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Comparative evaluation of some physical and mechanical properties of veneer-overlaid and non-overlaid… Filler, Merl Campbell 1961

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COMPARATIVE EVALUATION OP SOME PHYSICAL AND MECHANICAL PROPERTIES OP VENEEROVERLAID AND NON-OVERLAID PARTICLE BOARD by MERL C. FILLER, JR. B.S. 6f Wood U t i l i z a t i o n , Pennsylvania  1956  State U n i v e r s i t y  A T h e s i s s u b m i t t e d i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r the Degree o f Master o f F o r e s t r y i n the F a c u l t y o f F o r e s t r y  We accept the  t h i s t h e s i s as conforming t o  standard  r e q u i r e d from  candidates  f o r the Degree o f Master o f F o r e s t r y  Members o f the F a c u l t y o f F o r e s t r y The  U n i v e r s i t y o f B r i t i s h Columbia April  1961  In the  presenting  requirements  of  British  it  freely  agree for  that  thesis  an  advanced  for  Columbia, available  I  that  copying  gain  shall  by or  not  his  p a r t i a l  degree  fulfilment  at  the  Library  shall  reference  and  study.  I  extensive  may  be  granted  representatives.  allowed  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r #, Canada.  of  copying  this  without  by  of  the  It thesis  is  Columbia,  make  further this  Head  of  thesis my  understood  for  my w r i t t e n  of  University  the  publication be  in  that  for  purposes  or  agree  for  permission  scholarly  Department  this  f i n a n c i a l  permission.  ii  ABSTRACT  Three p a r t i c l e b o a r d s , one f l a k e b o a r d , one  multi-layer  b o a r d , and a plywood p a n e l , a l l o f 3 / 8 - i n c h t h i c k n e s s , were o v e r l a i d w i t h 1 / 2 0 - i n c h P h i l i p p i n e mahogany veneer, u s i n g a urea-formaldehyde  adhesive.  B o t h n o n - o v e r l a i d and  b o a r d s were s u b j e c t e d t o p h y s i c a l and m e c h a n i c a l i n v o l v i n g the g l u e l i n e and the boards  overlaid  tests  themselves.  R e s u l t s o f the g l u e - l i n e shear t e s t  i n d i c a t e d t h a t glue-,  l i n e f a i l u r e between the v e n e e r and the boards o n l y o c c u r r e d i n t h e boards o f h i g h e r d e n s i t y .  O v e r l a y i n g the  boards  d e c r e a s e d . d i m e n s i o n a l change i n a p l a n e p a r a l l e l t o t h e l e n g t h of the b o a r d but s l i g h t l y i n c r e a s e d i t p a r a l l e l t o t.  t h e w i d t h o f the b o a r d .  Boards composed o f f l a k e s had  s t r e n g t h p r o p e r t i e s t h a n those composed o f p a r t i c l e s .  better No  d e l a m i n a t i o n o f the b o a r d o c c u r r e d d u r i n g a c c e l e r a t e d a g i n g ; however, d e t e r i o r a t i o n i n t h e b o a r d c o r e was e x t e n s i v e . I n g e n e r a l , o v e r l a y i n g the boards tended t o minimize d i f f e r e n c e s i n s t r e n g t h p r o p e r t i e s between b o a r d s ,  and  improved the s t r e n g t h p r o p e r t i e s so as t o be almost comp a r a b l e to t h o s e o f plywood. i n the boards.  O v e r l a y i n g d e c r e a s e d warping  Some p h y s i c a l p r o p e r t i e s o f the b o a r d s ,  as r e s i s t a n c e t o warping  and f a c e - c h e c k i n g , were more  s a t i s f a c t o r y t h a n those o f plywood.  such  iii  ACKNOWLEDGEMENT  Acknowledgement  i s made t o W i l l i a m R. P r a n c i s o f the  Simpson L o g g i n g Company who i n s p i r e d t h e i n i t i a l work on t h i s t h e s i s , and t o Dr. R.W. Wellwood o f the U n i v e r s i t y o f B r i t i s h Columbia under whose.guidance t h e p r o j e c t was conducted and c a r r i e d t o c o m p l e t i o n .  Thanks a r e due t o  L e s l i e P a s z n e r f o r a s s i s t a n c e i n t e s t i n g and i n g a t h e r i n g d a t a , t o Dr. J.H.G. Smith f o r a i d i n a n a l y z i n g t h e s t a t i s t i c s , and t o Mr. R.W. manuscript.  The author i s g r a t e f u l t o M e s s r s . H.G.M. C o l b e c k ,  W.V. Hancock, W.M. the  Kennedy f o r r e v i e w i n g t h e  McGowan, P.L. N o r t h c o t t , and W.J. Smith o f  P o r e s t P r o d u c t s L a b o r a t o r i e s o f Canada, Vancouver, f o r  a s s i s t a n c e i n t h e o v e r l a y i n g and t e s t i n g phase o f t h e p r o j e c t . Acknowledgement  and thanks a r e made t o the s u p p l i e r s  o f p a r t i c l e h o a r d s and plywood, and t o Monsanto  Canada  L i m i t e d , Vancouver, f o r f u r n i s h i n g the a d h e s i v e , and f o r making a v a i l a b l e t h e i r t e s t i n g  equipment.  iv )  TABLE OF CONTENTS Page INTRODUCTION  . . . . .  1  MANUFACTURING PROCESS  5  PRODUCT VARIABLES Species  11  s e l e c t i o n and p r e p a r a t i o n  11  Adhesive m a t e r i a l s  14-  Curing  16  conditions  Product p r o p e r t i e s  17  Density  17  Dimensional s t a b i l i t y  18  P a r t i c l e and f l a k e o r i e n t a t i o n  20  Nail-holding a b i l i t y  21  Strength  properties  .  PROCEDURE  22 24-  Procurement o f m a t e r i a l  24-  Preliminary overlaying  26  F i n a l lay-up  30  TEST METHODS AND PROCEDURES  33  G l u e - l i n e shear  34-  M e c h a n i c a l t e s t s o t h e r t h a n g l u e - l i n e shear . . . .  34-  Physical tests  4-3  Accelerated  4-7  aging  Page DISCUSSION OP RESULTS  48  G l u e - l i n e shear Tension p a r a l l e l Static  48 t o l e n g t h and w i d t h o f s u r f a c e . .  bending  51 54  Modulus o f r u p t u r e  54  Modulus o f e l a s t i c i t y  55  Lateral n a i l resistance Nail-withdrawal resistance Dimensional  57 . . .  change  58 59  Warping  62  Accelerated aging  65  CONCLUSIONS AND RECOMMENDATIONS  68  BIBLIOGRAPHY  71  APPENDICES  74  A.  Tension P a r a l l e l  to Surface of Non-overlaid  and O v e r l a i d Boards and Plywood B.  A n a l y s i s of Variance of Tension P a r a l l e l to S u r f a c e as A f f e c t e d by O v e r l a y and G r a i n Direction  C.  Modulus o f Rupture o f N o n - o v e r l a i d and O v e r l a i d Boards and Plywood  D.  A n a l y s i s o f V a r i a n c e o f Modulus o f Rupture as A f f e c t e d by O v e r l a y and G r a i n D i r e c t i o n  E.  Modulus o f E l a s t i c i t y o f N o n - o v e r l a i d and O v e r l a i d Boards and Plywood  vi Page P.  A n a l y s i s o f V a r i a n c e o f Modulus  of E l a s t i c i t y  as A f f e c t e d by O v e r l a y and G r a i n D i r e c t i o n G.  L a t e r a l N a i l R e s i s t a n c e o f N o n - o v e r l a i d and O v e r l a i d Boards and  H.  A n a l y s i s of Variance of L a t e r a l N a i l Resistance as A f f e c t e d by  I.  Veneer-overlay  Nail-withdrawal Resistance of Non-overlaid Boards and  J.  Plywood  Plywood  A n a l y s i s of Variance of Nail-withdrawal R e s i s t a n c e as A f f e c t e d by  Veneer-overlay  vii  LIST OF TABLES Table I.  Page Moisture Content and S p e c i f i c G r a v i t y of Boards  II.  27  Amount of Delamination Occurring i n 4 - by 4 - i n c h Samples of Overlaid Board a f t e r 3 Cycles of a 4-hour Soak and a 20-hour Dry at 95°F . . .  III.  Thicknesses of Boards and Veneer Before and A f t e r Pressing  IV. V.  Glue-line Shear Test  A.  49  B.  49  Summary of Mechanical Properties of Non-overlaid Board  52  Summary of Mechanical Properties of Overlaid Board  VII.  29  A n a l y s i s of Variance f o r Glue-line Shear Test  VI.  29  52  Dimensional Change i n Thickness and Length of Panels Between 75 and 25 Percent Relative Humidity  VIII.  60  Warping i n Panels at 75 and 25 Percent Relative Humidity  63  viii  LIST OF FIGURES  Figure 1.  Page Schematic Drawing of M i l l e r - H o f f t Multi-Platen P a r t i c l e or Flake Board  Manufacturing  Process 2.  Interwood Glue Spreader Used f o r Applying Adhesive  3.  6  to Boards  31  Berthelson Oil-heated Hot-press f o r Bonding Veneer to P a r t i c l e Boards  4.  Cutting Plan of 2- by 4-foot Non-overlaid  31 and  Veneer-overlaid Boards and Plywood  35  5.  T i n i u s Olsen Universal Testing Machine  37  6.  T y p i c a l Load-deflection Curves  40  7.  L a t e r a l N a i l Resistance Test Assembly  42  8.  Nail-withdrawal Test Assembly  42  9.  Method Used f o r Measuring Twist i n Panels . . . .  45  10.  Thickness Measuring Micrometer D i a l  46  11.  Types of F a i l u r e Occurring i n Tension P a r a l l e l . .  46  12.  Accelerated Aging Samples  67  1  INTRODUCTION  D u r i n g t h e summer o f 1959» a t which time t h e author worked f o r the Simpson Logging Company o f S h e l t o n , Washington, a p r o j e c t was undertaken i n v o l v i n g the o v e r l a y i n g o f p a r t i c l e board w i t h v e n e e r .  A l i t e r a t u r e s u r v e y a t t h a t t i m e , and a  c u r r e n t one i n c o n j u n c t i o n w i t h t h i s s t u d y , r e v e a l e d l i t t l e i n f o r m a t i o n a v a i l a b l e on t h e p h y s i c a l and mechanical p r o p e r t i e s o f o v e r l a i d p a r t i c l e hoard.  The b a s i s o f t h i s p r o j e c t was t o  i n v e s t i g a t e f u r t h e r some o f t h e p r o p e r t i e s o f o v e r l a i d p a r t i c l e board. The development o f new uses f o r p a r t i c l e  board  promises t o have a f a r - r e a c h i n g e f f e c t on t h e wood-using industry.  P r e s e n t l y the uses o f p a r t i c l e hoard a r e many,  r a n g i n g from core s t o c k i n f u r n i t u r e t o h i g h l y d e c o r a t i v e wall paneling.  I f o v e r l a i d p a r t i c l e hoard c o u l d be developed  w i t h s t r e n g t h p r o p e r t i e s comparable might  t o plywood, such a p a n e l  serve a s t r u c t u r a l as w e l l as a d e c o r a t i v e purpose.  I t might he used as w a l l p a n e l i n g , movable p a r t i t i o n s , s h e l v e s , and s l i d i n g d o o r s .  Por t h e s e uses, b o t h the p h y s i c a l and  mechanical p r o p e r t i e s are important. Wood p a r t i c l e hoard may be d e f i n e d as a f l a t p a n e l composed o f d i s c r e t e p a r t i c l e s o f wood bonded t o g e t h e r with a suitable binder.  Veneer-faced o r v e n e e r - o v e r l a i d  2 p a r t i c l e board r e f e r s t o a p a n e l h a v i n g a f a c e and back p l y o f a wood v e n e e r .  G e n e r a l l y , when p a r t i c l e board i s o v e r l a i d ,  c r o s s - b a n d i n g i s p r o v i d e d i n o r d e r t o decrease  'telegraphing'  of t h e s u r f a c e p a r t i c l e s t h r o u g h the s u r f a c e o f the f a c e plies.  T h i s i s a l s o known as 'show-through'.  banding a l s o i n c r e a s e s d i m e n s i o n a l s t a b i l i t y .  The c r o s s One o b j e c t o f  t h i s study was t o determine t h e p r o p e r t i e s o f o v e r l a i d p a r t i c l e b o a r d i f c r o s s - b a n d i n g i s not c a r r i e d o u t . Marra  (16) d i v i d e s the t y p e s o f wood elements  i n t h e manufacture 'flakes'.  o f p a r t i c l e board i n t o  The term  used  ' p a r t i c l e s ' and  ' p a r t i c l e ' r e f e r s t o wood elements o f  s m a l l s i z e formed by hammermill a c t i o n on c h i p s o r p l a n e r shavings.  The term  ' f l a k e ' r e f e r s t o elements produced by  s p e c i a l c u t t e r heads on s o l i d wood.  Marra s t a t e s t h a t  flakes  are c h a r a c t e r i z e d by t h e i r a p p r e c i a b l e l e n g t h compared t o t h e i r thickness.  The wood g r a i n runs i n the f l a t ,  t u d i n a l d i r e c t i o n of the f l a k e .  T h i s nomenclature  f o l l o w e d i n t h e t e x t o f the t h e s i s .  longiw i l l be  U n f o r t u n a t e l y t h e word  ' p a r t i c l e b o a r d ' , as used i n the wood i n d u s t r y , has come t o mean any type o f wood c o m p o s i t i o n board, r e g a r d l e s s o f the p h y s i c a l elements going i n t o i t s make-up.  S i n c e boards a r e  produced by p a r t i c l e s , f l a k e s , o r by combinations o f b o t h , the word 'board' w i l l be used here i n r e f e r r i n g t o wood composition board of a general nature. Three boards o f the p a r t i c l e t y p e , one b o a r d o f the f l a k e t y p e , and one b o a r d c o n s i s t i n g o f a p a r t i c l e c e n t e r  3 and f l a k e s u r f a c e s , were used i n the e v a l u a t i o n .  F o r com-  p a r a t i v e purposes, an e x t e r i o r - g r a d e Douglas f i r plywood p a n e l was selected.  also included. This thickness  Boards o f 3/8-inch t h i c k n e s s were of hoard was  s e l e c t e d because i t  might he a p p l i c a b l e f o r b o t h s t r u c t u r a l and purposes.  decorative  Furthermore, some o f the p h y s i c a l d e f e c t s ,  such  as warping, might more r e a d i l y m a n i f e s t themselves w i t h a t h i n n e r hoard.  A b i g problem g o v e r n i n g the use o f p a r t i c l e  hoard i s dimensional s t a b i l i t y .  Another i s warping,  e s p e c i a l l y i n the f l a t - p r e s s e d type o f board used h e r e . Overlaying its  a h o a r d w i t h wood v e n e e r might  increase  s t r e n g t h p r o p e r t i e s enough t o enable i t t o be used as a  structural material.  Fujii  m a t e r i a l on p a r t i c l e b o a r d .  (6) s t u d i e d the e f f e c t o f o v e r l a y He s t a t e d t h a t the f l e x u r a l  s t r e n g t h and s t i f f n e s s o f the b o a r d c o u l d be  appreciably  i n c r e a s e d by o v e r l a y i n g w i t h a m a t e r i a l t h a t c o u l d a concentration  o f s t r e s s e s i n t e n s i o n and  absorb  compression.  Furthermore, the veneer o v e r l a y might t e n d t o d e c r e a s e d i m e n s i o n a l change i n the p a n e l .  The s m a l l component o f  l o n g i t u d i n a l s h r i n k a g e and s w e l l i n g o f the wood v e n e e r would r e s t r a i n d i m e n s i o n a l change i n the board, a t l e a s t i n the d i r e c t i o n o f the board p a r a l l e l t o the g r a i n o f the v e n e e r . I t was  the i n t e n t o f t h i s study.,; t h e r e f o r e , t o  make a comparative e v a l u a t i o n o f the p r o p e r t i e s of o v e r l a i d and n o n - o v e r l a i d h o a r d , and o v e r l a i d and n o n - o v e r l a i d  plywood.  4 More s p e c i f i c a l l y , the purposes were t o : 1.  D i s t i n g u i s h d i f f e r e n c e s e x i s t i n g i n the p h y s i c a l properties,  such as warping and d i m e n s i o n a l change,  between o v e r l a i d and n o n - o v e r l a i d 2.  Ascertain  board and plywood.  i f d i f f e r e n c e s e x i s t e d i n the  p r o p e r t i e s , such as t e n s i l e s t r e n g t h ,  strength  ultimate  s t r e n g t h i n bending, and s t i f f n e s s , between o v e r l a i d and n o n - o v e r l a i d 3.  4.  Determine  boards and plywood.  i f d i f f e r e n c e s e x i s t e d i n the p h y s i c a l  and m e c h a n i c a l p r o p e r t i e s p a r a l l e l and  perpendicular  t o the g r a i n of the f a c e veneer of the  panel.  Determine  i f d i f f e r e n c e s e x i s t e d i n the p h y s i c a l  and m e c h a n i c a l p r o p e r t i e s p a r a l l e l and  perpendicular  to the machine d i r e c t i o n of the b o a r d (the  longest  d i r e c t i o n o f a 4- by 8-foot b o a r d and the l o n g i t u d i n a l d i r e c t i o n o f the f a c e p l i e s o f plywood). The boards used i n t h i s study were o f the m u l t i p l a t e n f l a t - p r e s s e d type. manufacture  The type o f p r o c e s s used t o  t h i s type o f b o a r d i s d e s c r i b e d .  A review i s  a l s o made o f the m a n u f a c t u r i n g v a r i a b l e s and o f how v a r i a b l e s a f f e c t the p r o p e r t i e s  these  of the f i n i s h e d b o a r d .  5  MANUFAC TURING PROCESS  The p r o c e s s e s f o r m a n u f a c t u r i n g p a r t i c l e  hoard  are c l a s s i f i e d as the m u l t i - p l a t e n h o t - p r e s s , the e x t r u s i o n , and the c o n t i n u o u s - p r e s s i n g method.  Many r a m i f i c a t i o n s are  found i n the p r o c e s s i t s e l f , and the p r o c e s s e s used i n the manufacture  o f these hoards a r e not i d e n t i c a l .  Nonetheless,  the g e n e r a l f l o w scheme, shown i n F i g u r e 1, a p p l i e s w e l l enough to form an u n d e r s t a n d i n g of the g e n e r a l m u l t i - p l a t e n h o t - p r e s s m a n u f a c t u r i n g method.  The f o l l o w i n g p r o c e s s , as  o u t l i n e d , has been e x t r a c t e d from the Wood P a r t i c l e  Board  Handbook (11). 1  Raw,  green, wood m a t e r i a l , i n a c o a r s e form  such  as cordwood, e n t e r s the system a t a p r i m a r y r e d u c t i o n u n i t , which i s n o r m a l l y a k n i f e hog. e n t e r the system  Other t y p e s of wood r e s i d u e  a t the a p p r o p r i a t e p l a c e , depending  on  whether t h e y are d r y o r have a l r e a d y been reduced i n s i z e . T h i s l a t t e r m a t e r i a l i s u s u a l l y veneer c l i p p i n g s o r p l a n e r shavings.  The p r i m a r y hog reduces the m a t e r i a l i n t o a s i z e  s m a l l enough f o r f u r t h e r h a n d l i n g by a secondary, or hammerm i l l hog. conveyed  P a r t i c l e s l e a v i n g t h i s f i r s t hog are p n e u m a t i c a l l y t o a r o t a r y d r y e r where t h e y are d r i e d t o about  H e r e a f t e r r e f e r r e d t o as the Handbook  10  fines to boiler dry  wet w o o d  wood  wo.ste  was  feed  weightometer  resin  •  pump  hot-press unloa der  loader p re e ^^rnnr r n p r jes s 10 n rolls :  v  gravity  cauls  spacing  Figure  I.  Schematic  Carolina  of  MiIIer-Hofft  Multi-platen  Particle  or  Flake  Board  Process.  Source.- I n d u s t r i a l North  conveyor.  Diagram  Manufacturing  conveyor  Experimental  State  College.  P r o g r a m . 1956. W o o d R a l e i g h , p. 2 4 .  particle board  handbook.  7 p e r c e n t m o i s t u r e c o n t e n t , depending on the  requirements  the  particles  p a r t i c u l a r process.  conveyed t o the  After  secondary r e d u c t i o n u n i t  K i l n - d r i e d residue usually The  p a r t i c l e s are  s i z e t o he  p a r t i c l e s are  used i n the  screened and  desired  board.  These  From the  collector  oversize p a r t i c l e s  P a r t i c l e s " o f a c c e p t a b l e s i z e are  t o a second c o l l e c t o r . hogged, w h i l e the  the  grinding.  system a t t h i s p o i n t .  conveyed to a c o l l e c t o r .  f i n e s are removed.  as  e n t e r s the  are  for further  f i n a l r e d u c t i o n u n i t produces the  p a r t i c l e or flake  the  d r y i n g , the  and blown  L a r g e , o v e r s i z e p a r t i c l e s are  f i n e s are  of  sent to the  b o i l e r to be  reused  fuel. A c c e p t a b l e p a r t i c l e s are p a s s e d from the  collector  to a s t o r a g e b i n where a screw-type conveyor removes m a t e r i a l from the onto a  bottom a t a c o n s t a n t r a t e .  p a r t i c l e s are  'weightometer' which a u t o m a t i c a l l y c o n t r o l s  o f p a r t i c l e s as t h e y are mixer the  conveyed i n t o the  mixer.  p a r t i c l e s come i n t o c o n t a c t w i t h the  which i s s p r a y e d i n t o the the  The  p a r t i c l e mass.  same end  P a r t i c l e s and  of the  From the  controlled  a c r o s s the  rate  chip-spreading unit Here, on the  that  the  mixer t h a t  receives  t h o r o u g h l y mixed located  mixture i s f e d at  w i d t h of a f l a t ,  travels  In  amount  adhesive  r e s i n are  surge b i n the  the  resin  b e f o r e b e i n g d i s c h a r g e d i n t o a surge b i n , u s u a l l y a lower f l o o r .  fed  endless b e l t  c o n t i n u o u s l y beneath the  c h i p - s p r e a d i n g u n i t , the  mat  i s leveled  to  on a or bin. the  8 required thickness. to  M a t e r i a l which i s removed i s r e t u r n e d  t h e surge b i n . Beneath the c h i p s p r e a d e r i s a  conveyor  power-driven  which t r a v e l s a t the same r a t e o f speed as t h e b e l t .  M e t a l c a u l s are g r a v i t y f e d onto the conveyor  and pass  d i r e c t l y under t h e mass o f moving p a r t i c l e s as t h e y f a l l o f f the end o f t h e b e l t o f t h e s p r e a d e r u n i t .  The f a l l i n g o f the  mass a c t s t o a g i t a t e and d i s t r i b u t e the f i n e s throughout the mat.  The c a u l w i t h i t s mat t r a v e l s through an unheated p r e -  compression  unit.  T h i s mechanism c o n s i s t s o f an upper and  lower t r a c k which compacts the mat and a l s o shapes t h e s i d e s . In  some p r o c e s s e s t h e mat i s edge-trimmed f o l l o w i n g  compression.  Prom the c o l d - p r e s s i n g u n i t the c a u l p r o g r e s s e s t o a speed-up conveyor which causes a s p a c i n g between i t and the p r e c e d i n g c a u l .  S p a c i n g a l l o w s the l o a d e r time t o  r e c e i v e each mat and to charge the end o f each p r e s s c y c l e . of  the p r e s s w i t h a f u l l  The l o a d e r h o l d s t h e same number  c a u l s as does t h e hot p r e s s .  range from 4 t o 20. charge  load at  The number o f c a u l s may  When t h e l o a d e r has r e c e i v e d a f u l l  the p r e s s opens, and a f t e r d i s c h a r g e o f the c u r e d  b o a r d s , t h e new l o a d i s i n j e c t e d i n t o i t .  The p r o c e s s o f  l o a d i n g , c h a r g i n g the hot p r e s s w i t h the new l o a d , and unloading i s completely The  automatic.  p r e s s u n l o a d e r removes the p r e s s e d boards and  c a u l s from the p r e s s a t the completion  of the c u r i n g c y c l e .  9 A t t h i s p o i n t t h e cured hoards are a u t o m a t i c a l l y from the c a u l s . reloading while conditioning.  Cauls are returned t o the process f o r the boards are s t a c k e d  to allow a p e r i o d  A f t e r t h e r e q u i r e d c o n d i t i o n i n g p e r i o d the  hoards are edge-trimmed. he  separated  edge-trimmed b e f o r e  I n some p r o c e s s e s ,  the boards may  conditioning.  E s s e n t i a l l y , t h i s m u l t i - p l a t e n hot press  operation  may he b r o k e n down i n t o f o u r b r o a d phases; these a r e , particle  ( o r f l a k e ) p r e p a r a t i o n , p a r t i c l e t r e a t m e n t , mat  formation,  and hot p r e s s i n g . In the p r o c e s s  where a t h r e e - l a y e r h o a r d i s p r o -  duced, t h a t i s , a hoard w i t h a h i g h - q u a l i t y s u r f a c e f l a k e , and p a r t i c l e s i n the c e n t e r , t h e p r o c e s s  i s modified  somewhat.  A f t e r the wood e n t e r s the system, e i t h e r a t the d e b a r k e r o r a f t e r t h e d r y e r , t h e s u r f a c e f l a k e s and i n n e r p a r t i c l e s a r e channeled s e p a r a t e l y .  Each channel c o n t a i n s  r e d u c t i o n u n i t , storage dryer screens,  i t s own p r i m a r y  hopper, secondary r e d u c t i o n u n i t ,  conveying u n i t s , weightometer, wood-glue  m i x e r s , and p a r t i c l e  spreaders  f o r mat f o r m i n g .  One type  o f b o a r d used i n t h i s p r o j e c t c o n s i s t e d o f t h r e e - l a y e r c o n s t r u c t i o n , the surface being menziesii pine  o f Douglas f i r (Pseudotsuga  ( m i r b . ) F r a n c o ) f l a k e s , and the i n n e r core o f  (genus P i n u s ) p a r t i c l e s . C h i p s from the s e p a r a t e - f l o w  the mat-forming u n i t .  channels merge a t  I n d i v i d u a l c a u l s , moving on a  10 conveyor b e l t , p a s s beneath the c h i p - s p r e a d i n g u n i t s . u n i t s are so a r r a n g e d t h a t a t h i n mat f i r s t d e p o s i t e d on the c a u l .  o r bottom  layer i s  The c a u l i s moved t o the next  u n i t and the middle l a y e r i s d e p o s i t e d .  The c a u l i s a g a i n  moved to r e c e i v e the top l a y e r and the mat pressed.  These  i s then p r e -  Thus the p r o c e s s i s the same as the one  just  described. I t s h o u l d be n o t e d t h a t the p r o c e s s d e s c r i b e d here i s an example, and the p r o c e s s e s by which the boards used i n t h i s  study were made p o s s i b l y a l l had  variations.  I t i s not w i t h i n the scope o f t h i s r e p o r t t o e l a b o r a t e on the i n d i v i d u a l m a n u f a c t u r i n g methods.  11  PRODUCT VARIABLES  S p e c i e s s e l e c t i o n and p r e p a r a t i o n One  type o f b o a r d w i l l d i f f e r  and m e c h a n i c a l p r o p e r t i e s from a n o t h e r .  greatly i n physical I n a d d i t i o n t o the  v a r i a t i o n s e x i s t i n g i n the m a n u f a c t u r i n g p r o c e s s , t h e v a r i a t i o n i n the p r o p e r t i e s o f the s p e c i e s used i n the boards i s g r e a t , and the r e s u l t a n t p r o p e r t i e s o f the b o a r d a r e affected.  A l l boards used i n t h i s p r o j e c t were formed from  coniferous  species. I t i s s t a t e d i n the Handbook (11) t h a t  species  i s not the c o n t r o l l i n g f a c t o r i n p a r t i c l e b o a r d p r o d u c t i o n . A l t h o u g h hardwoods are g e n e r a l l y denser t h a n softwoods, the f a c t o r s o f hardness and c o m p r e s s i b i l i t y a r e the most i m p o r t a n t . Softwoods w i l l form more dense and compact boards t h a n h a r d woods under a g i v e n p r e s s u r e .  S i n c e t h e p a r t i c l e s o f the  softwoods can be r e a d i l y compacted, s t r o n g e r boards are o b t a i n e d because of b e t t e r bonding.  Strength p r o p e r t i e s of  the  b o a r d i n c r e a s e w i t h a d e c r e a s e i n the s p e c i f i c g r a v i t y o f  the  wood used i n the b o a r d . The breakdown o f ' p a r t i c l e s ' used i n wood  c o m p o s i t i o n - b o a r d p r o d u c t i o n as d e s c r i b e d by the Handbook i s i n t o s p l i n t e r - t y p e p a r t i c l e s , f l a k e s , and s h a v i n g s .  12 S p l i n t e r - t y p e p a r t i c l e s are oblong and may chunky shapes to n e e d l e - l i k e shapes.  range from s h o r t ,  F l a k e s , as  d e s c r i b e d , are t h i n , r e c t a n g u l a r p a r t i c l e s w i t h c o n t r o l l e d d i m e n s i o n s , and  already closely  are produced by a c u t t i n g a c t i o n  so t h a t f i b r e damage i s h e l d to a minimum.  Planer  shavings  are a l s o produced hy a c u t t i n g a c t i o n hut have no c o n t r o l l e d dimension or f i b r e o r i e n t a t i o n . Boards o b t a i n t h e i r s t r e n g t h i n two the i n d i v i d u a l wood f i b r e s and  ways, from  from the r e s i n bond.  A  given  amount o f r e s i n can e f f e c t i v e l y cover a c e r t a i n a r e a ; i f the area c o v e r e d and  i s too l a r g e , the r e s i n f i l m w i l l be  a weak bond w i l l r e s u l t .  w i d t h , and  T u r n e r (24) found t h a t l e n g t h ,  t h i c k n e s s a l l c o n t r o l the  p a r t i c l e , and  thin  surface area of  o f t h e s e , t h i c k n e s s had  the g r e a t e s t  the  effect.  G e n e r a l l y , bonding s t r e n g t h i n c r e a s e d as the w i d t h and o f the p a r t i c l e i n c r e a s e d .  Since  sawdust has  length  a large surface-  i  weight r a t i o i t r e q u i r e d more s u r f a c e a r e a bonding and h i b i t e d the lowest  strength properties.  ex-  Turner s t a t e d that  l a r g e , t h i n f l a k e s were the most d e s i r e d s i n c e they were more c o m p r e s s i b l e  and  a b e t t e r bond r e s u l t e d .  T u r n e r and Kern (25) found a c e r t a i n f l a k e t h i c k n e s s and  r e s i n c o n c e n t r a t i o n beyond which s t r e n g t h  p r o p e r t i e s o f the hoard d e c r e a s e d . f l a k e s had  I f boards w i t h  too low a c o n c e n t r a t i o n o f r e s i n on the  poor bonding would r e s u l t . t h a t no advantage was  There was  thin surface,  a converse l i m i t ,  g a i n e d hy i n c r e a s e d r e s i n amount.  in Thus  13 t h e r e i s an optimum p o i n t where b o t h f l a k e s i z e and r e s i n amount s h o u l d be m a i n t a i n e d . As the l e n g t h o f t h e p a r t i c l e i n c r e a s e s , the s t r e n g t h i n c r e a s e s , up t o a c e r t a i n p o i n t .  Too l a r g e  p a r t i c l e s tend t o have a s h i e l d i n g a c t i o n on the r e s i n  sprayed  i n t o the p a r t i c l e mass, thus c a u s i n g l a c k o f bonding.  Particle  w i d t h has l i t t l e total tensile  e f f e c t on b o a r d s t r e n g t h , assuming t h a t the  s t r e n g t h o f p a r t i c l e s , p a r a l l e l t o the g r a i n ,  v a r i e s w i t h w i d t h i n d i r e c t p r o p o r t i o n t o the f l a t which t r a n s f e r s t h e s t r e n g t h ( 1 1 ) . p a r t i c l e might  area  A g a i n , t o o wide a  t e n d t o have a s h i e l d i n g e f f e c t on the r e s i n .  There i s an optimum s i z e f o r t h i c k n e s s , l e n g t h and w i d t h . Particle  shape has the p r i m a r y e f f e c t on s t r e n g t h , w h i l e  r e s i n content i s secondary i n importance. Dimensional thickness.  s t a b i l i t y i s a l s o a f f e c t e d by p a r t i c l e  Wood which i s compressed tends t o s w e l l t o i t s  o r i g i n a l s i z e upon m o i s t u r e p i c k - u p , i f i t s m o i s t u r e c o n t e n t i s t h e same as t h e m o i s t u r e c o n t e n t o f the o r i g i n a l wood. Because t h i n n e r c h i p s need n o t be compressed as much as t h i c k e r ones f o r a board o f g i v e n s t r e n g t h , p a n e l s composed of t h i n n e r c h i p s have l e s s tendency t o s w e l l .  Heebink and  Harm (8) found t h a t boards produced w i t h 1 - i n c h - l o n g f l a k e s had l e s s d i m e n s i o n a l change t h a n b o a r d composed o f s h a v i n g s , slivers,  and sawdust.  They a t t r i b u t e d t h i s t o the i n c r e a s e d  b i n d i n g e f f i c i e n c y o f the r e s i n .  14 I t i s s t a t e d i n the Handbook (page 190)  that  K l a u d i t z found t h a t l a t e r a l n a i l - h o l d i n g a b i l i t y o f the hoard was  dependent  on the s p e c i f i c g r a v i t y , and t o some e x t e n t on  the p a r t i c l e s i z e , whereas p e r p e n d i c u l a r n a i l - h o l d i n g was  based e n t i r e l y on s p e c i f i c  ability  gravity.  I n a p r o j e c t such as t h i s , c o n s i d e r a t i o n must he given to p r o p e r t i e s other than strength.  Boards composed o f  s p l i n t e r s t e n d t o have gaps i n the s u r f a c e i f p a r t i c l e s o f the same s i z e a r e used throughout the b o a r d .  When s m a l l e r  p a r t i c l e s and f i n e s are i n t r o d u c e d i n t o the board the d i m e n s i o n a l s t a b i l i t y w i l l be reduced.  Unequal  distribution  of f i n e s r e s u l t s i n unequal expansion and c o n t r a c t i o n o f the b o a r d d u r i n g m o i s t u r e c o n t e n t changes,  s i n c e the s m a l l e r  p a r t i c l e s w i l l p i c k up a g r e a t e r p e r c e n t o f m o i s t u r e through t h e i r l a r g e r s u r f a c e a r e a p e r u n i t volume. Adhesive  materials Many m a t e r i a l s have been used t o bond wood  p a r t i c l e s t o g e t h e r , but f o r f l e x i b i l i t y ,  strength,  permanence t h e s y n t h e t i c r e s i n s are p r e f e r r e d . the urea-formaldehyde  r e s i n s predominate.  are a l s o used hut are somewhat more c o s t l y . Kitazawa, Duncan, and Hine  and  Of t h e s e  Phenolic resins Maxwell,  (18) suggest t h a t e x t e n s i v e  r e s e a r c h he made on the economical a p p l i c a t i o n o f p h e n o l i c r e s i n s i n h o a r d s , i n o r d e r t o c r e a t e more uses f o r the hoard.  They s t a t e t h a t p h e n o l i c - b o n d e d boards, once a c c e p t e d  15 by f i r e u n d e r w r i t e r s and b u i l d i n g code o f f i c i a l s ,  migbt  r e p l a c e plywood f o r s h e a t h i n g and e x t e r i o r u s e s . C u r r e n t l y , phenolic-urea-formaldehyde b e i n g used i n most c o m p o s i t i o n boards. formaldehyde  combinations  r e s i n s are  Melamine-urea-  a r e used o n l y to a l i m i t e d e x t e n t  because o f t h e i r g r e a t e r c o s t . C a t a l y s t s a r e used i n the c u r i n g o f the b o a r d , i n o r d e r t o h a s t e n a p o l y m e r i z a t i o n o r p o l y c o n d e n s a t i o n o f the resin.  The c a t a l y s t w i l l  board.  Too r a p i d a cure r e s u l t s i n an i n c o m p r e s s i b l e p a r t i c l e  or  a f f e c t the s u r f a c e q u a l i t y o f the  f l a k e , which w i l l m a n i f e s t i t s e l f outwardly as a  roughened s u r f a c e c o n d i t i o n  (11).  E x t e n d e r s , which a r e u s u a l l y f l o u r s , a r e added t o the r e s i n mix t o reduce r e s i n c o s t s and t o a i d i n t h e ' h o l d i n g ' o f the adhesive t o t h e p a r t i c l e s u r f a c e . a l s o a i d i n the d i s t r i b u t i o n o f the r e s i n f i l m .  Extenders  Miller  (17)  found t h a t s t r e n g t h p r o p e r t i e s , w i t h t h e e x c e p t i o n o f hardness,  i n c r e a s e d w i t h i n c r e a s e d amounts o f e x t e n d e r s .  He found t h a t adding an extender such as wheat f l o u r t o the mix had the same e f f e c t as i n c r e a s i n g t h e r e s i n by the same amount.  The same r e s u l t might have been a c h i e v e d by  i n c r e a s i n g p a r t i c l e m o i s t u r e content o r i n c r e a s i n g  resin  viscosity. A d d i t i v e s , a l t h o u g h not p e r t i n e n t t o t h i s  study,  might be p e n t a c h l o r o p h e n o l f o r p r e s e r v a t i v e measures, and wax f o r water r e p e l l e n c y .  16 S t u d i e s on r e s i n c o n t e n t o f p a r t i c l e board showed t h a t as r e s i n c o n t e n t was  increased strength p r o p e r t i e s of  the hoards i n c r e a s e d ( 1 1 ) .  A l s o , as r e s i n c o n t e n t i n c r e a s e d  p e r c e n t water a b s o r p t i o n d e c r e a s e d and t h i c k n e s s s w e l l i n g decreased.  I n c r e a s e s i n r e s i n content t h e r e f o r e tended t o  s t r e n g t h e n the bond and reduce s w e l l i n g . out t h a t r e s i n amount was which i t was  Marian (15)  pointed  not as important as the manner by  distributed.  Curing conditions A f t e r the r e s i n i s added, the p a r t i c l e hoard i s p l a c e d under c o n d i t i o n s of heat and p r e s s u r e t o e f f e c t bonding i n t o the f i n i s h e d p r o d u c t .  Temperature,  the  pressure,  t i m e , and m o i s t u r e content are a l l r e l a t e d t o the p r o d u c t i o n of the f i n i s h e d  board.  A m o i s t u r e c o n t e n t between 10 and 14 p e r c e n t i s the normal requirement o f the pre-compressed pressing.  mat b e f o r e h o t -  Excessive moisture w i l l lead to ' b l i s t e r s '  i n the p a r t i c l e board d u r i n g p r e s s i n g .  Too  little  reduces the p l a s t i c i t y of the wood p a r t i c l e s .  forming  moisture  Excessive  m o i s t u r e a l s o tends to r a i s e the r e s i n c o n c e n t r a t i o n i n the c e n t e r o f the hoard and to lower i t n e a r the s u r f a c e s . i s due t o r e s i n and m o i s t u r e m i g r a t i o n because  This  of the  d i f f e r e n c e s i n vapour p r e s s u r e s w i t h i n the board d u r i n g hot pressing.  To reduce s w e l l i n g and s h r i n k i n g the  final  m o i s t u r e c o n t e n t o f the h o a r d s h o u l d he as c l o s e as i s  17 f e a s i b l e t o the e q u i l i b r i u m moisture content will  experience The  Gottstein  (7)  i n service.  pressure  hoard and h o l d s  exerted  on the p a r t i c l e mass forms the  the p a r t i c l e s i n place while  the h i n d e r  found t h a t i n c r e a s i n g the f o r m i n g  s i g n i f i c a n t l y increased specific gravity. pick-up,  t h a t the board  The denser boards a l s o r e s i s t e d m o i s t u r e  and d i m e n s i o n a l  the b i n d e r .  pressure  s t r e n g t h p r o p e r t i e s as w e l l as  change was r e d u c e d .  Heat i s n e c e s s a r y i n board p r o d u c t i o n set  t o cure o r  The c u r i n g time must he l o n g enough f o r a  complete b o n d i n g o f the r e s i n .  Excessive  temperatures may  produce premature d r y i n g o f the s u r f a c e s , e x c e s s i v e cure  hardens.  (resulting i n brittle  resin  and f l a k y r e s i n ) , and s c o r c h i n g  of the surfaces. Product p r o p e r t i e s F o r an u n d e r s t a n d i n g o f the fundamental p h y s i c a l and  mechanical p r o p e r t i e s i n v e s t i g a t e d i n t h i s t h e s i s i t i s  e s s e n t i a l t h a t some c o n d i t i o n s a f f e c t i n g these p r o p e r t i e s be  examined. Density.  Density,  or s p e c i f i c gravity, i s a  measure o f the compactness o f the i n d i v i d u a l p a r t i c l e s o r f l a k e s and t h e a d d i t i v e s w i t h i n the h o a r d .  Strength  p r o p e r t i e s i n c r e a s e w i t h an i n c r e a s e i n d e n s i t y .  One o f  the problems i n h o a r d manufacture i s t o o b t a i n a  uniform  18 d e n s i t y throughout  the hoard.  When t h e p a r t i c l e s a r e unevenly  d i s t r i b u t e d o v e r the c a u l p r i o r to hot p r e s s i n g , the f i n i s h e d boards w i l l have a r e a s o f unequal d e n s i t y .  Later, i f  m o i s t u r e c o n t e n t changes o c c u r , the d i f f e r e n t d e n s i t i e s  will  cause uneveness o f d i m e n s i o n a l change and warping may take place (11). Dimensional s t a b i l i t y .  Many p r e s e n t a p p l i c a t i o n s  of p a r t i c l e o r f l a k e board r e q u i r e r e a s o n a b l e c o n t r o l  over  d i m e n s i o n a l change, hence t h i s i s a c r i t i c a l a r e a o f study i n board p r o d u c t i o n . S i n c e t h e m a t e r i a l i n p a r t i c l e board i s a r r a n g e d homogeneously, d i m e n s i o n a l changes a r e more u n i f o r m when compared w i t h whole wood.  T u r n e r and Kern  (25) l i s t t h e  v a r i a b l e s a f f e c t i n g the m o i s t u r e a b s o r b i n g a b i l i t y o f particle 1. 2. 3. 4. 5. 6. 7. 8. 9.  board: The volume o f the v o i d s i n and between the p a r t i c l e s , c a p i l l a r y passages t o the v o i d s , surface area of the p a r t i c l e s , d e n s i f i c a t i o n o f each p a r t i c l e b y the bonding p r e s s u r e , the amount o f p a r t i c l e s u r f a c e a r e a not c o v e r e d with r e s i n , p e r m e a b i l i t y of the r e s i n binder, depth o f i m p r e g n a t i o n o f each wood p a r t i c l e by resin, the o r i g i n a l m o i s t u r e content o f the wood p a r t i c l e s , and the n a t u r e o f tfye m o i s t u r e ( v i s c o s i t y , s u r f a c e tension, etc.). Any p r o d u c t i o n v a r i a b l e t h a t a f f e c t s these  also a f f e c t s dimensional s t a b i l i t y .  factors  Increase of r e s i n ,  i n c r e a s e o f bonding p r e s s u r e , and a d d i t i o n o f a wax  sizing  19 all  reduce m o i s t u r e  absorption.  One method t o combat the i n s t a b i l i t y o f the hoard would he t o o v e r l a y i t w i t h veneer.  some m a t e r i a l , i n t h i s case wood  The wood veneer, h a v i n g  o f l e s s than 1 p e r c e n t  (or swelling) value forces causing  a longitudinal  dimensional  shrinkage  would r e s t r a i n the  change i n the l e n g t h o f t h e b o a r d ,  p r o v i d i n g the g r a i n of the wood was p a r a l l e l t o the l e n g t h of the hoard.  Presumably, an o v e r l a y m a t e r i a l would n o t  reduce d i m e n s i o n a l  change i n t h i c k n e s s .  F o r a short  duration  the wood o v e r l a y might r e t a r d t h e m o i s t u r e from e n t e r i n g the board.  Over a l o n g p e r i o d the hoard would expand t o i t s  normal t h i c k n e s s .  I t i s p o s s i b l e t h a t l a t e r a l f o r c e s would  d e v e l o p from t h e o v e r l a i d board b e i n g  restrained i n i t s  l o n g i t u d i n a l movement and these f o r c e s m a n i f e s t i n the thickness d i r e c t i o n .  themselves  I f t h i s were the case an o v e r l a y  m a t e r i a l might i n c r e a s e d i m e n s i o n a l  change i n t h i c k n e s s .  D i m e n s i o n a l change i n the p a r t i c l e b o a r d , being  besides  due t o the normal s w e l l i n g and s h r i n k i n g o f wood, i s  a l s o due t o 'springback'.  S p r i n g b a c k r e f e r s t o the r e l e a s e  o f the compressive f o r c e s i n c u r r e d i n the board manufacture.  during  Boards composed o f l i g h t e r woods have a  g r e a t e r tendency to s p r i n g b a c k . moisture content,  Following  an i n c r e a s e i n  hoards composed o f t h i n n e r f l a k e s w i l l  swell l e s s , probably  because such hoards do not r e q u i r e as  much c h i p d e f o r m a t i o n f o r a g i v e n d e n s i t y , and t h e r e  i s more  s u r f a c e a r e a f o r the r e s i n t o e f f e c t i v e l y c o v e r t h e m a t e r i a l ( 2 4 ) .  20 P a r t i c l e and  flake orientation.  In the f l a t - p r e s s e d  hoards the p a r t i c l e s are o r i e n t e d l o n g i t u d i n a l l y i n the same d i r e c t i o n as the g r a i n i n wood. dimensional  Accordingly,^ most o f  the  change i s i n the t h i c k n e s s d i r e c t i o n o f the  S i n c e the p a r t i c l e s w i l l not  board.  l i e w i t h the i n d i v i d u a l g r a i n i n  each p a r t i c l e p a r a l l e l to the l e n g t h o f the board, the p a r t i c l e s should  e x e r t a r e s t r a i n i n g a c t i o n on each o t h e r to  reduce d i m e n s i o n a l and A a l t o (20) and  change i n l e n g t h and w i d t h .  Rahtu, Holm,  found t h a t d i f f e r e n c e s between the  l o n g i t u d i n a l dimensional  d i f f e r e n c e s e x i s t i n g , i f any,  transverse  change were not s i g n i f i c a n t . between the t r a n s v e r s e  The  and  l o n g i t u d i n a l d i r e c t i o n o f the b o a r d a r e a g a i n i n v e s t i g a t e d in this  thesis. As p r e v i o u s l y mentioned, t e l e g r a p h i n g o r show-  t h r o u g h i s the e f f e c t o f the or f l a k e s appearing  impression  of i n d i v i d u a l  through the o v e r l a i d veneer.  This i s  caused by the s w e l l i n g o f some of the  surface f l a k e s ,  r e s u l t i n g i n a roughened appearance.  Denser boards  to  t e l e g r a p h more than l i g h t e r ones (17).  veneering,  the  and  f o r the v e n e e r to w h o l l y  form a good bond.  more d i f f i c u l t When v e n e e r i n g , i s not  tend  Por ease of  s u r f a c e o f the board must be without  and d e p r e s s i o n s ,  particles  ridges  c o n t a c t the  surface  H i g h d e n s i t y boards are s a i d to  t o veneer s i n c e they do not care must be  'give' o r  taken t h a t the v e n e e r i n g  g r e a t enough to c r u s h the board  (21).  be  flatten. pressure  21 Nail-holding a b i l i t y .  Studies  have been made on  the n a i l - h o l d i n g e f f e c t o f p a r t i c l e b o a r d s .  Some o f the  f a c t o r s l i s t e d hy Kennedy and N i l e s (12) which a f f e c t l a t e r a l n a i l resistance are: II  1. 2. 3. 4. 5v 6. 7. 8. 9.  S i z e and shape o f n a i l , c o m p o s i t i o n of m a t e r i a l , p r e s s u r e between c o n t a c t i n g s u r f a c e s o f wood, f i n i s h o f c o n t a c t i n g wood s u r f a c e s , depth o f p e n e t r a t i o n , d i r e c t i o n o f n a i l i n g , whether r a d i a l o r t a n g e n t i a l , duration of load, rate of loading, l e n g t h o f time between d r i v i n g and t e s t i n g . H  For n a i l - w i t h d r a w a l  r e s i s t a n c e , Mack (14) found t h a t  the method o f d r i v i n g the n a i l , r a t e o f l o a d i n g , and l e n g t h of time between d r i v i n g and t e s t i n g had n e g l i g i b l e e f f e c t on resistance. factor.  S p e c i f i c g r a v i t y appeared t o be the c o n t r o l l i n g  Mack s t a t e d t h a t p r e - d r i l l i n g n a i l h o l e s  r e s i s t a n c e by r e d u c i n g  the r u p t u r e  improved  o f the f i b r e s around the  nail. Boards have l e s s r e s i s t a n c e t o n a i l w i t h d r a w a l and l a t e r a l n a i l movement t h a n normal wood.  W a k e f i e l d (26) found  t h a t boards f a i l e d i n l a t e r a l n a i l movement because o f a t e a r i n g around t h e n a i l r e s u l t i n g from f o r c e s on the wood. The By  f a c e o f t h e hoard might he s t r e n g t h e n e d w i t h an o v e r l a y . a p p l y i n g v e n e e r , t h i s m a t e r i a l might absorb some o f the  f o r c e s and t h e n a i l would n o t break away.  The n a i l -  w i t h d r a w a l t e s t was undertaken t o f i n d what degree o f improvement, i f any, might be o b t a i n e d  from  overlaying.  22 Strength properties*  Values a v a i l a b l e  s t r e n g t h p r o p e r t i e s o f wood c o m p o s i t i o n hoard range.  I n " F i b r e b o a r d and P a r t i c l e board"  on t h e  cover a wide  (5) t h e v a l u e s f o r  modulus o f r u p t u r e range from 1500 t o 7000 p s i , f o r modulus o f e l a s t i c i t y 150,000 t o 700,000 p s i , and f o r t e n s i l e p a r a l l e l t o t h e s u r f a c e , from 700 t o 3500 p s i .  strength  These v a l u e s  i n c l u d e boards made from p a r t i c l e s , s l i v e r s , and f l a k e s . v a l u e a g i s t e d i n the Handbook (11) a r e s i m i l a r . have a h i g h e r modulus o f r u p t u r e  F l a k e boards  (2000 t o 6500 p s i ) than  boards made from s p l i n t e r s o r p l a n e r shavings psi).  The  (1500 t o 4000  F l a k e boards a l s o have a h i g h e r modulus o f e l a s t i c i t y  (300,000 t o 650,000 p s i ) t h a n these o t h e r boards (150,000 t o 4-50,000 p s i ) . As a l r e a d y mentioned, p a r t i c l e s i z e and shape has a g r e a t e f f e c t on s t r e n g t h p r o p e r t i e s .  P a r t i c l e and f l a k e  types, i n order of decreasing strength p r o p e r t i e s are: flakes,  h e l i c a l flakes,  strands, excelsior,  s h a v i n g s , and sawdust ( 2 4 ) . an i n c r e a s e i n ' r e s i n content The  flat  f i b r e s , planer  B e s i d e s p a r t i c l e s i z e and shape, i n c r e a s e s s t r e n g t h o f t h e board,  r e s i n b i n d e r p e n e t r a t e s i n t o the f i n e m i c e l l a r s t r u c t u r e  o f the wood and p r e v e n t s t h e a d s o r p t i o n o f moisture  by t h e  c e l l u l o s e w h i c h o r d i n a r i l y l e a d s t o the s w e l l i n g o f wood. S t r i c k l e r (22) s t a t e d t h a t a l t h o u g h s p e c i e s o f wood, type o f r e s i n a d h e s i v e , r e s i n q u a n t i t y and d i s t r i b u t i o n , wax c o n t e n t , i f any, and s i z e and o r i e n t a t i o n  of p a r t i c l e s a l l  23 a f f e c t strength properties, the one f a c t o r most d i r e c t l y r e l a t e d to strength was hoard density. In t e s t i n g urea- and phenolic-bonded hoards under long-term loading, Bryan (2) found that strength reduction was approximately the same as f o r whole wood. F u j i i (6) o v e r l a i d 1/8-inch Douglas f i r veneer on a 3/8-131011 board made from planer shavings and increased the s t i f f n e s s value from 277,000 p s i to 1,900,000 p s i .  The  modulus of rupture value was increased from 1910 p s i to 11,100 p s i .  On a 3/8-inch m u l t i - l a y e r hoard with a f l a k e  surface, the values were increased from 618,000 p s i to 2,120,000 p s i f o r s t i f f n e s s , and from 3,130 p s i to 13,500 p s i f o r modulus of rupture.  In a l l cases i n bending, the grain of  the veneer was p a r a l l e l to the span of the specimen.  Fujii  found that cross-banding d i d not contribute appreciably to f l e x u r a l strength and s t i f f n e s s of the panels. There was reason to believe that the s o - c a l l e d P h i l i p p i n e mahogany veneer overlay used i n t h i s study might g r e a t l y increase the strength properties of the board.  Furthermore, the overlay should decrease dimensional  change i n the hoard i n the manner already described.  24  PROCEDURE  Procurement  of material  P i v e commercial b o a r d s , a l l o f the m u l t i - p l a t e n f l a t - p r e s s e d t y p e , and a plywood p a n e l were p r o c u r e d from companies i n t h e U n i t e d S t a t e s and Canada. S i n c e two boards were o b t a i n e d from each company, i t was assumed by t h e w r i t e r t h a t t h e s e boards r e p r e s e n t e d the t o t a l p o p u l a t i o n o f each make o f b o a r d .  Selection of  o n l y two boards o f each type was based on t h e premise t h a t v a r i a t i o n between t h e t y p e s o f boards was g r e a t e r t h a n v a r i a t i o n between i n d i v i d u a l boards o f each t y p e .  Further-  more, the o b j e c t was a l s o t o determine t h e e f f e c t o f t h e o v e r l a y veneer on t h e boards i n g e n e r a l .  Procurement o f  a d d i t i o n a l samples o f each board was p r e c l u d e d by t h e a d d i t i o n a l amount o f l a b o u r and m a t e r i a l s  involved.  The boards were d e s i g n a t e d by l e t t e r s and w i l l be so r e f e r r e d t o throughout the t e x t o f t h i s t h e s i s .  The  c o m p o s i t i o n o f each type o f b o a r d and t h e l e t t e r s a s s i g n e d t o each a r e shown below.  A l l boards were 2 f e e t by 4 f e e t  i n dimension and 3/8-inch i n t h i c k n e s s .  >  25 Board D e s i g n a t i o n  Type  Composition  A  particle  e a s t e r n white p i n e (Pihus s t r o b u s L.)  B  particle  southern pine (genus P i n u s )  particle  Douglas f i r (Pseudotsuga m e n z i e s i i (Mirb.) Franco)  flake  Douglas f i r p l a n e r shavings and f l a k e s cut from veneer cores  E  multi-layer  s u r f a c e f l a k e s o f Douglas f i r , and c e n t e r p a r t i c l e s o f white f i r (genus A b i e s ) , sugar p i n e ( P i n u s l a m b e r t i a n a D o u g l . ) , and ponderosa p i n e (Pinus ponderosa Laws.)  P  plywood  3-ply, s o l i d two s i d e s , BB, Douglas f i r , bonded w i t h phenolic r e s i n  Of t h e two boards from each type t e s t e d , one u s e d f o r the o v e r l a y and one was 1  was  t e s t e d w i t h o u t an o v e r l a y .  E x t r a boards f u r n i s h e d by the companies a l l o w e d p r e l i m i n a r y t e s t i n g to be conducted t o determine c o r r e c t p r e s s c o n d i t i o n s . The o v e r l a y v e n e e r was Shorea).  1 / 2 0 - i n c h P h i l i p p i n e mahogany  The v e n e e r was  p a t t e r n was  (genus  r a d i a l - s l i c e d , ribbon grain.  Grain  c o n s i s t e n t throughout, a requirement n e c e s s a r y  f o r warping t e s t s .  F o r bonding the veneer t o the b o a r d , a  urea-formaldehyde h o t - o r c o l d - s e t t i n g a d h e s i v e was  used.  Upon a r r i v a l i n the l a b o r a t o r y , the hoards were unpacked and p l a c e d on s t i c k e r s i n a h u m i d i t y room where t h e y reached a m o i s t u r e c o n t e n t i n e q u i l i b r i u m w i t h the  s u r r o u n d i n g atmosphere. atmosphere.  The veneer was p l a c e d i n the same  The hoards remained t h e r e f o r two weeks b e f o r e  p r e l i m i n a r y t e s t i n g was done on them. c l o s e d an average  moisture  c o n t e n t o f 7«8 p e r c e n t f o r the  boards and 7»2 p e r c e n t f o r the veneer M o i s t u r e c o n t e n t was based to  oven-dry weight.  T e s t samples d i s -  after conditioning.  on amount o f moisture i n samples  I n d i v i d u a l v a l u e s a r e shown i n T a b l e I .  V a l u e s f o r s p e c i f i c g r a v i t y b e f o r e and a f t e r p r e s s i n g a r e a l s o shown i n T a b l e I . Preliminary overlaying A p r e l i m i n a r y study was made on s m a l l samples b e f o r e p r e s s i n g o f the b o a r d s t o determine of  the e f f e c t i v e n e s s  the a d h e s i v e , and t o a r r i v e a t s a t i s f a c t o r y p r e s s i n g  conditions.  Boards A and B were o v e r l a i d a t t h r e e  different  p r e s s c o n d i t i o n s and w i t h t h r e e d i f f e r e n t g l u e  spreads.  C u r i n g was done on a C a r v e r l a b o r a t o r y p r e s s .  This press  i s h y d r a u l i c a l l y o p e r a t e d , w i t h 6- by 6 - i n c h p l a t e n s , e l e c t r i c a l l y heated, w i t h temperature of  that desired.  c o n t r o l w i t h i n 2}&°P  The a d h e s i v e used was from the same b a t c h  as t h a t used i n the f i n a l l a y - u p o f t h e 2- by 4 - f o o t p a n e l s . The  d i f f e r e n t p r e s s c o n d i t i o n s were: 1.  110°P f o r 20 minutes a t 1 2 5 p s i ,  2.  160°P f o r 1 5 minutes a t 1 2 5 p s i , and  3.  245°F f o r 7 minutes a t 1 2 5 p s i .  Table I.  Type  M o i s t u r e Content and G r a v i t y o f Boards  Moisture Content Before Lay-up (%)  Specific Gravity* Before Lay-up  Specific  Specific Gravity After Pressing  A  7.4  0.63  0.67  B  7.6  0.71  0.66  C  8.5  0.69  0.68  D  7.7  0.65  0.69  E  7.9  0.64  0.61  P  7.6  0.50  0.50  Veneer  -*  7.2  S p e c i f i c g r a v i t y based on oven-dry weight and volume.  28 On both types of panels, glue spreads of 40 and 60 pounds per thousand  square feet single glue l i n e were used  under the f i r s t press conditions. Under the second press conditions board A had glue spreads of 40 and 60 pounds, while board B had glue spreads of 3 0 and 40 pounds.  With  the t h i r d set of press conditions glue spreads of 30 and 40 pounds were used on both panels. A f t e r lay-up and pressing, the o v e r l a i d samples were trimmed to 4- by 4-inches and subjected to 3 cycles of the cold-soak delamination t e s t .  One cycle of t h i s  t e s t consisted of soaking the samples f o r 4 hours at room temperature,  and drying f o r 20 hours at 95°*' ( 3 9 ) .  Results of t h i s t e s t are shown i n Table I I . Delamination occurred only on the samples pressed at for 20 minutes. factor.  110°P  Amount of glue spread was not a c r i t i c a l  Because of the f e a r of b l i s t e r s or 'blows' occurring  during the f i n a l pressing of the boards, the t h i r d set of press conditions was  eliminated.  Steam forming i n the board  might s e r i o u s l y a f f e c t the board-to-veneer  glue-bond.  Press  conditions of 160°P f o r 15 minutes at 125 p s i were decided upon f o r the f i n a l pressing of the boards.  Although a  15-minute cure was probably longer than necessary f o r t h i s temperature,  i t was maintained to insure complete cure.  Conversations with a u t h o r i t i e s of Monsanto Canada Limited confirmed t h i s .  29 Table I I . Amount of Delamination Occurring i n 4- By 4-inch Samples of Overlaid P a r t i c l e Board A f t e r 3 Cycles of a 4-Hour Soak and 20Hour Dry at 95°F  Type  A  B  Glue Spread ( l b . per M sq.ft. S.G.L.)  Press conditions (% delamination) 110°P f o r 160°P f o r 245°F f o r 20 min.at 15 min.at 7 min. at 125 p s i 125 p s i 125 p s i  50  -  0.0  0.0  40  2.2  0.0  0.0  60  3.8  30  -  40  9.6  0.0  60  8.7  0.0  0.0 0.0  Table I I I . Thicknesses of Boards and Veneer Before and A f t e r Pressing Type  Thickness Boards ( i n . )  Single Thickness Veneer ( i n . )  Combined B+2V ( i n . )  Thickness After Pressing(in.)  A  0.380  0.052  0.484  0.461  B  0.384  0.052  0.488  0.469  C  0.372  0.052  0.476  0.466  D  0.386  0.052  0.490  0.471  E  0.374  0.052  0.478  0.458  P  0.373  0.052  0.477  0.465  30 Final  lay-up As n o t e d above, i t was  c o n d i t i o n s of 160°F a t 125 pressing.  d e c i d e d to use  p s i f o r 15  Minimum assembly time was  assembly time was  minutes f o r the 3 minutes.  15 minutes, hut t h i s was  the time i n v o l v e d i n f e e d i n g the p r e s s was An  press final  Maximum  not c r i t i c a l s i n c e negligible.  Interwood g l u e - s p r e a d i n g machine was  employed  t o d i s t r i b u t e the adhesive on the boards ( F i g u r e 2 ) . machine was double  e l e c t r i c a l l y d r i v e n , and capable o f s p r e a d i n g a  glue l i n e .  The  r o l l e r s o f the machine were c h a i n -  d r i v e n , w i t h a c c u r a t e mechanism f o r r a i s i n g and them.  lowering  A c c u r a t e g l u e spread o f 4-0 pounds p e r thousand  f e e t s i n g l e g l u e l i n e was throughout  the l a y - u p .  a l s o o b t a i n a b l e , and was  Pre-weighed p a p e r was  t h i s paper was  a g a i n weighed t o determine  bottom r o l l e r s . p r e v e n t foaming.  New  adhesive was  The 24—  attached to spreader  spread on top  and  c o n t i n u a l l y added t o  by 4-8-inch boards were put  the r o l l e r s o f the glue s p r e a d e r . l o o s e s i d e toward the a d h e s i v e , was  Veneer, w i t h the p l a c e d under and  through apparent over  hoard. A B e r t h e l s e n h y d r a u l i c h o t - p l a t e p r e s s was  cure the adhesive  (Figure 3).  T h i s p r e s s was  54— hy 5 4 - i n c h p l a t e n s , c o n t i n u o u s l y heated hy oil.  square  controlled  e x t r a sheets o f hoard and a f t e r p a s s i n g through the  the  This  Temperature checks  used  equipped  to  with  circulating  on the upper and lower p l a t e n s b e f o r e  Figure 3 .  B e r t h e l s e n O i l - h e a t e d H o t - p r e s s f o r Bonding Veneer t o P a r t i c l e Boards  32 p r e s s i n g i n d i c a t e d no d e v i a t i o n from the d e s i r e d 160°F which was  s e t on the machine c o n t r o l s .  psi  was capable  or  A maximum p r e s s u r e o f 400  o f b e i n g e x e r t e d over the e n t i r e p l a t e n a r e a ,  a t o t a l maximum p r e s s u r e o f 1,666,400 pounds.  Press  p l a t e s were o f f a b r i c a t e d s t e e l w i t h p r e c i s i o n - g r o u n d working surfaces.  The p r e s s was f u l l y  p r e s s u r e was m a i n t a i n e d  automatic;  a pre-set  f o r each p r e s s l o a d .  constant  A f t e r the  r e q u i r e d 15-minute c y c l e t h e p r e s s a u t o m a t i c a l l y opened. B o t h an e x t r a board and a s e c t i o n o f plywood were o v e r l a i d b e f o r e the f i n a l  o p e r a t i o n was begun.  p a n e l s were dead-stacked flatness.  A f t e r p r e s s i n g , the  f o r 24 hours t o i n s u r e complete  33  TEST METHODS AND PROCEDURES  A t the completion  o f the d e a d - s t a c k i n g  period,  specimens were c u t from each o v e r l a i d and n o n - o v e r l a i d as shown i n F i g u r e 4-.  test  panel  T h i s c u t t i n g arrangement a l l o w e d the  maximum number o f t e s t s and the r e q u i r e d number o f specimens i n each t e s t .  T e s t i n g was d i v i d e d i n t o f o u r phases: g l u e -  l i n e shear t e s t s , o t h e r s t r e n g t h t e s t s , m o i s t u r e t e s t s , and accelerated aging.  The s i z e and number o f specimens f o r each  t e s t a r e shown below. Size of Specimen ( i n . )  Test Clue-line  shear dry wet  1 by 3#  Number o f Specimens  1 by  5 5  Tension p a r a l l e l to surface parallel^ , perpendicular''  j, 2 by 12_T 2 hy 12  3 3  S t a t i c bending parallel perpendicular  3 by 143 by 14-  3 3  Lateral n a i l resistance  2 by 10  3  Nail-withdrawal  3 by  3  6  D i m e n s i o n a l change p a r a l l e l to g r a i n d i r e c t i o n ( l e n g t h o f p a n e l ) 2 hy 12 perpendicular to grain d i r e c t i o n (width o f p a n e l ) 2 hy 12  1  0  resistance  1  p  Grain of veneer o v e r l a y p a r a l l e l to length of t e s t specimen. ^ Grain of veneer o v e r l a y p e r p e n d i c u l a r to length of t e s t specimen. k Necked down t o a 1 - i n c h w i d t h over c e n t r a l 4- i n c h e s .  34 Size of Number o f Specimen ( i n . ) Specimens  Test  12 by  Warping Accelerated  12  2  by  6  3  2 by  2  3  3  aging  M o i s t u r e c o n t e n t and specific gravity  G l u e - l i n e shear G l u e - l i n e shear specimens were c u t a c c o r d i n g t o s p e c i f i c a t i o n s f o r p r e p a r i n g plywood g l u e - l i n e shear samples ( 3 ) .  Specimens were p r e p a r e d so t h a t shear was  a p p l i e d over a one-inch-square area.  T e s t i n g was done on a  plywood g l u e - l i n e t e s t i n g machine owned by Monsanto Limited.  Canada  Rate o f l o a d i n g was 600 t o 1000 pounds p e r minute.  Specimens were t e s t e d i n the d r y and wet  conditions.  P r e p a r a t i o n o f the wet specimens c o n s i s t e d o f a 48-hour soak i n water a t room temperature, an 8-hour d r y a t 145°P, f o l l o w e d by 2 c y c l e s o f a 16-hour soak and 8-hour d r y , t h e n a n o t h e r 16-hour soak. to  failure  Specimens were t e s t e d when wet.  Load  and percentage o f g l u e - l i n e , b o a r d , o r v e n e e r  f a i l u r e were r e c o r d e d . M e c h a n i c a l t e s t s o t h e r t h a n g l u e - l i n e shear These t e s t s i n c l u d e d s t a t i c b e n d i n g , t e n s i l e strength p a r a l l e l  t o the s u r f a c e , l a t e r a l n a i l  and n a i l - w i t h d r a w a l r e s i s t a n c e .  resistance,  F o r ease o f a p p l i c a t i o n  and f o r comparison of v a l u e s , the t e s t i n g methods, w i t h the  e x c e p t i o n of the l a t e r a l n a i l r e s i s t a n c e t e s t ,  followed  35 Legend.: 1.  glue-line  shear  samples 2.  static  bending  3.  tension  4.  lateral nail resistance  5.  nail  withdrawal  6.  dimensional change i n l e n g t h and thickness  7.  warping'  8.  moisture content and specific gravity  9.  accelerated aging  g  *  o  o  OJ  F i g u r e 4. G u t t i n g Plan of ¥'eneer-overlaid B o a r d s and  2- b y 4 - f o o t Plywood  parallel  Non-overlaid  and  36 those  suggested  by t h e Wood P a r t i c l e Board Committee  (28).  D e t a i l e d i n f o r m a t i o n o f specimen s i z e and t e s t i n g procedure are g i v e n i n ASTM s p e c i f i c a t i o n 1037 D ( 1 ) . content Moisture  Average  moisture  o f a l l specimens a t time o f t e s t i n g was 8.0 p e r c e n t . content was determined by t h e oven-dry method;  t h r e e 2 - hy 2 - i n c h samples were randomly s e l e c t e d from each hoard.  These samples were a l s o used t o determine  specific  gravity. T e n s i l e s t r e n g t h t e s t s were made on a Baldwin Southwark 6 0 , 0 0 0 pound, h y d r a u l i c a l l y - o p e r a t e d , u n i v e r s a l t e s t i n g machine.  S i x specimens were c u t from each type o f  o v e r l a i d and n o n - o v e r l a i d b o a r d . i n c h e s p e r minute.  Rate o f l o a d i n g was 0.04  In order t o evaluate  directional  p r o p e r t i e s w i t h i n b o t h t h e n o n - o v e r l a i d board and t h e o v e r l a i d b o a r d , t h r e e specimens were c u t w i t h t h e i r  length  5 p a r a l l e l t o t h e l e n g t h ^ o f t h e board, and t h r e e specimens w i t h t h e i r l o n g dimension p e r p e n d i c u l a r t o the l e n g t h o f the board.  R e s u l t s a r e r e p o r t e d i n Appendix A, and a  s t a t i s t i c a l a n a l y s i s of the data i s presented  i n Appendix B.  F l e x u r a l s t r e n g t h t e s t s were made on a T i n i u s O l s e n 2 0 , 0 0 0 pound u n i v e r s a l t e s t i n g machine ( F i g u r e 5 ) .  ^ F o r t h e n o n - o v e r l a i d hoards the l e n g t h o r l o n g e s t d i r e c t i o n o f a 4- hy 8 - f o o t board r e f e r s t o t h e 'machine d i r e c t i o n * . F o r the o v e r l a i d hoards, l e n g t h r e f e r s t o t h e l o n g i t u d i n a l d i r e c t i o n o f the g r a i n o f t h e veneer. I n t h i s study, g r a i n o f the veneer was p a r a l l e l t o machine d i r e c t i o n o f t h e h o a r d s .  38 Specimens were cut according 24 to 1 (28).  to a span-to-depth r a t i o of  Each specimen was  3 inches i n width, with a  span of 12 inches and a length of 14 inches. centre-loaded  at the rate of 0.24  Specimens were  inches per minute.  speed depended on unit rate of f i b r e s t r a i n and  This  was  c a l c u l a t e d from the following formula (28): ZL  2  N  =  ~  ,  where  N  =  rate of moving head, i n inches per minute,  Z  =  unit rate of f i b r e s t r a i n , i n inches per inch of outer f i b r e length per minute (0.005),  L  =  span, i n inches,  and  d  =  thickness of specimen i n inches.  The rounded portion of the loading block of the machine had a diameter equal to Vfi times that of the thickness of the specimen, or 3/4  inch.  were taken every 50 pounds of load on the  Deflection  readings  high-strength  specimens and every 20 pounds on the low-strength specimens. Maximum load was  recorded.  Load and d e f l e c t i o n at proportional  l i m i t s were v i s u a l l y i n t e r p o l a t e d from l o a d - d e f l e c t i o n curves drawn f o r each sample. machine head.  Deflections were read from the  39 Modulus of r u p t u r e and modulus o f e l a s t i c i t y were c a l c u l a t e d f o r each specimen from the f o l l o w i n g formulae (28):  R = 223E«  and  2bd^  p 3 L  E =  1  ,  where  4hd Y 3  R = modulus of r u p t u r e , i n p s i , E = modulus o f e l a s t i c i t y ,  in psi,  P - maximum l o a d , i n pounds, L = l e n g t h of span, i n i n c h e s , h = w i d t h o f specimen, i n i n c h e s , d = t h i c k n e s s of specimen, i n i n c h e s , P^  = l o a d a t p r o p o r t i o n a l l i m i t , i n pounds,  and  Y = c e n t e r d e f l e c t i o n at p r o p o r t i o n a l l i m i t , in inches. L o a d - d e f l e c t i o n c u r v e s were c o n s t r u c t e d and s t r e n g t h (modulus of r u p t u r e ) and elasticity) calculated.  stiffness  Por the m u l t i - l a y e r h o a r d  and  s t i f f n e s s terms should he c a l l e d the r u p t u r e and  elasticity'  and the plywood, the s t r e n g t h  convenient  for  a l l specimens.  'apparent  s i n c e the f o r e g o i n g  a p p l y to homogeneous m a t e r i a l s . was  (modulus o f  T y p i c a l c u r v e s are shown i n P i g u r e  6.  of  the  Por comparative  moduli  equations purposes i t  t o use these e q u a t i o n s when c a l c u l a t i n g Values  and  s t a t i s t i c a l analyses  p r e s e n t e d i n Appendices C through  P.  are  values  40  40Q  Figure 6. Typical Load-deflection Curves. Curve Number 1 represents p a r t i c l e board ('C^ with grain d i r e c t i o n of veneer overlay p a r a l l e l to span d i r e c t i o n . Curve Number 2 Is same non-overlaid board with long d i r e c t i o n of board p a r a l l e l to'span d i r e c t i o n .  41 F o r l a t e r a l n a i l r e s i s t a n c e , a t e s t was  devised  which s i m u l a t e d a c t u a l l o a d i n g c o n d i t i o n s f o r n a i l movement when i n s e r v i c e , f o r example, i n w a l l p a n e l i n g . the end of a 2 -  hy 1 0 - i n c h specimen was  In t h i s  n a i l e d to a 2-  4 - i n c h s t u d clamped on the base of the T i n i u s O l s e n machine.  N a t i o n a l B u i l d i n g Code (19) type  hy  testing  2 # - i n c h common, as p r e s c r i b e d by  N a i l type was  f o r w a l l sheathing.  test  the  F o r the same (10)  o f n a i l i n g the Housing and Home F i n a n c e Agency  recommend a 2 - i n c h n a i l . The  n a i l was  d r i v e n i n so t h a t i t s head was  w i t h the s u r f a c e o f the specimen. r i g h t angles  to the d i r e c t i o n of the n a i l .  shown i n F i g u r e 7«  Load was  i n c h e s per minute ( 2 8 ) . and  T e n s i o n was  a p p l i e d at  T h i s apparatus i s  a p p l i e d at the r a t e of  0.25  R e s u l t s are r e p o r t e d i n Appendix G  a s t a t i s t i c a l a n a l y s i s o f the d a t a i s p r e s e n t e d  Appendix  flush  in  H. The  n a i l - w i t h d r a w a l t e s t was  a l s o made on  T i n i u s O l s e n u n i v e r s a l t e s t i n g machine.  A 2-inch n a i l  d r i v e n p e r p e n d i c u l a r t o the s u r f a c e of the 3 - by sample, and  1/2  the h o a r d .  Specimens were adequately  i n c h of the n a i l was  A s t o p - d e v i c e was  the was  3-inch  l e f t p r o t r u d i n g from supported  c o n s t r u c t e d around the support  during n a i l i n g . to  prevent  the n a i l from b e i n g d r i v e n i n p a s t the 1 / 2 - i n c h mark. T e s t i n g was 72  hours.  made a f t e r n a i l s had remained i n samples f o r  F i g u r e 8.  Nail-withdrawal  T e s t Assembly  43 The was  t e s t i n g apparatus i s shown i n F i g u r e . 8.  a p p l i e d at the  values  and  r a t e of 0.06  range of v a l u e s  Load  i n c h per minute ( 2 8 ) . a  statistical  Specimens used to measure warping and  dimensional  a n a l y s i s are  f o r each hoard and  Average  shown i n Appendices I and  J.  Physical tests  change were f i r s t h u m i d i t y o f 75  conditioned  p e r c e n t and  i n i t i a l c o n d i t i o n i n g the reconditioned 25 p e r c e n t and was  f o r two  f o r two  temperature o f 68°F.  After  this  specimens were measured t h e n  more weeks at a r e l a t i v e h u m i d i t y o f  temperature o f 65°F-  done to induce warping and  panels.  weeks at a r e l a t i v e  T h i s second c o n d i t i o n i n g  d i m e n s i o n a l change i n the  L i n e a r measurements were taken on the l a s t  days o f each c o n d i t i o n i n g p e r i o d .  three  Specimens were wrapped i n  p l a s t i c bags when b e i n g t r a n s f e r r e d from the h u m i d i t y  cabinet  f o r measurements t o i n s u r e no moisture l o s s o r p i c k - u p . T e s t i n g was of warping and  d i v i d e d i n t o two  d e v i a t i o n of the  and bow.  f o u r t h corner  held f l a t .  Cup  was  Twist was  the m a c h i n e - d i r e c t i o n  Warp  was  the maximum  of the p a n e l w i t h the  other  measured as the maximum d e v i a t i o n  from the p l a n e s u r f a c e p e r p e n d i c u l a r  t o the f a c e g r a i n  on the n o n - o v e r l a i d  boards),  as the maximum d e v i a t i o n p a r a l l e l t o the f a c e ( p a r a l l e l to the machine d i r e c t i o n of the boards).  measurement  measurement o f d i m e n s i o n a l change.  measured as t w i s t , cup,  corners  phases:  and  grain  non-overlaid  (across bow  44 The  micro-ground  bottom p l a t e n o f t h e B e r t h e l s e n  h o t - p r e s s was used f o r measuring warp.  Four marks were made  on the p l a t e n f o r the f o u r c o r n e r s o f the p a n e l s .  T w i s t was  measured by p l a c i n g a stand-mounted d i a l micrometer on one of t h e c o r n e r s h e l d f l a t  a g a i n s t t h e p l a t e n , then moving t h e  micrometer up t h e p a n e l t o the f o u r t h c o r n e r n o t l y i n g i n the p l a n e .  The d i f f e r e n c e between t h e f i r s t and second  r e a d i n g s was t w i s t .  Care was taken t o i n s u r e t h a t t h e o t h e r  t h r e e c o r n e r s were h e l d f l a t  t o the p l a t e n s u r f a c e .  method i s i l l u s t r a t e d i n F i g u r e 9» i n t h e same way.  Cup and bow were measured  F o r t h e s e l a t t e r measurements t h e micrometer  would be moved from a c o r n e r h e l d f l a t h i g h e s t p o i n t o f cupping  o r bowing.  a c c u r a t e than u s i n g f e e l e r Dimensional  on t h e p l a t e n t o the  T h i s method was more  gauges o r a v e r n i e r c a l i p e r .  change was measured p a r a l l e l  l e n g t h and w i d t h o f each b o a r d . cut  This  Thus, two specimens were  from each b o a r d — o n e widthwise  each o f two p o i n t s a p p r o x i m a t e l y  to the  and one l e n g t h w i s e .  At  10 i n c h e s a p a r t on t h e  c e n t r e l i n e o f each specimen a s m a l l a r e a was rubbed w i t h a grease p e n c i l .  A fine  c r o s s was marked on t h e c e n t r e  line  w i t h a r a z o r b l a d e a t these two p o i n t s which were l a t e r as r e f e r e n c e p o i n t s f o r l e n g t h measurements. numbered A and B. two  The p o i n t s were  T h i c k n e s s measurements were made a t these  p o i n t s w i t h a p r e - z e r o e d Ames d i a l micrometer.  measuring apparatus  used  i s shown i n F i g u r e 10.  were made w i t h a metal r u l e r  Thickness  Length measurements  capable o f b e i n g r e a d t o 0.01 i n c h .  Readings were t a k e n w i t h a m a g n i f y i n g  lens (28).  Figure 9 « Method Used f o r Measuring Twist i n Panels. The zeroed d i a l micrometer was placed on one of three corners held f l a t on surface of p l a t e n (top photo), then moved to the corner out of plane of the surface (bottom photo).  ;ure 10.  Thickness Measuring Micrometer D i a l  Figure 11. Types of F a i l u r e Occurring i n Tension P a r a l l Samples A, B, and C are p a r t i c l e boards having brash-typ f a i l u r e s : D and E are f l a k e boards having s p l i n t e r i n g failures. Sample A, i s o v e r l a i d p a r t i c l e board with high-tensile strength p a r a l l e l to grain d i r e c t i o n of overlay, i n contrast to low t e n s i l e strength across grain, as i n sample D^. Sample F, represents high t e n s i l e strength, f a i l u r e of o v e r l a i d plywood.  splintering  47 A c c e l e r a t e d aging T h i s t e s t was  i n c o r p o r a t e d t o determine the amount  o f veneer d e l a m i n a t i o n , c h e c k i n g , and roughening, and t o note e f f e c t o f h o a r d d i s i n t e g r a t i o n .  The t e s t was m o d i f i e d  somewhat from t h a t suggested hy the Wood P a r t i c l e Committee ( 2 8 ) . formaldehyde c y c l e was  Board  Because o f i t s s e v e r i t y on the u r e a -  bonded hoards, the steaming phase o f the a g i n g  omitted.  As w i l l he f u r t h e r e x p l a i n e d , even  m o d i f i e d c y c l i n g t e s t was  too s e v e r e .  this  Specimens were  s u b j e c t e d to s i x c y c l e s o f a c c e l e r a t e d a g i n g , one c y c l e o f which c o n s i s t e d o f the f o l l o w i n g : 1.  Immersion i n water a t room temperature  f o r 4 hours.  2.  Storage i n r e f r i g e r a t o r a t 30°F f o r 20 h o u r s .  3.  H e a t i n g i n d r y a i r a t 145°P f o r 4 hours.  4.  Immersion i n water a t room temperature  5.  H e a t i n g i n d r y a i r a t 145°F f o r 16 h o u r s .  f o r 4 hours.  4-8  DISCUSSION OF RESULTS  Thicknesses of the hoards before and a f t e r pressing are shown i n Table I I I .  Thicknesses f o r the 3/8-inch hoards  ranged from 0.374- to 0.386 inches; plywood thickness was 0.373*  Boards A, B, and E had large v a r i a t i o n s i n thickness,  deviating as much as 0.018, 0 . 0 1 3 , and 0.022 inches, respectively.  A l l other hoards had tolerances w i t h i n 0.003  inch. Thickness of panels a f t e r pressing was smaller than the combined thicknesses of boards and veneer before lay-up. This decrease i n thickness a f t e r pressing was p o s s i b l y caused hy a small amount of compression  i n the boards and veneer  during pressing. Glue-line shear Results of t h i s shear t e s t are shown i n Table IV. Glue-line f a i l u r e i n both dry and wet t e s t s was l i m i t e d to boards B and C.  Board B had 50 percent g l u e - l i n e f a i l u r e  when tested dry and 10 percent when tested wet.  Board C  had 10 percent g l u e - l i n e f a i l u r e when tested both wet and dry. Glue-line f a i l u r e , where i t d i d occur, was on hoards having the highest s p e c i f i c gravity, namely hoards B and C. It i s p o s s i b l e that because of the denser surfaces of these  49 Table IV.  Glue-line Sheat Test Tested Wet  Tested Dry Load (lb)  Glue  70  46  0  0  100  20  30  76  10  20  70  10  30  60  71  10  20  70  81  0  10  90  53  0  0  100  E  82  0  15  85  68  0  0  100  F  75  0  40  60  91  0  5  95  Type  % Failure Veneer Core  Load (lb)  Glue  A  67  0  30  B  93  50  C  91  D  % Failure Veneer Core  Each value average of 5 specimens.  Table V.  Source of Variance  A n a l y s i s of Variance f o r G l u e - l i n e Shear Test  Degrees of Freedom  Boards (B) Treatment (T) Error Total Correction N.S.  5 1 5 11 1  Sum of Squares 1,190 588 595 2,373 66,603  Not s i g n i f i c a n t at the 5% l e v e l .  Mean Squares 238 588 119  F 2 . 0 0 0 N.S 4.941 N.S  50 two boards a poor glue bond may have r e s u l t e d d u r i n g p r e s s i n g . S u r f a c e hardness  t h e r e f o r e appeared t o i n f l u e n c e g l u e bond.  Board A, composed o f e a s t e r n white p i n e p a r t i c l e s w i t h a s m a l l percentage  o f h a r k , had t h e lowest shear v a l u e s .  Boards D and E were midway i n s t r e n g t h v a l u e .  When t e s t e d  d r y , some o f the f a i l u r e o c c u r r e d i n t h e veneer. wet,  When t e s t e d  the p a r t i c l e - t o - p a r t i c l e bonds were weakened and most  of the f a i l u r e  o c c u r r e d i n the board c o r e .  A l l shear v a l u e s  o f t h e boards d e c r e a s e d when t e s t e d wet except those o f t h e plywood.  The b r e a k i n g s t r e n g t h o f t h e o v e r l a i d plywood  i n c r e a s e d from 75 t o 91 p s i f o l l o w i n g t h e c o l d - w a t e r Because o f t h e g r e a t e r t e n s i l e  soak.  s t r e n g t h o f the Douglas f i r  p l i e s i n the plywood, much o f t h e wood f a i l u r e i n d r y shear was i n the o v e r l a y veneer.  The g r a i n o f t h e veneer o v e r l a y  was p a r a l l e l t o t h e g r a i n of the f a c e p l i e s o f the plywood. In g e n e r a l , t h e urea-formaldehyde  adhesive used t o  bond the veneer t o the hoards was s a t i s f a c t o r y when t h e boards were l a i d up a c c o r d i n g t o the p r e s s c o n d i t i o n s employed h e r e .  A l t h o u g h an a n a l y s i s o f v a r i a n c e ( T a b l e V)  i n d i c a t e d no s i g n i f i c a n t d i f f e r e n c e s between boards, o r between d r y and wet shear v a l u e s , t h e r e was a d e f i n i t e d e c r e a s e i n v a l u e s from the d r y t o the wet c o n d i t i o n w i t h the e x c e p t i o n n o t e d above o f t h e plywood.  Both shear v a l u e s  and wood f a i l u r e i n the veneer d e c r e a s e d when t h e samples were t e s t e d wet because  o f t h e weaker b o a r d c o r e .  tended t o e f f e c t a d e t e r i o r a t i o n o f t h e board c o r e .  Soaking  .51 Tension  p a r a l l e l to l e n g t h and w i d t h o f  surface  V a l u e s f o r t e n s i o n p a r a l l e l t o the s u r f a c e shown i n Table V I .  The  range of v a l u e s and  v a r i a n c e o f the main e f f e c t s and Appendices A and  B.  tensile  strength.  a n a l y s i s of  i n t e r a c t i o n s are g i v e n i n  O v e r l a i d boards had  v a l u e s than n o n - o v e r l a i d h o a r d s . g r a i n d i r e c t i o n was  are  significantly  higher  Of the o v e r l a i d hoards,  the most s i g n i f i c a n t f a c t o r a f f e c t i n g The  wood veneer, b e i n g v e r y h i g h i n t e n s i l e  s t r e n g t h p a r a l l e l to the g r a i n , had t e n s i l e s t r e n g t h of the p a n e l s .  the e f f e c t o f i n c r e a s i n g  Wood (veneer) has  a  low  t e n s i l e s t r e n g t h p e r p e n d i c u l a r t o the g r a i n d i r e c t i o n , i n g e n e r a l the o v e r l a i d boards had  lower t e n s i l e  and  strengths  t h a n n o n - o v e r l a i d boards when t e s t e d i n t h i s d i r e c t i o n . t h i s b a s i s i t appears t h a t p a r t i c l e and  On  f l a k e boards have  h i g h e r t e n s i l e s t r e n g t h t h a n wood a c r o s s the g r a i n . The  v e n e e r o v e r l a y tended t o minimize d i f f e r e n c e s  between b o a r d s .  D i f f e r e n c e s between b o a r d s , o v e r l a i d and  n o n - o v e r l a i d , were s i g n i f i c a n t a t the 5 p e r c e n t level.  A  ' s t u d e n t i z e d T' t e s t was  i n d i c a t e d t h a t the plywood p a n e l s tensile  performed and had  of the p a r t i c l e type, were  lower t h a n a l l o t h e r hoards, and board D, had  the h i g h e s t t e n s i l e  strength.  s t r e n g t h v a l u e s midway between the  the  significantly  s t r e n g t h v a l u e s t h a n a l l o t h e r boards.  boards A and B,  confidence results higher  Non-overlaid  significantly composed o f f l a k e s ,  Boards C and E had others.  tensile  .52 T a b l e V I . A. Type  Summary o f M e c h a n i c a l P r o p e r t i e s o f N o n - o v e r l a i d Board  T e n s i o n Modulus Modulus • Lateral NailParallel of' of Nail * Withdrawal (psi) Rupture E l a s t i c i t y R e s i s t a n c e Resistance (psi) (M p s i ) (lb) (lb)  A parallel perpend.  670 640  1,030 1,010  193 193  120  B parallel perpend.  960 860  1,970 1,510  356 280  160  C p a r a l l e l 1,440 perpend. 1 , 2 7 0  2,320 2,070  368 367  190  D p a r a l l e l 2,600 perpend. 2 , 5 9 0  3,920 3,770  548 548  210  E p a r a l l e l 1,190 perpend. 1,190  3,430 2,520  690 544  180  14,190 2,700  1,635 226  230  P p a r a l l e l 5,570 perpend. 570  B. Type  25 32 30 46 30 31  Summary o f M e c h a n i c a l P r o p e r t i e s o f O v e r l a i d Board T e n s i o n Modulus Modulus Parallel of of (psi) Rupture E l a s t i c i t y (psi) (M p s i )  Lateral NailNail * Withdrawal Resistance Resistance (lb) (lb)  A p a r a l l e l 3,680 perpend. 590  8,120 1,100  1,166 261  205  B p a r a l l e l 4,130 perpend. 1,010  8,940 1,610  1,045 188  220  C p a r a l l e l 4,390 perpend. 1 , 3 0 0  8,850 1,810  1,137 322  190  D p a r a l l e l 5,140 perpend. 2 , 2 7 0  9,400 3,230  977 396  200  E p a r a l l e l 4,020 perpend. 1,060  8,240 1,680  F p a r a l l e l 7,490 perpend. 3,060  10,830 2,490  1,062 275 1,384 119  195 210  40 59 46 54 33 30  * Specimens were p u l l e d so t h a t shear was a t r i g h t a n g l e s to d i r e c t i o n o f f a c e veneer.  53 A l t h o u g h d i f f e r e n c e s were not s i g n i f i c a n t , hoards A, B, and C had h i g h e r t e n s i l e  strength values p a r a l l e l to  the l o n g d i r e c t i o n o f the hoard than p e r p e n d i c u l a r t o i t . T e n s i l e s t r e n g t h v a l u e s f o r hoards D and E i n b o t h were  directions  similar. Boards composed o f f l a k e s had h i g h e r t e n s i l e  s t r e n g t h v a l u e s than those composed o f p a r t i c l e s . f i n d i n g s a r e i n agreement w i t h those o f T u r n e r Klauditz, particle  who size.  per unit area.  found t h a t bonding  These  (24) and  strength increased with  S m a l l p a r t i c l e s r e q u i r e more adhesive Furthermore,  hinder  l a r g e , t h i n f l a k e s a r e more  compressible, i n s u r i n g a b e t t e r surface-to-surface contact during  bonding. Plywood had the h i g h e s t t e n s i l e  s t r e n g t h w i t h two  p l i e s p a r a l l e l t o the d i r e c t i o n o f t e s t i n g ; these v a l u e s were much lower when one p l y was p a r a l l e l t o the d i r e c t i o n of t e s t .  O v e r l a y i n g w i t h veneer i n c r e a s e d t e n s i l e s t r e n g t h  i n b o t h d i r e c t i o n s , hut because of the normal arrangement o f the p l i e s the d i f f e r e n c e s were not minimized the boards. accounted  as t h e y were w i t h  C r o s s g r a i n i n the core p l y o f the plywood  f o r the low v a l u e i n t e n s i o n p e r p e n d i c u l a r t o the  l e n g t h of t h e g r a i n of the f a c e p l y .  Types of f a i l u r e s are  i l l u s t r a t e d i n F i g u r e 11.  Wood P a r t i c l e Board Handbook, p. 182.  54 S t a t i c bending Modulus of rupture.  Values f o r moduli of rupture  are shown i n Table VI, and the range of values and analysis of variance i n Appendices C and D. strength, g r a i n d i r e c t i o n of the veneer was factor.  the  Like t e n s i l e the most s i g n i f i c a n t  Differences between hoards were not s i g n i f i c a n t , hut  based on a wider i n t e r p r e t a t i o n of data, some conclusions could he drawn. The veneer overlay increased strength values of the hoards from 140 to 690 percent when tested p a r a l l e l to the grain.  Veneer overlaying also minimized the d i f f e r e n c e s  between boards.  Moduli of rupture values f o r o v e r l a i d board  with d i r e c t i o n of grain perpendicular to the span, with the exception of boards A and B, were lower than the values f o r the non-overlaid board.  Wood veneer with the grain at r i g h t  angles to the span contributed no strength to the board because of the lower f i b r e s t r e s s i n tension across the grain on the bottom, on convex surface, of the specimen under t e s t .  Because of the increased moment of i n e r t i a  without a corresponding  increase i n strength, c a l c u l a t e d  values f o r the o v e r l a i d board were lower than those of the non-overlaid hoard. to the g r a i n was  Strength of the veneer perpendicular  l e s s than the strength of the boards.  Again, strength of the hoards increased with p a r t i c l e s i z e ; non-overlaid boards D and E had the highest  55 s t r e n g t h v a l u e s i n bending. A had  the lowest  Non-overlaid had  Board D was  the h i g h e s t .  values f o r u l t i m a t e s t r e n g t h i n bending.  plywood w i t h the f a c e g r a i n p a r a l l e l to the  the h i g h e s t  s t r e n g t h i n bending.  W i t h the f a c e  b o a r d D.  non-  o v e r l a i d plywood were h i g h e r than those  the n o n - o v e r l a i d  and  of both  o v e r l a i d boards, w i t h the e x c e p t i o n  Modulus of r u p t u r e decreased  of  f o r the o v e r l a i d  plywood, presumably because of the l o w e r bending o f the o v e r l a y v e n e e r and  span  plies  p e r p e n d i c u l a r t o the span, s t r e n g t h v a l u e s f o r the o v e r l a i d and  Board  strength  the l a r g e r c r o s s - s e c t i o n a l a r e a  involved. A l t h o u g h not  s i g n i f i c a n t i n the  t e s t , a l l b o a r d s had h i g h e r d i r e c t i o n o f the  'studentized  s t r e n g t h v a l u e s i n the  long  board.  Modulus o f e l a s t i c i t y .  V a l u e s f o r moduli of  e l a s t i c i t y , o r s t i f f n e s s , are shown i n T a b l e V I , and range of v a l u e s  T'  and  a n a l y s i s of v a r i a n c e  and E, r e s p e c t i v e l y .  G r a i n d i r e c t i o n was  the  i n Appendices E the most  f a c t o r a f f e c t i n g s t i f f n e s s o f the o v e r l a i d boards. t e s t e d p a r a l l e l to the g r a i n of the veneer,  significant When  stiffness  v a l u e s , w i t h the e x c e p t i o n  of plywood, were i n c r e a s e d from  54  the veneer tended to e q u a l i z e  t o 500 p e r c e n t .  Again,  d i f f e r e n c e s between b o a r d s . v a l u e , had boards.  a higher value  Board A,  having  a low  stiffness  a f t e r o v e r l a y i n g than a l l other  56 S t i f f n e s s v a l u e s o f o v e r l a i d board d e c r e a s e d over those o f n o n - o v e r l a i d hoard when t e s t e d p e r p e n d i c u l a r t o the g r a i n of the veneer.  Board A was an e x c e p t i o n i n t h i s case.  The r e a s o n f o r the lower v a l u e s was t h a t the c r o s s - s e c t i o n a l areas i n c r e a s e d without a corresponding increase i n strength p r o p e r t i e s o f the veneer.  Fujii  (6) found the same r e s u l t s  when t e s t i n g the a f f e c t o f d i f f e r e n t o v e r l a y s on p a r t i c l e boards. The f o r m u l a used i n c a l c u l a t i n g modulus o f e l a s t i c i t y i s based on an i s o t r o p i c m a t e r i a l o f r e c t a n g u l a r cross-section.  As d i s c u s s e d , f o r t h e plywood and t h e m u l t i -  l a y e r h o a r d s , t h e s t i f f n e s s v a l u e s s h o u l d be c o n s i d e r e d as the  'apparent moduli o f e l a s t i c i t y , 1  s i n c e f o r comparative  purposes the c a l c u l a t i o n s were based on the r e c t a n g u l a r c r o s s - s e c t i o n a l areas o f the m a t e r i a l . N o n - o v e r l a i d boards A, B, and C were lower i n s t i f f n e s s than boards D, E, and F. h i g h e r v a l u e s t h a n the p a r t i c l e b o a r d s .  significantly  F l a k e b o a r d s had  This increase i n  s t r e n g t h f o r the f l a k e boards i s d i s c u s s e d i n the s e c t i o n under t e n s i l e  strength.  plywood because  S t i f f n e s s d e c r e a s e d i n the o v e r l a i d '  o f the lower bending s t r e n g t h , o r f i b r e  o f the P h i l i p p i n e mahogany veneer.  stress,  As i n bending, the  d i f f e r e n c e s i n s t r e n g t h v a l u e s between p a r a l l e l and p e r p e n d i c u l a r d i r e c t i o n s o f t h e plywood were l a r g e of the o r i e n t a t i o n o f the p l i e s .  because  57 V a l u e s were h i g h e r i n the l o n g i t u d i n a l of  the hoard.  direction  Prom a r e v i e w o f the t e n s i l e s t r e n g t h , u l t i m a t e  s t r e n g t h i n bending, and s t i f f n e s s p r o p e r t i e s , i t i s unders t a n d a b l e t h a t the wood elements might t e n d t o o r i e n t themselves  somewhat i n a l o n g i t u d i n a l d i r e c t i o n as t h e y  f a l l . onto the mat d u r i n g the m a n u f a c t u r i n g p r o c e s s . Lateral nail  resistance  T h i s t e s t was  done w i t h the i d e a o f d u p l i c a t i n g  l a t e r a l n a i l movement f o r c e s on a p a n e l i n a c t u a l for  example, when used as w a l l p a n e l i n g .  service,  Values are g i v e n  i n T a b l e V I , w i t h ranges and the a n a l y s i s of v a r i a n c e shown i n Appendices  G and H.  A l t h o u g h no s i g n i f i c a n t  differences  were apparent i n the a n a l y s i s o f v a r i a n c e , c o n c l u s i o n s were f o r m u l a t e d from the type o f f a i l u r e  of the b o a r d .  S h e a r i n g s t r e s s e s from the n a i l movement were a t r i g h t a n g l e s t o the g r a i n o f the veneer o f the o v e r l a i d b o a r d s , and a t r i g h t a n g l e s t o the machine d i r e c t i o n o f the n o n - o v e r l a i d boards.  The o v e r l a y i n c r e a s e d l a t e r a l  nail  r e s i s t a n c e f o r hoards A, B, ami E, but d i d not i n c r e a s e the  r e s i s t a n c e f o r plywood. On the o v e r l a i d boards the n a i l bent o r was  p u l l e d out from the s t u d a f t e r maximum l o a d was from between 200 the  t o 220  pounds.  n a i l on the o v e r l a i d b o a r d s .  being  reached at  No r u p t u r i n g o c c u r r e d around N o n - o v e r l a i d hoards A,  C, and E a l l f a i l e d hy a r u p t u r i n g of the wood elements  B,  58 around the n a i l . and  shear.  Figure  An  Boards f a i l e d by a combination  example o f t h i s type of f a i l u r e  of t e n s i o n  i s shown i n  7» Board D d i d not f a i l ;  o v e r l a i d boards,  the n a i l bent  Boards A and B had w i t h l o a d s of 120 Again, boards.  as i n the plywood and  the  and p u l l e d out from the  stud.  the lowest v a l u e s i n l a t e r a l n a i l r e s i s t a n c e , and 160  pounds, r e s p e c t i v e l y .  o v e r l a y i n g minimized  d i f f e r e n c e s between  L a t e r a l n a i l r e s i s t a n c e o f the n o n - o v e r l a i d boards  depended on t h e i r  composition.  Nail-withdrawal resistance Values  f o r n a i l - w i t h d r a w a l r e s i s t a n c e are  i n T a b l e V I , and v a l u e s f o r range and v a r i a n c e are shown i n Appendices I and boards had a s i g n i f i c a n t  effect  given  the a n a l y s i s o f J.  O v e r l a y i n g the  on withdrawal  values.  With  the e x c e p t i o n of plywood, n a i l - w i t h d r a w a l r e s i s t a n c e i n c r e a s e d f o r a l l boards. l a i d board  can be  The  h i g h e r v a l u e s f o r the  e x p l a i n e d i n two ways:  over-  1) the i n c r e a s e d  h o l d i n g a r e a a g a i n s t the n a i l , and 2) the p r e v e n t i o n by  the  v e n e e r of f i b r e break-away from around the bottom of the board  as the n a i l was  boards, results;  d r i v e n through.  Of the  non-overlaid?  the m u l t i - l a y e r board E and plywood had the however, these d i f f e r e n c e s were not  the 5 p e r c e n t c o n f i d e n c e  level.  lowest  significant  at  59 Nail-withdrawal resistance i s generally correlated with specific gravity.  In t h e s e r e s u l t s t h e hoards w i t h the  lowest v a l u e s a l s o had the lowest d e n s i t i e s . had the lowest r e s i s t a n c e v a l u e s .  Board A a g a i n  In a study such as t h i s ,  because o f the wide range o f v a l u e s f o r each board (Appendix  I ) and t h e v a r y i n g c o m p o s i t i o n o f each hoard, i t  is difficult withdrawal  t o make d e f i n i t e c o n c l u s i o n s r e l a t i n g t o n a i l -  r e s i s t a n c e being correlated with s p e c i f i c  gravity.  D r i v i n g the n a i l p e r p e n d i c u l a r t o the s u r f a c e o f t h e board is difficult.  A n a i l d r i v e n a t a s l i g h t angle from t h e  normal w i l l t e n d t o have a h i g h e r w i t h d r a w a l  r e s i s t a n c e (14-).  T h i s f a c t o r might have c o n t r i b u t e d t o t h e wide range o f v a l u e s . I t i s important  t o note t h a t withdrawal r e s i s t a n c e  of t h e hoards was comparable t o t h a t o f plywood.  F o r more  r e l i a b l e r e s u l t s the number o f r e p l i c a t e s s h o u l d be i n c r e a s e d . Dimensional  change  R e s u l t s o f dimension Table V I I .  Dimensional  change t e s t s a r e shown i n  change o f p a r a l l e l samples  t o change i n l e n g t h o f the e n t i r e b o a r d ,  and p e r p e n d i c u l a r  change r e f e r s t o change i n t h e width o f t h e board. decrease  corresponds  Average  i n t h i c k n e s s o f the n o n - o v e r l a i d boards i n g o i n g  from 75 t o 25 p e r c e n t r e l a t i v e h u m i d i t y was 5^1 p e r c e n t , and 4.5  p e r c e n t f o r the n o n - o v e r l a i d plywood.  F o r the o v e r l a i d  hoards and plywood, these v a l u e s were 4.0 p e r c e n t and 3 . 7 percent, r e s p e c t i v e l y .  O v e r l a y i n g tended  t o decrease  60  Table V I I .  D i m e n s i o n a l Change i n T h i c k n e s s and L e n g t h o f P a n e l s Between 75 and 25 P e r c e n t R e l a t i v e Humidity Non-overlaid  Type  Thickness (in) (%) *  Overlaid  Length ( i n ) (%)  Thickness (in) (%)  Length (in) (%)  A p a r a l l e l 0.16 perpend. 0.15  4.6  0.04 0.03  0.38 0.28  0.15 0.16  3.5  0.02 0.04  0.19 0.38  B p a r a l l e l 0.20 perpend. 0.18  5.6  0.04  0.02  0.38 0.19  0.16 0.17  3.8  0.00 0.04  0.00 0.37  C p a r a l l e l 0.19 perpend. 0 . 1 7  5.4  0.03 0.02  0.28 0.19  0.17  4.1  0.18  0.01 0.03  0.09 0.35  D p a r a l l e l 0.21 perpend. 0.21  6.1  0.02 0.02  0.20 0.20  0.21 0.16  4.3  0.00 0.03  0.00 0.28  E p a r a l l e l 0.13 perpend. 0.14  4.0  0.02 0.02  0.19  0.17  0.16  4.0  0.01 0.02  0.09 0.18  F p a r a l l e l 0.13 perpend. 0.20  4.5  0.00 0.03  0.00 0.28  0.16 0.16  3.7  0.01 0.03  0.10 0.29  0.19  Ave. d i m e n s i o n a l change f o r n o n - o v e r l a i d boards Ave. d i m e n s i o n a l change f o r n o n - o v e r l a i d boards and plywood Ave. d i m e n s i o n a l change f o r  o v e r l a i d boards Ave. d i m e n s i o n a l change f o r o v e r l a i d boards plywood  5*1%  5.0% 3*9%  and  Average o f p a r a l l e l and p e r p e n d i c u l a r measurements.  3.9%  61 dimensional  change i n t h i c k n e s s .  I t i s p o s s i b l e the veneer  a c t e d as a b a r r i e r , o r slowed moisture specimens.  I f the  pick-up  i n the  specimens had been c o n d i t i o n e d f o r a  l o n g e r p e r i o d i t i s p o s s i b l e t h a t the change i n t h i c k n e s s f o r the o v e r l a i d and n o n - o v e r l a i d boards would have been more n e a r l y  equal.  The  n o n - o v e r l a i d hoards A, B,  l a r g e r shrinkage  l o n g i t u d i n a l shrinkage  r a d i a l shrinkage  Plywood  i n l e n g t h because o f the  component o f the two  r a d i a l s w e l l i n g of the c e n t r e ply.cwould face p l i e s .  slightly  v a l u e s i n l e n g t h than i n width.  had n e g l i g i b l e s h r i n k a g e  two  and C had  small  face p l i e s .  be r e s t r a i n e d by  Any the  Widthwise i n the plywood, however, the o f the f a c e p l i e s was  r e s t r a i n e d only  s l i g h t l y by the l o n g i t u d i n a l s h r i n k i n g of the c e n t r e p l y . The  dimensional  hoards D and  change i n l e n g t h and w i d t h was  equal f o r  E.  O v e r l a y i n g tended t o reduce the i s o t r o p i c s h r i n k i n g p r o p e r t i e s o f the boards. o v e r l a i d boards was  S h r i n k i n g lengthwise  decreased  because o f the  i n the  restraining  a c t i o n of the v e n e e r due  t o i t s s m a l l component o f  l o n g i t u d i n a l shrinkage.  However, s h r i n k a g e  i n c r e a s e d because o f the l a r g e r a d i a l o f the veneer. shrinkage.  i n width  shrinkage  component  O v e r l a y i n g the plywood tended t o i n c r e a s e  W i t h the n o n - o v e r l a i d plywood the c e n t r e p l y  was  r e s t r a i n i n g two  p l i e s , but when o v e r l a i d , the c e n t r e p l y  was  r e s t r a i n i n g f o u r p l i e s , hence the i n c r e a s e d  shrinkage.  62 Boards A and E had t h e s m a l l e s t d i m e n s i o n a l change in  thickness.  gravity. boards,  These two hoards  a l s o had t h e lowest  specific  However, because o f the complex n a t u r e o f t h e i t i s difficult,  correlate specific  w i t h i n the scope  o f t h i s study, t o  g r a v i t y w i t h p e r c e n t d i m e n s i o n a l change.  V a r i a b l e s e n t e r i n t o the make-up o f t h e board,  such as r e s i n  amount, e f f e c t i v e n e s s o f r e s i n f i l m , p a r t i c l e s i z e , and amount o f wax a d d i t i v e s , which i n f l u e n c e the amount o f d i m e n s i o n a l change. Warping Amount o f t w i s t , cup, and how o c c u r r i n g i n the p a n e l s a t 75 and 25 p e r c e n t r e l a t i v e h u m i d i t y i s shown i n  7 Table V I I I .  G e n e r a l l y , warping'  a t 75 p e r c e n t and a t 25  p e r c e n t r e l a t i v e h u m i d i t y was a p p r o x i m a t e l y the same. O v e r l a y i n g the boards d e c r e a s e d warping d i f f e r e n c e s between b o a r d s .  and minimized  Plywood p a n e l s , b o t h  overlaid  and n o n - o v e r l a i d , e x h i b i t e d more warp than the b o a r d s . Of the hoards, A had the l a r g e s t amount o f t w i s t , cup, and bow.  Board B had a l a r g e amount o f warp a t 25  percent r e l a t i v e humidity.  Board E had no warping  o v e r l a i d , and v e r y l i t t l e when not o v e r l a i d . of  the hoards  The  when remainder  had v a r y i n g amounts o f warp f a l l i n g between  R e f e r s t o t w i s t , cup and how.  63  Table V I I I .  Warping i n P a n e l s a t 75 and 25 R e l a t i v e HumidityTwist  Cup  (0.001 i n . )  Type  75%  25%  A  85  85  B  0  C  Bow  (0.001 i n . ) 75%  25%  0  38  25  25  25  8  0  5  5  D  10  24  E  0  P  diff.  Percent  diff.  (0.001 i n . ) diff  75%  25%  7  24  50  26  10  2  0  15  15  3  6  3  5  7  2  14  7  0  7  5  3  2  23  23  0  5  5  0  0  0  165  16  149  15  9  4  5  7  2  A  0  0  0  8  21  13  0  0  0  B  0  6  6  13  14  1  4  2  2  C  5  2  3  0  0  0  2  10  8  D  5  0  5  2  0  2  0  0  0  E  0  0  0  0  0  0  0  0  0  P  93  10  83  12  12  0  7  0  7  Non-overlaid  Overlaid  64 these  two.  D i f f e r e n c e s , where they o c c u r r e d , d i d not  to f o l l o w a d e f i n i t e trend. t o 25 p e r c e n t samples and  75  When the p a n e l s went from  r e l a t i v e humidity,  warping decreased  increased i n others.  several instances reversed  appear  The  i n some  warping i n plywood i n  itself.  T h e o r e t i c a l l y , plywood c o n s t r u c t e d o f p l i e s s y m e t r i c a l l y about the n e u t r a l a x i s s h o u l d have o f the f a c e p l i e s e q u a l l y r e s t r a i n e d by no warping s h o u l d take p l a c e .  placed  shrinkage  the c e n t r e p l y ,  and  However, d i f f e r e n c e s i n  t h i c k n e s s between p l i e s and v a r i a t i o n s i n g r a i n d i r e c t i o n and  d e n s i t y w i t h i n the p l i e s o f the plywood accounted f o r  the l a r g e amount o f warp. Warping i n the b o a r d s can be a s c r i b e d t o f i n e s t h a t have f a l l e n or s e t t l e d to the bottom of the mat formation  i n the m a n u f a c t u r i n g p r o c e s s  homogeneous mass.  resulting in a  during non-  Furthermore, non-homogeneity of p a r t i c l e  s i z e can cause d i f f e r e n c e s i n s w e l l i n g o r s h r i n k i n g , r e s u l t i n g i n warp i n the p a n e l .  P a r t i c l e and  are composed of s m a l l elements of wood.  f l a k e boards  Wood s h r i n k s to a  n e g l i g i b l e degree i n the l o n g i t u d i n a l d i r e c t i o n as t o l a r g e r shrinkage  i n i t s r a d i a l and  compared  tangential directions.  By p l a c i n g these wood elements a c r o s s each o t h e r a t random as i s done i n b o a r d manufacture, the l a r g e r a d i a l t a n g e n t i a l shrinkage  and  components are r e s t r a i n e d by the  l o n g i t u d i n a l movement of the a d j a c e n t  particles.  small  Generally,  65 boards are c o n s t r u c t e d w i t h the l o n g i t u d i n a l d i r e c t i o n o f the  f i b r e s m a i n l y o r i e n t e d p a r a l l e l t o the p l a n e o f the p a n e l ,  hence t h i c k n e s s s w e l l i n g i s not  restrained.  A c c e l e r a t e d aging No d e l a m i n a t i o n o f the veneer o c c u r r e d a f t e r s i x c y c l e s o f t h i s t e s t , but i n t e r n a l d e t e r i o r a t i o n o f the board c o r e was  prevalent.  Because o f the s u b j e c t i v e n a t u r e o f t h i s  t e s t , comparisons  between boards were d i f f i c u l t  d e t e r i o r a t i o n was  i n the b o a r d where p a r t i c l e - t o - p a r t i c l e  f l a k e - t o - f l a k e a d h e s i o n was the  t o make. A l l or  l o s t a f t e r repeated c y c l e s of  test. Samples were i n s p e c t e d d u r i n g each phase o f e v e r y  cycle.  I n the f i r s t  c y c l e , boards A and B were the f i r s t  open i n the c o r e , f o l l o w e d by board E .  After.'its  to  initial  d e t e r i o r a t i o n , board E d i d not become a p p r e c i a b l y worse w i t h each c y c l e as d i d most o f the o t h e r b o a r d s .  After six  c y c l e s b o a r d A had almost c o m p l e t e l y opened i n the c e n t r e . Board B was  next.  The remainder of the boards had about the  same degree  o f d e t e r i o r a t i o n i n the c o r e .  Appearance  o f the  boards a f t e r f o u r and s i x c y c l e s i s shown i n F i g u r e 12. Roughness and t w i s t i n g of the veneer to  corresponded  the amount o f core opening; the more the core opened from  l o s s o f a d h e s i o n the more the f a c e veneer would t w i s t . C h e c k i n g was  absent on the veneer o f a l l boards, but  was  66 pronounced on the T h i s was angles  s u r f a c e o f the o v e r l a i d plywood samples.  because the f a c e v e n e e r was  t o the f a c e p l y of the plywood.  the case, presumably c h e c k i n g decreased.  The  o v e r l a y and  p l a c e d at r i g h t angles action  not p l a c e d a t r i g h t I f t h i s had  would have been  i t s grain  substantially  f a c e p l i e s o f the plywood, i f  to one  another would e x e r t  on each o t h e r d u r i n g m o i s t u r e c o n t e n t  commercial p r a c t i c e ,  been  restraining  changes.  In  the o v e r l a y veneer would be p l a c e d  d i r e c t i o n p a r a l l e l t o the g r a i n  f a c e p l i e s o f the plywood.  The  direction  alternative  the  i s to have  s p e c i a l l y c o n s t r u c t e d plywood where the g r a i n the o v e r l a y i s a t r i g h t a n g l e s  of  with  direction  to the g r a i n d i r e c t i o n  of  of  the  f a c e p l i e s o f the plywood. Boards composed o f p a r t i c l e s appeared t o undergo more d e t e r i o r a t i o n  than those  composed o f f l a k e s .  The  p a r t i c l e boards had more f a i l u r e because o f the l a r g e amount of s u r f a c e a r e a f o r the r e s i n b i n d e r t o c o v e r  effectively  as compared t o the r e l a t i v e l y s m a l l amount of s u r f a c e of the f l a k e  board.  area  Figure 12.  A c c e l e r a t e d Aging Samples. Type of d e t e r i o r a t i o n i n board core a f t e r f o u r c y c l e s i s shown i n top photo, and a f t e r s i x c y c l e s , i n bottom photo.  >3  68  CONCLUSIONS AND RECOMMENDATIONS  The f o l l o w i n g c o n c l u s i o n s have been made from this  study: 1.  Urea-formaldehyde  adhesive was s a t i s f a c t o r y when  bonding P h i l i p p i n e mahogany veneer t o p a r t i c l e and f l a k e board.  G l u e - l i n e f a i l u r e was minimal  and o c c u r r e d o n l y on hoards o f h i g h d e n s i t y . 2.  O v e r l a y i n g the b o a r d w i t h veneer i n c r e a s e d  tensile  s t r e n g t h p a r a l l e l t o the s u r f a c e , u l t i m a t e  strength  i n bending, and s t i f f n e s s i n t h e d i r e c t i o n o f the g r a i n o f t h e veneer, but g e n e r a l l y d e c r e a s e d these p r o p e r t i e s p e r p e n d i c u l a r t o the d i r e c t i o n o f the g r a i n of the veneer. 3.  Boards composed o f f l a k e s had h i g h e r s t r e n g t h p r o p e r t i e s than those composed o f p a r t i c l e s . O v e r l a i d plywood had s l i g h t l y h i g h e r s t r e n g t h v a l u e s than the o v e r l a i d b o a r d s .  4-.  V e n e e r i n g tended t o minimize d i f f e r e n c e s i n b o t h warping and s t r e n g t h p r o p e r t i e s between t h e boards. N a i l - w i t h d r a w a l r e s i s t a n c e and l a t e r a l r e s i s t a n c e were a l s o  increased.  nail  69 5.  A l t h o u g h not s i g n i f i c a n t i n a n a l y s e s of v a r i a n c e , t h e r e were s m a l l d i f f e r e n c e s i n s t r e n g t h p r o p e r t i e s between the l e n g t h and w i d t h d i r e c t i o n s o f most boards.  6.  V e n e e r i n g d e c r e a s e d warping but d i d not  appreciably  a f f e c t d i m e n s i o n a l change i n t h i c k n e s s and w i d t h "of the p a n e l s . the boards was  D i m e n s i o n a l change i n l e n g t h o f d e c r e a s e d by the veneer.  Plywood  e x h i b i t e d more warping than the b o a r d s . 7.  No d e l a m i n a t i o n o f the veneer o c c u r r e d a f t e r accelerated aging. was  Roughness and t w i s t o f veneer  r e l a t e d to amount of d e t e r i o r a t i o n i n the board  core.  P a r t i c l e boards d e t e r i o r a t e d more r e a d i l y  than the f l a k e b o a r d s . 8.  Board A, composed o f e a s t e r n white p i n e , had the lowest v a l u e s i n p h y s i c a l and mechanical  tests.  Board D of the f l a k e type and b o a r d E o f the m u l t i - l a y e r type had the h i g h e s t v a l u e s , and boards B and C were i n t e r m e d i a t e . Prom an a n a l y s i s o f the t e s t p r o c e d u r e s and subsequent  r e s u l t s , the f o l l o w i n g recommendations have been  formulated: 1.  In e v a l u a t i n g p a r t i c l e boards f o r use as p a r t i t i o n s o r w a l l p a n e l i n g , i t might be a d v i s a b l e t o use l a r g e r s i z e d samples when measuring warp.  For  70 intensive study, a more accurate device to measure d e v i a t i o n from the plane surface also needs to he incorporated. 2.  To measure dimensional change, a d i a l micrometer r i g i d l y mounted on a metal base would be more accurate than the method used here ( 2 8 ) . More r e p l i c a t e s should he taken f o r warping and dimensional change measurements.  3.  As used i n t h i s study, the l a t e r a l n a i l resistance t e s t was not as s a t i s f a c t o r y as might be desired. It d i d show d i f f e r e n c e s between non-overlaid hoards but  was not effective, on o v e r l a i d boards.  For  evaluation of n a i l resistance at varying distances from the edge of the board, the method described i n ASTM 1037 D (1) i s recommended. 4-.  Because of the wide range of values i n the n a i l withdrawal t e s t , more r e p l i c a t e s should be used.  71 BIBLIOGRAPHY  1.  American S o c i e t y f o r T e s t i n g M a t e r i a l s . 1958. Book of ASTM S t a n d a r d s . P a r t 6 . P h i l a d e l p h i a . 956 pp.  2.  Bryan, E.L. I960. Bending s t r e n g t h o f p a r t i c l e hoard under l o n g - t e r m l o a d . F o r . Prod. J o u r . 10(4-) .-200-204-.  3.  Canadian Standards A s s o c i a t i o n . 1952. S p e c i f i c a t i o n s f o r Douglas f i r plywood and western softwood c o n s t r u c t i o n plywood. Can. S t d . A s s o c . 0 1 2 1 - 1 9 5 7 . 18 pp.  4.  Douglas F i r Plywood A s s o c i a t i o n . 1942. T e c h n i c a l d a t a on plywood. P r t d . i n U.S.A. Form 4 2 - 7 0 . 52 pp.  5.  Food and A g r i c u l t u r e O r g a n i z a t i o n of the U n i t e d N a t i o n s . 1959. F i b r e b o a r d and p a r t i c l e hoard. Rept. t o U.N. Rome. 191 pp.  6.  F u j i i , J.S. 1958. The e f f e c t of o v e r l a y m a t e r i a l s on the f l e x u r a l p r o p e r t i e s o f commercial p a r t i c l e b o a r d . For. Prod. Jour. 8(8):219-224.  7.  G o t t s t e i n , J.W. 1950. Some s t u d i e s o f sawdust s y n t h e t i c r e s i n combination f o r hardboard manufacture. P r o c . F o r . P r o d . Res. Soc. 4 : 3 1 0 - 3 2 1 .  8.  Heebink, B.G., and R.A. Harm. 1959. S t a b i l i t y and s t r e n g t h o f oak p a r t i c l e h o a r d s . F o r . P r o d . J o u r . _3(7):197-202.  9.  H o f s t r a n d , A . J . 1958. R e l a t i o n s h i p o f s p e c i f i c g r a v i t y t o moduli o f r u p t u r e and e l a s t i c i t y i n commercial hardboard. F o r . Prod. J o u r . 8 ( 6 ) : 1 7 7 - 1 8 0 .  10.  Housing and Home F i n a n c e Agency. 1947. Technique o f house n a i l i n g . U.S.D.A., F o r . P r o d . Lab., Wash., D.C. 53 pp.  11.  I n d u s t r i a l E x p e r i m e n t a l Program. 1956. Wood p a r t i c l e hoard handbook. N o r t h C a r o l i n a S t a t e C o l l e g e . R a l e i g h . 303 PP.  12.  Kennedy, D.E., and G.H. N i l e s . 1952. H o l d i n g power o f n a i l s and screws i n e a s t e r n Canadian woods and b u i l d i n g boards. F o r . Prod. Lab. of Can., Ottawa. P r o j . 0 - 3 1 - 2 . 3 PP.  72 13.  Kloot, N.H. 1952. A survey of the mechanical properties of some f i b r e b u i l d i n g hoards. Aust. Jour, of App. S c i . 5(l):18-35.  14.  Mack, J.C. 1958« Some i n v e s t i g a t i o n s on test procedures i n nail-withdrawal t e s t s . Com. S c i . and Ind. Res. Org. Div. of For. Prod. Prog. Rept. No. 12. Melbourne. 7 PP»  15.  Marian, J.E. 1957. Adhesive and adhesion problems i n connection with p a r t i c l e board production. For. Prod. Jour. 8(6):172-176.  16.  Marra, G.G. 1958. and composition.  17.  M i l l e r , H.C.L. 1953« Chipcore - i t s c h a r a c t e r i s t i c s and production. For. Prod. Jour. _5(5) : 149-152.  18.  Maxwell, J.W., G. Kitazawa, T.F. Duncan, and J.M. Hine. 1959. Search f o r b e t t e r p a r t i c l e hoard adhesives. For. Prod. Jour. _)(10) :42A-46A.  19.  National Research Council of Canada. 1941. National b u i l d i n g code. N.R.C. No. 1068. Ottawa. 422 pp.  20.  Rahtu, H., C. Holm, and H. Aalto. 1958. On the properties of fibreboards and on t h e i r use f o r b u i l d i n g purposes V a l t i o n T e k n i l l i n e n Tutkimus-laitos. Tiedotus. S a r j a 3-Rakennus 2 1 . H e l s i n k i . 36pp.  21.  Smith, E.W., and F.I.M. Wood. I960. P a r t i c l e board as core stock f o r veneered panels. Wood 2 5 ( 2 ) : 7 2 - 7 5 »  22.  S t r i c k l e r , M.D. 1959- Properties of Douglas-fir f l a k e board. For. Prod. Jour. _)(7) :203-215.  23.  Talbott, J.W. 1957. Flapreg. Wash. State Bust, of Tech., Wash. State C o l l . 303 P P «  24.  Turner, H.D. 1954. E f f e c t of p a r t i c l e size and shape on strength and dimensional s t a b i l i t y of resin-bonded wood-particle panels. Jour. For. Prod. Res. Soc. 4(5):210-223.  25.  , and J.D. Kern. 1950. Relation of several formation v a r i a b l e s to properties of p h e n o l i c - r e s i n bonded wood-waste hardboard. U.S. Dept. of Agr. For. Prod. Lab. No. R1786. 13 pp.  26.  Wakefield, W.E. 1952. Resistance of wallboards to p u l l through of n a i l heads. For. Prod. Lab. of Can., Ottawa. Prog. Rept. No. 2. Prog: 0-313-1. 12 pp.  P a r t i c l e boards - t h e i r c l a s s i f i c a t i o n For. Prod. Jour. 8(12):11A-16A.  73 27.  Wangaard, F.F. 1 9 5 0 . The mechanical p r o p e r t i e s o f wood. John W i l e y and Sons, I n c . , New York. 377 pp.  28.  Wood P a r t i c l e Board Committee. No d a t e . Recommended t e s t i n g p r o c e d u r e s f o r wood p a r t i c l e hoard. N a t . Wood Mfg. A s s o c . C h i c a g o . 22 pp.  74  APPENDICES  A.  T e n s i o n P a r a l l e l t o S u r f a c e of N o n - o v e r l a i d and O v e r l a i d Boards and  B.  Plywood  A n a l y s i s of Variance of Tension P a r a l l e l to S u r f a c e as A f f e c t e d by O v e r l a y and G r a i n D i r e c t i o n  C.  Modulus  o f Rupture o f N o n - o v e r l a i d and O v e r l a i d  Boards and D.  Plywood  A n a l y s i s o f V a r i a n c e o f Modulus  o f Rupture as  A f f e c t e d by O v e r l a y and G r a i n D i r e c t i o n E.  Modulus  o f E l a s t i c i t y of N o n - o v e r l a i d ahd O v e r l a i d  Boards and P.  Plywood  A n a l y s i s o f V a r i a n c e o f Modulus  of E l a s t i c i t y  as  A f f e c t e d by O v e r l a y and G r a i n D i r e c t i o n G.  L a t e r a l N a i l R e s i s t a n c e o f N o n - o v e r l a i d and O v e r l a i d Boards and  H.  A n a l y s i s o f V a r i a n c e o f L a t e r a l N a i l R e s i s t a n c e as A f f e c t e d by  I.  Plywood  Veneer-overlay  N a i l - w i t h d r a w a l R e s i s t a n c e o f N o n - o v e r l a i d Boards and Plywood  J.  A n a l y s i s of V a r i a n c e o f N a i l - w i t h d r a w a l R e s i s t a n c e as A f f e c t e d by  Veneer-overlay  Appendix A.  Tension P a r a l l e l to Surface of Non-overlaid and Overlaid Boards and Plywood Non-overlaid mean(psi) range ( p s i )  Type  Overlaid mean(psi) range (ps:  A parallel perpend.  670 640  610- 750 •620- 650  3680 590  3650-3750 570- 610  B parallel perpend.  960 860  830-1040 840- 890  4130 1010  3850-4410 1000-1030  C parallel perpend.  1440 1270  1380-1490 1190-1330  4390 1300  4230-4544 1280-1330  D parallel perpend.  2600 2590  2570-2600 2300-2880  5140 2270  4990-5300 2110-2500  E parallel perpend.  1190 1190  1120-1270 1140-1210  4020 1060  3500-4400 970-1160  F parallel perpend.  5570 570  5200-6250 2 5 0 - 730  7490 3060  6670-8450 2410-3740  Appendix B.  Analysis of Variance of Tension P a r a l l e l to Surface as A f f e c t e d by Overlay and Grain Direction  Source of Variance Boards (B) Treatment (T) Grain d i r e c t i o n (G) BxT BxG TxG BxGxG Total Corr.  * *:  ***  Sum of Squares  Mean Squares  5 1  221,041 143,995  44,208 143,995  8.475** 27,606  1 5 . 5 1 5 23 1  257,716 6,833 84,062 84,609 26,082 824,338 1,386,723  257,716 1,367 16,812 84,609 5,219  49.409 0.262 3,223 16.221  Degrees of Freedom  level.  significant  at the  significant  at the 1% l e v e l ,  significant  at the 0.1% l e v e l .  ***  Appendix C.  Type  Modulus of Rupture of Non-Overlaid and Overlaid Boards and Plywood Non-overlaid mean(psi) range(psi)  Overlaid mean(psi) range(psi)  A parallel perpend.  1030 1010  960- 1080 950- 1040  8120 1100  7 9 3 0 - 8490 1090- 1120  B parallel perpend.  1970 1510  1910- 2000 1510- 1510  8940 1610  8470- 9350 1440- 1690  C parallel perpend.  2320 2070  2210- 2390 1970- 2120  8850 1810  8 7 2 0 - 9041 1800- 1820  D parallel perpend.  3920 3770  3 8 7 0 - 4030 3420- 3990  9400 3230  9270- 9480 2980- 3370  E  parallel perpend.  3430 2520  3420- 3510 2310- 2650  8240 1680  8 1 7 0 - 8340 1540- 1770  P parallel perpend.  14-190 2700  13380-14940 1640- 3660  10830 2490  10280-11260 2080- 2750  Appendix D.  Source of Variance Boards (b) Treatment (T) Grain d i r e c t i o n (G) BxT BxG BxGxT Total Corr.  Analysis of Variance on Moduli of Rupture As Affected by Overlay and Grain D i r e c t i o n Degrees of Freedom  Sum of Squares  Mean Squares  5 1  571,574 278,641  114,315 278,641  2.830, 6.899.  1 5 5 5 23 1  1,269,600 205,758 342,301 201,937 3,237,844 4,747,262  1,269,000 41,152 68,460 40,387  31.436 1.019 1.695* 9.H3  *  s i g n i f i c a n t at 5% l e v e l . **  s i g n i f i c a n t at 1% l e v e l .  P  *  Appendix E.  Modulus of E l a s t i c i t y of Non-Overlaid and Overlaid Boards and Plywood Non-overlaid Overlaid mean(lOpsi) range (lOpsi) mean(10p s i ) range(10p;  Type A parallel perpend.  193 193  1 9 3 - 193 193- 193  1166 261  1166-1166 258- 262  B parallel perpend.  356 280  3 5 6 - 356 280- 280  1045 188  1037-1062 188- 188  C parallel perpend.  368 367  368- 368 367- 367  1137 322  1137-1137 322- 322  D parallel perpend.  598 598  598598-  598 598  997 396  9 9 7 - 997 393- 399  E parallel perpend.  690 544  6 9 0 - 690 3 9 9 - 617  1062 275  950-1122 2 1 0 - 315  P parallel perpend.  1635 226  1475- 1867 1 9 1 - 278  1384 119  935-1609 111- 132  Appendix P.  Source of Variance Boards (B) Treatment (T) Grain d i r e c t i o n (G) BxT BxG TxG BxTxG Total Corr.  Analysis of Variance of Moduli of E l a s t i c i t y As Affected by Overlay and Grain D i r e c t i o n Sum of Squares  Mean Squares  F  5 1  411,602 230,880  82,320 230,880  2.258 6.334  1 5 5 l 5 23 1  1,933,473 310,124 736,461 554,496 182,254 4,359,298 8,580,104  1,933,473 62,025 147,292 . 554,496 36,451  Degrees of Freedom  s i g n i f i c a n t at the ***  level.  s i g n i f i c a n t at the 0.1% l e v e l .  53.043 1.702 4.041, 15.212  Appendix G.  L a t e r a l N a i l R e s i s t a n c e o f N o n - o v e r l a i d and O v e r l a i d Boards and Plywood Non-overlaid  m  Overlaid  Type Load-, LoadM e a n ( l b ) Range ( l b ) F a i l u r e x  Load LoadType Mean ( l b ) Range(lb) F a i l u r e  A  120  110-135  *  205  205-205  **  B  160  125-175  *  220  195-250  **  C  190  180-210  *  190  180-210  ***  D  210  195-225  ***  200  160-220  ** *  E  180  165-200  *  195  185-215  **  P  230  210-245  ***  210  205-225  ***  * board f a i l e d around n a i l e i t h e r i n . s h e a r , t e n s i o n , o r a combination o f t h e s e . ** n a i l b e n t . *** n a i l bent and was b e i n g p u l l e d out o f s t u d . each v a l u e t h e average o f 4 r e p l i c a t e s .  Appendix H.  Source o f Variance Boards (B) Treatment ( T ) Error Total  A n a l y s i s of Variance of L a t e r a l N a i l R e s i s t a n c e as A f f e c t e d by Veneer O v e r l a y  Degrees o f Freedom 5 1 5 11  Sum o f Squares 37.0 14.0 43.7 446.8  Mean Squares 7-40 14.00 8.74  F 0.847 1.602  Appendix I . W a i l - w i t h d r a w a l R e s i s t a n c e o f N o n - o v e r l a i d and O v e r l a i d Boards and Plywood  Type  Non-overlaid Load-Mean(lb) Load-Range(lb) 1  Overlaid Load-Mean(lb) Load-Range(lb)  A  25  23-27  40  31-54  B  32  19-40  59  49-70  C  30  21-40  46  34-63  D  46  39-54  54  42-67  E  30  20-40  33  28-36  P  31  25-41  30  24-34  1  Each v a l u e the average o f 6 r e p l i c a t e s .  Appendix J .  A n a l y s i s o f V a r i a n c e on N a i l - w i t h d r a w a l R e s i s t a n c e a s A f f e c t e d by V e n e e r - O v e r l a y  Source o f Variance Boards (B) Treatment ( T ) Error Total Correction significant  Degrees o f Freedom 5 1 5 11 1  Sum o f Squares  Mean Squares  658.0 385-3 256.7 1,300.0 17,328.0  131.6 385-3 51.3  a t the 5% l e v e l .  P 2.56 7.51*  

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