In the actual production process, the material can not leave the vertical roller mill freely from the discharge end. The discharge end of the vertical roller mill has the effect of inhibiting the discharge of large particles. The small particles can be discharged smoothly, while the large particles remain in the mill and continue to be ground.

This effect is called export classification. The classification function of the mill itself will affect the residence time of materials in the mill, and the inhibition effect of different discharge methods is different.

For lattice ball mill, the effect of lattice has a greater inhibition on the discharge of large particles, even if the lattice opening is large, it will also prevent the discharge of some large particles.