Press-Time Reduction By Preheating and Strength Improvement By Finger-Jointing Laminated Vaneer Lumber

Six-ply laminated-veneer-lumber (LVL) specimens were fabricated from finger-jointed, 1/4-inch (0.64 cm) rotary-cut western hemlock veneers using phenol-formaldehyde resin. The adhesive used for the finger-joints was phenol-resorcinol formaldehyde. Finger-joints were located at midspan in the outermost (tension and compression) laminae, and in a stepped fashion in the four inner laminae. The LVL Specimens had about 16 and 25 percent greater MOR and MOE, respectively than LVL specimens fabricated with unbonded butt joints. The effects on bending strength and bond quality of LVL made from preheated veneers were investigated. Variables included pressing time and platen temperature. MOR values did not vary significantly between platen temperatures of 178? and 204?C, nor with pressing times ranging from 8 to 14 minutes. Greater MOE values were obtained at the higher temperature, due to lower MCs and SGs of specimens pressed at this temperature. Shear strength values did not differ significantly between the two platen temperatures but did vary significantly with pressing time, increasing up to 10 minutes for pressing times. The average wood failure values obtained in both dry and wet shear test conditions were greater than the specified minimum value of 80 percent. Wood failure was better than shear strength as an indicator of the effects of temperature and pressing time on the bond quality of LVL specimens. Preheating the veneers resulted in a considerable reduction in required pressing time, with pressing schedules similar to those used in commercial plywood manufacture producing adequate bonds.

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