Circular rolling mill and rolling method using such a rolling mill

Abstract

A circular rolling mill includes a main chassis, a radial stand and at least one axial stand. The radial stand includes a roller and a mandrel. The axial stand includes an auxiliary chassis and tapered rollers. The mandrel is supported by an upper mandrel holder and selectively engaged with a lower mandrel holder. Each mandrel holder is integral in translation along a longitudinal axis of the main chassis, with at least one drive bar parallel to the longitudinal axis. The movement of the mandrel holders is controlled by a movement system located on the same side of the shaping roller as the mandrel. The auxiliary chassis slides along its longitudinal axis on the drive bars, which pass all the way through it. A mechanism moves the auxiliary chassis relative to the drive bars in translation parallel to the longitudinal axis.

Claims

1. A circular rolling mill for shaping annular workpieces, comprising: a main chassis; a radial stand comprising: a shaping roller for shaping an outer radial face of a workpiece to be rolled; and a mandrel for shaping an inner radial face of the workpiece to be rolled, supported by an upper mandrel holder and selectively engaged in a lower mandrel holder, each of the mandrel holders being integral, in translation along a longitudinal axis of said main chassis, with at least one drive bar parallel to the longitudinal axis of said main chassis, movement of the mandrel holders parallel to the longitudinal axis of said main chassis being controlled by a movement system located on the same side of said shaping roller as the mandrel; at least one axial stand, comprising: an auxiliary chassis slidably mounted, parallel to the longitudinal axis of said main chassis, on the drive bars of the mandrel holders, which pass all the way through it; and upper and lower tapered rollers for shaping lower and upper radial faces of the workpiece to be rolled; and a mechanism for translating said auxiliary chassis relative to the drive bars, parallel to the longitudinal axis of said main chassis.

2. The rolling mill according to claim 1, wherein a drive bar movement system is mounted on said main chassis on the side of said auxiliary chassis opposite the mandrel holders, the at least one drive bar extends between the movement system and the mandrel holders, and said auxiliary chassis is provided with openings for the at least one drive bar to pass through and for guiding movement of said auxiliary chassis on the at least one drive bar.

3. The rolling mill according to claim 1, wherein each mandrel holder is integral with two drive bars, distributed on either side of a median longitudinal plane of the rolling mill, and wherein said movement mechanism synchronizes movement of said auxiliary chassis along the two drive bars of one of the mandrel holders.

4. The rolling mill according to claim 3, wherein the drive bars, with respect to which said movement mechanism synchronizes movement of said auxiliary chassis, are integral with the lower mandrel holder.

5. The rolling mill according to claim 3, wherein said movement mechanism comprises a frame mounted on the two drive bars and immobilized in translation along the longitudinal axis of said main chassis on these two drive bars, as well as members for driving said auxiliary chassis along the drive bars, relative to the frame.

6. The rolling mill according to claim 5, wherein said frame is provided with two holes for the longitudinal bars on which it is mounted and immobilized to fit through.

7. The rolling mill according to claim 5, wherein said frame supports a motor for moving said auxiliary chassis along the drive bars and members for transmitting movement between the motor and said auxiliary chassis.

8. The rolling mill according to claim 7, wherein the motion transmission members comprise a belt and two parts of ball-screw systems, a belt and two parts of nut-and-screw systems or two parts of rack-and-pinion systems.

9. The rolling mill according to claim 5, wherein said frame carries at least one actuator for moving said frame and said auxiliary chassis away from each other parallel to the longitudinal axis of said main chassis.

10. The rolling mill according to claim 1, wherein an axial stand and a mandrel are provided on each side of said shaping roll, along the longitudinal axis of said main chassis, wherein said auxiliary chassis of each radial stand is slidably mounted, parallel to the longitudinal axis of said main chassis, on the drive bars of the mandrel holders located on the same side, which pass all the way through it, and wherein the circular rolling mill further comprises two mechanisms for moving said auxiliary chassis in translation relative to the drive bars, parallel to the longitudinal axis of said main chassis.

11. A method for rolling an annular workpiece by means of a rolling mill according to claim 1, comprising: shaping the radial outer and inner faces of the annular workpiece, by means of the shaping roller and mandrel, and the lower and upper axial faces, by means of the lower and upper tapered rollers; and adjusting, as a function of a diameter of the annular workpiece being rolled, a distance between the mandrel and a rear edge of the tapered rollers by actuating the mechanism for moving the auxiliary chassis along the drive bars.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be better understood and advantages beyond these will emerge more clearly in light of the following description of two embodiments of a circular rolling mill and a rolling method using its principle, given solely by way of example and made with reference to the accompanying drawings, in which:

[0024] FIG. 1 is a perspective concept view of a circular rolling mill according to the invention;

[0025] FIG. 2 is a perspective section along plane II in FIG. 1;

[0026] FIG. 3 is a perspective section along plane III in FIG. 1;

[0027] FIG. 4 is a semi-exploded perspective view of a mechanism for moving an auxiliary chassis belonging to the rolling mill of FIGS. 1 to 3;

[0028] FIG. 5 shows a longitudinal section of the circular rolling mill, in a rolling configuration different from that shown in FIGS. 1 to 3;

[0029] FIG. 6 shows, in two inserts A) and B), an enlarged version of box VI in FIG. 5, in first and second rolling configurations, the first configuration being that of FIG. 5;

[0030] FIG. 7 shows, in two inserts C) and D), partial sections similar to those of FIG. 6, when the rolling mill is in third and fourth rolling configurations;

[0031] FIG. 8 shows, in two inserts E) and F), partial sections similar to those shown in FIG. 6, when the rolling mill is in a fifth rolling configuration and after rolling has been completed; and

[0032] FIG. 9 is a view similar to FIG. 1 for a rolling mill according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0033] A circular rolling mill 1 shown in FIGS. 1 to 8 includes a main chassis 2 which extends along a longitudinal axis X2.

[0034] Main chassis 2 supports a radial stand 3 and an axial stand 4.

[0035] Rolling mill 1 is used to shape a workpiece 100 to be rolled, with an outer radial face 101, an inner radial face 102, an upper axial face 103, and a lower axial face 104.

[0036] Radial stand 3 includes a first roller 10 for shaping radial outer face 101 of workpiece 100 to be rolled, which is mounted so that it can rotate about a vertical axis Z10, defined by a support and drive assembly 12 including in particular an electric motor 14. Electric motor 14 is covered by a hood 15. When activated, electric motor 14 rotates the shaping roller about axis Z10.

[0037] 10A is an outer peripheral surface of shaping roller 10 which comes into contact with outer radial face 101 of workpiece 100 being rolled.

[0038] Radial stand 3 further includes a mandrel 20 which forms a second roller for shaping radial inner face 102 of workpiece to be rolled 100.

[0039] Mandrel 20 is supported by a first mandrel holder 22, or upper mandrel holder, which is mounted at the end of two drive bars 24 and 26. Mandrel holder 22 is also referred to as a cradle. Upper mandrel holder 22 carries a mechanism 28 for lowering/raising mandrel 20 along a longitudinal axis A20, which is vertical when mandrel 20 is installed in rolling mill 1. The lowering/raising mechanism is controlled by two electric motors 30 and 31 mounted on mandrel holder 22, from which mandrel 20 extends downwards.

[0040] Rolling mill 1 further includes a second mandrel holder 32, or lower mandrel holder, which defines a housing 33 for receiving the lower end of mandrel 20. Mandrel 20 is selectively engaged in housing 33, i.e., in lower mandrel holder 32, during the rolling phases, and released from this housing when loading a workpiece to be rolled or when unloading a rolled workpiece. Lower mandrel holder 32 is mounted at the end of two drive bars 34 and 36. Mandrel holder 32 may also be referred to as a cradle. Lower mandrel holder 32 is fitted with castors, only one of which can be seen in FIG. 2 with reference 38. The other castor is arranged symmetrically to the visible one, in relation to main chassis 2. Mandrel holder 32 rests, via its castors 38 and equivalent, on two tracks 52 at the top of main chassis 2. Castors 38 and equivalent facilitate movement of lower mandrel holder 32 along longitudinal axis X2.

[0041] Drive bars 24, 26, 34 and 36 extend parallel to longitudinal axis X2 of main chassis 2 and are superimposed in pairs, drive bar 24 being arranged above drive bar 34, while drive bar 26 is arranged above drive bar 36. Drive bars 24 and 26 are at the same horizontal level, as are drive bars 34 and 36.

[0042] P1 is a median longitudinal plane of rolling mill 1, which is vertical, located midway between the sides of main chassis 2 and includes longitudinal axis X2. Drive bars 24 and 26 are arranged on either side of median longitudinal plane P1, preferably symmetrically, while drive bars 34 and 36 are also arranged on either side of this plane P1, preferably symmetrically.

[0043] Upper and lower mandrel holders 22 and 32 hold mandrel 20 in a flat configuration against inner radial face 102 of workpiece 100 to be rolled while it is being rolled.

[0044] Each of drive bars 24, 26, 34 and 36 is moveable, parallel to the longitudinal axis X2, by means of a movement system 40 which includes an enclosure 42, two electric motors 44 and 45 and two angular gearboxes 46 and 47, each driven by one of electric motors 44 and 45. Each angular gearbox 46 or 47 drives two pinions 48 arranged on either side of mean longitudinal plane P1, each meshing with a rack 50 provided on one of drive bars 24, 26, 34 and 36.

[0045] Actuating electric motor 44 therefore enables drive bars 24 and 26, and therefore upper mandrel holder 22, to be moved parallel to longitudinal axis X2. Furthermore, actuating electric motor 45 enables drive bars 34 and 36, and therefore lower mandrel holder 32, to be moved parallel to axis X2. Motors 44 and 45 are synchronized so that the movements of mandrel holders 22 and 32 are also synchronized. Movement system 40 therefore controls movement of mandrel holders 22 and 32 parallel to longitudinal axis X2.

[0046] When loading workpiece 100 to be rolled onto rolling mill 1, or unloading same from the rolling mill after it has been rolled, mandrel holders 22 and 32 may be desynchronized to facilitate loading and unloading.

[0047] Movement system 40 is arranged along longitudinal axis X2 on the same side of shaping roller 10 as mandrel 20. In FIGS. 1 to 3 and 5, mandrel 20, mandrel holders 22 and 32 and drive system 40 are all positioned to the right of shaping roller 10 and its axis of rotation Z10. Rolling mill 1 is therefore compact.

[0048] When workpiece 100 to be rolled is in place in rolling mill 1, as shown in FIGS. 1 to 3 and 5 to 8 insert E), this part is subjected to radial compressive forces F1 and F2, exerted respectively by shaping roller 10 and by mandrel 20, on its inner and outer radial faces 101 and 102. The intensity of these radial compressive forces depends on the intensity of a thrust force exerted on mandrel holders 22 and 32 by electric motors 44 and 45, through drive bars 24, 26, 34 and 36, in the direction of shaping roller 10.

[0049] The movement of mandrel holders 22 and 32 by movement system 40 constitutes a primary movement within rolling mill 1, which makes it possible to exert radial compressive forces F1 and F2.

[0050] Axial stand 4 includes an auxiliary chassis 60 mounted on main chassis 2, and movable, relative to this chassis, along longitudinal axis X2.

[0051] Axial stand 4 includes a lower tapered roller 62 supported by auxiliary chassis 60 and rotated by an electric motor 63. Axial stand 4 further includes an upper tapered roller 64 rotated by an electric motor 65. A62 and A64 are axes of symmetry and rotation of tapered rollers 62 and 64 respectively. These axes are inclined both horizontally and vertically. They converge as they approach mandrel 20 and axis A20.

[0052] S62 and S64 are effective surfaces of tapered rollers 62 and 64 respectively. Active surfaces S62 and S64 refer to the surfaces of tapered rollers 62 and 64 which enable axial compressive forces F3 and F4 to be exerted. Larger diameter edges of active surfaces S62 and S64 are 62A and 64A, respectively. Active surfaces S62 and S64 are superimposed, i.e., vertically aligned, as are their edges 62A and 62B.

[0053] Distance d1 is the maximum distance, measured parallel to axis X2, between longitudinal axis A20 of mandrel 20 and rear edge 62A of active surface S62. Advantageously, distance d1 is measured at a horizontal portion of active surface S62. Distance d1 has a minimum value in the configurations of inserts A) and B) in FIG. 6 and C) in FIG. 7.

[0054] When the workpiece 100 to be rolled is in place in rolling mill 1, it is subjected to axial compressive forces F3 and F4 exerted respectively by upper tapered roller 64 and by lower tapered roller 62 on axial faces 103 and 104 of workpiece 100 being rolled.

[0055] Chassis 60 is inserted along longitudinal axis X2 between mandrel holders 22 and 32 on the one hand and movement system 40 on the other hand. In other words, movement system 40 is mounted on main chassis 2 on the side of auxiliary chassis 60 opposite mandrel holders 22 and 32.

[0056] To achieve this, chassis 60 is fitted with four sleeves 66, each of which defines a cylindrical volume V66 whose cross-section corresponds to that of drive bars 24, 26, 34 and 36.

[0057] In the example, drive bars 24, 26, 34 and 36 are circular in cross-section and volumes V66 are also circular in cross-section, with a diameter slightly greater than that of the drive bars.

[0058] Alternatively, drive bars 24, 26, 34 and 36 may have cross-sections other than circular, for example polygonal, in which case the geometry of volumes V66 is adapted accordingly.

[0059] Volumes V66 pass all the way through auxiliary chassis 60 and allow drive bars 24, 26, 34 and 36 to be guided in translation along the entire length of sleeves 66, through auxiliary chassis 60. In other words, auxiliary chassis 60 is slidably mounted on drive bars 24, 26, 34 and 36 and guided in longitudinal translation, parallel to axis X2, by the cooperation of sleeves 66 and the drive bars.

[0060] In addition, sleeves 66 allow forces, in particular weight or axial reaction forces, to be taken up by workpiece 100 being rolled, which limits the effect of the overhang of drive bars 24, 26, 34 and 36 with respect to movement system 40. This is particularly noticeable at upper drive bars 24 and 26, which support upper mandrel holder 22 and its accessories, including mandrel 20 and lowering/raising mechanism 28. This is less noticeable on lower drive bars 34 and 36, as the lower mandrel holder rests on tracks 52 via castors 38 and equivalent.

[0061] In addition, a mechanism 70 is provided to move auxiliary chassis 60, and therefore axial stand 4, along longitudinal axis X2, relative to the drive bars, i.e., relative to radial stand 3, in particular relative to lower drive bars 34 and 36.

[0062] More specifically, movement mechanism 70 includes a frame 72 fitted with two sleeves 74, the interior volume V74 of which forms a housing that may accommodate some of drive bars 34 and 36. The volumes or housings V74 go all the way through frame 72. Frame 72 is immobilized along drive bars 34 and 36, for example by screws, pins, or keys (not shown).

[0063] Frame 72 is elongated and extends transversely to longitudinal axis X2, between drive bars 34 and 36. It forms a beam resting on these two bars.

[0064] Advantageously, as may be seen in particular in FIG. 4, frame 72 consists of two sheet metal plates joined together and defining between them a volume for receiving accessories for movement mechanism 70.

[0065] Frame 74 supports an electric motor 76 which drives a belt 78, which partially surrounds pulleys 80, each integral with a worm screw 82. Belt 78 and pulleys 80 are mounted in frame 72, in the volume defined between the metal sheets of this frame, and protected by a cover 73.

[0066] Each worm screw 82 is engaged in a casing 84 fitted with ball bearings, not shown, designed to circulate in the threads of the worm screw in question.

[0067] In this way, a ball-and-socket joint is formed between elements 82 and 84.

[0068] As a result, rotating a worm screw 82 about its longitudinal axis has the effect of moving casing 84, in which it is engaged, parallel to longitudinal axis X2, relative to frame 72, which is fixed relative to drive bars 24, 26, 34 and 36, as explained above.

[0069] The two housings 84 are integral with auxiliary chassis 60, so that movement of these housings along the two worm screws 82 has the effect of simultaneously moving auxiliary chassis 60 relative to frame 72.

[0070] Belt 78 and the pulleys 80 synchronize movement of worm screws 82 around their respective longitudinal axes A82, thus synchronizing movement of housings 84 and moving auxiliary chassis 60 parallel to longitudinal axis X2, without any risk of it jamming relative to main chassis 2.

[0071] To this end, auxiliary chassis 60 is fitted with castors, two of which are shown in FIG. 2 with reference 68. Other castors are arranged symmetrically to those visible, in relation to plane P1. Castors 68 and equivalent enable auxiliary chassis 60 to move with minimum friction on tracks 52. Stabilizing castors 69 engaged against the sides of main chassis 2 ensure the stability of auxiliary chassis 60 and prevent it from tilting as it moves along the longitudinal axis X2 and during rolling.

[0072] As frame 72 is immobilized on drive bars 34 and 36, it acts as a fixed point for movement of auxiliary chassis 60 relative to these drive bars.

[0073] In this way, actuating electric motor 76 enables auxiliary chassis 60, and hence tapered rollers 62 and 64 which it supports, to be moved parallel to longitudinal axis X2, while lower mandrel holder 32 remains in a position fixed by drive bars 34 and 36, where mandrel 20 helps apply compressive forces F1 and F2 on radial outer and inner faces 101 and 102 of workpiece 100 being rolled. Movement of auxiliary chassis 60 and tapered rollers 62 and 64 by movement mechanism 70 constitutes a secondary movement, within rolling mill 1, which makes it possible to adapt the longitudinal position of tapered rollers 62 and 34, and therefore the points of application of axial compressive forces F3 and F4, while mandrel 20 remains in a position allowing application of radial compressive forces F1 and F2.

[0074] Thus, movement system 40 constitutes a primary movement system for mandrel 20 and mandrel holders 22 and 32, while movement mechanism 70 constitutes a secondary movement mechanism for auxiliary chassis 60 and tapered rollers 62 and 64, along longitudinal axis X2.

[0075] Starting from the configuration of insert A) in FIG. 6, where workpiece 100 is at the start of rolling, it is possible to exert compressive forces F1, F2, F3 and F4 on faces 101, 102, 103 and 104 respectively, by means of shaping roller 10, mandrel 20 and tapered rollers 62 and 64. This has the effect of gradually increasing an external diameter D100 of the part being rolled, as can be seen by comparing inserts A) and B) in FIG. 6 and insert C) in FIG. 7.

[0076] External diameter D100 is the diameter of radial face 101 of workpiece 100 being rolled.

[0077] In the configuration of insert C) shown in FIG. 7, diameter D100 of workpiece 100 being rolled is such that the part on which forces F3 and F4 are exerted is close to the largest-diameter edges 62A, 64A of each of tapered rollers 62 and 64, respectively. Tapered rollers 62 and 64 are in the same position as on inserts A) and B) in FIG. 6.

[0078] To allow rolling of workpiece 100 to continue, and as may be seen from comparing inserts C) and D) in FIG. 7, movability of auxiliary chassis 60 relative to mandrel holder 32 is used to move tapered rollers 62 and 64 back relative to mandrel 20, in direction D2 marked in insert D) in FIG. 7, by moving auxiliary chassis 60 along longitudinal axis X2, towards primary movement system 40, by means of secondary movement mechanism 70.

[0079] This ensures that active surface S62, respectively S64, of each tapered roller 62 and 64 remains overlapping workpiece 100 being rolled, even when its external diameter D100 increases beyond the sum of the thickness of workpiece 100, the radius of mandrel 20 and the initial value of distance d1 in the configuration of inserts A) and B) in FIG. 6. This enables forces F3 and F4 mentioned above to be exerted throughout the rolling of workpiece 100.

[0080] This movement of tapered rollers 62 and 64 in direction D2 is carried out without shifting mandrel holders 22 and 32 along longitudinal axis X2, which ensures that radial compressive forces F1 and F2 continue to be applied to outer and inner radial surfaces 101 and 102 of workpiece 100. This movement of tapered rollers 62 and 64 is carried out by activating electric motor 76 to move housings 84 in the direction of frame 72, i.e., also in direction D2, while frame 72 remains stationary along longitudinal axis X2, as do drive bars 34 and 36.

[0081] As workpiece 100 is rolled, electric motor 72 is activated to progressively move tapered rollers 62 and 64 in direction D2, thus reaching the configuration shown in insert E) in FIG. 8, which corresponds to the position of auxiliary chassis 60 shown in FIGS. 1 to 3.

[0082] Comparing inserts C), D) and E) in FIGS. 7 and 8 shows that movability of auxiliary chassis 60 along drive bars 24, 26, 34 and 36 makes it possible to increase the maximum permissible value of external diameter D100 of workpiece 100 being rolled, which makes rolling mill 1 more adaptable than rolling mills of the prior art.

[0083] At the end of the rolling operation, mandrel 20 is lifted from mandrel holders 22 and 32, to where it is extracted from housing 33 and brought above rolled workpiece 100. On the other hand, electric motor 49, which belongs to axial stand 4, is then actuated to lift upper tapered roller 62 with respect to lower tapered roller 64, thus achieving the configuration of insert F) in FIG. 8, where rolled workpiece 100 may be extracted from the rolling mill by means of a specific multi-axis robot or manipulator, not shown. This specific multi-axis robot or manipulator may also be used to load workpiece 100 to be rolled onto circular rolling mill 1.

[0084] During rolling, workpiece 100 is centered relative to mandrel 22 by means of two centering arms, only one of which may be seen in FIGS. 1 and 2 with reference 85. The two centering arms, 85 and equivalent, are arranged symmetrically relative to median longitudinal plane P1. Each centering arm is rotated about a vertical axis Z85 by an electric motor 86 and carries a centering roller 87 which bears against outer radial face 102 of workpiece 100 being rolled.

[0085] As tapered rollers 62 and 64 move backwards in the D2 direction, the value of distance d1 increases, as may be seen by comparing inserts C) and D) in FIG. 7 and insert E) in FIG. 8. This increase in the value of distance d1 is achieved by activating electric motor 76 as a function of the increase in external diameter D100 of workpiece 100 being rolled.

[0086] Thus, it is possible to implement on rolling mill 1 a method for rolling annular workpiece 100 which includes at least: [0087] a) shaping radial outer and inner faces 101 and 102 of annular workpiece 100 by means of shaping roller 10 and mandrel 20, as well as lower and upper axial faces 104 and 103 by means of the lower and upper tapered rollers 62 and 64; [0088] b) adjusting distance d1 as a function of diameter D100 of annular workpiece 100 being rolled, by actuating secondary mechanism 70 for moving auxiliary chassis 60 along drive bars 24, 26, 34 and 36, preferably by actuating electric motor 76 of this mechanism.

[0089] This type of method enables relatively large-diameter parts (100) to be rolled using a compact, relatively simple and therefore reliable rolling mill.

[0090] In the second embodiment of the invention shown in FIG. 8, elements similar to those of the first embodiment bear the same reference, possibly with the subscript A or B added. In what follows, if a reference is used in the description without being shown in FIG. 9 or shown in this figure without being mentioned in the description, it designates the same object as that bearing the same reference in the first embodiment, after removing the subscript A or B if any.

[0091] Circular rolling mill 1 of this second embodiment differs from the first embodiment in that radial stand 3 includes two mandrels not shown, each supported by an upper mandrel holder 22.sub.A or 22.sub.B and a lower mandrel holder 32.sub.A or a mandrel holder not shown located below the upper mandrel holder 22.sub.B. This circular rolling mill 1 also includes two radial stands 4A and 4B. In other words, the structure of the circular rolling mill of the first embodiment is symmetrical with respect to axis Z10 of rotation of shaping roller 10.

[0092] Circular rolling mill 1 of this second embodiment includes two sets of four drive bars 24.sub.A, 26.sub.A, 34.sub.A and 36.sub.A, on the one hand, and 24.sub.B, 26.sub.B, 34.sub.B and 36.sub.B on the other.

[0093] This embodiment is based on the known approach in circular rolling mills called MIRA, according to which a workpiece 100 to be rolled or already rolled can be loaded or unloaded from rolling mill 1 in parallel operation while another workpiece 100 is being rolled, on the other side of shaping roller 10.

[0094] In this second embodiment, the movement system is duplicated in the form of two primary movement systems 40.sub.A and 40.sub.B, while the movement mechanism is duplicated in the form of two secondary movement mechanisms 70.sub.A and 70.sub.B, enabling each of auxiliary carriages 60.sub.A and 60.sub.B to be moved independently of upper and lower mandrel holders 22.sub.A, 22.sub.B, 32.sub.A and equivalent, on either side of vertical axis of rotation Z10.

[0095] In this second design, two rolling arms 85.sub.A and 85.sub.B are provided on either side of the main chassis and are driven by electric motors 86.sub.A and 86.sub.B. This embodiment therefore includes four rolling arms and four motors for moving these arms. In FIG. 9, rolling arms 85.sub.A and 85.sub.B are shown with their rollers 87.sub.A and 87.sub.B spaced apart from workpiece 100 to be rolled.

[0096] A method of the type mentioned above may be implemented in alternating fashion on both sides of shaping roller 10 of circular rolling mill 1 of FIG. 9.

[0097] According to a variant of the invention not shown, the secondary drive mechanism(s) is/are mounted on upper drive bars 24 and 26 or equivalent. In another variant, the secondary drive mechanism(s) is/are mounted on both the lower drive bars and the upper drive bars. In this case, it is not possible to desynchronize mandrel holders 22 and 32.

[0098] According to another variant of the invention, not shown, each ball-screw system 82+84 may be replaced by a nut and worm system or by a rack and pinion system, which are also driven by a belt 78 of the type shown. According to another variant, also not shown, these systems can be replaced by actuators for moving frame 72 and auxiliary chassis 60 apart and together, parallel to longitudinal axis X2, and these actuators may be electric, pneumatic or hydraulic.

[0099] According to another non-represented variant of the invention, one or all of the mandrel holders is/are integral, in translation along longitudinal axis X2, with a single drive bar. Primary drive system 40 and secondary drive mechanism 70 are then adapted.

[0100] The above-mentioned operating modes and variants may be combined to generate new operating modes of the invention.