Applicability of Continuous Process Using Saturated and Superheated Steam for Boxed Heart Square Timber Drying

Abstract

This study aims to evaluate applicability for the continuous drying process using saturated and superheated steam for large-square timber. During drying of the boxed heart square timber, changes in moisture content were examined through the slices of the surface, inner and core layers. The results showed that there was a large moisture content difference between the surface and inner layers during saturated steam drying and between the inner and core layers during superheated steam drying. However, despite the moisture content difference between the layers, no surface check occurred, and an internal check occurred only near the pith or juvenile parts of the wood. The maximum value of the drying stress of the dried larch boxed heart square timber, calculated from the elastic strain of the slice and the tangential elastic modulus of the larch, was 1.30 MPa. The tangential tensile strength of the larch was estimated at 5.21 MPa under temperature and moisture content conditions when drying stress was at a maximum. That is, in the continuous drying process, the saturated and superheated steam did not generate a check in the surface because the drying stress of the wood did not exceed the tangential tensile strength. In further studies, the superheated steam drying conditions will need to be relaxed to suppress the occurrence of internal checks. Such studies would make the continuous drying process using saturated and superheated steam available for the drying of large-square timber.