What is the purpose of classification?
During the crushing process, the change in the size of the ore particles does not happen at the same time but is completed gradually. In each stage of pulverization, a part of the fine particles that meet the requirements is always produced. In the grinding process, in order to separate qualified fine particles in time, prevent over-crushing, and improve the productivity of the mill, classification equipment is required to complete the process. Qualified particles are sent to the sorting operation from the classification overflow (the sieve is the product under the sieve), and the coarse particles are returned to the mill for regrinding. Therefore, classification plays an important role in grinding operations.
How to choose grading equipment reasonably?
The grading equipment commonly used in concentrators are spiral classifiers, hydro-cyclones, and fine screens.
Spiral classifiers are classified into high weir type, submerged type, and low weir type according to the position of the spiral in the tank and the level of the overflow surface. The high weir type is suitable for separating the overflow that is larger than the grain size, so it is mostly used for the first stage of grinding, and the submerged type is suitable for separating the product smaller than the grain size, and it is mostly used in the second stage of grinding to form a closed circuit with the mill.
The working principle of the screw classifier: The spiral classifier equipment is based on the principle that the solid particles are different in size and specific gravity, so the sedimentation speed in the liquid is different. The fine mineral particles float in the water and overflow, and the coarse mineral particles sink to the bottom of the tank. A piece of grading equipment is pushed upward by a screw to perform mechanical grading. It can filter the powder ground out of the mill, and then screw the coarse material into the feed port of the mill using a spiral blade to filter out The fine material is discharged from the overflow pipe. Because of its simple structure, stable work, convenient operation, long service life, and other advantages, it has been widely used in mineral processing plants.
The hydro-cyclone separator is classification equipment that uses centrifugal force to accelerate the sedimentation of ore particles. It needs pressure to feed the ore, so it consumes a lot of power, but it has a small area, low price, large processing capacity, high classification efficiency, and very fine overflow. Stream products are mostly used in the grading equipment in the second stage of closed-circuit grinding.
The working principle of the hydro-cyclone: the slurry enters the shell along the tangential direction of the column through the feed pipe under pressure and makes a rotary motion in the shell. The coarse particles (or dense particles) in the slurry are greatly affected by the pressure. The centrifugal force enters the periphery of the revolving flow and flows downwards with the slurry flow at the same time, and is finally discharged from the grit nozzle at the bottom to become sediment; the centrifugal force of the fine particles is small, and they are in the center of the revolving flow and move upward with the slurry flow, and finally, by the overflow pipe The discharge becomes overflow.
Fine screen
Because the spiral classifier and hydro-cyclone are classified according to the different settling speeds of the mineral particles in the water medium, it is easy to produce the anti-enrichment of useful minerals in the sedimentation, resulting in the crushing of useful minerals. The fine screen is completely classified according to the geometric size of the ore particles and is hardly affected by the density and the classification efficiency is also high. Therefore, in recent years, the fine screen has been paid more and more attention in the grinding cycle as classification equipment.
