SU1755948A1 - Method of classification of powders - Google Patents

Abstract

Use: separation of fine materials into a number of narrow fractions in powder metallurgy, production of synthetic diamonds and other industries. SUMMARY OF THE INVENTION: The method includes introducing the powder onto a sieve cloth installed in a confined space, supplying additional particles and blowing the powder and additional particles with a gas stream. The extra particles have a soaking speed of 20-90 times that of the boundary grains of the powder and are fed to a sieve cloth. The gas flow rate is set equal to the soaring speed of the boundary powder grains, and the products are withdrawn along the periphery of the closed volume. 1 il.

Description

The invention relates to a technique for classifying polydisperse materials by particle size and can be used in powder metallurgy, the production of synthetic diamonds and other industries, primarily for the separation of fine powders into a number of narrow fractions.

A known method for the classification of powders, including the filing of the source material on the sieve and blowing it from the bottom by the gas stream.

The disadvantage of this method is the low separation efficiency caused by blocking the sieve holes with large particles of the material being classified.

The closest to the invention is the method of separation of granular materials by size, including the introduction of the initial powder on a sieve fabric installed in a confined space, blowing it from the bottom with a gas stream, followed by removing the separation products and feeding coarse-grained additional particles into the sub-gas stream.

Additional particles are picked up by the flow and move towards the sieve surface. When it hits, the sieves are partially cleaned, resulting in improved separation quality.

However, coarse powder accumulates on the screen surface during the separation process, which prevents the release of fine particles, which reduces the intensity of the process and the quality of the products. Not all of the grains stuck in the cells, powder grains are ejected from there by coarse particles. Some of them are crushed by blows, resulting in fractional flow

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becoming lower product changes, which also reduces the quality of separation. In addition, a high gas velocity is required to feed the coarse material to the surface of the sieve. Frequent impacts of large particles on the sieve polter lead to accelerated wear. As a result, the economics of the separation process are reduced,

The aim of the invention is to improve the quality of the classification.

The goal is achieved by the fact that in the method of classification of powders, including the introduction of powder on a sieve cloth installed in a closed volume, the supply of additional particles, the blowing of powder and additional particles from the bottom by a gas stream, their suspension, separation into fractions and the output of separated products , additional particles are fed to the screening cloth, while particles with a soaring speed, 20–90 times greater than the soaring speed of the boundary grains, are used as additional particles. , The gas flow rate is set equal to the velocity boundary Withania powder grains, and the output of products is carried out along the periphery of the enclosed volume.

The delivery of additional particles with a soaring speed to a sieve cloth installed in a closed volume is 20–90 times greater than the flow velocity and the soaring speed of the powder's border grains, which results in a uniform distribution of the mixture of material being divided allows to reduce the concentration of the powder at the surface of the web and speed up the passage of products through the sieve. Additional particles purify the sieve cloth, thanks to which the quality of separation is improved. The removal of powder along the periphery of a closed volume also increases the efficiency of the separation process.

The drawing shows a device for carrying out the proposed method.

The device comprises a container 1 with lower and upper flanges 2.3 and a feeder 4 located in it. A screen sieve 5 is installed in the lower flange 2. A duct 6 connected to the upper flange 3 is connected to a cyclone and a suction system (not shown). Between the flanges 2.3, along the perimeter of the web 5, a perforated surface 7 is installed, forming together with the web 5 and the flange 3 a closed volume. On the screen 5 are placed additional particles 8, having a soaring speed, 20-90 times greater than the speed

vitani boundary grains of the powder to be separated.

The method is carried out as follows. When the suction system is turned on, an air flow is generated that passes through the screen 5, the pores between the additional particles 8 and the box b (the direction of air flow is shown in solid lines). The flow rate is set equal to the soak rate of the boundary grain of the powder to be divided.

A feeder 4 feeds the polydisperse powder onto the screen 5 (the direction of movement of the powder particles is shown by dashed lines). Under the action of the flow, the particles 8 and the particles of the powder in a closed volume are transferred to a fluidized state. Since the soaring speed of additional particles v is 20–90 times the soaring speed of the boundary grains of the powder vp, and the flow rate w is equal to the soaring speed of the boundary grains, the fluidization of the particles 8 and the powder will be uniform. At a vitanization rate, fluidization becomes non-uniform: the proportion of gas passing through a closed volume and the pores between particles in the form of bubbles increases. At the soaring speed, the mixture of particles 8 and the powder lies almost motionless on the canvas 5 and does not go into a fluidized state, which has been established experimentally and follows from the analysis of literature data

The suspended particles of the powder are distributed along the height of the closed volume in such a way that large particles are below the sieve cloth and small (borderline) particles at the top, the soaring speed of which is equal to or less than w. Under the action of the stream, fine powder particles are carried away through the box 6 into the cyclone. The large ones pass through the web 5, and the particles of intermediate sizes are removed through the perforated surface 7. The additional particles, interacting with the powder, accelerate its removal into the separation products by pushing the powder through the screen sieve 5 and the perforated surface 7.

Thus, the introduction of additional particles on the screening cloth with a soaring speed v, 20-90 times the soaring speed of the boundary grains of the powder vp, and feeding the gas stream with a speed w equal to Vp, improves the quality of the separation process. The removal of powder particles around the periphery of a closed volume also improves the quality of separation. For carrying out the separation process, lower gas flow rates are required than in the known method, as a result of which

with the energy cost of carrying out the process and reduced particle abrasion. Below are the results of experimental tests on the model of the described device. The screen cloth in the form of a circle and a perforated surface are made of stainless steel mesh with a mesh size of 150 microns. The diameter of the web is 60 mm, the height of the perforated surface is 170 mm, the diameter of the container is 100 mm. The air flow is created by a vacuum cleaner. The separation is subjected to polydisperse powders of titanium carbide with a particle size

less than 63 microns. The boundary size 51 (i.e., the particle diameter over which separation is carried out) is 10 µm. The speed of such particles is 1.5 m / s. In the experience of the N 7 boundary

the size (51 is 15 µm, and the winding speed, 3–10 m / s. Expanded polystyrene particles poured on the sieve cloth were used as additional particles. The height of the bed in a stationary state is 40 mm. The test results are tabulated.

As can be seen from the presented data, in the absence of additional particles on the screen cloth, powder separation does not occur. In this case, the powder leaves the feeder and almost all of it passes through the screen into a large product. When the soaring speed of the particles of the layer is greater than indicated in the claims (experiment no. 5), the layer is not fluidized and separation does not occur. At a low soaring rate of additional particles of the layer (experiment No. 4), the homogeneous liquefaction is disturbed, the layer begins to boil, and almost all of the powder particles are brought to the surface.

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Some particles of the bed are carried away with the powder into the cyclone. And only in the specified range of soaring speeds does an intense powder classification occur.

Thus, carrying out the method on a laboratory model allows us to conclude that it works and is highly efficient. Compared with the basic object - classifier VTSK-4, the use of the proposed method in the separation of powders allows to increase the productivity of the process by 4-6 times and to reduce the air consumption for separation by 2.5-3 times. The technical characteristics of the classifier are reflected in the avenue of the international exhibition Khimi-82 (Moscow, Krasna Presn, September 2-16, 1982.).

Claims (1)

Claims: A method of classifying powders, including the introduction of powder onto a screening cloth installed in a confined space, the supply of additional particles, the blowing of powder and additional particles from the bottom by a gas stream, their suspension, separation into fractions and the output of separated products, characterized in that , in order to improve the quality of classification, additional particles are fed to the sieve cloth, while particles with a soaring speed of 20–90 times greater are used as additional particles, Withania velocity boundary grain powder, gas flow rate is set equal to the velocity boundary Withania powder grains, and the output of products is carried out along the periphery of that closed volume.