Since the beginning of the last century, many studies have been performed inudorder to improve our understanding on the milling process. Recently, Mishra andudRajamani (1992) applied the Discrete Element Method (DEM) to solve theudmilling problem. Since then, this method gained considerable success due to itsudability to predict load motion and power draw by tumbling mills as affected byudoperating conditions. The application of this method at an industrial stage requiresuda more rigorous validation in order to produce realistic output.udLifter profiles play a key role in the performance of tumbling mills since theyudinfluence the motion of mill charge. Since lifters change profiles during theiruduseful life due to wear, the performance of tumbling mills will correspondinglyudvary as a function of time. There is therefore a need to predict forces and wear onudmill lifters in order not only to chose or design an initial lifter profile whichudoptimizes tumbling mills performance over the lifters’ useful life but also toudevaluate lifter replacement time and type and also modifications which can beudperformed on lifters and/or operating mill conditions in order to extend the lifters’uduseful life. Despite the importance related to this subject, few works has beenuddone in this field.udIn this thesis, we firstly assess the ability of the Discrete Element Method toudmodel the tangential and normal forces exerted by the mill charge on lifters. Dataudfrom an experimental two-dimensional mill designed in order to record the normaludand tangential forces exerted on an instrumented lifter were available. Theudmeasured results obtained at different speeds and percentages of filling have beenudcompared to the Discrete Element Method simulated results in the sameudconditions. A good agreement has been found between the experimental and theudsimulated results in terms of toe, shoulder positions and amplitude of forces.ududAfter this validation of the DEM, we secondly assess the ability of this method toudpredict the wear of lifters in dry milling conditions. We derived a mathematicaludwear equation describing the removal of materials from lifters which takes intoudaccount all types of wear occurring in dry milling environment. We introduce audnew approach to implement this equation in the DEM code in order to produceudrealistic simulated profiles. Our new method developed has been tested againstudlaboratory and industrial data of evolving lifter profiles due to wear. Goodudagreement has been found between the simulated and the measured profiles.udThe variation of the load behaviour as a function of lifter wear in industrialudtumbling mills studied was also investigated in this thesis. The objectives were toudimprove the understanding of the grinding process and quantify the variation ofudload behaviour as a function of lifter wear. Lifter modifications were alsoudexplored in order to extend lifters useful life.udAn attempt was also made in this thesis to derive, from the description of the loadudbehaviour, equations in order to predict the wear of lifters without using theudDiscrete Element Method. Equations derived show the difficulty to use thisudapproach. Success in this case was achieved only in a particular case where noudsignificant changes occur in the load behaviour as a function of lifters wear. Thisudfinding confirms the DEM as the adequate tool to model forces and wear ofudtumbling mill lifters.udThe results obtained are of great economical significance since they can improveudthe profitability of mineral processing plants. A step forward in the use of theudDEM not only to design milling equipments but also to improve theudunderstanding, optimise and quantify the change occurring as a function of liftersudwear was achieved.
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