Study On The Respective Grinding Contribution And Corresponding Separated Quantitative Characteristics Of Impact And Abrasion Action Mechanisms In Cylindrical Mill Grinding

The cylindrical mill is widely used in the processing of solid mineral resources in mine,metallurgy,building materials,chemical industries etc.Improving the production and processing capacity of the mill and optimizing the particle size composition of the grinding products have very important practical significance for enhancing the economic efficiency of enterprises and the resource recovery rate.Theoretically,for the cylindrical mill,the grinding is mainly driven by the rotation of the mill cylinder to enhance the impact and abrasion effects and thus the size of the materials is reduced,which indicates that the movement status of the grinding medium is the key grinding factor.However,during the running process of mill,the impact and abrasion actions synchronously coexist and continuously occur,and the two actions may exert forces in different areas and transform to each other periodically.So it is very difficult to separate and quantitative characrerize the respective grinding contributions of the impact and abrasion actions.It is obvious that this problem limits the theoretical analysis of the grinding process and behavior,as well as its white-box process,and further affects the grinding simulation prediction and optimization.Therefore,three kinds of mineral samples of quartz,pyrrhotite and pyrite with relative simple minerals composition were chosed as the research subjects to conduct the experiments of drop weight,abrasion and cataracting in this thesis.Combined with MATLAB programming and Origin function fitting method,the grinding characteristics of the impact and abrasion actions in cylindrical mill,as well as the quantitative separation and coupling-change characteristics of their respective grinding contribution rates under cataracting condition were investigated by means of the population balance dynamics theory of grinding.The drop weight test was applied to investigate the impact crushing characteristics of three kinds of mineral samples and obtain the hardness grade results of the resistance to impact crushing ability and the relationship equation between the particle size and impact specific crushing energy,which revealed the influence rules of impact specific crushing energy and other factors on the crushing characteristics of mineral samples,and provided the most direct basic data of the crushing test for the population balance dynamics simulation of grinding.The drop weight test results of three kinds of mineral samples showed that the particle size compositions of the impact crushing products had a wide distribution range,covering all particle sizes from 0 to close to the size of the feed material,and impact specific crushing energy had a critical value and energy barrier effect,and the influences of other factors were affected by the impact specific crushing energy.In the low-speed grinding test of the cylindrical mill,the particle size distribution results and abrasion behavior characteristics of the grinding products were investigated by changing the grinding influence factors such as the feed size,sample type and grinding time.The results showed that low-speed grinding was a low-energy grinding process,and the product particle size composition was different from that obtained by impact crushing.The difference was highlighted by the uneven distribution of the product particle size,and the product particle size tended to distribute in the second coarse fractions near the original particle size of the feed itself and the fine fractions of-0.038 mm,which indicated that there were obvious abrasion behavior characteristics in the low-speed grinding process.The abrasion behaviors were affected by feeding particle size and mineral sample types.From the perspective of the generation rate of the fine fractions of grinding products,the smaller the mineral hardness or the feed size,the greater the generation rate of the same fine fractions.However,from the perspective of the crushing rate of the feed size,the correlation of the crushing rate and its growth rate of mineral samples with the feed size and mineral hardness were relatively complicated,and there was no obvious consistency rule.In the high-speed grinding test of the cylindrical mill,the particle size distribution and the grinding behavior characteristics of the grinding products were studied under cataracting condition.The results showed that the high-speed grinding was a high-energy grinding process,and the product particle size was composed of a large number of main particle sizes and distributed in a wide particle size range.This suggested that there were significant difference between the high-speed and low-speed grinding processes in the product particle size compositions,while the product particle size distribution under high-speed grinding was similar to that obtained by impact grinding.The breakage rates of the three kinds of mineral samples under cataracting condition were positively correlated with the grinding time,and also related to the mineral hardness.The breakage rates of pyrrhotite and pyrite were similar,both of which were larger than that of quartz,and quartz was the most difficult to be ground by comparison with the other two minerals.The generation speeds of each product size of the three kinds of mineral samples under cataracting condition were related to the hardness of the mineral samples.The generation rate of each grinding product size of quartz was always the smallest,while the generation rate was relatively large for pyrrhotite and pyrite,and the relative sizes of the two were related to the feed size.The generation rate of each product size under cataracting condition was higher than that of the abrasion grinding.Based on the results of the drop weight and cataracting test,a hypothetical impact grinding and its population balance dynamic model with only impact action were constructed,and the simulated grinding results were obtained by solving the model parameters.The construction methods and steps of simulation results of impact grinding mainly included the size grade classification of grinding products,the calculation of impact specific crushing energy,negative cumulative yield of any relative particle size and fracture distribution function,as well as the acquisition of selection function and Reid solution of the population balance equation.The results indicated that the selection function of the population balance kinetic equation showed a declining trend with the increase of grinding time.The selection function of the coarse fractions of the grinding products changed dramatically by comparison with the fine fraction,and the selection function decreased with the decrease of the feed size.Using the grinding efficiency as the indicator of the grinding effect could better reflect the achievement degree of the grinding purpose.The grinding efficiency was remarkably affected by the grinding methods.Among them,the efficiency of abrasion was obviously lower than that of the grinding under impacting and cataracting condition.The grinding efficiency under cataracting condition was the highest,while the grinding efficiencies under impacting and cataracting condition were closer and the change trends were also more similar.The grinding efficiency was closely related to the hardness of mineral samples.In most cases,the greater the hardness of the mineral,the lower the grinding efficiency of the qualified particle size.According to the normalization method,the total contribution rates of the impact and abrasion actions must be equal to 100% for the grinding effects of any particle size in actual grinding process,and the grinding efficiencies of impact and abrasion actions were coupled to the grinding efficiency under cataracting condition.The quantitative relationship of the grinding efficiency of the three grinding methods was established by introducing the coupling factor,and the calculation methods and quantitative results of the respective contribution rates of the impact and abrasion actions under cataracting condition were obtained,which would achieve the quantitative separation of the contribution rates of the two kinds of grinding actions under cataracting condition.Studies showed that the contribution rates of impact and abrasion actions under cataracting condition varied with grinding time.In general,the contribution rate of the impact action increased with the increase of grinding time,and gradually tended to be stable,while the contribution rate of abrasion action decreased with the increase of grinding time.Under the experimental conditions of this thesis,the impact action was the dominant contribution during the grinding process followed by the abrasion action.The contribution rates of the impact and abrasion actions under cataracting condition were also related to the feed size.The contribution rate of impact action decreased with the decrease of feed size,while the contribution rate of abrasion action increased inversely.The contribution rates of impact and abrasion actions under cataracting condition would fluctuate with the change of grinding conditions,and the fluctuation range was related to the hardness of the mineral sample.The respective contribution rates of impact and abrasion actions of quartz had the smallest fluctuation range,and for pyrrhotite and pyrite,the fluctuation ranges were relatively similar.In a word,a new grinding analysis method for quantitatively separating and characterizing the contribution rates of impact action and abrasion actions in the cylindrical mill was firstly proposed in this thesis.The complete technical route and test calculation steps that combined the test methods such as JK drop weight impact crushing,abrasion action and cataracting with the traditional dynamics fitting and population balance dynamics simulation method of grinding were established,which could realize quantitative the separation of contribution rates of the impact and abrasion actions under cataracting condition.The research results have innovated the method and approach of grinding analysis and enriched the theory of grinding analysis,which had important referential significance and practical guiding value for grinding simulation and optimization.