HGM Series of Three-rings and Medium-speed Micro-powder Grinder is widely used in making fine powder or ultra-fine powder, and the raw materials should be non-inflammable and non-explosive under the Moh's hardness less than 6 grade such as limestone, calcite, dolomite, kaolin, bentonite, talc, illite, pyrophillite, barite, meerschaum, fluorite, potash ore, etc. The lifetime of spare parts is relied on the hardness of raw materials, and is lowered once the Moh's hardness is up to 4-6 grades.