Structural Flakeboards and Composites 2975 



Press time: 5 minutes (including closing time of 45 to 60 sec) 



Resin content: 5-1/2 percent 



Core flakes: Random orientation, 0.025 inch thick, width-reduced, 



with special attention to sweetgum and hickory 

 Face flakes: 0.015-inch thick, mat water-sprayed on both sides just 

 prior to pressing 

 • Variable factors 



Panel density at 50 percent RH: 45, 47, and 49 Ib/cu ft 

 Face flakes 



(1) Random orientation; not width reduced 



(2) Aligned; sweetgum, hickory, and southern pine flakes re- 

 duced in width for ease of feeding through the aligning 

 mechanism 



Replications of boards: 3 



This three-layer design met target goals suggested by the Forest Service Task 

 Force on Panel Specifications for modulus of elasticity, modulus of rupture, and 

 internal bond strength at densities below 50 Ib/cu ft: 



Face flake orientation 

 Panel property at 50 percent RH Random Aligned 



Density (Ib/cu ft) 47.5 45.5 



IB (psi) 83 82 



MOE (psi) 800,000 1 ,090,000 



MOR (psi) 5,300 6,625 



Relationships of these properties to panel density are plotted in figure 24-38 

 (from which the foregoing tabulation was constructed). The target IB of 70 psi 

 was attained in both aligned and random boards at a panel density of 44.7 Ib/cu 

 ft. Target MOE of 800,000 psi required a random panel density of 47.5 Ib/cu ft, 

 however, at which density IB was 83 psi. The board with aligned faces had an 

 MOE of 1 ,090,000 at density of 45.5 Ib/cu ft, at which density IB was 82 psi. At 

 all densities, MOR of the aligned board was well above that of the random 

 board. 



The flakes for the panels just described were cut with sharp knives from wood 

 heated in water to 160°F. Subsequent experimentation showed a loss of a few 

 percentage points in MOR and IB in panels made from the same mix of flakes cut 

 from wood at 72°F. Another slight loss in values was discernible when knives 

 were allowed to become substantially dull. 



To evaluate the correlation between small- and large-panel properties. Price 

 (1978) fabricated 4- by 8-foot flakeboards using the prescription of Hse and 

 Koch\ At 46 Ib/cu ft, MOE values were comparable (table 24-12) to those 

 obtained by Hse and Koch; modulus of rupture and internal bond strengths were 

 also comparable. 



