US1692767A - Stranded sector-shaped conductor - Google Patents

Description

Nov. 20, 1928,.

STRANDED SECTOR SHAPED CONDUCTOR Filed March 31. 1928 WITNESSES wil/Lm.

INVENTOR harman, @mais Patented Nov. 20, 1928.

, UNITED 4STATES PATENT oFFlcE.

NORMAN C. DAVIS, OF IERTH AMBOY, NEW JERSEY, .ASSIGNOR TOGENERAL CABLE CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

STRANDED SECTOR-SHAPED CONDUCTOR.

Original application filed April 20. 1927, Serial No 185,096. Divided and this application led March 31, 1928. u serial no. 266,357.

This application isa division of application filed April 20, 1927, Serial No. 185,096, which is itself a continuation in part of an application filed Oct. 25, 1'924, Serial No. 745,883.

My invention relates to the making of sec-A tor-shaped conductors formultiple-conductor cables, and consists in ymethod of production.

It is advantageous, in the making of mullo tiple-conductor cables, particularly those of large size, that the conductors be composed, each of a number of smaller wires, stranded together in helical twist. A cable whose con ductors are so composed is flexible in far greater degree than a. cable Whose conductors consist, each vof a single solid wire.

In the kmaking of sector-shaped conductors (a shape advantageous, in that a cable of given circular mileage or cross section may be made of relatively small over-all dimensions) the formation of the `individual conductor out of an assembly of small Wires presents peculiar difliculties. If the sector shape be attained by a particular grouping of the wires, then stranding (that is to say, helical Winding of the wires about one another or about a common axis) becomes impossible. The shape-giving wires must extend straight away through the length of the conductor. Manifestlya conductor so. composed, with wires extendingstraight away throughout its length, is far less flexible, whether under cross-bending or under torsion, than a compound conductor whose constituent wires are stranded or spiraled in a. h'elix. Furthermore, a compound conductorwhose body isv built up of wires extending straight away throughout its length will, when bent or twisted, tend tov lose its characteristic and yimportant sector shape; its component wires will tend to become displaced; the kconductor as a whole will tend to assume circular cross-sectional form--4 this in far greater degree'than' if the constituent wires were stranded 'or spiraled.

If the compound sector be builtV up by binding a core bundle about with one ormore layers of stranded (that is to say, helically wrapped) wires, the core bundle itself being made up ofpar'allel straight-away wires of equal or of diverse diameters, grouped to sector shape in cross'section, or otherwise made u then, in consequence of therounding of t e anglesincident tothe wrapping on of the enveloping layer or layers, the sec-tor shape of the enveloped core is seriously compromised, and Ythe advantages sought are measurably unattained. This rounding of the corners increases directly with the number of binding layers applied.

If the sector shape be attained by rolling to sector-shape a conductor composed of a plurality of wires initially stranded helically in usual manner tosubstantially circular com- Vpact section, then the strains of crushing,

coming as necesssarily they do unequally at successive points upon the individual wires, produce deformation, and irregular deformation of the individual wires. The same wire is .at different points in its extent differently misshapen and in many cases almost cut through. One notable result of this rolling is that, electrically considered, the effective cross-sectional area of the conductor is greatly diminished. Therefore, the currentcarrying capacity of the conductor as awhole is greatly diminished-making it necessary v to allow an'excessiye additional area of metal before rolling, to give the necessary required effective area after the rolling operation. The economies incident to the sector-shape are then partially or wholly lost in countervailing diminution of capacity.

Indeed7 the difliculties here indica-ted are with other conductors to -areasonably short cabling lay. y

My invention consists in stranding `the wires of the conductor (that is to say,'bring` ing them together in a bundle in which the wires vare helically twisted), the bundlev itself being round, or approximately so. I shall hereafter throughout this specification use the phrase helically stranded to designate the grouping of the wires inthe manner indicated, and, inthe drawings about to be v described', clearly shown. The proportions of this bundle are such-the arrangement of the component-wires into a bundle `is such, that the bundle itself may in an ensuing operation be crushed to sector shape, and that without appreciably mutilating or misshaping at successive points the wires of which the bundle is composed. The resultwhen under torsion or bending. All this is accomplished without the vemployment of a core of straight-away wires or bars, to give the desired characteristic sector shape.

In the accompanying drawings Fig. I

shows in side elevation and diagrammati-- cally a collocation of wires helically strandedl according to my invention into a bundle, the bundle being adapted to be crushed according to my invention from circular cross-sectional shape to sector shape. Fig. II shows the same collocation in cross-section. Fig. III shows the bundle after the crushing` operation has been performed upon it. Figs.

IV and V and VI and VII are pairs of correlated diagrams, corresponding to Figs II and III, and illustrating the invention in further detail.

The invention consists essentially in stranding helically a number of'wires to a bundle of hollow format-ion, preferably circular in cross-section, or-substant-ially so, and then bringing the bundle to sector shape at the expense of the hollow space or spaces within the bundle; and this without mutilation of the component wires. In the bundle each wire is free of the others and in the shaping of the bundle the wires by virtue of such freedom may move, and do move, both laterally and longitudinally, and independently, to new relative arrangement, and there is no. localized mutilation, no appreciable irregular diminution in cross-sectional area at successive points in the length of a component wire.

The area of a circle is greater than the area of a sector of equalperiphery. If then a substantially or approximately circular bundle of tangent wires be formed with a hollow space within, and ifA such a bundle after being formed be brought tothe crosssectional shape of a sector of equal perimeter, the cross-sectional area of the bundle will be diminished. This diminution of area may be brought aboutwholly at the expense of the hollow-space, and without appreciable mutilation, of the individual wires irregularly at successive points in their length. My invention takes advantage of and realizes this possibility.

The simplest working out of the invention is attained in forming initially a hollow bundle o'f helically stranded wires. This simplest form is illustrated, with slight elaboration, in Figs. I-IV of the drawings. The bundle here consists of three successively enveloping layers of helically stranded wires (the number of layers is immaterial to the invention). The component wires of each layer are shown to be, and ordinarily will preferably be, tangent, or substantially so,

wire to wire. There is a hollow space within the innermost layer, and there are hollow spaces between the layers. Figs. I and II show they bundle when first assembled; Fig. III shows it when brought thereafter to sector shape. It will be observed, on comparing Figs. II and III that the hollow spaces initially present are ultimately eliminated. The bundle is in its initial stage (Fig. II) properly proportioned; each successive layer of wires is such in its extent, in the number of wires composing it, as t-o afford an inner space of proper size, so that when the sector shape is imposed upon the bundle the spaces will be diminished and preferably eliminated, the component wires will rearrange themselves and the component wires will closely overlie one another and the whole will become integrated in a unitary conductor, but without substantial mutilation of the component wires.

Another characteristic of the stranded, sector-shaped conductor of my invention is that it is susceptible to being twisted on its longitudinal laxis without loss of its essential sector shape. This is a characteristic which has not hitherto been attained ,hitherto it has been necessary, in making into a cable helically stranded sector-shaped conductors such as the art hitherto has known, to assemble the component conductors in a very long lay; that is to say, with a very gradual twist or turning about the cable axis-a very much longer lay than otherwise would be employed. This limitation has been imposed by the circumstance that, if a shorter lay were attempted, the strains set up within the individual conductor would cause` the component wires to shift in position, and the conductor as a whole to lose its essential sector shape. In the practice of my invention,

the otherwise normal operation of cable making is not disturbed. The component conductors may be united with the desired relatively short lay, and that without loss of the essential sector shape of the component conductors. The result is a completed cable which is flexible in highest degree, in contrast with the relatively stiff structure which alone hithertohas been attainable.

Inbuildingup thebundle diagrammatically shown in Fig. II mandrels may be employed, removable as building progresses; upon which mandrels the successive layers may be helically stranded. The mandrels for the outer layers will of course be hollow. The crushing of the bundle, from 'the circular shape of Fig. II with included spaces, to the sector shape of Fig. III with spaces eliminated, may be effected in any Way known to the art, with the qualification, that the component wires shall be free to move longitudinally as well as laterally, one relatively to another. The crushing ordinarily willfhe-,eifected between rolls, one or both of theilrtrllsbeing powerdriven and the bundle of. Wines advancing 1n response to the tract-ive effect of the rolls upon it'. .n

In Figs. I and II the successive layers -are shown standing in concentric arrano'ement, with no visible means of support. This concentricity will be substantially maintained, if the blank passes directl from the forming mandrels to the crushlng rolls, with no extended space between. But it will be understood that Figs. I and II may in this particular be taken to be diagrammatic. There can be no harm, nor disturbance of the described operation, if at the rtime when the blank enters the crushing rolls the assembled layers do not stand concentrically, but instead rest one upon another at t-he lowermost points of their peripheries. I

According to my= present invention I carry the crushing farther than to the point at which the component wires of the bundle are brought merely to tangency. That operation and its product are described and speciically claimed in my application Serial No. 185,096, alluded to above. For certain uses I have found that I may advantageously carry thecrushing step further and may not merely eliminate the tubular space of the initial blank (leaving a finished product in which the wires touch one another throughoutl the cross-section'of the finished article), but I may, by carrying the crushing step further, shape the wires one to another, changing them from circular cross-section to more or less completely polygonal cross-section. The individual wires in the finished article make tangency not along lines merely, but over facets producedfby such further crushing. The result is a helically stranded sectorshaped conductor whose over-all dimensions are 4less relatively to the effective cross-sectional area of conductor, when compared with a conductor produced by the method of my prior application; the resulting conductor has therefore characteristics which make it useful, and under certain conditions preferable to any stranded sector-shaped conductor hitherto known.

Referring to Figs. I, II, and III,the tubular blank as here shown is (as ordinarily it will be) multi-tubular, one tube being contained Within another. 'ithineach tube the helices in which the individual wires exvtend are turned all of them in the same direction and at the ama pitch. It is preferable that as betweenl the several tubes the direction of turning' of the 4helices shall be the same, and that the angle of pitch shall be substantially the same.

In forming from the blank of Fig. II the product of Fig. III, I carry the pressure further. I lnot merely eliminate (as described above) the tubular spaces within the blank,

but I compress the component strands beyond the point of tangency along lines. I change the cross-sectionall shape of'the individual strands, I bring them to modified polygonal cross-sectiomand in the finished article the adjacent strands lie in tangency over extended surfaces. This will appear on comparing the Figs. II and III, and on considering individual wires a, b, c, ai, and e. These' wlres initially are each of them round in cross-section. In the finished article these wires have been modified in cross-sectionalthe fact that adjacent Wires are laid in heliceswhich extend in the same direction and -at the saine degree of turning that makes possible this further crushing without loss in effectiveness of the finished article.

In this specific elaboration of my invention i each individual wire is elongated. The crosssectlonal area of conductor in the finished article is less than the cross-sectional area of conductor in the blank. The crushing and elongation of the individual wire is, it Will be remarked, an elongation which is uniform from point to point throughout the length of the wire. It 1s this substantial uniformity in elongation from point to point throughout the entire length of each wire that is essential to practical success.

In Figs. IV and V, I have shown that if the blank be a multi-tubular blank the successive tubes, instead of being spaced at intervals apart may be tangent. In this case kthe initial blank contains but one hollow space to be crushed out,-that which is found within the inner layer of wires. The crushking of the blank not only eliminates this space; but, as in the case already considered, it effects readjustment of the individual wires and the crushing of-l the individual wires one upon another, modifying the individual wires in cross-sectional shape, causing them to assume a polygonal cross-sectional shape, with the sides of the polygons coincident, as between adjacent Wires. In this crushing operation the individual wires are elongated and the length' of lay is increased, and, as between the two layers, the amount of elongation of individual wires is not`exactly the same; b ut in these respects the individual wires of the bundle respond to the crusliinr strain, and the result is a sectorshaped bundle such as that shown in Fi V whose component strands of substantially polygonal cross-section are of substantially uniform cross-section throughout the length yof the conductor, andA whose component i dividual components of substantiallyuniform cross-section throughout its length. The last-named characteristic is, as I have said, of controlling importance. Since in the blank the component wires extend in helical course, in the nished sector every wire will extend in a course which is not straightaway, and a course which I characterize as winding: a

In Figs. VI and VII a single tubular blank consisting of six wires is shown to be reduced according to the specific elaboration of my invention here under consideration to sector shape, and here the matter of the readjustment of the individual wires and the minute shaping of them may be more minutely considered, and the essence of my invention in its simplest form may there be studied and understood. l v

Turning now from thefdetails of the sev- 4eral iigures of drawing thus far considered.

to general observations, it is tobe remarked that the angular value of the sector produced will be such as may be desired. The conductors shown in most of the figures ofthe drawings are-intended for use inrthree-conductor cables, and the angular value of these sectors is 120. If the conductor were intended for a `four-conductor cable, the an for a two-conductor cable, the angular value Would'be 180. Such adaptations will be understood to be included in the contemplaductor which consists in forming a tubular v blank of individually free, helically stranded wires, each wire extending in a true helix, theturmf all of the helices extending in the same-directiom and while the component wires are individually free to move both longitudinally and transversely with respect to adjacentwires crushing andelon atin such blank and the component wires tereo and bringing the blank to sector shape with elimination of the tubular space within, and bringing the component wires to polygonal section with extended surfaces of contact between adjacent wires. l

-2. The method herein described of forming a stranded sector-shaped electrical conductor which consists in forming amultitubular blank of a succession of tubular layers, each layer, consisting of individually` free, helically stranded wires, each wire extendin lin a true helix, and the turn of all of the elices Within the blank extending in the same direction, and while the .component wires are individually free to move both longitudinally and transversely with respect to adjacent wires crushing and elongating the blank and the component wires thereof and bringing the blank to sector shape with relative rearrangement of the Wires' and with elimination of tubular space Within, and bringing the component wires to polygonal section with extended surfaces of contact between adjacent wires'.

In testimony whereof I have hereunto set m hand.

y i NORMAN C. DAVIS.

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