Effects of cutterhead diameter and log infeed position on size distribution of pulp chips produced by a chipper-canter

摘要

Effects of cutterhead diameter and log infeed position on the mechanism of chip formation and size distribution of black spruce chips produced by a chipper canter were evaluated. Two cutterhead diameters (448.7 and 661.5 mm) combined with three infeed positions or vertical distance from the cutterhead axis to the bedplate on which the log was supported, were tested. The mean angle between the chipping rake face with respect to the grain (mean attack angle) was calculated for each infeed position. The nominal linear cutting speed was fixed at 23.5 m/s. Rotation speed and feed speed were adjusted to obtain a nominal chip length of 25.4 mm. Ninety-six logs were transformed under frozen and unfrozen wood temperatures. The high-speed images showed that the attack angle and temperature of logs (frozen and unfrozen wood) played an important role in the mechanism of chip formation. Within a knife cut, the images also showed that chip thickness was mainly defined by radial-longitudinal and in a lesser degree by tangential-longitudinal splitting ruptures. Furthermore, chip size distribution was also affected by the cutterhead diameter, attack angle, and temperature condition. Mean chip thickness decreased as attack angle increased for both cutterhead diameters, regardless of wood temperature condition. Further, frozen logs produced thinner chips than unfrozen logs (regardless of the cutterhead diameter and/or attack angle). The maximum amount of pulpable chips was produced during the fragmentation of unfrozen logs at the greater attack angle for both cutterhead diameters. These results give useful information to estimate changes in chip size distribution that could occur within the studied range of infeed positions (or attack angles) and cutterhead diameters.