The materials that exploit from underground mine or open-pit mine or the crushed materials could be mixed together as different size of grains. In dressing plant, coal preparation plant and other industry departments, the materials should be classified into several grades with similar granularity before further processing. 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 and useful materials processing:
(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.
NS series high efficient vibrating screen manufactured by Luoyang Dahua Heavy Type Machinery Co., LTD. is a kind of circular vibrating screen with multilayer and high efficiency, which is designed by adopting the advanced technology from overseas. This machine is featured in reliable structure, strong exciting force, high screen efficiency, small noise, easy maintenance and safety operation etc. It is widely applied for grading in mining, construction, transportation, energy source and chemical industry.
The Classification of Screening Machine
原文：https://www.cnblogs.com/dahuacrusher/p/14731524.html