GB2519960A

GB2519960A - Sheathed cable

Info

Publication number: GB2519960A
Application number: GB1319340.4A
Authority: GB
Inventors: Jagannathan Mohanraj
Original assignee: Bridon Ltd
Current assignee: Bridon Ltd
Priority date: 2013-11-01
Filing date: 2013-11-01
Publication date: 2015-05-13
Also published as: WO2015063511A1; GB201319340D0

Abstract

A cable (1) for use in structural and civil engineering comprises a helical structure of a plurality of wires (4) that has a weather protection or an aesthetic finish, whilst still allowing inspection of the cable in situ. This is achieved by the provision of at least one translucent or transparent stripe (3) of no more than 4 times the radial depth of the sheath combined with transparent or translucent blocking material and lubricant within the opaque sections of the sheath (2). The sheath being applied with a cross headed extruder. The invention also provides a method of manufacturing, testing and inspecting the cable by visual, camera or instrument sensing change in colour and/or reflected energy.

Description

Sheathed Cable

Technical Field

The present invention relates to a cable comprising a sheath, and to a method of manufacturing a cable comprising a sheath. The present invention further relates to a method of inspecting a cable comprising a sheath and a structure comprtsing the cable

Background Art

There is a growing interest in the field of structural engineering for cables that include plastics sheathing, to provide long-term protection against corrosion.

The sheathing can also give an aesthetically pleasing appearance.

For example1 in civil engineering, cables sheathed in white or grey plastics material have been used. In offshore projects, sheathing may be a bright colour, for visibility, for example comprising a yellow component.

Problem to be Solved The present inventor has reaLised that sheathing cables prevents visual inspection of the cables after assembly. Further, although magnetic inspection methods can be used to check the kitegrity of cables, the inventor has realised that this may not be possible in many cases due to difficulty of access.

The present inventor has discovered that it is possible to sheath cables with transparent or translucent sheath that allows visual inspection for signs of degradation, such as broken wires and/or corrosion, whilst still affording environmental protection and offering an aesthetic finish.

Statement of Invention

The present invention provides a cable comprising a cable structure and a sheath, the sheath comprising at least one translucent or transparent section.

The present invention further provides a method of manufacturing a cable, comprising forming a sheath on the cable structure, the sheath comprising at least one translucent or transparent section.

The present invention further provides a method of inspecting a cable, wherein the cable comprises a sheath, comprising at least one translucent or transparent section, the method including inspecting the cable structure through the translucent or transparent section of the sheath.

The present invention further provides a structure comprising the cable of the invention.

Detailed Description of the Invention

Preferred and optional features of the invention will be described below.

According to the present invention, a cable can be provided comprising a cable structure and a sheath.

The cable structure is preferably a known cable structure. It may comprise a cable, rope or wire. It may be formed according to any known structure.

For example, it may comprise a plurality of filaments twisted into strands, the strands being twisted together to form the cable structure.

The cable structure may be formed of any suitable material. For example, it may comprise metallic wire, synthetic materials such as high strength composites, thermoplastic or natural materials such as naturai fibre, or any combination of these.

In a preferred embodiment, the cable structure is formed of steel, preferably galvanised steel.

The cable structure may be a spiral strand structure or a full lock cable structure, for example.

The cable structure may comprise blocking material or lubricant between strands or filaments of the cable.

According to a preferred embodiment, the lubricant or blocking material may be transparent or translucent.

Preferably, the lubricant or blocking material comprises a clear wax or thixotropic gel, being preferably a non-setting semi-solid that fully wets surfaces of the cable structure. Examples of such materials include petrolatum waxes and polymer gels. Preferably, by replacing air that would otherwise be present in the cable structure, the lubricant or blocking material can prevent the penetration of moisture etc. into or along the cable in the event of the sheath integrity being compromised.

Where a transparent blocking material is used, it may comprise thermoplastic material. It may be formed of the same kind of material as described below in relation to the sheath. It may be integral with the material of the sheath.

The sheath suitably comprises an annular layer of material on the outer circumference of the cable structure. Preferably, the sheath extends for at least part of the length of the cable.

Preferably, the sheath extends over at least pad of the circumference of the cable structure. It is preferred that the sheath extends over the whole of the circumference of the cable structure.

The sheath may directly contact at least pad of the outer periphery of the cable structure. The sheath may be spaced from at least part of the outer periphery of the cable structure, for example by lubricant or blocking material. In this case, the lubricant or blocking material is preferably transparent or translucent.

For the purposes of the present application, a section of sheath wilt be taken to be transparent if filaments or structures on at least pad of the surface of the cable of size not less than 0.5 mm are visually distinguishable. The inspection may be carried out by the naked eye or by a camera or instrument capable of sensing a change in colour and/or reflected energy. Preferably, inspection is carried out using visible light. Preferably, if a high degree of transparency is required, inspection can be carried out at an illumination of 500 lux. Ef a lower degree of transparency is accepted, inspection can be carried out at an illumination of 1000 lux.

Ft is preferable that at Least a portion of the sheath should be transparent as defined above. In this way, inspection of at least part of the surface of the cable structure can be carried out through the transparent section.

However, it may be sufficient in some cases for the sheath to be translucent.

That is, a certain amount of scattering of light may be tolerated, whereby an image cannot be seen clearly, if it is possible to detect discolouration of a surface which may be caused by corrosion.

For the purposes of the present application, a section of sheath will be taken to be translucent if it is possible to detect through the translucent section a predetermined difference in colour to a predetermined colour standard.

Preferably, if a high degree of translucency is required, inspection can be carried out at an illumination of 500 lux. If a lower degree of translucency is accepted, inspection can be carried out at an illumination of 1000 lux. It may be carried out by camera or instrument capable of sensing a change in colour and/or reflected energy, or by the naked eye. The predetermined difference and the predetermined colour standard may be defined in any suitable manner, for example with reference to numerical values (Munsell colour values, Pantone colours or other suitable references). Alternatively, the manufacturer of the cable may supply sample images to define the colour standard and the predetermined level of difference from the predetermined colour standard.

It may be necessary to remove a portion of the sheath, suitably a thickness equivalent to the radial thickness of the sheath, to determine translucency or transparency.

Preferably, the sheath comprises at least one translucent or transparent section and at least one section which is not translucent or transparent. The latter section may be referred to as an opaque section. Preferably1 the translucent or transparent section comprises at least 2% of the surface area of the cable, more preferably at least 5% of the surface area of the cable, being suitably about 10% of the surface area of the cable. Preferably, the translucent or transparent section comprises up to 70% of the surface area of the cable, more preferably up to 50% of the surface area of the cable, even more preferably up to 20% of the surface area of the cable, and suitably around 10% of the surface area of the cable.

There may be a plurality of translucent or transparent sections. For example, translucent or transparent sections may be formed at intervaLs along the length of the cable.

There may be at least one translucent or transparent section at each position along the length of the cable. The translucent or transparent sections in this case may be continuous with one another. The translucent or transparent section may be in the farm of at least one stripe.

In a preferred embodiment, the translucent or transparent section extends along the whole length of the cable. It may be formed in a spiral configuration, a sinuous or wavy configuration or it may extend substantially parallel to the axis of the cable. If the translucent or transparent section extends in a spiral, it will preferably have a different twist to the lay of the strands, so that each strand can be inspected at at least one position along the axial length of the cable.

It may have the opposite twist or the pitch of the twist may be different to the lay of the strands.

The section of sheath which is not translucent or transparent may be provided for aesthetic reasons, or at least in part for aesthetic reasons. It may comprise material which is selected wholly or partly for other properties, such as strength, abrasion resistance, etc. At any one axial position along the cable, there may be more than one translucent or transparent section.

Preferably, there is at least one translucent or transparent section extending along the length of the cable.

Preferably, the circumferential width of the translucent or transparent section is at least 5% of the outer circumference of the sheath, preferably around 10% of the outer circumference of the sheath. Preferably, it represents no more than 20% of the outer circumference of the sheath, preferably around 10% of the outer circumference of the sheath.

The radial depth of the translucent or transparent portion is suitably constant over the whole circumference of the cable structure. It is suitably at least 1% of the diameter of the cable, preferably at least 5% of the diameter of the cable.

Preferably, it is no more than 20% of the diameter of the cable, and preferably no more than 12% of the diameter of the cable.

Preferably, the circumferential width of the transparent or translucent section of the sheath in the circumferential direction is at least 0.5, preferably I and more preferably at least 15 times the radial depth of the transparent or translucent section. Preferably, it is no more than four times the radial depth, preferably no more than three times and preferably around twice the radial depth.

To make the radial depth of the translucent or transparent section significantLy thinner than the radial depth of the opaque section could introduce a potential weak spot and to make it significantly thicker wouLd expose it to mechanical damage during cable handling.

Preferably, the radial depth of the translucent or transparent portion is at least 0.5, preferably I and more preferably not more than 1.5 times the radial depth of the opaque section.

However, the translucent or transparent portion may bulge outwards to give an outwardly convex surface, as this would tend to magnify the image.

If there are a plurality of translucent or transparent sections, they may be spaced apart around the circumference, preferably at regular intervals.

For example, two stripes may be provided, located diametrically opposite one another. Where a plurality of translucent or transparent sections are provided, preferably, the sum of the circumferential extents is in the range 5-20% of the outer circumference of the sheath.

The translucent or transparent section may be coloured, for example for aesthetic reasons.

Preferably, the translucent or transparent section is formed of synthetic material, preferably thermoplastic. For example, it may comprise polyolefin (for example polypropylene and/or polyethylene) or amorphous polycarbonate.

Thermosetting resins such as vinyl-ester or polyurethane could be used.

However, this would normally require a pultrusion forming process, rather than an extrusion process If the cable structure comprises transparent or translucent lubricant or blocking material, it may be possible to detect corrosion or damage at a deeper level than the surface of the cable structure. Further, such lubricant or blocking material can help to reduce air pockets formed within the cable. Air pockets can lead to weakening of the bond between the cable structure and the sheath, corrosion, or interference of inspection of the cable structure. In particular, lubricant can wet the internal surface of the sheathing and minimise light reflection at its internal surface.

The cable of the present invention can be used in many applications.

For example, it may be used for structural cables. It may be used in civil engineering applications and offshore applications: For example, it may be used as cable for roof supports or bridge hangers.

If the translucent or transparent portion is axially aligned with the cable, for ease of inspection or aesthetic appearance, it may be desirable to arrange the translucent or transparent portion on, for example, the top and or the bottom of the cable. Typically, to achieve this, a cable may comprise an end anchorage comprising means for fixing the configuration of the cable with respect to the structure, for example at least one pin-secured open socket. The rotational location of the translucent or transparent portion relative to the socket pins would therefore be defined, taking into account of what the pin orientation would be on the structure.

The present invention provides a method of manufacturing a cable in which a sheath comprising at least one translucent or transparent section is formed on a cable structure.

The cable, the cable structure and the sheath may each be as described above.

Suitably, the sheath is formed by applying sheath material in molten or part molten form to a cable structure.

The sheath material may be applied under pressure onto the cable structure. It may alternatively be extruded to form a tubular structure which is brought in to contact with the cable structure, for example, by reducing pressure between the cable structure and the tubular structure.

Pressure extrusion may be used, particularly where the lubricant or blocking material is the same material as the sheath.

In an alternative embodiment (particularly where a previously introduced clear lubricant or blocking material is present) a tubular section of the jacket material may be extruded, preferably assisted by applying a partial vacuum to the cable structure. This can help to ensure that the sheath is tight on the cable structure and to minimize the risk of air entrapment within the sheath.

Preferably, the sheath is applied by a continuous melt extrusion process.

Preferably, a cross-head extruder is used.

Preferably, an extruder is used that comprises at least one passage for feeding a cable structure through at least one passage for feeding opaque sheath material and at least one passage for feeding transparent or translucent sheath material. The sheath material may be fed by any suitable means, such as a screw feeder.

In order to form the translucent or transparent section, a second extruder may be provided, preferably feeding the cross-head, to feed transparent/translucent material at a predetermined point in the extruder. Preferably, it is fed to a predetermined point in the annulus of an annular die that controls the melt as it exits the cross-head.

If more than one translucent/transparent section is required, more than one second extruder may be provided.

Where lubricant or blocking material is used, it is suitably applied during or after manufacture of the cable structure. Preferably, the translucent or transparent lubricant or blocking material is applied before application of the material of the sheath. However, it may be applied at the same time as the sheath.

The material of the transparent or translucent section may comprise clarifying agent. Preferably, the clarifying agent acts to control the crystallisation of the plastics material when the plastics material solidifies after extrusion and thereby controls transparency.

Preferably, the material comprising portions of the sheath which are not translucent or transparent are compatible with portions forming sections that are translucent or transparent, in the sense that they can be co-extruded and form an integral bond.

Preferably, the material of the opaque section of the sheath and the material of the transparent or translucent section of the sheath are identical except that the opaque section is provided with pigmentation which makes it opaque.

The method of inspection of the present invention may be carried out by any suitable means. Preferably, it is carried out visually. It may be carried out by the naked eye or by the use of a camera or instrument capable of sensing a change in colour and/or reflected energy. It may be necessary to illuminate the cable, for example using artificial light, for example a handheld torch.

The inspection may comprise the step of comparing the colour detectable through the translucent or transparent section with a colour reference to determine if it differs from the predetermined colour standard by a predetermined amount. For example, a colour chart may be provided indicating predetermined discolorations compared to the predetermined colour.

The present invention will be further described by way of example only, with reference to the accompanying drawings, in which:

Brief Description of Drawings

Figure 1 is a schematic view of a cable according to the present invention.

Figure 2 is a schematic cross-sectional view of a cable according to the present invention.

Figure 3 is a second embodiment of cable according to the present invention, shown in cross-section.

Figure 4 is a schematic cross-sectional view of first embodiment of a method of manufacturing a cable according to the present invenUon.

Figure 5 is a schematic cross-sectional view of second embodiment of a method of manufacturing a cable according to the present invention.

Detailed Description of the Drawings

Figure 1 is a schematic view of a section of cable which extends axially from left to right across the page. The cable comprises an opaque section of sheathing 2 formed of grey coloured polyolefin material which is not transparent or translucent. It is provided for environmental protection and pigmented for aesthetic reasons. The circumference of the sheathing comprises a transparent section 3 through which the cable structure 4 can be seen.

The transparent section 3 comprises a section which is integrally extruded with the opaque section 2 in a cross-head extruder and which allows the condition of the cable structure 4 to be inspected. In this way, breakage of cable structure filaments or discolouration due to rusting can be detected.

Figure 2 is a schematic cross-section view through the cabLe 1, not to scale.

Here, the cable structure is shown as a helical structure 4 comprising a plurality of wires which have been twisted together in a conventional manner. It can be seen that the sheath comprises two opaque sections 2 and two transparent sections 3 which are located diametrically opposite to one another.

Figure 3 is a schematic view, showing a cable in which the cable structure comprises a locked coil rope.

Figure 4 is a schematic cross-sectional view of first embodiment of a method of manufacturing a cable according to the present invention. A cable structure 4 is shown, being fed through a die of a cross head extruder 5. Two separate extruders are used to extrude opaque sheath material 6 and transparent or translucent sheath material 6 which coalesce to form a tubuLar structure which is brought into contact with the cable structure 4, for example, by reducing pressure between the cable structure 4 and the tubular structure.

Figure 5 is a schematic cross-sectional view of second embodiment of a method of manufacturing a cable according to the present invention. A cable structure 4 is shown being fed through a die of a cross head extruder. Two separate extruders are used to extrude opaque sheath material 6 and transparent or translucent sheath materiaL 6 which are forced under pressure in the die 5 into contact with the cable structure 4.

The present invention has been described above by way of example only and modifications can be made within the invention. The invention also extends to any individual features or any generalisation of any of the features disclosed or any combination of any generalisation of the features disclosed.

Claims

CLAIMS1. A cable comprising a cable structure and a sheath, the sheath comprising at least one translucent or transparent section.
2. The cable according to Claim 1, wherein the cable structure is formed of metallic wire.
3. The cable according to Claim 1 or 2, wherein the cable structure comprises a spiral strand structure or a full lock cable structure.
4. The cable according to any preceding Claim, wherein the cable structure comprises blocking material or lubricant between strands or filaments of the cable structure.
5. The cable according to Claim 4, wherein the lubricant or blocking material is transparent or translucent.
6. The cable according to Claim 4 or 5, wherein the sheath is spaced from at least part of the outer periphery of the cable structure, by lubricant or blocking material.
7. The cable according to any preceding Claim, wherein the sheath comprises at least one translucent or transparent section and at least one section which is not translucent or transparent.
8. The cable according to Claim 7, wherein the translucent or transparent section comprises at least 2% of the surface area of the cable.
9. The cable according to Claim 7 or 8, wherein the translucent or transparent section comprises at least 5% of the surface area of the cable.
10. The cable according to Claim 7, 8 or 9, wherein the translucent or transparent section comprises up to 70% of the surface area of the cable.
11. The cable according to any of Claims 7 to 10, wherein the translucent or transparent section comprises up to 50% of the surface area of the cable.
12.The cable according to any preceding Claim, wherein the translucent or transparent section is in the form of at least one stripe.
13. The cable according to any preceding Claim, wherein the translucent or transparent section extends substantially parallel to the axis of the cable.
14.The cable according to any precedrng Claim, wherein the circumferential width of the translucent or transparent section is at least 5% of the outer circumference of the sheath.
15.The cable accord[ng to any preceding Claim, wherein the circumferential width of the translucent or transparent section is up to 20% of the outer circumference of the sheath.
16.The cable according to any preceding Claim, wherein the radial depth of the translucent or transparent portion is at least 1% of the diameter of the cable.
17.The cable according to any preceding Claim, wherein the radial depth of the translucent or transparent portion is at least 5% of the diameter of the cable.
18.The cable according to any preceding Claim, wherein the radial depth of the translucent or transparent portion is no more than 20% of the diameter of the cable.
19. The cable according to any preceding Claim, wherein the circumferential width of the translucent or transparent portion of the sheath is at least 0.5 times the radial depth of the transparent or translucent section.
20.The cable according to any preceding Claim, wherein the circumferential width of the translucent or transparent portion of the sheath is no more than 4 times the radial depth of the transparent or translucent section.
21.The cable according to any preceding Claim, wherein the translucent or transparent section is coloured.
22. The cable according to any preceding Claim, wherein the translucent or transparent section comprise polyolefin or amorphous polycarbonate.
23.A method of manufacturing a cable in which a sheath comprising at least one translucent or transparent section is formed on a cable structure.
24.The method according to claim 23 wherein the sheath is formed by applyEng sheath material in molten or part molten form to a cable structure.
25.The method according to claim 23 or 24, wherein the sheath is applied by a continuous melt extrusion process.
26.The method according to any of claims 23 to 25, wherein the sheath is applied using a cross-head extruder.
27.A method of inspecting a cable, wherein the cable comprises a sheath, comprising at least one transLucent or transparent section, the method including inspecting the cable structure through the translucent or transparent section of the sheath.
28. The method of claim 27, wherein inspection is carried out visually.
29.The method of claim 27 or 28, wherein inspection is carried out by the naked eye or by the use of a camera or instrument capable of sensing a change in colour and/or reflected energy.
30. A structure comprising a cable according to any of claims I to 22.
31.A cable, substantially as herein described with reference to the accompanying drawings.
32.A method of manufacturing a cable, substantially as herein described with reference to the accompanying drawings.
33.A method of inspecting a cable, substantially as herein described with reference to the accompanying drawings.