RU2346221C1 - Method of vacuum-plasma melting of metals and alloys in skull furnace and facility for its implementation - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention concerns metallurgy field and can be used for manufacturing of chemically active and complex-alloyed metals and alloys for instance, such as titanium, zirconium, niobium, tantalum, chrome and alloys on its basis. In the method arc discharge is created in vacuum plasmatron with formation of vacuum plasma arc and effecting on it and metal melt by magnetic fields of two groups of electromagnets, top and bottom. Top group of electromagnets is provided for creating of oncoming to each other of basic and additional magnetic fields, providing regulation of vacuum plasma arc, forming, declining and moving it, and bottom group of electromagnets - for mixing of melt in horizontal and vertical planes. At that forming of vacuum plasma arc is implemented by means of extraction by basic magnetic field of arc column from interelectrode gap with formation of loop between plasmatron and molten pool by means of additional magnetic field. During melting process it is implemented induction values correction of basic and additional magnetic fields.

EFFECT: refining of melted metal and alloy by means of faithful reproduction of defined chemical composition and structure of received alloys at increasing of efficiency and productivity of facility.

23 cl, 2 dwg

Description

The invention relates to the field of metallurgy and can be used for the production of chemically active and complex alloyed metals and alloys, for example, such as titanium, zirconium, niobium, tantalum, chromium, etc. and alloys based on them.

A feature of the melting of chemically active metals and alloys is their increased affinity for oxygen. Therefore, the smelting of such metals is carried out in vacuum.

Reactive metals and alloys actively interact with oxygen. The consequence of this is that it is impossible to melt such metals and alloys in ceramic crucibles and in vacuum induction furnaces, since it is not possible to select crucible material that would not interact with the molten metal: when melted in a graphite crucible, the metal is contaminated with carbon, and in a ceramic crucible from refractory oxides - oxygen. In both cases, a decrease in the ductility of the metal is detected.

Known methods for melting reactive metals and alloys in vacuum arc furnaces with a consumable electrode in a copper mold (see patent RU No. 2294973, C22B 9/21). This invention relates to methods for vacuum arc melting of highly reactive metals, in particular titanium, and is implemented in vacuum arc furnaces with a consumable electrode and a water-cooled crystallizer. In these furnaces, an arc burns between the consumable electrode and the liquid metal in the upper part of the ingot throughout the entire heat. The main danger in vacuum-arc melting is burning the crystallizer wall with an electric arc, water penetrating into the furnace space and its interaction with liquid or hot metal with the creation of an explosive situation.

For normal operation in such furnaces, it is necessary to strictly observe the safety rules developed at enterprises at all stages of the technological process, including when installing the electrode and welding it to the cinder (see V. A. Gromata. Titanium metallurgy. M: Metallurgy, 1968 city, p. 482-484).

In a vacuum-arc melting of a consumable electrode, the possibility of metal contamination by the electrode material and the melting capacity is excluded. However, the creation and maintenance of large-scale production, which includes cumbersome and energy-intensive press equipment for the manufacture of long electrode electrodes from charge materials, is required.

To obtain uniformly complex chemical alloyed alloys, technologies of two, three or more multiple remelting of such materials are used in crystallizers with an increasing diameter, which is laborious and expensive. The disadvantages of this method include the fact that metals and alloys can only be obtained in a cylindrical shape.

In vacuum arc furnaces with a consumable electrode and with a rotary crucible, molten casting into molds is possible, including of a complex shape. In patent RU No. 2239757, F27B 14/04, a vacuum arc melting and casting installation is presented, intended for the production of castings from refractory and chemically active metals.

The technology for the production of castings using a consumable electrode in vacuum-arc skull furnaces has also been developed (Neustruev A.A., Khodorovsky GL Vacuum skull furnaces. M .: Metallurgy, 1967), based on the deposition of a molten metal bath in a copper cooled crucible and periodically casting the melt into molds. In the skull furnace, part of the molten metal solidifies on the inner surface of the wall of the cooled crucible, forming the so-called skull, a thick crust of solid metal. The skull eliminates the direct contact of liquid metal with the crucible material, eliminates their interaction and contamination of the melted alloy by the crucible material.

The disadvantages of existing vacuum arc skull furnaces with a consumable electrode are:

- the need to prepare a consumable electrode of the desired chemical composition, which requires additional production and, therefore, additional material costs;

- limited possibilities for trimming complex alloys due to increased explosion hazard;

- the difficult preparation of multicomponent alloys with a large difference in the melting temperatures of the starting metals due to the effect of the advanced melting, which is very difficult to overcome, since in the skull crucible the heating of the liquid bath occurs due to the arc energy burning between the consumable electrode (anode) and the metal bath ( cathode). In this case, the residence time of the melt in the skull crucible, after melting to the end of the metal, is minimized due to the rapid cooling of the melt.

To eliminate these drawbacks while maintaining all the advantages of vacuum arc skull molding, it is promising to use independent heat sources instead of a consumable electrode. The use of independent sources of heating in a vacuum arc skull furnace allows you to abandon the complex production of a consumable electrode and load a lump charge into the crucible.

Therefore, to more efficiently obtain chemically active and complex alloyed alloys in vacuum arc skull furnaces, a method for melting metals with a non-consumable electrode was proposed. In this case, a lump charge is loaded into the skull crucible, and its melting is carried out by creating an electric discharge between the non-consumable electrode and the charge, which is the anode. This method allows you to average the chemical composition in the liquid bath of the skull plate and complete all the physicochemical processes by increasing the residence time of the melt in the liquid state. However, it cannot provide accurate reproduction of a given chemical composition and structure of the resulting alloys due to contamination of the resulting alloys with a non-consumable electrode material.

The source of metal contamination when using, for example, a vacuum plasma torch as a non-consumable electrode, is a plasma torch electrode, the so-called hollow hot cathode, made of thermionic material and made in the form of tubes of various shapes or rods of tungsten or tantalum. When using a plasma torch vertically mounted above the crucible as a heat source (see, for example, patent RU No. 2184160, IPC С22В 9/20), the melt is contaminated with cathode material (tungsten) as a result of its splashing with the melt and erosion. When tungsten enters the alloy, defects are formed in the finished products. It should also be noted that a plasmatron vertically mounted above the crucible prevents the crucible from turning and makes it difficult to drain the metal at an adjustable speed.

The closest known to the claimed method of vacuum-arc melting of metals and alloys in a skull furnace and a device for its implementation in its essence and the achieved result is patent RU No. 2239757, IPC С22В 9/21, F27B 14/04.

According to the known method of vacuum-arc melting of metals and alloys in a skull furnace, the metal is loaded into a water-cooled crucible in the form of a charge, a vacuum is created in the furnace chamber, the charge is melted in a vacuum using an arc discharge, while the arc in the furnace burns to the molten metal, charge , which is the anode, and casting the obtained melt into the molds.

Known vacuum arc skull furnace (patent RU No. 2239757) contains a vacuum chamber in which a melting tank is placed, which is a water-cooled metal crucible having an upper edge and a bottom, a cathode holder with a cathode and located under the crucible bottom, at least one mold for plum metal.

The disadvantage of this method is the inability to accurately reproduce a given chemical composition and structure of the resulting alloys, especially complex alloyed, due to contamination of the resulting alloys with the cathode material and the lack of conditions for organizing uniform melting in the crucible of the starting metals.

Another disadvantage of the method of melting metals in a vacuum by a non-consumable electrode is the dispersion of the arc discharge and the occurrence of spurious arcs. This leads to local overheating of the charge, i.e. to reduce the quality of the resulting alloys, as well as to inefficient energy consumption.

In the process of melting due to settling of the charge and splashing out of liquid metal in the upper part of the skull and crucible, growths are formed (peaks, pockets, nastily). The formation of growths ultimately leads to a decrease in the quality of the resulting alloy, since due to the deterioration of melt mixing in the crucible, the melting process is hindered and the possibility of obtaining an alloy of a given chemical composition is reduced. In addition, the productivity of the process is reduced due to a decrease in the mass of the metal being drained.

The main disadvantage of the known vacuum arc skull furnace is the central location of the non-consumable electrode, leading to contamination of the alloy with undesirable impurities from the elements that make up the cathode material. The cathode is usually made of tungsten or alloyed tungsten. In the melting process, the destruction of the cathode material occurs. When placed directly above the charge, the cathode is sprayed with molten metal, and brittle alloys with low emission properties are formed on its surface. Particles of this alloy containing tungsten crumble and fall into the melt. The cathode loses its emission properties and begins to melt, like a consumable electrode. As a result of tungsten entering the alloy, defects are formed in the finished products.

The objective of the invention is to improve the quality of the melted metal and alloy due to the exact reproduction of a given chemical composition and structure of the resulting alloys while increasing the efficiency and productivity of the device.

The problem in part of the first object is solved due to the fact that in the method of vacuum arc melting of chemically active metals and alloys based on them in a skull furnace, which includes loading the charge into a water-cooled skull plate, creating a vacuum in the furnace chamber, melting the charge in vacuum with using an arc discharge and discharge of the obtained melt into molds, characterized in that the arc discharge is created in a vacuum plasmatron with the formation of a vacuum plasma arc and the metal melt is affected by magnetic l from two groups of electromagnets, upper and lower, while the upper group of electromagnets is designed to create opposing main and additional magnetic fields that control the vacuum plasma arc, forming, deflecting and moving it, and the lower group of electromagnets to mix the melt in horizontal and vertical planes in such a way that when the melt is mixed in a vertical plane, a convexity is formed on the surface of the melt mirror, and when the melt is mixed in th The horizontal plane is created by pulling the main magnetic field of the arc column from the interelectrode gap with the formation of a loop between the plasma torch and the molten metal bath using an additional magnetic field. Moving the arc while mixing the melt is carried out in the horizontal plane towards the movement of the melt, and when mixing the melt in the vertical plane, to places the formation of bulges, and in the process of smelting, the values of the induction of the main and additional magnetic fields are adjusted, and before draining the obtained melt into the molds it is kept in a skull crucible for 0.05-0.5 hours.

In this case, the magnitude of the magnetic field induction of the electromagnets, providing melt mixing in the vertical plane, can increase until a bulge, mainly spherical, appears on the surface of the melt mirror.

And the magnitude of the main magnetic field induction, proportional to the strength of the arc current, can be adjusted according to the flow rate of the plasma-forming gas in manual mode.

In addition, the magnitude of the induction of the main magnetic field, proportional to the strength of the arc current, can be adjusted according to the flow rate of the plasma-forming gas in automatic mode.

Moreover, with an increase in the consumption of plasma-forming gas from 0.1 m ³ / h to 10 m ³ / h, the magnitude of the induction of the main magnetic field can increase by 10-30%, and with a decrease in the consumption of plasma-forming gas from 0.1 m ³ / h to 0 , 05 m ³ / hour, the magnitude of the induction of the main magnetic field can be reduced by 20-40%.

In addition, the magnitude of the additional magnetic field induction, proportional to the arc voltage, can be corrected for the pressure in the furnace chamber in manual mode.

Also, the magnitude of the induction of the additional magnetic field, proportional to the arc voltage, can be corrected for the pressure in the furnace chamber in automatic mode.

Moreover, with increasing pressure in the furnace chamber from 10 ^-1 mm Hg up to 10 mmHg the magnitude of the induction of an additional magnetic field can increase by 10-30%, and with a decrease in pressure in the furnace chamber from 10 ^-1 mm Hg up to 10 ^-3 mm Hg the magnitude of the induction of an additional magnetic field can be reduced by 30-60%.

At the same time, in the melting process, controlled control of the arc current, plasma-forming gas flow rate, furnace pressure, arc length and magnetic field induction values is carried out.

When loading the mixture into the crucible, first the refractory components of the alloy are loaded, and its low-melting components are fed into the crucible at the end of the melting.

In addition, in the furnace chamber before the start of smelting, a vacuum of 10 ^-3 -10 ^-4 mm Hg can be created, and during the smelting process they can change the vacuum from 10 ^-3 to 1 mm Hg.

In addition, before draining the melt from the crucible, they can provide a deflection of the vacuum plasma arc to the place of formation of the growth on the skull to remove it.

The problem in part of the second object is solved due to the fact that in a device for vacuum-arc melting of chemically active metals and alloys based on them in a skull furnace containing a vacuum chamber of the skull furnace, in which there is a melting tank in the form of a water-cooled skull skull, located under crucible, at least one mold and a cathode holder located above the crucible with a cathode, characterized in that the cathode is made in the form of a vacuum plasmatron for converting a plasma forming gas into a plasma in vacuum conditions with the formation of a vacuum plasma arc, while the vacuum plasmatron is installed at an angle relative to the vertical axis of the crucible and is located on the periphery of the crucible outside the melt mirror, and the furnace additionally contains electromagnetic control systems for the vacuum plasma arc and melt mixing, which are two groups of electromagnets, the upper and the lower, while the upper group of electromagnets is designed to pull the arc from the interelectrode gap, forming it in the form of a loop and moving crucible from one sector to another and oppositely directed magnetic fields, and the lower group of electromagnets is designed to control the electromagnetic stirring of the melt in the horizontal and vertical planes, situated below the maximum permissible level of the melt in the crucible and contains magnets that create magnetic fields directed tangentially.

The hollow cathode may be made of a refractory thermionic material, such as tungsten. And the cathode holder is made of copper and water-cooled and has an axial hole for supplying a plasma-forming gas, such as argon.

In addition, the vacuum chamber of the furnace may include a gas pumping port connected to vacuum pumps.

The arc plasma torch and crucible can be connected to a constant current source using flexible current leads.

In addition, the mark of the maximum permissible level of the melt in the melting tank can be located at least 50-100 mm below the upper edge of the crucible.

In this case, part of the lower group electromagnets providing control of the electromagnetic mixing of the melt in the horizontal plane can be made in the form of solenoids, which are windings covering the crucible located in the cooled zone of the crucible.

In addition, the windings of the upper and lower groups of electromagnets are connected to the power source using a flexible current supply and are interconnected via a switch, ensuring their coordinated and alternating operation in automatic mode.

In addition, the water-cooled crucible is made of copper.

The crucible can also be made with the ability to move and contain a drain sock.

In this case, the crucible can be made rotatable relative to the horizon.

Molds can also be made with the possibility of movement.

In this case, the molds can be installed on a rotating casting table.

The technical result provided by the above set of essential features consists of:

- in eliminating the possibility of the products of the cathode material getting into the melt and contamination of the resulting melt with this material;

- to ensure intensive melting of the charge in the crucible without local overheating of the charge due to the organization of uniform melting in the crucible of the starting metals during arc deflection and scanning it along the surface of the charge;

- to increase the uniformity of the composition of the obtained alloy due to the increase in the efficiency of melt mixing due to turbulization of the liquid metal flows;

- in increasing the volume of liquid metal in the crucible due to the erosion of the peripheral layers of metal adjacent to the walls of the crucible, and reducing the thickness of the skull layer;

- to reduce the likelihood of liquid metal splashing out of the crucible and the formation of growths due to a decrease in the liquid metal wave incident on the crucible wall, due to the direction of the additional magnetic field, it is opposite to the main one, which leads to an increase in the mass of the melt being drained;

- in automating the melting process to provide the necessary control action to maintain the process within specified limits;

- to increase the residence time of the melt in the crucible until it is discharged, which allows to increase the averaging of the chemical composition of the resulting alloy in the volume of the crucible;

- in a faster, with an adjustable required speed, and convenient pouring of the melt into the molds, which allows to achieve the required temperature for discharge and to obtain the required metal structure;

- in the removal of the formed growths on the walls of the crucible, the appearance of which could not be avoided.

In addition, vacuum-arc skull furnaces equipped with a vacuum plasmatron, that is, vacuum-plasma furnaces, provide the possibility of using a neutral, oxidizing or reducing atmosphere, as well as smooth control of the heating power and pressure in the furnace chamber. These advantages are extremely important for the remelting of metal waste or a multicomponent lump metal charge having various physical and technological properties.

The essence of the proposed method of vacuum-arc melting of metals and alloys in a skull furnace is as follows.

The main part of the bulk charge is loaded into a water-cooled copper crucible. When loading the mixture into the crucible, first the refractory components of the alloy are loaded, and its low-melting components with high vapor pressure, for example, such as aluminum, are fed into the crucible at the end of the melting. The furnace is sealed and before starting melting in a chamber of the furnace create a vacuum of 10 ^-3 -10 ^-4 mm RT.article During the melting process, the vacuum is maintained at 10 ⁻³ −1 mm Hg.

To create an arc discharge, a vacuum plasmatron is used, in which the plasma-forming gas is converted into plasma under vacuum conditions, and the metal is melted using the resulting vacuum plasma arc. In the process of melting metal, the arc burns onto the charge, which is the anode. The plasma torch cathode is hollow, and gas is supplied through it to the furnace. An inert gas, for example argon, is used as the plasma-forming gas. This provides the necessary conditions for the smelting of chemically active, as well as multicomponent and complex alloys.

In this case, a vacuum plasma arc is created outside the limits of the melt mirror and act on the arc and melt by magnetic fields from two groups of electromagnets. This eliminates the possibility of contamination of the melt with the cathode material and ensures the absence of undesirable impurities in the resulting alloy. In this case, the system of electromagnets provides control of the plasma arc and efficient mixing of the melt for intensive melting of the charge in the crucible without local overheating, as well as reducing the occurrence of dispersion of the arc discharge and the appearance of spurious arcs.

During the operation of the furnace, one group of electromagnets, creating the primary and secondary magnetic fields that are in opposition to each other, provides control of the vacuum plasma arc, forming, deflecting and moving it along the surface of the charge. In this case, the main and additional magnetic fields are directed transversely to the vacuum plasma arc and exert a force on it to deflect and direct the arc into the melting zone. Another group of electromagnets provides melt mixing by mixing the melt in horizontal and vertical planes.

As a result of this, when the melt is stirred in a vertical plane, a bulge is formed on the surface of the melt mirror. The existence of a bulge signals that there are powerful vertically directed flows (jets) of liquid metal. In this case, the magnitude of the magnetic field induction of the electromagnets, providing control of the melt mixing in the vertical plane, is increased until a convex, mainly spherical, shape appears on the surface of the melt mirror.

When mixing the melt in a horizontal plane, the rotation of the liquid metal relative to the vertical axis of the crucible is created.

Mixing the melt in both horizontal and vertical planes increases the intensity of mixing and provides an increase in the volume of liquid metal in the crucible due to the erosion of the peripheral layers of the metal and a decrease in the thickness of the skull in the crucible, which makes it possible to increase the mass of the melt drained from the crucible.

In the process of creating a vacuum plasma arc, the arc column is pulled by the main magnetic field from the interelectrode gap to ensure arc burning on the molten metal (charge). Using an additional magnetic field, an arc is formed in the form of a loop, the upper end of which is attached to the plasmatron, and the lower end to the molten metal bath, which excludes the possibility of arc burning on the crucible wall. In the zone of attachment of the plasma arc to the metal, a so-called “anode spot” is formed. Pulling the column of the plasma arc from the interelectrode gap using the transverse arc of the main magnetic field, the induction of which is proportional to the strength of the arc current, and creating it in the form of a loop (the so-called "loop arc") using an additional magnetic field, the induction of which is proportional to the voltage of the arc, makes it possible the formation of the "anode spot" of the arc in the central part of the molten metal bath and reduces the effect of the intrinsic magnetic field of the arc on the melt, which leads to the formation of waves liquid metal. The opposite directions of the main and additional magnetic fields in this case reduce the wave of liquid metal incident on the wall of the crucible, and reduce the likelihood of liquid metal spilling out of the crucible, and also reduce the formation of growths resulting from the rolling of liquid metal on the side surface of the skull.

Before draining the melt from the crucible, the vacuum plasma arc is deflected to the place of formation of the growth on the skull to remove it, which makes it possible to increase the mass of the melt drained from the crucible.

When moving the melt in the horizontal plane towards the movement of the liquid metal, the movement of the arc is provided, and when the melt is mixed in the vertical plane, to the places where the bulges form, mainly of a spherical shape. By applying a magnetic field to the vacuum plasma arc, the arc is scanned by moving it along the surface of the melt mirror towards the metal flow, i.e. in the direction opposite to the direction of movement of the flow of liquid metal in the horizontal plane. While mixing the melt in a vertical plane, a plasma arc is introduced into the upper part of the bulges, mainly of a spherical shape. This creates a turbulization of the liquid metal flow and increases the mixing efficiency, as well as intensifies the melting process.

The creation of magnetic fields for moving the arc and mixing the melt is carried out alternately. This eliminates the mutual influence of magnetic fields and their distortion.

In the melting process, the induction of the main and additional magnetic fields is adjusted, while the current strength of the vacuum plasma arc is controlled by changing the parameters of the power source.

Correction of the magnitude of the induction of the main magnetic field when the flow rate of the plasma-forming gas supplied through the hollow cathode of the vacuum plasma torch, and the correction of the magnitude of the induction of the additional magnetic field depending on the gas pressure in the furnace chamber, as well as the regulation of the current by changing the parameters of the power source and the creation in the discharge chamber rarefied atmosphere allows you to fully automate the alloy preparation process, optimize the melting process and reduce energy consumption and per unit mass of the discharged melt.

In this case, the magnitude of the main magnetic field induction, which is proportional to the strength of the arc current, is adjusted for the flow rate of the plasma-forming gas in both manual and automatic modes. This applies briefly to the process of ignition of the arc. The magnitude of the additional magnetic field induction, proportional to the arc voltage, is corrected for the gas pressure in the furnace chamber in both manual and automatic modes.

To ignite the arc, a plasma-forming gas, for example argon or helium, is fed into the furnace chamber through the hollow cathode of the plasma torch. The main electromagnet located under the cathode and the additional electromagnet of the arc control system located on the opposite side of the crucible are switched on. The power source of the plasma torch is connected and, using an oscillator (high-frequency oscillation generator), an arc is ignited between the cathode and the upper flange of the crucible. The magnetic field of the main electromagnet instantly “blows” the arc from the crucible flange onto the charge, and the counter-directed magnetic field of the additional electromagnet prevents the arc from exiting onto the crucible wall, forming a loop arc. Next, the process of melting the charge is carried out without stopping the pumping of the chamber with a vacuum pump and adjusting the parameters affecting the course of the melting.

In metallurgical plasma furnaces, during certain periods of melting, the arc current is kept constant for quite long periods of time, while changing the technological parameters of the plasma torch, such as arc length, plasma gas flow rate, and pressure in the furnace chamber. These parameters affect the conditions of arc burning. The flow rate of the plasma-forming gas during the melting process is changed to solve technological problems, for example, for the nature of metal mixing, changes in the power released on the molten charge. The pressure in the furnace is increased, for example, to suppress the evaporation of the volatile components of the prepared alloys, and reduced to increase the efficiency of metal degassing.

When creating a rarefied gas atmosphere in the discharge chamber, in which the voltage is practically independent or weakly dependent on the arc length, the magnitude of the main magnetic field induction is adjusted depending on the plasma gas flow rate, and the magnitude of the additional magnetic field induction is adjusted depending on the gas pressure in the furnace chamber . In this case, the current of the plasma arc is regulated by changing the parameters of the power source.

It was found that in a rarefied atmosphere at a pressure of 10 ^-3 mm Hg up to 1 mmHg a change in the flow rate of the plasma-forming gas passed through the arc leads to a change in the electron-ion composition of the arc. A decrease in the consumption of plasma-forming gas leads to an increase in the number of electrons or, accordingly, to a decrease in the number of ions in the arc and to an increase in controllability of the arc by a magnetic field (the arc is more easily deflected and easier to bend under the influence of a magnetic field). On the contrary, an increase in the consumption of plasma-forming gas leads to a decrease in the number of electrons in the arc column or, accordingly, to an increase in the number of ions and to a decrease in controllability of the arc by means of a magnetic field (the arc deviates worse and bends more difficult). To obtain the same force from the side of the magnetic field on the arc with an increased consumption of plasma-forming gas, the magnitude of the magnetic field induction must be increased, and with a reduced - reduced.

Correction of the magnitude of the additional magnetic field induction in proportion to the arc voltage without correcting the magnitude of the induction by changing the pressure in the furnace and the plasma gas flow rate can lead to disruption of the process due to excessive or insufficient arc deflection, which will lead to a deterioration in the mixing of the metal, i.e. to reduce the quality of the obtained melt, as well as to reduce the melting rate of the mixture, i.e. to a decrease in productivity, and, in the event of an arc falling on the crucible wall, to an emergency.

The magnitude of the arc voltage depends not only on the length of the arc, but also on the pressure in the furnace chamber, which can vary both specifically during technological operations and spontaneously, for example, due to the evaporation of charge elements with high vapor pressure. In addition, the pressure also changes with a change in gas flow, which also leads to a change in arc voltage.

The automatic control system cannot recognize for what reason the voltage has changed: due to an increase in the length of the arc or because of a change in pressure in the installation chamber.

Therefore, in the proposed inventions in a skull furnace with a vacuum plasmatron installed outside the molten metal bath, it is proposed to correct the induction of the main and additional magnetic fields as follows.

With an increase in the consumption of plasma-forming gas from 0.1 m ³ / h to 10 m ³ / h, the magnitude of the induction of the main magnetic field is increased by 10-30%, and with a decrease in the consumption of plasma-forming gas from 0.1 m ³ / h to 0.05 m ³ / hour, the magnitude of the induction of the main magnetic field is reduced by 20-40%.

The magnitude of the additional magnetic field induction is increased by 10-30% with increasing pressure in the furnace chamber from 10 ^-1 mm Hg up to 1 mm Hg, and when the pressure in the furnace chamber decreases from 10 ^-1 mm Hg up to 10 ^-3 mm Hg the magnitude of the induction of the additional magnetic field is reduced by 30-60%.

This will provide optimal control of the vacuum plasma arc when changing the pressure of the plasma-forming gas and the pressure in the furnace chamber during arc burning in a rarefied atmosphere.

Thus, in the melting process, a controlled regulation of the current strength of the vacuum plasma arc, the flow rate of the plasma gas, the pressure in the furnace, the length of the vacuum plasma arc and the magnitude of the magnetic field induction are carried out.

Connecting the electromagnetic control systems of a vacuum plasma arc and melt mixing, setting and adjusting its parameters for forming and moving the arc (scanning) the arc along the charge surface and mixing the resulting melt ensures predetermined observance of the technological process while increasing the efficiency of melting of charge materials and increasing the productivity of the melting process.

The obtained melt is kept in a skull crucible for 0.05-0.5 hours and poured into molds with an adjustable speed. This allows you to intensify the averaging of the chemical composition of the resulting alloy in the volume of the crucible, and also provides an alloy with the necessary structure.

The invention is illustrated by drawings.

Figure 1 shows a General view of a device for vacuum-arc melting of metals and alloys in a skull furnace with a vacuum plasmatron mounted on the periphery of the crucible at an angle to its vertical axis.

Figure 2 shows a water-cooled metal crucible indicating the effects on the arc and melt during the melting of electromagnetic fields.

According to the invention, a device for vacuum-arc melting of metals and alloys in a skull furnace contains a vacuum chamber 1 of the skull furnace (Fig. 1), in which a melting tank is placed, which is a water-cooled metal crucible 2. The crucible 2 is made of copper and has an upper edge 3 and the bottom 4. The skull furnace also contains a cathode holder 5 with a cathode 6. The cathode 6 is hollow and is a vacuum plasmatron 7, in which the plasma-forming gas is converted into plasma under vacuum and using the resulting vacuum a smart plasma arc melts metal. The cathode 6 is installed at an angle relative to the vertical axis of the crucible and is located on the periphery of the crucible 2 outside the melt mirror. The skull furnace additionally contains a system 8 of electromagnetic control of a vacuum plasma arc and a system 9 of electromagnetic mixing of the melt, consisting of two groups of electromagnets, the top 10 and bottom 11. The upper group 10 of electromagnets is installed above the maximum permissible melt level in the crucible (not shown) and contains the main 12 and an additional 13 magnets creating counter-directional magnetic fields. The upper group of 10 electromagnets is designed to stretch the arc, form it in the form of a loop and move from one sector of the crucible to another. The lower group of 11 electromagnets is located below the maximum permissible melt level in the crucible and contains magnets that create tangentially directed magnetic fields. The lower group 11 of electromagnets provides control of the electromagnetic mixing of the melt in the horizontal and vertical planes. The maximum permissible melt level in the crucible 2 is located at least 50-100 mm below its upper edge 3.

The hollow cathode 6 is made of a refractory thermionic material, such as tungsten.

The cathode holder 5 is made of copper and water-cooled and has an axial hole (not shown) for supplying a plasma-forming gas, such as argon.

The electromagnets of the upper 10 and lower 11 groups are located in the cooled zone 14 of the crucible 2, one below the other, windings with ferromagnetic cores.

Part of the electromagnets of the lower group, providing control of the electromagnetic mixing of the melt in the horizontal plane, can be made in the form of solenoids 15, which are windings covering the crucible 2, located in the cooled zone 14 of the crucible 2.

A device for vacuum arc melting of metals and alloys in a skull furnace contains a direct current source 16 and a power source of electromagnets 25.

Water-cooled crucible 2 is made with the possibility of movement and contains a drain sock 18. The crucible 2 can be made rotatable relative to the horizon.

The skull oven contains 2 molds 17 located under the crucible, which are movable and mounted on a rotating casting table 19.

The skull furnace contains a dispenser 20 for loading the mixture into a crucible and a peephole 21.

The vacuum chamber 1 of the skull furnace contains a pipe 22 for pumping gas, connected to vacuum pumps (not shown).

A vacuum plasmatron 7 and a water-cooled metal crucible 2 are connected to a direct current source 16 using flexible current leads 23 and 24, respectively.

The windings of the upper 10 and lower 11 groups of electromagnets are connected to a power source 25 using a flexible current supply (not shown) and are interconnected via a switch 26, ensuring their coordinated and alternating operation in automatic mode.

The inventive device operates as follows.

At the beginning of the work, the bulk of the metal lump charge is loaded into the water-cooled copper crucible 2 through the batcher 20. When loading the charge into the crucible, the refractory alloy components are first loaded, and its low-melting components are fed into the crucible at the end of the melting.

Then, an inclined vacuum plasmatron 7 with a hollow hot cathode 6 is brought to the crucible 2 and set it to the position necessary for arc excitation. The vacuum plasmatron 7 is set so as to prevent the cathode 6 material from getting into the crucible 2 during charge melting, that is, the hollow tungsten cathode 6 of the plasma torch is located on the periphery of the water-cooled crucible 2, outside the metal mirror zone.

The molds 17 are brought under the crucible 2 to the position corresponding to the beginning of the discharge of the metal. Then carry out the sealing of the skull furnace, provide pumping gas from the chamber 1 of the furnace with vacuum pumps through the pipe 22 to a residual pressure of 10 ^-3 -10 ^-4 mm RT.article

Plasma-forming gas is supplied through the hollow cathode 6 to the furnace with a flow rate corresponding to the power of the hollow hot cathode 6 and the required vacuum in the furnace chamber 1 to carry out the process of melting the charge without turning off the pump chamber 1. Inert gas, argon, helium are usually used, but it is also possible to use active gases, nitrogen, methane, etc.

A direct current source 16 is connected through a flexible current supply 23 to the hollow cathode 6 of the plasma torch 7 and through a flexible current supply 24 to the crucible 2 and a discharge is excited using a high-frequency generator or voltage source (not shown) of several hundred volts.

The obtained discharge is maintained at a small power (units of kilowatts), sufficient to heat the cathode 6 to the temperature of thermionic emission, which is necessary to create a vacuum plasma arc. Vacuum plasma arc 30 at the time of ignition is shown in Fig.2. With this power, the arc can burn on the flange or wall of the crucible without smelting them.

Then the arc power is increased to the value necessary for carrying out the process of melting the charge (hundreds of kilowatts), and the arc is pulled by the magnetic field of the main magnets 12 to ensure the combustion of the vacuum plasma arc on the metal (charge), and also form an arc loop by the magnetic field of the additional magnets 13 to exclude the possibility of burning a vacuum plasma arc on the crucible wall. Thus get a vacuum plasma arc 31 in working condition (Figure 2).

The flow rate of the plasma-forming gas, the arc length, the vacuum in the furnace chamber 1, the arc power (current strength and arc voltage) are established, which correspond to the charge melting period.

Provide through a flexible current supply of electromagnets (not shown) the connection of the system 8 of electromagnetic control of the arc and the system 9 of mixing the melt to the power source 25 (Figure 1). Carry out the installation and regulation of the parameters of the arc to move (scan) it along the surface of the charge and mix the resulting molten metal to increase the efficiency of the melting of the charge materials.

The upper 10 and lower 11 groups of electromagnets of systems 8 and 9 of electromagnetic arc control and melt mixing work in concert and alternately. The windings of the upper and lower groups of electromagnets are interconnected via a switch 26 (Figure 1), ensuring their coordinated and alternating operation in automatic mode.

During the melting of the charge, when the bulk of the metal is in the solid state, the determining system 8 is the electromagnetic control of the arc. The arc control system provides the alternate inclusion of electromagnets of the upper group 10, moving the arc 31 from one sector of the crucible to another, as shown in Fig.2. Then the system 9 of the electromagnetic control of mixing the melt is turned on. Depending on the number of the electromagnet of the upper group 10 turned on, the system 9 of electromagnetic control of melt mixing includes solenoids 15 enclosing the crucible with a field direction that ensures metal rotation in the direction opposite to the vacuum plasma arc, or an electromagnet of the lower group 11 with the corresponding number, which provides the formation of a stream of liquid metal in the zone of the anode spot of the arc in the direction opposite to the arc 31.

After the pieces of the mixture are melted and a liquid metal bath is obtained on the entire surface of the crucible, the system of electromagnetic mixing of the liquid metal 9 becomes decisive, which should ensure that the bottom sections of the mixture are washed out by the liquid metal streams 33 and then average the temperature of the liquid metal over the entire volume of the crucible due to the effective mixing of the melt in the crucible . During this period, the main mode is the mode of mixing the melt in the vertical plane, which is ensured by the inclusion of electromagnets 11 of the lower group, the magnetic field of which interacts with currents flowing through the melt. This interaction leads to the emergence of forces that cause vertical movement of the masses of liquid metal, as shown in Fig.2. The magnitude of the magnetic field induction is chosen so that a spherical convex 32 appears on the surface of the melt under the action of the upward flow of the liquid metal. The existence of the convexity indicates that the mixing system 9 is working efficiently. To enhance mixing by organizing the turbulent movement of the melt, the vacuum plasma arc is sent directly to the formed bulge, which is carried out automatically according to the specified program by turning on the electromagnet of the upper group 10, the number of which corresponds to the number of the electromagnet of the lower group 11.

Before draining the melt from the crucible, the vacuum plasma arc is deflected to the place of formation of the growth 34 on the skull, the formation of which could not be avoided. This ensures the removal of growth, which makes it possible to increase the mass of the melt drained from the crucible. The formation of a build-up complicates the course of the melting process due to the deterioration of melt mixing in the crucible and reduces the possibility of obtaining an alloy of a given chemical composition, and also leads to a decrease in the process productivity due to a decrease in the mass of the metal being drained. Removal of the growth can be performed in manual mode.

After reaching the mass-average temperature of the metal, providing it with the necessary fluidity for successful casting, low-melting alloying alloy components with high vapor pressure, such as aluminum, are introduced from the dispenser 20 (FIG. 1).

The prepared alloy is drained into the molds 17 mounted on the table 19 of the casting machine, after the obtained melt is kept in a skull crucible for 0.05-0.5 hours. Drainage is carried out through the drain toe 18 of the crucible 2 by turning it around a horizontal axis. During casting, the crucible 2 or the molds 17 are moved to ensure that the jet of the liquid metal to be drained falls into the mold accurately.

Immediately after draining the liquid metal, the crucible is returned to its original (horizontal) position.

To organize a continuous cycle of operation of the furnace, the second and next loading of the charge into the crucible is carried out without depressurization of the furnace from the loading device - a screw loader or a tray (not shown) through the batcher 20 of charge materials, the first (previous) mold 17 is removed from the crucible and the second mold is placed under the crucible . Next, the process is repeated, starting with the supply of plasma-forming gas to the hollow cathode 6, without waiting for the complete evacuation of the furnace chamber 1.

Method implementation examples

Example 1. Smelting of heat-resistant nickel alloys.

In a vacuum-plasma skull oven designed in accordance with the scheme shown in Fig. 1, smelting of heat-resistant nickel alloys of the ZhS brand was carried out. A charge — alloy components in the form of pure metals — was loaded into a rotary skull plate with a capacity of about 200 kg (nickel). Two groups of electromagnets were placed in the cooled cavity of the crucible, four electromagnets in each group. The upper group of electromagnets of the electromagnetic arc control system was installed in the crucible at a distance of 60 mm from the top edge of the crucible. The lower electromagnets of the melt mixing system were placed at a distance of 120 mm from the upper edge of the crucible. To create an arc discharge, a vacuum plasmatron with a hollow cathode composed of tungsten rods of the VL-10 brand was used. The rods were inserted into a copper cooled cylindrical cathode holder with an axial hole for feeding argon into the cathode cavity. The vacuum plasmatron was installed at an angle of 30 ° relative to the vertical axis so that its cathode was located on the periphery of the crucible above the upper flange of the furnace.

A standard charge of pure metals was loaded into the crucible: plates of nickel, cobalt, titanium, niobium, molybdenum and tungsten sticks. The mass of the mixture was calculated so that after its melting the level of the liquid metal was 80 mm below the upper edge of the crucible. The mixture was loaded so that the refractory components were on top. An inclined plasmatron was brought to the crucible so that its hollow tungsten cathode was located outside the charge and outside the liquid metal mirror above the upper flange of the crucible, and set it in the position necessary for arc excitation, at a distance of 100 mm from the end of the cathode to the upper flange of the crucible. This arrangement of the plasma torch during the smelting of nickel alloys made it possible to obtain an alloy with a calculated tungsten content. After four similar melts carried out with a plasmatron vertically installed in the center of the crucible (before reconstruction of the furnace), the tungsten content in the alloy after the third and fourth melts exceeded the maximum allowable value by 6 and 7%, respectively, due to increased wear of the tungsten cathode of the plasmatron. In fact, this was the reason for the reconstruction of the furnace to change the position of the plasma torch and remove the cathode from the melting charge and the melt mirror.

A rotating casting table with molds with an inner diameter of 50 mm each was installed under the crucible.

Before melting, the furnace chamber was sealed and previously evacuated to 10 ⁻³ mm Hg. by pumping through a pipe connected to vacuum pumps.

A thyristor rectifier was used as a power source for the plasma torch, the positive output of which was connected to a pallet placed in the bottom of the crucible using a flexible, cooled current lead. As a result, the metal charge and molten metal acquired a positive potential and became the anode. The minus pole of the rectifier was connected to the cathode holder of the plasma torch. As a result, the tungsten electrode of the plasma torch acquired a negative potential and became a cathode.

Without stopping pumping, argon was fed into the furnace through a hollow cathode of the plasma torch with a flow rate of 0.4 m ³ / h. Then they turned on the power source of the plasma torch, briefly connected the oscillator and ignited an arc discharge. Using a plasma torch, a vacuum plasma arc was created outside the charge and the forming melt mirror. Under the influence of counter-directional magnetic fields of the main electromagnet located directly below the cathode and the additional electromagnet opposite to it, a loop arc was formed, as shown in FIG. It was impossible to start melting without using the main magnetic field, "blowing" the arc from the upper flange of the crucible, since with increasing current strength the arc melted the flange. In the absence of an additional magnetic field, the arc was tied to the far wall of the crucible.

Then, using the switch, the upper electromagnets were turned on alternately, with an interval of 2 s (the switching time of one electromagnet was 5 s), directing the arc to different sectors of the crucible, and the charge was melted on the entire surface of the crucible, forming a bath of molten metal. With manual control on / off of the electromagnets, the time of complete melting of the charge was 1.2 hours. If the settings for switching on the electromagnets were set using the controller and worked in automatic mode, the time for complete charge melting was about 40 minutes. If scanning was not performed, the melting time increased to 2 hours.

During the melting of the charge, the arc current was set and stabilized at 6 kA. The pressure in the furnace was set at 10 ^-1 mm Hg. The length of the arc during the melting of the charge was changed due to the settling of the charge. In proportion to the arc length, its voltage varied within 30-45 V. The magnitude of the magnetic field induction of the main electromagnet at an arc current of 6 kA was set to 0.02 T, and the magnitude of the additional electromagnet field induction was changed in direct proportion to the arc voltage: at 30 V - 0.04 T, 35 V - 0.05 T, 45 V - 0.06 T. In this case, the system of electromagnets not only provides control of the plasma arc, but due to the stabilization of the shape of the arc in a magnetic field, it also reduces the likelihood of dispersion of the arc discharge and the appearance of spurious arcs, which occurred during the operation of a plasma torch vertically mounted above the central part of the crucible.

During the melting of the charge, the pressure in the furnace gradually increased from 10 ^-1 to 1 mm Hg, the “anode spot” of the arc did not reach the middle of the crucible either, so the magnitude of the additional magnetic field was corrected — it was reduced to 0.03 T.

The time of melting the lump charge using the indicated methods of arc control and magnetic field correction did not exceed 40 minutes.

Three swimming trunks were carried out without using the system of electromagnetic mixing of the melt. The chemical composition of the alloy after the second heat did not meet the technical conditions. The niobium content turned out to be less than the maximum allowable value by almost 5%, tungsten - by 5%, which is associated with the enrichment of these skull elements due to the lack of melt mixing. The mass of the merged metal without electromagnetic mixing of the melt decreased by almost 35%. The thickness of the skull after the third melting increased to 35-45 mm in the upper part of the crucible, and a bottom skull with a thickness of 50-70 mm was formed in its lower part. In addition, in the upper part of the crucible in the area of the drain sock, a buildup was formed in the form of a visor hanging over the molten metal. In the presence of a visor, the metal merged past the sock and did not fall into the mold. Therefore, before draining the metal, the visor was removed. To do this, the arc control system was turned off, leaving the main electromagnet turned on to direct the arc to this visor, and the visor was fused with an arc for 5 minutes.

The remaining 16 heats were carried out with the coordinated operation of the system of electromagnetic mixing of the melt and the system of electromagnetic control of the arc. The work was carried out as follows.

After the formation of a molten metal bath to erode the bottom and peripheral layers of the charge and averaging the melt temperature, the metal was kept in a liquid state for 0.5 hours, heating the bath surface with a plasma arc, continuing mixing of the melt and scanning the arc.

To mix the melt in a vertical plane by creating vertically directed flows of liquid metal, the magnetic fields of the lower electromagnets were oriented tangentially with respect to the inner surface of the crucible.

To mix the melt in the horizontal plane by creating a rotational movement of the flows of liquid metal relative to the vertical axis of the crucible, the magnetic fields of the lower electromagnets were oriented vertically.

The magnitude of the magnetic field induction of the lower electromagnets while stirring the melt in a vertical plane was gradually increased until a convexity of a spherical shape appeared on the surface of the melt mirror and was further maintained at this level (approximately 0.03-0.04 T at an arc current of 6 kA). Periodic switching of the lower electromagnets led to the formation of bulges in different sectors of the crucible with the melt, which visually looked like the movement of the bulge along the surface of the melt. The arc was directed to the upper part of the bulge. This was done automatically using a controller, which essentially is a switch, indicated by 26 in FIG. 1. With the help of such a switch, the electromagnets are switched on in pairs. Depending on the number of the lower electromagnet turned on, the controller included an upper electromagnet with the corresponding number, the magnetic field of which ensured the direction of the arc to that sector of the crucible (bath) in which the bulge existed. In order to avoid the mutual influence of the upper and lower fields and their distortions, the lower and upper electromagnets were switched on not simultaneously, but alternately. The setting of the on-time of the electromagnets was set using the controller. The lower electromagnet was turned on for 15 seconds, and the upper electromagnet paired with it was turned on for 10 seconds immediately after the lower electromagnet was turned off. Then, the lower electromagnet was turned on again for 15 seconds, and the upper electromagnet was turned on for 10 seconds, etc. The total operating time of one pair of electromagnets was set to 200 seconds. Next, the first pair of electromagnets was turned off and the second pair was turned on. The alternate inclusion of the upper and lower electromagnets is possible due to the large inertia of the movement of the flows of molten metal. The existence of a bulge after disconnecting the lower electromagnets of the mixing system lasts approximately 10 seconds.

When mixing (rotating) the melt in the horizontal plane, the electromagnetic control systems operate in the same way as when mixing the melt in the vertical plane. The difference is that the controller includes pairs of electromagnets with other numbers, which provide the opposite direction of the arc with respect to the rotating inertial flow of liquid metal. The settings of the intervals for switching on the electromagnets were the same in both mixing modes.

Smelting of the charge was carried out in a skull of waste waste alloy, pre-fused to the walls of the crucible. The thickness of the skull in the upper part of the crucible after the first melting was 20-30 mm.

The molten metal in the crucible was poured into molds mounted on a rotary casting table. The discharge coefficient was close to unity, i.e. the mass of the fused metal on average was equal to the mass of the loaded charge (deviations on each heat did not exceed 10%). The resulting castings with a diameter of 50 mm and a total weight of about 200 kg were cut to study macro- and microstructure. The oxygen content was determined by the neutron activation method on templates cut from the central part of the cast rods, the nitrogen content was determined by vacuum melting.

When conducting heats according to the technology described above, a correspondence was observed between the calculated and experimental data. Smelting was carried out with the introduction of filling up to 0.3% carbon. Pieces of aluminum and titanium were loaded into the crucible from the dispenser 5-10 minutes after receiving the melt and its degassing.

The oxygen content in the melt before the addition of active elements was 0.025-0.04%, in the finished alloy - 0.015-0.030%.

Two melts were carried out with the feeding of fluorspar in the amount of 0.5% of the total charge. After the formation of a liquid bath, the surface of the melt was covered with a dense layer of inactive slag displaced by the plasma arc. If before draining with the help of an electromagnetic system the “anode spot” was shifted to the drain toe, and then the melt was gradually drained, then the slag partially remained in the crucible, partially left with the last portion of the metal without getting into the body of the casting. This made it possible to significantly reduce the pollution of the melt by non-metallic inclusions and reduce the oxygen content to 0.005-0.006%. The nitrogen content in this case was 0.0022-0.0027%. A similar oxygen content occurs in similar castings obtained by vacuum induction melting.

Example 2. Remelting waste titanium alloys.

Titanium alloys were melted in a vacuum-plasma furnace with a skull plate with an inner diameter of 400 mm and a vacuum plasmatron vertically mounted in the center of the crucible. In the absence of a system of arc deflection and electromagnetic mixing of the melt as the melt was carried out, the thickness of the skull gradually increased; in the upper part of the crucible a build-up appeared in the form of a visor, which made it difficult to drain the metal by turning the crucible. In theoretical loading of a charge weighing 60 kg, the mass of the metal poured from the crucible was 15-20 kg. After the fifth melting, the tungsten content of 0.15% was found in the obtained alloy. After the ninth smelting, the tungsten content in the alloy reached 0.2%. In this case, it was possible to visually see the wear of a hollow tungsten cathode, the shape of which was changed, and a melted metal layer was visible on its surface. When tapped on the cathode surface, the layer easily crumbled. In this regard, the conduct of swimming trunks was discontinued.

After the reconstruction of the furnace using the equipment described in example 1, the VT-5l titanium alloy conditioned casting waste was remelted. The mixture consisted of profitable parts of castings, risers, sprues, etc. Before remelting, the oxidized surface of the cut waste was cleaned by tumbling and bead-blasting. In addition, the waste was washed in hot water and an alkali solution, and then dried in an oven.

Lump titanium waste was loaded into the crucible with a slide, the top of which was shifted from the center of the crucible to the side of the inclined cathode mounted above the upper flange of the crucible outside the charge and the liquid metal mirror.

The furnace chamber was previously evacuated to 10 ^-4 mm Hg.

Before igniting the arc, the magnetic field of the main electromagnet was set to about 0.015 T, and the field of the additional electromagnet was 0.03 T. The argon flow rate at the start of smelting was set to 0.1 m ³ / h; the current strength of the vacuum plasma arc was stabilized at 5 kA. Under these conditions, the pressure in the furnace chamber was set at 5 · 10 ^-2 mm RT.article.

The bath formation time did not exceed 2 minutes. After melting the charge, the argon consumption was reduced to 0.05 m ³ / h, and the magnitude of the main magnetic field induction was reduced to 0.01 T. After about 5 minutes of melting after the charge was deposited, the arc length stabilized at 250 mm, however, the arc voltage gradually increased from 40 to 65 volts, since the pressure in the furnace gradually decreased from 5 · 10 ^-2 to 5 · 10 ^-3 mm Hg . Therefore, in order to avoid arc burning only in the crucible sector, located near the cathode, the magnitude of the additional magnetic field induction was adjusted - reduced to 0.02 T.

Mixing of the melt was carried out similarly to Example 1. The lower electromagnets were turned on in coordination with the upper ones (pairs) using a switch and a controller. To mix the melt in the vertical plane, the magnetic field induction of the lower electromagnets was increased until a spherical convexity appeared on the surface of the melt mirror. When melting titanium alloys, this required induction of 0.04-0.05 T. The lower electromagnet was turned on for 10 seconds, and the upper electromagnet paired with it was turned on for 5 seconds. Then again, for 15 seconds, the same lower electromagnet was turned on, and after it, for 5 seconds, the same upper electromagnet was turned on, etc. The total operating time of one pair of electromagnets was set to 90 seconds.

With the help of such a switch, the electromagnets are switched on in pairs. Depending on the number of the lower electromagnet turned on, the controller included an upper electromagnet with the corresponding number, the magnetic field of which ensured the direction of the arc to that sector of the crucible (bath) in which the bulge existed. In order to avoid the mutual influence of the upper and lower fields and their distortions, the lower and upper electromagnets were switched on not simultaneously, but alternately. The settings for turning on the electromagnets were set using the controller. The lower electromagnet was turned on for 10 seconds, and the upper electromagnet paired with it was turned on for 5 seconds immediately after the lower electromagnet was turned off. Then, the lower electromagnet was turned on again for 10 seconds, and the upper electromagnet was turned on for 5 seconds, etc. The total operating time of one pair of electromagnets was set to 90 seconds. Next, the first pair of electromagnets was turned off and the second pair was turned on. The alternate inclusion of the upper and lower electromagnets is possible due to the large inertia of the movement of the flows of molten metal. The existence of a bulge after disconnecting the lower electromagnets of the mixing system lasts up to 8 seconds.

Mixing (rotation) of the melt in the horizontal plane was carried out with the same time settings, organizing the opposite direction of the arc with respect to the rotating flows of liquid metal. In this case, instead of electromagnets, coreless solenoids covering the crucible were used (as shown in FIG. 2, item 15). The solenoids are turned on sequentially and in accordance with each other. For the formation of metal rotation using a solenoid, induction of 0.01-0.02 T was required near the inner surface of the crucible.

Exposure of the metal in the liquid state was carried out for 10 minutes, after which the metal was drained by turning the crucible.

The mass of the metal to be drained was approximately equal to the mass of the charged charge and amounted to 60 ± 5 kg.

Table 1 shows the chemical composition of the obtained alloy.

No. of swimming trunks Al Si O H N Mo Fe V one 5.22 0,092 0.12 0.010 0,03 <0.5 0.12 not upd. 2 6.12 0,086 0.16 0.012 0.02 <0.5 0.11 not upd. 3 6.10 0.128 0.11 0.010 0.02 <0.5 0.1 not upd. four 6.12 0.134 0.12 0.010 0,03 <0.5 0.12 not upd. Norm 4.1-6.2 <0.15 <0.22 <0.03 <0.05 <0.8 <0.3 <1.2

The content of tungsten and copper in the obtained castings was not found. Only after melting No. 2 in the alloy were “traces” of tungsten and copper fixed.

Manual adjustment of the field of electromagnets was not sufficiently effective, since several parameters were simultaneously changed during the smelting process. The length of the arc and its voltage changed due to the settling of the charge, the pressure in the furnace - due to the injection of argon into the furnace through a plasma torch, the flow rate of argon was changed to reduce the pressure before draining the metal and reduce its oxidation by simultaneously injecting argon into the furnace and, accordingly, increasing it. It was difficult for the operator to quickly understand the cause of the voltage change, which led to errors. As a result, the arc deflected either too much or too weakly. Automatic adjustment of the fields of electromagnets using a pressure sensor made it possible to timely correct the magnetic field induction of an additional electromagnet.

Thus, the claimed combination of essential features provides accurate reproduction of a given chemical composition and structure of the resulting alloys due to the melting process according to a given technology. At the same time, the skull eliminates direct contact of liquid metal with the crucible material, eliminates their interaction and contamination of the melted alloy by the crucible material, and the use of independent heat sources in vacuum arc skull furnaces allows loading a lump charge into the crucible, ensuring the necessary overheating and fluidity of the melt, and long metal exposure in a liquid state, preservation of alloying components in the alloy due to the possibility of their later introduction into the melt and complete averaging of the composition of Av, and involvement in the process of melting lumpy waste. The use of a vacuum plasma torch as a cathode also creates the possibility of creating a neutral, oxidizing or reducing atmosphere, as well as smooth control of the heating power and pressure in the furnace chamber. Placing the cathode in such furnaces outside the melt mirror, i.e. on the periphery of the furnace, it avoids contamination of the melt with undesirable impurities and improves its quality. In addition, the claimed combination of essential features makes it possible to make the crucible rotary, which makes it possible to discharge metal at an adjustable speed. Mixing of the melt intensifies the melting process and increases its uniformity. The melt mixing efficiency here also increases due to the direction of the arc in the zone of its optimal contact with the molten charge. This leads to an increase in the intensity of mixing of the liquid metal, to an increase in the quality of the alloy being prepared and the productivity of the process. These advantages are extremely important in the remelting of waste or a multicomponent lump mixture of metals having various physical and technological properties, as well as chemically active metals and their alloys.

Claims (23)

1. The method of vacuum-arc melting of chemically active metals and alloys based on them in a skull furnace, comprising loading the charge into a water-cooled skull crucible, creating a vacuum in the furnace chamber, melting the charge in a vacuum using an arc discharge and draining the melt into molds, different the fact that the charge is melted using a vacuum plasma arc formed by the arc discharge of a vacuum plasma torch, and the metal melt is also affected by magnetic fields from the upper and lower electron groups of magnets, while the upper group of electromagnets create opposing primary and secondary magnetic fields that control the formation, deflection and movement of the vacuum plasma arc, and the lower group of electromagnets mix the melt in horizontal and vertical planes, and when the melt is mixed in a vertical plane on the surface the melt mirrors form bulges, and when the melt is mixed in a horizontal plane, the melt rotates relative to along the vertical axis of the crucible of the skull, while the formation of the vacuum plasma arc is carried out by pulling the main magnetic field of the column of the arc from the interelectrode gap with the formation of a loop between the vacuum plasmatron and the bath of the melt using an additional magnetic field, moving the arc while mixing the melt in the horizontal plane is directed towards the movement of the melt , and when the melt is mixed in a vertical plane, to the places where the bulges are formed, moreover, during melting, Correction of the magnitude of the induction of the main and additional magnetic fields is called for, and before draining the obtained melt into the molds it is kept in a skull crucible for 0.05-0.5 hours. 2. The method according to claim 1, characterized in that the magnitude of the magnetic field induction of the lower group of electromagnets providing melt mixing in the vertical plane is increased until a bulge, mainly spherical, appears on the surface of the melt mirror. 3. The method according to claim 1, characterized in that the magnitude of the induction of the main magnetic field of the upper group of electromagnets, proportional to the strength of the arc current, is adjusted for the flow of plasma-forming gas in manual or automatic modes. 4. The method according to claim 3, characterized in that the magnitude of the induction of the main magnetic field of the upper group of electromagnets is increased by 10-30% with an increase in the consumption of plasma-forming gas from 0.1 to 10 m ³ / h, and with a decrease in the consumption of plasma-forming gas from 0 , 1 to 0.05 m ³ / h the magnitude of the induction of the main magnetic field is reduced by 20-40%. 5. The method according to claim 1, characterized in that the magnitude of the induction of an additional magnetic field of the upper group of electromagnets, proportional to the arc voltage, is adjusted according to the pressure in the furnace chamber in manual mode. 6. The method according to claim 5, characterized in that the magnitude of the induction of an additional magnetic field of the upper group of electromagnets is increased by 10-30% when the pressure in the furnace chamber increases from 10 ^-1 to 1 mm Hg, and when the pressure in the chamber decreases furnaces from 10 ^-1 to 10 ^-3 mm Hg the magnitude of the induction of the additional magnetic field is reduced by 30-60%. 7. The method according to any one of claims 1 to 6, characterized in that in the smelting process a controlled regulation of the arc current, the plasma gas flow rate, the pressure in the furnace, the arc length and the magnitude of the magnetic field induction of the electromagnets is carried out. 8. The method according to claim 1, characterized in that when loading the charge into the crucible, the refractory alloy components are first loaded, and its fusible components are fed into the crucible at the end of the melting. 9. The method according to claim 1, characterized in that a vacuum of 10 ⁻³ −10 ⁻⁴ mm Hg is created in the furnace chamber before starting to melt, and during the smelting process, the vacuum is varied from 10 ⁻³ to 1 mm Hg. 10. The method according to claim 1, characterized in that before the discharge of the melt from the crucible, the vacuum plasma arc is deflected to the place of formation of the growth on the skull to remove it. 11. Device for vacuum-arc melting of chemically active metals and alloys based on them in a skull furnace, containing a vacuum chamber of the skull furnace, in which a melting tank in the form of a water-cooled skull skull is located, at least one mold is located under the crucible and the cathode holder is located above the crucible with a cathode, characterized in that the cathode is made in the form of a vacuum plasmatron having the ability to convert a plasma-forming gas into a plasma under vacuum with the formation of a vacuum plasma arc, while the vacuum plasmatron is installed at an angle relative to the vertical axis of the skull crucible and is located on its periphery outside the melt mirror, and the furnace is equipped with electromagnetic control systems for the vacuum plasma arc and mixing the melt in the form of upper and lower groups of electromagnets, while the upper group of electromagnets is designed for pulling the arc from the interelectrode gap, forming it in the form of a loop and moving from one sector of the crucible to another, the maximum the active level of the melt in the crucible and contains the main and additional magnets that create counter-directional magnetic fields, and the lower group of electromagnets is designed to control the electromagnetic stirring of the melt in horizontal and vertical planes, located below the maximum permissible level of the melt in the crucible and contains magnets that create tangentially directed magnetic fields to the inner surface of the skull plate. 12. The device according to claim 11, characterized in that the vacuum plasmatron is made of a refractory thermionic material, for example, tungsten. 13. The device according to claim 11, characterized in that the cathode holder is made of copper and water-cooled and has an axial hole for supplying a plasma-forming gas, for example, argon. 14. The device according to claim 11, characterized in that the vacuum chamber of the furnace contains a pipe for pumping gas, connected to vacuum pumps. 15. The device according to claim 11, characterized in that the vacuum plasmatron and the water-cooled skull plate are connected to a constant current source using flexible current leads. 16. The device according to claim 11, characterized in that the mark of the maximum permissible level of the melt in the crucible is located at least 50-100 mm below its upper edge. 17. The device according to claim 11, characterized in that the part of the electromagnets of the lower group that control the electromagnetic mixing of the melt in the horizontal plane is made in the form of solenoids, which are windings covering the crucible located in the cooled zone of the crucible. 18. The device according to claim 11, characterized in that the windings of the upper and lower groups of electromagnets are connected to the power source using a flexible current supply and are interconnected via a switch, ensuring their coordinated and alternating operation in automatic mode. 19. The device according to claim 11, characterized in that the water-cooled skull plate is made of copper. 20. The device according to claim 11, characterized in that the water-cooled skull plate is movable and contains a drain toe. 21. The device according to claim 11 or 20, characterized in that the water-cooled skull plate is rotatable relative to the horizon. 22. The device according to claim 11, characterized in that the molds are moveable. 23. The device according to claim 11 or 22, characterized in that the molds are mounted on a rotating casting table.

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