Technical and Economic Considerations in the Platen Drying of Aspen Sapwood and Paper Birch Cut-Stock

Describes experiments on drying of aspen sapwood and paper birch in a 26 inch by 26 inch steam heated single opening hot press. Steel cauls were used between the platen surface and the wood surface; however, ventilated cauls or screens were not used. Maximum platen temperatures were 340?F. Aspen sample thicknesses ranged from 3/4 inch to 1-1/4 inches and birch sample thicknesses ranged from 1/2 inch to 1 inch. Drying times were determined by measuring the internal temperature of the specimen and extending the drying until the internal temperature rose to within 3?F of the platen temperatures. Aspen was found to be subject to drying defects in certain zones of the specimen, however birch dried defect free. Differences in moisture permeability in different portions of the aspen specimens are suggested to account for the drying defects. Fairly detailed production and cost analyses are given for aspen cut-stock and for kiln-drying production of aspen lumber. A comparison is given of estimated costs of drying aspen cut-stock by kiln-drying and by platen drying. It is concluded that platen drying of these species is technically feasible. No end defects developed during the drying, permitting drying stock of final length dimensions. Drying time for 4/4 green aspen was reduced from 10 days (kiln dry time) to 131 minutes for platen drying. Sample thickness had a pronounced effect on drying time. Below the 63 percent yield level, platen drying of 3/4 inch aspen is less costly than kiln-drying. Platen drying may have an economic advantage for highly permeable woods.

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