Materials pass the sieve grading is referred to screening. The used machine is called screening machine (or sieve for short).

Screening can be divided into following types in the process of mineral separation:

(1) Independent screening: This screening refers to the materials that to be screened is the finished product after screening. For example, in coal preparation plant, the raw coal after screening directly provides for customer use, this process is applied independent screening.

(2) Pre-screening: The process that prepared for further processing is called pre-screening. In dressing plant, if we take gravity concentration and electromagnetism separation, the ore should be in required size. Therefore, before separating, the ore must be classified in order to helpful for further process. 

(3) Auxiliary screening: This screening is worked together with crushing machine. The grain size should meet the requirement of crushing machine after screening, this type of screening is called auxiliary screening.