EP1226886A1 - System for driving and guiding a metal band - Google Patents

Abstract

The system for driving and guiding a strip product (2) has a squeezer (P) to apply a locking pressure to fixed (4) and moving (5) rollers. The squeezer consists of a hydraulic locking cylinder (110) for each of the mobile roller's bearings, with pistons (111) forming pressure chambers (12b) delivering hydraulic fluid at a locking pressure. The pressure chambers are linked to dampers for variations in strip thickness, absorbing a limited movement of the pistons with no substantial variation in hydraulic pressure.

Description

The invention relates to a drive and guiding a strip moving along a longitudinal axis, and applies specially for controlling the movement of a metal strip in a rolling plant.

To obtain a sheet, it is usual to start from a slab which first passes through a degreasing mill, then through a rolling mill finisher consisting of a series of rolling stands operating in tandem, until the desired thickness is obtained, the strip obtained being finally wound in a reel on a mandrel driven in rotation.

This winding must be carried out under a certain traction which is, however, less than the traction usually required for rolling.

On the other hand, the strip may tend, at the exit of the rolling, to shift laterally and it is necessary to center it before it is wound into a reel.

For this, it is usual to place, at the exit of the rolling and in upstream of the winder, a driving and guiding device which normally includes two cylindrical rollers mounted on both sides and across the tape running plane and between which is applied a pinch pressure of the strip, at least one of the rollers being rotated around its axis to control scrolling under tension of the strip thus clamped between the two rollers.

Preferably, the upper roller can be raised so that move away from the lower roller to facilitate the engagement of the tape on the winder or allow it to pass, for example towards a another winder placed downstream.

Usually the position of the upper roller is determined by adjustable stops according to the thickness of the strip but, to ensure proper training of the band, it is necessary to fine-tune the pinch pressure applied between the two rolls. It is useful, on the other hand, to be able to modulate the pressures applied, respectively, on each side of the strip, these may be slightly different to exercise, if necessary, a band refocusing effect.

The document FR-A-2459692, for example, describes a device for this type, in which the upper roller is applied, in the position of clamping on fixed stops and clamping pressure is applied to the bearings of the lower roller by cylinders of a special type allowing a presetting of the pressures applied, respectively, of the right side and left side of the band.

In another known arrangement described, for example, in the document FR-A-2346066, the upper roller is carried by a frame which can pivot around a horizontal axis under the action of a jack pneumatic, between a raised position allowing free passage of the band and a lowered position for pinching the band, the level is adjusted by fixed stops.

The upper roller is carried by two mounted bearings sliding, transverse to the running plane, in guides of the frame, and each associated with a double-acting pneumatic cylinder of adjustment of the pressure force applied to the strip on each side of it.

Such devices therefore make it possible to adjust the pressures applied to the strip to exert the tensile force necessary for lamination and, if necessary, to center it before winding.

It happens, however, that the strip presents, when scrolling, extra thicknesses due to a folding of the strip on itself, in especially for thin layers. When the upper roller is simply applied by its own weight, it can lift slightly to allow such extra thickness to pass, without modification pinch pressure. However, if the pinch pressure is applied by cylinders, these are subject, in case of excess thickness, to shocks that may disturb the pressure setting. In one device as described by document FR-A-2346066, is used, for apply pinch pressure, pneumatic cylinders that can absorb any extra thickness. However, the response time of a pneumatic cylinder is not negligible and it is therefore difficult, in in this case, to provide a real regulation allowing to refocus the band by modulating the pressures applied on the two bearings.

The object of the invention is to solve these problems by means of a driving and guiding device which allows to absorb excess thickness defects which may occur when the strip, without significantly modifying the forces applied, respectively, on the bearings of the pinch roller, on either side of the strip, these efforts can thus be modulated so as to permanently correct the centering of the strip to ensure a good winding of the reel.

The device according to the invention, while providing a reliable result, is relatively simple and inexpensive and can be adapted to existing devices without significant modification thereof.

The invention therefore relates, in general, to a device drive and guide a strip product comprising, at inside a frame, two cylindrical rollers mounted to rotate each around an axis perpendicular to the direction of travel, one at less of said rollers rotating on two guided movable bearings transverse to the strip running plane, means for pinching the strip between the two rollers by applying a adjustable clamping pressure on each of the movable bearings and means for controlling the rotation of at least one of said rollers, the clamping means comprising, for each movable bearing, a jack hydraulic clamping bearing on the frame and on the bearing and comprising a pressure chamber supplied with hydraulic fluid under clamping pressure.

In accordance with the invention, each clamping cylinder is associated to a means of damping variations in strip thickness designed to absorb a limited displacement of the piston in the direction opposite to the tightening direction, without appreciable variation in the pressure of tightening applied to each bearing by the corresponding cylinder.

This depreciation means comprises at least one room closed containing at least one damping fluid and communicating with the pressure chamber of the clamping cylinder, so that the fluid is subject to the clamping pressure applied to the piston of said cylinder, said damping chamber having a volume sufficient considering the compressibility of the fluid it contains for absorb a limited displacement of the piston of the clamping cylinder, without significant variation in the hydraulic clamping pressure applied by this one.

In a first embodiment, the room depreciation includes a single part forming a capacity communicating with the pressure chamber of the clamping cylinder by a largely open conduit and filled with the same hydraulic fluid, said capacity with sufficient volume taking into account the compressibility of said hydraulic fluid to absorb a limited displacement of the piston clamping cylinder.

Preferably, in another embodiment, the chamber depreciation comprises two parts, respectively a first link part forming a closed capacity connected with the pressure chamber of the jack through a first conduit largely open and filled with the same hydraulic fluid and at the same pressure tightening, and a second part which is put in communication with the first part by a second largely open conduit and filled with a gas under pressure so as to form a gas accumulator capable of to absorb the passage in the capacity of a quantity of fluid corresponding to a limited displacement of the piston without significant variation of the pressure of said hydraulic fluid.

Advantageously, the connecting duct between the pressure and the damping chamber has a section of sufficient passage to avoid any significant dynamic variation in the fluid pressure during a limited displacement of the cylinder piston Tightening.

According to another preferred characteristic, a shutter without inertia, such as a deformable membrane is placed in the second connecting conduit between the capacity and the accumulator to ensure the separation between hydraulic fluid and gas.

In another embodiment, the body of each cylinder of clamp is slidably mounted axially in an integral hollow body of the frame and limiting with said clamping cylinder body, a chamber filled with a gas, so as to constitute a pneumatic cylinder damping capable of absorbing a displacement of the body of the clamping cylinder determined by a limited displacement of the piston of said clamping cylinder.

Particularly advantageously, the pressure chamber of each clamping cylinder is supplied by a hydraulic circuit comprising means for limiting the clamping pressure preset to a value corresponding to the clamping force between the rollers necessary for the strip to run, the fluid contained in the chamber of damping being maintained at a pressure at least equal to the pressure limit applied on the piston of the clamping cylinder.

Advantageously, a means for measuring the lateral position of the strip is provided upstream of the guide device, and the information on the position of the tape provided by this means is used to control the tilting of the second roller of the guide device in order to correct, by a slight lateral displacement of the strip, a defect "saber", before winding the strip on the winder located in downstream of the guide device.

Preferably, the drive torque transmitted to the band by the rollers is modulated by the power supplied by the motors of these rollers, in order to optimally adjust the traction between the last rolling stand and the device, in particular to facilitate the measurement of the flatness of the strip.

The device of the invention makes it possible to absorb the shock of the strip at commitment and also allows - without inertia - to pass the extra thicknesses resulting in particular from folding or welding.

It is thus easier, by the modulation of the drive torque rollers, to adjust the traction between the last cage and the device without changing the winding tension at the winder.

The invention also covers other advantageous arrangements and will be better understood by the following description of certain modes of particular embodiments, given by way of nonlimiting examples and illustrated by the attached drawings in which:

Fig.1 is a side view of a drive device and tape guide according to the invention.

Fig. 2 is a vertical axial section along line II, II of FIG. 1, the gas accumulator being oriented differently.

Fig. 3 is a detail view, on an enlarged scale, of FIG. 2.

Fig. 4 is a regulation diagram for controlling the cylinders Clamping.

Fig. 5 shows an alternative embodiment of the device according to the invention.

Figure 6 shows another variant.

In Figures 1 and 2, there is shown schematically a device 1 for driving and guiding a metal strip 2 which has just been laminated and is going to be wound into a reel.

Such a device 1 is therefore located downstream of a last cage of rolling (not shown) and upstream of a winder (not shown) which ensures the winding. Band 2 is supported and driven by a roller conveyor-table T (Fig. 1) defining a plane substantially horizontal scrolling; centering along the axis of this conveyor is provided by guides not shown.

The device 1 comprises a fixed frame 3 comprising, each side of the strip, a vertical lateral support.

The strip 2 passes between two pinch rollers 4 and 5, the axes of rotation are parallel to the running plane and located in a transverse plane, said axes being perpendicular to the direction tape advance.

The lower roller 4 is supported by a shaft 41 rotatably mounted, at each end, in a fixed bearing 42 locked in one of the supports sides of the frame 3.

The upper roller 5 is supported by a shaft 51 rotatably mounted at each of its ends respectively in a rolling bearing 52 mounted in a housing, which can slide while being guided by a slide 53 formed on a support frame 6.

The rollers 4, 5 are rotated by means motors not shown, by means of cardan extensions.

The chassis 6 is articulated on the frame 3 around a horizontal axis 9, arranged upstream and above the roller 5. At least one cylinder hydraulic 7 is provided to raise the chassis 6 by rotating it, in the opposite clockwise direction according to Fig.1, around the axis 9. The cylinder 7 is articulated, in the lower part, on an axis carried by the frame 3 while in upper part the rod of the jack 7 is articulated on an axis carried by the chassis 6 opposite axis 9.

In the raised position, the chassis 6 is sufficiently spaced from the roller 4 to facilitate the start of winding or to let pass tape 2 freely to another winding equipment located in downstream and not shown in the drawing.

In the lowered position, the chassis 6 is applied by the jack 7 to adjustable stops 8 of the frame 3, the level of which can be adapted to the thickness of the strip S so that it is pinched between the two rollers 4, 5.

Pinching means P are provided to exert a force of tightening of the strip 2. As shown in FIGS. 1 and 2, these pinching means P comprise, on each side of the strip 2, a hydraulic cylinder 10 whose body 12 is fixed to the chassis 6 and whose piston 11 allows individual clamping pressure to be applied adjustable on the associated bearing 52, by means of a rod 13.

In the previous arrangement described in document FR-A-2346066, the two bearings of the upper roller were connected by a rod and a connecting rod, with a double-acting cylinder making it possible to apply, in a one way or the other, a force added algebraically to the weight of the roller.

In the invention, on the other hand, the clamping force is exerted only by the cylinders 10 which are preferably single acting, the weight of the roller 5 being collected by balancing jacks 20 which are supported on the lifting frame 6.

For this purpose, as shown in Figure 2, the rotation shaft of the roller 5 is extended by two pins 51 each threaded in a rolling bearing 54 having a housing which is fixed to the end of the rod a jack 20 whose body is provided with support parts engaging in a yoke attached to the lifting frame 6.

These jacks 20 collect the weight of the roller 5 and to exert on it an effort of recall upwards. Cylinders 10 can therefore be single acting, the rod 13 of each cylinder 10 being a simple pusher which bears, in the tightening direction, on the housing of the corresponding bearing 52.

Each cylinder 10 comprises a piston 11 slidably mounted in the bore of a cylinder 12 forming the cylinder body and fixed on the rod 13 which bears down on the bearing housing 52 of the roller 5. When the frame 6 is applied in the lowered position on the stops 8, as illustrated in Fig.1, the axis of the jack 10 is substantially vertical. The cylinder body 12 is closed at its upper end by a cover 12a removably attached, for example by means of screw.

A pressure chamber 12b is thus formed in the body of cylinder 12, between the piston 11 and the cover 12 a.

The jack 10 is a hydraulic jack fed by a pipe 10a connected to an orifice provided in the cover 12a and which opens into the volume located above the piston 11. On the pipe 10a is connected a servo valve which allows, for example, to connect the line 10a either to a source of pressurized liquid (not shown), either to the tarp (not shown), or to close the line 10a. The second chamber of the cylinder, on the other side of the piston 11, is connected by a channel 10b to a pipe 10c for returning to the sheet.

The cylinders 20 for balancing the weight of the roller 5 are supplied permanently with a slight overpressure so as to apply the bearings 54 on the ends of the pushers 13 of the jacks 10 while exerting thus an effort of recall upwards. As a result, the servo valves 30 supply of the cylinders 10 make it possible to precisely control the pinch pressures applied respectively to the sides of the strip, by means of a regulation system shown schematically in Figure 4.

A sensor 21 for measuring the lateral position of the strip is provided, above the strip 2, just upstream of the device 1. This sensor 21 includes, for example, a CCD camera (camera charge transfer system), but other means of measure can be used.

As illustrated in Fig. 4, the output signal from camera 21 is sent to the input of a gap shaping circuit 22. Leaving the circuit 22 is connected to an input of a comparator 23 including another input receives, via line 24, a setpoint for the cylinder 5 tilt control. Comparator 23 output is sent to an input of a microcomputer 25. Other inputs of this microcomputer 25 are respectively connected to a line 26 providing a pressure limit value, a line 27 providing a setpoint of the position of the rod 13, a line 28 receiving the sensor 15 information on the position measurement and a line 29 receiving information from the pressure sensor 16.

Through the use of hydraulic cylinders 10 for the application pinch pressure, response time is extremely short and we can therefore achieve pressure regulation allowing correct a possible off-center of the band.

However, if the strip 2 has an extra thickness, the passage of it between rollers 4 and 5 causes an upward impact on the jacks 10 which could disturb the regulation.

To avoid this drawback, there is provided, according to the invention, a damping means A which allows to absorb a limited displacement of piston 11, in the opposite direction to tightening, without appreciable variation of the clamping pressure applied to the bearing 52 and consists of a chamber B subjected to the clamping pressure and containing a fluid having a degree of compressibility which allows it to absorb upward movement of the piston.

In the embodiment of Figs. 1 and 2, the chamber depreciation B has two parts, respectively a part of link consisting of a capacity 14 which communicates with the room pressure 12b of the jack and a damping part consisting of a gas accumulator 17.

The capacity 14 consists of a recess in the cover 12, above the pressure chamber 12b, and contains the same hydraulic fluid. As shown in Fig. 2, the capacity 14 has a cylindrical shape, with a diameter greater than that of the bore of the body cylinder 12 and it communicates with the pressure chamber 12b by a duct 14a of sufficient section to avoid any dynamic variation sensitive to fluid pressure in capacity 14 during displacement of the piston 11.

A position sensor 15 can be arranged inside the capacity 14, along the axis of the jack 10, and is thus protected against external shocks. The position sensor 15 comprises a first part linked to the upper end of the rod 13 and a second part linked to the cover 12a and being able to move axially relative to the first part. On the other hand, a pressure sensor is connected to an orifice 16 provided on the cover to allow the effort exerted to be determined on the bearing 52 by the jack 10.

The second part of the damping chamber B includes a volume filled with gas, advantageously constituted by an accumulator gas 17 whose outer shape is substantially cylindrical and centered, preferably, on an axis orthogonal to that of the jack 10. The accumulator 17 is fixed laterally on the cover 12a which comprises a transverse passage duct 18 which opens into the capacity 14 to put it in communication with the accumulator 17. The diameter of the passage duct 18 is large enough to avoid a dynamic variation of the pressure during the passage of the liquid in capacity 14. The separation between the liquid in capacity 14 and the gas from the accumulator 17 is provided by a shutter without inertia, by example formed by a partition 19 applied to the bottom of a counterbore formed around the periphery of conduit 18.

The inflation pressure of the accumulator 17 is adjusted to a value slightly higher than a set pressure pressure limit in capacity 14 to exert the necessary effort on strip 2 during from its introduction and during its scrolling. This overpressure, which may vary depending on the product, is therefore collected, in operation normal, by the partition 19 for closing the duct 18.

The operation of the device is as follows.

Waiting for the arrival of the tape head 2, the device is closed by the jacks 7, the chassis 6 coming to be applied on the stops 8. The cylinder position control 10 adjusts, depending on the thickness of the strip, the spacing between the rollers 4 and 5. The rollers 4 and 5 are then rotated with a slight overspeed by compared to that of band 2.

After the tape head has passed between rollers 4 and 5, the clamping pressure is regulated by the cylinders 10 controlled in position, by means of a regulation system which may be of the type shown in figure 4.

At least one of the rollers is rotated so as to control the running of the strip under the desired tension for the rolling.

If an extra thickness occurs when the strip 2 runs, for example, in the event of folding, the roller 5 tends to lift and the rods 13 push up the pistons 11 which discharge the oil in the capacities 14 associated with each of the jacks 10. The overpressure which then occurs is transmitted by the shutter 19 to the contained gas in the accumulator 17 and is absorbed by a simple rise in pressure of this gas.

During the entire travel of strip 2, the effort required to the drive is maintained by a position regulation of the jacks 10 with application of a pressure limitation whose setpoint has been set for the thickness of the strip 2 considered.

This regulation is not likely to be disturbed in the event of passage an extra thickness thanks to the gas damping effect.

In case of deviation of the tape, on one side or the other, the sensor 21 detects this deviation and controls a tilting of the roller 5 in the direction which corrects the deviation detected. The tilting of the roller 5 is obtained by displacement of one of the lateral bearings 52 with respect to the other bearing, so that the axis geometric of roller 5 rocks slightly around an axis longitudinal orthogonal, the band tightening effort thus becoming stronger on one side than the other.

The strip 2 thus subjected to an asymmetrical tightening force is pushed back laterally, i.e. orthogonally to its direction longitudinal in advance, on the side of the lowest effort by a so-called "cherry stone".

Thanks to the regulation system according to the diagram in Fig. 4, the strip 2 is thus maintained in the axis of the winder and its defects, in particular that of "saber" (transverse deviation), are compensated for so as to allow winding without telescoping of the turns.

While strip 2 is engaged in the last cage rolling, we can modulate the torque of the drive motors rollers 4 and 5 so as to adjust an optimal level of traction between the last cage and the rollers 4 and 5, in particular not to mask, by excessive traction, flatness defects and to allow their measurement which takes place in the immediate exit area of the last rolling stand.

When the tail of strip 2 leaves the last cage rolling, it remains driven by the device 1 which plays its role of guidance according to the regulation scheme which has been described previously.

The device 1 of the invention makes it possible to absorb strong defects in excess thickness which may occur in the event of the band being folded back 2.

The damping effect can occur without delay, thanks to the dimensions of the conduit 18, to the gas contained in the accumulator 17 and to the shutter without inertia 19.

When the allowance has passed, the gas pressure in the accumulator 17 returns to its initial value, which is slightly higher than the limited pressure in capacity 14, and cylinder 10 then regains its normal operating conditions under regulation.

Response times are much lower than in known devices, due to the fact that the fluid intervening in the chamber 12b and the capacity 14 is a liquid.

Of course, the invention is not limited to the details of the mode of realization which has just been described and which can be the subject of variants does not deviating from the protective framework defined by the claims.

We could consider, for example, that the room damping B either in a single part filled with oil, giving capacity 14 sufficient volume to absorb limited displacement of piston 11, without excessive variation in fluid pressure hydraulic taking into account its compressibility. The gas accumulator G could then be eliminated.

But the gas accumulator could also be made from another way.

For example, Fig.5 shows an alternative embodiment in which identical elements or playing roles similar to elements already described above are designated by the same references or by the sum of the number 100 and references previous, without their description being repeated.

In this case, each damping means A comprises a pneumatic cylinder 31 having a cylindrical body 32 fixed to the chassis 6 centered on the axis of the hydraulic cylinder 110 for adjusting the pressure of nip.

The bottom 112a of the clamping cylinder 110 is widened so as to constitute a piston mounted sliding in the body 32 of the jack tire 31, the rod of which is formed by the body 112 of the actuator tightening 110.

Chamber 117 of this pneumatic cylinder 31, limited by the bottom 112a of the jack 110, on the side opposite the rod 113, forms a volume G filled with pressurized gas and acts as the gas accumulator described previously with reference to FIGS. 1 to 4. The displacement towards the top of piston 111 and rod 113, authorized by gas compression in volume G, absorbs shocks due to variations thickness of the strip 2 or at its entry between the rollers 4 and 5. The body 112 can be guided by a vertical axial extension 112d, of smaller diameter, which passes tightly through a bore of the upper body 32.

In normal operation, the piston 111 is pressed against a lower stop 32a of the body 32, and the clamping force of the strip 2 is provided by the hydraulic cylinders 110 and the oil pressure in these cylinders. In the event of excess thickness of the strip 2, the entire jack 110 has tendency to lift and the piston 111 moves away from the stop 32a in compressing the gas contained in the chamber 117 of the pneumatic cylinder 31 which dampens the passage of the additional thickness without appreciable modification of the clamping pressure applied by the jack 110 on the bearing 52 on roller 5.

Furthermore, it has been observed that, in the embodiment of the Figure 1, the sliding mounting of chocks 52 of the roller 5 drives friction which, even if minimal, can have an effect hysterisis that could disrupt regulation, given the large precision allowed by the invention.

To further improve this precision it would be possible, as the shows figure 6, to mount the bearings 152 of the roller 5 on two connecting rods 153 articulated on the chassis 6 around bearings 62 for which friction is negligible.

In this case, the body 112 of the cylinder 110 is mounted with a clearance lateral in a housing 61 of the chassis 6 and is supported thereon by an articulation 18, so as to follow the slight offset of the bearings 152 due to the rotation of the connecting rods 153.

Claims (18)

Device for driving and guiding a strip product (2) traveling in a longitudinal direction, comprising a support frame (3), two cylindrical rollers (4, 5) arranged on either side of a plane strip running means (2) and rotatably mounted each about an axis substantially parallel to said mean plane and perpendicular to the running direction, respectively a first roller (4) rotating on two fixed bearings (42) and a second roller (5) rotating on two mobile bearings (52, 152) guided transversely to the running plane of the strip, means (P) for pinching the strip (2) between the two rollers (4, 5) by applying a adjustable clamping pressure on each of the movable bearings (52, 152) of the second roller (5) and of the means for controlling the rotation of at least one of said rollers (4, 5), the clamping means (P) comprising, for each movable bearing (52, 152), a hydraulic clamping cylinder (10, 110) having a c orps (12, 112) bearing on the frame (3) and a piston (11, 111) slidingly mounted in the body (12, 112) and associated with a rod (13, 113), bearing on the movable bearing ( 52) corresponding to the second roller (5), said piston (11,111) limiting, in the body (12, 112) of the jack (10, 110), a pressure chamber (12b, 112b) supplied with hydraulic fluid under a pressure of clamping, characterized in that each clamping cylinder (10, 110) is associated with a means (A) damping of the variations in thickness of the strip, designed to absorb a limited displacement of the piston (11, 111) in the direction opposite to the tightening direction, without appreciable variation in the hydraulic tightening pressure applied to each bearing (52, 152) by the corresponding jack (10, 110). Device according to claim 1, characterized in that the damping means (A) comprises at least one closed chamber (B) containing at least one damping fluid and communicating with the pressure chamber (12b) so that the fluid damping is subjected to the clamping pressure applied to the piston (11, 111) of the jack (10, 110), said damping chamber (B) having a sufficient volume, taking into account the compressibility of the fluid which it contains, to absorb a limited displacement of the piston (11, 111) of the clamping cylinder (10), without appreciable variation in the hydraulic clamping pressure applied thereto. Device according to claim 2, characterized in that the closed damping chamber (B) forms a capacity (14) communicating with the pressure chamber (12b) of the jack (10, 110) by a largely open conduit (14a) and filled with the same hydraulic fluid, said capacity (14) having a sufficient volume, taking into account the compressibility of said hydraulic fluid, to absorb a limited displacement of the piston (11, 111) without appreciable variation in the pressure of the fluid in the pressure chamber (12b) and the capacity (14). Device according to claim 2, characterized in that the damping chamber (B) comprises two parts, respectively a first connecting part forming a closed capacity (14) placed in communication with the pressure chamber (12b) of the jack by a first conduit (14a) widely open and filled with the same hydraulic fluid and at the same clamping pressure, and a second part (17) which is placed in communication with the first part (14) by a second conduit (14b) widely open and filled with a gas under pressure so as to form a gas accumulator (G) capable of absorbing the passage in the capacity (14) of a quantity of fluid corresponding to a limited displacement of the piston (11, 111) without variation significant pressure of said hydraulic fluid. Device according to claim 4, characterized in that a shutter without inertia such as a deformable membrane (19) for separation between the hydraulic fluid and the gas is placed in the second conduit (14b) for connection between the capacity (14) and the accumulator (G). Device according to one of claims 3, 4 or 5, characterized in that the conduit (14a, 14b) connecting the pressure chamber (12b) and the damping chamber (B, 14) has a passage section sufficient to avoid any appreciable dynamic variation of the fluid pressure during a limited displacement of the piston (11, 111) of the clamping cylinder (10,110) Device according to claim 4, characterized in that the gas accumulator (17) is arranged on one side of the jack and has the shape of a cylindrical assembly with an axis orthogonal to that of the jack (10). Device according to one of claims 3 and 4, characterized in that the capacity (14) provided in the body (12) of the hydraulic cylinder (10) has sufficient dimensions to place there a means for measuring the position of the piston , such as a position sensor (15). Device according to claim 2, characterized in that the body (112) of each clamping cylinder (110) is slidably mounted axially in a hollow body (32) fixed on the frame (3) so as to constitute a limiting piston 112, inside said body (32), a pressure chamber (117) filled with a gas, the assembly forming a pneumatic damping cylinder (B) capable of absorbing a displacement of the body (112) of the cylinder tightening (110) determined by a limited displacement of the piston (111) of said clamping cylinder (110). Device according to one of Claims 2 to 9, characterized in that the pressure chamber (12b) of each clamping cylinder (10, 110) is supplied by a hydraulic circuit comprising means for limiting the clamping pressure preset at a value corresponding to the clamping force between the rollers (4, 5) necessary for the movement of the strip (2). Device according to claim 10, characterized in that the fluid (G) contained in the damping chamber (B) is maintained at a pressure at least equal to the pressure limit applied to the piston (11,111) of the clamping cylinder (10,110). Device according to one of the preceding claims, characterized in that it comprises means for measuring (21) the lateral position of the strip (2) placed upstream, in the direction of travel of the guide device (1) , and that the information on the position of the strip provided by this measuring means (21) is used to control the tilting of the second roller (5) of the guide device in order to correct a defect in the centering of the strip. Device according to claim 12, characterized in that the means for measuring the lateral position of the strip (2) comprises a digital camera (21). Device according to one of the preceding claims, characterized in that the drive torque transmitted to the strip (2) by the rollers (4,5) is modulated by the power supplied by the motors of these rollers, in order to adjust optimally the traction between the last rolling stand and the drive device (1). Device according to one of the preceding claims, in which the axes of the rollers are situated in a substantially vertical plane, characterized in that it comprises a lower roller (4) placed below the strip and rotatably mounted on two fixed bearings , and a roller (5) placed above the strip and rotatably mounted on two movable bearings. Device according to claim 15, characterized in that the movable roller (5) is carried by two bearings (52) slidably mounted between fixed guide faces (53), in a direction transverse to the plane of travel of the strip (2 ). Device according to claim 15, characterized in that the movable roller (5) is carried by two bearings (152) fixed respectively to the ends of two guide rods (153) articulated around a fixed axis (62), each jack clamp (110) being mounted so as to follow an offset of the bearings (152) due to the rotation of the connecting rods (153) during the application of the clamping pressure. Driving and guiding device according to one of the preceding claims, characterized in that the movable roller (5) and all of the clamping means (P) are mounted on a frame (6) rotatably mounted on the frame (3) around a fixed axis (9) and applied, in the clamping position, to a fixed stop (8) by a jack (7) capable of rotating the chassis (6) around the axis (9) up to a position spaced from the strip running plane (2).

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