Study On Experiment And Simulation Of Charge Motion In Ball Mills

Main problems of ball mills such as low grinding efficiency, high power consumption, harsh noise and high rate of wear of liner and charge have been existing in relative industrial applications for a long time. Study on charge motion of ball mills, especially the microscopic process of grinding behaviour, can help to improve the performance of ball mills in dealing with these defects. Some research has been done on charge motion of ball mills since the last century. Although related achivements come out, branches of their study methods seem to be difficult to apply in the field of microscopic process of grinding behaviour. The discrete element method (DEM) has its advantages in tracking of both the dynamics activities of the charge and the entire variation process. Thus, the DEM prediction possesses great potential in study of charge motion of ball mills. It is opening with the theoretical analysis of one single ball movement in a ball mill in this dissertation, discussing about the critical factors which would effect on movement of the single ball. In order to put insight into the motion principles for the realistic media system of ball mills, an experiment has been exerted. In the mean time, information about the static and dynamical situations of the system has been returned from the experiment. The results from the experiment provide a reference for the simulation tests and help to correct the simulation parameters. The simulation tests also provide large amounts of results that are relatively difficult to obtain by experiment. In the last stage, charge motion and its related problems are simulated by the discrete element method.The main contents and innovations of this dissertation can be summarized as follows:(1) Theoretical analysis of movement of a single ball in a ball millTwo cases of the charge motion of single ball medium, that is in one case the ball moves without rotary, in the other case the ball is with some rotary were discussed respectively by theoretical method. In the first case, the charge motion of single ball medium without rotary is divided into two motion stages which are motion stage with static friction and motion stage with dynamic friction. While in the other case the charge motion of single ball medium with some rotary is divided into two motion stages which are motion stage with pure rolling and motion stage with both rolling and sliding. The separating positions of the charge motion of one single ball of the two cases are solved. The critical factors which have influence on the charge motion of single ball medium are found by discussing the variation law of the separating positions of the two cases.(2) Study on charge motion by experimentThe side viewing cover of the physical ball mill model is made of transparent plexiglass material, which is convenient for observation and shooting in the experiment. There is only one layer of balls in the ball mill by adjusting the tube length. The charge motion of the one layer of balls is shot by high-speed camera and the shooting results can be analyzed clearly and easily.(3) Determination of simulation parametersCharge motion in ball mills is simulated. The results from experiments and simulation tests are compared to judge whether they match with each other. If not, the possible reasons are analyzed and next test is prepared by adjusting some parameters. And if they do match, the simulation parameters of the test are considered to be suitable in some extent.(4) Simulation study on charge motionIssues such as charge motion, power draw, and effect of ball size and liner shape on charge motion and power draw are simulated by the discrete element method. And the effects of a wide range of operating parameters such as the mill speed, the filling ratio of balls, the ball size and the surface geometry of liner on charge motion and power draw have been studied.On the bottom, the discrete element method is feasible to study on charge motion of ball mills with only one layer of balls. And the results got from study of charge motion in this specific case are valuable and meaningful to explore the principles of the dynamics of more practical ball mill system.