Optimum veneer peeling temperatures for selected softwood species using big roller bars

Driven by the need for productivity and recovery, rotary veneer peeling for softwood plywood manufacturing has changed from the use of a small 5/8-inch (15.88 mm) diameter roller bar to a big roller bar with diameter ranging from 2.50 to 3.75 inches (63.50 to 95.25 mm). This study focused on the effects of conditioning temperature on veneer quality using a big roller bar. A 4-ft (1.22 m) pilot plant rotary lathe consisting of a 3-inch (76.20 mm) diameter roller bar was used to peel a total of 130 logs. The peeling study was conducted on three commonly used conifers, namely, western white spruce, lodgepole pine and Douglas fir. The laboratory results indicated that increasing log temperature led to increase in veneer surface roughness and thickness variation, but decrease in lathe checks. The optimum log temperatures under the slow-speed laboratory peeling condition were 85–100°F (29–38 °C). Considering knife wear, lathe vibration and fast peeling speed, the optimum peeling temperatures for typical softwood plywood mills were found to be 85–95°F (29–35 °C) for spruce, 95–100°F (35–38 °C) for lodgepole pine, and 110–120°F (43–49 °C) for Douglas fir. These temperatures were significantly lower than 130°F (54 °C) previously suggested based on a small roller bar. The results of this study have been widely implemented by the Canadian softwood plywood industry with confirmed benefits of energy-saving and veneer quality improvement.