WOOD COMMINUTION AND MATERIAL FLOW IN A LABORATORY CHIP REFINER

Experiments conducted on a 12 in. Sprout-Waldron laboratory refiner we re used to characterize chip fracture, material comminution, and flow in a disc refiner. These experiments included high-speed video observa tions of chip fracture in the entrance zone of the refiner; tests with chips of uniform size to characterize comminution; stall tests bz whi ch material al different locations in the refining zone was observed; and tracer studies to measure the overall material residence time dist ribution in the refiner. We found that cracks induced in chips by the chipping process were vital to allow their rapid breakdown into coarse fragments during refining. We offer a new hypothesis to explain why m any of these fragments have rounded edges by observing that edges are more likely to be exposed to the grinding action of passing bars. We a lso propose that brooming of fragment ends may be a significant mechan ism for fibre separation. A theoretical analysis of the number of impa cts, refining intensity, and specific refining power was used to compa re the laboratory refiner with a typical pilot-plant unit This shows t hat the laboratory refiner cannot reproduce both the refining intensit y and specific refining power of a pilot-plant refiner and that a plat e pattern with a greater bar density would be necessary to allow this.