JPS586251A - Wet type classifying method - Google Patents

Abstract

PURPOSE:To classify powder in a wet type with high accuracy by introducing liquid dispersed with the powder to be classified into beds wherein >=3 layers of granular packings of constant grain sizes are packed at the closest packing under differential pressures. CONSTITUTION:Liquid contg. the powder 5 to be classified is introduced into beds 2 packed into >=3 layers at the closest packing between metal screens or meshed trays 3 of openings smaller than spherical bodies by using differential pressures. While the liquid is passed between the clearances of the packings by this process, the powder 5 is classified. In this way, it is possible to remove coarse particles larger than distribution widths as well as to screen the particles of the same grain sizes by shapes and to eliminate clogging easily by backflowing.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for classifying wet powder with high precision. In recent years, there has been a need for techniques for precisely processing ceramics and the like, so it is desired to classify the abrasive grains with high precision so that they have a strict particle size distribution.

That is, in order to increase the processing speed of polishing, the coarser the grain size of the abrasive grains, the higher the processing efficiency, but if the width of the grain size distribution is wide, the finish of the polished surface will be rough. %, when coarse particles exceeding the particle size range are mixed in, scratches occur due to the coarse particles, resulting in a poor finished surface. Therefore, it is desirable that the abrasive grains used for precision machining have a particularly narrow particle size distribution and that coarse particles larger than the particle size range are mixed in.

As conventional methods for classifying abrasive grains, the most commonly used dry method is a method using a sieve, and the wet method is a water sieve method. When using a method using a sieve, the width of the particle size distribution cannot be determined when the particle size of the classified material is measured using a photographic method due to variations in the opening of the sieve and irregularities in the shape of the abrasive grains. It has the disadvantage of being wide and shifting toward the larger side. If particles with elongated shapes are mixed in, it is possible to sort them to some extent using a shape sorter, but this is not possible when the particles are small in size. When a sieve is used for a long period of time, it becomes clogged and efficiency decreases, but once the sieve is clogged, it cannot be recovered. In addition, in the case of abrasive grains that require strict classification, a Lo-Tap sieve shaker is used, but its capacity is small.

On the other hand, the water WtJ method is a method that takes advantage of the fact that the settling speed of abrasive grains in a liquid, mainly water, differs depending on the particle size. It is necessary to strictly control physical properties such as the viscosity and specific gravity of the liquid, and for this purpose, complicated and complicated means must be used. Also, since the water sieve method collects particles with the same final velocity as they settle in the liquid, elongated particles are classified as being equivalent to spheres with the same final velocity, regardless of shape. Therefore, there is a drawback that the shape of the particles obtained is non-uniform. Also, is it necessary to repeat the same operation for microparticles that are smaller than the target particle size range? However, it is difficult to remove coarse particles larger than the particle size range, and the presence of these coarse particles is a drawback of the abrasive material that deteriorates its quality as an abrasive material for precision machining.

Furthermore, since the water sieve method has a small processing capacity per unit cross-sectional area and time, it is necessary to operate a plurality of devices in parallel for large-scale processing, which requires a large floor area and increases construction costs.

The present invention relates to a wet classification method that improves the drawbacks of the dry sieving method and the wet water sieving method, and has the advantage of being able to remove coarse particles that are larger than the distribution width. At the same time, the present invention provides a method that has the advantage that it is possible to sort out the shapes of particles of the same particle size, and that clogging can be easily cleared by backflow.

The invention will now be explained with reference to the accompanying drawings. FIG. 1 is an example schematically showing the method of the present invention, and FIG. 2 shows an example in which a plurality of packed layers are stacked and used. FIGS. 3 and 4 compare the particle size distributions of particles before being classified by this method and particles after being classified using a photographic method.

In the figures, especially in FIG. 1, the portion corresponding to the sieve of this classification device is composed of three or more layers of close-packed spheres (1). This packed layer (2) is arranged between a flat wire mesh or a perforated plate (3) with an opening smaller than the diameter of the two upper and lower spheres, and the wire mesh or perforated plate is secured by a suitable tightening means such as a rubber gasket. The washer (4) is tightened to hold down the packed layer and prevent each sphere from freely vibrating and changing the distance between the spheres. From above this packed bed, the powder to be classified (
A liquid containing 5) is introduced from above to below using a pressure difference, and is classified into powder while passing through the gap between the fillers.

Arrows indicate the direction of liquid flow. The diameter of particles that can pass through the packed bed is 15.5% or less of the diameter of the filler, and this method reliably prevents coarse particles larger than the distribution width from passing through. Further, if the particles are of the same size, elongated particles cannot pass through the packed bed and are removed, so the shape of the particles classified by the sieving method is also carried out at the same time. As the classification continues, powder may get caught in the packed bed and cause clogging, but in this case, only the fluid is allowed to flow backwards to remove it. In addition, if there is a lot of clogging, the packed bed can be disassembled and removed, so it can be used repeatedly.
Furthermore, there is no disadvantage such as unusability. Furthermore, since the particles are introduced by the pressure difference of the liquid, the time required for classification is very short and it is easy to expand the method to an industrial scale.

As a method of utilizing the present invention, as shown in FIG. 2, a plurality of packed beds may be stacked at intervals in descending order of particle size from above. Particles that have passed through the first stage packed bed following the liquid flow in the direction of the arrow 1ml, that is, the particle size is 31
Of the particles that are 1 &51% of the diameter of the spheres constituting the 11th stage packed bed, 1% of the diameter of the spheres constituting the 2nd stage packed bed
Particles with a particle size of 5.5- or less are likewise forced by the liquid stream to the next stage.

Particles accumulated between each packed layer can be removed by appropriate means. In FIG. 2, water is introduced from the inlet (6) in the direction of the arrow and taken out from the bottle outlet (7). or,
When a blockage occurs, use the arrow 1o1 from the inlet port (8).
This can be solved by supplying water in the direction of and causing it to flow backwards. According to such a multi-stage classification method, powders can be classified into powders having a narrower particle size distribution width than conventional ones according to the selection of spheres in the packed bed. In view of the above points, the method of the present invention greatly improves the accuracy of classification.

It is desirable that the sphere of the filler used to carry out the present invention be a true sphere with constant dimensions;
Glass balls and steel balls are also suitable as fillers because they are manufactured in various sizes.

By the way, the sieve specified by JISK has a ratio of 0 openings.
The ratio decreases in order, but the smallest is nominal size 57
There are only up to μ. Therefore, the size of the sphere corresponds to the 0 opening of the sieve specified in JIS, for example, the nominal size 25.
When spheres of 0# to 57s are used as a multi-stage packed bed and the spheres with a smaller diameter are classified, they are classified into a series of spheres with a narrow particle size range having a diameter approximately 15.5% of the original sphere series. . Using each of the obtained spheres as a multi-stage packed bed, and then classifying the spheres with smaller diameters, the process of sequentially repeating the process until the particle diameters of the spheres constituting the packed bed are uniform allows for fine particles that do not have a sieving standard. By further extending in the direction, a packed layer with a zero opening ratio of W can be created. Therefore, by using this method to create a packed bed with a ratio of 0 + 4, it is possible to distinguish particles of several microns by the ratio, and even fine particles can be significantly narrowed compared to conventional classification methods. It becomes possible to classify into ranges.

Next, an example will be described.

In this example, a mesh with a nominal size of 8B# is stretched perpendicularly to the longitudinal direction of the tube in a glass tube with an inner diameter of 8 m, and is fixed with a rubber gasket and a washer.
A glass ball (one that passed through a #125 sieve and remained on a #125 sieve) was placed on top and tapped several times from below to form a close-packed layer. The packed bed of glass bulbs is about 10 to 11 stages. The upper surface of the packed bed was pressed and fixed with a net having a nominal size of 88j in the same manner as the lower surface.

Connect the lower end of the glass tube to a suction flask, then connect the suction flask to a vacuum pump and while suctioning, add 1 g of 20/Boj diamond powder classified by the water sieve method.
was mixed with water at a temperature of more than 100 °C and thoroughly stirred, and the mixture was poured over the packed bed. The flow rate of water passing through the pipe is approximately 8
d/rn i n, -. The particle size distribution of the diamond powder sample before being classified by this method and the diamond powder recovered after classification was measured by an enlarged photo test method, and the results are shown in FIG. 3. The horizontal axis of FIG. 3 shows the biaxial average diameter in microns, and the vertical axis shows the number of particles in units of microns.

The particle size of the diamond powder sample that was only classified using the water sieve method is widely distributed from 17.5μ to 57s, as shown by the solid line in FIG. On the other hand, the particle size distribution of the particles remaining on the packed bed (dotted chain line) and the particles that passed through the packed bed (dashed line) are clearly different, and the latter has a narrow particle size distribution range from 17.5 to 50 s. It can be seen that particles with a large particle size are completely removed.

Example 2 Inner diameter 8 with water inlet and classified particle outlet in the middle
In the glass tube of (2), an inlet port was installed using the same method as in Example t.
Two layers of glass bulb packed layers were set up above and below the outlet. The glass bulbs used for the upper first stage packed layer were 425/3.
84μ, the glass bulb used for the second stage filling layer is 58475
50s, and the layer thickness was about 13-14 layers each. Connect the lower end of the glass tube to a suction flask, and while suctioning with a vacuum pump, mix 1 g of diamond powder sifted through a 65157p electronic sieve with 5001st or higher water, stir well, and add the mixture to the first stage packed bed. Injected from above.

The flow rate of water passing through the tube was approximately 201 Ij/min. Measure the particle size distribution of the diamond powder before classification by this method and the diamond powder at each stage after classification,
The results are shown in Figure 4. As shown by the solid line in Figure 4, the diamond powder simply sifted with a 65157p electronically shaped sieve has a wide distribution (distribution) from 42μ to 7Sμ, but the particles remaining on the first stage after classification by this method ( One-point chain m>
, particles obtained from the middle of the first and second stages (double-dashed line)
In the particle size distribution of the particles obtained from the bottom of the second stage (dashed line), the peaks are shifted in order, indicating that they are well classified. In particular, the particles recovered from between the first and second stages were 57
It is distributed in a narrow range from # to 69μ, and the second
It can be seen that the particles that passed through the stage are also distributed in a narrow range from 45# to 65s. It can be seen that particles with a particularly large particle size are removed.

[Brief explanation of the drawing]

FIG. 1 is an example schematically showing the present invention, and FIG. 2 shows an example in which a plurality of packed layers are stacked one on top of the other. 3 and 4 show the particle size distribution curves of the classified sample and the powder after classification. Patent Applicant Ishizuka Research Institute Co., Ltd. Figure 4 Shibuchi I 12 No Na is 1st Ward Department Kinji Support 8 Ru "Ero's Assignment Now Procedural Amendment (Method) % Expression % Engineering Incident Indication 1988 Patent Application No. 1041'78
No. 2 Title of the invention Wet classification method 3 Relationship with the case of the person making the amendment Patent applicant 4 Date of amendment order November 5, 1980 (shipment date
(November 24, 1981) 5. Subject of amendment Figure 6. Contents of amendment As shown in the attached sheet

Claims (1)

[Claims] +1) Three or more close-packed layers of spherical fillers with a constant particle size are formed, and a dispersed liquid such as powder to be classified is passed through one of the packed layers using a pressure difference. A wet classification method for powder, which is characterized by the following. (2) The wet classification method according to item 1, wherein a plurality of packed beds according to item 1 having different particle sizes of spheres are stacked at intervals in descending order of particle size.