When the mill is in closed circuit grinding, there should be a proper cycle load. In production practice, it has been shown in a certain range that the production efficiency of grinding equipment such as ultrafine mills, centrifugal ultrafine mill, etc. The increase of the ratio increases, and under the condition of a large sand return ratio, the fluctuation of the powder mill efficiency will have a small impact on the productivity of equipment such as ultrafine grinding. When the sand return ratio is too small, it does not show the advantages of closed-circuit grinding. Therefore, appropriately increasing the sand return ratio has certain benefits. Usually, the sand return amount of a rod mill is smaller than that of a ball mill. This is because the voids in the unit media volume of the rod mill are relatively small, so there is less material to hold. Professional ultra-fine pulverizers and other grinding equipment, as well as more technical information on grinding machines, are all in SBM.