Charge behaviour and power consumption in ball mills: sensitivity to mill operating conditions, liner geometry and charge composition

Abstract

Discrete element method (DEM) modelling has been used to systematically study the effects of changes in mill operating parameters and particle properties on the charge shape and power draw of a 5-m ball mill. Specifically, changes in charge fill level, lifter shape (either by design or wear) and lifter pattern are analysed. The effects of changes to the properties of the charge (ball fraction, ball and rock shape, type of ball and rock size distributions and the lower cutoff of the rock size distribution) can all be interpreted in terms of their effects on the shear strength of the charge. Some changes increase the shear strength leading to higher dynamic angles of repose of the charge, higher shoulder positions and higher power consumption for sub-critical speeds. For super-critical speeds, they lead to lower power consumption, due to lower particle mobility as the particles lock together better. Changes to the charge that weaken the interlocking of particles have the opposite effect on the charge shape and power consumption. The combination of these effects means that the speed for which peak power consumption occurs is predominantly determined by the shear strength of the charge material and the fill level. This demonstrates the sensitivity of mill behaviour to the charge characteristics and the critical importance of various assumptions used in DEM modelling.