2922 



Chapter 24 



Some, but not all, authorities believe that disk flakers (figs. 18-265 and 18- 

 266) offer next best control over flake thickness, and drum flakers (figs. 18-268 

 and 18-269) slightly less. Most agree that ring flakers (figs. 18-270 through 18- 

 272) afford least control of flake dimensions. 



Price and Lehmann (1978) compared three-layer structural flakeboards of 

 sweetgum, southern red oak, and mockemut hickory made from 2-1/4-inch- 

 long, 0.020-inch-thick flakes cut from green wood on a shaping-lathe headrig 

 and on disk, drum, and ring flakers. The ring flaker produced 23.8 percent fines 

 (from chips 2-1/4 inches long); the drum, lathe, and disk produced only 7,7, 3.5, 

 and 2.2 percent fines, respectively (figs. 18-274ABC). 



1.2 



.3 1.4 I.I 1.2 



COMPACTION RATIO 



1.4 



Figure 24-4. — Bending strength (modulus of rupture) related to compaction ratio of 1/2- 

 inch-thick southern red oak and mockernut hickory panels made from 2-1/4-inch- 

 long, 0.020-inch-thick flakes cut on four types of flakers. Panels fabricated at the 

 target density of 52.6 Ib/cu ft are accentuated. (Left) Initial strength at 50-percent 

 relative humidity. (Right) Tested after accelerated aging. (Drawing after Price and 

 Lehmann (1978.) 



When oak and hickory boards were evaluated, bending strength and stiffness 

 were higher in those made from shaping-lathe-cut flakes (figs. 24-4 and 24-5), 

 and internal bond strength was greatest in panels of ring-cut flakes (fig. 24-6 and 

 24-7). Linear expansion values were low in panels of shaping-lathe-cut flakes 

 pressed to low compaction ratios (i.e., ratio of panel density to wood density) 

 and in those of drum-cut flakes pressed to high compaction ratios (fig. 24-8 

 bottom). Thickness swell in these oak and hickory panels, when subjected to the 

 ovendry- vacuum-pressure-soak cycle, or to change in relative humidity from 30 



