December 1999Volume 51 Issue 12
Millsoft -- simulation software for tumbling-mill design and trouble shooting
Mining Engineering, 1999, Vol. 51, No. 12, pp. 24-30
Rajamani, R.K.; Mishra, B.K.; Songfack, P.; Venugopal, R.
ABSTRACT:The mill power draft and grinding efficiency depend on the motion of the grinding charge and the ensuing ball collisions that utilize the electric power and cause particle breakage. The movement of balls and rocks in tumbling mills has been of interest since the beginning of the century when Davis (1919) first studied single ball trajectories. In the following decades, the profile of the cascading charge began to figure in mill power prediction. The effort was to locate the center of gravity of the cascading charge, so that the mill power could be calculated from a torque formula. Empirical correlations sprang up to calculate the mill power draft from design and operating parameters. Notable among them is Bond’s formula for mill power and maximum ball diameter (Bond, 1952, 1953). The formula for ball size takes into account the ore work index, mill speed and mill diameter, as well as the feed size of the ore. Based on plant data, Dunn (1976, 1989) modified this formula but maintained Bond’s key variables. Curiously, mill diameter and mill speed figure in the expressions, presumably in lieu of the impact energy produced in the ball mass. As will be shown, the underlying ideas in such an empirical formulation can be expanded via rigorous physics of the phenomena.
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