GB2078019A - Heat-recoverable closure device - Google Patents

Abstract

A closure device for enclosing part of an elongate bundle of electrical wires or a fibre optic bundle 2, comprises a hollow, generally tubular, dimensionally heat-recoverable body 1 having an outlet portion 5 adapted to be positioned about, and recovered onto, the bundle, and an internal surface on which a circumferentially extending reservoir of adhesive 8 is located, the internal surface having a region adjacent to the edge of the adhesive remote from the outlet portion which, at least on recovery of the body, provides an annular constriction 9 in the body, and a zone 11 adjacent to the edge of the said region remote from the adhesive which, on recovery of the body encloses a volume of greater transverse cross- sectional area than that enclosed by the constriction. The arrangement is such that, when the closure device is recovered the annular constriction 9 and outlet portion 5 will contract radially onto the bundle and the adhesive will be forced into the bundle. <IMAGE>

Description

SPECIFICATION Closure device This invention relates to closure devices for enclos ing parts of elongate bundles of wires or filaments.

Closure devices have been used extensively for enclosing wires, connections and electrical equip ment in cables and harnesses in order to insulate any bare electrical conductors, to protect the wires, connections or equipment from mechanical abuse and to prevent moisture from contacting the electrical conductors. Recently, such closure devices have been formed in an expanded, dimensionally heat recoverable configuration so that they may be positioned about the part of the cable or harness to be protected and recovered onto the cable or harness by application of heat.In order to protect the enclosed objects from ingress of moisture, the closure device may be provided with a coat of adhesive, either during manufacture or, in the case of epoxy adhesives, during application, so that a seal is formed between an outlet of the closure device and the jacket of the cable or harness.

The present invention provides a closure device for enclosing part of an elongate bundle of wires or filaments which comprises a hollow, generally tubu lar, dimensionally heat-recoverable body having an outlet portion adapted to be positioned about, and recovered onto, the bundle, and an internal surface on which a circumferentially extending reservoir of adhesive is located, the internal surface having a region adjacent to the edge of the adhesive remote from the outlet portion which, at least on recovery of the body, provides an annular constriction in the body, and a zone adjacent to the edge of the said region remote from the adhesive which, on recovery of the body encloses a volume of greater transverse cross-sectional area than that enclosed by the con striction, the arrangement being such that, when the closure device is recovered over a bundle of wires or filaments, the annular constriction and outlet portion will contract radially onto the bundle and the adhesive will be forced into the bundle.

As stated above, the body of the closure device is dimensionally heat-recoverable. Heat-recoverable articles may, for example, be produced by deform ing a dimensionally heat-stable configuration to a dimensionally heat-unstable configuration, in which case the article will assume, or tend to assume, the original heat-stable configuration on the application of heat alone.

According to one method of producing a heat recoverable article, a polymeric material is first extruded or moulded into a desired shape. The polymeric material is then cross-linked or given the properties of a cross-linked material by means of chemical cross-linking initiators or by exposure to high energy radiation, for example a high energy electron beam or atomic pile radiation. The cross linked polymeric material is heated and deformed and then locked in the deformed condition by quenching or other suitable cooling methods. The deformed material will retain its shape almost indefinitely until exposed to a temperature above its crystalline melting temperature, for example about 120 C in the case of polyethylene.Examples of heat-recoverable articles may be found in US Patent Specification No. 2,027,962 and UK Patent Specification No. 990,235, the disclosures of which are incorporated herein by reference. As is made clear in US Patent No. 2,087,962, however, the original dimensionally stable heat-stable configuration 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.

Any polymeric material to which the property of dimensional recoverability may be imparted, may be used to form the articles. Preferably the article comprises a polymeric material to which the property of dimensional recoverability has been imparted by crosslinking and deforming the material. Polymers which may be used to form the polymeric material include polyolefins such as polyethylene and ethylene copolymers for example with propylene, butene, vinyl acetate or ethyl acrylate, polyamides, polyurethanes, polyvinylchloride, polyvinylidene flouride, elastomeric materials such as those described in UK Specification No. 1,010,064 and blends such as those disclosed in UK Specifications Nos. 1,284,082 and 1,294,665, the disclosures of which are incorporated herein by reference.

Preferably the device is formed from a polyolefin or a blend of polyolefins, and especially it comprises polyethylene.

In general, the adhesive reservoir may comprise any adhesive that can be caused to flow at the recovery temperature of the closure device, for example it may be a mastic or a hot-melt adhesive, preferably a hot-melt adhesive. Examples of hotmelt adhesives that may be used include those based on polyamides, vinyl and acrylic homo- and copolymers, such as ethylene-vinyl acetate and ethylene-ethyl acrylate copolymers, polystyrene, polyesters and polyolefins. Care should be taken to match the type of adhesive with the material of the closure member used so that adequate bonding is obtained. Thus, for example, when a polyolefin is used as the material, an ethylene-vinyl acetate adhesive is suitable.Similarly, where the material for the cover is based on a segmented polyester, for example, as commercially available under the trade name "Hytrel" from DuPont, a polyester hot-melt adhesive is preferred.

The closure device according to the invention has the advantage that it can be used to protect connections, terminations or other moisture sensitive parts of wire or filament bundles from ingress of moisture when the bundle is unjacketed. This has not been possible using previously proposed closure devices since any adhesive coat on the closure would not in general penetrate the bundle and prevent moisture from travelling along the interstices between the wires or filaments. Moreover, increasing the quantity of adhesive would not necessarily cause it to penetrate the bundle since the adhesive will preferentially spread out axially along the surface of the bundle.When the closure according to the present invention is recovered onto a bundle of appropriate size, however, the annular constriction and outlet portion contract radially onto the bundle and limit the axial extent along which any substantial quantity of adhesive can flow on the surface of the bundle, thereby causing the adhesive to penetrate the bundle. In order to prevent the adhesive flowing axially along the interstices in the bundle by too great an extent and reaching any equipment, termination or connection enclosed by the closure member, a zone is provided adjacent to the edge of the construction forming region which, on recovery of the body, encloses a volume of greater transverse crosssectional area than that enclosed by the constriction, so that a space is provided between the bundle and the internal surface of the body.On recovery of the closure device about the bundle, the pressure within the space will be less than in the adhesive reservoir, and adhesive that has been forced along the bundle through the constriction will be able to move radially outwards into the space so that the axial extent of travel of the adhesive is limited.

The closure device according to the invention may in general have any configuration that is suitable for its intended use, for example it may have one or more additional outlets adapted to be recovered onto the bundle and/or one or more other outlets.

Thus the closure member may be in the form of a cap having only one outlet or, where it is intended to be used as a splice cover it may have two substantially coaxial outlets, one at each end. Where it is intended to cover a branch-out in a bundle it may have three or more outlets. The device is particularly suitable for enclosing the termination of the bundle at a connector in which case the device has two outlets, one adapted to be recovered onto the bundle and the other to be recovered onto the connector.In this case the outlets are usually located at each end of the body and may be coaxial or oriented at 90 to each other or at any angie between 90 and 180 . The device need be provided with the adhesive reservoir, constriction-forming region and adjacent zone to prevent moisture ingress only from the outlet portion to be recovered over the bundle since there will usually be a sufficiently tight fit between the connector and the outlet portion to be recovered over it to prevent ingress of moisture through that outlet.

Preferably the body has a further constriction forming region adjacent to the edge of the first space forming zone remote from the said outlet portion and optionally a further associated space forming zone adjacent to the further constriction forming region. Such an arrangement has the advantage that, on recovery of the body about the bundle, the pressure in the space defined by the further space forming zone will be less than that in the space defined by the first space forming zone, so that adhesive that does flow through the further constriction will then tend to flow radially outwards, thereby further limiting the extent of flow of the adhesive along the bundle.If desired, one or more further constriction forming regions and associated space forming zones may be provided although the provision of two such regions is usually sufficient to prevent axial flow of the adhesive to the connection or equipment.

Of course it is possible to provide a constriction forming region and associated space forming zone at the edge of the adhesive facing the outlet portion although there is usually no advantage in this since the outlet portion itself will contract onto the bundle to reduce the flow of adhesive along the bundle through the outlet and, in any case, there is no significant disadvantage if some adhesive does flow through the outlet portion. Preferably the outlet portion will be in the form of an elongate tube having a wall thickness that decreases toward the outer end in order that forces tending to bend the bundle with respect to the closure device, which may be occasioned by mishandling will be taken up by the outlet portion.In such a closure device the - increased axial length of the outlet portion will reduce the tendency of adhesive to flow out through the outlet portion.

A preferred closure device according to the invention has a shoulder region in the internal surface of the body for positioning any wide parts of the object to be enclosed, such as the edge of a connector or a cable clamp, before the device is recovered. The shoulder region is preferably substantially heatstable, that is, it is not dimensionally recoverable or is dimensionally recoverable only to a small extent so that it conforms to the corresponding part of the object to be positioned before recovery of the device.For certain devices, such as those intended to enclose the termination of a bundle at a connector, it is advantageous for the surface of the shoulder to face away from the outlet adapted to be positioned about the bundle and especially advantageous for it to be located in part of the device having a large wall thickness so that, where the bundle is provided with a clamp for protecting the connections of the wires or filaments from any load applied to the bundle, the clamp may be accommodated in the shoulder region. When the device has been recovered onto the bundle and connector, any axial load applied to the bundle will be taken up by the clamp and the connector via the wall of the closure device instead of the connections of the wires or filaments.The body may also have a region in its interval surface which, on recovery of the body, forms a second shoulder that abuts the side of the clamp remote from the said outlet portion so that the two shoulders together prevent any axial movement of the clamp.

The body of the closure device according to the.

invention may be manufactured by moulding the body in an initial configuration, that is, in the configuration that it is intended to have when recovered onto the bundle, from a crosslinkable polymeric material, crosslinking the polymeric material, deforming the body and cooling the body to retain it in its deformed configuration. The body may be formed by injection, compression or transfer moulding and is preferably crosslinked before removal from the mould by means of chemical crosslinking agents, e.g. peroxides, incorporated in the polymeric material. In addition, it may be advantageous to incorporate one or more co-curing agents such as triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, ethylene glycol dimethacrylate, trimethylol propane trimethacrylate, pen taerythritol tetramethacrylate, allyl methacrylate and vinyl methacrylate.

After the polymeric material has been crosslinked and removed from the mould, the body is expanded while hot, for example pneumatically or by sliding the body along a tapered mandrel. The adhesive may be introduced into the body in a number of ways, for example hot adhesive may be injected into the body during or after expansion of the body, or, preferably, a ring of adhesive is placed around a mandrel and the expanded body is positioned about the mandrel and adhesive and is allowed partially to recover by application of heat so that it contracts onto the adhesive.

The closure device may be used in connection with bundles of wires or filaments which are simply laid parallel to each other or are laid together helically as in a cable. The device is particularly suitable for enclosing parts of bundles of optical fibres.

Two forms of closure device according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional elevation along the axis of one form of device according to the invention after recovery onto a bundle of wires or filaments; and Figure 2 is a sectional elevation along the axis of a second form of device according to the invention after recovery onto a bundle of wires or filaments.

Referring to Figure 1 of the accompanying drawings a closure device in the form of a boot has a generally tubular body 1 that has been recovered over part of a fibre optic bundle 2. The body has an outlet 3 which is designed to be recovered over a connector or adaptor 4 of the fibre optic bundle and an outlet portion 5 adapted to be recovered over the bundle as shown in Figure 1. The outlet portion 5 has a relatively thin wall thickness which decreases in a direction away from the main body of the closure in order to spread any strain on the bundle which may be caused by bending it with respect to the closure device.

The bundle may be expected, in certain cases, to be subjected to an axial load and so is provided with a clamp 6 having spaces at its periphery through which groups 6a of the filaments pass. The body 1 has an internal shoulder 7 which has a smaller diameter than the clamp 6 so that the clamp can be accurately positioned within the body. The shoulder 7 may, in one form of the device, have a smaller diameter than that of the clamp 6 even when the body 1 is in its expanded state so that the clamp may be positioned before recovery of the body, or it may, in its expanded state, have a greater diameter than that of the clamp to allow the clamp and bundle to be inserted into the body through the outlet portion 5.

A hollow cylindrical reservoir 8 of a hot-melt adhesive is located on the internal surface of the body 1 between the shoulder 7 and the outlet portion 5. The internal surface of the body 1 is provided with a region adjacent to the edge of the reservoir remote from the outlet portion 5 which, when the body is recovered onto the bundle, forms an annular constriction 9 that contracts onto, and presses against, the bundle 2, and a zone 10 adjacent to the said region, which, on recovery of the body, does not contract onto the bundle but leaves a space 11 between the internal surface of the body and the bundle 2. As shown in Figure 1, the space 11 extends from the annular constriction 9 to the shoulder 7.

The closure device may be formed by moulding and curing a polymer blend in a configuration substantially as shown but with the annular constriction 9 and outlet portion 5 of slightly narrower internal diameter than the external diameter of the bundle intended to be covered and the moulded body is then pushed along a tapered polytetrafluoroethylene mandrel while hot to expand it, thereby flattening the constriction 9 and forming a generally cylindrical internal surface. After quenching, the body is removed and placed over a second mandrel of slightly smaller diameter about which a ring or band of adhesive has already been positioned, and the body is heated to allow it to recover onto the mandrel without melting the adhesive. The body is then quenched and removed from the mandrel.The shape of the second mandrel may be such as to allow the region of the body forming the shoulder 7 to recover fully so that the shoulder 7 of the formed closure device is not heat-recoverable.

In order to enclose the end of the bundle 2, the closure device so formed is first positioned over the bundle and adaptor 4 and moved along the bundle to expose the region of the bundle on which the clamp 6 is to be secured. After the clamp has been secured on the bundle, the device is moved along the bundle toward the adaptor until the clamp 6 abuts the shoulder 7 of the body, and the body is then recovered onto the bundle by application of heat to the outer surface of the body, for example by means of a hot air gun. As the body becomes hot the annular constriction 9 reappears and the constriction and outlet portion 5 contract onto the bundle 2. In addition, the adhesives 8 becomes soft or molten and is forced into the bundle and through the constriction by recovery of the surrounding portion of the body 1.Because the pressure in the adhesive within the bundle is greater than the pressure within the space 11, some adhesive 12 will flow radially outwards from the bundle into the space 12 where it will solidify on cooling rather than flowing axially along the bundle toward the adaptor 4 orthe clamp 6 and associated collars 6b.

In addition, when the body is recovered onto the bundle, a further constriction 7b is formed on the side of the clamp 6 opposite the shoulder 7 in order to prevent any movement of the clamp toward the outlet 3.

Figure 2 shows a modification of the closure device in which, on recovery thereof, a further annular constriction 13 is formed. The further annular constriction also contracts onto the bundle 2 when the body is recovered and divides the space 11 into two separate spaces 1 lea and 11 b. The pressure within space 11b is less than that within space 11a and so the tendency of the molten adhesive to flow along the bundle toward the adaptor is reduced.

The closure device shown in Figure 2 differs from that shown in Figure 1 also in that the constriction 7b is absent, thus allowing the installed device to be pulled back along the bundle to expose the connector 4 and clamp 6 on reheating. As will be appreciated, the provision or otherwise of the constriction 7 depends solely on whether it is desired to enable the device subsequently to be pulled away from the connector and is independent of other features of the device.

The closure device may be provided with an eyelet 14 so that a dust cap for the adaptor 4 can be retained on the device.

Claims (12)

1. A closure device for enclosing part of an elongate bundle of wires or filaments which comprises a hollow, generally tubular, dimensionally heat-recoverable body having an outlet portion adapted to be positioned about, and recovered onto, the bundle, and an internal surface on which a circumferentially extending reservoir of adhesive is located, the internal surface having a region adjacent to the edge of the adhesive remote from the outlet portion which, at least on recovery of the body, provides an annular constriction in the body, and a zone adjacent to the edge of the said region remote from the adhesive which, on recovery of the body encloses a volume of greater transverse crosssectional area than that enclosed by the constriction, the arrangement being such that, when the closure device is recovered over a bundle of wires or filaments, the annular constriction and outlet portion will contract radially onto the bundle and the adhesive will be forced into the bundle.

2. A device as claimed in claim 1, wherein the internal surface has a further region which, at least on recovery of the body, provides an annular constriction in the body, the further region being adjacent to the edge of the said zone remote from the adhesive.

3. A device as claimed in claim 1, wherein the internal surface has a plurality of regions each of which, at least on recovery of the body, provides an annular constriction in the body, and each of which being separated from the or each other such region adjacent thereto by a zone which, on recovery of the body, encloses a volume of greatertransverse cross-sectional area than that enclosed by each constriction.

4. A device as claimed in claim 2 or claim 3, wherein the internal surface has a further such zone that is separated from the adhesive by all the constriction forming regions.

5. A device as claimed in any one of claims 1 to 4, wherein the outlet portion is in the form of an elongate tube having a wall thickness that decreases toward its outer end.

6. A device as claimed in any one of claims 1 to 5, wherein the internal surface is provides with as substantially dimensionally heat-stable shoulder region.

7. A device as claimed in any one of claims 1 to 6, wherein the adhesive is a hot-melt adhesive.

8. A device as claimed in claim 7, wherein the adhesive is based on a polyamide, vinyl or acrylic homo- or copolymer, polystyrene, a polyester or a polyolefin.

9. A device as claimed in any one of claims 1 to 8, wherein the body has one or more outlets in addition to the said outlet portion.

10. A closure device substantially as described with reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.

11. A method of protecting a wire bundle and associated connector from moisture, which comprises es recovering a device as claimed in any one of claims 1 to 10 thereabout.

12. A wire bundle in which a device as claimed in any one of claims 1 to 10 has been recovered thereabout.