EP0392952A1 - Method of and installation for casting thin metallic products - Google Patents

Abstract

According to the method in accordance with the invention, for the continuous casting of thin metallic products, the molten metal is cast into an ingot mould whose walls define a casting space 7 of elongated transverse section and the thickness of the product emerging from the ingot mould is reduced, while the core thereof is still unsolidified, to the thickness desired for the said thin metallic product. According to the invention, the cast metal is caused to solidify on the surface in the ingot mould so that the solidified skin of the product emerging from the ingot mould forms, on each edge, a solidified wall of rounded transverse section containing the still unsolidified metal, and the reduction in thickness is effected so that the said rounded solidified wall progressively folds over on itself. In order to form the said wall of rounded section, the ends 9 of the said section of the casting space are rounded in a convex shape. <IMAGE>

Description

The present invention relates to a process for the continuous casting of thin metallic products, in particular steel, such as thin slabs, according to which the molten metal is poured into a mold of elongated section and the thickness of the product from the mold is reduced. directly at the outlet thereof while the core of said product is not yet solidified.

It also relates to a casting installation, allowing the implementation of this process, comprising a mold with cooled fixed walls and a device located directly downstream of the mold, intended to reduce the thickness of the cast product to bring it to the 'final thickness desired for the thin product, this device comprising two clamping members, for joining or at least bringing the solidified walls of the product from the ingot mold, generally constituted by cylinders acting on said product in the manner of rolling cylinders.

Such methods and installations are already known, aiming to produce thin slabs, that is to say whose width is generally greater than three times the thickness, the latter being less than about 120 mm.

For example, it has already been proposed to pour the liquid metal into an ingot mold, the small faces of which have a small width compared to the width of the large faces. In particular in order to be able to penetrate the pouring nozzle between the large faces, the mold has, at least in its upper part, a central flare, the large faces then having for example a section in the form of a "gendarme hat". To reduce the cast product to a rectangular section, either the enlargement is gradually reduced from the top to the bottom of the mold, where it finds a rectangular section, or the cast product passes immediately downstream of the mold between two cylinders which bring the large faces of the product together to bring them parallel to each other.

It has also been proposed to flow into a mold of substantially constant elongated rectangular section, the nozzle then having a strongly flattened section so as to be able to be inserted between the walls of the mold.

In all cases, the thickness of the product from the mold is reduced immediately downstream of it, while the core is not yet solidified, to bring the cast product to the desired thickness.

However, these methods have a major drawback resulting from the rolling of the edges of the product from the mold. In fact, as indicated above, the rolling is carried out while the core of the product is still liquid. In fact it is not really a rolling, but rather a crushing of the product from the mold to bring closer until contact the solidified skins of the large faces thereof. The central part of the large faces therefore does not undergo significant elongation during this crushing. By cons, due to the solidification of the edges of the product in the mold, these are actually laminated which leads to deformation and elongation of the edges. It follows that the thin slabs obtained by these methods may have defects of the "long edge" type well known to laminators.

In addition, the rolling of the edges requires a force for tightening the thickness reduction cylinders, much greater than the force necessary to bring the solidified skins closer to the central parts of the large faces, which leads to oversizing the device ensuring the "rolling" .

The purpose of the present invention is to solve the problems set out above, and to allow obtaining thin products, such as thin slabs, of good quality, while limiting the dimensions and therefore the size of the installation. Manufacturing.

With these objectives in view, the present invention relates to a process for the continuous casting of thin metallic products, such as thin slabs, according to which the molten metal is poured into an ingot mold of elongated section and the thickness of the product is reduced. from the mold, while the core thereof is not yet solidified, up to the desired thickness of said thin metallic product.

According to the invention, this method is characterized in that the cast metal is led to solidify superficially in the mold so that the skin solidified from the edges of the product from the mold forms, on each edge, a solidified section wall rounded transverse containing the metal not yet solidified, and the thickness is reduced so that said rounded solidified wall gradually folds back on itself.

According to a particular arrangement of the invention, this process is characterized in that the thickness reduction is continued until the longitudinal edges of said rounded solidified wall are practically in contact with one another.

The invention also relates to a continuous casting installation for thin metal products, comprising a mold whose walls define a casting space of elongated cross section, and a thickness reduction device placed downstream of the mold to reduce the thickness of the product from the mold.

According to the invention, this installation is characterized in that the ends of said section of the pouring space are rounded convex.

According to a particular arrangement of the invention, the sides of the central part of said section are convex, and preferably connect to said ends so that the section of the mold is of elliptical shape.

According to another arrangement, the sides of the central part of the section are straight, at least in the lower part of the mold.

According to yet another arrangement, the perimeter of said section is substantially constant over the entire height of the mold, the section passing progressively, from the top to the bottom of the mold, from a substantially circular shape to a very elongated elliptical shape, or to a form having two elongated parallel rectilinear sides, connected at their ends by semicircles.

As will no doubt already be understood, the principle of the invention is to form in the mold a product of elongated cross section, not solidified to the core, the skins solidified from the edges being able to be, during the reduction in thickness later, folded back on themselves, instead of being crushed by rolling.

The invention will be better understood, and other characteristics and advantages will appear on reading the description which will be given by way of example of an installation and a method for manufacturing thin steel slabs.

• - la figure 1 est une représentation schématique en coupe d'une installation de coulée conforme à l'invention ;
• - la figure 2 est une représentation en perspective de l'espace de coulée de la lingotière ;
• - la figure 3 représente une variante de la forme de cet espace de coulée ;
• - la figure 4 représente la section du bord du produit à la sortie de la lingotière dans une installation selon l'Art Antérieur ;
• - la figure 5 représente l'évolution de la section du bord du produit lors de la réduction d'épaisseur.

Reference is made to the appended drawings in which:

• - Figure 1 is a schematic sectional representation of a casting installation according to the invention;
• - Figure 2 is a perspective representation of the casting space of the mold;
• - Figure 3 shows a variant of the shape of this casting space;
• - Figure 4 shows the section of the edge of the product at the outlet of the mold in an installation according to the Prior Art;
• - Figure 5 shows the evolution of the section of the edge of the product during the thickness reduction.

In FIG. 1 is shown schematically in longitudinal section an installation for casting thin slabs comprising an ingot mold 1 whose cooled walls 2 delimit a casting space 7, and two thickness reduction cylinders 4 arranged downstream of the ingot mold and spaced apart by a distance equal to the desired thickness of the slab 5, less than the width of the outlet section of the mold.

During casting, liquid metal 3 is supplied with the casting space 7, in a conventional manner. The metal solidifies on contact with the walls of the mold to form solidified skins 6. The different casting parameters are adjusted so that at the outlet level a of the mold, the core of the product is still liquid.

The product extracted from the mold 1 then passes between the cylinders 4 where it undergoes a reduction in thickness which has the effect of bringing the solidified skins 6 almost until contact, giving the product the desired thickness.

In accordance with an arrangement of the invention, the casting space has a shape such as that shown in FIG. 2. At its upper part, the inlet section 10 of the casting space 7 at level 0 of the mold. has an enlarged elliptical shape which allows in particular the easy introduction of a liquid metal supply nozzle of the conventional type. As a variant, this section can even be practically circular.

The outlet section 11, at level a of the mold, is also elliptical but of very elongated shape. Between levels higher 0 and lower a , the section evolves regularly while keeping a constant perimeter.

According to another variant, represented in FIG. 3, the space of casting 7 ′ has an outlet section 11 ′ which has two parallel rectilinear sides 12 connected at their ends by semicircles 13.

The basic idea of the invention is to shape the mold so that the edges of the product extracted therefrom are rounded. This configuration can also be obtained by means of an ingot mold whose perimeter of the section is not constant over its height. It is however preferable to keep a constant perimeter, at least in the lower part of the mold, so that the solidified skin does not undergo elongation or compression, in the plane transverse to the direction of casting, which could lead to surface cracks or wrinkles.

As already pointed out, the aim of the present invention is to eliminate or at least limit the rolling of the edges of the product extracted from the ingot mold during the reduction in thickness produced by the cylinders 4.

To better understand how the particular shape of the ingot mold achieves this result, reference is made to FIGS. 4 and 5.

FIG. 4 represents the section of an edge of a product poured into an ingot mold according to the prior art, the small walls of which are flat and perpendicular to the edges of the large walls. On leaving such an ingot mold, the product has on its edges a skin 20 solidified in contact with the small walls of the ingot mold, the outer surface of which is perpendicular to those of the skins 21 formed in contact with the large walls. When it is desired to reduce the thickness of this product, the skins 21 can easily be brought close to each other since the core 22 of the product is not yet solidified. On the other hand, the end skin 20 is compressed, according to the arrows 23, between the thickness reduction cylinders. This solidified skin is therefore really laminated. It follows an elongation thereof, while the skins 21 which are simply brought closer to each other, retain their size, which creates in the final product the defect of "long edge" already mentioned.

Figure 5 shows the evolution of the section of an edge of the product obtained at the outlet of the mold according to the invention.

FIG. 5 a represents the section at the outlet level a of the ingot mold, a section which is preserved until the surface of the product comes into contact with the cylinders 4. The solidified skin forms a curved wall 30 which contains the still liquid metal 31.

When the product comes into contact with the cylinders 4 (level b in FIG. 1) these begin by bringing the skins 6 formed on the walls of the ingot mold into each other in the central zone 8 where the radius of curvature of the ellipsoidal section of the mold is the largest. Against by the skin 30, formed in the end zones 9, of smaller radius of curvature, is practically not deformed (FIG. 5 b ), the longitudinal edges 32 of the skin 30 retaining their relative spacing.

At level c (FIG. 5 c ) the reduction in thickness is greater. The two parts 30 ′, 30˝ of the skin 30, located on either side of the plane P of longitudinal symmetry are folded over one another, the junction line 33 of these two parts 30 ′, 30˝ , being moved laterally outwards.

At level d , close to the level of the axes of the cylinders, the reduction in thickness ends, the edges 32 of the skin 30 are practically in contact with one another, the two parts 30 ′ and 30˝ thereof. these having completely folded over each other.

Thus, thanks to the rounded shape of the edges of the casting space, it is possible to reduce the thickness of the product from the ingot mold practically without rolling the edges. In addition, the effort required to fold the two parts 30 ′, 30˝ of the skins 30 of the edges one on the other, is much less than that which would be necessary to crush the skin 20 of a product with small flat faces .

It will be noted that for this purpose the cooling in the mold is carried out so that the thickness of the skin solidified on the short sides of the product is less than the half thickness of the final product, substantially up to the level of the iron cylinders.

The invention is not limited to the preferred forms of ingot mold which have been described above by way of example. In particular, insofar as the supply of liquid metal to the mold can be carried out by a flattened nozzle, or by other means, such as for example a lateral supply, the mold can have a constant section over its entire height. , such as that of the outlet section 11 ′ shown in FIG. 3.

Claims (7)

1) Process for continuous casting of thin metallic products, such as thin slabs, according to which the molten metal is poured into an ingot mold of elongated section (1) and the thickness of the product from the ingot mold is reduced, while the core thereof is not yet solidified, up to the desired thickness of said thin metal product (5), characterized in that the cast metal (3) is led to solidify superficially in the mold so that the solidified skin of the product from the mold forms, on each edge, a solidified wall (30) of rounded cross section containing the metal not yet solidified (31), and the thickness is reduced so that said rounded solidified wall gradually folds in on itself. 2) Method according to claim 1, characterized in that the thickness reduction is continued until the longitudinal edges (32) of said rounded solidified wall are practically in contact with one another. 3) Installation for continuous casting of thin metallic products, comprising an ingot mold (1) whose walls define a casting space (7) of elongated cross section, and a thickness reduction device (4) placed downstream of the ingot mold to reduce the thickness of the product from the mold, characterized in that the ends (9) of said section of the casting space are rounded convex. 4) Installation according to claims 3, characterized in that the sides of the central part (8) of said section are convex. 5) Installation according to claim 3, characterized in that the sides of the central part (8) of said section are rectilinear, at least in the lower part of the mold. 6) Installation according to claim 3, characterized in that said section is of elliptical shape. 7) Installation according to claim 3, characterized in that the perimeter of said section is substantially constant over the entire height of the mold.

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