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Drying and equalization of western hemlock to Japanese equilibrium moisture content Wallace, John Wilkes

Abstract

Density sorted, matched-samples of Western hemlock {Tsuga heterophylla (raf.)[SargP were dried in three different drying technologies in order to quantify the physical changes of kiln dried wood when exposed to the equilibrium moisture contents of a typical Japanese winter. Moisture sorption and desorption was monitored for 14 weeks by sampling board weight, dimensions, shell and core moisture contents and warp. All three technologies, a conventional kiln, a radio frequency vacuum kiln and a superheated steam vacuum kiln are capable of drying to a target average moisture content of 19% at the core with acceptable standard deviation. Product quality was good with all three drying technologies. The difference of 7% in equilibrium moisture content between Tokyo and Vancouver is large enough to elicit a response in shell moisture content, dimensions and warp. However, the responses found should be expected when wood is examined in context of its natural variability. Drying Western hemlock to 19% moisture content at the core should be considered the maximum target MC. A target MC of 15% moisture content at the core would optimize the drying time and stability as the lumber is equalized to Japanese conditions.

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