Brief introduction of screening principles

Screening is the process dividing different particle sizes of granular materials into several levels through single or multi-screen surface evenly cloth hole. The particles greater than mesh sieve will be left at the plane, called the sieve material. And particles smaller than mesh sieve, called sieve material.

Granular material’s screening process can be seen as two periods: Firstly, the fine particles smaller than the mesh size reach the screen surface through the material layer composed of coarse particles; In order to achieve these two phases, there must be relative movement between the material and the screen surface. Therefore, screen box should have the appropriate movement characteristics, on the one hand the material on the screen surface is at a loose state; On the other hand, coarse particle on the sieve so ensure that the fine particles can smoothly through sieve.

Specific screening process are: a large number of particles have different size, mixed granular material is into the screen surface, only a part of the particles are in contact with the screen surface. Only some part are in contact with the screen surface, the material contacting the screen surface is not particles less than sieve. Most particles smaller than mesh size are located throughout the entire material layer.

Due to the movement of the screen box, the material layer on the screen surface has loosed, so that the existed large particles’ large gap further expand, small particles took the opportunity to move to the lower deck through the gap. At the same time, due to the small clearance of small particles, large particles cannot pass through; therefore, large particles continually move in motion. So the original messy arrangement of the particles occurs, that the particle size will separate. Thus forming the situation that the small particles are at the bottom, the coarse particles are at the top. Eventually, the fine particles arriving the screen surface will through sieve if they are less than the sieve. Therefore, achieving the separation of coarse and fine particles, and completing the screening process. However, in actual screening, a fully sufficient separation doesn’t exist. In general, some part of undersize product are left in the screen overflow.