GB2163895A

GB2163895A - A cable and a method of producing same

Info

Publication number: GB2163895A
Application number: GB08422160A
Authority: GB
Inventors: Nigel Shackleton
Original assignee: FOTHERGILL CABLES Ltd
Current assignee: FOTHERGILL CABLES Ltd
Priority date: 1984-09-01
Filing date: 1984-09-01
Publication date: 1986-03-05
Also published as: GB8422160D0

Abstract

In order to protect elements 15, such as optical fibres or delicate wires, from damage, they are located in holes 13 formed longitudinally through a core 10 and a sheath 16 is provided around the core 10. Slits 11 may be provided to minimise compression stresses on the elements 15 when the cable is bent. The core 10 is produced by extrusion and the elements 15 are inserted into the holes 13 at the same time. <IMAGE>

Description

SPECIFICATION A cable and a method of producing same This invention relates to a cable particularly but not exclusively an optical fibre cable, and a method of producing same.

There are a number of different types of optical fibre cables available. One such cable compr ses a central core of supporting material with optical fibres laid in grooves in its outer surface, which is then covered with an outer sheath. The disadvantage of this type of cable is that the optical fibres are still liable to be damaged.

The object of this invention is to provide a cable construction which will afford greater protection to optical fibres or other elements extending thoreth- rough.

With this object in view, the present invention provides a cable comprising a central core of supporting material having a number of holes ru ining longitudinally therethrough and a sheath surrounding said core.

The central core may be made of malleable plastics or other suitable material.

In use, each hole will contain one or more optical fitires or other elements, such as wires, which requite protection against damage.

If n-quired, additional reinforcement can be providea by a reinforcing member running down the centm of the core, and our running down one or more of the holes.

If rc quired, in order to ensure the optical fibres are not subjected to compression stresses wnen the cable is bent, the central core can be slit into segments and if necessary, for additional protection against compression stresses, the slits can be made with a helical or reverse helical twist along the length of the core.

Thes invention also comprises a method of manufactuiing the aforesaid cable by extruding m.terial through a die and a tip which forms holes s( as to form the central core, simultaneously insertiiig ele menus to be protected into the holes by way of tubes provided on the tip and applying a tubular sheath over the core by extrusion or otherwise.

Any reinforcing member(s) may also be inserted into the holes in the central core by way of tubes provided on the tip of the extrusion die.

The die is advantageously provided with fingers to form slits in the central core as it is extruded and thus subdivide the latter into segments. Any helical or reverse helical twist may be imparted to the segments and intervening slits by means of a twist unit downstream of the extrusion die.

The invention will be described further, by way of example, with reference to the accompanying drawing in which the single figure is a cross-section though a preferred practical embodiment of the cable of the invention.

As illustrated, a preferred embodiment of the cable of the invention comprises a central core 10 cf malleable plastics having four equidistant slits 11 in its periphery which effectively divide the core 10 into tour lobes or segments 12. Arranged between the slits 11, centrally of each segment 12, are four holes 13 running longitudinally of the core 10. At the centre of the core 10 there is a reinforcing member in the form of a wire or bundle of wires 14. In each hole 13 there extends an element or elements requiring protection against damage, such as one or more optical fibres 15. The core 10 is surrounded by a tubular sheath 16, also of plastics material.

It will be appreciated that the cable provides particularly effective protection for the optical fibres 15 since they are completely surrounded by core material and thus less vulnerable to external knocks and disturbances compared to previous cables where they were simply covered by the material of the sheath. The slitting of the core 10 minimises compression stresses on the optical fibres 15 when the cable is bent.

In the exemplified embodiment the slits 11 ran generally parallel with the axis of the cable. However, in further embodiments the slits 11 may be arranged with a helical or reverse helical twist for additional protection of the optical fibres 15 against compression stress.

Many other variations are possible. For example, the number and disposition of holes 13 and slits 11 may vary from those in the illustrated embodiment and reinforcing member may additionally or alternatively be provided in the holes 13. Also the cable is not confined to use with optical fibres and other elements, such as delicate wires, may be thus encased and protected.

In manufacturing the cable illustrated in the drawing the core 10 is formed by continuously extruding molten plastics material through a die having fingers which form the slits 11 and thus subdivide the core 10 into segments 12. A tip is also provided as part of the extrusion unit and this forms the holes 13. The optical fibres 15 and the reinforcing member 14 are inserted into the holes 13 and into the centre of the core 10 respectively through tubes provided on the tip. The tubular sheath 16 is applied by a second extrusion unit downstream of that producing the core 10.

For production of cables in which the slits are arranged with a helical or reverse helical twist a twist unit impaiting an appropriate twist to the core is provided between the core extrustion unit and the sheath extrusion unit.

1. A cable comprising a central solid core of supporting 3 material having a number of holes formed longitudinally therethrough for reception of elements, such as optical fibres or wires, which require protection against damage, and a sheath surrounding said core.

2. A cable as claimed in claim 1 including a reinforcing member extending down the centre of the core and/or down one of the holes.

3. A cable as claimed in claim 1 or 2 wherein slits are provided around the periphery of the core thereby dividing the core into lobes or segments.

4. A cable as claimed in claim 3 wherein the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A cable and a method of producing same This invention relates to a cable particularly but not exclusively an optical fibre cable, and a method of producing same. There are a number of different types of optical fibre cables available. One such cable compr ses a central core of supporting material with optical fibres laid in grooves in its outer surface, which is then covered with an outer sheath. The disadvantage of this type of cable is that the optical fibres are still liable to be damaged. The object of this invention is to provide a cable construction which will afford greater protection to optical fibres or other elements extending thoreth- rough. With this object in view, the present invention provides a cable comprising a central core of supporting material having a number of holes ru ining longitudinally therethrough and a sheath surrounding said core. The central core may be made of malleable plastics or other suitable material. In use, each hole will contain one or more optical fitires or other elements, such as wires, which requite protection against damage. If n-quired, additional reinforcement can be providea by a reinforcing member running down the centm of the core, and our running down one or more of the holes. If rc quired, in order to ensure the optical fibres are not subjected to compression stresses wnen the cable is bent, the central core can be slit into segments and if necessary, for additional protection against compression stresses, the slits can be made with a helical or reverse helical twist along the length of the core. Thes invention also comprises a method of manufactuiing the aforesaid cable by extruding m.terial through a die and a tip which forms holes s( as to form the central core, simultaneously insertiiig ele menus to be protected into the holes by way of tubes provided on the tip and applying a tubular sheath over the core by extrusion or otherwise. Any reinforcing member(s) may also be inserted into the holes in the central core by way of tubes provided on the tip of the extrusion die. The die is advantageously provided with fingers to form slits in the central core as it is extruded and thus subdivide the latter into segments. Any helical or reverse helical twist may be imparted to the segments and intervening slits by means of a twist unit downstream of the extrusion die. The invention will be described further, by way of example, with reference to the accompanying drawing in which the single figure is a cross-section though a preferred practical embodiment of the cable of the invention. As illustrated, a preferred embodiment of the cable of the invention comprises a central core 10 cf malleable plastics having four equidistant slits 11 in its periphery which effectively divide the core 10 into tour lobes or segments 12. Arranged between the slits 11, centrally of each segment 12, are four holes 13 running longitudinally of the core 10. At the centre of the core 10 there is a reinforcing member in the form of a wire or bundle of wires 14. In each hole 13 there extends an element or elements requiring protection against damage, such as one or more optical fibres 15. The core 10 is surrounded by a tubular sheath 16, also of plastics material. It will be appreciated that the cable provides particularly effective protection for the optical fibres 15 since they are completely surrounded by core material and thus less vulnerable to external knocks and disturbances compared to previous cables where they were simply covered by the material of the sheath. The slitting of the core 10 minimises compression stresses on the optical fibres 15 when the cable is bent. In the exemplified embodiment the slits 11 ran generally parallel with the axis of the cable. However, in further embodiments the slits 11 may be arranged with a helical or reverse helical twist for additional protection of the optical fibres 15 against compression stress. Many other variations are possible. For example, the number and disposition of holes 13 and slits 11 may vary from those in the illustrated embodiment and reinforcing member may additionally or alternatively be provided in the holes 13. Also the cable is not confined to use with optical fibres and other elements, such as delicate wires, may be thus encased and protected. In manufacturing the cable illustrated in the drawing the core 10 is formed by continuously extruding molten plastics material through a die having fingers which form the slits 11 and thus subdivide the core 10 into segments 12. A tip is also provided as part of the extrusion unit and this forms the holes 13. The optical fibres 15 and the reinforcing member 14 are inserted into the holes 13 and into the centre of the core 10 respectively through tubes provided on the tip. The tubular sheath 16 is applied by a second extrusion unit downstream of that producing the core 10. For production of cables in which the slits are arranged with a helical or reverse helical twist a twist unit impaiting an appropriate twist to the core is provided between the core extrustion unit and the sheath extrusion unit. CLAIMS

4. A cable as claimed in claim 3 wherein the slits are formed with a helical or reverse helical twist along the length of the core.

5. A method of manufacturing the cable claimed in any preceding claim comprising extruding material through a die including a tip which forms holes so as to form the central core, simultaneously inserting elements to be protected into the holes by way of tubes provided on the tip and applying a tubular sheath over the core.

6. A method as claimed in claim 5 further including inserting a reinforcing element into a hole in the central core by way of a tube provided on the tip of the die.

7. A method as claimed in claim 5 or 6 wherein the die is provided with fingers to form slits in the periphery of the central core as it is extruded and thus subdivide the latter into lobes or segments.

8. A method as claimed in claim 7 wherein a twist unit is located downstream of the extrusion die and is operative to impart a helical or reverse helical twist to the slits of the central core before application of the sheath.

9. A cable substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

10. A method of manufacturing the cable claimed in any of claims 1 to 4 substantially as hereinbefore described.