Patent ID: 8757387

Claim:
A classification device for classifying particles by size, comprising: an upper impeller-type rotor, a lower end of which is covered with a cover disc without penetration hole and an upper end of which is covered with an upper cover disc with a first frustoconical penetration hole; a lower impeller-type rotor, an upper end of which is covered with a cover disc without penetration hole and a lower end of which is covered with a lower cover disc with a second frustoconical penetration hole, the lower cover disc with the second frustoconical penetration hole being disposed below the upper impeller-type rotor and the lower impeller-type rotor; an upper particle discharge chamber configured to discharge particles of a first size from the upper impeller-type rotor; a lower particle discharge chamber disposed below the upper particle discharge chamber, and configured to discharge particles of a second size from the lower impeller-type rotor; and an outlet pipe provided below the lower impeller-type rotor and configured to discharge particles of a size larger than the first and second sizes, wherein the upper impeller-type rotor and the lower impeller-type rotor are provided so that axes thereof are coincident and the first ends face with each other forming a gap therebetween in an axial direction, wherein the penetration holes of the upper cover disc and the lower cover disc extend through an entire thickness of the upper cover disc and the lower cover disc, respectively, wherein a diameter of the first frustoconical penetration hole increases from an upper surface of the upper cover disc to a lower surface of the upper cover disc in the axial direction, and a diameter of the second frustoconical penetration hole increases from a lower surface of the lower cover disc to an upper surface of the lower cover disc in the axial direction, and wherein diameters of the penetration holes of the upper cover disc and the lower cover disc are different.