Effect of using a hot-press to suppress surface checks in sugi boxed heart square timbers during the drying process

摘要

The high temperature drying method has become popular for drying sugi (Cryptomeriajaponica D.Don) boxed heart square timbers in Japan because it shortens the drying time and suppresses surface checks. However, it is well known that internal cracks and surface discoloration often occur in sugi boxed heart square timbers during the drying process. We investigated the effect of using a hot-press for suppressing surface checks in sugi boxed heart square timbers during the drying process. That is to say, the objective of this study was to reduce the damage of timbers during the drying process by shortening the high temperature drying time. The treatment for suppressing surface checks in timber is to form a surface drying set in it. This report presents the effect of using a hot-press for the formation of a surface drying set in sugi boxed heart square timbers. The results of this study are summarized below. (1) The inside of the sugi boxed heart square timbers showed almost no drying with this surface treatment. (2) Surface drying of the sugi boxed heart square timbers could be carried out uniformly with 30 min of hot-pressing with hardly any influence from the wide variations in moisture content. However, there was no good progress in drying over the 2nd layer under any of the test conditions. (3) Higher plate heating temperatures resulted in deeper heating in the sugi boxed heart square timbers. (4) In this surface treatment, the drying set was formed in the 1st layer under each test condition. However, in the 2nd and 3rd layers, the drying set was hardly formed. (5) In this study, two types of plates were used: a flat plate with a smooth surface and a slit plate with grooves cut into the surface to make it easier for it to release vapor. However in these results, the effect of creating slits was not apparent.