Pressure Resistant Cable

Abstract

A land lines communication cable system resistant to shock pressures comprises an integral tensile unit wherein tensile tapes covering the cable lengths are secured to splice cases, and an integral compressive unit wherein a plurality of both cable lengths and splice boxes are filled with an intercommunicating incompressible pasty composition.

Parent Case Text

This is a division of application Ser. No. 116,845 filed Feb. 19, 1971 now abandoned.

Description

BACKGROUND OF THE INVENTION

Communication cables, which in this application are construed to include cables for communicating not only voice signals but signals other than voice signals including what are sometimes designated control cables, are herein designated land lines cables as distinguished from submarine cables. Such cables in combination with splices and/or auxiliarly equipment such as amplifiers comprise a cable system which may be buried in whole or in part. While it has been known to protect cables, including communications cables, from mechanical damage by covering them with armor wires or tapes, this has not provided protection against gaseous pressure waves that pass through interstices in the armor, or tensile forces so great in extent that they affect areas beyond the termination of the armor. Conventional cables, even if they are protected by armor, can be crushed by high external gas pressures so that the conductors within the cables are severed or shorted to each other by the destruction of their insulation. Although it has been known to fill communication cables with pasty compositions to keep out moisture, such compositions have not constituted any protection against local crushing pressures since a filling of composition would yield under pressure either by being extruded to an opening in the cable sheath or swelling or bursting the sheath at a low-pressure area.

SUMMARY

We have invented a land lines communication cable system at atmospheric pressure that is highly resistant to destruction by severe external shock pressures. This system comprises a plurality of lengths of cable each comprising a plurality of insulated communications conductors and a tubular sheath, such as a polymeric extrudate, surrounding the conductors and a plurality of layers of high-tensile-strength armor tapes surrounding the sheath. Our system also comprises at least one connection between the cable lengths comprising a splice between the conductors of the different cable lengths and a splice case enclosing the splice and, possibly, auxilliary apparatus. The splice case is characterized by the fact that, although it is normally maintained at atmospheric pressure, it has substantial hoop strength and is capable of withstanding high tensile and compressive shock forces. The case comprises means at both ends for securing the armor tapes of different lengths of cable so that tensile stresses are carried through one of the lengths, the case, and the tapes of another length acting as one continuous tensile member. An incompressible pasty composition fills all void spaces within the cable sheaths and the splice case and can flow from one to the other under a high pressure differential. Since, however, the case is filled with composition and has an exceedingly high hoop strength the composition in the cable has no outlet to flow into when a portion of the cable is subject to compression. It cannot burst out of a remote section of the cable itself because of the high tensile strength of the armor tapes.

A preferred embodiment of cable for our system comprises a continuous extruded tubular polymeric sheath surrounding a plurality of insulated communication conductors, a corrugated steel shielding tape wrapped with an overlapped longitudinal seam to surround the sheath, and a continuous extruded polymeric jacket over the shielding tape. This tape has an overlapping portion of itself and would be free to yield under compression in the absence of pasty filler. A first layer of high-tensile-strength armor tapes is helically wrapped around the cable jacket with one direction of lay and is directly covered with another layer of high-tensile-strength armor tapes with a reverse direction of lay. In addition to their structural effect the armor tapes provide additional electric and magnetic shielding of the conductors and we have found that this shielding is enhanced as a result of the separation of the armor tapes from the corrugated shielding tapes by the extruded sheath. A continuous, polymeric, outer jacket is extruded over the second layer of armor tapes. These jackets and also the sheath, preferably comprise a polyolefin and our system may comprise a number of splice boxes and cover a distance miles in extent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view, partly in section, of the cable system of our invention.

FIG. 2 shows a cut-away pictorial view of a cable of our invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A cable system, designated generally by the numeral 10, comprises a plurality of cable lengths 11, 12, 13, 14 15 with interconnections 16, 17, 18 comprising splice cases 19, 21, 22 of which we shall describe the interconnection 16 and splice case 19 in more detail hereinbelow. The structure of a cable 23 forming the cable lengths 11-15 is shown in detail in FIG. 2 to comprise a plurality of insulated conductors 24, twisted into pairs in a known manner. Each of the insulated conductors has a copper wire 26 and a surrounding wall of polyethylene insulation 27. Our invention is, of course, not limited by the particular type of communication conductors in the cable 23 which may include coaxial cables, quads, unpaired conductors, and, indeed some additional strands other than communication conductors. 25 pairs of the insulated conductors 24 are stranded together to form a core 28. In the illustrated cable the conductors are No. 16 Awg (American Wire Gage) solid copper with 20-mil walls of solid polyethylene insulation, and the core formed by these conductors is wrapped with an 0.016-inch-thick tape 29 of SBR (styrene-butadiene rubber) backed with polyester film. A sheath 31,90 mils thick, of low-density polyethylene is extruded over the core 28 and over this has been folded a ten-mil corrugated shielding tape 32 of low-carbon, tin-coated steel. Over the steel tape 32 is extruded a 120-mil jacket 33 of low-density polyethylene to a diameter of 1.845 inch. A plurality of high-tensile strength tapes 34 are wrapped around the jacket 33 in two layers 36 and 37. The tapes 34 are rolled from copper-clad steel to a dimension of 0.050 .times. 0.200 inch, the layer 36 being applied with a 12 1/2 inch right hand lay and the layer 37 with a 12 1/2 inch left hand lay. The reverse lays of the layers 36 and 37 keep the cable balanced under tension and the pitch diameter of the armor tape layers is long enough to provide an extremely high tensile strength for the cable as a whole, easily withstanding a pull of 30,000 pounds without damage, while at the same time being short enough to provide the hoop strength necessary to confine the contents of the core when portions of the cable are subjected to compression.

In addition the armor tapes 34 reinforce the shielding effect of the tape 32. The shielding effect of the armor layers 36, 37 is enhanced by the reverse lays of the two layers and the close spacing of the tapes within each layer. A pasty composition 38 fills the space between the conductors 24 in the core 28. This composition is essentially incompressible and preferably will be water insoluble and have a high dielectric strength. A suitable composition is described in U.S. Pat. NO. 3,539,708.

An overall low density polyethylene jacket 39 is extruded over the layer 37 providing mechanical and moisture protection to the cable 23. The large size and weight of the cable 23 limits the continuous length that can be delivered to any installation site so that connections will be required even in the absence of amplification or branching of the cable system.

To make a connection such as the interconnection 16, the wires 26 of the cable lengths 11 and 12 can be spliced by any suitable means of which several are known, after cutting away the overlaying layers as shall be explained. The splice is finally protected by the heavy splice case 19 which is formed by bolting together upper and lower flanged sections 41, 42 with a large plurality of bolts and nuts 44 to provide a very high hoop strength. The ends of the sections 41, 42 bolt to end plates 46, 47 by means of cap nuts 48. The end plates 46, 47 have circular grooves 49 scored for firm gripping of the armor tapes 34 which are wrapped around steel rings 51 shaped to fit the grooves 49 on one face 52 and flattened on the other face 53. The flattened surface 53 serves to grip the ends of the tapes 34 against a scored surface 54 of a facing plate 56 which is locked against the ring 51 by means of long bolts 57 which thread into taps in the plate 46. A gusseted stub tube 58 fits a counter bore 59 in the facing plate 56, the plate 56 and tube 58 having an inside diameter closely fitting over the layer 37. The case 19 encloses a split inner steel casing 61 having thin tubular extensions 62 that fit closely over the shielding tape 32 and make electrical contact with the shielding 32, such as by being wired down upon the tape or soldered to it so that the casing 61 affords shielding continuity between tapes 32 of the two lengths 11, and 12, and so on. Thus throughout our system the shielding is continuous. Similarly the case 19 itself provides shielding continuity as well as structural continuity of the layers 36, 37. The splices in the wires 26 are staggered within the casing 61 and the tapes 29, 32 and sheath, 31 are cut off so that they extend a short distance within the casing 61 to expose the conductors 24 for splicing. The jacket 33 is cut off so that it extends within the case 19 a short distance from the extension 62. The tapes 34 are cut so as to leave enough free length for wrapping around the ring 51, and the jacket 39 is cut just short of abutting the tube 58.

Surrounding the splice in the wires, the casing 61 is completely filled with the pasty composition 38 forming a continuum with the composition in the cable cores. Outside of the casing 61 composition fills the remaining space in the case 19. There is, in fact, a continuous pressure contact of the composition 38 within our system including the cable lengths 11, 12, 13, 14, 15 and cases 19, 21, 22. The case 22 is bifurcated at one end to provide for a branched splice but each of bifurcations 63, 64 is provided with plates 56, 46 and ring 51 to anchor the tape armors in the manner of the case 19.

We have invented a new and useful cable system of which the foregoing description has been exemplary rather than definitive, and for which we desire an award of Letters Patent as defined in the following claims.

Claims

1. A cable for a land lines communication system resistant to destruction by high external shock pressures comprising:

A. a plurality of insulated communication conductors,

B. a wrapping comprising polyester film, surrounding said conductors,

C. a continuous, extruded, tubular polymeric sheath directly covering said polyester film,

D. an incompressible pasty composition completely filling all void spaces within said sheath at atmospheric pressure,

E. a corrugated steel shielding tape wrapped with an overlapped longitudinal seam surrounding said sheath,

F. a continuous extruded tubular polymeric jacket surrounding said shielding tape,

G. a first layer of high-tensile-strength copper-clad steel armor tapes helically wrapped around said jacket with a selected direction of lay,

H. a second layer of high-tensile-strength copper-clad steel armor tapes helically wrapped over said first layer with a direction of lay in reverse of the direction of said first layer,

I. a continuous extruded polymeric outer jacket surrounding said second

2. The cable of claim 1 wherein said sheath and said jackets comprise polyethylene.