Pressurized final steam conditioning

In New Zealand, to reduce final moisture content variation and drying stress it is standard practice to final steam condition the lumber at 100?C and 100 percent relative humidity. To assess the effectiveness of pressurized final steam conditioning, four matched series of radiata pine sample boards were dried at 160?C dry bulb and 100?C wet bulb then steamed for varying durations under pressure at 2.8 bars pressure (giving conditions of 130?C dry bulb and 130?C wet bulb). Effectiveness of steaming was assessed by measuring moisture pickup, moisture content gradient, and strain (using the McMillan strip technique). Compared to standard atmospheric pressure steaming, pressurized steaming was more rapid and gave more effective stress relief. One hour of pressurized steaming achieved at least as good a result as the current commercial practice of 3 hours of atmospheric pressure steaming for 40-mm-thick radiata. The improved steaming effectiveness was attributed to a more complete softening of the wood in the pressure steaming. Subject to no adverse thermal degradation, pressurized steam conditioning offers an effective means of rapidly eliminating dying stresses,. Work is currently being done to evaluate the effect of pressure steaming on mechanical properties as well as the benefits of pressured drying.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member