Effect of Prefreezing on Press-Drying of Black Walnut Heartwood

A hot press was employed to evaluate the possibly beneficial effect of prefreezing on walnut heartwood boards to be high-temperature dried. High-temperature drying has been shown to save both time and energy. One-half- and one-inch walnut heartwood boards, prefrozen at -10?F, and unfrozen controls, were press-dried at either 2500F or 300?F, and at 50, 100, or 150 pounds per square inch of pressure. Freezing prior to press-drying significantly reduced thickness shrinkage, depth of collapse, and number of honeycombing checks. The benefits of prefreezing were more pronounced in 1-inch than in 1/2-inch boards. Temperatures higher than 250?F and pressures greater than 50 pounds per square inch adversely affected most of the drying characteristics observed. Therefore, press conditions of 250?F and 50 pounds per square inch are the maximums at which you can still receive the benefits of prefreezing walnut heartwood boards without the adverse effect of higher temperatures and pressures.

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