y i n g r a t e s of "2x4" PCH specimens 47 Table 7. Number of "2x4" PCH specimens w i t h i n t e r n a l checking 4 8 Table 8. Largest i n t e r n a l check s i z e f o r "2x4" PCH specimens 4 8 Table 9. Test of mean valu e s f o r "2x4" PCH lumber 51 Table 10. I n i t i a l moisture content and green s p e c i f i c g r a v i t y of "4x4" PCH lumber 53 Table 11. Average moisture contents i n a l l 4 loads of "4x4" PCH specimens 55 Table 12. K i l n - d r y i n g time of "4x4" PCH specimens 58 Table 13. D r y i n g r a t e s of "4x4" PCH specimens 58 Table 14. Number of "4x4" PCH specimens w i t h i n t e r n a l checking 68 Table 15. Lar g e s t i n t e r n a l check s i z e f o r "4x4" PCH specimens 68 Table 16. Test of mean values f o r "4x4" PCH lumber 71 Table 17. F i n a l moisture contents of "4x4" PCH specimens w i t h i n t e r n a l c hecking 75 Table 18. Regression l i n e s 79 v i i i Table 19. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of "4x4" PCH specimens 87 Table A - l . Targeted and f i n a l weights i n a l l 8 loads of PCH specimens 100 Table A-2. Observed and expected f r e q u e n c i e s of "2x4" PCH specimens one week a f t e r d r y i n g 101 Table A-3. Observed and expected f r e q u e n c i e s of "4x4" PCH specimens one week a f t e r d r y i n g 103 Table A-4 . C r i t i c a l and c a l c u l a t e d " t " v a l u e s 106 Table A-5. Average i n i t i a l moisture contents i n a l l 4 loads of "4x4" PCH specimens 108 i x ACKNOWLEDGEMENTS The author would l i k e t o express h i s g r a t i t u d e t o F o r i n t e k Canada Corp. f o r t h e i r f i n a n c i a l support of h i s Master of F o r e s t r y (Wood Science) s t u d i e s . The use of t h e i r r e s e a r c h f a c i l i t i e s throughout t h i s study i s a l s o g r e a t l y a p p r e c i a t e d . F i n a l l y , the author would l i k e t o thank a l l those people who a s s i s t e d w i t h h i s study. In p a r t i c u l a r , a s s i s t a n c e by h i s a d v i s o r , Dr. S. Avramid i s , U.B.C. F a c u l t y of F o r e s t r y , r e s e a r c h s c i e n t i s t s Drs. J.F.G. Mackay and L.C. O l i v e i r a and t e c h n o l o g i s t s messrs S. M c l n t y r e and D.M. Wright, F o r i n t e k , i s a p p r e c i a t e d . x ABBREVIATIONS USED CD : c o n v e n t i o n a l d r y i n g CS : c o n d i t i o n i n g sample D : d i s c a r d DB : dry - b u l b (temperature) e : expected frequency EMC : e q u i l i b r i u m moisture content FCMC : f i n a l core moisture content FCSMCD : f i n a l c o r e - s h e l l moisture content d i f f e r e n c e FMC : f i n a l moisture content FSMC : f i n a l s h e l l moisture content FW : f i n a l weight GW : green weight HTD : high-temperature d r y i n g IMC . : i n i t i a l moisture content KS : k i l n specimen MC : moisture content MCS : moisture content s e c t i o n o : observed frequency NO : number ODW : oven-dry weight p : p r o p o r t i o n PCH : P a c i f i c Coast hemlock PVA : p o l y v i n y l a c e t a t e x i R2 : c o e f f i c i e n t of d e t e r m i n a t i o n s 2 : pooled estimate u : average WB : wet-bulb (temperature) X 2 : c h i - s q u a r e "2x4" : 2 by 4 inches "4x4" : 4 by 4 inches x i i 1. INTRODUCTION In 1984, F o r i n t e k ' s Western Laboratory c a r r i e d out e x p l o r a t o r y t e s t s t o i n v e s t i g a t e t o what extent temperature c o u l d be i n c r e a s e d i n the d r y i n g of B r i t i s h Columbia framing lumber (28) . Two inches t h i c k by 4 inches wide by 3 f e e t l o n g (51 mm by 102 mm by 0.91 m) specimens of P a c i f i c Coast hemlock (PCH) lumber were high-temperature d r i e d at f o u r d i f f e r e n t l e v e l s of a i r temperature, 225, 250, 275 and 300°F (107.2, 121.1, 135.0 and 148.9°C) . The r e s u l t s i n d i c a t e d t h a t PCH can stand h i g h d r y i n g temperatures w i t h minimal degrade i n terms of su r f a c e checks, end s p l i t s and warp. However, v a r y i n g amounts of i n t e r n a l c hecking were found, p a r t i c u l a r l y i n the specimens d r i e d at the two hi g h e s t temperatures. Temperatures of above 212°F (100°C) have been used f o r a long time i n the d r y i n g of t e x t i l e s and paper. Since the t e x t u r e of these m a t e r i a l s i s o f t e n very l o o s e and only t h i n l a y e r s are d r i e d at one time, the moisture d i s t r i b u t i o n i n s i d e the m a t e r i a l i s not c r i t i c a l . The take-up of the evaporated or b o i l e d - o f f moisture at the s u r f a c e of the m a t e r i a l i s the r e a l concern. On the other hand, i n high-temperature d r y i n g (HTD) of lumber, not on l y has the water t o be evaporated as q u i c k l y as p o s s i b l e , but the d i s t r i b u t i o n of moisture content (MC) w i t h i n each board i s very c r i t i c a l . Indeed, lumber has t o be d r i e d as u n i f o r m l y as p o s s i b l e over the e n t i r e c r o s s - s e c t i o n i n 1 order t o minimize i n t e r n a l s t r e s s e s which can e v e n t u a l l y r e s u l t i n d r y i n g d e f e c t s . When moisture i s d i f f u s i n g through the board d u r i n g d r y i n g , moisture g r a d i e n t s are set up between the s h e l l and the core i n a way t h a t the MC of the former i s always lower than t h a t of the l a t t e r . Since the moisture d i f f u s i o n through these two d i s t i n c t areas does not occur at the same r a t e , d i s s i m i l a r d i m e n s i o n a l changes are i n e v i t a b l e . These changes i n two bodies which are at t a c h e d t o each other, are the reason why i n t e r n a l s t r e s s e s develop d u r i n g lumber d r y i n g . The p r o b a b i l i t y of degrade o c c u r r i n g as a r e s u l t of d r y i n g s t r e s s e s i s i n c r e a s e d when the d r y i n g c o n d i t i o n s are made so severe as t o g i v e very steep moisture g r a d i e n t s . Past r e s e a r c h has shown t h a t d r y i n g at h i g h temperatures, low r e l a t i v e h u m i d i t i e s , or a combination of both, causes e x c e s s i v e l y steep moisture g r a d i e n t s i n a number of wood s p e c i e s (5,30). I t i s known t h a t one of the major problems i n d r y i n g PCH lumber i s the l a r g e v a r i a t i o n i n MC between and w i t h i n the boards (21,22, 31, 39) . This problem has been d i s c u s s e d by K o z l i k (19) and i s a t t r i b u t e d t o heartwood t h a t o f t e n c o n t a i n s s i n k e r heartwood (wetwood) which reaches the d e s i r e d f i n a l moisture content (FMC) two t o f i v e times more s l o w l y than normal heartwood. D r y i n g lumber which c o n t a i n s s i n k e r heartwood may r e s u l t i n steep moisture g r a d i e n t s r e s p o n s i b l e f o r i n t e r n a l s t r e s s e s and e x c e s s i v e degrade. 2 One cannot expect HTD t o r e s u l t i n very s h o r t d r y i n g c y c l e s without any impact on q u a l i t y . Since the degrade l o s s e s can o f f s e t time savings when PCH i s high-temperature d r i e d , the lumber i s c u r r e n t l y d r i e d under lower temperatures. However, i f one can minimize degrade l o s s e s , i . e . dry PCH lumber at hig h temperatures without steep moisture g r a d i e n t s r e s p o n s i b l e f o r h i g h i n t e r n a l s t r e s s e s , i t i s l i k e l y t h a t a change t o HTD w i l l be made. The purpose of t h i s study was t o t e s t the hy p o t h e s i s t h a t immediate steam c o n d i t i o n i n g a f t e r HTD c o u l d minimize i n t e r n a l c h e c k i n g i n PCH lumber. 3 2. LITERATURE REVIEW 2.1 H i g h - t e m p e r a t u r e d r y i n g o f P a c i f i c C o a s t hemlock Western hemlock (Tsuga h e t e r o p h v l l a (Raf.) Sarg.) and a m a b i l i s f i r (Abies a m a b i l i s (Dougl.) Forbes) are two important lumber s p e c i e s h a r v e s t e d on the coast and the i n t e r i o r wet b e l t s of B r i t i s h Columbia. These two softwood s p e c i e s grow t o g e t h e r and are commercially named P a c i f i c Coast hemlock (PCH) or hem-f i r . Not a l l s i z e s and t h i c k n e s s e s of PCH lumber manufactured i n B r i t i s h Columbia are k i l n - d r i e d . One reason i s t h a t s h i p p i n g from the c o a s t a l r e g i o n i s based on volume r a t h e r than on weight (28) . One more reason why lumber i s shipped green i s a t t r i b u t e d t o the l a c k of k i l n schedules t h a t w i l l e f f e c t i v e l y dry the lumber i n a sho r t p e r i o d of time and w i t h minimum degrade (1). The major commercial system used t o dry PCH lumber i s c o n v e n t i o n a l k i l n - d r y i n g . C o n v e n t i o n a l k i l n - d r y i n g systems use d r y i n g temperatures up to 212°F (100°C) although they are u s u a l l y i n the range of 100 t o 190°F (37.8 t o 87.8°C). These systems i n c l u d e steam-heated dry k i l n s and e l e c t r i c a l d e h u m i d i f i c a t i o n d r y e r s . In both systems, lumber i s d r i e d i n a c l o s e d chamber i n which temperature, r e l a t i v e h umidity and v e l o c i t y of the a i r can be c o n t r o l l e d . Such c o n v e n t i o n a l systems p r o v i d e good d r y i n g q u a l i t y i n a r e l a t i v e l y s h o r t time (44). One d r y i n g system c u r r e n t l y under i n v e s t i g a t i o n , t h a t c o u l d 4 a c c e l e r a t e the d r y i n g time of PCH lumber, i s high-temperature k i l n - d r y i n g . As i n c o n v e n t i a l k i l n - d r y i n g systems, lumber i s d r i e d i n a k i l n i n which temperature, r e l a t i v e h u m i d ity and v e l o c i t y of the a i r are c o n t r o l l e d , but d r y i n g temperatures over 212°F (100°C), up t o about 240°F (115.6°C), are used (44). HTD i s e c o n o m i c a l l y a t t r a c t i v e because d r y i n g i s extremely f a s t . Therefore, a m i l l can process i t s i n v e n t o r y u s i n g l e s s k i l n c a p a c i t y compared t o t h a t r e q u i r e d i n c o n v e n t i o n a l d r y i n g (CD). A m i l l can make some s u b s t a n t i a l energy savings because the t o t a l d r y i n g energy requirements per u n i t of lumber decrease as temperatures i n c r e a s e (28,44). There are at l e a s t two reasons t h a t may e x p l a i n why HTD i s extremely f a s t . When wood i s exposed t o an atmosphere i n which the amount of water vapour i s l e s s than w i t h i n the wood i t s e l f , i t l o s e s moisture. The r a t e at which t h i s moisture d e s o r p t i o n takes p l a c e , depends on the r e l a t i v e h umidity i n s i d e the k i l n . The lower the r e l a t i v e humidity, the f a s t e r i s the d r y i n g . A low r e l a t i v e humidity i n c r e a s e s the c a p i l l a r y f low of moisture from the wood and s t i m u l a t e s d i f f u s i o n of water by l o w e r i n g the MC at the s u r f a c e (33) . Besides low r e l a t i v e h u m i d i t i e s , HTD i s a l s o extremely f a s t because of h i g h a i r temperatures (above the b o i l i n g p o i n t of water) . As soon as the temperature i n s i d e the wood reaches 212°F (100°C) , water t u r n s i n t o steam c a u s i n g a pre s s u r e i n excess of t h a t i n the k i l n . T h i s p r e s s u r e d i f f e r e n t i a l a c c e l e r a t e s the r a t e at which water 5 evaporates out of the wood (40) . HTD was i n v e s t i g a t e d f o r the f i r s t time i n Canada about 4 8 years ago. P r e l i m i n a r y i n v e s t i g a t i o n s were i n i t i a t e d at the Canadian F o r e s t Products Laboratory i n Ottawa on e a s t e r n s p e c i e s . Western s p e c i e s i n c l u d i n g D o u g l a s - f i r , western hemlock, and western red cedar were a l s o i n v e s t i g a t e d but t o a l e s s e r e x t e n t . L a d e l l (24) r e p o r t e d t h a t , i n g e n e r a l , softwood lumber can be d r i e d at hig h temperatures i n a remarkably short time and w i t h l i t t l e degrade. Very l i t t l e end or s u r f a c e c h e c k i n g was observed i n hemlock and D o u g l a s - f i r . In view of the l a r g e number of s p e c i e s and s i z e s t h a t needed t o be high-temperature t e s t e d i n Canada, i t was decided two years l a t e r t o extend HTD on the western c o a s t . In 1954, the Vancouver F o r e s t Products Laboratory began i n v e s t i g a t i o n s i n t o HTD of 1 i n c h t h i c k (25 mm) D o u g l a s - f i r and western hemlock (12). Only s l i g h t and medium checking o c c u r r e d i n some of the f a s t d r i e d lumber when the l o a d was removed from the k i l n at low temperatures. However, severe face checking was found when the l o a d was removed at e l e v a t e d temperatures. Up t o 1957, t e s t s were e s s e n t i a l l y made on o n l y 1 i n c h t h i c k (25 mm) m a t e r i a l . HTD i n v e s t i g a t i o n s were next expanded to t h i c k e r m a t e r i a l . Schedules were developed f o r 7/4 inches t h i c k (44 mm) western hemlock lumber i n 4, 6, and 8 inches (102, 152, and 203 mm) widths (22) . T o t a l k i l n time was reduced up to 19% i n d r y i n g 2 by 8 inches lumber, from 19 t o 37% f o r 2 by 6 6 inches lumber, from 14 t o 39% f o r 2 by 4 inches lumber when compared t o c o n v e n t i o n a l schedules. Degrade was not i n c r e a s e d and, i n g e n e r a l , checking was s i m i l a r i n most i n s t a n c e s when comparing the c o n v e n t i o n a l t o the high-temperature schedules. In a d i f f e r e n t study (39), two types of western hemlock and balsam f i r lumber, common and c l e a r , were high-temperature d r i e d and compared w i t h commercial d r y i n g u s i n g c o n v e n t i o n a l temperatures. The lumber, 7/4 inches t h i c k (44 mm) by 4 t o 12 inches wide (102 t o 305 mm) i n len g t h s of 14 t o 22 f e e t (4.27 to 6.71 m), was d r i e d i n 15% l e s s time u s i n g HTD than the us u a l commercial p r a c t i c e . The l o s s i n value due t o degrade i n the common dimension was comparable f o r both types of d r y i n g . In the c l e a r grades the l o s s e s i n value were about 9% hi g h e r f o r HTD than f o r CD. I n t e n s i v e q u a l i t y i n v e s t i g a t i o n s were then c a r r i e d out when d i f f e r e n t B r i t i s h Columbia softwood s p e c i e s i n c l u d i n g Douglas-f i r , western hemlock and western red cedar were high-temperature d r i e d (36,37,38). R e s u l t s i n d i c a t e d t h a t the most s e r i o u s d e f e c t a s s o c i a t e d w i t h HTD was i n t e r n a l c h ecking. I t was a l s o found t h a t the degrade can be minimized u s i n g a two-stage schedule. CD was a p p l i e d u n t i l the lumber was d r i e d t o an average MC very c l o s e t o the f i b e r s a t u r a t i o n p o i n t and then the s w i t c h was made t o HTD. Some darkening of wood was observed, but a d r y i n g time r e d u c t i o n of 15 t o 30% over c o n v e n t i o n a l schedule times was achieved. 7 The e f f e c t of HTD on q u a l i t y and p r o p e r t i e s of western hemlock was l a t e r i n v e s t i g a t e d i n more d e t a i l . The d i f f e r e n c e i n MC between the d r i e s t and w e t t e s t boards of a d r i e d l o a d , i . e . the FMC range, was found t o be s m a l l e r when h i g h temperatures were used r a t h e r than c o n v e n t i o n a l ones. I n c r e a s i n g temperature a l s o had the g r e a t e s t i n f l u e n c e i n l o w e r i n g the wood e q u i l i b r u m moisture content (EMC), i . e . the MC at which wood does not g a i n or l o s e m o i s t u r e . The h i g h e r the temperature, or the lower the r e l a t i v e humidity, the lower was the EMC (9,20,21,37,38). K i l n time was reduced by one-half or more compared to c o n v e n t i o n a l d r y i n g f o r f o u r d i f f e r e n t types of boards: sapwood, normal heartwood, young-growth s i n k e r heartwood and old-growth s i n k e r heartwood (23) . With e i t h e r schedule, normal heartwood d r i e d t w i c e as f a s t as the t h r e e other wood types t o 30% MC, and 25% f a s t e r t o 15% MC. Old-growth heartwood had the l o n g e s t k i l n time, and some boards c o n t a i n e d h i g h MC areas. HTD i n t e n s i f i e d i n t e r n a l c hecking and c o l l a p s e i n sapwood and s i n k e r heartwood. F i n a l l y , experiments were c a r r i e d out t o i n v e s t i g a t e t o what extent d r y i n g of PCH c o u l d be a c c e l e r a t e d without compromising the q u a l i t y of the f i n a l product. Two by 4 inches (51 by 102 mm) PCH lumber was d r i e d at four d i f f e r e n t l e v e l s of a i r temperature, 225, 250, 275 and 300°F (107.2, 121.1, 135.0 and 148.9°C), and-three l e v e l s of a i r v e l o c i t y , 300, 600 and 900 f t . / m i n . (1.5, 3.0 and 4.6 m/s) . R e s u l t s i n d i c a t e d t h a t the 8 l o s s of moisture per u n i t of time, i . e . the d r y i n g r a t e , was s t r o n g l y a f f e c t e d by both temperature and a i r v e l o c i t y . The hi g h e r the a i r temperature, or the hig h e r the air . v e l o c i t y , the hi g h e r was the d r y i n g r a t e . V i s i b l e degrade was minimal i n terms of s u r f a c e checks, end s p l i t s and warp. However, v a r y i n g amounts of i n t e r n a l checking were found, p a r t i c u l a r l y i n the boards d r i e d at the two h i g h e s t temperatures (28). 2.2 I n t e r n a l c h e c k i n g A c c o r d i n g t o Bramhall and Wellwood (4), s t u d i e s of d r y i n g degrade made i n B r i t i s h Columbia have shown t h a t the most s e r i o u s q u a l i t y l o s s r e s u l t s from checking and s p l i t t i n g of wood. Furthermore, i t i s d i f f i c u l t t o a c c e l e r a t e the d r y i n g process without c a u s i n g more lumber t o check (see High-temperature d r y i n g of P a c i f i c Coast hemlock). In view of the above, i t was the i n t e n t i o n of the present review t o cover lumber checking w i t h more emphasis on the e f f e c t of high temperatures on i t s development. When wood i s d r i e d , the s u r f a c e f i b e r s immediately reach a MC l e v e l c o rresponding t o the ambient c o n d i t i o n s . This MC i s always lower than t h a t of the f i b e r s a t u r a t i o n p o i n t . These f i b e r s are r e s t r a i n e d from s h r i n k i n g f u l l y , because the adjacent l a y e r a s h o r t d i s t a n c e i n t o the wood i s s t i l l above the s a t u r a t i o n p o i n t and does not s h r i n k . In consequence, the wood 9 i n the s u r f a c e l a y e r i s s t r e t c h e d , i . e . put under t e n s i o n , w h i l e t h a t of the i n n e r l a y e r s i s compressed. I f the moisture g r a d i e n t set up between the s u r f a c e and i n n e r l a y e r s i s steep, i t i s p o s s i b l e t h a t the t e n s i l e s t r e s s may exceed the s t r e n g t h of the wood across the g r a i n which i n t h i s case w i l l be even lower, because of the g r e a t e r p l a s t i c i t y a s s o c i a t e d w i t h HTD. The h i g h e r the d r y i n g temperatures, the h i g h e r the p l a s t i c i t y (see C o n d i t i o n i n g ) and lower the s t r e n g t h and e l a s t i c p r o p e r t i e s of wood are (11,18). I f t h i s occurs, s u r f a c e checking w i l l r e s u l t . I f the moisture g r a d i e n t i s only moderately steep, the t e n s i l e s t r e s s i n the s u r f a c e l a y e r may exceed the e l a s t i c l i m i t of the wood, de v e l o p i n g a permanent s t r e s s r a t h e r than s u r f a c e c h e c k i n g . This permanent s t r e s s i s known as t e n s i o n set (5,8,30) . As the next l a y e r t o the s u r f a c e d r i e s , i t w i l l tend to s h r i n k and hence be converted from a zone under compression to one under t e n s i o n . Tension set can be induced i n each s u c c e s i v e l a y e r from the s h e l l t o the core of the wood as i t s h i f t s from b e i n g under compression t o be i n g under t e n s i o n . Once again, i f the moisture g r a d i e n t t h a t i s set up through the board i s q u i t e steep, i t i s p o s s i b l e t h a t the t e n s i l e s t r e s s may exceed the s t r e n g t h p r o p e r t i e s of t h i s zone. The wood w i l l then f a i l under i n t e r n a l t e n s i o n , t h a t i s , develop i n t e r n a l checking (5) . F i g u r e 1 shows a t y p i c a l sequence of t r a n s v e r s e r e s i d u a l s t r e s s e s t h a t developed d u r i n g CD of 2 inches t h i c k red oak 10 F i g u r e 1. T r a n s v e r s e r e s i d u a l s t r e s s e s i n l u m b e r a t v a r i o u s s t a g e s o f c o n v e n t i o n a l d r y i n g ( a f t e r M c M i l l e n 1958) CO to ID £C r— CO CO CO UJ a: o. 2 o o 2 g CO z DAYS DRYING 18 28 36 50 11 heartwood lumber (29). Since the MC g r a d i e n t i s steepest d u r i n g the e a r l y stages of d r y i n g , the g r e a t e s t l e v e l of s t r e s s i n t e n s i o n i s a l s o p r esent then (34). Therefore, i n t e r n a l c hecking can u s u a l l y be avoided by e n s u r i n g t h a t severe s t r e s s e s do not develop when the MC of the s h e l l and core of the d r y i n g board i s above the f i b e r s a t u r a t i o n p o i n t . E x c e s s i v e l y h i g h a i r temperatures are avoided u n t i l a l l the f r e e water has been evaporated from the e n t i r e board. In t h i s way lumber can be k i l n - d r i e d w i t h a combination of a c o n v e n t i o n a l temperature schedule f o l l o w e d by a h i g h -temperature schedule when the MC of the d r y i n g board i s l e s s than t h a t of the f i b e r s a t u r a t i o n p o i n t . Past r e s e a r c h has shown t h a t l e s s checking developed u s i n g such a combination (2,3,37). • However, t h i s i s not always the case. Past r e s e a r c h has a l s o shown t h a t , when the core of the board has developed a maximum t e n s i l e s t r e s s and the d r y i n g temperature i s s i g n i f i c a n t l y i n c r e a s e d , the s t r e n g t h p r o p e r t i e s of t h i s zone w i l l decrease due t o the p l a s t i c i z i n g e f f e c t of the heat. The r e s u l t of t h a t w i l l be f a i l u r e under i n t e r n a l t e n s i o n , t h a t i s , i n t e r n a l c h e c k i ng (41,42). I f high-moisture-content pockets are present i n the core of the board, i n t e r n a l c hecking w i l l be accentuated. Mackay (26) found out t h a t c o l l a p s e develops i n the form of severe shrinkage when these wet pockets dry out. This c o l l a p s e r e s u l t s i n a weakened board more l i k e l y t o p u l l 12 apart under t e n s i l e s t r e s s e s a f t e r s t r e s s r e v e r s a l (29). F i n a l l y , lumber having h i g h MC may be i n c o m p l e t e l y d r i e d l e a v i n g the core wet. As i n lumber w i t h wet pockets, such lumber i s more l i k e l y t o develop i n t e r n a l checking (10,25,27). Water i n wood moves 12 t o 15 times f a s t e r along the g r a i n than i t does across i t (33). Therefore, lumber l o s e s moisture f a s t e r l o n g i t u d i n a l l y than across the g r a i n . Unless a slower and more uniform e v a p o r a t i o n of moisture i s achieved, l o n g i t u d i n a l moisture g r a d i e n t s w i l l develop w i t h i n the d r y i n g board. Accompanying these l o n g i t u d i n a l moisture g r a d i e n t s are l o n g i t u d i n a l d r y i n g s t r e s s e s r e s p o n s i b l e f o r end checking (45). I f the moisture g r a d i e n t i s only moderately steep, the end checks are u s u a l l y s m a l l and do not extend very f a r back i n t o the wood. However, i f the moisture g r a d i e n t i s steep, l a r g e r end checks develop, and as the i n t e r n a l l a y e r s are converted from a zone under compression t o one under t e n s i o n , these end checks may go a l l the way across the i n t e r i o r l a y e r s of the d r y i n g board. This form of i n t e r n a l checking can extend from one end of the board t o the other, depending upon the l o n g i t u d i n a l d r y i n g s t r e s s e s (29) . One way t o reduce or e l i m i n a t e these l o n g i t u d i n a l moisture g r a d i e n t s and d r y i n g s t r e s s e s i s t o p a i n t the ends of the boards w i t h m o i s t u r e -r e s i s t a n t c o a t i n g s . Such end c o a t i n g s , t o be e f f e c t i v e , must be a p p l i e d b e f o r e the wood has d r i e d a p p r e c i a b l y and end checks have formed (33). 13 \ \ 2.3 C o n d i t i o n i n g K i l n schedules u s i n g c o n d i t i o n i n g treatments were recently-developed at F o r i n t e k Canada Corp. i n Vancouver t o k i l n - d r y 4 inches t h i c k by 4 inches wide (102 by 102 mm) s u r f a c e d PCH lumber i n a c c e p t a b l y s h o r t p e r i o d s of time and w i t h l i t t l e or no degrade (1) . The lumber was c o n d i t i o n e d f o r 24 hours at 150°F (65.6°C) dry-bulb (DB) and 14 6°F (63.3°C) wet-bulb (WB) temperatures, t h a t r e s u l t e d i n a r e l a t i v e humidity of approximately 90%. This long humidity treatment r e s u l t e d i n s t r e s s r e l i e f , moisture r e d i s t r i b u t i o n and disappearance of many of the end and s u r f a c e checks t h a t were present b e f o r e t h a t s t e p . In view of the above, the procedure proposed i n t h i s study t o d i m i n i s h the occurrence of i n t e r n a l checking was s t r e s s r e l i e f immediately a f t e r d r y i n g . The r e l i e f of t e n s i o n s e t s and i n t e r n a l s t r e s s e s r e s p o n s i b l e f o r i n t e r n a l checking i s accomplished e s s e n t i a l l y by the a d d i t i o n of moisture and heat t o the outer l a y e r s of the lumber at the end of the d r y i n g schedule. I f enough water i s added t o the s u r f a c e and i t s adjacent l a y e r , compressive s e t s are induced which are oppo s i t e t o , and tend t o r e l i e v e , the t e n s i o n s e t s which developed e a r l i e r d u r i n g d r y i n g . I n t e r n a l s t r e s s e s a l l the way across the cr o s s s e c t i o n can be r e l i e v e d t h i s way when h i g h temperatures are ma i n t a i n e d f o r a long enough p e r i o d of time (29) . 14 A c c o r d i n g t o Kininmonth and W i l l i a m s (17), c o n d i t i o n i n g should be c a r r i e d out immediately a f t e r d r y i n g . I f not, one or two end checks c o u l d extend c o n s i d e r a b l y d u r i n g c o o l i n g and i n subsequent st o r a g e , t o r e s u l t i n e x c e s s i v e i n t e r n a l checking (see I n t e r n a l checking) . One of the best methods t o achieve good c o n d i t i o n i n g i n the s h o r t e s t l e n g t h of time i s through the use of steam s u p p l i e d by low pr e s s u r e b o i l e r s . The q u a l i t y of the steam i s always c l o s e to. s a t u r a t i o n so t h a t h i g h e r r e l a t i v e h u m i d i t i e s and EMCs can be achieved at h i g h e r temperatures. High p r e s s u r e steam on the other hand i s g e n e r a l l y much d r i e r . I t c o n t a i n s more heat and l e s s moisture per pound of steam produced. One e f f e c t i v e method t o achieve s a t u r a t e d c o n d i t i o n s at h i g h temperatures d u r i n g c o n d i t i o n i n g i s t o i n j e c t water i n t o the steam spray l i n e . M i x i n g of water w i t h h i g h p r e s s u r e steam can reduce c o n d i t i o n i n g time by one-half of the time needed f o r c o n d i t i o n i n g of hot lumber. Devices i n s t a l l e d i n the spray l i n e system f o r water i n j e c t i o n e l i m i n a t e c o o l i n g time, e f f e c t i v e l y r a i s e the r e l a t i v e humidity and save steam (4 6). Both methods were t e s t e d by Kininmonth and W i l l i a m s on 1 and 2 inches t h i c k (25 and 51 mm) r a d i a t a pine lumber and gave e x c e l l e n t r e s u l t s (16,17). When c o n d i t i o n i n g was c a r r i e d out immediately a f t e r d r y i n g (4 hours at 100°C) u s i n g low p r e s s u r e , s a t u r a t e d steam, severe i n t e r n a l checking extending from the ends of lumber and from the d i s t o r d e d g r a i n around the knots, was l i m i t e d t o s l i g h t c h e c k i n g near the ends (40 t o 80 mm) and around the knots. 15 S i m i l a r r e s u l t s were a l s o o b t a i n e d w i t h h i g h p r e s s u r e steam (by c o o l i n g the l o a d t o about 80°C, by i n j e c t i n g water i n t o the spray l i n e and then steaming at 85 t o 90°C) . However, t h i s second method i n c r e a s e d the maintenance c o s t s (due t o the c o r r o s i v e a c t i o n of the water d r o p l e t s ) and the d r y i n g time. S t r e s s r e l i e f i s a l s o f a s t e r and more e f f e c t i v e i f c a r r i e d out at h i g h temperatures. The p o s s i b i l i t y of s t r e s s r e l i e f by thermal expansion should not be overlooked when wood i s c o n d i t i o n e d u s i n g h i g h a i r temperatures. Any expansion of t h i s nature, however, should not be of s u f f i c i e n t magnitude t o cause the wood t o expand beyond i t s e l a s t i c l i m i t (7). S t r e s s e s t h a t would a r i s e from thermal expansion caused by h i g h e r c o n d i t i o n i n g temperatures would be minor compared t o those developed e a r l i e r from moisture changes. Another source t h a t c o u l d cause s t r e s s r e l i e f , i s the p l a s t i c i z i n g e f f e c t of temperature on wood. H i l l i s (13) suggests t h a t h i g h temperatures, when maintained f o r a s u f f i c i e n t time, can cause the l i g n i n s i n the middle l a m e l l a and the l i g n i n s and h e m i c e l l u l o s e s around the m i c r o f i b r i l s t o s o f t e n r a t h e r than f r a c t u r e under t e n s i o n s e t s and i n t e r n a l s t r e s s e s . In the presence of moisture, s o f t e n i n g of wood accentuates (6) so t h a t i t s mechanical b e h a v i o r can be changed from g l a s s - l i k e to s e m i - p l a s t i c . The a d d i t i o n of moisture to the s u r f a c e f i b e r s at the end of d r y i n g causes them t o s w e l l . When the wood i s more p l a s t i c i n c h a r a c t e r , the r a t e and the amount of s w e l l i n g i n c r e a s e r e s u l t i n g i n a f a s t e r and b e t t e r 16 s t r e s s r e l i e f . 3. MATERIALS AND METHODS 3.1 Phase I One shipment of n i n e t y , 14 f e e t l o n g (4.27 m) , p i e c e s of green roughsawn PCH lumber was o b t a i n e d from a l o c a l s a w m i l l . I m p e r i a l nominal and a c t u a l m e t r i c t h i c k n e s s and width of the p i e c e s were 2 by 4 inches ("2x4") and 51 by 102 m i l l i m e t r e s , r e s p e c t i v e l y . The lumber was commercially produced from logs h a r v e s t e d on the Queen C h a r l o t t e I s l a n d s i n an area c l o s e t o S a n d s p i t . There was no p a r t i c u l a r sawing p a t t e r n so t h a t the annual r i n g s d i d not have a s p e c i f i c d i r e c t i o n and t h e r e was no s e p a r a t i o n between heartwood and sapwood. Each p i e c e of lumber was randomly assigned a number ranging from 1 to 90. The p i e c e s were sawn as f o l l o w s , t o p r o v i d e four k i l n loads of n i n e t y , 36 inches long (91.4 cm), k i l n specimens (KSs) and two s e t s of n i n e t y , 1 i n c h long (2.5 cm), moisture content s e c t i o n s (MCSs) . F i r s t , one MCS was sawn 10 inches (25.4 cm) away from one end of each p i e c e of lumber, t o make up one s e t of MCSs. The MCSs were put i n a p l a s t i c bag i n order t o keep t h e i r MC unchanged. Four KSs were sawn next f o r k i l n l oads #1, #2, #3 and #4, r e s p e c t i v e l y . F i n a l l y , the second set of MCSs was o b t a i n e d . F i g u r e 2 i l l u s t r a t e s t h i s sawing p a t t e r n . Every p i e c e of lumber was sawn i n such a way t h a t i t s f o u r KSs were l a b e l l e d on the same top f a c e . XX-Y was the code used 18 F i g u r e 2. S a wing p a t t e r n o f "2x4" PCH lumber D MCS KS KS . KS KS MCS D K S : K ILN S P E C I M E N (3 feet) M C S : M O I S T U R E C O N T E N T S E C T I O N (1 inch) D : D I S C A R D (10 inches) 19 t o l a b e l each KS where XX and Y were the i d e n t i f i c a t i o n numbers of the p i e c e of lumber i t was sawn from and the run number t h a t the specimen was used i n , r e s p e c t i v e l y . The l a b e l given t o the KS sawn from p i e c e of lumber #12 i n l o a d #2, f o r i n s t a n c e , was 12-2. A MCS was l a b e l l e d XX-R or XX-L, R and L, s t a n d i n g f o r r i g h t or l e f t , i n d i c a t i n g from which end i t was sawn. Immediately a f t e r sawing, the KSs were coated w i t h a heavy coat of p o l y v i n y l a c e t a t e (PVA) at both ends t o minimize end-d r y i n g b e f o r e and d u r i n g the e x p e r i m e n t a l k i l n - d r y i n g . Once s e a l e d , the lumber was s t o r e d o u t s i d e under p l a s t i c wrap. Water was sprayed on the p l a s t i c t o reduce any s i g n i f i c a n t changes i n the MC of the specimens. Once the lumber was s e a l e d and s t o r e d , the MCSs were weighed (± 0.1 g) u s i n g a d i g i t a l b alance. They were then immersed i n water to measure t h e i r green volume (± 0.1 cm3) and oven-dried at 103°C (± 2°C). Twenty-four hours l a t e r , they were weighed once more and t h e i r green MC and s p e c i f i c g r a v i t y were c a l c u l a t e d . The k i l n used i n t h i s experiment was a 3 by 3 by 3 f e e t (0.91 m) l a b o r a t o r y - s c a l e u n i t . The l o a d r e s t e d on a s c a l e so t h a t change of weight, and t h e r e f o r e MC, c o u l d be monitored over time. A i r v e l o c i t y through the l o a d was set at 750 fpm (3.8 m/s) w i t h no r e v e r s a l of flow. The aluminum s t i c k e r s were 5/4 inches wide (32 mm) by 3/4 i n c h t h i c k (19 mm) and were p l a c e d 3 f e e t a p a r t , i . e . at each end of the KSs. A p a r t i c u l a r l o a d i n g 20 p a t t e r n was used so t h a t i n a l l f o u r runs, the KSs sawn from the same o r i g i n a l p i e c e of lumber had the same k i l n l o c a t i o n . The l a b e l l e d top face of each KS a l s o faced the top of the k i l n . D r y i n g was c a r r i e d out at 300°F (148.9°C) DB and approximately 212°F (100.0°C) WB temperatures, r e s u l t i n g i n a r e l a t i v e humidity and EMC of 22% and 1.4%, r e s p e c t i v e l y (35). The k i l n was set t o t u r n i t s e l f o f f when the l o a d weight c o r r e s p o n d i n g t o an average of 12% MC, was reached (see Appendix 7.1). The c o n d i t i o n i n g p e r i o d scheduled was s t a r t e d when the a i r temperature i n the k i l n was down t o 185°F (85.0°C). Three d i f f e r e n t l e v e l s of c o n d i t i o n i n g time, 2, 4 and 6 hours, were c a r r i e d out once f o r runs #2, #3 and #4, r e s p e c t i v e l y . In a l l runs, c o n d i t i o n i n g was done at 185°F (85.0°C) DB and 180°F (82.2°C) WB temperatures, r e s u l t i n g i n a r e l a t i v e h umidity of approximately 90%. One lo a d , run #1, was k i l n - d r i e d without c o n d i t i o n i n g f o r comparison purposes. The k i l n schedule i s i l l u s t r a t e d i n F i g u r e 3 and l i s t e d i n Table 1. A f t e r e i t h e r d r y i n g (run #1) or c o n d i t i o n i n g (runs #2, #3 and #4), the specimens were l e f t i n the k i l n i n order t o c o o l down t o room temperature, i . e . 23°C. The f o r t y - f i v e specimens l a b e l l e d w i t h an odd number were then cross-sawn i n t o t h r e e , 12 inches long (30.5 cm), c o n d i t i o n i n g samples (CSs)-. A l l t h r e e CSs were immediately l a b e l l e d f o r i d e n t i f i c a t i o n purposes. F i g u r e 4 shows the sawing p a t t e r n used. The remaining f o r t y -f i v e specimens of the charge were kept at room temperature 21 F i g u r e 3. K i l n s c h e d u l e o f t h e "2x4" s p e c i m e n s 350 DRY-BULB WET-BULB 300 111 cc QC 250 HI Q. LU 200 Green MOISTURE CONTENT (% 12% 22 Figure 4. Sawing pattern of the "2x4" specimens f o r i n t e r n a l checking evaluation Table 1. K i l n schedule of the "2x4" specimens DB (°F) WB (°F) MC (%) 300 212 GREEN 185 180 12 i n s i d e the l a b o r a t o r y and cut a c c o r d i n g t o the same p a t t e r n one week l a t e r . Every CS was checked immediately a f t e r c u t t i n g t o determine the e x t e n t , i f any, of i n t e r n a l checking. The l o n g e s t and the l a r g e s t i n t e r n a l checks observed i n each d r y i n g run were recorded. The l e n g t h s and widths of the checks were measured u s i n g a d i g i t a l c a l i p e r (± 1 mm) and a width gage (± 0.1 mm), r e s p e c t i v e l y . The width gage used i s shown i n F i g u r e 5. The number of CSs w i t h one or more i n t e r n a l check (s) was a l s o recorded. Two weeks a f t e r d r y i n g , the core MC of each CS was measured u s i n g a d c - r e s i s t a n c e moisture meter. One MC measurement was f i r s t taken 4 inches (10.2 cm) away from one end, 1 i n c h deep (2.5 cm) i n t o the wood. This procedure was repeated at the other end so t h a t f o r each CS, two core MC measurements were taken as shown i n F i g u r e 6. F i n a l l y , samples w i t h i n t e r n a l and end checking were i d e n t i f i e d and recorded. 24 F i g u r e 5. W i d t h gage 25 F i g u r e 6. P o i n t s a t w h i c h t h e c o r e m o i s t u r e c o n t e n t o f e a c h c o n d i t i o n i n g sample were t a k e n 4 11 4 " 4 26 3.2 Phase I I A shipment of f o r t y - e i g h t , 13 f e e t l o n g (3.96 m) , p i e c e s of s u r f a c e d PCH lumber was obta i n e d . I m p e r i a l nominal and a c t u a l m e t r i c t h i c k n e s s and width of the p i e c e s were 4 by 4 inches ("4x4") and 105 by 105 m i l l i m e t r e s , r e s p e c t i v e l y . The lo g s o r i g i n a t e d from the Nimpkish V a l l e y on Vancouver I s l a n d . KSs were e s s e n t i a l l y c u t , k i l n - d r i e d and c o n d i t i o n e d i n the same way as i n Phase I . Only the sawing p a t t e r n and d r y i n g schedule used were d i f f e r e n t . As can be seen i n F i g u r e 7, one, 36 inches l o n g (91.4 cm), KS was f i r s t sawn from one end of each p i e c e of lumber, t o make up k i l n l o a d #1. One MCS was sawn next to make up one MC s e t . Two more KSs f o r k i l n loads #2 and #3, r e s p e c t i v e l y , one more MCS and one l a s t KS f o r k i l n l o a d #4 were f i n a l l y o b t a i n e d from each p i e c e of lumber. D r y i n g was c a r r i e d out at 275°F (135.0°C) DB and 180°F (82.2°C) WB temperatures, r e s u l t i n g i n a r e l a t i v e humidity and EMC of approximately 16% and 1.1%, r e s p e c t i v e l y (35). The k i l n schedule i s i l l u s t r a t e d i n F i g u r e 8 and l i s t e d i n Table 2. A f t e r e i t h e r d r y i n g (run #5) or c o n d i t i o n i n g (runs #6, #7 and #8) , the specimens were l e f t i n the k i l n i n order t o c o o l down to room temperature. The twenty-four specimens l a b e l l e d w i t h an odd number were then cross-sawn i n t o 13, 10 and 13 inches l o n g (33.0, 25.4 and 33.0 cm) samples. A 1 i n c h long (2.5 cm) MCS was sawn opp o s i t e t o each coated end of each 13 27 F i g u r e 7. S a wing p a t t e r n o f "4x4" PCH l u m b e r K S M C S K S K S M C S K S K S : K ILN S P E C I M E N (3 feet) M C S : M O I S T U R E C O N T E N T S E C T I O N (1 inch) 28 F i g u r e 8. K i l n s c h e d u l e o f t h e "4x4" s p e c i m e n s 350 DRY-BULB WET-BULB 300 LU DC C 250 UJ CL UJ l -200 Green 12% MOISTURE CONTENT (% 29 Table 2. K i l n schedule of the "4x4" specimens DB (°F) WB (°F) MC (%) 275 180 G R E E N 185 180 12 inches l o n g (33.0 cm) samples and l a b e l l e d on i t s top f a c e . The remaining 12 inches long (30.5 cm) samples were the CSs used f o r i n t e r n a l c h e c k i n g e v a l u a t i o n . F i g u r e 9 i l l u s t r a t e s the sawing p a t t e r n d e s c r i b e d . The MCSs were then sawn i n three equal p a r t s . The top and bottom p a r t s of each MCS were put i n the oven at 103°C (± 2°C) f o r 24 hours i n order t o e s t a b l i s h f i n a l s h e l l moisture content (FSMC) . The ce n t e r p a r t was sawn one more time i n t h r e e equal s m a l l e r p i e c e s . The c e n t e r p i e c e was oven - d r i e d i n order t o o b t a i n i t s f i n a l core moisture content (FCMC) . The two o u t s i d e p i e c e s were d i s c a r d e d (Figure 10) . The remaining twenty-four specimens l a b e l l e d w i t h an even number were kept at room temperature and cut u s i n g the same p a t t e r n one week l a t e r . In each run, every CS was checked immediately a f t e r c u t t i n g t o determine the e x t e n t , i f any, of i n t e r n a l c hecking. The l o n g e s t and the l a r g e s t i n t e r n a l checks found were recorded the same way as i n Phase I . Samples w i t h i n t e r n a l checking were 30 F i g u r e 9. Sawing p a t t e r n o f t h e "4x4" s p e c i m e n s f o r i n t e r n a l c h e c k i n g e v a l u a t i o n C S M C S . C S M C S C S 12" 1" 10" 1" 12" C S : C O N D I T I O N I N G S A M P L E M C S : M O I S T U R E C O N T E N T S E C T I O N 31 F i g u r e 10. Core and s h e l l p a r t s o f a "4x4" m o i s t u r e c o n t e n t s e c t i o n A : S H E L L PART B : C O R E PART D : D I S C A R D 32 i d e n t i f i e d and recorded. 4. RESULTS AND DISCUSSION 4.1 Phase I As can be seen i n Table 3, t h e r e was a l a r g e v a r i a t i o n i n IMC between the "2x4" p i e c e s of PCH lumber. The average IMC was 69.7%, ranging from 40.0 t o 164.5%. F i g u r e 11 shows the d i s t r i b u t i o n of IMCs and as can be seen, a g r e a t e r p o r t i o n of the lumber had IMCs ranging from 40 t o 80%. Table 3. I n i t i a l moisture content and green s p e c i f i c g r a v i t y of "2x4" PCH lumber MIN MAX AVG INITIAL MOISTURE CONTENT (%) 40.0 164 .5 69.7 GREEN SPECIFIC GRAVITY 0.303 0.553 0.397 The green s p e c i f i c g r a v i t y a l s o showed a c o n s i d e r a b l e v a r i a t i o n between the p i e c e s , ranging from 0.303 t o 0.553 (Table 3) . A g r e a t e r p a r t of the lumber had s p e c i f i c g r a v i t i e s ranging from 0.360 t o 0.420 (Figure 12). I t i s l i k e l y t h a t the p i e c e s w i t h low s p e c i f i c g r a v i t y were a m a b i l i s f i r and those w i t h h i g h s p e c i f i c g r a v i t y were western hemlock (see Phase I I ) . O v e r a l l the average green s p e c i f i c g r a v i t y was 0.397. 34 Figure 11. I n i t i a l moisture content frequency d i s t r i b u t i o n of "2x4" PCH lumber 50 20-40 40-60 60-80 80-100 100-120 120-140 140-160 160-180 INITIAL MOISTURE CONTENT (%) 35 Figure 12. Green s p e c i f i c g r a v i t y frequency d i s t r i b u t i o n of "2x4" PCH lumber .30-.33 .33-.36 .36-.39 .39-.42 .42-.45 .45-.48 .48-.51 .51-.54 .54-.57 SPECIFIC GRAVITY 36 Table 4 shows the k i l n - d r y i n g time of lumber f o r a l l d r y i n g runs. D r y i n g times from green t o the t a r g e t e d 12% MC were q u i t e c l o s e , r a n g i n g from 24.00 hours f o r run #4 t o 26.50 hours f o r run #1. C o o l i n g from 300 t o 185°F (148.9 t o 85.0°C) DB temperature p r i o r t o c o n d i t i o n i n g was done i n a r e l a t i v e l y s hort time, ra n g i n g from 45 minutes f o r run #3 t o 2.00 hours f o r run #2. In run #1, no c o n d i t i o n i n g was i n v o l v e d so t h a t lumber was k i l n - d r i e d i n only 26.50 hours. In run #4, lumber was c o n d i t i o n e d f o r 6.00 hours r a i s i n g the t o t a l k i l n - d r y i n g time t o 31.00 hours. Comparing F i g u r e s 13, 14, 15 and 16, d r y i n g r a t e s i n each run were s i m i l a r . A n o t i c e a b l e d i f f e r e n c e , however, was the hi g h e r MC ob t a i n e d i n l o a d #2 befor e c o o l i n g and c o n d i t i o n i n g . As can be seen i n Table 5, both MCs befor e c o o l i n g i n loads #3 and #4 were 12.1% compared t o 13.2% i n l o a d #2. The hi g h e r MC may e x p l a i n why run #2 had a r e l a t i v e l y l onger c o o l i n g time s i n c e the thermal c o n d u c t i v i t y of wood i n c r e a s e s w i t h i t s MC (33) . A h i g h e r MC may have i n c r e a s e d the q u a n t i t y of heat t h a t flowed through the wood when i t s s u r f a c e s were c o o l e d down. This r e l e a s e of heat may have s l i g h t l y i n c r e a s e d the a i r temperature i n the k i l n r e s u l t i n g i n a lo n g e r c o o l i n g p e r i o d . D r y i n g r a t e s of a l l runs were then p l o t t e d a g a i n s t t h e i r average MCs (Figures 17, 18, 19, and 20) i n order t o e v a l u a t e any d i f f e r e n c e s t h a t might e x i s t . The change i n the d r y i n g r a t e as d r y i n g progressed was again s i m i l a r at each run. When the 37 Table 4. K i l n - d r y i n g time of "2x4" PCH specimens RUN # KILN-DRYING TIME (hours) I DRYING I COOLING 1 CONDITIONING I TOTAL 1 1 26.50 j 26.50 2 1 25.25 1 2.00 1 2.00 I 29.25 3 1 24.50 1 0.75 1 4.25 I 29.50 4 1 24.00 1 1.00 1 6.00 I 31.00 Table 5. Average moisture contents i n a l l 4 loads of  "2x4" PCH specimens RUN # MOISTURE CONTENT (%) I BEFORE | COOLING | BEFORE | CONDITIONING | AFTER DRYING | AND CONDITIONING 1 -- 1 12.2 2 1 13 2 1 12.2 1 12.8 3 1 12 1 1 11.6 1 12.2 4 1 12 1 1 11.5 1 12.4 38 Figure 13. P l o t of average moisture content against time f o r run #1 (no conditioning) 80 60 Z LLI I-8 40 Ul DC O 20 1 , 1 , 1 , 1 , I , | , i _ 0 5 10 15 20 25 30 TIME (hours) 39 Figure 14. P l o t of average moisture content against time f o r run #2 (2 hours of conditioning) DRYING 0 5 10 15 20 25 30 TIME (hours) 40 Figure 15. P l o t of average moisture content against time f o r run #3 (4 hours of conditioning) DRYING 0 5 10 15 20 25 30 TIME (hours) 41 Figure 16. P l o t of average moisture content against time f o r run #4 (6 hours of conditioning) Figure 17. P l o t of drying rate against average moisture content f o r run #1 (no conditioning) Figure 18. P l o t of drying rate against average moisture content f o r run #2 (2 hours of conditioning) 80 60 40 20 MOISTURE CONTENT (%) 44 Figure 19. P l o t of drying rate against average moisture content f o r run #3 (4 hours of conditioning) 5 80 60 40 20 MOISTURE CONTENT (%) 45 F i g u r e 20. P l o t o f d r y i n g r a t e a g a i n s t average m o i s t u r e c o n t e n t f o r run #4 (6 hours o f c o n d i t i o n i n g ) d e s i r e d DB and WB temperatures were reached, the d r y i n g r a t e was maximum. T h e r e a f t e r , lumber MC and d r y i n g r a t e c o n s t a n t l y decreased s i m i l a r l y f o r a l l d r y i n g runs. Average d r y i n g r a t e s of a l l runs were f i n a l l y c a l c u l a t e d and, as shown i n Table 6, were r e l a t i v e l y c l o s e , ranging from 2.20% of MC per hour f o r run #1 t o 2.40% of MC per hour f o r run #4. For a l l d r y i n g runs, the h i g h e r the average d r y i n g r a t e , the s h o r t e r was the d r y i n g time from green t o the t a r g e t e d 12% MC. Table 6. Dr y i n g r a t e s of "2x4" PCH specimens RUN # DRYING RATE (% MC/hour) * MIN MAX AVG 1 + 0.15 + 4.89 +2.20 2 - 0.90 + 4.33 +2.25 3 - 1.04 + 4 .45 +2 .32 4 - 0.59 + 4.26 +2.40 * : e x c l u d i n g c o o l i n g and c o n d i t i o n i n g + : moisture l o s s : moisture g a i n Table 7 shows the number of specimens t h a t developed i n t e r n a l checking i n each d r y i n g run. When the specimens were cut immediately a f t e r d r y i n g and c o n d i t i o n i n g , no i n t e r n a l 47 Table 7. Number of "2x4" PCH specimens w i t h i n t e r n a l checking 3' SPECIMENS CUT AT 1' FROM THE END RUN # j AFTER DRYING 1 WEEK AFTER DRYING 1 LEFT RIGHT MAX. % 1 LEFT RIGHT MAX. % j j A 1 1 0 0 0 0 1 5 6 6 112 \ ] [ / \ 2 1 q ' 0 • 0 0 1 0 3 3 1 1 [ 3 1 o 0 0 0 1 1 3 3 4 1 0 0 0 0 1 1 2 2 4 LEFT, RIGHT : number of d e f e c t i v e specimens found at that end MAX. : maximum number of d e f e c t i v e specimens at one or both ends % : percentage of d e f e c t i v e specimens at one or both ends Table 8. Largest i n t e r n a l check s i z e f o r "2x4" PCH specimens RUN # 3' SPECIMENS CUT AT 1 FROM THE END I AFTER DRYING | 1 WEEK AFTER DRYING I LENGTH (mm) 1 WIDTH (mm) | LENGTH (mm) | WIDTH (mm) 1 1 0 1 0 | 40 | 0 4 2 1 0 1 0 | 35 | 0 6 3 1 0 1 0 | 32 | 1 0 4 1 0 1 0 | 31 1 0 5 48 checking was found. I n t e r n a l checking o c c u r r e d l a t e r d u r i n g subsequent storage at room temperature so t h a t f o r runs #1, #2, #3 and #4, 13, 7, 7 and 4% of the specimens, r e s p e c t i v e l y , were found w i t h i n t e r n a l c hecking at one or both ends when cut one week a f t e r d r y i n g . Kininmonth and W i l l i a m s (17) o b t a i n e d s i m i l a r r e s u l t s w i t h 2 inches t h i c k (51mm) r a d i a t a p i n e lumber. A c h i - s q u a r e s t a t i s t i c , t e s t i n g p r o p o r t i o n s independance, was a l s o run i n order t o determine whether or not the p r o p o r t i o n of specimens w i t h i n t e r n a l c hecking was the same a f t e r 0, 2, 4 and 6 hours of c o n d i t i o n i n g . Appendix 7.2 shows how the t e s t was done. The r e s u l t s i n d i c a t e d t h a t the p r o p o r t i o n of d e f e c t i v e specimens one week a f t e r d r y i n g was about the same f o r a l l d r y i n g runs. This i s c o n t r a r y t o what Kininmonth and W i l l i a m s r e p o r t e d . In t h e i r study, i n t e r n a l c hecking was s i g n i f i c a n t l y reduced u s i n g c o n d i t i o n i n g immediately a f t e r k i l n -d r y i n g . Table 8 shows the l a r g e s t s i z e of i n t e r n a l check found i n each run. I n t e r n a l check l e n g t h s ranged from 4 0 mm f o r run #1 to 31 mm f o r run #4 and widths ranged from 0.4 mm f o r run #1 t o 1.0 mm f o r run #3. Two weeks a f t e r d r y i n g , each CS was v i s u a l l y examined i n order t o determine which specimens were more l i k e l y t o develop ch e c k i n g . The CSs of the d e f e c t i v e specimens were found w i t h end checks. Two reasons c o u l d e x p l a i n t h e i r presence. F i r s t l y , they c o u l d have been the r e s u l t of i n t e r n a l checks found e a r l i e r 49 when the KSs were cross-sawn i n t o CSs f o r i n t e r n a l checking e v a l u a t i o n . Secondly, they c o u l d have developed t h e r e a f t e r as the ends of the cut p i e c e s d r i e d out. I t can be seen i n Appendix 7.3 t h a t i n 26 p i e c e s of the i n i t i a l 14 f e e t l o n g (4.27 m) lumber, 4 out of -4 KSs developed c h e c k i n g problems. Conversely, i n 20 p i e c e s of lumber, a l l 4 KSs were f r e e from c h e c k i n g . IMCs and green s p e c i f i c g r a v i t i e s of both types of p i e c e s (with and without checking) were f i r s t compared u s i n g a " t " t e s t . Appendix 7.4 shows how t h i s t e s t was done and Table 9 c o n t a i n s the r e s u l t s o b t a i n e d . IMC showed an i n s i g n i f i c a n t d i f f e r e n c e f o r both types of p i e c e s u s i n g a 10% l e v e l of s i g n i f i c a n c e . S p e c i f i c g r a v i t y a n a l y s i s r e v e a l e d a s i g n i f i c a n t d i f f e r e n c e at the 1% l e v e l . This i m p l i e s t h a t p i e c e s of lumber w i t h low s p e c i f i c g r a v i t i e s were probably not l i k e l y t o develop c h e c k i n g problems as shown i n F i g u r e 21. F i n a l l y , the core MCs o b t a i n e d f o r the d e f e c t i v e specimens were compared w i t h the ones o b t a i n e d f o r the n o n - d e f e c t i v e specimens. KSs w i t h h i g h core MCs were more l i k e l y t o develop checking. Two reasons may e x p l a i n why some specimens had h i g h FCMCs. The f i r s t reason c o u l d be the c o n s i d e r a b l e v a r i a t i o n i n s p e c i f i c g r a v i t y observed among them. Green s p e c i f i c g r a v i t i e s as h i g h as 0.553 were found i n some of the p i e c e s of lumber. A c c o r d i n g t o O l i v e i r a (32), h i g h d e n s i t y hemlock lumber e x h i b i t s much slower d r y i n g r a t e s . Such lumber may be o n l y p a r t i a l l y d r i e d at the end of the d r y i n g c y c l e , l e a v i n g the core wet. The 50 Table 9. Test of mean values f o r "2x4" PCH lumber LUMBER WITH CHECKING 1 LUMBER WITHOUT CHECKING 2 PROPERTY . CONCLUSION MIN MAX AVG STD MIN MAX AVG STD IMC (%) 41.8 150.9 70.8 27.5 44.1 115.7 61.2 15.0 Not s i g . at the 10% l e v e l GREEN SPECIF. GRAVITY 0.342 0.497 0.419 0.038 0.303 0.406 0.355 0.031 S i g . at the 1% l e v e l CORE MC (%) 3 11.5 26.8 17.2 3.7 8.9 14.9 10.9 1.4 S i g . at the 1% l e v e l 1 : checking developed i n a l l 4 k i l n specimens 2 : no checking observed i n a l l 4 k i l n specimens 3 : core moisture content 2 weeks a f t e r d r y i n g second reason c o u l d be the l a r g e v a r i a t i o n i n MCs observed among them. A c c o r d i n g to K o z l i k (19), t h i s problem i s due t o the e x i s t e n c e of s i n k e r heartwood which has a d r y i n g r a t e two t o f i v e times slower than normal heartwood. Wet pockets, a c h a r a c t e r i s t i c of s i n k e r heartwood, were observed i n some CSs when they were checked f o r i n t e r n a l c h ecking. The.specimens w i t h a high FCMC were not on l y found t o have checking problems but a d d i t i o n a l l y , the degrade observed was a l s o much more severe. For t h a t reason, i t was decided i n Phase I I t o perform a more d e t a i l e d i n v e s t i g a t i o n . Such specimens were b e l i e v e d to develop steep MC g r a d i e n t s t h a t f a v o r e d i n t e r n a l checking development. 51 Figure 21. P l o t of green s p e c i f i c g r a v i t y against i n i t i a l moisture content f o r "2x4" PCH lumber > O U a. O ui QL </> 0.56 i B 0.54 -0.52 -0.5 - m m 0.48 -0.46 - m . ° o ° m 0.44 -0.42 -% MM a s m • 0 a a B  um mm m n m a 0.4 - u • lp ++ H m m El 0.38 - % + + rfr1 T ES . m m • J i • • 0.36 -0.34 -+ i El + + E B SI + g 0.32 -0.3 -+ + + + i i + i i i i 1 1 1 1 1 1 1 30 50 70 90 110 130 INITIAL MOISTURE CONTENT (%) 150 170 m Checking developed In 1 or more kiln specimen (s) + All 4 kiln specimens free from checking 52 4.2 Phase I I As was r e p o r t e d f o r "2x4" PCH lumber, t h e r e was a l s o a c o n s i d e r a b l e v a r i a t i o n i n IMC d i s t r i b u t i o n i n the "4x4" PCH lumber (Table 10). The IMC ranged from 31.8 t o 122.1% w i t h an average value of 60.9%. F i g u r e 22 shows t h a t a major p o r t i o n of the lumber p o p u l a t i o n had IMCs t h a t ranged between 4 0 and 60%. Table 10. I n i t i a l moisture content and green s p e c i f i c g r a v i t y  of "4x4" PCH lumber MIN MAX AVG INITIAL MOISTURE CONTENT (%) 31.8 122.1 60.9 GREEN SPECIFIC GRAVITY 0.312 0.464 0.376 A c o n s i d e r a b l e v a r i a t i o n i n IMC was observed between and w i t h i n specimen boards. The average IMC f o r the specimens i n runs #5, #6, #7 and #8 was 55.1, 54.8, 57.9 and 62.9%, r e s p e c t i v e l y (Table 11). As mentioned e a r l i e r , KSs f o r runs #5 and #6 were cut from one end w h i l e KSs f o r runs #7 and #8 were cut from the other end. One c o u l d conclude t h a t the shipped p i e c e s of lumber were d r i e r at one end compared to the o t h e r . 53 Figure 22. I n i t i a l moisture content frequency d i s t r i b u t i o n of "4x4" PCH lumber 22 • i " I 1 ' ' '\ ' ' " " ' ' \ ' ' " ' ' \ ' ' " 20-40 40-60 60-80 80-100 100-120 120-140 INITIAL MOISTURE CONTENT (%) 54 Table 11. Average moisture contents i n a l l 4 loads of "4x4" PCH specimens RUN # I IMC %) MC (%) | BEFORE | COOLING I BEFORE I CONDITIONING | AFTER DRYING | | AND CONDITIONING| ONE WEEK AFTER DRYING AND ' CONDITIONING 5 I 55 1 -! 1 8.7 | 7.8 6 1 54 8 1 7. 8 1 8.1 1 8.1 | 7.2 7 1 57 9 I 10. 0 1 10.0 I 10.5 | 8.6 8 1 62 9 1 13. 5 1 13.5 1 14.1 | 11.9 The average green s p e c i f i c g r a v i t y of "4x4" PCH lumber was 0.376, ranging from 0.312 t o 0.464 (Table 10). F i g u r e 23 shows t h a t the normal d i s t r i b u t i o n may be not the best model f o r the d i s t r i b u t i o n of s p e c i f i c g r a v i t y . A l a r g e p r o p o r t i o n of the p i e c e s of lumber had green s p e c i f i c g r a v i t i e s r a n g i n g from 0.320 to 0.380 w h i l e an even l a r g e r p r o p o r t i o n had s p e c i f i c g r a v i t i e s r a n g i n g from 0.380 to 0.420. Ac c o r d i n g t o Jessome (14), s p e c i f i c g r a v i t i e s of unseasoned a m a b i l i s f i r and western hemlock are 0.360 (± 0.038) and 0.409 (± 0.038), r e s p e c t i v e l y . Compared t o western hemlock, the s p e c i f i c g r a v i t y of a m a b i l i s f i r i s r e l a t i v e l y low and c l o s e r t o the f i r s t range. The s p e c i f i c g r a v i t y g i ven f o r western hemlock i s h i g h e r and c l o s e r t o the second range. Therefore, i t i s l i k e l y t h a t lumber i n the f i r s t range i s a m a b i l i s f i r w h i l e lumber i n the second one i s 55 Figure 23. Green s p e c i f i c g r a v i t y frequency d i s t r i b u t i o n of "4x4" PCH lumber 26 .30-.32 .32-.34 .34-.36 .36-.38 .38-.40 .40-.42 .42-.44 .44-.46 .46-.48 SPECIFIC GRAVITY 56 western hemlock. FMCs immediately a f t e r d r y i n g and c o n d i t i o n i n g i n loads #5, #6, #7 and #8 were 8.7, 8.1, 10.5 and 14.1%, r e s p e c t i v e l y (Table 11) . Such a wide v a r i a t i o n i n the FMCs can be a t t r i b u t e d t o the l a r g e v a r i a t i o n i n IMC observed w i t h i n each p i e c e of lumber. In a l l k i l n l o a d s , the h i g h e r the IMC, the hi g h e r was the FMC. Table 12 shows k i l n - d r y i n g time of "4x4" PCH lumber. D r y i n g times ( e x c l u d i n g c o o l i n g ,and c o n d i t i o n i n g ) f o r runs #5, #6, #7 and #8 were 106.50, 106.25, 84.50 and 71.25 hours, r e s p e c t i v e l y . As was found i n Phase I f o r "2x4" PCH lumber, the hi g h e r the average FMC (Table 11) and d r y i n g r a t e (Table 13), the s h o r t e r was the d r y i n g time i n a l l d r y i n g runs. C o o l i n g times were r e l a t i v e l y s hort except f o r run #7 which was 7.25 hours. The k i l n shut down l a t e at n i g h t and c o n d i t i o n i n g was s t a r t e d o n l y e a r l y the next morning. The DB and WB temperatures were down t o 100°F (37.7°C) and 70°F (21.1°C), r e s p e c t i v e l y . A c c o r d i n g t o Kininmonth and W i l l i a m s , such a lo n g c o o l i n g p e r i o d should have been avoided because i n t e r n a l c hecking was more l i k e l y t o develop even before the c o n d i t i o n i n g treatment takes p l a c e (see C o n d i t i o n i n g ) . R e s u l t s which are shown l a t e r i n the t e x t i n d i c a t e d t h a t t h i s was not the case i n t h i s p a r t i c u l a r run s i n c e most i n t e r n a l c hecking o c c u r r e d once c o n d i t i o n i n g was c a r r i e d out d u r i n g subsequent storage at room temperature. 57 Table 12. K i l n - d r y i n g time of "4x4" PCH specimens RUN # KILN DRYING TIME (hours) I DRYING I COOLING | CONDITIONING | TOTAL 5 1 106.50 - ! - ! 106.50 6 I 106.25 1 1.50 1 2.25 I 110.00 7 1 84 .50 1 7.25 1 4.25 I 96.00 8 I 71.25 1 0.00 1 6.00 I 77.25 Table 13. Drying r a t e s of "4x4" PCH specimens RUN # DRYING RATE (% MC/hour) " MIN MAX AVG 5 - 0 20 + 1 64 + 0 44 6 + 0 11 + 1 80 + 0 44 7 + 0 13 + 2 09 + 0 57 8 + 0 19 + 2 20 + 0 69 e x c l u d i n g c o o l i n g and c o n d i t i o n i n g moisture l o s s moisture gain 58 F i g u r e s 24, 25, 26 and 27 show the change i n MC over time f o r a l l d r y i n g runs. Two p l o t s were made f o r each d r y i n g run. The f i r s t p l o t shows the expected change i n MC over time assuming the IMC and FMC before c o n d i t i o n i n g of a l l d r y i n g runs equal t o 60.9 and 12.0%, r e s p e c t i v e l y . The second p l o t was made to c o r r e c t the o r i g i n a l p l o t u s i n g the l o a d i n i t i a l and f i n a l average MCs (Appendix 7.5). For a l l d r y i n g runs, i t shows t h a t c o n d i t i o n i n g was not c a r r i e d out at the d e s i r e d 12% FMC. F i n a l l y , d r y i n g r a t e s of a l l runs were p l o t t e d a g a i n s t t h e i r average MCs (Figures 28, 29, 30 and 31). As n o t i c e d i n Phase I f o r "2x4" PCH lumber, the d r y i n g r a t e was again at maximum when the d e s i r e d DB and WB temperatures were reached. T h e r e a f t e r , lumber MC and d r y i n g r a t e c o n s t a n t l y decreased i n a l l d r y i n g runs. C o n d i t i o n i n g of "4x4" lumber was not recommended by Kininmonth and W i l l i a m s because degrade from i n t e r n a l checking was too e x c e s s i v e . I t was claimed t h a t s t r e s s r e l i e f at the end of d r y i n g was not j u s t i f i e d s i n c e most of the degrade oc c u r r e d d u r i n g d r y i n g when such lumber was high-temperature k i l n - d r i e d . Table 14 shows the number of specimens t h a t developed i n t e r n a l c h e c k i ng i n each d r y i n g run. When specimens were cut immediately a f t e r d r y i n g and c o n d i t i o n i n g , 18% of them on the average, had a l r e a d y developed i n t e r n a l checking at one or both ends. One week l a t e r , 34% of the specimens were found w i t h i n t e r n a l checks. A s t a t i s t i c a l a n a l y s i s u s i n g the z value was 59 F i g u r e 24. P l o t o f a v e r a g e m o i s t u r e c o n t e n t a g a i n s t t i m e f o r r u n #5 (no c o n d i t i o n i n g ) ADJUSTED DATA 0 20 40 60 80 100 TIME (hours) 60 F i g u r e 25. P l o t o f a v e r a g e m o i s t u r e c o n t e n t a g a i n s t t i m e f o r r u n #6 (2 h o u r s o f c o n d i t i o n i n g ) 70 ADJUSTED DATA ACTUAL DATA 20 40 60 TIME (hours) 80 100 120 61 F i g u r e 26. P l o t o f a v e r a g e m o i s t u r e c o n t e n t a g a i n s t t i m e f o r r u n #7 (4 h o u r s o f c o n d i t i o n i n g ) Figure 27. P l o t of average moisture content against time f o r run #8 (6 hours of conditioning) 63 Figure 28. P l o t of drying rate against average moisture content f o r run #5 (no conditioning) 2.5 64 Figure 29. P l o t of drying rate against average moisture content f o r run #6 (2 hours of conditioning) 65 F i g u r e 30. P l o t o f d r y i n g r a t e a g a i n s t a v e r a g e m o i s t u r e c o n t e n t f o r r u n #7 (4 h o u r s o f c o n d i t i o n i n g ) Figure 31. P l o t of drying rate against average moisture content f o r run #8 (6 hours of conditioning) 2.5 ' 70 60 50 40 30 20 10 0 MOISTURE CONTENT (%) 67 Table 14. Number of "4x4" PCH specimens w i t h i n t e r n a l checking RUN # j 3' SPECIMENS CUT AT 1' FROM THE END j AFTER DRYING 1 1 WEEK AFTER DRYING I LEFT RIGHT MAX. % 1 LEFT RIGHT MAX. % 5 I 5 6 6 25 | 6 5 6 25 6 1 7 2 7 29 | 9 8 9 38 7 1 3 0 3 13 I 10 5 10 42 8 1 1 1 1 4 1 8 5 8 33 LEFT, MAX. % number of d e f e c t i v e specimens found at that end maximum number of d e f e c t i v e specimens at one or both ends percentage of d e f e c t i v e specimens at one or both ends Table 15. Largest i n t e r n a l check s i z e f o r "4x4" PCH specimens RUN t | 3' SPECIMENS CUT AT 1 FROM THE END AFTER DRYING 1 1 WEEK AFTER DRYING LENGTH (mm) I WIDTH (mm) | LENGTH (mm) | WIDTH (mm) 5 1 63 1 1.5 1 47 | 1 6 6 1 44 1 2.1 I 91 1 3 5 7 1 30 1 1.6 1 59 | 2 1 8 1 35 1 0.8 I 61 1 1 5 68 run i n order t o determine whether the p r o p o r t i o n s of specimens w i t h i n t e r n a l checking were the same at the end of d r y i n g and c o n d i t i o n i n g and one week l a t e r (Appendix 7.6) . R e s u l t s showed t h a t the p r o p o r t i o n of specimens w i t h i n t e r n a l checking was g r e a t e r one week a f t e r d r y i n g . This means t h a t most i n t e r n a l c hecking developed a f t e r d r y i n g and c o n d i t i o n i n g , c o n t r a r y to Kininmohth and W i l l i a m s ' r e s u l t s . Therefore, c o n d i t i o n i n g immediately a f t e r d r y i n g was j u s t i f i e d i n t h i s case. In runs #5, #6, #7 and #8, 25, 38, 42 and 33% of the specimens, r e s p e c t i v e l y , were found w i t h i n t e r n a l checking one week a f t e r d r y i n g and c o n d i t i o n i n g . A c h i - s q u a r e s t a t i s t i c , t e s t i n g p r o p o r t i o n s independence, was performed and r e s u l t s showed t h a t the p r o p o r t i o n of specimens w i t h i n t e r n a l checking problems one week a f t e r d r y i n g was about the same i n a l l d r y i n g runs (Appendix 7.2). As observed i n "2x4" PCH lumber, c o n d i t i o n i n g immediately a f t e r d r y i n g d i d not reduce i n t e r n a l c h e c k i ng development f o r "4x4" PCH lumber. The z value was a l s o used t o determine whether the p r o p o r t i o n of d e f e c t i v e specimens found i n the "4x4" lumber was high e r than t h a t i n the "2x4" lumber (Appendix 7.6). One week a f t e r d r y i n g and c o n d i t i o n i n g , an average of 8% of the "2x4" specimens were found w i t h i n t e r n a l checking compared t o 34% f o r the "4x4" ones. R e s u l t s have shown t h a t these two p r o p o r t i o n s were s i g n i f i c a n t l y d i f f e r e n t at the 1% l e v e l . Not o n l y were the "4x4" specimens more l i k e l y t o develop i n t e r n a l checking, but 69 the s i z e of the checks observed was a l s o more important. As can be seen i n Tables 8 and 15, maximum le n g t h s and widths of the i n t e r n a l checks one week a f t e r d r y i n g and c o n d i t i o n i n g were on average 1.9 times longer and 3.7 times wider i n the "4x4" specimens than i n the "2x4" ones. The f i r s t r a t i o (1.9 times longer) was expected s i n c e "4x4" lumber i s two times t h i c k e r than "2x4" lumber. However, the second r a t i o (3.7 times wider) shows t h a t i n t e r n a l checking was more severe i n the former specimens than t h a t i n the l a t t e r ones. Based on our f i n d i n g s , one c o u l d agree w i t h Kininmonth and W i l l i a m s and conclude t h a t c h e c k ing i n the t h i c k e r specimens i s more e x c e s s i v e q u a l i t a t i v e l y and q u a n t a t i v e l y . The FMC of each specimen was c a l c u l a t e d u s i n g the f o l l o w i n g e q u a t i o n : FMC = 1/9 x FCMC + 8/9 x FSMC ( 1 ) where FCMC and FSMC are the f i n a l core and s h e l i MCs (Figure 10), r e s p e c t i v e l y . FMCs of i n t e r n a l l y checked specimens were then compared w i t h c h e c k - f r e e ones u s i n g a " t " t e s t (Appendix 7.4) . I t can be seen i n Table 16 t h a t , immediately a f t e r d r y i n g and c o n d i t i o n i n g , FMC showed a very s i g n i f i c a n t d i f f e r e n c e f o r both types of specimens at the 1% l e v e l . I n t e r n a l l y checked specimens were found w i t h low FMCs. When the specimens were cut one week a f t e r d r y i n g and c o n d i t i o n i n g , d e f e c t i v e specimens were found w i t h low MCs again. However, FMCs of both types of 70 Table 16. Test of mean valu e s f o r "4x4" PCH lumber LUMBER WITH INTERNAL LUMBER WITHOUT INTERNAL CHECKING 1 CHECKING 2 CONCLUSION MIN MAX AVG STD MIN MAX AVG STD IMC (%) 31.8 55.3 44.1 8.0 32.4 116.8 63.8 21.9 S i g . at the 1% l e v e l GREEN SPECIF. GRAVITY 337.2 451.9 382.9 31.0 312.3 464.4 372.9 - 45.1 Not s i g . at the 10% l e v e l 3' SPECIMENS WITH INTERNAL CHECKING 3' SPECIMENS WITHOUT INTERNAL CHECKING CONCLUSION AVG FMC AFTER DRYING (%) 6.3 12.2 8.2 1.5 6.0 25.1 11.0 3.8 S i g . at the 1% l e v e l FMC ONE WEEK AFTER 4.9 11.2 8.2 1.7 4.9 22.1 8.9 2.9 Not s i g . at the 10% l e v e l DRYING (%) i n t e r n a l checking developed i n 3 or 4 k i l n specimens i n t e r n a l checking developed i n 0 or 1 k i l n specimen 71 specimens were not found s i g n i f i c a n t l y d i f f e r e n t at the 10% l e v e l . T h i s i m p l i e s t h a t both types of specimens reached a s i m i l a r EMC a f t e r one week of storage at room temperature. F i n a l l y , specimen MCs were i n v e s t i g a t e d i n more d e t a i l t o determine at which l e v e l i n t e r n a l c h e c k ing was more l i k e l y to occur. As can be seen i n F i g u r e s 32 and 33, more i n t e r n a l c h e c k i ng was found when specimen MCs ranged from 7% t o 8%. Table 17 shows t h a t 96% and 100% of the d e f e c t i v e specimens were found o v e r - d r i e d (below 12% MC) , when cut immediately a f t e r d r y i n g and c o n d i t i o n i n g , and one week l a t e r , r e s p e c t i v e l y . This may e x p l a i n why i n t e r n a l checking developed a f t e r d r y i n g and c o n d i t i o n i n g i n t h i s experiment c o n t r a r y t o Kininmonth and Williams'' r e s u l t s . In t h i s experiment, lumber was d r i e d t o 13.5% MC or l e s s b e f o r e c o n d i t i o n i n g (Table' 11) . In t h e i r experiment, i n t e r n a l checking developed d u r i n g d r y i n g because lumber was d r i e d t o a lower MC, 10% or l e s s . Kauman (15) suggests t h a t c o n d i t i o n i n g s hould be c a r r i e d out when lumber average MC i s above 15%. Below t h a t , i n t e r n a l s t r e s s e s r e s p o n s i b l e f o r i n t e r n a l checking cannot be r e l i e v e d because the wood i s too s t i f f , i . e . not p l a s t i c enough, t o r e l a x . In t h i s experiment, c o n d i t i o n i n g was c a r r i e d out at 8.1, 10.0 and 13.5% average MC f o r runs #6, #7 and #8, r e s p e c t i v e l y . Such low MCs may e x p l a i n why i n t e r n a l c h e c k ing was not s i g n i f i c a n t l y reduced by c o n d i t i o n i n g treatments i n t h i s experiment. 72 Figure 32. F i n a l moisture content frequency d i s t r i b u t i o n of "4x4" d e f e c t i v e specimens immediately a f t e r drying and c o n d i t i o n i n g 50 6-7 7-8 8-9 9-10 10-11 11-12 12-13 FINAL MOISTURE CONTENT (%) 73 Figure 33. F i n a l moisture content frequency d i s t r i b u t i o n of "4x4" d e f e c t i v e specimens one week a f t e r drying and c o n d i t i o n i n g Table 17. F i n a l moisture contents of "4x4" PCH specimens w i t h i n t e r n a l checking 3' SPECIMENS CUT | FMC RANGE (%) I NO OF DEFECTIVE | I SPECIMENS | % ! 6 7 1 3 | 13 0 7 - 8 1 11 1 47 8 1 8 - 9 I 3 | 13 0 AFTER DRYING AND | 9 - 10 ! 3 | 13 0 CONDITIONING | 10 - 11 1 1 1 4 3 11 - 12 1 1 1 4 3 12 - 13 1 1 1 4 3 j 1 23 I 100 0 i 4 5 1 1 1 2 6 | 5 - 6 1 4 I 10 5 1 6 - 7 1 6 I 15 8 1 WEEK AFTER DRYING I 7 - 8 1 8 | 21 1 AND CONDITIONING | 8 - 9 1 6 | 15 8 1 9 - 10 1 7 | 18 4 | 10 - 11 1 5 I 13 2 11 - 12 1 1 1 2 6 1 38 I 100 0 75 The f i n a l c o r e - s h e l l MC d i f f e r e n c e (FCSMCD) of each specimen was c a l c u l a t e d u s i n g the f o l l o w i n g e q u a t i o n : FCSMCD = FCMC - FSMC ( 2 ) FCSMCDs of a l l d r y i n g specimens were p l o t t e d a g a i n s t t h e i r FMCs. F i g u r e 34 shows the s c a t t e r e d p o i n t s o b t a i n e d f o r the non-d e f e c t i v e specimens cut immediately a f t e r d r y i n g and c o n d i t i o n i n g . The p o i n t s f o l l o w c l o s e l y a s t r a i g h t l i n e i n d i c a t i n g t h a t FCSMCD and FMC are t o some extent l i n e a r l y r e l a t e d . The f o l l o w i n g r e g r e s s i o n l i n e was ob t a i n e d t o express t h a t l i n e a r r e l a t i o n s h i p : FCSMCD .= -10.20 + 1.96 FMC ( 3 ) Fi g u r e 35 shows the s c a t t e r e d p o i n t s o b t a i n e d f o r the d e f e c t i v e specimens. The f o l l o w i n g second r e g r e s s i o n l i n e was found: FCSMCD = -12.40 + 2.30 FMC ( 4 ) Both r e g r e s s i o n l i n e s show a good l i n e a r r e l a t i o n s h i p between the two v a r i a b l e s . The c o e f f i c i e n t s of d e t e r m i n a t i o n (R2) f o r r e g r e s s i o n l i n e s 3 and 4 are 0.87 and 0.81, r e s p e c t i v e l y (Table 18) . Both r e g r e s s i o n l i n e s a l s o show t h a t a decrease i n the specimens' MCs r e s u l t e d i n ' a decrease i n t h e i r c o r e - s h e l l MC d i f f e r e n c e s . However, above EMC, r e g r e s s i o n l i n e 4 p r e d i c t s h i g h e r c o r e - s h e l l MC d i f f e r e n c e s than does l i n e 3. This c onfirms Salamon's f i n d i n g s (36) t h a t i n t e r n a l l y checked lumber 76 Figure 34. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of non-defective specimens cut immediately a f t e r drying and c o n d i t i o n i n g Figure 35. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of d e f e c t i v e specimens cut immediately a f t e r drying and c o n d i t i o n i n g Table 18. Regression l i n e s SPECIMENS | Y REGRESSION LINE R2 I FCMC AFTER DRYING Y = -11.03 + 3.05 X 0 90 | FCMC ONE WEEK I AFTER DRYING Y = - 5.17 + 2.22 X 0 88 I FSMC AFTER DRYING Y = 1.38 + 0.74 X 0 97 DEFECTIVE | | FSMC ONE WEEK 1 AFTER DRYING Y = 0.65 + 0.85 X 0 99 | FCSMCD AFTER DRYING Y = -12.40 + 2.30 X 0 81 | FCSMCD ONE WEEK | AFTER DRYING Y - - 5.82 + 1.37 X 0 70 | FCMC AFTER DRYING Y - - 9.06 + 2.74 X 0 94 | FCMC ONE WEEK | AFTER DRYING Y => - 4 . 61 + 2.13 X 0 96 | FSMC AFTER DRYING Y - 1.13 + 0.78 X 0 99 NON-DEFECTIVE I I FSMC ONE WEEK I AFTER DRYING Y = 0.58 + 0.86 X 0 99 | FCSMCD AFTER DRYING Y - -10.20 + 1.96 X 0 87 | FCSMCD ONE WEEK | AFTER DRYING Y = - 5.18 + 1.27 X 0 86 X : SPECIMEN' FMC (%) 79 has s t e e p e r f i n a l moisture g r a d i e n t s than i n n o n - d e f e c t i v e lumber. F i n a l core and s h e l l MCs of a l l KSs cut immediately a f t e r d r y i n g and c o n d i t i o n i n g were p l o t t e d a g a i n s t t h e i r FMCs. F i g u r e s 36 and 37 show the s c a t t e r e d p o i n t s o b t a i n e d f o r the n o n - d e f e c t i v e and d e f e c t i v e specimens, r e s p e c t i v e l y . As can be seen i n Table 18, the r e g r e s s i o n l i n e s found f o r the d e f e c t i v e specimens p r e d i c t h igher core MCs and lower s h e l l MCs than f o r the n o n - d e f e c t i v e specimens. Table 18 a l s o g i v e s the r e g r e s s i o n l i n e s found f o r the specimens cut one week a f t e r d r y i n g and c o n d i t i o n i n g . F i g u r e s 38 (FCSMCDs of no n - d e f e c t i v e specimens), 39 (FCSMCDs of d e f e c t i v e specimens), 40 (FCMCs and FSMCs of n o n - d e f e c t i v e specimens) and 41 (FCMCs and FSMCs of d e f e c t i v e specimens) i l l u s t r a t e them. Once again, the d e f e c t i v e specimens were found w i t h h i g h core and low s h e l l MCs r e s u l t i n g i n steep c o r e - s h e l l moisture content g r a d i e n t s . However, t h e i r moisture g r a d i e n t s were not as steep as the ones recorded one week e a r l i e r s i n c e the lumber kept l o s i n g water d u r i n g storage at room temperature. Table 19 g i v e s the FCSMCDs o b t a i n e d i n a l l d r y i n g runs. The average FCSMCD i n the c o n t r o l run (run #5) immediately a f t e r d r y i n g was 7.9%. Average FCSMCDs immediately a f t e r c o n d i t i o n i n g i n runs #7 and #8 were 9.9 and 16.7%, r e s p e c t i v e l y . This may e x p l a i n why more specimens were found d e f e c t i v e one week a f t e r c o n d i t i o n i n g i n those two runs than t h a t i n the c o n t r o l run 80 Figure 36. F i n a l core and s h e l l moisture contents of non-defective specimens cut immediately a f t e r drying and c o n d i t i o n i n g Figure 37. F i n a l core and s h e l l moisture contents of d e f e c t i v e specimens cut immediately a f t e r drying and c o n d i t i o n i n g Figure 38. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of non-defective specimens cut one week a f t e r drying and c o n d i t i o n i n g Figure 39. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of d e f e c t i v e specimens cut one week a f t e r drying and c o n d i t i o n i n g Figure 40. F i n a l core and s h e l l moisture contents of non-defective specimens cut one week a f t e r drying and c o n d i t i o n i n g Figure 41. F i n a l core and s h e l l moisture contents of d e f e c t i v e specimens cut one week a f t e r drying and c o n d i t i o n i n g Table 19. F i n a l c o r e - s h e l l moisture content d i f f e r e n c e s of  "4x4" PCH specimens 1 RUN # I TIME OF MEASUREMENT I FCMC (%) FSMC (%) FCSMCD (%) MIN MAX AVG MIN MAX AVG MIN MAX AVG 1 5 I AFTER DRYING I 8 . 9 31. 3 15. 7 | 5. 9 11. 9 7. 9 1 2. 4 19.9 7.9 11 WEEK AFTER DRYING| 7 . 9 24. 5 12. 3 1 5. 5 11. 1 7. 3 1 2. 3 15.1 5.1 1 6 |AFTER CONDITIONING I 7. 7 34 . 6 13. 7 | 5. 8 11. 8 7. 4 1 1. 9 22.8 6.4 |1 WEEK AFTER I 6. 4 23. 7 11. 4 1 4 . 7 10. 1 6. 7 | 1. 2 13.6 4.7 |CONDITIONING | 1 7 I AFTER CONDITIONING I 10. 7 35. 9 19. 3 1 6. 8 15. 1 9. 4 1 3. 7 20.8 9.9 | 1 WEEK AFTER I 9. 2 25. 8 13. 6 ! 6. 2 11. 4 8. 0 1 2 . 5 14.4 5.6 I CONDITIONING I 1 8 1 AFTER CONDITIONING I 15. 5 64. 0 29. 0 1 8. 8 20. 2 12. 2 1 6. 7 43.8 16.7 I 1 WEEK AFTER I 12. 1 41. 3 20. 2 1 7. 9 19. 7 10. 9 1 4 . 1 21.5 9.3 [CONDITIONING | (Table 14). P i e c e s of lumber w i t h such h i g h FCSMCDs may have b u i l t up s t r e s s e s c o n s i d e r a b l e enough t o develop i n t e r n a l c h e c k i n g d u r i n g storage at room temperature. In run #6, the average FCSMCD immediately a f t e r c o n d i t i o n i n g was 6.4% and lower than t h a t i n the c o n t r o l run a f t e r d r y i n g . However, the number of specimens found w i t h i n t e r n a l checks one week l a t e r was not reduced s i n c e most of the degrade o c c u r r e d d u r i n g d r y i n g . Indeed, i n t e r n a l checking o c c u r r e d d u r i n g d r y i n g i n run #6 because lumber was d r i e d to a lower MC bef o r e c o n d i t i o n i n g , i . e . 8.1% compared t o 10.0 and 13.5% i n run #7 and #8, r e s p e c t i v e l y 87 (Table 11). FCSMCDs one week a f t e r d r y i n g and c o n d i t i o n i n g were l e s s than one week e a r l i e r . T h i s i m p l i e s t h a t lumber kept l o s i n g water d u r i n g storage r e s u l t i n g i n lower s h e l l and core MCs as shown i n Table 19. F i n a l l y , i t can be seen i n Appendix 7.7 which of the i n i t i a l p i e c e s of lumber developed i n t e r n a l c h e c k ing problems. On one hand, 10 p i e c e s were found w i t h i n t e r n a l checking i n 3 KSs or more. On the other hand, 29 p i e c e s were n o n - d e f e c t i v e or found w i t h i n t e r n a l checking i n o n l y 1 KS. F i g u r e 42 i l l u s t r a t e s specimens found i n t e r n a l l y checked. Non-defective specimens are a l s o shown f o r comparison purposes. IMCs and green s p e c i f i c g r a v i t i e s of both types of p i e c e s were compared u s i n g a " t " t e s t as shown i n Appendix 7.4. R e s u l t s have shown t h a t IMC s i g n i f i c a n t l y i n f l u e n c e d i n t e r n a l checking development (Table 16) . P i e c e s of lumber w i t h low IMCs were more l i k e l y t o develop i n t e r n a l checking. Many specimens cut from those l e n g t h s were found o v e r - d r i e d and i n t e r n a l l y checked. Green s p e c i f i c g r a v i t y showed an i n s i g n i f i c a n t d i f f e r e n c e at the 10% l e v e l . 88 Figure 42. Examples of d e f e c t i v e and non-defective specimens of "4x4" PCH lumber 89 5. CONCLUSION Three f e e t long (0.91 m) specimens of "2x4" and "4x4" PCH lumber were c o n d i t i o n e d immediately a f t e r HTD i n order to minimize f i n a l moisture g r a d i e n t s and r e s i d u a l s t r e s s e s r e s p o n s i b l e f o r i n t e r n a l checking problems. No i n t e r n a l checking was found when the "2x4" specimens were cross-sawn upon completion of c o n d i t i o n i n g . I n t e r n a l checking developed l a t e r d u r i n g subsequent storage at room temperature. For 0, 2, 4, and 6 hours of c o n d i t i o n i n g , 13, 7, 7 and 4% of the specimens, r e s p e c t i v e l y , were found d e f e c t i v e at one or both ends when cut one week a f t e r d r y i n g and c o n d i t i o n i n g . S t a t i s t i c a l l y , c o n d i t i o n i n g d i d not s i g n i f i c a n t l y reduce i n t e r n a l checking, although 4% of d e f e c t i v e specimens among those c o n d i t i o n e d f o r 6 hours i s r e l a t i v e l y low compared t o 13% of d e f e c t i v e specimens when no c o n d i t i o n i n g was i n v o l v e d . I t c o u l d be suggested t h a t a d i f f e r e n c e of 9% would i n d i c a t e s u b s t a n t i a l savings f o r the d r y i n g i n d u s t r y a n n u a l l y , a l t e r n a t i v e l y i t c o u l d be co n s i d e r e d t h a t the f i n a n c i a l l o s s e s a s s o c i a t e d w i t h 4% of the lumber being i n t e r n a l l y checked are too g r e a t . Therefore, more r e s e a r c h i s needed i n order to e s t a b l i s h i f i n t e r n a l checking can be reduced even more by u s i n g c o n d i t i o n i n g treatments immediately a f t e r d r y i n g . . The degrade observed i n the "4x4" specimens was more e x c e s s i v e than i n the "2x4" ones. Some o v e r - d r i e d specimens 90 were found t o be i n t e r n a l l y checked a f t e r d r y i n g and c o n d i t i o n i n g even though most degrade o c c u r r e d d u r i n g storage at room temperature. For 0, 2, 4 and 6 hours of c o n d i t i o n i n g c a r r i e d out immediately a f t e r d r y i n g , 25, 38, 42 and 33% of the specimens, r e s p e c t i v e l y , were found i n t e r n a l l y checked at one or both ends when cut one week a f t e r d r y i n g and c o n d i t i o n i n g . Specimens w i t h high FCSMCDs and low FMCs were found d e f e c t i v e . When cut immediately a f t e r d r y i n g and c o n d i t i o n i n g , 96% of the d e f e c t i v e specimens were found o v e r - d r i e d below 12% MC. This p r o p o r t i o n i n c r e a s e d t o 100% when specimens were cut one week l a t e r . Therefore, an a p p r o p r i a t e recommendation would be to segregate lumber i n t o s e v e r a l moisture c l a s s e s i n order t o minimize i n t e r n a l checking due t o o v e r - d r y i n g . A second recommendation would be t o c o n d i t i o n the lumber at h i g h e r MCs. This way, l e s s boards w i t h low MCs would develop i n t e r n a l checking d u r i n g d r y i n g . However, such a method should be i n v e s t i g a t e d c a r e f u l l y because i t i m p l i e s long c o n d i t i o n i n g treatments which are c o n t r a r y t o the aim of re d u c i n g d r y i n g times by the use of HTD.- I f not, boards w i t h h i g h e r MCs, and t h e r e f o r e steeper moisture g r a d i e n t s , would develop i n t e r n a l c hecking d u r i n g subsequent st o r a g e . Based on these f i n d i n g s alone, one l a s t recommendation would be t o p r a c t i c e i n t e r m i t t e n t c o n d i t i o n i n g . For i n s t a n c e , a f i r s t c o n d i t i o n i n g treatment c a r r i e d out when the wood i s more p l a s t i c i n c h a r a c t e r , i . e . above 15% MC, c o u l d be combined w i t h a second treatment at 12% 91 MC. This way, moisture g r a d i e n t s and i n t e r n a l s t r e s s e s would be minimized and a b e t t e r and f a s t e r s t r e s s r e l i e f would be achieved. 92 6. LITERATURE CITED 1. 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S t r e n g t h t e s t s p e r p e n d i c u l a r t o the g r a i n of timber at v a r i o u s temperatures and moisture c o n t e n t s . J o u r n a l of the C o u n c i l f o r S c i e n t i f i c and I n d u s t r i a l Research ( A u s t r a l i a ) , 9(4):265-276. 12. GUERNSEY, I.W.. 1957. High-temperature d r y i n g of B r i t i s h Columbia softwoods. F o r e s t Products J o u r n a l , 7(10) :368-371. 13. HILLIS, W.E. 1975. The r o l e of wood c h a r a c t e r i s t i c s i n high-temperature d r y i n g . J o u r n a l of the I n s t i t u t e of Wood Science, 7 (2): 60-67. 14. JESSSOME, A.P. 1977. Strength and r e l a t e d p r o p e r t i e s of woods grown i n Canada. F o r i n t e k Canada Corp., Ottawa. F o r e s t r y t e c h n i c a l r e p o r t No. 21, 37 p. 15. KAUMAN, 16 W.G. 1982. Les c o n t r a i n t e s en cours de sechage. Leurs mesures - comment l e s e v i t e r ? 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Proceedings 21st annual meeting Western Dry K i l n Clubs, M i s s o u l a , Montana, p. 55-61. C.J. 1973. E f f e c t of k i l n c o n d i t i o n s on the dimensional s t a b i l i t y of D o u g l a s - f i r and western hemlock. Fo r e s t Products J o u r n a l , 23(9):85-92. 94 21. KOZLIK, C.J. 1981. Shrinkage of western hemlock heartwood a f t e r c o n v e n t i o n a l and high-temperature k i l n -d r y i n g . F o r e s t Products J o u r n a l , 31(12) :45-50 . 22. KOZLIK, C.J. and L.W. HAMLIN. 1972. Reducing v a r i a b i l i t y i n f i n a l moisture content of k i l n - d r i e d hemlock lumber. F o r e s t Products J o u r n a l , 22(7):24-31. 23. KOZLIK, C.J. and J.C. WARD. 1979. C o n v e n t i o n a l and h i g h -temperature k i l n - d r y i n g of sapwood, normal heartwood, and s i n k e r heartwood of dimension lumber from young-growth western hemlock. Proceedings 30th annual meeting Western Dry K i l n Clubs, Washington-Idaho-Montana Seasoning Club, p. 33-53. 24. LADELL, J.L. 1955. High-temperature d r y i n g of lumber. Timber of Canada, 16 (7) :19-22 . 25. LARSON, T.D., ERICKSON, R.W. and R.S. BOONE. 1986. Comparison of d r y i n g methods f o r paper b i r c h SDR f l i t c h e s and studs. F o r e s t Products Laboratory, Fo r e s t S e r v i c e , U.S. Department of A g r i c u l t u r e . Research paper No. FPL-465, 13 p. 26. MACKAY, J.F.G. 1976. Delayed shrinkage a f t e r s u r f a c i n g of high-temperature k i l n - d r i e d n o r t h e r n aspen dimension lumber. F o r e s t Products J o u r n a l , 26 (2) :33-36. 27. MACKAY J.F.G. 1983. Superheated-steam d r y i n g of aspen 2 x 4 lumber. F o r i n t e k Canada Corp., Vancouver. Unpublished r e p o r t , 9 p. 28. MACKAY, J.F.G. 1984. A c c e l e r a t e d d r y i n g of B r i t i s h Columbia framing lumber. F o r i n t e k Canada Corp., Vancouver. Unpublished r e p o r t , 13 p. 29. MCMILLEN, J.M. 1958. S t r e s s e s i n wood d u r i n g d r y i n g . F o r e s t Products Laboratory, F o r e s t S e r v i c e , U.S. Department of A g r i c u l t u r e . Report No. 1652, 52 p. 30. MCMILLEN, J.M. 1963. A study of d r y i n g s t r e s s e s i n ponderosa p i n e . Proceedings 15th annual meeting Western Dry K i l n Clubs, C o r v a l l i s , Oregon, p. 48-53. 95 31. OLIVEIRA, L.C., MACKAY, J.F.G. and D.M. WRIGHT. 1989. D i f f i c u l t i e s d u r i n g i n d u s t r i a l d r y i n g of hemlock and p o t e n t i a l gains by u s i n g a c c e l e r a t e d schedules. Proceedings Western Dry K i l n A s s o c i a t i o n , Washington-Idaho-Montana Seasoning A s s o c i a t i o n , p. 108-118. 32. OLIVEIRA, L.C. 1990. Personnal communication Canada Corp., Vancouver. F o r i n t e k 33. PANSHIN, A.J. and C. de ZEEUW. 1980. Textwood of Wood Technology. Fourth e d i t i o n . McGraw-Hill Book Company. 722 p. 34. RASMUSSEN, 35. ROSEN, H.N E.F. and G. VOORHIES. 1952. The r e l i e f of casehardening s t r e s s e s i n a i r c r a f t lumber. F o r e s t Products Laboratory, F o r e s t S e r v i c e , U.S. Department of A g r i c u l t u r e . Report No. 1371, 15 p. 1979. Psychometric r e l a t i o n s h i p s and e q u i l i b r i u m moisture content of wood at temperatures above 212°F. Symposium on Wood Mois t u r e Content - Temperature and Humidity R e l a t i o n s h i p s , V i r g i n i a P o l y t e c h n i c I n s t i t u t e and State U n i v e r s i t y , B l a c k s b u r g , V i r g i n i a . p. 12-19. 36. SALAMON, M. 1961. K i l n - d r y i n g of B r i t i s h Columbia softwoods at high temperatures. Proceeedings 13th annual meeting Western Dry K i l n Clubs, Medford, Oregon. p. 29-35. 37. SALAMON, M. 1965. E f f e c t of high-temperature d r y i n g on q u a l i t y and s t r e n g t h of western hemlock. F o r e s t Products J o u r n a l , 15 (3) : 122-126. 38. SALAMON, M. 1966. E f f e c t s of d r y i n g s e v e r i t y on p r o p e r t i e s of western hemlock. F o r e s t Products J o u r n a l , 16(1):39-46. 39. SALAMON, M. and C.F. MC BRIDE. 1965. A comparison of western hemlock and balsam f i r d r i e d at high and c o n v e n t i o n a l temperatures. Proceedings 17th annual meeting Western Dry K i l n Clubs, P o r t l a n d , Oregon, p. 50-57. 96 40. SCHNEIDER, A. 1972. Zur Konvektionstrocknung von S c h n i t t h o l z b e i extrem hohen Temperaturen. E r s t e M i t t e i l u n g : Trocknungsverlauf und Brettemperaturen b e i Trocknungstemperaturen von 110 b i s 180°C. Holz a l s Roh- und Werkstoff, 30:382-394. 41. STAMM, A.J. 194 6. Passage of l i q u i d s , vapors and d i s s o l v e d m a t e r i a l s through softwoods. F o r e s t Products Laboratory, F o r e s t S e r v i c e , U.S. Department of A g r i c u l t u r e . T e c h n i c a l b u l l e t i n No. 929 , 80 p. 4 2 . STAMM, A.J. and W.K. LOUGHBOROUGH. 1 9 4 2 . V a r i a t i o n i n shrinkage and s w e l l i n g of wood. T r a n s a c t i o n s of the ASME, J o u r n a l of Energy Resources Technology, 63 (329) : 3 7 9 - 3 8 6 . 43. WALPOLE, R.E. 1982 e d i t i o n . I n t r o d u c t i o n t o S t a t i s t i c s . T h i r d Macmillan P u b l i s h i n g Co. 521 p. 44. WENGERT, E.M. and F.M. LAMB. 1988. Matching a d r y i n g system to a m i l l ' s requirements. F o r e s t I n d u s t r i e s , t e c h n i c a l r e p o r t on lumber d r y i n g , 115 (7) :T1-T5 . 45. WENGERT, E.M. and F.M. LAMB. 198 9. End C o a t i n g of lumber to prevent end checking. Proceedings of the IUFRO, I n t e r n a t i o n a l Wood Dr y i n g Symposium, S e a t t l e , Washington. p. 164-168. 46. WINKEL, L.D. 1955. Casehardening s t r e s s r e l i e f of ponderosa p i n e . Western Pine A s s o c i a t i o n , P o r t l a n d , Oregon. Research note No. 4.214, 8 p, 97 7. APPENDICES 98 1. L o a d w e i g h t a t 12% m o i s t u r e c o n t e n t In t h i s experiment, the k i l n l o a d r e s t e d on a s c a l e so t h a t change of weight, t h e r e f o r e MC, c o u l d be monitered over time. In each run, the k i l n was set t o t u r n i t s e l f o f f when the l o a d weight corres p o n d i n g t o an average of 12% MC was reached. IMC and green weight (GW) of l o a d #1, f o r i n s t a n c e , were 69.7% and 259.9 kg, r e s p e c t i v e l y . These data were f i r s t f i t t e d t o the f o l l o w i n g equation t o c a l c u l a t e the l o a d oven-dry weight (ODW): ODW = GW / (IMC + 1) (5) The ODW found was 153.2 kg. F i n a l l y , the weight corresponding t o the t a r g e t e d 12% MC was c a l c u l a t e d u s i n g the f o l l o w i n g e q u a t i o n : weight at 12% MC = 1.12 x ODW (6) In t h i s p a r t i c u l a r run, the k i l n was set t o t u r n i t s e l f o f f when the weight on the s c a l e was down t o 171.6 kg. Table A - l g i v e s the t a r g e t e d and f i n a l weights (FWs) ob t a i n e d f o r a l l d r y i n g runs. 2. T e s t i n g s e v e r a l p r o p o r t i o n s 2.1 "2x4" sp e c i m e n s The c h i - s q u a r e (X2) t e s t procedure d i s c u s s e d by 99 Table A - l . Targeted and f i n a l weights i n a l l . 8 loads of PCH specimens RUN # | LOAD IMC1 GREEN OVEN-DRY TARGETED2 FINAL 3 | WEIGHT WEIGHT WEIGHT WEIGHT ! <%) (kg) (kg) (kg) (kg) i 1 69.7 259.9 153.2. 171. 6 171. 8 2 1 69.7 257 . 9 152 . 0 170 .2 171.4 3 1 69.7 259.5 152.9 171.2 171. 6 4 1 69.7 262 .2 154 .5 173.0 173 . 6 5 1 60.9 279 . 9 174 .0 194 . 9 196 .1 6 1 60.9 273.8 170.2 190 . 6 190 .7 7 1 60.9 282 . 6 175.6 196.7 196.8 8 1 60.9 294 . 6 183.1 205 .1 205.2 1 : average IMC of the i n i t i a l p i e c e s of lumber 2 3 at 12% MC bef o r e c o o l i n g and c o n d i t i o n i n g Walpole(43) was used to t e s t whether or not the p r o p o r t i o n of d e f e c t i v e specimens was the same a f t e r 0, 2, 4 and 6 hours of c o n d i t i o n i n g . L e t t i n g p l t p 2, p 3 and p 4 represent the p r o p o r t i o n of specimens found i n t e r n a l l y checked one week a f t e r d r y i n g and c o n d i t i o n i n g i n l o a d #1, #2, #3 and #4, r e s p e c t i v e l y , and u s i n g the f o l l o w i n g s i x - s t e p procedure, we had: 100 1. N u l l h y p o t h e s i s : p : = p 2 = p 3 = p 4 • . 2. A l t e r n a t i v e h y p o t h e s i s : p l f p 2, p 3 and p 4 were not eq u a l . 3. L e v e l of s i g n i f i c a n c e : 0.10. 4. C r i t i c a l r e g i o n : X 2 > 6.251 f o r 3 degrees of freedom. 5. Computations : Corresponding t o the observed f r e q u e n c i e s ox = 6 and o 5 = 39, we found ex = ( (45x14)/180) = 3.5 and e 5 = ( (45x166)/180) = 41.5. A l l o t h er expected f r e q u e n c i e s were found the same way and d i s p l a y e d i n Table A-2. Table A-2. Observed and expected f r e q u e n c i e s of "2x4" PCH  specimens one week a f t e r d r y i n g SPECIMENS | CONDITIONING TIME (hrs) TOTAL | 0 2 4 6 |DEFECTIVE I 6 (3 5) 3 (3 5) 3 (3 .5) 2 (3 5) 1 14 | |NON-DEFECTIVE| 39 (41 5) 42 (41 5) 42 (41 .5) 43 (41 5) 1 166 | | TOTAL | 45 45 45 45 180 I Then, X 2 = (((6 -3.5) 2)/3.5) + (((3 -3.5) 2)/3.5) + ... + ( ( (42-41 . 5) 2)/41.5) + ( ( (43-41 . 5) 2)/41.5) = 2.788 101 6. D e c i s i o n : Accept the n u l l h y p o t h e s i s and conclude t h a t the p r o p o r t i o n of d e f e c t i v e specimens one week a f t e r d r y i n g and c o n d i t i o n i n g was about the same f o r a l l d r y i n g runs. 2.2 "4x4" spe c i m e n s L e t t i n g p l f p 2, p 3 and p 4 represent the p r o p o r t i o n of specimens found d e f e c t i v e one week a f t e r d r y i n g and c o n d i t i o n i n g i n l o a d #5, #6, #7 and #8, r e s p e c t i v e l y , and u s i n g the s i x - s t e p procedure g i v e n by Walpole, we had: 1. N u l l h y p o t h e s i s : p : = p 2 = p 3 = p 4. 2. A l t e r n a t i v e h ypothesis : p l r p 2 , p 3 and p 4 were not e q u a l . 3. L e v e l of s i g n i f i c a n c e : 0.10. 4. C r i t i c a l r e g i o n : X2 > 6.251 f o r 3 degrees of freedom. 5. Computations : Corresponding t o the observed f r e q u e n c i e s ol = 6 and o 5 = 18, we found e1 = ((24x33)/96) = 8.3 and e 5 = ((24x63)/96) = 15.8. A l l o t h er expected f r e q u e n c i e s were found the same way and d i s p l a y e d i n Table A-3. Then, X 2 - ( ( (6-8 .3) 2)/8 .3) + ( ( (9-8.3) 2)/8.3) + ... + ( ( (14-15.8) 2)/15.8) + ( ( (16-15.8) 2)/15.8) = 1.616 6. D e c i s i o n : Accept the n u l l h y p o t h e s i s and conclude t h a t the p r o p o r t i o n of d e f e c t i v e specimens one week a f t e r d r y i n g and 102 c o n d i t i o n i n g was about the same f o r a l l d r y i n g runs. Table A-3. Observed and expected f r e q u e n c i e s of "4x4" PCH specimens one week a f t e r d r y i n g 1 SPECIMENS | CONDITIONING TIME (hrs) TOTAL 0 2 4 6 1 I DEFECTIVE ] 6 (8.3) 9 (8.3) 10 (8 .3) 8 (8.3) | 33 | I NON-DEFECTIVE I 18 (15.8) 15 (15.8) 14 (15 .8) 16 (15.8) 63 | I TOTAL | 24 24 24 24 96 | 3. Summary o f d r y i n g q u a l i t y o f "2x4" PCH lumber F i g u r e A - l shows which "2x4" specimens were found w i t h and without checking. The runs t h a t the specimens were used i n and the o r i g i n a l boards which they were cross-sawn from are i n d i c a t e d . 4. T e s t s c o n c e r n i n g means The p h y s i c a l p r o p e r t i e s of the "2x4" and "4x4" specimens were compared by a t e s t of s i g n i f i c a n c e ("t" t e s t ) of the mean val u e s f o r a l l p r o p e r t i e s . Table A-4 g i v e s the r e s u l t s f o r the comparison of the d e f e c t i v e and no n - d e f e c t i v e specimens mean 103 F i g u r e A - l . D e f e c t i v e and n o n - d e f e c t i v e s p e c i m e n s "2x4" PCH lumber 104 F i g u r e A - l . ( C o n t i n u e d ) 14' ORIGINAL BOARD# RUN# 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 USEE | | 3' SPECIMEN WITHOUT CHECKING 3' SPECIMEN WITH CHECKING 105 Table A-4. C r i t i c a l and c a l c u l a t e d " t " v a l u e s TYPE OF I LUMBER I PROPERTY I AVERAGE | STANDARD I I DEVIATION | SAMPLE SIZE t VALUE CONCLUSION j I CRITICAL CALCULATED 2"X4"X14' I ! j ! NON-DEFECTIVE I DEFECTIVE I IMC (%) | 61.2 70.8 1 15.0 | 1 27.5 I 20 26 1 -1 68 -1.40 Not S i g . at the 10% l e v e l NON-DEFECTIVE I DEFECTIVE | GREEN SPEC. I GRAVITY | 0 . 355 0.419 1 0.031 I 1 0.038 | 20 26 1 -2 69 -6.03 S i g . at the 1% l e v e l NON-DEFECTIVE| DEFECTIVE I CORE MC (%) | 10.9 17.2 1 1.4 I 1 3.7 | 20 26 1 -2 69 -7.21 S i g . at the 1% l e v e l 4"X4"X13' | ! i i NON-DEFECTIVE I DEFECTIVE I IMC {%) | 63.8 44.1 1 21.9 I I 8.0 | 29 10 1 +2 71 +2.76 Si g . at the 1% l e v e l NON-DEFECTIVE I DEFECTIVE | GREEN SPEC. I GRAVITY | 0.373 0.383 1 0.045 | 1 0.031 | 29 10 1 -1 69 -0.65 Not S i g . at the 10% l e v e l 4"X4"X3' | NON-DEFECTIVE| DEFECTIVE I FMC (%) | AFTER DRYING| 11.0 8.2 1 3.8 I 1 1.5 I 73 23 1 +2 63 +3.44 S i g . at the 1% l e v e l NON-DEFECTIVE I DEFECTIVE | FMC (%) | 1 WEEK AFTERI DRYING | 8.9 8.2 1 2.9 I 1 1.7 I 58 38 1 +1 66 +1.34 Not S i g . at the 10% l e v e l 106 v a l u e s . Every time a " t " t e s t was performed, the f o l l o w i n g s i x -step procedure g i v e n by Walpole was used. For i n s t a n c e , l e t t i n g u x and u 2 represent the average IMCs of the "2x4" p i e c e s of lumber i n which a l l 4 KSs were found checked and f r e e from checking, r e s p e c t i v e l y , we had: 1. N u l l h y p o t h e s i s : u x = u 2. 2. A l t e r n a t i v e h ypothesis : u1 and u 2 were not e q u a l . 3. L e v e l of s i g n i f i c a n c e : 0.10. 4. C r i t i c a l r e g i o n : t < -1.68 f o r 44 degrees of freedom. 5. Computations : The pooled estimate (s 2) of the common v a r i a n c e was f i r s t c a l c u l a t e d . s 2 = ( (20-1) (15.0 2) + (26-1) (27 .52) )/(20+26-2) = 526.85. Then, t = (61.2-70.8)/( (526.85) ( (1/20) + (1/26) ) 1 / 2 = -1.40 6. D e c i s i o n : Accept the n u l l h y pothesis and conclude t h a t the average IMCs of both types of p i e c e s were r e l a t i v e l y the same at the 10% l e v e l . 5. Average i n i t i a l moisture contents i n a l l 4 loads of "4x4" PCH specimens Table A-5 g i v e s the GWs, FWs and average FMCs obt a i n e d i n a l l f o u r loads of "4x4" PCH specimens. GW, FW and FMC of l o a d #5, f o r i n s t a n c e , were 279,9 kg, 196.1 kg and 8.7%, r e s p e c t i v e l y . These data were f i t t e d i n the f o l l o w i n g equation 107 t o c a l c u l a t e the l o a d ODW: ODW = FW / ( FMC + 1) (7) The ODW found was 180.4 kg. F i n a l l y , the l o a d IMC was c a l c u l a t e d u s i n g the f o l l o w i n g e q u a t i o n : IMC = ( GW - ODW ) / ODW (8) The IMC found f o r run #5 was 55.1%. Average IMCs of a l l d r y i n g runs are gi v e n i n Table A-5. Table A-5. Average i n i t i a l moisture contents i n a l l 4 loads  of "4x4" PCH specimens RUN # | LOAD i IMC (%) FMC* (%) GREEN WEIGHT (kg) OVEN-DRY WEIGHT (kg) FINAL* WEIGHT (kg) 5 1 55 . 1 8.7 279.9 180 .4 196 .1 6 • 1 54 . 8 8 .1 273.8 176 . 8 191.1 7 1 57 . 9 10.5 282.6 178 . 9 197 .7 8 ' 1 62 . 9 14 .1 294 . 6 180.8 206.3 * : a f t e r d r y i n g and c o n d i t i o n i n g 108 6. Testing the d i f f e r e n c e between two proportions 6.1 "4x4" specimens found d e f e c t i v e immediately and one week a f t e r drying and c o n d i t i o n i n g To t e s t the hypothesis t h a t the p r o p o r t i o n s of "4x4" specimens found i n t e r n a l l y checked when cross-^-sawn immediately a f t e r d r y i n g and c o n d i t i o n i n g (px) and one week a f t e r t h a t p e r i o d (p2) were equal, the f o l l o w i n g s i x - s t e p procedure d i s c u s s e d by Walpole (43) was used: 1. N u l l h y p o t h e s i s : P i = p 2-2. A l t e r n a t i v e h y p o t h e s i s : P i < p 2 • 3. L e v e l of s i g n i f i c a n c e : 0.01. ; 4. C r i t i c a l r e g i o n : z < -2.33. 5. Computations : The pooled estimate of the p r o p o r t i o n p corr e s p o n d i n g t o the observed p r o p o r t i o n s p x and p 2 was f i r s t c a l c u l a t e d : . ' P i = 17/96 = 0.177, p 2 = 33/96 = 0.344, p = ( (17 + 33)/(96 + 96)) = 0.260. Then, the z value t e s t i n g p x and p 2 was o b t a i n e d z = ( (0.177-0.344)/( (0.260) (0.740) ( (1/96) + (1/96) ) ) 1 / 2 = -2.64. 6. D e c i s i o n : Rej e c t the i n i t i a l h y p o t h e s i s and conclude t h a t the p r o p o t i o n of d e f e c t i v e specimens found immediately a f t e r d r y i n g and c o n d i t i o n i n g was s m a l l e r than t h a t one week l a t e r . 109 6.2 "2X4" and "4x4" specimens f o u n d d e f e c t i v e one week a f t e r d r y i n g and c o n d i t i o n i n g As i n s e c t i o n 7.61, the z value was used t o t e s t the hy p o t h e s i s t h a t the p r o p o r t i o n s of "2x4" (p x) and "4x4" (p2) specimens found i n t e r n a l l y checked one week a f t e r d r y i n g and c o n d i t i o n i n g were e q u a l . The f o l l o w i n g s i x - s t e p procedure given by Walpole (43) was used: 1. N u l l h y p o t h e s i s : p 1 = p 2. 2. A l t e r n a t i v e h y p o t h e s i s : p x < p 2. 3. L e v e l of s i g n i f i c a n c e : 0.01. 4. C r i t i c a l r e g i o n : z < -2.33. 5. Computations : Pi = 14/180 = 0.078, p 2 = 33/96 = 0.344, p = ( (14 + 33)/(180 + 96)) = 0.170, z = ( (0.078-0.344)/( (0.170) (0.830) ( (1/180) + (1/96) ) ) 1 / 2 = -5.60. 6. D e c i s i o n : Rej e c t the i n i t i a l h y p o t h e s i s and conclude t h a t the p r o p o t i o n of "2x4" specimens found d e f e c t i v e one week a f t e r d r y i n g and c o n d i t i o n i n g was s m a l l e r than t h a t the "4x4" ones . 7. Summary o f d r y i n g q u a l i t y o f " 4 x 4 " PCH lumber F i g u r e A-2 shows which "4x4" specimens were found w i t h and 110 F i g u r e A -2. D e f e c t i v e and n o n - d e f e c t i v e s p e c i m e n s o f "4x4" PCH lumber 13' ORIGINAL BOARD # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 RUN # 5 6 7 8 I I 3' SPECIMEN WITHOUT INTERNAL CHECKING • K a m i 3' SPECIMEN WITH INTERNAL CHECKING F i g u r e A-2. ( C o n t i n u e d ) 13'ORIGINAL RUN# BOARD # 5 6 7 8 46 47 48 3' SPECIMEN WITHOUT INTERNAL CHECKING I M l 3' SPECIMEN WITH INTERNAL CHECKING 112 without i n t e r n a l c hecking. The runs t h a t the specimens were used i n and the o r i g i n a l boards which they were cross-sawn from are i n d i c a t e d . 113 

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