FR2645463A1 - METHOD AND INSTALLATION FOR CASTING THIN METAL PRODUCTS - Google Patents

Abstract

According to the method according to the invention, for the continuous casting of thin metal products, the liquid metal is poured into an ingot mold whose walls define a casting space 7 of elongated cross section and the thickness of the product obtained from the ingot mold, while the core thereof has not yet solidified, to the desired thickness of said thin metallic product. According to the invention, the cast metal is caused to solidify superficially in the ingot mold so that the solidified skin of the product from the ingot mold forms, on each edge, a solidified wall of rounded cross section containing the metal not yet solidified, and we achieves the reduction in thickness so that said rounded solidified wall gradually folds back on itself. In order to form said wall of rounded section, the ends of said section of the casting space are rounded convex.

Description

METHOD AND INSTALLATION OF CASTING

THIN NETWORK PRODUCTS

  The present invention relates to a process for the continuous casting of thin metal products, in particular steel, such as thin slabs, in which the molten metal is cast in an elongate mold and the thickness of the product from the mold is reduced. directly at the exit of it while the heart

  said product is not yet solidified.

  It also relates to a casting installation, allowing the implementation of this method, comprising a cold fixed-wall mold and a device located directly downstream of the mold, intended to reduce the thickness of the cast product to bring it to the surface. final thickness desired for the thin product, this device comprising two pinch members, to bring together or at least bring closer the solidified walls of the product from the mold, generally constituted by cylinders acting on

  said product in the manner of rolling rolls.

  Such methods and installations are already known, aimed at producing thin slabs, that is to say the width of which is generally greater than three times the thickness, this being

less than about 120 mm.

  For example, it has already been proposed to cast the liquid metal in an ingot mold whose small faces have a small width relative to the width of the large faces. In particular in order to be able to penetrate the casting 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 "cocked hat". To bring back the cast product to a rectangular section, the enlargement is gradually reduced from the top to the bottom of the mold, where it finds a rectangular section, the cast product passes immediately downstream of the mold between two cylinders which bring the big faces closer to

  produced to bring them parallel to each other.

  It has also been proposed to flow in an ingot mold of rectangular section substantially constant constant, the nozzle then having a strongly flattened section to be inserted between

the walls of the mold.

  In all cases, the thickness of the product from the mold is reduced immediately downstream thereof, while the core is not yet solidified, to bring the cast product to the desired thickness. However, these processes have a major disadvantage resulting from the rolling of the edges of the product from the mold. Indeed, 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 ingot mold to bring to contact the solidified skins of the large faces thereof. The central part of the large faces therefore does not undergo significant elongation during this crash. On the other hand, because of the solidification of the edges of the product in the mold, they are actually rolled, which leads to deformation and elongation of the edges. It follows that the thin slabs obtained by these processes may have

  defects of the type "long edges" well known laminators.

  In addition, the rolling of the edges requires a clamping force of the rolls of thickness reduction, much greater than the effort required to bring the solidified skins of the central parts of the large faces, which leads to oversize the device

ensuring "rolling".

  The object of the present invention is to solve the problems set out above, and to allow obtaining thin products, such as slabs, of good quality, while limiting the

  dimensions and therefore the size of the manufacturing facility.

  With these objectives in view, the present invention relates to a process for continuously casting thin metal products, such as thin slabs, in which the liquid metal is cast in an elongate mold and the thickness of the product is reduced. from the mold, while the core thereof is not yet solidified, to the desired thickness of said thin metal product. According to the invention, this process is characterized in that the cast metal is caused to solidify superficially in the mold so that the solidified skin of the edges of the product resulting from the mold form, on each edge, a solidified section wall. cross-section containing the not yet solidified metal, and the reduction in thickness is performed so that said wall

  solidified rounded folds gradually on itself.

  According to a particular embodiment of the invention, this process is characterized in that the reduction in thickness is continued until the longitudinal edges of said rounded solidified wall are

  practically in contact with each other.

  The invention also relates to a continuous casting plant for thin metal products, comprising an ingot 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 casting space are convex rounded. According to a particular embodiment of the invention, the sides of the central part of said section are convex, and preferentially connect to said ends so that the

  section of the mold is elliptical.

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

mold.

  According to another provision, the perimeter of said section is substantially constant over the entire height of the mold, the section passing gradually from the top to the bottom of the mold, a substantially circular shape to a very elongated elliptical shape, or to a shape having two parallel rectilinear elongated sides connected at their ends by semicircles. As will have probably already been understood, the principle of the invention is to form in the mold a product of elongated cross-section, not solidified at heart, the solidified skins of the edges may be, during the reduction of thickness later, folded on themselves, instead of being crushed by rolling. The invention will be better understood, and other features and

  advantages will appear, on reading the description that will be

  an example of an installation and a method of

  manufacture of thin steel slabs.

  Reference is made to the accompanying 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 product edge at the outlet of the mold in an installation according to the prior art; FIG. 5 represents the evolution of the section of the edge of the

  produced during the reduction of thickness.

  In Figure 1 is shown schematically in longitudinal section a thin slab casting installation comprising a mold 1 whose cooled walls 2 delimit a casting space 7, and two cylinders 4 of thickness reduction disposed downstream of the mold and spaced apart a distance equal to the desired thickness of the slab 5, less than the width of the exit section

of the mold.

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

  outlet of the mold, the heart of the product is still liquid.

  The product extracted from the mold 1 then passes between the rolls 4 where it undergoes a reduction in thickness which has the effect of bringing practically to the point of contact, the solidified skins 6

  giving the product the desired thickness.

  According to an embodiment 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 the level 0 of the mold has an enlarged elliptical shape which allows in particular the easy introduction of a liquid metal feed nozzle of conventional type. Alternatively, 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 the upper levels 0 and lower a, the section evolves regularly in

keeping a constant perimeter.

  According to another variant, represented in FIG. 3, the space of

  7 'has an outlet section 11' which has two sides 12 recess

  parallel tilines connected at their ends by semicircles 13.

  The idea underlying the invention is to conform the mold so that the edges of the product that is extracted 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 cracks or surface creases.

  As already pointed out, the object of the present invention is to eliminate or at least limit the rolling of the edges of the product extracted from the mold during the thickness reduction.

performed by the cylinders 4.

  To better understand how the particular shape of the mold makes it possible to arrive at this result, reference will be made to the figures

4 and 5.

  Figure 4 shows the section of an edge of a product cast in a mold according to the prior art, the walls of small dimensions are flat and perpendicular to the edges of the walls of large size. At the outlet of such an ingot mold, the product has on its edges a skin 20 solidified in contact with the small-sized walls of the mold, whose outer surface is perpendicular to those of the skins 21 formed in contact with the large-sized walls. When it is desired to reduce the thickness of this product, the skins 21 can easily be brought closer to one another 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 really laminated. It follows an elongation thereof, while the skins 21 which are simply close to one another, retain their dimension, 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. 5a shows the section at outlet level a of the mold, which section is preserved until the surface of the product comes into contact with the rolls 4. The solidified skin

  forms a curved wall 30 which contains the still liquid metal 31.

  When the product comes into contact with the rolls 4 (level b in FIG. 1), the latter begin by bringing the skins 6 formed on the walls of the mold into the central zone 8 where the radius of curvature is brought closer to one another. of the ellipsotal section of the mold is the largest. On the other hand, the skin 30, formed in the end zones 9, of smaller radius of curvature, is practically not deformed (FIG. 5b), the longitudinal edges 32 of

  the skin 30 retaining their relative spacing.

  At level c (Figure 5c) 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" , get

  finding moved laterally outward.

  At the level d, adjacent to the level of the axes of the rolls, the reduction in thickness ends, the edges 32 of the skin 30 are practically in contact with each other, the two parts 30 'and 30 "

  of it having completely folded one over the 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 mold without substantially rolling the edges. Moreover, 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. 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 liquid metal supply of the mold can be carried out by a flat nozzle, or by other means, such as for example a lateral feed, the mold may have a constant cross-section along its entire height, such as that

  of the outlet section 11 'shown in FIG.

7 2645463

Claims (6)

  1) A process for continuously casting thin metal products, such as thin slabs, in which the liquid metal is cast in an elongate mold (1) and reduces the thickness of the product from the mold, while the the core thereof is not yet solidified to the desired thickness of said thin metal product (5), characterized in that the cast metal (3) is allowed to solidify superficially in the mold so that the solidified skin of the product from the ingot mold forms, on each edge, a solidified wall (30) of rounded cross section containing the not yet solidified metal (31), and the thickness reduction is carried out so that said rounded solidified wall   gradually withdraws on itself.   2) Process according to claim 1, characterized in that the reduction in thickness is continued until the longitudinal edges (32) of said rounded solidified wall are   practically in contact with each other.   3) Installation for continuous casting of thin metal 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 mold for reducing the thickness of the product from the mold, characterized in that the ends (9) of said section of the casting space are convex rounded.   4) Installation according to claims 3, characterized in that   that the sides of the central portion (8) of said section are convex. ) 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 elliptical in 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.