抄録
The high-temperature setting method, which enables rapid kiln-drying for square timber with pith, has spread in many saw mills in Japan. It has been supposed that obvious drying tension set, which is formed at the shell of timber without back-splitting, results in generation of sufficient compressive stress at the shell, and reducing surface checks significantly. In the paper, we investigated the differences in internal stress between indoor and outdoor storage with sugi (Cryptomeria japonica D. Don) square timber kiln-dried by the method. The compressive stress was expressed as released strain measured by the slicing technique. Main results were shown below.
- Strong compressive stress was observed at the shell of the timber which was stored indoor for five years.
- On the other hand, the compressive stress obviously decreased at the shell of the timber which was stacked outdoor and covered with a corrugated panel for six years.
- The compressive stress might be reduced by loss of tension set which was caused by moisture variation during long outdoor storage.
- The hygro-thermal recoverable component of set seemed to be melted, which had been assumed to be recovered only by boiling.
From the above results, the indoor storage had little effect on the compressive stress at the shell of timber kiln-dried by the method, but the outdoor storage decreased the surface stress. Further research is needed for explanation of the time-dependent change for practical uses. For practical outdoor uses, the risk of occurrence of surface checks might increase as time passes.
