Reducing Variability in Final Moisture Content of Kiln-Dried Western Hemlock Lumber

This study investigated presteaming of western hemlock lumber to minimize the nonuniformity of final moisture content. Presteaming from 4 to 24 hours and drying with conventional or high-temperature (above 212?F) schedules did not promote uniform drying. Schedules were developed for high-temperature (above 212?F) drying of 2-inch dimension lumber in 4, 6, and 8-inch widths. Total kiln time was reduced from zero to 19 Percent in drying 2 by 8-inch lumber, from 19 to 37 percent for 2 by 6-inch lumber, from 14 to 39 percent for 2 by 4-inch lumber, and 50 percent on 4/4 vertical grain shop lumber when compared to commercial schedules. Degrade was not increased and generally final moisture contents were more uniform with high-temperature drying. Lack of uniformity of final moisture contents is attributed directly to wet pockets or streaks in the heartwood. Segregation of sinker or heavy stock on the green chain can be accomplished with a high, degree of accuracy (about 98 percent). Through good segregation practices, the uniformity of final moisture contents would be improved and total kiln time would be reduced, because sinker stock represents a low percentage of the lumber production in given mill.

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