A study of charge motion in rotary mills, with particular reference to the grinding action

Abstract

The objective of this study was to develop a fundamental understanding of the action of the grinding charge in a mill, and to then correlate this with the metallurgical performance of different mill-liners. To achieve these overall objectives it was first necessary to develop suitable experimental techniques, and the development of these techniques became a large part of the objective of the study. The motion of balls deep within the charge of a rotary grinding mill was investigated. Novel investigative techniques were used to track the motion of the balls, including X-ray filming at 50 frames per second of both the front and side views of a transparent mill, and gamma-camera filming of a radioactive ball. Analysis of the trajectories of the balls revealed several phenomena in the milling action that have not been reported until now. It was observed that the paths of the balls are smooth, that they spiral in and out of the charge, and that the grinding does not take place by rotary nipping of the ore between the balls.