About grinding balls
Release time:
2012-11-25
Currently, the widely used types of grinding balls both domestically and internationally are high carbon high alloy cast grinding balls and high carbon low alloy forged or cast grinding balls. In dry production processes such as thermal power plants and the cement industry, the vast majority use high and low chromium cast iron grinding balls. In the wet processes of mining, high carbon low alloy grinding balls are more commonly applied. There are many types of grinding balls in the domestic market, and due to the imperfections of the market economy, the use of grinding balls is not determined by process efficiency, leading to a high degree of randomness. The main varieties include chromium-based high alloy cast iron types, such as Cr8, Cr12, Cr15, Cr18, Cr24, Cr26, and low chromium cast iron types, such as Cr2 and martensitic cast iron.
Currently, the widely used types of grinding balls both domestically and internationally are high carbon high alloy cast grinding balls and high carbon low alloy forged or cast grinding balls. In dry production processes such as thermal power plants and the cement industry, the vast majority use high and low chromium cast iron grinding balls. In wet processes in mining, high carbon low alloy grinding balls are more commonly applied.
There are many types of grinding balls in China. Due to the imperfections in the market economy, the use of grinding balls is not determined by process efficiency, leading to a high degree of randomness. The main varieties include chromium-based high alloy cast iron, such as Cr8, Cr12, Cr15, Cr18, Cr24, Cr26, and low chromium cast iron like Cr2 and martensitic cast iron. In terms of wear resistance, martensitic cast iron and low chromium cast iron are on the same level. Their differences lie in the production process. High alloy cast iron has excellent wear resistance; the higher the alloy content, the better the wear resistance, while also providing good economic benefits. There has been a misunderstanding that high chromium balls are well-suited for cement mills but not for power plants. In fact, both domestic and international thermal power plants have a good record of using high chromium balls extensively, such as in Wuxi, Zouxian, Yueyang, Xingtai, Hengyang, and MaTou power plants, which prefer to use high chromium balls over others. High chromium cast iron grinding balls are rapidly becoming popular in power plants. In dry grinding processes in power plants and cement plants, the wear of high chromium balls is only 15 to 50 grams per ton. Using high chromium balls not only saves costs, reduces labor for workers, and lowers electricity consumption of the mills, but also reduces the waste of limited human resources. It should be said without reservation: high chromium balls can be called environmentally friendly grinding balls, green grinding balls.
The varieties of forged and rolled balls are mainly high carbon chromium molybdenum alloy and medium to low carbon manganese alloy. The processes for forging and rolling balls are simple, and the manufacturing costs are low. Considering economic benefits, low chromium alloy grinding balls are generally used in wet processes in mining, with wear typically around 500 to 700 grams in iron, copper, and molybdenum mines. Increasing the hardness of low chromium alloy balls is the most effective way to reduce wear. We have increased the hardness of low chromium balls to around HRC55, resulting in wear of about 550 grams in copper mines. Due to production process reasons, the quality of forged balls should be slightly better than that of rolled balls.
However, when the diameter exceeds 110mm, it is recommended to use high-carbon chromium-molybdenum low-alloy forged balls, mainly considering that the breakage rate of large-diameter cast balls may be higher. The carbon content of forged balls is generally around 1%, with chromium content less than 2%. The hardness of low-chromium cast balls should generally be around HRc48, and efforts should be made to increase the hardness of low-chromium cast iron balls to enhance economic benefits. The low-chromium cast iron grinding balls we produced in collaboration with an Indian factory have a hardness of up to HRc55, with minimal difference between the core and surface hardness. They demonstrate a good cost-effectiveness ratio in power plants, mines, and cement industries. The diameter of grinding balls in thermal power plants should generally not exceed φ60mm. In cement and mining, the ball diameter should be matched according to the mill diameter, the surface shape of the lining, and the feed particle size. There is only one principle for matching: to minimize the diameter of the grinding balls as much as possible, because the ball mill is a grinding machine, and it is inappropriate for it to undertake even a small part of the crushing function.
Under the premise of material selection, the grading of grinding balls is very important. An ideal grading of grinding balls combined with an ideal surface shape of the lining can enable the mill to achieve maximum working efficiency. The correct choice of material is the fundamental guarantee for maintaining the ideal grading of grinding balls and the ideal surface shape of the lining in the best condition over the long term.
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