Classification: It is a process of dividing mixed materials with different particle sizes into several narrow grades with similar particle sizes in the medium according to their different sedimentation rates.

According to the different functions in the grinding circuit, classification can be divided into: pre-classification, inspection classification and control classification.

Pre-grading: It means that the material before grinding is pre-separated by the classifier to pre-separate qualified fine particles that do not need to be ground, and only the unqualified coarse particles are sent to the grinding machine for grinding to reduce unnecessary grinding and lightening the load of the mill.

Inspection and classification: It is to classify the products after grinding, and return the unqualified coarse-grained fractions to the grinding machine for regrinding to control the particle size of the grinding products.

Control classification: divided into two situations, namely overflow control classification and sand settling control classification: the former is to classify the overflow of the first classification again to obtain finer overflow products; the latter refers to the first classification of the overflow. The classified sand is re-classified to obtain coarse-grained materials with less fine-grained content and sent back to the mill for re-grinding, which can more effectively prevent over-grinding.

Classification equipment, the classification equipment used for closed-circuit grinding cycle includes spiral classifier, hydrocyclone and fine screen.

The following mainly explains the spiral classifier, screw blades, bearings at the upper and lower ends supporting the screw shaft, screw shaft transmission and lifting mechanism. Classification: According to the position in the tank and the height of the slurry surface, it is divided into three types: submerged type, high weir type and low weir type.

According to the different number of spirals, it can be divided into: single-screw and double-screw classifiers; the specifications of the spiral classifier are represented by the diameter of the spiral.

The working principle of the spiral classifier working principle: the ore pulp after grinding is fed into the inclined installed semicircular water tank from the ore feeding port of the classifier. With the low-speed rotation of the screw and the continuous stirring of the pulp, most of the fine and light particles are suspended on the top and overflow from the overflow weir to become overflow products, while the coarse and heavy particles will settle at the bottom of the tank and become sand, is conveyed to the discharge port of the classifier by the screw, and then returned to the mill for regrinding.