US3766309A - Electric cable with corrugated metallic sheath - Google Patents

Abstract

An electric cable having one or more insulated cores surrounded by a corrugated metal sheath and having a tubular covering intermediate the core and the sheath which covering is softer than the core and is deformed by the sheath corrugations which are embedded therein. The covering may be wrapped tapes of crepe paper or expanded foam synthetic resin or a tube of synthetic resin extruded over the core or cores.

Description

United States Patent [1 1 Calzolari et al.

[ 1 ELECTRIC CABLE WITH CORRUGATED METALLIC SHEATI-I [76] Inventors Pietro Calzolari, Viale Restelli No. 37; Sergio Longoni, Via A. Mario, 67, both of Milan, Italy [22] Filed: July 13, 1971 [21] Appl. No.: 162,199

[30] I Foreign Application Priority Data July 14, 1970 Italy 27395 A/70 [52] US. Cl, 174/102 D, 174/110 F, 174/122 R [51] Int. Cl. HOlb 7/20 [58] Field of Search 174/102 R, 102 D,

174/105 R, 106 R, 106 D, 107', 28, 29, 110 F, 110 SR, 120 R, 120 FP,12O SR, 122 R [56] References Cited UNITED STATES PATENTS 3,557,301 l/1971 Priaroggia 174/102 D 2,995,616 8/1961 Nicolas 174/102 D 2,890,263 6/1959 Brandes et a]. 174/29 3,590,141 6/1971 Mildner 174/107 X 3,173,990 3/1965 Lamons.... 174/102 D 3,394,400 7/1968 Lamons..... 174/102 R 3,130,256 4/1964 Mildner 174/107 X FOREIGN PATENTS OR APPLICATIQNS 1,047,896 12/1958 Germany 174/110 F Primary Examiner-Bernard A. Gilheany Assistant Examiner--A. T. Grimley Attorney-Lorimer P. Brooks et al.

[5 7] ABSTRACT An electric cable having one or more insulated cores surrounded by a corrugated metal sheath and having a tubular covering intermediate the core and the sheath which covering is softer than the core and is deformed by the sheath corrugations which are embedded therein. The covering may be wrapped tapes of crepe paper or expanded foam synthetic resin or a tube of synthetic resin extruded over the core or cores.

4 Claims, 2 Drawing Figures Patented Oct. 16, 1973 s a My W Wm m B26 v w a m&4% 3% 5 ELECTRIC CABLE WITH GQRRUGATED METALLIC SHEATH .ble, under operating conditions.

In the prior art, cables covered with corrugated metallic sheaths, for example, an aluminum sheath, a gap was left between the sheath and the cable core contained therein with the object of avoiding damage to the core during the external metallic sheath forming process.

Frequently, due to particular layout requirements, under working conditions, telecommunication, power transmission or control, cables encounter surroundings which subject them to strong unidirectional vibrations, for example, in the subsoil of a motorway or when arranged in vertical wells, so that only the sheath is firmly fixed while the cable core has to support its own weight. In these exceptional circumstances, it is' possible that the stresses which tend to move the core with respect to the sheath exceed the maximum detachment resistance between the two parts.

When these conditions are present, slipping occurs between the sheath and cable core which can cause serious trouble, e.g. breaks, contact between ducts, etc., which trouble in the main, though not exclusively, is found at the critical points, such as near the junctions and terminals.

The present invention serves to eliminate the abovementioned problems, with a cable with corrugated metallic sheath in which the anchoring force applied to the sheath is transmitted by the latter to the core of the cable thus preventing the relative slipping between sheath and core during operation, while offering the maximum assurance that the core of the cable will retain unaltered its integral structure.

In particular, the present invention concerns an electric cable comprising a core contained in a corrugated metallic sheath, characterized by the fact that it also comprises a soft tubular covering, protecting and engaging said core, the corrugations of the sheath embedding themselves, for at least a part of their depth, in the soft tubularcovering, so that the corrugations of the sheath deform the covering and grip it.

- The attached drawings illustrate, by way of example,

preferred embodiments of cables produced in accordance with the invention as follows, and in such drawings:

FIG. 1 represents a longitudinal axial, partial section of an electric cable with a corrugated metallic sheath according to a preferred form-of the invention; and

FIG. 2 represents a longitudinal axial, partial section of an electric cable with corrugated metallic sheath according to a further form of the invention.

The electric cable which could be of the telecommunication, power transmission or control type, comprises a core 11 surrounded by a corrugated metallic sheath 12, preferably of aluminum. The space between the corrugated-'matallic sheath 12 and the core 11 of thecable, is'occupied by a soft tubular covering 13 in which the helical corrugations 14 of the metallic sheath are embedded for the whole of their depth.

The core 11 shown in FIG. 1 comprises a conductor 17, either solid or stranded, surrounded by one or'more layers of insulation 18 which may in turn be surrounded by one or more layers of insulation, conductive material or semi-conductive material 19. Such layer or layers 19 are covered by an outer protective layer or layers 20, such as a wrapping of non-conductive material or a metal sheath. However, the core 11 may take any conventional form or the core may be a plurality of separately insulated conductors contained within the cov ering 13. i

The material of the covering 13 is softer, i.e. more readily deformable, than the outer covering of the core 11, so that it may be deformed as shown in FIG. 1 without applying pressure to the core 11 which would cause any substantial deformation thereof. The covering 13 frictionally engages the exterior of the core 11 so as to resist slipping of the core 11 with respect thereto. The material of the covering 13 is self-sustaining and resilient and is to be distinguished from sealing compounds sometimes used to fill the corrugations of the sheath 12, the latter compounds being flowable and having a low shear strength and therefore, offering little resistance to slipping between the sheath 12 and the core 11.

According to a preferred embodiment, the covering 13 on the core 11 of the cable is formed by helically winding or longitudinally applying, during the manufacturing process, one or more tape-like elements, for example, tapes of crepe paper, or of synthetic material, such as, for example, expanded foam. This soft tubular covering 13 of a suitable thickness, provides protection for the core 11, during the corrugating phase of the sheath 12. Preferably, its thickness is at least equal to the spacing, if any, between the smallest interior surface of the sheath 12 and the core 11 plus at least onehalf the interior depth of the corrugation.

During said corrugating phase, the work is carried out in such a way that the corrugation of the sheath 12 depresses, or becomes embedded in, the covering 13 which, being soft, adapts itself to the internal shape of said sheath 12, while providing in all cases, a sufficiently protecting layer between the lowest points l4, 15, etc. of the helical corrugations and the core 11.

In this way an interengagement is obtained between the soft tubular covering 13 and the corrugated metallic sheath 12 which tightly fastens to the latter the core 11 of the cable 10, ensuring in addition that the integral structure of the core 11 is preserved during the corrugating phase and preventing the danger of slipping between the core 11 and the sheath 12 during operation.

According to another embodiment, the soft tubular covering 13 can also be obtained by the extrusion of synthetic material on to the core 11 of the cable 10.

In addition, the sheath 12 can be embedded in the covering 13, for the whole of the depth of its corrugations, as in FIG. 1, or for at least a part of said depth, so that spaces 17 are left between the soft tubular covering l3 and the highest point 16 of the corrugations, as shown in FIG. 2.

As will be noted, both the embodiments completely of aluminum or any other type of conducting metal, during operation.

The construction details of the cable of the invention can, of course, be changed according to requirements, without departing from the principles of the invention.

What is claimed is:

1. An electric cable comprising at least one core including a conductor surrounded throughout its length by at least one layer of insulating material, a corrugated metal sheath surrounding said core, and a tube of solid material intermediate said core and said sheath with the corrugations of said sheath embedded in said tube for preventing slipping of said core and said sheath relative to each other in a direction extending longitudinally of said cable when said cable is suspended by said sheath, said tube being formed by at least one tape made of an insulating material different from that of and having at least a portion of its interior in frictional engagement with the exterior of said core thereby to provide a tube of tape of solid material between said core and said sheath in frictional engagement with both said sheath and said core which substantially prevents significant relative movement between said core and said sheath longitudinally of said cable when said cable is suspended by said sheath, said material of said tape being softer than the material of said core so as to permit deformation and compression of said tube by said corrugations of said sheath without substantial deformation of said core and said material of said tape also being self-sustaining and resilient and having a shear strength sufficient to prevent said relative movement without shearing thereof.

2. A cable as set forth in claim 1, wherien said tape is made of crepe paper.

3. A cable as set forth in claim 1, wherein said tape is helically wrapped around said core.

4. A cable as set forth in claim 1, wherein said tape extends longitudinally of said core.

Claims (4)

1. An electric cable comprising at least one core including a conductor surrounded throughout its length by at least one layer of insulating material, a corrugated metal sheath surrounding said core, and a tube of solid material intermediate said core and said sheath with the corrugations of said sheath embedded in said tube for preventing slipping of said core and said sheath relative to each other in a direction extending longitudinally of said cable when said cable is suspended by said sheath, said tube being formed by at least one tape made of an insulating material different from that of said layer, deformable by the corrugations of said sheath and having a normal exterior size in the absence of deformation thereof by said corrugations which is greater than the minimum diameter of said corrugations so that portions of said tube at least partially fill said corrugations and said tube encirculing said core and having at least a portion of its interior in frictional engagement with the exterior of said core thereby to provide a tube of tape of solid material between said core and said sheath in frictional engagement with both said sheath and said core which substantially prevents significant relative movement between said core and said sheath longitudinally of said cable when said cable is suspended by said sheath, said material of said tape being softer than the material of said core so as to permit deformation and compression of said tube by said corrugations of said sheath without substantial deformation of said core and said material of said tape also being self-sustaining and resilient and having a shear strength sufficient to prevent said relative movement without shearing thereof.

2. A cable as set forth in claim 1, wherein said tape is made of crepe paper.

3. A cable as set forth in claim 1, wherein said tape is helically wrapped around said core.

4. A cable as set forth in claim 1, wherein said tape extends longitudinally of said core.

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