IL39280A

IL39280A - Electrical cable with a protected core

Info

Publication number: IL39280A
Application number: IL39280A
Authority: IL
Original assignee: Fmc Corp
Priority date: 1971-05-11
Filing date: 1972-04-24
Publication date: 1974-11-29
Also published as: BE782909A; ZA722700B; BR7202806D0; AU4155372A; FR2137682A1; DE2218412A1; GB1396594A; CH556089A; IT957809B; US3701840A; PH9819A; AT318732B; AU468436B2; CA961127A; IL39280A0; FR2137682B1; ES402507A1; SE7205899L; NL7205399A

Description

BJaia na»V ya * o»n ^ Electrical cable with a reteeted core The present invention is directed to an electrical cable having an improved protective barrier for the conductor core thereof.

Described in the United States Patent 3,244,799 is an electrical cable having a conductor core formed of a plurality of individually insulated conductor wires, a corrugated tape or strip of polyester film surrounding the conductor core, and an outer protective covering, which includes a metallic shield and a jacket of thermoplastic material which- is applied while still in a molten condition „ The corrugated tape employed in such electrical cable is formed of single thickness (non-laminated) polyester film, with the corrugations thereof being uniform and extending longitudinally thereof, and may be either wound spirally about the conductor core or applied longitudinally thereto with their longitudinal edges overlapped „ In electrical cables as described in the cited patent, the corrugated tape provides air spaces in the area between the conductor core and the surrounding metallic shield which serve to insulate the core against the transfer of heat applied to the metallic shield during jacketing of the cable with the molten thermoplastic material. These air spaces also pneumatically cushion the conductor core against mechanical forces applied to the cable and which might otherwise damage the core insulation.

It is well known in the art that polyester film is well suited for use as a protective barrier in electrical cables since such film does not absorb moisture, has a low Such leakage, of course, involves a waste of materials, creates processing problems and, most important, provides electrical cables with variable and unreliable characteristics Significantly, when corrugated barrier tapes, as heretofore described, are employed in the manufacture of jell-filled electrical cables, there is a pronounced tendency for the electrical insulating jell to escape.

It appears that this effect is due to the longitudinal corrugations in the barrier tape serving as flow channels for the jell, permitting such jell to travel freely toward overlapping edges of the tape at which leakage may occur. Accordingly, a primary object of this invention is to provide an improved protective barrier for a conductor core of an electrical cable.

Another object of this invention is the provision of an electrical cable having a conductor core surrounded with a protective barrier formed of embossed polymeric film, and particularly polyethylene terephthalate film, which affords mechanical protection, thermal insulation, dielectric protection, and electrical stability for such core.

Still another object of the present invention is to provide a protective barrier which is adapted to form an essentially liquid-tight seal about a conductor core of an electrical cable.

A further object is to provide an electrical cable having an electrical insulating jell contained between a conductor core and a protective barrier formed A still further object is to provide, for use in electrical cables, a protective barrier having embossments which are adapted to interlock with each other when overlapped and thereby form an essentially fluid-tight joint therebetween.

These and other objects of the invention are achieved by the use of an embossed polymeric film as a protective barrier between a conductor core and an outer protective covering of an electrical cable. This protective barrier is preferably formed of polyethylene terephthalate film and is hereafter described as such. However, films formed of other polymeric materials may be employed, providing such films do not absorb moisture, have a low dielectric constant, low dissipation factor, high dielectric strength and are capable of being embossed and permanently retaining such embossments.

The embossed polyester film forming the protective barrier of the present invention is applied as a tape or strip, either longitudinally or spirally about the conductor core, with its longitudinal edges in overlapping relationship. Once applied, the embossments on such tape form air spaces between the conductor core and an overlying metallic sheath which, together with a jacket of thermoplastic material, constitutes the protective outer covering of the cable. These contained air spaces serve as a thermal insulation and pneumatically cushion the conductor core from external forces. arrangement thereof, and are separated from each other only by linear portions of the film.

In electrical cables, the embossed polyester film of the present invention affords the above-described advantages regardless of whether its embossed or recessed side is in facing relationship with the conductor core.

For a greater understanding of this invention, reference is made to the following detailed description and accompanying drawing in which Figure 1 is a side view of an electrical cable which incorporates the protective barrier of the present invention, with portions of such cable being broken away to illustrate various elements thereof; Figure 2 is a transverse section through the electrical oable taken substantially along the line II-II of Figure 1; Figure 3 is a plan view of a portion of the protective barrier employed in the cable show in Figure 1; Figure 4 is a vertical section take substantially along the line IV-IV of Figure 3 Figure 5 ii a vertical section taken substantially along the line V-V of Figure 3, and Figure 6 is a section! similar to that shown in Figure 3, taken through overlapping edge portions of the protective barrier.

With reference to Figures 1 and 2 of the drawing, the electrical cable there illustrated is indicated generally by the character 11 and includes a conductor core 13 composed of a plurality of individually insulated wires, a protective barrier 15, an electrical insulating tive barrier 15, a metallic sheath 19 over the protective barrier 15, and a jacket 21 of thermoplastic material.

The cable 11 is assembled in the conventional manner with the core wires being first passed through a bath of molten jell 17, and then squeezed together to force out excess jell and to fill all voids in the remaining jell. Protective barrier 15, in the form of a tape or strip, is then applied longitudinally of the conductor core 13 with its longitudinal edges in overlapping relationship. After-which, the metallic sheath 19 is provided over the wrapped core and is covered with a molten thermoplastic material to form the jacket 21 thereon.

Illustrated in greater detail in Figures 3-5 is the protective barrier 15 which is formed of a film of polyethylene terephthalate having a normal flat thickness of perhaps .05 mm. Polyethylene terephthalate films of greater thickness can be employed, providing they are capabl of being embossed and permanently retain the embossment or deformations set therein. Embossing of the polyethylene terephthalate film may be achieved in any convenient manner, as for example by heating such film to a temperature below its softening point, followed by nipping such film, under relatively high pressure, between a cool, engraved metal roll and a rubber covered back-up roll.

The pattern of the embossments 23 formed in the polyethylene terephthalate film are of like size and configuration and are preferably in a closely-packed array so that only linear portions of the original film appear between adjacent embossments. The perimeters of the and desirably are of polygonal configuration, as for example of a hexagonal pattern as illustrated, to facilitate a close packing thereof.

More particularly, in the protective barrier 15 shown in Figures 3-5, the hexagonal embossments 23 are arranged in substantially parallel rows, as indicated by the lines 25, with the embossments in the directly adjacent rows being in staggered relationship with each other. With this arrangement, only linear portions 27 of the original film remain between adjacent embossments 23. The lengths of these individual linear portions 27 will, of course, depend upon the particular configuration and size of the embossments themselves.

The staggered array of the closely spaced embossments provides very restricted circuitous paths along which flow of the jell 17 during cable assembly is difficult and continually retarded. More important, as illustrated in Figure 6, overlapping edge portions of the barrier 15 interlock with each other, that is, embossments 23 projecting from the surface of one of such overlapping edge portions mate and are gripped firmly with depressions 29 in the surface of the other of such overlapping edge portions. As a result of this firm interlocking, these overlapping edge portions of the protective barrier 15 together provide a compact and snug or essentially liquid-tight joint. - -

Claims

39230/2 CLAIMS8

1. An electrical cable having a conductor core, a protective barrier for said core, which barrier does not absorb moisture and has a lov dielectric conten , low dissipation factor and a high dielectric strength, a metallic shield disposed over said protective barrier, and a continuous covering of a solidified plastic material on said metallic shield, characterised in that the protective barrier is formed of a flexible polymeric film enveloped about said conductor core with its longitudinal edge portions in overlapping relationship, and the flexible polymeric film having rows of permanently pre-se , substantially like, individual embossments projecting from one surface thereof, said individual embossments being closely packed arid in substantially abutting relationship with each other, and permanently pre-set, substantially like, individual depressions in the other surface thereof, the depressions being aligned v/ith the embossments, and the rows of embossments in the polymeric film being arranged in substantially parallel relationship,

2. A cable according to Claim 1, characterized in that the embossments in each of the rows of embossments are i staggered relationship with the embossments in the rows directly adjacent thereto.

3. A cable according to Claim 2, characterized in that the perimeters of the embossments are of polygonal contour and the portion of the film between adjacent embossments are linear.

4. A cable according to Claim 2 or 3, characterized in that the eiabossments projecting from one surface of the film interlock with depressions in the other surface of the film along the overlapping portions thereof. 39280/2 ~i

5. , A cable according to any one of the preceding claims, characterised in that an electrical insulating gel is between said conductor core and the polymeric film.

6. An electric cable substantially as hereinbefore described by way of example and with reference to the accompanying drawings- For the Applicants DR. REINHOLD COEDS! AND PARTNERS ISJCB