A three-dimensional analysis of media motion and grinding regions in mills

Arising from the collection of numerical routines (validation toolbox) developed for validating discrete element method (DEM) predictions of charge motion in grinding mills, a range of rigorous charge analysis techniques have been developed. These provide descriptors of the motion and grinding regimes in a mill that hitherto have not been presented in the literature. To make the analysis meaningful, the descriptions of the charge motion were expressed as mathematical relationships that are applicable over the full range of charge motion that can be experienced in a rotary mill. iginal division of the charge using the concept of the equilibrium surface, as proposed by Powell and Nurick (1996) [A study of charge motion in rotary mills. Part 1 – Extension of the theory. Miner. Eng. 9 (2), 259–268], has been refined to provide a surface that can be analytically derived from positional data. From this the position of the centre of circulation (CoC) of the charge can be objectively determined. The rate of circulation of the charge is calculated from knowledge of the position of the CoC. Improved techniques are presented for determining the shoulder and toe positions of the bulk charge. Plots of velocity, acceleration, interaction force, frequency of passing through a particular region, etc. can be expressed as a function of position in the mill. h a consistent analytic characterisation of the charge, the influence of varying the operating conditions on the motion of the charge and the formation and intensity of different grinding regimes can be derived. This paper presents the methods to perform such an analytic characterisation and discusses how they may be used to improve milling efficiency.