GB2101505A

GB2101505A - Cable manufacture

Info

Publication number: GB2101505A
Application number: GB08119362A
Authority: GB
Inventors: Kenneth Taylor; Colin Stanley Parfree; David Ian Strong
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1981-06-23
Filing date: 1981-06-23
Publication date: 1983-01-19
Also published as: FR2508180B1; AU8493882A; JPS584105A; GB2101505B; FR2508180A1

Abstract

A method of providing a cladding layer on a stranded cable element including extruding an oversize metallic tube (8) directly over a stranded layer (7) of a cable by means of a continuous extrusion process such as a friction extrusion machine (26). The tube (8) is allowed to cool before being subsequently drawn down and swaged into intimate contact with the stranded layer (7) by means of suitable dies and/or rolls (27). When the cable core incorporates optical fibres (3), as in an optical fibre submarine cable, this cladding method avoids the high temperatures and pressures associated with friction extrusion techniques adversely affecting the optical fibres. <IMAGE>

Description

SPECIFICATION Cable manufacture This invention relates to methods of manufacturing cables and in particular to methods of providing cables with a cladding layer and is applicable to both stranded rope cables and telecommunications cables.

One known construction of optical fibre cable for submarine use comprises one or more optical fibres located within a tubular electrical conductor, over which there is a cylindrical strain member, comprising for example one or more layers of stranded steel wires, and over the strain member is formed an electrically conductive tube, comprising copper tape wrapped longitudinally with the edges butted and the seam being welded to provide hermeticity. The tubular electrical conductor may comprise a C-section aluminium tube obtained by the friction extrustion technique, and formed into a closed tube around the optical fibres as disclosed in our co-pending Application No. 8021035 Serial No. (C.S. Parfree-P.

Worthington 1 5-9). A dielectric layer is extruded over the copper tube and further sheathing and armouring may be applied, if required, depending on the intended use of the cable.

Depending on their length, such optical fibre cables require repeaters, at intervals, to amplify the signal. These repeaters are powered electrically, the power being supplied from a terminal via the tubular metal conductor comprising the tubular electrical conductor, the cylindrical strain member and the electrically conductive tube. In designing the cable to meet the necessary requirements, it is important that the cable should have good flexibility, should be resistant to high pressures and to the action of the sea, and be available in long lengths.

It is an object of the present invention to provide a cable cladding method which can be used particularly, but not exclusively, in the manufacture of optical fibre submarine cable such that the cable meets the above requirements.

According to one aspect of the present invention there is provided a method of manufacturing a cable including a cladding layer arranged on a stranded cable element, comprising the steps of coaxially extruding an oversize metallic tube directly over the stranded cable element by a continuous extrusion process, and subsequently deforming the extruded tube into intimate contact with the stranded cable element, whereby the stranded cable element is not adversely affected by the heat and pressure of the extrusion process.

According to another aspect of the present invention there is provided an optical fibre submarine cable comprising one or more optical fibres arranged within a protective tube, one or more layers of strain members stranded over the protective tube, a metallic tube in intimate contact with the outermost layers of strain members, which metallic tube was coaxially extruded oversize directly over the outermost layer and subsequently deformed onto the outermost layer of strain members, and a layer of dielectric extruded over the deformed metallic tube.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a cross-section through an optical fibre cable core at one stage during cable manufacture; Fig. 2 shows a cross-section through a completed optical fibre submarine cable, and Fig. 3 shows, schematically, a process for manufacturing an optical fibre submarine cable and incorporating the process of the present invention.

An optical fibre cable core shown in Fig. 1 comprises a small strength member 1, comprising, for example, a wire, and a plurality of optical fibres 2, eight are shown, held together around the strength member 1 to comprise an optical fibre preform 3.

The preform 3 is arranged in an aluminium tube 4, which comprises a C-section extruded by a friction extrusion machine, that has been closed around the preform 3 by suitable dies or rolls subsequently to the preform being arranged therein. The tube 4 may be hermetically sealed by welding or soldering at the abutting faces 5 if desired.

A layer of high tensile steel wires 6 are stranded helically over the tube 4 in a conventional manner, typically fourteen wires being employed. Alternatively more or less wires per layer or more than one layer can be employed.

The layer of steel wires 6 comprises a strain member 7 (tensile strength member).

An oversize aluminium tube 8 is then directly extruded coaxially over the stranded strength member 7 by a continuous extrusion process, such as a friction extrusion process. Continuous extrusion processes avoid the stop/start steps inherent with discontinuous extrusion processes, such as billet extrusion, and enable long lengths to be extruded with substantially constant properties.

The tube 8 is subsequently drawn down and swaged onto the stranded strength member 7, using suitable dies or a combination of dies and rolls, to the form shown at 8' in Fig. 2. The tube material fills at least the interstitial spaces between the wires 6 and is in intimate contact with the layer 7 of stranded wires 6. The tube 8', the layer 7 of wires 6 and the tube 4 form a composite electrical conductor for power transmission to the repeaters which is sufficiently flexible for submarine use, which is hermetically sealed and can be made in long lengths. In addition the construction is resistant to the high pressures encountered on the sea bed and thus protects the optical fibres therefrom.

The tube 8 is initially extruded oversize such that it is a loose fit and not in intimate contact with the steel wires 6 of strength member 7. Thus the elements within the tube 8 are not directly subjected to the high temperatures and high pressures inherent in the continuous extrusion process and, in particular, the optical fibres are not adversely affected thereby. The drawing down and swaging is performed when the tube 8 has cooled sufficiently that damage to the inner elements of the cable will not be caused.

Typically the tube is extruded oversize such that a 25% decrease in the overall cross-sectional area thereof is required in the drawing down and swaging step.

The process for making the optical fibre cable described above with reference to Figs. 1 and 2 will now be described briefly with respect to Fig. 3.

C-Section aluminium tube 4 is produced by a friction extrusion machine 20, friction extrusion machines are disclosed, for example, in UK patent specifications Nos. 1370894 and 1467089. The extruded tube 4 is fed to a series of form rolls and dies 21, either directly or via a store (not shown), just prior to which series of form rolls and dies 21 the optical fibre preform 3 is fed from a reel 22.

The C-Section tube 4 is drawn through form rolls 23' and dies 23" by a hauler 24. The first set of form rolls 23' is effective to close the gap in the 'C", and the second set of dies 23" is effective to plastically deform the closed C-Section tube to reduce its external diameter by a predetermined value in the range of 5 to 10% of the initially closed diameter.

The closed C-section tube 4' containing the optical fibre preform 3 is then fed through a strander 25 to apply the layer 7 of steel wires 6.

The predetermined size to which the closed C Section tube is reduced in the second set of dies, is calculated so that the layer 7 of steel wires 6, or the first layer of multi-layer steel wires, exactly touch each other and touch the outer surface of the C-Section tube. This is important since, if the tube is too large, the external pressure caused by the wires will cause the first or only layer of wires to bed into the aluminium tube, thus causing elongation, which is undesirable since it can result in fracture of the optical fibres.

The steel strand covered core is then passed through a friction extrusion machine 26 which extrudes the oversize tube 8 thereover.

Subsequently the oversize tube 8 is drawn down and swaged onto the steel strands 6 at a die or die/roll station 27. An extruder 28 extrudes the dielectric layer 9 over the drawn down tube 8'. A further extruder 29 may be employed to apply sheath 11, and a conventional armoury machine 30 may be employed to apply armoury wires 12.

It is important that the aluminium C-Section tube 4 is provided in long lengths, since welding together shorter lengths causes problems in achieving the desired accuracy in the outer diameter of the closed and deformed C-Section effected by the dies 23. The split dies described in our co-pending application No. 8021035 are employed to assist in achieving the required long lengths. Likewise, it is important that the tube 8 is provided in long lengths and thus continuous extrusion thereof, as with friction extrusion machines, is desired.

Since the aluminium tube 8 is formed as a cylindrical tube, and not as in the prior art by longitudinally wrapping a copper tape around the core and subsequently welding the longitudinal seam. a more hermetic structure is produced than hitherto, even if the C-Sectioned tube is not welded at its adjacent faces, since copper tape weld imperfections cannot be ruled out. In addition, the copper tape welding of the prior art method is a fairly hazardous operation since, if the copper is contaminated or deformed, burnthrough, i.e. melting of the copper and underlying wires, occurs and thus can badly affect the cable's components and its performance, and requires considerable machine stoppage time to correct.

The forming of an oversize aluminium tube 8 and its subsequent drawing down and swaging involves the use of processing which is less prone to fault than the prior art and results in improved hermeticity.

Whereas the invention has been described with reference to optical fibre cables, it can alternatively be employed with any standard rope or cable over which it is desired to provide a cladding layer such as an hermetic metallic sheath, which rope or cable may include components which are liable to be adversely affected by the high temperatures and pressures involved if the sheath is extruded directly thereover. It is particularly applicable where long lengths of hermetic cladding with coherent properties, size and strength for example, are required.

The optical fibre cable shown in Fig. 2 preferably comprises the following: a central strand 1 comprising a high tensile steel wire clad in copper, in turn clad in polypropylene. The external diameter of the polypropylene 1.53 mm.

Around this are eight clad optical fibres each with an external diameter of 0.85 mm, and these are surrounded by a C-Section aluminium tube whose external diameter after swaging down is 6.71 mm, reduced from 9.91 mm, and the C-Section tube is surrounded by twelve high tensile steel wires each having a diameter of 2.31 mm. A sheath of low density polythene is extruded over the steel wires to a diameter of approximately 12 mm and a high density polythene jacket is extruded onto the sheath to an overall external diameter of 22 mm.

In place of the sheath and jacket a single integral sheath of low density polythene could be used instead. Outer armouring, for shallow water areas, would comprise about 20 plough steel wires each of around 7 mm in diameter.

Claims

CLAIMS 1. A method of manufacturing a cable including a cladding layer arranged on a stranded cable element, comprising the steps of coaxially extruding an oversize metallic tube directly over the stranded cable element by a continuous extrusion process, and subsequently deforming the extruded tube into intimate contact with the stranded cable element, whereby the stranded cable element is not adversely affected by the heat and pressure of the extrusion process. 2. A method as claimed in claim 1 , whereas the stranded cable element comprises one or more optical fibres arranged within a protective tube, over which protective tube one or more layers of strain member wires are stranded, and wherein the method further includes extruding dielectric over the deformed extruded tube. 3. A method as claimed in claim 2, wherein the protective tube comprises a C-Section metallic tube extruded by a continuous extrusion process and deformed by dies and/or rolls into a circular section around the optical fibre or fibres. 4. A method as claimed in claim 3, wherein a sheath is extruded over the dielectric. 5. A method as claimed in claim 4, wherein armouring is provided over the sheath. 6. A method as claimed in any one of the preceding claims, wherein the oversize metallic tube is extruded from aluminium. 7. A method as claimed in any one of the preceding claims, wherein the continuous process is a friction extrusion process. 8. A method as claimed in claim 2, wherein a plurality of optical fibres are arranged about a central strain member as an optical fibre preform. 9. An optical fibre submarine cable comprising one or more optical fibres arranged within a protective tube, one or more layers of strain members stranded over the protective tube, a metallic tube in intimate contact with the outermost layer of strain members, which metallic tube was coaxially extruded oversize directly over the outermost layer and subsequently deformed onto the outermost layer of strain members, and a layer of dielectric extruded over the deformed metallic tube. 10. An optical fibre submarine cable as claimed in claim 9, further comprising a sheath extruded over the dielectric. 11. An optical fibre submarine cable as claimed in claim 10, further comprising armouring arranged over the sheath. 12. A method of manufacturing a cable substantially as herein described with reference to and as illustrated in the accompanying drawings. 1 3. An optical fibre submarine cable substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings. New claims or amendments to claims filed on 2/2/82. Superseded claims. All. New or amended claims.

1. A method of manufacturing an optical fibre cable comprising one or more optical fibres arranged within a protective tube including one or more layers of strain members, the method including the steps of coaxially extruding an oversize metallic tube directly over the outermost strain member layer and subsequently, such that the optical fibres are not adversely affected by the heat and pressure of the extrusion process, deforming the oversize extruded tube into intimate contact with the outermost strain member layer, whereby to hermetically seal the optical fibres.

2. A method as claimed in claim 1, wherein the one or more layers of strain members are provided by stranding one or more layers of strain member wires over the optical fibres.

3. A method as claimed in claim 1 or 2 wherein the optical fibre or fibres is or are arranged in a first tube over which the strain member layer or layers are provided, and wherein the first tube comprises a C-Section metallic tube extruded by a continuous extrusion process and deformed by dies and/or rolls into a circular section about the optical fibres of fibres.

4. A method as claimed in any one of the preceding claims wherein the oversize metallic tube is extruded by a continuous extrusion process.

5. A method as claimed in any one of the preceding claims, further including the step of extruding dielectric over the deformed tube that was extruded oversize.

6. A method as claimed in claim 5, wherein a sheath is extruded over the dielectric.

7. A method as claimed in claim 6, wherein armouring is provided over the sheath.

8. A method as claimed in any one of the preceding claims, whrein the oversize metallic tube is extruded from aluminium.

9. A method as claimed in any one of claims 3 to 8, wherein the continuous extrusion process is a friction extrusion process.

10. A method as claimed in any one of the preceding claims, wherein a plurality of optical fibres are arranged about a central strain member as an optical fibre preform.

11. An optical fibre cable comprising one or more optical fibres arranged within a protective tube including one or more layers of strain members and an extruded metallic tube in intimate contact with the outermost layer of strain members, which metallic tube was coaxially extruded oversize directly over the outermost layer and subsequently deformed onto the outermost layer of the strain members, whereby to hermetically seal the optical fibres.

12. A cable as claimed in claim 11, wherein the strain member layers comprise layers of stranded strain member wires.

13. A cable as claimed in claim 11 or claim 12, including a layer of dielectric extruded over the deformed metallic tube.

14. A cable as claimed in claim 13, further comprising a sheath extruded over the dielectric.

1 5. A cable as claimed in claim 14, further comprising armouring arranged over the sheath.

1 6. A method of manufacturing an optical fibre cable substantially as herein described with reference to and as illustrated in the accompanying drawings.

1 7. An optical fibre cable substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.