Stress-Based Kiln Drying of Gmelina arborea Roxb. Lumber
Wency H. Carmelo1, Ramon A. Razal2*,
Chrysline Margus N. Piñol3, and James Fuller4
1Forest Products Research and Development Institute,
College, Laguna 4031 Philippines
2Department of Forest Products and Paper Science, University of the Philippines Los Baños
College of Forestry and Natural Resources, College, Laguna, Philippines
3Institute of Mathematical Sciences and Physics,
University of the Philippines Los Baños College of Arts and Sciences,
College, Laguna, 4031 Philippines
4Fuller Drying Labs, Orange, Virginia 22960 USA
The study evaluated the kiln drying of 25-mm thick Gmelina arborea Roxb. lumber using conditions based on changing shrinkage rates following the procedure developed by Fuller under US Patent No. 5,873,182 dated 23 February 1999. For comparison, a separate kiln drying run was done following conventional, moisture content (MC)-based drying schedule. To monitor shrinkage, a linear variable differential transducer was mounted across a sample board that was coupled to a data acquisition system. Real-time shrinkage data was processed and the graph of dynamic shrinkage versus time provided information on peak stress, stress reversal and reduction of shrinkage rates. These transitions were taken as signals to advance kiln drying conditions to the next step prescribed in the MC-based drying schedule, which allowed prompt changes in kiln settings. The early transition in internal kiln drying conditions resulted to reduction in kiln drying time by 30 to 36%. The quality of the dried lumber was evident in the more uniform final moisture content distribution of the dried boards, less steep moisture gradient, and the absence of residual stresses in the boards dried in a kiln where changing shrinkage rates were used as basis for operation and control.
Drying is one of the most important steps in the processing of wood. The quality of finished products depends to a large extent on the moisture present in the wood at the time of manufacture. For fast wood drying with minimal drying degrade, proper kiln settings as well as appropriate kiln drying schedules (KDS) must be followed. . . . . read more
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