Surface shrinking and swelling behavior of boxed-heart timber of sugi (Cryptomeria japonica) during drying using high temperature setting treatment
2018
Toba, K. (Forestry and Forest Products Research Institute (Japan)) | Kobayashi, I. | Yamamoto, H. | Kurita, S.
The purpose of this study is to investigate the temporal changes in the surface dimensional behaviors of the boxed-heart timber of sugi (Cryptomeria japonica) during drying processes. Tangential surface strain was continuously measured during drying schedule which consisted of eight hours of steaming, 24 hours of high temperature setting treatment, and the following steam drying. Decreasing trends of surface strain were always found both in a few hours immediately after the beginning of steaming and steam drying. Especially, the drastic shrinking was found in the samples with flat square of sawing pattern (-0.7% on average), while the samples with square of sawing pattern showed smaller one (-0.2% on average). These drying shrinkage were considered to be progressed only in the surface of timber, because their average moisture contents showed almost constant values. On the other hand, some increasing trends were found in the latter period of steaming and the beginning of high temperature setting treatment. Large scale of surface strains with more than 0.1%, which was difficult to explain by the thermal expansion and releasing of residual stresses, is considered to be due to the effects of the prelude of surface cracking.
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