Effect of the rotation speed on the size distribution of black spruce pulp chips produced by a chipper-canter

The effect of the cutterhead rotation speed of a chipper-canter on the size distribution of chips produced from black spruce (Picea mariana) logs was evaluated. Four rotation speeds were selected and the feed speed was adjusted to obtain the same nominal chip length of 27.5 mm for each condition. For each speed, 15 logs that were 152.4 mm in the small-end diameter were fragmented under frozen wood conditions (-15°C to -5°C) in winter and unfrozen wood conditions (11°C to 16°C) in summer. The chipper-canter was adjusted to obtain a cant that was 101.2 mm wide. The results showed that weighted mean chip thickness decreased from 6.65 mm to 5.67 mm in winter and from 7.30 mm to 6.16 mm in summer when rotation speed was increased from 546 to 783 rpm. The reduction in chip thickness resulted in an increase of acceptable chips (2 to 8 mm thick), a decrease of overthick chips (more than 8 mm thick), but an increase in fines, pin chips, and fragile or thin chips. However, the increase of these rejects was compensated by the decrease in the overthick fragments and by the benefits from the increase in the feed rate of the chipper-canter. Winter temperatures produced more fines, pin chips, and fragile or thin chips but increased the acceptable chips at the expense of the overthick fraction. These results provide the basis to estimate the changes in chip size within the range of the cutting speeds considered.