Influence of radial force and rake angle on ring debarking efficiency of frozen and unfrozen black spruce logs

The effects of the radial force applied by a ring tip debarker and the rake angle on debarking quality of frozen and unfrozen black spruce logs were studied. A one-arm ring debarker prototype was built, which controlled the radial force, the rake angle, and the cutting and feed speeds. The experiment consisted of debarking logs using three radial forces for each temperature (- 20 degrees C and + 20 degrees C) with three rake angles (73 degrees, 80 degrees, and 87 degrees). The cutting and feed speeds were kept constant with a tip overlap of 20% and average tip edge radius of 78 mu m. Debarking quality was evaluated by two criteria: the proportion of bark remaining on log surfaces and the amount of wood in bark residues. Log characteristics, i.e. dimensions, eccentricity, bark thickness, knot features, bark/wood shear strength, as well as basic densities of sapwood and bark were measured. The radial force had a significant effect on debarking quality of frozen and unfrozen logs. The proportion of bark on log surfaces decreased but the amount of wood in bark residues increased as radial force increased. Thus, the radial forces of 18.9 N/mm and 18.2 N/mm were suggested for better removing frozen and unfrozen barks, respectively. In addition, the studied rake angles did not affect any of the debarking quality indicators for unfrozen logs. However, a tool with a rake angle of 87 degrees was better for removing bark of frozen logs without negatively affecting fiber loss. Regression equations were established in order to predict the optimal radial force and rake angle taking into account the log characteristics.