The steel ball used in ball mill can be divided into casting ball and forging ball. Generally, the diameter of casting ball is less than 120mm, which is used in ball mill; large diameter mill or semi autogenous mill requires larger diameter of steel ball, which is basically forged steel ball. The casting ball can be divided into chromium casting and non chromium casting, in which the content of low chromium ball is 1-4%, that of medium chromium ball is 5-9%, and that of high chromium ball is more than 10%. The wear resistance of medium and low chromium cast balls is poor and the comprehensive cost performance is not high. High chromium wear-resistant ball has good performance, but poor impact toughness. It is easy to crack when used in large-diameter mill. The forging ball is divided into ordinary forging steel ball and new type oblique cutting roll forging steel ball.
The common forged steel ball is made of bearing steel, heated at high temperature and forged by air hammer and other equipment. After heat treatment, the surface hardness can reach hrc48. However, due to the poor hardenability of the material, the quenching depth is only about 15mm, and the core hardness is generally only HRC 30, so the unit consumption is high. The new type of oblique cutting roll forged steel ball is made of B3 steel (high carbon steel) bar, which is heated at high temperature and rolled in the oblique cutting roll forging machine. After quenching, the quenching depth can reach about 30mm, the surface hardness HRC is more than 58, and the impact toughness is greater than 21 joules. The disadvantage is that the cost is high.
The average wear of the steel ball is 300g / T and the unit price is 1500 yuan higher than that of the common casting ball. In order to further reduce the wear and production cost, the concentrator has carried out the application test of duplex wear-resistant cast steel ball
(1) At present, the diameter of steel ball with diameter of 180 mm is too large to fully play the role of grinding, resulting in the reduction of refined powder grade.
(2) The test results show that the grinding fineness of 5522 mill and the production capacity of – 200 mesh can be effectively improved by using the steel ball with a diameter of 150 mm.
(3) The unit consumption and unit cost of φ 150 mm multiphase wear-resistant casting steel ball are reduced by 26.88% and 22.75% respectively compared with that of forged steel ball with diameter of 180 mm. In addition, the crushing rate and out of roundness index meet the production requirements.
(4) In order to further improve the grinding fineness of 5522 mill and ensure the processing capacity of mill per hour, it is suggested that 180 mm steel balls and 150 mm steel balls should be used in a certain proportion.