Influence of spreading rate and gluing pressure on PVAc glue joints effectiveness

The changes in glueline shear strength on European beech bonded with five polyvinyl acetate (PVAc) and one polyurethane (PU) adhesives at pressure levels of 0,15 N/mm2, 0,3 N/mm2, 0,5 N/mm2 and at three spread rates were evaluated. Spread rates were either the suitable one, either lower and higher than the suggested value; similarly, the press was set up to reach either the suitable gluing pressure, either lower and higher than the suggested value. All the possible "spread rate vs gluing pressure" combinations were tested. The specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal testing machine. Increasing of spread rate created stronger glue lines, and the magnitude was more evident comparing low spread rates with suggested. Best gluing results were obtained increasing spread rate. Gluing pressure had a lower influence than spread rate in glue lines strength, and results revealed values suggested by technical sheets and higher values were most of the time the best ones.