Effect of Low Vacuum Medium Temperature Drying on Reduction of Residual Stress and Correction of Warp of Japanese Cedar Timber

Abstract

Abstract In Japan, the increasing utilization of large-diameter logs has become an important issue, and effectively utilizing these logs has been a key topic of discussion. When producing timber-without-pith from large-diameter logs, unavoidable warp occurs due to the release of residual stress within the logs. And warp is the most serious processing problem compared to other factors as cracks. Warp can adversely affect the production efficiency and economic returns of the timber. Utilizing high-temperature drying with load to those timber has achieved significant drying effects, and residual stress-induced warp was corrected and maintained at the same level for up to six months after drying. However, high-temperature drying comes with drawbacks such as high energy consumption which connects to long treatment period and potential for thermal degradation. To achieve the same effect as high-temperature drying to correct warp, and to reduce residual stress, but with shorter treatment period and avoid thermal degradation, this study applied low vacuum medium temperature drying to large-diameter logs. Through this method, effective drying is achieved, residual stress is reduced and warp are corrected to a certain extent. Low vacuum medium temperature drying is practical as a drying method for timber from large-diameter logs because it is effective in reducing residual stress and correcting warping, while at the same time shortening the treatment period and avoiding thermal degradation.