Some concentrators did not adjust the size of the opening of the classifier during the equipment installation, and the operator did not pay attention to it during the vertical roller mill operation.which would also affect the grinding operation invisibly. The lower opening of the classifier is low, and the ore sedimentation area is large, so the amount of returned sand is increased, and the fineness of grinding is relatively fine.The lower opening of the classifier is large, the ore sedimentation area is large, and the water flow is relatively smooth, so the amount of returned sand is increased, and the fineness of grinding is relatively fine. In the same way, when the opening on the classifier is low and large, the amount of returned sand will increase and the fineness of grinding will be relatively finer. Otherwise, on the contrary, the grinding fineness becomes coarser.