EP0477045A1 - Apparatus for twin-roll continuous casting - Google Patents

Abstract

Apparatus for continuous casting between twin rolls 1, 2 with parallel axes, defining between them and with two fixed lateral walls 3 a casting space for a molten metal, each lateral wall comprising at least one lateral part 6, placed against the plane end front surface of one of the rolls, and consisting of a disc portion with an external diameter equal to that of the said adjacent roll, and a central part 12, opposite the said casting space, made from an insulating refractory material. <??>The said disc portion is produced from a material which has characteristics of thermal conductivity and mechanical strength which are greater than those of the said refractory material and is a frustoconical disc portion whose face with the greatest radius of curvature is located towards the roll, and whose frustoconical surface is in contact with the insulating material of the said central part. <??>The invention applies to the continuous casting of thin metal products, notably from steel. <IMAGE>

Description

The present invention relates to the continuous casting of metals, in particular steel, between two cylinders of parallel axes driven in rotation in opposite directions, to obtain thin products.

It is known that in this type of casting, one of the problems is the confinement, towards the ends of the cylinders, of the molten metal fed into the casting space defined between the cylinders. One solution to this problem is to use fixed side walls held in a sealed manner against the cylinders, and in particular against the end surfaces of the latter. To prevent the molten metal from solidifying on contact with these walls and forming a solidified metal wedge which would prevent the correct formation of the edges of the cast product, it is already known to use for these side walls a sufficiently insulating material, which avoids or at least limits this solidification. Such an insulating refractory material however generally has insufficient mechanical properties to be maintained in contact with the movable cylinders without causing rapid wear of this material.

To solve this problem, it has already been proposed in the patent application published under the number FR 2636259 to produce side walls of which only a central zone is formed of insulating material. Two metal tabs placed on either side of this material penetrate slightly between the cylinders by marrying their curvature. In addition to better mechanical strength, these tabs promote sealing between cylinders and side walls because the solidified metal skins extend over these fixed tabs on which the edges of the skins slide, thus covering the cylinder-side wall joint.

It has also been proposed, in French patent application No. 89 08086 in the name of the present applicant, a side wall comprising at least one lateral part, for example metallic, facing the planar front surface of a cylinder, and of which the surface opposite the casting space is an extension of the surface of said cylinder, and is connects to a front part of said wall, recessed therein with respect to the side part, so as to form in the wall a hollow zone laterally extending the casting space.

The present invention proposes to provide another solution to the problem mentioned above.

With this objective in view, the invention relates to a continuous casting installation between two cylinders with parallel axes defining between them and with two fixed side walls a casting space for a molten metal, each side wall comprising at least a lateral part, placed against the flat front end surface of one of the cylinders, and consisting of a disc portion of outside diameter equal to that of said adjacent cylinder, and a central part, opposite said casting space, in insulating refractory material, this installation being, according to the invention, characterized in that said disc portion is made of a material having good thermal conductivity and mechanical resistance characteristics superior to those of said refractory material. and is a portion of frustoconical disc whose face having the greatest radius of curvature is situated towards the cylinder, and the frustoconical surface is in contact with the insulating material of said central part.

Since the disc portion opposite the front end surface of the cylinder is resistant to friction, it can be pressed against the cylinder with sufficient force to ensure sealing, without risk of deterioration or wear. The central part in insulating material avoids an excessive solidification of the metal and the formation of the corner mentioned at the beginning of this thesis. During casting, this central part can be worn by the metal which digs it, but in doing so the metal which penetrates into the hollow thus formed approaches the frustoconical surface of the disc portion, kept at low temperature among other things due to its thermal conductivity and its proximity to the cooled surfaces of the cylinders. It follows that this metal solidifies on the surface, the wall thus solidified hooks into the insulating refractory material and forms a sort of slide in which the liquid metal can flow to the level of the neck between the cylinders, where, solidified, it constitutes the edge of the product.

As will be better understood below, the constitution of the side wall according to the invention makes it possible, at the start of casting, to form an autocreuset, constituted by the skin of metal solidified in the insulating refractory material, which stabilizes due to the proximity of the disc portions, thus prevents the progression of wear of said refractory material, and thus allows the continuation of the casting. Thanks to the taper of the portions of discs, the horizontal section of this self-crucible near the neck, takes a C shape whose thickness of the branches decreases towards their ends, so that the spacing between these branches is substantially constant, which makes it possible to obtain the edges of the cast product of thickness substantially equal to the thickness of the central zone thereof.

According to a particular arrangement, the frustoconical surface of the disc portion may include asperities, such as spikes, which improve the attachment of the insulating material and therefore the maintenance of the autocreuset on its edges.

According to another arrangement, the central part of insulating refractory material can be made up of several of these materials arranged in successive layers having characteristics of mechanical resistance and / or thermal insulation varying gradually from the material located towards the casting space. , which has the highest insulation coefficient.

The disc portions, or at least the area of larger diameter thereof, may be coated or made of a material resistant to heat and having in particular good mechanical strength at high temperature, such as zirconia, and more can be cooled, by example by an internal circulation of a cooling fluid.

Other characteristics and advantages will emerge from the description which will be given by way of example of an installation for the continuous casting of thin steel products, in accordance with the invention.

• la figure 1 est une représentation partielle d'une installation de coulée continue entre deux cylindres, en vue de dessus et en coupe selon un plan horizontal ;
• la figure 2 est une vue frontale, à échelle réduite, de la paroi d'obturation selon la flèche F de la figure 1 ;
• les figures 3a à 3c sont des schémas montrant l'évolution, au début de la coulée, de la partie centrale de la paroi latérale, à proximité du col entre les cylindres ;
• la figure 4 est une vue schématique frontale de la paroi latérale en régime de coulée établi ;
• la figure 5 est une vue schématique de la paroi, en régime établi, en coupe selon la ligne V-V de la figure 4 ;
• la figure 6 est une vue frontale de la paroi latérale selon une première variante ;
• les figures 7a et 7b sont des vues en coupe de la paroi de la figure 6 aux niveaux repérés respectivement a et b sur cette figure;
• la figure 8 est une vue frontale de la paroi latérale dans une seconde variante ;
• les figures 9a et 9b sont des vues en coupe de la paroi de la figure 8, aux niveaux repérés respectivement a et b sur cette figure ;
• la figure 10 est une vue partielle en coupe d'une autre variante, dans le cas d'une installation de coulée entre cylindres déplaçables axialement l'un par rapport à l'autre ;
• la figure 11 est une vue de détail, agrandie, de la zone centrale de la paroi dans le cas d'un matériau réfractaire isolant en plusieurs couches.

Reference is made to the appended drawings in which:

• Figure 1 is a partial representation of a continuous casting installation between two cylinders, in top view and in section along a horizontal plane;
• Figure 2 is a front view, on a reduced scale, of the closure wall according to arrow F of Figure 1;
• Figures 3a to 3c are diagrams showing the evolution, at the start of casting, of the central part of the side wall, near the neck between the cylinders;
• Figure 4 is a schematic front view of the side wall in established casting regime;
• Figure 5 is a schematic view of the wall, in steady state, in section along the line VV of Figure 4;
• Figure 6 is a front view of the side wall according to a first variant;
• Figures 7a and 7b are sectional views of the wall of Figure 6 at the levels marked respectively a and b in this figure;
• Figure 8 is a front view of the side wall in a second variant;
• Figures 9a and 9b are sectional views of the wall of Figure 8, at the levels marked respectively a and b in this figure;
• Figure 10 is a partial sectional view of another variant, in the case of a casting installation between cylinders movable axially relative to each other;
• FIG. 11 is an enlarged detail view of the central zone of the wall in the case of a material refractory insulating in several layers.

The continuous casting installation between cylinders partially shown in FIG. 1, comprises two cylinders 1 and 2 with parallel and horizontal axes, driven in rotation and two lateral walls for closing the casting space, such as wall 3 , located towards the ends of the cylinders and held against the front surfaces 4, 5 of the cylinders.

The side wall 3, shown in Figure 1 in section along a horizontal plane at the axes of the cylinders and in front view in Figure 2, has two side parts 6 each consisting of a portion of frustoconical disc of larger outside diameter equal to that of the cylinders, so that the face 7 of these portions of discs having the greatest radius of curvature is situated against the front surface 4, 5 of the adjacent cylinder, and that the edge 9 of the bevel formed by the frustoconical surface 8 and the face 7 of these disc portions is opposite the edge formed by the edge of the cylindrical surface 10 of the corresponding cylinder.

In the drawing of FIG. 2, the cylinders are represented only by the trace 10 'of their cylindrical surface, and it can be seen that this trace merges with the edge 9 of the disc portions.

The angle of the bevel, that is to say the angle at the base of the tapered disc portion is 5 to 85 degrees, and preferably about 30 °.

The disc portions constituting the lateral parts 6 of the closure wall 3 are made of a material having good mechanical characteristics, resistant to wear, and preferably having a low coefficient of friction to limit the forces due to the possible friction of the cylinders on these portions of discs. We could for example make them out of cast iron, steel, copper, and reduce friction by lubrication.

It will also be noted that the mechanical strength of the material constituting the disc portions also makes it possible to avoid the deterioration of these if, following the wear of the insulating refractory, the cast metal, in the course of solidification, comes into contact with them. The progression of wear is stopped or at least greatly slowed down, and metal infiltration between these disc portions and the cylinders is thus avoided.

The disc portions 6 may also, in the vicinity of the edge 9, be coated or made of a material having a particularly high mechanical resistance at high temperature and preferably unlikely to be wetted by the molten molten metal, and inert to the contact of the liquid steel to avoid deterioration of the edges 9 of the disc portions, or the attachment of cast metal thereon, in the event that molten metal is brought, during casting, into contact with said edges. It is possible, for example, to use a ceramic deposit (for example zirconia) on a metallic or ceramic substrate, or to produce the disc portion in the form of a monolithic piece of ceramic or composite ceramic, or else to use an antioxidant coating.

In addition, these disc portions can be cooled, for example by circulation of a cooling fluid in channels 11 produced in the disc portions, the cooling thus caused having to be sufficient to maintain the region near the edge at a temperature lower than that where damage could occur, without having a cooling effect on the cast metal.

Between the two disc portions 6, in the central part of the side wall 3, is placed an insulating refractory material 12, in leaktight contact with the frustoconical surfaces 8 of the disc portions 6. This central part made of insulating refractory material is contained towards the rear of the wall 3 by a support plate 13, on which the disk portions 6 are fixed.

To improve the anchoring of the refractory insulating material on the disc portions 6, and in particular near the neck between the cylinders, the frustoconical surface of these is provided with asperities, such as pins 14 which penetrate into said insulating refractory material, or hollows, produced for example by drilling, into which said material penetrates.

Furthermore, the central part 12 preferably comprises an overhang 15 relative to the plane of the faces 7 of the disc portions, which is inserted between the cylinders.

The insulating refractory material has a thermal conductivity of less than 0.35 W / mK, that is to say that it must be sufficiently insulating to avoid solidification of the metal on contact, and have good dimensional stability during large temperature variations. We can for example use a fibrous refractory, for example composed of alumina fibers impregnated with zirconia gel (for example of the type marketed under the name of Procelit or Procal).

To better understand the advantages of the side wall according to the invention, the diagrams in Figure 3 represent the evolution of this wall at the start of casting.

FIG. 3a represents, on an enlarged scale, the central zone of the side wall before the start of the casting in a plane situated slightly above the neck between the rolls. We therefore see the wall and the overhang 15 which penetrates slightly between the cylinders.

After a relatively short casting time, the cast metal 22 has worn off the insulating refractory material by eliminating the overhang 15 and by slightly digging the central part, as shown in FIG. 3b.

As the casting continues, the metal continues to dig the insulating refractory and creates in it a cavity 16 of rounded section. The solidified skin 17 which then forms in this cavity clings to the insulating refractory material, forming the autocreuset mentioned above.

It will be noted that the autocreuset 17 occupies in the insulating refractory material a larger space than that existing, at the same level, between the cylinders. This extra width is authorized by the particular constitution of the side walls according to the invention, and in particular by the fact that the disc portions 6 are frustoconical.

In addition this extra width of the autocreuset allows the edges of the cast product to retain a thickness substantially equal to the general thickness of the product. It will indeed be understood that the edges of the final product are obtained from the metal being solidified which moves, simultaneously with the metal passing between the cylinders, in the vertical gutter formed by the autocreuset which is fixed to it relative to the side wall.

It will also be understood that once the autocreuset is formed, it protects the insulating refractory material from direct contact with the molten metal, preventing the progression of its wear, which makes it possible to ensure the stability of the process for the pursuit of casting.

It will also be noted that the skins 23 of metal, solidified in contact with the cylinders and moving with them, are not linked to the skin 16 forming an autocreuset.

In the drawings of FIGS. 4 and 5, the side wall has been shown in the established casting regime, respectively in plan and in horizontal section at the level of line V V, situated clearly above the neck. We see the V-shaped digging resulting from the wear of the refractory insulating material by the edges of the metal skins 23 solidified on the cylinders. The depth and width of the wear marks 18 increases downwards, until they meet to form the cavity 16, shown in FIG. 3c, seat of the autocreuset 17.

It will also be noted that the formation and stability of the autocreuset results from the thermal equilibrium which is established between the cast metal and the various parts of the installation and in particular of the side wall. This is why the insulating refractory material, in contact with which the molten metal is brought to the start of the casting, must be very insulating in order to avoid premature solidification of said metal between the edges of the rolls. Furthermore, it is desirable that the autocreuset, once formed, be as stable as possible. To this end, the central part of the wall can be produced in the form of a composite part shown in FIG. 11 formed of several layers 12a, 12b, 12c of different refractory materials arranged vertically, whose mechanical resistance characteristics increase and those of thermal insulation correlatively decrease from the plane of the faces 7 of the disc portions towards the support plate 13. Thus at the very beginning of the casting, it is the thermal insulation aspect which is predominant, during the first contact of the molten metal with the insulating refractory material, while during the formation of the autocreuset, the digging of the central part leads the auotcreuset to reach mechanically more resistant layers which limit its progression and, once arrived in steady state ensure a better seat for this one.

The last layer, or the support plate itself, constitutes a safety plate to avoid any risk of molten metal flow in the event of a breakthrough in the autocreuset. They may for example be made of a hard material which does not deform by expansion, such as silica.

According to a variant, represented in FIGS. 6 and 7, the portions of discs comprise in their lower part close to the neck between the cylinders, a clearance 19 consisting in removing, until the bottom of the side wall, the bevelled part of said disc portions , this clearance being filled by a widening 20 corresponding to an insulating refractory material, which is consequently in contact with the front faces of the cylinders over the height of this clearance. The presence of the insulating material, softer than the material constituting the disc portions, allows the edges of the product, solidified near the neck, to flourish, outside the grip of the cylinders. The rolling force at the neck and at the edges of the rolls can thus be reduced, which prevents deterioration of said rolls. edges.

The height of this clearance, above the neck will preferably be close to a length of arc β of 2 ° measured at the periphery of the cylinders.

According to another variant shown in Figures 8 and 9, the disc portions are released in the same area as above only over part of their thickness, leaving a thinned part 21 of disc in contact with the cylinders, which avoids direct contact of the refractory material with the cyclinders, while largely retaining the possibility of the opening of the edge of the cast product, mentioned above.

These clearances also allow the passage through the refractory material of a possible excess thickness of the edge of the product which could result from a too large momentary widening of the autocreuset.

In the drawing of FIG. 10, there is shown, in section at the neck, an application of the invention in the case of casting between two axially offset cylinders, for example in an installation allowing the casting of products of variable width by relative axial displacement of the cylinders.

In this case the side wall is not symmetrical, as in the previous examples, with respect to the median plane P of the installation parallel to the axes of the cylinders. This wall 30 is formed on the side where it is in contact with the front face of the cylinder 1 ′ (lower part of the drawing in FIG. 10), in the same way as in the examples described above, and comprises a portion of frustoconical disc 6 ′ fixed to a support plate 13 ', and a central part 12' made of insulating refractory material. The other side of the wall 30 (upper part of FIG. 10) is constituted by a tongue 31 placed against the cylindrical surface of the cylinder 2 ', for example of the same material as the disc portion 6', this tongue also being in bevel, shaped to match the curvature of the cylinder 2 ', and also fixed to the support plate 13'. The material insulating refractory 12 'fills the space between the disc portion 6' and the metal tongue 31.

This side wall is in fact equivalent to that of the variant, adapted to axially offset cylinders, of the wall described in the French patent application n ° 89 08086 already cited, to which reference may be made for more details, and to which applied the principle of the wall according to the present invention.

It will easily be understood that the particular arrangement in FIG. 10 allows the axial displacement of the cylinder 2 'relative to the cylinder 1 ′ and to the wall 30, allowing the width of the cast product to be varied.

It will also be understood that in the case of this variant the autocreuset, which forms in a similar manner to what has been explained previously, is not symmetrical with respect to the plane P, but offset towards the side of the disc portion 6 ', which causes the formation of a bank of the product slightly bent with respect to the general plane of the thin product obtained. This apparent defect is not however detrimental when the edges of the product are subsequently dropped, after casting, for example by shearing. On the contrary, in this case the falling of the banks can be facilitated.

The invention is not limited to the examples and variants described above, and includes any provisions resulting from the combination of said examples or variants.

Claims (13)

1) Installation for continuous casting between two cylinders (1,2) with parallel axes defining between them and with two fixed side walls a casting space for a molten metal, each side wall (3) comprising at least one lateral part (6), placed against the flat end surface (4,5) of one end of one of the cylinders, and consisting of a portion of disc of outside diameter equal to that of said adjacent cylinder, and a central part (12), facing said casting space, made of insulating refractory material, characterized in that said disc portion is made of a material having thermal conductivity and mechanical resistance characteristics greater than those of said refractory material, and is a frustoconical disc portion of which the face having the greatest radius of curvature is located towards the cylinder, and the frustoconical surface (8) is in contact with the insulating material of said central part. 2) Installation according to claim 1, characterized in that the angle at the base of the frustoconical disc portion (6) is between 5 and 85 °. 3) Installation according to claim 1, characterized in that the insulating refractory material is an alumina fiber. 4) Installation according to claim 1, characterized in that the central part consists of several layers (12a, 12b, 12c) of materials having characteristics of increasing mechanical resistance from the layer (12a) located towards the space of casting 5) Installation according to claim 1, characterized in that the disc portions are made of cast iron, steel, copper, molybdenum or one of their alloys. 6) Installation according to claim 1, characterized in that the frustoconical surface of the disc portions has asperities (14). 7) Installation according to claim 1, characterized in that the disc portions are coated or formed, in their area of larger diameter, by a material having good mechanical strength at high temperature. 8) Installation according to claim 7, characterized in that said material is zirconia. 9) Installation according to claim 1, characterized in that the disc portions are cooled. 10) Installation according to claim 1, characterized in that the disc portions have, in the area near the neck between the cylinders, a clearance (19), this clearance being filled with an insulating refractory material (20). 11) Installation according to claim 10, characterized in that said clearance is achieved over the entire thickness of the disc portion. 12) Installation according to claim 10, characterized in that said clearance is produced over a part of the thickness of the disc portion leaving a thinned portion (21) of this disc portion in contact with the cylinder. 13) Installation according to claim 1, characterized in that the central part (12) has an overhang (15) penetrating between the cylinders.

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