A Developmental Study of Drying System Applying RF-Heating/Vacuum Method to The Boxed-Heart Heavy Timbers Like Logs.

在日本，杉经常被用作原木或方柱的箱心木材.由于心材横截面大，咏叹调大，很难在短时间内干燥。这与干燥成本的增加有关。并且，由于收缩各向异性的存在，杉心材在干燥过程中容易产生严重的龟裂。RE/真空干燥法是一种快速、无缺陷的干燥方法。本研究对经稀土/真空干燥的原木和箱心方材及其与热处理或发汗干燥相结合的干燥方法进行了内应力和干燥永久变形的测定。通过这些调查，情况变得清楚如下。(1)RE/真空干燥法干燥的杉木原木，当干燥后横截面上的水分分布趋于均匀时，应力表现为较大的张应力。通过80 ℃热处理1天，这些大的拉应力在表面层消失，表面裂纹得到改善。(2)采用窑干与真空干燥相结合的干燥方法，改善了箱心方材的干燥时间和表面缺陷。表面裂纹减少的原因之一似乎是窑干前阶段所作的干燥装置。(3)通过蒸腾干燥，只有液材的含水率降低。因此，在真空干燥过程中，箱心方材横截面外侧的含水率比内侧的含水率低，表面裂纹减少。

In Japan, sugi is very often used as a boxed- heart timber of log or square column. It is difficult to dry these timbers in a short time, as having a big cross section and large aria of heart wood. It connects with the increase of the drying cost. And the severe checks occur easily for the boxed heart timbers of sugi during drying , because of anisotropic shrinkage. RE/vacuum drying method is wellknown for an effective means of rapid and checkless drying. But When the moisture distribution became approximately uniform after drying, surface check often occurred.In this research, measurment of internal stress and drying set was performed on the sugi log and boxed-heart square timber dried with RE/vacuum method and it's combination with heat treatment or transpirational drying. As a result of these investigations, it became clear as follows. (1) These stresses of Sugi logs dried with RE/Vacuum method were relatively large tension , when the moisture distribution in the cross section became approximately uniform after drying. By the heat treatment of 80ﾟC for 1 day, these large tensile stresses at the surface layer disappeared and surface checks were improved. (2) The conbination method of kiln- drying and RE/Vacuum drying improved these drying time and surface check for the boxed-heart square timbers. It seems that one of the reason for surface check decrease is drying set made at the former stage of kiln- drying. (3) By the transpirational drying, moisture content of only sap wood was decreased. So the moisture contents of outer part in the cross section of the boxed-heart square timbers became approximately lower than inner part during RE/Vacuum drying, and surface checks were decreased comparing with untreated.