GB1579123A

GB1579123A - Cables

Info

Publication number: GB1579123A
Application number: GB17034/76A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1976-04-27
Filing date: 1976-04-27
Publication date: 1980-11-12
Also published as: FR2349931B1; FR2349931A1; JPS52131188A

Description

(54) CABLES (71) We, STANDARD TELE PHONES AND CABLES LIMITED, a British Company, of 190 Strand, London, W.C.2., England, do 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: This invention relates to submarine cable suitable for use in underwater telecommunications links.

In the past it has been customary in manufacturing submarine coaxial cables to form the return conductor from a flat copper or aluminium strip which is longitudinally applied around the dielectric of the cable and the edge regions of the strip overlap one another. In the case of aluminium only, we insert a flat polypropylene tape approximately 2 thou thick by l" wide in between the overlapped longitudinal edge regions to act both as a mark (that is to say it is normally black and therefore any twisting in the cable can be detected by virtue of a projecting portion of the tape) and to provide insulation between the longitudinal edge regions which has been thought to be preferable to intermittent electrical contact which might occur when bare edge regions overlap one another.

It has never been considered necessary to provide an additional moisture barrier such as is described for example in British Patent Specifications 886,417 and 1,071,762 simply because results over the years have not shown such a barrier to be necessary. For one thing the cable has a solid polythene dielectric of a substantial thickness (approximately 2" thick), a fairly thick polythene outer sheath (about 8" thick) and the metal return conductor between the two does act to a large extent as a barrier against any further ingress of moisture which may over the years eventually permeate the sheath.

It is an object of the present invention to improve the water-resistance of the return conductor.

According to one aspect of the present invention there is provided a submarine coaxial cable comprising: a central strength member; an inner coaxial conductor; a return coaxial conductor comprising a longitudinal tape with longitudinal edge regions adjacent each other; rigid dielectric material between the inner and return conductors; a sheath surrounding the return conductor; and sealing means, including a strip or tape engaging said longitudinal edge regions only, to prevent moisture passing between the edge regions, whereby the sealed coaxial return conductor also acts as a moisture barrier against moisture ingress to said dielectric material.

In one embodiment at least one overlapped region is formed with a longitudinal rib to provide a longitudinal pressure seal, the deformation occurring at the contact with the crest of the rib.

Preferably the rib is formed in one or both overlapped surfaces of the return conductor, but it can also be provided on an intermediate insulating tape of, for example, polypropylene.

According to a further aspect of the present invention the longitudinal edge regions overlap one another; said sealing means comprises a tape of deformable material interposed between the edge regions; and said tape forms a pressure seal at the edge regions incorporating a longitudinally-extending region deformed by external pressure.

According to yet another aspect of the present invention the previously-mentioned polypropylene tape is replaced by an adhesive tape which has been bonded by heating to the overlapped edge regions of the return conductor. The tape or edges can once again be formed with longitudinal beads or ribs.

Preferably the heat is applied during the tandem forming of the return conductor and extrusion of an outer waterproof plastics sheath will bond the overlapped edges via the tape. The tape can be an EVA copolymer or can be polyethylene. The tape could comprise a metal core or other flexible substrate coated with a thin layer of adhesive material or having a longitudinal bead of adhesive material on each side, which will become bonded to the overlapped edges of the return conductor by the application of heat, preferably during the extrusion of the plastics sheath.

Another aspect of the present invention resides in replacing the polypropylene tape by a tape of insulating material more resilient than polypropylene. A suitable material could be neoprene in the form of a tape about an inch wide and between 5 thou and 10 thou thick. The compressive stress of the outer plastics sheath squeezes the more resilient material to form an effective watertight seal. Alternatively a continuous tape of neoprene of circular cross section could be used, preferably seated in a groove in the return conductor edge region.

Reference will now be made to the drawings accompanying the Provisional Specification in which: Figure 1 is a cross section of a submarine coaxial cable according to an embodiment of the present invention, Figure la is a cross section of a tape of a submarine coaxial cable according to another embodiment of the invention Figure 2 shows schematically an apparatus suitable for making the embodiment of Figure 1 and Figures 3, 4, 5, 6, 7 and 8 show partial sections of submarine coaxial cables according to other embodiments of the invention.

Referring to Figure 1 a submarine cable comprises a central tensile strength member 1, preferably of high tensile steel wires, an inner conductor 2 of copper or aluminium, a dielectric 3 preferably of polyethylene and a return conductor 4 of copper or aluminium.

The whole is surrounded and encapsulated by a polyethylene outer sheath 5.

The edge regions 6 and 7 of the return conductor 4 are each formed with a longitudinal rib 8 and 9 respectively which each form a longitudinal region of increased pressure on an intermediate insulating tape 10 of polypropylene.

It would be possible to have only one rib, i.e. either the rib 8 or the rib 9 and it would also be possible to have a rib formed on the polypropylene tape as shown in Figure la.

Here the tape 10' is shown as having two ribs 11 and 12 and these would be in place of the ribs 8 and 9 shown in the return conductor 4 in Figure 1.

The ribs in the return conductor 4 of Figure 1 preferably have a smooth crosssectional shape, i.e. they are not sharply pointed and preferably have a height above the surface of the return conductor of between '2 and 10 thou. The ribs described above in combination with or integral with the tape form a pressure sealing mechanism greater than 2 thou thick.

Referring now to Figure 2 there is shown schematically and in cross-section the return conductor tape 4 of Figure 1 (on a different scale) passing between forming rollers 13, 14, 15 and 16 at a stage in the manufacturing process in which the tape is just starting to be formed to a curved shape from its original flat shape as it comes off the reel of tape. These forming rollers have cooperating annular ribs 13' and 16' and annular grooves 14' and 15' respectively.

These co-operating annular ribs and grooves form the longitudinal ribs 8 and 9 as shown in Figure 1. Subsequently, although not shown, other forming rollers would urge the strip into a circular configuration to completely embrace the dielectric with the surface of the edge region of the longitudinal tape and the surfaces of the polypropylene tape overlapping one another.

Referring now to Figure 3 there is shown an embodiment in which the polypropylene tape has been replaced by a tape of insulating material which is more resilient than polypropylene. In this particular case the tape 17 is made of neoprene and would, prior to being compressed between the overlapping edges 6 and 7 of return conductor 4, have a thickness of between 2 thou.

and 10 thou. and it would be about an inch wide.

Referring now to Figure 4 a polypropylene tape 18 is disposed between the overlapping edge regions 6 and 7 of the return conductor 4 and each edge region has a longitudinal groove 19 and 20. Disposed in each groove is a neoprene seal 21 and 22 which, prior to being squeezed between the surfaces of the groove and the polypropylene tape, is of circular cross section as indicated in the lead lines between the reference numerals 21 and 22 and in situ positions of these seals in the cable. These seals would have an original diameter between 10 and 30 thou. The depth of the grooves would be between 5 and 10 thou.

Referring now to Figure 5 there is shown a coaxial cable in which the polypropylene tape has been replaced by an adhesive copolymer strip 23, preferably an EVA (Ethyl Vinyl Acetate) tape which has been bonded to the facing surfaces of the overlapping edge regions 6 and 7 by the application of heat. Alternatively a low density polyethylene tape could bc used for the tape 23. This softens at about 120"C. A "bonding" temperature preferably in the range 180 to 2000C is envisaged and is preferably derived from the heat of the extruded outer sheath 5 alone without the addition of further heat, although other sources of heat are not excluded. By "bonding" we do not mean a molecular bond.Inspection of the cable has revealed that the polyethylene tape has softened and been deformed by squeezing between the overlapped edge regions of the return connector until its thickness has been reduced from about 5 thou + 1 thou. to only 2 thou. i.e. it has been reduced in thickness by over half its original thickness. It has not stuck irremovably to the return conductor and can be peeled away if pulled. However the deformation ensures any trapped air bubbles are removed and an effective seal is produced.

It would be possible to replace the tape 23 with a strip of compound which will react with water vapour should this find its way into the overlap region. This compound would undergo a chemical change in contact with water vapour such as to prevent water vapour passing through the overlap regions and into the dielectric 3.

Furthermore, the tape 23 could be modified to comprise a thinner metal tape coated on both sides with an adhesive plastics material which bonds with the overlying surfaces of the overlap edge regions 6 and 7 by the application of heat, preferably in the range 180 to 200"C.

The plastics material 23 could be applied in tandem with the return conductor forming using an extruded bead or a printed bead of plastics material which becomes spread out when compressed between the overlapping edge regions 6 and 7 of the return conductor 4. Thus the extrusion or printing of the bead could be simultaneous with the forming of the return conductor. Alternatively, the extruded bead could be applied utilising an overlap knife.

Referring now to Figure 6 there is shown a coaxial submarine cable in which a polyproylene tape 24 is disposed between the overlapping edge regions 6 and 7 of the return conductor 4. Between the return conductor 4 and the peripheral overlapping edge 7a there is applied an adhesive fillet 25 of a water-impervious mastic which adheres to the return conductor 4 and the overlapping peripheral edge 7a. A similar fillet 26 provides a seal between the peripheral under-lapping edge 6a and the return conductor 4. Preferably as shown the overlapping peripheral edge 7a is chamfered to give a greater surface area of contact with the fillet of mastic. This material could for example be COMPOUND TP 3003A (Telcon Plastics Ltd). The underlapping edge 6a could similarly be chamfered although this is not shown in the drawing. It would also be possible to make do with just one fillet either 25 or 26.

Referring now to Figure 7 there is shown a submarine coaxial cable having a polypropylene tape 27 positioned between the overlapping edge regions 6 and 7 of the return conductor 4. In addition a metal tape 28 overlies the edge region 7 and, by a similar amount, the return conductor 4 on the other side of the peripheral edge 7a.

This metal tape 28 is coated with an adhesive plastics material which bonds to the edge regions 7 and the conductor 4. Alternatively the tape 28 could be provided with longitudinal beads of adhesive plastics material which bond with region 7 and conductor 4 over only selected longitudinal areas, i.e.

the metal tape, under those circumstances, would not be bonded to the return conductor over the whole width of the tape 28.

Alternatively the edge regions 6 and 7 need not overlap but could lie side-by-side as shown in Figure 8, sealed once again by the tape 28 as described with reference to Figure 7.

WHAT WE CLAIM IS: 1. A submarine coaxial cable comprising: a central strength member; an inner coaxial conductor; a return coaxial conductor comprising a longitudinal tape with longitudinal edge regions adjacent each other; rigid dielectric material between the inner and return conductors; a sheath surrounding the return conductor; and sealing means including a strip or tape engaging said longitudinal edge regions only to prevent moisture passing between the edge regions, whereby the sealed return coaxial conductor also acts as a moisture barrier against moisture ingress to said dielectric material.

2. A submarine coaxial cable according to claim 1, wherein said longitudinal edge regions overlap one another; said sealing means comprises a tape of deformable material interposed between the edge regions; and said tape forms a pressure seal at the edge regions incorporating a longitudinally-extending region deformed by external pressure. submarine 3. A submarine coaxial cable according to claim 1, wherein: said longitudinal edge regions overlap one another; said sealing means comprises a tape of plastics material interposed between the longitudinal edge regions; said sheath comprises extruded plastics material and exerts an external pressure on the return conductor; and said tape softens at a temperature similar to the extrusion temperature of the sheath whereby a longitudinally-extending region of the tape lying between the overlapped edge regions has been deformed by the external pressure. submarine 4. A submarine coaxial cable according to claim 4 wherein the tape originally 5 thou

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

180 to 2000C is envisaged and is preferably derived from the heat of the extruded outer sheath 5 alone without the addition of further heat, although other sources of heat are not excluded. By "bonding" we do not mean a molecular bond. Inspection of the cable has revealed that the polyethylene tape has softened and been deformed by squeezing between the overlapped edge regions of the return connector until its thickness has been reduced from about 5 thou + 1 thou. to only 2 thou. i.e. it has been reduced in thickness by over half its original thickness. It has not stuck irremovably to the return conductor and can be peeled away if pulled. However the deformation ensures any trapped air bubbles are removed and an effective seal is produced.

It would be possible to replace the tape 23 with a strip of compound which will react with water vapour should this find its way into the overlap region. This compound would undergo a chemical change in contact with water vapour such as to prevent water vapour passing through the overlap regions and into the dielectric 3.

Furthermore, the tape 23 could be modified to comprise a thinner metal tape coated on both sides with an adhesive plastics material which bonds with the overlying surfaces of the overlap edge regions 6 and 7 by the application of heat, preferably in the range 180 to 200"C.

The plastics material 23 could be applied in tandem with the return conductor forming using an extruded bead or a printed bead of plastics material which becomes spread out when compressed between the overlapping edge regions 6 and 7 of the return conductor 4. Thus the extrusion or printing of the bead could be simultaneous with the forming of the return conductor. Alternatively, the extruded bead could be applied utilising an overlap knife.

Referring now to Figure 6 there is shown a coaxial submarine cable in which a polyproylene tape 24 is disposed between the overlapping edge regions 6 and 7 of the return conductor 4. Between the return conductor 4 and the peripheral overlapping edge 7a there is applied an adhesive fillet 25 of a water-impervious mastic which adheres to the return conductor 4 and the overlapping peripheral edge 7a. A similar fillet 26 provides a seal between the peripheral under-lapping edge 6a and the return conductor 4. Preferably as shown the overlapping peripheral edge 7a is chamfered to give a greater surface area of contact with the fillet of mastic. This material could for example be COMPOUND TP 3003A (Telcon Plastics Ltd). The underlapping edge 6a could similarly be chamfered although this is not shown in the drawing. It would also be possible to make do with just one fillet either 25 or 26.

Referring now to Figure 7 there is shown a submarine coaxial cable having a polypropylene tape 27 positioned between the overlapping edge regions 6 and 7 of the return conductor 4. In addition a metal tape 28 overlies the edge region 7 and, by a similar amount, the return conductor 4 on the other side of the peripheral edge 7a.

This metal tape 28 is coated with an adhesive plastics material which bonds to the edge regions 7 and the conductor 4. Alternatively the tape 28 could be provided with longitudinal beads of adhesive plastics material which bond with region 7 and conductor 4 over only selected longitudinal areas, i.e.

the metal tape, under those circumstances, would not be bonded to the return conductor over the whole width of the tape 28.

Alternatively the edge regions 6 and 7 need not overlap but could lie side-by-side as shown in Figure 8, sealed once again by the tape 28 as described with reference to Figure 7.

WHAT WE CLAIM IS: 1. A submarine coaxial cable comprising: a central strength member; an inner coaxial conductor; a return coaxial conductor comprising a longitudinal tape with longitudinal edge regions adjacent each other; rigid dielectric material between the inner and return conductors; a sheath surrounding the return conductor; and sealing means including a strip or tape engaging said longitudinal edge regions only to prevent moisture passing between the edge regions, whereby the sealed return coaxial conductor also acts as a moisture barrier against moisture ingress to said dielectric material.
2. A submarine coaxial cable according to claim 1, wherein said longitudinal edge regions overlap one another; said sealing means comprises a tape of deformable material interposed between the edge regions; and said tape forms a pressure seal at the edge regions incorporating a longitudinally-extending region deformed by external pressure. submarine
3.A submarine coaxial cable according to claim 1, wherein: said longitudinal edge regions overlap one another; said sealing means comprises a tape of plastics material interposed between the longitudinal edge regions; said sheath comprises extruded plastics material and exerts an external pressure on the return conductor; and said tape softens at a temperature similar to the extrusion temperature of the sheath whereby a longitudinally-extending region of the tape lying between the overlapped edge regions has been deformed by the external pressure. submarine
4. A submarine coaxial cable according to claim 4 wherein the tape originally 5 thou

+ 1 thou thick is now 2 thou + 1 thou thick where it is deformed.
5. A submarine coaxial cable according to claim 3 or claim 4 wherein said tape is low-density polyethylene.
6. A submarine coaxial cable according to claim 1, wherein: the sealing means comprises a metal tape overlying the edge regions and adhesive material bonding the metal tape to the edge regions.
7. A submarine coaxial cable according to claim 1, wherein: said longitudinal edge regions overlap one another; the sealing means comprises at least one strip of resilient material interposed between the overlapped edge regions; and said sheath exerts a compressive force on the overlapped edge regions whereby the resilient material is resiliently deformed between the edge regions.
8. A submarine coaxial cable according to claim 3, wherein: said longitudinal edge regions each have a longitudinal rib which each form a longitudinal region of increased pressure on the interposed tape.
9. A submarine cable according to claim 1 wherein: a fillet of water-impervious mastic adheres to one edge region of the return conductor and to the adjacent edge of the other edge region.
10. A submarine coaxial cable substantially as hereinbefore described with reference to the accompanying drawings.