EP0850116B1 - Electromagnetic device for use with a continuous-casting mould - Google Patents

Abstract

PCT No. PCT/DE96/01554 Sec. 371 Date Jun. 1, 1998 Sec. 102(e) Date Jun. 1, 1998 PCT Filed Aug. 13, 1996 PCT Pub. No. WO97/07911 PCT Pub. Date Mar. 6, 1997A stationary continuous casting mold, especially for casting steel, with an electromagnetic device having a plurality of stirrer elements which are arranged in pairs on the outer wall of the continuous casting mold at a distance from one another and are connected to an electric a.c. voltage. The stirrer elements include at least two pairs and the stirrer elements of each pair are arranged opposite one another and so as to be rotated at an angle relative to one another in an X-shaped configuration in a plane parallel to the casting direction. All pairs are arranged at substantially the same height.

Description

The invention relates to a stationary continuous casting mold, in particular for casting steel, with an electromagnetic device comprising a plurality of partial stirrers, which in pairs arranged at a distance from each other on the outer wall of the continuous casting mold and to a electrical alternating voltage with appropriate phase position to generate a rotating electromagnetic force field are connected.

Stationary continuous casting molds are suitable for carrying out the method for casting steel in the immersion tube casting process, in which the immersion tube extending into the continuous casting mold is immersed in the melt. It is known to influence the solidification during the continuous casting of high-melting metals, such as steel, by generating rotating electromagnetic fields in the stationary continuous casting mold by stirring. A stirring device for stationary continuous casting molds with two part stirring devices which can be operated independently of one another and which are arranged one behind the other in the casting direction on the outer wall of the continuous casting mold is known, for example, from DE-OS 38 19 492. The electromagnetic rotating fields are generated in the mold. In particular, this stirring device is intended to achieve a uniform, finer microstructure of the cast strand, a uniform distribution of non-metallic inclusions, better heat dissipation, etc.
From JP-A-60 040654 a stirrer arrangement is known, in which two opposing stirrers are rotated through an angle.
To generate the magnetic flux, the stirring device ("Herrmann, E., Manual of Continuous Casting, Aluminum-Verlag GmbH, Düsseldorf 1958, pages 417-429") can be formed, for example, from a plurality of electromagnets made of horseshoe-shaped transformer sheets, which are arranged vertically or horizontally on the wall of the Continuous casting mold are arranged. The induction flow goes from one leg of the horseshoe to the other through the molten metal. The molten metal passed through the mold is subjected to a continuous mechanical circulation flow due to the magnetic fluxes generated. The stirring device is operated such that the electromagnets, the magnetic field of which, for example, propagates in the direction of the vertical axis of the mold, are controlled in such a way that the direction of the maximum magnetic flux rotates about the vertical axis of the mold. This is intended to achieve a good circulation of the metal melt with good efficiency at the same time.

The stirring of the melt with such a stirring device has different Disadvantage. So, despite the stirring, there are regular swellings on the Surface of the melt, with the result that casting powder and slag particles on Immersion tube can be drawn into the strand shell area. Another disadvantage is that, despite the stirring, bridges of solidified metal kept interspersed Form the ceramic inlet pipe and mold wall in the upper area of the continuous casting mold. This type of stirring also still results in a jam of Overheating heat in the inner area of the mold, which leads to the formation of dendrites reinforced, which then mostly undesirably as globulites on the Apply the solidification front of the melt. Although with the known device uniform solidification front can be achieved, ribbons are formed in the melt negative segregation.

It is the object of the present invention to provide an electromagnetic device for specify a stationary continuous casting mold, in which the melt in the Continuous casting mold is stirred so that swellings on the surface of the melt, the formation of bridges of solidified metal between the ceramic inlet pipe and Mold wall in the upper area of the continuous casting mold and a jam of Overheating heat in the inner area of the mold is avoided.

The invention solves the problem by the in the characterizing part of Claim 1 specified features. Due to the characteristic features of subclaims 2 to 7 is the inventive device of the stationary Continuous casting mold can be designed in an advantageous manner.

The invention provides that the electromagnetic device at least two Includes pairs of partial stirrers and the partial stirrers of each pair are arranged opposite one another, namely at an angle x-shaped rotated against each other, the rotation in a plane parallel to Pouring direction takes place. All pairs are essentially the same height arranged.

This ensures that the originally vertical flow velocities the molten metal in the area of the inlet pipe vice versa, or at least greatly reduced, whereby one Temperature stratification with strong vertical flow reduction is counteracted that the partial stirring devices each have a horizontal Stir the molten metal. The electromagnetic Facilities each lead to an upward spiral Rotational movement of the molten metal in the middle of the mold, what causes superheated steel to move up from the bottom of the mold, which in turn solidifies the melt between the ceramic inlet pipe and Mold wall (so-called bridging) prevented. By the invention electromagnetic device there is a horizontal and vertical Rotation of the melt. These rotational movements generated in the melt effectively prevent the formation of white tapes (tapes with negative Segregation).

The electromagnetic device continues to improve the Degree of purity of the cast strand, since the reduction is more vertical Currents in the melt floating impurities into the Slag zone favors.

Advantageously, in the case of a stationary continuous casting mold with a rectangular, so-called beam-blank cross-section proposed to provide two pairs of partial stirrers, the partial stirrers of the pairs facing each other on the broad sides are arranged. Both pairs generate independently in the between them, a mold area lying in a helical upward direction Rotational movement with opposite direction of rotation, whereby the currents of the Steel melt in the stationary continuous casting mold in the area of the dip tube influence each other so that also around the dip tube a helical upward rotational movement of the melt occurs.

The control of the partial stirrer with a stationary continuous casting mold rectangular cross section with two pairs of partial stirrers is simplified if the partial stirrers of each pair are electrically connected in series.

The electromagnetic according to the invention has a particularly good effect Set up when the amount of the angle by which the partial stirrer is opposite the Casting direction are arranged rotated, is in the range between and 30 ° and 60 °.

In a favorable embodiment, the partial stirrers are in the form of coils with one ferromagnetic U-shaped core. This makes a strong one Generate a magnetic field in the stationary continuous casting mold with little effort.

An easy to use adaptation to different casting conditions achieved by an intended actuator through which the partial agitator each Pair can be rotated against each other during operation. So it can electromagnetic device can be optimally set with little effort. The Partial stirrers are expediently mounted in rotatable holders for this purpose can be adjusted by an actuator. The control is usually done either controlled by hand or using a specified setting algorithm. As The manipulated variable can be, for example, the frequency of the swells on the surface of the Serve melt, but it can also be the depth of the formed on the dip tube Inlet funnel of the molten metal can be used.

Fig. 1

eine schematische räumliche Darstellung einer stationären Stranggießkokille zum kontinuierlichen Gießen von Metallen mit einer erfindungsgemäßen elektromagnetischen Einrichtung,

Fig. 2

eine Draufsicht auf die in Fig. 1 dargestellte stationäre Stranggießkokille mit dem Anschlußschema der Teilumrührer der elektromagnetischen Einrichtung an eine Wechselspannungsquelle und

Fig. 3

eine schematische räumliche Darstellung einer stationären Stranggießkokille nach Fig. 1 mit den durch die erfindungsgemäße elektromagnetische Einrichtung in der Schmelze induzierten mechanischen Kraftfeldern.

An embodiment of a stationary continuous casting mold for the continuous casting of metals, in particular steel, with an electromagnetic device according to the invention is described below with reference to the schematic drawing. This shows in:

Fig. 1

2 shows a schematic spatial representation of a stationary continuous casting mold for the continuous casting of metals with an electromagnetic device according to the invention,

Fig. 2

a plan view of the stationary continuous casting mold shown in Fig. 1 with the connection diagram of the partial stirrer of the electromagnetic device to an AC voltage source and

Fig. 3

is a schematic spatial representation of a stationary continuous casting mold according to FIG. 1 with the mechanical force fields induced in the melt by the electromagnetic device according to the invention.

As shown in Fig. 1, a stationary continuous casting mold 10 for Continuous casting of metals on a continuous casting mold by four Mold walls 11, 12 made of metal, namely two broad sides 12 and two narrow sides 11, is formed. The continuous casting mold 10 is open at the top and bottom; the lower one Cross-sectional area through which the metal strand leaves the mold is normal less than or equal to the upper cross-sectional area of the continuous casting mold 10. The Mold walls 11, 12 enclose the mold cavity 13 into which a dip tube 14 protrudes, which has one or more outflow openings at the free end. In the mold cavity 13 is molten metal that continuously over the dip tube 14 can be fed and through the lower mold outlet opening is continuously discharged. The molten metal solidifies on contact with the cooled mold walls 11, 12 in the continuous casting mold 10, so that a shell is formed. The thickness of this shell gradually increases as the metal Continuous casting mold 10 happens until it as a strand from the lower part of the Continuous casting mold 10 emerges. The shell must exit 10 from the continuous casting mold have a sufficient thickness because the strand was not at that time is completely solidified to hold back the molten core that eventually solidifies and forms a solid strand.

The pouring level in the mold cavity 13 is above the Outflow opening of the dip tube 14 and is covered with mold powder. The mold powder serves as a lubricant and reduces the friction between the outer surface of the Melt and the mold walls 11, 12.

The continuous casting mold 10 is provided with an electromagnetic device 20, from the partial stirrers 21-24 arranged on the mold walls 11, 12 is formed. The partial stirrers 21-24 are in pairs 21, 24 and 22, 23 interconnected. In the exemplary embodiment, there are two pairs 21, 24 and 22, 23 provided that are arranged to the right and left of the pouring direction A, the partial stirrer a pair 21, 24 and 22, 23 opposite each other on the broad sides 12 of the continuous casting mold 10. As can be seen in FIG. 1, the partial stirrers 21, 24 and 22, 23 of a pair against each other in a plane parallel to the casting direction twisted by an x-shape. The angle through which the partial stirrers of a pair are arranged rotated relative to each other, is preferably in the range between and 30 ° and 60 °. In the exemplary embodiment, the partial stirrers are a pair rotated by 45 ° against each other, i.e. the rotation of the partial stirrer Pair is (2 times 45 ° equal) 90 °. The exact angle is determined in a known manner according to the phase position of the AC voltage, which is used to excite the partial stirrer 21 - 24 cares. As in the exemplary embodiment, the partial stirrers 21-24 are turned on AC voltages connected in the order of the partial stirrer 21 - 24 differ by a phase difference of 45 °, so for the Angle by which the partial stirrer of a pair rotates against each other to be arranged, a value of 45 °.

Each partial stirrer 21-24 has a ferromagnetic U-shaped design Core. In the exemplary embodiment, the core is an iron core that consists of Dynamo sheet is made and carries coils made of copper wires. The cross section of the Cores are rectangular; the pole shoes lie on the mold walls 11, 12 on. The magnetic fields generated by the partial agitators 21-24 penetrate through the Mold walls 11, 12 into the mold cavity 13 and penetrate the molten metal.

According to the law of induction, there is a voltage in the moving melt induced, which is equal to the derivative of the magnetic flux over time. From of the induced voltage resulting electric currents cause after Biot-Sarvart's law a force effect in the melt, the vectorial Product of induction and current is proportional. That induced by the magnetic field The force field in the melt leads to mechanical currents, which cause stirring of the Cause melt.

Each pair of partial stirrers 21, 24 and 22, 23 is operated independently of one another and connected in phases so that in the mold cavity 13 between the Partial stirrers 21, 24 and 22, 23 each have a resulting rotating magnetic field is generated that a rotating mechanical force field in the melt, as in FIG. 3 shown, which originates in the left mold half near the front broad side 12 and in the right half near the rear broad side 12. The rotating force field is upwards, but towards the opposite one Mold wall directed, i.e. there are force components in both vertical and in the horizontal direction. So it will be in the left and right mold halves opposing force fields induced, one in the left half of the mold in the middle to the left outer wall and in the right half of the mold one from the middle generate rotating flow in the melt to the right wall. Here are in middle part of the mold the vertical components of the force fields upwards directed; however, the horizontal vector components run in opposite directions for two mold halves. The distance between the partial agitator pairs 21, 24 and 22, 23 is so chosen so that the melt performs a stirring movement in the area of the immersion tube, without the melt entering the mold through the dip tube already in Immersion tube is braked. Outside the dip tube is the electromagnetic one Braking effect of the device 20 is quite desirable.

In the central area of the mold, the partial agitator pairs 21, 24 and 22, 23 consequently produces a constant upward flow of hot melt; the melt becomes an upward spiral rotation imposed. This is the natural direction of movement of the melt in the The mold cavity 13 faces in the opposite direction, so that it is inside the mold cavity 13 at least partially to suppress the natural movement of the melt comes and the associated swellings on the surface with the disadvantages the drawing of casting powder and slag particles into the strand shell area be prevented.

The electromagnetic device 20 enables a reversal of the vertical Flow directions in the stationary continuous casting mold with the advantages mentioned with simultaneous horizontal stirring of the melt.

Due to the simultaneous horizontal stirring in the left and right part of the Chill is counteracted by temperature stratification, the overheating heat degraded evenly. Forming dendrites are stirred away, which then accumulate as globulites on the solidification front of the melt. Due to the horizontal and vertical stirring of the melt will make the formation more negative Segregation (so-called white bands) prevented.

FIG. 2 shows a top view of the stationary continuous casting mold shown in FIG. 1. In addition, the connection scheme of the partial agitators 21-24 is the electromagnetic one Device 20 shown. As can be seen in FIG. 2, the pairs are 21, 24 and 22, 23 the electromagnetic device 20 each electrically connected in series. So are the upper terminals of the coils 25, 27 and 26, 28 connected to each other. By the series connection can the partial stirrers of a pair 21, 24 and 22, 23 on one normal AC voltage source.

The same effect is of course also with multi-phase by 120 ° to each other phase-shifted three-phase currents can be achieved if a corresponding asymmetrical spatial arrangement of the partial agitator pairs 21, 24 and 22, 23 is used.

An actuator is used to adapt to different casting conditions (not shown) by which the partial stirrers of each pair 21, 24 and 22, 23 can be rotated against each other during operation, so much the same to optimally set the electromagnetic device 20. The partial agitators 21, 24 and 22, 23 are conveniently mounted in rotatable brackets that the actuator can be adjusted. The control is usually carried out by a microprocessor, either controlled by hand or based on a predetermined one Setting algorithm. The frequency of the Surges on the surface of the melt serve, but it can also be the depth of the suction funnel of the molten metal that forms on the immersion tube become.

Of course, the electromagnetic device 20 may also be of a variety of Partial agitator pairs 21, 24 and 22, 23 can be constructed, each in a subspace the stationary continuous casting mold the corresponding described above generate magnetic rotating fields with a corresponding sense of rotation, what by correct control of the partial agitator pairs and a corresponding one Angular rotation of the partial stirrers of a pair 21, 24 and 22, 23 against each other can be adjusted.

REFERENCE SIGN LIST:

Continuous casting mold

10th

Narrow sides

11

Broadsides

12th

Mold cavity

13

Dip tube

14

electromagnetic device

20th

Partial stirrer

21-24

Do the washing up

25-28

Pouring direction

A

Claims (7)

1. A stationary continuous casting mould, in particular for steel casting, with an electromagnetic device comprising a plurality of sub-stirrers which are arranged in pairs spaced relative to one another on the outer wall of the continuous casting mould and are connected to an electric alternating voltage with appropriate phase position for the generation of a rotating electromagnetic force field,
   characterised in that
   the sub-stirrers (21 - 24) comprise at least two pairs (21, 24 and 22, 23) and the sub-stirrers of each pair (21, 24 and 22, 23) are arranged opposite each other, twisted by an angle relative to each other in a plane parallel to the casting direction so as to form an x-shape, and all the pairs (21, 24 and 22, 23) are arranged at substantially the same height.
2. A continuous casting mould according to claim 1,
   characterised in that,
   in the case of a stationary continuous casting mould with a rectangular cross section, the sub-stirrers of the pairs (21, 24 and 22, 23) are arranged opposite each other on the broad faces (12).
3. A continuous casting mould according to claim 1 or claim 2,
   characterised in that
   the sub-stirrers of each pair (21, 24 and 22, 23) are connected electrically in series.
4. A continuous casting mould according to claim 3,
   characterised in that
   the sub-stirrers (21, 24 and 22, 23) connected electrically in series are each connected to alternating voltages phase-shifted by 90°.
5. A continuous casting mould according to any one of claims 1 to 4,
   characterised in that
   the angle by which the sub-stirrers (21, 24 and 22, 23) are each twisted relative to one another is from 30° to 60°.
6. A continuous casting mould according to any one of claims 1 to 7,
   characterised in that
   the sub-stirrers (21, 24 and 22, 23) take the form of coils (25 - 28) with a ferromagnetic U-shaped core.
7. A continuous casting mould according to any one of claims 1 to 6,
   characterised in that
   an actuator is provided by means of which the sub-stirrers of each pair (22, 24 and 22, 23) may be twisted relative to one another in predeterminable manner during operation.

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