GRINDER

PROBLEM TO BE SOLVED: To provide a grinder capable of remarkably improving grinding efficiency by performing grinding in a state near to surface contact, also performing various modes of grinding with only such a single grinder and accordingly, grinding of even a composite material and further, consistently performing various degrees of grinding from coarse grinding to medium-degree grinding into a powder having about 100 μm particle size. SOLUTION: This grinder is provided with: stationary grinding outer rings 53a, 53b and 53c each having a cylindrical inner surface, and rotors 52a, 52b and 52c each rotatably placed inside the corresponding one of the outer rings 53a, 53b and 53c in a concentric manner with the outer ring 53a, 53b or 53c, so as to form a prescribed space 54 between the rotor 52a, 52b or 52c and the outer ring 53a, 53b or 53c; wherein the respective combinations of the outer rings 53a, 53b and 53c and the rotors 52a, 52b and 52c are vertically and concentrically stacked up in several (e.g. three) tiers. In the grinder, since the grinding is performed in the space between the cylindrical inner surface of each of the outer rings 53a, 53b and 53c and the outer peripheral surface of the corresponding one of the rotors 52a, 52b and 52c, the grinding section is formed by these surfaces to effect surface contact of a material to be ground with the grinding section and therefore the grinder has very high grinding efficiency as compared with a conventional line-contact type grinder. Conversely, in order to obtain nearly equivalent grinding efficiency to that of such a conventional grinder, the grinder can be operated at a lower rotational speed than that of this conventional grinder, to enable drastic reduction in noise and vibration of the grinder, minimization of the rise in temperature of a material to be ground and prevention of any change in property of a fine powder produced.