EP0792706A1 - Casting cylinder of continuous casting apparatus with one or two cylinders - Google Patents

Abstract

The cylinder consists of a hub (2), a coaxial shell (3) and two supporting and centering flanges (5,6) between them. Each flange has a truncated conical surface (51,61) which engages with a corresponding surface (34,35) on the inside of the shell situated in a zone in which variations in the shell's inner diameter as a result of expansion are virtually nil. The flanges are pressed towards one another by springs (74), and the hub and shell also have axial stops (24,33) and pressure elements (80,81). The flanges and the shell have connecting channels (7,8,53,54) for circulating a coolant, with additional channels (32) in the shell located in the outer of its two layers (37).

Description

The invention relates to the continuous casting of metals, in particular steel, on one or between two cylinders, and more particularly the constitution of a cylinder of a continuous casting installation according to the aforementioned technique.

It is known that, with the aim of obtaining directly by casting molten metal thin metal products, such as thin strips a thickness of a few millimeters, in particular in steel, a particular casting technique has been developed. , commonly called continuous casting between cylinders. This technique consists in pouring molten metal into a casting space formed between two cooled cylinders with parallel axes and two lateral closing walls generally disposed against the front end surfaces of the cylinders. The metal solidifies on contact with the walls of the cylinders and, by rotation of the latter in opposite directions, a metal strip is extracted, at least partially solidified, the thickness of which is substantially equal to the distance separating the two cylinders. This technique makes it possible to obtain, directly from the molten metal, thin strips of metal, in particular steel.

The small thickness of these strips allows them to be directly laminated by cold rolling.

Another casting technique is also known, intended to obtain even thinner products, according to which the molten metal, spilled on the surface of a single cylinder driven in rotation, solidifies entirely in contact with the cylinder to form a continuous metal strip. .

The cylinders used for the implementation of these casting techniques are generally cooled internally and comprise a hub and a ferrule arranged coaxially, means for axial and rotational connection of the ferrule on the hub and means for supporting and centering the ferrule on the hub.

Such cylinders are described, for example, in document FR-A-2 711 561. This document describes a cylinder comprising a hub supporting a ferrule made of a material which is a good conductor of heat, for example a copper alloy. The ferrule has channels for circulation of a cooling fluid oriented parallel to the axis of the cylinder.

The axial positioning of the ferrule on the hub is ensured by a shoulder of the hub, located at the axially median plane of the cylinder, on which a corresponding shoulder, produced on the internal surface of the ferrule, is held in abutment. The centering of the ferrule is ensured by flanges whose outer surface is conical and cooperates with conical bores formed on the edges of the ferrule. The two flanges can slide axially on the hub, and they are returned to one another by elastic return means. Thus, the centering of the shell is ensured, and preserved when the shell deforms under the effect of expansions due to heating during casting. In addition, as illustrated in FIGS. 4 and 5 of the aforementioned document, the extreme zones of the outer edges of the conical bores of the ferrule are detangled, so as to come to be applied progressively to the conical surface of the flanges, when the edges of the shell is deformed under the effect of differential expansion between the outer surface of the shell and its colder internal surface, and this without the areas of the conical surfaces, respectively of the flanges and of the shell, initially in contact move away from each other.

This provision is only of interest when the edges of the ferrule are thin, and it is therefore necessary to ensure the largest possible contact surface at the conical surface between the flange and the ferrule.

The present invention aims to propose a new embodiment of the centering of the ferrule on the hub of a casting cylinder, particularly suitable when, unlike the aforementioned technique, the ferrule has a relatively large thickness at the edges. It will be noted that such a thick ferrule on its edges has the advantage of being less subject to deformations, in particular localized deformations. In addition, a ferrule with thin edges, centered and supported only by the tapered ends of the ends, implies that its axially middle part is significantly thicker than the edges. Contrary to this, a thick ferrule can keep an almost constant thickness over its entire length; the shape of its section through a radial plane is generally continuous over its entire length, that is to say that it has only slight variations in thickness from one edge to the other, and therefore that the deformations inevitable that it undergoes during casting remain homogeneous over its entire width.

Another advantage of using thick ferrules is that they can be made, in their thickness, of several layers of different materials. For example, the material of the outer layer, in contact with the cast metal, can be particularly suitable for ensuring rapid solidification of the cast metal in contact with it, and the material of the inner layer being more suitable for ensuring the overall mechanical strength. of the shell.

The invention therefore aims to ensure the concentricity of such a ferrule and the hub both hot and cold, and despite the inevitable deformations due to expansion, to obtain a strip of quality metal, with perfect regularity of thickness and longitudinal profile. It also aims to facilitate the manufacture of the shell and to ensure better sealing of the coolant circuits at the interface between the flanges and the shell.

With these objectives in view, the invention relates to a casting cylinder for a continuous metal casting installation on one or between two such cylinders, this cylinder comprising a hub and a ferrule arranged coaxially, and two flanges for support and radial centering of the ferrule on the hub, characterized in that each flange has a frustoconical part which cooperates with a corresponding frustoconical surface of the bore of the ferrule, said frustoconical surface being located in an area where the variations in internal diameter of the shell due to expansion deformations are substantially zero.

The radial centering of the ferrule on the flanges is therefore ensured by these frustoconical surfaces. As the latter are located in an area where the variations in internal diameter of the ferrule, due to expansion deformations, are substantially zero, centering is therefore always ensured by the same ferrule-flange contact zones which remain more or less fixed in position, even when the shell is thermally deformed, and define the position references of the shell which are the same when cold and when hot. And as the centering of the flanges on the hub is also ensured, and not liable to be disturbed by thermal deformations since it is carried out in an area of the cylinder where the temperature is substantially constant, it follows that the concentricity of the ferrule relative to the cylinder shaft is permanently ensured, whatever the temperature variations of the shell.

The axial position of the points where the variations in internal diameter of the shell due to the deformations of dilation thereof are substantially zero can be determined by calculation models or experimentally. We can thus determine the deformation of the shell as a function of the parameters of construction and use of the cylinder. This deformation of the shell is illustrated, intentionally exaggerated, in Figure 3 of the accompanying drawings. In this figure has been schematically and partially shown the ferrule 3 in section by a radial plane of the cylinder. The dashed line represents the shape of the cold shell, the mark 31 'designating the exterior surface of the shell, and the mark 31 "designating its internal surface, the generator of which has been here, for the sake of simplification of the drawing, represented by a simple straight line. The solid line represents the hot shell, deformed under the effect of thermal expansion. Note that a first effect of the heating of the shell is a radial expansion, leading to an increase in the diameter of the shell, illustrated by arrow F _1. If the temperature of the shell, when hot, was homogeneous, this radial expansion would be practically the only observable effect, with a purely axial expansion. But in practice, during casting, the outer surface layer of the shell heats up much more strongly, in contact with the cast metal, than the interior of the shell which remains at low temperature due to the intense cooling i internal to which it is subjected, resulting in differential expansion which causes an elongation, in the axial direction, of the outer layer of the shell, greater than that of the inner layer. This differential expansion therefore results in a bending deformation of the ferrule, illustrated by the arrow F ₂ in FIG. 3, which tends to bring the edge of the ferrule towards the axis of the cylinder. For equivalent heat exchange conditions, this deformation is all the smaller when the shell is thick under the cooling channels, since this thick and cold part prevents the deformation of the area located above the channels. For a thick ferrule, this deformation leads to the internal diameter of the ferrule on its edges becoming less than its cold diameter, the generatrix of the internal surface of the ferrule thus deformed cutting the line of this cold generatrix at a point AT.

Thus it is noted that there is a point, or a zone of small dimension, where the variations in diameter of the shell, resulting from the combination of the effects of radial expansion and axial differential expansion, are substantially zero, the bending compensating for the increase in diameter, and where, consequently, the section also remains practically cylindrical. It is more particularly in this zone that, in accordance with the invention, a frustoconical surface which bears on the corresponding frustoconical parts of the flanges is arranged in the bore of the ferrule.

The distance between these zones of substantially constant diameter made on each side of the shell (in the axial direction), may however vary slightly between the cold and hot states of the shell, due to the overall expansion of the shell in the axial direction . This is why, preferably, the flanges are slidably mounted on the hub, and the cylinder comprises elastic means for bringing the two flanges together towards one another.

According to a preferred arrangement, intended to ensure the axial positioning of the ferrule on the hub while leaving the flanges the possibility of moving slightly axially, the cylinder comprises means of axial abutment of the ferrule on the hub, located in a plane substantially axially median of the cylinder, and pressure means for exerting an axial force on said abutment means, while leaving the ferrule the possibility of expanding radially, without modifying its axial positioning defined by said stop.

According to another preferred arrangement, the internal surface of the ferrule comprises at least one cylindrical bore adjacent and coaxial to each frustoconical surface, each flange comprises a cylindrical part placed in this bore, and channels for supplying cooling fluid to the ferrule are made in the flange and in the shell at the level of said cylindrical part.

Said cylindrical bore can be produced between the frustoconical surface and the edge of the shell. In this case, a radial clearance is provided, when cold, between the cylindrical bore and the corresponding cylindrical part of the flanges, to allow the reduction in hot diameter, explained above, of the edges of the ferrule, deformable joints ensuring the sealing between the flanges channels and those of the ferrule.

According to another arrangement, said bore can also be produced towards the middle of the cylinder, that is to say opposite, with respect to the frustoconical surface, of the preceding arrangement.

According to yet another arrangement, such cylindrical bores and corresponding cylindrical parts of the flanges, can be produced on either side of the conical bearing, the radial clearance, on the side outside the conical part, being preserved. this game allows on the one hand not to add constraints of hooping of the ferrule and, on the other hand, authorizes a modification of the convex by playing on the cooling or the conditions of heat exchange between the steel in the mold and the ferrules.

Whatever the embodiment chosen from the three preceding arrangements, an advantage resulting from the situation of said channels at the level of the bores cylindrical and cylindrical parts of the flanges is that the seal between flanges and ferrule is more easily achievable, and more reliable, than if these channels passed, as provided in the document FR-A-2711561 already cited, at a surface of conical bearing.

Other characteristics and advantages will appear in the description which will be given of a cylinder of a continuous casting installation between two such cylinders of thin steel products.

• la figure 1 est une vue en demi coupe radiale d'un cylindre conforme à l'invention,
• la figure 2 est une vue d'un bord d'un cylindre dans une variante de réalisation,
• la figure 3 représente schématiquement les déformations de dilatation de la virole, comme cela a déjà été expliqué précédemment.

Reference is made to the appended drawings in which:

• FIG. 1 is a view in radial half-section of a cylinder according to the invention,
• FIG. 2 is a view of an edge of a cylinder in an alternative embodiment,
• Figure 3 schematically shows the expansion deformations of the shell, as already explained above.

• un arbre 1 relié à un mécanisme d'entraînement en rotation, non représenté,
• un moyeu 2 lié rigidement à l'arbre 1, par exemple par frettage et/ou clavetage, et usiné après montage sur l'arbre, coaxialement à celui-ci,
• une virole 3, coaxiale au moyeu 2, et qui constitue un élément démontable et interchangeable du cylindre,
• des moyens de liaison axiale de la virole sur le moyeu, comportant des moyens 4 de butée axiale,
• deux flasques 5, 6 assurant le support et le centrage de la virole 3 sur le moyeu 2.

The casting cylinder, shown in Figure 1, includes:

• a shaft 1 connected to a rotary drive mechanism, not shown,
• a hub 2 rigidly connected to the shaft 1, for example by shrinking and / or keying, and machined after mounting on the shaft, coaxially with the latter,
• a ferrule 3, coaxial with the hub 2, and which constitutes a removable and interchangeable element of the cylinder,
• means of axial connection of the ferrule on the hub, comprising means 4 of axial stop,
• two flanges 5, 6 providing support and centering of the ferrule 3 on the hub 2.

The rotational connection of the ferrule on the hub is ensured, as will be seen below, on the one hand, by the flanges 5, 6 and their assembly means and, on the other hand, by the means 4 axial stop and pressure means on this stop.

The ferrule 3 consists of two coaxial layers 37, 38 made of different materials, the outer layer 37 being made of a material which is a good conductor of heat, such as copper or a copper alloy, and the inner layer 38 being made of a material of greater mechanical resistance, for example stainless steel SUS 304. It comprises, near its external surface 31, cooling channels 32 connected at their ends to channels 7, 8 supply and return d 'cooling water .

The hub 2 has a middle part 21 of larger diameter than its axial end parts 22, 23. The middle part 21 of the hub 2 has a shoulder 24, located in a plane P substantially median of the cylinder, and orthogonal to its axis .

The ferrule 3 has, inside, a corresponding shoulder 33, and therefore also located in the plane P.

The centering, in the direction of the axis, of the ferrule 3 on the hub 2 is ensured by pressing the shoulder 33 of the ferrule on the shoulder 24 of the hub, which precisely defines the positioning of the ferrule relative to to the hub and therefore relative to the entire casting installation. The symmetry of position of the ferrule relative to the median plane of the cylinder is thus ensured and preserved even when the ferrule expands axially during casting, the axial displacements of the edges of the ferrule, caused by this expansion, taking place in a manner symmetrical with respect to said median plane.

It will be noted that, due to said radial expansion of the shell during casting, the internal diameter of the latter, in its median part, increases, as has been explained in relation to FIG. 3, and the radial centering of the ferrule cannot therefore be ensured by the middle part 21 of the hub which remains cold, the diameter of which practically does not vary, and which, during cold mounting, has a certain diametral clearance relative to the ferrule.

This radial centering is ensured by the two flanges 5, 6, centered on the end parts 22, 23 of the hub and being able to slide slightly, practically without play, thereon. Each flange has a frustoconical part 51, 61 which cooperates with the surface of a bore 34, 35 of also frustoconical shape with the same conicity, produced inside the ferrule 3, in an area where the variations in internal diameter of the ferrule, due to the expansion deformations thereof, are substantially zero, as explained above.

The flanges 5, 6 are pulled towards each other by elastic approximation means, acting in the axial direction of the cylinder to press the frustoconical parts 51, 61 of the flanges against the frustoconical bores 34, 35 of the ferrule, so as to ensure its centering and its support. It should be noted that the radial centering of the ferrule on the hub is ensured only by the conical ferrule-flange bearing surfaces, which makes it possible to keep this centering even when the middle part of the ferrule moves away from the hub when hot , under the effect of the thermal expansion, as indicated above.

The means for resiliently bringing the flanges towards one another may consist of means for pulling the flanges towards the central part 21 of the hub, acting independently on each flange.

Preferably, as shown in FIG. 1, these approximation means comprise means for elastic connection of the flanges to each other, constituted by a system of tie rods 71 distributed circumferentially, which connect the flanges by passing freely through bores drilled in the middle part 21 of the hub. These tie rods 71 pass through corresponding holes in the flanges 5, 6 and carry adjustment nuts 73 at their ends.

Elastic elements, such as for example elastic washers 74, are placed between the nut 73 and the flange 6, so as to exert a pulling force on the flanges towards one another while allowing their spacing. The tensile force is adjusted, by the nuts 73, so as to apply the flanges against the conical bores of the ferrule with sufficient force to support the spacing force undergone by the cylinders during casting without risking that effort does not cause, because of the tapered surfaces, a separation of the flanges and a retraction of the ferrule towards the axis of the cylinder, and to prevent sliding in rotation, while allowing a slight sliding in the axial direction, when , when hot, the distance between the tapered bores varies as a result of the axial and radial expansion of the ferrule.

The centering of the flanges 5, 6 on the parts 22, 23 of the axial end of the hub 2 is ensured by sliding resin injected into zones 26 arranged for this purpose between the flanges and the hub, or by other means such as bearings or oil seal making it possible to minimize the clearance between hub and flange, for example of the order of 0.05 mm on the diameter, while retaining good qualities of axial sliding of the flanges on the hub, to avoid seizures and subsequent disturbances in the movements of the flanges.

To ensure the transmission of the rotational drive torque between the hub and the flanges, it is possible to use a rotation connection system of known type, not shown, for example keys or other rotation connection means ensuring continuity of the passage of the couple while allowing freedom of translation in the direction axial.

Thus, the transmission of the drive torque from the hub to the ferrule is ensured by this connection system between the hub and the flanges, and by friction between the flanges and the ferrule.

The transmission of the torque by the means indicated above is preferably supplemented by a friction drive at the shoulders of the hub 24 and of the ferrule 33.

To this end, the cylinder includes pressure means for pressing the shoulder 33 of the ferrule on the shoulder 24 of the hub. These means comprise an elastic flange 80 fixed on the hub 2 and pressing on the ferrule by means of one or more spacers 81. This spacer can be a continuous ring placed between the ferrule 3 and the central part 21 of the hub 2, or else be segmented and thus form a plurality of independent push-pieces in the form of tiles placed in longitudinal grooves produced at the interface between ferrule and hub, as indicated in the document FR-A-2711561 already cited.

This ring or these thrust parts are pressed against a second shoulder 36 of the ferrule, arranged near the shoulder 33 and opposite to it. These provisions make it possible to give the ferrule a continuous shape of regular section over its entire width, which makes it possible to minimize its hot deformations by making them symmetrical with respect to the median plane P.

The taper angle of the tapered seats is large enough to avoid any risk of jamming of the flanges in the ferrule. Furthermore, the length of the conical surfaces in contact is small so that the difference in internal diameter of the shell on either side of each frustoconical surface 34, 35 is also small and therefore the thickness of the shell varies only very little over its entire width. the length of Conical surfaces in contact is however sufficient to provide a sufficient contact area to withstand the efforts of spacing of the cylinders generated by the cast metal.

The location, in the axial direction, of the frustoconical surfaces 34, 35 is determined experimentally and / or by a calculation model which makes it possible, in a manner known per se, to determine the deformation of the hot shell as a function of its geometry, of the nature of the material or materials that compose it, and parameters such as the water flow in the cooling channels, the heat exchange coefficients, etc. One can then determine the point or the zone of the profile of the interior surface of the ferrule where the radial dilations compensate for the bending deformations.

By way of example, for an overall water flow rate in all the channels of the shell of 400 m ³ / h, the shell having a width of 1300 mm, and with an average extracted heat flow of 8 MW / m ² , this point is calculated at 560 mm from the median plane of the cylinder.

• minimisation des mouvements relatifs entre flasques et virole, obtenue en situant ces portées au plus près de la zone où la déformation de bombé (flexion de la section radiale) de la virole compense sa dilatation radiale,
• minimisation de la déformation de la virole sous l'effet des efforts axiaux exercés sur celle-ci par les flasques,
• stabilité de la position des flasques sous les efforts exercés en cours de coulée par le produit coulé sur la virole et retransmis aux flasques via les dites portées coniques, en jouant sur l'angle de conicité pour que la résultante des actions de la virole sur les flasques passe entre les zones 26 de portée de chaque flasque sur le moyeu 2.

The position of the conical bearing surfaces thus determined can be corrected to take account of the other forces exerted on the shell and its support and centering means, and will then result from a compromise between the following objectives:

• minimization of the relative movements between the flanges and the ferrule, obtained by locating these spans as close as possible to the zone where the bulging deformation (bending of the radial section) of the ferrule compensates for its radial expansion,
• minimization of the deformation of the shell under the effect of the axial forces exerted on it by the flanges,
• stability of the position of the flanges under the forces exerted during casting by the cast product on the ferrule and retransmitted to the flanges via the said conical surfaces, by playing on the angle of conicity so that the result of the actions of the ferrule on the flanges passes between the zones 26 of range of each flange on the hub 2.

In the example shown in Figure 1, each flange 56, comprises, on the side of the larger diameter of the frustoconical part 51, 61, a cylindrical part 52, 62 which is located in a cylindrical bore 39.40 produced in the ferrule between the frustoconical surface 34, 35 and the edges of said shell. A radial clearance, of the order of 0.6 to 0.8 mm when cold is provided between said cylindrical parts of the flanges and the corresponding bores of the ferrule, to allow the reduction, explained above, of the diameter of the edges of the hot shell.

The cooling water supply and return channels 7, 8 open onto the inner surface of the shell in the said cylindrical bore, where they communicate with respective channels 53, 54 made in the flanges, which communicate with each other. same with main channels 27, 28 arranged in the hub. Seals 55 seal these channels at the interface between the cylindrical part of the flange and the corresponding cylindrical bore of the ferrule.

In the variant shown in FIG. 2, the cylindrical part 52 ′ of the flange 5 and the corresponding cylindrical bore 39 ′ of the shell, at the level of which the channels 7, 8, 53, 54 pass, are located on the other side of the frustoconical bearing zone, that is to say on the side of the smallest diameter thereof. In the area between the conical bearing surface and the edge of the ferrule, the latter also comprises a cylindrical bore in which is housed a second cylindrical part 55 of the flange, with minimal clearance allowing the deformation of the ferrule already explained, this clearance can however be in this variant more important.

Whatever the embodiment, the communication of the respective channels of the ferrule and the flange at a cylindrical interface makes it possible to facilitate the corresponding machining operations and to ensure a better seal at this interface.

The flanges 5, 6 are preferably made of a material having a coefficient of expansion equal to or close to that of the material of the hub, which guarantees the centering of the flanges on the hub, even when these parts undergo temperature variations which, even if they remain weak, are in practice inevitable.

On the other hand, the frustoconical part of the flange will be made, or will include a coating layer, in a material with a low coefficient of friction, to facilitate its sliding against the frustoconical surface of the ferrule, during micro-displacements which can nevertheless occur between these surfaces.

Claims (11)

Casting cylinder for a continuous metal casting installation on one or between two such cylinders, this cylinder comprising a hub (2) and a ferrule (3) arranged coaxially, and two flanges (5, 6) for support and radial centering ferrule on the hub,
characterized in that each flange has a frustoconical part (51, 61) which cooperates with a frustoconical surface (34, 35) corresponding to the bore of the ferrule, said frustoconical surface being located in an area (A) where the variations internal diameter of the shell due to expansion deformations are substantially zero. Cylinder according to claim 1, characterized in that the cylinder comprises elastic means (71, 74) for bringing the two flanges together towards one another. Cylinder according to claim 1 characterized in that it comprises means (24, 33) for axial abutment of the ferrule on the hub, located in a substantially axially median plane of the cylinder, and pressure means (80, 81) for exert an axial force on said abutment means. Cylinder according to claim 1, characterized in that the internal surface of the ferrule comprises, at least one cylindrical bore (39, 40, 39 ') adjacent and coaxial to each frustoconical surface (34, 35), each flange (5, 6 ) has a cylindrical part (52, 62, 62 ') placed in this bore, and channels (7, 8; 53, 54) for supplying the coolant for the ferrule are made in the flange and in the ferrule at level of said cylindrical part. Cylinder according to Claim 4, characterized in that the said cylindrical bore (39, 40) is produced between the frustoconical surface (34, 35) and the edge of the ferrule. Cylinder according to Claim 4, characterized in that the said cylindrical bore (39 ') is produced towards the middle of the cylinder with respect to the frustoconical surface (34). Cylinder according to claim 4, characterized in that cylindrical bores and corresponding cylindrical parts of the flanges are produced on either side of each conical part. Cylinder according to claim 1, characterized in that the ferrule (3) comprises two coaxial layers (37, 38) made of different materials. Cylinder according to claim 8, characterized in that cooling channels (32) are formed in an external layer (37) of the shell. Cylinder according to claim 1 characterized in that each flange (5, 6) is made essentially of a material having a coefficient of expansion substantially equal to that of the material of the hub (2). Cylinder according to one of claims 1 or 10, characterized in that the frustoconical part (51, 61) of each flange is made, at least on the surface, of a material promoting sliding.

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