EP0286533B1 - Metal strip or sheet-rolling method and installation - Google Patents

Description

For the rolling of metal products in strip form, rolling mill trains are used, each of which consists of a cage comprising two spaced apart support columns connected by crosspieces and between which is mounted a set of superimposed rollers whose axes are parallel and placed in the same plane. Each cylinder is rotatably mounted around a shaft carried at its two ends by support members housed respectively in the two columns of the cage.

Rolling mills of different types can be produced. The so-called "quarto" rolling mills have four rolls, respectively two working rolls between which the rolled product passes and bearing on the side opposite the product, each on a support roll. One can also consider other arrangements, for example passing the strip between a working cylinder and a counter-cylinder bearing on the cage, the working cylinder being applied, on the opposite side, against a bearing cylinder on which is exerted the clamping force. The "sexto" type rolling mills, on the contrary, include intermediate rolls interposed between the support rolls and the working rolls.

The cylinders bear on each other along substantially parallel bearing lines and directed along a generator whose profile, normally rectilinear, depends on the applied forces and the resistance of the cylinder. Generally, the tightening force is applied by screws or jacks interposed between the cage and the ends of the shaft of the upper support cylinder, the lower support cylinder, or counter-cylinder bearing directly on the cage. . Apart from the latter, the other cylinders must therefore be able to move slightly relative to the cage and they are therefore carried by support members mounted to slide vertically inside the corresponding columns of the cage.

Since the clamping force is applied to the two ends of the upper support cylinder and the laminated product, of variable width, does not cover the entire length of the working rolls, each cylinder can bend under the action of the applied forces and this results in a variation in thickness of the passage space of the strip between the working rolls, the edges of the strip thus being able to be thinner than the central part.

For a long time, attempts have been made to correct these thickness defects on the cross section of the rolled product and various means have been used for this purpose.

In particular, it has been proposed to use support cylinders having a slightly domed external profile capable of compensating for the deflection of the cylinder under the action of the clamping force so that the generator contacting the corresponding working cylinder is substantially straight. However, this profile can only be determined as a function of an average rolling force.

The possibilities of correction are increased by using cylinders with variable bulging comprising a central shaft on which is threaded a deformable cylindrical casing whose profile can be determined by application of thrust forces between the shaft and the casing to compensate for the deflection of the shaft as a function of the rolling force.

In a known embodiment, the central shaft, which is rotatably mounted around its axis, is provided by its periphery with a recess closed towards the outside by the deformable casing, the latter being connected to the shaft sealingly at both ends so as to constitute a closed annular space into which a fluid is introduced under an adjustable pressure.

It is thus possible, by inflation of the envelope, to vary the profile thereof.

In another known embodiment used in particular in the paper industry, the peripheral wall of the support cylinder is constituted by a tubular envelope rotatably mounted around two bearings on the central shaft, the latter being fixed in rotation and forming a support beam on which bear a plurality of envelope holding pads distributed along a support generatrix, and extending radially between the support beam and the internal face of the envelope with interposition of a lubricating film allowing the rotation of the envelope. Each pad rests on the support beam by means of at least one jack making it possible to individually adjust the radial position of the pad as a function of the profile to be given to the support line in order to correct the defects in thickness and flatness. of the strip measured downstream of the rolling mill by known devices. It is thus possible to distribute the corrections over the width of the strip so as to quickly correct localized thickness or flatness defects.

Since the purpose of rolling is to produce flat products with a thickness as constant as possible, it makes sense to use symmetrical installations comprising, on each side of the product, a variable crown cylinder whose profile is adjusted to compensate for the deflection of the shaft so that the support line on the corresponding working cylinder is as straight as possible. However, this sag cannot always be fully compensated and, in addition, the working rolls, which generally have a small diameter, may tend to ovalize under the action of the forces applied. This is why, it has also been proposed to complete the correction of the profile of the support cylinders by a cambering effect of the working cylinders obtained by application of bending forces on the two ends of the shaft of each cylinder.

Each working cylinder is in fact carried at its ends by bearings housed in chocks slidably mounted in the corresponding columns of the cage, and the relative positioning of which can be adjusted by means of hydraulic jacks exerting thrust forces in opposite directions. on ears attached to each chock. One can thus achieve a so-called "positive" bending by tightening the chocks of the two working rolls, to compensate for an excess thickness of the edges of the product or else a so-called negative bending by spacing the chocks of the two working cylinders to compensate for an excess thickness of the part central product.

The invention therefore applies preferably but not limited to a rolling mill of the quarto type comprising, inside a support cage, four cylinders with parallel axis and superimposed along a clamping plane, rotatably mounted each around a shaft carried at its two ends by support members housed in the columns of the cage, respectively two working cylinders providing between them an elongated space for the passage of the product and bearing each on the opposite side on a cylinder d '' support of which at least one is of the variable crown type comprising a cylindrical envelope rotatably mounted on a central shaft and means for adjusting the profile of the envelope by applying thrust forces between the central shaft and the wall internal of the casing, the clamping force being applied to the ends of the shaft of the support cylinder and the working cylinders being associated with bending means by applying force bending ts on the ends of their shafts. EP-A-0 140 776, on which the preambles of claims 1 and 5 are based, describes a laminior of this type.

Until now, in order to achieve, under the best possible conditions, a control of the flatness and the regularity of thickness of the laminated product, it seemed normal to use symmetrical installations comprising in particular two support cylinders with variable bulging. However, such devices are expensive and use delicate components liable to deteriorate, which significantly increases the cost of production and operation of the rolling mill.

The subject of the invention is a method and an installation for implementing the method, making it possible to optimally correct defects in thickness and flatness of the product and capable of being implemented in a more simple and less expensive, each rolling mill stand being in fact equipped with a single support cylinder with variable bulging, the other support cylinder being a solid counter-cylinder bearing directly on the cage by the ends of its shaft of rotation and being able to deform freely under the action of the clamping force by forming a concave support line towards the product.

The method according to the preamble of claim 1 is characterized in accordance with the invention, in that, the cage being equipped with means for bending the two working cylinders by applying bending forces to the ends of the shaft of each cylinder, the profile of the deformable envelope of the cylinder with variable bulge is adjusted so as to form a convex support line towards the product and substantially parallel to the support line of the counter-cylinder and the camber is adjusted individually of each working cylinder so as to maintain constant the thickness of the rolling space over the entire width of the product, by applying to the ends of the shafts of each working cylinder bending forces whose direction and intensity are individually adjusted for each end of each cylinder by resting directly on the column of the cage, the product having, at the exit of the cage, a curved cross section capable of being subsequently rectified by known means.

Preferably, the bending of the two working cylinders is carried out by application of thrust forces in one direction or the other on the support members of their shafts and the position of each is adjusted separately. support member of each working cylinder to keep the thickness of the rolling space constant. To this end, the support members of the working cylinders being constituted by chocks mounted sliding along the corresponding columns of the cage and on which bear camber cylinders, according to another essential characteristic, the camber cylinders are associated by groups independent of each other and corresponding respectively to each chock of each working cylinder, each group of jacks bearing directly on the corresponding column of the cage and being associated with a separate control means for the individual adjustment of the effort of camber applied on each end of each cylinder.

According to another preferred characteristic, the adjustment of the external profile of the support cylinder and of the camber of the working cylinders is carried out automatically by referring to a model taking into account the dimensional and resistance characteristics of the various organs and of the product and capable of determine the corrections to be made to the profile of the deformable envelope and to the position of each support member from thickness and flatness measurements made on the strip downstream of the rolling mill, so as to keep the thickness of the film constant 'passage space of the strip over the entire width thereof.

To this end, according to another characteristic of the invention, the shape of the support line of each working cylinder on the product is determined from the measurements made downstream and according to the forces applied and the corrections to be made to the profile of the support cylinder and to the camber of the working cylinders by comparing the profiles of the support lines to keep them parallel to one another and spaced apart by a constant distance corresponding to the thickness to be given to the product .

However, the invention will be better understood from the detailed description of a particular embodiment, given by way of example and shown in the accompanying drawings.

Fig. 1 is a schematic overview of the rolling mill stand and its regulation system.

Fig. 2 is a schematic view of rolling mill in section through a plane transverse to the axes of the rolls.

Fig. 3 is a front view of a particular embodiment.

Fig. 4 is a detailed view, in cross section, of the bending means.

In FIGS. 1 and 2, a quarto-type rolling mill is schematically represented comprising a set of four superimposed rolls with parallel axes placed in a vertical clamping plane P, respectively two working rolls 1 and 2 framed by two support rolls , respectively upper 3 and lower 4 and between which a strip product passes 5. The assembly is conventionally placed inside a rolling stand 6 comprising two vertical columns 61. As can be seen in FIG. 1 , each cylinder 1, 2, 3, 4 is rotatably mounted around a shaft, respectively 11, 21, 31, 41 the ends of which are carried by support members 12, 22, 32, 42 housed in windows 62 provided in the two columns 61 of cage 6.

These provisions are well known and do not require any particular explanation. Generally, the tightening force is applied by screws or jacks 63 to the two ends of the shaft 31 of the upper support cylinder 3 and is collected by the lower support cylinder 4 whose shaft 41 is supported its two ends, directly on the cage 6, the product 5 thus being clamped between the two working cylinders 1 and 2 along contact generators 13, 23 each defining a line support.

It is understood that, if the rollers were perfectly rigid, the two support lines 13 and 23 would be rectilinear and parallel, the rolled product 5 being perfectly flat and of constant thickness. However, it is obviously impossible to avoid the bending of the various cylinders under the applied forces, all the more so since the width (l) of the product is less than the length (L) of the support cylinders and that, as a result, the product n 'exerts a reaction on the working rolls only in the central part of these, the ends remaining free and therefore being able to come together, which leads to a thinning of the edges of the product.

On the other hand, as the clamping force is applied to the two ends of the shaft 31 of the support cylinder 3 and the counter-cylinder 4 receiving the force bears on the cage by the ends of its shaft 41 , the trees tend to flex as shown, exaggeratedly, in Figure 1, which, in a full cylinder causes a corresponding deformation of the cylinder casing.

To compensate for this inevitable deflection of the shaft, according to an already well-known arrangement, the upper support cylinder 3 is a cylinder with variable crowning and, more precisely, with a deformable envelope. It in fact comprises a tubular cylindrical casing 33 rotatably mounted around the shaft 31 and bearing, moreover on the latter, by means of a series of retaining pads 34 each associated with a thrust cylinder 35 supplied by a hydraulic circuit which passes through a bore 36 formed along the shaft 31. Preferably, the jacks 35 are supplied separately and under individually adjustable pressures so as to be able to precisely adjust the profile of the casing 33 and in particular of the support line 37 on the working cylinder 1. Generally, the installations of this type are symmetrical the two support cylinders being with deformable envelope. On the contrary in the installation according to the invention, the lower support cylinder 4 is a full cylinder consequently constitute a simple counter-cylinder for absorbing the pressure transmitted by the working cylinder 2.

Each working cylinder 1 or 2 also consists of a full cylinder of fairly small diameter, rotatably mounted around a shaft whose ends 11, 21 are carried by bearings mounted in chocks 7 housed in the corresponding windows 62 of the cage 6b and mounted sliding in the direction of the clamping plane P passing through the axes of the cylinders.

To this end, as shown in detail in Figure 4, each chock 7 is provided with vertical guide faces 71 sliding along slides 72 formed on support pieces 73 fixed on the columns 61 of the cage 6 and in which are housed sets of hydraulic cylinders (8) (FIG. 2) bearing, in both directions, on the chocks 7 in order to adjust the position thereof along the slides 72.

According to a fairly conventional arrangement, each chock 7 is provided, on either side of the plane of symmetry P, with two ears 74 and associated with two pairs of jacks, respectively upper 81 and lower 82, the bodies of which are mounted in the support parts 73 and whose rods bear in opposite directions on the two horizontal faces of the ears 74. In this way, by putting under pressure one or the other of the two pairs of jacks 81, it is possible to move each chock 7 for, respectively, removing it or bringing it closer to the horizontal plane Pʹ of passage of the product 5 between the cylinders 1 and 2.

It is understood that, if each working cylinder 1 or 2 is allowed to flex freely under the action of the forces applied in one direction by the product 5 and in the other by the corresponding support cylinder, the chocks 7 of said cylinder 1 (2) will assume, inside the windows 62 of the cage, an equilibrium position which depends on the profile of the support cylinder and the distribution of pressures on the product 5. On the other hand, by acting on one or the other of the pairs of jacks 81, 82, the working cylinder 1 (2) is bent in one direction or the other which modifies the profile of the support line 13 (23) and therefore the distribution of pressures on the product 5.

Usually, it is said that a positive bending is carried out when the chocks 7 are removed from the plane Pʹ of the product 5 by increasing the pressure in the central part of the product and a negative bending when the chocks 7 are brought closer to the plane Pʹ of product 5 by increasing the pressure on the edges of the product.

To check the regularity of thickness and flatness of the strip 5 after rolling, various known means can be used, for example using a flatness measuring roller 51 placed downstream of the cage 6 and on which the strip runs while being subject to some tension. Measuring members placed along the roller 51 make it possible to detect the variations along its width of the force applied by the strip and to deduce therefrom the flatness defects. Another measuring device 52 makes it possible to measure the thickness of the strip and, optionally, to check the regularity of the latter over the width.

There are several known systems for measuring the flatness and the thickness of the laminated strip; a flatness measuring roller is described in detail, for example, in patent FR 2,538,537 from the same company.

In Figure 1, there is shown in an exaggerated manner the deformations of the cylinders.

In general, the clamping force is applied to the upper support cylinder 3, transmitted to the product 5 and collected by the lower support cylinder 4.

Since the forces are applied to the ends of the shafts 31 and 41 of the two support cylinders, the latter tend to bend, their axes taking a curved shape turning its concavity towards the product. It is therefore natural to use a symmetrical cage comprising two support cylinders with variable bulging so that the deformation of the envelope compensates for the bending of the shaft and that each support cylinder has a support line as much as possible straight for the corresponding working cylinder.

In the installation according to the invention, on the contrary, an asymmetrical support cage is used comprising a single support cylinder with a deformable envelope, normally the upper support cylinder 3 on which the clamping forces are applied, the cylinder lower support 4 being a simple full cylinder which is allowed to flex freely under the action of the forces applied.

According to a first characteristic of the invention, instead of simply compensating for the deflection of the shaft 31 of the upper cylinder so that the support line 37 is substantially rectilinear, the bulging of the casing 33 will be further increased so that the support line 37 is convex towards the product 5 and preferably has a curvature substantially equal to that of the support line 47 of the lower cylinder 5 which results from the free bending of the latter.

Therefore, the two working cylinders 1 and 2 also take a curved shape, the support lines 13 and 23 being substantially parallel and concave upwards.

It follows that, instead of making a product as flat as possible, we will on the contrary accept that the product 5 has at the outlet of the rolling mill, a curved shape. Admittedly, it is quite surprising to deliberately regulate the rolling process to produce a curved product, but, in fact this curvature of the product at the outlet of the rolling mill does not present any significant drawback since it has been known for a long time to correct such defects after rolling by known devices known as "anti-tiles".

On the other hand, the fact that the product has a curved cross section does not hinder in any way the correction of the flatness and thickness defects which can be done in particular by playing on the bending forces applied on the two working rolls 1 and 2 .

However, in the arrangements known up to now, one acted symmetrically on the two working rolls by spreading their chocks from one another for a positive bending or by bringing them together for a negative bending. In the process according to the invention, on the contrary, the two working rolls which are undergoing are acted on separately, one a positive bending and the other a negative bending to adapt to the shape of the lower support cylinder. As a result, the cambering system 8 is different from those which were usually used and which were supported in opposite directions on the chocks of the two working rolls.

The bending system 8 is shown in detail in Figures 3 and 4. As can be seen, the sets of cylinders 81, 82, 81ʹ, 82ʹ acting respectively on the cylinders 1 and 2 are mounted in the guide parts 73 but separated one another. Indeed, for technological reasons, the bodies of the positive cambering cylinders 82, 82ʹ consist of the same part 83 incorporated in the support part 73, but the chambers of the cylinders are separated from one another by a partition 84 and supplied separately and under individually adjustable pressures, which allows the two cylinders 82, 82ʹ for positioning chocks 7, 7ʹ to be adjusted independently of each other, each cylinder bearing directly on the column 61 of the rolling mill , via the support piece 73.

Thanks to these provisions, one can, on the one hand adjust the profile of the support line 37 of the upper support cylinder 3 to make it substantially parallel to the support line 47 of the lower cylinder 4 and on the other hand , separately check the bending of the working rolls 1 and 2, so as to produce a curved product but of constant thickness, the regularity of this can be corrected at any time according to the thickness and flatness measurements made in downstream.

To adjust the profile of the upper support cylinder and the camber of the working cylinders, various known regulation systems can be used. Such a system is in particular described in detail in patent FR 83.16341 filed on October 14, 1983 by the same company.

The product 5 therefore emerges curved from the rolling mill and is straightened in a device of the "anti-tile" type 53 which does not require a detailed description, such devices being well known.

An installation for implementing the method has been shown, for example, schematically in FIG. 1.

This figure shows symbolically the stand 1 of the rolling mill with its four cylinders, the clamping cylinders 63 and the means 8 for applying bending forces to the shafts 11, 21, of the working rolls 1 as well that means 51 for checking the flatness and 52 for measuring the thickness, represented in front of the cage 6.

The actions of these different organs are commanded and controlled by a regulation system 9 associated with a model 90, preferably a mathematical model.

The bending of the shaft 31 under the effect of the clamping cylinders 63 is measured by displacement sensors 38 placed at its ends.

The pressures in the different control cylinders pads 34 are determined individually by a hydraulic control assembly 39.

Each bending device 8 exerting a bending force on one end of the shaft of a working cylinder 1 or 2 is associated with a sensor 75 providing a signal representative of the position of the corresponding chocks 7 and with a hydraulic assembly 85 of adjustment of the forces exerted in one direction or the other by the groups of jacks 81 or 82.

These various measurement devices emit signals representative, respectively, of the clamping force applied by the jacks 63, of the deformation of the central shaft 31 of the upper support cylinder 3, of the positive or negative bending of the working cylinders 1 and 2, and of the thickness of the sheet which are applied to the various inputs 91, 92, 93, 94 of the regulation system 9.

The mathematical model 90, in which all the structural and dimensional characteristics of the cage and the cylinders as well as of the rolled product have been introduced determine, depending on the tightening force applied by the jacks 63 and the product characteristics, the profile of the support line 47 of the lower cylinder 4 and the pressures to be applied to the pads 34 by means of the hydraulic control member 39 so that the support line 37 of the upper cylinder 3 has a shape convex towards the strip and of the same curvature as the support line 47, according to the regulation process described in patent FR 83 16341 already cited.

It is possible, in the same way to determine the equilibrium positions, that is to say without bending effort, chocks 7 of the two working cylinders 1 and 2, corresponding to this curvature of the support lines 37 and 47 of the support cylinders 3 and 4. In addition, the flatness defects detected, during operation, by the control device 51 are also transformed into signals applied to an input 95 of the regulation system 9 which, via the hydraulic assembly 39, determines the forces which must be applied by the various holding pads 34 to consequently correct the profile of the support line 37 The regulation system 9, with reference to the indications contained in the mathematical model 90 then determines the profile of the support lines 13 and 23 of the two support cylinders resulting from the different forces applied over the width of the sheet and which can be materialized in different ways, for example digitally or analogically on a screen 96 associated with the regulator 9. It is thus possible to detect a lack of parallelism between the support lines 13 and 23 of the two working cylinders 1 and 2 where it would result in a variation in thickness of the product over its width and to individually make the desired corrections to the various cambering devices 8 agissan t separately on the ends of the shafts of the two working rollers. These corrections can be made manually by an operator or else automatically, by comparing the shape of the support lines 13 and 23 determined by the mathematical model 90 or else by varying their spacing over the length of the two cylinders. In fact, the individual control of the cambering forces applied to each end of each working cylinder makes it possible to optimally control the shapes of the support lines to compensate for an irregularity in the thickness of the laminating space 50.

Of course, the invention is not limited to the details of the process and of the installation which have just been described and which could be modified, in particular to adapt to other regulation systems without departing from the principles that have been defined and are the subject of the claims.

For example in the embodiment described, the camber of the cylinders is adjusted by acting on the position chocks but the invention also applies to arrangements in which a bending torque is applied directly to each end of each cylinder.

On the other hand, the invention has been described in its preferred application to a quarto rolling mill but it can be applied to other types of rolling mill, for example of the sexto type with intermediate rolls provided with bending means, or else to three-cylinder rolling mills. The product then passes between the working cylinder and a counter-cylinder corresponding to the lower support cylinder and that, according to the invention, is allowed to deform freely under the force applied, the upper support cylinder being of the type deformable casing with adjustable profile and the bending forces being applied to the single working cylinder to correct thickness irregularities.

Likewise, in the embodiment described above, a support cylinder with a rotating envelope was used, maintained by pads, this arrangement making it possible to obtain a particularly precise adjustment of the profile of the support generator, but it would be possible to 'apply the invention using other means for adjusting the profile of the support cylinder, in particular by inflating the envelope.

Claims (7)

1. Process for the rolling of a metal product in band form by passage through a rolling mill comprising, inside a stand (6), at least four rolls (1, 2, 3, 4) mounted for rotation about parallel axes and disposed in a pressure application plane (P), each on a shaft (11, 21, 31, 41) carried at its two ends by support means (12; 22; 32; 42) housed in two columns (61) of the stand (6), respectively two work rolls (1, 2) between which is formed an elongate space (50) for the passage of the product (5) in band form and which, on the opposite side to the said space, bear respectively against a coacting roll (4) taking the pressure load and against a variable camber backup roll (3) having a deformable cylindrical Casing (33) which is mounted on a central shaft (31) and whose profile can be adjusted by the application of thrust loads between the central shaft (31) and the inner face of the casing (33), and means (63) for applying a pressure load to the ends of the shaft (31) of the backup roll (3), the coacting roll (4) deforming under the action of the pressure load to form a line of support (47) which is concave in the direction of the product (5), characterised in that, the stand (6) being equipped with means (8) for cambering the two work rolls (1, 2) by applying bending loads to the ends of the shaft of each roll (1, 2), the profile of the deformable casing (33) is adjusted in such a manner as to form a line of support (37) which is convex in the direction of the product (5) and is substantially parallel to the line of support (47) of the coacting roll (4), and in that the camber of each work roll (1, 2) is individually adjusted in such a manner as to maintain a constant thickness of the roll pass (50) over the entire width of the product (5), by applying to the ends of the shafts of each work roll (1, 2) bending loads whose direction and intensity are adjusted individually for each end of each roll (1, 2) by bearing directly against the column of the stand (6), the product (5) on leaving the stand (6) having an incurved transverse profile capable of being subsequently straightened by known means.
2. Rolling process according to Claim 1, characterised in that when the cambering of the two work rolls (1, 2) is effected by the application of thrust loads in one direction or the other to the support means (12, 22) of their shafts, the position of each support means (12, 22) of each work roll (1, 2) is adjusted separately in relation to a position of equilibrium in order to maintain a constant thickness of the roll pass (50).
3. Rolling process according to one of the preceding claims, characterised in that the adjustment of the external profile of the backup roll (3) and of the camber of each work roll (1, 2) is effected automatically by reference to a model (90) taking into account the dimensional and resistance characteristics of the different components and of the product (5) and adapted to determine the corrections to be made to the profile (37) of the deformable casing (33) and to the position of each support means (12, 22) of the work rolls, based on measurements of thickness and flatness made on the band downstream of the rolling mill, in such a manner as to maintain a constant thickness of the space (50) for the passage of the product (5) over the entire width of the latter.
4. Rolling process according to Claim 3, characterised in that the shape of the line of support (13, 23) of each work roll (1, 2) on the product is determined on the basis of measurements made downstream and in dependence on the loads applied, and in that the corrections to be made to the profile of the backup roll (3) and to the camber of the work rolls (1, 2) are determined by comparison of the profiles of their lines of support (13, 23) in order to keep the said lines parallel to one another and spaced a constant distance apart corresponding to the thickness to be given to the product (5).
5. Rolling installation for carrying out the process according to one of Claims 1 to 5, having a support stand (6) comprising two spaced columns (61), at least four rolls (1, 2, 3, 4) each mounted for rotation about a shaft (11, 21, 31, 41) carried, at each end, by support means (12, 22, 32, 42) housed in the columns of the stand (6), respectively two work rolls (1, 2) and two backup rolls (3, 4), means (63) for applying a pressure load to the ends of the shaft (31) of one of the backup rolls (3), the ends of the shaft (41) of the other backup roll (4) being supported on the stand (6), one of the backup rolls (3) being of the variable camber type having a cylindrical casing (33) mounted on a central shaft (31) and associated with means for adjusting the profile of the casing (33), and the other backup roll (4) being a simple solid coacting roll, characterised in that, the stand (6) being equipped with means (8) for cambering the two work rolls (1, 2) by applying bending loads to the ends of their shafts (11, 21) and the backup coacting roll (4) forming, under the effect of the pressure load, a concave line of support (47) for the corresponding work roll (2), the work roll cambering means (8) comprise separate means (81, 82) (81', 82') for applying a bending load to each end of the shaft (11, 21) of each work roll (1, 2), the said cambering means being supported separately on the stand and being adjusted individually.
6. Rolling installation according to Claim 5, in which the support means (12, 22) of the work rolls consist of chocks (7) mounted for sliding along the corresponding columns (61) of the stand (6), and the cambering means (8) consist of hydraulic jacks (81, 82) for adjusting the positioning of the said chocks, characterised in that the cambering jacks (81, 82) (81', 82' are associated in groups independent of one another and corresponding respectively to each chock (7) of each work roll (1, 2), each group of jacks bearing directly on the corresponding column (61) of the stand (6) and being associated with a separate control means (75, 85) for the individual adjustment of the positioning of each chock (7).
7. Rolling installation according to Claim 6, characterised in that the separate control means (75, 85) of each group of cambering jacks are associated with a device (9) for automatic regulation by reference to a mathematical model (90) established in accordance with the dimensional and resistance characteristics of the different components of the rolling mill and of the rolled product (5) and adapted to determine, on the basis of thickness and flatness measurements made on the product (5) at the outlet of the stand (6) and in dependence on the loads applied, the corrections to be made to the external profile (37) of the backup roll (3) whose casing is deformable and to the position of each chock (7) in relation to its position of equilibrium, in such a manner as to maintain a constant thickness of the space (50) between the work rolls (1, 2) over their entire length.

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