US2527172A - Reinforced soldered-seam metal sheathed cable - Google Patents

Description

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REINFORCED soLDERED-SEAM METAL smmn CABLE Filed Nov. 20, 1945 2 Sheets-Shoot 2 l5 /5 gf l F/Ga 6 F/GS Patented Oei. 24, 1950 REINFORCED SOLDEBED-SIAM METAL SHEATHED CABLE Charles James Beaver, Bowden, and Edward Leslie Davey, Timperley, England, mignon to W. T. Glover & Company Limited, Manchester, Lancashire, England, a British company Application November 20, 1945, Serial No. 629,808 In Great Britain November 24, 1944 2 Claims.

This invention relates to electric cables of the kind which, when in service, work with a substantial difference of pressure between the inside and outside of the sheath which covers the dielectric of a core or of a group of cores. the pressure difference being due to the application of fluid under high pressure inside the sheath. The invention is particularly applicable for use with the Glover high pressure gas-filled cable (see the Journal of the Institution of Electrical Engineers, volume 91, part II, page 35 and U. S. Patent Specification No. 2,067,169).

The invention is concerned with the improved construction of the part of the cable immediately surrounding the dielectric. In this improved construction the sheath is replaced by an envelope made from thin metal tape which is formed to shape by running it longitudinally on the core (or group of cores) bending it transversely to enclose the core and to form flanges, lying side by side and projecting radially where the edges of the curved portion of the tape meet, joining these flanges, by soldering, and bending the united flanges over so as to lie upon or close to the exterior of the adjacent wall of the envelope and then binding the envelope with reinforcing metal tape applied helically with short lay, with or without a layer of bedding between it and the sheath. The metal tape envelope takes the place of the usual lead sheath with substantial advantages. It can be made of only a few mils thickness, whereas a lead sheath is of the order of 100 mils in thickness.

The tape used for the envelope is preferably of soft copper, but brass or other suitable strong, soft metal may be used. For the reinforcement, metals such as hard brass. steel, phosphor bronze or cadmium copper may be used. In addition to serving their normal function as reinforcement,

they assist the envelope by retaining the flangey in its position against the wall of the envelope. In this position the soldered joint between the flanges is nearly wholly in shear and the shear stress may be reduced to a desirable low value by giving an appropriate circumferential width to the flanges.

Owing to the differences in the mechanical' properties of the metal tapes used for the envelope and for the reinforcement, it can be provided that the greater part of the load due to the pressure is carried by the reinforcing tapes so that the stress in the envelope can be kept low.

To enable the invention to be more fully understood and readily carried out a description of a preferred form of construction and of its method of manufacture will now be given by way ci' example and with the aid of the accompanying diagrammatic drawings wherein:

Figure 1 is a perspective view of the stepped end of a gas-filled cable with a pressure retaining envelope constructed in accordance with the invention,

Figure 2 is a side elevation of a machine for manufacturing the envelope of the cable shown in Figure 1,

Figure 3 is a plan of the machine shown in Figure 2, and

Figures 4, 5, 6, 7, 8 and 9 are cross-sectional views taken on the lines IV-IV, V--V. VI-VI, VII-VII, VIII--VIIL and IX-IX, respectively of Figure 2 and on an enlarged scale as compared with Figures 2 and 3, showing successive stages of the manufacture of the envelope.

As will be seen from Figure 1 of the drawings the cable comprises a stranded conductor i, of

which the surface has been smoothed somewhat as by drawing through a die, and a dielectric 2 built up of pre-impregnated paper tapes. Over the dielectric is a conductive screen 3 which in turn is surrounded by a layer of copper woven fabric tape 4 by which is meant a woven fabric tape in which are incorporated a number of fine copper wire warps 4a. This is enclosed in an envelope li formed by applying a flat strip longitudinally to the outside of the core and folding it round to flt the core and to leave two flanges t which are secured by a illm of solder 'i and are bent to lie against the envelope 5, by a method to be described. Surrounding this metal envelope is a layer 8 of copperV woven fabric tape similar to the tape l and serving as a bedding for a reinforcing metal tape l applied helically with a short lay. Over the reinforcement layer is a protective sheath or covering iii.

The preferred method of manufacturing the envelope l will now be explained. The ,cable core il consisting of conductor I, dielectric 2. conductive screen 3 and copper woven fabric tape 4 is drawn through a guide l2 and over a grooved roll il. Above the roll i3 is a reel Il carrying a fiat coil of thin metal tape i5. This tape is drawn on' the coil and passed under a cylindrical roller II with a flange il at each end which holds it in contact with the top surface of the core in the position shown in Figure 4, which is a crosssection on the line IV--IV of Figure 2. From the rolls I3 and I6 the core il and strip I5 are drawn through a second pair of rolls, the lower roll i8 of which is in the form of a disc with a grooved periphery of approximately semi-circular shape. The upper roll i! has in its periphery a circumferential groove u-shaped section, the walls of which fold the tape i5 into the form of an inverted U-shaped channel of which the semicylindrical part lies in engagement with the upperhali'ofthecore ",auhowninl'igun.

3 On leaving the rolls I8 and I9 the core and the tape are drawn through another set of rolls comprising a roll 20 with a semi-circular groove which holds the tape I5 in contact with the upper half of the core I I and a pair of side rolls 2 I which bend the sides of the inverted channel into engagement with the lower half of the surface of the core and the margins of the tape into flanges 6 which lie close to each other and extend vertically downwards below the core, as shown in Figure 6. Preferably the inner surfaces of these flanges are tinned, the tinning operation being performed before the tape is applied to the core. As they leave the rolls 20 and 2I, the flanges are passed through a bath 22 containing a non-corrosive iiux, for example a mixture of rosin (colophony) and rosin oil, and then through a bath 23 containing molten solder. The solder used should preferably be one having a melting point above 200 C., so that there is a suitable margin between its melting point and the melting point of the metal used during the installation of the finished cable for making a plumbed joint between the envelope and some other part such as the gland of a joint box or termination. An example of a suitable solder is one consisting of 56% tin and 44% lead, and when this solder is used, the bath will be held at a temperature of approximately 280 C. On leaving the solder bath 23 the core I I and its envelope 5 pass through three more groups of rolls. The first group consists of an upper roll 24 with a peripheral groove of semi-circular cross-section and a pair of side rolls 25 with transversely curved surfaces which engage the two lower quadrants of the envelope and with cylindrical surfaces which squeeze the soldered joint down to a thickness which will result in the joint having an optimum shear strength. This thickness will depend mainly on the temperature of the solder in the bath and to a lesser extent on the type of solder used (see British Non-Ferrous Metals Research Associations Research Monograph No. 1 entitled Tin Solders by S. J. Nightingale and O. F. Hudson). With the example of solder given above the optimum joint thickness is 0.004 inch. The following group of rolls consists of an upper grooved roll 26 and a single side roll 2l which engages a lower quadrant of the envelope and presses the jointed flanges through an angle of about 45 as shown in Figure 8. The third set consists of a pair of grooved rolls 28 and 29 which press the jointed flanges still further so that they lie alongside the surface of the envelope as shown in Figure 9. After passing through a guide 30 the metal tape enveloped core is given its binding of reinforcing metal tape, preferably after applying a layer of bedding to the envelope.

The presence of the layer of copper woven fabric l over the screen 3 surrounding the dielectric 2 (see Figure 1) serves to prevent the envelope from being caused to adhere to the screen II when the soldered joint is being made. In cases where the dielectric contains free impregnating compound, this layer, or alternatively a cover strip extending longitudinally on the core so as to lie between the joint and the core, will also serve to prevent the free compound from running into the space between the flanges before they are united and thus from contaminating the surfaces before they have been soldered together.

It will be appreciated that by the improved method of gas-impervious envelope for the core,

` a considerable saving of metal results and that,

owing to the reduction in circumference, this is accompanied by a small saving in the parts which surround the envelope. At the same time there is obtained an envelope with a much higher fatigue limit than a lead sheath.

What we claim as our invention is:

1. A high tension power cable comprising a pressure-resistant, gas-impervious covering enclosing an insulated electric conductor charged 'with gas under superatmospheric pressure, said covering comprising a longitudinally seamed sheet metal envelope having overlapping longiwhich the other overlies the outer surface of the folded edge. solder uniting the contiguous surfaces of the longitudinal edges and means for holding the soldered seam in a position where the stress exerted on it by the gas pressure to which the envelope is subjected is substantially wholly a shear stress, said means comprising a helical lapping of short lay of reinforcing metal tape surrounding said envelope and retaining the soldered edges in position against the wall of the envelope.

2. A high tension power cable comprising a pressure-resistant, gas-impervious covering enclosing an insulated electric conductor charged with gas under superatmospheric pressure, said covering comprising a longitudinally seamed sheet metal envelope having overlapping longitudinal edges of which one is folded back and lies against the outer wall of the envelopeand of which the other overlies the outer surface of the folded edge and a thin film of solder extending over substantially the whole outer surface of the folded back edge and uniting substantially the whole of said surface to the contiguous surface of the overlying edge, and means for holding the soldered seam in a position where the stress exerted on it by the gas pressure to which the envelope is subjected is substantially a shear stress, said means comprising a helical lapping of short lay of reinforcing metal tape surrounding said envelope and retaining the soldered edges in position against the wall of the envelope.

CHARLES JAMES BEAVER.. EDWARD LESLIE DAVEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Y Date OTHER REFERENCES Sil-Fos and Easy-Flo, Bulletin No. 12, page 5, published by Handy and Harman, 82 Fulton Bt.,

New York, N. Y., 113-112 Lit.

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