Drying softwood in a vacuum dryer. A comparison of drying results in a vacuum drier and a conventional kiln

摘要

Drying quality of 75 x 150 mm Pinus Sylvestris lumber dried in a DWT vacuum dryer and a conventional drying kiln was compared. Two drying tests were made in the DWT dryer with drying programs suggested by DWT to average moisture contents of 17% in 105 h and 9.6% in 209 h. The conventional kiln dried the wood in 180 h to an average moisture content of 23.8%. Drying climate was registered by electronic thermometers in addition to the control systems of both the dryers. Condensed water and energy consumption in the DWT dryer were measured. Average moisture content, moisture gradient within the planks, standard deviation and systematical variation of moisture content between the planks were measured by dry sample tests after drying. Drying packages were weighed before and after drying. Remaining tension was measured by means of prong tests. Drying checks and quality degrade due to drying was determined through visual inspection. The average final moisture content of the DWT drying tests was 17% and 9.6% with standard deviations of 2.8% and 2.2% respectively. The conventional kiln showed a final moisture content of 23.8% and a standard deviation of 4.5%. Approximately 21% of the wood dried in the conventional kiln and of the wood dried to 17% in the DWT dryer was degraded due to drying defects, the degrading was mainly due to checking. The degrade of the wood dried to 9.6% in the DWT dryer was approximately 10%.