FI59499B - FRAMEWORK FOR THE FRAMEWORK OF TELECOMMUNICATIONS CABLE TELECOMMUNICATIONS CABLES - Google Patents

Description

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FINLAND — FINLAND OD PKanttihakemu * - PattfiantAkning 75188U

(22) H »k * ml * p» hri— · AmOknlnfidag 25.06.75 '* (23) Alkuplhr »—Glltlghaudag 25.06.75 (41) Become Public - Bllvlt offtntllg 29.12.75

Patents and Registration. .... _. . ,, ...

_ * ,,. , (44) Date of issue. -

Patent 'OCh rtjllttrityrallin Amökan utlifd oeh utl.tkriftun puMIcsrtd 30. oU. 8l

(32) (33) (31) stuoiksu * —Begird prlorttet 28.06.7U

Holland-Holland (NL) 7 ^ 087 ^ 0 (71) N.K.F. Kabel BV, Schieweg 9, Delft, The Netherlands (NL) (72) Frederik Hendrik Kreuger, Delft, Jacobus Petrus Ignatius van Kesteren, Leidschedam, The Netherlands (NL) (7M Oy Kolster Ab (5l) Longitudinally watertight long distance cable manufacturing method and longitudinally watertight telecommunication cable made by this method - Förfarande for framställning av en i längdriktningen vattentät telekommunikationskabel och enligt förfarandet framställd i längdriktningen vattentät tele-kommun ik at i on r. k ab e 1

The present invention relates to a method of manufacturing a longitudinally watertight telecommunication cable having a plurality of strands 1. coated with a synthetic insulating material. The gaps between the conductors and the space between the cable core and the sheath are filled with a substance that prevents water from penetrating the cable core in the longitudinal direction of the cable.

These types of cables are already known. Bottom-laid cables can be penetrated into the heart of the cable by holes created by mechanical damage to the cable sheath. Such defects may be due to base sagging or mechanical force. In a cable core consisting of cable strands or twisted-wire 1. as is usually the case with a telecommunication cable, water entering the cable can propagate longitudinally through the void space between the conductors 2,59499 and the space between the cable core and the sheath. When each conductor is insulated with plastic, the ingress of water into the cable is not detected until it has penetrated quite a long time, whereby the electrical properties of the cable deteriorate. Again, correcting such a deterioration in electrical properties is a very difficult task. However, the ingress of water into the cable can be prevented by placing a very "thick-flowing" material or foam in the cable along its entire length or in certain blocks, i.e. at regular intervals for a certain length of part in the longitudinal direction of the cable. The very thick liquids proposed for this purpose are usually paraffin-type substances, petroleum waxes, petroleum jelly and the like. Such materials are melted or heated to a low viscosity and then pressed between the conductors and into the space between the cable core and the sheath. Once the substance has solidified, it forms a waterproofing in the cable. However, the downside of these substances is that they become liquid again as the temperature of the cable rises. This can happen, for example, when the cable on the cable reel has to be exposed to the sun's rays for a long time. Due to the gravity, the molten insulating material in the cable then flows into the lower parts of the cable on the cable reel, whereby there is insufficient water insulation between the conductors, or uninsulated points remain in other parts of the cable. This is a disadvantage, especially when the insulating material is placed in certain blocks of the cable. Another disadvantage of this structure is that when polyethylene insulation comes into contact with some paraffin-like substances, their electrical and mechanical properties deteriorate over time.

When the gaps between the conductors and the space between the core and the sheath of the cable are filled with foamed synthetic material, different kinds of difficulties arise again. Namely, foaming is a method which is difficult to control and which usually starts immediately after the foam-forming mixture has been sprayed from the tank. The formation of foam may therefore be complete even before the space between the conductors and the space between the core and the sheath of the cable is completely filled with insulating material. Another drawback is that, in general, a cable with foamed synthetic material in the core as an insulating material becomes rigid, which in turn can cause difficulties when winding the cable on a spool and immersing it in the ground.

When power cables with only a small number of conductors of circular cross-section are manufactured, the spaces between the conductors and the space around them are filled with silicone rubber of circular cross-section in the form of silicone rubber, which cures on its own at room temperature. The vulcanizing agent is added to the filler only shortly before the start of the treatment in question.

However, the disadvantage of this method is that when the manufacturing process stops po. wires containing material become easily clogged.

As a result, the use of such a self-vulcanizing filler material in the manufacture of telecommunication cables causes difficulties, especially when the insulating material is placed in the cable in certain blocks to prevent water from penetrating inside the cable.

The object of the present invention is to provide a method by which a permanently flexible, longitudinally watertight cable can be produced in which the waterproofing material cannot flow during heating and thus damage the actual insulation of the conductor.

According to the invention, this is achieved by using a method characterized in that the silicone rubber, which cures under the influence of air moisture, is fed between the conductors of the strands 1. and around the core, after which a sheath is applied to the core of the cable.

The silicone season, which cures under the influence of air humidity, is different from the silicone season which cures at ambient temperature in that in the former the vulcanization begins only when the rubber comes into contact with the air containing moisture. Instead, in the latter type of rubber, vulcanization begins as soon as the substances in the mixture are mixed. Thus, the ambient air and its humidity have no effect on the start of the process in this case.

Silicone rubbers that cure under the influence of air humidity are already known and are widely available. They usually comprise a mixture of diorganopolysiloxane (diorganopolysiloxaneX filler, for example silica) and also a crosslinking agent, for example ethyl silicate and, of course, another vulcanization catalyst. silicone oil or a volatile solvent can be used for this purpose, either as such or mixed with a rapidly volatile solvent, and the vulcanised material is then permanently elastic, and tests have shown that the silicone rubbers used for this purpose adhere well to commonly used conductor insulation materials such as polyethylene and polyvinyl chloride. on the other hand, the material can be easily removed with the bare hands from the conductor insulation.

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A further advantage of silicone rubbers which vulcanize at ambient temperature due to the humidity of the air is that the vulcanization process is relatively slow. As a result, a sheath consisting of an overlapping film can be arranged on the core of the cable even before the end of the vulcanization step. Thus, all the gaps between the conductors and the space between the core and the sheath of the cable are filled po. agent.

When the core of the cable is placed in the sheath surrounding it, the part of the material which has not had time to be completely vulcanized but is still plastic is now compressed into all the spaces between the core of the cable and the sheath. Under normal conditions, the moisture remaining in the core of the cable after attaching the sheath is sufficient in the vulcanization process to achieve complete vulcanization of the silicone rubber. When the silicone rubber was vulcanized in blocks in the experiment, it was found that the blocks could be detached from the conductor layers. If the core of the cable has several conductors twisted together, for example star-stranded cables, the above-mentioned layer arrangement can be obtained by placing a new layer of conductors or conductor bundles on top of the previous layer, which is vulcanized at ambient temperature. After vulcanization, the silicone rubber layers, which are successively made in the same place, form a uniform, water-impermeable barrier. This is also the case when the core is made by twisting several wiring harnesses together. In this latter cable manufacturing process, in which the core of the cable is formed, unvulcanized silicone rubber is placed in and around the wiring harnesses such that after joining the bundles, the silicone rubber therein forms a uniform mass at each block location in the cable core.

The telecommunication cable games produced by the method according to the invention remain constantly flexible, so that there are no difficulties when winding them on cable reels or installing them in place on the object in question. In addition, the experiments showed that during the installation work, the silicone rubber can be removed from the conductors quite simply by hand.

Example

The core of a telephone cable comprising 150 asterisked twisted-pair conductors, each again comprising a 0.32 mm diameter copper conductor coated with a 0.32 mm polyethylene insulation layer, was formed by twisting the core into three successive layers of asterisked four turns, 9 »15» 21, 27 »34 and 41 star alloy helical conductors alternately as left and right threads.

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A film formed of "linear" polyester was wrapped around each layer, with the exception of the outer layer, as an open thread.

A silicone rubber surface (vulcanized at ambient temperature under the influence of air humidity) was made at regular intervals (l m) about 10 cm in length on the core and each successive layer of asterisked threads. For this purpose, Silastic 738 RTV (manufactured by Dow Corning Corporation) was used, which is reported to be silicone rubber that cures at room temperature under the influence of air humidity.

The film made of linear polyester was wrapped overlapping around the core of the cable. Thereafter, a jacket was injected onto the heart.

"In order to determine the tightness of the waterproofing, a certain amount of cable made in the above way was connected horizontally to a vertical pipe with water one meter above the cable. After six weeks, it could be seen that the water had only reached the first silicone rubber barrier.

Claims (4)

6,59499 A method of making a longitudinally watertight long-distance communication cable having a plurality of plastic insulated conductors, a substance which prevents water from penetrating the cable in the axial direction, thereby being inserted between the conductors and in the space between the cable core and the sheath. at ambient temperature under the influence of atmospheric moisture, is placed between the conductors and in the space around the core of the cable, after which a sheath closely associated with it is made on the core of the cable. A method according to claim 1, characterized in that the silicone rubber, which cures at ambient temperature under the influence of air humidity, is placed in blocks in the space between the cable core and the sheath. Method according to Claim 2, characterized in that, when the core of the cable is formed, a layer of silicone rubber is applied on top of the second conductor layer around the core, which cures at ambient temperature under the influence of air humidity. A longitudinally watertight telecommunication cable, the core of which consists of a plurality of conductors and between them and in the space between the cable core and the sheath a substance preventing water penetration into the cable core in the longitudinal direction of the cable, characterized by the method according to claims 1-3.