US 3383704 A
Description (OCR text may contain errors)
May 14, 1968 R. J. scHoERNER ET AL 3,383,704
MULTI STRAND CABLE Filed Jan. l0, 1967 United States Patent O 3,383,704 MULTISTRAND CABLE Roger J. Schoerner and Bobby A. Rowland, Carrollton, Ga., assignors to Southwire Company, Carrollton, Ga., a corporation of Georgia Filed Jan. 10, 1967, Ser. No. 608,306 6 Claims. (Cl. 57-145) ABSTRACT F THE DISCLOSURE What is disclosed herein is a multistrand cable which avoids the spiralling and other undesirable characteristics of a conventional uncompacted cable and which avoids the lack of flexibility and other undesirable characteristics of a conventional compact cable, Specifically, the cable disclosed herein is a multistrand cable having a core strand which is of substantially circular cross-section and having a plurality of layer strands, each of which is of substantially circular cross-section and each of which has a relatively attened region along its length that is limited in width to that width which can be achieved by deforming without causing the cable to have the undesirable characteristics of a conventional compact cable.
The present invention relates to multistrand cable. More particularly, the present invention relates to multistrand electrical cable wherein imprinting of the insulating cover and any tendency to spiral have been substantially eliminated while retaining good overall physical properties including flexibility.
The usual method presently employed to form multistrand electrical cable involves helically stranding a plurality of individual wire strands about a central core strand in one or more layers without deformation of any of the strands. This type of cable is generally referred to as conventional uncompacted cable. The resulting crosssection of the cable comprises a core strand surrounded by one or more concentric arrays of individual strands wherein each strand including the core strand is of circular cross-sectional configuration. After stranding the cable is normally covered with a suitable insulating material such as neoprene or a polyolen by an extrusion-coating process.
Several problems exist with cable formed in this manner. First, since no effort is made to reduce the cable diameter a maximum amount of insulating material is necessary to provide a cover for the cable. This amount of insulating material is further increased due to the superficial valleys on the cable which are created by the individual strands of circular cross-section forming the outermost concentric array. Second, the stranding operation does not form a particularly tight-stranded cable. As a result the extrusion-coating process, which operates at relatively high pressures, forces insulating material into the internal interstices between the individual strands of the cable thereby causing what is commonly referred to as imprinting in the resultant insulating cover. Third, relatively long lengths of the cable have a pronounced tendency to assume an elongated spiral configuration. This g, spiralling in the cable is caused by kinks in the core strand or in one or more of the layer strands. It is also caused by unequal tension placed on the individual strands as a result of the stranding operation.
In an effort to overcome these problems it has previously been proposed to highly compress the stranded cable to the extent that the internal interstices are eliminated and the valleys are reduced to a minimum in size. This has been accomplished by passing the cable immediately after being stranded through a high compression die. The
3,383,704 Patented May 14, 1968 resulting cross-section of the cable comprises the usual core strand surrounded by one or more concentric arrays of individual strands; however, each strand including the core strand has been deformed to the extent that its original cross-section has been altered to resemble a polygonal conguration. All of these deformed strands nest together to form a substantially continuous cross-sectional surface wherein only lines of juncture between the individual strands remain in place of the interstices. From a practical view, there is a limit on the size of cables which may be compressed in this manner since high pressures are required for the compressing operation and it becomes increasingly diicult to achieve the necessary pressures as the diameter of the cable is increased.
Stranded cable which has been compressed in this manner is generally referred to as compact cable. Because of the compactness of the cable the extruded insulating cover does not suffer from imprinting and also less insulating material is necessary to completely cover the cable due to its reduced diameter` Moreover, the compressive forces required to produce compact cable essentially remove any kinks which may be in the individual strands and substantially equalize the tension forces among the strands thus eliminating the spiralling characteristic which is present in the completely uncompacted cable.
There do exist some serious drawbacks in forming compact cabie. First, the required compression forces are so high that the stranded cable is subject to frequent breakage as it is drawn through the compression die, particularly with cables of relatively large diameters. Second, a very large drawing force is required thus increasing power consumption. Third, and probably most important, the metal strands become cold worked as they pass through the compression die and consequently their physical properties are altered. By far the most irnportant effect on physical properties is the loss in flexibility and elongation when considering that the product comprises electrical cable.
Therefore, in accordance with the present invention there is provided a multistrand electrical cable which does not suffer from the spiralling characteristics nor imprinting of the insulating cover as are present in the conventional Vuncompacted cable yet substantially has the desirable physical properties such as flexibility and elongation which .are not present in compact cable.
Briefly described, the stranded electrical cable of the present invention in its most simple construction is formed by helically stranding a plurality of individual Wire strands about a central core strand in a concentric array forming a single layer. Thereafter the stranded product is passed through a sizing die to substantially deform or flatten only the outermost surface of the single-layered cable. This degree of deformation has been found to be sufficient to substantially eliminate the internal stresses set up within the strands during the stranding operation which cause spiralling. The resulting cable comprises a core strand, having a substantially circular cross-sectional configuration, sur-rounded by a single concentric array of helically wound individual strands whose surface portions corresponding to and forming the outermost surface of the cable have been flattened. The remaining surface portions of the individual strands retain their smoothly curved configurations.
Thus, another readily apparent feature of the present invention as compared to the conventional uncompacted cable is that less insulating material is required due to the reduction in size of the valleys on the surface of the cable and a reduced effective diameter of the cable. In addition, as compared to the formation of compact cable, the formation of the cable of the present invention requires much less compression and drawing force thereby significantly decreasing potential breakage of the stranded cable as it passes through the sizing die. Of course, larger diameter cables are also capable of being formed in accordance with the present invention as a result of the lower forces required. 1
These and other features and objects of the present invention will become more apparent from the following discussion and the accompanying drawings wherein:
FIGURE 1 is a cross-sectional view of the stranded electrical cable comprising the present invention in its most simple construction.
FIGURE 2 is a schematic view illustrating the manner in which the cable shown in FIGURE l is formed.
FIGURE 3 is a cross-sectional view of another embodiment of the stranded electrical cable comprising the present invention wherein two concentric arrays of individual strands are provided around a central core strand.
FIGURE 4 is a schematic view illustrating the manner in which the cable shown in FIGURE 3 is formed.
With reference to FIGURE l, there is shown one ernd bodiment of the multistrand electrical cable, generally designated by numeral 1t), which includes a core strand 11 surrounded by a single concentric layer of helically wound strands 12 which are in tight surface contact with the core strand. The core strand 11 is substantially circular in cross-section while strands 12, originally of circular cross-section, have been deformed in those regions 13 of their surfaces which correspond to and form the outer surface of the cable. While this deformation may be somewhat exaggerated in the drawings, fairly perceptible corners 14 and 14' bounding each side of the deformed regions 13 are present. The remaining surface regions 15 of the strands 12 substantially retain their original roundness. That is, the surface region 15 of each strand 12 essentially defines a continuous curve extending from corner 14 to corner 14' with no intermittent tiattened areas.
Due to the cross-sectional configurations of the strands, interstiees 16 are formed on the interior of the cable between strands 12 and core strand 11 while superficial valleys 17 are formed on the exterior of the cable between the strands 12. The interstices 16 are sealed from valleys 17 by the tight contact 1S between adjacent strands 12. This contact seal is sufficient to effectively prevent coating materials from entering the interstices during an extrusion coating operation which may be subsequently performed on the cable. Thus, as pointed out previously, imprinting in the insulating cover of the cable is eliminated.
In addition, it is pointed out that the deformed regions 13 of the cable produce a corresponding decrease in the depth of the valleys 17 and in the effective diameter of the cable. Therefore, less coating material is required to ll the valleys and cover the cable to provide an insulating sheath.
As previously described, the strands 12 are in tight engagement with each other as well as with core strand 11. These strands are also under substantially equal tension and possess no kinks, all of which directly results from the manner in which the cable is formed to produce the deformed regions 13 on strands 12. The cable, as a result, may be unrolled from its carrier spool and lie in a substantially straight-line path exhibiting no tendency to spiral.
Formation of the above-described multistrand cable may be accomplished using a conventional stranding machine in combination with an appropriate sizing die, all of which is schematically represented in FIGURE 2 as one embodiment. This apparatus includes a spool 2t) from which the core strand 11 is supplied. The core strand is fed axially into the entrance end of the sizing die 25. Surrounding the core strand as it passes to the die is a concentric array of supply spools 21 containing strands 12. These supply spools are mounted on a rotatable frame (not shown) of a conventional stranding machine, such Cil as those shown and described in United States Patent No. 1,691,337 and United States Patent No. 2,156,652, among others. While the frame rotates the strands 12 are fed to the sizing die concurrently with the core strand 11 whereupon they becorne helically wound about the core strand 11. The helically wound structure is then drawn through the die thereby forcing the strands 12 into tight arrangement around the core strand while their outermost surfaces are deformed to form regions 13 as shown and described with reference to FIGURE 1. A suitable lubricant, such as a mineral oil, may be used during the drawing operation to reduce the drawing force necessary and the resulting multi-strand electrical cable 10 is thereafter withdrawn from the die 25 and wound upon a suitable spool 26 for subsequent treatment such as an extrusion coating process.
The sizing die merely defines a sizing aperture for the strands 12 and core strand 11. It may be formed by a plurality of rolls arranged so that their axes approximate a circle in much the same manner as some rolling mills. However, it is preferred that the sizing die comprise a block of hard metallic material such as tungsten carbide having the sizing aperture extending therethrough while gradually tapering along its relatively long length.
In deforming the surfaces of strands 12 within the sizing die 25 the strands actually become cold-worked to a limited degree. The amount of cold-working which takes place is limited to cause removal of kinks and equalization of tension among the strands and does not have any significant effect on the physical properties of the strands. The removal of kinks and the equalization of tension among the strands is quite significant in the final multistrand electrical cable in that the cable has no tendency to spiral as is characteristic of conventional stranded cables.
While the multistrand electrical cable is lformed by sizing the cable at the point of stranding in FIGURE 2 it should be understood that the stranding operation may take place separately in advance of the sizing operation.
As previously pointed out, multistrand electrical cable having a greater number of individual strands than the cable of FIGURE 1 may also be formed in accordance with the present concepts. Briefly, these larger size multistrand cables may be formed by stranding and sizing successive layers of strands about a central core strand in much the same manner as illustrated in FIGURE 2. As a result, the strands of each layer are deformed in those surface regions forming the outer periphery of the same layer, and are forced into tight arrangement about the inner portion of the cable structure which is surrounded by the layer.
This will be better understood with reference to FIG- URE 3 wherein a two-layered multistrand electrical cable 1s illustrated. Specifically, the cable includes an inner cable structure comprising a c-ore strand 31 surrounded by a single layer of helically wound strands 32. The Strands 32 are in tight engagement with the core strand 31. This lnner cable structure has been sized to produce fiattened regions 33 on strand 32 which for-m the outer periphery of the inner cable structure along with the valleys 34 between the strands. As is apparent, the inner cable structure is identical with the structure of the single-layered cable described with respect to FIGURE 1.
Surrounding the inner cable structure is a second layer of s trands 36 which are helically Wound in a direction opposlte 'to the strands 32. The strands 36 are similarly flattened m regions 37 forming the outer periphery of the cable along with the valleys 38 between the strands. Each liattened region 37 is bounded by corners 39 and 39' while the remaining surface region v4t) substantially retains its roundness or continuous curvature. Internal interstices 41, which periodically cross over the valleys 34 of the inner cable structure, are effectively sealed from the valleys 33 by the tightness of the contact at 42 between adjacent strands 36. In addition, the strands 36 are in tight contact with the flattened regions 33 of the strands 32.
Formation of the above-described two layer multistrand electrical cable, as Well as cables of more than two layers, essentially involves duplication of the steps involved in forming a single layer cable. Thus, for example, in FIG- URE 4 there is shown the core strand 31 being axially fed from a supply spool 50 to a first sizing die 55. The strands 32 forming the rst layer of the cable are simultaneously fed to the die from spools 51 mounted -on a rotating frame (not shown) of a conventional stranding machine. The inner cable structure 45 is thereafter withdrawn rfrom the sizing die 55 and axially fed to a second sizing die `60. Strands 36 are also fed to the die from spools 52 in the same lmanner as strands 32 are fed to die 55, with the exception that the frame is rotating in the opposite direction. The resulting two-layer multistrand electrical cable 46 as described with respect to FIGURE 3 is withdrawn from the Vdie V60 and wound upon a spool `61.
In this embodiment it should be understood that both layers of strands are cold-Worked in their flattened regions to a limited degree by the dies 55 and 60. The cold-working is limited to removal of kinks in the strands and equalizing the tension among the strands within each layer. This essentially reduces the internal stresses built up within the strands during the stranding operation. The physical properties, such as flexibility and elongation, remain substantially unaffected.
Thus, in accordance with concepts disclosed above, a multistrand electrical cable, having one or more layers of strands, may be conveniently constructed to possess the major advantageous features now possessed individually by conventional cable and compact cable without sulfering from the corresponding disadvantageous features.
The following examples will serve to additionally point out certain aspects of the invention.
Example 1 Six individual aluminum strands were stranded about an aluminum core strand and the stranded structure was passed through a sizing die. The diameter of each strand, including the core strand, was approximately 24.3 mils and the minimum diameter of the sizing aperture of the die was about 71 mils.
The resulting multistrand electrical cable had a maximum diameter of about 72 mils. The cable exhibited good properties of flexibility and elongation and had no tendency to spiral when laid out along a path without being anchored.
Example 2 A cable was formed as described in Example 1 and, in addition, an insulating sheath was extruded thereover. There was no evidence of imprinting in the sheath.
Example 3 An AWG No. 1 copper cable was formed in accordance with the following specifications. Six individual copper strands were stranded about a copper core strand. Each of the strands was approximately 111.5 mils in diameter. The stranded structure was then passed through a sizing die having an aperture of 318. mils minimum diameter.
The resulting multistrand electrical cable had a maximum diameter of 319` mils and exhibited good properties of flexibility and elongation. No tendency to spiral was present.
Example 4 A double-layer AWG No. aluminum cable was formed in accordance with the following specifications. Six individual aluminum strands were stranded about an aluminum core strand, each of the strands being approximately 23.5 mils in diameter. The stranded structure was passed through a sizing die having an aperture of about 68 mils minimum diameter. The resulting single-layer cable had a maximum diameter of about 69 mils. Twelve individual aluminum strands, each of about 23.5 mils in diameter, were then stranded about the single layer cable and passed through a second sizing die having an aperture of about 113 mils minimum diameter.
The resulting multi-strand electrical cable had a maximum diameter of about 114 mils and exhibited good properties of flexibility and elongation. The cable had substantially no tendency to spiral when laid out in an unanchored position.
Example 5 A double-layer AWG No. 2 copper cable was formed in accordance with the following specifications. Six copper strands were stranded about a copper core strand and passed through a sizing die having an aperture of about 172 mils minimum diameter. Each of the strands was initially about 60.3 mils in diameter. The resulting single-layer cable, having a maximum diameter of about 173 mils, was stranded with twelve additional copper strands, each of about 60.3 mils in diameter. The stranded structure was passed through a second sizing die having an aperture .of 287 mils minimum diameter.
'The resulting multistrand electrical cable had a maximum diameter of about 288 mils and was covered with an insulating sheath by extrusion. The cable possessed good properties of flexibility and elongation. No tendency to spiral was exhibited and no imprinting in the insulating sheath was found.
Example 6 A three-layer copper cable of AWG No. 300 was formed in accordance with the following specifications. Six copper strands were stranded about a copper core strand, each of the strands being approximately 91.8 mils in diameter. The stranded structure was then passed through a sizing die having an aperture of 262 mils minimum diameter. The resulting single-layer cable, having a maximum diameter of about 263 mils, was then stranded with twelve additional strands, each being about 91.8 mils in diameter. The stranded structure was drawn through a Second sizing die having an aperture of about 437 mils minimum diameter and the resulting doublelayer cable had a maximum diameter of about 438 mils. The double-layer cable was then stranded with an additional eighteen strands, ea'ch of about 83.3 mils in diameter. The thus stranded structure was drawn through a third sizing die having an aperture of about 611 mils minimum diameter and a three-layer cable of about 614 mils in diameter was produced.
The three-layer multistrand cable was covered with an insulating sheath by the usual extrusion coating process. The sheath showed no signs of imprinting. 'Ihe cable, in general, exhibited good properties .of flexibility and elongation and had no tendency to spiral.
Additional tests were performed on cables having strands of different diameters than those listed above as well as four-layer cables. The results obtained in all instances were in agreement with those obtained in Examples 1-6.
From the above detailed description it will be readily apparent to those skilled in the art that multistrand cables of any numbers of layers of strands may be made in accordance with the concepts of the invention. It is further pointed out that while only copper and aluminum strands have been mentioned in connection with the examples, strands of other metals may be employed, such as bronze, silver, brass, Steel, gold, magnesium, nickel, tungsten, zinc and alloys of the same.
Moreover, from Examples 1-6 and the foregoing general description of embodiments of the invention, it Iwill now be understood that a multistrand cable embodying the invention disclosed herein is characterized by a relaively flattened region 13, 33 or 37 which extends along the length of each layer strand 12, 32 or 36 and which is positioned in the perimeter of the layer strand 12, 32
or 36, so that it defines that portion of the perimeter which is most remote from a core strand 11 or 31. It will also be understood that the width of a region 13, 33 or 37 is limited so that the cross-section of a layer strand 12, 32 or 36 remains substantially circular. This limiting of the width of a region 13, 33 or 37 serves to provide substantial wedge-shaped valleys 17, 34, and 37 between adjacent layer strands 12, 32 or 36 and to otherwise provide a cable which does not have the undesirable physical properties which are characteristic of a prior art compact cable. However, even a region 13, 33 .or 37 which is limited in width provides a cable which does not have the undesirable properties of a prior art uncompacted cable.
In connection with the width of a region 13, 33 or 37, it will be noted from FIGS. l and 3 that the portion of the perimeter of a layer strand 12, 32 or 36 which is defined by a region 13, 33 or 37 is approximately twentyone percent of the perimeter. When the Examples 1-6 are manufactured and examined, it will be found that the portion of the perimeter of a layer strand 12, 32 or 36 which is dened by a region 13, 33 or 37 is also approximately twenty-one percent or less.
Thus, from a production standpoint, it will be understood that a multistrand cable embodying the invention is a cable which had a region 13, 33 or 37 along each layer strand 12, 32, or 36 so as to avoid the undesirable characteristics of a conventional uncornpacted cable but in which the region 13, 33 or 37 is limited to a Width that defines less than twenty-two percent of the perimeter of a layer strand 12, 32 or 36 so as to avoid the undesir- Y able characteristics of a conventional com-pact cable. It will also be understood that many variations and moditications may be made without departing from the spirit and scope thereof and therefore, it is intended that the present invention be limited only as defined in the appended claims.
1. In a multistrand cable, a core strand of substantially circular cross-section, and a plurality of layer strands helically wound about said core strand, each of said layer strands being of a substantially circular cross-section and each of said layer strands having a relatively flattened region extending along its length, said relatively attened region being formed -by deforming a layer strand so as to provide in the perimeter of a layer strand a portion of said perimeter which is most remote from said vcore strand and which is less than twenty-two percent of said perimeter.
2. The cable of claim 1 in which the core strand and layer strands are formed from a metal selected from the group consisting of aluminum, copper, silver, brass, bronze, gold, magnesium, nickel, tungsten, steel, zinc, and alloys .of the same.
3. The cable of claim 1 in which there are at least two layers of helically wound layer strands surounding the core strand with each successive layer Ibeing helically wound in a direction opposite to the preceding layer.
4. The cable of claim l1 in which each of the layer strands is in sealing engagement with the adjacent layer strands to effectively seal off the internal interstices of the cable.
S. The cable of claim 1 in which an insulating sheath surrounds said layer strands.
6. The cable of claim f1 in which said plurality of layer strands are a irst plurality .of layer strands and including a second plurality of layer strands helically wound about said irst plurality of layer strands.
References Cited UNITED STATES PATENTS 251,114 12/1881 Hallidie 57-145 1,742,172 2/1929 Atwood 57-138 XR 2,071,709 2/1937 Riddle 57--145 XR 1,888,076 1l/1932 Evans 57-161 XR 2,978,860 4/1961 Campbell 57-145 3,195,299 7/1'965' Dietz 57--149 3,234,722 2/ 1966 Gilmore 57-145 3,295,310 1/1967 Beighley 57-145 FOREIGN PATENTS 330,916 4/1903 France.
14,121 8/1891 Great Britain.
278,233 10/1927 Great Britain.
FRANK J. COHEN, Primary Examiner.
DONALD WATKINS, Examiner.