Using the dem to relate drop ball tests to semi-autogenous grinding

Samukute, Shwarzkopf Oliver
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The Drop Ball Test (DBT) is a common quality control procedure used in many grinding media-manufacturing units to evaluate the quality of manufactured balls by subjecting a sample to an impact fracture test. Whilst DBTs have provided reasonable data over many years, the quantitative comparison of the energy that the balls are subjected to during the DBT and in high impact loading environments such as Semi-Autogenous Grinding (SAG) mills remains a grey area. The Discrete Element Method (DEM) is a numerical technique that can provide a much more detailed description of the grinding media collision behaviour in both DBTs and SAG mills. The DEM allows simulation of the collision behaviour in various systems that involve interaction of many particles. The DEM model applied in this work uses a spring-sliderdashpot to calculate contact forces and the net resultant is used to compute acceleration, velocity and distance moved by the particles by applying Newton’s laws of motion. The objective of this work was to quantify the energy that grinding balls are exposed in both the DBT and SAG environments. Using the DEM, simulations where conducted in both environments to evaluate extent of ball impact loading. The impact energy spectra obtained from the DEM simulation of various ball sizes in the DBT was used to quantify the energy the balls are subjected to. The data showed that larger 125mm steel balls are exposed to relatively higher energy levels and have higher probability of fracture than smaller 115mm and 100mm balls. From the SAG mill simulations, ball trajectories were evaluated to determine the energy that the grinding media is exposed to. Increasing ore:ball ratios showed the extent of ore cushioning and reduction in energy that the balls are exposed to. Using the DBT data and DEM impact energy spectra obtained from both the DBT and SAG simulations, empirical models were developed that attempt to predict ball fracture in the DBT and try to relate ball fracture in the DBT to ball endurance in the SAG environment. A reasonable estimation of the energy that the balls are exposed in both the DBT and SAG mill was achieved. However, establishment of simulation parameters that specifically apply to the material of ball construction is recommended for future studies. From the results analysed, it was concluded that a more accurate determination of simulation parameters of the specific material of construction has the prospect of achieving improved ball fracture predictions
A dissertation submitted to the Faculty of Engineering and Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science, Johannesburg, 2019
Samukute, Shwarzkopf Oliver (2029) Using the dem to relate drop ball tests to semi-autogenous grinding,University of the Witwatersrand,