EP0290423B1 - Device for continuously manufacturing a thin metal strip - Google Patents

Description

The present invention relates to a device for the continuous production of a thin metal strip according to the preamble of claim 1. By thin metal strip is meant, within the meaning of the present invention, a metal strip whose thickness does not not exceed about 10 mm. To fix the ideas, reference will be made here to the manufacture of a steel strip. It must however be considered that this particular application has no other purpose than to illustrate the object of the present invention, and that the method is in fact applicable to any other metal.

For essentially economic reasons, it is currently sought to produce thin strips directly by casting liquid steel between two cooled supports of appropriate width, which would make it possible to eliminate, at least in part, the hot rolling process.

Various techniques are currently known, in particular casting between two rollers and casting between two strips, the rollers, respectively the strips, moving so as to drive the metal strip formed.

In these techniques, controlling the flow of metal and heat exchange along the width of the metal strip presents serious difficulties which lead to significant transverse variations in the thickness and in the microstructure of this strip. In addition, the edges of the metal strip are irregular and frequently affected by cracks, and they must be rectified by an additional shearing operation.

There is also known a process for continuously manufacturing a thin metal strip by casting molten metal, said strip having a constant width and not being subject to the abovementioned drawbacks; this process, which was the subject for example of US patent No. 2,477,030 of July 26, 1949, Belgian patent No. 546,497 of July 27, 1956 and European patent application No. 85.308.004.2 (publication No. 0 182 531) of 4.11.1985; these rather particular technologies are normally implemented in installations comprising a horizontal casting section.

Document JP-A-60 261654 also discloses a device for manufacturing a strip by helical cutting of a tube cast by centrifugation. Here too, the metal is poured in a horizontal direction and the device comprises a single rotary section, provided with cooling means and secured to a casting container which is also rotary.

The object of the present invention is to provide a particular device for implementing the process for the continuous production of a thin metal strip from a molten metal, into which said metal is poured by centrifugation into a tube having the desired thickness and in that said metal tube is cut along a helical line, in order to form a continuous strip.

According to the present invention, a device for the continuous production of a thin metal strip from a molten metal, which comprises a tubular mold for forming a layer of metal along the wall of the mold, with means cooling in which is applied to said layer of metal a cooling causing the complete solidification of said metal into a solid tube and with an apparatus for cutting said tube along a helical line, is characterized in that said mold is mounted in a vertical position and in what it comprises at least two successive sections in which the metal is forced to flow from top to bottom in a thin blade animated by a movement of gyration along the interior wall of said mold.

In the device of the invention, the molten metal successively passes through a tubular mold in which it is forced to flow from top to bottom in a thin blade animated by a movement of gyration along the interior wall of said mold, and in which there is applied a cooling which causes a partial solidification of said metal, then an element comprising secondary cooling means causing complete solidification of said metal into a solid tube, and finally an apparatus for cutting said tube along an inclined helical line of an angle appropriate to the desired width of the metal strip.

According to a particular characteristic, at least the second of said sections can rotate around its longitudinal axis.

In addition, the first section is advantageously equipped with means for distributing the molten metal on its interior wall as well as means for imparting to said molten metal a movement of gyration along said interior wall.

According to an advantageous embodiment of the invention, said first section has an internal section which increases in the direction of progression of the molten metal through said first section.

According to a particular variant of this modality, the internal section of said first section increases continuously over at least part of the length thereof; in particular, this continuous increase in the internal section can be regular, so as to give this first section a frustoconical shape over the corresponding part of its length.

This continuous increase in the internal section can however follow any law, for example a law which gives said first section a parabolic internal profile.

Also according to the present invention, said first section is made of a material which is a good conductor of heat, in particular copper. Therefore, the molten metal can undergo controlled cooling in this first section, so as to be in a pasty state, that is to say partially solidified, at the outlet of said first section. The vigorous stirring carried out during cooling ensures a sufficiently low viscosity of the pasty mixture.

Still according to the present invention, the means for distributing the molten metal on the inner wall of said first section comprise a nozzle with closed end and having one or more lateral ducts for exit from the molten metal.

Although a single outlet duct can ensure a sufficient flow of molten metal, it has however proved advantageous to provide at least two outlet ducts, uniformly distributed over the periphery of the nozzle in order to ensure such a regular distribution. as possible of the molten metal in said first section.

Optionally, said outlet conduits can be oriented so as to give the molten metal which leaves therefrom a movement having a tangential component relative to the interior wall of said first section. It is thus possible to initiate the turning movement of the molten metal in said first section.

This tangential component can itself be inclined relative to a horizontal plane, in order to limit the dynamic effects of the impact of the molten metal against the interior wall of said first section.

Finally, the means for imparting to the molten metal a movement of gyration along the wall of said first section can be constituted by any mechanical drive device known per se.

The secondary cooling means are preferably fixed and produce a sheet of water which flows at high speed along the metal tube during solidification.

Downstream of said secondary cooling means is arranged a device for cutting said tube along a helical line.

This device comprises drive rollers imparting to the metal tube a combined movement of axial progression and rotation, as well as at least one cutting tool oriented so as to carry out the cutting along the desired helical line.

Other features and advantages of the present invention will appear on reading the detailed description given below by way of example and in which reference is made to the appended figures.

Figure I schematically shows a longitudinal section through a device according to the invention for the manufacture of a thin metal strip from molten steel. The device of the invention is installed under a container, not shown, such as a ladle, equipped with a pouring nozzle 1. This device essentially consists of a mold comprising a first section H1 and a second section H2, a cooling system H3 and a cutting device 9, 10.

The first section H1 consists of a tubular element 3 provided with a distributor plate 2 which ensures the formation of a film of molten steel and its flow on the interior surface of this tubular element 3; it also includes an inductor intended to impart to this steel film a rotational movement which ensures its good contact with the wall as well as its uniform distribution along this wall. In the illustrated variant, the inductor 4 is arranged around the tubular element 3; it goes without saying that this inductor 4 could, without departing from the scope of the invention, be arranged inside the tubular element 3 or even partly outside and partly inside said element.

The second section H2 of the mold consists of an ingot mold 6 made of copper, cooled with water and driven in a rotational movement around its longitudinal axis. This ingot mold is supported by a device 7 allowing its rotation.

The cooling system H3 comprises means for forming a sheet of homogeneous water flowing at high speed along the cast steel tube.

Finally, the cutting device comprises rollers 9 imparting to the cast steel tube a spiral movement which ensures both the rotation and the axial progression of the steel tube. These rollers 9 are followed by a cutting tool, for example a slitting disc 10, which operates the cutting of the steel tube along the desired helical line.

This cutting device can also be associated with a pipe 13 for injecting a neutral gas such as argon, inside the cast steel tube.

This device works as follows.

The liquid steel flowing from the nozzle 1 is deflected by the distributor plate 2 so as to form a steel film on the inner wall of the refractory tubular element 3. The inductor 4 prints this steel film a gyratory movement at a predetermined speed. The steel film enters the ingot mold 6 which rotates about its longitudinal axis and which thus maintains the gyratory movement of the steel film. A lubricant is added to the ingot mold at 5. The cooling applied by the ingot mold 6 causes the steel film to solidify, which then leaves the ingot mold in the form of a tube in the pasty state. This tube is cooled vigorously, in the device 8, by a sheet of water which flows at high speed along its outer surface. The argon blown through the pipe 13 also contributes to the cooling of the interior surface of this tube. At the outlet of the device 8, the solidified steel tube 11 is gripped by rollers 9 which impart to it a movement of rotation and axial progression, then the tube is cut by a disc 10 into a continuous strip 12 of width B.

The width B of the strip 12 can be modified by simply varying the angle α of inclination of the cutting propeller, that is to say the orientation of the disc 10 and the rollers 9, as well as the speed tube rotation 11.

For example, a steel having an initial overheating of 25 ° C. was poured continuously, at a rate of 20 t / h, into a tube with an outside diameter D = 150 mm and a thickness E = 3 mm. The extraction speed of the tube was 0.5 m / s.

According to the value of the angle α and of the speed N of rotation of the tube 11, bands of different width B were produced, according to the table below:

The strips obtained had a very fine solidification structure and homogeneous properties throughout their section. Their width was constant, and their edges were regular and without defects.

The method of the invention offers great flexibility of conduct, because of the ease with which it is possible to modify the width and the thickness of the metal strips produced. In addition, the strips produced do not have any profile and flatness defects, which are common and difficult to avoid in the other processes.

Figure II illustrates the particular embodiment of the device of the invention, in which the first section of the mold has a frustoconical shape.

This figure shows a nozzle 1, fitted to a casting container, not shown, the end of which is introduced into a first section H1 of the casting mold. This first section H1 consists of an element frustoconical 3 in copper, the section of which increases towards the second section H2. The frustoconical element 3 is equipped with means, known per se and not shown, on the one hand to rotate it around its longitudinal axis and on the other hand to ensure its cooling.

The nozzle 1 has a closed end, and two lateral outlet conduits 14, inclined downwards in the direction of the internal wall of the frustoconical element 3.

The diameter of the outlet section of the frustoconical element 3 is slightly less than the diameter of the inlet section of the second section H2 of the casting mold.

Furthermore, the second section H2 of the casting mold and the cooling system H3 conform to those of the device shown in Figure I and described above.

This modality of the device of the invention operates as follows.
The molten metal, in particular steel, coming from the casting container, not shown, escapes from the nozzle 1 by the lateral conduits 14. It comes into contact with the inner wall of the frustoconical element 3 and, as a result from the rotation of the latter, it forms a uniform metal film 15 on this interior wall.

The inclination of the rotating inner wall forces the metal to progress downward, while the cooling means, not shown, cause the appearance of a solidified fraction which gives the metal a pasty state.

The pasty metal then enters the second section H2 of the mold, then in the cooling system H3, as described in the document cited in the introduction.

As an example of implementation of this device, we used a frustoconical section H1 having a length of 0.35 m, an outlet section of 0.15 m in diameter and an opening angle of 30 °. A steel having an initial overheating of 25 ° C. was poured, with a flow rate of 20 t / h; the frusto-conical element rotated at a speed of 1100 rpm. Under these conditions, the speed of the steel film at the outlet of the frustoconical element was 10 m / s and the solid fraction in the steel reached 30% there.

It goes without saying that the invention is not limited to the embodiment which has just been described and illustrated. Various modifications can be made to it, in particular in the internal profile of the first section of the casting mold, without leaving the framework defined by the claims which follow.

Claims (10)

1. Device for the continuous manufacture of a thin metal strip from a molten metal, which comprises a tubular mould for forming a layer of metal along the wall of the mould, with cooling means in which a cooling causing the complete solidification of the said metal into a solid tube is applied to the said layer of metal and with an apparatus for cutting the said tube along a helical line, characterised in that the said mould is mounted in a vertical position and in that it comprises at least two successive sections (H1; H2; H3) in which the metal is forced to flow downwards in a thin sheet (15)driven into a gyration movement along the inner wall of the said mould.

2. Device according to Claim 1, characterised in that the first of the said sections comprises means (2) for distributing the molten metal over the inner wall of the said mould.

3. Device according to Claim 2, characterised in that the said means for distributing the molten metal over the inner wall of the said mould comprise a nozzle with a closed end (14) having one or more lateral outlet channels for the molten metal.

4. Device according to any one of Claims 1 to 3, characterised in that at least the second (H2) of the said sections can rotate about its longitudinal axis.

5. Device according to Claim 4, characterised in that the first of the said sections comprise means (4) for imparting to the molten metal a gyration movement along its inner wall.

6. Device according to any one of Claims 1 to 5, characterised in that at least one of the said sections of the said mould is provided with cooling means (6) for causing a partial solidification of the said metal.

7. Device according to any one of Claims 1 to 6, characterised in that the first of the said sections has an internal cross-section which increases in the direction of the progression of the metal through the said first section.

8. Device according to Claim 7, characterised in that the said internal cross-section increases according to a law which gives the said first section a parabolic inner profile over the corresponding part of the length of the latter.

9. Device according to any one of Claims 1 to 8, characterised in that the said cutting apparatus comprises rollers (9) for driving the said metal tube in terms of rotation and in terms of axial progression, as well as at least one cutting tool (10) oriented so as to carry out the said cutting along the desired helical line.

10. Device according to any one of Claims 1 to 9, characterised in that it comprises means (13) for introducing an inert gas inside the said solidified metal tube.

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