GB2239134A

GB2239134A - Heat shield for a cable joint

Info

Publication number: GB2239134A
Application number: GB9022057A
Authority: GB
Inventors: Peter Deusser; Christa Wenzel; Olaf Holzmann
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1989-10-14
Filing date: 1990-10-10
Publication date: 1991-06-19
Anticipated expiration: 2010-10-10
Also published as: DE3934426A1; GB2239134B; GB9022057D0

Abstract

A heat shield to be provided around a cable end (1) within the end region (6) of a heat shrink sleeve (2) of a cable joint. The heat shield consists of an elongate heat shielding tape for forming about the cable end (1) a plurality of turns (4, 11) arranged adjacent to each other without overlap in the shape of a spiral. The tape may be in the form of a rope (8) coated with adhesive (9) or a flat spiral (10) formed with holes (18), the core (13) of which is coated with adhesive 14. <IMAGE>

Description

1

DESCRIPTION

PED89178 HEAT SHIELD FOR A CABLE JOINT This invention relates to a heat shield for provision around the end of a cable within the end region of a heat shrink sleeve of a cable joint.

DE-A-3521369 discloses such a heat shield which consists of a heatresistant piece of film material which is wound around a cable end and acts as a barrier against the heat produced during the heat-shrinking operation of a shrink sleeve. Acting thus, damaging a heat- sensitive cable jacket can be prevented. So as to ensure that the known heat shield adheres to the cable jacket, its surfaces facing the cable are provided at least in certain regions with adhesive areas which perform their adhesive action at room temperature.

It is an aim of the present invention to provide a heat shield of such a shape that a simple application of the heat shield on the cable jacket is possible.

Accordingly, in a first aspect the present invention provides a heat shield for provision around the end of a cable within the end region of a heat shrink sleeve of a cable joint, the heat shield comprising an elongate heat shielding tape for forming about the cable end a plurality of turns arranged adjacent to each other without overlap in the shape of a spiral, for example of the screwthread type.

As there are no areas of overlap, a heat shield in accordance with the invention has no discontinuities in the form of longitudinal bulges which might otherwise interfere with the sealing efficiency.

At least those surfaces of the heat shield that are contiguous to the cable end may advantageously be coated with fusible adhesive which conveniently melts at the temperature used for shrinking the heat shrink sleeve and fills intermediate spaces of the spiral, optionally in combination with an interior fusible adhesive layer of the heat shrink sleeve. Adhesive bridges can thus be formed 2 PHD89178 between the individual turns of the spiral from the exterior to the interior surfaces of the heat shield, so that an effect aimed at in the prior-art case by using recessed portions which are distributed in the form of a lattice is achieved in a simple manner. Consequently, the cable joint can be sealed in a reliable manner at the cable lead-in side.

The fusible adhesive provided on the heat shielding tape conveniently has a melting temperature which is not higher than that of an internal fusible adhesive coating of the shrink sleeve.

A heat shield in accordance with the invention adheres to the cable jacket even if adhesives are used at temperatures other than room temperature.

The heat shielding tape may have a substantially rectangular crosssection. This results in a small number of broad turns which can be applied in a relatively fast manner on the cable end. To improve the permeability, the rectangular heat shielding tape may be provided with apertures or holes. For the same reason, the rectangular heat shielding tape may have a fabric-like, grid-like or net-like structure.

In another embodiment the heat shielding tape may have a substantially circular cross-section. Such a heat shielding tape can be used, as can also rectangular or square cross-section heat shielding tapes, as a universal structural element for heat shields of different sizes.

A circular cross-section heat shielding tape which may advantageously be coated or enveloped by a fusible adhesive, provides a heat shield of a simple structure. With such a circular cross-section tape the proportion of areas of contact of adjacent turns can be relatively large, so enabling a better bond between the interior and exterior fusible adhesive layers.

The heat shielding tape of a heat shield in accordance with the invention may be wound around a cable end to form a helix without having been preformed or preshaped as a helix. In such a case it is advantageous to use materials which have only a low degree of resilience or rebound and which are in essence subject to 1 3 PHD89178 plastic deformation during bending or wrapping round the cable end. The initial part of the turn applied first and the end region of the turn applied last can, if required, be fixed by applying an adhesive which becomes effective at room temperature. The further turns may then stay in place without any additional measures to secure them.

A heat shield in accordance with the invention may comprise an elastically resilient material shaped into the form of a spiral and may, for example, comprise a heat shielding tape having a resiliently rebounding core which tape is formed into a helical tube whose inner diameter is less than the outer diameter of the cable end before being provided on the cable end. Thus, without using any additional means, a heat shield in accordance with the invention is reliably secured because the elastically resilient tape grips tightly around the cable end.

A particularly simple application is obtained when the turns of the helical tube are adhered, for example glued or cemented, to each other before they are provided on a cable end and the helical tube is slit in the longitudinal direction. The longitudinal slit in the heat shield is elastically flared for the lead-in of the cable end.

During the heating operation for shrinking the heat shrink sleeve the temperature decreases from the exterior to the interior. Therefore it is preferably provided that the fusible adhesive on the heat shielding tape (and any internal fusible adhesive coating of the heat shrink sleeve) have a fusing temperature which is not higher than the heat-shrinking temperature of the heat-shrink sleeve.

The melting temperature of the fusible adhesive applied onto the heat shield or on the heat shielding tape should, particularly in the regions facing the cable end, be so low and less than 900C or preferably less than 800C, that the material of the cable jacket does not unduly soften.

The invention also provides a method of forming a protective cover over a cable joint between the ends of two cables, which 4 PHD89178 method comprises providing a heat shield in accordance with the first aspect around at least one cable end, applying a heat shrinkable film material around the two cable ends and heat-shrinking the heat shrinkable film material so that the heat-shrinkable film material tightly surrounds the at least one heat shield and the cable ends.

In another aspect, the invention provides a cable joint arrangement comprising a joint formed between the ends of two cables and a protective cover provided over the joint, the protective cover comprising a heat shield in accordance with the first aspect provided over at least one of the cable ends and a heat-shrink sleeve formed around the cable ends over the at least one heat shield.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which Figure 1 is a partly cross-sectional view of the cable lead-in region of a cable joint on which the heat shield in accordance with the invention is provided; Figure 2 illustrates to a larger scale, the manner in which a heat shield in accordance with Figure 1 is applied; and Figure 3 shows a modified form of a heat shield of the invention.

Referring now to the drawing, and in particular Figure 1, there is shown a cable joint arrangement comprising a cable joint between two cable ends 1 (only one of which is shown in Figure 1) and a protective cover. The protective cover comprises a heat shield 5 formed by a heat shielding tape in the form of a plurality of turns 4 wound around at least one preferably both, of the cable ends 1 to form a spiral or helix, for example of the screwthread type, and a heat-shrinkable shrink film material 2 applied around the joint between the two cable ends 1. The contiguous ends of the heat- shrinkable film material 2 which have bulging profiles are clamped together by means of a connecting clamp 3, so that a closed tube is obtained. The shrink film material 2 is heated to the shrinking temperature, which causes the dimensions in the PHD89178 peripheral direction to be reduced. The shape shown in Figure 1 is then obtained with the end region 6 of the shrink film material 2 tightly surrounding the heat shield 5.

When heat shrink film material 2 is heated to the shrinking temperature, fusible adhesive layers provided on the interior side of the shrink film material 2 and on the heat shield 5 melt. The heat shield 5 ensures that no excessive temperatures are transferred to the surfaces of the cable end 1 and so to its jacket. The temperature produced on heating the shrinkable film 2 should be sufficiently high to soften the fusible adhesive layers adjacent to the cable end 1 but should be sufficiently low that the jacket of the cable end 1 is not unduly affected.

The fusible adhesive portions of the heat shrinkable film 2 and of the heat sleeve 5 are fused in such a manner that the region between the end region 6 of the heat shrinkable film 2 and the cable end 1 is free from cavities and is sealed tightly. The radial permeability required therefore of the heat shield 5 is provided in the solution in accordance with the invention by the connecting parts between adjacent turns 4 of the heat shield 5.

For simplicity, Figure 1 shows the cross-sections of the turns 4 in their original state. However, the fusible adhesive layers of the turns 4 do indeed fuse when heat shrink film material 2 is heated to the shrinking temperature, so that, after shrinking, in practice no separate crosssectional forms of the turns 4 can be distinguished.

During the heating operation for shrinking the heat shrinkable film material 2 the temperature decreases from the exterior to the interior. Therefore it is preferably provided that the fusible adhesive on the heat shielding tape, and any internal fusible adhesive coating of the heat shrink material have a fusing temperature which is not higher than the heat-shrinking temperature of the heat- shrink material or sleeve.

The melting temperature of the fusible adhesive applied onto the heat shield or on the heat shielding tape, must, more specifically in the regions facing the cable end, be so low and 6 PHD89178 less than 900C or preferably less than 800C, that the material of the cable jacket does not unduly soften.

The heat shield 5 and the manner of application to the cable end 1 will now be described in detail with reference to Figure 2. First, a tubular helix 7 of the screw-thread type is formed from a heat shielding tape. This tape consists o an elastically resilient or rebounding core 8, which is enveloped by a fusible adhesive layer 9. The inner diameter Di of the tubular helix 7 is less than the outer diameter Da of the cable end 1, so that, when the tubular helix 7 is wound or wrapped around the cable end 1 as shown in Figure 2 for the portion 71 of the tubular helix 7, the tubular helix 7 fits tightly around the cable end 1.

Although the heat shielding tape shown in Figures 1 and 2 is of circular cross-section, the cross-section of a heat shielding tape could alternatively be chosen to be rectangular, so that then a compact cavity-free tubular helix is obtained.

The elastically resilient material forming the core 8 should be both heatresistant and heat-isolating. Particularly suitable materials are crosslinked polyethylenes, polyesters or MF (polyvinylidenefluoride). The cross-sectional area of the heat shielding tape, including the fusible adhesive layer 9, should be in the range of from 5 to 20 m2. Where the core 8 has a larger cross-section, the wire 8 can efficiently be in the form of a cord or a rope, for which hemp andlor synthetic resin andlor glass fibres can be used. A metal wire, for example of steel or aluminium, would also be suitable for the core 8.

Although in the arrangement described above, the preformed tubular helix 7 has effectively to be unwound to enable the tape to be wrapped round the cable end, the turns of the tubular helix 7 may be glued to each other before being applied to the cable end. In this case, the tubular helix 7 will be slit longitudinally to allow the tubular helix 7 to be provided around the cable end 1. The longitudinal slit may be elastically flared for the lead-in of the cable end.

The core 8 might, however, alternatively be formed from a C 1 7 PHD89178 material which is not elastically resilient or reboundable, as will be described with reference to Figure 3.

In Figure 3 the tubular helix 10 consists of turns 11 of a heat shielding tape of a rectangular cross-section. The heat shielding tape has a core 13 which is surrounded on all sides by fusible adhesive 14. The heatresistant and heat-isolating material of the core 13 is not elastically resilient or reboundable, rather on bending the core 13 is subjected in essence only to plastic deformation. In the example shown in Figure 3, the rectangular cross-section heat shielding tape is directly wound around the cable end 1 without previously being formed into a tubular helix 7 as was the case in the example shown in Figure 2. The initial region 15 and the end region 16 of the heat shielding tape can, if so required, be fixed on the cable end 1 using adhesives which become effective at room temperature.

Should the connecting lines between the turns 11 of the heat shielding tape not be sufficient to obtain a sufficient number of connecting parts between the exterior and the interior fusible adhesive layers, the heat shielding tape can be provided with apertures 18. Particularly advantageous are also fabric-like grid-like or net-like structures for the core 13. Cores assembled from fibre elements are flexible and have lower recovery forces than solid cores. They allow penetration of the fusible adhesive.

1 8 PHD89178

Claims

CLAIM(S)

1. A heat shield for provision around the end of a cable within the end region of a heat shrink sleeve of a cable joint, the heat shield comprising an elongate heat shielding tape for forming about the cable end a plurality of turns arranged adjacent to each other without overlap in the shape of a spiral.

2. A heat shield as claimed in Claim 1, wherein at least the areas of the heat shield contiguous with the cable jacket are coated with fusible adhesive.

3. A heat shield as claimed in Claim 2, wherein the fusible adhesive has a melting temperature which is not higher than that of an internal fusible adhesive coating of the shrink sleeve.

4. A heat shield as claimed in Claim 1, 2 or 3, wherein the elongate heat shielding tape comprises an elastically resilient material shaped into the form of a spiral.

5. A heat shield as claimed in Claim 4, wherein the heat shielding tape has an elastically rebounding core and, before being applied to the cable end, is formed into the shape of a helical tube having an inner diameter less than the outer diameter of the cable end.

6. A heat shield as claimed in Claim 5, wherein the turns of the helical tube are glued to each other before being applied on a cable end and the helical tube is slit longitudinally.

7. A heat shield as claimed in any one of the preceding claims, wherein the heat shielding tape has a substantially rectangular cross-section.

8. A heat shield as claimed in Claim 7, wherein the rectangular cross-section heat shielding tape is provided with apertures.

9. A heat shield as claimed in Claim 7 or 8, wherein the rectangular cross-section heat shielding tape has a fabric-like, lattice-like or net-like structure.

10. A heat shield as claimed in any one of Claims 1 to 6, wherein the heat shielding tape has a substantially circular cross-section.

9 PHD89178

11. A heat shield as claimed in Claim 10, wherein the circular cross-section heat shielding tape has an outer coating of fusible adhesive.

12. A heat shield as claimed in Claim 10 or 11, wherein the circular cross-section heat shielding tape has a core which consists of a cord or a rope.

13. A heat shield as claimed in Claim 12, the cord or rope is made of hemp, synthetic resin material, glass fibres or several of these materials.

14. A heat shield as claimed in any one of the Claims 10 to 13, wherein the circular cross-section heat shielding tape contains a metal wire.

15. A heat shield for provision around the end of a cable, substantially as hereinbefore described with reference to the accompanying drawing.

16. A method of forming a protective cover over a cable joint between the ends of two cables, which method comprises providing a heat shield in accordance with any one of the preceding claims around at least one cable end, applying a heat shrinkable film material around the two cable ends and heat-shrinking the heat shrinkable film material so that the heat-shrinkable film material tightly surrounds the at least one heat shield and the cable ends.

17. A method according to Claim 16, which further comprises clamping longitudinal edges of the heat shrinkable film material together to form a sleeve around the cable ends prior to heat shrinking.

18. A method of forming a cable joint between the ends of two cables substantially as hereinbefore described with reference to the accompanying drawing.

19. A cable joint arrangement comprising a joint formed between the ends of two cables and a protective cover provided over the joint, the protective cover comprising a heat shield in accordance with any one of claims 1 to 15, provided over at least one of the cable ends and a heat-shrink sleeve formed around the cable ends over the at least one heat shield.

PHD89178

20. A cable joint arrangement according to Claim 19, wherein each of the cable ends is provided with a heat shield in accordance with any one of Claims 1 to 15.

21. A cable joint arrangement according to Claim 19 or 20, wherein the heat-shrink sleeve is formed by a heat shrunk heat-shrinkable film material wrapped aroun d the cable joint over the heat shield(s) and having its longitudinal edges clamped together by a connecting clamp.

22. A cable joint arrangement substantially as hereinbefore described with reference to the accompanying drawings.

Published 1991 atThe Patent Office. State House. 66171 High Holborn. London WC I R 47P. Further copies may be obtained from Sales Branch. Unit a Nine Mile Point. Cvnnfebnfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray, Kent.