WO1996026566A1

WO1996026566A1 - Cable seal insert

Info

Publication number: WO1996026566A1
Application number: PCT/GB1996/000342
Authority: WO
Inventors: Jacques Brusselmans; Hendrik Graulus; Jos Vandepoel
Original assignee: Nv Raychem S.A.; Raychem Limited
Priority date: 1995-02-21
Filing date: 1996-02-14
Publication date: 1996-08-29
Also published as: AU4672096A; GB9503502D0; AR001353A1

Abstract

A cable seal insert (7) for use in sealing a cable entry in a sealed enclosure, which seal insert (7) has: i) two opposed faces (11, 12); ii) at least one aperture (15) for cable or other elongate article, said aperture (15) extending through said opposed faces (11, 12); and iii) an edge for receiving a gasket for sealing the enclosure; characterised in that: a) the two opposed faces (11, 12) are each formed from a layer of rubber (17, 18) or equivalent material; and b) the two layers of rubber (17, 18) are separated from each other by a layer of gel (19) or equivalent material.

Description

CABLE SEAL INSERT

The present invention relates to improvements in the sealing of sealed enclosures having openings for the entry of elongate articles, e.g. cables.

It is known to provide sealing enclosures comprising two substantially rigid casing members, e.g. base and cover, which are fitted together when the enclosure is formed and in which the joint between the two parts is sealed by a sealing strip in the form of an O-ring. Such enclosures are used for example to protect splices in telecommunications cables which may contain metallic conductors or optical fibres. Such enclosures must be provided with means for allowing entry of one or more cables into the enclosure, and for sealing the enclosure at the point at which the cable enters.

One way in which this has been done is to provide an opening in the wall of the base of the enclosure leading into a recess which intersects a surface of that part which abuts against a surface of the cover of the enclosure mentioned above. A rubber insert is provided with one or more central apertures into which an elongate member, e.g. a cable, can be inserted. The rubber insert is then introduced into the recess mentioned above, where it contacts the walls of the recess and corresponding parts of the cover and the gasket. The insert has a flat edge at the point at which it comes into contact with the gasket.

A slot may be provided in the insert to allow it to be opened to insert a cable laterally into the aperture.

The arrangement described above has various disadvantages, in particular it is necessary to coat the rubber insert with grease in order to obtain a seal, and the rubber insert is unable to accommodate cables over a significant range of sizes or shapes. The grease has to be applied by hand before the enclosure is assembled. It would be desirable to provide a cable sealing insert which did not, for example, require the manual application of grease before use.

According to the present invention a cable seal insert is provided for use in sealing a cable entry in a sealed enclosure, which seal insert has: i) two opposed, preferably flat, faces; ii) at least one aperture for a cable or other elongate article, said aperture extending through said opposed faces; and iii) a, preferably flat, edge for receiving a gasket for sealing the enclosure, characterised in that a) the two opposed faces are each formed from a layer of rubber or equivalent material; and b) the two layers of rubber or equivalent material are separated from each other by a layer of gel or equivalent material.

The opposed faces are formed of rubber or equivalent material. They are thus elastically deformable but differ from the gel in being harder, i.e. in having a smaller cone penetration than the gel. The rubber or equivalent material may be a natural rubber or a synthetic elastomer or similar material. It may be, for example, a thermoplastic elastomer, such as one based on styrenic or other block copolymers, or it may be an EPDM rubber. The rubber or equivalent material preferably has a Shore A hardness in the range 26-90, particularly between 60 and 80.

Preferred gels which may be used in the present invention usually contain substantial proportions of oil and it is thus desirable to select a rubber which is resistant to softening or swelling by oil.

The gel. or various different pieces of gel, may serve to form a seal to the enclosure and to the gasket, and preferably directly to the cables, and the rubber may serve to contain the gel and to store compressive energy when the enclosure is closed. That compressive energy can maintain the gel under pressure during service of the product, thereby enhancing the seal between cables and enclosure.

When a rubber gasket is used it may be necessary to stretch it slightly to fit it into place. This will generate forces tending to pull the gasket inwards, and thus away from the centre of the flat edge of the insert. It may therefore be desirable that the seal insert have a gel or other sealing material extend transversely across the middle of the flat edge to ensure that the gasket contact the gel. In order that the insert be insertable into the casing of the enclosure either way around it is preferable that the gel extend completely across the flat edge (rather than from the centre of the flat edge to one side of it).

It will be apparent that the or each aperture in the seal insert is not required to be at any geometric centre of the insert. It is sufficient that it be surrounded by the seal insert on all sides.

The cable seal insert is preferably bounded by a single curved edge in addition to the (preferably) flat (gasket) edge to correspond to recesses in the enclosure casing. However, depending on the shape of the parts of the casing intended to receive the seal insert, other shapes may be used.

The seal insert preferably has a slit extending from an edge, preferably not the flat (gasket) edge, to the central aperture to allow the insert to be opened for the lateral insertion of an elongate article e.g. a cable.

The man skilled in the art, after reading this specification, will be able to select a gel or other sealing material that is suitable for use in the seal of the invention. The material is preferably sufficiently soft that it can deform to accommodate various cable sizes and to fill any interstices that would otherwise remain. The material should additionally be resistant to water and sufficiently rugged that it be able to withstand installation and, preferably, several so-called re-entries. For most purposes we prefer that the material have a Stevens Voland hardness from of at least 50g, preferably at least 60g. Preferred maximum values are 150g, preferably 130g and we prefer the value to be between 90g and 120g. Stevens Voland hardness is measured on a Stevens LFRA Texture Analyser having a stainless steel circular spindle of diameter of about 0.64cm, the measurement being taken at a penetration of 4mm. The material preferably has elasticity, and in particular preferably has an elongation to break of at least 100%, preferably at least 200%, more preferably at least 300%.

A preferred class of materials is that of liquid-extended polymers, in particular oil-extended polymers. Preferred materials may be classified as mentioned above as gels. See US 4634207 (Debbaut), the disclosure of which is incorporated herein by reference. Gels may be thermosetting or thermoplastic.

Suitable materials for the gel can be made by gelling a curable polyurethane, a silicone or a suitable block copolymer in the presence of substantial quantities of an extender fluid that is compatible with the network polymer, such as mineral oil in the case of a block copolymer system, and/or vegetable oil and/or a plasticizer. In the present invention any of these materials can be used, but we particularly prefer a gel that comprises an extender oil with a styrene tri- block copolymer with the optional addition of di-block material. Examples therefore include ethylene propylene-styrene or other diblook copolymers and various triblock copolymers such as a styrene- ethylene-butylene-styrene (SEBS) or a styrene-ethylenepropylene-styrene or a styrene-ethylenepropylene/ethylenebutylene-styrene block copolymer extended by a mineral oil. Suitable block copolymers of these types are marketed under the Trade Marks Kraton and Septon. The amount of block copolymer, relative to the amount of oil, can be varied to achieve the desired softness. Preferred gels may contain between 5 and 25%, and more preferably between 10 and 25%, by weight of block copolymer respectively.

In some instances other materials such as soft rubbers or other elastomers may be used as alternatives to gels. Where soft rubbers are used instead of gels, they will still differ by their lower hardness values from the rubber forming the opposed faces of the seal. An advantage of gels and of rubbers is that their cohesive strength is greater than their adhesive strength to cables and other commonly encountered substrates, and as a result they can be readily and cleanly removed. Gels may however excel over rubbers in that they can be softer and can wet the substrate to be sealed and themselves when overlapped, thereby achieving a superior seal.

A preferred gel used in the present invention is distinguished from rubbers by having a relatively high cone penetration e.g. from 100-350 (lO^mm). Gels in general have higher cohesive strength than adhesive strength so that two portions of gel cohere to each other more strongly than they adhere to surfaces to which they are applied.

In use elongate articles, e.g. cables, are introduced into the apertures of the inserts. The seal inserts are then introduced into recesses in one part of the casing forming the enclosure. The second part of the casing is then attached to the first part so as to bring an O-ring or other sealing gasket between the two parts into contact with the (preferably flat) edge(s) of the sealing insert(s). The recesses into which the inserts are received, are preferably of such a size that the opposed flat faces are moved towards one another to put the gel under pressure, thereby displacing it sideways so as to form a seal to the cable, to the recesses in which the inserts are located, and to the gasket.

The invention will now be illustrated by reference to the accompanying drawings, in which:

Figure 1 is a plan view of a cable entry portion of the base of an optical fibre splice enclosure;

Figure 2 is a cross-section of the base and cover portions of the enclosure along a line corresponding to II-II of Figure 1 ; Figure 3 is a perspective view of a known cable seal insert for use with the splice enclosure;

Figure 4^' is a perspective view of a cable seal insert according to the invention; and

Figure 5 shows the effect of axial compression of the insert of the invention in producing a desired displacement of gel.

As shown in figures 1 and 2, an enclosure, e.g. for optical fibre splices comprises a base (1) and a cover (2), between which there is defined a central cavity which may contain conventional arrangements for making or organising splices between optical fibres or electrical conductors. These do not themselves form part of the invention and are not shown in the interests of clarity. Recesses in the lid receive a rubber or other gasket (3) which provides a seal between the base and cover when the base and cover are fastened together by screws (e.g. 4). The base is provided with projecting cable guides (5). These are open at the top and define a passage extending into the interior of the base to allow entry of optical fibre cables into the base. The passage is so shaped that the cables can be lowered into the passages from above. A recess (6) is provided in the base in the path of each cable passage. This recess may have a generally U-shaped base, and is shaped so as to receive the cable seal insert (7) as shown in Figure 2. The insert (7) is positioned so that its U-shaped lower part (7a) fits in the U-shaped base of the recess and so that its flat upper edge (7b) contacts gasket (3).

As shown in Figure 2 there is no cable in place in the seal insert and the central aperture is blocked by a removable insert (8).

The cover (2) is shaped so as to provide cable guide means (9) which co-operate with the cable guide means of the base to form a closed passage. The cover also has recesses shaped so as to receive the projecting parts (10) of the cable inserts of Figure 2 when they are in place in the base. The gasket (3) may be so positioned that it is in contact with the inner side (7c) of the flat edge of the cable seal insert when the cover is fixed to the base.

The cable seal insert (7) of Figures 2 and 3 is a one piece rubber moulding having opposed flat faces (11, 12) a curved edge (7a) and an upper flat edge (7b). A central aperture (15) is provided for receiving a cable. A slit (16) in the insert may extend from the curved edge (11) to the central aperture (15) and allows the insert to be opened along the line of the split for the lateral insertion of a cable into the aperture.

The cable seal insert according to the invention is shown in Figure 4. The two opposed faces (11, 12) are formed from layers of rubber or equivalent material ill, 18). A layer of gel (19) lies between the rubber (17, 18). An aperture (15) of substantially uniform cross-section extends through each face (11, 12) and through the layer of gel (19). Portions of the rubber layers may be cut away at the middle of the top flat edges and the cutaway portions filled with gel (20, 21). A slit (16) may join the central aperture (15) to the outside curved edge (11). When the insert is placed in the recess provided in the base the opposed end faces are pressed together thereby putting the gel under pressure, so helping to seal the cable entry aperture (15). When the cover is placed over the base the rubber gasket sealing the joint between the base and cover will be over the gel either along the centre of the insert or in the cut-away middle portion of the rubber layer, so helping to give a good seal.

The gels or equivalent material can be seen to extend to the external edges of the insert around its entire periphery (although some of the periphery is hidden from view). As a result, the gel can form a continuous uninterrupted seal around the whole of the insert. Also, the gel can be seen to extend inwardly to the cavity (15), and as a result form a seal completely around a cable within the insert. This allows a gel seal (or equivalent) to be formed between the cable and the enclosure into which the seal insert is positioned. As the seal insert is pushed into a recess in an outlet of the enclosure, it may be axially compressed (as shown in Figure 5) due to the two rubber layers being forced together, depending on the relative dimensions of the recess and the insert. This deforms the gel (or equivalent) radially inwards and outwards, producing beads 22, 23 respectively, forcing it against the cable and the outlet of the enclosure. For clarity, figure 5 shows the axially compressed seal insert without cable or enclosure. Because of the ability of the gel to be deformed or displaced in this way, the seal insert of the invention is able to accommodate and seal cables over a wide range of sizes and cross- sectional shape.

Claims

1. A cable seal insert for use in sealing a cable entry in a sealed enclosure, which seal insert has: i) two opposed faces; ii) at least one aperture for a cable or other elongate article, said aperture extending through said opposed faces; and iii) an edge for receiving a gasket for sealing the enclosure; characterised in that: a) the two opposed faces are each formed from a layer of rubber or equivalent material; and b) the two layers of rubber are separated from each other by a layer of gel or equivalent material.

2. The cable seal insert according to claim 1 wherein the rubber or equivalent has a Shore A hardness of 26 to 90.

3. The cable seal insert according to Claim 1 or Claim 2, wherein the two opposed faces are substantially flat.

4. The cable seal insert according to any preceding claim, wherein the edge for receiving the gasket is substantially flat.

5. The cable seal insert according to Claim 4, wherein the insert is bounded by a single curved edge in addition to the substantially flat edge.

6. The cable seal insert according to any one of the preceding claims wherein a slit extends from an edge to the or each aperture to allow the insert to be opened for lateral insertion of a cable or other elongate article.

7. The cable seal insert according to any one of the preceding claims wherein the gel has one or more of: a cone penetration of from 100-350 (10^" mm); an ultimate elongation of at least 200%: and a Stevens Voland hardness from 60g to 130g.

8. An enclosure comprising a substantially rigid casing comprising a base and cover sealed together in use by a gasket, and having means for allowing entry of at least one cable to the enclosure, and wherein the or each cable entry means is sealed in use by a cable seal insert received in a recess in the casing and abutting against the gasket sealing between the base and cover, characterised in that the insert is an insert according to any one of claims 1 to 7.