US 3073889 A
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Description (OCR text may contain errors)
Jan. 15, 1963 A. MoQRE ELECTRIC SUBMARINE CABLE'S 2 Sheets-Sheet 2 Filed Aug. 3, 1959 lnverlor H.A.MOORE By a ,tz
Attorney United States Patent Ofice 3,073,889 Patented Jan. 15, 1963 3,073,889 ELECTRIC SUBMARINE CABLES Hayden A. Moore, London, England, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Fiied Aug. 3, 1959, Ser. No. 831,135 Claims priority, application Great Britain Aug. 15, 1958 Claims. (Cl. 174-102) This invention relates to electric submarine cables.
A submarine cable of the coaxial conductor type is known in which the central conductor consists of stranded metal wires around which is a copper tape applied in overlapping helical turns. It is also known to apply the copper tape longitudinally with the edges formed into a continuous box seam. The dielectric separating this central conductor from an outer conductor is a solid dielectric such as polythene applied by extrusion.
Ditiiculty has arisen in the extrusion process because air in the interstices between the strands expands as a consequence of the heat in the extruder and forms air bubbles in the dielectric. Proposals have been made to fill the interstices between the strands with a suitable dielectric such as a mixture of polythene and polymerised isobutylene. Apart from ditficulty in controlling the diameter of the conductor there has been trouble with bursting of the sealed copper tube at the seam. There is also some danger of increasing the A.C. resistance of the conductor with this method.
It has, therefore, been proposed to remove the air from the interstices between the conductor strands by passing the stranded conductor through a heated and evacuated chamber, immediately before the conductor passes into the extrusion machine, but this has not proved successful.
According to the present invention copper tape is wrapped longitudinally around the stranded centre member and the seam of the tape is hermetically sealed.
The invention will be better understood from the following description of one embodiment thereof taken in conjunction with the accompanying drawings in which:
FIG. 1 is a cross-section of a core of a Submarine cable according to the invention and FIG. 2 is a perspective view showing a method of making such core.
Referring to the drawings, FIG. 1 shows a cross section of a core of a Submarine cable. This core consists of a strand 1 of metal wires surrounded in known manner by a copper tape 2 folded longitudinally about the strand 1 with the meeting edges formed into a box seam 3. According to the present invention the meeting edges of the box seam 3 are sealed by means of a filament 4 of plastic material, which is illustrated as being an organic thermoplastic material such as polythene which has been heated to cause it to ow between the meeting edges of the box seam and so seal the seam.
One method of applying a filament of polythene is shown in FIG. 2. The polythene filament 4 is led through a tube 5 so that it is applied immediately under the meeting edges of the copper tape 2 as the box seam 3 is formed. The method of folding the copper tape longitudinally and forming a box seam is well known and need not therefore be described.
The core shown in the drawings was formed with a strand *1 of 19 mild steel wires and the polythene filament 4 was 0.03 inch in diameter. This core formed the inner conductor of a Submarine coaxial cable and a dielectric of polyethylene 6 was extruded around this core and enclosed in a conductor 7. The core was heated in the usual manner at the entry to the extrusion machine by means of gas flames and the heat so applied caused the polyethylene of the filament 4 to flow between the meeting edges of the box seam and between the conductors adjacent to the box seam and the copper tape 2 thus hermetically sealing the metal strands within the copper tape.
With such a construction the difficulties formerly occurring have been overcome and no air bubbles have been formed in the surrounding dielectric.
It is clear that the heat sealing of the box seam could be eii'ected by any convenient form of heating such as high frequency induction heating of the copper tube or D.C. resistance heating through a contact roller. It is also clear that the heating could be carried out immediately after the seam is formed or during the formation of the seam.
Although the filament 4 has been described as being of an organic thermoplastic material it could equally be a plastic metal such as lead which would flow under the heat applied.
While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.
What we claim is:
l. In an electric cable, a core, a metal tape folded longitudinally of itself as a sheath about the core with the lateral edges of the tape formed into a box seam, a length of plastic material disposed inside said sheath and contiguous with the core and said box seam to provide a seal for said seam, a solid dielectric surrounding the seamed metal tape and an outer conductor surrounding the dielectric.
2. Electric cable as claimed in claim 1 in which the said length of plastic material is a filament of thermoplastic organic material.
3. Electric cable as claimed in claim 1 in which said length of plastic material is composed of polyethylene.
4. Electric cable as claimed in claim 1 in which the said length of plastic material is composed of lead.
References Cited in the file of this patent UNITED STATES PATENTS 2,492,568 i Gillis Dec. 27, 1949 2,711,439 Smith June 21, 1955 FOREIGN PATENTS 83,383 Switzerland Dec. 1, 1919