Predrying Before Press-Drying to Reduce Drying Defects in Hardwoods

A major technical problem in press-drying hardwood lumber from the green condition is the nearly certain occurrence of major drying defects. A new approach is suggested in this paper where low-temperature predrying entire boards is followed by manufacture into clear cuttings and then press-drying these cuttings to the desired final moisture content (MC). With this technique, quality can be maintained with accompanying reductions in energy consumption and drying time. One-inch-thick red oak, pecan, hickory, yellow-poplar, and soft maple were manufactured into clear cuttings in the green condition and press-dried to 7 percent MC. The second half of the experimental material was predried at 85?F to 25 percent MC as entire boards and then manufactured into cuttings and press-dried to 7 percent. A large number of defects–collapse, surface checking, and honeycomb–developed in lumber press-dried from the green condition. Pre-drying to 25 percent MC before press-drying maintained quality over press-drying from the green in all species. Red oak and soft maple cuttings were good enough to be suitable for any use. With this process, drying time from 25 to 7 percent MC can be reduced from a matter of days in a kiln to less than 1 hour in a press, and quality can be maintained.

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