GB2173052A - Heat shielded shrink fit sleeving for cables - Google Patents

Abstract

A cable 1 has metal fabric 5 wrapped around it before a heat shrink sleeve 2 is shrunk onto the cable (for example, to protect a cable repair). The fabric may have perforations 7 in addition to its inherent porosity or mesh. The member is more flexible and provides more reliable sealing than foil or film. <IMAGE>

Description

SPECIFICATION Improved heat shield This invention concerns an improved heat shield, more especially it concerns a heat shield for the protection of cables.

In the technique of protecting cable joints by covering the joint with a heat shrink sleeve, it is often advantageous to protect some or all of the cables against excessive heat from the heat source used to initiate heat shrinkage, such as a gas flame gun or hot air gun. It is particularly useful to protect the insulation of small diameter cables which may otherwise soften and distort under the recovery forces of the heat shrink sleeve. Failure of the insulation may occur at the time of fitting the sleeve or the insulation may become weakened and prone to failure at a later date.

The use of aluminium foil is commonplace as a wrapping around cable joints and individual cables, for various reasons including its ability to act as a heat shield. We refer to UK Patent No.2,075,771B in which a heat shield of metal foil and having both a heat-activatable adhesive and a pressure-sensitive adhesive on an internal surface is wrapped around at least one cable. The metal foil is required to have sufficient stiffness substantially to prevent radial distortion or indentation of the foilsurrounded cable portion during heat recovery of the sleeve.

We have now discovered that certain other materials, not being metal foils, and in which such a specified stiffness is not a necessity, may be used with certain advantages and the avoidance of disadvantages, to perform a heat shield function and certain other functions.

The present invention provides a kit for covering an elongate substrate, comprising a heat shrinkable sleeve and a metal fabric heat protection member capable of being wrapped around one or more parts of the substrate.

The metal fabric may have perforations in addition to its characteristic porosity or mesh.

The present invention also provides a method of protecting an elongate substrate using a heat shrinkable sleeve, comprising wrapping one or more parts of the substrate with a heat protection member composed of a metal fabric, and heat shrinking the sleeve over at least part of the wrapped substrate.

The invention further provides a protected elongate substrate comprising the product of the above-mentioned method.

Heat shrink sleeves suitable for use in the present invention are well known articles available commercially and also widely described in the patent literature. Preferred sleeves may be onepiece sleeves or, more preferably, split sleeves, and may be formed from polyolefins such as polyethylene, especially those which have been partially cross-linked, for example by radiation. It is conventional to have the inside of the sleeve coated with a mastic or a hot-melt adhesive, so that a seal between the shrink down sleeve and a substrate is formed to substantially eliminate the possibility of liquid or vapour leakage.

If two or more cables or other substrates emerge from one end of the heat shrink sleeve, it is preferred to nip the ends of the sleeve together between the cables using a clip, before heat shrinking the sleeve onto the cables/substrate.

The heat protection member is preferably rectangular or square in shape and may be dimensioned according to the expected dimensions of the substrate to be covered. Preferably, the member is of such a size as to wrap at least once round the substrate, although, if desired or necessary, two or more members may be used to achieve at least a single wrap of the substrate.

Preferably, the heat protection member is a fine woven fabric. Most preferably, the member is an expanded metal mesh. Alternatively, the member may be a non-woven fabric, for example, a fine metal gauze or a fabric of non-woven metal fibres bonded together by any method capable of retaining the integrity of the fabric under normal conditions of use, such as mechanical twisting, bonding by adhesive or spot welding. Preferred metals are aluminium, copper, a copper alloy or stainless steel, although other metals or alloys may be used. The metal may have a protective coating, such as anodising, zinc metal in the case of talvanised steel, a protective polymeric film forming coating, including lacquers and varnishes, polymers such as polyethylene or PVC and paints.

The porosity or mesh size of the fabric is preferably of 0.01 to 10mm, more preferably 0.5 to 7.5mm, and in woven fabrics, the metal fibre or wire may be from 0.01 to 5mm in diameter, preferably 0.5 to 3mm in diameter. In the case of the smaller diameter pores or mesh, such as those in the range 0.01 to 3mm, it may be desirable to provide relatively large perforations in addition. These perforations may be of any shape although it is convenient to have regularly spaced perforations of regular shape, for example round, diamond, square or, preferably, rectangular, and the perforations may be of any size from about 5 to 30mm across. The perforations may be punched out of the fabric after manufacture of the fabric or may be incorporated in the manufacturing process of the fabric.

A main intended use of the member is to protect and increase the diameter of relatively small diameter cables to decrease or eliminate the damage done to the cable insulation during shrinking of the heat-shrinkable sleeve around it and to minimise the problems of sealing of the heat shrink sleeve around small diameter substrates.

It is preferred to provide the heat protection member with at least one area, on at least one major face, of an adhesive. The adhesive may be a tacky contact adhesive intended to retain the member in a desired position on a substrate; the adhesive area may be applied to the substrate or may contact another part of the same or a different member to retain the member(s) around the substrate. Suitable contact adhesives are commercially available and preferably have a Ring and Ball softening point in the range 55 to 1000C. Preferably, the area(s) of contact adhesive are protected before use by a release paper or film, and such films or papers, e.g. siliconised paper, are well known.

In one embodiment, the heat protection member may have a film, eg of 0.3-0.6mm thick, of a tacky hot melt adhesive applied to the whole of a major face of a sheet of expanded aluminium, and the adhesive may then be covered by a release paper or film. In another embodiment, a rectangular sheet of expanded aluminium has applied three parallel 20mm wide strips of a tacky contact adhesive of 0.07mm thickness across the width of the sheet at each end and across the centre. Each strip may be protected by a release paper or the whole of the face may be covered by a release paper, or film.

The heat protection member may have at least one area, on at least one major face opposite to that major face carrying an area of contact adhesive, of a hot melt (sealing) adhesive which melts at the temperatures experienced within the heat shrink sleeve during such heat shrinkage. Suitable hot melt adhesives are suitably nontacky at ambient temperatures, are preferably sufficiently flexible not to hinder wrapping of the member around the substrate. If the hot melt adhesive is relatively rigid in the thickness applied, which thickness is suitably 0.1 to 1 mum; it is desirable to apply the adhesive in many discrete areas to facilitate wrapping. Suitable hot-melt adhesives are commercially available, and preferred adhesives have Ring and Ball softening points in the range 90 to 140"C.

The hot melt sealing adhesive on the wrapping member is preferably of such a viscosity in its molten state during heat shrinking of the heat-shrinkable sleeve that it will flow through under the pressure exerted by the heat shrink sleeve. The adhesive should be compatible with the adhesive coating the inside of the heat shrink sleeve, as well as with any contact adhesive present.

The heat protection member may carry a deposit of a thermochromic temperature indicator which changes colour, desirably permanently and unambiguously, when the member has reached a temperature at which the hot melt sealing adhesive on the inside of the heat shrink sleeve, and, if present, the hot melt sealing adhesive on the member itself, melts and flows to fill any interstices between the member and the sleeve, to fill the pores or mesh and perforations of the fabric and bond the sleeve, member and substrate together in a leak-resistant manner.

Certain heat shrink repair kits currently marketed include an item which is known as a liner, which is a sheet of plastics or card having a coronet shape at two opposite ends.

The liner may be wrapped around a cable repair and the points of the coronet brought together to form a regular shape, and the heat shrink sleeve is shrunk onto the liner rather than directly onto the repaired cable. It may be desirable to provide a heat protection member according to the present invention around the liner to provide additional protection to the liner. For such use, a fabric having very fine mesh or pores of the order of 0.1-0.3 mm and without perforations, should be used. The heat protection members of the present invention are significantly more resistant to penetration by sharp objects than plastic films or metal foils which may enclose the liner or be laminated therewith.In its preferred use, however, to protect a relatively small diameter substrate, and its preferred embodiments, the member of the present invention exhibits a greatly improved modulus of elasticity compared to that of the known metal foil which is required to be stiff to prevent damage to the substrate. A protected substrate according to the present invention is capable of exhibiting greatly improved compliance to flexing and/or vibration of the substrate without mechanical failure or failure of the adhesive bond which seals the heat shrink sleeve to the substrate against leakage of liquid or vapour.

Two embodiments of the present invention are illustrated in the accompanying drawings, in which Fig. 1 is a perspective view of a kit according to the present invention, in use, and Fig.2 is schematic cross-section of the wrapping member of the present invention.

Referring first to Fig. 1, a substrate is a cable, 1 (in Fig. 1 only a single cable is shown for simplicity), and a cable splice (not shown) is to be protected. A split heat shrink sleeve, 2, is applied over the cable splice, and comprises a neck portion, 3. held together in an assembled condition by a relatively flexible metal channel, 4. The sleeve 2 has an internal layer or deposit of a hot melt sealing adhesive (not shown).

Referring now to both Figs. 1 and 2, a heat protection member, 5, comprises a woven metal gauze, 6, of 1 mum diameter copper wire, having a regular array of perforations, 7, of size 25mm by 2.5mm. On one face is applied a layer, 8, of a non-tacky hot melt sealing adhesive, and the other face carries a layer, 9, of a tacky contact adhesive. The member is applied to the area of cable at the end of the sleeve 2, so that it extends within and outside the sleeve, by wrapping it firmly around the cable so that the layer 8 is external, and the layer of contact adhesive is pressed onto the outer surface of the layer 8 to hold the member in position.

When the sleeve is shrunk using, for example, a propane/butane flame, onto the splice, the hot melt sealing adhesive on the inside of the sleeve and the layer 8 melt and flow through at least the perforations 7, and preferably but not necessarily through the pores or mesh of the metal gauze, to bond the member to the cable insulation and the sleeve to the member. An exceptionally strongly bonded product results, which is very resistant to failure of the seal because of vibration or flexing owing to the high flexibility of the gauze.

An alternative heat protection member has a metal fabric which is 2.5mm galvanised steel wire twisted to give a mesh of 6mm. A preferred protection member is an expanded aluminium having a mesh size of 3.17 X 1.81mm and strand dimensions of 0.28 X 0.30mm. In these cases, no perforations are necessary.

A test was carried out to compare the heat protection performance of a conmercial product comprising a stiff aluminium foil having a number of rectangular perforations, as described in UK Patent No 2,075,771B, and a prototype protection member of expanded aluminium as mentioned above, carrying a film of tacky contact adhesive. Themocouples were attached to cable pieces before the known foil product and the protection member of the invention were applied around the cable pieces.

A further sample of cable had no heat protection applied over the thermocouple. Pieces of heat shrinkable sleeve were positioned over the cables and were caused to shrink by applying a propane/butane flame. Under identical conditions, the temperature at the cable surface was 91"C for the assembly without any heat protection, 70"C for the assembly having the commercial foil product and 60"C for the assembly having the prototype expanded metal heat protection member.

Claims (20)

1. A kit for covering an elongate substrate, comprising a heat shrinkable sleeve and a metal fabric heat protection member capable of being wrapped around one or more parts of the substrate.

2. A kit according to claim 1, wherein the fabric has a porosity or mesh size of 0.1 to 10 mm.

3. A kit according to claim 2, wherein the fabric has a porosity or mesh size of 0.5 to 7.5 mm.

4. A kit according to any one of the preceding claims, wherein the fabric has perforations in addition to its porosity or mesh.

5. A kit according to claim 4, where the perforations are from 5 to 30 mm across.

6. A kit according to any one of the preceding claims, wherein the fabric carries a layer on one major face thereof, of a contact adhesive.

7. A kit according to any one of claims 1 to 5, wherein the fabric carries a layer of a hot melt sealing adhesive on one major face thereof.

8. A kit according to claim 7, wherein the hot melt sealing adhesive is carried in discrete portions to facilitate wrapping of the member around a substrate.

9. A kit according to claims 6 and 7, wherein the the layers of contact adhesive and hot melt sealing adhesive are on opposite major faces of the fabric.

10. A kit according to any one of the preceding claims, wherein the fabric of the wrapping member is a metal gauze.

11. A kit according to any one of claims 1 to 9, wherein the fabric of the member is expanded metal.

12. A kit according to claim 1, substantially as hereinbefore described.

13. A method of protecting an elongate substrate, using a heat shrinkable sleeve, comprising wrapping one or more parts of the substrate with a heat protection member comprising a metal fabric, and heat shrinking the sleeve over at least part of the wrapped substrate.

14. A method according to claim 13, wherein the member is wrapped around a liner which is constructed around the substrate.

15. A method according to claim 13, wherein the member is wrapped around a portion of the substrate at the point at which it emerges from the sleeve.

16. A method according to claim 15, wherein the member is wrapped around a relatively small diameter substrate.

17. A method according to claim 16, wherein the substrate is a cable branchout having a plurality of cable portions, and one at least of said cable portions has a member wrapped around.

18. A method according to any one of claim 13 to 17, wherein the wrapping member carries, on the surface facing the substrate, a layer of contact adhesive.

19. A method according to claim 13, substantially as hereinbefore described.

20. A protected elongate substrate having a part of the substrate wrapped with a metal fabric heat protection member and a surrounding heat shrunk sleeve, prepared by a method according to any one of the claims 13 to 19.