Method and apparatus for grinding material particles

Abstract

A grinding apparatus includes a roller mill in which material particles are pre-ground, a tube mill connected to the roller mill through a fluidized-bed-type classifying device in which the material particles are classified by size and a circulation line is connected between the classifying device and the roller mill, wherein a fluidized portion of the pre-ground particles, which consists of a fine material component is fed into a tube mill, a remaining portion of the pre-ground particles, which consists of course material and some amount of fine material not fed into the tube mill is returned to the roller mill through the circulation line where the remaining portion of the pre-ground particles is again crushed together with newly fed material particles in the roller mill. The fluidized-bed-type classifying device is provided with a first chute through which the fine material component flows out to the tube mill and a second chute connected to the circulation line through which the remaining portion is returned to the roller mill. The inner hollow space of the fluidized-bed-type classifying device is divided into an air introduction section and a fluidized bed section by a porous partition plate arranged horizontally with inclination toward the second chute. The fluidized bed section communicates with both the tube mill and the roller mill and the air introduction section communicates with the material fluidizing air which has a controllable flow rate.