WO1998042055A1

WO1998042055A1 - Recoverable article

Info

Publication number: WO1998042055A1
Application number: PCT/GB1998/000811
Authority: WO
Inventors: David Ions; Philip Roland Winfield; Josef Toerringer; George Gansbuehler; Sean Michael Lewington
Original assignee: Raychem Limited
Priority date: 1997-03-19
Filing date: 1998-03-18
Publication date: 1998-09-24
Also published as: GB9705696D0; AU6414398A

Abstract

A recoverable article comprising an inner resilient tubular member (2) that is held in a laterally expanded configuration by engagement with outer holdout means (8), wherein the outer surface of the inner member (2) is provided with a plurality of cavities (6) and wherein the holdout means (8) is helically located around the inner member (2) so as to occupy the cavities (6), thereby to provide the holdout engagement.

Description

RECOVERABLE ARTICLE

This invention relates to a recoverable article for, and method of, enclosing an elongate substrate. The substrate may comprise for example a cable, which may be an electrical power or telecommunications cable, and in particular a cable connection. The cable connection may comprise a joint, or splice, between two, or more, cables, or a termination of a cable, for example on to a terminating lug or bushing connected to electrical equipment such as switchgear or a transformer. The termination may comprise an adapter, for example an elbow.

The invention will be further particularly described with reference to an in-line joint between two electric power cables, but it is to be understood that this is by way of example only and not by way of limitation.

Joints between two power cables, whether either or both are polymeric or paper insulated cables, need to be enclosed within a protective arrangement that includes an electrically insulating layer. Heat shrink technology has been applied for this purpose for many years, with products available from Raychem and others. However, technologies that do not require heat are also employed. Push-on sleeves and elbows are available but unlike heat shrinkable products, these have severe range-taking limitations that necessitate a large inventory. Other so-called cold applied solutions require a tubular elastomeric sleeve to be radially expanded and mounted on a rigid holdout member, the internal diameter of which is larger than the maximum outer diameter of the cable joint to be enclosed. One example of the latter is the PST sleeve available from 3M, as exemplified in US-A-3515798. Such a sleeve has an inner holdout member that consists of a continuous narrow strip of tough flexible material in the form of a rigid closed helix having adjacent coils interconnected. The held out sleeve is mounted over the cable joint and the helical strip is then unwound, thus allowing the insulating stretched elastic cover to shrink down onto the joint. However, it is inconvenient having to unwind the holdout strip helically around the extended cable, especially if the work has to be done in the confined space of a trench or manhole. Another example of a cold applied arrangement is disclosed in US-A-3824331 (AMP), in which a resilient tubular cover is supported in a stretched condition by an easily removable external one piece support member, each end of the cover being rolled back over the outside of the support. The cover and support member are mounted on an internal sleeve in the form of a longitudinally slit tube held in a state of increased diameter by a dividing strip in the shape of an I-beam. When in position over the cable joint, removal of the dividing strip longitudinally from the slit allows the inner tube to be squeezed and then freely withdrawn from the cover. The cover ends are then unrolled onto the adjacent cable sections and the external support member is removed. It will be appreciated that such an arrangement requires an inner and an outer holdout member, each of which has to be removed. EP-B-O 530 952 (3M) discloses a cover assembly in which an elastomeric tube is held out in a stretched condition on an inner support core. The core is frangible such that application thereto of a force beyond that produced by the tube causes breakage of the core so as to allow contraction of the elastomeric tube onto the substrate. The fragments of the collapsed core remain within the tube and must therefore be as small as possible to facilitate accommodation therewithin.

With each of these arrangements, the holdout member is disposed internally of the sleeve that is to be applied to the substrate cable. Thus, the sleeve cannot conveniently have an internal coating, of gel, mastic or adhesive for example, applied thereto. This problem, is avoided by the recoverable sleeve assembly disclosed in US-A-4410009 (Sigmaform), in which an inner elastomeric tube is maintained in a radially-stretched condition by having an outer rigid tube surrounding and secured to the outer surface thereof. The outer tube is a rigid thermosetting adhesive polyurethane whereby the outer tube is sufficiently adhesive to hold the inner tube in its stretched condition but will peel from the inner tube upon impact of force. US-A-4070746 (Raychem) discloses a recoverable tubular article in which an elastomeric sleeve is retained in a radially expanded condition by an outer constraint that is bonded thereto. The restraint is sufficiently strong to retain the sleeve in its expanded form under ordinary conditions of storage, but is susceptible to attack by solvents that weaken the bond sufficiently to allow the elastomeric sleeve to peel away from the restraint and to recover towards its original state. US-A-4233731 (Raychem) discloses a dimensionally-recoverable article comprising a hollow resilient member which has been expanded to a dimensionally unstable configuration in which it is retained by a keeper positioned between and separating two parts of the hollow member away from the path of recovery thereof The keeper is made from a material that weakens or changes its shape upon heating and/or chemical treatment, for example by being chemically degradable when subjected to a solvent. In one embodiment a single wedge of fusible material is interposed in the break in the circumference of a split tube of beryllium copper alloy. In another embodiment a tubular member made from an engineering plastics material has dovetailed protuberances on its outer surface between which strips of a polycarbonate are inserted to maintain the expanded configuration. EP-A0590469 (Kabelmetal) discloses a recoverable elastomeric tubular article that is held in its expanded state by thermoplastic bracing means in the form of a profile applied helically to the outer surface of the expanded tube.

It is an object of the present invention to provide a recoverable article and its method of manufacture, in which the article is held out in its expanded configuration by an advantageous external holdout means so as not to interfere with any inner layer, of gel, adhesive or mastic material for example, which may be applied internally thereof as a coating or which may be located around the substrate to be enclosed.

Thus, in accordance with one aspect of the present invention, there is provided a recoverable article comprising an inner resilient tubular member that is held in a laterally expanded configuration by engagement with outer holdout means, wherein the outer surface of the inner member is provided with a plurality of cavities, and wherein the holdout means is helically located around the inner member so as to occupy the cavities, thereby to provide the holdout engagement.

Preferably, the cavities comprise a plurality of channels that extend longitudinally of the article, preferably parallel to one another.

Preferably, the outer surface of the inner member is castellated.

In a preferred embodiment, the holdout means comprises a strip of material that has projections on one surface thereof for engaging respective ones of the cavities of the inner member. The strip may be helically wound around the inner member with the projections being trapped within successive ones of longitudinal channels in the outer surface that extend parallel to each other and to the axis of the tubular member. The backing strip and projections may be integrally formed, and thus be of the same high modulus polymeric material, or alternatively the projections may be formed of a high modulus polymeric material and the backing strip of an elastomeric material, for example to accommodate any variation in the tolerances of the arrangement of the cavities. The helix may be formed by an open winding such that successive turns are spaced apart from each other.

A simple peeling action by hand of the holdout means from one end to the other subsequently allows recovery of the inner member, under the action of its recovery forces, to, or towards, its unexpanded configuration into close conformity with the substrate to be enclosed.

The holdout means may be applied in a flowable form, such as sand or other granular material, and held in place by a wrapping of polymeric or other suitable material. The flowable material may be a hardenable, or curable, material, such as plaster of paris, cement, a curable epoxy resin system or other thermoset, which may or may not require a wrapping.

In general, however, whether or not the holdout means is flowable, it may be desirable to enclose the article of the invention within an outer sheath to enhance retention of the holdout means during storage and transport.

The holdout means may comprise foam, preferably high density foam, which may be formed in strips to fit channels in the outer surface of the inner member for example, or which may be foamed in situ to fill the expanded cavities.

The holdout means may be formed, especially when of strip configuration, of material that exhibits good resistance to compression in the transverse direction, whilst exhibiting more flexibility, or brittleness, in the longitudinal direction of the inner member, thereby to facilitate controlled removal thereof, and thus controlled recovery of the inner member. Cardboard has been found to be a suitable material, for example a material comprising composite layers of Kraft board approximately 0.9mm thick. Wooden laths, fibre board or plasterboard are also suitable materials. In the latter case, a board comprising a layer of plaster 9mm thick laminated between layers of cardboard giving an overall thickness of about 10mm has been found suitable. Such holdout means are comparatively cheap and are also bio-degradable. It is also envisaged, however, that the holdout means of the article of the invention may be polymeric, preferably bio-degradable.

The holdout means may be extruded on to the outer surface of the inner tubular member.

Advantageously, the cavities, for example the longitudinal channels, in the outer surface of the inner member are re-entrant so as to enhance retention of the holdout means.

It will be appreciated that the shaping of the cavities has to be such as to ensure that the inner member is retained in its expanded configuration under expected conditions of storage and transport to its place of application and then to be released without the need for undue force, preferably manually, when the article is to be applied to a substrate. The shaping of the interface between the inner member and the holdout means will thus depend on factors such as (i) the material of the inner tubular member and of the holdout means, in particular the relative hardness, and (ii) the force within the expanded tubular member tending to cause it to recover, which will itself depend on the material, the expansion ratio of the member, and its thickness. Thus, for example a thickwalled inner member made of highly expanded, relatively high modulus material would require a relatively greater amount of mechanical interlocking by the holdout means due to its relatively high recovery forces.

The inner member is preferably made from polymeric, preferably elastomeric material.

The inner member may form part of an enclosure for an electric cable splice, termination, or the like, and may be formed from electrically conductive material, for example for forming electrical continuity across, and/or electrical screening of, the joint. The inner tubular member may have one, or more, further layers on its inner surface, which may be co-extruded therewith. For example, an electrically insulating layer and/or an electrically stress grading polymeric layer may be co-extruded internally with the inner member. Such an additional layer may have different mechanical properties from the inner member, for example by being more resilient so as to enhance conformity with the substrate, for example a cable splice. There may also be an innermost electrically conductive layer, for example extending along only part of the length of the other layer (s), to provide a Faraday cage. An inner layer of gel, mastic or adhesive may be provided to enhance conformability and sealing, for example to exclude air and/or moisture, with the substrate. It is also envisaged that such a sealant layer may be applied separately to the substrate.

In accordance with another aspect of the present invention, there is provided a substrate, for example a cable joint, termination or elbow, enclosed by a recovered article in accordance with the said one aspect of the present invention.

In accordance with a further aspect of the present invention, there is provided a method of manufacturing a recoverable article that comprises an inner resilient tubular member and outer holdout means, wherein (a) the tubular member is provided with a plurality of cavities in its outer surface; (b) the tubular member is laterally expanded; (c) the holdout means is applied helically around and along the expanded tubular member so as to occupy the cavities; and (d) the tubular member is allowed to relax such that it is held in an expanded configuration by the holdout means.

The recoverable article manufactured by the method of the invention may have one or more of the features of the article in accordance with the said one aspect of the invention.

Recoverable articles, their methods of manufacture, and an in-line electrical cable joint, each in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is an isometric view of one embodiment of the article in its partially recovered state; Figure 2 shows one embodiment of the holdout means of the article of

Figure 1; Figure 3 shows another embodiment of the holdout means; Figure 4 is an end view of the inner tubular member of the article as extruded; Figure 5 is an end view of the expanded article of Figure 4;

Figure 6 is an end view of an alternative inner tubular member;

Figures 7 and 8 show isometric views of two further embodiments of the article; and Figure 9 is an isometric view of a recovered article forming part of an inline power cable splice.

Referring to Figures 1, 2, 4 and 5, the recoverable article comprises a tubular right cylindrical conductive elastomeric inner member 2 of relatively high modulus, that has a castellated outer surface. The outer surface defines lands 4 with twelve circumferentially equi-spaced channels 6 that extend entirely along the member 2 parallel to each other and to the longitudinal axis thereof. A holdout strip 8 of relatively high modulus polymer is wound as an open helix around and along the inner tubular member 2 when in its expanded configuration (Figure 5). The strip 8 is of rectangular section and has a series of inner generally cubic projections 10 that engage successive channels 6 as the strip is wound in an open helix around the member 2. The inner member 2 has been co-extruded with a cylindrical innermost component 12 of relatively low modulus insulating elastomer.

The coextruded composite article 2, 12 (Figure 4) is expanded on to a mandrel (not shown) to about twice its original diameter (Figure 5). In the expanded condition, the holdout strip 8 is wound thereonto with its projections 10 locking into the channels 6. The mandrel is then removed. The inwards recovery force of the elastomeric components then tends to urge the castellated bands 4 circumferentially on to the projections 10 thereby enhancing their retention and the holding out of the article 2, 12.

As shown in Figure 6, the channels 14 of the modified inner castellated member 16 with its innermost layer 18, may be made re-entrant, so as further to enhance the retention of the member 16 in its expanded configuration. The holdout strip 8 may conveniently extend beyond the end of the article 2 so as to provide a tab that can be pulled so as manually to unwind the strip out of the channels 10 thereby to allow the article 2, 12 to recover progressively from one end thereof to the other, as can be seen in Figure 1.

It is envisaged that two holdout strips may be employed, each covering part, preferably half, of the length of the recoverable article, so that recovery may take place from the centre to one end by removing one of the strips, and from the centre to the other end by removing the other strip. In some applications such an arrangement may be preferable to ensure exclusion of air from within the article as it recovers on to the substrate.

The holdout strip 8 of Figure 2 has been formed by extruding a cylindrical tube with a castellated inner surface and then performing an in-line helical cutting operation. As an alternative, the strip 18 of Figure 3 is extruded as a continuous tape that is subsequently helically wound on to the inner member. As a further alternative, the holdout strip may be extruded directly on to the inner member whilst it is held in its expanded configuration (Figure 5). An advantage of the latter embodiment is that the filling of the channels at discrete intervals is assured, without the need for close control of tolerances that is required for the preformed structures of Figures 2 and 3.

Referring to Figure 7, the castellated component 20 and the cylindrical innermost component 22 correspond to the composite article 16, 18 of the embodiment of Figure 6. The holdout strip 24 is extruded on to the expanded composite article 20, 22. In order to get a progressive installation when the holdout strip 24 is removed, the expanded article is rotated under the extruder head and then stopped. It is then moved axially a short distance and rotation continued to produce the pattern shown.

The holdout means of the embodiments so far described is released by a continuous unwinding in one sense circumferentially around the article. In some instances, however, it may be desirable, due to difficulty of access for example, not to have to unwind all the way around the article. Referring to Figure 8, the relatively hard castellated conductive inner member 20 and cylindrical insulating innermost member 22 correspond to the article of the embodiment of Figure 7. The holdout means of the embodiment of Figure 8, however, does not require a 360° movement for release of the composite article 20,22 from its expanded configuration. In this embodiment, the holdout means is extruded on to the expanded composite article in a manner similar to that of Figure 7, except that following each linear extrusion along a channel, the sense of rotation is reversed. In this way, the holdout strip 26 is subsequently removable in a to-and-fro motion and not by continuous rotation in the same sense.

Figure 9 shows an article 140, which may be in accordance with any one of the preceding embodiments, in its recovered condition on an in-line electric power cable splice. The article 140 consists of a castellated electrically conductive resilient member 142 and an innermost layer 144 of polymeric electrically insulating material. Each cable has an outer polymeric jacket 146, folded back earth screen wires 148, and primary dielectric 150. Prior to the recovery of the article 140, the region around the connector of the cable conductors (not shown) has been enclosed within a layer 152 of stress controlling material, that has been compressed into conformity with the underlying components by the recovery of the article 140, thereby excluding air from the splice region. Although not shown, it will be understood that an outer protective jacket is to be applied to the splice as shown in Figure 9 so as to encompass the article 140 and to seal on to each cable jacket 146. Electrical continuity across the joint, via the conductive layer 142, between the cable wires 148 will also be made. Advantageously, the outer protection jacket is as disclosed in British Patent Application No.9626364.5, the entire contents of which are included herein by this reference.

Claims

1. A recoverable article comprising an inner resilient tubular member that is held in a laterally expanded configuration by engagement with outer holdout means, wherein the outer surface of the inner member is provided with a plurality of cavities, and wherein the holdout means is helically located around the inner member so as to occupy the cavities, thereby to provide the holdout engagement.

2. An article according to claim 1, wherein the cavities comprise a plurality of channels that extend longitudinally of the article, preferably parallel to one another.

3. An article according to claim 2, wherein the tubular member is of substantially right-cylindrical configuration and the channels extend substantially axially thereof.

4. An article according to any one of the preceding claims, wherein the cavities are re-entrant, thereby to enhance the holding out of the inner member.

5. An article according to any one of the preceding claims, wherein the outer surface of the inner member is castellated.

6. An article according to any one of the preceding claims, wherein the holdout means comprises at least one strip of material that has projections thereon for engaging respective ones of the cavities of the inner member.

7. An article according to any one of claims 1 to 6, wherein the holdout means is applied to the inner tubular member in a flowable form and allowed to harden.

8. An article according to any one of the preceding claims, wherein the holdout means is extruded on to the inner member.

9. An article according to any one of the preceding claims, wherein the holdout means comprises:

(a) a particulate material; or

(b) a cured material; or

(c) high density foam; or

(d) compacted fibrous material; said material being retained in place by an enveloping cover, if necessary.

10. An article according to any one of the preceding claims, wherein the holdout means is releasable mechanically, preferably manually, from the inner member.

11. An article according to any one of the preceding claims, wherein the holdout means comprises form-stable, preferably bio-degradable, material.

12. An article according to claim 11 , wherein the holdout material is polymeric.

13. An article according to any one of the preceding claims, wherein the inner tubular member is electrically conductive.

14. An article according to any one of the preceding claims, wherein the inner tubular member is made from polymeric, preferably elastomeric, material.

15. An article according to any one of the preceding claims, comprising an additional, radially inner, resilient tubular arrangement on which the inner tubular member is mounted, preferably integrally therewith.

16. An article according to claim 15, wherein the additional tubular arrangement comprises at least one tubular member that is more resilient than the inner resilient tubular member.

17. An article according to claim 15 or claim 16, wherein the additional tubular arrangement comprises an electrically insulating tubular member and/or an electrically stress-controlling tubular member.

18. An article according to any one of claims 15 to 17, wherein the additional tubular arrangement is made from polymeric material.

19. An article according to any one of claims 15 to 18, comprising an innermost electrically conductive layer radially inwards of the additional tubular arrangement, and preferably located only in a longitudinally central region of the article so as to provide a Faraday cage.

20. A recoverable article substantially as hereinbefore described with reference to the accompanying drawings.

21. An elongate substrate, preferably an electrical component, including an electric cable splice, termination or elbow, enclosed by a recovered article in accordance with any one of the preceding claims.

22. A method of manufacturing a recoverable article that comprises an inner resilient tubular member and outer holdout means, wherein (a) the tubular member is provided with a plurality of cavities in its outer surface; (b) the tubular member is laterally expanded; (c) the holdout means is applied helically around and along the expanded tubular member so as to occupy the cavities; and (d) the tubular member is allowed to relax such that it is held in an expanded configuration by the holdout means.

23. A method according to claim 22, wherein the cavities comprise a plurality of channels that extend longitudinally of the tubular article, preferably parallel to one another, and the holdout means comprises at least one strip of material that has projections thereon for engaging respective ones of the channels as the strip is helically wound around the tubular member.