GB1602875A - Flexible electric cables with corrugated insulation and process for their manufacture - Google Patents

Abstract

This is a flexible cable, insulated by means of a material which would possess, under the conditions of use of the cable, an insufficient flexibility. This cable includes one or more profiles, wound over the core (1), on which profiles the insulation is deposited thus forming corrugations. Flexibility is achieved by the movement of the corrugations and by the compression (squashing) of the profile. Application to cables for low temperatures or to cables for which the insulation would be relatively rigid at the use temperature. <IMAGE>

Description

(54) FLEXIBLE ELECTRIC CABLES WITH CORRUGATED INSULATION AND PROCESS FOR THEIR MANUFACTURE (71) We, PRECICABLE, of 138 rue Michel Carre 95100 Argenteuil, France, a body corporate organised under the laws of France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to flexible electric cables with corrugated insulation and to a continuous process for their manufacture.

Flexible electric cables are necessary for various purposes, either because of the course over which they have to be moved for their installation or because the apparatus to which they are to be connected executes frequent movements of varying amplitude.

In these cables, the flexibility of the conductive core is obtained by joining together elementary strands of small diameter. which may frequently be less than 1 millimetre and may even be as little as a tenth of a millimetre.

The conventional insulators, such as thermoplastic polymers, are generally considered to be sufficiently flexible at room temperature but not at the low temperatures encountered .outdoors or in deep freeze installations, where they are liable to lose most of their flexibility.

Special insulators, for example those based on fluorine derivatives. which are particularly sought after for their dielectric qualities and their resistance to fire, have a rigidity which makes them unusable for the manufacture of insulated flexible cables other than those of very small dimensions.

For short cables, it has been attempted to overcome this difficulty by using insulators in the form of a corrugated flexible tube of insulating material which is threaded over the conductive core. This solution, however, is inapplicable to the insulation of cables hundreds of metres or even kilometres in length. It is also rather laborious and, due to the considerable clearance which is necessary between the flexible tube and the core in order to enable one to be threaded over the other, a considerable volume of air is enclosed in the cable, with all the known disadvantages which this entails.

This invention provides a flexible insulated cable of indefinite length, cable comprising a conductive core and a surrounding insulating material which is relatively rigid under the conditions of use of the cable, character ised in that the insulating material is main tained in a non-slipping relationship to the conductive core and in corrugated shape by means of a hollow profiled member or members interposed between the conductive core and the insulating matenal.

This invention also provides a process for the continuous manufacture of an insulated flexible cable as just defined, in which process the insulation is deposited on a support which has previously been provided with a hollow profiled member or members adapted to form and to support the corrugations of the insulating material.

The term "support" denotes the one, or more than one, conductor which may be either bare or, in certain cases, covered with a first, insulating or semiconductive layer.

This invention covers flexible cables insulated by a material which would have insufficient flexibility under dle conditions of use of the cable. They compris: one or more hollow profiles wound over the core, on which profiles are deposited the insulation which thus forms corrugations. The flexibility is provided by the movement of the corrugations and by flattening of the profiles.

The invention also covers the use of the cables at low temperatures or in situations where the insulation would be relatively rigid under the operating conditions.

Among the various methods for depositing the insulation on the support, extrusion and taping are particularly important.

The various methods of carrying out the invention are illustrated in the accompanying figures in which: Figures 1 to 4 represent longitudinal seo tions of cables according to the invention in which the profile or profiles are wound spirally round the length of the cable. Figure 3 showing a multi-conductor cable- and Figure 4 a cable in which the core has previously been covered with a semi-conductive layer.

In Figure 1, a conductive core 1, elementary strands of which are shown schematically, is provided with an insulation 3 which has been deposited by extrusion to form a series of transverse corrugations 4.

The volume of empty space S depends on the shape of the profile. In the embodiment shown, the profiled member consists of a tube 6 which can be flattened when the cable is bent, thereby improving the flexibility of the insulating sheath. The tube 6 is wound spirally over the whole length of the core.

In Figure 2, the profile 8, again wound spirally, is tublar and approximately triangular in cross-section.

By choosing the pitch at which the profile is wound spirally round the cable so as to be either substantially equal to, or significantly different from, the pitch at which the core is twisted and either equal to or opposite in sense, the flexibility of the whole arrangement can be varied slightly according to the practical requirements for its use.

Figure 3 shows an embodiment in which the flexible cable comprises two conductors 12 and 13 with a first insulation 14 to which is applied, according to the invention, a profile 15 which supports the corrugated external insulator 3. The same arrangement may also be used for multi-wire cables.

Figure 4 represents an embodiment in which the conductive core has previously been covered with a semi-conductive sheath.

In Figures 3 and 4, the corrugated insulation 3 is thus connected to the conductive core through an intermediate layer which may be either insulating or semi-conductive.

In all cases, bending of the cable even over a small radius of curvature causes virtually no displacement of the corrugated sheath in relation to the conductive core.

Due to the corrugations supported by the profile, deformations of the insulating sheath under compression or stretching are within the range of elastic deformation of the material of the insulator so that when the cable is bent it suffers no permanent deformation.

Continuous manufacture of flexible insulated cables according to this invention comprises placing the profile in position and depositing the insulation thereon.

The profile may be placed in position in in the form of a succession of heat-welded rings. However, it is frequently more convenient, especially if the profiles are tubular, to wind them in one or more spirals as shown in Figures 1 to 4. The pitch and sense of these spirals may be chosen according to the degree of flexibility required, maximum flexibility being obtained if the profiles are wound at the same pitch and in the same sense as the strands of the conductive core.

The rings or spirals may be circular in crosssection but they may have any other desired shape, for example, elliptical or polygonal.

It is also possible to use several distinct hollow profiles which may be of any desired cross-sectional shape, wound in separate spirals.

The insultating material is deposited from an extruder head by the techniques commonly employed for the continuous manufacture of insulated cables. The insulation, which is extruded in a pasty state, forms corrugations due to a controlled depression, and solidifies in contact with the support.

The insulation may also be deposited by taping. In that case, the taped cable must be subjected to heat which enables corrugations to be formed on the profiles by sotening or by the effect of heat shrinkage of the material constituting the tape.

The invention may be performed for any types of insulations commonly used for the manufacture of electric cables but its advantages are particularly marked in cases where the insulation is excessively rigid under the conditions under which the cable will be used. This applies mostly to polymers when they are subjected to low temperatures as well as to several fluorinated polymers such as E.T.F.E. (copolymer of ethylene and tetrafluoroethylene) or F.E.P. (fluoroethylenepropylene), which have hitherto been unusable for the manufacture of flexible insulated cables other than cables of very small diameter.

The profile may be manufactured from the same material as the insulation itself but, without departing from the scope of the invention, it may also be made of a different material, which may be insulating, conductive or semi-conductive.

The invention is further illustrated by the following example.

Example A flexible insulated cable having a core 70 mm2 in cross-section composed of elementary strands 0-25 mm in section of tin plated electrolytic copper was produced according to the invention.

Three tubular profiles of E.T.F.E. (copolymer of ethylene and tetrafluoroethylene) having an external diameter of 2-5 mm and an internal diameter of 1 9 mm were first wound round the core in three distinct spirals. The pitch of each spiral was 30 mm and the sense of winding was opposite to that of the strands of the core.

A layer of E.T.F.E. 1-2 mm in thickness was then deposited by extrusion. This layer assumed a corrugated form as shown in Figure 5.

The resulting cable could be wound and unwound on a mandrel 50 mm in diameter without any effort and without damage to the insulation.

By comparison, an insulating layer of E.T.F.E. having the same average thickness as in the previous cable was directly extruded over a core 70 mm2 in cross-section. The resulting cable could only be wound over a mandrel 400 mm in diameter and only with considerable effort. When attempts were made to wind it over a mandrel 300 mm in diameter, the insulation tore in the stretched parts. In both cases, the cable did not spontaneously resume its initial form after it had been bent.

In addition to the advantages resulting from the flexibility conferred on the cables according to the invention, it was found that the corrugations of the sheath, since they reduce the number of points of contact, have the effect of considerably facilitating the winding, unwinding and stretching of the cable and the handling and positioning thereof in general. Conversely, the increased external surface area of the cable, which is approximately double that of the external surface of a conventional cable of the same cross-section, improves cooling of the cable and enables a substantially higher average current intensity to be used than in an identical cable which is covered with a smooth insulation.

WHAT WE CLAIM IS: 1. A flexible insulated electric cable of indefinite length, cable comprising a conductive core and a surrounding insulating material which is relatively rigid under the conditions of use of the cable, characterised in that the insulating material is maintained in a non-slipping relationship to the conductive core and in corrugated shape by means of a hollow profiled member or members interposed between the conductive core and the insulating material.

2. A flexible insulated electric cable according to claim 1, in which the hollow profiled members are transversely placed rings.

3. A flexible insulated electric cable according to claim 1, in which a hollow profiled member is wound spirally around the core.

4. A flexible insulated electric cable according to any one of claims 1 to 3, in which the insulator is a copolymer of ethylene and tetrafluoroethylene.

5. A process for the manufacture of a flexible insulated electric cable according to any one of claims 1 to 4, in which process insulation is deposited on a support which has previously been provided with a hollow profiled member or members adapted to form and to support the corrugations of the insulating material.

6. A process for the manufacture of a flexible insulated electric cable according to claim 5, in which the insulation is deposited by extrusion.

7. A process for the manufacture of a flexible insulated electric cable according to claim 5, in which the insulation is deposited by taping.

8. A process according to claim 5, substantially as herein described with reference to the accompanying drawings and/or the specific example.

9. Cables manufactured by a process as claimed in any of claims 5 to 8.

10. A cable according to claim 1, substantially as herein described with reference to the accompanying drawings and/or the specific example.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. By comparison, an insulating layer of E.T.F.E. having the same average thickness as in the previous cable was directly extruded over a core 70 mm2 in cross-section. The resulting cable could only be wound over a mandrel 400 mm in diameter and only with considerable effort. When attempts were made to wind it over a mandrel 300 mm in diameter, the insulation tore in the stretched parts. In both cases, the cable did not spontaneously resume its initial form after it had been bent. In addition to the advantages resulting from the flexibility conferred on the cables according to the invention, it was found that the corrugations of the sheath, since they reduce the number of points of contact, have the effect of considerably facilitating the winding, unwinding and stretching of the cable and the handling and positioning thereof in general. Conversely, the increased external surface area of the cable, which is approximately double that of the external surface of a conventional cable of the same cross-section, improves cooling of the cable and enables a substantially higher average current intensity to be used than in an identical cable which is covered with a smooth insulation. WHAT WE CLAIM IS:

1. A flexible insulated electric cable of indefinite length, cable comprising a conductive core and a surrounding insulating material which is relatively rigid under the conditions of use of the cable, characterised in that the insulating material is maintained in a non-slipping relationship to the conductive core and in corrugated shape by means of a hollow profiled member or members interposed between the conductive core and the insulating material.

2. A flexible insulated electric cable according to claim 1, in which the hollow profiled members are transversely placed rings.

3. A flexible insulated electric cable according to claim 1, in which a hollow profiled member is wound spirally around the core.

4. A flexible insulated electric cable according to any one of claims 1 to 3, in which the insulator is a copolymer of ethylene and tetrafluoroethylene.

5. A process for the manufacture of a flexible insulated electric cable according to any one of claims 1 to 4, in which process insulation is deposited on a support which has previously been provided with a hollow profiled member or members adapted to form and to support the corrugations of the insulating material.

6. A process for the manufacture of a flexible insulated electric cable according to claim 5, in which the insulation is deposited by extrusion.

7. A process for the manufacture of a flexible insulated electric cable according to claim 5, in which the insulation is deposited by taping.

8. A process according to claim 5, substantially as herein described with reference to the accompanying drawings and/or the specific example.

9. Cables manufactured by a process as claimed in any of claims 5 to 8.

10. A cable according to claim 1, substantially as herein described with reference to the accompanying drawings and/or the specific example.