JPH078353B2 - Screening method using spiral groove and its equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and an apparatus for classifying powder into coarse particles and fine particles with a separation diameter of about 10 to 200 μm.

A drawback of conventional classifiers is that they generally have poor classification accuracy.

First, when classifying devices, they are roughly classified into those that do not use a screen and those that do.

The one without a screen has an air flow classification mechanism, and the biggest drawback regarding its accuracy is that large coarse particles having a size larger than the separation diameter are mixed in the fine particles.

The classification method is that the particles are classified into coarse particles and fine particles by the centrifugal force proportional to the diameter of the particles at the separation point in the classification chamber and the strength of the adjusted centripetal flow. Classification accuracy is low because it is not completely dispersed in the flow, the air flow is a vortex instead of rectification, and the separation field is a point or line in the classification chamber. It is only to compare.

Next, the type that uses a screen is generally a rigid type, and the method is that the powder dispersed in the air stream is collided with a vertical screen and coarse powder is passed through below the opening of the screen. It is separated into powder and fine powder.
However, not all of the fine powder passes through just by colliding with the screen once, and the coarse powder containing a large amount of fine powder falls and is discharged by gravity.

To compensate for this, there is a method to keep the powder in a floating state inside the screen, but the primary dispersed air flow from the top side and the clogging prevention air flow from the side surface create a vortex inside the screen, and let the coarse powder fall. Then, naturally, most of the fine powder also falls to the coarse powder side and is discharged.

Lastly, the horizontal type does not have the effect of gravity to discharge the coarse powder, so that the movement and discharge functions of the powder inside the screen become insufficient. If the air flow on the inlet side is fast, fine powder will flow out directly from the discharge port, and if it is slow, it will be deposited inside the screen and will be discharged without reaching the mesh surface.
This is also true for flat screens, which is a cause of low classification accuracy.

It is an object of the present invention to provide a sieving method and a device for realizing high classification accuracy, which is low in classification accuracy in which a large amount of fine powder remains in coarse powder of the prior art.

In the case of a powder having a small particle size, for example, wheat flour, a force of attracting each other is exerted between the particles, and the particles are likely to be aggregated into “damage”. 0 for flour.
13mm or less, but generally 1mm when making bread dough
Remove the lumps with a tea strainer with a small opening. This is because it is easy to aggregate with an opening of 1 mm or less, which is difficult to pass through.

In this way, the smaller the particle size, the more reliable the dispersion, and the individual particles need to pass through the mesh. In the present invention, when the powder enters the screen by the primary air flow blown from the outer peripheral gap of the feeder outlet, the powder is dispersed in the air stream, and once collided with the screen, the powder reached the screen with insufficient dispersion. The object is fluidized by the rotation of the screen and the movement of the spiral groove, and further the secondary air flow is blown out from the gap of a certain width under the net to be dispersed, and it has a mechanism that acts until it reaches the outlet.

Subsequent accurate classification means that particles slightly smaller than the size of the mesh pass through. However, particles do not enter the opening at once, and many of them hit the wire of the net and are repelled. In other words, it is necessary to increase the chances of contacting the net. In the present invention, a net is wound around the outside of the spiral groove to form a screen cylinder, and the field of separation is formed into a spiral zone of the net by rotating, and the separating force is applied for a long time.

When fine powder is sucked from the lower part of the casing through a cyclone, the airflow inside the casing is slow except for the primary air flow and the outlet of the secondary air flow. It becomes a swirl toward the exit.

Therefore, the particles that once jumped up inside the screen ride on this vortex and reach the net.

An embodiment of the present invention will be described with reference to the drawings,
A screen 4 is formed by forming a through hole in a closed casing 15 and winding a mesh 5 around the spiral groove 4 to form a cylinder. The inside of the groove is a partition wall, the outside is the mesh 5, and the stroke is the length of the mesh. 5, 10, 11 can be rotated and sealed on the drive wheel 9.
13 The air flow control valve 3 is installed so that it can be installed in one of the holes and supplies the primary air flow blown out from the outer peripheral gap of the feeder 2 to one hole 3
And a primary air reservoir 16, a primary air flow supply device consisting of a gap between the feeder 2 outlet and the primary air reservoir is attached, a lid having a coarse powder outlet 12 is attached to the other hole, and the cylindrical screens 4, 5,
On the lower side of 10, 11, there is installed a secondary air flow supply device consisting of an air volume control valve 7 that blows out toward the powder amount from the lower surface of the net and a secondary air reservoir 8 having an air outlet of a certain width, and the casing.
The lower part of 15 is characterized by having a suction port that also serves as a fine powder outlet 6 and connects to a cyclone.

To explain the mechanism below, the raw material powder is supplied from the screw feeder 2 and is dispersed by the primary space flow blown from the outer peripheral gap of the feeder outlet of the primary air reservoir 16 through the attached air volume control valve 3. The dispersed powder reaches the net 5 along the spiral groove 4. When air is sucked from the fine powder outlet 6, the secondary air flow is blown from the lower surface of the net 5 toward the powder layer through the air volume control valve 7 through a gap of a constant width on the upper surface of the secondary air reservoir 8. At the same time, the drive wheel 9 allows the mesh 5, the spiral groove 4, and the mesh frame.
10, when the screen consisting of the mesh fixing band 11 rotates,
The powder once attached and deposited on the screen floats and disperses from the lower surface of the net 5 from which the secondary air flow blows along the groove, and the fine powder rides on the vortex from the upper and side surfaces of the net 5 and sequentially passes through the screen. This operation is repeated until the coarse powder reaches the coarse powder outlet,
The coarse powder outlet 12 is discharged through a rotary valve, and the fine powder is collected from the fine powder outlet 6 through a cyclone and a bag filter.

The effect of the present invention is less than fine powder which is said to be difficult to sieve by sieving in classified coarse particles and having a low fine particle mixing ratio, that is, fine powder is sieved again using a finer mesh. That is, it is possible to obtain a sieved product having a uniform particle size range.

[Brief description of drawings]

 1 is a cross-sectional view showing an example of the present invention. FIG. 2 is a cross-sectional view taken along the line AA of FIG.

Claims (3)

[Claims] 1. In the classification of powders, the powders dispersed in an air stream are made to spirally flow along a mesh so that the separation field is made into a spiral zone of the mesh, and it is allowed to act for a long time. The characteristic sieving method. 2. In a powder classifying apparatus, a through hole is formed in a closed casing, and a net is wound around the through hole to form a cylinder, the inside of which is a partition wall of the groove, and the outside of which is a mesh. , The stroke can rotate the screen consisting of the groove length,
It is attached so that it can be sealed, and one of the holes is equipped with a device that supplies the primary air flow blown from the outer peripheral gap of the feeder outlet.
A lid with a coarse powder outlet is attached to the other hole, a device for supplying a secondary air flow blown from the lower surface of the net is installed below the cylindrical screen, and a cyclone that also serves as a fine powder outlet is provided at the bottom of the casing. A sieving device having a suction port connected to it. 3. A sieving apparatus according to claim 2, wherein a thin plate having a hole formed outside the spiral groove is wound around the spiral groove.