Classification device

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.