Grinding metal ores with ball mill is dissociative grinding for the purpose of dissociative minerals. It is only a means to break the ore by the striking force of steel balls to reach a certain particle size, and the real purpose is for the monomer dissociation of useful minerals and gangue minerals. In the grinding process, steel balls are the implementer of crushing force and the medium of crushing energy. Whether the size of steel balls is reasonable or not determines the transmission of crushing energy, the degree of dissociation and the size of over-crushing. Excessive steel ball size will not only cause unnecessary energy consumption and material consumption, but also affect the particle size distribution and dissociation characteristics of grinding products. The hazards of oversize steel balls mainly include the following. Harm of oversize ball mill.

1. If the ball diameter is too large, it is difficult to improve the monomer dissociation degree of the target mineral. When the impact force of steel ball is too large, the ore is broken through along the direction with the largest crushing force, and the crushing of ore particles is not selective. When the impact force of steel ball is moderate, the ore particles will be broken along the joint surface between different minerals, which is beneficial to the dissociation of useful minerals and gangue minerals. Because the binding force among particles in various parts of rock and mineral is extremely uneven, the binding force among particles in mineral unit cell is the strongest. On the other hand, the bonding force on the crystal plane between unit cells is weak, only 75% of the bonding force in the crystal. However, the bonding force on the interface of different mineral crystals is much smaller than that on the crystal plane of the same mineral. Therefore, accurate ball diameter, that is, accurate crushing force, can increase the probability of selective dissociation of minerals, and make the monomer dissociation degree of ground products good, which is beneficial to subsequent separation operations.

2. Excessive ball diameter will lead to the intensification of the down-homogenization of the particle size of grinding products. The larger the ball diameter, the more energy is transmitted and the larger the crushing force is. Moreover, because of the non-selectivity of ball crushing, the crushed ore particles are severely over-crushed, and the ball diameter is large. At the same ball loading rate, the number of balls is less, the probability of crushing is less, and the number of blows to the ore particles is less, which leads to the aggravation of the grinding phenomenon of the ore particles. Therefore, the non-fine grinding of ore particles and the increase of over-grinding phenomenon make the product particle size distribution uneven, which will not only affect the follow-up fine grinding operation, but also lead to poor particle size characteristics of selected materials, and the wear of pipelines and sand pumps will be intensified due to the most severe wear of coarse ore particles on equipment, which will increase the production cost of concentrator.

3. If the ball diameter is too large, the wear of the medium will increase. The unit consumption of steel balls abroad is generally about 0.8 kg/t. The domestic average is 1.5 ~ 1.6 kg/t, and some even reach 3.0 kg/t. This is related to the material and processing quality of steel balls. Hard nickel alloy steel balls and liners are generally used abroad, while carbon steel balls are mostly used in China. However, too large a ball diameter is also one of the reasons. Because the wear of steel balls is related to the weight, the consumption of big balls is higher than that of small balls. At the same time, the larger the ball diameter, the larger the impact force, and the increase of broken balls of steel balls is also one of the reasons for the increase of medium wear.

4. In addition, if the ball diameter is too large, it will cause many problems. The larger ball diameter enhances the impact of the mill liner, the liner and the screw head of the fixed liner are seriously worn, the cylinder is easy to leak slurry, and the life of the liner is shortened. For example, after the steel ball with a diameter of 100mm is used to replace the steel ball with a diameter of 125mm in rough grinding in a gold concentrator, not only the slurry leakage phenomenon of the cylinder is greatly reduced, but also the service life of the lining plate is increased from 4 months to more than 6 months. If the ball diameter is too large, the working noise of the mill will increase, because part of the crushing energy of the mill is converted into acoustic energy. At the same time, the large ball diameter will also cause the increase of grinding energy consumption.