EP0976466B1 - Method and device for the manufacture of a tube from strip material - Google Patents

Abstract

The method of making thin wall metal tubes involves cold forming a thin metal blank into an increasing curved section with the edges (4) closed and then welded together. The partially formed blank (3) is first twisted around a quarter turn and, prior to welding closed, is rotated back slightly. The claims also include a machine for carrying out the method.

Description

The invention relates to a method for producing a tube - preferably with a small wall thickness - made of tape material, wherein the initially flat strip material - made of metal, especially steel - in several forming stations one behind the other in the conveying direction is formed into the tube by the edges of the strip material more and more bent and curved towards each other.

The invention further relates to a device for producing a Pipe made of metallic strip material with a relatively small diameter and small wall thickness with several in the feed direction of the Workpiece pairs of rollers arranged one behind the other for gradual and then increasing deformation and curvature of the edges of the Workpiece in the feed course towards each other, with first pairs of rollers attack on the top and bottom of the workpiece and in the Area in which the curved edges form undercuts, Pairs of rollers are provided on the outside of the curved Attack edges.

Such manufacture of a tube is known (see e.g. US-A-4 460 118). Usually the initially band-shaped workpiece always becomes cold subjected to greater deformation of the edges. The in the feed direction the first pairs of rollers have somewhat interlocking shapes that bend the strip material so far that the curved Margins to the previous cross section of the tape a little more than stand at right angles.

From this degree of deformation can no longer form roll in this Wise with an undercut, sometimes already to one Grip pipe preformed workpiece. It is therefore known to start such a degree of deformation on the outer sides without drive Rollers provide the bent areas of the workpiece in the next pass press closer together and the pipe bend to complete. However, this often leads to an offset of the two edges to each other, the later in a welding device would have to be compensated, so that the resulting pipes in relative large tolerances become out of round.

The invention is therefore based on the object of a method and a device for the production of pipes of the entry to create the type with which the edges to be welded with greatest possible accuracy even before a welding station or Welding device meet, so that in particular pipes with thin walls and pipes with small diameters can be produced.

The method defined at the outset is used to solve this task characterized in that when the edges are curved so far are that they form an undercut that is partially shaped Workpiece in a first turning section by about a quarter turn is twisted and then further deformed, the between the Edges located slot in the further course of the passage of the Deformation is reduced and that before the final welding of the slot the workpiece in a second turning section again rotated back and then the edges moved towards each other welded become.

So it becomes the workpiece while it is being deformed by a belt first twisted into a tube after the first deformation steps, so that the edges forming the undercut are no longer opposite stand up from the original course, but lie aside, so that the roles attacking them on the outside, like the previous ones Forming rolls, have horizontal axes and can be driven, which significantly improves the precision of the further deformation in the feed benefits. This means that scoring can also occur on the outside of the pipe caused by the different peripheral speeds largely non-driven side rollers with vertical axes be avoided. In addition, arises in the workpiece a certain tension leading to a very precise location, in particular the edges, contributing so that their movement towards each other can be influenced accordingly.

If the slit is narrow enough in this way, the previous one becomes Partial rotation reversed, so that afterwards the resulting one very precise slot between the edges in the usual way can be welded shut. Trials have shown that on this A ratio of pipe diameter to wall thickness of 7: 1 to 80: 1 is possible. The pipe diameters range from just 3 mm to almost 40 mm possible with wall thicknesses of approximately 0.15 mm to 1 mm. Here results there is also a high precision of the outer diameter in a very low tolerance range. Thus, in this procedure Cold formed tubes with high precision and high speed getting produced.

It is useful if the workpiece in the second Is rotated back by the same angle by which it is previously twisted on the first turn. So that has Workpiece in the end practically again the position that a conventional also has a workpiece formed into a tube, only during the deformation a twist first in one and then again in the opposite direction. But this enables the advantageous and expedient deformation by means of driven Form rollers also in an area where the undercut has already increased so that a form roll no longer in the approximately C-shaped cross section of the workpiece for further deformation and can interfere with curvature.

It is therefore expedient if after the first rotation section on the Mold rollers attacking the workpiece are driven around horizontal axes and the workpiece as it continues to deform Form rolls is pushed in the feed direction. Since so far in this area and degree of deformation on a workpiece outside attacking form rollers with their axes of rotation transverse to the previous form rolls had to be oriented, they were normally without drive and were therefore unable to feed anything contribute. This not only resulted in less accuracy, but also could also lead to traces on the outside of the pipe which its feed practically sets these rollers in rotation had to. Since these form rolls now also around horizontal axes can be driven with the previous ones Form rollers are driven together easily, which also Feed positively influenced.

The form rollers behind the second turning section also rotate around horizontal axes and pull the workpiece in Feed direction. So it is in this area of the Form rollers actively moved in the feed direction, which is the quality of the Manufacturing benefits.

The drives of the driven form rollers can thus be synchronized be, the synchronization is carried out in particular mechanically. This allows the peripheral speeds of the form rollers Requirements of the workpiece and its material in the best possible way to adapt in the sense that a tube of high quality is created.

The torsion angle in the course of the first turning section and the second Rotation distance can be selected between 75 ° and 100 °. So it is possible to predefine a torsion angle or even to set it to make adjustable so that it differs from case to case Ratios and / or materials and / or dimensions can be adjusted.

The device used to solve the problem mentioned at the beginning with several pairs of rollers is characterized in that between the pairs of rollers on both sides of the workpiece and the pairs of rollers acting on the outside of the curvatures a turning section and a turning device for twisting the Workpiece by about a quarter turn and that behind that the outside of the curved edges attacking pairs of rollers Axes of rotation are arranged parallel to the axes of rotation of the front the rotating path and rotating device are rollers that these form rollers arranged behind the turning section also with are connected to the drive and that in the feed direction behind them to reduce the distance between the edges to be bent serving form rollers another turning section and turning device to twist the workpiece back and at least one behind Pair of rollers arranged to bring the edges closer to the welding process are.

A device is therefore proposed in which - of the Turning devices apart - all pairs of rollers parallel, horizontal Can have axes of rotation, so that they are also driven synchronously can. Accordingly, not only is the deformation accurate, but also also the feed of the originally band-shaped workpiece, see above that it is appropriately controlled to a tube of high accuracy can be deformed even if this pipe is only a small one Wall thickness and possibly only a small diameter Has. Experiments have shown that the edges are so precise move to each other, that a correspondingly accurate welding without special welding slot control, even by means of laser welding is possible. This takes advantage of the fact that the torsion Workpiece and thus the slot under a certain tension stand so that they maintain a correspondingly precise location.

The first rotating device and / or the second rotating device can have at least one pair of rollers, one roller an annular groove and whose other roles have a matching ring projection, the axes of rotation of these rollers transversely and approximately around the Angle of rotation of the workpiece compared to the previous pairs of rollers are arranged pivoted, the workpiece with its up reached at this point cross section between the ring groove and fits the annular projection. The user must therefore Workpiece, if the end face of this pair of rollers of the turning device reached accordingly twisted insert what it from this pair of rollers of the rotating device in the twisted accordingly or again turned back position is held so that the subsequent part of the workpiece the desired torsion and / or reverse torsion. The rotating device is therefore practical a bracket formed by two rollers, through which the Partially shaped tube in a certain position is fixed during the further run, namely in the ab this twisted location. The pair of roles used for this purpose represents a structurally simple additional solution and does not require any own drive, but could of course also have its own drive exhibit.

For optimization or to adapt to different ones Workpieces and materials can be made from at least one workpiece existing rotating device form-fitting pair of rollers and especially the pair of roles in terms of orientation the axes of rotation can be pivoted transversely to the feed direction and be ascertainable. This means that it can be used for pipe production Preselected torsion angles within appropriate limits and be set.

The swivel angle for the rotating device can be about 25 °, in particular about 3 ° to 10 °, adjustable and can be opposite the axes of rotation in the feed direction before the turning distance located form rollers between 75 ° and 100 °, in particular approximately 80 ° to 90 °.

Further configurations of the device, in particular with regard to the number of pairs of roles before or after the or Turning distances are the subject of claims 11 to 13. They give appropriate numbers and arrangements to one hand with as possible little, but on the other hand enough precise pairs of roles Deformation of an originally flat band, for example made of steel, to a pipe, in particular with a wall thickness, e.g. from under Allow 1 mm so that a precise welding of the edges is possible, which gives a tube of high precision, so that this can even be suitable to manufacture cannulas from it.

Even better edge training and precision in the field of later weld seam can be achieved if the first pair of rollers to bend the edges of the workpiece a pair of rollers for rolling the edges of the edges are upstream. So that the edges before the actual bending with great accuracy on a bring uniform shape, which at the same time in the subsequent Bending the workpiece to different degrees of deformation Inside and outside are taken into account, so a corresponding precise gap with optimal geometry at the two edges bending for the subsequent welding process.

Fig.1

eine Seitenansicht und

Fig.2

eine Draufsicht einer erfindungsgemäßen Vorrichtung mit Paaren von Umformrollen und in Vorschubrichtung dazwischen angeordneten Drehstrecken mit Drehvorrichtungen für ein ursprünglich bandförmiges Werkstück, welches im Vorschubverlauf zu einem Rohr geformt wird,

Fig.3

die einzelnen Rollenpaare vom ersten Eintritt des Werkstückes in die Vorrichtung bis zur Fertigstellung einschließlich auch einer Kalibrierung, wobei die einzelnen Formrollen teilweise nur mit den einander zugewandten Hälften ab ihren Mittellinien dargestellt sind und dieselbe Numerierung wie in Fig.1 und 2 aufweisen,

Fig.4

jeweils den Querschnitt des Werkstückes im Fortschritt der Verformung von einem ursprünglich bandförmigen Ausgangsmaterial bis hin zu dem endgültig geformten Rohr, wobei der Arbeitsvorschritt in Fig.4 von unten nach oben verläuft,

Fig.5

in gegenüber Fig.3 vergrößertem Maßstab und im Längsschnitt die Formgebung der Formrollenpaare in ihrem Wirkbereich auf das Werkstück, wobei der Verformungsfortschritt in zwei Spalten jeweils von oben nach unten dargestellt ist und zwar zunächst in der linken Spalte ganz von oben ausgehend von einem ebenen Band über mehrere Umformschritte, die sich in der rechten Spalte wiederum von oben nach unten fortsetzen,

Fig.6

eine erste Drehvorrichtung entgegen der Vorschubrichtung, also in Richtung des Pfeiles "A" in Fig.7 gesehen,

Fig.7

eine Seitenansicht der Drehvorrichtung gemäß Fig.6,

Fig.8

eine der Fig.6 entsprechende Ansicht einer in Vorschubrichtung zweiten Drehvorrichtung mit Blickrichtung in Richtung des Pfeiles "B" in Fig.9 sowie

Fig.9

eine Seitenansicht der zweiten Drehvorrichtung gemäß Fig.8.

An embodiment of the invention is described below with reference to the drawing. It shows in a partly very schematic representation:

Fig.1

a side view and

Fig.2

2 shows a top view of a device according to the invention with pairs of forming rollers and rotating sections arranged in between in the feed direction with turning devices for an originally band-shaped workpiece, which is formed into a tube in the course of the feed,

Figure 3

the individual pairs of rollers from the first entry of the workpiece into the device up to the completion including also a calibration, the individual form rollers being shown in part only with the halves facing one another from their center lines and having the same numbering as in FIGS. 1 and 2,

Figure 4

in each case the cross section of the workpiece in the progress of the deformation from an originally band-shaped starting material to the finally shaped tube, the working step in FIG. 4 running from the bottom upwards,

Figure 5

on an enlarged scale compared to FIG. 3 and in longitudinal section, the shape of the pairs of form rollers in their effective area on the workpiece, the progress of the deformation being shown in two columns from top to bottom, initially in the left column from the top starting from a flat band several forming steps, which continue in the right column from top to bottom,

Figure 6

a first rotating device against the feed direction, that is seen in the direction of arrow "A" in Figure 7,

Figure 7

6 shows a side view of the rotating device according to FIG. 6,

Figure 8

6 shows a view corresponding to FIG. 6 of a second rotating device in the feed direction, looking in the direction of arrow "B" in FIG. 9 and

Figure 9

a side view of the second rotating device according to Figure 8.

A device designated as a whole by 1 is used for manufacturing a tube 2 made of metallic strip material 3, also in the following "Workpiece 3" called, the device 1 due to the Features and details described below are suitable is, pipes with a relatively small diameter and relatively smaller To produce wall thickness.

The device 1 has several in the feed direction of the Workpiece 3 roller pairs 01, 02, 03 arranged one behind the other and 04 and in the feed direction according to arrow Pf1 in FIG Distance to pairs of rollers 05 and 06 and with a further distance Roller pairs 07 and 08 as well as 09 and finally roller pairs 10 to 13 to calibrate on, causing a gradual deformation with increasing curvature of the edges 4 of the workpiece 3 in Feed course is carried out towards each other, this gradual deformation in Figure 4 in a schematic representation is indicated from the bottom up. One can see in Fig.4 in the bottom representation shows the initial cross section of the band-shaped Workpiece 3, which according to those located above Cross sections are deformed more and more until according to the very top these schematic cross-sectional representations, the tube 2 is formed.

3 and 5 are first pairs of rollers 01 to 04 - in the Technical terminology also called "stitch 01" to "stitch 04" - provided the top and bottom of the workpiece 3 at the same time attack while in the area where the curved edges 4 form the undercuts 5 indicated in FIG. 4, pairs of rollers 05 and 06 are designed and arranged so that their roles attack on the outside of the curved edges of the workpiece 3, as it is particularly evident in Fig.5 in the "stitch 05" and as "Stitch 06" designated individual representations can be seen, wherein additionally between the support rollers 05a and 06a which reach between the edges are indicated in Fig.5.

It can be seen especially in Fig.5 in connection with Fig.4 that between the "stitch 04" and the "stitch 05" the workpiece 3 by almost a quarter turn is twisted and can be seen in Fig. 1 and 2 between the pairs of rollers 04 and 05 also a corresponding, as first turning distance for this torsion process, in which a first rotating device 6 is arranged, which is shown in FIG and 7 again separately and with regard to their form rolls within 5 is shown as "stitch 04/05".

Behind this first rotating device 6 there are already mentioned pairs of rollers 05 and 06 whose roles on the outside attack the curved edges 4 of the workpiece 3. Between the pair of rollers 04 and the pair of rollers 05 this quarter turn of the Workpiece 3 takes place, the pairs of rollers 05 and 06 with their Rotation axes parallel to the rotation axes in front of the rotation path located roller pairs 01 to 04 and arranged according to Fig.2 Drive gear 7 can be driven synchronously, so that the pairs of form rollers 01 to 04 and the form roller pairs 05 and 06 a common one Drive with the gear 7 and a motor 8 can have that Workpiece 3 is also subjected to a feed in the area, in which the form rollers on the outside of the curved edges 4 attack and no longer the workpiece 3 itself between them record, as in the roller pairs 01 to 04.

In the feed direction behind this to reduce the distance of the Forming rollers to be bent towards each other 4 is one further or second turning section with a turning device 9 recognizable with which the workpiece is twisted back or is turned back, after which two more in the exemplary embodiment Roller pairs 07 and 08 for the final approximation of the edges 3 for follow the welding process. The tool sets 09 are expediently around compression rollers, while the roller pairs 10 to 13 serve for the final calibration of the tube 2.

The first rotating device 6 and also the second rotating device 9 point according to Figures 6 and 7 and 8 and 9 and also according to 5 each a pair of rollers, consisting of two rollers 61 and 62 or 91 and 92, the roller 61 according to FIG. 6 having an annular groove and the other roller 62 of the first rotating device 6 one to do so have matching ring projection and the axes of rotation 63 of these rollers 61 and 62 across and about the angle of rotation of the workpiece 3 opposite the preceding pairs of rollers are arranged pivoted. there is indicated in Figure 5 that the workpiece 3 with its cross section between the annular groove and the annular projection of these rollers 61 and 62 fits and thus form-fitting in the rotated position is held and fixed, although at the same time a feed he follows.

The roller 91 also has an annular groove according to FIGS. 8 and 5, while the Roller 92 engages the workpiece at its slot has an annular projection, which is also in an annular groove is arranged to the now adapted to the final pipe Cross section of the workpiece 3 according to Fig. 5, stitch 06/07 consider.

In both rotating devices 6 and 9, the workpiece 3 form-fitting against the previous twisting and torsion held so that the twist or torsion during the feed occurs gradually at all cross-sectional areas of the workpiece and the workpiece is deformed according to the feed.

It is indicated in Figure 6 as well as in Figure 8 that the one existing the workpiece 3 form-fitting pair of rollers Rotating device 6 and 9 and in particular their respective pair of rollers with respect to the orientation of the axes of rotation 63 and 93 transverse to Feed direction can be pivoted and locked according to arrow Pf1 is, for the first rotating device according to Figure 6 in the embodiment a swivel angle of 8 ° and for the second rotating device 9 a pivoting angle of 4 ° is indicated according to FIG. So can the torsion of the workpiece 3 in the course of the turning distance between the roller pairs or stitches 04 and 05 also from case to case corrected or adjusted and to the workpiece, its dimensions and its material can be adjusted.

The swivel angle for the workpiece 3 within the rotating device 6 and also in turn in the rotating device 9 can also via a larger angle difference can be changed or - always constant angle of rotation - be different. Are conceivable Angle of rotation of approximately 75 ° to 100 ° and in particular approximately 80 ° to 90 ° or - as in the exemplary embodiments - deviations of 90 °, that are smaller than 10 °.

Figures 1 and 2 show that a first set of pairs of rollers from "stitch 01" to "stitch 04" for the first deformation of the edges 4 and their curvature compared to the starting position as a sheet metal strip trained workpiece 3 up to the turning distance with the first Rotating device 6 comprises four pairs of rollers. It has shown, that this is a convenient number of forming rolls around the sheet metal strip so far to prepare and in terms of cross section deform that it is then outside for further deformation of the curvatures of the edges is to be recorded, but what about a quarter turn is twisted.

Behind the first rotating device 6 are in the embodiment two pairs of rollers 05 and 06 to approximate those curved in cross section Edges 4 towards each other and behind it the second rotating device 9 arranged. The pairs of rollers 07 and 08 behind the second rotating device 9 also have rollers rotating about horizontal axes on. It is then followed by upsetting rolls 09, too can rotate around vertical axes. In the further feed process then closes a calibration part with the roller pairs 10 to 13 and finally the welding device 14.

1 and 2 it can also be seen that a first pair of rollers 100 before the subsequent pairs of roles 01 to 04 slightly different is trained. It is the pair of roles, which in Fig. 5, left column at the top with "before stitch 01" is designated and is also indicated schematically in FIG. The first pair of rollers 01 for bending the edges 4 of the workpiece 3 is upstream of this pair of rollers and is used for rolling the Edges of the edges 4, so that these after the bending of the cross section to a circle despite the different radii of curvature of the Inside and outside of the workpiece a narrow, practically constant gap practically over the entire material thickness form with each other, which makes welding easier.

With the device 1 described above, a tube 2 can be made from a Workpiece 3 in. initially as a flat strip material several forming stations one behind the other in the conveying direction and pairs of rollers are made by the edges 4 of the Workpiece 3 more and more bent and in the feed direction be curved towards each other. This happens first in the Roller pairs 01 to 04.

If the edges 4 are curved so far that they have an undercut 5 form, the partially already curved and shaped workpiece 3 twisted about a quarter turn in a first turning section and then further deformed to the tube 2, the between the Edges 4 located slot in the further course of the feed 4 and 5 is reduced, initially in the slot still engage corresponding annular guide projections can. Before the final closing and welding of the Edges 4 limited slot, the workpiece 3 in a second Rotation distance - by means of the second rotating device 9 - again rotated back, then the edges 4 finally together be welded. If necessary, one can also be used beforehand Calibration take place.

The workpiece 3 can in the second rotational path by means of the second Rotating device 9 rotated back about the same angle to which it was previously on the first turning route by means of the first Rotating device 6 is twisted. To deform the edges 4 the workpiece is close to each other except for a small slot width during its advance compared to its normal orientation twisted what due to the length of the turns and the elasticity the material of the workpiece 3 is possible.

Advantageously, after the first turning section on the workpiece 3 attacking form rollers 05 and 06 around horizontal Axes rotate and are driven so that the workpiece 3 at its further deformation from these form rollers 05 and 06 in Feed direction is pushed.

Rotate the form rollers 07 and 08 behind the second turning section also around horizontal axes, are driven and pull the workpiece 3 in the feed direction, so that practically all form rolls the device 1 also for the feed and further transport of the workpiece. The drives of the driven form rollers before and after the turning sections are driven synchronized, as schematized in Fig.2 by the gear 7 and the motor 8 and the outputs 7a and a connecting shaft 7b between the two gears 7 is indicated. Only the calibration part with the calibration rollers 10 to 13 in turn have their own motor 81 and an associated gear 71.

Depending on the workpiece and dimensions, the torsion angle can vary the first rotation section and accordingly also in the second rotation section be selected and set. In the exemplary embodiment in Fig. 6 a variation of this angle by 8 °, in Figure 8 such a 4 °.

To manufacture a tube 2 from a cross-section originally flat, band-shaped workpiece 3, this is in several successive forming stations formed by pairs of forming rollers Step by step more curved in cross-section until the tube shape is reached. If the edges 4 of the workpiece 3 so are widely curved so that they each form an undercut, So form rollers can no longer intervene so far that they Can continue to shape the inside of the cross section, that will partially shaped workpiece 3 in a first rotational path by approximately twisted a quarter turn and in this twisted position in further feed deformed such that the between the Edges 4 located slot reduced in the further feed course becomes. Before the final approach or closing and welding of the slot, the workpiece 3 is in a second rotational path rotated back again, after which the edges 4 are welded.

Claims (14)

1. Process for producing a preferably thin-walled tube (2) from strip material, wherein the initially flat strip material is shaped in a plurality of shaping stations arranged one behind the other in the direction of conveying to form the tube, the edges (4) of the strip material being bent round more and more and curved towards each other, characterised in that when the edges (4) are curved so far that they form an undercut (5) the partially shaped workpiece (3) is twisted through roughly a quarter turn in a first rotation zone and is then deformed further, the gap between the edges being reduced as the advance and deformation continue, and before the final closing and welding of the gap the workpiece is turned back again in a second rotation zone and then the edges (4) which have been brought towards one another are welded together.
2. Process according to claim 1, characterised in that in a second rotation zone the workpiece is turned back again through roughly the same angle as the one through which it was twisted previously in the first rotation zone.
3. Process according to claim 1 or 2, characterised in that after the first rotation zone, shaping rollers (05, 06) acting on the workpiece (3) are driven about horizontal spindles and the workpiece (3) is pushed in the direction of advance by these shaping rollers (05, 06) as deformation continues.
4. Process according to one of claims 1 to 3, characterised in that shaping rollers (07, 08) acting after the second rotation zone also rotate about horizontally disposed spindles and pull the workpiece (3) along in the direction of advance.
5. Process according to one of claims 3 or 4, characterised in that the drives of the driven shaping rollers are synchronised in operation before, between and after the rotation zones and the synchronisation is effected by mechanical means, in particular.
6. Process according to one of claims 1 to 5, characterised in that the angle of torsion in the first rotation zone and/or the second rotation zone is selected, more particularly set, to be between 75° and 100°.
7. Apparatus (1) for producing a tube (2) from metal strip material (3) with a relatively small diameter and thin walls, having a plurality of pairs of rollers (01,02,03,04) arranged one behind the other in the direction of advance of the workpiece (3) for gradually and then increasingly deforming and curving the edges (4) of the workpiece (3) towards each other as the workpiece advances, wherein first pairs of rollers (01 to 04) act on the top and bottom of the workpiece (3) and pairs of rollers that act on the outsides of the curved edges are provided in the area where the bent edges (4) form undercuts (5), characterised in that between the pairs of rollers acting on both sides of the workpiece and the pairs of rollers acting on the outsides of the curves, are provided a rotation zone and a rotation device (6) for twisting the workpiece through roughly a quarter turn and thereafter the pairs of rollers acting on the outsides of the curved edges are mounted with rotation axes which are parallel to the rotation axes of the rollers located before the rotation zone and rotation device, in that these shaping rollers arranged after the rotation zone are connected to the drive and that behind these shaping rollers that serve to reduce the spacing between the edges (4) which are to be bent towards each other, in the direction of advance, are provided another rotation zone and rotation device (9) for twisting the workpiece and turning it back again and after this is provided at least one pair of rollers for bringing the edges (3) together for the welding operation.
8. Apparatus according to claim 7, characterised in that the first rotation device (6) and/or the second rotation device (9) has/have at least one pair of rollers, one roller (61) of which has an annular groove while the other roller (62) has an annular projection that fits said annular groove, the rotation axes (63) of these rollers (61, 62) being arranged transversely of the previous pairs of rollers and pivoted relative thereto by roughly the angle of rotation of the workpiece (3), and in that the cross section of the workpiece (3) fits between the annular groove and the annular projection.
9. Apparatus according to claim 7 or 8, characterised in that the rotation device (6, 9) consisting of at least one pair of rollers which grips the workpiece (3) by interlocking engagement and in particular the pair of rollers is pivotable and fixable in relation to the orientation of the rotation axes transversely of the direction of advance (Pfl).
10. Apparatus according to claim 9, characterised in that the pivot angle for the rotation device (6; 9) is adjustable by about 25°, particularly about 3° to 10°, and is between 75° and 100°, particularly about 80° to 90° relative to the rotation axes of the shaping rollers located before the rotation zone in the direction of advance.
11. Apparatus according to one of claims 7 to 10, characterised in that a first set of pairs of rollers for the first curving and deformation of the edges relative to the starting position of the workpiece (3) which is in the form of a sheet metal strip up to the rotation zone comprises about three to six, preferably four or five pairs of rollers.
12. Apparatus according to one of claims 7 to 11, characterised in that behind the first rotation device (6) are provided at least two pairs of rollers (05, 06) for bringing the curved edges (4) together and behind them is provided the second rotation device (9).
13. Apparatus according to one of claims 7 to 12, characterised in that the pairs of rollers after the second rotation device (9) have rollers some of which rotate about horizontal axes and some of which rotate about vertical axes and behind them is mounted the welding apparatus (14).
14. Apparatus according to one of claims 7 to 13, characterised in that upstream of the first pair of rollers which serve to bend the edges (4) of the workpiece (3) is provided a pair of rollers for rolling the rims of the edges (4).

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