During the Industrial minerial processing procedures, there is a basic step that efficiently decreases rapidly with fineness and  carried out on relatively coarse material. Screening has generally three purposes.
1. Prevent the entry of undersize into crushing machines to increase efficiency and save energy;
2. Ensure every oversize material are processed;
3. The end product would be of similar size to meet a specified requirement.

There are two types of screens, which are stationary screens and moving screens. The stationary screen is used to select the coarse material. It usually consists of a series of heavy parallel bars set in a frame. The moving screens are more diversified and can be used in various applications. The most commonly seen moving screens are revolving screens, shaking screens, reciprocating screens, gyratory screens, vibrating screens and so on. According to move directions, there are horizontal motion and vertical motion.