In the vertical roller mill, the size and proportion of steel vertical rollers have a great influence on the productivity and working efficiency of the mill. For coarse and hard materials, larger steel vertical rollers should be selected, for fine and brittle materials, with smaller diameter steel vertical rollers, the impact times of steel vertical rollers in the mill increase with the decrease of vertical roller diameter, and the grinding between vertical rollers increases.

The clearance is dense with a decrease of spherical diameter. Therefore, it is better to choose the vertical roller with a larger mass and smaller diameter (loose density) as the grinding medium. The size of the vertical roller mainly depends on the particle size of the material to be ground, and the diameter and speed of the mill can be considered appropriately. Formula (1-15) is an empirical formula for spherical diameter and feed size.

After choosing the maximum diameter and minimum diameter of steel vertical rollers according to technological requirements, material properties, mill specifications and various parameters, and then matching grade, using curves, the accumulative percentage of the mass of each corresponding steel vertical rollers loaded into the mill can be found, the actual percentage of the mass can be calculated, and the loading quality of steel vertical rollers at all levels can be obtained.