Mechanistic modeling and simulation of a wet planetary ball mill

Abstract

The planetary mill is one of the most commonly used mills for ultrafine grinding in the laboratory, given its ability to reach higher intensity of the collisions as the result of increase in rotational frequency and ball acceleration without the undesired centrifugation of the grinding charge. Several attempts have been made in the literature to develop a predictive model of this mill, with limited success. The work applies the mechanistic UFRJ mill modeling approach to predict the size distribution in a laboratory planetary mill, on the basis of single-particle slow compression data obtained using a micro compression tester, besides simulations using the discrete element method. At first, careful verification of the Hertz-Mindlin contact parameters was conducted using a video recording system that moves along with the jar during milling. Grinding tests were conducted with hematite for the mill operating at frequencies that varied from 150 to 300 rpm, resulting in generally very good agreement between model and experiments. However, agreement between the two was found to reduce for the highest rotational frequency studied. This was attributed to the reduction in grinding efficiency in the experiments that was not observed in the simulations, which resulted in predicted values overestimating fineness of the product. Finally, simulations were compared to experiments for quartz, silicon carbide and blast furnace slag under identical conditions and it was shown that the model provided very good predictions, with the exception of quartz.