Effects of high-temperature and low-humidity treatment on the drying characteristics of Mongolian pine boxed-heart square timber

Appropriate high-temperature and low-humidity (HT-LH) treatment conditions can improve drying quality of Mongolian pine (Pinus sylvestris var. mongolica Litv) boxed-heart square timber. In this study, the timber with a cross section of 120 mm × 120 mm was first steamed at 95°C for 12 h, followed by HT-LH treatment at various temperatures (105-135°C) and durations (6-12 h). The effects of treatment temperature and duration on the moisture distribution, temperature distribution, drying rate, stress and drying checks were investigated. The results indicate that at temperatures up to 120°C, increasing the temperature and the treatment duration effectively enhances the drying rate during HT-LH treatment but reduces the drying rate in the subsequent conventional drying stage. Steam treatment mainly modified the spatial distribution of moisture content without significantly changing the overall moisture content, thereby improving moisture uniformity in the timber. Surface checks were poorly suppressed when the surface temperature did not exceed 100°C during HT-LH treatment. HT-LH treatment at 120°C for 10-12 h effectively suppresses surface checks in wood, however, HT-LH treatment induces severe internal checks.