FR2508180A1 - OPTICAL FIBER CABLE AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Abstract

THE INVENTION CONCERNS THE MANUFACTURE OF A FIBER OPTIC CABLE IN WHICH THE CONDUCTIVE TUBE SURROUNDING THE FIBERS IS COVERED WITH ONE OR MORE LAYERS OF STRANDED STEEL WIRES 7 ENSURING THE MECHANICAL RESISTANCE OF THE CABLE AND AN EXTERNAL CONDUCTIVE TUBE 8 IS FORMED ON THE LAST LAYER OF STEEL WIRE. THE EXTERNAL TUBE 8 IS MANUFACTURED BY EXTRUSION OF AN OVERSIZED TUBE AROUND THE LAST LAYER OF STRANDED WIRES 7, PREFERABLY CONTINUOUS BY MEANS OF A FRICTION MACHINE. AFTER COOLING, THIS TUBE IS STRETCHED AND LAMINATED BY ADEQUATE DIES OR ROLLS SO THAT IT TIGHTLY ENSURES THE LAYER OF THREADS 7. THE TUBE OBTAINED 8 PROVIDES A SEALING OF THE FIBERS MORE HERMETIC THAN THE WELDED COPPER STRIP AND LONG WELDING TECHNOLOGY ANTERIOR. THE INITIAL OVERSIZING OF THE TUBE PROVIDED FOR BY THE INVENTION PREVENTS THE FIBERS FROM DAMAGED BY THE HIGH TEMPERATURES AND PRESSURES OF THE FRICTION EXTRUSION PROCESS. MAIN APPLICATION TO THE MANUFACTURING OF UNDERWATER OPTICAL CABLES.

Description

The present invention relates to methods of manufacturing cables and,

  more particularly, cable sheath coating methods that apply to stranded wire or cable and reinforced core telecommunication cables.

  steel wires, especially optical fiber submarine cables.

  Optical fiber cables for underwater use generally comprise one or more optical fibers surrounded by a tubular electrical conductor on which one or more layers of stranded steel wires form a cylindrical, tensile strength member. A copper strip is wound longitudinally around the strands and its two edges are joined and welded to form a hermetic conductive tube The inner tubular conductor may be constituted by a C-profile aluminum tube obtained by the friction extrusion technique and then formed to constitute a closed tube around the optical fibers, as described by the British patent application No. 8021035 A dielectric layer is extruded on the copper tube and the cable can still be provided with an outer sheath and an armor according to the use considered. Depending on their length, these fiber optic cables will have to be equipped with repeaters, located

  at regular intervals, to amplify the signal.

  The power supply to the repeaters is provided by a terminal and uses the circuit formed by the stranded steel wires and the two conductive tubes surrounding these wires. The cable must be designed to have a good flexibility, a sufficient resistance to high pressures and to the action of the marine environment and it must be available

in great length.

  An object of the present invention is to provide a method of coating a stranded layer of a cable, this method being applicable in particular to the manufacture of optical fiber submarine cables having the above characteristics, but not

not limited to this application.

  According to the main characteristic of the invention, the method of manufacturing a cable comprising a coating layer on a stranded element of the cable consists in extruding directly and coaxially on the stranded element, by a continuous extrusion process, a metal tube of larger diameter than the strand, then deforming the extruded tube to tightly clamp the strand on which the heat and pressure produced by the extrusion process did not

thus no adverse effect.

  Another feature of the invention resides in an optical fiber submarine cable comprising one or more fibers arranged in a protective tube, one or more layers of tensile elements stranded on the protective tube, a tube metal in intense contact with the outer layer of the stranded elements, this tube having been extruded coaxially and directly on the outer layer of the stranded elements with a diameter greater than this layer, and then deformed to come into contact with the layer, and a layer of dielectric extruded on the

metal tube thus Tétreint.

  The invention will be better understood when reading

  of the following detailed description, made as a

  of non-limiting example, with reference to the appended figures which represent FIG. 1, a cross-sectional view of an optical fiber cable core, at a certain stage of a method of manufacturing the cable according to the invention ; FIG. 2 is a cross-sectional view of an optical fiber cable completed in FIG. 3, a diagrammatic view of an optical fiber submarine cable manufacturing installation in which the method according to the invention is integrated. . The core of the optical fiber cable of FIG. 1 comprises a small central carrier 1, for example a wire, and a plurality of optical fibers 2 held around the carrier 1 in a cylindrical rod 3. For example,

  the illustrated core comprises an 8-fiber rod.

  The ring 3 is contained in an aluminum tube 4 coming from the extrusion of a C-profile by a friction machine and the closure of this profile around the rod 3 by adjacent dies or rollers. If necessary, the tube 4 can be hermetically sealed by soldering

  or welding the longitudinal faces 5 placed end to end.

  A layer of steel wire 6 of high mechanical strength is bandaged on the tube 4, in conventional manner It typically comprises fourteen son, according to the example provided by the figure, but it is obviously possible to use a plus or fewer wires per layer and more layers The steel wire layer is a reinforcing element

  7 of the mechanical resistance of the cable.

  An aluminum tube 8 is then extruded directly and coaxially on the reinforcing strand 7 by a continuous extrusion process, in particular a friction extrusion process, with a diameter greater than that of the strand 7 Extrusion processes continuously avoid the start and stop phases inherent to discontinuous processes, the extrusion of billets, tubes of great length can thus be extruded

  with very homogeneous properties.

  The tube 8 is finally stretched and stamped or pushed onto the reinforcing strand 7 by means of a combination of dies and rolling trains to form the coating tube 8 'shown in FIG. 2. The material of the tube 8' fills at least the interstitial spaces between the wires 6 and is in close contact with the

  outer layer or the single layer 7 of stranded wires 6.

  The tube 8 ', the layer 7 and the tube 4 thus constitute a composite electrical conductor capable of transmitting energy to the repeaters, sufficiently flexible for submarine applications, hermetically sealed and available in long lengths The described structure can withstand at the high pressures of the seabed and

  thus effectively protects optical fibers.

  The tube 8 is initially extruded to a sufficient size to fit freely on the reinforcing element 7, without coming into close contact with the wires 6 of this element. The cable components located inside the tube 8 are therefore not not directly subjected to the high temperatures and pressures which characterize the continuous extrusion process and, more particularly, no adverse effect is exerted on the optical fibers The drawing and rolling of the tube 8 on the stranded layer 7 is performs after sufficient cooling to avoid further

  any damage to the internal elements of the cable.

  Typically, the initial extrusion of the tube 8 takes place at a diameter such that a contraction of 25% of this diameter is necessary during the operations.

drawing and rolling.

  The method of manufacturing the optical fiber cable according to FIGS. 1 and 2 will now be described with reference to FIG. 3. A C-aluminum profile is produced by a friction extruder 20, such a machine being for example of the type The open tube 4 is drawn directly or via a storage drum through a series of dies and forming rollers 21 which is located immediately after the introduction of the invention. cylindrical rod 3 containing the optical fibers, in the tube 4, the rod 3 being unwound from the coil 22 The tube 4 is entralné by a traction roller 24 and passes through a first set of forming rollers 23 'which serves to close the profile at C and a second set of dies 23 "which plastically deforms the closed profile to reduce its internal diameter to a predetermined value. This value corresponds typically

  at a decrease of the initial diameter of 5 to 10%.

  The closed tube 4 'containing the fiber optic core 3 is then pulled through a stringer 25 which

2508 180

  the coating of a layer 7 of steel son 6.

  The diameter at which the closed C-profile tube is reduced by the second set of dies is calculated so that the wires 6 of the layer 7 are placed exactly against each other and in contact with the outer surface of the C C adaptation is important, because if the tube was too large, the external pressure exerted by the son of the first or the only layer 7 could lead them to fit into the aluminum tube This would cause an elongation of the tube which

  could lead to the fracture of optical fibers.

  The core of the cable covered with steel strands then passes through a friction extruder 26 which covers it with the oversize tube 8. The latter is stretched and compressed on the strands 6 in a stretching and rolling station 27 An extruder 28 produces the dielectric layer 9 on the shroud tube 8 'A second extruder 29 can be used to cover the cable with a sheath 11 and a conventional machine 30 for him

  apply armor wires 12 over this sheath.

  It is important that the C-profile aluminum tube 4 is produced in great length because the welding of several short-length tube sections does not make it possible to achieve the required accuracy for the outer diameter of the tube which is closed and deformed by the dies 23 Split dies described in British Patent Application No. 8021035 may be

  used to provide the required long lengths.

  It is also important that the tube 8 is produced in great length, which makes it desirable to use a continuous extrusion process of the type obtained with

friction extrusion machines.

  Since the aluminum tube 8 is formed as a cylindrical tube and not, as in the prior art, by longitudinally winding a copper strip around the core of the cable by welding the strip edge to edge, one achieves a more hermetic structure than before, even though the C-profile tube is not welded along its adjacent edges, since imperfections in the welding of a copper strip can not be eliminated. , the welding operation of the copper strip performed in the prior art is rather random because, if the copper is contaminated or deformed, it can occur a deep burn of the cable, that is to say a melting of the Copper and underlying wires that severely affect the components and characteristics of the cable and require a shutdown

  extended machines to remove the cause.

  The forming of an oversize aluminum tube and the subsequent stretching and rolling operations involve the use of much more reliable manufacturing processes than those of the prior art and provide improved hermeticity. Although the invention has been described with reference to optical fiber cables, it can be applied to any cable or cable on which it is desired to form a coating such as a hermetic metallic sheath, this rope or cable comprising components which can be damaged by the high temperatures and the high pressures necessary for the direct extrusion of this sheath The invention applies more particularly to the manufacture of a hermetic coating of great length with a great constancy of certain properties, for example diameter and mechanical strength. The optical fiber cable shown in FIG. 2 preferably has the following structure: a central carrier 1 made of a very strong steel wire

  coated with copper, the whole being sheathed with polypropylene.

  The outer diameter of the polypropylene rod is 1.13 mm. Eight coated optical fibers, each having an external diameter of 0.85 mm, are mounted around this rod and they are surrounded by an aluminum tube 4 having a C-profile. whose outer diameter is initially 9.91 mm and decreased to 6.71 mm after forming The tube 4 formed is surrounded by twelve steel wires of great

  mechanical strength each having a diameter of 2.31 mm.

  A low density polyethylene sheath is extruded on the steel wires to a diameter of about 12 mm and a high density polyethylene sheath is extruded on the sheath to a total outer diameter of 22 mm. Low density can be used in place of the sheath and outer casing assembly. External armor, required for shallow water applications, can consist of approximately 20 hard steel wires.

some 7 mm in diameter.

  It is obvious that the description which

  preceding was given as a non-limitative example

  and that other variants can be envisaged without

  to go beyond the scope of the invention.

Claims (10)

  A method of manufacturing an optical fiber cable comprising one or more fibers arranged in a protective tube including one or more layers of mechanical resistance elements (7), characterized in that it comprises the extrusion operations of an oversized coaxial metal tube (8), directly on the outer layer of mechanical strength elements (7) and so that the optical fibers (2) are not adversely affected by heat and pressure due to extrusion subsequently deforming the extruded tube (8 ') to bring it into very close contact with said outer layer of strength members.  The method according to claim 1, wherein said layer or layers of strength elements (7) are produced by stranding one or more resistant wire layers (6) on the optical fibers (2). Method according to claim 1 or 2, wherein said optical fibers (2) are arranged in a first tube (4) around which the layer or layers of mechanical resistance elements (7) are stranded, said first tube comprising a layer C-profile metal extruded by a continuous extrusion process and deformed by dies (23 ') or rolling rolls (23 "), or by a set (21) of dies and rollers into a circular profile around of the optical fiber.   4 Process according to any one of   preceding claims, wherein said tube   overdimed metal (8) is extruded by a continuous extrusion process.   Process according to any one of   preceding claims, wherein a layer   dielectric (9) is also extruded onto the deformed tube (8 ') which has been previously extruded at a upper diameter (8).   The method of claim 5, wherein   a sheath (11) is extruded onto the dielectric (9).   The method of claim 6, wherein an armor (12) is formed on said sheath (11). Process according to any one of   preceding claims, wherein the metal tube   suffydimensionné (8) is made of extruded aluminum.   9 Process according to any one of   Claims 3 to 8, wherein said process   Continuous extrusion is a process of extrusion by friction (25).   Process according to any one of   preceding claims, wherein a plurality of fibers   optics (2) are arranged around a central carrier   (1) the cable in an optical fiber holder (3).   11 An optical fiber cable comprising one or more fibers arranged in a protective tube including one or more layers of strength members and an extruded metal tube (8 ') in close contact with the outer layer of strength members ( 7), characterized by   the fact that said metal tube has been extruded directly   said outer layer (7) as a D-sized coaxial tube (8) and subsequently deformed to closely enclose said layer and seal   thus hermetically said fibers (2).   Cable according to claim 11, wherein said layers of strength elements (7)   consist of strands of resistant wires (6).   Cable according to claim 11 or 12, wherein a dielectric layer (9) is also extruded   on the deformed metal tube (8 ').   Cable according to claim 13, wherein a   sheath (11) is extruded onto the dielectric (9).   Cable according to claim 14, wherein a   armor (12) is formed on said sheath (11).