EP1694455B1 - Magnetic brake for continuous casting moulds - Google Patents

Abstract

The invention relates to a continuous casting mold, in particular a thin slab mold in which the flow of a liquid metal in the mold is influenced by a magnetic field generated by permanent magnets, wherein the permanent magnets have, over the width and/or height thereof, different magnetic strengths or are spaced from each other by different distances for a different field strength. To provide for variation of the magnetic field strength, the permanent magnets are differently adjusted in groups for changing a field strength distribution.

Description

The invention relates to a continuous casting mold, in particular thin-slab mold, are applied in soft permanent magnets for influencing the flow of the liquid metal in the mold by a magnetic field generated by the mold, wherein the permanent magnets above the width and / or height different magnet strengths or different distances to each other have a different field strength and can be moved in different groups to the mold for a different field strength distribution, wherein the permanent magnets are arranged in the water box of the continuous casting mold and can be adjusted for direct contact with the mold plate.

The use of magnetic means to decelerate and even out liquid metal streams is a known technique and has been described in several technical documents. The parts of the plant listed in the documents all have large masses which make it difficult to oscillate the casting mold required for operation. In addition, the equipment is very expensive.

The document EP 0 880 417 B1 describes a magnetic brake for the casting of metal in a mold, consisting of a magnetic core and from a supplied with electrical DC or low-frequency alternating current coil. Further, a magnetic return is provided to close the magnetic circuit.

Advances in development in the field of permanent magnets (hard ferrites, rare earth magnets) have in the meantime opened up a new use of possible field strengths of permanent magnets, which make permanent magnets suitable for use as an alternative to the above electromagnets.

It has therefore already been proposed to use the equipment previously used for the electromechanical brake (EMBr) for generating the magnetic field (field coil, electrical control, outer yoke for conducting the magnetic Flow, etc.) by permanent magnets, which are used directly on the mold.

The document EP 0 568 579 describes a method for controlling the flow of molten metal into the non-solidified metal portions of a casting mold, supplying at least one molten metal primary stream thereto and forming a casting in the mold, thereby producing at least one static magnetic field of poles adjacent to the mold are arranged and consist of permanent magnets, wherein the magnetic field serves to brake and split the primary flow of molten metal flowing into the mold and to control secondary currents, wherein the magnetic field is arranged substantially over the entire Width of the strand formed in the mold acts. The magnetic field strength is to vary in the plane which extends perpendicular to the casting direction and at the level at which the magnetic field strength reaches its maximum value, within an interval of 60 to 100% of this maximum value, while the field strength at a level with the highest surface / meniscus of the molten metal has a maximum value of 500 gauss. The magnetic field is controlled and distributed by providing the magnetic poles movable and / or with adjustable core elements.

The document EP 0 040 383 (B1 ) describes a method for stirring the non-solidified areas in a cast strand, wherein the strand is formed in a mold and a pouring stream flows through a pouring tube or directly into the mold. Where the pouring stream penetrates into the melt already present in the mold, at least one static magnetic field acting in the melt is produced, which brakes the pouring stream and splits it in such a way that its momentum is weakened or consumed. A device provided for this purpose can consist of one or more permanent magnets.

The document JP 08155610 has a mold of rectangular design, at the four corners of each permanent magnets for generating magnetic fields south and north are arranged.

The document EP 0 568 579 A discloses a continuous casting mold, in which permanent magnets are attached to influence the flow of the liquid metal on the mold, wherein the magnets have different magnetic field strengths, because they are adjustable via einschlebbare magnetic and non-magnetic core elements.

Permanent magnets have the same magnetic induction field strength a much shorter design and thus drastically reduced masses. There is no need for additional means to conduct the magnetic flux in the form of an outer yoke. If necessary, it is sufficient to use the existing within the mold ferromagnetic materials to close the magnetic flux circuit.

However, the use of permanent magnets requires other approaches. Although permanent magnets are listed as possible static magnetic field sources in the prior art, only equipment is described for the case of magnetic field generation via current coils with DC or AC, but not permanent magnets.

Since permanent magnets have no switch for switching on and off, this requires special safety measures for installation and maintenance of the equipment. Unlike alternating current operation, however, special processes and equipment for starting up a continuous casting machine are also required.

wobei B₀ die Induktionsfeldstärke eines der Permanentmagneten ist, z der Abstand von einem der Magnete aus gemessen, d der Abstand zwischen den Magneten und h die wirksame Höhe des Magneten ist. Die wirksame Höhe h wird durch Messung bestimmt. Zudem ist π die Zahl Pi (= 3,14...) und cosh ist der Kosinus Hyperbolikus (siehe Abbildung 1).In the case of the magnetic brake, permanent magnets for generating the magnetic field are present on both sides of the casting mold in this case. The induction field strength B in this arrangement follows in their distance in the space between the permanent magnets of the formula: $$\mathrm{B}\left(\mathrm{z}\right)\mathrm{=}\mathrm{2}\mathrm{\cdot }{\mathrm{B}}_{\mathrm{0}}\mathrm{-}\cosh \frac{\mathrm{\pi }\mathrm{\cdot }\left[\mathrm{z}\mathrm{-}\frac{\mathrm{d}}{\mathrm{2}}\right]}{\mathrm{H}}$$

where B _{0 is} the field strength of one of the permanent magnets, z is the distance from one of the magnets, d is the distance between the magnets, and h is the effective height of the magnet. The effective height h is determined by measurement. In addition, π is the number Pi (= 3.14 ...) and cosh is the cosine hyperbolic (see Figure 1).

The object of the invention is to provide means for varying the magnetic field strength of permanent magnets on a continuous casting mold.

The object is achieved according to the invention in that the permanent magnets are movable on pivotable adjusting means to the mold for adjusting the field strength.

wobei Φ der magnetische Fluss, B die magnetische Feldstärke, A die Durchtrittsfläche zur Gießkokille und cos der Kosinus des Winkels zwischen dem Vektor der magnetischen Feldstärke und dem Flächennormalenvektor der Durchtrütsfläche ist Die Veränderung des magnetischen Flusses erfolgt über die Feldschwächung B gemäß der Formel B(z) und dem Winkel. Im Falle der mechanischen Verschiebung als Änderung des Abstandes erfolgt die Änderung von Φ nur über die Feldschwächung B gemäß der o. g. Formel über B(z).This happens, for example, by changing the distance of the magnets from each other, by rotation of the carrier of the permanent magnets of the casting mold away. There are other possibilities by means of rotating spindles. In the case of rotation of the magnet carrier away from the casting mold, the field weakening follows the following formula: $$\mathrm{\Phi }\mathrm{=}\overrightarrow{\left|\mathrm{B}\right|}\mathrm{\cdot }\overrightarrow{\left|\mathrm{A}\right|}\mathrm{\cdot }\cos \left(\mathrm{<}\left(\overrightarrow{\mathrm{B}},,\overrightarrow{\mathrm{A}}\right)\right)$$

where Φ is the magnetic flux, B the magnetic field strength, A the passage area to the casting mold and cos the cosine of the angle between the vector of the magnetic field strength and the area normal vector of the Durchtrütsfläche is the change of the magnetic flux via the Field weakening B according to the formula B (z) and the angle. In the case of the mechanical shift as a change of the distance, the change of Φ is made only via the field weakening B according to the above formula over B (z).

The rotation facilitates the separation of the magnets from the passage surface, because according to the regulations for mounting these permanent magnets it is necessary to set them on one edge and then place them on the support with a constantly decreasing angle (see Figure 3). The magnets are not placed directly on the carrier of ferromagnetic material, but for ease of detachment for rotation or mounting a layer of non-ferromagnetic material is placed between them. This can be austenitic steel, but it is also sufficient for a 1 mm thick plastic plate. The uneven distances of the magnets to the passage surface associated with the rotation are magnetically balanced by a passage body through the water box of the casting mold made of ferromagnetic material.

There are 2 types of casting mold, the mold with recess for an externally supplied magnetic brake and the design with the magnetic brake integrated in the water box. For both applications the following devices are required:

Casting mold with window for externally supplied magnetic brake:

The magnetic field generated by the permanent magnets must remain adjustable in its field strength. For this purpose, the permanent magnets are mounted on the teeth of a rake, which engages in the support ribs of the water boxes of the casting mold. A device makes it possible to adjust the distance of the teeth to the mold by displacement. This makes it possible to vary the magnetic field in its strength. The device can be moved by mechanical spindle or by hydraulic cylinder.

Casting mold with integrated magnetic brake:

The previous electrical device for generating the magnetic field is removed and on the then exposed ferromagnetic block (passage window) in the water box, a device for holding the permanent magnets is mounted. This device can be moved by rotation and thus the magnetic field strength can be varied. The device can be moved by a mechanical spindle or by hydraulic cylinders. In addition, it is possible to make this device rotatable about an axis at the bottom and thus to provide a variable distance between the permanent magnet and ferromagnetic block. In addition, the magnetic field strength can also be adjusted.

Permanent magnets are so strong that they can not be produced over a large area. Such a magnet would be exploded by its own field forces, i. to be torn apart. It is therefore necessary to produce large-area magnets for the width of a continuous casting mold of many individual magnets which are glued on a large-area carrier made of ferromagnetic material to the magnetic flux densities of the many individual magnets to a large magnetic flux, which then the metallurgical effects in the mold has to unite. This is significant in that, because you can set by the same orientation of the magnetic poles, small magnets not arbitrarily close together, finally, the same name poles of the magnets repel. One is thereby forced to make the magnetic carrier multi-layered, since in the second layer by permanent magnets the still open interstices of the first layer must cover.

Furthermore, with a ruler or rake (comb-shaped brake), the magnets must not only sit on the teeth of the Rulers, but also on the back of the magnetic carrier (Rulers) made of ferromagnetic material and again in several layers, since otherwise not the required magnetic flux density in the metallurgical part of the mold achieved.

Claims (2)

1. Continuous casting mould, particularly thin slab mould, in which permanent magnets for influencing of the flow of the liquid metal in the mould by way of a magnetic field generated at the mould are mounted, wherein the permanent magnets have magnetic strengths which are different over the width and/or height or different spacings relative to one another for a different field strength, and are movable in groups differently at the mould for a different field strength distribution, wherein the permanent magnets are arranged in the water tank of the continuous casting mould and are adjustable for direct contact with the mould plate, characterised in that the permanent magnets are movable on pivotable setting means at the mould for adaptation of the field strength.
2. Continuous casting mould according to claim 1, characterised in that the setting means for the permanent magnets are constructed as rotary devices or as rotary spindles.

Images