Modeling Nipped Breakage Mass Of Particle Beds And Comminution Mechanism Of Ball Mill

The ball milling as one of the main powder processing devices has been widely used in many powder processing industries such as cement,ceramic,glass,mineral powder,painting.The powder processing is the energy intensive industry,and the ball milling is the most energy-consumption equipment in the powder processing.In order to improve the efficiency of ball milling,many researchers think that the more impact energy,the more beneficial for the powder broken.While they give too little care to the broken characteristics of these unconfined particles which stay on the media,as the particles will slip rapidly when be impacted by the media,and only a small part of the particle will been nipped and been broken.However,the nipped configuration of particle beds including the nipped height and range has an important effect on the breakage mass and the energy consumption.But there is shortage for the study of the nipped configuration of particle beds and its breakage mechanism.The modeling the comminution processing in ball milling only depends on trial mill and empirical equations,and the media diameter,particle size and the impact energy have not been considered.It is difficult to improve and optimize the comminution processing in ball mill.In order to analyze comminution mechanism of ball mill,a study on the nipped configulation of particle beds and the model of breakage mass was carried out.The height of the nipped particles is calculated by the compression test of the unconfined particles beds and the mathematical model of the nipped height of quartz particle beds has been built.The influence of the bed height,impact energy,ball diameter and particle size on the nipped height and range of particle beds has been analyzed by the falling ball impact tests,and the mathematical model of the nipped configuration of the unconfined particles bed has been established.The mass of incomplete breakage in low impact energy and complete breakage in high impact energy are analyzed and a single-impact breakage mass model is established based on the nipped particles configuration.The selection function and breakage function for the single-impact breakage mass of the particle beds has been set up according to the population balance model(PBM),combined with the impact energy spectra of the media in ball mill.The comminution process model in ball mill has been built as well.Finally,the grinding experiments have been carried out in the testing ball mill.The outcome predicted by the comminution process model is basically consistent with the experimental result,thus the mass model has been proved correctly.The mainly study innovation results in this article are listed as following:(1)For the phenomenon that most of the particles are pushed out of the nipped area and only a few particles are caught and broken when particles are compressed by media,A method to measure the statically nipped height of particle beds has been presented.According to leap features of the stress force when particles are broken,the distances between media are measured by displacement sensor and the mathematical model of the nipped height of quartz particles has been built.(2)The duration of impact breakage is very short,and the measure of the nipped height and range is difficult.A method to determine the nipped height and range of particle beds has been put forward according to the trend of the particle breakage mass.Few particles in unconfined beds are broken before nipped and the effect of initial height of particle beds is unobvious.It is concluded that the bed height of the nipped particles is the stack height with 2 layers particles by the falling ball impact test.The influence of bed height,impact energy,impact velocity,ball size,and particle size on nipped configuration has been analyzed,and the mathematical model of nipped range has been set up.(3)According to the significant difference of breakage mass of particle beds in different impact energy levels,the breakage mass increases linearly with the input energy in low energy levels but slowly in high energy levels.The mass of nipped particles is the turning point of breakage mass increasement.A method to distinguish the low energy impact and high energy impact has been put forward according to the mass of nipped particles,which provides the theoretical support for the construction of the model of incomplete and complete breakage mass,and makes up for the deficiency in calculating breakage mass based on the impact energy.(4)In order to improve the energy efficiency and make up for the deficiencies of research in macro-view,a method of modeling the comminution process in ball mill based on single-impact breakage mass and impact energy spectra has been proposed,combined with the microscopic model of the nipped particle beds and the macroscopic media movement.The selection function and breakage function of particle breakage are built based on the nipped configuration of particle beds.The microscopic factors such as ball diameter and particle are incorporated into the function.In this paper,a method of modeling the comminution process in ball mil based on single-impact breakage mass and impact energy spectra has been proposed,and the comminution mechanism of the ball mill has been studied,these will provide the theoretical foundation for predicting the comminution outcome,optimizing the parameter and designing the ball-milling devices.