Shrinkage of Western Hemlock Heartwood After Conventional and High-Temperature Kiln-Drying

Two groups of end-matched specimens of unseasoned 2- by 6-inch western hemlock (Tsuga heterophylla) dimension lumber and vertical-grain 2- by 6-inch clear lumber containing varying amounts of sinker heartwood were kiln-dried and equilibrated to 11, 6, and zero percent moisture content. Conventional (186?F) and high-temperature (230?F) schedules were used. Before kiln-drying, each specimen was surfaced on four sides to 1.7 by 6 inches, cut to 20-inch lengths, measured for width and thickness, and weighed. The measurement areas were given four classifications: normal (no sinker heartwood), streak, band, and sinker. Measurements and weights were recorded again after kiln-drying and equalizing. Specimens with normal heartwood shrank similarly with both schedules. High-temperature drying of streak, band, and sinker heartwood specimens produced greater shrinkage than conventional drying of matched specimens. Sinker specimens shrank least after kiln-drying, followed by band, streak, and normal specimens. Total shrinkage was nearly equal for the four heartwood classifications. Adjustment of measurements of shrinkage of the vertical-grain specimens to a 90? ring angle did not indicate any differences in total shrinkage except in 4 of 12 comparisons in the tangential plane.

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