DE10128168C1 - Production of metal ingots in a mold comprises re-melting several melting electrodes by exchanging the electrodes according to an electroslag re-melting process in a controlled atmosphere - Google Patents

Abstract

Production of metal ingots (10) in a mold (1) comprises re-melting several melting electrodes (21) by exchanging the electrodes according to an electroslag re-melting process in a controlled atmosphere. During the electrode exchange when the hood (17) holding the electrodes is open, a protective gas is introduced into the mold via a slag layer (13) through a gas feed device (4) which sits gas-tight on the mold. The gas feed device tapers toward the hood relative to the mold cross-section. AN Independent claim is also included for a device for producing the metal ingots. Preferred Features: The hood with the melting electrode is placed on the gas feed device to continue the re-melting process. The protective gas is argon or nitrogen. While the protective gas is being introduced through the gas feed device, waste gases are removed from the melt region of the mold using a waste gas line (7).

Description

The invention relates to a method for producing metal blocks according to the preambles of claims 1 and 2 and a device for this purpose according to the preambles of claims 6 and 7.

In such processes, the slag performs several functions:

• 1. It forms the electrical heating resistor between the Melting electrode and the metal block and / or the mold for the generation of the heat of fusion.
• 2. It forms a heat store for the duration of the electrodes change.
• 3. It cleans the metal of the consumable electrode (s), which is in shape of melted drops through the slag layer in the Melting lake or swamp sinks over the metal block.
• 4. It melts any alloying elements to be added before these sink into the melting lake.
• 5. It melts further slag to be added.

The shielding gas also has several functions:

• 1. It protects the melting electrode that is hot at the bottom Slag and the molten metal against unwanted influences the ambient air such as oxygen and moisture (water or hydrogen).
• 2. It takes from the consumable electrode and from the Slag layer of rising gaseous impurities and toxic compounds such as B. sulfur dioxide from the Sulfur content of the consumable electrode and fluoride certain, metallurgically related slag components and leads them away, possibly to an exhaust gas treatment system.
• 3. It prevents embrittlement of the metal block, in particular those caused by the influence of hydrogen and oxygen.
• 4. It prevents changes in the reactivity of the slag towards the metals.

These functions of slag and protective gas are without special Precautions when changing electrodes are impaired.

By US-3,777,041 it is with an electro-slag remelt oven known throughout the remelting of a single Electrode into the mold itself above the slag an inert gas like Introduce argon or nitrogen and one on the upper mold edge Arrange ring body that surrounds the electrode as closely as possible. However, consumable electrodes are usually irregularly shaped, so that the annular gap must be dimensioned sufficiently large. The gas losses are correspondingly high. A hood surrounding the electrode and an electrode rod penetrating this are however also little planned like an electrode change.

A similar system with protective gas supply is also in the attachment by Jäger / Koch / Cerwenka "Characteristics of the ESR and VAR Processes in the Production of High-Performance Nickel-Base Alloys "in" subject reports metallurgical practice metal processing ", Vol. 25, No. 4, 1987,  Pages 307 to 313 described in which the sealing effect of a ring body opposite the melting electrode through a labyrinth tion is improved. In this case an electrode change is necessary give; however, there is a hood that could limit gas consumption not described, rather is above the labyrinth seal Suction ring provided, which suggests significant leaks. Suction is necessary because some of the possible emitting slags contain highly toxic fluorides and also because Remelting often releases sulfur contained in the steels, that burns to toxic sulfur dioxide.

By US-3,989,091 it is with an electro-slag remelt oven known, on the upper mold edge an annular body with radial arrange inward nozzles through which throughout the Remelting in the annular gap between the melting electrode and a protective gas is introduced into the mold, except for the slags mirror drops. An electrode change would be possible, but it is Gas consumption through convective rise of the protective gas Warm up considerably because there is no hood covering the electrode surrounding the ring body and the escape of the protection could prevent gases.

An electro-slag remelting furnace is known from AT-PS 343 300, in which the entire mold is arranged within an oven chamber, which is flooded with nitrogen. In one of the embodiments for the purpose of changing electrodes inside the furnace chamber least a supply electrode arranged after the melting of the first electrode can be brought into its melting position. The Chamber volume and the construction work are large, and the gas consumption is considerable.

By US-4 117 253 it is with an electro-slag remelt oven known the distance between the housing of the electrodes drive and the upper mold edge during the remelting of one To bridge the electrode sealed by a cylindrical jacket,  which surrounds the electrode and provides protection through the slag gas atmosphere can be maintained. For changing electrodes However, this jacket must be lowered telescopically over the mold are so that the protective gas escapes and the slag and thus the Molten metal exposed to the influence of atmospheric oxygen are. In addition, the jacket must have a correspondingly large diameter have.

US Pat. No. 4,953,177 and the corresponding EP 0 407 021 A1 Electro-slag remelting furnace known in which abge on the mold seals a hood is placed through which an electrode rod is passed through. The seal is made using an invertible textile membrane. To avoid the influence of oxygen, the A protective gas such as argon is introduced into the upper end of the mold. With a sequential melting of several electrodes by changing electrodes is not concerned with this writing, rather it is about surveillance and Regulation of the composition of the gas atmosphere in the furnace.

DE 39 01 297 C2 is an electro-slag remelting plant known in which an axially divided on the upper edge of a mold Hood is placed, which is sealed so far when remelting that no toxic gases can escape, and at which only small amounts of inert gases and / or dry air must be supplied so that Plants for the generation of dry air and exhaust gas purification very much can be dimensioned smaller. It is the successive Melting of electrodes described by changing electrodes, however, no information is given as to how the slag is when changing electrodes by opening or removing the hood could be protected against atmospheric oxygen.

DE 195 05 743 A1 describes the electrode change in an electrical system slag remelting plant described, the one mold and two hoods has, which for the purpose of changing electrodes alternately from Mold can be lifted off. Here, however, is the slag again briefly exposed to the ambient air and its oxygen. Means that  could prevent this are not specified.

From DE 24 25 032 B2 it is known that casting blocks are easily deformable high-melting iron and metal alloys after the Electroslag remelting process from at least one self-consumable electrode (consumable electrode) in a liquid-cooled To produce mold. By connecting the mold with a hood or bell should have a pressure of at least 20 bar or 2 MPa, preferably more than 50 bar or 5 MPa, upright from a gas that does not react with the slag be preserved. This is done in a three-part pressure chamber that consists of a pressure vessel, the bell and a lid, the Pressure chamber surrounds the mold or the mold as a pressure chamber is trained. Pressure chamber and bell are about the same height, and the melting electrode has a length such that it is in the Initial state about half in the bell and half in the mold or pressure chamber. This suggests that an electric change is not intended during the construction of a block. This would also be absurd, because then the pressure chamber would have to be opened the pressure breaks down and the slag comes with the Ambient air in contact, which is stated to be very harmful.

The length relationships of the electrode and block are due to this, that the electrode has a significantly smaller diameter than the mold must have to avoid short circuits between the two. Also the Aspect ratios make it unnecessary to change electrodes conclude. When changing electrodes, one should at least switch on strongly preheated electrode are used at its lower end already exposed to atmospheric oxygen during its transport to the mold would be and would oxidize significantly. Both following a cold Electrode as well as adding an oxidized electrode as well Collapse of the high pressure gas atmosphere would result in the finished block as a disturbance of its composition and structure impact construction, so that the block would not be usable. A gas feeding device between bell and mold is not only not  disclosed; it would also be ineffective because of the high pressure gas atmosphere could not be maintained. The gas loss would be considerable, e.g. B. at 50 bar or 5 MPa operating pressure 50 times free chamber volume.

The invention is based on the object of a method and to provide a device of the type described in the introduction, at those for the maintenance of a controlled or inert gas atmosphere only small amounts of gas in the area of slag and / or electrode are needed and where the slag and / or the electrode at However, changing electrodes does not have the harmful influence of acid substance and / or moisture is exposed to the ambient air or become.

The solution to the problem is the one specified at the beginning Method according to the invention by the features in the characteristics of the Claims 1 and 2 and in the device specified above according to the invention by the features in the characteristics of the patent claims 6 and 7.

The object is completely achieved by the invention, in particular, a method and an apparatus of the beginning described genus specified in which for the maintenance of a controlled or inert gas atmosphere above the slag and / or only small amounts of gas are required on the circumference of the electrode and where the slag and / or the electrode in the electrodes nevertheless do not change the harmful influence of oxygen and / or is exposed to the humidity of the ambient air.

In addition, the functions of slag specified at the beginning remain and preserve protective gas as much as possible.

The expression "with the hood open" includes the following options: It can be a closed hood on the perimeter, the raised to change electrodes and, if necessary, also move sideways  and / or is pivoted. But it can also be one on the Scope sectored hood, from trade to electrodes change one or more sectors swung out sideways or move so that the electrodes can be changed by hanging a new, possibly preheated electrode by a special manipulator is possible. This possibility can be expanded, however, that the Subdivided hood additionally raised and, if necessary, also moved sideways and / or is pivoted.

In the course of further refinements of the method according to the invention, it is particularly advantageous if - either individually or in combination -:

• - The hood with the subsequent melting electrode Continuation of the remelting process on the gas supply device is put on,
• - At least one gas from the group argon and Nitrogen is used and / or if
• - During the supply of protective gas through the gas supply device device through an exhaust pipe exhaust gases from the melting range of the Chill can be removed.

In the course of further refinements of the device according to the invention, it is particularly advantageous if — either individually or in combination:

• - The hood has a smaller internal cross section than the mold and if the intermediate ring is tapered towards the hood. is
• - The hood is a feedthrough that can be supplied with protective gas for the Has electrode rod,
• - The feed device of the hood is designed as a nozzle ring, the  surrounds the electrode rod at the top of the hood,
• - The gas supply device has an exhaust pipe through which Exhaust gases can be removed from the melting area of the mold, and / or if
• - The hood consists of sectors, one of which is the sector Electrode change is removable from the other sector.

Two exemplary embodiments of the subject matter of the invention and their modes of action are explained in more detail below with reference to FIGS. 1 to 3.

Show it:

Fig. 1 is a vertical section through a first embodiment of an electro-slag Umschmelzofens during Schmelzbetrie bes

Fig. 2 shows a detail from Fig. 1 during the electrode change and

Fig. 3 shows a vertical section through a second embodiment of an electroslag remelting furnace during the melting operation.

In Fig. 1, a cylindrical mold 1 of conventional design with cooling water connections 2 and 3 is shown. On this mold 1 , a Gaszu management device 4 in the form of an intermediate ring 5 is attached, which via a supply line 6 to a gas source for a protective gas, for. B. nitrogen or - preferably - argon, is connected. Mixtures of these gases with different proportions are also suitable. The furnace atmosphere of contaminated exhaust gas is sucked off through an exhaust pipe 7 . As shown, the intermediate ring 5 is in the form of a hollow truncated cone, the larger base surface of which rests on the upper annular surface of the mold 1 by means of a seal 8 .

In the starting phase, not shown, the bottom of the mold 1 was closed by a cooled and later lowerable base plate 9 , a so-called extraction table. The metal block 10 being formed rests on this, the upper side of which bears a sump 12 made of cleaned metal melt via a phase boundary 11 . In turn, a molten slag layer 13 floats on the latter, the composition of which depends on the metallurgical requirements of the remelting process. In order to be able to influence the composition of an alloy, the intermediate ring 5 is also connected to a container 15 with alloy elements via a feed channel 14 . A similar device can also be provided for the supply of slag for the starting phase and possibly further slag, since this is partially removed as a block skin during the remelting process.

A cylindrical hood 17 is placed on the intermediate ring 5 by means of a flange 16 and has a feed-through 18 for an electrode rod 19 at its upper end. This is connected to a drive, not shown, for the vertical feed. The bushing 18 encloses the electrode rod 19, which is smooth on the surface, as closely as possible and is connected via a feed line 20 to a source of a protective gas.

The bushing 18 is surrounded by a further feed device 28 for a protective gas, which is designed as an annular channel 28 a, from which a nozzle ring 29 extends. The supply takes place via a supply line 30 with a shut-off valve 31 . This has the following relevance: The melting electrode 21 must be preheated at the lower end outside the mold 1 to about 600 ° C., so that no electrically insulating slag film is formed there, which would temporarily delay the remelting process. This would have negative consequences for the block structure. On the other hand, the hot metal would react with the atmospheric oxygen to form oxides. This is now at least largely prevented by the protective gas emerging from the nozzle ring 29 , which forms a kind of falling protective gas curtain due to the vertical nozzle direction in connection with the greater density, which is indicated by the arrows 32 .

On the electrode rod 19 - replaceable - a melter electrode 21 is attached. At the end of the remelting of this electrode 21, remains to protect the electrode rod 19 and the jig not shown, an electrode 21 a back rest, the underside of which is indicated by dashed lines. Details of such a melting process are known and are therefore not explained in detail.

As shown, the hood 17 surrounds the melting electrode 21 as close as possible in order to keep the gas volume, the gas consumption and the ambient air possibly introduced when changing the electrodes as low as possible.

In Fig. 2 the same parts as in Fig. 1 are given the same reference numerals. The following is also shown: The intermediate ring 5 is also provided with a seal 22 on its upper side. The hood 17 was raised by means of a lifting drive, not shown, and can be pivoted laterally away from the mold 1 in the direction of arrows 23 or 24 and there - after removal of the electrode residue 21 a - can be fitted with a new melting electrode 21 .

As shown, the hood 17 has a significantly smaller internal cross section (according to the diameter D1) than the mold 1 (according to the diameter D2). The conical intermediate ring 5 creates the conditions for a largely stepless transition and also for an advantageous constriction of the opening 25 , whereby the effect of the inert gas coating of the slag is increased. However, the arrangement is not limited to a rotationally symmetrical system.

The supply of protective gas and the removal of furnace gases is advantageously distributed over the circumference of the intermediate ring 5 , which is indicated by the dash-dotted lines 26 and 27 . The shielding gas has the following effect during the electrode change: Cold shielding gas sinks to the surface of the slag due to its higher density in the hot furnace gases. Argon is inherently denser, which increases the protective effect. After fulfilling its protective function, the gas rises again and is drawn off via the exhaust line 7 . Contamination of the ambient air, even if only temporarily, is thereby minimized.

After loading the hood 17 with the new melting electrode 21 , the hood 17 is retracted again via the opening 25 or pivoted and lowered into the position according to FIG. 1, whereupon the remelting process after the lowering of the new melting electrode 21 with only a brief interruption of 1 can be continued to 2 minutes in FIG. 1. This process can be repeated practically any number of times. From Fig. 2 it can also be seen that the protective gas veil according to the arrows 32 still extends over the lower end of the melting electrode, so that the protective function is fully fulfilled even during the transport of the new melting electrode 21 . After the Nachchargie ren the shut-off valve 31 can be closed to save gas.

The hood 17 can be at least one additional hood which is already equipped with a new melting electrode 21 and which is kept ready in the waiting position outside the melting position. As a result, the duration of the electrode change can be considerably shortened, the influence on the crystal structure of the metal block 10 can be reduced, and its structure can be significantly improved and homogenized.

Fig. 3 shows - while maintaining the previous reference numerals - a hood 17 , which consists of two semi-cylindrical sectors 17 a and 17 b. Of these, the sector 17 b can be moved by means of a driving or swiveling mechanism (not shown) for changing electrodes in the direction of arrow 17 d into the position 17 c shown in broken lines, which greatly simplifies the manipulations when changing electrodes and reduces the overall height of the system. The bushing 18 and the feed device 28 are undivided, rather a concentric parting line with a seal 33 runs in a semicircular shape. Two diametrically opposed, axially parallel separation joints 34 are indicated by a dashed line.

The hood 17 according to FIG. 3 no longer has to be lifted - if the height is appropriate - to change the electrodes, but only opened to the side, provided suitable manipulators for the preheated melting electrodes are required. However, it is also possible here to additionally lift the hood 17 by means of a lifting drive (not shown) and to move or pivot it sideways as a whole.

LIST OF REFERENCE NUMBERS

1

mold

2

Cooling water connection

3

Cooling water connection

4

Gas supply means

5

intermediate ring

6

supply line

7

exhaust pipe

8th

poetry

9

baseplate

10

metal block

11

phase boundary

12

swamp

13

slag layer

14

feeding channel

15

container

16

flange

17

Hood

17

a sector

17

b sector

17

c position

17

d arrow

18

execution

19

electrode rod

20

supply line

21

consumable

21

a Electrode residue

22

poetry

23

arrow

24

arrow

25

opening

26

line

27

line

28

feeder

28

a ring channel

29

nozzle ring

30

supply line

31

shut-off valve

32

arrows

33

poetry

34

joints
D1 diameter
D2 diameter

Claims (12)

1. A method for producing metal blocks ( 10 ) in a mold ( 1 ) by successively remelting a plurality of melting electrodes ( 21 ) by changing electrodes after the electroslag remelting process in a controlled atmosphere under a slag layer ( 13 ), the melting electrodes ( 21 ) held by means of an electrode rod ( 19 ) in an at least largely gas-tight hood ( 17 ) and fed into a melting area of the mold ( 1 ) and residues ( 21 a) of the melting electrodes ( 21 ) are removed again from the melting area, characterized in that during the electrode change with the hood open ( 17 ) into the mold ( 1 ) above the slag layer ( 13 ) by a gas-tight ring-shaped gas supply device ( 4 ) seated on the mold ( 1 ), which tapers towards the hood ( 17 ) in relation to the mold cross-section a protective gas is introduced. 2. Method for producing metal blocks ( 10 ) in a mold ( 1 ) by successively remelting several melting electrodes ( 21 ) by changing the electrodes after the electroslag remelting process in a controlled atmosphere under a layer of slag ( 13 ), the melting electrodes ( 21 ) held by means of an electrode rod ( 19 ) in an at least largely gas-tight hood ( 17 ) and fed into a melting area of the mold ( 1 ) and residues ( 21 a) of the melting electrodes ( 21 ) are removed again from the melting area, characterized in that during the electrode change in the hood ( 17 ), a protective gas is introduced, which at least the lower end of the melting electrode ( 21 ) washes. 3. The method according to claim 1, characterized in that the hood ( 17 ) with the subsequent melting electrode ( 21 ) to continue the remelting process on the gas supply device ( 4 ) is placed. 4. The method according to at least one of claims 1 to 3, characterized characterized in that at least one gas from the Group argon and nitrogen is used. 5. The method according to claim 1, characterized in that during the supply of protective gas through the gas supply device ( 4 ) through an exhaust pipe ( 7 ) exhaust gases are removed from the melting area of the mold ( 1 ). 6. Device for producing metal blocks ( 10 ) by successively remelting a plurality of melting electrodes ( 21 ) by changing the electrodes by the electro-slag remelting process in a controlled atmosphere under a slag layer ( 13 ), with a mold ( 1 ), an electrode rod ( 19 ) for the melting electrode ( 21 ) to be remelted and with an at least largely gas-tight hood ( 17 ) surrounding the electrode rod ( 19 ) and the melting electrode ( 21 ), from which the melting electrodes can be guided into a melting region of the mold ( 1 ) and by means of which Remains ( 21 a) of the melting electrode ( 21 ) can be removed again from the melting area, characterized in that an annular gas supply device ( 4 ) is arranged between the hood ( 17 ) and the mold ( 1 ) and is gas-tight on the mold ( 1 ) sits and tapered towards the hood ( 17 ) in relation to the mold cross section and through which a protective gas can be introduced into the mold ( 1 ) above the slag layer ( 13 ) during the electrode change with the hood ( 17 ) open. 7. Device for producing metal blocks ( 10 ) by successively remelting a plurality of melting electrodes ( 21 ) by changing the electrodes by the electro-slag remelting process in a controlled atmosphere under a slag layer ( 13 ), with a mold ( 1 ), an electrode rod ( 19 ) for the melting electrode ( 21 ) to be remelted and with an at least largely gas-tight hood ( 17 ) surrounding the electrode rod ( 19 ) and the melting electrode ( 21 ), from which the melting electrodes can be guided into a melting region of the mold ( 1 ) and by means of which Remains ( 21 a) of the melting electrode ( 21 ) can be removed again from the melting area, characterized in that the hood ( 17 ) is provided with a feed device ( 28 ) for a protective gas, through which the melting electrode ( 21 ) at least at its lower end End can be flushed with the protective gas. 8. The device according to at least one of claims 6 and 7, characterized in that the hood ( 17 ) has a smaller internal cross section than the mold ( 1 ). 9. The device according to at least one of claims 6 and 7, characterized in that the hood ( 17 ) has a feedable with protective gas feedthrough ( 18 ) for the electrode rod ( 19 ). 10. The device according to claim 7, characterized in that the feed device ( 28 ) of the hood ( 17 ) is designed as a nozzle ring ( 29 ) which surrounds the electrode rod ( 19 ) at the upper end of the hood ( 17 ). 11. The device according to claim 6, characterized in that the gas supply device ( 4 ) has an exhaust pipe ( 7 ) through which exhaust gases can be removed from the melting area of the mold ( 1 ). 12. The device according to at least one of claims 6 and 7, characterized in that the hood ( 17 ) consists of sectors ( 17 a, 17 b), of which one sector ( 17 b) for changing electrodes from the other sector ( 17th a) is removable.