RU2648615C1 - Method of plasmochemical metal refining in vacuum and plasmotron for its implementation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to non-ferrous metallurgy and can be used for refining metals in the melt state. Method includes heating and melting the metal in the melting pot, in the vacuum chamber, and cyclic plasma treatment of the alternating current of the melt surface, which contains the treatment period using moistened argon, the dry argon treatment period, the vacuum distillation period and the flux feeding period. Plasma torches are installed vertically above the surface of the melt and provide the possibility of highly effective plasma-chemical treatment of the melt surface in the vacuum at the high electrode resource. At the end, the melt is slowly cooled and the ingot is formed. Part of the ingot, where the impurities are concentrated, is separated.

EFFECT: method and plasmatron allow to increase the efficiency of plasma-chemical refining of any metals and to remove impurities.

2 cl, 2 dwg

Description

The invention relates to the metallurgy of non-ferrous metals and can be used to produce pure metals and alloys by refining in a melt state.

A known method comprising heating a silicon crucible to obtain a melt and treating the melt with a plasma torch directed at an acute angle to a surface containing an inert gas and water vapor, heating and melting the crude silicon in a cylindrical quartz crucible in vacuum using a graphite heater , then the silicon melt is processed using a system of three dual-mode plasmatrons with anodes isolated from the casing and a system for supplying water to the anode channel, first with dry argon plasma at a constant current of 50-80 A, then with humidified argon plasma at an alternating current of 100-200 A, after which a polycrystalline silicon ingot is formed by slow cooling of the melt in a quartz crucible (See RU 2465202 C2, application filing date: 17.11.2010, published on 27.10. 2012).

This method has several significant disadvantages. The surface treatment of the melt is carried out in one zone located between the plasma torches, where a high gas pressure is created, which is necessary for stable arc burning, as a result of which impurities with a low vapor pressure are slowly removed from the melt. Impurities with a vapor pressure lower than that of the metal are not removed at all. Evaporated impurities are deposited on the heater parts, damaging them, and on the plasma torch bodies, from where, after peeling, they fall back into the melt, polluting it. Large losses of heat absorbed by the plasmatron bodies from the chamber. A small resource of a tungsten cathode when using water vapor as a plasma-forming gas, necessary for the implementation of plasma-chemical processing processes.

The widely used principle of direct heating by electric arc gas discharge is implemented in many designs of arc and plasma-arc furnaces, which in turn are used in metallurgy of ferrous and non-ferrous metals. To obtain pure metals, vacuum plasma arc furnaces are particularly interesting, in which the melting and purification of metal is carried out under reduced pressure, using the thermal energy of an electric arc that directly affects the metal. Such equipment allows refining of metals using the vacuum distillation mechanism.

A known design of a melting plasma torch, including a water-cooled case, channels for supplying a plasma-forming gas, parallel to the axis of the plasma torch and connected to a vertically located water-cooled nozzle, electrical insulation, electric network, tungsten electrode-cathode, electrode holder, characterized in that the plasmatron is additionally equipped with a second channel for a plasma-forming gas supply with a nozzle, the nozzles being installed symmetrically about the axis of the plasma torch at an angle of 30-35 ° to the vertical the axis of the electrode holder (See RU 2524173 C1, application filing date: 02/13/2013, published 07/27/2014).

The disadvantages of this design include the impossibility of carrying out processes of melting and refining in vacuum, which is necessary for refining a metal by vacuum distillation, because of the need to create high pressure plasma-forming gases necessary for the stable operation of a tungsten cathode; low resource of a tungsten cathode when using water vapor and other active gases as a plasma-forming gas, the use of which accelerates the mechanism of metal refining by vacuum distillation; low efficiency of the process due to high heat loss due to the lack of thermal insulation of the cooled parts of the plasma torch from the inner space of the melting furnace.

The objective of the present invention is to eliminate the disadvantages of the known method and increase the efficiency of plasma-chemical refining of any metals and the efficiency of removing impurities by increasing the number of melt surface treatment zones in which low gas pressure is created, which contributes to the evaporation of impurities; organization of buffer gas flows, contributing to the effective removal of vaporized impurities and preventing their deposition on plasmatrons and heater parts; introducing powdered fluxes into the melt, in order to remove impurities, with a low vapor pressure; thermal shielding of plasmatron cases to reduce heat loss from the chamber.

To solve this problem, a method of plasma-chemical refining of metals in vacuum is carried out, including heating the metal in a crucible placed in a vacuum chamber using a graphite heater to obtain a melt and treating the melt with a plasma torch containing an inert gas and water vapor, and in accordance with the invention, the surface the melt is treated with alternating current plasma using one or more of the plasmatrons proposed in this application, mounted vertically above the surface of the melt and soda neighing cathode, anode with a high-pressure chamber, a throttling channel and a mixing chamber, an additional plasma-forming gas supply pipe flushed by cooling water, with a capillary installed inside, a DC arc power supply, two semiconductor diodes, a current limiting inductor, internal and external cylindrical screens installed axially symmetric with respect to plasmatrons, at a distance of 5-10 millimeters from the surface of the melt, from the spaces between the inner and outer cylindrical cranes pump gases, argon and flux powder are fed into the spaces between the plasma torches and the inner cylindrical screens, the treatment is carried out in cycles consisting of a treatment period using moistened argon, a treatment period using dry argon, a vacuum distillation period and a flux supply period, then the melt is slowly cooled and form an ingot.

The objective of the present invention is also to eliminate the disadvantages of the known plasma torch and increase the efficiency of plasma-chemical refining of any metals and the efficiency of removing impurities by introducing new elements into the design and their interconnections, allowing the processes of melting and refining in vacuum using active plasma-forming gases, to implement a highly efficient metal refining process by vacuum distillation, while maintaining optimal working conditions for tungsten Vågå cathode ensuring its maximum resource; to increase the efficiency of the melting process, through the use of thermal insulation of plasma torch parts from the interior of the melting furnace.

The invention is further explained with the help of schematic drawings, in which FIG. 1 illustrates a diagram of an implementation of the claimed method using the proposed plasma torch; FIG. 2 illustrates the design of the claimed plasmatron.

As shown in FIG. 1 and 2, the method is implemented in a device in which there is a steel vacuum chamber 1 with water-cooled walls and a hole 2 for pumping gases. At least one plasmatron for plasma-chemical refining of metals is installed in chamber 1. In this embodiment, three plasma torches are vertically mounted in chamber 1, each of which contains a body 3 made of steel pipe, pressed into a copper holder 5, a tungsten cathode 4, mounted in an insulator 6. A tungsten cathode 4, a copper holder 5 and an insulator 6 are placed in anode 7 electrically connected to the housing 3. The housing 3 is connected to the positive pole of the power source of the DC arc 8, see FIG. 1. The tungsten cathode 4 is connected to the negative pole of the power source of the DC arc 8, see FIG. 1. The tungsten cathode 4, the copper holder 5 and the insulator 6 limit the volume of the high-pressure chamber 9 made in the anode 7, which is connected through the throttling channel 10 to the mixing chamber 11, see FIG. 2. The pipeline of the main plasma-forming gas 12 is connected to the high-pressure chamber 9 through a channel 13 configured to provide a vortex direction of gas movement in the high-pressure chamber 9, see FIG. 2. Washed by cooling water forcedly supplied to the housing, the additional plasma-forming gas supply pipe 14, in which the capillary 15 is axially symmetrically located, communicates with the mixing chamber 11, see FIG. 2. The positive pole of the power supply of the DC arc 8 is connected to the cathode of the first semiconductor diode 16, the anode of which is connected to the current limiting inductor 17, see FIG. 1. The negative pole of the DC arc power source is connected to the anode of the second semiconductor diode 18, the cathode of which is connected to the current limiting inductor 17, see FIG. 1. The housing 3 is placed in an inner cylindrical screen 19 made of a quartz tube, placed axially symmetrically with respect to the housing, at a distance of 5-10 millimeters from the surface of the metal melt 22, see FIG. 1. and FIG. 2. A thermally insulating screen 20, a heating element 21, and a crucible 23, into which the metal 22 is charged, are placed in the chamber 1, see FIG. 1. The space bounded by the thermally insulating screen 20 is separated from the inner cylindrical screen 19 by an external cylindrical screen 24 made of graphite and placed axially symmetrically with respect to the inner cylindrical screen, at a distance of 5-10 millimeters from the surface of the melt, see FIG. 1. and FIG. 2. The space between the outer and inner cylindrical screens is connected to the volume of the chamber 1, from where the gases are evacuated, see FIG. one.

A device for implementing the method operates as follows. Gases are pumped out of the chamber 1 through the opening 2, see FIG. 1. Argon is introduced into the space bounded by the housing 3 and the inner cylindrical screen 19, see FIG. 1. and FIG. 2. Using a heater 21, a metal loading melt 22 is obtained, see FIG. 1. Plasma-chemical processing of the surface of the melt loading metal is carried out in cycles starting from the processing period using moistened argon, as follows. Argon is supplied to the main plasma forming gas supply line 12 and the additional plasma forming gas supply line 14, see FIG. 2. Next, turn on the power source of the DC arc 8, see FIG. 1 and initiate a discharge between the tungsten cathode 4 and the anode 7, see FIG. 2. Plasma jet 25, see FIG. 1, leaving the throttling channel 10 through the mixing chamber 11, see FIG. 2 moves to the surface of the melt loading metal 22, see FIG. 1. The throttling channel 10 creates resistance to the flow of argon supplied to the mixing chamber 11, as a result of which a high plasma-forming gas pressure is generated near the tungsten cathode 4, which is necessary for its stable operation, see FIG. 2, with a minimum gas pressure above the surface of the melt loading metal 22, see FIG. 1, necessary for the efficient evaporation of impurities. Argon flow in the throttling channel 10, see FIG. 2, counteracts the penetration of water vapor, impurities and metals from the surface of the melt loading metal 22, see FIG. 1 to the tungsten cathode 4, see FIG. 2, which they can damage. Next, water is supplied to the capillary 15, as it moves along the capillary, the water evaporates and, leaving the capillary, mixes with a stream of argon supplied through an additional plasma-forming gas supply pipe 14, see FIG. 2. The resulting mixture enters the mixing chamber 11, see FIG. 2, where a jet of plasma 25 captures it and carries it to the surface of the melt loading metal 22, see FIG. 1. Evaporation of water is accompanied by absorption of heat and a decrease in temperature. The cooling water circulating in the housing 3 under pressure heats the walls of the additional plasma-forming gas supply pipe 14, the flow of argon and the capillary wall 15 moving along it, see FIG. 2, preventing the possibility of freezing of water in the capillary. Current limiting inductors 17 are connected to lines A, B, and C of an industrial AC 400 V 50 Hz network, see FIG. 1. Conditions are created for ignition of an alternating current arc discharge, the electrodes of which are the surface of the metal loading melt 22, see FIG. 1 under plasmatrons, tungsten cathodes 4 and anodes 7 of plasmatrons, see FIG. 2. Through the use of semiconductor diodes 16 and 18 and current limiting chokes 17, see FIG. 1, tungsten cathodes 4 perform only the function of cathodes, and anodes 7 only the function of anodes, see FIG. 2, in an AC discharge whose value is limited. Moreover, only argon is located near the tungsten cathode 4, see FIG. 2. Thus, conditions are created to prevent any damage to the tungsten cathodes 4 and anodes 7, see FIG. 2. Next, the water supply to the capillary 15 is stopped, see FIG. 2, and otherwise, similarly to the previous one, a treatment period using dry argon is realized. During processing, a treatment zone is formed under each plasmatron, in the center of which an arc gas discharge of alternating current acts on the surface of the metal charge melt, which alternately performs the functions of the cathode and anode, as a result of which it is subjected to intense heating, bombardment by argon, oxygen and hydrogen ions. As a result of this effect, insoluble slag films covering the surface of the melt of the metal loading are destroyed and evaporate, and conditions are created for the evaporation of impurities. Argon streams displace the upper layers of the metal loading melt, together with the products of slag evaporation, in the low-pressure gas region, limited by internal and external cylindrical screens, where impurities evaporate from the upper layers of the metal loading melt, from where they are pumped out together with the products of evaporation of slag and argon without settling on plasmatrons. During processing, under the influence of a mechanical plasma pulse, the mass of the metal loading melt is mixed in the direction indicated by arrows 26, see FIG. 1, providing the passage of the entire mass of the melt loading metal through the processing zone. Argon streams indicated by arrows 27, see FIG. 1, the slag is moved along the surface of the metal loading melt to the treatment zones, where they are destroyed and removed in a similar way. Argon streams and external screens 24 prevent the exit of vaporized impurities and metal droplets into the space bounded by the heat-insulating screen 20, where they can damage the details of the heater 21, see FIG. 1. In the period of vacuum distillation, turn off the arc of alternating and direct current, stop the flow of argon into the supply pipelines of the main 12 and additional 14 plasma-forming gas, see Fig. 2. Impurities evaporate with the overheated and slag-free surface of the metal loading melt and argon flows, are displaced in the low-pressure gas region, limited by internal 19 and external 24 cylindrical screens, see Fig. 1, from where they are pumped out. During the flux supply period, flux powders with argon are fed into the spaces between the bodies 3 and the inner cylindrical screens 19, see FIG. 1. and FIG. 2. Powder particles are introduced into the metal loading melt and, reacting with impurities, form insoluble solid compounds (slags) that float to the surface, from where they are removed during the next treatment cycle. Next, the metal loading melt is slowly cooled, forming an ingot so that the crystallization front moves in one direction, displacing the remaining impurities into the removed part of the ingot.

The proposed method and the plasma torch for its implementation, completely eliminates the disadvantages inherent in the prototype. Additionally, unlike the prototype method allows you to refine almost all metals. Additionally, unlike the prototype, the proposed method uses a fluxing mechanism that allows you to remove impurities that cannot be removed by the above mechanisms.

Claims (2)

1. A plasma torch for plasma-chemical refining of metals in vacuum, containing a water-cooled case, a channel for supplying a plasma-forming gas, an anode and a tungsten cathode, a high-pressure chamber made in the anode, connected through a throttling channel to a mixing chamber, and an additional plasma-forming gas supply pipe washed with cooling water with an installed inside the capillary, the inner cylindrical screen and the outer cylindrical screen placed around the said housing connected to positively m pole of the DC arc power source, while the tungsten cathode is connected to the negative pole of the DC power source, and the positive pole of the DC arc power source is connected to the cathode of the first semiconductor diode, the anode of which is connected to the current limiting inductor, and the negative pole of the arc power source DC is connected to the anode of the second semiconductor diode, the cathode of which is connected to a current limiting inductor. 2. A method of plasma-chemical refining of metals in vacuum, comprising heating with a graphite metal heater in a crucible placed in a vacuum chamber to obtain a melt and treating the surface of the melt with alternating current plasma containing argon, characterized in that the melt surface is treated using at least at least one plasmatron according to claim 1, while gases are pumped out of the space bounded by the inner and outer cylindrical screens of the plasmatron and connected to the volume of the vacuum chamber chemical treatment of the surface of the melt is carried out in cycles consisting of a treatment period using moistened argon, a treatment period using dry argon, a vacuum distillation period and a flux supply period, while flux powder with argon is fed into the space bounded by the inner cylindrical screen, after which the melt slowly cool and form an ingot with the movement of the crystallization front in one direction and the displacement of impurities in the removed part of the ingot.

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