Method and system for producing a helical pipe, and mould at least for aligning or calibrating a helical pipe

Abstract

The invention relates to a method for producing a helical, at least aligned or calibrated pipe having a longitudinal axis, the method comprising the following steps: A) providing a helical prefabricated metal pipe having a plurality of turns; B) supporting the prefabricated pipe in the circumferential direction at a first support position and at a second support position in each case across a plurality of turns such that an outer circumference of the plurality of turns lies on a first straight line at the first support position and on a second straight line at the second support position; C) clamping a first end of the prefabricated pipe; D) clamping a second end of the prefabricated pipe; E) rotating the first end and the second end relative to one another about the longitudinal axis such that an outer diameter of the plurality of turns is reduced or increased; F) supporting the prefabricated pipe in the circumferential direction at a third support position across a plurality of turns such that the outer circumference of the plurality of turns lies on a straight line at the third support position; G) releasing at least the first end or the second end of the prefabricated pipe such that the outer circumference of the plurality of turns lies on a third straight line at the third support position; H) heating the prefabricated pipe to a target temperature; and I) removing the at least aligned or calibrated pipe.

Description

[0001] Method and system for producing a helical tube and mold at least for straightening or calibrating a helical tube

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for manufacturing a helical oriented tube from a helical prefabricated tube.

[0004] The present disclosure also relates to a mold at least for straightening or calibrating a helical, prefabricated tube.

[0005] Furthermore, the present disclosure relates to a system for producing a helical, oriented tube.

[0006] BACKGROUND

[0007] Metal tubes with a helical shape that are subjected to pressurized fluid must be manufactured with a high degree of precision to withstand such high internal pressure without deformation. For example, such a helix must have a diameter defined within specified tolerances and constant across all its threads.

[0008] Helical tubes for pressure applications are cold-wound to avoid structural changes that can occur with hot winding. Cold winding results in partial elastic deformation of the tube. After cold winding, the helix expands slightly. The diameter of the helix then hardly corresponds to a nominal diameter. Furthermore, the diameter of the helix can increase or decrease along the helix's longitudinal axis. However, if the diameter of the individual helix threads varies along the longitudinal axis, exposure to a fluid under high pressure can cause the helix to open further.

[0009] It is therefore an aspect of the present disclosure to provide a method and a mold for producing a helical, at least directed or calibrated tube, wherein the directed tube meets defined requirements for the precision of the individual threads of the helix over the length of the helix. SUMMARY OF THE INVENTION

[0010] The aforementioned aspect is disclosed by a method for producing a helical, at least directed or calibrated tube according to the independent claim 1 directed thereto.

[0011] For this purpose, the method for producing the helical, at least oriented or calibrated tube with a longitudinal axis comprises the steps:

[0012] A) Providing a helical, prefabricated metal tube having a plurality of turns,

[0013] B) supporting the prefabricated pipe in the circumferential direction at a first support position and at a second support position, each over a plurality of turns, so that an outer circumference of the plurality of turns lies on a first straight line at the first support position and on a second straight line at the second support position,

[0014] C) clamping a first end of the prefabricated pipe,

[0015] D) clamping a second end of the prefabricated pipe,

[0016] E) rotating the first end and the second end relative to each other about the longitudinal axis so that an outer diameter of the plurality of threads decreases or increases,

[0017] F) supporting the prefabricated pipe in the circumferential direction at a third support position over a plurality of turns, so that the outer circumference of the plurality of turns lies on a straight line at the third support position,

[0018] G) releasing at least the first end or the second end of the prefabricated pipe so that the outer circumference of the plurality of threads at the third support position lies on a third straight line,

[0019] H) Heating the prefabricated pipe to a desired temperature and

[0020] I) Removing the pipe which has at least been straightened or calibrated.

[0021] It has been found that a prefabricated tube can only be cold wound into an insufficiently precise helix. However, cold winding of the prefabricated tube into a helix is ​​necessary in order not to change the structure of the tube, which is produced, for example, by cold forming. After cold winding, the helix springs open, making it difficult to adjust the outer diameter of the individual threads to a nominal diameter. In addition, the outer diameter of the helix usually changes over the course of the helix. The method of the present disclosure is therefore based on the idea of ​​either reducing the outer diameter of the helix of the prefabricated tube or enlarging the inner diameter of the helix of the prefabricated tube by twisting the first end relative to the second end of the tube.The individual threads of the helix are then supported from the outside or inside at a predetermined diameter, preferably using a mold, and the twisting of the tube ends is released. Supporting the individual threads prevents the helix from expanding or contracting. Each individual thread now has the diameter specified by the support. Finally, the prefabricated and supported tube is heated to a predetermined target temperature so that the tube no longer expands or contracts after the support is released (e.g., by removing it from the mold).

[0022] The disclosed method serves at least to straighten or calibrate the helical, prefabricated tube. A helical, at least straightened or calibrated tube is produced.

[0023] Through straightening, the helix threads acquire a defined outer and / or inner diameter along the helix's longitudinal axis. In one embodiment, the outer diameter and / or inner diameter of the helix is ​​approximately constant across the longitudinal axis after straightening. However, embodiments are possible in which the outer diameter and / or inner diameter of the helix increases or decreases across the longitudinal axis.

[0024] Through calibration, each individual thread of the helix receives an outer and / or inner diameter defined within specified tolerances and determined by the shape. In one embodiment, the method according to the disclosure allows for fine calibration.

[0025] In one embodiment of the disclosed method, the helix of the tube is both directed and calibrated.

[0026] For straightening or calibrating, the first end and the second end of the prefabricated pipe are clamped and then the first end and the second end are rotated relative to each other around the longitudinal axis of the helix, so that the helix either expands (its outer circumference increases) or is twisted (its outer circumference decreases). During or after the twisting of the first and the second end relative to each other, the helix of the prefabricated pipe is supported in the circumferential direction at at least three support positions, namely the first support position, the second support position and the third support position, each over a plurality of turns, so that the outer circumference of the plurality of turns lies on a straight line at each of the three support positions. Once the prefabricated helix is ​​supported in the circumferential direction at at least three support positions, at least the first or the second end can be released again.The threads of the helix are then held at their defined outer diameter at the three support positions.

[0027] According to one embodiment, the first end and the second end are rotated relative to each other in such a way that only a predominantly elastic deformation or an exclusively elastic deformation of the prefabricated pipe occurs. In such an embodiment, the rotation does not result in cold straightening of the pipe.

[0028] If, in one embodiment of the disclosure, the outer circumference of the helix or its threads is reduced by twisting the first end and the second end of the tube relative to each other about the longitudinal axis of the helix, the prefabricated tube must be supported externally at at least three support positions. If, in one embodiment of the disclosure, the outer circumference of the helix or its threads is increased by twisting the first end and the second end relative to each other, the tube must be supported internally at the three support positions. This support thus prevents the helix from springing open after twisting.

[0029] In one embodiment of the disclosure, the helical prefabricated tube is made of stainless steel. In one embodiment of the disclosure, the stainless steel is a nickel-containing alloy or a titanium-containing alloy.

[0030] In one embodiment of the disclosure, providing the helical prefabricated tube in step A) comprises cold forming a billet into the prefabricated tube, for example by cold pilger rolling or cold drawing, and winding the prefabricated tube into the helix.

[0031] In one embodiment of the disclosure, providing the prefabricated pipe in step A) comprises helically winding the prefabricated pipe at a temperature of 50% or less of the recrystallization temperature of a material of the prefabricated pipe. In this application, winding at a temperature of 50% or less of the recrystallization temperature of the material of the prefabricated pipe is referred to as cold winding. In one embodiment of the disclosure, the winding in step A) takes place at room temperature.

[0032] In one embodiment of the disclosure, the twisting in step E) is carried out such that the prefabricated pipe is deformed elastically, predominantly elastically or completely elastically.

[0033] In one embodiment of the disclosure, the twisting of the first end and the second end of the helical prefabricated tube in step E) occurs at a temperature of 50% or less than the recrystallization temperature of the material of the prefabricated tube. In one embodiment of the disclosure, the twisting in step E) also occurs at room temperature.

[0034] In one embodiment of the disclosure, before releasing the first end or the second end in step G) and during heating in step H), the first straight line, the second straight line, and the third straight line are parallel to the longitudinal axis. In this way, the tube acquires a directional shape with a constant outer diameter of the helix along the length of the helix's longitudinal axis.

[0035] In one embodiment of the disclosure, the support in at least step B) or step F) during the twisting in step E) comprises advancing at least the first straight line, the second straight line, or the third straight line in a radial direction perpendicular to the longitudinal axis. In this way, the support of the helical, prefabricated tube is adjusted during the twisting in step E). This takes into account the increase or decrease in the outer diameter of the helix during the twisting.

[0036] In one embodiment of the disclosure, prior to twisting in step E), at least two of the first straight line, the second straight line, and the third straight line form an angle with the longitudinal axis. This position of the straight line relative to the longitudinal axis takes into account the initial situation in which the helix has an outer diameter that varies in the direction of the longitudinal axis.

[0037] In one embodiment of the disclosure, the third support position is spaced 120° from the first support position and from the second support position in the circumferential direction. Such an arrangement is particularly useful when the prefabricated pipe is supported at exactly three support positions. In one embodiment of the disclosure, the target temperature in step H) is at least 70% of the recrystallization temperature of a material of the prefabricated pipe. In this way, the prefabricated pipe is tempered so that it becomes stress-relieved and the restoring forces are tempered out of the originally elastic deformation due to the twisting in step E). In one embodiment of the disclosure, the target temperature in step H) is at most 130% of the recrystallization temperature of the material of the prefabricated pipe.

[0038] In one embodiment of the disclosure, the target temperature in step H) is at least 80% of the recrystallization temperature of the material of the prefabricated pipe. In another embodiment, the target temperature in step H) is at most 120% of the recrystallization temperature of the material of the prefabricated pipe.

[0039] Typically, the recrystallization temperature of a metal is in a range of 500 °C to 1,300 °C, especially of a stainless steel, in a range of 550 °C to 1,050 °C.

[0040] The aforementioned aspect is also addressed by a mold at least for straightening or calibrating a helical, prefabricated pipe according to the independent claim 11 directed thereto. For this purpose, the mold comprises a first support section, a second support section, and a third support section. The first support section is arranged at a first support position in a circumferential direction relative to the helical, prefabricated pipe that can be received in the mold.

[0041] The second support section is arranged at a second support position in the circumferential direction relative to the helical, prefabricated tube that can be received in the mold. The third support section is arranged at a third support position in the circumferential direction relative to the prefabricated tube that can be received in the mold. The first support section and the second support section are each designed such that an outer circumference of a plurality of threads of the helix lies on a first straight line at the first support position and on a second straight line at the second support position. The mold also has a first clamping device for clamping a first end of the prefabricated tube. The third support section is movable between a closing position that closes the mold and a release position that releases the mold, wherein the prefabricated tube can be introduced into the mold in the release position.The third support section is also designed such that during operation of the mold in the closing position of the third support section, the outer circumference of the plurality of flights at the third support position lies on a third straight line.

[0042] In one embodiment of the disclosure, at least one of the first support portion, the second support portion, and the third support portion has a comb-like structure with a plurality of part-circular arc-shaped recesses such that, during operation of the mold, the plurality of turns of the prefabricated tube are supported both in a radial direction perpendicular to the longitudinal axis of the helix and in an axial direction parallel to the longitudinal axis.

[0043] In one embodiment of the mold, at least one of the first support portion, the second support portion, and the third support portion is adjustable in the radial direction so that the reduction or enlargement of the outer diameter of the helix can be accommodated during rotation of the first end and the second end of the helical prefabricated tube relative to each other.

[0044] In one embodiment, the mold comprises a second clamping device and optionally a drive unit for pivoting the second clamping device relative to the first clamping device. The second clamping device is provided for clamping a second end of the prefabricated pipe, wherein the drive unit is operatively connected to the second clamping device such that the second clamping device is pivotable by means of the drive unit, so that, with a prefabricated pipe clamped in the first clamping device and the second clamping device, the outer diameter of the plurality of threads can be changed.

[0045] The aforementioned aspect is also addressed by a system for producing a helical, oriented tube, wherein the system comprises a mold in one embodiment as previously described, a drive unit, and a second clamping device. The second clamping device is provided for clamping a second end of the prefabricated tube, wherein the drive unit is operatively connected to the second clamping device such that the second clamping device is pivotable by means of the drive unit, so that when a prefabricated tube is clamped in the first clamping device and in the second clamping device, the outer diameter of the plurality of threads can be changed. In such a system, the mold is separable from the drive unit and the second clamping unit, so that the parts required for tempering the helix in the mold do not need to be brought into the furnace.The aforementioned aspect is also achieved by a system for producing a helical, at least oriented or calibrated tube, wherein the system comprises a mold according to an embodiment as previously described and a furnace with a furnace muffle, wherein the furnace muffle is configured such that the mold, with a prefabricated tube accommodated therein, can be received in the furnace muffle. Tempering is carried out in the furnace according to step H) of the method disclosed herein.

[0046] The features of the system as described above can also be combined with each other.

[0047] SHORT DESCRIPTION OF THE CHARACTERS

[0048] Further advantages, features, and applications of the present disclosure will become apparent from the following description of variants and the accompanying figures. The foregoing and the following detailed description of variants will be better understood when read in conjunction with the accompanying figures. The illustrated embodiments are not limited to the precise arrangements and instrumentation shown. In the figures, like elements are designated by identical reference numerals.

[0049] Figure 1 is a schematic isometric top view of a first variant of the mold with a helical tube received therein before heating.

[0050] Figure 2 is a schematic isometric top view of another variant of the mold with a helical tube received therein before heating.

[0051] Figure 3 is a flow diagram of a method for straightening a helical prefabricated pipe having a shape as shown in Figures 1 or 2.

[0052] DETAILED DESCRIPTION Figures 1 and 2 each show a mold 1 in which a helical, prefabricated tube 2 made of a titanium-containing stainless steel alloy is accommodated. The mold 1 serves to align and calibrate the prefabricated helix from the prefabricated tube 2.

[0053] Figure 3 schematically shows a flow chart for the process for straightening the helix. The flow chart also includes the preparation of the helical, prefabricated tube 2.

[0054] The need to straighten the prefabricated tube 2 or the helix wound therefrom arises from the manner in which the helical tube is prepared (step 100 in Figure 3). The prefabricated tube 2 is a tube 2 cold-formed by cold pilger rolling (step 120 in Figure 3) from a billet (preparing the billet in step 110 in Figure 3). This tube 2 is initially straight after cold pilger rolling 120 and is then wound into a helix at room temperature (step 130).

[0055] Due to the cold winding 130 of the straight, prefabricated tube into the helical shape, this helix springs open after winding. In the process, the outer diameter of the individual threads 3 of the tube 2 typically increases unevenly along the longitudinal axis 4 of the helix. If the interior of such a tube helix with an outer diameter that changes along the longitudinal axis 4 is subjected to a fluid under high pressure, the helix experiences further expansion and may not be able to withstand the pressure. Therefore, the helix must be straightened and calibrated (step 200 in Figure 3) after winding. In the examples discussed here, the straightening 200 of the helix takes place so that after the straightening and calibration 200, the outer diameter of the helix in the direction of the longitudinal axis 4 does not change and remains constant.

[0056] The mold 1 consists of three first, second and third support sections 5, 6, 7 distributed over the circumference of the helix of the tube 2. These are arranged in the circumferential direction around the longitudinal axis 4 at a distance of 120° each, so that they optimally support the individual threads of the helix (step 210 in Figure 3).

[0057] Each of the support sections 5, 6, 7 has a comb-like structure, each with a partially circular cutout 8 for accommodating a thread of the helix of the tube 2. A first clamping device 9 is provided on the side of the tube, in which a first end 10 of the tube 2 is clamped (clamping the first end in step 220 in Figure 3). To carry out the method according to the invention, the second end 11 of the tube is clamped in a second clamping device (not shown in the figures) (clamping the second end in step 230 in Figure 3).

[0058] This second clamping device does not actually belong to the mold 1, but rather to a system for straightening the helical, prefabricated tube 2. The second clamping device is mounted on a drive unit so that the second clamping device can be pivoted about the longitudinal axis 4. The twisting of the first end and the second end of the tube is designated by reference numeral 240 in the flow chart of Figure 3.

[0059] If the first end 10 and the second end 11 of the tube are both clamped, a pivoting movement of the second clamping device about the longitudinal axis 4 of the tube leads to a rotation of the first end 10 and the second end 11 of the tube 2 relative to one another. This rotation, in turn, causes the helix of the tube 2 to constrict or widen, depending on the direction of rotation. In the embodiments shown, the rotation of the first end 10 and the second end 11 relative to one another occurs in such a way that the outer diameter of the helix of the tube 2 decreases. Therefore, the support sections 5, 6, 7 are arranged such that they support the individual threads 3 of the tube 2 from the outside.

[0060] In the embodiment of Figure 1, the helical, prefabricated tube is first received between the first support section 5 and the second support section 6, then the first end 10 and the second end 11 of the tube 2 are rotated relative to each other and finally the third support section 7 is placed in such a way that, together with the first and second support sections 5, 6, it holds the helix with a reduced but constant outer diameter.

[0061] Compared to the embodiment of Figure 1, the mold 1 of Figure 2 is modified in that during the rotation 240 of the first end 10 and the second end 11 of the tube 2 relative to one another, the three support sections 5, 6, 7 are advanced in the radial direction. In this way, the decreasing radius during the rotation can be taken into account. In addition, the three support sections 5, 6, 7 can be pivoted relative to the longitudinal axis 4 such that the equalization of the outer diameters of the threads 3 in the longitudinal direction 4 is compensated during the rotation 240. In step 250, the second end 11 of the tube 2 is released again, so that the threads 3 of the tube 2 are held at the same outer diameter only by the support sections 5, 6, 7.

[0062] In the next step, the mold containing the helical, prefabricated tube supported by support sections 5, 6, and 7 is annealed in a shaft furnace at a temperature of approximately 90% of the recrystallization temperature of the titanium alloy of tube 2 (step 260 in Figure 3). In this way, the stress and thus the restoring force that expands the helix of tube 2 are thermally eliminated. Finally, the fully straightened and calibrated tube is removed from mold 1 in step 270.

[0063] For the purposes of original disclosure, it is noted that all features as they become apparent to a person skilled in the art from the present description, the drawings, and the claims, even if they were specifically described only in conjunction with certain other features, can be combined both individually and in any combination with other features or groups of features disclosed herein, unless this has been expressly excluded or technical circumstances make such combinations impossible or pointless. A comprehensive, explicit presentation of all conceivable combinations of features is omitted here solely for the sake of brevity and readability of the description.

[0064] While the invention has been illustrated and described in detail in the drawings and the foregoing description, this illustration and description are given by way of example only and are not intended to limit the scope of the invention as defined by the claims. The invention is not limited to the disclosed embodiments.

[0065] Modifications of the disclosed embodiments will be apparent to those skilled in the art from the drawings, the description, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain features are claimed in different claims does not exclude their combination. Reference signs in the claims are not intended to limit the scope of protection. List of Reference Signs

[0066] 1 form

[0067] 2 helical prefabricated pipes

[0068] 3 courses

[0069] 4 Longitudinal axis

[0070] 5 support section

[0071] 6 support section

[0072] 7 Support section

[0073] 8 partially circular cutout

[0074] 9 Clamping device

[0075] 10 first end of the pipe

[0076] 11 second end of the pipe

[0077] 100 Preparing the helical prefabricated tube

[0078] 110 Providing a magnifying glass

[0079] 120 cold pilger rolling of the hollow shell to the prefabricated pipe

[0080] 130 Winding the prefabricated pipe into a helix

[0081] 200 Straightening and calibrating the helical prefabricated pipe

[0082] 210 supports of the prefabricated pipe

[0083] 220 Clamping the first end of the pipe

[0084] 230 Clamping the second end of the pipe

[0085] 240 Twisting the first end relative to the second end

[0086] 250 Releasing the second end of the tube

[0087] 260 Heating the pipe

[0088] 270 Removing the straightened and calibrated tube

Claims

Patent claims 1. A method for producing a helical, at least oriented or calibrated tube with a longitudinal axis (4), the method comprising the steps A) Providing (100) a helical, prefabricated tube (2) made of metal with a plurality of threads (3), B) supporting (210) the prefabricated pipe (2) in the circumferential direction at a first support position and a second support position, each over a plurality of turns (3), so that an outer circumference of the plurality of turns (3) lies on a first straight line at the first support position and on a second straight line at the second support position, C) clamping (220) a first end (10) of the prefabricated pipe (2), D) clamping (230) a second end (11) of the prefabricated pipe (2), E) rotating (240) the first end (10) and the second end (11) relative to each other about the longitudinal axis (4) so ​​that an outer diameter of the plurality of threads (3) decreases or increases, F) supporting (210) the prefabricated pipe (2) in the circumferential direction at a third support position over a plurality of turns (3) so that the outer circumference of the plurality of turns (3) lies on a straight line at the third support position, G) releasing (250) at least the first end (10) or the second end (11) of the prefabricated pipe (2) so that the outer circumference of the plurality of threads (3) lies on a third straight line at the third support position, H) Heating (260) the prefabricated pipe (2) to a desired temperature and I) Removing (270) the at least straightened or calibrated tube.

2. Method according to the preceding claim, wherein the twisting (240) in step E) is carried out in such a way that the prefabricated pipe (2) is predominantly elastically deformed.

3. The method according to any one of the preceding claims, wherein the providing (100) of the prefabricated pipe (2) in step A) comprises a helical winding (130) of the prefabricated pipe (2) at a temperature of 50% or less of the recrystallization temperature of a material of the prefabricated pipe (2).

4. Method according to one of the preceding claims, wherein before the release (250) in step G) and during the heating in step H), the first straight line, the second straight line and the third straight line are parallel to the longitudinal axis (4).

5. Method according to one of the preceding claims, wherein the supporting (210) in at least step B) or step F) during the rotating in step E) comprises advancing at least the first straight line, the second straight line or the third straight line in a radial direction perpendicular to the longitudinal axis (4).

6. Method according to the preceding claim, wherein before the twisting (240) in step E) at least two of the first straight line, the second straight line and the third straight line form an angle with the longitudinal axis (4).

7. The method according to any one of the preceding claims, wherein the first support position and the second support position have a minimum angular distance of 180 degrees or less in the circumferential direction.

8. The method according to any one of the preceding claims, wherein the third support position is circumferentially spaced from the first support position by 90 degrees or more and is circumferentially spaced from the second support position by 90 degrees or more.

9. The method according to any one of the preceding claims, wherein the third support position is spaced from the first support position and the second support position by a distance of approximately 120 degrees in the circumferential direction.

10. Method according to one of the preceding claims, wherein the target temperature in step H) is at least 70% of the recrystallization temperature of a material of the prefabricated pipe (2).

11. Mould (1) at least for straightening or calibrating a helical, prefabricated tube (2) with a longitudinal axis (4) of the helix, the mould (1) having a first support section (5), a second support section (6), wherein the first support section (5) is arranged at a first support position in a circumferential direction relative to a helical, prefabricated tube (2) that can be received in the mold (1) during operation of the mold, wherein the second support section (6) is arranged at a second support position in the circumferential direction relative to the helical, prefabricated tube (2) that can be received in the mold (1) during operation of the mold, and wherein the first support section (5) and the second support section (6) are each configured such that an outer circumference of a plurality of threads (3) of the helix lies on a first straight line at the first support position and on a second straight line at the second support position, a first clamping device (9) for clamping a first end (10) of the prefabricated tube (2), and a third support section (7),wherein the third support section (7) is arranged at a third support position in the circumferential direction relative to the prefabricated pipe (2) that can be received in the mold (1) during operation of the mold (1), wherein the third support section (7) is movable between a closing position that closes the mold (1) and a release position that releases the mold (1), wherein the prefabricated pipe (2) can be introduced into the mold (1) in the release position, and wherein the third support section (7) is designed such that, during operation of the mold (1), in the closing position of the third support section (7), the outer circumference of the plurality of threads (3) at the third support position lies on a third straight line.

12. Mold (1) according to the preceding claim, wherein at least one of the first support section (5), the second support section (6) and the third support section (7) has a comb-like structure with a plurality of part-circular arc-shaped depressions (8), so that in the operation of the mold (1) the plurality of threads (3) of the prefabricated tube (2) is supported both in a radial direction and in an axial direction.

13. The mold (1) according to claim 11 or 12, wherein at least one of the first support portion (5), the second support portion (6) and the third support portion (7) is adjustable in the radial direction.

14. Plant for producing a helical, at least oriented or calibrated pipe, the plant comprising a mold (1) according to one of claims 11 to 13, a drive unit and a second clamping device, the second clamping device being provided for clamping a second end (11) of the prefabricated pipe (2), the drive unit being operatively connected to the second clamping device in such a way that the second clamping device can be pivoted by means of the drive unit, so that when the prefabricated pipe (2) is clamped in the first clamping device (9) and in the second clamping device, the outer diameter of the plurality of threads (3) can be changed.

15. Plant for producing a helical, at least oriented or calibrated tube, the plant comprising a mold (1) according to one of claims 11 to 13 and a furnace with a furnace muffle, the furnace muffle being designed such that the mold (1) with a prefabricated tube (2) received therein can be received in the furnace muffle.

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