In the crushing process exerted on the solid external forces are rolling, shearing, impact, grinding four. Rolling is mainly used in coarse and medium crushing, suitable for hard materials and large pieces of material crushing; shearing is mainly used in fine crushing, suitable for toughness material crushing; impact is mainly used in medium crushing, fine grinding, ultra-fine grinding, suitable for brittle material crushing; grinding is mainly in the fine grinding, ultra-fine grinding, suitable for small and fine particles of crushing. The actual crushing process is often the simultaneous action of several external forces.