Discrete element modelling of lifter stresses in tumbling mill

The discrete element code PFC3D has been used to model lifter stresses within a large tumbling mill. The intensity of the induced stresses (shear and normal) is directly proportional to the intensity of lifting action and liner/lifter wear. Results show that, for the modelled case, the magnitude of the stresses decreases as the number of lifters increase. Hence, longer intervals between relining can be expected for a mill with a larger number of lifters. However, it appears that beyond a critical number, a further increase in the number of lifters will not result in significant further reduction of stress. Distribution of the impact energy is also affected by the number of lifters. With very few lifters, the dominant form of energy consumption will be low intensity abrasion events. With larger numbers of lifters, high intensity impacts will be more frequent. Net power draw will be at a minimum for very small numbers of active lifters. As the number of lifters increases, power draw increases and eventually reaches a relatively stable value. Further work will be required to investigate the effect of lifter shape on the induced stresses. It appears to be possible to determine the number and shape of lifters that will result in the optimal power draw, while simultaneously minimising liner/lifter wear.