Gluability of platen-dried Douglas-fir veneer

Graduation date: 1981This study was undertaken to determine whether Douglas-fir (Pseudotsuga\ud menziesii (Mirb.) Franco) veneer could be platen-dried and then\ud sucessfully glued into two-ply parallel-laminated panels.\ud A range of veneer thicknesses, platen temperatures and final dry\ud moisture contents were examined. Thicknesses included were nominal\ud 0.1, 0.2, 0.3 and 0.4 inches; platen temperatures were 325, 375, 425\ud and 460°F. Drying of both sapwood and heartwood was carried out to\ud final moisture contents of either one, five or nine percent.\ud Gluebond quality was evaluated using shear strength and percentage\ud wood failure as criteria. Three aging methods were employed: none,\ud vacuum-pressure soaking and cyclic boiling.\ud The effective limit on subsequent gluability of platen-dried veneers\ud was found to be a function of both platen temperature and drying time.\ud Thin veneers (0.1 and 0.2 inch) typical of commercial plywood operations\ud were most gluable after drying at the lowest platen temperature\ud examined, 325°F. However, 0.4 inch thick veneers were best dried at a high platen temperature, 460°F, and had laminate shear strengths\ud equivalent to thin veneer panels.\ud Shear strength after vacuum-pressure aging appeared to be the best\ud method of performance evaluation of parallel-laminated platen-dried\ud veneers. Percentage wood failure was uniformly high for all veneer\ud thicknesses and platen temperatures. Shear strength was only moderately\ud predictable empirically; platen temperature and temperature x\ud drying time were the most important influences on subsequent mechanical\ud capacity.\ud Drying times to five percent moisture content varied from less than\ud one minute for 0.1 inch veneer at 460°F to approximately 20 minutes\ud for 0.4 inch sapwood veneer dried at 325°F.\ud Volumetric shrinkage after platen-drying at all temperatures at 35\ud psi and air drying at 425°F were approximately equal. Thickness shrinkage\ud was greater for platen-dried veneer, but tangential shrinkage was\ud lower