GB2048140A - Continuous casting of metal strip - Google Patents

Abstract

Molten metal is cast continuously into a channel-shaped mould (4) carried by and movable with a generally horizontally disposed support system (5). An electromagnetic inductor or linear motor (8) is suitably positioned, for example above the mould just upstream of a weir box (2), and is operable to generate within the cast molten metal a travelling magnetic field sufficient to fix in space the position of the heel (7) of the cast metal. <IMAGE>

Description

SPECIFICATION Continuous casting of metal This invention relates to the continuous casting of metal strip and particularly but not exclusively to the continuous casting of steel strip.

Various proposals have been made previously for continuously casting metal strip. For example in U.S.A. patent 3703204 there is disclosed the concept of casting molten metal into a horizontal moving trough-shaped mould of so-called ablative material, such as papier mache, which is charred or burned onto the molten metal to form a mould surface during its solidification therein. Also known are strip casting machines employing opposed moving belts between which molten metal is introduced.

In accordance with one aspect of the invention, there is provided apparatus for the continuous casting of metal strip which comprises a movable generally horizontally disposed support system, a channel-shaped mould carried by and movable continuously with the support system past a feed station for continuously casting molten metal into the channel-shaped mould and means operable to promote within molten metal leaving the casting station an electro-magnetic force to oppose movement of molten metal in a direction counter ta the direction of movement of the support system.

In accordance with a further aspect of the invention,there is.provided a method of continuously casting molten metal from a casting station into a channel-shaped mould movable continuously past the casting station, which method includes the step of promoting within molten metal leaving the casting station an eiectro-magnetic force which opposes movement of molten metal in a direction counter to the direction of movement of the mould.

The electro-magnetic force may be promoted within the molten metal by an electro-magnetic inductor, e.g. a linear motor, positioned above or below the support system and immediately preceding or following the casting station. The inductor may be operated to fix in space the position of the heel of the metal cast into the mould, the thickness of the cast strip being controlled by varying the rates at which the molten metal is cast into the mould and/or the velocity of the mould.

The mould is preferably manufactured from a thermally insulating and non-combustible material; additionally, the mould material is preferably non-oxidizable at high temperatures and substantially insoluable in the molten metal.

Such a material may comprise for example a fibrous alumino-silicate paper, alumina-paper, silica-paper or zirconia paper of the type available under the trade names Triton Kaowool, Saffil and Refrasil.

Alternatively, the mould may be produced from a reusable refractory material such as fused silica or high alumina; the refractory material may comprise a multiplicity of abutting refractory tiles provided with upstanding edge dams along their non-abutting sides. The tiles together with the edge dams may be cast or pressed to shape.

Other features of the invention will become apparent from the following description, given herein solely by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a diagrammatic side elevational view in section of one embodiment of continuous casting apparatus in accordance with the invention; and Figure 2 is a transverse cross-sectional view taken on line Il-Il of Figure 1.

As illustrated in Figures 1 and 2, molten steel is poured from a tiltable ladle 1 into a weir box 2 positioned above the strip casting apparatus. The rate at which the molten steel is delivered to the weir box, and consequently to the casting apparatus, is controlled by varying the angle of tilt of the ladle in dependence upon the weight of metal contained in the ladle as measured by load sensors 3 positioned below the ladle.

The casting apparatus comprises a channeishaped mould 4 carried upon a horizontally movable support system 5. The direction of movement of the mould 4 and support system 5 is indicated by arrow 6. The support system 5 may comprise the upper flight of a channel-shaped endless conveyor belt manufactured from, for example, a non-strain, non-quench ageing steel strip. Alternatively, the support system may comprise a multiplicity of wheeled trolleys movable in a generally horizontal plane around a continuous track. Examples of suitable forms of such support systems are described and illustrated in our co-pending patent applications, Nos. (Serial No.1526192) 27704/74, (Serial Nos. 1551755) 25932/76 and(1551754)2593 and (1551754)25931/76.

The mould 4 is produced from a refractory, thermally insulating and non-combustible material. In addition the refractory material is preferably non-oxidizable at high temperatures and substantially insoluable in molten steel.

Sacrificial materials which satisfy these requirements include fibrous alumino-silicate, alumina, silica and zirconia paper of the type available under the trade names Triton Kaowool, Saffil and Refrasil. Materials which can be used repeatedly include fused silica or high alumina refractory tiles formed with upstanding edge dams along their non-abutting sides. The titles together with their edge dams may be cast or pressed into shape.

As molten steel is cast into the mould 4 from the weir box 2, a proportion of it tends to travel within the mould in a direction counter to the direction of mould movement to form a heel 7.

This tendency is increased as the metal casting rate, and/or the thickness of the layer of cast molten metal, is increased. Because of this tendency, it has hitherto been impracticable to cast steel strip in a controlled manner at thicknesses greater than the equilibrium or minimum spreading thickness of the steel. At thicknesses below equilibrium thickness, surface tension forces operate to prevent spreading of the cast steel.

Positioned above the support system 5 immediately preceding the point at which molten steel is cast from the weir box 2 into the mould 4, is an electro-magnetic inductor or linear motor 8 which is operable to generate a travelling magnetic field. When the liquid metal heel 7 flow back within the mould and enters the region of the magnetic field, eddy currents are induced which act to oppose movement of the metal in a direction counter to the direction of travel of the support system thereby to fix in space the position of the heel 7 of the molten steel within the mould.

With the heel 7 held in this manner, strip of thickness greater than equilibrium thickness can be cast simply by increasing the casting rate of the molten steel and/or by changing the velocity of the support system and consequently the mould. In addition the profile of the heel 7 can be controlled to eliminate defects, such as laps, produced in the under surface of the cast strip caused by an erratically shaped heel.

As the mould travels away from the weir box 2, the cast steel solidifies and is separated from the mould at a suitable position downstream of the weir box.

As illustrated, the linear motor 8 is positioned above and immediately following the casting station. By so positioning the motor, the hydrodynamic forces which would otherwise tend to cause some of the liquid metal to flow back within the mould 4 in a direction counter to the direction of mould movement, are offset by electrical forces induced by the magnetic field. The tendency for the liquid movement to form a heel by flowing backwardly from the point of metal delivery is thereby minimised of eliminated.

Claims (12)

1. Apparatus for the continuous casting of metal strip which comprises a movable generally horizontally disposed support system, a channelshaped mould carried by and movable continuously with the support system past a feed station for continuously casting molten metal into the channel-shaped mould and means operable to promote within molten metal leaving the casting station an electro-magnetic force to oppose movement of molten metal in a direction counter to the direction of movement of the support system.

2. Apparatus, as claimed in Claim 1 , wherein the electro-magnetic force is promoted within the molten metal by an electro-magnetic inductor.

3. Apparatus as claimed in Claim 2, wherein the electro-magnetic inductor is positioned above or below the support system and immediately preceding or following the casting station.

4. Apparatus as claimed in Claim 2, wherein the inductor is operated to fix in space the position of the heel of the metal cast into the mould, the thickness of the cast strip being controlled by varying the rates at which the molten metal is cast into the mould and/or the velocity of the mould.

5.. Apparatus as claimed in any one of claims 2 td -4 wherein the inductor is a linear motor.

6. Apparatus as claimed in any preceding claim wherein the mould is manufactured from a thermally insulating and non-combustible material.

7. Apparatus as claimed in Claim 6, wherein the mould material is non-oxidizable at high temperatures and substantially insolubie in the molten metal.

8. Apparatus as claimed in Claim 7, wherein the mould material comprises a fibrous aluminosilicate paper, or alumina-paper or sitica-paper or zirconia paper of the type available under the trade names Triton Kaowool, Saffil and Refrasil.

9. Apparatus, as claimed in Claim 6 or Claim 7, wherein the mould is produced from a re-usable refractory material such as fused silica or high alumina.

10. Apparatus, as claimed in Claim 9, wherein the refractory material comprises a multiplicity of abutting refractory tiles provided with upstanding edge dams alohg their non-abutting sides.

11. A method of continuously casting molten metal from a casting station into a channelshaped mould movable continuously past the casting station, which method includes the step of promoting within molten metal leaving the casting station an electro-magnetic force which opposes movement of molten metal in a direction counter to the direction of movement of the mould.

12. Apparatus for continuous casting metal strip substantially as herein described with reference to the accompanying drawings.

1 3. A method of continuously casting molten metal substantially as herein described with reference to the accompanying drawings.