CH686169A5 - Method for producing tubular metal sheath, and sheath obtained by method - Google Patents

Abstract

The method consists of progressively forming a thin metal strip (22) in a forming unit (28) until one of its longitudinal edges partially overlaps the other edge and thus produces a sheath with closed cross section. The strip is coated beforehand on at least one of its faces with another material, the overlapping edges of the strip being joined to one another by means of a laser-beam welding unit (36) without prior preparation of these edges. The laser beam is adjusted so that it penetrates 90% of the total thickness of the overlapping edges of the formed strip (22). The thickness of the metal strip lies in the range 0.02-0.3 mm. The strip edges are joined to one another by a continuous longitudinal weld seam. Alternatively, they are joined to one another by two continuous weld seams running parallel. The sheath is made of a material belonging to group formed by copper, aluminium, steel and their alloys.

Description

1

CH 686 169 A5

2

Description

The invention relates to a method of manufacturing a metallic tubular envelope and an envelope obtained according to this method. More particularly, the invention relates to a method for manufacturing a flexible tubular casing, from a thin metal strip which is covered on at least one of its faces with a layer of another material, the tubular casing. being for example intended, in combination with a longitudinal element extending inside and an insulating sheath, to form cables capable of transporting electrical or optical signals, or else flow conduits or the like.

According to known methods, tubular casings of this type are generally obtained continuously from a metallic strip which passes through a series of forming rollers to give the strip the form of a closed casing in which the longitudinal edges are brought into juxtaposition to form a longitudinal joint line along which a TIG or similar welding is carried out. According to a particular application, the tubular envelope can be formed around a longitudinal element such as a conductor embedded in an insulator or even such as a simple tube, then this tubular envelope is covered with a layer of a material. insulating for example by an additional extrusion operation.

Although apparently satisfactory, this method nevertheless has drawbacks.

Indeed, the fact of having to bring the longitudinal edges in juxtaposition or edge to edge requires the use, on the one hand, of a precise forming machine, and on the other hand, of a tape having dimensional tolerances, in particular in its width which are constant and tight which results in high manufacturing costs.

Furthermore, when the tubular envelope extends around a conductor embedded in an insulator or around a simple tube, it is necessary to subject the envelope to an additional calibration operation in which the tubular envelope is brought in close contact with the conductor or the tube. This additional operation increases the production time and thereby increases the cost of the finished product.

Furthermore, to achieve reliable edge-to-edge welding, it is necessary according to this method to use metal ribbons having thicknesses at least greater than 0.3 mm. This therefore leads to the production of tubular envelopes having a high rigidity so that they can only be difficultly bent, and this only along large radii of curvature. This therefore results in a restrictive limitation of the field of application of this type of tubular casing.

In addition, this method makes the welding of the longitudinal edges very difficult to carry out when the tubular envelope is formed from a tape of which at least one of the faces is covered with a layer of another material because it is then necessary to prepare the surfaces to be welded. However, there are many applications for which the tubular envelope must include on its outer and / or inner faces a thin layer of another material, for example an outer layer of a synthetic material to form a primer layer, in particular if the tubular envelope is intended to be covered with an insulating sheath or simply to protect the tape during its storage and its handling.

The main object of the invention is therefore to remedy the drawbacks of the aforementioned prior art by providing a simple, effective and economical method for producing flexible tubular casings which can be easily produced from thin metal ribbons and of which at least one of the faces can be covered with a layer of another material.

To this end, the invention relates to a method of manufacturing a tubular casing, intended in particular for the production of cables, tubes or the like as defined by claim 1 of the patent.

The overlapping of the longitudinal edges before the welding operation thus allows the use of tapes of small thickness and width having no particular dimensional tolerances since the problem of making an edge-to-edge seal disappears. Thus, the tubular casings obtained are, on the one hand, easier to handle since they are more flexible, and on the other hand inexpensive to manufacture. The great flexibility of the envelopes obtained according to the method of the invention widens the field of application thereof compared to that of tubular envelopes manufactured according to the methods of the prior art. Also, the fact of welding the longitudinal edges together using a laser beam device makes it possible to produce a quality weld that the strip is covered on one of its faces with a layer of another material such as synthetic material or not.

According to one embodiment of the method according to the invention, the step of fixing the edges comprises the production of a longitudinal continuous weld bead. A perfectly sealed tubular envelope is thus obtained.

According to one embodiment of the method of the invention, the step of fixing the edges comprises the simultaneous production of two parallel longitudinal weld beads.

Thanks to this characteristic, the reliability of the sealing of the envelope is easily increased without thereby slowing down the manufacture of the tubular envelope and increasing its cost.

The invention also relates to a tubular casing, intended in particular for the production of cables, tubes or the like, characterized in that it is formed of a metal strip covered on at least one of its faces with a layer of another material, and in that said tape comprises two longitudinal edges folded transversely, one of the longitudinal edges of the tape said upper edge partially covering the other longitudinal edge said lower edge and in that the upper edge is held on the lower edge by at least one laser weld bead.

5

10

15

20

25

30

35

40

45

50

55

60

65

2

3

CH 686 169 A5

4

Other advantages and characteristics of the invention will appear more clearly on reading the following description of exemplary embodiments, the description being given purely by way of illustration in conjunction with the accompanying drawings, among which:

- fig. 1 is a sectional view of a first embodiment of a tubular casing according to the invention shown in the context of an application to a coaxial cable;

- fig. 2 is a sectional view of a first embodiment of a tubular casing according to the invention shown in the context of an application to a pipeline; and

- fig. 3 and 4 are sectional views of a second embodiment of a tubular casing according to the invention respectively in the applications of FIGS. 1 and 2; and

- fig. 5 is a schematic representation of a device allowing the implementation of the method according to the invention.

The description of the process for manufacturing a tubular casing which will follow will be made in the context of two particularly advantageous applications of the tubular casing of the invention, namely to a first application to a coaxial cable and a second application to a flow duct.

Of course the tubular casing obtained according to the manufacturing method of the invention is not limited to these applications and other applications can be envisaged. By way of example, the tubular envelope of the invention could also be advantageously used to make cables comprising optical fibers.

Referring to fig. 1, we see a cross-sectional representation of a coaxial cable designated by the general reference 1, the cable 1 being produced from an envelope 2 according to the invention.

The coaxial cable 1 comprises a conductive element 4 embedded in a layer of electrical insulating material 6. The conductive element 4 can be made of copper or any other conventional conductive material and the layer of insulating material 6 can be solid or in the form a foam, made of a plastic material, such as cellular polyethylene foam or the like.

The layer of insulating material 6 is tightly surrounded by a tubular casing 2 formed from a metal or metal alloy strip, the longitudinal edges 8, 10 of which are folded back so that the longitudinal edge 8, said upper edge partially covers the longitudinal edge 10 said lower edge.

The two longitudinal edges 8, 10 are fixed together by means of a continuous weld bead 12. In the example shown, the weld is an autogenous laser weld and the weld bead 12 is formed by the metal of the upper longitudinal edge 8 which has undergone complete melting and the metal of the part of the lower edge 10 which has undergone a partial merger. The cord 12 extends along the entire length of the upper edge 8 so that the tubular casing 2 is perfectly waterproof.

The tubular casing 2 can advantageously be made of steel, copper, aluminum or their alloys, but it can also be made of any other conductive material.

The thickness of the ribbon from which the tubular casing 2 is made is preferably between 0.02 and 0.30 mm. The tubular casing 2 which is produced from a thickness included in the range mentioned above advantageously has great flexibility.

The cable 1 finally comprises a layer of an electrical insulating material 14 such as polyethylene, which tightly surrounds the tubular envelope 2.

Referring now to FIG. 2, we see a cross-sectional representation of a pipe 16 such as a pipe of a heat transfer fluid produced from an envelope 2 according to the invention and in which the elements identical to those described above have been designated by the same reference numbers.

The structure of the pipe 16 differs from that of the coaxial cable 1 which has just been described only in that the conductive element 4 embedded in the insulating layer 6 is replaced by a simple tube 18 made of polyethylene or a material analog plastic.

In this case, it will be noted however that the tubular casing 2 has only an oxygen barrier function in order to avoid on the one hand premature aging of the plastic material forming the tube 18 and on the other hand corrosion of the system (not shown) associated with line 16 is used. Likewise, the layer of insulating material 14 will not be chosen specifically as a function of its electrical insulation properties but rather for its thermal insulation properties.

Referring now to Figs. 3 and 4, there is respectively seen a cross section of a coaxial cable 1 and of a pipe 16 made from a second embodiment of an envelope 2 according to the invention. The structure of this cable and of the pipe is respectively of the same type as that of the cable 1 and of the pipe 16 described in conjunction with FIGS. 1 and 2.

Unlike the embodiment of the envelope 2 described in conjunction with FIGS. 1 and 2, the upper longitudinal edge 8 of FIGS. 3 and 4 covers the lower longitudinal edge 10 over a greater part and the longitudinal edges 8, 10 are fixed together using two continuous longitudinal weld beads 12.

Referring also to FIG. 5, we see the schematic representation of a device 20 for implementing the method of manufacturing a tubular casing 2 according to the invention applied to the manufacture of a coaxial cable 1 or a pipe 16, such as described in conjunction with fig. 1 to 4.

In this device 20 a metal strip 22 is delivered continuously from a distribution coil 24 conventionally driven by a motor-ductor (not shown).

The ribbon 22 is formed by a continuous strip of a metal or a metal alloy having a

5

10

15

20

25

30

35

40

45

50

55

60

65

3

5

CH 686 169 A5

6

good aptitude for cold deformation. The width of the ribbon is greater than the circumference of the envelope 2 which it is desired to manufacture for reasons which will appear clearly in the following description. In the example described, the ribbon 22 is further provided on its two faces with a thin layer of another material (not shown), in this case a synthetic material. Preferably, this synthetic material is of the same nature or even identical to that of the material of the elements with which it will be in contact in the rest of the process.

The ribbon 22, after having run over return pulleys 26 arrives at a forming station 28. This forming station 28 comprises conventional means such as a series of forming rollers (not shown) through which the longitudinal edges 8 , 10 of the ribbon 22 are progressively folded transversely to form the closed tubular casing 2 in which the upper longitudinal edge 8 partially covers the lower longitudinal edge 10. The overlap width must be sufficient to be able to subsequently weld an edge 8 on the other 10.

The device 20 also comprises, upstream of the forming station 28, a distribution coil 30 of a continuous longitudinal element 32, such as a conductor coated with a layer of insulating material or a tube, depending on the desired final product. . The distribution reel 30 is also conventionally driven by a geared motor (not shown) and the longitudinal element 32 travels at the same speed as the ribbon 22 on a series of return pulleys 34 to the forming station 28. The longitudinal element 32 then travels parallel to the ribbon 22 and so that the tubular envelope 2 can be formed around the longitudinal element 32 so that the latter extends coaxially inside the tubular envelope 2 and in close contact with the latter.

Leaving the forming station 28, the tubular casing 2 passes through a welding station 36 comprising a conventional laser beam welding device. This device produces a laser beam which produces the continuous longitudinal weld bead 12 along the longitudinal edges 8, 10 superimposed on the envelope 2.

According to a variant of the method, the laser beam welding device 36 can comprise two optics so as to separate the laser beam into two and simultaneously produce two parallel longitudinal weld beads 12.

Advantageously, the welding device is adjusted so that the energy provided by the laser beam can bring the molten material to approximately 90% of the total thickness of the two overlapping longitudinal edges 8, 10. Thus, unlike the methods of the prior art, the welding can be easily controlled so that any deterioration of any internal coating of the tubular casing 2 and of the longitudinal element 32 located inside the casing 2 is avoided.

Once the welding has been carried out, the tubular casing is directed to an extrusion station 38

conventional in which it is coated with the layer 14 forming a sheath, this layer being made for example of polyethylene. It should be noted in this connection that the thin layer which covers the external surface of the tubular casing 2 promotes the attachment of the extruded material 14 to the tubular casing 2.

At the outlet of the extrusion station 38, a finished flexible product is obtained comprising a tubular casing 2 forming a coaxial cable 1 or a pipe 16 of pipe or the like in combination with the longitudinal element 32 around which the tubular casing 2 has been formed and depending on the nature of the longitudinal element 32. In this regard, the longitudinal element 32 can take very diverse forms and in particular the form of optical fibers contained in tubes of very small diameter (1 to 10 mm ).

The finished product is then conventionally stored on a receiving reel 40.

Claims (11)

Claims 1. Method of manufacturing a tubular casing, intended in particular for the production of cables, tubes or the like comprising the steps consisting in: - bring a ribbon made of a metallic material - gradually shaping said ribbon by folding the longitudinal edges of said ribbon until a closed tubular envelope is obtained in which one of the longitudinal edges partially covers the other longitudinal edge, characterized in that said ribbon is previously covered on at least one of its faces directed outwards from a layer of another material and in that the superimposed longitudinal edges are fixed together by means of a laser beam welding device without prior preparation of the longitudinal edges. 2. Method according to claim 1, characterized in that the laser beam device is adjusted so that the laser beam penetrates over approximately 90% of the total thickness of the two longitudinal edges of the overlapping ribbon. 3. Method according to one of claims 1 and 2, characterized in that the thickness of the metal strip extends in a range from 20 to 300 micrometers. 4. Method according to one of claims 1 to 3, characterized in that the step of fixing the edges comprises the production of a continuous longitudinal weld bead. 5. Method according to one of claims 1 to 3, characterized in that the step of fixing the edges comprises the simultaneous production of two longitudinal weld beads. 6. Tubular casing obtained according to the method according to one of the preceding claims, intended in particular for the production of cables, tubes or the like, characterized in that it is formed of a metal strip covered on at least one of its faces d 'a layer of another material, and in that said tape comprises two longitudinal edges folded transversely, one of the longitudinal edges of the tape said upper edge overlapping 5 10 15 20 25 30 35 40 45 50 55 60 65 4 7 CH 686 169 A5 partly the other longitudinal edge called the lower edge and in that the upper edge is held on the lower edge by at least one laser weld bead. 7. Tubular casing according to claim 6, characterized in that it is made from a material belonging to the family comprising copper, aluminum, steel and their alloys. 8. Application of the manufacturing method according to one of claims 1 to 5 for obtaining a cable or a tube, characterized in that it consists in providing a longitudinal element around which said envelope is shaped then welded . 9. Application of the manufacturing method according to claim 8, characterized in that said element is formed by a tubular element which extends in close contact with the inner surface of said envelope. 10. Application of the manufacturing method according to claim 8, characterized in that said element is formed by a conductor embedded in an insulator. 11. Application of the manufacturing method according to one of claims 8 to 10, characterized in that it consists in providing an insulating sheath extending in close contact with said layer of synthetic material of said welded tubular casing. 5 10 15 20 25 30 35 40 45 50 55 60 65 5