Structural Flakeboards and Composites 



2953 





RANDOM FREE FALL 



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ELECTROSTATIC 

 FIELD- ALIGNMENT 



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FORMING LINE 



Figure 24-23. — Schematic diagram of electrical alignment of flakes. (Drawing after 

 Moloney 1980.) 



24-7 PRESSING 



Platen-type hot presses convert the formed mat of flakes into a bonded panel 

 of desired thickness by densifying it to develop adequate contact between flakes, 

 and by heating it to glue-line temperatures at which the binder cures rapidly. In a 

 typical flakeboard pressed to 0.5-inch thickness the mat would be about 25 

 flakes thick if the flakes were deposited with no voids and not compressed from 

 their original average thickness of 0.020 inch. Because voids are present in mats 

 of flakes, mats must be compressed to reduce the void volume and increase 

 contact between individual flakes (fig. 24-26). Variation in flake thickness 

 increases void volume and the need for compression. Generally, compression 

 required to achieve adequate bonding between thin flakes of dense hardwoods 

 may be about 20 percent, i.e. , the density of the pressed panel may be about 20 

 percent greater than the density of the flakes from which the panel is made. The 

 degree of compression is usually expressed as compaction ratio — 1.20 in the 

 example cited. Because wood of the most dense species (e.g., white oak or 

 hickory) has about twice the compression strength of the least-dense species 

 (e.g., yellow-poplar), the degree of compression of individual flakes varies 

 significantly in a panel with a mixture of species. 



