Apparatus for producing fine metal powders

 

The invention relates to powder metallurgy, to a device for the production of fine metal powders by condensation from the vapor phase. In the proposed device, containing a metal evaporator, a plasma generator in the form of a nozzle-anode and cathode, the camera condensation and powder collection chamber connected with the evaporator of metal through the nozzle-anode according to the invention, the nozzle-anode made supersonic, the cathode is placed in the nozzle-anode, and the evaporator is made in the form of a vacuum melting furnace. Provided the process of obtaining a fine powder with the process of remelting of the metal and consequent saving of energy required for melting metal and capture the evaporating metal. 1 Il.

The invention relates to the field of powder metallurgy, in particular to the production of fine metal powders by condensation from the vapor phase.

Known methods for producing metal powder from the gas phase during arc spraying of metals, evaporation of metals in the atmosphere of inert gas, the evaporation of metals in vacuum and others [1]. In these methods, various methods carry out heating of the evaporated metal to a high temperature at which the low temperature, where is the condensation of the metal vapor in the gas volume and on the cold walls of the chamber.

Known devices are stand-alone camera, pumped up to a certain pressure or filled with inert gas, in one of which are the evaporators /crucibles, boats, electric arc/, and the other cooled parts of the camera are collections of powder.

Known methods and devices include two opposite stages: first, the necessary heating of the evaporated metal to a high temperature to obtain a metal vapor and, secondly, rapid forced cooling of the obtained vapor to create the conditions in which they glut.

And on the cooling rate and the degree of supersaturation of the metal vapour vary the size of the obtained powder. With a slow cooling rate vapor, which corresponds to the known methods [1], the range of particle sizes is very wide. Therefore, in the resulting product, except for particles with desired size, contains particles of very small size, to catch which is very difficult.

In metallurgy when the vacuum remelting of metals, on the contrary, it is necessary to use techniques that reduce the loss remelted metal evaporation. For example, prerana reach 7% [2]. Remelting of metals is carried out in a wide range of pressures of the inert gas from 10^-2mm RT.article to tens of atmospheres [2]. The increased pressure in the furnace by introducing inert gas into the furnace substantially reduces the rate of evaporation of the metal, but this measure causes complication melting equipment.

When remelting of Nickel and Nickel-based alloys solves the problem of removal of the metal or alloy of harmful impurities such as lead, arsenic, zinc and others [2]. Moreover, it should be noted that these impurities emitted into the atmosphere that are harmful not only to metals, but also for humans and the environment.

The disadvantages of vacuum remelting of metal are metal loss by evaporation during the melting and removal of the gas environment of the metal vapour from the furnaces, which cause harm to humans and the environment.

The known method of production of fine metal powders [3]. In the known method, the metal powders are served in the plasma jet two independent burners, components with each other at a right angle. In the hot zone of the powders melt and evaporate, and in cold regions of the jet is the condensation of the vapors in fine powder. The process takes place in the isolated working volume.

To spending on evaporation source metal powder.

Known apparatus for producing fine metal powders [4] . The known device comprises a node melting and evaporation of the metal, the plasma generator and camera collecting powder.

The disadvantages of the known devices [4] should be attributed to the evaporation of the metal in the evaporator, as it requires significant energy costs.

As the closest analogue for the proposed device is invited to consider the device for the production of fine metal powders containing metal evaporator, a plasma generator in the form of a nozzle-anode and cathode, the camera condensation and powder collection chamber connected with the evaporator of metal through the nozzle-anode (see EN 2116868 C1, class B 22 F 9/12, publ. 10.08.1998).

The objective of the invention is the saving of metal by reducing emissions of metal vapor vacuum furnaces for melting metal.

The technical result consists in the combination process to obtain fine powder with the process of melting metal, and dealt with this saving of energy required for melting metal and capture the evaporating metal.

The technical result is achieved in that in the apparatus for producing fine metal powders containing ISPU with the evaporator of metal through the nozzle-anode, according to the invention, the nozzle-anode made supersonic, the cathode is placed in the nozzle-anode, and the evaporator is made in the form of a vacuum melting furnace.

When the vacuum remelting of metal formed of a pair of metal before getting in a suction system, is passed through an electric arc, burning in front of a critical section of a supersonic nozzle and supersonic speed releases in the camera condensing and collecting the powder. The process of production of fine metal powder with the process of remelting of the metal leads to saving of energy required for melting and vaporization of the metal, and reducing emissions of metal vapor in the surrounding atmosphere.

Gas atmosphere furnaces for vacuum remelting, containing pairs of metals in contact in the region of the nozzle, in which an electric arc, is heated to high temperatures /T>10⁴To/. At the end of the gas through a supersonic nozzle-anode extension and sharp cooling /10⁴-10⁷To/from/ gas flow. Moreover, the cooling rate depends on the initial temperature of the expired gas environment. The higher the temperature the initial expiration, the greater the initial cooling rate. As a result of this sharp kondensation and further coagulation of the particles into larger particles. Such particles are less affected by the gas flow and easily assembled in the collections of the powder.

Slow change of temperature of gas medium, which corresponds to the flow of the gas environment on the suction vacuum line such conditions glut metal vapor is not generated. In the result, are formed of very fine metal particles, which are almost impossible to catch and, therefore, they, together with the gases are ejected through these pumping systems in the environment.

An example of the production of fine metal powders is as follows. A pair of metal produced in furnaces for melting metal, is passed through an electric arc burning between the cathode and the nozzle-anode in subcritical section of the nozzle. In the post arc gas environment containing a pair of metal is heated to high temperatures10⁴Because the Nozzle-anode is throttling element and serves to create a pressure differential. At the end of the hot gas environment in the chamber condensing and collecting powder with low pressure leads to expansion and a sharp cooling of the gas mixture, resulting in a high degree of supersaturation of the metal vapour. As a result of strong PE the condensation of the metal vapor continues by joining the nuclei of certain atoms of the metal. Simultaneously with this, there is coagulation of the particles into larger particles. At some distance from the nozzle-anode, on which the density of metal atoms due to their condensation becomes very small, the interaction between the individual metal atoms and a condensation nuclei, and between nuclei does not occur, the growth of particles stops. Formed particles poured down the camera and after the termination of the process of remelting removed from it.

When remelting of metals that can form nitrides, for example, when the melting of titanium, chamber volume, which occurs after the gas environment, it is advisable to add nitrogen. In the interaction of metal particles with residual nitrogen atmosphere can be formed valuable powder is titanium nitride. Adding a camera other reaction gases, oxygen or carbon, will take the form of powders of oxides or carbides of metals.

To perform the described method of producing fine metal powders offered the device shown in the drawing.

From otkachnoj vacuum line 1 connecting the furnace for remelting metal 2 with the vacuum evacuation system 3, is given pipe 4 connecting magist chamber 5 through the pipe 6 to the same vacuum system 3. Highway 1 has a valve 9 and the outlet 4 - valve 10. At the bottom of the chamber 5 is equipped with a valve 11. Metered flow of the reaction gas in the chamber 5 is carried out using a flowmeter 12 and control valve 13. Power to the electrodes 6 and 7 are supplied from the constant current source 14. Sypko resulting powder from the chamber 5 passes through the valve 11 into the container 15.

The device operates as follows. At the initial stage of the process of melting metal are pumped out of the furnace for remelting metal 2 by the vacuum pump system 3 adsorbed gases when closed, the gate valve 10 and open the valve 9. When the temperature in the furnace, which starts the evaporation of remelted metal, the valve 10 is opened, and the valve block 9 and carry out the ignition of the arc between the cathode 7 and the nozzle-anode 6. Power to the electrodes supplied from the power source 14. Then to complete the process of melting metal pumping out from the furnace 2 are carried out through the pipes 4 and 8. Formed during sudden adiabatic cooling of the hot gas environment of the metal powder is poured down the camera 5, and accompanying gases discharged from the chamber 5 through the pipe 8 by a vacuum pump system 3. Upon receipt of the nitrides, the 12 and control valve 13. Upon completion of the cycle of melting metal /or more cycles of the obtained fine powder is poured into the container 15 through the valve 11.

The use of the proposed device for the production of fine metal powders, which uses the drawback existing in metallurgy production, namely metal loss by evaporation during the melting of the metal in vacuum furnaces, allows to reduce the emission of metal vapor contained in the gas furnaces in the smelting of metal, and, therefore, reduce their harmful effects on humans and the environment. Simultaneously, the possibility of production of fine metal powders, as well as nitrides, carbides and oxides, which can be used directly in powder metallurgy.

Sources of information 1. Romanowski W., Engels S. Hochdisperse Metalle. - Berlin: Akademik - Verlag, 1982. - 171 s.

2. Lakomski Century. And. Plasma-arc remelting. - Kyiv: Tekhnika, 1974. - 336 S.

3. Pat. Japan 51-13262, CL 01 F 15/06.

4. Pat. Japan 61-179806, CL 22 F 9/14.

5. Sutugin A. G., Grimberg A. N. Condensation of the steam by cooling submerged jet //thermal physics of high temperatures, 1975, T. 13, 4, S. 787-795.

Claims

The device is a nozzle-anode and cathode, the camera condensation and powder collection chamber connected with the evaporator of metal through the nozzle-anode, characterized in that the nozzle-anode made supersonic, the cathode is placed in the nozzle-anode, and the evaporator is made in the form of a vacuum melting furnace.