Fundamental Studies on the Ball Mill Crushing

Abstract

The authors investigated the variation of crushing mechanism of a ball mill relative to mill speed, and found that crushing mechanism of the mill at 70 per cent of the critical speed was mainly represented by the impact compression. Whereupon they applied Eqs. (2)-(7)-relation between the crushing condition and the net work input to crushing by impact compression-to the ball mill crushing. By these Eqs., the authors' assumption on the effect of density, size and drop height of the ball on the capacity of the mill were proved to be nearly in accord with the expcrimental results.(a) The relation of the ball load to the capacity of the mill at the normal speed, i.c., 70 per cent of the critical speed, might be expressed by Eqs. (10)-(14). In case the total ball load is proportional to the weight of one ball at constant specific weight and constant number of balls, the relation is given by Eq. (10), but, when the ball load is proportional to the number of balls at constant specific weight and constant ball size, it is given by Eq. (11). On the other hand, in case the ball load is proportional to the specific weight at constant size and number of balls, it is given by Eq. (14).(b) The relation of the mill diameter to the capacity may be expressed by Eqs. (16) and (17). Of the two mills, having equal ball charge rate to the mill volume, but different diameters, the mill with the larger diameter has greater efficiency. So does the mill having the balls of smaller specific weight.