The structure of the ball mill is very simple. The main working part is a rotary cylinder, which pulverizes and grinds the materials by the impact and grinding action of the grinding medium loaded in the cylinder. When the mill rotates at different speeds, the grinding medium in the barrel may appear in three basic motion states, as shown in the figure. If the speed is too slow, the grinding media and materials will be brought to a height equal to the dynamic friction angle by the cylinder due to friction, and then slide down under the action of gravity, which is called the "falling state" (Figure a). This situation has a strong grinding effect on the materials. Effect, but the impact effect is weak, and the crushing effect on large materials is not good. If the rotation speed is too fast, the grinding medium and the material-attached cylinder rotate together with it, which is called the "turnover state" (picture c). In this case, the grinding medium has no impact and grinding effect on the material. The rotation speed is moderate, and the grinding medium is lifted to a certain height and then dropped down in a near parabolic trajectory, which is called the "throwing state" (Figure b). At this time, the grinding medium has a greater impact on the material, and the crushing effect is better.
The movement state of the grinding medium in the ball mill cylinder
In the throwing state, the cylinder speed of the ball mill needs to be lower than the critical speed nc. If the critical speed exceeds the critical speed, the ball layer close to the axis of the cylinder will gradually achieve centrifugalization. This requires the ball mill to have an appropriate operating speed, too fast or too slow will affect the working efficiency of the ball mill. This is the root cause of the low efficiency of the ball mill. According to the principle of impact collision, the collision velocity required for particle crushing increases as the particle size decreases. When the material is crushed to a certain degree , even if the ball mill operates at an appropriate speed, it is difficult to meet the collision rate required for particle crushing, which is why it is difficult to refine the material after grinding to a certain particle size in the ball mill.
This article is excerpted from "Research on New Pulping System and Application of Ceramics with Internal Circulation Effective Grinding Machine as the Main Equipment".
