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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., L a v a l 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 o f F o r e s t r y  Ve  a c c e p t t h i s t h e s i s as conforming t o the r e q u i r e d  THE  standard  UNIVERSITY OF BRITISH COLUMBIA A p r i l 1991  ©  J o e l Dubois, 1991  In  presenting this  degree at the  thesis in  University of  partial  fulfilment  of  of  department  this thesis for or  by  his  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  representatives.  an advanced  Library shall make it  agree that permission for extensive  scholarly purposes may be her  for  It  is  granted  by the  understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department The University of British Columbia Vancouver, Canada  DE-6 (2/88)  ABSTRACT  The p u r p o s e o f t h i s s t u d y was t o e v a l u a t e t h e e f f e c t i v e n e s s of  steam  conditioning  internal Pacific  checking Coast  conditioning  immediately  resulting  hemlock time,  2,  from  lumber.  after  drying  to  reduce  high-temperature  drying  of  Three  levels  of  4 and 6 h o u r s ,  different were c a r r i e d  o u t on 2  i n c h e s wide by 4 i n c h e s t h i c k by 3 f e e t l o n g (51 mm by 102 by  mm  0.91 m) , and on 4 i n c h e s wide by 4 i n c h e s t h i c k by 3 f e e t  long  (105 mm by 105 mm by:0.91'm), s p e c i m e n s .  purposes,  c o n t r o l s o f b o t h s i z e s o f specimens  For comparison were a l s o  high-  temperature d r i e d without c o n d i t i o n i n g . Analysis of the r e s u l t s  indicated that i n t e r n a l checking  was n o t s i g n i f i c a n t l y r e d u c e d 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 d e v e l o p a f t e r w a r d s d u r i n g s t o r a g e a t room t e m p e r a t u r e , and t h a t t o t a l degrade o b s e r v e d i n t h e "4x4" specimens was more e x c e s s i v e t h a n t h a t i n t h e "2x4" ones. The d e f e c t i v e "4x4" specimens were f o u n d o v e r - d r i e d the  (below  t a r g e t e d 12% m o i s t u r e c o n t e n t ) w i t h h i g h c o r e - s h e l l m o i s t u r e  content d i f f e r e n c e s . specimens'  More i n t e r n a l c h e c k i n g was f o u n d when t h e  f i n a l m o i s t u r e c o n t e n t r a n g e d from 7 t o 8%.  T A B L E OF CONTENTS  ABSTRACT  i i  TABLE OF CONTENTS  i i i  LIST OF FIGURES  v  LIST OF TABLES  viii  ACKNOWLEDGEMENTS  x  ABBREVIATIONS USED  xi  1 . INTRODUCTION  1  2 . LITERATURE REVIEW  4  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  4  2.2 I n t e r n a l c h e c k i n g  9  2 . 3 Conditioning  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 w e i g h t a t 12% m o i s t u r e c o n t e n t  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  iii  2.2 "4x4" specimens  102  3. Summary o f d r y i n g q u a l i t y o f "2x4" PCH lumber  103  4. T e s t s c o n c e r n i n g means  103  5. A v e r a g e i n i t i a l m o i s t u r e c o n t e n t s  i n a l l 4 loads  o f "4x4" PCH specimens  107  6. T e s t i n g t h e d i f f e r e n c e between two p r o p o r t i o n s 6.1 "4x4" specimens f o u n d d e f e c t i v e i m m e d i a t e l y 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 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 7. Summary o f d r y i n g q u a l i t y o f "4x4" PCH l u m b e r . . .  iv  109 109 110 110  L I S T OF  F i g u r e 1.  FIGURES  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 lumber a t various stages of conventional d r y i n g  11  F i g u r e 2.  Sawing p a t t e r n o f "2x4" PCH lumber  19  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" specimens  22  F i g u r e 4. F i g u r e 5.  Sawing p a t t e r n o f t h e "2x4" specimens f o r i n t e r n a l checking evaluation W i d t h gage  23 25  F i g u r e 6.  P o i n t s at which the core moisture  content  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  26  F i g u r e 7.  Sawing p a t t e r n o f "4x4" PCH lumber  28  F i g u r e 8. F i g u r e 9.  K i l n s c h e d u l e o f t h e "4x4" specimens Sawing p a t t e r n o f t h e "4x4" specimens f o r i n t e r n a l checking evaluation  29  F i g u r e 10. F i g u r e 11. F i g u r e 12. F i g u r e 13. F i g u r e 14. F i g u r e 15. F i g u r e 16. F i g u r e 17.  31  Core and s h e l l p a r t s o f a "4x4" m o i s t u r e content s e c t i o n  32  I n i t i a l moisture content frequency d i s t r i b u t i o n o f "2x4" PCH lumber  35  Green s p e c i f i c g r a v i t y f r e q u e n c y d i s t r i b u t i o n o f "2x4" PCH lumber  36  P l o t of average moisture content t i m e f o r r u n #1 (no c o n d i t i o n i n g )  against 39  Plot" of average moisture content a g a i n s t t i m e f o r r u n #2 (2 h o u r s o f c o n d i t i o n i n g )  40  P l o t of average moisture content a g a i n s t t i m e f o r r u n #3 (4 h o u r s o f c o n d i t i o n i n g )  41  P l o t of average moisture content a g a i n s t t i m e f o r r u n #4 (6 h o u r s o f c o n d i t i o n i n g )  42  P l o t of d r y i n g r a t e a g a i n s t average moisture c o n t e n t f o r r u n #1 (no c o n d i t i o n i n g )  43  v  Figure  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 c o n t e n t f o r r u n #2 (2 h o u r s o f c o n d i t i o n i n g ) ....44  Figure  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 c o n t e n t f o r r u n #3 (4 h o u r s o f 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 c o n t e n t f o r r u n #4 (6 h o u r s o f 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 m o i s t u r e c o n t e n t 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 o f "4x4" PCH lumber  54  Green s p e c i f i c g r a v i t y f r e q u e n c y d i s t r i b u t i o n o f "4x4" PCH lumber. . .  56  P l o t of average m o i s t u r e content t i m e f o r r u n #5 (no c o n d i t i o n i n g )  60  F i g u r e 23. F i g u r e 24. F i g u r e 25. F i g u r e 26. F i g u r e 27. F i g u r e 28.  against  P l o t o f average m o i s t u r e content 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 )  .61  P l o t of average m o i s t u r e content 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 )  62  P l o t of average m o i s t u r e content a g a i n s t t i m e f o r r u n #8 (6 h o u r s o f c o n d i t i o n i n g )  63  P l o t of d r y i n g r a t e a g a i n s t average moisture c o n t e n t f o r r u n #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 c o n t e n t 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 ) ....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 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 ) ....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 m o i s t u r e c o n t e n t f o r r u n #8 (6 h o u r s o f 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 o f "4x4" d e f e c t i v e specimens i m m e d i a t e l y 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 n a l moisture content frequency d i s t r i b u t i o n o f "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  F i g u r e 33.  vi  F i g u r e 34.  F i g u r e 35.  F i g u r e 36.  F i g u r e 37.  F i g u r e 38.  F i g u r e 39.  F i g u r e 40.  F i g u r e 41.  F i g u r e 42. Figure A - l . F i g u r e A-2.  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 o f n o n - d e f e c t i v e specimens c u t i m m e d i a t e l y 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 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 o f d e f e c t i v e specimens c u t i m m e d i a t e l y 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 n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f n o n - d e f e c t i v e specimens c u t i m m e d i a t e l y 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 n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f d e f e c t i v e specimens c u t i m m e d i a t e l y 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 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 o f n o n - d e f e c t i v e specimens c u t 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 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 o f d e f e c t i v e specimens c u t 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 n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f n o n - d e f e c t i v e specimens c u t 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 n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f d e f e c t i v e specimens c u t 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  Examples o f d e f e c t i v e and n o n - d e f e c t i v e specimens o f "4x4" PCH lumber  89  D e f e c t i v e and n o n - d e f e c t i v e specimens o f "2x4" PCH.lumber  104  D e f e c t i v e and n o n - d e f e c t i v e specimens o f "4x4 PCH lumber  I l l  ,r  vii  L I S T OF T A B L E S  T a b l e 1.  K i l n s c h e d u l e o f t h e "2x4" specimens  24  T a b l e 2.  K i l n s c h e d u l e o f t h e "4x4" specimens  30  T a b l e 3.  I n i t i a l m o i s t u r e c o n t e n t and g r e e n s p e c i f i c g r a v i t y o f "2x4" PCH lumber  34  T a b l e 4.  Kiln-drying  38  T a b l e 5.  Average m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f  t i m e o f "2x4" PCH s p e c i m e n s  "2x4" PCH specimens  38  T a b l e 6.  D r y i n g r a t e s o f "2x4" PCH specimens  47  T a b l e 7.  Number o f "2x4" PCH specimens w i t h i n t e r n a l checking L a r g e s t i n t e r n a l check s i z e f o r "2x4" PCH  48  specimens  48  T a b l e 9.  T e s t o f mean v a l u e s f o r "2x4" PCH lumber  51  T a b l e 10.  I n i t i a l m o i s t u r e c o n t e n t and g r e e n s p e c i f i c g r a v i t y o f "4x4" PCH lumber Average m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f  53  "4x4" PCH specimens  55  T a b l e 12.  Kiln-drying  58  T a b l e 13.  D r y i n g r a t e s o f "4x4" PCH specimens  58  T a b l e 14.  Number o f "4x4" PCH specimens w i t h i n t e r n a l checking L a r g e s t i n t e r n a l check s i z e f o r "4x4" PCH  68  specimens  68  T a b l e 16.  T e s t o f mean v a l u e s f o r "4x4" PCH lumber  71  T a b l e 17.  F i n a l m o i s t u r e c o n t e n t s o f "4x4" PCH s p e c i m e n s with i n t e r n a l checking Regression l i n e s  75 79  T a b l e 8.  T a b l e 11.  T a b l e 15.  T a b l e 18.  t i m e o f "4x4" PCH specimens  viii  T a b l e 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  T a b l e A - l . T a r g e t e d and f i n a l w e i g h t s i n a l l 8 l o a d s o f PCH specimens T a b l e A-2. T a b l e A-3.  O b s e r v e d and e x p e c t e d f r e q u e n c i e s o f "2x4" PCH specimens one week a f t e r d r y i n g  87 100 101  O b s e r v e d and e x p e c t e d f r e q u e n c i e s o f "4x4" PCH specimens one week a f t e r d r y i n g  103  T a b l e 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  T a b l e A-5.  Average i n i t i a l m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f "4x4" PCH specimens  108  ix  ACKNOWLEDGEMENTS  The Canada  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 Corp.  Forestry  for their  (Wood S c i e n c e )  facilities  financial  support  studies.  The use o f t h e i r  throughout t h i s  study i s a l s o g r e a t l y  Finally,  t h e author would l i k e  assisted  with  h i s study.  a d v i s o r , D r . S. A v r a m i d i s , scientists  Drs.  J.F.G.  o f h i s Master of research  appreciated.  t o t h a n k a l l t h o s e p e o p l e who  In p a r t i c u l a r ,  assistance  U.B.C. F a c u l t y o f F o r e s t r y , Mackay  t e c h n o l o g i s t s m e s s r s S. M c l n t y r e appreciated.  x  and  L.C.  by h i s research  Oliveira  and  and D.M. W r i g h t , F o r i n t e k , i s  A B B R E V I A T I O N S USED  CD  :  conventional  drying  CS  :  conditioning  sample  D  :  discard  DB  :  dry-bulb  (temperature)  e  :  expected  frequency  EMC  :  e q u i l i b r i u m moisture  FCMC  :  f i n a l core moisture  FCSMCD  :  f i n a l c o r e - s h e l l moisture content  FMC  :  f i n a l moisture  FSMC  :  f i n a l s h e l l moisture  FW  :  final  weight  GW  :  green  weight  HTD  :  high-temperature  drying  IMC  .:  i n i t i a l moisture  content  content content  content  KS  :  kiln  MC  :  moisture  MCS  :  moisture content  o  :  observed  NO  :  number  ODW  :  oven-dry  p  :  PCH  :  P a c i f i c C o a s t hemlock  PVA  :  p o l y v i n y l acetate  content  specimen content section  frequency  weight  proportion  xi  difference  R  2  s  2  :  coefficient  :  pooled  of d e t e r m i n a t i o n  estimate  u  :  average  WB  :  wet-bulb  X  :  chi-square  "2x4"  :  2 by 4 i n c h e s  "4x4"  :  4 by 4 i n c h e s  2  (temperature)  xii  1.  In  INTRODUCTION  1984, F o r i n t e k ' s  exploratory  tests  Western  to investigate  Laboratory  t o what  extent  c o u l d be i n c r e a s e d i n t h e d r y i n g o f B r i t i s h lumber  (28) .  lumber  levels  out  temperature  Columbia  framing  Two i n c h e s t h i c k by 4 i n c h e s wide b y 3 f e e t l o n g  (51 mm b y 102 mm by 0.91 m) specimens (PCH)  carried  were  o f P a c i f i c C o a s t hemlock  high-temperature  o f a i r temperature,  121.1, 135.0 and 148.9°C) .  dried  at four  different  225, 250, 275 and 300°F  (107.2,  The r e s u l t s i n d i c a t e d t h a t PCH c a n  s t a n d h i g h d r y i n g t e m p e r a t u r e s w i t h m i n i m a l degrade i n terms o f s u r f a c e c h e c k s , e n d s p l i t s and warp. of  However, v a r y i n g amounts  i n t e r n a l c h e c k i n g were found, p a r t i c u l a r l y i n t h e specimens  d r i e d a t t h e two h i g h e s t t e m p e r a t u r e s . Temperatures long  time  texture  o f above 212°F  i n the drying  of these materials  (100°C) have been u s e d  of t e x t i l e s  and p a p e r .  Since the  i s o f t e n v e r y l o o s e and o n l y  l a y e r s a r e d r i e d a t one t i m e , t h e m o i s t u r e d i s t r i b u t i o n the m a t e r i a l i s not c r i t i c a l .  fora  thin inside  The t a k e - u p o f t h e e v a p o r a t e d o r  b o i l e d - o f f moisture at the surface of the material i s the r e a l concern.  On t h e o t h e r hand, i n h i g h - t e m p e r a t u r e d r y i n g (HTD)  of  lumber,  n o t o n l y has t h e w a t e r t o be e v a p o r a t e d as q u i c k l y  as  possible,  but the d i s t r i b u t i o n  w i t h i n each board i s v e r y c r i t i c a l .  of moisture Indeed,  content  lumber  (MC)  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 o v e r t h e 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 in drying  result  defects.  When m o i s t u r e i s d i f f u s i n g t h r o u g h t h e b o a r d d u r i n g d r y i n g , m o i s t u r e g r a d i e n t s a r e s e t up between t h e s h e l l and t h e c o r e i n a way t h a t t h e MC o f t h e f o r m e r i s a l w a y s l o w e r t h a n t h a t o f t h e latter.  S i n c e t h e m o i s t u r e d i f f u s i o n t h r o u g h t h e s e two d i s t i n c t  a r e a s does n o t o c c u r a t t h e same r a t e , d i s s i m i l a r  dimensional  changes a r e i n e v i t a b l e .  These changes i n two b o d i e s w h i c h a r e  attached  a r e t h e r e a s o n why i n t e r n a l  t o each o t h e r ,  stresses  d e v e l o p 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 o f degrade o c c u r r i n g as a r e s u l t o f d r y i n g stresses  i s increased  when t h e d r y i n g  conditions  a r e made so  s e v e r e as t o g i v e v e r y s t e e p m o i s t u r e g r a d i e n t s .  Past  research  has  low  relative  shown  that  drying  at high  temperatures,  h u m i d i t i e s , or a combination of both, moisture gradients It lumber  causes e x c e s s i v e l y  i n a number o f wood s p e c i e s  steep  (5,30).  i s known t h a t one o f t h e major p r o b l e m s i n d r y i n g PCH i s the large  variation  i n MC between  and w i t h i n t h e  b o a r d s (21,22, 31, 39) . T h i s p r o b l e m 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  heartwood content  (wetwood) w h i c h r e a c h e s t h e d e s i r e d (FMC) two  heartwood. result  t o heartwood t h a t o f t e n c o n t a i n s  Drying  i n steep  to five  times  more  lumber w h i c h c o n t a i n s  moisture  s t r e s s e s and e x c e s s i v e  gradients  degrade.  2  final  slowly  than  sinker  moisture normal  s i n k e r h e a r t w o o d may  responsible  for internal  One cannot e x p e c t HTD t o r e s u l t i n v e r y s h o r t d r y i n g c y c l e s w i t h o u t any i m p a c t  on q u a l i t y .  S i n c e t h e d e g r a d e l o s s e s can  offset  time  s a v i n g s when PCH i s h i g h - t e m p e r a t u r e  lumber  i s c u r r e n t l y d r i e d under l o w e r t e m p e r a t u r e s .  dried, the However,  i f one c a n m i n i m i z e degrade l o s s e s , i . e . d r y PCH lumber a t h i g 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  will  be made. The p u r p o s e o f t h i s s t u d y was t o t e s t t h e h y 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 m i n i m i z e  c h e c k i n g i n PCH  lumber.  3  internal  2. L I T E R A T U R E 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  Western amabilis f i r  hemlock  (Tsuga  (Abies a m a b i l i s  Coast  heterophvlla  hemlock  (Raf.)  Sarg.)  and  (Dougl.) F o r b e s ) a r e two i m p o r t a n t  lumber s p e c i e s h a r v e s t e d on t h e c o a s t and t h e 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 s o f t w o o d s p e c i e s grow t o g e t h e r  and a r e c o m m e r c i a l l y named P a c i f i c C o a s t hemlock fir.  Not a l l s i z e s and t h i c k n e s s e s o f PCH lumber  i n B r i t i s h Columbia are k i l n - d r i e d .  (PCH) o r hemmanufactured  One r e a s o n i s t h a t s h i p p i n g  from t h e c o a s t a l r e g i o n i s b a s e d on volume r a t h e r t h a n on w e i g h t (28) . One more r e a s o n why lumber i s s h i p p e d g r e e n i s a t t r i b u t e d to  the lack  of k i l n  schedules that  will  effectively  dry the  lumber i n a s h o r t p e r i o d o f t i m e and w i t h minimum degrade ( 1 ) . The  major  commercial  conventional kiln-drying.  system  used  t o d r y 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 systems use  d r y i n g t e m p e r a t u r e s up t o 212°F (100°C) a l t h o u g h t h e y a r e u s u a l l y i n t h e range o f 100 t o 190°F (37.8 t o 87.8°C). i n c l u d e steam-heated dryers.  d r y k i l n s and e l e c t r i c a l  I n b o t h s y s t e m s , lumber  These  systems  dehumidification  i s d r i e d i n a c l o s e d chamber  i n w h i c h t e m p e r a t u r e , r e l a t i v e h u m i d i t y and v e l o c i t y o f t h e a i r can  be  controlled.  Such  conventional  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 short time (44). One d r y i n g s y s t e m 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 t h e d r y i n g t i m e o f PCH lumber, kiln-drying. dried  i s high-temperature  As i n c o n v e n t i a l k i l n - d r y i n g s y s t e m s ,  in a kiln  i n which  temperature,  relative  lumber i s  h u m i d i t y and  v e l o c i t y o f t h e a i r a r e 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), a r e u s e d ( 4 4 ) . 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 e x t r e m e l y fast.  Therefore, a m i l l  can p r o c e s s 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 c a n make some s u b s t a n t i a l e n e r g y s a v i n g s because  t h e t o t a l d r y i n g e n e r g y r e q u i r e m e n t s p e r u n i t o f lumber d e c r e a s e as t e m p e r a t u r e s i n c r e a s e  (28,44).  There a r e a t l e a s t two r e a s o n s t h a t may e x p l a i n why HTD is  extremely f a s t .  When wood i s exposed  w h i c h t h e amount o f w a t e r v a p o u r itself,  i t loses moisture.  t o an atmosphere i n  i s l e s s t h a n w i t h i n t h e wood  The r a t e  at which  this  moisture  d e s o r p t i o n t a k e s p l a c e , depends on t h e r e l a t i v e h u m i d i t y i n s i d e the k i l n . drying.  The l o w e r t h e r e l a t i v e h u m i d i t y , t h e f a s t e r i s t h e A low r e l a t i v e h u m i d i t y i n c r e a s e s t h e c a p i l l a r y  flow  o f m o i s t u r e from t h e wood and s t i m u l a t e s d i f f u s i o n o f w a t e r by lowering  t h e MC  humidities,  HTD  temperatures temperature into  steam  at the surface i s also  (33) .  extremely  fast  Besides  low r e l a t i v e  because  of high a i r  (above t h e b o i l i n g p o i n t o f water) . As soon as t h e i n s i d e t h e wood r e a c h e s 212°F (100°C) , w a t e r t u r n s  causing a pressure i n excess of that  i n the k i l n .  This 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  5  water  e v a p o r a t e s o u t o f t h e wood (40) . HTD was i n v e s t i g a t e d f o r t h e f i r s t t i m e i n Canada about 4 8 years  ago.  Canadian species.  Preliminary  Forest  investigations  Products  Western  Laboratory  species  were i n i t i a t e d i n Ottawa  including  on  Douglas-fir,  at the eastern western  hemlock, and w e s t e r n r e d c e d a r were a l s o i n v e s t i g a t e d b u t t o a lesser extent.  Ladell  (24) r e p o r t e d t h a t , i n g e n e r a l ,  softwood  lumber c a n be d r i e d a t h i g h t e m p e r a t u r e s i n a r e m a r k a b l y s h o r t time  and w i t h  little  degrade.  Very  little  end o r s u r f a c e  c h e c k i n g was o b s e r v e d i n hemlock and D o u g l a s - f i r . In  view  of the large  number o f s p e c i e s and s i z e s  that  needed t o be h i g h - t e m p e r a t u r e t e s t e d i n Canada, i t was d e c i d e d two y e a r s l a t e r t o e x t e n d HTD on t h e w e s t e r n c o a s t . the  Vancouver  F o r e s t P r o d u c t s L a b o r a t o r y began  i n t o HTD o f 1 i n c h t h i c k (12).  I n 1954,  investigations  (25 mm) D o u g l a s - f i r and w e s t e r n hemlock  O n l y s l i g h t and medium c h e c k i n g o c c u r r e d i n some o f t h e  f a s t d r i e d lumber when t h e l o a d was removed from t h e k i l n a t low temperatures.  However, s e v e r e f a c e c h e c k i n g was f o u n d when t h e  l o a d was removed a t e l e v a t e d t e m p e r a t u r e s . Up t o 1957, t e s t s thick to  material.  thicker material.  thick 152, to  (25 mm)  were e s s e n t i a l l y  made on o n l y 1 i n c h  HTD i n v e s t i g a t i o n s were n e x t expanded  S c h e d u l e s were d e v e l o p e d f o r 7/4 i n c h e s  (44 mm) w e s t e r n hemlock lumber i n 4, 6, and 8 i n c h e s (102, and 203 mm)  widths  (22) .  T o t a l k i l n t i m e was r e d u c e d up  19% i n d r y i n g 2 by 8 i n c h e s lumber,  6  from 19 t o 37% f o r 2 by  6 i n c h e s lumber,  from 14 t o 39% f o r 2 by 4 i n c h e s lumber  compared t o c o n v e n t i o n a l s c h e d u l e s . and,  i n general,  comparing In  when  Degrade was n o t i n c r e a s e d  c h e c k i n g was s i m i l a r  i n most i n s t a n c e s when  the conventional t o the high-temperature schedules.  a different  study  ( 3 9 ) , two t y p e s o f w e s t e r n  hemlock and  b a l s a m f i r lumber, common and c l e a r , were h i g h - t e m p e r a t u r e d r i e d and  compared  temperatures. i n c h e s wide  with  commercial  The lumber,  drying  using  7/4 i n c h e s t h i c k  conventional  (44 mm) by 4 t o 12  (102 t o 305 mm) i n l e n g t h s o f 14 t o 22 f e e t (4.27  t o 6.71 m), was d r i e d i n 15% l e s s t i m e u s i n g HTD t h a n t h e u s u a l commercial p r a c t i c e .  The l o s s i n v a l u e due t o degrade  common d i m e n s i o n was comparable  i n the  f o r both types of drying.  t h e c l e a r g r a d e s t h e l o s s e s i n v a l u e were about  In  9% h i g h e r f o r  HTD t h a n 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 t h e n c a r r i e d o u t 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 , w e s t e r n hemlock and w e s t e r n r e d c e d a r were h i g h - t e m p e r a t u r e dried  (36,37,38).  Results indicated  that  t h e most  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 e c k i n g . found  that  schedule.  t h e degrade  c a n be m i n i m i z e d  CD was a p p l i e d  until  using  t h e lumber  serious  I t was a l s o a  two-stage  was d r i e d  t o an  a v e r a g e MC v e r y c l o s e t o t h e f i b e r s a t u r a t i o n p o i n t and t h e n t h e s w i t c h was made t o HTD. but  a drying  time  Some d a r k e n i n g o f wood was o b s e r v e d ,  reduction  o f 15 t o 30% o v e r c o n v e n t i o n a l  s c h e d u l e t i m e s was a c h i e v e d .  7  The  effect  hemlock was in  MC  o f HTD  on  and  properties  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 .  between t h e d r i e s t  i.e.  quality  the  FMC  temperatures Increasing  range, were  and w e t t e s t b o a r d s  was  found  used  temperature  to  rather  also  be  the  The  western  difference  of a d r i e d  smaller  than  had  of  when  conventional  greatest  l o w e r i n g t h e wood e q u i l i b r u m m o i s t u r e c o n t e n t  load, high ones.  influence  in  (EMC), i . e . t h e  MC a t w h i c h wood does not g a i n o r l o s e m o i s t u r e .  The h i g h e r t h e  temperature, or the lower the r e l a t i v e humidity, the lower the  EMC  (9,20,21,37,38).  K i l n t i m e was  r e d u c e d by o n e - h a l f o r  more compared t o 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 of  boards:  sapwood,  heartwood  and  schedule,  normal  normal  dried  o t h e r wood t y p e s t o 30% MC, growth  heartwood,  heartwood  had  the  c o n t a i n e d h i g h MC a r e a s .  and  HTD  what  extent  experiments drying  of  (23) .  t w i c e as 25%  faster  longest k i l n  fast  air  PCH  either  the three  t o 15% MC.  t i m e , and  Old-  some  boards  heartwood.  were c a r r i e d PCH  could  out t o i n v e s t i g a t e  be  accelerated  compromising the q u a l i t y of the f i n a l product. (51 by 102 mm)  sinker  With as  types  i n t e n s i f i e d i n t e r n a l c h e c k i n g and  c o l l a p s e i n sapwood and s i n k e r Finally,  young-growth  o l d - g r o w t h s i n k e r heartwood heartwood  was  to  without  Two by 4 i n c h e s  lumber was d r i e d a t f o u r d i f f e r e n t l e v e l s o f  t e m p e r a t u r e , 225,  250,  275  and  300°F  (107.2,  121.1,  135.0  and 148.9°C), a n d - t h r e e l e v e l s o f a i r v e l o c i t y , 300, 600 and  900  ft./min.  the  (1.5, 3.0  and 4.6  m/s) .  8  Results indicated that  loss of moisture per unit strongly  o f t i m e , i . e . t h e d r y i n g r a t e , was  a f f e c t e d by b o t h t e m p e r a t u r e  and a i r v e l o c i t y .  The  higher t h e a i r temperature, or t h e higher the air. v e l o c i t y , the higher  was t h e d r y i n g  rate.  Visible  degrade was m i n i m a l i n  terms o f s u r f a c e c h e c k s , end s p l i t s and warp. amounts o f i n t e r n a l  However, v a r y i n g  c h e c k i n g were found, p a r t i c u l a r l y  i n the  b o a r d s d r i e d a t t h e two h i g h e s t t e m p e r a t u r e s ( 2 8 ) .  2.2  Internal  checking  A c c o r d i n g t o B r a m h a l l and Wellwood ( 4 ) , s t u d i e s o f d r y i n g degrade  made  serious  quality  wood.  i n British loss  Furthermore,  process  without  temperature  Columbia  results  have  from  more  i t was t h e i n t e n t i o n  lumber  checking  with  more  t h e most  to accelerate the drying  lumber  to  check  d r y i n g o f P a c i f i c Coast hemlock).  above,  that  c h e c k i n g and s p l i t t i n g o f  i ti s difficult  causing  shown  of the present emphasis  (see H i g h -  I n view of the review  t o cover  on t h e e f f e c t  of high  t e m p e r a t u r e s on i t s development. When wood i s d r i e d ,  the surface fibers  a MC l e v e l c o r r e s p o n d i n g t o t h e ambient always  lower than that  of the f i b e r  immediately  conditions.  reach  T h i s MC i s  saturation point.  These  f i b e r s a r e 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 , b e c a u s e t h e a d j a c e n t layer  a  short  distance  into  t h e wood  s a t u r a t i o n p o i n t and does n o t s h r i n k .  9  is still  I n consequence,  above t h e t h e wood  i n t h e 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 . p u t under t e n s i o n , w h i l e that  of the inner  layers  i s compressed.  I f the  moisture  g r a d i e n t s e t up between t h e s u r f a c e and i n n e r l a y e r s i s s t e e p , it  i s possible that the t e n s i l e  o f t h e wood a c r o s s lower, The  s t r e s s may e x c e e d t h e s t r e n g t h  the g r a i n which i n t h i s  case w i l l  be even  because o f t h e 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  higher  the d r y i n g temperatures, the higher  HTD.  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 l o w e r t h e 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 o f wood a r e (11,18). result.  I f the moisture  I f this  occurs,  surface  checking  will  gradient i s only moderately steep, the  t e n s i l e s t r e s s i n t h e s u r f a c e l a y e r may e x c e e d t h e e l a s t i c l i m i t o f t h e wood, d e v e l o p i n g checking.  This  a permanent s t r e s s r a t h e r t h a n  permanent  stress  i s known  as  surface  tension set  (5,8,30) . As  the next l a y e r t o the s u r f a c e  s h r i n k and hence be c o n v e r t e d one under t e n s i o n .  dries,  i twill  tend t o  from a zone under c o m p r e s s i o n t o  T e n s i o n s e t can be i n d u c e d i n e a c h s u c c e s i v e  l a y e r f r o m t h e s h e l l t o t h e c o r e o f t h e wood as i t s h i f t s b e i n g under c o m p r e s s i o n t o b e i n g under t e n s i o n . the moisture steep,  s t r e n g t h p r o p e r t i e s o f t h i s zone.  Figure stresses  tension, 1  Once a g a i n , i f  g r a d i e n t t h a t i s s e t up t h r o u g h t h e b o a r d i s q u i t e  i t i s possible that the t e n s i l e  internal  from  shows that  a  that  The wood w i l l t h e n f a i l under  i s , develop  typical  sequence  developed during  10  s t r e s s may e x c e e d t h e  internal of  checking  transverse  CD o f 2 i n c h e s  thick  (5) .  residual r e d oak  Figure  1.  Transverse r e s i d u a l s t r e s s e s i n lumber various stages of conventional d r y i n g (after McMillen 1958)  at  CO CO UJ  a: o.  CO  to  2 o o  —£rCOC 2 ID  g CO  z DAYS DRYING  28  18  11  36  50  h e a r t w o o d lumber ( 2 9 ) . S i n c e t h e MC g r a d i e n t i s s t e e p e s t d u r i n g t h e e a r l y s t a g e s of  drying,  the  greatest level  present then (34).  of  stress  i n tension i s  also  T h e r e f o r e , i n t e r n a l c h e c k i n g can u s u a l l y be  a v o i d e d by e n s u r i n g t h a t s e v e r e s t r e s s e s do not d e v e l o p when t h e MC  o f t h e s h e l l and c o r e o f t h e d r y i n g b o a r d i s above t h e f i b e r  saturation point. until  a l l the f r e e water  board. of  a  I n t h i s way  has been e v a p o r a t e d  that  schedule  s c h e d u l e when t h e MC of the  shown t h a t  less  from t h e  entire  lumber can be k i l n - d r i e d w i t h a c o m b i n a t i o n  c o n v e n t i o n a l temperature  temperature than  E x c e s s i v e l y high a i r temperatures are avoided  fiber  f o l l o w e d by  of the d r y i n g board  saturation  checking developed  point.  Past  u s i n g such  a  high-  i s less  research a  has  combination  (2,3,37). • However, t h i s i s not a l w a y s t h e c a s e . also  shown t h a t ,  maximum  tensile  significantly  P a s t r e s e a r c h has  when t h e c o r e o f t h e b o a r d stress  and  the  drying  has  developed  temperature  a is  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 d e c r e a s e due t o t h e p l a s t i c i z i n g e f f e c t o f t h e h e a t .  The  r e s u l t o f 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 n g (41,42). present  i n the  accentuated.  core  Mackay  I f high-moisture-content pockets are  of the board,  internal  checking w i l l  be  (26) f o u n d out t h a t c o l l a p s e d e v e l o p s i n  t h e form o f s e v e r e s h r i n k a g e when t h e s e wet  pockets dry  T h i s c o l l a p s e r e s u l t s i n a weakened b o a r d more l i k e l y  12  to  out. pull  apart  under  tensile  stresses  after  stress  reversal  (29).  F i n a l l y , lumber h a v i n g 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 t h e c o r e wet.  As i n lumber w i t h wet p o c k e t s , s u c h  more l i k e l y t o d e v e l o p i n t e r n a l c h e c k i n g  lumber i s  (10,25,27).  Water i n wood moves 12 t o 15 t i m e s f a s t e r a l o n g t h e g r a i n t h a n i t does a c r o s s i t ( 3 3 ) . T h e r e f o r e , lumber l o s e s m o i s t u r e 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 . and  more  uniform  evaporation  of  Unless a slower  moisture  is  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 t h e s e l o n g i t u d i n a l m o i s t u r e g r a d i e n t s a r e  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 c h e c k i n g ( 4 5 ) . If  the moisture  checks  gradient  i s only moderately  steep,  t h e end  a r e u s u a l l y s m a l l and do n o t e x t e n d v e r y f a r back  t h e wood.  However, i f t h e m o i s t u r e g r a d i e n t i s s t e e p ,  end  develop,  checks  and as t h e i n t e r n a l  from a zone under c o m p r e s s i o n checks  may  end  of  longitudinal eliminate stresses resistant  larger  are converted  t o one under t e n s i o n , t h e s e end  go a l l t h e way a c r o s s t h e i n t e r i o r  d r y i n g board. one  layers  layers  of the  T h i s form o f i n t e r n a l c h e c k i n g c a n e x t e n d the  board  drying  these  to  the  stresses  longitudinal  i s t o p a i n t t h e ends coatings.  into  other,  (29) . moisture  depending  One  way  to  gradients  of the boards  upon reduce  from the or  and d r y i n g  with  moisture-  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 t h e wood has d r i e d a p p r e c i a b l y and end c h e c k s have formed ( 3 3 ) .  13  \  \  2.3  Conditioning  K i l n s c h e d u l e s u s i n g c o n d i t i o n i n g t r e a t m e n t s were r e c e n t l y d e v e l o p e d a t F o r i n t e k Canada Corp. i n V a n c o u v e r t o k i l n - d r y 4 inches  t h i c k by 4 i n c h e s  lumber i n a c c e p t a b l y no  degrade  150°F  (1) .  90%.  (DB) and 14 6°F  resulted This  in  long  surfaced  PCH  o f t i m e and w i t h l i t t l e o r  The lumber was c o n d i t i o n e d  that  approximately  (102 by 102 mm)  short periods  (65.6°C) d r y - b u l b  temperatures,  wide  a  f o r 24 h o u r s a t  (63.3°C) w e t - b u l b relative  humidity  humidity  treatment  (WB) of  resulted i n  s t r e s s r e l i e f , m o i s t u r e r e d i s t r i b u t i o n and d i s a p p e a r a n c e o f many of  t h e end and s u r f a c e  checks t h a t  were p r e s e n t  before  that  I n v i e w o f t h e above, t h e p r o c e d u r e p r o p o s e d i n t h i s  study  step.  to  diminish  the occurrence  of i n t e r n a l  r e l i e f immediately a f t e r drying. internal  stresses  responsible  checking  was  stress  The r e l i e f o f t e n s i o n s e t s and for  internal  checking  is  a c c o m p l i s h e d e s s e n t i a l l y by t h e a d d i t i o n o f m o i s t u r e and heat to  the outer  schedule. adjacent to,  l a y e r s o f t h e lumber  I f enough w a t e r  i s added t o t h e s u r f a c e  and i t s  l a y e r , compressive sets are induced which are opposite  and t e n d  to relieve,  e a r l i e r during drying. cross  a t t h e end o f t h e d r y i n g  the tension  sets  which  I n t e r n a l s t r e s s e s a l l t h e way a c r o s s t h e  s e c t i o n c a n be r e l i e v e d t h i s way when h i g h  are maintained  developed  f o r a l o n g enough p e r i o d o f t i m e  14  temperatures (29) .  According  t o Kininmonth  and W i l l i a m s  (17),  s h o u l d be c a r r i e d o u t i m m e d i a t e l y a f t e r d r y i n g . two  conditioning  I f n o t , one o r  end c h e c k s c o u l d e x t e n d 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  storage, to result  (see I n t e r n a l c h e c k i n g ) .  i n excessive internal  checking  One o f t h e b e s t methods t o a c h i e v e  good c o n d i t i o n i n g i n t h e s h o r t e s t l e n g t h o f t i m e i s t h r o u g h t h e use o f steam s u p p l i e d by l o w p r e s s u r e b o i l e r s .  The q u a l i t y o f  t h e steam i s a l w a y s 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 humidities  and EMCs c a n be a c h i e v e d  at higher  temperatures.  H i g h p r e s s u r e steam on t h e o t h e r hand i s g e n e r a l l y much d r i e r . It  c o n t a i n s more heat  produced.  and l e s s  moisture  p e r pound  o f steam  One e f f e c t i v e method t o a c h i e v e s a t u r a t e d c o n d i t i o n s  at high temperatures t h e steam s p r a y l i n e .  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  into  M i x i n g o f w a t e r w i t h h i g h p r e s s u r e steam  can r e d u c e c o n d i t i o n i n g t i m e by o n e - h a l f o f t h e t i m e needed f o r c o n d i t i o n i n g o f h o t lumber. system  f o r water  Devices i n s t a l l e d i n the spray l i n e  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,  r a i s e t h e r e l a t i v e h u m i d i t y and save steam (4 6 ) . were t e s t e d by K i n i n m o n t h (25 and 51 mm) (16,17). drying  effectively  B o t h methods  and W i l l i a m s on 1 and 2 i n c h e s t h i c k  r a d i a t a p i n e lumber and gave e x c e l l e n t  When c o n d i t i o n i n g was c a r r i e d o u t i m m e d i a t e l y  (4 h o u r s  results after  a t 100°C) u s i n g l o w p r e s s u r e , s a t u r a t e d steam,  s e v e r e i n t e r n a l c h e c k i n g e x t e n d i n g from t h e ends o f lumber and from t h e d i s t o r d e d g r a i n a r o u n d t h e k n o t s , was l i m i t e d t o s l i g h t checking  near  t h e ends  (40 t o 80 mm)  15  and a r o u n d  the knots.  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 cooling spray  the load  line  second  80°C,  t o about  by i n j e c t i n g  water  and t h e n s t e a m i n g a t 85 t o 90°C) .  method  increased  t h e maintenance  costs  into the  However,  this  (due t o t h e  c o r r o s i v e a c t i o n o f t h e w a t e r d r o p l e t s ) and t h e d r y i n g t i m e . 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 a t h i g h temperatures. thermal  expansion  The p o s s i b i l i t y o f s t r e s s r e l i e f by  should  not  be  overlooked  conditioned using high a i r temperatures.  when  wood i s  Any e x p a n s i o n o f t h i s  n a t u r e , however, s h o u l d not be o f s u f f i c i e n t magnitude t o cause t h e wood t o expand beyond i t s e l a s t i c l i m i t  (7). Stresses that  w o u l d a r i s e from t h e r m a l e x p a n s i o n c a u s e d by h i g h e r c o n d i t i o n i n g t e m p e r a t u r e s would be minor compared t o t h o s e d e v e l o p e d e a r l i e r from m o i s t u r e changes. relief, Hillis  A n o t h e r s o u r c e t h a t c o u l d cause s t r e s s  i s the p l a s t i c i z i n g  effect  of temperature  on  wood.  (13) s u g g e s t s t h a t h i g h t e m p e r a t u r e s , when m a i n t a i n e d f o r  a s u f f i c i e n t t i m e , can cause t h e l i g n i n s i n t h e m i d d l e l a m e l l a and t h e l i g n i n s soften  rather  and h e m i c e l l u l o s e s a r o u n d t h e m i c r o f i b r i l s t o  than  fracture  under  tension  of moisture,  sets  and  internal  softening  o f wood  stresses.  In the presence  accentuates  (6) so t h a t i t s m e c h a n i c a l b e h a v i o r c a n be  from g l a s s - l i k e t o s e m i - p l a s t i c .  changed  The a d d i t i o n o f m o i s t u r e t o  t h e s u r f a c e f i b e r s a t t h e end o f d r y i n g c a u s e s them t o s w e l l . When t h e wood i s more p l a s t i c amount o f s w e l l i n g  increase  i n character,  resulting  16  t h e r a t e and t h e  i n a faster  and b e t t e r  stress  relief.  3.  3.1  Phase  One  M A T E R I A L S AND  I  shipment o f n i n e t y ,  g r e e n roughsawn PCH  were 2 by  respectively. harvested  on  Sandspit.  the  feet long obtained  actual metric  4 inches  The  14  lumber was  I m p e r i a l n o m i n a l and pieces  METHODS  There was  51 by  commercially  Queen C h a r l o t t e  Islands  no p a r t i c u l a r  m) , p i e c e s  from a l o c a l  thickness  ("2x4") and  lumber was  (4.27  sawmill.  and  width  of  the  102  millimetres,  produced from i n an  area  logs  close  s a w i n g p a t t e r n so t h a t  Each p i e c e o f lumber was f r o m 1 t o 90.  and  content (25.4 one  two  cm)  s e t s of n i n e t y ,  t o keep t h e i r MC  o f MCSs was  (MCSs) .  away from one  s e t o f MCSs.  l o a d s #1,  #2,  The  (91.4  cm),  1 inch long one  MCS  (2.5 was  four  kiln  specimens  cm),  moisture  sawn 10  inches  end o f e a c h p i e c e o f lumber, t o make up MCSs were put  unchanged.  #3 and #4,  obtained.  long  First,  i n a p l a s t i c bag  F o u r KSs  respectively.  in  were sawn n e x t f o r  order kiln  F i n a l l y , the second set  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 .  E v e r y p i e c e of lumber was KSs  sapwood.  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  sections  no  randomly a s s i g n e d a number r a n g i n g  k i l n l o a d s o f n i n e t y , 36 i n c h e s (KSs)  to the  a n n u a l 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 s e p a r a t i o n between h e a r t w o o d and  of  sawn i n s u c h a way  were l a b e l l e d on t h e same t o p f a c e .  18  XX-Y  was  that i t s four t h e code u s e d  F i g u r e 2. S a w i n g p a t t e r n o f " 2 x 4 " PCH l u m b e r  D  MCS  KS  KS .  KS  KS  KS  : K I L N S P E C I M E N (3 feet)  MCS  : 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 i n c h e s )  19  MCS  D  t o l a b e l e a c h KS where XX and Y were t h e i d e n t i f i c a t i o n numbers o f t h e p i e c e o f lumber i t was t h e s p e c i m e n was KS  sawn f r o m and t h e run number t h a t  used i n , r e s p e c t i v e l y .  sawn f r o m p i e c e o f lumber #12  12-2.  A MCS  was  r i g h t or l e f t ,  l a b e l l e d XX-R  The  l a b e l given to  the  for instance,  was  i n l o a d #2, o r XX-L,  R and  i n d i c a t i n g from w h i c h end  i t was  L,  standing  for  sawn.  I m m e d i a t e l y a f t e r s a w i n g , t h e KSs were c o a t e d w i t h a heavy coat of p o l y v i n y l acetate drying  before  and  during  s e a l e d , t h e lumber was was  (PVA) the  a t b o t h ends t o m i n i m i z e  experimental  t h e MC  of the  Once weighed  Water  s i g n i f i c a n t changes i n  lumber  0.1  g)  was  using  sealed  and  a digital  stored,  balance.  the  MCSs  were  They were  then  immersed i n w a t e r t o measure t h e i r g r e e n volume (± 0.1 oven-dried  Once  specimens.  the  (±  kiln-drying.  s t o r e d o u t s i d e under p l a s t i c wrap.  s p r a y e d on t h e p l a s t i c t o r e d u c e any  end-  a t 103°C (± 2°C).  w e i g h e d once more and  cm )  and  3  T w e n t y - f o u r h o u r s l a t e r , t h e y were  t h e i r g r e e n MC  and  s p e c i f i c g r a v i t y were  calculated. The (0.91  m)  kiln  used i n t h i s  e x p e r i m e n t was  laboratory-scale unit.  The  m/s)  A i r v e l o c i t y through the w i t h no  inches  wide  3 feet apart,  r e v e r s a l of flow. (32 mm)  by  3/4  set  a t 750  fpm  feet so  (3.8  aluminum s t i c k e r s were  inch thick  (19 mm)  i . e . a t each end o f t h e KSs.  20  3  c o u l d be m o n i t o r e d o v e r  l o a d was The  3 by  l o a d r e s t e d on a s c a l e  t h a t change o f w e i g h t , and t h e r e f o r e MC, time.  a 3 by  and  were  5/4  placed  A p a r t i c u l a r loading  p a t t e r n was u s e d so t h a t i n a l l f o u r r u n s , t h e KSs sawn from t h e same o r i g i n a l p i e c e o f lumber had t h e same k i l n l a b e l l e d t o p f a c e o f each KS a l s o  location.  The  faced the top of the k i l n .  D r y i n g was c a r r i e d o u t a t 300°F (148.9°C) DB and a p p r o x i m a t e l y 212°F (100.0°C) WB t e m p e r a t u r e s , r e s u l t i n g i n a r e l a t i v e h u m i d i t y and EMC o f 22% and 1.4%, r e s p e c t i v e l y ( 3 5 ) . The k i l n  was s e t t o t u r n i t s e l f o f f when t h e l o a d  weight  c o r r e s p o n d i n g t o an a v e r a g e o f 12% MC, was r e a c h e d (see A p p e n d i x 7.1). air  The c o n d i t i o n i n g p e r i o d s c h e d u l e d was s t a r t e d when t h e  temperature  different  i n the k i l n  was down t o 185°F  (85.0°C).  l e v e l s o f c o n d i t i o n i n g t i m e , 2, 4 and 6 h o u r s , were  c a r r i e d o u t once f o r runs #2, #3 and #4, r e s p e c t i v e l y . runs,  Three  conditioning  was  done  (82.2°C) WB t e m p e r a t u r e s , approximately  90%.  conditioning  a t 185°F  resulting  One l o a d ,  f o r comparison  and #4), t h e specimens  i n a relative  purposes.  The k i l n  and 180°F  humidity of without  schedule i s  i n T a b l e 1.  ( r u n #1) o r c o n d i t i o n i n g  were l e f t  down t o room t e m p e r a t u r e ,  DB  r u n #1, was k i l n - d r i e d  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 After either drying  (85.0°C)  In a l l  i n the k i l n  i . e . 23°C.  (runs #2, #3  i n order t o cool  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 t h e n c r o s s - s a w n i n t o t h r e e , 12 inches long CSs  were  (30.5 cm), c o n d i t i o n i n g samples  immediately  labelled  (CSs)-.  A l l three  for identification  purposes.  F i g u r e 4 shows t h e sawing p a t t e r n u s e d . f i v e specimens  The r e m a i n i n g  o f t h e c h a r g e were k e p t a t room  21  forty-  temperature  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" specimens  350 DRY-BULB  WET-BULB  300  111  cc QC  HI Q.  250  LU 200  12%  Green  MOISTURE CONTENT (%  22  Figure  4. Sawing p a t t e r n o f t h e "2x4" specimens f o r i n t e r n a l checking evaluation  T a b l e 1. K i l n s c h e d u l e o f t h e "2x4" specimens  DB  (°F)  WB  (°F)  300  212  185  180  MC  (%)  GREEN 12  i n s i d e t h e l a b o r a t o r y and c u t a c c o r d i n g t o t h e same p a t t e r n one week l a t e r . E v e r y CS was c h e c k e d i m m e d i a t e l y a f t e r c u t t i n g t o d e t e r m i n e t h e e x t e n t , i f any, o f i n t e r n a l c h e c k i n g . largest  internal  recorded.  checks  observed  The l o n g e s t and t h e  i n each  drying  The l e n g t h s and w i d t h s o f t h e c h e c k s  using a d i g i t a l  were measured mm),  respectively.  The w i d t h gage u s e d i s shown i n F i g u r e 5.  The  number  with  one  (± 1 mm)  were  (± 0.1  o f CSs  caliper  run  o r more  and a w i d t h gage  internal  check (s)  was  also  recorded. Two weeks a f t e r d r y i n g , t h e c o r e MC o f e a c h CS was measured u s i n g a d c - r e s i s t a n c e moisture meter. first (2.5  taken 4 inches cm)  into  One MC measurement  was  (10.2 cm) away from one end, 1 i n c h deep  t h e wood.  This procedure  was  repeated  at the  o t h e r end so t h a t f o r each CS, two c o r e MC measurements were t a k e n 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 c h e c k i n g were i d e n t i f i e d and r e c o r d e d .  24  F i g u r e 5. W i d t h  25  gage  Figure  6.  Points at which the core moisture content each c o n d i t i o n i n g sample were t a k e n  4  4 "  11  26  4  of  3.2 P h a s e I I  A shipment o f f o r t y - e i g h t , of  surfaced  PCH  actual metric inches  lumber  was  13 f e e t l o n g  obtained.  t h i c k n e s s and w i d t h  (3.96 m) , p i e c e s  Imperial  of the pieces  nominal  and  were 4 by 4  ("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  l o g s o r i g i n a t e d from t h e N i m p k i s h V a l l e y on V a n c o u v e r 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 t h e same way schedule  as i n Phase I .  O n l y t h e s a w i n g p a t t e r n and d r y i n g  u s e d 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 i n c h e s l o n g (91.4 cm), KS was f i r s t sawn f r o m one end o f each p i e c e o f lumber, t o make up k i l n l o a d #1.  One MCS was sawn n e x t  t o make up one MC s e t . Two more KSs f o r k i l n  l o a d s #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 o f lumber. out  a t 275°F  resulting and  (135.0°C) DB  i n a r e l a t i v e humidity  i n Table  After either drying  and EMC  an odd number  inches long  temperatures,  of approximately  16%  i s illustrated  2.  ( r u n #5) o r c o n d i t i o n i n g (runs #6, #7  #8) , t h e specimens were l e f t  down t o room t e m p e r a t u r e . with  (82.2°C) WB  1.1%, r e s p e c t i v e l y ( 3 5 ) . The k i l n s c h e d u l e  i n F i g u r e 8 and l i s t e d  and  and 180°F  D r y i n g was c a r r i e d  i n the k i l n  The t w e n t y - f o u r  were t h e n  cross-sawn  i n order t o cool  specimens into  (33.0, 25.4 and 33.0 cm) s a m p l e s .  labelled  13, 10 and 13 A 1 inch long  (2.5 cm) MCS was sawn o p p o s i t e t o each c o a t e d end o f e a c h 13  27  F i g u r e 7. S a w i n g p a t t e r n o f " 4 x 4 " PCH l u m b e r  KS  MCS  KS  KS  MCS  KS  : K I L N S P E C I M E N (3 feet)  MCS  : 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  KS  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" specimens  350 DRY-BULB  WET-BULB  300  LU  DC C  UJ  250  CL  UJ l200  12%  Green  MOISTURE CONTENT (%  29  T a b l e 2. K i l n s c h e d u l e  DB  o f t h e "4x4" specimens  WB  (°F)  MC  (°F)  275  180  185  180  (%)  GREEN  12  i n c h e s l o n g (33.0 cm) samples and l a b e l l e d on i t s t o p f a c e . remaining  The  12 i n c h e s l o n g (30.5 cm) samples were t h e CSs u s e d f o r  i n t e r n a l checking evaluation.  F i g u r e 9 i l l u s t r a t e s the sawing  pattern  described.  The MCSs were  then  sawn  parts.  The t o p and b o t t o m p a r t s o f each MCS  i n three  equal  were p u t i n t h e  oven a t 103°C (± 2°C) f o r 24 h o u r s i n o r d e r t o e s t a b l i s h shell  moisture  content  (FSMC) .  The c e n t e r p a r t was  more t i m e i n t h r e e e q u a l s m a l l e r p i e c e s . oven-dried (FCMC) . remaining  i n order to obtain i t s f i n a l  final  sawn  one  The c e n t e r p i e c e  was  core moisture  content  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 ( F i g u r e 10) . twenty-four  specimens l a b e l l e d  with  an even  The  number  were k e p t a t room t e m p e r a t u r e and c u t u s i n g t h e same p a t t e r n one week l a t e r . In e a c h r u n , e v e r y CS was c h e c k e d i m m e d i a t e l y to  determine  the extent,  l o n g e s t and t h e l a r g e s t  i f any, o f i n t e r n a l  after  cutting  checking.  The  i n t e r n a l c h e c k s f o u n d were r e c o r d e d t h e  same way as i n Phase I .  Samples w i t h i n t e r n a l  30  checking  were  Figure  9. S a w i n g p a t t e r n o f t h e " 4 x 4 " s p e c i m e n s for i n t e r n a l checking evaluation  CS  12"  MCS  1"  . CS  10"  MCS  1"  CS  : CONDITIONING  MCS  : MOISTURE CONTENT  12"  SAMPLE  31  SECTION  CS  F i g u r e 10. C o r e and s h e l l p a r t s o f a moisture content section  A  : S H E L L PART  B  : C O R E PART  D  :  DISCARD  32  "4x4"  i d e n t i f i e d and r e c o r d e d .  4. RESULTS AND D I S C U S S I O N  4.1 P h a s e  I  As c a n be seen i n T a b l e 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 t h e "2x4" p i e c e s o f PCH lumber. 69.7%,  ranging  distribution  from  40.0  t o 164.5%.  The a v e r a g e IMC was  Figure  11  shows t h e  o f IMCs and as can be seen, a g r e a t e r p o r t i o n o f  t h e lumber had IMCs r a n g i n g from 40 t o 80%. T a b l e 3. I n i t i a l m o i s t u r e c o n t e n t and g r e e n s p e c i f i c g r a v i t y o f "2x4" PCH lumber  MIN  MAX  AVG  40.0  164 .5  69.7  0.303  0.553  0.397  I N I T I A L MOISTURE CONTENT (%)  GREEN SPECIFIC  The  green  GRAVITY  specific  gravity  also  showed a  considerable  v a r i a t i o n between t h e p i e c e s , r a n g i n g from 0.303 t o 0.553 ( T a b l e 3) . A g r e a t e r p a r t o f t h e lumber 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 0.360 t o 0.420  (Figure 12).  I t i s l i k e l y that the pieces  w i t h l o w 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 t h o s e w i t h h i g h s p e c i f i c g r a v i t y were w e s t e r n hemlock  (see Phase  t h e a v e r a g e g r e e n s p e c i f i c g r a v i t y was 0.397.  34  II).  Overall  F i g u r e 11. I n i t i a l m o i s t u r e c o n t e n t f r e q u e n c y o f "2x4" PCH lumber  distribution  50  20-40  40-60  60-80  80-100 100-120 120-140 140-160 160-180  INITIAL MOISTURE CONTENT (%)  35  F i g u r e 12. Green s p e c i f i c g r a v i t y f r e q u e n c y o f "2x4" PCH lumber  distribution  .30-.33 .33-.36 .36-.39 .39-.42 .42-.45 .45-.48 .48-.51 .51-.54 .54-.57 SPECIFIC GRAVITY  36  T a b l e 4 shows t h e k i l n - d r y i n g t i m e o f lumber f o r a l l d r y i n g runs.  D r y i n g t i m e s from g r e e n t o t h e t a r g e t e d 12% MC were q u i t e  close, run  ranging  #1.  from 24.00 h o u r s f o r r u n #4 t o 26.50 h o u r s f o r  Cooling  from  300  to  185°F  (148.9  to  85.0°C)  DB  t e m p e r a t u r e 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 h o r t time, #2.  ranging  f r o m 45 m i n u t e s f o r r u n #3 t o 2.00 h o u r s f o r r u n  I n r u n #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  kiln-dried  in  only  26.50  hours.  In  run  conditioned  f o r 6.00 h o u r s r a i s i n g t h e t o t a l  #4,  lumber  was  kiln-drying  time  t o 31.00 h o u r s . Comparing F i g u r e s run  were s i m i l a r .  13, 14, 15 and 16, d r y i n g r a t e s i n each  A n o t i c e a b l e d i f f e r e n c e , however, was t h e  h i g h e r MC o b t a i n e d  i n l o a d #2 b e f o r 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 T a b l e 5, b o t h MCs b e f o r e  c o o l i n g i n loads  and  #4 were 12.1% compared t o 13.2% i n l o a d #2.  may  e x p l a i n why  r u n #2 had a r e l a t i v e l y  since the thermal (33) . flowed This  The h i g h e r  longer  c o n d u c t i v i t y o f wood i n c r e a s e s  cooling with  #3 MC  time  i t s MC  A h i g h e r MC may have i n c r e a s e d t h e q u a n t i t y o f heat t h a t through release  t h e wood when i t s s u r f a c e s of  heat  temperature i n the k i l n  may  have  slightly  resulting  were c o o l e d increased  i n a longer  down.  the a i r  cooling period.  D r y i n g r a t e s o f a l l runs were t h e n p l o t t e d a g a i n s t t h e i r a v e r a g e MCs  (Figures  17,  18,  19,  and  d i f f e r e n c e s t h a t might e x i s t . drying progressed  was a g a i n  20)  i n order  to evaluate  any  The change i n t h e d r y i n g r a t e as  s i m i l a r a t each r u n .  37  When t h e  T a b l e 4.  K i l n - d r y i n g t i m e o f "2x4" PCH specimens  RUN #  KILN-DRYING TIME  I  COOLING  (hours)  I  DRYING  1 CONDITIONING I  1  1  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  j  TOTAL  26.50  T a b l e 5. A v e r a g e m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f "2x4" PCH specimens  RUN #  MOISTURE  I |  BEFORE COOLING  | |  CONTENT  BEFORE CONDITIONING  --  1  (%)  | |  AFTER DRYING AND CONDITIONING  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 o f average m o i s t u r e c o n t e n t f o r r u n #1 (no c o n d i t i o n i n g )  against  time  80  60 Z LLI I8 40 Ul  DC  O  20  1 0  ,  1 5  ,  1  , 10  1  , 15 TIME (hours)  39  I 20  ,  | 25  ,  i_ 30  F i g u r e 14. P l o t o f average m o i s t u r e c o n t e n t a g a i n s t f o r r u n #2 (2 hours o f c o n d i t i o n i n g )  time  DRYING  0  5  10  15 TIME (hours)  40  20  25  30  F i g u r e 15. P l o t o f average m o i s t u r e c o n t e n t a g a i n s t f o r r u n #3 (4 hours o f c o n d i t i o n i n g )  time  DRYING  0  5  10  15 TIME (hours)  41  20  25  30  F i g u r e 16. P l o t o f average m o i s t u r e c o n t e n t a g a i n s t f o r run #4 (6 hours o f c o n d i t i o n i n g )  time  Figure  17. 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 #1 (no c o n d i t i o n i n g )  Figure  80  18. 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 #2 (2 hours o f c o n d i t i o n i n g )  60  40 MOISTURE CONTENT (%)  44  20  Figure  19. 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 run #3 (4 hours o f c o n d i t i o n i n g )  5  80  60  40 MOISTURE CONTENT (%)  45  20  Figure  20.  P l o t of drying r a t e against average moisture c o n t e n t f o r r u n #4 (6 h o u r s o f c o n d i t i o n i n g )  d e s i r e d DB and WB t e m p e r a t u r e s were r e a c h e d , t h e d r y i n g r a t e was maximum.  Thereafter,  lumber  MC  and d r y i n g  decreased s i m i l a r l y f o r a l l d r y i n g runs. o f a l l r u n s were f i n a l l y  rate  constantly  Average d r y i n g  rates  c a l c u l a t e d and, as shown i n T a b l e 6,  were r e l a t i v e l y c l o s e , r a n g i n g from 2.20% o f MC p e r hour f o r r u n #1 t o 2.40% o f MC p e r hour f o r r u n #4.  For a l l drying  the h i g h e r t h e average d r y i n g r a t e , t h e s h o r t e r  runs,  was t h e d r y i n g  t i m e f r o m g r e e n t o t h e t a r g e t e d 12% MC. T a b l e 6. D r y i n g  r a t e s o f "2x4" PCH s p e c i m e n s  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 loss moisture gain Table  7  shows  i n t e r n a l checking cut  *  immediately  t h e number  o f specimens  i n each d r y i n g r u n . after  drying  that  When t h e specimens were  and c o n d i t i o n i n g ,  47  developed  no  internal  T a b l e 7. Number o f "2x4" PCH specimens w i t h i n t e r n a l c h e c k i n g 3' SPECIMENS CUT AT 1' FROM THE  RUN #  j 1  AFTER DRYING  LEFT  RIGHT  0  0  q  ' 0  1 WEEK AFTER DRYING  %  1  0  0  1  0  0  MAX.  j 1  1  END  LEFT  RIGHT  j  ]  5  6  6  1  0  3  3  1  3  1  o  0  0  0  1  1  3  3  4  1  0  0  0  0  1  1  2  2  RIGHT  A  112 \  / \  [  2  LEFT, MAX. %  %  MAX.  : : :  •  1  1  [  4  number o f d e f e c t i v e s p e c i m e n s f o u n d a t t h a t e n d maximum number o f d e f e c t i v e s p e c i m e n s a t one o r b o t h ends p e r c e n t a g e o f d e f e c t i v e s p e c i m e n s a t one o r b o t h ends  T a b l e 8. L a r g e s t i n t e r n a l check s i z e f o r "2x4" PCH specimens 3' SPECIMENS CUT AT 1  RUN #  I  AFTER DRYING  (mm)  1  |  WIDTH  (mm)  1 WEEK AFTER DRYING  I  LENGTH  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  |  FROM THE END  LENGTH  (mm)  |  WIDTH  (mm)  c h e c k i n g was  found.  Internal  checking occurred l a t e r during  subsequent  s t o r a g e a t room t e m p e r a t u r e so t h a t f o r r u n s #1,  #3 and #4,  13, 7, 7 and 4% o f t h e specimens,  #2,  r e s p e c t i v e l y , were  f o u n d w i t h i n t e r n a l c h e c k i n g a t one o r b o t h ends when c u t week  after  drying.  Kininmonth  and  s i m i l a r r e s u l t s with 2 inches thick A chi-square s t a t i s t i c ,  Williams  (17)  one  obtained  (51mm) r a d i a t a p i n e lumber.  t e s t i n g p r o p o r t i o n s independance,  was a l s o r u n i n o r d e r t o d e t e r m i n e whether o r not t h e p r o p o r t i o n of and was  specimens  w i t h i n t e r n a l c h e c k i n g was  6 hours of c o n d i t i o n i n g . done.  The  results  Appendix  indicated  t h e same a f t e r 0, 2, 4 7.2  that  shows how the  the  test  proportion  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 t h e same f o r all  drying  Williams  runs.  reported.  This In  i s contrary their  study,  to  what  Kininmonth  and  checking  was  internal  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 drying . T a b l e 8 shows t h e l a r g e s t s i z e o f i n t e r n a l check f o u n d i n each r u n . to 1.0  31 mm mm  I n t e r n a l check l e n g t h s ranged from 4 0 mm f o r r u n #4 and w i d t h s r a n g e d from 0.4  f o r run  Two  o r d e r t o d e t e r m i n e w h i c h specimens  end c h e c k s .  The  #1  f o r r u n #1 t o  #3.  weeks a f t e r d r y i n g , each CS was  checking.  mm  f o r run  CSs  v i s u a l l y examined i n  were more l i k e l y t o d e v e l o p  o f t h e d e f e c t i v e specimens  were f o u n d  Two r e a s o n s c o u l d e x p l a i n t h e i r p r e s e n c e .  with  Firstly,  t h e y c o u l d have been t h e r e s u l t o f i n t e r n a l c h e c k s f o u n d e a r l i e r  49  when t h e  KSs  were c r o s s - s a w n  evaluation.  Secondly,  the  the  ends  of  into  CSs  for internal  t h e y c o u l d have d e v e l o p e d  cut  pieces  d r i e d out.  checking  t h e r e a f t e r as  I t can  be  seen  A p p e n d i x 7.3  t h a t i n 26 p i e c e s o f t h e i n i t i a l 14 f e e t l o n g  m)  4  lumber,  Conversely,  i n 20  checking. pieces  out  o f -4  KSs  developed  p i e c e s o f lumber, a l l 4 KSs  IMCs and  A p p e n d i x 7.4  9 c o n t a i n s the difference  significance.  shows how  r e s u l t s obtained.  for  (4.27  problems.  were f r e e from  green s p e c i f i c g r a v i t i e s of both types  ( w i t h and w i t h o u t c h e c k i n g )  "t" test.  checking  in  both  types  of  were f i r s t  compared u s i n g a  t h i s t e s t was IMC  done and  showed an  pieces  of  using  a  Table  insignificant 10%  level  of  Specific gravity analysis revealed a s i g n i f i c a n t  d i f f e r e n c e a t t h e 1% l e v e l .  T h i s i m p l i e s t h a t p i e c e s o f lumber  w i t h low s p e c i f i c g r a v i t i e s were p r o b a b l y not l i k e l y t o c h e c k i n g p r o b l e m s as shown i n F i g u r e 21.  develop  F i n a l l y , the core  MCs  o b t a i n e d f o r t h e d e f e c t i v e specimens were compared w i t h t h e ones obtained MCs  f o r the non-defective  specimens.  were more l i k e l y t o d e v e l o p Two  r e a s o n s may  e x p l a i n why  KSs  with high  core  checking. some specimens had h i g h FCMCs.  The f i r s t r e a s o n c o u l d be t h e 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  as 0.553 were f o u n d i n some o f t h e p i e c e s o f l u m b e r . to  Oliveira  slower at  (32),  high  drying rates.  d e n s i t y hemlock  Such lumber may  be  lumber  According  exhibits  much  only p a r t i a l l y d r i e d  t h e end o f t h e d r y i n g c y c l e , l e a v i n g t h e c o r e wet.  50  high  The  T a b l e 9. T e s t o f mean v a l u e s f o r "2x4" PCH lumber  LUMBER WITH CHECKING PROPERTY  2  . MIN  IMC  LUMBER WITHOUT CHECKING  1  AVG  STD  MIN  MAX  AVG  STD  41.8  150.9  70.8  27.5  44.1  115.7  61.2  15.0  GREEN SPECIF. GRAVITY  0.342  0.497  0.419  0.038  0.303  0.406  0.355  0.031  CORE MC  11.5  26.8  17.2  3.7  8.9  14.9  10.9  1.4  1 2 3  (%)  MAX  CONCLUSION  : : :  (%)  3  Not s i g . a t t h e 10% l e v e l S i g . a t t h e 1% l e v e l S i g . a t t h e 1% l e v e l  c h e c k i n g developed i n a l l 4 k i l n specimens no c h e c k i n g o b s e r v e d i n a l l 4 k i l n s p e c i m e n s c o r e m o i s t u r e c o n t e n t 2 weeks a f t e r d r y i n g  second r e a s o n c o u l d be t h e l a r g e v a r i a t i o n i n MCs o b s e r v e d among them.  According to Kozlik  (19), t h i s  e x i s t e n c e o f s i n k e r heartwood which five  times  slower  than  normal  problem  i s due t o t h e  has a d r y i n g r a t e two t o  heartwood.  Wet p o c k e t s ,  c h a r a c t e r i s t i c o f s i n k e r heartwood, were o b s e r v e d when t h e y were c h e c k e d  a  i n some CSs  f o r i n t e r n a l checking.  The.specimens w i t h a h i g h FCMC were n o t o n l y f o u n d t o have checking problems but a d d i t i o n a l l y , a l s o much more s e v e r e . II  t o perform  were  believed  t h e degrade o b s e r v e d was  F o r t h a t r e a s o n , i t was d e c i d e d i n Phase  a more d e t a i l e d t o develop  investigation.  steep  i n t e r n a l c h e c k i n g development.  51  MC  gradients  Such specimens that  favored  F i g u r e 21. P l o t o f green s p e c i f i c g r a v i t y a g a i n s t m o i s t u r e c o n t e n t f o r "2x4" PCH lumber  0.56 i  initial  B  0.54 0.52 m  0.5 -  m  0.48 -  > O U a. O ui QL  </>  m  0.46 0.44 0.42 0.4 -  .  °  MM  m  a m  B  u  H  % +  n  m  +  0.38 -  + rfr +. m mi•  i  T  El J  m  a m  1  0.36 -  El  • •  ES  SI  0.34 -  +  0.32 0.3 30  m  o°  a s • 0 a m mm u • lp + %  +  B  E  + +  i  +  g  +  +  i  50  +  i  i  i  i  1 1 1 1 70 90 110 130 INITIAL MOISTURE CONTENT (%)  m Checking developed In 1 or more kiln specimen (s) + All 4 kiln specimens free from checking  52  1  1 150  1  170  4.2  Phase I I  As  was  reported  considerable lumber  of the  variation  (Table 10).  average value  f o r "2x4"  The  in  IMC  IMC  o f 60.9%.  PCH  lumber,  distribution  r a n g e d from 31.8  F i g u r e 22  lumber p o p u l a t i o n  had  there  was  i n the  also  "4x4"  a PCH  t o 122.1% w i t h  an  shows t h a t a m a j o r p o r t i o n  IMCs t h a t r a n g e d between 4 0  and  60%. T a b l e 10.  I n i t i a l moisture content o f "4x4" PCH lumber  I N I T I A L MOISTURE CONTENT (%)  GREEN SPECIFIC GRAVITY  A considerable  #5,  #6,  respectively  #7  and  (Table 1 1 ) .  and  #6 were c u t from one  cut  from the  other  MAX  AVG  31.8  122.1  60.9  0.464  v a r i a t i o n i n IMC  end.  The #8  was  a v e r a g e IMC  was  55.1,  end w h i l e KSs  0.376  o b s e r v e d between f o r the  54.8,  57.9  As m e n t i o n e d e a r l i e r , KSs  One  f o r r u n s #7  p i e c e s o f lumber were d r i e r a t one  end  and  specimens i n and  62.9%,  f o r runs and  c o u l d conclude t h a t the  53  gravity  MIN  0.312  w i t h i n specimen b o a r d s . runs  and g r e e n s p e c i f i c  compared t o t h e  #8  #5  were  shipped other.  F i g u r e 22. I n i t i a l m o i s t u r e c o n t e n t f r e q u e n c y o f "4x4" PCH lumber  distribution  22  • i  20-40  "  I  40-60  1  '  '  '\ '  '  60-80  "  "  '  '\'  '  "  80-100  INITIAL MOISTURE CONTENT (%)  54  '  '\'  '  "  100-120  120-140  T a b l e 1 1 . Average m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f "4x4" PCH specimens  RUN #  I  IMC  MC  %)  I BEFORE I CONDITIONING  | BEFORE | COOLING  (%)  | AFTER DRYING | ONE WEEK AFTER | AND CONDITIONING| DRYING AND ' CONDITIONING  !  -  1  8.7  |  7.8  8.1  1  8.1  |  7.2  1  10.0  I  10.5  |  8.6  1  13.5  1  14.1  |  11.9  5  I  55 1  6  1  54 8  1  7.8  1  7  1  57 9  I  10. 0  8  1  62 9  1  13.5  The a v e r a g e g r e e n s p e c i f i c g r a v i t y o f "4x4" PCH lumber was 0.376, r a n g i n g from 0.312 t o 0.464 ( T a b l e 1 0 ) .  F i g u r e 23 shows  t h a t t h e n o r m a l d i s t r i b u t i o n may be n o t t h e b e s t model f o r t h e distribution  of specific  gravity.  A large proportion  of the  p i e c e s o f lumber had g r e e n 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 t o 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 ranging specific hemlock  from  0.380  gravities  t o 0.420.  fir  According  t o Jessome ( 1 4 ) ,  amabilis  f i r and w e s t e r n  o f unseasoned  a r e 0.360 (± 0.038) and 0.409 (± 0.038),  Compared t o w e s t e r n hemlock, i s relatively  the specific  l o w and c l o s e r  first  gravity  to the f i r s t  s p e c i f i c g r a v i t y g i v e n f o r w e s t e r n hemlock to t h e second range.  gravities  respectively. of amabilis range.  The  i s h i g h e r and c l o s e r  T h e r e f o r e , i t i s l i k e l y t h a t lumber i n t h e  range i s a m a b i l i s f i r w h i l e lumber i n t h e s e c o n d one i s  55  F i g u r e 23.  Green s p e c i f i c g r a v i t y f r e q u e n c y o f "4x4" PCH lumber  distribution  26  .30-.32 .32-.34 .34-.36 .36-.38 .38-.40 .40-.42 .42-.44 .44-.46 .46-.48 SPECIFIC GRAVITY  56  w e s t e r n hemlock. FMCs i m m e d i a t e l y 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 s #5, #6, #7  and  #8 were  (Table  11) .  8.7,  Such  a  8.1,  wide  10.5  variation  a t t r i b u t e d t o the large v a r i a t i o n p i e c e o f lumber.  and  In a l l k i l n  14.1%, r e s p e c t i v e l y  i n t h e FMCs  c a n be  i n IMC o b s e r v e d w i t h i n  each  l o a d s , t h e h i g h e r t h e IMC, t h e  h i g h e r was t h e FMC. Table  12  Drying times #6,  #7  shows  kiln-drying  time  o f "4x4" PCH  lumber.  ( 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 r u n s #5,  and #8  respectively.  were  106.50,  106.25,  84.50  and 71.25 h o u r s ,  As was f o u n d i n Phase I f o r "2x4" PCH lumber, t h e  h i g h e r t h e average  FMC  ( T a b l e 11) and d r y i n g r a t e  (Table 13),  t h e s h o r t e r was t h e d r y i n g t i m e i n a l l d r y i n g r u n s . t i m e s were r e l a t i v e l y hours.  The k i l n  short except  f o r r u n #7 w h i c h  down t o 100°F  According  was 7.25  s h u t down l a t e a t 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 t h e next morning. were  Cooling  The DB and WB t e m p e r a t u r e s  (37.7°C) and 70°F  t o Kininmonth  and W i l l i a m s ,  (21.1°C), such  respectively.  a long  cooling  p e r i o d s h o u l d have been a v o i d e d b e c a u s e i n t e r n a l c h e c k i n g was more l i k e l y  t o d e v e l o p even b e f o r e t h e c o n d i t i o n i n g  t a k e s p l a c e (see C o n d i t i o n i n g ) . in  the text  particular  indicated run since  that most  R e s u l t s w h i c h a r e shown l a t e r  this  was  internal  not t h e case checking  c o n d i t i o n i n g was c a r r i e d o u t d u r i n g subsequent temperature.  57  treatment  i n this  occurred  once  s t o r a g e a t room  T a b l e 12. K i l n - d r y i n g t i m e o f "4x4" PCH specimens  RUN #  KILN DRYING TIME  I  DRYING  I  COOLING  -  | CONDITIONING |  !  106.50  2.25  I  110.00  1  4.25  I  96.00  1  6.00  I  77.25  1  106.50  6  I  106.25  1  1.50  1  7  1  84.50  1  7.25  8  I  71.25  1  0.00  RUN  #  -  TOTAL  !  5  T a b l e 13. D r y i n g r a t e s  (hours)  o f "4x4" PCH specimens  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  excluding cooling moisture loss moisture gain  and c o n d i t i o n i n g  58  Figures  24, 25, 26 and 27 show t h e change i n MC o v e r t i m e  f o r a l l d r y i n g runs. The  first  plot  Two p l o t s were made f o r e a c h d r y i n g r u n .  shows  the expected  change  i n MC  over  time  a s s u m i n g t h e IMC and FMC b e f o r e c o n d i t i o n i n g o f a l l d r y i n g runs e q u a l t o 60.9 and 12.0%, r e s p e c t i v e l y .  The s e c o n d p l o t was made  to correct the o r i g i n a l p l o t using the load i n i t i a l a v e r a g e MCs (Appendix 7.5). conditioning Finally,  was  drying  For a l l d r y i n g runs,  not c a r r i e d  the  desired  Thereafter, a l l drying  12% FMC.  r a t e s o f a l l r u n s were p l o t t e d a g a i n s t  f o r "2x4" PCH lumber, t h e d r y i n g  when  i t shows t h a t  out a t t h e d e s i r e d  a v e r a g e MCs ( F i g u r e s 28, 29, 30 and 3 1 ) . I  and f i n a l  DB  and  WB  As n o t i c e d i n Phase  r a t e was a g a i n  temperatures  a t maximum  were  reached.  lumber MC and d r y i n g r a t e c o n s t a n t l y d e c r e a s e d i n runs.  Conditioning  of  "4x4" lumber  was  n o t recommended  K i n i n m o n t h and W i l l i a m s b e c a u s e degrade f r o m i n t e r n a l was  their  too excessive.  by  checking  I t was c l a i m e d t h a t s t r e s s r e l i e f a t t h e end  o f d r y i n g was n o t j u s t i f i e d s i n c e most o f t h e degrade  occurred  d u r i n g d r y i n g when s u c h lumber was h i g h - t e m p e r a t u r e k i l n - d r i e d . T a b l e 14 shows t h e number o f specimens t h a t d e v e l o p e d checking  i n each  drying  run.  When  specimens  internal were c u t  i m m e d i a t e l y 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% o f them on t h e a v e r a g e , had a l r e a d y d e v e l o p e d i n t e r n a l c h e c k i n g ends.  One week l a t e r ,  i n t e r n a l checks.  a t one o r b o t h  34% o f t h e specimens were f o u n d  with  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 t h e z v a l u e was  59  Figure  24.  Plot o f average moisture content f o r r u n #5 (no c o n d i t i o n i n g )  against  time  ADJUSTED DATA  0  20  40  60 TIME (hours)  60  80  100  Figure  25. P l o t o f average moisture content against 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 )  time  70 ADJUSTED DATA ACTUAL DATA  20  40  60 TIME (hours)  61  80  100  120  Figure  26.  P l o t of average moisture content against 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 )  time  F i g u r e 27. P l o t o f average m o i s t u r e c o n t e n t a g a i n s t f o r run #8 (6 hours o f c o n d i t i o n i n g )  63  time  F i g u r e 28. 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 #5 (no c o n d i t i o n i n g )  2.5  64  Figure  29. 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 run #6 (2 hours o f c o n d i t i o n i n g )  65  Figure  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 )  F i g u r e 31. 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 run #8 (6 hours o f c o n d i t i o n i n g )  2.5  ' 70  60  50  40 30 MOISTURE CONTENT (%)  67  20  10  0  T a b l e 14. Number o f "4x4" PCH specimens w i t h i n t e r n a l checking  j  3'  j  RUN #  AFTER  SPECIMENS CUT AT 1'  1  DRYING  I  LEFT  RIGHT  MAX.  5  I  5  6  6  1  7  7  1  8  1  LEFT, MAX. %  FROM THE END  1 WEEK AFTER DRYING  %  RIGHT  MAX.  6  5  6  25  |  9  8  9  38  13  I  10  5  10  42  4  1  8  5  8  33  %  1  6  25  |  2  7  29  3  0  3  1  1  1  LEFT  number o f d e f e c t i v e s p e c i m e n s f o u n d a t t h a t end maximum number o f d e f e c t i v e s p e c i m e n s a t one o r b o t h ends p e r c e n t a g e o f d e f e c t i v e s p e c i m e n s a t one o r b o t h ends  T a b l e 15. L a r g e s t i n t e r n a l check s i z e f o r "4x4" PCH specimens 3'  RUN  t |  SPECIMENS CUT AT 1  1  AFTER DRYING  LENGTH  (mm)  I  WIDTH  (mm)  |  FROM THE END  1 WEEK AFTER DRYING  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  r u n i n o r d e r t o d e t e r m i n e whether t h e p r o p o r t i o n s with i n t e r n a l checking  were t h e same a t t h e end o f 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) . that  the proportion  greater checking  o f specimens  o f specimens w i t h  one week a f t e r d r y i n g .  R e s u l t s showed  internal  checking  T h i s means t h a t most  was  internal  d e v e l o p e d 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 t o  Kininmohth  and W i l l i a m s '  results.  Therefore,  conditioning  i m m e d i a t e l y 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 c a s e . In  runs  #5,  #6,  #7 and #8,  specimens, r e s p e c t i v e l y , week a f t e r testing  drying  25, 38, 42 and 33% o f t h e  were f o u n d w i t h i n t e r n a l c h e c k i n g  and c o n d i t i o n i n g .  proportions  independence,  A chi-square  was p e r f o r m e d  one  statistic, and  showed t h a t t h e p r o p o r t i o n o f specimens w i t h i n t e r n a l  results checking  p r o b l e m s one week a f t e r d r y i n g was about t h e same i n a l l d r y i n g runs  (Appendix  conditioning checking The  7.2).  As  observed  immediately a f t e r  in  "2x4" PCH  lumber,  d r y i n g d i d not reduce  internal  development f o r "4x4" PCH lumber. z  value  was  also  used  t o determine  whether  the  p r o p o r t i o n o f d e f e c t i v e specimens f o u n d i n t h e "4x4" lumber was h i g h e r t h a n t h a t i n t h e "2x4" lumber after  drying  (Appendix 7 . 6 ) . One week  and c o n d i t i o n i n g , an a v e r a g e o f 8% o f t h e "2x4"  s p e c i m e n s were f o u n d w i t h i n t e r n a l c h e c k i n g the  "4x4" ones.  compared t o 34% f o r  R e s u l t s have shown t h a t t h e s e 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 a t t h e 1% l e v e l . "4x4"  Not o n l y were t h e  specimens more l i k e l y t o d e v e l o p i n t e r n a l c h e c k i n g , b u t  69  t h e s i z e o f t h e c h e c k s o b s e r v e d was a l s o more i m p o r t a n t .  As can  be seen i n T a b l e s 8 and 15, maximum l e n g t h s and w i d t h s o f t h e i n t e r n a l c h e c k s 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  specimens longer)  times  was e x p e c t e d  that  specimens  and 3.7  t h a n i n t h e "2x4" ones.  t h a n "2x4" lumber. shows  longer  internal  since  times  wider  The f i r s t  "4x4" lumber  t h a n t h a t i n t h e l a t t e r ones.  ratio  (1.9 t i m e s  i s two t i m e s  However, t h e second r a t i o c h e c k i n g was more  i n t h e "4x4"  thicker  (3.7 t i m e s w i d e r )  severe  i n t h e former  Based on o u r f i n d i n g s ,  one c o u l d agree w i t h K i n i n m o n t h and W i l l i a m s and c o n c l u d e t h a t checking  in  the  thicker  specimens  is  more  excessive  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 o f each specimen was c a l c u l a t e d u s i n g t h e f o l l o w i n g equation: FMC = 1/9 x FCMC + 8/9 x FSMC  ( 1 )  where FCMC and FSMC a r e t h e f i n a l 10), r e s p e c t i v e l y .  c o r e and s h e l i MCs  FMCs o f i n t e r n a l l y c h e c k e d  specimens  t h e n 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 7.4) .  (Figure were  (Appendix  I t can be seen i n T a b l e 16 t h a t , i m m e d i a t e l y 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 v e r y s i g n i f i c a n t d i f f e r e n c e f o r b o t h t y p e s o f specimens  a t t h e 1% l e v e l .  specimens were found w i t h low FMCs.  Internally  checked  When t h e specimens were c u t  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 found  with  low MCs  again.  However,  70  FMCs  of both  were  types of  T a b l e 16. T e s t o f mean v a l u e s f o r "4x4" PCH lumber  LUMBER WITH INTERNAL CHECKING  LUMBER WITHOUT CHECKING  1  INTERNAL 2  CONCLUSION  IMC  (%)  GREEN  SPECIF.  GRAVITY  MIN  MAX  AVG  STD  MIN  31.8  55.3  44.1  8.0  32.4  116.8  337.2  451.9  382.9  31.0  312.3  464.4  3' SPECIMENS WITH INTERNAL CHECKING  MAX  AVG  STD  63.8  21.9  372.9  - 45.1  S i g . a t t h e 1% l e v e l  Not s i g . a t t h e 10% l e v e l  3' SPECIMENS WITHOUT INTERNAL CHECKING  CONCLUSION  AVG  FMC AFTER DRYING  (%)  FMC ONE WEEK AFTER DRYING (%)  internal internal  6.3  12.2  8.2  1.5  6.0  25.1  11.0  3.8  S i g . a t t h e 1% l e v e l  4.9  11.2  8.2  1.7  4.9  22.1  8.9  2.9  Not s i g . a t t h e 10% l e v e l  checking developed checking developed  i n 3 or 4 k i l n i n 0 or 1 k i l n  specimens specimen  71  specimens  were n o t f o u n d  level.  This implies  similar  EMC  Finally,  after  specimen  that  was  b o t h t y p e s o f specimens  reached a  o f s t o r a g e a t room t e m p e r a t u r e .  MCs  investigated  were  As c a n be seen  checking  d i f f e r e n t a t t h e 10%  one week  determine at which l e v e l occur.  significantly  found  when  i n more  detail  to  i n t e r n a l c h e c k i n g was more l i k e l y t o i n F i g u r e s 32 and 33, more i n t e r n a l specimen  MCs  ranged  from  7% t o 8%.  T a b l e 17 shows t h a t 96% and 100% o f t h e d e f e c t i v e specimens were found  over-dried  (below  12% MC) , when  cut immediately  after  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 . may e x p l a i n  why i n t e r n a l c h e c k i n g d e v e l o p e d  conditioning Williams'' 13.5%  i n this  results.  MC  experiment In t h i s  contrary  experiment,  or less before conditioning  experiment,  This  after drying  and  t o Kininmonth  and  lumber  was d r i e d t o  (Table' 11) .  In t h e i r  i n t e r n a l checking developed d u r i n g drying  because  lumber was d r i e d t o a l o w e r MC, 10% o r l e s s . Kauman  (15) s u g g e s t s t h a t  conditioning  out when lumber a v e r a g e MC i s above 15%. stresses because relax.  responsible  s h o u l d be c a r r i e d  Below t h a t , i n t e r n a l  f o r i n t e r n a l c h e c k i n g c a n n o t be r e l i e v e d  t h e wood i s t o o s t i f f ,  i.e.  not p l a s t i c  enough, t o  I n t h i s e x p e r i m e n t , c o n d i t i o n i n g was c a r r i e d o u t a t 8.1,  10.0 and 13.5% a v e r a g e MC f o r runs #6, #7 and #8, r e s p e c t i v e l y . Such  low  MCs  significantly  may  explain  reduced  by  why  internal  conditioning  experiment.  72  checking  treatments  was  not  in  this  F i g u r e 32. F i n a l m o i s t u r e c o n t e n t f r e q u e n c y d i s t r i b u t i o n o f " 4 x 4 " d e f e c t i v e specimens i m m e d i a t e l y a f t e r d r y i n g and c o n d i t i o n i n g  50  6-7  7-8  8-9 9-10 10-11 FINAL MOISTURE CONTENT (%)  73  11-12  12-13  F i g u r e 33. F i n a l m o i s t u r e c o n t e n t f r e q u e n c y d i s t r i b u t i o n o f "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  T a b l e 17. F i n a l m o i s t u r e c o n t e n t s o f "4x4" i n t e r n a l checking  3' SPECIMENS CUT  |  FMC  RANGE  (%)  I I  NO OF DEFECTIVE SPECIMENS  PCH specimens w i t h  | |  %  !  1  6  7  1  3  |  13 0  7 -  8  1  11  1  47 8  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  1  23  I  100 0  j  i  4  5  1  1  1  2 6  |  5 -  6  1  4  I  10 5  1 1 WEEK AFTER DRYING I AND  CONDITIONING  6 -  7  1  6  I  15 8  7 -  8  1  8  |  21 1  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  final  core-shell  MC  difference  (FCSMCD)  s p e c i m e n was c a l c u l a t e d u s i n g t h e f o l l o w i n g  of  each  equation:  FCSMCD = FCMC - FSMC  ( 2 )  FCSMCDs o f 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. Figure  34 shows t h e s c a t t e r e d  defective  specimens  cut  obtained  immediately  after a  and  straight  line  indicating  FCSMCD and FMC a r e t o some e x t e n t  The f o l l o w i n g r e g r e s s i o n  closely  drying  The  related.  follow  f o r t h e non-  conditioning. that  points  points  l i n e was o b t a i n e d  linearly  t o express  that l i n e a r r e l a t i o n s h i p : FCSMCD .= -10.20 + 1.96 FMC Figure  ( 3 )  35 shows t h e s c a t t e r e d p o i n t s o b t a i n e d  specimens.  The f o l l o w i n g s e c o n d r e g r e s s i o n  for the defective l i n e was f o u n d :  FCSMCD = -12.40 + 2.30 FMC Both r e g r e s s i o n the  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  two v a r i a b l e s .  regression 18) .  ( 4 )  The c o e f f i c i e n t s o f d e t e r m i n a t i o n  l i n e s 3 and 4 a r e 0.87 and 0.81,  Both r e g r e s s i o n  lines also  (R ) 2  respectively  show t h a t  for  (Table  a decrease i n the  s p e c i m e n s ' MCs r e s u l t e d i n ' a d e c r e a s e i n t h e i r c o r e - s h e l l MC differences. higher  However, above EMC, r e g r e s s i o n  core-shell  MC  differences  than  does  line line  4 predicts 3.  This  c o n f i r m s 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 c h e c k e d lumber  76  Figure  34. F i n a l c o r e - s h e l l m o i s t u r e c o n t e n t d i f f e r e n c e s o f n o n - d e f e c t i v e specimens c u t i m m e d i a t e l y 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 35. F i n a l c o r e - s h e l l m o i s t u r e c o n t e n t d i f f e r e n c e s o f d e f e c t i v e specimens c u t i m m e d i a t e l y a f t e r d r y i n g and c o n d i t i o n i n g  T a b l e 18. R e g r e s s i o n SPECIMENS  DEFECTIVE  |  Y  REGRESSION  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  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  |  Y - - 9.06 + 2.74 X  0 94  | FCMC ONE WEEK | AFTER DRYING  Y => - 4 . 61 + 2.13 X  0 96  |  Y -  1.13 + 0.78 X  0 99  Y =  0.58 + 0.86 X  0 99  Y - -10.20 + 1.96 X  0 87  Y = - 5.18 + 1.27 X  0 86  | | FSMC ONE WEEK 1 AFTER DRYING  FCMC AFTER DRYING  FSMC AFTER DRYING  FCSMCD AFTER DRYING  | FCSMCD ONE WEEK | AFTER DRYING  SPECIMEN'  R  Y = -11.03 + 3.05 X  |  :  LINE  I FCMC AFTER DRYING  NON-DEFECTIVE I I FSMC ONE WEEK I AFTER DRYING  X  lines  FMC (%)  79  2  has  steeper  final  moisture  g r a d i e n t s than  i n non-defective  lumber. F i n a l c o r e and s h e l l MCs o f a l l KSs c u t i m m e d i a t e l y conditioning  were  plotted  drying  and  Figures  36 and 37 show t h e 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 t h e  n o n - d e f e c t i v e and d e f e c t i v e specimens,  against  their  after  respectively.  FMCs.  As can be  seen i n T a b l e 18, t h e r e g r e s s i o n l i n e s f o u n d f o r t h e d e f e c t i v e specimens p r e d i c t h i g h e r c o r e MCs and l o w e r s h e l l MCs t h a n f o r the non-defective Table  specimens. found  f o r the  specimens c u t 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 .  Figures  38  18 a l s o  (FCSMCDs  defective specimens)  of  gives the regression l i n e s  non-defective  specimens), and 41  40  specimens),  (FCMCs and FSMCs  (FCMCs and FSMCs  39  (FCSMCDs  of  of non-defective  of defective  specimens)  i l l u s t r a t e them. Once a g a i n , t h e d e f e c t i v e specimens were found w i t h h i g h c o r e and low s h e l l MCs r e s u l t i n g i n s t e e p moisture content g r a d i e n t s .  core-shell  However, t h e i r m o i s t u r e g r a d i e n t s  were n o t as s t e e p as t h e ones r e c o r d e d one week e a r l i e r s i n c e t h e lumber k e p t l o s i n g water d u r i n g s t o r a g e a t room t e m p e r a t u r e . Table  19 g i v e s t h e FCSMCDs  obtained i n a l l d r y i n g runs.  The a v e r a g e FCSMCD i n t h e c o n t r o l r u n ( r u n #5) i m m e d i a t e l y a f t e r d r y i n g was 7.9%. A v e r a g e FCSMCDs i m m e d i a t e l y a f t e r c o n d i t i o n i n g in  r u n s #7 and #8 were 9.9 and 16.7%, r e s p e c t i v e l y .  T h i s may  e x p l a i n why more specimens were f o u n d 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 t h o s e two runs t h a n t h a t i n t h e c o n t r o l r u n  80  F i g u r e 36. F i n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f n o n - d e f e c t i v e specimens c u t i m m e d i a t e l y a f t e r d r y i n g and c o n d i t i o n i n g  Figure  37. F i n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f d e f e c t i v e specimens c u t i m m e d i a t e l y a f t e r d r y i n g 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 m o i s t u r e c o n t e n t d i f f e r e n c e s o f n o n - d e f e c t i v e specimens c u t 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 39. F i n a l c o r e - s h e l l m o i s t u r e c o n t e n t d i f f e r e n c e s o f d e f e c t i v e specimens c u t 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 40. F i n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f n o n - d e f e c t i v e specimens c u t 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  Figure  41. F i n a l c o r e and s h e l l m o i s t u r e c o n t e n t s o f d e f e c t i v e specimens c u t 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  T a b l e 19. F i n a l c o r e - s h e l l m o i s t u r e c o n t e n t d i f f e r e n c e s o f "4x4" PCH specimens  1  RUN #  I TIME OF MEASUREMENT I  FCMC  MIN  1  5  MIN  MAX  MIN  AVG  MAX  AVG  31. 3 24. 5  15. 7 12. 3  | 1  5. 9 5. 5  11. 9 11. 1  7. 9 7. 3  1 1  2. 4 2. 3  19.9 15.1  7.9 5.1  7. 7 6.4  34 . 6 23. 7  13. 7 11. 4  | 1  5. 8 4 .7  11. 8 10. 1  7. 4 6.7  1 |  1. 9 1. 2  22.8 13.6  6.4 4.7  10. 7 9. 2  35. 9 25. 8  19. 3 13. 6  1 !  6.8 6.2  15. 1 11. 4  9. 4 8. 0  1 1  3. 7 2 .5  20.8 14.4  9.9 5.6  15. 5 12. 1  64. 0 41. 3  29. 0 20. 2  1  1  8. 8 7. 9  20. 2 19. 7  12. 2 10. 9  1 1  6.7 4 .1  43.8 21.5  16.7 9.3  |AFTER CONDITIONING I |1 WEEK AFTER I |CONDITIONING |  1  7  I AFTER CONDITIONING | 1 WEEK AFTER I CONDITIONING  I I I  1 AFTER CONDITIONING I I 1 WEEK AFTER I [CONDITIONING |  (Table 14). built  AVG  8 .9 7 .9  6  8  MAX  FCSMCD (%)  (%)  I AFTER DRYING I 11 WEEK AFTER DRYING|  1  1  FSMC  (%)  P i e c e s o f lumber  up s t r e s s e s  w i t h s u c h h i g h FCSMCDs may have  c o n s i d e r a b l e enough  t o develop  c h e c k i n g d u r i n g s t o r a g e a t room t e m p e r a t u r e .  internal  I n r u n #6,  the  a v e r a g e FCSMCD i m m e d i a t e l y a f t e r c o n d i t i o n i n g was 6.4% and l o w e r than that i n the c o n t r o l run a f t e r d r y i n g . o f specimens  However, t h e number  f o u n d w i t h i n t e r n a l c h e c k s one week l a t e r was n o t  reduced  since  most  Indeed,  internal  o f t h e degrade  checking  occurred  during  occurred during drying  drying.  i n run  #6  b e c a u s e lumber was d r i e d t o a l o w e r MC b e f 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%  87  i n r u n #7 and #8, r e s p e c t i v e l y  (Table 11). less  than  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 one  week e a r l i e r .  This  implies that  l o s i n g water d u r i n g storage r e s u l t i n g MCs  as shown i n T a b l e Finally,  i t can  KSs or  one  kept  s h e l l and  core  19. be  seen  i n Appendix  i n i t i a l p i e c e s o f lumber d e v e l o p e d On  i n lower  lumber  7.7  which  of  the  i n t e r n a l checking problems.  hand, 10 p i e c e s were found w i t h i n t e r n a l c h e c k i n g  o r more. found  On  with  t h e o t h e r hand, 29 p i e c e s were  internal  checking  in  only  1  non-defective  KS.  i l l u s t r a t e s specimens found i n t e r n a l l y c h e c k e d . specimens  are  in 3  Figure  42  Non-defective  a l s o shown f o r c o m p a r i s o n p u r p o s e s .  IMCs  and  g r e e n s p e c i f i c g r a v i t i e s o f b o t h t y p e s o f p i e c e s were compared u s i n g a " t " t e s t as shown i n A p p e n d i x 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 c h e c k i n g development ( T a b l e 16) . develop  P i e c e s o f lumber w i t h low IMCs were more l i k e l y t o  internal  l e n g t h s were f o u n d  checking.  Many  o v e r - d r i e d and  specimens  cut  from  i n t e r n a l l y checked.  those 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 a t t h e level.  88  10%  F i g u r e 42. Examples o f d e f e c t i v e and n o n - d e f e c t i v e o f "4x4" PCH lumber  89  specimens  5.  Three f e e t l o n g lumber  were  minimize  (0.91 m) specimens o f "2x4" and "4x4" PCH  conditioned  final  CONCLUSION  immediately  moisture  gradients  responsible f o r i n t e r n a l checking No i n t e r n a l were  checking  cross-sawn  checking  upon  developed  temperature.  and  HTD  i n order  residual  to  stresses  problems.  was f o u n d when t h e "2x4" specimens  completion  later  after  during  of c o n d i t i o n i n g .  Internal  subsequent  a t room  storage  F o r 0, 2, 4, and 6 h o u r s o f c o n d i t i o n i n g , 13, 7,  7 and 4% o f t h e s p e c i m e n s , r e s p e c t i v e l y , were f o u n d d e f e c t i v e at  one  or both  conditioning. reduce  ends  when  c u t one  week  after  drying  and  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  internal  checking,  among t h o s e c o n d i t i o n e d  although  4% o f d e f e c t i v e  specimens  f o r 6 h o u r s i s r e l a t i v e l y low compared  t o 13% o f 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 . It  c o u l d be s u g g e s t e d t h a t  substantial  savings  for  a d i f f e r e n c e o f 9% w o u l d i n d i c a t e the  drying  a l t e r n a t i v e l y i t c o u l d be c o n s i d e r e d associated with too  great.  annually,  that the f i n a n c i a l  4% o f t h e lumber b e i n g  Therefore,  industry  more r e s e a r c h  losses  i n t e r n a l l y checked are 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 c h e c k i n g can be r e d u c e d 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 excessive  degrade than  observed  i n t h e "4x4" specimens  i n t h e "2x4" ones.  90  Some o v e r - d r i e d  was  more  specimens  were  found  to  be  internally  checked  after  c o n d i t i o n i n g even though most degrade o c c u r r e d a t room t e m p e r a t u r e .  drying  during  and  storage  F o r 0, 2, 4 and 6 h o u r s o f 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% o f t h e  s p e c i m e n s , r e s p e c t i v e l y , were f o u n d i n t e r n a l l y c h e c k e d a t one o r b o t h ends when c u t 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 h i g h FCSMCDs and l o w FMCs were f o u n d d e f e c t i v e . When c u t i m m e d i a t e l y  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% o f t h e  d e f e c t i v e specimens were f o u n d o v e r - d r i e d b e l o w 12% MC. proportion later.  i n c r e a s e d t o 100% when specimens were c u t one week  Therefore,  segregate  This  lumber  an a p p r o p r i a t e into  several  minimize i n t e r n a l checking  recommendation w o u l d be t o  moisture  classes  i n order  to  due t o o v e r - d r y i n g .  A s e c o n d recommendation w o u l d be t o c o n d i t i o n t h e lumber a t h i g h e r MCs.  T h i s way, l e s s b o a r d s w i t h l o w MCs w o u l d d e v e l o p  i n t e r n a l checking during drying. be  However, s u c h a method s h o u l d  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 l o n g c o n d i t i o n i n g  treatments times  which  are contrary  by t h e use o f HTD.-  therefore checking  steeper during  moisture  subsequent  t o t h e aim o f r e d u c i n g  drying  I f n o t , b o a r d s w i t h h i g h e r MCs, and gradients, storage.  would develop  internal  Based on t h e s e  findings  a l o n e , one l a s t recommendation w o u l d be t o p r a c t i c e i n t e r m i t t e n t conditioning. carried  For instance,  a first  conditioning  o u t when t h e wood i s more p l a s t i c  treatment  i n character, i . e .  above 15% MC, c o u l d be combined w i t h a s e c o n d t r e a t m e n t  91  a t 12%  MC. be  This  way,  minimized  moisture gradients and  a better  and  and i n t e r n a l s t r e s s e s  faster  achieved.  92  stress  relief  would  would  be  6. L I T E R A T U R E C I T E D  1.  AVRAMIDIS, S and J.F.G. MACKAY. 1988. Development o f k i l n s c h e d u l e s f o r 4 - i n c h by 4 - i n c h P a c i f i c C o a s t hemlock. F o r e s t P r o d u c t s J o u r n a l , 3 8 ( 9 ) : 4 5 - 4 8 .  2.  BOONE, R.S. 1984. H i g h - t e m p e r a t u r e k i l n - d r y i n g o f 4/4 lumber from 12 hardwood s p e c i e s . F o r e s t Products Journal, 34(3):10-18.  3.  BOONE, R.S. 1986. H i g h - t e m p e r a t u r e k i l n - d r y i n g r e d maple lumber - some o p t i o n s . F o r e s t P r o d u c t s J o u r n a l , 36(9):19-25.  4.  BRAMHALL, G. and R.W. WELLWOOD. 1976. K i l n - d r y i n g o f w e s t e r n C a n a d i a n lumber. Western F o r e s t P r o d u c t s L a b o r a t o r y , Vancouver. Information r e p o r t No. VP-X-159, 112 p.  5.  CECH, M.Y.  6.  CHOW, S.-Z. and K . J . PICKLES. 1971. Thermal s o f t e n i n g and d e g r a d a t i o n o f wood and b a r k . Wood and F i b e r , 3 (3) : 166-178.  7.  CHURCHILL, J.W. 1954. The e f f e c t o f t i m e , t e m p e r a t u r e and h u m i d i t y on t h e r e l i e f o f c a s e h a r d e n i n g stresses. F o r e s t Products J o u r n a l , 4(5):264270 .  8.  ELLWOOD, E.L. 1953. P r o p e r t i e s o f b e e c h i n t e n s i o n p e r p e n d i c u l a r t o t h e g r a i n and t h e i r r e l a t i o n t o drying. F o r e s t Products J o u r n a l , 3(5):202-209.  9.  ERICKSON, R.W., PETERSON, M.D. and T.D. LARSON. 1984. Obtaining uniform f i n a l moisture content i n the high-temperature d r y i n g o f paper b i r c h f l i t c h e s . F o r e s t Products J o u r n a l , 34(2):27-32.  1964. Development o f d r y i n g s t r e s s e s d u r i n g high-temperature k i l n - d r y i n g . Forest Products J o u r n a l , 14 (2) :69-76.  10. ESPENAS, L.D. 1971. S h r i n k a g e o f D o u g l a s - f i r , w e s t e r n hemlock, and r e d a l d e r as a f f e c t e d by d r y i n g conditions. Forest Products Laboratory, Forest S e r v i c e , U.S. Department o f A g r i c u l t u r e . Report No. D-12, 16 p.  93  11. GREENHILL, W.L. 1936. Strength t e s t s p e r p e n d i c u l a r to the g r a i n o f t i m b e r a t v a r i o u s t e m p e r a t u r e s and moisture contents. 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 R e s e a r c h ( 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. Forest Products Journal, 7(10) :368-371.  13.  H I L L I S , W.E.  14.  JESSSOME, A.P. 1977. S t r e n g t h and r e l a t e d p r o p e r t i e s o f 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, W.G.  16  KININMONTH, J.A. and J.B. MAUD. 1982. Recent changes i n t i m b e r d r y i n g methods u s e d i n New Z e a l a n d . 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R e p o r t No. D-9, 32 p.  19.  1970. Problems o f d r y i n g w e s t e r n hemlock KOZLIK, C.J. •heartwood t o a u n i f o r m f i n a l m o i s t u r e c o n t e n t . P r o c e e d i n g s 2 1 s t a n n u a l m e e t i n g W e s t e r n Dry K i l n C l u b s , M i s s o u l a , Montana, p. 55-61.  20.  KOZLIK, C.J. 1973. E f f e c t o f k i l n c o n d i t i o n s on t h e d i m e n s i o n a l s t a b i l i t y o f D o u g l a s - f i r and w e s t e r n hemlock. F o r e s t P r o d u c t s J o u r n a l , 2 3 ( 9 ) : 8 5 - 9 2 .  94  21. KOZLIK, C . J . 1981. S h r i n k a g e o f w e s t e r n hemlock h e a r t w o o d a f t e r c o n v e n t i o n a l and h i g h - t e m p e r a t u r e k i l n drying. F o r e s t P r o d u c t s J o u r n a l , 31(12) :45-50 . 22. KOZLIK, C . J . and L.W. HAMLIN. 1972. R e d u c i n g v a r i a b i l i t y i n f i n a l m o i s t u r e c o n t e n t o f k i l n - d r i e d hemlock lumber. F o r e s t P r o d u c t s J o u r n a l , 2 2 ( 7 ) : 2 4 - 3 1 . 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 t e m p e r a t u r e k i l n - d r y i n g o f sapwood, n o r m a l heartwood, and s i n k e r h e a r t w o o d o f d i m e n s i o n lumber from young-growth w e s t e r n hemlock. P r o c e e d i n g s 3 0 t h a n n u a l m e e t i n g Western D r y K i l n C l u b s , Washington-Idaho-Montana S e a s o n i n g C l u b , p. 33-53. 24. LADELL, J . L . 1955. H i g h - t e m p e r a t u r e d r y i n g o f lumber. Timber o f Canada, 16 (7) :19-22 . 25. LARSON, T.D., ERICKSON, R.W. and R.S. BOONE. 1986. Comparison o f d r y i n g methods f o r p a p e r b i r c h SDR f l i t c h e s and s t u d s . F o r e s t P r o d u c t s L a b o r a t o r y , F o r e s t S e r v i c e , U.S. Department o f A g r i c u l t u r e . R e s e a r c h p a p e r No. FPL-465, 13 p. 26. MACKAY, J.F.G. 1976. D e l a y e d s h r i n k a g e a f t e r s u r f a c i n g o f h i g h - t e m p e r a t u r e k i l n - d r i e d n o r t h e r n aspen d i m e n s i o n lumber. Forest Products Journal, 26 (2) :33-36. 27. MACKAY J.F.G. 1983. S u p e r h e a t e d - s t e a m d r y i n g o f aspen 2 x 4 lumber. F o r i n t e k Canada C o r p . , V a n c o u v e r . U n p u b l i s h e d 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 o f B r i t i s h C o l u m b i a f r a m i n g lumber. F o r i n t e k Canada Corp., Vancouver. U n p u b l i s h e d 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 P r o d u c t s L a b o r a t o r y , F o r e s t S e r v i c e , U.S. Department o f A g r i c u l t u r e . R e p o r t No. 1652, 52 p. 30. MCMILLEN, J.M. 1963. A s t u d y o f 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 C l u b s , 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 o f hemlock and p o t e n t i a l g a i n s by u s i n g a c c e l e r a t e d schedules. P r o c e e d i n g s Western D r y K i l n A s s o c i a t i o n , Washington-Idaho-Montana S e a s o n i n g A s s o c i a t i o n , p. 108-118. 32. OLIVEIRA, L.C. 1990. P e r s o n n a l c o m m u n i c a t i o n Canada Corp., V a n c o u v e r .  Forintek  33. PANSHIN, A . J . and C. de ZEEUW. 1980. Textwood o f Wood Technology. Fourth e d i t i o n . M c G r a w - H i l l Book Company. 722 p. 34. RASMUSSEN, E.F. and G. VOORHIES. 1952. The r e l i e f o f c a s e h a r d e n i n g 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 P r o d u c t s L a b o r a t o r y , F o r e s t S e r v i c e , U.S. Department o f A g r i c u l t u r e . R e p o r t No. 1371, 15 p. 35. ROSEN, H.N  1979. P s y c h o m e t r i c 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 m o i s t u r e c o n t e n t o f wood a t t e m p e r a t u r e s above 212°F. Symposium on Wood M o i s t u r e C o n t e n t - Temperature and H u m i d i t y 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 University, Blacksburg, V i r g i n i a . p. 1219.  36. SALAMON, M.  1961. K i l n - d r y i n g o f B r i t i s h C o l u m b i a softwoods a t h i g h temperatures. Proceeedings 1 3 t h a n n u a l m e e t i n g Western D r y K i l n C l u b s , Medford, Oregon. p. 29-35.  37. SALAMON, M.  1965. E f f e c t o f h i g h - t e m p e r a t u r e d r y i n g on q u a l i t y and s t r e n g t h o f w e s t e r n hemlock. F o r e s t P r o d u c t s J o u r n a l , 15 (3) : 122-126.  38. SALAMON, M.  1966. E f f e c t s o f 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 o f w e s t e r n hemlock. Forest Products Journal, 16(1):39-46.  39. SALAMON, M. and C.F. MC BRIDE. 1965. A c o m p a r i s o n o f w e s t e r n hemlock and b a l s a m f i r d r i e d a t h i g h and conventional temperatures. Proceedings 17th a n n u a l m e e t i n g Western D r y K i l n C l u b s , P o r t l a n d , Oregon, p. 50-57.  96  40. SCHNEIDER, A. 1972. Zur K o n v e k t i o n s t r o c k n u n g von S c h n i t t h o l z b e i e x t r e m hohen T e m p e r a t u r e n . E r s t e M i t t e i l u n g : T r o c k n u n g s v e r l a u f und B r e t t e m p e r a t u r e n b e i T r o c k n u n g s t e m p e r a t u r e n von 110 b i s 180°C. H o l z a l s Roh- und W e r k s t o f f , 30:382-394. 41. STAMM, A.J.  42.  194 6. Passage o f l i q u i d s , v a p o r s and d i s s o l v e d m a t e r i a l s through softwoods. Forest Products L a b o r a t o r y , F o r e s t S e r v i c e , U.S. Department o f 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.  STAMM, A . J . and W.K. LOUGHBOROUGH. 1 9 4 2 . Variation in s h r i n k a g e and s w e l l i n g o f wood. T r a n s a c t i o n s o f the ASME, J o u r n a l o f Energy R e s o u r c e s T e c h n o l o g y , 63 (329)  :379-386.  43. WALPOLE, R.E. 1982 edition.  Introduction to S t a t i s t i c s . Third M a c m i l l a n P u b l i s h i n g Co. 521 p.  44. WENGERT, E.M. and F.M. LAMB. 1988. Matching a drying system t o a m i l l ' s r e q u i r e m e n t s . 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 o f lumber t o p r e v e n t end c h e c k i n g . P r o c e e d i n g s o f t h e IUFRO, I n t e r n a t i o n a l Wood D r 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 P i n e A s s o c i a t i o n , P o r t l a n d , Oregon. R e s e a r c h n o t e No. 4.214, 8 p,  97  7. A P P E N D I C E S  98  1.  Load weight a t 12% m o i s t u r e  content  I n t h i s e x p e r i m e n t , t h e 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 o f w e i g h t , t h e r e f o r e MC, c o u l d be m o n i t e r e d o v e r  time.  I n e a c h r u n , t h e k i l n was s e t t o t u r n i t s e l f o f f when t h e l o a d weight corresponding and  green weight  t o an a v e r a g e o f 12% MC was r e a c h e d .  (GW) o f l o a d #1, f o r i n s t a n c e , were 69.7% and  259.9 k g , r e s p e c t i v e l y . f o l l o w i n g equation  These d a t a  were f i r s t  fitted  ODW  to  the targeted  to the  t o c a l c u l a t e t h e l o a d o v e n - d r y w e i g h t (ODW):  ODW = GW / (IMC + 1) The  IMC  (5)  f o u n d was 153.2 k g . 12% MC  F i n a l l y , t h e weight  was  calculated using  corresponding the following  equation: w e i g h t a t 12% MC = 1.12 x ODW  (6)  I n t h i s p a r t i c u l a r r u n , t h e k i l n was s e t t o t u r n i t s e l f o f f when t h e w e i g h t on t h e s c a l e was down t o 171.6 k g . the  targeted  and f i n a l  weights  (FWs) o b t a i n e d  Table A - l gives f o r a l l drying  runs.  2.  Testing  several  proportions  2.1 " 2 x 4 " s p e c i m e n s  The  chi-square  (X ) t e s t p r o c e d u r e d i s c u s s e d by 2  99  T a b l e A - l . T a r g e t e d and f i n a l w e i g h t s i n a l l . 8 l o a d s o f PCH specimens  RUN #  LOAD  |  |  <%)  GREEN WEIGHT (kg)  IMC  1  OVEN-DRY WEIGHT (kg)  TARGETED WEIGHT (kg)  2  FINAL WEIGHT (kg) 3  !  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 : a v e r a g e IMC o f t h e i n i t i a l p i e c e s o f lumber a t 12% MC 2 b e f o r e c o o l i n g and c o n d i t i o n i n g 3 W a l p o l e ( 4 3 ) was u s e d t o t e s t whether defective  or not t h e p r o p o r t i o n of  specimens was t h e same a f t e r 0, 2, 4 and 6 h o u r s o f  conditioning.  Letting p  l t  p , p and p r e p r e s e n t t h e p r o p o r t i o n 2  3  4  o f specimens f o u n d i n t e r n a l l y c h e c k e d 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 p r o c e d u r e , we had:  100  1. N u l l h y p o t h e s i s 2. A l t e r n a t i v e  :p = p :  hypothesis  3. L e v e l o f s i g n i f i c a n c e 4. C r i t i c a l r e g i o n 5. C o m p u t a t i o n s  2  = p = p • . 3  :p  l f  4  p , p 2  and p  3  were n o t e q u a l .  4  : 0.10.  : X > 6.251 f o r 3 d e g r e e s o f freedom. 2  : Corresponding t o the observed frequencies  o  = 6 and o = 39, we f o u n d  e  = ( (45x14)/180) = 3.5 and e = ( (45x166)/180) = 41.5.  x  x  All  5  5  o t h e r e x p e c t e d f r e q u e n c i e s were f o u n d t h e same way and  d i s p l a y e d i n T a b l e A-2. T a b l e A-2. O b s e r v e d and e x p e c t e d f r e q u e n c i e s o f "2x4" PCH specimens one week a f t e r d r y i n g  SPECIMENS  CONDITIONING TIME  |  0  2  TOTAL  (hrs)  |  6  4  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  |  180  I  |DEFECTIVE  |  TOTAL  | 45  45  45  45  Then, X  2  = ( ( ( 6 - 3 . 5 ) ) / 3 . 5 ) + ( ( ( 3 - 3 . 5 ) ) / 3 . 5 ) + ... 2  2  + ( ( (42-41 . 5) ) / 4 1 . 5 ) + ( ( (43-41 . 5 ) ) / 4 1 . 5 ) 2  2  = 2.788  101  6. D e c i s i o n  : A c c e p t t h e n u l l h y p o t h e s i s and c o n c l u d e t h a t t h e  p r o p o r t i o n o f 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 t h e same f o r a l l d r y i n g r u n s .  2.2  "4x4" specimens  Letting  p  p ,  l f  p  2  and p  3  represent  4  the proportion  of  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 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 t h e s i x - s t e p p r o c e d u r e g i v e n by W a l p o l e , we had: 1. N u l l h y p o t h e s i s : p  :  = p  2  = p  2. A l t e r n a t i v e h y p o t h e s i s : p 3. L e v e l o f s i g n i f i c a n c e 4. C r i t i c a l r e g i o n 5. C o m p u t a t i o n s  : X  2  l r  3  and p  were n o t e q u a l .  4  > 6.251 f o r 3 d e g r e e s o f freedom.  : Corresponding t o the observed frequencies  e  = ((24x33)/96) = 8.3 and e  All  2  : 0.10.  = 6 and o  1  4  p ,p  o  l  = p .  3  5  = 18, we f o u n d 5  = ((24x63)/96) = 15.8.  o t h e r e x p e c t e d f r e q u e n c i e s were f o u n d t h e same way and  d i s p l a y e d i n T a b l e A-3. Then, X 2  ( ( (6-8 . 3 ) ) / 8 .3) + ( ( ( 9 - 8 . 3 ) ) / 8 . 3 ) + ... 2  2  + ( ( (14-15.8) )/15.8) 2  + ( ( (16-15.8) )/15.8) 2  = 1.616 6. D e c i s i o n  : A c c e p t t h e n u l l h y p o t h e s i s and c o n c l u d e t h a t t h e  p r o p o r t i o n o f d e f e c t i v e specimens  102  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 t h e same f o r a l l d r y i n g  runs.  T a b l e A-3. O b s e r v e d and e x p e c t e d f r e q u e n c i e s o f "4x4" PCH specimens one week a f t e r d r y i n g  1  SPECIMENS  |  CONDITIONING  0  I DEFECTIVE  ]  6  I NON-DEFECTIVE I 18  I  TOTAL  (8.3) (15.8)  | 24  TIME  2  9 15  TOTAL  (hrs)  4  (8.3) (15.8)  24  (8 .3)  8  14 (15 .8)  16  24  24  10  6  1  (8.3)  |  (15.8)  33  |  63  |  96  |  3. Summary o f d r y i n g q u a l i t y o f " 2 x 4 " PCH l u m b e r  F i g u r e A - l shows w h i c h "2x4" specimens were f o u n d w i t h and without checking. the  original  The runs t h a t t h e specimens were u s e d i n and  boards  which  they  were  cross-sawn  from a r e  indicated.  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 o f t h e "2x4" and "4x4" specimens were compared by a t e s t o f s i g n i f i c a n c e values f o r a l l properties. comparison  of the defective  ("t" t e s t ) o f t h e mean  T a b l e A-4 g i v e s t h e r e s u l t s f o r t h e and n o n - d e f e c t i v e  103  specimens  mean  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 " 2 x 4 " PCH l u m b e r  104  specimens  Figure A-l.  ( Continued )  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  |  T a b l e 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 LUMBER  I I  PROPERTY  I  AVERAGE  | I  STANDARD DEVIATION  I |  SAMPLE SIZE  j 2"X4"X14'  !  I  NON-DEFECTIVE I IMC DEFECTIVE I  (%)  |  NON-DEFECTIVE I GREEN SPEC. I | DEFECTIVE | GRAVITY NON-DEFECTIVE| CORE MC DEFECTIVE I  (%) |  61.2 70.8  1 1  15.0 27.5  0 . 355 0.419  1 1  0.031 0.038  10.9 17.2  1 1  1.4 3.7  ! 4"X4"X13'  i  |  NON-DEFECTIVE I IMC DEFECTIVE I  VALUE  CONCLUSION  !  20 26  1  -1 68  -1.40  Not the  20 26  1  -2 69  -6.03  |  S i g . at the 1% l e v e l  I |  20 26  1  -2 69  -7.21  S i g . at the 1% l e v e l  1  +2 71  +2.76  S i g . at t h e 1% l e v e l  1  -1 69  -0.65  Not the  1  +2 63  +3.44  S i g . at the 1% l e v e l  1  +1 66  +1.34  Not the  | I  I  S i g . at 10% l e v e l  i  |  63.8 44.1  1 I  21.9 8.0  I |  29 10  NON-DEFECTIVE I GREEN SPEC. I | DEFECTIVE | GRAVITY  0.373 0.383  1 1  0.045 0.031  | |  29 10  3.8 1.5  I I  73 23  2.9 1.7  I I  58 38  4"X4"X3'  {%)  j  t  I C R I T I C A L CALCULATED  S i g . at 10% l e v e l  |  NON-DEFECTIVE| FMC (%) | DEFECTIVE I AFTER DRYING|  11.0 8.2  NON-DEFECTIVE I FMC (%) | DEFECTIVE | 1 WEEK AFTERI DRYING |  8.9 8.2  1 1 1  1  106  S i g . at 10% l e v e l  values.  E v e r y t i m e a " t " t e s t was p e r f o r m e d , t h e f o l l o w i n g s i x -  s t e p p r o c e d u r e g i v e n by W a l p o l e was u s e d . u  x  and u  lumber  2  r e p r e s e n t the average  i n which  a l l 4 KSs were  For instance,  letting  IMCs o f t h e "2x4" p i e c e s o f found checked  and f r e e  from  c h e c k i n g , 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 y p o t h e s i s : u  1  3. L e v e l o f s i g n i f i c a n c e 4. C r i t i c a l r e g i o n 5. C o m p u t a t i o n s  2  2  were n o t e q u a l .  : 0.10.  : t < -1.68 f o r 44 d e g r e e s o f freedom.  : The p o o l e d e s t i m a t e (s ) o f t h e common 2  v a r i a n c e was f i r s t s  and u  calculated.  = ( (20-1) (15.0 ) + (26-1) (27 .5 ) )/(20+26-2) = 526.85. 2  2  Then, t = ( 6 1 . 2 - 7 0 . 8 ) / ( (526.85) ( (1/20) + (1/26) )  1/2  6. D e c i s i o n  = -1.40  : A c c e p t t h e n u l l h y p o t h e s i s and c o n c l u d e t h a t t h e  a v e r a g e IMCs o f b o t h t y p e s o f p i e c e s were r e l a t i v e l y  the  same a t t h e 10% l e v e l .  5. Average i n i t i a l PCH specimens  moisture  contents i n a l l 4 loads of  T a b l e A-5 g i v e s t h e GWs, all #5,  FWs and a v e r a g e FMCs o b t a i n e d i n  f o u r l o a d s o f "4x4" PCH s p e c i m e n s . for  instance,  respectively.  were  "4x4"  279,9  kg,  GW,  FW and FMC o f l o a d  196.1  kg  and  8.7%,  These d a t a were f i t t e d i n t h e f o l l o w i n g e q u a t i o n  107  t o c a l c u l a t e t h e l o a d ODW: ODW = FW / ( FMC + 1) The  ODW  found  was  (7) 180.4 k g .  Finally,  the load  IMC was  calculated using the following equation: IMC = ( GW - ODW ) / ODW  (8)  The IMC f o u n d f o r r u n #5 was 55.1%.  A v e r a g e IMCs o f a l l d r y i n g  r u n s a r e g i v e n i n T a b l e A-5. T a b l e A-5. A v e r a g e i n i t i a l m o i s t u r e c o n t e n t s i n a l l 4 l o a d s o f "4x4" PCH specimens  RUN #  i  5 6  LOAD  |  1 • 1  IMC  FMC*  (%)  (%)  GREEN WEIGHT (kg)  OVEN-DRY WEIGHT (kg)  FINAL* WEIGHT (kg)  55 .1  8.7  279.9  180 .4  196 .1  54 .8  8 .1  273.8  176 . 8  191.1  1  57 .9  10.5  282.6  178 . 9  197 .7  8 ' 1  62 .9  14 .1  294 . 6  180.8  206.3  7  * : 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. T e s t i n g t h e d i f f e r e n c e between two  6.1  proportions  "4x4" specimens found d e f e c t i v e i m m e d i a t e l y a f t e r d r y i n g and c o n d i t i o n i n g  To  test  the hypothesis  that  and one  the proportions  week  o f "4x4"  s p e c i m e n s f o u n d i n t e r n a l l y c h e c k e d when cross-^-sawn i m m e d i a t e l y after  drying  period  and c o n d i t i o n i n g  (p )  were  2  equal,  d i s c u s s e d by W a l p o l e 1. N u l l h y p o t h e s i s  (p ) and one week x  the  following  corresponding first  procedure  : Pi = p 2  : Pi < p • 2  3. L e v e l o f s i g n i f i c a n c e : 0.01.  5. C o m p u t a t i o n s  six-step  that  (43) was u s e d :  2. A l t e r n a t i v e h y p o t h e s i s  4. C r i t i c a l r e g i o n  after  ;  : z < -2.33.  : The p o o l e d  estimate  of the proportion  t o the observed proportions  p  x  and p  calculated:  p  was  2  .'  P i = 17/96 = 0.177, p  2  = 33/96 = 0.344,  p = ( (17 + 3 3 ) / ( 9 6 + 96))  = 0.260.  Then, t h e z v a l u e t e s t i n g p  x  and p  2  was  obtained  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  : Reject  the i n i t i a l  hypothesis  and c o n c l u d e  that  t h e p r o p o t i o n o f d e f e c t i v e specimens f o u n d i m m e d i a t e l y 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 t h a n t h a t one week l a t e r .  109  6.2  "2X4" a n d " 4 x 4 " s p e c i m e n s d r y i n g and c o n d i t i o n i n g  As  i n section  hypothesis specimens  that  7.61, t h e z v a l u e  the proportions  found i n t e r n a l l y  c o n d i t i o n i n g were e q u a l . by W a l p o l e  f o u n d d e f e c t i v e o n e week  was  used  after  t o t e s t the  o f "2x4" (p ) and "4x4" (p ) x  c h e c k e d one week  2  a f t e r d r y i n g and  The f o l l o w i n g s i x - s t e p p r o c e d u r e g i v e n  (43) was u s e d :  1. N u l l h y p o t h e s i s  : p  1  = p .  2. A l t e r n a t i v e h y p o t h e s i s  2  : p  x  < p . 2  3. L e v e l o f 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. C o m p u t a t i o n s : P i = 14/180 = 0.078, p  2  = 33/96 = 0.344,  p = ( (14 + 3 3 ) / ( 1 8 0 + 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  : Reject  the p r o p o t i o n  the i n i t i a l  hypothesis  o f "2x4" specimens  and c o n c l u d e t h a t  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 was s m a l l e r t h a n t h a t t h e "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 w h i c h "4x4" specimens were f o u n d w i t h and  110  F i g u r e A-2. D e f e c t i v e a n d n o n - d e f e c t i v e " 4 x 4 " PCH l u m b e r  specimens o f  RUN #  13' ORIGINAL BOARD # 5  6  7  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 I I •Kami  3' SPECIMEN WITHOUT INTERNAL CHECKING 3' SPECIMEN WITH INTERNAL CHECKING  8  F i g u r e A-2. ( C o n t i n u e d )  13'ORIGINAL BOARD #  RUN# 5  6  7  46 47 48  IM l  3' SPECIMEN WITHOUT INTERNAL CHECKING 3' SPECIMEN WITH INTERNAL CHECKING  112  8  without  internal  checking.  The runs t h a t  t h e specimens  were  u s e d i n and t h e o r i g i n a l b o a r d s w h i c h t h e y were c r o s s - s a w n from are  indicated.  113  

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