The grinder uses the materials to be ground as the media, through mutually impacting and grinding to realize crushing. Tube mill: Inside the cylinder, there are some grinding media. Under the friction force and centrifugal force, the media and materials feed into the cylinder are lifted to a certain height with the cylinder rotating around the horizontal axis. If their gravity are large than the centrifugal force, the materials will drop down, and to be crushed by the impacting force. At the same time, the movement between the grinding media also has the function of grinding for the materials during the rotation process.