Structural Flakeboards and Composites 2945 



for long periods (7 to 10 minutes) while intermittently placed spray nozzles 

 disperse a fog of resin comprised of the finest possible droplets. Liquid resin is 

 usually applied to southern hardwood flakes at rates of 4 to 7 percent, resin 

 solids basis, of the ovendry weight of the flakes. Figure 24-2 (top) depicts a 

 panel made of flakes on which resin has been uniformly applied in desired small 

 droplets. 



In 1980 the literature contained no in-depth studies of the technology of 

 applying liquid resins to flakes of the southern hardwoods on an industrial scale. 

 It is likely that industrial plants will incorporate 1.0 to 1.5 percent of water- 

 emulsified slack wax (based on ovendry weight of flakes) with the liquid resin. 

 This wax, a byproduct of oil refining, provides some short-term resistance to 

 water penetration into fabricated panels, and also may ease flake handling and 

 mat forming problems by lowering friction coefficients of flake surfaces. 



Liquid resin and its additives can be introduced into industrial blenders by air 

 spray, airless spray, or centrifugal distribution from spinning disks or tubes. 

 Airless sprays, operated at 600 to 800 psi, introduce less air into a blender than 

 air sprays, but have smaller nozzles which may clog and afford less turbulence 

 than air sprays. 



Long-retention-time blenders. — Long-retention-time blenders for liquid 

 resin are continuous-feed machines that approach the action of laboratory blend- 

 ers of the drum type. Flakes must be tumbled gently to minimize breakup and 

 production of fines, and must mix efficiently so all surfaces are exposed to resin 

 fog in a short time. Blender capacity of 5 to 8 tons per hour enables most 

 flakeboard mills to meet production requirements with three to five blenders. 

 The resin atomization system should avoid small-diameter orifices prone to 

 plug. In a blender designed by Nyberg and Beattie\ liquid resin is fogged 

 centrifugally within the blender from one or more 1 1 -inch-diameter disks driven 

 hydraulically at speeds up to 5,000 rpm (fig. 24-20). The 8- to 10-foot-diameter 

 drum, with anti-slip internal ribs, is continuously loaded with flakes to a depth of 

 1 or 2 inches and rotated at a speed at which the flakes cling to the surface of the 

 drum, but drop when near the top to repeat the cycle. Drum length is about 24 

 feet. 



Short-retention-time blenders. — Short-retention-time blenders which re- 

 quire only seconds, instead of minutes, to apply resin take little space, can be 

 adjusted quickly, and can be readily cleaned, have gained favor in the United 

 States. These blenders (fig. 24-21) feature a small-diameter short tube in which a 

 paddle agitator revolves at 500 to 700 rpm. Spray nozzles at the inlet end apply 

 resin to only a portion of the flakes, uniform distribution being accomplished 

 mainly by violent tumbling action during flake transit from inlet to outlet. The 

 blender illustrated in figure 24-21 (bottom) is 42 inches in diameter, 108 inches 

 in axial length, and is powered by a 75-hp motor. About 40 tons per hour 

 (ovendry basis) of flakes can be blended with resin and wax. Wilson and Hill 

 (1978) suggest that multiple short-retention-time blenders arranged in series 

 achieve better resin application than single blenders. 



^Nyberg, D. W. , and N. W. Beattie. 1980. Improved blending capabilities for waferboard. Paper 

 given at Canadian Waferboard Symposium, November 18-20, 1980, Ottawa, Canada. 



