Study On Charge Dynamic Behaviour Of Ball Mills

Ball mill is one of the indispensable grinding equipment which is crucial to the basic industries such as mining,cement,ceramic and thermal power.The power consumption of ball mill is the highest during the process of particle size reduction,accounting for 50%~60% of total power consumption.Besides,the total power consumption of ball mill accounts for 5% of national power generation,resulting in a lot of energy dissipation.However,energy dissipation of ball mill is strongly sensitive to the charge dynamic behavior,which is the main research direction for intensive studying and improving the grinding theory.Currently,the variation of charge dynamic behavior,collision energy and energy dissipation are not thoroughly investigated.This dissertation was financially supported by National Natural Science Foundation of China(General Program,Multi-body impact-tribology coupling behavior of large ball mill).Aiming at the problem of energy dissipation during milling process,the charge dynamic behavior in ball mills is investigated to seek the intrinsic mechanism and variation of the dynamic behavior with different mill operations,which will be beneficial to optimize the grinding efficiency and consequently provide the basic theory and data support to design new energy-saving ball mills.The main content of this study includes: Calibrating the charge contact parameters compared with discrete element numerical simulations and experimental validations.Establishing the region distribution characteristics of velocity and collision energy based on the position density limit.Theoretical study the motion of the grinding media in order to study the variation of motion parameters.A predicting model of charge dynamic behavior was established to investigate the effect of the feature parameters on mill power.Researching the particle breakage behavior and its energy distribution based on breakage experiments of iron ore samples.Firstly,the experiments of angle of repose of iron ore particle was investigated to study the effect of lifting velocity of container and particle size on angle of repose,and therefore the predicted model of angle of repose was established.Considering the irregular shape of iron ore particles,the irregular geometrical model was established according to the sphere clump method,in order to obtain the optimum number of sphere clump.The discrete element modelling of irregular particle was investigated,and the predicted model between angle of repose and the inter-particle contact parameters was established to validate the the optimum number of sphere clump on the basis of the swing-arm slump tester.The contact parameters of charge were calibrated according to the numerical simualtions and experiments verification,which will supply the accurate input parameters for the follow-up numerical simulations.Secondly,the motion of grinding media was therectical studied and a conception of dimensionless of lifter height was proposed to analysis the effect of mill operation parameters on motion parameters of grinding media.The position density limit was proposed on the basis of mesh generation,and the region distribution characteristics of velocity and collision energy were addressed.A mathematical model,predicting the effect of mill operation parameters on charge feature parameters,was obtained to study the variations of charge feature parameters,and thereby establishing and verifying the mill power model.Furthermore,the theretical model validation was then carried out on the basis of the experiments of charge dynamic behaviour.Finally,the experiments of grinding kinetics of iron ore particles were conducted,and the non-linear population balance modelling was used to investigate the breakage behaviour of iron ore particles.The correlation of breakage behavior of iron ore particles and collision energy was described based on the charge dynamic behavior.Considering the impact behavior of grinding media in ball mills,the impact breakage experiments under high strain rate was carried out on the basis of SHPB method.The impact breakage behavior of iron ore under high strain rate was studied,as well as the impact energy dissipation and fragment-size distribution of iron ore.