GB2113925A - Heat-recoverable articles - Google Patents

Abstract

A heat-recoverable sleeve 2 for enclosing splices or joints 1 in pressurised cables or supply lines is given increased resistance to peeling away from the cable or line by insertion of auxiliary means, preferably a U- or V-shaped flexible strip 6, which may be heat-recoverable, between the sleeve and the cable or supply line. The ends of the strip 6 are preferably closed and are preferably overlapped and bonded to each other when the strip is placed around the cable or supply line. A release foil 8 may be positioned inside the U- or V- shape of the strip to resist bonding together of the opposed arms thereof, and the foil may carry adhesive to bond it to one of the arms and may protrude beyond the ends of the arms so that the foil adhesive can help to locate the strip on the cable or supply line. <IMAGE>

Description

SPECIFICATION Heat-recoverable articles This invention relates to heat-recoverable articles and their use in the insulation and protection of substrates such as supply lines.

Heat-recoverable articles, especially heatshrinkable articles, are now widely used in many areas where insulation, sealing and encapsulation are required. Usually these articles recover, on heating, towards an original shape from which they have previously been deformed, but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.

In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Patents 2,027,962; 3,086,242 and 3,957,372. As is made clear in, for example, U.S. Patent 2,027,962, the original dimensional heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heatstable article is deformed to a dimensionally heat unstable form in a separate stage.

In other articles, as described, for example, in British Patent 1,440,524, an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating, weakens and thus allows the elastomeric member to recover.

Heat-shrinkable sleeves find many applications especially in the connection and termination of wires, cables and pipes. However, there are other applications where it is desirable to provide a connecting, insulating or protective heatrecoverable member for elongate objects such as cables and pipes where the ends are not accessible or, if they are accessible, where it undesirable to disconnect or otherwise displace them. For such applications so-called "wraparound" sleeves have been developed. Basically these are heat-recoverable sheets which can be wrapped round the substrate to form a generally tubular shape and which, in general, are provided with fastening means for holding them in the wrapped-up configuration during recovery.

Typically such fastening means are mechanical in nature and comprise, for example, rigid clamps" pins or channel members which co-operate with suitable shaped moulded or extruded protuberances adjacent to the overlapping edges of the heat-recoverable sheet. Various types of fastening means are described, for example in U.S.

Patent 3,379,218 and British Patents 1,115,470; 1,211,988 and 1,346,479. In other applications, however, the sheet may be held in the wrappedup configuration during recovery by means of an adhesive which may, in some cases, be applied on site.

Heat-recoverable sleeves and wrap-around sleeves have been successfully employed in many fields of application. One particularly important field in which they are employed is in the protection of communication system cables, Such cables must periodically be spliced to connect successive portions and to provide access for branch cables and terminals. At the splices so effected the protected sheaths must be disturbed thus providing an opportunity for moisture and other contaminants to reach and damage or destroy the unprotected conductors and the splice. For this reason splice cases have been developed to protect and seal the splice and the cable ends.Especially useful splice cases and materials and components for use therein are described, for example, in German OS 2,543,338, 2,543,314,2,543,346, 2,635,000 and 2,539,275, the disclosures of which are incorporated herein by reference. Another important type of splice case is described and claimed in British Patent No. 1,431,167, the disclosure of which is also incorporated herein by reference.

The splice cases mentioned above have proved extremely successful in practice in many types of cables including, especially, pressurised cables, i.e.

those in which a small pressure of, for example, up to about 2 kg/cm2, typically about 0.5 kg/cm2, is maintained in order to prevent the ingress of water through a damaged cable jacket. The application of splice cases to such pressurised cables is discussed in the Patents mentioned above and also in British Patent Application No. 35338/75 and in German OS 2,638,448, the disclosures of which are incorporated herein by reference.

Such splice cases are provided with outer heatrecoverable sleeves which are shrunk down over the splice when the latter has been completed. It will be appreciated that the ends of the heatshrinkable sleeve, which may be a wrap-around sleeve, are shrunk down firmly over the cables forming the splice and, for this purpose, they are generally provided with a heat activatable adhesive to provide a good seal to the cables.

However, the presence of the splice case itself precludes the central portion of the heatrecoverable sleeve from complete recovery and, therefore, in a pressurised cable the pressure within the splice case tends to force the heatrecoverable sleeve away from the cables and, in particularly, puts the adhesive layer in the region at which the heat-recoverable sleeve first contacts the cable under considerable strain, rendering it liable to failure by peel. A further complication is that the counteracting recovery force of the heatrecoverable sleeve tends to relax with time down to some limit value.Failure can, in general, be avoided by, for example, ensuring that a sufficient length of heat-recoverable sleeve is shrunk down on each cable and by other means such as solvent cleaning of the cable jackets, abrasion of the jacket surfaces and flame brushing, and at relatively low pressures employed to date the splices have readily met the test requirements of the users. However, at slightly higher pressures, which are now proposed for use in pressurised cables, the problem becomes more severe, especially bearing in mind that the expected life time of the joints is from 20 to 30 years and in view of the fact that, in practice, cable preparation is dependent upon the skill of the operator.It will, in any case, be appreciated that similar problems may arise in other applications in which external or internal forces may tend to cause the sleeve to come out of contact with the substrate.

The present invention provides a method of recovering a heat-recoverable article on or about a substrate, wherein there is interposed between the article and the substrate at least one flexible auxiliary member which is adapted to eliminate or to reduce the effect of a force tending to cause the heat-recoverable article to be brought out of contact with said substrate.

By "flexible" we mean able to be deformed by a force which will, in the absence of the member, lead to the article being brought out of contact with the substrate. In general, therefore, the article will be deformed to enhance the contact of its surfaces with the article and the substrate.

Accordingly, while the member is to be responsive to such forces it should not itself be rupturable or caused to flow thereby at least when interposed between the article and the substrate.

As will be appreciated from the following discussion, the invention is generally applicable to any use of heat-recoverable article including, for example, those in which the article is a heatexpansible article which is adapted to contact the inner surface of a utility line such as a duct.

Reference is made in-this respect to British patent No.1,245,119 and British Patent Application No.

45725/76, the disclosures of which are also incorporated herein by reference. It will also be appreciated that the concept of the present invention may be applicable to situations in which no heat-recoverable article is used but in which, nonetheless, forces derived from internal pressure or some other cause tend to put an interface in danger or failure by peel.

However, for convenience, the invention will now be described in more detail with reference to the use of heat-shrinkable sleeves in the protection of splices in pressurised cables.

Accordingly, the essence of one aspect of the present invention is to provide one or more auxiliary members which isolate the interface region from the forces which would otherwise tend to cause peel at the interface and which, preferably, do so by themselves accommodating those forces. In one embodiment of the present invention the auxiliary member presents to such forces a re-entrant or concave surface, and preferably the member comprises a strip of generally U- or V-shaped cross-section, the base of which lies at or adjacent the interface between the heat-shrinkable sleeve and the cable and the arms of which are attached, e.g. by adhesive, to the heat-shrinkable sleeve and the cable jacket, respectively, in the direction of the splice. The strip is preferably flexible at least insofar that it is able to respond to pressure by opening out, so as to enlarge the U or V.Thus the strip may, for example, be made from a flexible polymeric material, cross-linked polyethylene being especially preferred or may, in some applications, be hinged at its base, this being achieved for example by the provision of a relatively flexible region at the base of an otherwise relatively rigid strip. If desired the strip may be reinforced along its length so as to provide it with some structural strength and, in certain applications it may be desirable to provide it with further reinforcement at spaced apart regions along its length.

The strip may be provided as a continuous length which is cut to size and wrapped around the circumference of the cable or may be provided as standard size lengths for this purpose; for large diameter cables it may be appropriate to use two or more of such standard size lengths. In other embodiments it may be appropriate to provide the U- or V-shaped strip as a continuous annular member which is positioned around the cable. The strip may, for example, be moulded or extruded. In all cases the strip-can, if desired, itself be heatrecoverable so that it can be caused to recover and firmly grip the cable. The material of the strip should preferably be non-meltable below about 180at and should be capable of adhering to the hot melt or other adhesives commonly employed in splicing.It should also be sufficiently thick that it does not tear or crack under the strains and pressures involved. Cross-linked flat polyethylene sheet having a thickness of 0.3 to 0.5 mm is particularly suitable.

In those applications where the strip is to be wrapped around the cable it will be necessary for the ends to overlap and the length of the strip is, therefore, preferably, from 1.25 to 1.75 times that of the circumference of the cable jacket. In order properly to secure the overlapping ends of the strip to each other, the side walls of each end of the strip are preferably bonded together, for example, by peroxide so as to provide flat end portions which are themselves bonded to each other in the overlapping region. As mentioned above, in some cases, it may be desirable to use two lengths of strip in order to form an annular member about the circumference of the cable.

Once again, the overlapping ends of the strips will preferably be flattened to facilitate bonding. In all embodiments it will be advantageous to mark the strips so as to indicate to the operator where the minimum region of overlap should occur. The strip may, for example, be provided with a coloured region where overlap is to occur. In some embodiments the strip may be attached to the inner surface thereof prior to recovery. However, in presently preferred embodiments the strip is provided as a separate member which becomes attached to the inside of the heat-recoverable sleeve by adhesion with the hot melt or other adhesive provided on the inner surface thereof.

The other side of the strip is itself preferably provided with an outer layer of the same or a similar adhesive for adhesion to the cable. In some cases it may be preferable to use a mastic which may give better wetting and sealing at low temperatures and allow less cable preparation.

It will be preferable to provide means for maintaining the strip in the desired position during recovery. In this respect it may be possible, as mentioned above, to provide a heat-recoverable strip which is initially shrunk onto the cable. In other embodiments the strip may itself be resilient, e.g. made from a natural or synthetic elastomer or may be provided with a resilient component such as a coil spring in order to grip the cable. However, the strip may advantageously be retained in position by providing a material coated with a contact adhesive which adheres to the side of the U- or V-shaped strip adjacent the cable and to the cable itself. Such a material may, for example, by a tape of thin foil provided on its upper surface with a release agent (in order to prevent the two sides of the U- or V-shaped strip from sticking together) and on its lower side with a contact adhesive.

In all embodiments of the present invention it will be preferred to provide some means to ensure that the sides of the U- or V-shaped strip do not stick together and, in this respect, it may be appropriate to provide a release foil as an insert between the said sides. It may also be desirable for the release foil to extend some distance, for example about 15 mm, from the edge of the strip towards the splice towards the splice, in order to prevent the sleeve from sticking to the cable jacket between the strip and splice.

It will be appreciated that the present invention may be used in many applications and, in particular, is not limited to applications in which the heat-recoverable article is a simple heatshrinkable tubular sleeve. Thus it may, for example, be used where branch-off connections are being made, and in this respect, is suitable for use together with the clips and fork members described and claimed in British Patent Applications Nos. 79.1 1714and 79.11713, respectively, the disclosures of which are incorporated herein by reference.

Suitable materials and adhesives for use in the method of the present invention are described in the various Patents referred to herein and will, in any case, be known to those skilled in the art.

The present invention also provides auxiliary members, especially the above described U or Vt shaped strips, for use in the method of the present invention. For example, the invention provides a flexible auxiliary member for use in recovering a heat-recoverable article on or about a substrate, said member being adapted to be interposed between the article and the substrate and comprising a strip of generally U- or V-shaped cross-section coated on at least one exterior surface by an adhesive or a mastic.

In another aspect, the invention also provides a splice in a pressurised cable or a joint in a pressurised supply line protected by a sleeve provided with one or more flexible auxiliary members interposed between the sleeve and the cable or supply line and so positioned as to present a re-entrant or concave surface to the forces generated by the internal pressure of the cable or supply line such that the forces which would otherwise tend to cause peel at an interface between the sleeve and the cable or supply line are reduced or eliminated. The invention also provides a kit of parts comprising a sleeve and an auxiliary member as aforesaid for protecting a splice in a pressurised cable or a joint in a pressurised supply line.

Various embodiments in accordance with the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal cross-section through one end of a conventional cable splice; Figure 2 is a longitudinal cross-section through one end of a protected cable splice; Figure 3 shows a V-strip as used in the arrangement shown in Figure 2; Figure 4 is a cross-section along the line n'-a of Figure 3; Figure 5 shows the application of the V-strip of Figures 3 and 4 to a cable; Figure 6 is a transverse cross-section along the line ssp of Figure 2; Figure 7 is a similar cross-section to that shown in Figure 6; Figure 8 is a transverse cross-section taken through a break-out splice; Figure 9 shows an application for a tubular Vstrip; and Figure 10 shows a further form of V-strip provided with a spring component.

Referring now to the drawings, in Figure 1 there is shown an end portion of a protected splice made by a conventional method such as, for example, one of those described in the patents referred to above. As can be seen, the splice 1 (which is not shown in detail) is protected by a heat-recoverable sleeve 2 which is shrunk, at the end shown, about cable 3. The pressure within the cable indicated by arrows tends to cause failure of the bond between the sleeve 2 and the cable 3, especially at interface 4. A hot melt adhesive 5 is typically provided on the inner surface of the sleeve 2 at least in those regions in which it contacts the cable 3.

In Figure 2 there is shown an arrangement in accordance with the present invention in which a V-strip 6 made from cross-linked polyethylene is positioned between the sleeve 2 and the cable 3 so that the base thereof lies at or adjacent the interface 4.

As is shown more clearly in Figures 3 and 4 the V-strip 6 is provided on its lower side with a layer of hot melt adhesive or mastic 7 and on its upper side is contacted by the hot melt adhesive layer 5 provided on the inner surface of the sleeve 2. In order to secure the V-strip in position prior to recovery it is also provided on the upper surface of its lower side with a silicone foil tape 8 which is itself provided with a lower layer of contact adhesive 9. As is shown most clearly in Figure 3 the ends of the V-strip 10 and 11 are closed, for example by bonding with a peroxide and, as is shown most clearly in Figure 6 the overlapping ends are secured together so as to give a degree of overlap.

Figure 5 shows the instalment of the V-strip 6 prior to recovery. As shown, the cable 3 is preferably provided with a suitable marking line 12 at a predetermined distance from another line 13 which represents the position of the end of the heat-recoverable sleeve 2 (Figure 2). Preferably the distance between lines 12 and 13 is from 1 to 3 times the width of the V-strip. The V-strip 6 is itself marked at 14 so as to indicate the necessary degree of overlap. The zone 14 may, for example, by coloured.

The width of the V-strip 6 is typically from 30 to 60 mm and the siliconed foil 8 preferably projects a further 20 to 40 mm beyond the lower edge thereof.

Figure 6 shows the position of a single V-strip in cross-section on the line ,B/30f Figure 2, and in Figure 7 there is shown how, for a large diameter cable, there may be employed two Vstrips 1 5 and 1 6 which overlap in areas 1 7 and 18.

Figure 8 shows how the V-strip may be employed at a branch-off cable termination employing a clip 1 9 in accordance with the teachings of British Patent Applications Nos.

79.11713and 79.11714. As can be seen the smaller branch-off cable 20 is provided with a single V-strip 21 whereas the larger main cable 22 is provided with two overlapping V-strips 23 and 24.

Figure 9 shows how a pre-installed tubular Vstrip 25 may be used in conjunction with a valve member 26. This valve member may, for example, be that used to pressurise the splice case.

Figure 1 0 shows a further form of V-strip 27 which in this case is provided at its base 28 with a spring component 29 which is pre-installed, preferably with an overlap of 0.75 turns, and which operates to grip the V-strip firmly in place on a substrate such as a cable prior to recovery.

Claims (10)

1. A splice in a pressurised cable or joint in a pressurised supply line protected by a sleeve provided with one or more flexible auxiliary members interposed between the sleeve and the cable or supply line and so positioned as to present a re-entrant or concave surface to the forces generated by the internal pressure of the cable or supply line such that the forces which would otherwise tend to cause peel at an interface between the sleeve and the cable or supply line are reduced or eliminated.

2. A splice or joint according to Claim 1, wherein the auxiliary member(s) carries or incorporates means for holding it in position on the cable or supply line.

3. A splice or joint according to Claim 1 or 2, wherein the auxiliary member(s) comprise(s) at least one strip of substantially U-shaped or V shaped cross-section, the arms of which cross section are respectively attached to the sleeve and the cable or supply line.

4. A splice or joint according to Claim 3, wherein the flexibility of the strip is such that the U- or V-shaped cross-section is able to open out in response to the pressure applied thereto within the pressurised cable or supply line.

5. A splice or joint according to Claim 30r 4, wherein the strip incorporates spring means capable of holding it around the cable or supply line.

6. A splice or joint according to any of Claims 2 to 5, wherein the strip is wrapped around the cable or supply line with the ends of the strip overlapping.

7. A splice or joint according to Claim 6, wherein the ends of the strips are bonded to each other where they overlap.

8. A splice or joint according to any of Claims 2 to 7, wherein the arms of the U- or V-shaped cross-section are bonded together at or near the ends of the strip.

9. A splice or joint according to any of Claims 2 to 8, wherein the strip has a release foil inserted between the arms of U- or V-shaped cross-section to reduce the likelihood of the arms adhering to each other.

10. A strip according to claim 1, substantially as herein described with reference to any of Figures 2-10 of the accompanying drawings.

10. A splice or joint according to Claim 9, wherein the release foil protrudes beyond the strip edge toward the splice so as to reduce the likelihood of the sleeve adhering to the cable or supply line between the strip and the splice.

11. A splice or joint according to Claim 10, wherein the release foil carries adhesive on one of its main surfaces which adhesive bonds the foil to the inner surface of one of the arms of the U- or V shaped cross-section and is capable in use of bonding the protruding portion of the foil to the cable or supply line to help position the strip thereon.

1 2. A splice or joint according to any one of the preceding Claims, wherein the auxiliary member(s) is/are made from flexible polymeric material.

1 3. A splice or joint according to Claim 12, wherein the auxiliary member(s) is/are made from cross-linked polyethylene.

14. A splice or joint according to any of the preceding Claims, wherein the auxiliary member(s) is/are made from heat-recoverable material and has/have been shrunk around the cable or supply line.

15. A splice or joint according to any of the preceding Claims, wherein the sleeve is at least partly made of heat-recoverable material and has been heat recovered about the cable or supply line.

1 6. A splice or joint according to Claim 1, substantially as described with reference to Figures2 to 6, or 7, or 8, or 9, or 10 of the accompanying drawings.

17. A strip of flexible material having a substantially U-shaped or V-shaped cross-section suitable for use as the auxiliary member in a splice or joint according to any of the preceding Claims.

18. A strip according to Claim 17 having the arms of the U- or V-shaped cross-section bonded to each other at the ends of the strip.

19. A strip according to Claim 1 7 or 18, having adhesive material on its outer surface capable of attaching the arms of the U- or V-shaped cross section to the sleeve and the cable or supply line respectively when the strip is used in the said splice or joint.

20. A strip according to Claim 1 7 having between the arms of the U- or V-shape a release foil which carries adhesive on one of its major surfaces, the adhesive bonding the foil to one of the said arms and the foil protruding beyond the said arms so that the adhesive carried by the protruding portion can be used to bond the foil to a substrate, thereby helping to position the strip thereon.

21. A strip according to any of Claims 17 to 20, which is made of heat-shrinkable material.

22. A strip according to any of Claims 17 to 21, which incorporates spring means capable of holding the strip around a cable or supply line.

23. A strip according to Claim 1 7 substantially as described with reference to any one of Figures 2 to 10 of the accompanying drawings.

24. A method of recovering a heat-recoverable article on or about a substrate, wherein there is interposed between the article and the substrate at least one flexible auxiliary member which is adapted to eliminate or to reduce the effect of a force tending to cause the heat-recoverable article to be brought out of contact with said substrate.

25. A method according to Claim 24, wherein the auxiliary member carries means for holding it in position on the substrate prior to the heat recovery of the said article.

26. A method according to Claim 24 or 25, wherein the substrate is a spliced or jointed pressurised cable or supply line and the article is a heat-shrinkable sleeve.

27. A method according to Claim 24,25 or 26, wherein the auxiliary member comprises at least one strip substantially U-shaped or V-shaped cross-section, and the arms of the said crosssection are respectively attached to the said article and the said substrate.

28. A method according to Claim 27, wherein the flexibility of the strip is such that the U- or Vshaped cross-section is able to open out in response to pressure applied thereto.

29. A method according to Claim 27 or 28, wherein the strip is wrapped around the substrate with the ends of the strip overlapping.

30. A method according to Claim 29, wherein the ends of the strip are bonded to each other where they overlap.

31. A method according to any of Claims 27 to 30, wherein the arms of the U- or V-shaped crosssection are bonded together at or near the ends of the strip.

32. A method according to any of Claims 27 to 31, wherein a release foil is inserted between the arms of the U- or V-shaped cross-section of the strip to reduce the likelihood of the arms adhering to each other.

33. A method according to Claim 32, wherein the release foil protrudes beyond the arm ends of the U- or V-shaped cross-section and the strip is positioned so that the foil reduces the likelihood of direct bonding between the portions of the article and the substrate which are adjacent to the concave side of the strip.

34. A method according to Claim 33, wherein the foil carries adhesive on one of its main surfaces which adhesive bonds the foil to the inner surface of one of the arms of the U- or V-shaped cross-section, and is used to bond the protruding portion of the foil to the substrate to help position the strip thereon.

35. A method according to any of Claims 24 to 34, wherein the auxiliary member(s) is/are made of flexible polymeric material.

36. A method according to Claim 35, wherein the auxiliary member(s) is/are made from crosslinked polyethylene.

37. A method according to any of Claims 24 to 36, wherein the auxiliary member(s) is/are made of heat-shrinkable material and is/are positioned around the substrate and subsequently heatshrunk to grip the substrate.

38. A method according to Claim 24 substantially as described with reference to any of Figures 2 to 6,or7, or 8,or 9,or 10 of the accompanying drawings.

39. An article produced by a method according to any of Claims 24 to 38.

40. A sleeve-protected splice or joint in a pressurised cable or pressurised supply line produced by a method according to any of Claims 24 to 38.

41. A kit of parts comprising a sleeve and an auxiliary member capable of being assembled into a splice or joint according to any of Claims 1 to 16.

New claims or amendments to claims filed on 28 February 1983 Superseded claims 1-41.

New or amended claims:

1. A sealing strip which can be wrapped around a cable or supply line and over which a recoverable sleeve can be recovered to form an enclosure with said strip being positioned at a junction between the cable or line and the sleeve, said strip comprising: (a) an elongate member of an air impermeable polymeric material having first and second surfaces which converge at a longitudinal edge of the member such that the first surface can contact the cable or line and the second surface can contact the sleeve; and (b) an adhesive or mastic layer on at least one of said first and second surfaces which is adhered to and which extends along said elongate member and which is adapted to secure the elongate member to the cable or supply line; said polymeric material being flexible and said first and second surfaces being arranged such that an angle between the first and second surfaces can increase in response to pressure within the enclosure thereby reducing or eliminating peel at said junction.

2. A strip according to claim 1, in which the layer (b) is provided by an adhesive strip which is adhered to one of said first and second surfaces.

3. A strip according to claim 2, which additionally comprises a longitudinal foil strip which extends from a longitudinal edge of said elongate member in a direction away from the elongate member, said foil or strip being coated with an adhesive or matic.coating.

4. A strip according claim 3, in which the coating on the foil strip is a pressure sensitive or contact adhesive coating.

5. A strip according to any preceding claim, in which the layer (b) comprises hot-melt adhesive.

6. A strip according to any preceding claim in which the elongate member is substantially Uor V-shaped in cross-section.

7. A strip according to claim 6, in which the arms of the U- or V-shaped cross-section are bonded to each other at the ends of each strip.

8. A strip according to claim 6 or 7 having between the arans of the U-or V-shaped crosssection a release foil which carries adhesive on one of its major surfaces, the adhesive bonding the foil to one of the said arms, and the foil protruding beyond the said arms so that adhesive carried by the protruding portion can be used to bond the foil to the cable or line.

9. A strip according to any preceding claims, in which the elongate member (a) is made of heatshrinkable material.