EFFECTS OF FRACTIONAL BALL FILLING OF A VIBRATION MILL ON THE RATE OF GRINDING - RESULTS OF NUMERICAL-ANALYSIS OF BALL MOTION

The effects of fractional ball filling on the behavior of balls and their collision characteristics in a vibration mill were investigated by image analysis with a video recorder as well as by a numerical calculation method called the "discrete block method". It was made clear that an increase in fractional ball filling causes an increase in frequency but a decrease in average intensity of ball collisions, and that it results in acceleration of the circulation speed of the balls in the reverse direction to that of circular vibration of the mill. A good correlation independent of vibration conditions and fractional ball filling was obtained between the rate constant of grinding determined by grinding experiments with glass beads as a feed material and the effective crushing collision frequency of balls calculated by the simulation and defined as the frequency of ball collisions whose intensity is greater than the strength of feed particles. From these results, it was made clear that there is an optimum fractional ball filling, depending on the strength of the feed materials and vibration conditions of the mill, that maximizes the rate of grinding.