The grinding process of the grinding machine is not spontaneous and irreversible, so it must rely on the external force on the material to overcome the cohesion of the internal particle. The size of cohesion, even for the same material, is very different.

Cohesion can be divided into two types: one is that the cohesion is applied to the interior of the crystal, and the other is between the crystal and the crystal. The physical properties of two kinds of cohesive force are the same, the difference is the numerical value, the former is much larger than the latter. It broken process is a very complex material size change process, mainly has the strength of the material, hardness, toughness, shape, size, humidity, density and homogeneity, etc., related to many factors cannot be estimated. The external conditions, such as the interaction and distribution of the material mass in the broken moment, are also the important factors affecting the crushing process. All these factors complicate the change in the size of the process, so much so that it is not possible to come up with a rigorous and complete theory of theory to explain the process.

The size of cohesion depends on the properties and structure of the crystal itself, and it is also related to various defects in the crystal structure. These defects may be macroscopic and microscopic cracks. Due to the existence of cracks, the connection between the crystal groups has weakened.

According to the nature of crystal structure and particle inter-atomic forces, can theoretically calculated crystal cohesion, as for the cohesion between the crystal structure and particle size, and all the lower material block caused by sexual factors, give attention to two or morethings, for the moment, can not be calculated.