EP2446980B1 - Scaffold tube and method for processing tube ends - Google Patents

Description

The invention relates to a scaffolding tube according to the preamble of claim 1 and a method for machining pipe ends by plastic cold forming according to the preamble of claim 7.

From the prior art tubes are known, the end of which is tapered, so that the tapered end can be inserted, for example, in the opposite end of a similar or similar pipe. Such pipes are used for example for the construction of tents and are known in particular from scaffolding. The pipe ends of such pipes are tapered such that the outer diameter of the tapered pipe end substantially corresponds to the inner diameter of the unrinned pipe. However, a small clearance is required so that the tapered pipe end can be inserted into another tube of the same type, without it comes to clamping between the two tubes.

Several methods for producing a tapered pipe end are known from the prior art. Thus, the taper, for example by rotating rollers or by pulling the tube by means of a molded sleeve, also called die or Einziehwerkzeug be generated. For example, it is off DE 20 2008 017 196 U1 a device for retracting a pipe end known. The mold sleeve, in which the pipe end is pressed in the axial direction, is conically tapered on the inside, so that after the Einziehvorgang a conically formed transition region between the tapered pipe end and the non-tapered pipe. This has the consequence that a tube that is attached to the tapered end of the tube, does not rest on a smooth bearing surface. As a result, an overall length that is extremely subject to tolerances results, in particular in the case of several plugged-together tubes. This is because the axial bearing point of an attached pipe is subject to several uncertainty factors, such as wear or diameter tolerances, due to the conical transition region between the tapered pipe end and the unrinned pipe. In addition, the conical transition region often results in an attached tube being clamped to the conical transition region and can no longer or only with difficulty be pulled off the tapered tube end.

For this reason, it is also known to compress the tube after retraction of the pipe end in the region of the transition, so that from the conical transition, an axial contact surface is formed. As a result of the upsetting process, a bead bulges outward in a region of the non-tapered tube adjoining the transition. A method for producing such a pipe end is for example made DE 2654439 A1 known. Also the DE 1972690 U disclosed a scaffolding tube having a bead between the tapered end and the undeformed tube.

Scaffolding tubes with a bead between the tapered tube end and the undeformed tube have the disadvantage that they can not be pushed through retaining clips, for example, due to the radially outwardly projecting bead, which are only loosened and not fully opened for mounting or dismounting a scaffold. Also, there may be other applications requiring the passage of a scaffolding tube through an opening that substantially matches the outside diameter of the undeformed tube. This is not possible with pipes having an outwardly projecting bead.

While scaffold tubes with a bulge created by compression provide a good axial bearing surface for an attached tube, the load transfer into the undeformed region of the tube above the bead is not optimal. The bead forms a kind of resilient element between the axial bearing surface and the undeformed region of the scaffolding tube. For larger axial forces, which act on a system of several assembled scaffolding tubes, it may also happen that the bead between the axial bearing surface and undeformed tube area is further compressed. On the one hand, this leads to a change in length of the scaffold tube, on the other hand, this can also cause the mated tubes can not be pulled apart or clamp due to the deformation.

From the prior art, it is also known to provide the tapered pipe end as a separate component to insert into an undeformed tube with larger diameter and then preferably to weld from the inside with the larger pipe. Although this creates a clean bearing surface, the load transfer into the scaffolding tube is optimal, but this procedure is complicated and expensive to manufacture. In addition, during the welding process, thermal distortion of the tubes may occur, which may result in the scaffolding tubes becoming stuck when nesting and pulling apart.

Out WO 2005/021326 A2 There is known a canted tube which serves to secure a bumper and is adapted to absorb energy by deformation. The overturn tube comprises a larger diameter section and a smaller diameter section thereafter. The two sections are connected by a double fold. The double fold is a loose double fold whose folds do not lie directly against each other. Upon axial loading of the telescoping tube, the portion of the smaller diameter tube plunges into the portion of the larger diameter tube with continuous deformation of the double seam. OBJECT OF THE PRESENT INVENTION It is to provide a scaffolding tube with a tapered tube end that provides a good axial bearing surface between the tapered region and the undeformed tube while providing optimum load transfer. In addition, it should be avoided that a bead protrudes significantly beyond the outer circumference of the undeformed tube to the outside. The tube should also be easy to manufacture and cheap to manufacture. It is a further object of the present invention to provide a method for producing such a pipe or for machining pipe ends.

The object is solved by the features of independent claim 1 of the present invention. The invention is based on a scaffolding tube having a first section and having a second section adjoining the first section, wherein the first section has a first cross section with a first outer contour and a first inner contour, and the second section has a second cross section with a second outer contour and have a second inner contour. Furthermore, the second section can be inserted into a tube whose cross section corresponds to the first cross section. According to the invention, it is provided that the first section and the second section are integrally connected to one another via a double fold, wherein the fold layers of the double fold abut one another directly.

The solution according to the invention offers the advantage that a precisely defined axial contact surface exists between the tapered second section and the unrestrained first section. Due to the double fold, whose folds lie directly against one another, it is further ensured that the tube in the region of the double fold is not significantly widened beyond the outer contour of the first section. The tube can therefore be inserted through openings which correspond in their cross-section substantially to the outer circumference of the tube. Due to the fact that the folds of the double fold lie directly against each other, an optimal load transfer is ensured. The double fold can hardly be deformed by axially acting forces under normal use. By integral connection between the first portion and the second portion is meant that the first portion and second portion are not connected by a weld or other joint, but consist of a single continuous tube. The scaffold tube according to the invention is easy to manufacture and inexpensive to manufacture.

The scaffold tube according to the invention consists of metal, preferably of steel. Preferably, the tube is a hollow cylindrical tube, but also tubes with different cross-section, such as a rectangular cross-section with rounded corners are conceivable. The tube of the invention may also have a poligonal cross-section. Preferably have first section and second section of the tube over the entire length thereof or almost the entire length of a constant cross-section.

Advantageous embodiments of the present invention are the subject of the dependent claims.

According to a particularly preferred embodiment of the present invention, the tube in the region of the double fold has an outer contour which substantially corresponds to the first outer contour. If the tube in the region of the double fold has only a slightly larger outer contour than the undeformed first section of the tube, then the tube can be pushed through loosened fastening tube clamps. It is particularly advantageous if the outer contour in the region of the double fold exactly corresponds to the first outer contour and thus the tube is wider at no point than in the area of the undeformed first section.

In a further preferred embodiment of the present invention, the second outer contour corresponds to the first inner contour minus a small clearance. This ensures that nested tubes have a good fit and at the same time it is possible to easily insert the tubes into each other and pull apart.

In a particularly preferred embodiment of the present invention, the second section represents one end of the tube and is chamfered on the outside at the free end. The chamfer facilitates nesting of the tubes.

In a further particularly preferred embodiment of the present invention, the second portion has a free end, wherein an at least partially plate-shaped component with a front, a back and a passage opening is fitted onto the second portion, so that the second portion penetrates the passage opening and the Front side of the component abuts a formed by the double fold axial stop of the tube, and further wherein the free end of the second portion is flanged radially outwardly on the back of the component. As a result, another component can be fixed at the end of the tube, wherein a simple, stable and extremely accurate fixation of the additional component is possible. Due to the axial stop, which is formed by the double seam, a precise alignment of the tube can be ensured perpendicular to the plane of the partially plate-shaped member. By crimping the free end of the second section a positive connection between the tube and additional component in the axial direction is achieved. By a high contact pressure when crimping the free end of the second portion on the back of the additional component can also be an additional adhesion between the pipe and the additional Component can be achieved. The passage opening in the additional area-wise plate-shaped component is preferably formed so that there is a slight clearance between the passage opening and the outer contour of the second section. As a result, the additional component can be attached easily and without great effort to the second section of the tube. Between the passage opening of the additional component and the second portion of the tube may also be a press fit.

Preferably, the length of the second portion of the tube is dimensioned so that the radially outwardly flanged on the back of the component free end terminates at least with the outer contour of the cross section of the first portion or even slightly more radially outwardly protrudes. This ensures a secure and stable cohesion between the pipe and the additional component.

Most preferably, the at least partially plate-shaped component is a base plate of a ceiling support. The scaffolding tube according to the invention is itself designed as a ceiling support in this case, wherein the base plate of the ceiling support is simple, inexpensive, stable and extremely precise attached to the pipe end.

The beading of the free end of the second portion on the back of the additional component is preferably carried out by rolling over the protruding over the back of the plate-shaped member portion of the second portion.

The invention further provides a method for processing pipe ends by cold plastic working, by which in particular the above-described invention scaffolding tube can be prepared. The method according to the invention comprises a plurality of method steps. In a first method steps, the end of a tube is drawn in, so that the tube after the drawing process has an undeformed first section with a first cross section, a second section deformed by the insertion process with a second cross section, and a transition between the first section and the second section wherein the second cross section is smaller than the first cross section. In the first method step, therefore, only a first tapering of the pipe end takes place. In a subsequent process step, an outward circumferential bead is produced in a region of the first section immediately adjacent to the transition by swaging the tube in this region. After this process step, the bead is folded over the transition in the direction of the free end of the second portion, so that a double seam is formed, via which the first portion is connected to the second portion.

By turning over the bead is achieved that the outer contour of the tube in the region of the double fold substantially corresponds to the outer contour of the first section. Furthermore, this also ensures that the folds of the double fold abut each other directly. By the method according to the invention, a clearly defined axial abutment surface is created for a tube plugged onto the tapered section of the tube. Furthermore, the method according to the invention provides a tube with a tapered end, which ensures optimum axial force introduction via the axial bearing surface. The method according to the invention can be carried out extremely quickly and enables simple and cost-effective production. At the same time, the manufacturing tolerances are very low.

Further advantageous embodiments of the method according to the invention are the subject of the dependent claims.

In a particularly preferred embodiment of the present invention, a mold sleeve is used for the insertion process, the inner contour is tapered in the axial direction, wherein the mold sleeve is pressed onto the tube for pulling the pipe end in the axial direction. Such mold sleeves are known from the prior art and are also referred to as dies or Einziehwerkzeuge or dies. With a molded sleeve, the pipe end can be rejuvenated extremely quickly and precisely.

In a further preferred embodiment of the present invention, the second portion of the tube for generating the bead is supported on the outside by a support sleeve, which is driven to produce the bead on the second portion and at least a portion of the first portion, wherein in the inner contour of the support sleeve Is formed in the region of the bead to be produced a circumferential groove, in which bulges the bead during the upsetting operation to the outside. The support sleeve ensures that the tube is compressed such that the bead forms in a clearly defined area. In addition, the shape of the bead can be suitably specified by the geometry of the circumferential groove.

In a further particularly preferred embodiment of the present invention, the upsetting operation is carried out by means of a mandrel, with which an axially directed pressing force is exerted on the free end of the second section. This allows a simple to perform and exactly controllable type of compression.

In a further preferred embodiment of the present invention, the turning over of the bead takes place by pulling off the support sleeve in the direction of the free end of the second portion, wherein the free end is axially supported by the mandrel. This represents a very particularly preferred embodiment of the method according to the invention, since the method thereby becomes extremely fast and cost-effective. The support sleeve also forms the tool for the process step of turning over the bead.

Preferably, the support sleeve has a first end and a second end, wherein the first end of the support sleeve is located during the compression process in the region of the first portion, and wherein the groove is formed such that the inner contour of the support sleeve starting is tapered ramp-like from a maximum cross section of the groove in the direction of the first end. If the pipe to be machined is a hollow-cylindrical pipe, the ramp-like taper is a conical taper of the inner contour of the support sleeve. The ramp-like taper allows easy removal of the support sleeve and a precise turning of the bead produced in the previous process step. The ramp-like taper makes the support sleeve to a calibration tool with which the outer contour defined in the region of the generated double fold can be returned to an exact diameter, for example the outer diameter of the undeformed tube.

Further, the angle of the ramp-like taper to the longitudinal axis of the support sleeve is preferably a maximum of 15 degrees. As a result, the removal of the support sleeve is particularly facilitated.

If the cross section of the inner contour at the first end of the support sleeve essentially corresponds to the outer cross section of the first section, then the outer contour in the region of the double rebate can essentially be returned to the outer contour of the undeformed tube in the region of the first section. Preferably, the cross section of the inner contour at the first end of the support sleeve corresponds to the outer cross section of the first portion of the tube plus a small clearance.

In a further particularly preferred embodiment of the present invention, the drawing-in process and the upsetting process take place in a single process step, with the mold sleeve and the support sleeve being combined to form a single tool. As a result, only one tool is required for the entire process, as a result of which the method according to the invention becomes particularly fast. The process is very cheap. Experiments have shown that this combination of molded sleeve and support sleeve is suitable for a single tool only for Rohrendenverjüngungen up to a certain length. Also, this particularly rapid variant of the method according to the invention is possible only with pipes made of certain materials and with a certain thickness range of materials.

The tube must be supported axially for processing by the method according to the invention during the drawing-in process and the compression process in the region of the first section.

An embodiment of the present invention will be explained in more detail below with reference to drawings.

• Fig. 1 eine Seitenansicht eines erfindungsgemäßen Rohrs,
• Fig. 2 eine isometrische Ansicht des erfindungsgemäßen Rohrs aus Fig. 1,
• Fig. 3 einen Längsschnitt durch das erfindungsgemäße Rohr aus den Fig. 1 und 2,
• Fig. 4 einen Längsschnitt durch eine Formhülse zur Herstellung des erfindungsgemäßen Rohrs aus den Fig. 1 bis 3,
• Fig. 5 einen Längsschnitt durch ein mittels der Formhülse aus Fig. 4 bearbeitetes Rohr,
• Fig. 6 einen Längsschnitt durch eine Stützhülse und einen Stützdorn zur weiteren Bearbeitung des in Fig. 5 gezeigten Rohrs,
• Fig. 7 einen Längsschnitt durch ein mittels der in Fig. 6 gezeigten Apparatur bearbeiteten Rohrs in einem Zwischenstadium,
• Fig. 8 eine Schrägansicht eines erfindungsgemäßen Rohrs, das als Deckenstütze ausgebildet ist, und
• Fig. 9 einen Längsschnitt durch das als Deckenstütze ausgebildete Rohr aus Fig. 8.

Show it:

• Fig. 1 a side view of a tube according to the invention,
• Fig. 2 an isometric view of the tube of the invention Fig. 1 .
• Fig. 3 a longitudinal section through the pipe according to the invention from the Fig. 1 and 2 .
• Fig. 4 a longitudinal section through a molded sleeve for the production of the tube according to the invention from the Fig. 1 to 3 .
• Fig. 5 a longitudinal section through a means of the molded sleeve Fig. 4 machined pipe,
• Fig. 6 a longitudinal section through a support sleeve and a mandrel for further processing of in Fig. 5 shown tube,
• Fig. 7 a longitudinal section through a means of in Fig. 6 shown apparatus of processed pipe in an intermediate stage,
• Fig. 8 an oblique view of a pipe according to the invention, which is designed as a ceiling support, and
• Fig. 9 a longitudinal section through the trained as a ceiling support pipe Fig. 8 ,

For the following statements applies that the same parts are designated by the same reference numerals.

An inventive tube 1 is in the FIGS. 1 to 3 shown. The tube 1 comprises a first portion 10 and a second portion 20, which are connected to each other via a double seam 30. The tube is a hollow cylindrical scaffolding tube whose end is tapered and formed by the second section 20. It should be noted that the invention is not limited to the hollow cylindrical tube shown. Also conceivable would be other deviating from the hollow cylindrical shape cross sections such as oval, triangular, rectangular or other poligone cross sections.

The second section 20 of the tube 1 is tapered such that a tube of the same type with the wider side can be plugged onto this second section 20. The outer diameter of the tapered portion 20 must be to be slightly smaller than the inner diameter of the first portion 10 so that there is little play between the nested tubes. The play ensures that the pipes can simply be plugged into each other and pulled apart. The tube is further chamfered at the free end 7 of the second portion 20 by a chamfer 40, whereby the nesting of the tubes is facilitated.

In Fig. 1 it is shown that the second portion 20 has a continuous transverse bore 8 into which a bolt can later be inserted for locking the nested tubes. The other tube, not shown, must also have a hole to do so.

In Fig. 3 showing a longitudinal section through the tube 1, the double seam 30, via which the first portion 10 is connected to the second portion 20, shown in more detail. The double fold 30 consists of the three fold layers 2, 3 and 4, which abut each other directly. The outer fold layer 4 is the extension of the first portion 10 of the tube 1. The middle fold layer 3 abuts against the inner contour 11 of the first portion 10 and is connected both to the outer layer 4 and the inner layer 2 in one piece and without a joint. The inner fold layer 2 in turn merges into the second section 20 of the tube 1. The outer contour 22 of the second section lies in the region of the double fold 30 directly against the middle fold layer 3.

The constant diameter of the outer contour 12 of the first portion 10 is slightly widened before the double fold 30, as well as the constant diameter of the inner contour 21 of the second portion 20 is slightly tapered in front of the double fold 30. It is thereby achieved that the outer diameter of the second section 20 approximately corresponds to the inner diameter of the first section 10, although between the two sections in the region of the double fold 30, the middle fold layer 3 is arranged.

The method for producing the pipe according to the invention from the Fig. 1 to 3 will be described below on the basis of FIGS. 4 to 7 explained.

The Fig. 4 shows a molded sleeve 50 by means of which the tube end of an initially undeformed tube 1 'is drawn with a constant diameter. The inner contour 51 of the rotationally symmetrical molded sleeve 50 has an opening 57 into which the tube 1 'is inserted for the Einziehvorgang. For drawing in the tube 1 ', either the tube 1' can be pressed into the molded sleeve 50, or the shaped sleeve 50 can be pressed onto the tube 1 '. After the opening 57, the inner contour 51 of the molded sleeve 50 initially has a cylindrical region 52. In this cylindrical portion 52, the tube 1 'is guided only. The diameter of the cylindrical portion 52 therefore corresponds approximately to the outer diameter of the undeformed tube 1 'or is slightly larger.

After the cylindrical portion 52, the inner contour 51 of the molded sleeve 50 is tapered. By the taper 53, the outer diameter of the tube 1 'is brought to the desired outer diameter of the later second section 20. The already tapered part of the tube 1 'introduced into the mold sleeve 50 is guided or radially supported after the taper 53 with the aid of the guide sleeves 54, 55 and 56. This avoids undesirable deformation, for example, bending of the tapered portion of the pipe 1 ', which may occur due to machining.

The intermediate product achieved by the process step described above is in Fig. 5 shown. The tube 1 'now has a first section 10 and a second section 20, which already correspond in their cross section to the finished tube. First section 10 and second section 20 are interconnected by a tapered transition 5.

For further processing, the in Fig. 5 shown intermediate in the in Fig. 6 shown support sleeve 60 introduced. Also for this purpose, either the pipe can be moved in the axial direction when the support sleeve 60 is stationary. It is also possible to hold the tube and drive the support sleeve 60 on the pipe end. The inner contour 61 of the support sleeve 60 is divided into several sections. At the first left end 63, the cross section of the inner contour 61 corresponds to the later outer diameter of the double fold 30 of the tube 1. This diameter corresponds either to the outer diameter of the first section 10 or is slightly larger. The inner contour 61 further has a groove 62, wherein the inner contour is tapered starting from this groove 62 in the direction of the first end 63 ramp-like or conical. This conical taper is designated by the reference numeral 65. Starting from the groove 62 in the direction of the right second end 64 of the support sleeve 60, the inner contour 61 substantially corresponds to the outer contour 22 of the second portion 20 of the tube 1 '. At the end 64, the inner contour 61 has a second conical taper 67, by the chamfer 40 is generated at the free end 7 of the subsequent tube when inserting the tube 1 'in the support sleeve 60.

At the right end of this second conical taper 67 ends a coaxial with the support sleeve 60 arranged support mandrel 70. With the help of this support mandrel 70 is exerted on the free end 7 of the inserted into the support sleeve 60 tube 1 'an axial pressing force. The length of the support sleeve 60 is dimensioned such that the in Fig. 5 shown conical transition 5 between the first portion 10 and the second portion 20 in the region of the groove 62 of the inner contour 61 comes to rest. Due to the axial pressing force, the tube 1 'is compressed in the region of the transition 5, so that in the groove 62 of the in Fig. 7 shown bead 6 is formed.

In the last step, the in Fig. 6 shown support sleeve 60 withdrawn to the right of the tube 1 '. The mandrel 70 remains unchanged while in position and supports the free end 7 of the tube 1 'in the axial direction. By removing the support sleeve 60 of the in Fig. 7 shown bead 6 by the ramp-like taper 65 in the inner contour 61 of the support sleeve 60 is transposed over the shortened transition 5 to the right, so that in Fig. 3 shown double seam 30 with the adjacent folded layers 2, 3 and 4 is formed. The ramp-like conical taper 65 has with respect to the longitudinal axis 66 of the support sleeve 60 preferably at an angle of at most 15 degrees.

For processing pipe ends by the process according to the invention, the in Fig. 6 shown support sleeve to a certain length of the tapered portion can also be used as a molded sleeve. The drawing of the pipe end and the production of the circumferential bead by compression of the tube can then be done in one operation. In addition, only a single tool is required.

The Fig. 8 and 9 show an inventive tube 1, which is designed as a ceiling support. The pipe end of the pipe 1 is formed substantially the same as the pipe according to the Fig. 1 to 3 and also includes a first portion 10 having a larger diameter and a second portion 20 having a smaller diameter. Unlike the tube from the Fig. 1 to 3 At the end of the tube a plate 80 is fixed, which forms a base plate and thus a foot of a ceiling support. The second portion 20 of the tube 1 is slightly shorter for the purpose of securing the base plate 80 as in the embodiment of Fig. 1 to 3 executed. The base plate 80 is attached to the second portion 20 of the tube 1, so that the second portion 20 penetrates a passage opening 83 of the base plate 80. The passage opening 83 corresponds in its diameter substantially to the outer diameter of the second portion 20, wherein a slight clearance between the second portion 20 and the passage opening 83 is provided to allow easy attachment of the base plate 80 to the second portion 20. The base plate 80 abuts in the axial direction with its front side 81 against an axial stop 31, which is formed by the double fold 30 of the tube 1. The free end 7 of the second portion 20 is flanged radially outwardly on the back 82 of the plate 80. By appropriate contact pressure when crimping a positive connection is generated to the existing between pipe 1 and base plate 80 positive connection. The length of the second portion 20 is dimensioned such that the free flanged end 7 extends in the radial direction at least as far outward as the axial stop 31 on the opposite front side 81 of the base plate 80. The base plate 80 is arched to the through hole 83, so that the flanged free end 7 of the second section terminates with a bearing surface of the base plate 80. The base plate 80 may equally serve as a foot or as a ceiling support element of the ceiling support.

Claims (15)

1. Scaffold tube (1) with a first portion (10) and with a second portion (20) adjoining the first portion (10), the first portion (10) having a first cross-section with a first external contour (12) and a first internal contour (11), and the second portion (20) having a second cross-section with a second external contour (22) and a second internal contour (21), and the second portion (20) can be inserted in a tube, the cross-section of which corresponds to the first cross-section, characterised in that the first portion (10) and the second portion (20) are integrally joined to one another via a double fold (30), and the fold layers (2, 3, 4) of the double fold (30) lie directly one against the other.
2. Scaffold tube (1) as claimed in claim 1, characterised in that the scaffold tube (1) has an external contour in the region of the double fold (30) which essentially corresponds to the first external contour (12).
3. Scaffold tube (1) as claimed in one of claims 1 or 2, characterised in that the second external contour (22) corresponds to the first internal contour (11) minus a slight clearance.
4. Scaffold tube (1) as claimed in one of claims 1 to 3, characterised in that the second portion (20) constitutes one end of the scaffold tube (1) and is chamfered on the outside at the free end (7).
5. Scaffold tube (1) as claimed in one of claims 1 to 3, characterised in that the second portion (20) has a free end (7), and an at least partially plate-shaped component (80) with a front face (81), a rear face (82) and an orifice (83) is fitted onto the second portion (20) so that the second portion (20) extends through the orifice (83) and the front face (81) of the component (80) lies against an axial stop (31) of the scaffold tube (1) formed by the double fold (30), and the free end (7) of the second portion (20) is also folded radially outwards back towards the rear face (82) of the component (80).
6. Scaffold tube (1) as claimed in claim 5, characterised in that the scaffold tube (1) is designed as a deck support and the component is a base plate (80) of the deck support.
7. Method of processing tube ends by plastic cold forming, in particular to produce a scaffold tube (1) as claimed in one of claims 1 to 6, comprising the following method steps:

   - drawing in one end of a tube (1') so that, after the drawing-in operation, the tube (1') has a first portion (10) with a first cross-section, a second portion (20) with a second cross-section formed during the drawing-in operation and a transition (5) between the first portion (10) and the second portion (20), the second cross-section being smaller than the first cross-section,

   - producing an outwardly directed, circumferentially extending bead (6) in the region of the transition (5) or in a region of the first portion (10) directly adjoining the transition (5) by compressing the tube (1') in this region,

   - folding the bead (6) back across the transition (5) in the direction of the free end (7) of the second portion (20) so that a double fold (30) is created, and the first portion (10) is joined to the second portion (20) via the double fold (30), characterised in that the fold layers (2, 3, 4) of the double fold (30) lie directly one against the other.
8. Method as claimed in claim 7, characterised in that a forming tube (50) is used for the drawing-in operation, the internal contour (51) of which tapers in the axial direction, and the forming tube (50) is pressed in the axial direction onto the tube (1') in order to draw in the tube end.
9. Method as claimed in one of claims 7 or 8, characterised in that, in order to produce the bead (6), the second portion (20) is supported on the outside by a support sleeve (60) which is moved onto the second portion (20) and at least a region of the first portion (10) in order to produce the bead (6), and a circumferentially extending groove (62) is formed in the internal contour (61) of the support sleeve (60) in the region where the bead (6) is to be produced, into which the bead (6) cambers outwards during the compressing operation.
10. Method as claimed in one of claims 7 to 9, characterised in that the compressing operation is implemented by means of a mandrel (70), by means of which an axially directed pressing force is applied to the free end (7) of the second portion (20).
11. Method as claimed in one of claims 9 or 10, characterised in that the bead (6) is folded back by pulling the support sleeve (60) in the direction of the free end (7) of the second portion (20), during which the free end (7) is axially supported by the mandrel (70).
12. Method as claimed in claim 11, characterised in that the support sleeve (60) has a first end (63) and a second end (64), and the first end (63) of the support sleeve (60) lies in the region of the first portion (10) during the compressing operation, and the groove (62) is designed so that the internal contour (61) of the support sleeve (60) tapers in a ramp-type arrangement starting from a maximum cross-section of the groove (62) in the direction of the first end (63).
13. Method as claimed in claim 12, characterised in that the angle of the ramp-type taper (65) with respect to the longitudinal axis (66) of the support sleeve (60) is at most 15 degrees.
14. Method as claimed in one of claims 11 to 13, characterised in that the cross-section of the internal contour (61) at the first end (63) of the support sleeve (60) essentially corresponds to the external cross-section of the first portion (10).
15. Method as claimed in one of claims 9 to 14, characterised in that the drawing-in operation and compressing operation are run in a single method step and the forming tube (50) and support sleeve (60) are combined in a single tool.

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