GB2227501A

GB2227501A - Cable anchorage

Info

Publication number: GB2227501A
Application number: GB8901735A
Authority: GB
Inventors: Charles Jeremy Brown
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1989-01-26
Filing date: 1989-01-26
Publication date: 1990-08-01
Also published as: JPH02285911A; GB8901735D0; FR2642184A1

Abstract

The ends of wire tensile strength members 2, 3 are clamped between surfaces of radiused blocks 4, 5, 6, which surfaces lie at an angle of 45 DEG to 135 DEG to the axis of the clamped cable. The blocks are retained by threaded member 9. Further strands may be clamped between further blocks. The clamping surfaces may be roughed, e.g. by ribbing or by grit such as tungsten carbide grit. The orientation of clamping surfaces is said not to crush core 1 which may contain optical fibres. <IMAGE>

Description

CABLE ANCHORAGE.

This invention relates to a cable anchorage, particularly for anchoring a submarine cable to a submersible housing such as a splice chamber or the like, but not exclusively so.

According to the present invention there is provided an anchorage for a cable wire tensile strength member comprising first and second clamping parts for clamping between them the wire member, means for holding the parts clamped together, and wherein the first and second clamping parts have respective clamping surfaces which lie at a substantial angle to the longitudinal axis of the cable.

One of the advantages of having the clamping surfaces at a substantial angle e.g. 300 to the longitudinal axis is the ability to accommodate larger numbers of strand wires. In addition it enables the anchorage to be designed to accommodate several stranded layers by means of additional clamping members one behind the other one additional clamping member for each respective additional stranded layer.

Furthermore there is much less likelihood of damage to the sensitive optical core in an optical fibre cable.

The preferred clamping angle with respect to the longitudinal axis of the cable, is 900 and the smallest practical angle would be 450 to the longitudinal cable axis.

The anchorage according to the present invention offers advantages over the prior art taper clamp terminations. In particular with the prior art the assembly process causes relative movement between the strand wires of different layers which causes an uneven distribution of load between the strand layers. Also because of the strong radial force caused by the taper effect, there is always the possibility of crtzse sensitive optical package. In particular in an optical fibre submarine cable having a conductive pressure resistant tube directly beneath the strength member wires, this tube can be pinched, thereby putting pressure on the sensitive optical package within.

It has also been found that with a taper clamp termination, there is a shearing mechanism in gripping the high tensile steel wires which tends to reduce the designed maximum tensile strength of the wires.

Furthermore, the taper clamp termination is limited to use with single or double layers of strand wires. It is not practical to use it with more than three layers of stranding because it is almost impossible to ensure good wire distribution over the tapered clamping surfaces and even load distributiob between different layers.

Finally it is difficult to separate the component parts of a conventional taper clamp after these parts have been assembled owing to the substantial friction against relative movement of the parts.

In order that the invention can be more clearly understood reference will now be made to the accompanying drawing which shows in longitudinal cross-section and somewhat schematically, a universal cable anchorage according to an embodiment of the present invention.

Referring to the drawing, an optical fibre submarine cable is shown in part, comprising a conductive metal tube 1 closely surrounded by inner and outer tensile strength strand layers 2 and 3 emaining parts of the submarine cable ail. For example within the pressure resist. tube 1 would be the optical fibre package and around the outside of the strand wires would be an insulating jacket sufficient to enable the pressure resistant tube 1 to conduct electricity for powering regenerators with or without the conductivity of the associated strand wires, the jacket providing insulation against the sea earth.

The anchorage comprises a first clamping block 4 having a clamping surface 4a and a trumpet shaped lead surface 4b enabling the outer strand wires 3 to follow a bend radius designed such that the surface strains in the wires do not exceed 48. This has been shown to be a limiting value so that the ultimate tensile strength of the high tensile steel strand wires 3 do not fall below 95% of their expected strength. Clearly for larger diameter wires there will need to be a larger bend radius.

The ends 3a of the outer strand wires 3 are clamped between the clamping surface 4a of block 4 and the clamping surface 5a of block 5 adjacent thereto.

It is to be noted that the clamping surfaces lie at a substantial angle to the longitudinal axis 1A of the cable. In this particular embodiment the angle is 900 so that the clamping pressure is parallel to the cable axis and the clamping surface is normal to the cable axis. It is not however essential for the clamping 0 0 surface to be 90 ; it could in fact be 90 plus or minus 450.

Block 5 also has a trumpet shaped wire lead surface whose radius is designed so that surface strains in the wires 2 do not exceed 48. The ends of wires 2 (2A) are clamped between the clamping surface Sc of block 5 and the co-operating clamping surface 6a of block 6.

Preferably at least one of the clamping surfaces of each of the blocks is roughened. Either hardened steel ribbed surface such as suggested in BT patent application or by grit evenly dispersed and bonded to the surface in a manner described in or co-pending Patent Application (our reference C.J. Brown - 1). The ribbed surface is adequate for softer wire e.g. mild steel, and the grit would be necessary for harder wires e.g. high tensile steel wires.

The three blocks 4, 5 and 6 are clamped in the longitudinal direction by a thin-walled outer casing 7 which has a screw-threaded end portion 8 into which a screw-threaded member 9 is inserted.

The casing 8 has an inwardly-directed annular shoulder 10 which resists the clamping force of the screw threaded member 9. As screw threaded member 9 is screwed into the casing the blocks 4, 5 and G become squeezed together so that the wire ends 3a and 2 heceDn- firmly clamped between the clamping surfaces of te blocks.

Claims

CLAIMS.

1. An anchorage for a cable wire tensile strength member comprising first and second clamping parts for clamping between them the wire member, means for holding the parts clamped together, and wherein the first and second clamping parts have respective clamping surfaces which lie at a substantial angle to the longitudinal axis of the cable.

2. An anchorage as claimed on claim 1 wherein said angle is 900.

3. An achorage as claimed in claim 1 or claim 2, wherein at least one of the surfaces is roughened to increase its grip on the wire tensile strength member.

4. An anchorage as claimed in claim 3 wherein the roughening comprises grit firmly held on said surface.

5. An anchorage as claimed in claim 4 wherein said grit is tungsten carbide grit.

6. An anchorage as claimed in any preceding claim, comprising a third clamping part, the second and third clamping part having respective clamping surfaces arranged to clamp between them a further tensile member of the cable.

7. An anchorage as claimed in claim 6, wherein the clamping surfaces for clamping the further wire tensile member lie at a substantial angle to the longitudinal axis of the cable.

8. An anchorage substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.