EP1283333A1 - Method of manufacturing an exhaust gas catalyst - Google Patents

Abstract

The production of an exhaust gas catalytic converter comprising a catalyst in a housing with two end connectors comprises taking a tube (30) long enough to make two housings, indenting the tube in the middle, cutting the tube at the indentation (36) to make two workpieces, charging each piece with catalyst, and indenting the charging end of each piece.

Description

The invention relates to a method for producing a Exhaust gas catalytic converter according to the preamble of claim 1.

Catalytic converters of the type mentioned are under other used in motor vehicles for cleaning exhaust gases. The catalytic converter is usually made of a metal housing formed in which a catalyst insert is arranged is. A ceramic body is usually used as the catalyst insert, a so-called monolith used by one Numerous flow channels run through and on its surface coated with a catalytically active substance is. Often, the catalyst insert has a cotton padding with which the ceramic body is wrapped in the housing is used.

DE 197 34 198 A1 describes a process for the production known an exhaust gas catalytic converter, in which from a sheet First the housing of the catalytic converter is deep-drawn is, at the same time the first connection piece of the exhaust gas catalytic converter is molded on the housing. Subsequently the catalyst insert is inserted into the housing and the second connecting piece is drawn in by rolling.

DE 197 23 939 A1 discloses a method for manufacturing a catalytic converter, in which as a starting material a tube is used, one end of which is open is drawn in by non-cutting forming. Then will into the still open insertion of the pipe the catalyst insert introduced. After installing the catalyst insert the still open introductory part becomes the second Connection piece of the catalytic converter by non-cutting forming moved in.

The method known from DE 197 23 939 A1 draws is already characterized by high productivity. The housing of the catalytic converter is made of relatively thin sheets is manufactured, sheet thicknesses of approx. 1.5 are usual mm. There is the shape of the connector on Housing the risk of wrinkles due to excessive tangential Compressive stresses. Furthermore, the housings of catalytic converters often made of difficult to deform materials, especially stainless steels, which are also manufactured tend to wrinkle.

To avoid this, this known method the tube from the inside with the help of an internal mandrel when pulling in of the connecting piece supported. Despite this measure can chipless forming in this known method however, they are often only carried out in stages, to avoid wrinkling. When using a Press-rolling process for pulling in the connecting piece is so a lot of roll overflows required to shape the connecting pieces. This results in a relatively long production time.

When forming the second connection piece on the housing there is also the problem that the connection piece usually not molded against an internal mandrel can. Hence one is compared to the molding of the first connecting piece even larger number of forming steps required with even lower forming speeds have to run to education to avoid wrinkles.

It is an object of the invention to provide a particularly efficient method for producing an exhaust gas catalytic converter.

The invention solves the problem by a method with the Features according to claim 1. Advantageous further developments of the The inventive method result from the following Description, the drawing and the dependent Claims.

In the method according to the invention, the pipe is in its Dimension the length so that a double workpiece emerges from the tube can be manufactured. In a first step becomes an intermediate section of the tube between its two Ends retracted, whereby the double workpiece is formed becomes. In this way, two workpieces formed at the same time two connecting pieces, whereby the manufacturing time compared to the known methods significantly reduced. At the same time, the formation of wrinkles avoided when pulling in the intermediate section of the tube, since the pipe material on both sides of the intermediate section the pipe material in the forming area of the intermediate section supports. This ensures the kink stability of the pipe material in the forming area compared to that during forming acting tangential compressive stresses so far increased wrinkling in the intermediate section when Reshaping is prevented. The fact that this Process step a wrinkling on the tube almost is excluded, the pipe can be compared with a the known process much higher forming speed in the intermediate section. When moving in can the contour of the connection piece in a single Infeed can be molded, creating an additional Shortening the manufacturing time results.

Then the pipe is drawn in the area Intermediate section separated, the two individual workpieces be formed from the double workpiece. After this Inserting the catalyst inserts into the workpieces, the The catalyst inserts can be inserted before or after Separation of the intermediate section will be made each individual workpiece at its introducer to form the second connecting piece retracted.

In a preferred method variant of the invention The intermediate section of the tube is symmetrical molded between its ends so that the individual workpieces formed after the separation at least show approximately identical dimensions. In this way it is possible to have two from one tube at a time to produce identical individual workpieces.

To speed up the manufacturing process as a whole, it is furthermore advantageous to put the pipe immediately after pulling it in to separate the intermediate section, since the introduction of the Catalyst inserts in the individual workpieces is simplified and drawing in the introducers of the individual workpieces separate processing stations take place simultaneously can. Furthermore, it is in this process variant of Advantage if the retraction of the intermediate section and the Separation of the double workpiece into the two single workpieces done in a single setup so that the pipe not pulled out after pulling in the intermediate section and in a subsequent processing device for Disconnect must be clamped again. This gives a particularly high level of manufacturing accuracy, since the different Processing steps on one and the same machine can be carried out.

The tube is formed with a particularly preferred one Process variant with the help of at least two forming rollers. By using the forming rolls results on the one hand the advantage that with appropriate adjustment the forming rollers have a correspondingly large degree of design freedom in the shaping, in particular of the pipe transitions is given in the connecting piece. on the other hand becomes particularly gentle through the use of the forming rollers The connecting pieces on the pipe are pulled in. at this method variant is in particular the use of three forming rollers are advantageous, evenly over the circumference of the pipe are distributed, because of this Arrangement of the forming forces that lead to bending of the Tube during forming, from the forming rollers mutually absorbed and thus balanced become.

Especially when using pipes with thin walls is also proposed when pulling in the intermediate section the pipe from the inside of the pipe to support the intermediate section with even higher forming speeds form, because a buckling of the Tube is almost excluded by the inner support. To support the intermediate section, the Use of an internal mandrel suggested in the pipe is introduced. In a particularly preferred process variant become two inner mandrels in both ends of the tube introduced to each other in the area of the intermediate section come to the plant. The use of an internal mandrel also has the advantage that with appropriate design the outer contour of the inner mandrel the inner contour of the Tube to be manufactured housing of the catalytic converter defined can be formed.

It is also proposed to introduce the Tube when pulling in the connector from the inside to support her in this process step to avoid undesired wrinkling. This one too Process variant can preferably be used to support the pipe an internal mandrel used in the introducer of the pipe when pulling in the second connecting piece becomes.

In a preferred method variant of the invention Manufacturing process is to pull in the introducer used at least one forming roller that against an at least partially conical Thorn is formed. Through an axial and radial feed movement the forming roll becomes the workpiece area to be formed each between a section of the conical Dorns and the forming roller performed.

In a particularly advantageous development of this method variant the conical mandrel is synchronized with move the feed movement of the forming roll axially, so that the edge of the workpiece area to be formed is supported and temporarily between the mandrel and the forming roll is led. In this way, wrinkles can be avoided or arisen Wrinkles are rolled smooth.

Furthermore, when using a mandrel, it is proposed that to insert a mandrel with a cylindrical section, which when pulling in the tube to form a cylindrical Pipe section, for example to form the connecting piece, leads.

In a particularly preferred variant of the method it is also proposed that when pulling the tube pulled pipe sections to the finished connecting piece to mold. This allows for subsequent processing steps dispensed for finishing the connecting piece become.

Because exhaust gas catalysts have a wide variety of cross-sectional shapes are also proposed, not only in cross section to use circular tubes as the starting material, but according to the final cross section of the one to be manufactured Housing the exhaust gas catalytic converter to use pipes in the Cross section are not rotationally symmetrical. So in particular cross-sectionally oval or elliptical tubes used as starting material.

It may also be necessary for catalytic converters be that the connecting piece is offset to the longitudinal axis of the Housing run. To also such catalytic converters to be able to manufacture with the method according to the invention, is in a particularly preferred process variant proposed the tube when forming about an axis of rotation to rotate, with the tube parallel with its longitudinal axis runs offset to the axis of rotation. The connecting pieces the housing will then be concentric about the axis of rotation of the tube so that the connection piece after pulling in the pipe offset to the longitudinal axis of the tube are formed on this.

Alternatively, it is also possible to use the tube with its longitudinal axis inclined at a predetermined angle to the axis of rotation to run so that when pulling in of the pipe connecting piece created at an angle formed inclined to the longitudinal axis of the tube extending on this are.

It is also proposed to train those who are moving in Shape the connection piece so that it fits with your Axes of symmetry are offset from one another.

In a particularly preferred variant of the invention Procedures are used to reshape the tube at the same time several forming rolls are used, the forming rolls radially and optionally also axially be delivered. The forming rollers can in their outer contour be designed in such a way that by forming formed outer profile of the tube in its shape final shape of the catalytic converter corresponds. At the same time, through the use of forming rolls extremely gentle and economical production of the catalytic converters possible.

So when using at least one forming roll for forming of the pipe also pipes with non-rotationally symmetrical Cross-sectional shapes can be formed also proposed the forming roller when retracting the Tube between a maximum and a minimum infeed position radially adjustable. This procedure for non-cutting production of non-rotationally symmetrical parts basically known.

According to the method is provided to form a defined one Deviation from the rotational symmetry of the forming roller during a single revolution of the pipe between the maximum and the minimum infeed position radially adjust, the radial adjustment of the forming roller during a single revolution from the angle of rotation of the Tube depends.

This method is used to feed the forming roll used in particular an electronically controllable actuator, controlled by an electronic control unit which is a delivery path for the forming roll the angle of rotation of the tube, given geometry data of the Pipe and the exhaust gas catalytic converter to be formed (target data) and a correction factor.

Should also tubes from the inventive method high-strength materials are formed, it is also proposed before and, if necessary, also during forming of the pipe the pipe to a temperature above the To heat the recrystallization temperature of the pipe material, whereby the tube material has less resistance to deformation opposes.

Fig. 1

eine geschnittene Seitenansicht eines Abgaskatalysators;

Fig. 2

eine geschnittene Seitenansicht eines Rohrs beim Ausformen eines Doppelwerkstücks zur Fertigung zweier Gehäuse zweier Abgaskatalysatoren;

Fig. 3

eine geschnittene Seitenansicht, in der die Fertigung eines zweiten Anschlussstutzens eines der Gehäuse gezeigt ist;

Fig. 4

eine geschnittene Seitenansicht, in der die Fertigung des zweiten Anschlussstutzens eines der Gehäuse unter Verwendung eines zylindrischen Innendorns gezeigt ist;

Fig. 5

eine geschnittene Seitenansicht, in der die Fertigung des zweiten Anschlussstutzens eines der Gehäuse unter Verwendung eines konischen Innendorns gezeigt ist;

Fig. 6

eine geschnittene Seitenansicht eines nicht rotationssymmetrischen Rohrs nach dem Ausformen zu einem Doppelwerkstück;

Fig. 7

eine geschnittene Vorderansicht des Rohrs nach Fig. 6;

Fig. 8

eine geschnittene Vorderansicht eines im Querschnitt ovalen Rohrs nach dem Ausformen der Anschlussstutzen;

Fig. 9

eine Seitenansicht, in der das Ausformen des Doppelwerkstücks nach einer zweiten Verfahrensvariante gezeigt ist, bei der die Anschlussstutzen versetzt zur Längsachse des Rohrs an diesem ausgeformt werden;

Fig. 10

eine Vorderansicht, in der die verschiedenen Verfahrensschritte beim Ausformen des Doppelwerkstücks gezeigt sind;

Fig. 11

eine geschnittene Seitenansicht eines Abgaskatalysators mit ovalem Querschnitt, der nach dem Verfahren nach Fig. 9 gefertigt worden ist;

Fig. 12

eine Vorderansicht des Abgaskatalysators nach Fig. 11; und

Fig. 13

eine geschnittene Seitenansicht, in der eine dritte Verfahrensvariante zum Fertigen eines Abgaskatalysators gezeigt ist.

The method according to the invention is explained in more detail below on the basis of three design variants with reference to the drawing. In it show:

Fig. 1

a sectional side view of an exhaust gas catalytic converter;

Fig. 2

a sectional side view of a tube when molding a double workpiece to produce two housings of two catalytic converters;

Fig. 3

a sectional side view, in which the production of a second connection piece of one of the housings is shown;

Fig. 4

a sectional side view, in which the manufacture of the second connection piece of one of the housings is shown using a cylindrical inner mandrel;

Fig. 5

a sectional side view showing the manufacture of the second connection piece of one of the housings using a conical inner mandrel;

Fig. 6

a sectional side view of a non-rotationally symmetrical tube after being formed into a double workpiece;

Fig. 7

a sectional front view of the tube of FIG. 6;

Fig. 8

a sectional front view of a cross-sectionally oval tube after molding the connecting piece;

Fig. 9

a side view, in which the molding of the double workpiece is shown according to a second method variant, in which the connecting pieces are formed offset to the longitudinal axis of the tube on this;

Fig. 10

a front view, in which the various process steps in the molding of the double workpiece are shown;

Fig. 11

a sectional side view of an exhaust gas catalyst with an oval cross section, which has been manufactured by the method of FIG. 9;

Fig. 12

a front view of the catalytic converter according to Fig. 11; and

Fig. 13

a sectional side view, in which a third process variant for manufacturing an exhaust gas catalytic converter is shown.

In Fig. 1 is a sectional side view of an exhaust gas catalytic converter 10 shown, for example in motor vehicles is used for cleaning exhaust gases. The catalytic converter 10 has a housing 12 made of a stainless Steel is made. In the housing 12 is a catalyst insert 14 added. The catalyst insert 14 is formed from a ceramic monolyte 16 in which a Many flow channels are formed through which Exhaust gas flows, and its surface with a catalytic active substance is coated. To the ceramic monolyte 16 is a cushion mat 18 laid, the ceramic monolyte 16 completely encloses and this in the housing 12 in a defined location. The housing section 20, in which the catalyst insert 14 is received, goes to everyone its ends to form a transition contour 22 each in a connection piece 24. The connecting pieces 24 serve as an inlet or outlet for the exhaust gas catalytic converter 10, the individual exhaust pipes, not shown the exhaust system to the connecting piece 24 in a known manner Way releasably attached.

2 shows a first variant of the invention Process for producing the catalytic converter shown in FIG. 1 10 shown. To manufacture the catalytic converter 10 is a tube 30 made of a stainless Steel used to make the housing 12 of the catalytic converter 10 formed by the inventive method becomes. The tube 30 is dimensioned in its length so that made a total of two catalytic converters 10 from the tube can be, as will be explained later.

The tube 30 is first with its two ends 32 and 34 into the spindles (not shown) of a pressure rolling machine used. Then an intermediate section 36, the formed symmetrically between the two ends 32 and 34 is drawn in with the aid of a first forming roller 38. The Forming roller 38 is continuously fed radially while at the same time the tube 30 about an axis of rotation R in Rotation is offset. The outer contour 40 of the forming roller 38 is designed such that the outer contour 40 the forming roller 38, the transition contours 22 and the connecting piece 24 two housing 12 are made, the merge with their connecting pieces 24. there becomes the hollow cylindrical shape of the connecting piece 24 formed by a cylindrical peripheral surface 42 which symmetrically between the end faces of the forming roller 38 the outer contour 40 is shown.

A double workpiece 44 is formed by this method, in which the ends 32 of two housings 12 are each formed in their final shape. there becomes wrinkled by the shape of the tube 30 in the intermediate section 36 prevented because the pipe material in Forming area of the intermediate section 36 from the tube material is supported on both sides of the intermediate section 36, whereby the buckling stability in the forming area is comparatively high is high.

After the formation of the intermediate section 36, the double workpiece 44 using a cutting roller (not shown) divided into two individual workpieces 46, the following be processed separately.

In a development of the previously described method variant becomes the tube 30 when the intermediate section is formed 36 additionally supported from the inside. To this Purpose are in the two open ends 32 and 34 of the Rohrs 30 Innendorne 48 introduced in the area of Intermediate section 36 with their end faces to each other Plant come. The Innendorne 48 are designed so that the outer contour 49 of the later inner contour of the Pipe 30 corresponds. After positioning the inner arbors 48, the forming roller 38 is fed radially and the tube 30 with the previously described method step. After pulling in, the inner arbors 48 are removed again pulled out the tube 30 and the double workpiece formed 44 with the help of a cutting roller in the two individual workpieces 46 separated.

The inner arbors 48 can have a shoulder 49 of larger diameter, at which the pipe ends 32, 34 come to rest. A compression can occur when the inner mandrels 48 move together for material accumulation in intermediate section 36. Vice versa is also a dilution by appropriate delivery the forming roller 38 possible.

After the tube 30 has been cut into each individual workpiece 46 first the ceramic monolyte wrapped with the mat 18 16 through the still undeformed end 34 of the tube 30 inserted into the tube 30. Then the tube 30th with its deformed end in the spindle (not shown) another spinning mill.

3 shows, after tightening the tube 30 in the Spindle the still undeformed end 34 through which the catalyst insert 14 was introduced with the help of a second Forming roller 50 to the transition contour 22 and the second Connection piece 24 shaped. Here too is the outer contour 52 of the form roller 50 with a cylindrical peripheral surface 54 provided so that the connection piece 24 is finished is formed without subsequent processing of the connecting piece 24 is required.

4 shows a modified method step in Cut shown, when pulling in the second end 34 of the tube 30, an inner mandrel 56 is additionally used, which is inserted into the open end 34 of the tube 30 as it is drawn in becomes. The inner mandrel 56 has a cylindrical Support surface 58 and a radially protruding from this Waistband 60 on. With the help of the cylindrical support surface 58 the inner contour of the connecting piece 24 is defined formed, while the collar 60 an axial flow of the Pipe material limited.

5 is an alternative embodiment of the Method step for pulling in the second end 34 of the Tube 30 shown in section. With this process variant becomes the second end 34 with the help of a third forming roller 62 reshaped in the opposite of the two previously described Design variants on the outer peripheral surface of the Press roller 62 has only one radially circumferential forming edge 64 is trained. Furthermore, this embodiment variant a conical mandrel 66 is used, which is a conical Support surface 68 and an adjoining this has cylindrical support surface 70. The cylindrical Support surface 70 is on the end face of the conical Dorns 66 provided and goes into the flared conical Support surface 68 over.

To deform the second end 34 of the tube 30, the conical Mandrel 66 with its cylindrical support surface 70 in the open second end 34 of the tube 30 inserted. Subsequently the third forming roller 62 is fed radially and move axially at the same time. In the same way the conical mandrel 66 synchronizes with the feed movement of the forming roller 62 move axially, whereby to avoid wrinkles the workpiece area to be reshaped at least temporarily between the forming edge 64 of the third forming roller 62 and a surface portion of the cylindrical support surface 68 of the conical mandrel 66 is guided, as FIG. 5 shows. The infeed movements between the forming roller 62 and the conical mandrel 66 are continued as long as until the forming roller 62 in the area of the cylindrical Support surface 70 arrives. From this point on, the forming roll 62 only axially with respect to the conical mandrel 66 adjusted, which makes the high cylindrical connecting piece 24 is shaped like the dashed lines in Fig. 5 shows.

The previously described with reference to FIGS. 2 to 5 Process variants can also be used for forming pipes 30a and 30b with non-rotationally symmetrical cross sections are used, as shown in Fig. 6 to 8 are. Thus, the tube 30a shown in FIGS. 6 and 7 has an O-shaped cross-section. That in Fig. 8 tube 30b shown, however, shows an oval shape, such as it is particularly common in exhaust gas catalysts 10.

These tubes are used to pull in the connecting piece 24 30a and 30b with non-rotationally symmetrical cross sections a process for non-cutting shaping not rotationally symmetrical Parts used. With this procedure the forming roll 38, 50 or 62 is fed in a controlled manner, so that from the initially not rotationally symmetrical pipe cross-section the hollow cylindrical connecting piece 24 is formed is, while at the same time the transition contour 22nd arises.

9 and 10 is a method variant of the invention Procedure shown. With this process variant the pipe 30 with its longitudinal axis S around the amount X is offset to the axis of rotation R in the spinning roll machine (not shown) used. Subsequently the intermediate section 36 on the tube 30 by a total three forming rollers 38 formed while the tube 30th rotates about the axis of rotation R. The forming rollers 38 are delivered radially with different amounts, such as 10 shows what caused the retracted intermediate section 36 axially offset with respect to the longitudinal axis L of the tube 30 this is shaped, as shown in FIG. 9. Then will the resulting double workpiece 44 in the previously described Way divided into two individual workpieces 46, in the catalyst insert 14 is used for each individual workpiece 46 and the still undeformed end 34 of each individual workpiece 46 in a corresponding manner to the catalytic converter 10a reshaped.

11 and 12 show an exhaust gas catalytic converter 10b, that with the method described above from a cross section oval tube 30b has been manufactured. With this Exhaust gas catalytic converter 10b became the single workpiece 46 for molding of the second connecting piece 24, however, offset in parallel inserted into the press rolling machine so that the two finished connecting piece 24 offset from each other and formed offset to the longitudinal axis of the tube 30b on this are.

Fig. 13 shows a third method variant in which the Tube 30 with its longitudinal axis L below a predetermined Angle α inclined to the axis of rotation R in the spindle 72 the press rolling machine and the intermediate section 36 has been formed. Then the so formed Double workpiece 44 separated in the manner described above, 46 catalyst inserts into the resulting individual workpieces 14 used and the still open ends 34 of the Single workpieces 46 drawn. Again, this will be the case Individual workpiece 46 to be formed with its longitudinal axis L below a predetermined angle α inclined to the axis of rotation R of the spindle 72 inserted into this. The second end 34 is then shaped with the help of a forming roller 74, that arises when the second end 34 is drawn in Connection piece 24 inclined at the angle α to the longitudinal axis L of the tube 30 or the individual workpiece 46 is continuously formed on this.

Claims (17)

Method for producing an exhaust gas catalytic converter (10), which has a housing (12) with two connecting pieces (24) and a catalyst insert (14) arranged in the housing (12), wherein: the catalyst insert (14) is inserted into a tube (30) forming the housing (12) and the ends (32, 34) of the tube (30) for forming the connecting pieces (24) are drawn in by non-cutting shaping, characterized, that the length of the tube (30) is such that a double workpiece (44) can be manufactured, that the tube (30) is drawn in at an intermediate section (36) between its two ends (32, 34), that the tube (30) is cut off in the region of the drawn-in intermediate section (36), two individual workpieces (46) being formed, and that each individual workpiece (46) is drawn in at its inlet (34) after the insertion of the catalyst insert (14). Method according to claim 1,
characterized in that the intermediate section (36) of the tube (30) is formed symmetrically between its ends (32, 34). Method according to claim 1 or 2,
characterized, that the tube (30) is cut off immediately after the intermediate section (36) is drawn in, in particular by a cutting roller, and that the intermediate section (36) is pulled in and separated, in particular in one clamping. The method of claim 1, 2 or 3,
characterized in that the tube (30) is formed by at least two forming rollers (38, 50, 62). Method according to one of claims 1 to 4,
characterized, that the intermediate section (36) is supported during the drawing in from the inside of the tube (30) and that at least one inner mandrel (48) is inserted into the tube (30) to support the intermediate section (36). Method according to one of claims 1 to 5,
characterized, that at least the edge of the insertion end (34) of the tube (30) is supported from the inside of the tube (30) when being drawn in, and that a mandrel (56, 66) is used for support, which is inserted into the introducer (34). Method according to claim 6,
characterized in that the introducer (34) is pressed against the mandrel (66), which is at least partially conical, when at least one shaping roller (62) is drawn in. Method according to claim 7,
characterized in that the conical mandrel (66) is moved axially synchronized with the feed movement of the forming roller (62), so that the workpiece area to be formed is supported and at least temporarily guided between the conical mandrel (66) and the forming roller (52). Method according to one of claims 5 to 8,
characterized in that the mandrel (48, 56, 66) has a cylindrical section (42, 54, 70) which leads to the formation of a cylindrical pipe section (24) when the pipe (30) is drawn in. Method according to one of the preceding claims,
characterized in that when the pipe (30) is pulled in, the drawn-in pipe sections are formed into the finished connecting pieces (24). Method according to one of the preceding claims,
characterized in that a non-rotationally symmetrical, in particular oval, tube (30) is used. Method according to one of the preceding claims,
characterized, that the tube (30) rotates about an axis of rotation (R) during the forming, that the tube (30) runs parallel to the axis of rotation (R) with its longitudinal axis (L) and that the connecting pieces (24) that arise when the tube (30) is drawn in about the axis of rotation (R) are formed offset on the longitudinal axis (L) of the tube (30). Method according to one of claims 1 to 11,
characterized, that the tube (30) rotates about an axis of rotation (R) during the forming, that the tube (30) extends with its longitudinal axis (L) at a predetermined angle (α) inclined to the axis of rotation (R) and that the connecting pieces (24) formed when the pipe (30) is drawn in about the axis of rotation (R) are formed at an angle (α) inclined to the longitudinal axis (L) of the pipe (30) and extends thereon. Method according to one of the preceding claims,
characterized in that the retracted connecting pieces (24) with their axes of symmetry (S) run offset from one another. Method according to one of the preceding claims,
characterized, that several forming rollers (38, 50, 62) are used for forming the tube (30) at the same time and that the forming rollers (38, 50, 62) are fed radially and optionally also axially at the same time. Method according to one of the preceding claims,
characterized, that at least one shaping roller (38, 50, 62) is used for shaping the tube (30), that in order to form a defined deviation from the rotational symmetry, the forming roller (38, 50, 62) is radially adjusted between a maximum and a minimum infeed position during a single rotation of the tube (30) and that the radial adjustment of the forming roller (38, 50, 62) during a single revolution depends on the angle of rotation of the tube (30). Method according to one of the preceding claims,
characterized in that the tube (30) is heated to a temperature above the recrystallization temperature of the tube material before the forming.

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