Drying characteristics of log cross sections of Japanese cedar during hybrid kiln drying combined with dielectric heating

This study was carried out to investigate drying times, residual drying stresses, and drying defects during the hybrid kiln drying combined with dielectric heating (hybrid kiln drying) of 50-mm-thick log cross sections (LCs) of Japanese cedar. Compared to the drying times of the controls and the E-S1s in which sapwood zones of both sides of cross section of them were end-taped with one sheet of Japanese traditional paper, a longer drying time was required for the E-S2/H1s in which sapwood zones of them were done with two sheets of Japanese traditional paper and heartwood zones done with one sheet of it within a LC. For all of the end-taping treatments without formation of V-shaped cracking, the residual drying stresses along tangential direction in the bark side were lower than the tensile strength perpendicular to grain of Japanese cedar. The final MCs of the circumferential slices cut from the control, E-S1, and E-S2/H1 were so even in the range of 11.4% MC to 14.4% MC. The E-S2/H1s could be dried without any drying defects, while fine checks were found on the heartwood zone of the E-S1s, and especially, the controls were defected by severe heart checks and V-shaped cracks, and fine border checks.