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UBC Theses and Dissertations

Schedule and post-drying storage effects on Western Hemlock squares quality Rohrbach, Katrin


This study intends to explore the effects of two drying schedules with options of conditioning and post-drying storage on the drying speed and quality of western hemlock timbers. Western hemlock (Tsuga heterophylla), the species of interest in this study, is one of British Columbia's most abundant tree species that accounts for 75 to 80% of British Columbia's exports to Japan. It is usually combined with amabilis fir (Abies amabilis) for processing and economical purposes. Hemlock is difficult to dry due to its compression wood, wetpockets and large spread of initial moisture content and basic density. Consequently, it seems practical to dry hemlock by itself. In this study, hemlock was dried using two different schedules with optional conditioning and optional seven day post-drying storage in a covered and climatized space. These eight experimental runs were compared to a control run, which utilized an established drying schedule. To assess the kiln dried timber quality, twist, diamonding, and checks were evaluated using pre-drying and post-drying and/or post-storage measurements. Drying times and casehardening were also considered. Data analysis and evaluation illustrated that conditioning and the harsher schedule reduced casehardening, while the milder schedule developed less twist and diamonding. Even though it appears that the control run developed less shape distortions than the treatment runs, the control run required longer drying times. When using the harsher schedule the kiln was immediately available for the next run, and the dried timber could be stored in a covered area in order to level out the moisture gradients and alleviate casehardening. As a subsequent step, the timber could be planed to reduce twist, diamonding and superficial checks.

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