Drying and Impregnation for Heavy Timbers of Sugi Heartwood III ー Preservative Penetration Observed on Boxed-Heart Square Timber of Sugi, Dried with Either The High-Temperature Setting Treatment or The Medium-Temperature Drying Adding Radio-Frequency Heating ー

For the development of manufacturing technology of boxed-heart Sugi timber with appropriate preservative treatment, we have been examining the effects of the drying method before impregnation on the quality of the products with preservative treatment. We used boxed-heart Sugi timber from Nara and Oita which were treated either by medium-temperature drying, by a combination of medium-temperature drying and radio-frequency heating, by a high-temperature setting drying, or by a combination of high-temperature setting drying and radio-frequency heating. We investigated the penetration of the timber preservatives as well as the dimensional change before and after the impregnation. As a result, we confirmed that there were parts with insufficient penetration in boxed-heart Sugi timber from the above prefectures which were dried by a high-temperature setting treatment. Moreover, there were some cases in which such timbers had lower solution uptake and penetration ratio of preservatives than those that were dried with medium-temperature. Also, back split was necessary in order to prevent surface checks during drying process after impregnation and curing process. Lastly, using radio-frequency heating in addition to medium-temperature for drying before impregnation showed a possibility of producing materials without poor penetration, reduced solution uptake or penetration ratio in short time.