EP0490800B1 - Cylinder for single-roll or twin-roll continuous casting. - Google Patents

Abstract

The cylinder comprises an outer sleeve 6, made from a material which is a good conductor of heat, and a central core 2. The sleeve is connected to an underlying support piece 3 over their entire contact surface by means of a metallurgical connection without melting produced by diffusion welding by means of isostatic hot compression. <IMAGE>

Description

The present invention relates to the continuous casting of strips of metal, in particular steel, on a cylinder or between two cylinders. More specifically, it relates to this type of casting rolls which are commonly constituted by a rigid internal core and an energetically cooled external ferrule, in contact with which the cast metal cools and solidifies to form the strip which is extracted. continuously due to the rotation of the cylinder (s).

The ferrule is commonly cooled from the inside, for example by circulation of a cooling fluid in channels drilled through its thickness. To ensure vigorous cooling of the cast metal, the material constituting the shell is a good conductor of heat, namely copper or one of its alloys.

Furthermore, this ferrule must be rigid enough not to deform, while not cracking, under the effect of mechanical and thermal stresses to which it is subjected during repeated casting cycles.

It must also be rigidly linked to the cylinder core to avoid any relative displacement.

As a result, in industrial installations where the diameter and the width of the cylinders are large, the shell is a large piece, massive and thick because it must in particular include the cooling channels and mechanical anchoring means on the core. .

Such a ring is described for example in EP-A-0428464 (the French patent application ^No. 2,654,372 issued May 17, 1991). This document describes a casting cylinder for continuous casting on or between two such cylinders, comprising a core and a ferrule rigidly linked to the core in its middle part and over its entire circumference by a dovetail or T-shaped slide assembly. The ferrule is in contact of the core over its entire width and it is held by its edges thereon by means allowing axial displacement but preventing the radial displacement of said edges of the shell relative to the core.

However, the manufacture of such parts poses many problems. It is in particular difficult to obtain, during the molding of the shell, sufficient homogeneity of the metal which constitutes it. In addition, the machining operations necessary for producing the cooling channels and the means for connecting to the core are generally difficult to carry out in the copper alloys used. In the end, these materials are expensive.

The object of the present invention is to eliminate or at least reduce these drawbacks, without harming the thermal and mechanical characteristics of the shell, in particular its resistance to cracking.

With these objectives in view, the invention relates to a casting cylinder of a continuous casting installation on one or between two such cylinders comprising an outer ferrule made of copper or copper alloy and a central core, characterized in that the ferrule is linked to an underlying cylindrical support part over their entire contact surface by a non-fusion metallurgical connection produced by diffusion-welding, the support part being made of a steel whose coefficient of expansion is equal to or greater than that ferrule material.

As can be understood, the idea underlying the invention consists in opting for a support piece which expands as much, or even more, with heat than the constituent material of the shell, so as to obtain, after their hot assembly (welding-diffusion) and return to ambient temperature, placing the shell in compression preload favorable to its resistance in use in contact with the cast metal.

The core can itself constitute the support part, or, preferentially, this support part is an annular part whose external surface is cylindrical, and which includes inside means for mechanical connection to the core.

The ferrule, made of copper or a copper alloy, is therefore not very capable of undergoing significant mechanical stresses. Thanks to the invention, there is in fact produced a composite part which has at its periphery the characteristics required thermally, and inside the mechanical characteristics necessary to resist the various mechanical stresses which are exerted on the cylinder during casting.

In addition, the machining operations necessary for the connection of the ferrule-support part assembly to the cylinder core are more easily achievable on steel or cast iron of which the support part can for example be made.

Finally, the necessary quantity of copper or copper alloy necessary for the shell can be reduced, which reduces the cost of the cylinder.

According to a particular arrangement, the cylinder comprises at the interface between the ferrule and the support part a thin layer of a metal or alloy capable of being assembled by diffusion welding on the one hand with the metal constituting the ferrule and on the other share with that of the support piece.

According to a variant, cooling channels are drilled in the thickness of the shell parallel to its axis, supply and return channels cross the ferrule-support part interface and tubes are placed in these supply and return channels at the interface so as to seal between them and on the one hand the ferrule and on the other apart from the support piece.

According to another variant, the cylinder has grooves made at the shell-support part interface, and tubes are placed in these grooves and tightly connected at their ends with on the one hand the shell and on the other hand the part. of support.

• on usine la virole et la pièce-support ;
• on place la virole autour de la pièce-support ;
• on réalise la liaison virole-pièce de support par soudage diffusion par compression isostatique à chaud.

A method of manufacturing a casting cylinder according to the invention is characterized in that:

• the ferrule and the support part are machined;
• the ferrule is placed around the support piece;
• the ferrule-support part connection is made by diffusion welding by hot isostatic compression.

• préalablement à la réalisation de la liaison virole-pièce de support, on soude ces deux pièces sur les bords de leurs surfaces en contact ;
• l'usinage de la virole comporte la réalisation de rainures à la surface interne de celle-ci, et préalablement à la réalisation de la liaison virole-pièce de support, on place dans ces rainures des tubes qu'on lie de manière étanche à leurs extrémités d'une part à la virole et d'autre part à la pièce de support.

According to specific provisions of this process:

• prior to making the ferrule-support part connection, these two parts are welded to the edges of their contacting surfaces;
• the machining of the ferrule includes the production of grooves on the internal surface thereof, and prior to the production of the ferrule-support part connection, tubes are placed in these grooves which are tightly connected to their ends on the one hand to the ferrule and on the other hand to the support piece.

• la figure 1 est une vue demi-coupe axiale d'un cylindre conforme à l'invention ;
• la figure 2 est une vue de détail du bord de l'ensemble virole-pièce de support lors de sa réalisation, selon une première variante ;
• la figure 3 est une vue similaire dans une seconde variante ;
• la figure 4 est une vue partielle en coupe selon la ligne IV-IV de la figure 3.

Other characteristics and advantages of the cylinder according to the invention will appear in the description which follows, given with reference to the appended drawings in which:

• Figure 1 is an axial half-sectional view of a cylinder according to the invention;
• Figure 2 is a detail view of the edge of the ferrule-support piece assembly during its production, according to a first variant;
• Figure 3 is a similar view in a second variant;
• FIG. 4 is a partial sectional view along the line IV-IV of FIG. 3.

The casting cylinder 1 shown in FIG. 1 comprises a core 2, an annular support piece 3 held on the core by two annular flanges 4 and tie rods represented only by their axes 5.

The external ferrule 6 made of copper alloy is assembled on the support part 3 by diffusion welding, this assembly being carried out beforehand by hot isostatic compression, which leads to obtaining a composite part ferrule-support part, which will be called hereinafter "composite ferrule".

Diffusion welding by hot isostatic compression makes it possible to obtain a diffusion bond in the solid state. This assembly technique requires a high pressure and a moderate temperature of the parts to be assembled which does not reach their melting temperature as is the case in conventional welding. The high pressure of the two parts on each other leads to intimate contact of the facing surfaces and to the production of a metallic junction without pores by reciprocal diffusion of the metals through the interface.

The use of this technique for the production of said composite ferrule makes it possible to obtain a resistant connection of the ferrule 6 on the support part 3. This part 3 can then be made of a less expensive material than that of the ferrule 6, and which, moreover, can be more easily machined.

The composite ferrule (3,6) may comprise at the interface between the ferrule 6 and the support part 3 a thin layer of a metal or alloy, for example nickel or an iron-nickel alloy with 42% nickel, which is able to be assembled by hot isostatic compression with one and the other of the constituent metals of the shell and of the support piece, which allows for example to produce these in metals difficult to assemble directly by this technique .

The ferrule 6, made of a material having good thermal conductivity and sufficient mechanical resistance characteristics at relatively high temperatures, above 400 ° C., is for example made of a Cu-Cr-Zr alloy, preferably in the state hyper soaked.

The support part is a material having good mechanical characteristics at room temperature, easily machinable, and whose coefficient of expansion is preferably equal to or greater than that of the shell material, such as for example austenitic cast iron GS to 18 % Ni or type 304 austenitic stainless steel.

The core is preferably made of steel or stainless steel.

• les ébauches de la virole et de la pièce de support sont réalisées classiquement par exemple par moulage ;
• les surfaces destinées à être soudées sont usinées de manière que la virole puisse être mise en place autour de la pièce-support avec un jeu réduit. Avant assemblage, les surfaces sont préparées, cette préparation pouvant consister en un nettoyage, décapage, ou traitement mécanique ou chimique, par exemple nickelage électrolytique sur une épaisseur de 50 à 100 µm ;
• une fois assemblées, une soudure est réalisée sur les bords de l'interface 9 entre la virole 6 et la pièce de support 3 pour assurer l'étanchéité de l'interface ;
• les deux pièces ainsi assemblées sont soumises alors à une compression isostatique à chaud, par exemple à 900°C, sous une pression de 100 Mpa pendant une heure, pour réaliser la liaison par soudage-diffusion.

In general, the manufacture of the composite shell comprises the following steps:

• the blanks of the shell and of the support part are produced conventionally, for example by molding;
• the surfaces intended to be welded are machined so that the ferrule can be placed around the support piece with reduced play. Before assembly, the surfaces are prepared, this preparation possibly consisting of cleaning, pickling, or mechanical or chemical treatment, for example electrolytic nickel plating on a thickness of 50 to 100 μm;
• once assembled, a weld is made on the edges of the interface 9 between the ferrule 6 and the support part 3 to seal the interface;
• the two parts thus assembled are then subjected to hot isostatic compression, for example at 900 ° C., under a pressure of 100 Mpa for one hour, to make the connection by welding-diffusion.

The composite shell thus obtained can then be machined, or undergo the specific heat treatments necessary to obtain the metallurgical characteristics required for its use.

Note here all the advantage of the choice of materials indicated above, that is to say the alloy Cu-Cr-Zr for the shell and the stainless steel E304 for the support. In fact, the expansion coefficients of these materials are close to each other, that of stainless steel E304 however being slightly higher than that of the Cu-Cr-Zr alloy. It follows that in the cooling phase of the heat treatments applied to the ferrule-support assembly, the support tends to retract slightly more than the ferrule, which ensures, after thermal treatments, compression of the ferrule. The shell thus prestressed has better resistance to cracking.

It may be advantageous to carry out certain machining of the ferrule 6 before it is assembled on the support part 3.

In the case shown in Figure 2, cooling channels 7 are drilled axially in the shell, as well as holes 10 intended to allow the supply or return of a cooling fluid. Corresponding holes 10 'are made in the support piece 3. In this case, after the ferrule has been placed around the support piece, tubes 11 are introduced into the holes 10 and 10' so as to cover the interface 9 and seal it, this seal being also provided on the edges of the shell by the welds 12. The tubes 11 therefore allow on the one hand to ensure sealing of the interface required during the hot isostatic compression operation, and on the other hand to balance the pressure inside the cooling channels 7 to avoid the risk of their deformation due to the high pressures applied at the periphery of the shell.

In the case shown in Figures 3 and 4, cooling channels 7 are located at the shell-support part interface. Grooves 13 are machined inside the shell 6 before it is assembled on the support part 3. It will be noted that it is easier to machine such grooves than to drill orifices over a great length. Tubes 14 are placed in these grooves and, after the ferrule has been placed on the support part, welded at their ends 15. The sealing of the interface 9 is thus ensured, as is the pressure balancing of the inside the tubes 14.

The invention is not limited to the embodiments described above by way of examples.

In particular, hot isostatic compaction can be carried out by the technique of coating the assembled parts with a sealed container outside of which the pressure is applied.

Claims (8)

1. Casting roll of an installation for continuous casting onto one such roll or between two such rolls, comprising an outer shell (6) made of copper or copper alloy and a central core (2), characterized in that the shell is bonded to a subjacent cylindrical support piece (3), over their entire contact area, by a fusionless metallurgical bond produced by diffusion welding, the support piece being made of a steel whose expansion coefficient is equal to or greater than that of the material of the shell (6).
2. Roll according to Claim 1, characterized in that the support piece (3) is an annular piece which has a cylindrical external surface and which includes, on the inside, means of mechanically bonding to the core.
3. Roll according to Claim 1, characterized in that the core constitutes the support piece.
4. Roll according to Claim 1, characterized in that the support piece is made of stainless steel.
5. Roll according to Claim 1, characterized in that the shell (6) is made of a Cu-Cr-Zr alloy.
6. Roll according to Claim 1, characterized in that it includes, at the interface (9) between the shell and the support piece, a thin layer of a metal or alloy capable of being joined by diffusion welding, on the one hand to the metal making up the shell and, on the other hand, to that making up the support piece.
7. Roll according to Claim 1, characterized in that cooling channels (7) are drilled into the thickness of the shell, parallel to its axis, feed and return channels pass through the shell/support-piece interface and tubes (11) are placed in these feed and return channels in the region of the interface so as to ensure sealing between them and, on the one hand, the shell and, on the other hand, the support piece.
8. Roll according to Claim 1, characterized in that it includes grooves (13) produced at the shell/support-piece interface and tubes (14) are placed in these grooves and bonded in a sealed manner at their ends to, on the one hand, the shell and, on the other hand, the support piece.

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