In the multilevel allocation of the grinding balls of a ball mill, the requirements in many aspects mainly depend on the average diameter of the grinding ball, such as the impact force of the steel balls, the times of impact, and so on. It means that the grinding balls of different specifications have an effect on them. In the two-stage allocation of the grinding balls, the impact force of the steel ball and the times of impact are determined by the diameter of the bigger ball, while the control of the material flow speed is determined by the diameter of the smaller ball and the amount of the filled materials. It can relieve the contradiction between the impact force, the times of impact, and the control of the flow speed of the materials. Compared with other kinds of allocation methods, the two-stage allocation of the grinding balls is more simple.

According to the changes of the outputs, with the increase of the hardness and the particle size of the materials, in the multilevel allocation of the grinding balls, the contradiction between the impact force of the steel balls and the control of the material flow speed will become more obvious. And the output will decrease obviously. However, in the two-stage allocation of grinding balls, this contradiction doesn’t exist. Because in this allocation method, the big grinding balls and the small ones can meet the requirements of the impact force and the control property of the materials respectively. Therefore, the output does not change obviously, which can prove the advantage of the two-stage allocation of grinding balls.

By adopting the two-stage allocation of grinding balls, the output is higher. And it is of energy conservation. Besides, it can reduce the times of cleaning the grinding cavity, which can increase the operation rate of a ball mill.

The so-called two-stage allocation of grinding balls is to choose two kinds of grinding balls with different size specifications, whose diameters are quite different, to finish the allocation for a ball mill. Its principle is that the space between the big grinding balls can be filled by the small balls, which can improve the stacking density of steel balls. Thus, on one hand, the impact force and impact times in the first grinding cavity can be increased. On the other hand, the higher stacking density of grinding balls can make the materials be ground well. In the two-stage allocation of grinding balls, the big grinding balls are used to crush the materials. The small grinding balls are used to fill the space between the big balls, which can increase the stacking density of the grinding media to control the flow speed of materials and improve the grinding property of the ball mill. And the small grinding balls have the function on transferring energy. They can transfer the impact force and energy produced by the big balls to the materials. Besides, they can squeeze the thick particles of the materials out of the space between the big balls then send them to the impact area with big grinding balls.