Continuous grinding in a small wet ball mill. Part V. A study of the influence of media shape

Abstract

The influence of change in grinding media shape on the grinding behaviour of trace quantities of quartz within an environment of calcite in a small continuous wet ball mill has been studied using steel spheres, cubes, long, short and equi-cylinders, and hexagonal “cylinders” Their dimensions were chosen so that a unit of each shape weighed the same as a one-inch sphere. Standard charges of 90.5 lb. of each shape were used. The results show that the shape of grinding media had a significant effect on both the first-order breakage rate constants ( k′) and the breakage function. Spheres had the most selective rate function (i.e. relatively high breakage rates for coarser sizes and low for finer), and cubes and cylinders the least selective. Breakage functions for cylinders and cubes indicated that these shapes produced fewer fines in any single breakage event than spheres or hexagons. Media shape had a marked effect on the average residence time of particles in the mill but little effect on the type of flow through the mill. Simulated grinds using the dynamic model of breakage and the appropriate experimentally determined breakage functions, rate functions and distributions of residence time showed that spherical media handled the greatest throughput and produced the most closely sized product.