After a long period of rotation and impact, the sample gradually changes from large pieces to small pieces, and small pieces to powder. The ball mill is the basic grinding equipment in a laboratory. Factories also often uses large-scale ball mill to manufacture powder.
The faster the rotation speed, the greater mechanical force can be generated. The collision frequency can improve the grinding efficiency. However, with too fast rotation speed, it may reduce the frequency of grinding ball falling down and hitting the sample. It will reduce the efficiency. Too high a rotation speed may also cause the grinding jar to lose its adhesion stability and even cause danger to the operator.
A basic ball mill only rotates in one axis, and the forces in the other axial directions rely solely on the dispersion of forces in the other axial directions while grinding beads rolling. Some ball mills are designed with a swing mechanism, and the mechanical force extends to the other two axis and increase the collision force of the grinding beads in 3D direction. However, the increased mechanical complexity may influence the stability and durability of the machine during operation.
Basically, the longer the running time, the finer the sample will be ground.
The two conditions affects the degree of freedom and collision distance between the sample and the grinding ball. Excessive empty space reduces the frequency of collision between the sample and the grinding beads. Otherwise, a crowded space makes the grinding beads and the sample have almost no distance in between, and the gravitational acceleration reduced, only rely on the weight of the grinding beads. A proper size of jar and empty space inside is also important.
The size of the grinding beads will affect the size distribution of the voids. In some occasions, mixed grinding balls with different sizes can have better grinding results. In addition, the more grinding balls filled, the greater the total weight. With the assistance of gravity, it is helpful to improve the grinding efficiency, too. However, the condition of empty space mentioned above and the upper limit of weight that a ball mill can drive must be considered.
Besides, a ball mill with weight and speed compensation and overload protection helps control conditions.