Structural Flakeboards and Composites 



2949 



can be accomplished by separating incoming logs — and their flakes — into two 

 species classes, with low-density wood in one and high-density wood in another. 

 The two classes should be about equal in volume. For small (6-inch dbh) 

 stemwood of all pine-site hardwoods, this division point will be at a density of 

 about 0.569 (based on green volume and ovendry weight) or a weight per cubic 

 foot of 35.5 pounds (ovendry basis). Larger stemwood will have slightly lower 

 density. 



Because species composition varies, each procurement area will have a differ- 

 ent species mix, and therefore a different dividing point between the high- and 

 low-density classes. Some typical panel properties for a number of particular 

 mixes are given in section 24-16. 



Table 24-1 1 . — Single-species flakeboard densities'-^ at which target specifications^ for 

 mechanical properties and dimensional stability can be met (Data from Hse 1975c) 



Species 



Lb/cuft — -- 



Sweetbay 35.9 37.2 30.4 49.5 



Red maple 40.0 41 .6 33.9 49.5 



Sweetgum 40.9 42.3 34.5 49.5 



Black tupelo 38.8 >49.5^ 32.7 44.5 



White ash 48.3 50.0 40.8 49.5 



Southern red oak 49.9 5 1 .6 42. 1 44.5 



Hickory 52.5 54.3 44.3 49.5 



Post oak 54.8 56.7 46.3 <44.5^ 



White oak 57. 1 59.0 48. 1 <44.5^ 



^Flakeboards from which these values were derived were 0.5 inch thick made from 3-inch-long, 

 0.015-inch-thick, 3/8-inch-wide veneer flakes. 



^Based on volume and weight at equilibrium at 80°F and 50 percent RH (i.e., at an MC of about 

 5.9 percent). 



•'Goals of the Forest Service Task Force on Panel Specifications. 



"^In 30-90 percent RH exposure test. 



^Indicates undetermined value larger than 49.5. 



^Indicates undetermined value smaller than 44.5. 



BOARD LAYERING 



Experienced researchers agree that face flakes of structural panels containing 

 dense woods such as the oaks and hickories should be thin (e.g., 0.015 inch) and 

 core flakes should be thicker (e.g., 0.025 inch). To accomplish this construc- 

 tion, the mat must be formed in three layers — a core and two faces. In 1/2-inch 

 panels, the core layer may be about 1/4-inch thick and each face layer about 1/8- 

 inch thick. Flakes in all layers can be randomly placed, producing panels with 



