This report addresses issues about productivity, recovery and quality concerning veneer peeling in plywood mills. It was demonstrated that green veneer can be composed using a stitching technique. The maximum stitching speed was 50 ft/min which was slower than a current veneer composer. Stitched veneer did not have a significant effect on bending properties, but shear strength was slightly reduced which could be caused by the existence of stitching threads between the glueline.
The roller bar diameter size had a significant influence on veneer quality. In general, peeling veneer with a 1” diameter roller bar resulted in the smoothest veneer with the most uniform thickness. The veneer thickness and roughness between 1.0” and 2.56” diameter roller bars were significantly different, but the difference in veneer quality between 1.75” and 2.56” diameter roller bars was not significant. Further, the difference in veneer quality between 1.0” and 1.75” diameter roller bars was not significant except for veneer roughness.
Knife height also had a significant effect on veneer quality. Setting the knife at the spindle center proved to be the best. Veneer thickness at this setting was consistently closest to the target, and had the smoothest surfaces and smallest lathe checks. Average veneer thickness was lowest as well. While higher or lower settings created rougher veneer, higher settings were more forgiving than lower ones. For best results, the peeling knife should therefore be set at 0.0” to 0.015” above the spindle center.
Incisor teeth pattern affected veneer quality. Narrower teeth and a wider gap resulted in better veneer quality in terms of veneer curl-up (flatness) and green and dry veneer thickness variations. However, the effect of incisor teeth patterns on veneer roughness and lathe checks seemed to be negligible.
The validation tests revealed that an optimum lathe setting for the smooth roller bar was the following: pitch angle (PA) =89.50, vertical gap (VG)=0.425” and horizontal gap (HG) = 0.1”, and the optimum lathe setting for the incisor bar was the following: PA=90.50, VG=0.388” and HG=0.1” to 0.11” when peeling 1/8-inch veneer.
The peeling computer program VPeel® was successfully upgraded to allow users to define profiles of pitch angle and horizontal gap. This feature will help the veneer product industry to define optimum lathe settings.