NZ195449A - Method and apparatus for making optical fibre cable - Google Patents

Description

ORIGINAL Priority Dat&[s): | .CornpSsts Specification FiSed: J I Class: . -Q'6: 1^84 PubiicEtion Date: P.O. JoLrn"-~", No: .

NEW ZEALAND THE PATENTS ACT, 1953 COMPLETE SPECIFICATION " i-J b V - l-H: "OPTICAL FIBRE SUBMARINE CABLE' A ^ " 'r t WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a. patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement 1 954 49 This invention relates to optical fibre cables, particularly to such cables for submarine use.

British Patent 1,550,588 discloses an optical fibre cable which includes one or more optical fibres located within a / tubular electrical conductor over which there is a cylindrical strain member. Optical fibre cables offer the advantage for submarine telecommunication systems, of propagating the signal over relatively long distances before the signal needs amplification in a repeater. It is estimated that the repeater spacing can be as much as 30 or even 50 km in optical fibre submarine communication systems in the near future.

The repeaters are powered electrically, the power being supplied from a terminal via the tubular metal conductor comprising, in the aforementioned patent, the tube 2 surrounded by the cylindrical strength member 3 and the copper tape 4. In designing a 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 method of making an optical fibre cable in which the above requirements can be met.

Accordingly there is provided a method of making an optical fibre cable, comprising providing a hollow metallic conductor extruded by a friction extrusion technique, placing one or more 195449 optical fibres into the hollow conductor, sizing the conductor to reduce its external diameter to a predetermined value by drawing it through one or more forming dies which are split to enable maintenance or cleaning thereof to take place without breaking the conductor or the optical fibre/s, and completing the cable including applying a tensile strength member around the conductor. For a submarine cable completion would also include applying a dielectric layer over the strength member.

Preferably the hollow conductor comprises a C-section tube which is closed and further plastically deformed to reduce its external diameter to the predetermined value.

Preferably the reduction in external diameter of the closed C-section tube is in the range of 5 to 10% of the initially-closed diameter.

Preferably the conductor is made of aluminium or aluminium alloy.

Conveniently the forming dies also effect closure of the gap in the "C" prior to reducing the diameter of the tube.

In order that the invention can be clearly understood reference will now be made to the accompanying drawings wherein:- Fig. 1 shows schematically a process for manufacturing an optical fibre cable in accordance with an embodiment of the 195 present invention, Fig. 2 shows the C-section aluminium tube as formed by the friction-extrusion technique, and Fig. 3 is a cross-section through one embodiment of a cable 5 formed by the process shown in Fig. 1.

Fig. 4 depicts an end view of a die case, Fig. 5 depicts a sectional view of the die case of Fig. 4, Fig. 6 depicts one half of a die pellet that may be fitted in the die case of Figs. 4 and 5, and 10 Figs. 7 and 8 depict cross-sections of part of an optical fibre cable respectively before and after it has been drawn through a train of dies as depicted in Figs. 4, 5 and 6.

Referring to Fig. 1 of the drawings a hollow metal conductor in the form of a C-shaped section aluminium tube 1 is ex-15 truded from a friction extrusion machine 2 to a store 3 indi cated by dotted lines. Friction extrusion machines are disclosed in UK patents 1,370,894 and 1,467,089 and reference could with advantage be made thereto. It may be possible to do away with store 3 and feed the extruded tube 1 directly to a 20 series of dies 4, just prior to which an optical fibre preform is fed from a reel 6. The optical fibre preform comprises a plurality of optical fibres 7 held together around a king wire 8, as shown in greater detail in Fig. 3.

The C-sectioned tube is drawn through the dies by a reel 9 25 and the first set of dies 41 is effective to close the gap in - 4 „ t the "C". Alternatively the closing may be effected by a rolling mill using profiled wheels. The second set of dies 4" is effective to plastically deform the closed C-section tube to reduce its external diameter to a predetermined value in the 5 range 5 to 10% of the initially closed diameter.

The closed C-section tube 1' containing the optical fibre preform is then fed through a strander or stranders (10 and 11) to apply one or two layers of steel wires 12 and 13 respectively, shown in detail in Fig. 3, to form a tensile strength member. 10 The predetermined size to which the closed C-section tube is reduced in the second set of dies, is calculated so that the first layer of tensile strength members 12 exactly touch one another and touch the outer surface of the C-section tube. This is important since, if the tube is too large, the external 15 pressure caused by the layers of strength members and externally applied pressure will cause the first layer of wires to bed into the aluminium tube, thus causing elongation which is undesirable.

At a further station 14 in the manufacturing process, a longitudinally applied copper tape 15 is formed by a set of 20 forming rolls 16 round the strength members.

The emergent cable element 17 is passed into a plastics extruder 18 in which a dielectric layer 19 of polythene is extruded around the element 17 to form the finished cable 20.

It may or may not be necessary to apply a sheath 21 in a 25 further extrusion machine 22. Over this sheath 21 may be 1 0 * 195449 applied armouring wires if the cable is to be used for submarine electrocommunication systems in shallow waters. The armouring is not shown in Fig. 3.

It is important that the aluminium C-section tube is pro-5 vided 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 tube effected by the dies 4. It has been found that weaknesses can occur at the weld subsequent to its passage through the dies 4. To make it 10 possible to use long lengths of aluminium tubing it is proposed that split-dies be used for the dies 4, so that these can be removed and cleaned when galling occurs, without the need to break the tubing 3 or the optical fibre preform 5.

A train of four wire sizing dies to convert the hollow 15 C-section aluminium tube containing optical fibres into closed tubing around the fibres is shown in Figs. 4 to 8. The tube acts both as a conductor for electrical power and as a pressure-resistant tube to withstand high hydrostatic pressures such as are experienced on the ocean floor.

Referring to Figs. 4 and 5, two semi-cylindrical blocks and 31 are machined from separate cylinders of EN24 steel. Jig-boring is used to provide holes 32 for dowels and holes 33 for pair of screws (not shown) by which one block is secured to the other. The two blocks, which are to form the two halves of I Wkk f the die case, are then assembled, and provided with a main bore 34 for housing the two identical die pellet halves 35 (not shown in Figs. 1 and 2) therein. The die pellet halves are also made from separate pieces of tungsten carbide die pellet stock. Both pieces, which are annular, are cut with a diamond wheel to leave major segments which are just larger than half. These are brazed into their respective die case halves. Since the die pellet inserts are at this stage just larger than halves they protrude a short distance above the machined faces of the die case halves. They are then diamond ground flush with those machined faces. Next the two halves of the die case are assembled and the existing hole through the die pellet halves is enlarged by spark erosion machining before being given a final polish to size with diamond polish. The bore has a cylindrical throat 36, typically about 2.5 mm long which is preceded by a long taper 37 having a semi-vertical angle of about 10°. Downstream of the throat at 38 the bore is chamfered at about 45°.

A train of four such dies can be used with the throat diameters of 9.0, 8.8, 8.3 and 7.5 mm respectively to close an extrusion of C-section aluminium duct 1 around a set of plastics coated optical fibres 7 which have been introduced in the duct through the opening in its side. The tube 1 which is made of 99.5% commercial grade aluminium, starts with a 9.9 mm overall diameter before closing, a 6.5 mm internal diameter, and a 86° opening between the jaws 53. After closing, the overall diameter is 7.5 mm and the internal diameter in a typical drawing down operation is about 4.3 mm. When operating at a drawing speed of about 6 metres per minute it is found that aluminium pick-up in the dies becomes noticeable after drawing about 2 km 5 of the tube. The amount of tube that can be drawn before this occurs is however variable within a wide range depending upon die lubrication. Once aluminium pick-up has occured, it is a matter of only a few minutes to take each die apart, clean it, and re-assemble it ready for continuation of the drawing 10 operation.

Claims (11)

195449 What we claim is:-

1. A method of making an optical fibre cable, comprising the steps of providing a hollow metallic conductor extruded by a friction extrusion technique, placing one or more optical fibres into the hollow conductor, sizing the conductor to reduce its external diameter to a predetermined value by drawing it through one or more forming dies which are split to enable maintenance or cleaning thereof to take place without breaking the conductor or the optical fibre/s, and completing the cable including applying a tensile strength member around the conductor.

2. A method as claimed in claim 1 wherein the hollow conductor comprises a C-section tube, and including placing said one or more optical fibres into the tube, closing the tube and further plastically deforming the tube to reduce its external diameter to the predetermined value.

3. A method as claimed in claim 2 wherein the external diameter of the closed C-section tube is reduced by 5 to 10% of the initially closed diameter.

4. A method as claimed in any one of the preceding claims wherein the conductor is made of aluminium or aluminium alloy.

5. A method as claimed in any one of the preceding claims wherein each forming die comprises a die case and a die pellet each formed in two or more parts which are capable of being assembled around, and dismantled from around the conductor without access to either end thereof. - 9 - 195449

6. A method as claimed in claim 5 wherein the component parts of the die case are dowelled together and secured by bolts.

7. A method as claimed in any one of the preceding claims wherein the tensile strength member is applied by stranding one or more layers of high tensile wires around the conductor.

8. A method as claimed in any one of the preceding claims wherein a dielectric layer is extruded over the strength member.

9. A method of manufacturing an optical fibre cable substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

10. A method of manufacturing an optical fibre cable substantially as hereinbefore described with reference to the accompanying drawings.

11. An optical fibre cable made by a method according to any preceding claims. INTERNATIONAL STANDARD ELECTRIC CORPORATION P.M. Conrick Authorized Agent 5/1/1223 10