When screening materials with screens, it can be classified into the following three categories according to the sequence to screen out the coarse grain, medium grain and fine grain.

1. From coarse to fine.

Overlap several screens with different mesh size, with the largest mesh on the top and gradually minishing in order. This screening sequence has many advantages. The large-mesh sieve surface is more solid and wear-resisting. When materials are firstly screened on the large-mesh sieve surface, through being distributed by several layers of sieves, only a small amount of fine-grade materials are sent to the small-mesh screen, effectively preventing the fragile small-mesh screen surface from being damaged. This device has a compact structure and covers an small area. But the screening work of the lower layers couldn’t be seen,and the sieve surface is inconvenient to change. Besides, the transportation of the screened materials is relatively difficult, for they are all discharged from the sieve bottom.

2. From fine to coarse

The most remarkable advantage of the screening order from fine to coarse is that the screening operations is completed on the single layer, easy to operate and transport and convenient to replace the sieve surface, with each grade of material discharged from the corresponding chute. However, because the coarse grained and medium grained materials have to go through the small mesh screen, making the sieve surface wear increase.

3. The blended screening

In order to overcome part of the shortcomings of the above two kinds of screening sequences and keep their virtues, the blended screening arranges the easy-to-wear small mesh screen beneath the medium mesh screen, convenient for installation and maintenance.