GB2172153A - Cable joint enclosures and supports therefore - Google Patents

Abstract

A sheet metal support for forming at least one tapered end of a cable joint has an end portion which is divided into a plurality of parallel sided or tapered fingers, each finger comprising a relatively flexible proximal part, a relatively stiff medial part forming a substantial part of the length and a relatively flexible distal part, beyond which there may be a relatively stiff end part. The relatively flexible parts may be weakened by reducing their width, (see fingers 12, 13, 16, 17 and 18), by localised annealing (see finger 14) or by machined or rolled grooves (see finger 15). The medial part may be stiffened by imparting transverse curvature to it. The support is primarily designed for use with a heat shrunk outer covering, and ensures uniform shape when the shrinking covering is allowed to establish the taper in the support. <IMAGE>

Description

SPECIFICATION Cable joint enclosures and supports therefor This invention relates to enclosures suitable for joints in cables used in the transmission of electrical energy and/or of electric and/or optical signals, and to supports for the joint enclosures.

In our British Patent No. 1065431 we described a joint enclosure in which at least one tapering end portion was supported by a rec angular metal sheet having along each of two opposite edges or along one edge a plurality of slits dividing part of the sheet into fingers which were caused to overlap one another over a part of their lengths with their free ends embracing the sheath of the cable or of one of the cables. Others have been prepared to sacrifice the virtually limited range-taking capacity of this type of support in order to have the finger-ends lie flat on the surface of the cable, and have used tapered fingers.In some cases a small hole has been punched at the closed end of each slit, primarily in order to reduce risk of tearing before the joint enclosure is completed but with the additional effect of creating a distinct flexing point at the base of each finger.

These known arrangements are reasonably satisfactory when the taper is formed by hand (or with a noose of tape or string) prior to the application of an outer covering, but it is sometimes difficult to achieve the desired rigi dity in the finished enclosure without making the fingers difficult to bend to a neat and consistent shape, and when the joint enclo sure is formed by collapsing a heat-shrink sleeve onto the support without previously securing the fingers in their final positions there is a risk (especially if the sleeve is not uniformly heated) that the finger-ends will settle in longitudinally-displaced positions resulting at best in an untidy joint end and at worst in an enclosure that fails to make a fluid-tight seal round the cable.

The present invention reduces or substantially eliminates this risk.

The support of the present invention com prises a sheet-metal blank (which will normally but not necessarily be rectangular) having at least one end portion divided to form a plural ity of fingers and is distinguished by the fact that each finger comprises: a relatively flexible proximal part; a relatively stiff medial part forming a substantial part of its length; and a relatively flexible distal part.

The relatively flexible distal part may extend to the end of the finger, or there may be a relatively stiff end part, the purpose of the distal part in either case being to allow the end of the finger to lie flat (in a longitudinal sense) on the surface of the cable so that pratically all of the taper is formed by the medial part.

The fingers may be parallel-sided and overlap or they may be tapered. Except in very unusual circumstances all the fingers (of one edge when two are formed into fingers) will have like longitudinal dimensions and in most cases they will be substantially identical.

The required distribution-of flexibility and stiffness may be achieved by weakening the proximal and distal parts or by stiffening the medial part or by both stiffening the medial part and weakening at least one of the proximal and distal parts. A preferred way of weakening the proximal part consists in reducing its width by punching or otherwise forming apertures at the base of the slits between the fingers, and the same technique can be used for the distal apart. Alternatives include local reduction of thickness, partial slitting without removal of metal, and for some metals local annealing of a sheet that is otherwise in a relatively hard condition. A preferred way of stiffening the medial part comprises imparting transverse curvature to it.

The joint enclosure of the invention includes at least one tapered end formed by a support comprising at least one of the fingered sheets described and an outer covering of heat-shrink or other conforming fluid-tight insulating material. When two separate fingered sheets are used, they may together form the whole support or they may form only the end portions with a middle portion formed of plain sheet metal or other suitable material. In most cases a longitudinal seam between sheet metal edges will be formed. In some cases an unsecured overlap seam may be acceptable, but in most cases we prefer to use a rolled seam (similar to those used for the side seams of tinplate cans), preferably projecting on the inside only. If desired, a seam-welded joint or an overlapped joint secured by sopt-welding, rivetting, adhesive or other suitable means could be used.

In the accompanying drawings, Figs. 1, 2 and 3 are diagrammatic plan views of portions of three supports in accordance with the invention and Fig. 4 is a composite "sampler" illustrating a variety of possible modifications.

The support of Fig. 1 is similar to the support shown in Figs. 1 and 2 of Patent No.

1065431 except that each of the fingers comprises a distal relatively flexible portion 1 formed by a reduction in the width of the fingers consequent upon punching a series of round holes 2 at the bases of the slits 3, a relatively stiff medial section 4 of full width, a distal relatively flexible zone 5 formed by a second row of round holes 6 and an end portion 7 lying beyond the distal relatively flexible portion. The fingers are slightly twisted, as by forming the slits 3 by a shearing action, to ensure consistent overlap.Compared with the support of Patent No. 1065431, the device of Fig. 1 forms a more conical, less rounded, taper with the end portions 7 each lying with its under-edge flat on the cable and its overedge flat on the surface of the underlying finger, so that the risk of the extreme end of the finger digging into the cable and failing toslide into its intended final position is considerably reduced.

The supports of Figs. 2 and 3 provides tapered fingers that are not intended to overlap, and are designed for laser cutting, though they could also be formed wholly or in part by CNC punching. The proximal regions 8 are formed in broadly the same way as those of Fig. 1, but the holes 9, instead of being round, are of a rounded three-cornered shape in the case of Fig. 2 or an "obround" shape (i.e. a shape bounded by equal parallel sides and two semicircles) in the case of Fig. 3, both designed to give the required degree of flexibility while reducing the risk that a conductive object might penetrate through the holes without contacting the metal.The medial sections 10 are stiffened by creasing longitudinally to the kind of profile shown by the appended cross-section, and distal portions 11 are neither weakened or stiffened, so that there is no distinct end portion.

In Fig. 4, each of the individual fingers 12 to 18 illustrates a slightly different way of obtaining the required relatively stiff and relatively flexible sections. Fingers 12 and 13 are similar to those of the Fig. 2 example, except that the holes, 19, 20 respectively, are of alternative shapes. Finger 14 is made from hard-rolled metal sheet but with proximal and distal flexible zones, 21 and-22 respectively, formed by localised annealing. Finger 1 5 has flexible portions 23 and 24 formed by machined or rolled grooves (preferably formed before blanking out to form the finger) extending part-way through the thickness of the metal. Finger 16 is similar to the Fig. 1 example except that it is tapered, and the notches 25 and 26, being laser cut, are deeper and narrower. Fingers 17 and 18 differ from finger 16 in having holes 27, 28 within the width of the finger instead of notches at the edges. Some of these variants can be combined, but the use of different kinds of finger on the same support is not recommended.

Claims (8)

1. A support for a cable joint enclosure comprising a sheet metal blank having at least one end portion divided to form a plurality of fingers distinguished by the fact that each finger comprises: a relatively flexible proximal part; a relatively stiff medial part forming a substantial part of its length; and a relatively flexible distal part.

2. A support as claimed in Claim 1 in which each finger further comprises a relatively stiff end part.

3. A support as claimed in Claim 1 or Claim 2 in which the proximal part is weakened to make it relatively flexible by forming enlargements at the base of the slits between the fingers.

4. A support as claimed in any one of Claims 1 -to 3 in which the medial part of each finger is stiffened by imparting transverse curvature to it.

5. A joint enclosure including at least one tapered end formed by a support as claimed in any one of the preceding claims and an outer covering of conforming fluid-tight insulating material.

6. A joint enclosure as claimed in Claim 5 in which the outer covering is heat shrunk on to the support.

7. A support for a cable joint substantially as described with reference to and as shown in Fig. 1 or Fig. 2 or Fig. 3 or including fingers which are substantially as one of those shown in Fig. 4.

8. A cable joint enclosure including a support claimed in Claim 7.