A method for rapid cooling of the molten ceramic material

 

(57) Abstract:

The invention relates to methods for producing fused powdered ceramic materials. Developed process that provides rapid cooling of the molten ceramics by entering jet of molten ceramics in turbulent fluid flow. Jet ceramics is broken into small particles that harden when passing through the cyclone and then separated from the flow stream and collected in the form of fine dry particles of a ceramic material. The method allows to obtain a fused ceramic material, which can be cooled with a minimum emission of dust to obtain a relatively homogeneous spherical particles. 6 C.PF-ly, 3 ill.

The present invention relates to fused powdered materials. More specifically, the invention relates to methods for producing such fine materials, particularly ceramics. It is well known that the material obtained in the molten state, must be quickly cooled to the desired temperature. This can be done by pouring the melt into water, but it releases a lot of steam and requires a large amount of water. In addition, water may is military material to the cooling medium type of steel balls or in the cavity between thick steel plates. Cooling of the material on steel balls is always associated with the issue Department of the frozen product from the cooling medium. If the material is placed between the steel plates, the latter quickly lose their cooling properties and must be replaced after a certain period of time. Air or water cooling solves both of these problems, but its disadvantage is that it cannot provide the primary material that can be crushed to particles of all sizes that are required in the production of abrasive materials.

However, for ceramic and refractory materials, it is preferable to use air cooling of molten materials. In this process the stream of molten material is injected into a stream of cold air pumped under high pressure. Turbulence breaks up the flow of material into droplets, which are then cooled by air, and around the droplets formed by the shell, whose thickness increases up until all the drop will not harden. This process is described in U.S. patent N. 3.831.857, N. 4.897.111 (where instead of air is used liquefied gas in turbulent flow), and also in British patent N. 1.478.087 (which Ispolkom patent N. 2.146.662-A. Receipt of ceramic powders by rapid cooling of the melt is also known from SU 1444323 A1. These processes are also not without problems, as it is found that the composition of the droplet/particle must go through as much as 5 meters before the shell will be strong enough to withstand the forces of interaction between particles, which could damage the membrane and cause fusion of the colliding particles. In addition, this process produces a large quantity of dust that pollutes the environment and must be registered by the respective filters.

Now developed a new method that allows to obtain a fused ceramic material, which can be cooled with a minimum emission of dust to obtain a relatively homogeneous spherical particles. This method can be used to produce various ceramics including Zirconia stabilized with yttrium, alumina, a mixture of alumina and zirconium oxide, magnesium oxide, etc.

General description of the invention

In accordance with the present invention developed a process for rapid cooling of the molten ceramic material which comprises feeding a stream of molten keetsa into droplets, captured turbulent flow and cooled. The cooled droplets are then subjected to further cooling and separated from the fluid flow in the cyclone separator, and flow is introduced tangentially to the wall of the cyclone separator.

In a preferred process variant, the flow of fluid consists of water droplets or contains water droplets captured by the air flow, you can use the flow of the medium containing only air. However, the presence of water is desirable because water drops considerably increases the efficiency of cooling of the molten ceramic drops. Also found that instead of air can be used with other gases type carbon dioxide and nitrogen. However, the obvious advantages of air due to its low cost and availability usually make this choice most preferred.

In a preferred embodiment of the invention, air or mixture of air and water is pumped through the arcuate slit with the concave side of the arc upward. The flow rate of the gas is such that captured the molten material cannot penetrate through the gas stream, which forms a sort of canal, along which is moved the nutrient inlet for the flow in the upper part of the funnel and the outlet opening in its lower part. Flow enters through the inlet so that it flows around and along the inner wall of the separator in a spiral up to exit through the outlet. In the course of the process air and the water vapor generated during cooling of the ceramic melt, if the cooling medium contains water), produced through the upper part of the cyclone. Frozen droplets and not evaporated water (if water is included in the cooling of the mixture) are released through the bottom of the cyclone and separated. Then the particles pass through a stage of drying.

It is often desirable to provide a cyclone internal baffles to suppress vortex jet, which can cause vibration, able after some time to break the integrity of the system. The upper part of the cyclone can be provided with a gas removal system, but it is most expedient to perform the upper part of such a length that the cover of the apparatus would be above the entry opening material. In this case, the upper part of the cyclone can be opened without any problems.

Given the significant heat transfer of the cooling medium in the cyclone, it is desirable to provide at least part of the cyclone by a cooling jacket to absorb the generated heat. If the cyclone entered the water horse the second case you can display particles with sufficient residual heat to natural drying without the use of a separate dryer. In this case, the drying can be performed by simple physical extraction of water, when the particles of the material to dry in air in a thin layer on a conveyor belt.

The present invention can be most successfully applied in the manufacture of processed materials that are required in the form of small crystals. The invention is of particular importance in the production of zirconium refractory materials where rapid cooling in an oxidizing environment reduces the amount of nitride and carbide components in the final product. In refractory industry fully oxidized products are considered the most beneficial. This can also be attributed to rapid cooling of the abrasive materials based on aluminum oxide and zirconium, where rapid hardening tends to stabilize the tetragonal form crystals of zirconium oxide, which improves abrasive properties. In addition, by adjusting the turbulence of the flow, it is possible to obtain particles of the material divided by size, which can be used directly or further crushing or classification by size, as abrasive materials.

In the drawings shows:

Figure 1 is a vertical cross-section of the device>Figure 3 is a variant of the device, which uses water gun.

Description of the preferred variants of the invention

The following describes different ways of the invention with reference to the attached drawings.

The figure 1 shows a furnace 1, which is used to receive the molten ceramic material. From the furnace the molten material through the outlet 2 is fed to the input 4 of the cyclone 6. The melt flow fond of flow of air, water or a mixture of air and water passing through the nozzle 3. Additional cooling water may also be introduced through the annular gap 5 at the entrance 4 to the cyclone 6. Exciting fluid nozzle operates under high pressure, creating a turbulent zone between the outlet and the inlet of the cyclone, so the flow of the melt is broken into small droplets, which has hardened and cooled at the inlet to the cyclone. The extension 7 of the cyclone above the point at which the material enters the cyclone, which prevents the escape of particulate material from the cyclone while the system is running.

The cyclone can be equipped with baffles (not shown), providing a more uniform cooling and reduce possible vibration. When the thread exits qi is the material is fed onto the conveyor belt 10.

It is also possible and advisable to place another cooling system before the cyclone, so that the whole of the molten product was hardened to the inlet of the cyclone, which is used for further cooling of the ceramic product and water separation. One variant of such additional cooling system is a "water cannon", and variant system equipped with such a device, shown in figure 3. The molten product is poured from the furnace 1 through the drain hole 2, and the flow of the cooling medium is supplied from the nozzle 3 and is directed down the length of the water gun 14 with plenty of water rings 15, the jet which is directed into the barrel of the gun at a certain angle along its length. Before each ring has a reflective aperture to prevent settling of the product on the rings and possible steam explosion. Output water gun is located at the entrance to the cyclone.

The advantage of this system is that if necessary, you can use a large amount of cooling water. In addition, by using a water gun with plenty of cooling rings with selectors, it is possible to accurately adjust the amount of cooling water. The water cannon can be separated from the cyclone or Monterosa environment can only be water, only air or a mixture of both these environments. In one preferred embodiment of the invention in air-water flow of the air is supplied under pressure of 6.3 MPa, and the water is under a pressure of about 3 ATM through the half-open tube with a diameter of one inch. In this case the product was a zirconium oxide stabilized with yttrium oxide (about 5% weight. yttrium). Obtained with this device the final product had a particle size less than 100 mesh and consisted mainly of coarse quarter-inch pellets.

Usually by spraying water (without air) out large particles, few of which have a size less than 40 mesh. Use only air provides the obtaining of much smaller particles, and the combination of water with air to give an intermediate distribution of particles by size, however, the higher the speed of flow of the spray liquid through the nozzle 3, the better the dispersion and the smaller the size of the obtained particles. As you might expect, the flow of molten ceramics also affects the roughness of the particles: the higher the flow rate of the melt, the coarser particles of the product under any flow of the cooling medium.

The effectiveness of the proposed device were evaluated using the water was the screen by passing water under pressure 3 ATM through an annular nozzle. With less than 3% weight. the coarse product is passed through a sieve with a mesh size of 40 mesh.

If the air pressure of 5.6 ATM is fed through the inlet nozzle and the water screen, the resulting product consists of much smaller particles.

When using ceramics, including 10% aluminum oxide, 5% of silicon oxide and 85% of zirconium oxide, by spraying water through the annular nozzle when the air passes only through the air nozzle, the efficiency of 99.78% of the product deposited on the sieve with mesh size of 70 mesh. and 90.6% of delayed sieve with a mesh size of 30 mesh. Only 42,28% weight. have a particle size of 12 mesh.

When using the same ceramic, but without water flow from the annular nozzle, and the air mixture flow of water through the inlet nozzle, observed the same picture when 99,79% weight. remain on a sieve with a mesh size of 70 mesh and approximately 40,47% weight. particles have a particle size greater than 12 mesh.

Using only the air in the inlet nozzle without the use of water through an annular nozzle distribution of particle size was somewhat more uniform, when only 91.2% in weight. was retained on a sieve with a mesh size of 70 mesh 59,75% weight. on a sieve with a mesh size of 30 mesh and only 19,17% of the particles have a size greater than 12 the AP molten ceramic into turbulent flow of the at least one fluid medium, in which a jet of molten ceramic is broken into a stream of droplets captured by the flow of the medium in the form of solidified particles are introduced into the cyclone tangentially to the wall of the cyclone.

2. The method according to p. 1, characterized in that the ceramic material is selected from the group consisting of magnesium oxide, aluminum oxide, zirconium oxide, mixtures of aluminum oxide with zirconium oxide and aluminum oxide or zirconium with the addition of small amounts of yttrium, silica, magnesium oxide and mixtures thereof.

3. The method according to p. 1, wherein the turbulent flow of fluid comprises air, or water, or a mixture of air and water.

4. The method according to p. 1, wherein the turbulent flow of the fluid entrains the molten ceramic water through the screen.

5. The method according to p. 1, wherein the turbulent flow of the fluid injected in the neck with a water gun.

6. The method according to p. 1, characterized in that the cyclone is equipped with internal baffles to break up the mixture of fluid with ceramics on individual particles.

7. The method according to p. 1, characterized in that the temperature of the cyclone is regulated so that the particles at the outlet of the cyclone retain the amount of residual is

 

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