Fiberboards 275 1 



of orientation than are longer fibers (fig. 23-6). Long fibers are more easily 

 aligned, by electrical or mechanical means, in one of the principal board dimen- 

 sions, to enhance board properties in the direction of alignment. 



WOOD FURNISH 



In preference to more expensive roundwood, southern fiberboard plants in- 

 creasingly use residue chips from sawmill and veneer plants, and whole-tree 

 forest-residual chips. Bark-free sawmill chips must be screened to remove their 

 fines content and blended in inventory to maintain a uniform species mix. 

 Whole-tree chips contain considerable bark (table 17-6) which not only weakens 

 boards and contributes significantly to waste- water contamination, but contains 

 grit that accelerates wear of refiner plates and conveyors. 



Whole-tree chips will not yield highest quality hardboard substrates for high- 

 gloss finishes, but are suitable for embossed boards permitting surface imperfec- 

 tions from bark and shives. 



Sawdust, which is cheaper than pulp chips, can be incorporated in fiberboards 

 but board strength is diminished. To compensate for such strength loss, board 

 density can be increased; e.g., a sawdust component of 20 percent of total 

 furnish would require a board density of about 71 pounds per cubic foot. Such 

 high densities can cause major processing difficulties such as blistering during 

 pressing. 



Bark may also be incorporated in fiberboards, but strength properties of 

 resulting boards will be diminshed and color darkened. Strength properties are 

 not the sole quality indicators for many board uses, however, and boards con- 

 taining considerable percentages of sawdust and bark are manufactured. 



23-5 PREPARATION OF RAW MATERIAL 



Mechanical pulping with defibrators and refiners requires wood in homoge- 

 neous form, i.e., pulp chips, fed at a uniform and continuous rate. The technol- 

 ogy for preparing and handling these pulp chips is extensive; interested readers 

 are referred to other sections of this text for aspects of the subject as follows: 

 Subject Reference 



Roundwood harvest Chapter 16 



Merchandising decks for tree-length wood Sect. 16-6 



Raw-material measurement Chapter 27 



Debarking of roundwood Chapter 17 



Chipping Sect. 18-24 



Whole-tree chipping Sects. 16-5 and 16-10 



Chip debarking and cleaning Sect. 17-7 



Chip handling Sect. 16-16 



Deterioration of chips during storage Figs. 11-21 through 1 1-24 and related 



text, Sects. 16-16, 16-17, and 25-9 



The steps in preparing wood for defibration are summarized in figure 23-7. 



