Device for joining a fibre-optic cable and a junction box, and process for manufacturing said device

(74) Prosecutor Civil Service. Henrik Levkowetz,

JK THorsens Patentbureau A / S, Oslo.

(30) Priority requests 16.11.8α, FR, _No.> 8417532.

(54) The designation of the invention PURCHASES A CONNECTION BETWEEN A CABLE AND A CONNECTION BOX AND PROCEDURE FOR ITS MANUFACTURING.

(57) Summary

A coupling device forms a connection between an optical fiber cable junction box and an axial support member (2) in the cable and consisting of a composite material comprising fibers, or a fiber braid. The fibers (4) at the outer end of the axial support (2) are then spread in fan form to a tassel and. firmly embedded in cold-polymerized resin (5) fills a cavity (6) which forms part of the junction box.

(56) Publications cited none.

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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for connecting an optical fiber cable and its carrier consisting of a fibrous composite material or a fiber braid, with a junction box, and in particular high voltage carrier cables.

The invention also relates to a method of manufacturing such a device. It has already been proposed in the applicants' French patent application no. 2,524,986 is a connecting device between the outer ends of two submerged optical fiber cables, each cable comprising an optical fiber core as well as a steel wire casing screwed to the core, while a copper tube is pulled over this casing and an insulating layer, a return conductor and protective screen, while the cable joint itself for each cable end comprises a fastening portion, a tapered wedge for spreading the sheath forming steel wires, as well as a curable synthetic resin plug in which the ends of the steel wires are embedded as they are wedged between the attachment portion and the tapered wedge.

Such a cable joint, however, is quite complicated and hardly suitable for joining a cable with a non-metal axial support element, especially by jointing tubular support cables or with a central core provided with optical fiber grooves and with an axial carrier member of composite material (glass fibers / epoxy resins, glass fibers / polyester resins, aromatic polyamide fibers / polyester resins) or of high strength braided non-metallic fibers (eg carbon fibers). The outer ends of such cables must be securely held in junction boxes and must be capable of absorbing tensile forces corresponding to an extension of at least 0.8% without breaking or sliding.

It is thus an object of the present invention to provide a connecting device which securely holds the outer end of the cable in question in the junction box, and allows said cable end to withstand a tensile force corresponding to an extension of at least 0.8% without breakage or slip of material, while at the same time connection is of simple design as well as easy to manufacture.

The invention thus relates to a device for connection between a junction box for an optical fiber cable and an axial support element in the cable and consisting of a composite material comprising fibers or fiber braid.

In accordance with the prior art, the connecting device according to the invention has as a special feature that the fibers at the outer end of the axial support element are spread in fan form to a tassel and firmly embedded in cold-polymerized resin, which fills a cavity forming part of the junction box. .

The invention also relates to a method for producing a connecting device as stated above in the case of the cable in question having an axial support element consisting of a composite material comprising glass fibers, the method according to: According to the invention, the outer end of the axial support element is burnt to separate the glass fibers and spread them in fan form to a tassel which is then fed into cold polymerizable resin which fills a cavity forming part of the junction box, after which the resin allowed to polymerize.

In case the axial support of the cable is constituted by one. fiber braid, the method according to the invention extends. in that the fibers at the end of the braid are spread in fan form to form a tassel, whereupon the fiber tassel is fed into a cold polymerizable resin which fills a cavity forming part of the junction box and the resin is then allowed to polymerize.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawing, the only figure of which is a partial section through a connection between a junction box and a carrier for a high voltage conduit, the carrier cable having a grooved central stem of plastic material and a composite support member consisting of glass fibers and epoxy resin.

The center stem 1 has an axial support member 2 as well as an outer sheath

2A and ends at a point 3. The axial support has a diameter of about 0.5 - 2 mm and is made of glass fibers with a diameter of about 20 µm coated with epoxy resin in which the fibers are twisted together and such that the glass constitutes 70% by weight of the composite glass / resin material. The support member extends beyond the endpoint 3 over a length of about 50 mm. Then the glass fibers are spread out in the form of a brush 4 with a length of 25-30 mm. This fiber brush is inserted into a pulp of epoxy resin 5 located inside a container 6 in a piece with the corresponding junction box, which is not shown. With regard to the optical fibers of the cable, not shown, these are connected to corresponding fibers at the outer end of another cable, which is known in a known way into a cavity in the junction box in such a way that an excess length of glass fibers, e.g. as described in published French Patent Application No. 2,524,986. or the corresponding U.S. Patent Application No. 482,358. The mutual separation of the glass fibers in the composite material in the core of the cable core as well as the spread of the fan ends in fan form is achieved by burning the outer end of the core. This also serves to remove lubricant that may still be found on the glass fibers, which will also improve the adhesive connection of the fibers with the cold polymerizable resin, e.g. an epoxy resin.

Breakage tests have been carried out on a core of plastic material and with a support element consisting of a composite material of fiberglass and resin. The core rod was arranged vertically and by spreading the glass fibers in fan form to a tassel, each of its outer ends was connected to a plug of cold polymerized epoxy resin arranged in a junction box.

The lower junction box was then subjected to a pulling force which produced an extension of the core rod by 1%. No fracture and no slip of material were detected at the end of an 8-month observation period. Tensile strength tests are also performed on the carrier with an end attached to an anchoring box. The carrier then burst at an extension of about 5%, showing that the tensile strength of assembled carrier and junction box is not less than the tensile strength of the carrier alone. This strength corresponds to a force of 400 kg to produce rupture in a core rod with a diameter of 2 mm, and a force of 285 kg to achieve rupture in a rod with a diameter of 1.2 mm.