Drying Sweetgum Veneer with Combinations of Impinging Hot Air and Microwave Energy

Sweetgum veneer utilized in the manufacture of crates and boxes is very susceptible to mold and decay if wet pockets remain after drying. These are due to differential drying rates between the highly permeable sapwood and the extremely impermeable heartwood. A combination microwave-impinging hot air drier was employed to investigate the drying behavior of 1/7-inch-thick veneers. Significant reductions in drying time were obtained using only impinging air jets at temperatures up to 400?F or with impinging hot air and microwave energy of either 1, 2.5, 5, 10, or 15 kW. Drying time to 15 percent moisture content (MC) was decreased from 17.1 to 4.4 minutes at air temperatures of 200?F and 3.5 to 2.1 minutes at 400?F with the addition of microwave energy of 5 or 15 kW, respectively. Besides shortening the drying time, the addition of microwaves at lower energies resulted in a satisfactory moisture leveling both within and between the veneer samples. Optimal moisture uniformity was obtained at a microwave energy of 2.5 kW. Higher energies decreased uniformity. If the veneer is held under restraint by rollers, veneer of acceptable quality, as based upon color, flexibility, and warpage, was obtained at all conditions tested.

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