To provide a method for performing efficiently dry classification of a powder of a highly electrostatically charged substance with a vol. specific resistivity measured by a charging method of at least 1011 Ωcm.
An agitating type cylindrical sieving machine is used as a classifier and a raw material powder fed from a raw material feeding hole 1 is carried to one end of a cylindrical screen 3 and is scattered on the inside face of the screen 3 by means of a blade 4 rotating at high speed. As the blade has a twisted angle, the raw material powder is moved in the left side direction of the figure on the inside face of the screen 3. In this case, the raw material powder is pushed on the inside face of the screen 3 by action of the blade 4 rotating at high speed, and very fine vibration is generated on the face of the screen 3 corresponding to the front and the back of this pushed blade 4. While this vibration prevents the screen 3 from being clogged, it makes powder particles with a smaller size than the opening of the screen 3 pass through to the outside and the particles are discharged from an outlet 5 for the fine particles.
KANAHOSHI NAOHIKO
TSUNO NOBUYUKI
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