Structural Flakeboards and Composites 2993 



On average, Hse found that the low-density species were slightly more stable 

 than the high density ones; white oak panels were the least stable. All 49.5-lb/cu 

 ft boards, except hickory and post oak, expanded more than either 44.5 or 39.5- 

 Ib/cu ft boards of the same species. Red maple, sweetbay, and sweetgum were 

 the most stable among the 44.5-lb/cu ft boards. Among 39.5-lb/cu ft boards, 

 sweetgum and sweetbay were the most stable. 



Post (1961) found that scarlet oak flakeboard made from veneer flakes had 

 least linear expansion if flakes were about 0.012 to 0.015 inch thick. 



Comparison of single-species boards made from flakes cut on industrial 

 flakers. — Price and Lehmann (1978) evaluated linear expansion of boards com- 

 posed of flakes cut on ring, disk, drum, and shaping-lathe flakers. When ex- 

 posed to the ovendry-vacuum-pressure-soak test, southern red oak, hickory, and 

 sweetgum boards made with lathe flakes were most stable (figs. 24-8 and 24- 

 12). Lathe flakes also made the most stable sweetgum boards as tested by a 24- 

 hour water soak. When cycled between 30 and 90 percent RH, oak and hickory 

 boards had most linear stability if made from lathe or drum flakes. 



Heebink and Lehmann (1977) made flakeboards of yellow-poplar, red oak, 

 and hickory from randomly oriented 1 -inch-long flakes 0.015 inch thick cut in 

 the 0-90 direction by cross-grain planing. Linear expansions they observed in 

 the single-species boards of 40 Ib/cu ft density bonded with phenol-formalde- 

 hyde resin (6 percent resin content) were as follows: 



Condition Yellow-poplar Red oak Hickory 



Percent 



0-90 percent RH 0.21 0.29 0.29 



30-90 percent RH .11 .17 .16 



30-day water soak .20 .36 .25 



24-hour water soak .12 .17 .17 



In a study of phenolic-bonded 1/2-inch-thick flakeboard made from randomly 

 oriented 0.020-inch-thick, 3-inch-long sweetgum flakes cut on a shaping lathe, 

 R. C. Tang and E. W. Price found (Final Report FS-SO-3201-12, dated March 

 31, 1982, Pineville, La.) that linear expansion was at follows: 



Relative humidity cycle Linear expansion 



Percent 



35 to 95 0.153 



55 to 95 .118 



These observations were made with an optical comparator. 



Price (1978), using calipers to measure between pins fitted in grommeted 

 holes, found that yellow-poplar and southern pine boards made with 3-inch- 

 long, 0.015-inch-thick face flakes and 0.025-inch-thick core flakes cut on a 

 shaping-lathe had linear expansion — averaged across 4-foot and 8-foot panel 

 directions — after a 24-hour water soak, as follows (table 24-20): 



