Hybrid kiln drying system with radio frequency heating for hinoki boxed-heart timber with round edges

To avoid the formation of checks during the drying of hinoki (Chamaecyparis obtusa Endl.) boxedheart timber with round edges, a comparative investigation on the kiln drying and the hybrid drying, the high temperature and low humidity (HT/LH) treatment stage combined with radio frequency (RF) heating, was carried out in this study. The results showed that the hybrid drying could effectively prevent the occurrence of both surface checks and internal checks in the hinoki boxed-heart timber with round edges. Moreover, the hybrid drying time was significantly shortened to 15 hours. The combination of RF heating at the stage of HT/LH treatment resulted in at least following beneficial consequences: reduction of the surface temperature decreasing, attenuation of the tensile stress, promotion of the internal drying, relaxation of the moisture gradient, and inhibition on the extreme drying stress. Therefore, a wood drying strategy with high speed, free of both surface and internal checks could be realized through hybrid drying.