WO1990000470A2

WO1990000470A2 - Forming branch-off enclosures

Info

Publication number: WO1990000470A2
Application number: PCT/GB1989/000738
Authority: WO
Inventors: Peter Ian Lee; Raymond Charles Foss; Karl-Heinz Marx
Original assignee: Bowthorpe-Hellermann Limited
Priority date: 1988-07-05
Filing date: 1989-06-30
Publication date: 1990-01-25
Also published as: WO1990000470A3; AU3866789A

Abstract

In forming a sealed enclosure around a cable branch-off, a generally U-shaped clip is applied to an end of a heat-shrinkable sleeve positioned around the branch-off, and heat is applied to shrink the sleeve. The clip is formed of an electrically insulating material resistant to the high temperatures of a torch used to apply heat to shrink the sleeve, e.g. a thermally resistant aromatic polymer.

Description

FORMING BRANCH-OFF ENCLOSURES

This invention relates to a method of forming an enclosure around jointed substrates such as power or tele¬ communications cables. This invention further relates to a kit for use in carrying out the method and also to a clip used in the method- United Kingdom patent specification No. 1 604 81 discloses a method of forming a sealed enclosure around a branch-off in e.g. an electricity supply line. The method comprises placing a heat-shrinkable sleeve around the branch-off, applying a U-shape clip to an end of the sleeve between two branching cables extending from that end of the .sleeve, the clip serving to pinch together opposite portions of the sleeve between the two branches, and then applying heat to the sleeve causing it to shrink and seal around the two branches at the end of the sleeve. United Kingdom patent specification 1 604 981 teaches the use of a metal U-shape clip, so that it will facilitate the applicΞtion of heat to the adjacent regions of the heat-shrinkable sleeve and thus ensure that an adhesive lining of the sleeve will be fully melted in order to form an effective seal with the cable branches. Speci¬ fication 1 604 98I acknowledges Belgian patent No. 833 9'β ,r.e use of U-sr.ap c clips made from poly- acry-on: ri-.e αι; ac:e.^ scy e-e coDθ--vmer. styrene acrylonitrile resins or filled polymers (preferably glass-filled polyamide), but specification 1 604 981 further teaches that clips of such materials would not be suitable for use in the method to which it relates. However, the use of metal clips in underground cable joints is found to be undesirable because of potential electrical conduction and corrosion problems. These risks are reduced if the metal clip is coated with epoxy resins but this coating is prone to damage, for example if the joint is pulled through a duct.

In accordance with this invention as seen from one aspect, there is provided a method of forming a sealed enclosure around a branch-off, comprising disposing a heat- shrinkable sleeve around the branch-off, applying a generally U-shaped clip to an end of the sleeve between two branching elements emerging from that end of the sleeve, the clip serving to pinch together the opposite portions of the sleeve between the two branches, and applying heat to the sleeve causing it to shrink and seal around the two branches at said end of the sleeve, the clip comprising an electrically insulating material resistant to high tem¬ peratures such as those to which the clip 'would be subjected by a torch which may be used to apply the heat to the sleeve. In accordance wit this invention .is seen from a second aspect, there is provided a kit for carrying out the above-defined method, comprising a heat-shrinkable sleeve and at least one generally U-shaped clip comprising an electrically insulating material resistant to high tem¬ peratures such as those to which the clip would be subjec- ted by a torch which may be used to apply heat to the sleeve to cause it to shrink.

1^ α.cco^vι;-ι^vιΛs wi*^*^ this irventic . ^ seen f^o ~ third aspect, there is provided a generally U-shaped clip for use in he above-defined method, the clip comprising temperatures such as those to which the clip would be subjected by a torch which may be used to apply heat to the sleeve to cause it to shrink.

Preferably the material of the clip is able to resist a temperature of at least 250°C for a period of at least 5 minutes.

The clip may be formed of wood treated with fire retardant. Preferably, however, the material of the clip comprises a thermally resistant aromatic poly- mer. The latter is typically a linear polymer contain¬ ing aromatic nuclei (such as benzene rings) in the back¬ bone thereof, with, preferably, no aliphatic hydrocarbon groups in the backbone. Any carbon in the backbone is preferably in the aromatic nuclei mentioned above; any further carbon atoms are preferably present in carbonyl groups. Examples of suitable such thermally resistant polymers are polyphenylene sulphide and polyphenylene oxide. Such a thermoplastic material may, if desired, contain reinforcing filler, which again should be thermally resistant. Other possible materials are aromatic polya ides (aramids), polybenzimidazole, and polyether ether ketones (the latter being known as "PEEK" polymers.

Clips of thermoplastics materials can be formed by standard manufacturing techniques such as injection moulding or compression moulding. The clips can there¬ fore be made more cheaply than the prior art metal clips, which must be made by diecasting or pressing. In carrying out the method of enclosing the branch-off, the clip may be applied to the end of the heat-shrinkable sleeve between the two branching elements so as to pinch together opposite portions of the sleeve, then heat may be applied to the sleeve from a propane gas torch to cause the sleeve to recover. The clip is however able to resist the heat to which it is subjected by the torch. In an alternative embodiment of the method, the clip may be applied after the heat has been applied to the sleeve, although in this case preferably the opposite portions of the sleeve are pinched together between the two branches using a pair of tongs before the heat is applied.

Further because the clips may be formed by moulding, design restrictions which apply to metal castings and press- ings are removed. Preferably, the inner end of the clip slot is radiused to reduce the risk of the end of the heat- shrinkable sleeve splitting. Preferably also, the clip tapers in thickness from the outer edge to the inner edge of each of its two prongs: this allows the two adjacent branch elements to rest closer together.

A further problem with the use of U-shaped clips for holding together opposite portions of the heat-shrink sleeve between the two branches concerns the tendency for the clip to progressively slip off, or "milk off". In accordance with this invention as seen from a fourth aspect, there is provided a method of forming a sealed enclosure around a branch-off, comprising disposing a heat-shrinkable sleeve around the branch-off, applying a generally U-shaped clip to an end of the sleeve between two branching elements emerging from that end of the sleeve, the clip serving to pinch together the opposite portions of the sleeve between the two branches, and applying heat to the sleeve causing it to shrink and seal around the two branches at said end of the sleeve, the clip having the facing inner edges of its two prongs tapering towards each other towards their free ends so that the clip once applied is resistant to slipping off.

In accordance with this invention as seen from a fifth aspect, there is provided a kit for carying out the method defined in the last preceding paragraph, comprising a heat-shrinkable sleeve and at least one generally U- shaped clip, the facing inner edges of the two prongs of the clip tapering towards each other towards their free ends. In accordance with this invention as seen from a sixth aspect, there is provided a generally U-shaped clip for use in the method defined above, the facing inner edges of the two prongs of the clip tapering towards each other towards their free ends. Embodiments of this invention will now be des¬ cribed by way of example only and with reference to the accompanying drawings, in which:

FIGURE 1 is a side elevation of a generally U- shaDed clio: FIGURE 2 is a longitudinal section through the clip on the line II-II of Figure 1;

FIGURE 3 is a cross-section through the clip on the line III-III of Figure 1 ; FIGURE 4 is an end view of the clip in the direction of arrow A in Figure 1 ;

FIGURE 5 is a side elevation of a clip of modified shape; and

FIGURE 6 is a view of a sealed enclosure being formed around a branch-off using a clip as shown in Figures 1 to 4.

Referring to Figures 1 to 4 of the drawings, there is shown a generally U-shaped clip formed of electrically insulating thermo-plastics materials as mentioned previously, and formed by injection moulding or compression moulding. The clip is generally flat but as shown in Figure 3 each of its two prongs 1,2 tapers in thickness from its outer edge 3 to Its inner edge 4. Also, each prong tapers from its inner end to its free end, and the facing Inner edges 4 of the two prongs 1 , 2 taper towards each other towards the free ends of the prongs. At the web-end of the U- shaped clip, the clip is formed with portion 5 projecting away from the prongs and this portion 5 Is formed with an aperture 6 for use in removing the clip from the joing sleeve should this prove necessary. This aperture 6 is thus outside the load bearing areas of the clip. The Inner end of the slot between the two prongs is radiused, as shown at 7 in Figure 2, and all the other edges of the clip are radiused so that the clip is free of any sharp edges.

In accordance with this invention, a kit for use in a method of enclosing a branch-off comprises a heat- shrinkable sleeve together with at least one clip such as shown in Figures 1 to -. In carrying out an embodiment of this method, the sleeve 20 is disposed around the branch- off and the clip is applied to one end of the sleeve between two branching elements 22, 24 (e.g. cables) emer¬ ging from that end of the sleeve, the clip serving to pinch opposite portions of the sleeve together between those elements (Figure 6). Then a propane gas torch is used to apply heat to the sleeve, causing it to shrink and embrace the point, sealing around the two branch cables at the end of the sleeve from which these emerge. Preferably the sleeve has an adhesive coating on its inner surface, which coating is melted by the application of heat to flow and complete the seal between the sleeve and the cables, the adhesive setting as the sleeve is allowed to cool.

As explained previously, the material of the clip is resistant to the temperatures to which it is subjected by use of the torch. However, in an alternative method, the clip may be applied after the heat is applied to the sleeve, preferably in this case the opposite portions of the sleeve at its end being pinched together between the two cables using a pair of tongs, before the heat is applied. Further as expalined above, because of the tapering shape of the slot between the two prongs 1,2 of the clip, the clip is resistant to slipping off or "milk¬ ing off" once it is applied to the end of the sleeve. In addition to the advantages of the clip as referred to already in this specification, there is a further advantage as follows. It it becomes necessary to repair a joint, ^'the current practice is to cut it open leaving the clip(s) in position, repair the joint then re- seal the joint by recovering a tubular sleeve about it. This tubular sleeve covers the whole joing including the original clip(s) and is lined with an adhesive sealant which is required to bond to the clip(s) to provide an effective moisture barrier. Such adhesive are found to adhere to a limited extent to the coatings provided on the metal clips used hitherto, but we have gound that they bond better to the thermoplastics materials specified above for the clips in accordance with this invention. Referring to Figure 5, a modified clip is shown, again being generally U-shaped and flat but with its two prongs 11, 12 tapering In thickness from its outer edge 13 to its inner edge 14 and with each prong tapering from its inner end to its free end. The facing inner edges 14 of the two prongs 1, 2 taper towards each other, from the inner end towards the free ends, but then diverge at a substantially greater angle over portions 15 adjacent the free ends of the prongs. The clip has a generally rec¬ tangular outline with the outer edges is of the two prongs diverging at a small angle over portions 16 adjacent the free ends of the prongs. The free ends of the prongs 11, 12 are rounded as shown. Because this clip presents a wide entry to the slot between the two prongs, the clip is easy to push onto the end of the heat-shrink sleeve. The clip shown in Figure 5 may be formed of any of the electrically insulating materials mentioned previously.

Claims

1) A method of forming a sealed enclosure around a branch-off, comprising disposing a heat-shrinkable sleeve around the branch-off, applying a generally U-shaped clip to an end of the sleeve between two branching elements emerging from that end of the sleeve, the clip serving to pinch toge¬ ther the opposite portions of the sleeve between the two branches, and applying heat to the sleeve causing it to shrink and seal around the two branches at said end of the sleeve, the clip comprising an electrically insulating material resis¬ tant to high temperatures such as those to which the clip would be subjected by a torch which may be used to apply the heat to the sleeve.

2) A method as claimed in claim 1 , in which the material ooff tthhee cclliipp iiss aabbllee ttoo rreessiisstt aa tteemmperature of at least 250 c for a period of at least 5 minutes.

3) A kit for carrying out the method claimed in claim 1 , the kit comprising a heat-shrinkable sleeve and at least one U-shaped clip comprising an electrically insulating material resistant to high temperatures such as those to which the clip would be subjected by a torch which may be sued to apply heat to the sleeve to cause it to shrink.

4) A kit as claimed in claim 3. in which the material ooff tthhee cclliipp iiss aabbllee ttoo rreessiisstt aa tteermperature of at least 250 c for a period of at least 5 minutes,

5) A kit as claimed in claim 4, in which the material of the clip comprises a thermally resistant aromatic polymer.

6) A generally U-shaped clip for use in the method claimed in claim 1 , the clip comprising an electrically in¬ sulating material resistant to high temperatures such as those to which the clip would be subjected by a torch which may be used to apply heat to the sleeve to cause it to shrink. 7) A clip as claimed in claim 6, in which said electri¬ cally insulating material is able to resist a temperature of at least 250 c for a period of at least 5 minutes.

8) A clip as claimed in claim 7, in which the material of the clip comprises a thermally resistant aromatic polymer.

9) A method of forming a sealed enclosure around a branch-off, comprising disposing a heat-shrinkable sleeve around the branch-off, applying a generally U-shaped clip to an end of the sleeve between two branching elements emerging from that end of the sleeve, the clip serving to pinch tog¬ ether the opposite portions of the sleeve between the two branches, and applying heat to the sleeve causing it to shrink and seal around the two branches at said end of the sleeve, the clip having the facing inner edges of its two prongs tapering towards each other towards their free ends so that the clip once applied is resistant to slipping off.

10) A kit for carrying out the method claimed in claim 9, comprising a heat-shrinkable sleeve and at least one generally U-shaped clip, the facing inner edges of the two prongs of the clip tapering towards each other towards their free ends.

11) A generally U-shaped clip for use in the method claimed in claim 9, the facing inner edges of the two prongs of t.ie clip tapering towards each other towards their free ends.