JPH03137973A - Screening method and apparatus utilizing spiral groove - Google Patents

Abstract

PURPOSE:To enhance classifying accuracy by allowing a powder dispersed in an air stream to spirally flow along a net to allow a separation field to act as a band for a long time. CONSTITUTION:A raw material powder 1 is supplied from a screw feeder 2 and dispersed by the primary air stream blown off from a primary air sump 16 to reach a net 5 along a spiral groove 4 and, when air is sucked from a fine powder outlet 6, the secondary air stream from the gap of the upper surface of a secondary air sump 8 is blown off from the under surface of the net 5. At the same time, when a screen consisting of the net 5, the spral groove 4, a net frame 10 and a net fixing band 11 is rotated by a drive wheel 9, the powder once bonded to and accumulated on the spiral groove 4 is floated and dispersed from the under surface of the net 5 through which the secondary air stream is blown off along the groove 4 and successively passes through the screen from the upper and side surfaces of the net 5. This operation is repeated many times until the powder reaches an outlet 12 and coarse particles are discharged out of the outlet 12 and fine particles are collected from the fine powder outlet 6 through a cyclone and a bag filter.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method and apparatus for classifying powder into coarse particles and fine particles with a separation diameter of about 10 to 200 E/cm millimeters.

BACKGROUND OF THE INVENTION A drawback of conventional classifiers is that they generally have low classification accuracy.

First, when classifying classifiers, there are two types: those that do not use a screen and those that do. For those that do not use a screen, there is an air flow classifier, but the biggest drawback in terms of accuracy is that coarse particles larger than the separation diameter are mixed in with the fine particles.

The classification method is that the particles are classified into coarse and fine particles at a separation point in the classification chamber using centrifugal force proportional to the diameter of the particles and the strength of the adjusted centripetal airflow. The classification accuracy is low because the airflow is not rectified but a vortex, and the separation field is a point or line within the classification chamber. Classification accuracy is determined by comparing the average particle size before and after classification. This is also shown by ζ.

Next, for those that use a screen, a vertical type is common, and the method is to make the powder dispersed in the air flow collide with a vertical screen, and by passing fine powder below the opening of the screen, coarse particles are removed. It separates into fine particles.

However, all the fine particles were destroyed by the debris that collided with the screen.
does not pass through the screen, and coarse powder containing a large amount of fine powder falls and is discharged by gravity.

To compensate for this, there is a method of keeping the powder in a suspended state inside the screen, but the floating speed of the particles is premised on rectification.

However, the inside of the screen becomes a whirlpool state due to the primary dispersion airflow from the upper side and the anti-clogging flow from the side (it is also necessary to ensure the discharge of the paddy flow), and this effect is not so great.

Finally, in the case of a horizontal type, the function of moving and discharging the powder inside the screen is insufficient because there is no effect of gravity on the discharge of coarse particles. If the airflow on the inlet side is fast, fine powder will flow directly from the discharge port, and the movement of coarse particles due to the clogging prevention airflow from the bottom, the coarse particle movement guide plate of the cylindrical screen, and the strong mesh slope of the flat screen. It is ineffective if the powder is not deposited on the screen, which goes against classification, which is based on dispersing the powder in the airflow.
Classification accuracy is low.

This invention solves the above-mentioned drawbacks and meets the social demand for producing powder with uniform particle size.

The mechanism will be explained below with reference to the drawings. Raw material powder 1 is supplied from a screw feeder 2, and is dispersed by a primary air flow blown out from an outer circumferential gap at a feeder outlet of a primary air reservoir via an attached air volume control valve 3. The dispersed powder follows the spiral groove 4 and reaches the net 5 (place of separation). When air is sucked through the fine powder outlet 6, a secondary air flow is blown out from the lower surface of the screen 5 through a gap of a certain width on the upper surface of the secondary air reservoir 8 through the air volume control valve 7. At the same time, when the screen consisting of the net 5, helical groove 4, net frame 1o, and net fixing band 11 is rotated by the drive wheel 9, the powder that has adhered and accumulated in the helical groove 4 is blown along the groove by the secondary air flow. The lower surface of the net 5 floating,
The particles are dispersed and pass through the screen sequentially from the top and side surfaces of the net 5. This operation is repeated many times at J leading to exit 12,
Coarse particles are discharged from the outlet 12 via a rotary valve, and fine particles are collected from the fine powder outlet 6 via a cyclone and a bag filter.

In other words, the substance of this invention is a screen with a mesh wrapped around a spiral groove, which is rotated and utilizes air flow and suction to quickly discharge separated fine powder and remove powder in the process of being separated. The essence of the method is to disperse the coarse particles in an air stream at a band-shaped separation site provided along a spiral groove, and to move the coarse particles reliably toward the coarse particle outlet without repeatedly applying a separating force to discharge the coarse particles.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing one example of this invention. Figure 2 is a cross-sectional view taken along line A-A in Figure 1.

Claims (1)

[Scope of Claims] (1) In the classification of powder, the powder dispersed in the air flow is caused to flow spirally along a net, so that the separation field is a zone and the action is performed over a long period of time. Characteristic sieving method (2) In the classification device, a screen is formed by wrapping a mesh around the outside of a spiral groove to form a cylinder, the inside is the partition wall of the groove, the outside is the screen, and the stroke is the length of the groove. (3) The sieving device described in (2), in which a thin plate with holes is wrapped around the outside of a spiral groove. (4) An air volume control valve with a certain gap between the screw feeder and the outer periphery of its outlet. A powder quantitative supply and dispersion device attached to the sifting device described in item (2), comprising an air reservoir with a