AU1772892A - Cable sealing - Google Patents

Description

CABLE SEALING

The present invention relates to a cable seal, and in particular to a telecommunications cable splice case.

Cable splice cases have the following function. Where a cable splice is to be made, cable jackets have to be stripped back from the cable ends in order to connect the internal conductors. Once the conductors have been connected, the environmental protection previously provided by the cable jacket has to be made good across the splice in order to prevent corrosion or other damage of the conductors and connectors. This is done by building a so-called splice case across the splice from intact cable jacket of the incoming cable to intact cable jacket of the outgoing cable.

For many years now such cable splice cases have been made by positioning a heat-shrinkable sleeve, internally-coated with a hot- melt adhesive, around the splice, and heating it. Heat causes the adhesive to become activated and the sleeve to shrink into tight engagement around the incoming and outgoing cables. The heat- shrunk sleeve is quite strong and stiff and provides good mechanical strength between the cables. That is important since axial pull along the cables, bending of the cables, and vibration etc. are all likely to arise during service of the cable, and these loads must not be carried by the internal conductors and connectors. It can be seen that the axial loads will be carried across the splice from jacket to jacket by the sleeve. A further point, of course, is that the environmental seal provided by the splice case must remain intact in spite of these mechanical forces acting on the cables. Splice cases are tested, for example, for axial load strength and the requirements are quite severe. For a splice between pressurized cables a typical test is carried out over a temperature range from -15 to 45 °C with an internal pressurization of 70 Kpa with the cables axially loaded to 1000N. The splice must remain pressure tight after 24 hours. A disadvantage of heat-shrinkable sleeves, however, is that an open-flame torch is generally needed to install them and they can be difficult to re-enter (by which is meant removal of the splice case to gain access to the splice without damaging the splice). Effort has recently been directed towards designing a splice case that avoids the need either to heat-shrink a sleeve or to heat-activate an adhesive.

WO90/05401 (Raychem) discloses a splice case that does not require heat for installation, and that as a result is easy to re-enter. Sealing is, in its preferred embodiments, provided by a gel, in particular one having an elongation of at least 100% and a compression set at 70°C of less than 30%. The sealing material is put under compression to seal an annular gap between the cables to be sealed and a surrounding housing.

A disadvantage under some conditions is that the gel does not have the strength to provide the overall splice case with certain mechanical properties such as axial pull strength.

Provision is therefore made in the splice case of WO 90/05401 to provide a mechanical connection across the splice. Armour or other strength member of the cables is secured to a flange (illustrated in the present figure 2) by securing means such as a bolt.

Various other known means of providing mechanical strength may be mentioned. US 3663740 (Deltett) discloses a splice case for use on several different types of sheathed or armoured telephone cables. The case includes grippers for securely anchoring the sheaths of the cables to prevent tension loads damaging the splice. An exterior of the gripper is provided with an annular groove which mates with a part of the case to prevent relative axial movement. The gripper is formed of two mating halves, and an epoxy material is injected to fill a space between them, thereby securing the gripper to the cable.

US 4262167 (3M) discloses a cable splice case for communications cables, comprising a two part outer shell, divided perforate end plates and a cable collar for each cable end. The cable collar is grooved to receive an end plate gasket. A preferred form of collar is in two parts and fits together over a mastic winding between two washers on the cable to form a hermetically sealed cable end structure. Strain relief is supplied by means of reinforced braces, two or more of which are to be uniformly spaced and strapped to the cable end inwardly of the end plates. The braces grip the outer cable sheath with extended tangs and are held in place by a hose clamp. Uprights of the braces abut against the ends of the cable collars as they extend through end plates within the case.

In US2771502 (Bell Telephone Laboratories) cable jackets at a splice are longitudinally slit and peeled back to provide tabs that are clamped between end plates.

The use of hose clamps securing cables to flanges of splice case end pieces is disclosed in DE 3536598 (Siemens).

We have now devised an improved technique for providing axial pull strength that can avoid problems of the prior art; for example in preferred embodiments it avoids the need for epoxy bonding, metal parts such as hose clamps, and for splitting of cable jackets. In particular, we have devised a clamp that can be self- tightening.

Thus, the invention provides a device for providing an environmental seal around a cable, which comprises:

(a) a structural member that can surround the cable, (b) a sealing material that can seal a gap between the cable and the structural member, and

(c) means for transmitting axial load on the cable to the structural member, the means (c) comprising:

(i) a first part that can abut the structural member,

(ii) a second part that can be fixed to the cable, and

(iii) a third part that can provide a flexible connection between the first and second parts and/or that can cause self-tightening of the means (c) onto the cable in response to axial load on the cable.

The invention also provides a device for providing an environmental seal around a cable, which comprises:

(a) a structural member that can surround the cable,

(b) a sealing material that can seal a gap between the cable and the structural member, and

(c) means for transmitting axial load on the cable to the structural member, the means (c) comprising:

(i) a first part that can abut the structural member,

(ii) a second part that can be fixed to the cable, and

(iii) a substantially frusto-conical third part that tapers from the first part to the second part.

The invention further provides means for transmitting axial cable load, comprising (i) a first part that can abut an end piece of a splice case;

(ii) a second part that can be fixed to a cable; and

(iii) a third part that can provide a flexible and/or substantially frusto-conical connection between the first and second parts and/or can provide self-tightening between the second part and the cable on axial movement of the cable relative to the first part.

The device of the invention is preferably used to form at least part of a cable splice case. In particular, an assembly may be provided for forming a cable splice, which comprises:

(i) a first device of the invention,

(ii) a second device of the invention, and

(iii) a cover, preferably of wraparound design, having two open ends within each of which can be positioned respectively the first and second devices.

In this way, an in-line splice case can be made. Either or each of the first and second devices may accommodate more than one cable in order that a branched cable splice be sealed.

A butt splice can be sealed in a similar way. Here a single device of the invention can be used at an open end of a cover (preferably dome shaped) having a single open end.

We prefer that the third part of the means (c) be flexible and be deformed by axial movement of the cable relative to the structural member that causes the second part to move towards the first part. The device is preferably arranged so that such cable movement results from tension pulling the cable out of a splice case. This device could, however, be arranged to resist pushing of a cable into a splice case. Also, a single device could be designed to resist forces in each direction, or two devices could be used one resisting force in one direction, and the other resisting force in the other direction.

As mentioned above, the device may be self-tightening. For example, deformation of the third part may bring a part of means (c), generally the second part, towards the cable. This may arise through the second part having a substantially frusto-conical shape or otherwise being tapered. The smaller end is fixed to the cable, and as the cable moves, the smaller end is forced towards the large end causing the tapered surfaces to buckle inwardly and grip the cable. The smaller end may be fixed to the cable by any suitable means. It may itself grip the cable, or some fixing means such as a hose clamp or a tie wrap may be used. A preferred tie wrap has an eye at one end through which the other end passes, and a saw tooth surface such that it self-locks.

The means (c) preferably comprises a plastics material, especially polypropylene, and it preferably contains no metal. The three functional parts referred to above are preferably mutually integral. '

Its precise shape is not critical but we prefer that it be substantially frusto-conical, optionally with substantially cylindrical extensions at each end. References herein to frusto-conical and cylindrical refer not only to complete surfaces but also to frames whose envelopes have those shapes. In fact, we prefer that the third part of the means (c) comprises legs that extend from a collar (the first part) and that can be bent inwardly to form the desired taper. We prefer four or more such legs circumferentially-spaced around the collar. The device is preferably of wrap-around design, allowing it to be installed around a cable without access to a free end of the cable. In the above example, the collar may be longitudinally slit, allowing it to be opened, and re-closed around the cable. The slit may double- back on its path across the collar so that mere circumferential tension in the collar does not open it; some relative longitudinal displacement either side of the slit being necessary. Other means of interlocking may, however, be employed, including those requiring additional parts.

Interlocking may also be provided between the first part of the means (c) and the structural member. This may be provided for ease of installation and/or to restrict movement of means (c) away from as well as towards the structural member.

Both a structural member and a sealing material are required for environmental sealing because, of course, neither can do the job alone: the structural member can not itself reliably seal to the cable without difficulties in installation and close tolerances in manufacture, and a sealing material does not have the strength to provide an entire splice closure. We prefer that the structural member (which may comprise two or more parts) not only provides some of the closure, but also serves to retain, and if need be deform by pressurizing efc, the sealing material.

In particular we prefer that the structural member be at least partially hollow, the sealing material being provided partially within the hollow and partially extending from it to seal any gap between the member and the cable.

Means (d) (which may be provided by the structural member) may be provided for putting the sealing material under compression thereby forcing it towards the cable and/or the structural member. This may comprise first and second end pieces: that face one another; between which the sealing material can be positioned; having respective holes through each of which the cable can pass; and that can be moved towards one another by said means (d).

The first and second end pieces may additionally be driven towards one another by some means such as one or more bolts, optionally fitted with a coil or other spring such that a substantially constant compressive force on the sealing material remains notwithstanding slight displacement of the sealing material.

The structural member or the end pieces that comprise it may comprise simple plates with holes for the cables, or they may have more complex construction. In particular, they are preferably of wrap-around design. For example, the structural member may comprise an inner part and one or more outer parts that can form at least part of an annulus around the inner part, leaving between them a hole through which the cable can pass. A recess may be defined by the inner and outer parts within which can be received the first part of means (c).

The first part of means (c) will in general have a larger cross- sectional size than that of a hole in the structural part. It could, however, be smaller and some catch be provided to prevent it passing entirely through the structural part. It may of course be located within a hole in the part, particularly within a tapered hole or a hole with a step-wise change in cross-section.

The sealing material preferably comprises a gel. We prefer a liquid-extended polymer composition preferably having a cone penetration value (measured by a version of ASTM D217) within the range from 30-400 (10" ^ mm); an ultimate elongation (measured by ASTM D412) greater than 100% with substantial elastic deformation to an elongation of at least 100%. Two or more gels or other materials of different properties may be used together, for example a softer gel to provide a seal and a harder gel to locate the softer gel and to apply pressure to it.

Gels may be made from a variety of materials, for example oil extended polyurethanes or from silicones. We prefer, however, oil- extended block copolymers. Reference may be made to US 3676387 (Lindlof), US 3827999 (Crossland), US 4176240 (Sabia), US 4369284 (Chen), and WO 88/00603 (Raychem).

Useful compositions may be made comprising at least 400, preferably at least 500, more preferably at least 700, especially 650- 750 parts by weight of an extender liquid such as a plasticizing oil per 100 parts by weight of a block copolymer. Preferred block copolymers comprise hard and elastomeric blocks, and suitable polymers comprise styrene - ethylenebutylene - styrene tri-block copolymers. Suitable examples are marketed by Shell under its trademark Kraton, in particular Kraton G1651. Other block copolymers may be used, and in general we prefer a polymer having hard and elastomeric blocks and having a molecular weight from 250,000 to 270,000. Further details of preferred materials may be obtained from WO 90/05401 (Raychem), the disclosure of which is incorporated herein by reference.

The invention is further illustrated with reference to the accompanying drawings in which

Figure 1 shows a prior art splice case;

Figure 2 shows a prior art means for transmitting axial load;

Figure 3 shows a new means for transmitting axial load;

Figure 4 shows the means of Figure 3 installed in a splice case; Figure 5 shows a wrap-around version of the means of Figure

3;

Figures 6A, 6B and 6C show installation and use of the means of Figure 3; and

Figure 7 shows several means for transmitting axial load moulded as an integral piece.

Figures 1 and 2 illustrate the prior art and are taken from WO 90/05401 (Raychem).

In Figure 1 a splice case 1 has been installed around a splice 2 between telecommunications cables 3. Seals at each end of the splice case are formed from a structural member 4 and a sealing material 5, such as a gel. The structural member may comprise first and second end pieces 6, 7 between which is positioned a sealing material. These end pieces may be brought together by a bolt 8 carrying a spring. The seals at each end of the splice case are bridged by a central part 9.

Figure 2 shows a means 10 for transmitting axial load from cables 3 to a structural member 4, such as that illustrated in Figure 1. The means 10 comprises a flange 11 that is bolted to the structural member 4, together with hose clamps 12 that are tightened around the cables and in turn connected to the flange 11. In this way axial load on the cables of Figure 1 can be transmitted through the splice case rather than through the conductors and connectors of the splice.

A new means 10 for transmitting axial cable load is illustrated in Figure 3. It is easy to install and need not require modification (such as the provision of threaded screw holes) of a structural member with which it is used. It comprises a first part 13, preferably in the form of a collar, second part 14, preferably in the form of legs, that can be fixed to a cable (for example with a tie wrap), and a third part 15 that can provide a flexible connection between the first and second parts. Preferably the third part can cause self-tightening of the means 10 onto the cable. The means 10 preferably comprises polypropylene, and it is preferably resiliently deformable so that deformation produced by axial cable pull is reversed when the cable is relaxed. Means 10 can therefore be reusable.

Figure 4 shows the means 10 installed at an end seal of the splice case of Figure 1. A tie wrap is used to hold the first parts 14 against the cable 3, but it is omitted from the drawing for clarity._. The first part 13 can be seen to have a larger cross-sectional size than a hole in the structural member through which the cable 3 passes.

Where means 10 is to be used on a splice case end seal carrying more than one cable, as at the right hand side of Figure 1, further features may be desirable. The structural part of the right hand end seal of Figure 1 may comprise an inner part and an outer annulus that surrounds it, a hole for the cable being provided between the inner part and the annulus. The edge of the annulus may be recessed relative to that of the inner part (or vice versa), and the first part 13 of means 10 may have an extension part way around its circumference to match such a recess. The means 10 of Figure 3 has such an extension.

The means 10 is preferably of wrap-around design in order that it be installable around a cable without access to the cable end. Preferably the first part 13 has means for locking the part 13 in the wrapped around configuration, and an example of such means is illustrated as interlocking projections 16 in Figure 5.

Means 10 is shown being installed and resisting axial cable pull in Figures 6 A, 6B and 6C. In Figure 6 A means 10 has been positioned around cable 3. The second part 15 can be seen to have a roughened, adhesive, or serrated surface 17 to aid fixing to the cables. In Figure 6B, the second parts 15 have been secured to the cable by means of a tie wrap 18.

The cable is then subjected to axial pull as shown by the arrow 19. The third parts 14 can deform as shown by the arrows 20 in Figure 6C to cause the means 10 to self -tighten onto the cable. It may be preferable for the legs (the third part) to be stiff, at least relative to a join region between them and the first part and/or between them and the second part. Thus, a living hinge or other means of pivoting, provided for example by a line of weakness, may be provided between the third part and either of both of the other parts. In this way, axial loads could be transmitted without significant bending if desired. A self-tightening action could still result.

The means for transmitting axial load illustrated in figure 7 can be bent, folded or otherwise deformed to deal with four cables. Similar means may be made for other numbers of cables such as 2, 3, 5 or 6. The means may comprise a backbone 21 and several first parts 22 that can abut or engage a structural member, several second parts 15 that can engage a cable, and several third parts 14 that can deform. The second parts may have serrations or other deformations that extend in each of two directions to allow the means to transmit axial load in each of those two directions.

Claims (23)

1. A device for providing an environmental seal around a cable, which comprises:

(a) a structural member that can surround the cable,

(b) a sealing material that can seal a gap between the cable and the structural member, and

(c) means for transmitting axial load on the cable to the structural member, the means (c) comprising:

(i) a first part that can abut the structural member,

(ii) a second part that can be fixed to the cable, and

(iii) a third part that can provide a flexible connection between the first and second parts and/or that can cause self-tightening of the means (c) onto the cable in response to axial load on the cable.

2. A device for providing an environmental seal around a cable, which comprises:

(a) a structural member that can surround the cable,

(b) a sealing material that can seal a gap between the cable and the structural member, and

(c) means for transmitting axial load on the cable to the structural member, the means (c) comprising:

(i) a first part that can abut the structural member, (ii) a second part that can be fixed to the cable, and

(iii) a substantially frusto-conical third part that tapers from the first part to the second part.

3. A device according to claim 1 or 2, in which the third part is flexible and is deformed by axial movement of the cable relative to the structural member that causes the second part to move towards the first part.

4. A device according to claim 3, in which the deformation brings a part of the means (c) towards the cable, the relative movement of the cable thereby causing tightening of the means (c) onto the cable.

5. A device according to any preceding claim, in which the third part comprises two or more legs circumferentially spaced around the cable.

6. A device according to any preceding claim, in which the first, second and third parts are mutually integral.

7. A device according to any preceding claim, in which means (c) is of wrap-around form.

8. A device according to claim 7, in which longitudinal edges of means (c) can be mutually interlocked to secure means (c) in a wrapped-around form.

9. A device according to any preceding claim, in which means (c) additionally comprises:

(iv) fixing means for fixing the second part to the cable.

10. A device according to claim 9, in which the fixing means (2) comprises a tie wrap or a hose clamp.

1 1. A device according to any preceding claim, in which the first part and the structural member can mutually interlock, thereby restricting movement of means (c) towards and away from the structural member.

12. A device according to any preceding claim, in which the structural member is at least partially hollow, the sealing material being provided partially within said hollow and partially extending from it to seal said gap.

13. A device according to any preceding claim, which additionally comprises:

(d) means for putting the sealing material under compression thereby forcing it towards the cable and/or towards the structural member.

14. A device according to claim 13, in which the structural member comprises first and second end pieces:

that face one other; between which the sealing material can be positioned, having respective holes through each of which the cable can pass; and that can be moved towards one another by said means (d).

15. A device according to any preceding claim, in which the structural member comprises an inner part and one or more outer parts that can form at least part of an annulus around the inner part, leaving between them a hole through which the cable can pass.

16. A device according to claim 15, in which the first part of means (c) can be received in a recess defined by the inner and outer parts.

17. A device according to claim 14, 15 or 16, in which the first part of means (c) has a cross-sectional size greater than that of a hole in the structural part.

18. A device according to any preceding claim, in which the sealing material comprises a gel.

19. An assembly for forming a cable splice case, which comprises:

(i) a device according to any preceding claim; and

(ii) a cover having an open end within which can be positioned the device (i).

20. An assembly for forming a cable splice case, which comprises:

(i) a first device according to any preceding claim;

(ii) a second device according to any preceding claim;

(iii) a cover having two open ends within which can be positioned respectively the first and second devices (i) and (ii).

21. An assembly according to claim 19 or 20, in which the means (c) is positioned at the side of a structural member remote from the end of the cover at which the structural member is positioned, such that axial movement of the cable out of the cover is restricted.

22. An assembly according to claim 21, in which the structural member comprises first and second end pieces that face one another and between which the sealing member is positioned; the means (c) being positioned at the side of the end piece remote from the end of the cover at which the structural member is positioned, such that axial movement of the cable out of the cover tends to move the end pieces toward one another causing the sealing material to be compressed.

23. A means for transmitting axial cable load, comprising:

(i) a first part that can abut an end piece of the splice case;

(ii) a second part that can be fixed to a cable, and

(iii) a third part that can provide a flexible and/or substantially frusto-conical connection between the first and second parts and/or can provide self-tightening between the second part and the cable on axial movement of the cable relative to the first part.