Drying of Veneers in a Fluid Bed

African mahogany (Kha a ivorensis), European beech (Fagus sylvatica) , and obeche (Triplochitron scleroxylon) veneers 1/16 and 1/6 inch in thickness were dried in a fluid bed or a platen dryer. The samples dried in the fluidized bed were 9 by 9 inches and those in the platen dryer 9 inches by 4 feet. The temperature of the fluidized bed was varied from 150? to 175? to 200?C. The temperature of the platen dryer was 155?C. Twenty samples were run for each combination of variables. Particles used in the fluidized bed were silicone-coated glass balls 0.2 to 0.3 millimeter in diameter (called ballotini), or washed river sand approximately 0.3 millimeter in diameter. Air pressure of 2 pounds per square inch introduced from the porous tile at the bottom of the bed caused the ballotini to be fluidized. A pressure of 5 pounds was needed to fluidize the sand. Thermostatically controlled electrical resistance heaters inserted in pockets through the sides of the bed and over the porous tile bottom controlled the temperature of the bed within .5?C. (?F.). In early trials the ballotini stuck to the green veneer and reduced heat transfer. To overcome this, wire brushes were moved over the surface at a rate of six double strokes per minute. The brushing procedure has been patented (provisional Patent No. 37,812). The sand did not adhere to the veneer and did not need to be brushed. Results of drying in a fluidized bed show that the brushed ballotini gave the fastest drying with slightly longer time for the unbrushed sand and the slowest drying with the unbrushed ballotini. A comparison of the time required to dry veneer to 8 percent moisture content in a fluidized bed with brushed ballotini and a platen dryer both at 155?C. (311?F.) showed that the fluidized bed required about one-half as much time. The authors conclude that the fluidized bed has promise as a commercial means of drying veneer.

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