Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
1999-09-03
2002-01-08
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C138S106000
Reexamination Certificate
active
06337440
ABSTRACT:
BACKGROUND OF THE INVENTION
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 U.S. Pat. No. 3,515,798. 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 U.S. Pat. No. 3,824,331 (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 U.S. Pat. No. 4,410,009 (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. U.S. Pat. No. 4,070,746 (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. U.S. Pat. No. 4,233,731 (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.
SUMMARY OF THE INVENTION
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 out in a laterally expanded configuration by engagement with an outer holdout means, wherein the outer surface of the inner member is provided with a plurality of channels extending therealong and the holdout means occupies the channels so as to provide said holdout engagement, wherein the holdout engagement is arranged to be weakened mechanically without any substantial change in the molecular structural properties of the holdout means, thereby to allow recovery of the inner tubular member towards its unexpanded configuration.
Preferably, the mechanical weakening of the holdout engagement is effected by a change in shape of the holdout means.
The article of the present invention is thus arranged to recover by mechanical weakening that does not involve the application of heat or a chemical treatment, including the application of a solvent, with the advantage of simplification of installation on a substrate.
Preferably, the holdout means comprises a plurality of strips that are disposed as a tight fit in respective ones of the channels. Each strip may comprise a plurality of longitudinally spaced-apart holdout members that substantially fill its cavity at discrete positions along its length, successive holdout members of each strip being linked together. The holdout members may be integral with the links therebetween, and may be of a high modulus polymeric material. Alternatively, the links, which may be provided by a continuous backing layer for example, may be formed from an elastomeric layer and the discrete holdout members may be of a high modu
Costigan Philip
Gansbuehler George
Ions David
Lewington Sean Michael
Toerringer Josef
Myers Bigel & Sibley & Sajovec
Nguyen Chau N.
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