Investigation of the mechanisms responsible for high speed impact crusher performance

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This thesis is an appraisal of developmental work done on an impact crusher. This work covered spans of contributions from a few student projects, whose data is used to evaluate the performance of impact crusher. To do this some drop weight tests were done on two material types, quartz and limestone. Milling kinetics studies were also done on these two materials in a batch ball mill to determine the breakage and selection function. DEM simulation was used to evaluate and compare ball milling crushing mechanism with that of single rotor impact crusher under various operating conditions: rotor speed and feed size distribution. The results showed crushing or grinding rate increased with rotor speed, as well as the number of repeated passes to re-crush the product. This naturally suggested an improved design by introducing an additional rotor to correspond to two passes on each batch test. To evaluate the design prior to building the re-designed crusher, discrete element method (DEM) simulation was done to generate the data that was used to compare the current design (single-rotor) with the new (double-rotor). According to DEM simulation output, the double rotor crusher has a potential to more than double the performance at relatively lower rotor speed as it shifts the impact energy spectra into more effective breakage region.
A dissertation submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2022