US2289732A - Electrical conductor - Google Patents

Description

July 14, 1942.

S. J. ROSCH ELECTRICAL CONDUCTOR Filed March 16, 1940 r f INVENTQR Jaz/222226Z J /Pos v ATTQRNEYS Patented July 14, 1942 ELECTRICAL CONDUCTOR i Samuel Joseph Resch, Yonkers, N. Y., assignor to Anaconda Wire and Cable Company, New York, N. Y., a corporation of Delaware 'Application March 16, 1940, serial No. 324,294

8v Claims.

This invention relates to electrical conductors and has for its object the provision of an improved electrical conductor of the stranded wire type and method oi' making the same.

i Electrical conductors of the stranded wire type must frequently be so constructed as to inhibit the conduction of water, acids, alkalies and oils through the interstices between the individual.

metallic conductors or wires thereof, whether the conductor is operating at atmospheric or higher pressures. 'I'his is particularly true of cables or conductors destined to operate in oil refineries, at the bottom of oil wells, at certain locations in submarine boatsl and in other similar installations. Conductors or cables for such uses have heretofore been commonly made by extruding a layer of unvulcanized rubber compound over the central strand and extruding similar layers of unvulcanized rubber compound over each of the surrounding layers of stranded wires. The outermost layer of stranded wires was covered with the requisite thickness of whatever type of insulation was deemed necessary, and it was expected that the stranded conductor, and especially the core or inner strands, would be pressure-tight against air or such liquids as would not affect the unvulcanized rubber compound used for lling the strand interstices. In most cases, the main outer` insulation of the stranded conductor or cable was a rubber compound requiring vulcanization. During the vulcanization of this main insulation, the rubber compound used for filling the strand interstices also became vulcanized to a greater or less extent, and in some cases became bonded to thel main vulcanized insulation. Stranded conductors of this construction possess certain disadvantages, among which may be enumerated the following:

1. The diameter of the stranded conductor is materially increased due to the presence of a layer of rubber of substantial thickness between the stranding layers. This increase in diameter is substantial since it is impractical to extrude a layer of u';.vulcanized rubber compound over a small diameter in less than M34 inch thickness. and over larger diameters in less than .025 inch thickness, which produces an increase in diameter of .030 inch and .050 inch, respectively, for each such application. Some of this increase in diameter might be eliminated by sinking or pressing the strands into the rubber layer, but in actual practice only a relatively slight decrease in diameter can be accomplished in this way.

2. Since it is impractical and uneconomical to place andoperate a rubber extruding machine' between each section of the stranding apparatus so as to apply the extruded layers of rubber simultaneously with the stranding operation, it is necessary to strand each layer of wires separately and to apply the layer of extruded rubber over each strand in a. separate operation. Naturally, this tends to considerably increase the cost of producing a stranded conductor of this type. For example, a 61 wire stranded conductor contairs four stranding layers which are commonly built up in one operation on a stranding apparatus of four sections. Where it is desired to extrude a layer of rubber over each stranding layer, it is necessary to first take the central strand and insulate it with a layer. of rubber, then to apply six wires over the core thus formed, after which the 7 wire strand is taken to the extrusion machine in order to cover the 7 wire strand with a layer of rubber. The 7 wire core is then brought back to the stranding machine in order to wind the next layer o f twelve additional wires thereon. Then the 19 wire core is taken over to the extrusion machine and covered with a layer of rubber, and so on until the last layerof 24 wires is applied.

3. The rubber compound used for filling the interstices of the metallic conductors supports combustion during any arc that is established in consequence of a cable failure or short circuit, such rubber compounds being `good supporters of combustion. The rubber compound is also deleteriously affected by contact with oil, and contact Vwith other chemicals, particularly aceticacid,

exercises a bad solvent effect on the rubber compound.

With the foregoing considerations in mind, I

' have developed a new and improved conductor which will carry out all of the functional duties of a conductor of the foregoing type and yet do so without the disadvantages hereinbefore rected. The conductor of the invention comprises an inner metallic conductor strand, which may be a single conductor or avgroup of stranded conductors, surrounded by an outer layer of stranded conductors and having a lattice-like structure of tough plastic insulation between the,inner and outer strands with the solid portions of the lattice-like structure filling interstitial vspaces between conductors and the openings of the latticelike structure permitting direct contact'be-tween radially adjacent conductors. Ordinarily, the conductor will have a plurality of concentric layers of spirally-stranded metallic conductors with adjacent layers having opposite directional spirality and the characteristic lattice-like structure of 4the invention will `be arranged between the adjacent layers of the stranded conductors.

The plastic insulation is preferably a synthetic resin base withsuch incorporated agents, where necessary, as will impart to the lattice-like struc,- ture suitable ame, acid-, alkali, oil, and

moisture-proofness as the finished conductor.

tion its characteristic lattice-like structure.

The novel features of the invention will be better understood from the following description taken in conjunction with the accompanying drawing, in which:

Fig. 1 illustrates a stranded electrical conductor or cable embodying the invention,

Figs. 2 and 3 are cross-sections of stranded conductors embodying the invention,

Fig. 4 is a detail view of a piece of the plastic insulation, illustrating'its characteristic latticelike structure, and

Fig. 5 diagrammatically illustrates an appa-- ratus for making the conductor of the invention in accordance with the method of the invention.

The conductor of the invention, illustrated in Fig. 1, comprises a :single central strand 6 surrounded by the next outer layer l of spirallystranded metallic conductors. In this embodiment of theinvention the central strand 6 is not covered with insulation. The stranded layer of conductors 1 is surrounded by concentric layers 8, 9 and I0 of spirally stranded metallic conductors, )with the conductors of adjacent layers (i. e. 1 and 8; 8 and 9; 9 and it, respectively) having opposite directional spirality. T he metallic conductors may be tinned copper Wires of any appropriate diameter.

A latticelike structure II of tough plastic insulation is interposed between the adjacent layers or strands 'I and 8, 8 and 9, and d and Ill, respectively. Preferably, the plastic insulation is non-adhering'and may be readily stripped from the metallic conductors. When so stripped, the insulation will exhibit lattice-like structure as illustrated -in Fig. 4.

When in position in the conductor of the invention, the solid portions I2 of the insulation will iill interstitial spaces between conductors while the openings I3 of the insulation permit close contact between radially adjacent metallic conductors, as illustrated in Figs. 2 and 3. Fig. 2 is a cross-section of the conductor illustrated in Fig.l 1, while Fig. 3 is a cross-section of a similar conductor in which the lattice-like structure of plastic insulation is interposed -between the central single strand 6 and the next outer strand 1.

Referring now to the apparatus illustrated in Fig. 5, the central strand 6, paid off from a supply reel I5, is led through the first section I6 of the stranding apparatus, which may be of the present standard construction. 'I'he section IB co- .operating with the closing die I9 applies a spirally wound layer of metallic conductors around the central strand 6, thus producing the strand I.

.The strand l is led througha taping head or device which applies to or winds on the strand 'l one or more la) ers I I' of thermo-plastic insulation in the form of a tape. The width of the tape will vary depending upon the diameter of the strand over which it is wound. The thickness of the tape will also vary, depending upon the volume of the interstices to be nlled and the amount of iilling material required. Since there may be a price differential making certain combinations of width and thickness of the tape prohibitive in cost, I can overcome any such distaining the closing die 2|.

its characteristic advantage by varying the number of taping heads 20, or I can vary the volume of filling material per unit length of conductor by applying the tape with the lap varying from an open butt to a 50% or greater over-lap.

'I'he strand 1, now covered with one or more layers of the spirally .wound tape of plastic insulation Il', is led through the second section I1 of the stranding machine, where another strand or layer 8, of metallic conductors is wound over the layer of plastic insulation II. A1- tho'g'h the strand 8 is calculated to fit snugly about the inner core, this snug fit can only be accomplished by compressing the strand 8 until the conductors thereof sink through the underlying layer ofirm, tough plastic insulation until radially adjacent conductors are in contact with one another. To this end, I provide, at the point of vstrand convergence, a closing. die 2l whose internal diameter is equal to a value corresponding to the theoretical diameter that should prevail had the intervening layer of plastic insulation Il" not been, applied. vThe stranded core will be unable to pass through the die 2| when the plastic insulation II is a synthetic resinous materiaL since such materials are extremely tough 'and have a flow point of approximately 350 F. or'even higher. Accordingly, a series of burners 22 of the Bunsen or similar type, capable of directing a gas flame at suitable high pressure at an object to be heated, are mounted with their iiames directed on a metallic structure con- In this manner suicient heat is applied to soften the plastic inf sulation Il and to permit the conductors of the strand 8 to sink in and cut through the plastic material, thereby enabling these conductors to make physical contact with the underlying conductors. The burners 22 supply heat at such a rate that the layer of insulation II' achieves its softening temperature at the production speeds customary with stranding operations so as not to retard production.

The resulting stranded conductor next passes through another taping head or device 23, similar to the device 2U, and one or more layers II of plastic insulation in the form of tape are applied around the layer or strand 8. Another strand or layer of metallic conductors 9 is then spirally wound around the insulation II" by the third section I8 of the stranding apparatus. A closing die 24, heated by burners 25, compresses the strand 9 around the softened insulation II to bring radially adjacent metallic conductors substantially into contact and to force the softened insulation into interstitial spaces between conductors.

As the number of metallic conductors, or their size, comprising a given strand or layer becomes larger, it may not be possible to provide suicient heat through the burners 22 or 25 to effect the necessary softening ofthe underlying plastic insulation. The metallic conductors are at room temperature, or possibly even lower, when applied on the stranding apparatus', and consequently they serve to dissipate heat from the metallic housings of the closing dies 2i and 24.

eter are drilled on the inner side of the ring thus formed so as to enable jets of gas andair to be projected toward the center thereof. The ring burner 26 is mounted in any appropriate manner in a vertical position concentric with the converging conductors of the strand 9. The combination of gas and air flowing through the orifices of the ring burner is ignited, and the length of each jet of flame is regulated by a valve 21. In this manner a circle of ame of any desired magnitude encompasses the individual conductors of the strand 9 and preheats them to the desired temperature.

The plastic insulation applied, heated and compressed iny accordance with the method of the invention is a substantially homogeneous and perforated tube of firm, tough, flexible, plastic material. The insulation does not adhere to the metallic conductors and may be readily stripped or removed by cutting it for a given length parallel to the axis of the cable or stranded conductor. tangular section of the plastic insulation so removed or stripped from a cable. In this section there are a series of cross hatchings, the angles at which they occur correspondingto the angle of lay of the inner or outer strands between which the layer of plastic insulation was compressed. The openings or perforations are those portions of the insulation which were cut through by the overlying strand. The solid portions of the insulation occupied or filled the interstitial spaces between conductors. y

The plastic insulation may consist of any appropriate plastic material, preferably containing such additional agents, where necessary, as will render it llame-prooi, acid-proof, alkali-proof, oil-proof and moisture-proof. In practicing the invention I prefer to make the plastic insulation of a suitable resinous base with such additional materials as may be required to meety the service for which the completed conductor is intended. I have obtained satisfactory" results with polyvinyl chloride and other synthetic resins of this general type. Any resinous material which will not support combustion and will perform the functions required of a conductor in resisting the Fig. 4 of the drawing illustrates a receects of gaseous or liquid pressure as well as y diameter wire, should have a theoretical diameter of .470". The actual diameter of a cable so constructed was .471". 'I'he actual diameter of a cable embodying my invention and constructed substantially in accordance with Figs.- 1 and 2 of the drawing had a diameter of .475". A similar 61 wire cable with a layer of unvulcanized rubber between adjacent strands, as heretofore made, has Ia diameter of .620" or more.`

I claim:

1. A stranded electrical conductor comprising a metallic conductor core surrounded by a layer of stranded metallic conductors, and a homogeneous lattice-like structure of tough plastic insulation between said core and said surrounding layer of conductors with the Vsolid portions of said structure lling interstitial spaces -between conductors and the openings of the lattice-like struca plurality of concentric layers of spirally wound ture permitting direct contacty between radially adjacent conductors. A

2. A stranded electrical conductor comprising a plurality of concentric layers of spirally stranded metallic conductors with' adjacent layers having opposite directional spilality, and a lattice-like structure of synthetic'resi'n ,oasebetween adjacent layers of conductors with the thick portions of the lattice-like structure lling interstitial spaces between conductors while ythe open portions-of the structure permit direct contact between radially adjacent conductors.

3. A stranded electrical conductor comprising 4a core of stranded metallic conductors surrounded by a layer of. stranded metallic conductors, and a layer of non-adhering plastic insulation between said core andl said surrounding layer of conductors filling interstitial spaces between the conductors while permitting direct contact between radially adjacent conductors in consequence of which relationship the plastic insulation has a substantially homogeneous lattice-like structure.

4. A stranded. electrical conductor comprising a metallic conductor strandV surrounded by a layer of spirally stranded metallic conductors, and a substantially homogeneous and perforated tube of tough plastic insulation between said strand and the surrounding layers of metallic conductors with radially adjacent conductors contacting through the perforations of the tube while the solid portions of the tube occupy interstitial spaces between conductors.

5.AA stranded electrical conductor comprising a plurality of concentric layers of spirally wound stranded metallic conductors with the conductors of adjacent layers having opposite directional spirality, and a lattice-like structure of tough plastic insulation between adjacent layers of conductors with radially adjacent conductors contacting through the openings of said structure while the solid portions of the structure occupy interstitial spaces between conductors.

6. A stranded electrical conductor comprising ametallic conductor core surrounded by a layer of stranded metallic conductors, and a substantially homogeneous and uniformly perforated tube of tough plastic insulation between said core and said surrounding layer of conductors with radially adjacent conductors contacting through the perforations of the tube and the solid portions of the tube occupying interstitial spaces between conductors. v

7. A stranded electrical conductor comprising a metallic conductor core surrounded by a layer of stranded metallic conductors, and a tough. iiexible and lattice-like structure of synthetic resin base between said core and said surrounding layer of conductors with radially adjacent conductors contacting through the openings of the lattice-like structure and the solid portions of the lattice-like structure occupying interstitial spaces between conductors.

8. A stranded electrical conductors comprising y the solid portions of the tube occupying interstitial spaces between conductors.

SAMUEL JOSEPH ROSCH.

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