Using variable glue spread rates to control bond quality and reduce glue consumption in pine plywood production

This study is a follow-up to research conducted on the use of glue application rate to control gluebond formation in southern pine plywood. The thrust of research in the past has been to modify the resin and/or glue mix to tolerate the broad range of material and manufacturing conditions that affect plywood bonding. The objective of this study was to further investigate the use of glue application rate to influence bond formation resulting in improved bond quality and reduced resin consumption. Test panels were manufactured in a full factorial experimental design with three levels of veneer roughness, three levels of veneer moisture content, three levels of veneer temperature, two levels of assembly time, and two glue application rate strategies. With each combination replicated, a total of 216 test panels were made and tested using the standard vacuum/pressure soak test. The results show that the variable application rate strategy (VARS) yielded 8.3 percent higher average wood failure than the constant application rate while using 13.1 percent less glue mix. Expanding the range of application rates for VARS compared to the previous study improved its effectiveness in dryout conditions. VARS can effectively extend the range of tolerable gluing conditions to produce acceptable bonds while significantly reducing glue consumption. VARS was especially effective in eliminating the detrimental effects of veneer roughness on bond quality. The improvements of the VARS schedule used in this study suggest that further studies may yield improved results over this schedule. It would be cost effective to use a response surface experimental method that would produce data to be used to model the bond formation process. The models can be used to develop optimized equations for wood failure and glue consumption depending on the objectives of the manufacturer.