EP0800879B1 - Water cooled mould for manufacturing ingots, process for continuous casting and process for electro-slag refining - Google Patents

Description

The invention relates to a short, water-cooled, below open mold for making blocks or strands according to the preamble of claim 1. Also recorded the invention a device with such a mold for the continuous casting of metals and a method for Electroslag remelting.

Both for continuous casting and for electroslag remelting of metals - and in particular of Steels - become water-cooled short molds that are open at the bottom used, the inserts mostly made of copper or copper alloys are manufactured. These bets can either be tubular - and in a water tank the cooling water flows around - or they are like this is particularly the case with large flat formats (slabs) Case is composed of several thick-walled copper plates, which are then held in a support structure. With these plate molds, the cooling water is over a distribution ring single, attached in the plates Cooling holes, fed and at the other end of the mold again from the cooling holes to a collector and further in led the return. There are also monoblock molds thick-walled, mostly forged rings known, in which the cooling water as well - as with the Plate molds - guided over individual cooling holes becomes.

The one in electro-slag remelting for special process variants used so-called stand molds, the one whole remelting block should not be here to be viewed as.

Rather, molds of interest here enable this Making strands or blocks that last considerably longer are as the water-cooled molds, with the conventional Continuous casting the strand formed in the mold subtracted either vertically or in an arc becomes. When electroslag is remelted, it can be in the mold formed block either by lowering a bottom plate subtracted down, or it can be Chill mold can be lifted in the way that on a fixed base plate a remelting block is built.

In all casting processes, reoxidation is avoided of the metal to be cast by the surrounding one Atmosphere of great importance. This question appears on the Electroslag remelting largely solved, since here the liquid metal sump is covered by a slag bath and is protected from direct air access. The The electrode tip also melts within of the slag bath so that direct contact of the liquid metal with the surrounding atmosphere avoided becomes.

The continuous casting was initially done in air, trying was, by adding oil in the area of the pouring level to limit the oxidation of the metal. The Introduction of mold powder to cover the mold level and the use of dip tubes for the supply of the liquid Metal in the mold has further improvements here guided.

Most casting powders, however, have an acidic composition, ie components such as SiO ₂ and Al ₂ O ₃ predominate compared to CaO and MgO. In addition, high amounts of carbon often have to be added to ensure the properties required for continuous casting.

For steels with the highest degree of purity, there is today Demand for pouring under basic slags at the same time complete coverage of the mold level and especially that formed in contact with the mold wall Meniscus. This requirement can not or today are not adequately met because basic slags have higher Have melting points and by the liquid Metal heat alone cannot be kept liquid can - all the more than they usually have more energy emitted to the environment through radiation as acidic flakes or powder mixtures.

Also in the electro-slag processes, in which the mostly basic slag due to the metal mirror the passage of current from the electrode to the block is heated and so that it is kept fluid, are the conditions not always ideal on the meniscus. Especially in manufacturing it always comes from blocks of large diameter again that the power supply must be reduced, in order to keep the melting sufficiently low and thus ensure a good block structure. It can happen here that the heat supply at the meniscus of the metal sump is no longer sufficient to have a good block surface free of To achieve tears and grooves.

But also with a modified electro slag process for strand melting of small strand-like cross sections in either continuous mold-like straight molds or in - belonging to the prior art - upward T-shaped Expanded molds can be used for the desired Melting rate required power or current not derived from the casting cross-section alone can otherwise cause the metal sump to overheat and continue to train an unfavorable Solidification structure comes.

To counteract this disadvantage, attempts have been made in Japan to part of the stream from the slag bath via the Derive mold wall. However, this can lead to occurrence of micro arcs between the meniscus of the Slag baths and the mold wall come. this leads to erosion of the copper of the mold at the level of the Slag bath and thus to a significant reduction the mold life.

To get around the problems outlined above would be it is desirable to introduce energy into one on the meniscus of the melting sump liquid, electrical to be able to control conductive slag bath independently, without affecting the melting rate or the bottom temperature be directly influenced. In principle, this could now by using one or more in the slag bath immersing non-consumable electrodes happen like this has already been suggested elsewhere.

When making small cross-sections, this separates Possibility for space reasons in general. At the Generate large cross-sections - and long remelting times - Such non-consumable electrodes become strong heated, with which graphite, but also tungsten or molybdenum as Eliminate materials because they are caused by atmospheric oxygen would be oxidized very quickly.

DE-A-1 483 646 describes a method for producing Cast blocks described with directional solidification, at which the surface of the melting sump by an overlying Slag layer is kept warm; the latter is produced in a predetermined area of the mold is connected to a power source. The slag bath is heated by the current transfer between two poles, one of them through the slag bath / smelter interface as well as the other from one into that Slag bath immersed - and also to that power source connected - power supply electrode formed becomes. That electrode is otherwise not identical to that metal forming the ingot; it is either as separate supply element on the slag layer set or attached to the top of the mold wall; an insulating intermediate piece is imperative in it Ceramic between the electrode and the mold required to avoid an otherwise occurring short circuit prevent. Alternatively, the second pole can also be from one directed towards the slag bath charge carrier beam a source that is not immersed in the slag bath be formed. That which solidifies in the mold Metal can be extracted from a slag bath as liquid metal Pouring ladle, as granules from a container or in form be fed to a self-consuming electrode.

GB-A-1 413 508 discloses a mold in its mold wall installed a non-consumable current-carrying element as well as via a rectifier with the power supply is connected that both the electrode and the Pouring cross section - in relation to the non-edible element - are always electrically negatively polarized.

According to US-A-3 768 543 is used to manufacture metal blocks from small pieces of metal particles in one several parts of existing water-cooled mold a meltable one between two water-cooled elements Metal electrode installed so that it is partially through the Cooling effect of these elements protected and with one pole is connected to a power source. One below the meltable electrode arranged mold element jumps inside in front. There is also a lower mold part, in which the with the second pole of the power source connected block is molded; this is against the below the mold element arranged in the fusible electrode electrically isolated by an insulating packing. The Electricity flows here between the partial melting electrode in the mold wall and the Block.

A system and a method according to DE 2 620 823 are intended in particular for the production of narrow slabs i.e. rectangular block formats, can be useful, whereby among other things consumable used, their cross-sectional area 1.05 to 20 times the cross-sectional area of the produced Blocks is. For the implementation of the procedure a slag bath is formed in the mold, in which both Immerse consumable and non-consumable electrodes. When using electrodes, their cross-sectional area larger than the cross-sectional area of the manufactured Blocks is, molds are expanded funnel-shaped upwards used.

The auxiliary electrodes discussed here have the disadvantage that they are not an integrated part of the mold wall and only partially immerse in the slag bath. Above of the hot slag are auxiliary electrodes on almost Heated slag temperature and in contact with the ambient air oxidized very quickly, leaving only an insufficient Durability is achieved.

Against this background, the inventor's goal set the difficulties discussed above and Eliminate problems.

The teachings of the independent lead to the solution of this task claims; the subclaims give favorable designs on.

According to the invention, the water-cooled copper elements Mold wall formed at least one not directly water-cooled current-carrying element installed so that this in a region which determines the position of the slag bath (20) is therefore in contact with the slag bath, and also completely below the surface of the slag bath is arranged, but not up to the mirror of the liquid metal is enough; over this element is a Contact can be made to a power source that according to Claim 1 on the other hand to an edible electrode or the resulting block or the one bearing it Base plate is connected.

As a material for these current-conducting elements preferably uses graphite in a manner known per se, but also high-melting metals, such as Tungsten, molybdenum or the like are suitable.

In a particular embodiment, the upper part of the Chill mold that receives the slag bath and into which current-carrying element (s) is / are installed, funnel-shaped be expanded. This may be particularly true in manufacturing of strands of small cross-section with a diameter or a side length of less than 300 mm of interest his.

A further embodiment of the mold according to the invention provides that the built-in current-conducting element (s) is / are electrically insulated from the copper part of the mold by installing non-conductive elements. Refractory ceramic materials such as fireclay, Al ₂ O ₃ , MgO etc. come into consideration as the material for the non-conductive elements.

When installing at least two current-carrying elements these can also be compared to each other by additional installation non-conductive elements between the individual current-conducting elements Elements.

Depending on the embodiment, the mold according to the invention enables a number of different arrangements and process variants with electroslag remelting or with Continuous casting, the most important of which are described below become.

Fig. 1:

einen Längsschnitt durch eine rohrförmige Kokille bei Verwendung für das Elektroschlacke-Umschmelzen;

Fig. 2:

den Längsschnitt durch die rohrförmige Kokille zum Einsatz beim Stranggießen;

Fig. 3:

den schematischen Aufbau einer ESU-Anlage im Längsschnitt mit Gleitkokille unter Verwendung der rohrförmigen Kokille nach Fig. 1;

Fig. 4:

den Längsschnitt durch eine andere Ausgestaltung der Kokille;

Fig. 5:

den Querschnitt durch Fig. 4 nach deren Linie V-V.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; this shows schematically in

Fig. 1:

a longitudinal section through a tubular mold when used for electro-slag remelting;

Fig. 2:

the longitudinal section through the tubular mold for use in continuous casting;

Fig. 3:

the schematic structure of an ESCU in longitudinal section with sliding mold using the tubular mold according to Fig. 1;

Fig. 4:

the longitudinal section through another embodiment of the mold;

Fig. 5:

the cross section through Fig. 4 along the line VV.

Fig. 1 shows the schematic structure of a tubular Mold 10 for so-called electro-slag remelting (ESU). In their water-cooled lower Chill part 12, a remelting block 16 is formed and so deducted from the mold 10 that the meniscus one liquid sump 18 in that lower water-cooled Mold part 12 is located. Above is a liquid To recognize slag bath 20, in which an edible Electrode 22 is immersed.

In the area of the slag bath 30 there is either total annular or one of several parts or Sections existing - not directly water-cooled - current-conducting element 24, which - as shown here - of also not water-cooled and not current-conducting outer elements 26 relative to the lower one Chill part 12 and any existing upper water-cooled mold part 14 electrically isolated can be.

The inflows of the mold parts 12, 14 for the cooling water are designated 28 for the sake of clarity Drains with 30.

In a simplified embodiment, is for a Range of possible uses of the upper water-cooled Mold part 14 and / or the non-water-cooled, non-current-conducting elements 26 can be dispensed with.

Basically, the mold 10 described above is also suitable for continuous casting, as shown in FIG. 2. Again, the meniscus of the liquid Bottom 18 of the strand 32 withdrawn from the mold 10 covered by the liquid slag bath 20, which in the Area of the not directly cooled current-conducting element 24 and the - also not directly cooled - not current-conducting elements 26 is held. That all in one liquid widening upward intermediate vessel 34 Metal 36 arrives in the flow direction x via an immersion tube 38 as a pouring jet 40 directly into the liquid sump 18.

There is now one for heating the slag bath 20 Range of options, the main of which is the 3, 4 can be seen.

Fig. 3 offers the schematic structure of an ESCU system Sliding mold using the one shown in Fig. 1 Mold 10 on. The installation of a current-carrying element 24 in the area of the slag bath 20 enables a number of Variants for connecting the system to a power source 42 for alternating or direct current through corresponding Switching switches 44, 46, 48, 50 can be achieved can.

A current flow like that of conventional electroslag remelting is common arises when the switches 44 - in line 45 between current source 42 and electrode 22 - and switch 48 - in line 49 between current source 42 and a base plate 52 - are closed when open Switch 46; the latter is the current-carrying element 24 assigned.

In contrast, with switches 44 and 48 closed Switch 46 in line 47 closed as well as the Switch 50 integrated in line 47 to a switching point 54 placed, the total melt flow over the Electrode 22 passed into the slag bath 20. For the Return are the current-carrying element 24 in the Chill mold 10 and the base plate 52 are available which the block 16 sits on. The respective partial flows adjust themselves according to the resistances. At this Operating mode can not be on the installation of the outer current-conducting elements 26 in the mold 10 become.

If the switch 48 is now opened, the entire Current over the current-conducting built into the mold 10 Element 24 and switches 46 and 50 via switching point 54 returned to the power source 38. Switching point 48 is with Line 49 connected.

Another option is when the switches are closed 44, 46 and 48 switch 50 to a switching point 56 lay, which is connected to line 45. In this case the power supply to the slag bath 20 takes place both via the Electrode 22 as well as that built into the mold 10 current-conducting element 24 corresponding to the respective Resistors while returning the entire Melt flow to power source 42 via block 16 and Base plate 52 happens. This operating mode requires mandatory the installation of not water-cooled, not current-conducting elements 26.

If the switch 44 is now opened, then the Slag bath 20 immersed electrode 22 and the current the entire power supply takes place in the mold 10 integrated current-conducting element 24.

While in electro-slag remelting a number of There are switching options when it comes to continuous casting 2 when installing a current-conducting element 24, which against the lower water-cooled mold part 12 due to non-current-conducting, not water-cooled elements 26 is electrically isolated, only one switching option, the Strand 32 is through pouring stream 40 with metal bath 36 in the distributor or intermediate vessel 34 constantly conductive connected. For heating the slag bath 20 here the feed of the melt stream from one is not represented current source via the current-conducting element and the return either through strand 32 or that Metal bath 36 in the distributor or tundish 34.

4 shows an embodiment of the mold 10 according to the invention, in which two current-conducting elements 24 _a and 24 _{b are} insulated from the lower water-cooled mold part 12 and the upper water-cooled mold part 14 by non-current-conducting elements 26 and horizontally from one another by likewise non-current-conducting intermediate elements 58 are. In this case, it becomes possible to connect one current-conducting sub-ring 24 _a to one pole of a current source (not shown here) and the second current-conducting sub-ring 25 _b to the other. The current flows through the slag bath 20 between the two current-conducting parts 24 _a , 24 _b .

Of course, there is also the possibility of three to arrange mutually insulated current-conducting elements and connect each to a pole of a three-phase source, with a rotating movement in the slag bath 20 and a good one Temperature compensation is achieved. At higher currents can thus also a rotational movement of the liquid sump 18 be effected.

Claims (10)

1. Short, water-cooled, open-bottomed chill mould (10) for the manufacture of bars or billets (16), in which a casting level defining a liquid pool (18) is covered by an electroconductive slag of a slag bath (20) which is arranged in a region that determines the position of the slag bath (20) and that is defined by the slag surface, and the bar or billet (16) is shaped in the lower portion of the chill mould (10) and removed therefrom either by lifting the chill mould (10) or by lowering the bar or billet (16) by means of a bottom plate, wherein at least one electroconductive element (24) is provided and the latter is designed so that it can be connected to a current source (42) which on the one hand comes into contact with the slag bath (20) and on the other hand does not extend as far as the level of the liquid metal, characterised in that the electroconductive element (24) is not directly water-cooled and is installed in the chill mould wall (12) composed of water-cooled and non-current-carrying elements (12, 14) in the region that determines the position of the slag bath (20), and in case of operation lies completely below the slag bath surface, wherein the current source (42) is designed so that it can be connected to a consumable electrode (22) and/or the resulting bar (16) and/or a bottom plate (52) supporting it underneath.
2. Chill mould according to claim 1, characterised in that the electroconductive, non-water-cooled element(s) (24) is/are made of the metal W, Mo or Nb.
3. Chill mould according to claim 1 or 2, characterised in that the upper portion of the chill mould (10) which holds the slag bath (20) and contains the electroconductive, non-water-cooled element (24) widens in a funnel shape.
4. Chill mould according to any of claims 1 to 3, characterised in that the electroconductive, non-water-cooled element(s) (24) installed in the chill mould wall (12) is/are electrically completely insulated from the water-cooled portions of the chill mould by elements (26, 58) which do not conduct the electrical current.
5. Chill mould according to any of claims 1 to 4, characterised in that in the chill mould wall (12) consisting of water-cooled elements are installed at least two not directly water-cooled, electroconductive elements (24) which are completely insulated from each other by elements (26, 58) that do not conduct the current and are not directly water-cooled, and each connected to a terminal of the current source (42).
6. Chill mould according to claim 4 or 5, characterised in that the elements (26) that do not conduct the electrical current are insulated horizontally from each other by non-electroconductive intermediate elements (58) (Fig. 5).
7. Apparatus for the continuous casting of metals using a chill mould (10) according to any of the preceding claims, in particular claims 4 to 6, characterised by an immersion tube (38) which conducts the liquid metal out of a distributor (34) into the metal pool (18) covered in the chill mould (10) by the liquid, electroconductive slag of the slag bath (20), wherein for heating the slag electrical current is conducted between the billet (16) and non-water-cooled, electroconductive elements (24) installed in the chill mould wall (12) in the region of the slag bath (20).
8. Method for the electroslag remelting of metals with consumable electrode using a chill mould according to one or more of claims 1 to 6, characterised in that the melt stream supplied to the slag bath over the consumable electrode is conducted away over the non-water-cooled, electroconductive element(s) installed in the chill mould wall.
9. Method for the electroslag remelting of metals into a bar using a chill mould according to any of claims 1 to 6, characterised in that the melt stream is supplied over the non-water-cooled, electroconductive element(s) installed in the chill mould wall and conducted away over the bar and a bottom plate supporting it underneath.
10. Method for the electroslag remelting of metals using a short, water-cooled, open-bottomed chill mould for the manufacture of bars or billets, in which a casting level defining a liquid pool is covered by an electroconductive slag of a slag bath which is arranged in a region that determines the position of the slag bath and that is defined by the slag surface, and the bar or billet is shaped in the lower portion of the chill mould and removed therefrom either by lifting the chill mould or by lowering the bar or billet, wherein electroconductive elements are provided and the latter are designed so that they can be connected to a current source, characterised in that both supply and return of the melt stream are carried out over non-water-cooled, electroconductive elements that are installed in the chill mould wall.

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