Optimizing the mill lining and the grinding media in tumbling mills

The grinding mill is probably the most common unit operation in mineral pro cessing. There is, however, much that can still be done in the way of optim ization. This paper discusses the results of a well-controlled pilot-scale test in which the performance of a tumbling mill equipped with a convention al rubber lining and lifter bars was compared to a tumbling mill equipped w ith a smooth rubber lining of the magnetic type. The results indicate that the smooth lining is about 14% more effective with respect to energy consum ption. By optimizing the size of the grinding media, the mill capacity can be increased in many grinding operations. In this specific case, grinding w ith a-20-mm ball charge required 26% less grinding energy than grinding wit h a-30-mm ball charge. The energy savings can, in most cases, be converted to an increase in capacity. The wear of the grinding media is difficult to assess over a short test period, bur the results suggest that the wear is s omewhat less when a smooth lining is used. A determination of the weal of t he linings was not included in this study, but it is generally accepted tha t the use of magnetic linings reduces the lining costs dramatically. Comput er simulation using the Millsoft code developed by Mishra er al. confirms a nd explains the increased effectiveness of comminution when a smooth lining and smaller grinding balls are used.