GB2056191A - Improvements in, or relating to, cable seals - Google Patents

Abstract

A method for sealing one or more cable cores to a sheath around the core or cores, or to a cable gland or other fitting, comprises filling a space defined between the core or cores, the cable sheath, and/or cable gland or other fitting, with a hardenable or curable compound (12) which has a low shrink characteristic on hardening or curing. <IMAGE>

Description

SPECIFICATION Improvements in, or relating to, cable seals This invention relates to the sealing of cable cores to a sheath around the cable in order to prevent gases or liquids, which may be dangerous, from passing into the cable at a termination of the cable. The invention finds particular application in flame-proof glands for cables, where the gases may be combustion or explosion products.

When sheathed cables which do not have full moulded cores, and thus have spaces between the conductor elements and other structural elements and the cable sheath, are terminated, for instance in flame-proof or water-proof glands, there is the possibility of communication through the gland and the spaces in the cable structure between a casing or other space to which the gland is attached and the exterior of the cable sheath, either through failure of the sheath in the case of a flame-proof gland in an explosion, or through a leak in the sheath in the case of a water-proof gland.

Previous known techniques have involved placing a specially adapted gland around the termination of the cable where the core is to be sealed to the sheath, and surrounding the end of the cable sheath and the individual conductors which may be projecting from the sheath at the termination with a hardenable or curable compound. The gland has been so desiged that before the compound hardens or cures it can be subjected to pressure. The subjection to pressure has been necessary as the compounds used for sealing the cable core undergo a considerable shrinkage when they harden or cure and thus, if they are not subjected to pressure do not adequately seal either to the cable core or to the gland body.Again, the compounds have been highly viscous in their raw state, and the subjection to pressure has been necessary to ensure that the compound enters all the interstices between the structure of the cable.

These known techniques require the use of a specially adapted gland whenever a cable core is to be so sealed. Accordingiy, it is an object of the present invention to provide a method which can be used to seal a cable core without the need for subjection to pressure. It is a further object of the invention to provide a method which can be used to seal cable cores with conventionai glands secured to them.

According to one aspect of the present invention a method for sealing a cable comprises filling a space defined between the exposed cable cores, the cable sheath and optionally a body such as a gland containing the cable with a hardenable compound which has a low shrink characteristic on hardening.

Preferably the compound is such that in its raw state it is sufficiently viscous to be easily applicable to the cable cores and sheath for instance with a spatula, and as a stage in its hardening or curing becomes less viscous so as to run more easily into the interstices between the cable structure elements, the body and the sheath.

Preferably the compound has a high resistance to pressure when hardened or cured so as to resist gas pressures during an explosion thus rendering the cable termination-flame-proof.

Preferably the compound has a high resistance to water absorption so as to render the cable termination suitable for under water applications.

Preferably the compound is an epoxy compound of the class which inciudes the semiflexible epoxy compound of putty like consistency manufactured and sold by Devcon Limited of Theale, Berkshire, under the Trade name "Devcon U.W." According to a further aspect the invention provides a cable termination sealed in accordance with any one of the above methods embodying the invention.

In order to promote a fuller understanding of the above, and other, aspects of the invention some embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a section through a gland and cable core according to the invention; Figure 2 is a section similar to Figure 1 with a single wire armour cable attached to the gland; Figure 3 is a section similar to Figure 1 with a wire braided armour cable attached to the gland, the gland and the cable having both an inner and an outer seal; Figure 4 is a section similar to Figure 2 including both an inner and an outer seal between the gland and the cable; Figure 5 is a section similar to Figure 4 including a metallic earth continuity diaphragm;; Figure 6 is a view giving details of the diaphragm of Figure 5 in its free state before assembly; Figure 7 shows the filling of a gland in an inverted position.

Figure 8 shows a water-proof gland embodying the invention.

Figure 9 shows a variation of the embodiments of Figure 4, and Figures 10 and 11 show variations of the embodiment of Figure 1.

In the gland cable termination shown in Figure 1, a cable 1 is attached to a gland 2 which is secured to an enclosure 3. The cable 1 has a elastomeric sheath 4 which surrounds a series of cores 5 and it is the space between the end of the sheath 4 and the protruding cores 5 which is required to be sealed.

The assembly of the device is as follows: the cable 1 is prepared by cutting back the sheath 4 at the required location to expose the cores 5.

The gland 2 which may be of known or conventional design per se, is then attached to the cable 1 by means of a compression nut 6 threadably engaging a body member 7 so that a seal 8 is compressed in the body member 7 to grip the sheath 4. A skid washer 9 may be interposed between the nut 6 and the seal 8. A sleeve portion 10 of the body 7, which is externally threaded for attachment to the enclosure 3, defines a chamber which encloses the end of the sheath 4 and the exposed cores 5. The chamber encloses approximately equal lengths of sheath 4 and exposed cores 5.The inner surface of the sleeve portion 10 and the portion of the seal 8, defining an end to the chamber, are coated as indicated at 11 with a release agent in the form of a silicon grease 1 A compound 12 is then inserted into the chamber such that it more than fills the chamber and completely surrounds those portions of the sheath 4 and cores 5 located in the chamber The compound 12 is a hardenable or curable compound which is inserted into the chamber in its raw or unhardened or cured state.

When the compound has hardened the gland 2 is ready for attachment to the enclosure 3 by means of threadably engageable portions on the sleeve portion 10 and the enclosure 4. An earth tag 13 may be used between the body 7 and the enclosure 3.

The silicon grease release agent is provided in the sleeve portion 10 and seal 8 in order that the cable 1 may be removed from the gland 2 with the compound attached to it, thus avoiding destruction of the seal which it effects.

In the embodiment shown in Figure 2 the cable 1 a is a single layer wire armour cable, the wire armour 14 being held in the gland 2a by means of an armour clamp ring 15, in known mannerperse.

Figure 3 shows a wire braided armour cable 1 b secured in a gland 2b, the wire braiding 1 6 being held in the gland 2b by means of an armour clamp ring 17. In this embodiment an outer seal 18 is provided in addition to the seal 8, such that an outer sheath covering the wire braiding 16 6 is also sealed to the gland.

Figure 4 shows the arrangement of a gland 2c, similar to gland 2b, which acts to retain a single layer wire armoured cable 1 a and provide the two seals 8 and 18 of Figure 3.

Figure 5 shows the arrangement of a gland similar to that of Figure 4 but incorporating a metallic earth continuity diaphragm 1 9 between the seal 8 and the compression nut 6. The continuity diaphragm is shown in more detail in Figure 6. The diaphragm 1 9 acts to provide earth continuity between the gland body and the sheath 20 of the cable, which in this instance is a metallic sheath, surrounding the cores 5.

In each of the embodiments shown in Figures 2 to 5, the space in the sleeve portion 10 of the body is filled with compound as discussed with reference to Figure 1.

The material of the compound 12 preferably has a very low shrinkage characteristic as it hardens or cures so that in the finished termination there is a minimum space between the compound and the sleeve portion 10. The material should also be self-curing whether it is surrounded by air, oil or water for example, and should be capable of withstanding high constant pressures. The compound should also be resistant to chemicals and petro-chemicals and vapours of petro-chemicals.

By using a compound with suitable characteristics it is possible to render the termination of the cable flame-proof so that when the gland is constructed to meet the requirements of a flame-proof device, the entire assembly may be accepted as flame-proof. By using a compound with suitable characteristics it is possible to render the termination of the cable water-proof so that when the gland is constructed to be water-proof the entire assembly can be water-proof, even when an external portion of the cable sheath has a leak in it.

The compound is preferably an epoxy resin compound which is curable on the addition of a catalyst, and is preferably sufficiently viscous in its raw state that it can be applied to the termination with a spatula while becoming less viscous with time before curing to a hard semi-flexible body, so that while less viscous it can run into the interstices between the cores of the cable and between them and the sheath of the cable to effect a complete seal. The compound is preferably one of the class of compounds which includes the epoxy compound sold by Devcon Limited under the Trade name or Trade Mark "Devcon U.W." which is in its raw state a putty like compound.

The glands of Figures 1 to 5 are preferably filied with compound while the cable is in place and assembled in the gland, with the gland sleeve portion 10 facing upwards. In the alternative, the compound may be placed in the sleeve portion 10 when it is facing downwards with the cable in place and the remainder of the gland components assembled to the body after the compound has been placed. In this last arrangement the cores 5 may be bound as shown at 21 in Figure 7 to prevent the compound from running downwards out of the sleeve portion 10 before it has cured.

When any of the glands of Figures 1 to 5 are to be used as water-proof glands, an external heat shrinkable sheath may be applied as indicated at 22 in Figure 8. The sheath 22 may be internally coated with a sealing compound before it is applied.

Figure 9 shows an arrangement similar to that of Figure 4 above. In the arrangement of Figure 9 the seal ring 8 has been omitted while the skid washer 9 has been retained. In this arrangement the compound 12 is made to fill the space which would have been occupied by the seal ring 8; and the threaded sleeve 24 on which the armour of the cable is gripped by means of the clamp ring 14 in a similar manner to the previous embodiments, is used to limit the spread of compound 12 as it is put in position around the cable cores 5. The sleeve 24 is then tightened onto the compound 12 after it has cured to grip it and retain the cable in the gland. The cable sheath 4 is, in this arrangement, stripped back at least to a point generally in line with the inner edge of the sleeve 24, and preferably further as shown in the Figure 9. The compound 12 is preferably chosen to be of a type which will adhere to the cable cores indicated at 4 so that in the finished arrangement the cable is retained in the gland at least in part through the medium of the cured compound 12.

The inner bore of the gland body 7 is treated with silicon grease before the compound 12 is placed in position to prevent the compound 12 adhering to the body. The frusto-conical seat 25 in the body of the gland into which the seal ring 9 would have been driven on tightening of the sleeve 24, serves to seal against the corresponding frusto-conical surface on the plug formed by the compound 12 after it is cured. This provides a pressure tight seal around the periphery of the plug, and this may optionaliy be enhanced by the provision of an 0 ring indicated at 26.

If desired, the skid ring 9 may be omitted in the arrangement of Figure 9. The other embodiments discussed above may be utilised in a similar manner to that discussed with regard Figure 9 by the omission of the seal ring 9 and or the skid washer 9. The material used for the compound 12 is preferably a two part epoxy resin putty which has the property of adhesion to synthetic plastics materials and/or rubber materials such as will be used as insulating material around the cores of the cable.

Figure 10 shows a further arrangement of a gland similar to that shown in Figure 1 only adapted for a wire armoured cable, in which the gland 7 is screwed into a flanged sleeve 50 for attachment to the wall 51 of an equipment compartment. In such an arrangement the compound 12 may adhere directly to the gland body 7 and the silicon grease need not in this case be applied. Figure 11 shows a further similar arrangement in which the gland body 7 is screwed into a screw threaded shouldered sleeve 52 which is retained in an aperture in a wall 51 by means of lock nuts 53. Again the compound 12 may adhere to the gland body 7.

Claims (10)

1. A method for sealing one or more cable cars to a sheath around the core or cores, or to a cable gland or other fitting, comprising filling a space defined between the core or cores, the cable sheath, and/or a cable gland or other fitting, with a hardenable or curable compound which has a low shrink characteristic on hardening or curing.

2. A method as claimed in Claim 1, in which the compound is such that in its raw state it is viscous, and becomes less viscous before hardening or curing.

3. A method as claimed in Claim 1 or 2 in which the compound is such that, when hardened or cured, it will resist the gases of an explosion.

4. A method as claimed in Claim 1, 2 or 3, in which the compound is such that, when hardened or cured, it is impervious to water.

5. A method for sealing one or more cable cores to a sheath around the core or cores, or to a cable gland or other fitting, substantially as herein described with reference to the accompanying drawings.

6. A cable termination sealed in accordance with the method of any preceding Claim.

7. A cable gland assembled to a cable, in which the core or cores of the cable are sealed to the body of the gland in accordance with the method of any one of Claims 1 to 6.

8. A cable gland as claimed in Claim 7 in which the body of the gland has a generally parallel bore to define said space.

9. A cable gland as claimed in Claim 7 or 8 in which the bore opens out to a generally conical seat defining an enlarged diameter part of said space.

10. A cable gland as claimed in Claim 9, in which means is provided for urging said compound into the generally conical seat after it has been cured, to seal in pressure tight fashion against the seat.

1 A cable gland as claimed in Claim 9 or 10, in which an '0' ring seal is interposed between the compound and the body of the land.

1 2.'A cable gland substantially as herein described with reference to the accompanying drawings.