Study On Breakage And Size Distribution Behaviour Of Iron Ore Particle In Ball Mills

The ball mill depends on the liner to lift grinding media to impact and grind mineral particles for meeting the needs of different particle size distribution in mineral plant.As indispensable grinding equipment,it is widely used in cement,chemical,metallurgical,ceramic industries with the highest energy consumption.However,the research on charge load behaviour is relatively simple and lacking the method of establishing the discrete element model of ball mill.Moreover,the particle breakage mechanism of ball mill has not been fully understood.This dissertation was financially supported by National Natural Science Foundation of China(General Program,Multi-body impact-tribology coupling behaviour of large-scale ball mill).The key problems of charge load and particle breakage behaviour were studied by combining experiment and DEM numerical simulation.The main contents of this study includes: Determination and analysis of contact parameters in the discrete element model of iron ore particles.Study on motion of grinding media in ball mills.Study on discrete dynamics of charge group in ball mills.Study on impact breakage behaviour of iron ore particles by dropping ball.Experimental studies of iron ore particle breakage and size distribution optimization.The purpose of this dissertation is to explore the changing law of charge motion and analyze the mechanism of breakage and size distribution of iron ore particle in ball mills,which will be beneficial to improve milling efficiency and reduce energy consumption.Firstly,aiming at the lack of sufficient understanding of the physical and mechanical properties of iron ore particles and the lack of methods to calibrate the contact parameters of discrete element model,the basic properties of iron ore particles were determined,the strength of single iron ore particles was explored,the variation of shape characteristic parameters of iron ore particles was analyzed,the geometric model of iron ore particles was constructed,and the contact parameters of iron ore particles needed for DEM numerical simulation were calibrated.It provides key parameters for the subsequent DEM numerical simulation of ball mill.Secondly,based on the classical milling theory,the motion characteristic equations of different layers of grinding media were constructed.An instrumented ball measuring device was designed to explore the angular velocity and acceleration of grinding media in ball mill.Additionally,the correctness of model established by DEM numerical simulation was verified through the instrumented ball data and the ball mill power.It provides an accurate model for the further study of the impact discrete dynamics of charge group in ball mill.Next,based on Φ520 mm×260 mm ball mill,the impact discrete dynamics numerical simulation of ball mill under different mill speed and filling level was carried out to analyze the variation of characteristic parameters of charge group.A prediction model of ball mill power based on mill speed,mass of charge group and centre of mass was established.The EDEM meshing method was used to explore the distribution of energy and frequency of collisions in charge groups.It provides a theoretical basis for the design of energy-saving and cost-reducing of ball mill.Then,based on the dropping ball impact test rig,the single-particle dropping ball and the multi-layer particle dropping ball impact breakage experiment were carried out to analyze the effect of the layer of iron ore particles,the size of iron ore particles,the dropping height of steel ball and the continuous impact number of steel ball on the impact breakage behaviour of iron ore particle.The breakage probability model and the breakage size distribution model of iron ore particles were constructed to reveal the mechanism of particle breakage in ball mill.Finally,based on the particle breakage model,the grinding experiment of iron ore particle under different mill speed and filling level was carried out to explore the characteristics of iron ore particle breakage size distribution.Analyzing the effect of mill speed and filling level on the kinetic parameters,selection function and breakage function of iron ore particle,and establishing the evaluation index of product size distribution.It provides a basic data support to reduce the energy consumption of iron ore particles and improve the grinding efficiency.