1. Field of the Invention
This invention relates to a powder classifier provided with a rotatable classification rotor in a casing for classifying powder under the influence of centrifugal force and airflow. More particularly, it relates to a powder classifier capable of handling a large amount of powder with a simplified internal mechanism.
2. Description of the Prior Art
Various techniques for classifying powder have been proposed in the art. One of such conventional techniques is known as powder classifier, for example, disclosed in Japanese Patent Published Application No. 57-11269, which is provided with a rotatable classification rotor for classifying powder by using rotation of the classification rotor and airflow.
The powder classifier rotates a classification rotor at high speed in the casing, the classification rotor equipped with a plurality of powder classifying vanes therearound, while ventilating the classification rotor from the periphery to the center. The airflow and the centrifugal force caused by the rotation act on powdery flow to classify the powder particles in accordance with the boundary defined by a desired particle size.
As discussed above, the classification rotor is equipped with the plurality of powder classifying vanes. Stated more specifically, an air introduction path is formed to be directed toward the inside of the rotor from the position where the powder classifying vanes are provided, and a powder introduction port or powder intake is formed above the classification rotor along the circumference thereof from which powder particles fall onto the powder classifying vanes. A powder supply port is provided on the upper center of a casing for supplying the powder as a raw material therefrom. The powder supplied is fed from the powder intake to the powder classifying vanes within the classification rotor, i.e., fed into a classification chamber while being scattered on the upper surface of the classification rotor. In the classification chamber, the centrifugal force of the powder classifying vanes and the air flowing into the center of the classification rotor act on the powder. In other words, fine powder particles with a small diameter that is very susceptible to air viscous resistance are carried by the airflow to the central portion and taken out from a fine powder outlet, while coarse powder particles having a large diameter that is very susceptible to the centrifugal force are scattered to the outer edge of the classification rotor by the centrifugal force and collected to a coarse powder outlet provided on the outer peripheral of the rotor. The powder is thus classified in accordance with the boundary defined by a desired particle size.
Such a conventional powder classifier is also provided with a balance rotor, unitarily with the classification rotor, so that the air passing through the classification rotor is introduced through the balance rotor from the center of the classification rotor into the fine powder outlet provided in the outer edge of the classification rotor. The balance rotor is provided with a view to regulating the flow of air passing through the classification rotor or a vent cavity or ventilating the vent cavity smoothly go that the powder can be classified in accordance with the desired value.
Since in the conventional classifier the balance rotor is coupled to the lower portion of the classification rotor, the flow can be balanced in the vertical direction. Such a balance rotor, however, makes the entire mechanism of the powder classifier complicated and the rotor large scale to increase the weight. The heavy rotor causes an increase in output of a drive mechanism for driving the rotor to rotate.
Further, since in the powder classifier the vent path from the classification rotor to the balance rotor is bent substantially at 180 degree and the sectional area of the path is increased from the center to the circumference, the ventilating speed is reduced and hence the classified powder particles could be accumulated or adhere to the inner surface of the vent path. The powder particles adhered may cause lowered permeability or clogging of the vent path. Because the entire mechanism is complicated, it is difficult to disassemble the classification rotor and it takes much time to clean the inside of the classification rotor for keeping its sanitary conditions or remove clogging powder particles from the vent path.