Suthon Srivaro, Taweesin Wongprot, Nirundorn Matan, and Buhnnum Kyokong

pp. 475 - 483

Abstract

Lumber drying is the most energy and time consuming process within the rubberwood lumber industry. The aim of this study was to develop an effective drying schedule for rubberwood lumber by accelerating the moisture movement out of lumber without degrading the lumber during drying. The study explored the effect of dry bulb temperature (60°C, 75°C and 90°C), steaming at the beginning of drying, predrying of lumber prior to drying, and top loading of lumber on the drying characteristics and lumber quality (bow, crook, twist, end splitting and color) of 30mm thick rubberwood lumber under the target EMC at 4% and air velocity of 4m/s. Accelerated conventional temperature drying of lumber at 90°C reduced the
drying time by ~50% from 117 hours to 54 hours but increased the energy consumption by 22% with respect to the conventional temperature drying at 60°C. The average activation energy for drying was 26 kJ/mol. Drying temperature had very little effect on quality of lumber after drying (bow, crook, twist, end splitting and color). Steaming at the beginning of drying
and predrying of lumber prior to drying reduced and increased the percentage of end splitting, respectively. A top load of about 300 kg/m² slightly decreased twist. Drying at higher temperatures produced more casehardening within the lumber but conditioning at higher temperatures was more effective in releasing the residual stress generated by drying. After conditioning at high temperatures prong of less than 0.5° casehardening was obtained.