If the feed particle size is large and the discharge particle size is small, two-level milling or multi-level milling is often required. Different milling levels also have certain requirements for LM vertical roller mill types.Generally, vertical roller mill is often used as primary mill, while counterattack vertical roller mill, conical vertical roller mill and hammer vertical roller mill are used as secondary mill or even tertiary mill.Consider the impact of material water content on milling productivity. When the water content is too large, fine-grained materials will agglomerate or stick to coarse-grained materials due to the increase of humidity, so as to increase the viscosity of materials.When a certain viscosity is reached, the materials will be bonded in the vertical roller mill inlet and milling chamber, which greatly reduces the ore discharge speed, aggravates the blockage of inlet and outlet, and reduces the productivity.