Study Of Material And Processing Of Large Scale Diameter Mill Ball

The large diameter grinding balls with higher comprehensive performance are widely used in the mine with the development of large diameter ball mills in recent years. However, the fragmentation, the burst and poor wear resistance of grinding balls, which caused by the principal contradiction between the hardness and stress, are considered as three main failure styles when grinding balls are worked in the ball mills. In view of these, a material and a forging process for new large-diameter grinding ball were researched in the paper.The experiments of lean alloy steel for industrial produce of grinding balls were designed. Effects of alloy elements on microstructure and properties of grinding balls were discussed. The lean alloy steel was based on the medium-carbon steel, and composed of silicon, manganese, chrome, molybdenum and a small number of boron. The mechanical tests, microstructure analysis and economical evaluation for 150 mm diameter grinding balls after forged in the air cooling processing were carried out. From the above, an optimum material of designed grinding ball materials was determined. The results of experiments indicated that the microstructure of the grinding ball is homogeneous, and a needle-like matrix composed of lower bainite, a little martensite and residual austenite. Moreover, the hardness is 51-52 HRC, and the volume hardness is 52.6 HRC, the toughness is 16 J/cm2. Compared with other material grinding balls, the new type grinding balls not only possess a higher hardness, but also present good toughness properties.The forging press molding was determined to product the large diameter grinding balls, mainly including the billet material preparation, process of forging press and after forging. The effects of different forging press processes on grinding ball properties were also discussed. The results showed that the toughness of grinding ball was greatly influenced by the forging press process, while the forging press process had a very small influence on the hardness.Next, the effects of low-temperature heat treatment on the properties of large diameter grinding balls were investigated. The results indicated that the grinding ball treated by air hardening and tempering at 250℃had better properties, the volume hardness was 60.7 HRC. the inner hardness was 60 HRC, the surface hardness was 61 HRC and the toughness was 24 J/cm2. Nevertheless, the relevant heat treatment parameters need to further optimize study.In the end, the impact abrasive wear resistance of the large diameter grinding balls and the 65Mn was characterized. The abrasive wear mechanism of these two kinds of grinding balls was contrastively analysis. Results revealed that the wear patterns of the new type large diameter grinding balls were as follows:interaction wear between the fatigue wear and wear caused by many plastic deformations, while the wear mechanism of the 65Mn grinding balls plastic deformation. In addition, the abrasiveness of large diameter grinding balls was 40% higher than that of 65Mn grinding balls.A kind of material for producing the large diameter grinding balls with good comprehensive mechnical properties was prepared successfully, which provides theoretical and practical foundation for the application and further study of the large diameter grinding balls.