Structural Flakeboards and Composites 

 AT 50% R.H. 





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 k 



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2927 



AFTER ACCELERATED AGING 



1.2 



1.3 



1.5 1.2 



compaction ratio 



1.3 



1.4 



1.5 



Figure 24-11. — Modulus of elasticity related to compaction ratio of 1/2-inch-thick 

 sweetgum panels made from 2-1/4-inch-long, 0.020-inch-thick flakes cut on four 

 types of flakers. (Left) Tested at 50-percent relative humidity. (Right) Tested after 

 accelerated aging cycle. (Drawing after Price and Lehmann 1978.) 



FLAKE DRYING^ 



Southern hardwood flakes will, for the most part, be cut from green, heated 

 stemwood of species having average moisture content of about 79.3 percent 

 (dry-weight basis). In most cases, the wood will be sorted, prior to flaking, into 

 at least two species classes according to wood specific gravity. The high-density 

 woods including the ash, hickory and oak species will have moisture contents 

 from about 47 to about 74 percent; low-density woods such as sweetbay, sweet- 

 gum, and yellow-poplar will range from 100 to 120 percent moisture content, 

 dry-weight basis (table 8-2). These particles will generally be 1-1/2 to 3 inches 

 long and 0.015 to 0.025 inch thick. To dry such flakes, industry in North 

 America largely relies on rotating-drum driers direct-fired by oil, natural gas, or 

 dry wood waste. 



Rotary-drum dryers. — The rotary-drum-type dryer flash dries surface mois- 

 ture from the wood particles and drives moisture from the interior of the particle 

 to the surface. Hot gases of combustion and excess air are pulled through the 

 drum by an induction fan. The small and light weight particles are air-conveyed 

 through the dryer in a matter of seconds. Heavy and large particles are air- 

 conveyed in the high temperature and high velocity channels of the dryer but 

 begin to drop out of the gas stream as the velocity diminishes. 



'^With addition of illustrations and introductory material, this subsection is largely taken from 

 Raddin (1975). 



