A METHOD OF MOUNTING A TIGHT-FITTING TUBE SECTION OR SOCKET ON A CABLE

Abstract: In a method of mounting a tight-fitting tube section or sleeve on a cable, the tube section/sleeve is internally provided with a plurality of slide rails, through which radial expansion may be effected during mounting, and through which the friction during mounting is reduced significantly. The rails are removed after the mounting.

Description: A method of mounting a tight-fitting tube section or socket on a cable The present invention concerns a method of mounting a tight-fitting tube section or a sleeve on a cable or the like. Various methods are known for mounting tube sections or sleeves on cables, e.g. as described in the German Offenlegungsschrift 2 621 641. This prior art concerns in particular a relatively large sleeve whose frictional force is reduced in consequence of the radial expansion which is effected by means of compressed air; however, on the other hand, sealing means are provided at the ends of the sleeve which involve increased frictional resistance against the cable to keep the air inside the sleeve. The Danish Patent Specification 150 428 likewise concerns a method where the frictional force is reduced by means of radial expansion effected with compressed air. However, cables are frequently assembled at locations where com- pressed air is not readily available, and compressed air methods are therefore not always equally applicable. Further, the sleeve is stretched in an axial direction and returns to its original shape only slowly. The US Patent Specifications 3 515 798 and 3 946 480 as well as the EP Patent Specification 117 092 all mention the same method, the so-called cold shrinking process wherein an elastically shrinkable, tubular cover is first expanded mechanically, and then a plastics strip, wound in a helix like e.g. a helical spring, is placed inside said cover. It is stored in this state by the manufac¬ turer and the wholesaler. When a cable joint is to be provided, such a pre-fabricated sleeve is obtained, and when the cover has been moved inwardly over the joint, the plastics strip is pulled out by a pull at the end which faces inwardly and then outwardly under all other coils. This entails that a certain withdrawal force is necessary, and at the end from which pulling is performed constantly, the end being pulled off must be wound around the cable in step with the release of the individual 5 coils inside the sleeve, which is extremely cumbersome. Moreover, it is very inexpedient that these pre-fabricated sleeves are to be stored in a highly expanded state until needed, because the expansion gives rise to a certain permanent deformation of the elastic, tubular cover. Iff and because the cover is frequently made in a rubber material which does not withstand very great, outer mecha¬ nical influences, e.g. in the form of cratches which may expand into big cracks, which will be detrimental to the electrical resistance of the sleeve. 15 It is also known to apply tight-fitting tube sections or sleeves by means of various known slide means, but frequently the means are pushed like a bank in front of the application end and thus do not contribute to reducing the friction. 20 Known is also a so-called hot shrinking process wherein a sleeve of a particularly cross—linked material is ex¬ panded very strongly by heat and is then cooled and thereby maintains its strongly expanded shape, is applied to a cable joint and then heated again to shrink around 25 the joint. This, however, requires quite special mate¬ rials, heating equipment and expansion equipment. The object of the present invention is to provide a me¬ thod of mounting a tube section or a sleeve over prefer¬ ably a cable end or joint, wherein only little friction 30 occurs between the tube section and the cable, which is not vitiated by the above-mentioned drawbacks and which lends itself for pre-fabrication. This object is achieved in that the method is performed as stated in the characterizing portion of claim 1 since the rails, which are placed in the longitudinal direc¬ tion, exert almost no friction during the application because of their special profile and material, they are extremely easy to remove after the application, the sleeve or the tube is not radially expanded in storage and has none of the above-mentioned drawbacks. By the invention and in connection with the application, automatic venting of the tube section or the sleeve is obtained at the same time, from within and outwardly, which is very important since entrapped air may cause electrical discharges in case of use on high-voltage cables. Preferably, the tube section or the sleeve is made of silicone rubber and the rails of PTFE, PE or another suitable plastics material. By their profile, the rails are engaged with one another either completely or partly so that they mutually support one another in maintaining a circular profile, but may additionally be provided with a supporting bushing or rod internally to assist in this function, said bushing or rod being removed immediately before application. The invention will be explained more fully by the follow¬ ing description of a preferred embodiment with reference to the drawing, in which figs. 1 and 2 show rails positioned from the end, and up to an assembling bushing and extending right through, respectively, figs. 3, 4 and 5 are end views illustrating the rails in various stages in the mounting of the tube section in accordance with the method of the invention, and fig. 6 shows examples of various useful profiles for performing the method. Fig. 1 shows a cable sleeve with a tube section 1 sur¬ rounding a cable conductor joint with a conductor 2 and a conductor assembling bushing 3, which has been placed inside the tube section or the sleeve prior to the mount¬ ing of the sleeve. The rails 5 are positioned from both insertion ends and adjoin the assembling bushing_ The sleeve is shown with the cables 7 inserted at both sides, which causes the tube section to be expanded so that, in this state, the rails do not support one another any¬ more, but a gap 8 is established between them. In this state, the rails may be removed very easily, either singly or several at a time. Fig. 2 shows another type of cable joint 9 where the rails 5 extend through it and protrude from both ends of the joint. The tube section or the sleeve is first moved somewhat inwardly over one cable end, and then the conductor joint is made, and the tube section or the sleeve is positioned centrally over the joint, follow¬ ing which the rails 5 are removed quite easily, and the tube section or the sleeve fits quite close over the cable joint. Fig. 3 shows a section A-A from fig. 1 or 2 with the assembly seen from the end, prior to removal of the rails 5. Fig. 4 shows the same view as fig. 3, but with the rails removed. Fig. 5- shows a tube section or sleeve 1 with rails 5 and inserted supporting bushing 10, which may be a ne¬ cessary auxiliary feature for certain profile types in the building of a circular profile of the rails. Fig. 6 shows various examples of useful profiles for rails 5, which support one another by their convex 13 and concave 12 faces in the formation of a circular cross- section. It will be appreciated that the method may be applied to various cable joints such as e.g. assembling sleeves, stop sleeves and end sleeves. The method of the inven¬ tion also provides the advantage that tube sections or sleeves may be manufactured and stored in a pre-fabri- cated state without being stretched in advance. The same tube section or sleeve may be caused to accommodate seve¬ ral cable diameters and cable geometries owing to its very great elasticity, which it retains in contrast to known sleeves of the type which loses part of their elas- tic power when stored for a long time in an expanded state.

Claims: P a t e n t C l a i m s 1. A method of mounting a tight-fitting tube section (1) or sleeve on a cable, wherein said tube section or sleeve is unexpanded or only slightly expanded in a radial direction when mounted, and is maintained in this state until finally positioned over a joint, c a r a c ¬ t e r i z e d in that the tube section or the sleeve is internally provided with longitudinally extending rails (5) which support one another and are so formed as to have a friction cancelling or reducing effect during the application of the. tube section, and then the rails are easily removed. 2. A method according to claim 1, c h a r a c t e r ¬ i z e d in that the rails are positioned inside the tube section so as to define a cavity within the rails, the internal area of said cavity being smaller than the cross-sectional area of the cable, the rails used being sufficiently rigid to expand the tube section evenly in step with the insertion of the cable into it. 3. A method according to claim 1 or 2, c h a r a c ¬ t e r i z e d in that the rails (5) have a friction reducing profile. 4. A method according to claims 1-3, c h a r a c t e r ¬ i z e d in that one or more supporting devices (10) may be placed on the internal side of the rails (5). 5. A method according to claims 1-4, c h a r a c t e r ¬ i z e d in that the rails (5) are in one piece through the entire sleeve. 6. A method according to claims 1-4, c h a r a c t e r - i z e d in that the rails (5) are inserted from their respective ends of the sleeve. 7. A method according to claims 1-5, c h a r a c t e r i z e d in that two or more of the friction cancelling or reducing means may be in one piece. 8. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the mounted sleeve may be disassembled without damage and be re-assembled by re-inserting the rails (5) into the sleeve. 9. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the tube section (1) or the sleeve may accommodate several cable diameters. 10. A method according to any of the preceding claims, c h a r a c t e r i z e d in that the tube section (1 ) or the sleeve may be applied to various cable geometries,

Inventors: NIELSEN OLE KJAER, NIELSEN, OLE, KJAER
Applicants: NORDISKE KABEL TRAAD
Application year: 1988
Main classification: H02G15
IPC codes: H01R4, H02G15