GB2172139A - Armoured cable - Google Patents

Abstract

In a method of making an armoured cable 1 in which the armouring elements 4 are completely embedded in a corrosion-protective sheath 3 without contact with each other or with the inner and outer surfaces of the sheath, the spacing is obtained by prespinning a spacing string 17 of insulating material around each armour wire 4. Alternatively a sheath (5, Fig. 2) having helical grooves (6) is extruded over the core 2. Armour wires (4) are fed to the grooves and covered by extrusion (Fig. 3). In another embodiment a sheath (15 or 16 Fig. 4) around the armouring wire spaces the wires. <IMAGE>

Description

SPECIFICATION Armoured cable This invention relates to armoured cables and methods of making them. Although particularly applicable to cables for conveying/transferring telecommunication signals, the invention is also considered to be useful in connection with other types of armoured cables such as electrical power cables. In the following specification the expression "cable core" is intended to include any cable core having at least one electrical conductor and/or optical fibre which is arranged within a sheath of insulation material.

Cable cores are normally provided with some sort of external armouring, the type of which is chosen in accordance with local requirements. The most common armouring used comprises one or more sets of steel wires or tapes which are wound around the cable core. The steel wires/tapes are usually galvanised and embedded within corrosionprotective layers of Jute or polypropylene impregnated with asphalt or bitumen. Depending upon the mechanical conditions along the cable route it may also be required to enclose the armouring wires/tapes within a waterproof corrosion-protective sheath of plastic or rubber. Problems may arise in connection with such constructions, because if the outer sheath is damaged, water may enter the steel armour layer and corrosion will start at places where the galvanisation layer is not perfect.

Once the duter protective sheath is damaged and water enters at one place the water will not only'flow along the nearest armouring steel wire/tape, it will also flow to neighbouring steel wires/tapes and the risk of corrosion of the steel armour is great.

In recent years there have been suggested several means and processes for filling cable cores and other parts of cables with waterrepellent and moisture-prevention powder, jellies and other materials.

It has also been suggested to embed fully armouring wires or threads within the outer protective sheath. If the wires are embedded in the sheath separately and so that neighbouring wires are not in contact with each other, a hole in or a rupture of the sheath will not automatically give water access to more than one armour wire.

With previously known processes for separately embedding armour wires in a corrosion protective sheath it has been difficult to obtain the desired results. The sheath must be pressure-extruded and even if the armour wires are guided at desired positions within the sheath at the inlet of the pressure extruder, it often happens that the wires are displaced from the desired positions in the final product.

The displacements are often so great that some of the wires are in mechanical contact with each other, some are in contact with the cable core and that some are in contact with the outer surface of the sheath. This uncontrolled situation is probably due to the fact that the wires have to be stranded around the cable while the sheath material is in its molten state.

In addition to the above mentioned drawbacks caused by uncrontrolled positioning of the armour wires, it is also a drawback that the sheath will be more sensitive to tearing.

The main object of the present invention is to provide a method by which there can be obtained a cable in which the armour wires are separately and completely embedded in a corrosion protective sheath without contact with each other or with the inner and outer surfaces of the sheath.

According to the invention in its broadest aspect there is provided a method of making an armoured cable having a number of armouring elements embedded in a corrosionprotective sheath which comprises the steps of guiding the armouring elements into desired positions around the circumference of the cable during application of the sheath, characterised in that the desired positioning of the armouring elements relatively to each other and to the cable core is obtained by introducing spacing devices in the sheath.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a general cross-section of a cable according to the present invention, Figure 2 illustrates one embodiment of the invention, Figure 3 illustrates a lay-out for making the cable shown in Fig. 2, Figure 4 illustrates two alternative embodiments of the invention, Figure 5 illustrates what is considered to be the most desirable embodiment of the invention, and Figure 6 illustrates a process for making a cable shown in Fig. 5.

In Fig. 1 a cable 1 includes a cable core 2 surrounded by a sheath 3 including a number of armour wires 4. It should be noted that the armour wires are separated from each other and that they are completely embedded within the sheath. It should also be noted in connection with the embodiments illustrated in Figs.

2, 4 and 5 that separating means 5, 15, 16 and 17 in the final product will be completely integrated with the sheath 3 so that the appearance of the final product will be similar or identical to that of Fig. 1.

In the embodiment shown in Fig. 2, a separating sheath 5 with grooves 6 is extuded over the cable core 2 with the grooves forming helical tracks for accommodation of the armour wires 4. A process for making the cable configuration of Fig. 2 is illustrated in Fig. 3 wherein the cable core 2 enters an extruder 10 in which the separating sheath 5 is extruded onto the core. The grooved cable core 11 is then, in tandem with extrusion of the sheath 5 or in a later process, passed to an extruder 13 together with the armour wires 4 which are paid off reels 12. At the outlet of the pressure extruder 13 the sheath 5 will be completely incorporated and integrated with the sheath supplied by the extruder 13 to provide the outer sheath 3 of the cable 1.

In Fig. 4 there are illustrated two embodiments of the invention, showing that the desired spacing may be obtained by arranging spacing devices 15 or 16 on the individual armour wires 4. It will probably be desirable to provide the armour wires 4 with the spacing devices 15, 16 in a separate process and not in tandem with extrusion of the sheath 3.

Using spacing devices 15 will probably have the drawback that the molten sheath material 3 will not easily penetrate into the spaces between the cable core 2 and these devices.

However, by using the arrangement of Fig. 3 where the armour wires 4 (which in this case are provided with spacing devices or simply sheaths 15) are applied to the cable core within the sheath extruder 13, good results may be obtained. The spacing devices may have various configurations 16, as illustrated.

In Fig. 5 is illustrated what is considered to be the preferred embodiment of the present invention. Each armour wire 4 is provided with a spacing string 17 of insulation material. The string 17 is preferably spun around the armour wire 4. When these thus prepared armour wires are stranded or subjected to other means applied to the cable core 2 while applying the outer sheath 3, the sheath material 3 will flow around all the armour wires 4. As mentioned, in the final product the separating strings 17 will be completely integrated with the sheath 3.

The strings 17 may be applied to the armour wires 4 in a separate process, but it is also possible to do this in a tandem operation as illustrated in Fig. 6. The cable core 2 enters the extruder 13 from the left and the finalised cable 1 as indicated in Fig. 1 leaves the extruder to the right. Each armour wire 4 (only two wires are shown) is provided with a separating string 17 before the armour wires are stranded around the cable core 2.

In the processing equipment illustrated in Figs. 3 and 6 the cable core 2 and finalised cable 1 may be rotated about their own axis from a rotating pay-off to a rotating take-up, while the prepared armour wires 4 are supplied from a stationary pay-off arrangement.

Claims (10)

1. A method of making an armoured cable having a number of armouring elements (4) embedded in a corrosion-protective sheath (3) which comprises the steps of guiding the armouring elements into desired positions around the circumference of the cable during application of the sheath, characterised in that the desired positioning of the armouring elements relatively to each other and to the cable core is obtained by introducing spacing devices (5, 15, 16, 17) in the sheath.

2. A method according to claim 1, characterised in that the spacing devices are introduced on the cable core and/or on the armouring elements (4) prior to application of the sheath (3).

3. A method according to claim 1 or 2, characterised in that the spacing devices (5, 15, 16, 17) are made of a material which, during application of the sheath (3), will be completely bonded to the sheath.

4. A method according to claim 3, characterised in that the spacing devices are made of the same material as the sheath.

5. A method according to claim 4, characterised in that the sheath is extruded at temperature/pressure conditions securing cdm- plete incorporation and integration of the spacing devices in the sheath.

6. A method according to claim 1, characterised in that the spacing devices are in the form of strings (17) which are spun/wound around at least some of the armouring elements (4).

7. A method according to claim 6, characterised in that at least one spacing string (17) is spun around each armouring element (4) prior to positioning of the armouring elements.

8. An armoured cable made by a method according to any one of the preceding claims.

9. A method of making an armoured cable substantially as described with reference to the accompanying drawings.

10. An armoured cable substantially as described with reference to the accompanying drawings.