WO2010041830A2

WO2010041830A2 - Vacuum system for vacuum melting and casting metal, and vacuum melting and casting method using same

Info

Publication number: WO2010041830A2
Application number: PCT/KR2009/005319
Authority: WO
Inventors: 고동근
Original assignee: 주식회사 엔티티
Priority date: 2008-10-10
Filing date: 2009-09-18
Publication date: 2010-04-15
Also published as: WO2010041830A3; KR20090126170A; TW201020042A

Abstract

The present invention relates to a vacuum system for vacuum melting and casting metal, and a vacuum melting and casting method using same, and more particularly, to a vacuum system for vacuum melting and casting metal, said vacuum system comprising: a vacuum pump device (256); a vacuum melting chamber (20) which is connected to the vacuum pump device (256) to enable metal melting under a vacuum condition, and which has an interior equipped with a melting furnace (110); a material injection tube (120) connected to the vacuum pump device (256) to provide metal material (01) into the vacuum melting chamber (20) under a vacuum condition; and a casting device (400) connected to the vacuum pump device (256) and the vacuum melting chamber (20) to perform casting by using the molten metal supplied from the vacuum melting chamber (20) under a vacuum condition. The present invention also relates to a vacuum melting and casting method using the vacuum system.

Description

Vacuum system for vacuum melting and casting of metals and vacuum melting and casting method using the same

The present invention dissolves metal in a vacuum state when casting a specific molding by melting the metal, injects the molten molten metal into the casting apparatus in a vacuum state, and also can be cast in an environment in which the inside of the casting apparatus is maintained in a vacuum state The present invention relates to a vacuum system for vacuum melting and casting of a metal and a vacuum melting and casting method using the same.

In general, a die casting machine dissolves metals such as aluminum alloys, zinc alloys, magnesium alloys, and copper alloys in the air, and casts the molten metal obtained from the melt in the air.

However, in the case of melting and casting in the air, due to inflow of gas into the air during melting of the metal and bubble formation during casting, moldability such as foaming defects, surface defects, and unfilling of die-casting products occurs, resulting in low product productivity. The energy loss is also enormous, and there is a problem in that the work environment is avoided due to the poor working environment due to gas generation.

In addition, the active metal such as magnesium is produced in a mixed gas atmosphere of SF ₆ and CO ₂ to emit a considerable amount of greenhouse gases, causing a lot of difficulties in production as well as air pollution.

The first object of the present invention for overcoming the above-mentioned problems is to make it possible to work in a vacuum state when dissolving the casting metal to obtain a pure metal molten metal from which an impure gas is removed, and also to vacuum the pure molten metal. The present invention provides a vacuum system for vacuum melting and casting of metals and a vacuum dissolving and casting method using the same, which can be press-fitted into a mold through an old mold and a molten metal supply pipe, and at the same time, environmentally friendly casting can be performed.

A second object of the present invention is to provide a vacuum system for vacuum dissolution and casting of a metal, and a vacuum dissolving and casting method using the same, in which dissolution and casting of an active metal such as magnesium alloy can be safely performed in a vacuum state.

The present invention for achieving the first object as described above, the vacuum pump device (256); A vacuum dissolution chamber 20 connected to the vacuum pump device 256 to enable dissolution of a metal in a vacuum state and having a molten crucible 110 therein; A material input pipe 120 connected to the vacuum pump device 256 to inject a metal material 01 in a vacuum state into the vacuum dissolution chamber 20; And a casting apparatus 400 connected to the vacuum pump device 256 and the vacuum melting chamber 20 to cast the molten metal supplied from the vacuum melting chamber 20 in a vacuum state. It is characterized in that the melting and the injection and casting into the casting apparatus.

The present invention for achieving the second object is provided with a first sensor 47 for detecting the amount of oxygen and hydrogen in the vacuum dissolution chamber 20, the vacuum dissolution chamber 20 in accordance with the detection of the first sensor Inert gas filler 21 is connected to one side so that the inert gas is injected into the inert gas when the first sensor 47 provided in the vacuum dissolution chamber 20 detects the amount of oxygen and hydrogen and increases more than the allowable value. Inert gas filled in the filling container 21 is injected into the vacuum melting chamber 20 to prevent the magnesium alloy molten metal from reacting with oxygen.

According to the vacuum system for vacuum melting and casting of the metal and the vacuum melting and casting method using the same according to the present invention, aluminum alloys, copper alloys, magnesium alloys, zirconium alloys and other special alloys, etc., can be maintained while maintaining the desirable characteristics of the die casting machine. Since metals can be easily dissolved in a vacuum state, impurities gas is removed and casting is also easily performed in a vacuum state, which can significantly reduce microbubbles, thereby minimizing casting defect rate, increasing productivity, and making the work environment more environmentally friendly. This has the advantage of being able to produce reliable, high quality products at low cost.

Moreover, even when the active metal is dissolved, the amount of oxygen and hydrogen is automatically managed, thereby injecting an inert gas when a risk factor is generated, thereby suppressing the reaction of the active gas with oxygen.

1 is a main structural diagram of a vacuum system for vacuum melting and casting of the present invention.

2 is a schematic diagram of a vacuum system connected to a vacuum melting die casting machine according to a first embodiment of the present invention.

3 to 12 is a diagram showing the operation of each process of the vacuum system for showing the vacuum melting and casting method of the present invention.

13 is a block diagram of a vacuum system connected to a vacuum gravity mold casting machine according to a second embodiment of the present invention.

14 is a block diagram of a vacuum system connected to a vertical vacuum forging machine according to a third embodiment of the present invention.

15 is a schematic diagram of a vacuum system connected to a vertical vacuum squeeze casting machine according to a fourth embodiment of the present invention.

V1: first valve V2: second valve

V3: third valve V4: fourth valve

V5: fifth valve V6: sixth valve

V7: 7th valve V8: 8th valve

V9: 9th Valve V10: 10th Valve

20: vacuum melting chamber 21: inert gas filling machine

22: 1st auxiliary vacuum tank 23: 2nd auxiliary vacuum tank

47: oxygen and hydrogen sensor 55: oxygen and hydrogen sensor

65: oxygen and hydrogen sensor 110: molten crucible

120: material input pipe 200: material loading plunger

256: vacuum pump device 150: sleeve

155: molten metal pressure plunger 300: molten metal inlet blocking plunger

400: casting apparatus 450: mold

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a schematic diagram of main components of a vacuum system for vacuum melting and casting according to the present invention.

1, the vacuum system of the present invention includes a vacuum pump device 256 for sucking air; A vacuum dissolution chamber 20 connected to the vacuum pump device 256 so that a heating means (not shown) is provided to dissolve the casting metal in a vacuum state and a melt crucible 110 is provided therein; A material input pipe 120 having a material loading plunger 200 at one side thereof connected to the vacuum pump device 256 so that the metal material 01 can be introduced into the vacuum dissolution chamber 20 in a vacuum state; The sleeve 150 is connected to the vacuum melting chamber 20 to inject molten metal in a vacuum state, and the molten metal injected into the sleeve 150 in a vacuum state is connected to the vacuum pump device 256. It is composed of; casting apparatus 400 including a mold (450) for molding a specific product.

Here, the casting apparatus 400 including the sleeve 150 and the mold 450, the vacuum dissolution chamber 20 for dissolving metal, and the material injection tube 120 are rapidly maintained in a vacuum state, and A first auxiliary vacuum tank 22 is installed between the mold 450 and the vacuum pump device 256 so as to maintain the same degree of vacuum inside, and between the vacuum dissolution chamber 20 and the vacuum pump device 256. The second auxiliary vacuum tank 23 is installed on the material input pipe 120 and the first auxiliary vacuum tank 22, while the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank ( 23) are interconnected.

The casting apparatus 400 is not limited as long as it enables the molten molten metal, including the sleeve 150 and the mold 450, to be molded into a specific product, and is a vacuum melting die casting machine as an example of such a casting apparatus 400. , Horizontal die casting machine, vacuum gravity mold casting machine, vertical vacuum melt forging machine, vertical vacuum squeeze casting machine, but the present invention is not limited to the described apparatus.

2 is a configuration diagram of a vacuum system in which the casting apparatus 400 is connected to a vacuum melting die casting machine according to the first embodiment of the present invention, wherein the vacuum melting die casting machine is devised by the present inventor, Korean Patent No. 10 -0578257 may be a vacuum melting die casting machine.

1 and 2, the connection portion of each device is preferably provided with a valve so as to be in communication with each other or closed in accordance with the inspection or abnormality of each device or various situations.

To this end, a first valve V1 is provided between the vacuum dissolution chamber 20 and the sleeve 150, and a second valve V2 is provided between the material injection pipe 120 and the vacuum dissolution chamber 20. A fourth valve V4 is provided between the mold 450 and the first auxiliary vacuum tank 22.

In addition, a third valve V3 is installed between the material input pipe 120 and the material loading plunger 200. When the third valve V3 is opened, the casting metal may be introduced into the material input pipe 120. If the state is closed, on the contrary, it means a state in which metal is introduced into the material input pipe 120.

A fifth valve V5 is provided between the material input pipe 120 and the first auxiliary vacuum tank 22, and a tenth valve V10 is provided between the first auxiliary vacuum tank 22 and the vacuum pump device 256. Is installed, and each auxiliary vacuum tank 22 is opened when the eighth valve V8 is installed between the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23. Reference numeral 23 can maintain the same degree of vacuum.

A seventh valve V7 is provided between the vacuum melting chamber 20 and the second auxiliary vacuum tank 23, and a ninth valve V9 between the second auxiliary vacuum tank 23 and the vacuum pump device 256. ) Is installed, the operation of the vacuum system of the present invention according to the opening and closing of each valve will be described in detail later.

On the other hand, the vacuum dissolution chamber 20 is installed with a first sensor 47 for detecting the amount of oxygen and hydrogen inside, the inert gas charger 21 filled with an inert gas and the vacuum dissolution chamber 20 and When the metal dissolved in the vacuum dissolution chamber 20 dissolves an active metal such as magnesium alloy, lithium alloy, or zirconium alloy by connecting the sixth valve V6 to the sixth valve V6, the sixth valve V6 is connected as necessary. It can be opened to allow the inert gas to be introduced into the vacuum melting chamber 20.

That is, magnesium alloys, lithium alloys, zirconium alloys among metals can be dissolved only in a vacuum state because they ignite when they come into contact with oxygen when dissolved in air. Therefore, during the dissolution of the active metal in the vacuum dissolution chamber 20, oxygen or hydrogen flows into the vacuum dissolution chamber 20, which is a significant risk, and thus, the first sensor before the oxygen and hydrogen flows into the vacuum dissolution chamber 20 and ignites. When the 47 senses the amount of oxygen and hydrogen and detects an abnormality and transmits it to a control panel (not shown), the control panel closes the first valve V1 and the seventh valve V7 and then the sixth valve V6. Open to fill the inert gas in the inert gas filler 21 into the vacuum dissolution chamber 20 to prevent the reaction with oxygen in advance to enable safe operation.

The inert gas mainly uses argon gas, and may also use a mixed gas of SF ₆ and CO ₂ , and may be used by appropriately mixing different kinds of gases depending on the nature of the dissolved metal.

The first auxiliary vacuum tank 22 rapidly evacuates the molding part of the mold 450, the sleeve 150, and the material input pipe 120, and communicates with the second auxiliary vacuum tank 23 to form a vacuum dissolution chamber ( 20), the molding portion of the mold 450, the sleeve 150, the material input pipe 120, the second auxiliary vacuum tank 23 can be maintained at the same vacuum level, each secondary vacuum tank 22 (23) ) May be provided with a second sensor (55, 65).

The

second sensors

55 and 65 are devices for first detecting the amount of oxygen and hydrogen before oxygen and hydrogen are introduced into the vacuum melting chamber 20. When oxygen and hydrogen are detected by the sensor 55 installed in the first auxiliary vacuum tank 22, the operation of the vacuum pump device 256 is stopped and the fourth valve V4, the fifth valve V5, and the eighth valve ( V8), the ninth valve V9 and the tenth valve V10 are closed to check the cause of the abnormality. In addition, when oxygen and hydrogen are detected by the sensor 65 installed in the second auxiliary vacuum tank 23, the operation of the vacuum pump device 256 is stopped and the seventh valve V7, the eighth valve V8, and the ninth valve are stopped. By closing the valve V9 and the tenth valve V10, the cause of the abnormality can be checked. As described above, the

second sensors

55 and 65 become primary safety devices before oxygen and hydrogen are introduced into the vacuum melting chamber 20.

3 to 12, the operation method of the vacuum system of the present invention will be described as follows, through which the vacuum system configuration of the present invention will be more clearly described.

3 to 12 are operation state diagrams for each process of the vacuum system for showing the vacuum melting and casting method of the present invention.

S1: vacuuming stage of each secondary vacuum tank

As shown in FIG. 3, the first valve V1, the second valve V2, the fourth valve V4, the fifth valve V5, the sixth valve V6, the seventh valve V7, and the eighth valve ( V8) When the vacuum pump device 256 is operated with the third valve V3, the ninth valve V9, and the tenth valve V10 open, the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 22 are closed. The inside of the auxiliary vacuum tank 23 is in a vacuum state (1 × 10 ^-3 Torr to 1 × 10 ^-5 Torr). The opening of the third valve V3 pushes the metal material to be dissolved into the material input pipe 120. It is to put.

If the oxygen and hydrogen amount is detected by the oxygen and

hydrogen sensors

55 and 65 installed in the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23, the operation of the vacuum pump device 256 is stopped. Check and remove the cause of error and restart. At this time, the operating range of the oxygen and hydrogen sensor is set in accordance with the type of metal to be dissolved.

S2: vacuuming step of the vacuum melting chamber

As shown in FIG. 4, the tenth valve V10 is closed and the seventh valve V7 is opened to vacuum the inside of the vacuum dissolution chamber 20, and the vacuum pump device 256 continues to operate. At this time, even if the vacuum pump device 256 continues to operate for a predetermined time, if oxygen and hydrogen in the vacuum melting chamber 20 or the second auxiliary vacuum tank 23 is detected as more than necessary, the operation of the vacuum pump device 256 is stopped. After the cause is removed, the vacuum pump device 256 is restarted to maintain the inside of the vacuum dissolution chamber 20 in a vacuum state.

S3: High vacuum stage of the first vacuum auxiliary tank

As shown in FIG. 5, the seventh valve V7 and the ninth valve V9 are closed, the tenth valve V10 is opened, and the vacuum pump device 256 is continuously operated to maintain the vacuum degree in the first vacuum auxiliary tank 22. It is made higher than the 2nd vacuum auxiliary tank 23. At this time, when the inside of the second vacuum auxiliary tank 23 is (1 × 10 ^-3 Torr to 1 × 10 ^-5 Torr) vacuum, the first vacuum auxiliary tank 22 is (1 × 10 ^-5 Torr to 1 × 10 ^-7 Torr) can be maintained in a vacuum state.

S4: vacuuming the material input tube and preparing the metal material

As shown in FIG. 6, the metal material 01 is pushed into the material injection plunger 200 into the material insertion plunger 200 and then repositioned. Then, the third valve V3 is closed and the material is inserted into the plug hole of the third valve V3. When the plunger 200 passes and stops, the third valve V3 is completely closed.

At this time, the fifth valve V5 is opened to maintain the vacuum degree such as the vacuum degree in the vacuum discharging chamber 20 in the material injection pipe 120. In addition, the fourth valve V4 is opened to coalesce the mold 450 and to vacuum the space between the molding part and the sleeve. As a result, the material input pipe 120, the mold 450, the sleeve 150, and the first auxiliary vacuum tank 22 maintain the same degree of vacuum.

S5: same evacuation step of each device

As shown in FIG. 7, the eighth valve V8 is opened to form the first auxiliary vacuum tank 22, the second auxiliary vacuum tank 23, the molding part of the mold 450, the sleeve 150, and the material input pipe 120. ) To maintain the same vacuum degree (about 1 × 10 ^-3 Torr to 1 × 10 ^-5 Torr), and then open the seventh valve V7 to allow the vacuum dissolution chamber 20 to maintain the same vacuum degree. At this time, the vacuum pump device 256 stops operation when the required degree of vacuum is reached, and operates when it does not reach.

S6: input phase of metal material

As shown in FIG. 8, the second valve V2 is opened, and the metal material 01 in the material introduction pipe 120 is pushed into the molten crucible 110 in the vacuum melting chamber 20 using the material loading plunger 200. After loading, the material loading plunger 200 is positioned in the material input pipe 120.

S7: Melting step of metal material

As shown in FIG. 9, the second valve V2, the fourth valve V4, the fifth valve V5, the seventh valve V7, and the eighth valve V8 are closed, and the ninth valve V9 is opened. The vacuum pump device 256 is operated to maintain a high degree of vacuum in the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23. At this time, dissolution of the metal material 01 charged into the solubility crucible 110 of the vacuum dissolution chamber 20 starts.

S8: vacuum holding step of the vacuum melting chamber

When melting of the metal material starts, as shown in FIG. 10, the seventh valve V7 and the first valve V1 are opened, the material loading plunger 200 is returned to its original position, and the third valve V3 is opened.

At this time, when the metallic material is an active metal that may ignite when it comes into contact with oxygen, if the first sensor 47 installed in the vacuum melting chamber 20 detects oxygen and hydrogen above a predetermined allowable value, the first valve V1 and After the seventh valve V7 is closed, the sixth valve V6 is opened to release the gas in the inert gas charger 21 into the vacuum dissolution chamber 20 in an instant, thereby preventing the ignition of the metallic material. Play a role.

S9: Melt Filling and Forming Step

When dissolution is completely performed in the molten crucible 110 in the vacuum melting chamber 20, as shown in FIG. 11, the seventh valve V7 is closed and the molten crucible is inclined to inject molten metal into the sleeve 150 of the casting apparatus. A predetermined product is molded in a mold 450 in which a cavity, which is a molding space, is formed.

When the step S9 is completed, as shown in FIG. 12, the first valve V1 is closed and the process returns to the above-described step S1, thereby ending one cycle of the vacuum melting and casting process.

13 is a configuration diagram of a vacuum system connected to a vacuum gravity mold casting machine according to a second embodiment of the present invention, and FIG. 14 is a configuration diagram of a vacuum system connected to a vertical vacuum melt forging machine according to a third embodiment of the present invention. 15 is a schematic diagram of a vacuum system connected to a vertical vacuum squeeze casting machine according to a fourth embodiment of the present invention.

In the case of the second to fourth embodiments of the present invention, the same operation as the vacuum system of FIG. 1 is performed in the same manner, and it is classified according to the characteristics of the casting apparatus 400.

The casting device 400 includes at least a sleeve 150 and a mold 450, and may further include a molten metal injection hole blocking plunger 300 as shown in FIGS. 14 and 15 according to the characteristics of the apparatus. The molten metal pressure plunger 155 may be further provided.

At this time, the vacuum melting die casting machine of FIG. 2 is a device proposed by the present invention, and the configuration of Korean Patent No. 10-0578257 may be referred to, and the vacuum gravity mold casting machine of FIG. 13 may refer to the configuration of Korean Patent No. 10-0572581. The vertical vacuum molten forging machine of FIG. 14 may refer to Korean Patent No. 10-0572589. In addition, since the vertical vacuum squeeze casting machine of FIG. 15 may refer to the configuration of Korean Patent No. 10-0572583, detailed configuration and operation thereof will be omitted.

As described above, although the present invention has been described with reference to one embodiment shown in the drawings, this is merely an example, and those skilled in the art may make various modifications and other equivalent embodiments therefrom. It will be understood that such modifications and other embodiments are included in the following claims.

Claims

A vacuum pump device 256;

A vacuum dissolution chamber 20 connected to the vacuum pump device 256 to enable dissolution of a metal in a vacuum state and having a molten crucible 110 therein;

A material input pipe 120 connected with the vacuum pump device 256 to inject a metal material 01 into the vacuum dissolution chamber 20 in a vacuum state;

The sleeve 150 is connected to the vacuum melting chamber 20 to inject molten metal in a vacuum state, and the molten metal injected into the sleeve 150 in a vacuum state is connected to the vacuum pump device 256. A casting device 400 including a mold 450;

Vacuum system for vacuum melting and casting of the metal, characterized in that consisting of.
The method of claim 1,

A first auxiliary vacuum tank 22 between the mold 450 and the vacuum pump device 256;

And a second auxiliary vacuum tank 23 interposed between the vacuum dissolution chamber 20 and the vacuum pump device 256.

The material input pipe (120) is a vacuum system for vacuum melting and casting of metal, characterized in that interconnected with the first secondary vacuum tank (22).
The method of claim 2,

At least one or each of the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23 is provided with a second sensor for sensing the amount of oxygen and hydrogen vacuum for melting and casting the metal system.
The method of claim 2,

The vacuum system for vacuum melting and casting of the metal, characterized in that the first secondary vacuum tank 22 and the second secondary vacuum tank 23 are in communication with each other.
The method of claim 1,

The vacuum dissolution chamber 20 is provided with a first sensor 47 for detecting the amount of oxygen and hydrogen, and inert to the sixth valve (V6) on one side so that inert gas is injected in accordance with the detection of the first sensor Vacuum system for vacuum melting and casting of a metal, characterized in that the gas filler 21 is connected.
The method of claim 4, wherein

The first valve (V1) provided between the vacuum dissolution chamber 20 and the sleeve 150,

A second valve V2 provided between the material input pipe 120 and the vacuum melting chamber 20;

A third valve (V3) formed at the inlet of the material input pipe (120),

A fourth valve V4 provided between the mold 450 and the first auxiliary vacuum tank 22;

A fifth valve V5 provided between the material input pipe 120 and the first auxiliary vacuum tank 22;

A seventh valve V7 provided between the vacuum melting chamber 20 and the second auxiliary vacuum tank 23;

An eighth valve V8 provided between the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23;

A ninth valve V9 provided between the second auxiliary vacuum tank 23 and the vacuum pump device 256;

And a tenth valve (V10) provided between the first auxiliary vacuum tank (22) and the vacuum pump device (256).
The method according to any one of claims 1 to 6,

The casting device 400, vacuum melting die casting machine, horizontal die casting machine, vacuum gravity die casting machine, vertical vacuum melt forging machine, vertical vacuum squeeze casting machine, characterized in that for any one of the vacuum melting and casting Vacuum system.
A vacuum melting and casting method using a vacuum system for vacuum melting and casting of a metal according to any one of claims 1 to 7,

A vacuuming step (S1) of each of the auxiliary vacuum tanks operating the vacuum pump device 256 to vacuum the inside of the first auxiliary vacuum tank 22 and the second auxiliary vacuum tank 23;

A vacuum dissolving step (S2) of the vacuum dissolution chamber in which the inside of the vacuum dissolution chamber 20 for dissolving the metal material is brought into a vacuum state;

A high vacuuming step (S3) of the first vacuum auxiliary tank so that the degree of vacuum in the first vacuum auxiliary tank 22 is higher than the degree of vacuum in the second vacuum auxiliary tank (S3);

Injecting the metal material (01) to be dissolved in the material input pipe 120 into the material insertion plunger 200, and vacuuming the material input pipe and preparing the metal material (step) to make the material input pipe 120 in a vacuum state ( S4);

The vacuum degree in the molded part of the first auxiliary vacuum tank 22, the second auxiliary vacuum tank 23, the mold 450 and the inside of the sleeve 150, the material injection pipe 120 and the vacuum dissolution chamber 20 is the same. The same evacuation step (S5) of each device in communication with each other so as to maintain the same;

A metal material introduction step (S6) for introducing the metal material (01) in the material injection pipe (120) into the molten crucible (110) in the vacuum melting chamber (20) with the material loading plunger (200);

Dissolving step (S7) of the metal material to dissolve the metal material (01) in the melting crucible 110 by the heating means;

A vacuum holding step (S8) of the vacuum dissolution chamber to operate the vacuum pump device 256 to maintain the vacuum state inside the vacuum dissolution chamber 20 and

Method of melting and casting the metal, characterized in that the molten metal is injected into the sleeve (150) of the casting device to form a predetermined product in the mold (450).
The method of claim 8,

When the metal material is the active metal in the dissolution step (S7) of the metal material, when the first sensor 47 installed in the vacuum melting chamber 20 detects oxygen and hydrogen above the allowable value, it is stored in the inert gas charger 21. Method for dissolving and casting metal, characterized in that the gas is injected into the vacuum melting chamber (20).