The purpose of this study was to determine flatwise and edgewise bending strength ("MOR") and stiffness ("MOE") of spruce and pine 1.5-inch by 3.5-inch by 48-inch laminated veneer lumber ("LVL") specimens parallel to grain. The experimental spruce and pine data was pooled together to give a combined spruce-pine data set.
Appendix 1 to Forestry Canada No. 35, Contract no. 1812L007 on
lumber and laminated veneer strength.
In part 1 of the present project, work was completed to show how deviations from recommended moisture content of the lumber, gluing surface preparation and gluing surface condition affect the strength and durability of the glue-wood bond for face and edge-glued laminates. In the final phase of the project, Part 2, edge- and face-glued laminates were prepared at two different moisture contents, 9 and 19% m.c. using the following three pressing methods: room temperature platen, hot platen and radio-frequency pressing. The laminates were evaluated to determine how deviations from recommended moisture content, assembly time, glue spread and platen pressure affect the strength and durability of the glue-wood bond. The study undertaken was intended to replicate the range of gluing practices seen in western Canada.
Cross-linked polyvinyl acetate (PVAC) adhesive was used to edge and face glue wood using the above three pressing methods and experimental variables.
As was found in Part 1 of this two year project, the moisture content of the wood had a substantial effect on the bond quality and delamination of both edge- and face-glued samples. Further, deviations from recommended manufacturer’s assembly time, glue spread or platen pressure resulted in poor bond quality or high delamination in many cases for the face-glued laminates. Of these four gluing and wood variables, moisture content had the greatest negative impact on bond performance while the other three gluing variables had about the same negative impact. The edge-glued laminates showed better bond quality and much more tolerance in gluing for deviations from recommended gluing practices.
At 19% moisture content (m.c.) all three pressing methods mentioned above showed a similar negative impact on bond performance for the face-glued laminates for a wide variation in the three gluing variables, assembly time, platen pressure and glue spread. For the edge-glued laminates at 19% m.c., there was a more severe impact on bond performance for the RF pressing method for a wide variation in the three gluing variables. At 9% m.c., all three pressing methods showed good performance for the edge-glued laminates for a wide variation in the gluing variables whereas for the face-glued laminates, each of the three pressing methods showed considerable negative impact on bond performance.
At 9% m.c. both the face- and edge-glued laminates made using recommended gluing conditions and three different pressing methods described above met the ASTM D1101, SKH NRP-7071 and JAS No. 112 standards specifications for delamination, shear strength and wood failure. However at 19% m.c., the face-glued laminates made using recommended gluing conditions failed to meet the delamination requirements in the ASTM D 1101 and SKH NRP-7071 standards for all three pressing methods.