Automated condition monitoring of mill ball size distribution and grate open area

Abstract

Grinding media in coarse grinding tumbling mills constitute the biggest consumable cost to a comminution processing plant, therefore it is critically important to minimize associated wear. Secondly, efficient grinding is dependent on tight control of the desired ball size distribution, or else optimum impact breakage cannot be assured. Despite the significance of minitoring ball size distribution for mill operation, no practically deployable systems are currently in industry use to measure it. This paper describes a new method for highly accurate, comprehensive, and rapid determination of ball size distribution.Accurate SAG and AG mill product size control is dependent on appropriate Grate Open Area dimensions. Wear of the grate hole edges or in the plate thickness results in an increase of the open area due to the tapered hole cross section, which can result in oversize product exiting the mill. Conversely, some grate castings feature peening of the edges during mill operation, thereby decreasing open area, and therefore preventing the desireed top size product from exiting the mill.SAG mill throughput requires grate holes to remain open or else throughput is restricted. Many grates in operation are pegged by grinding media to varying degrees of severity. This paper introduces a comprehensive, accurate and rapid method to measure and track the size and pegging status of each and all grate holes in situ, and therefore provides tracking information on the Open Area of a SAG mill. This enables operators to control the primary mill product size and therefore the opportunity to stabilize downstream processes.