Electrical conductors are customarily fabricated by stranding together a plurality of wires in concentric layers. The natural geometry of such a construction is that when round wires of the same diameter are used to form a stranded conductor, six wires fit around a single core wire, twelve wires fit around the layer of six wires, eighteen wires fit around the layer of twelve wires and so on with each successive layer containing six wires more than are contained in the layer around which they are being stranded. Conductors of this configuration are known as concentric lay conductors. The number of individual wires contained in any conductor having "n" layers of wire and being so constructed is calculated by the algebraic equation X=3n.sup.2 +3n +1 where X represents the number of wires forming the conductor and n represents the number of layers being stranded about the central wire. Concentric lay conductors have the disadvantage of being relatively large in diameter for a given cross section of conducting metal. This is due to the open spaces or interstices between the wires. This interstitial space adds only to the bulk of the conductor and does not contribute to its conductivity.
Reduction of the diameter of a concentric lay conductor is practiced through a process known as compacting. Such a process is taught in U.S. Pat. No. 1,943,087. In this process, the stranded conductor is radially crushed and metal from the round wires is forced to flow into the interstices. The result is a conductor having a smaller diameter than an equivalent concentric lay conductor.
The aforementioned patent taught the art of compacting stranded conductors by means of pressure rolls. More recently, U.S. Pat. No. 3,760,093 teaches that it is also feasible to effect the compacting by pulling the conductor through a wire drawing type die between the application of each layer of wires as the conductor is being stranded.
Compacting such a stranded conductor, however, changes the geometric dimensional relationships so that a layer having six more wires than the underlying layer no longer fits naturally onto the conductor. The aforementioned compact conductor patent teaches, and the teaching is generally followed in commerce, that, to compensate for the reduction in diameter of the conductor core by compacting, the individual diameters of wires used in succeeding layers of the conductor should be reduced.
Significant disadvantages exist in conductors formed either by rolling the ,stranded, conductor, as taught in U.S. Pat. No. 1,943,082; or by drawing the conductor through a drawing type die between the application of each successive layer of wires, as taught in U.S. Pat. No. 3,760,093. One disadvantage is that the individual wires are characterized by wide variations of their physical properties. This is due to uneven work hardening of the wires as a result of each wire's position within the stranded structure. Wires located closer to the center of the conductor receive a greater amount of work hardening than those strands near the surface. This increased amount of work hardening results in higher unit tensile strengths, higher hardness numbers, and lower elongations. Another disadvantage of these methods of compacting a stranded conductor is that as the conductor is compacted, the individual wires impress substantial indentations into each other at every point where one wire crosses another one. This is a natural result of compressing and plastically deforming the individual wires where they cross each other in their opposing lay. Such an indentation reduces the cross section of the conductor and creates a weak point which is more succeptable to failure. When such conductors are exposed to the tensions and compressions normally encountered in their intended use, they fail earlier than they would had they been constructed of wires having uniform physical properties and no indentions.
The use of stranded conductors constructed of individual wires with some wires shaped to eliminate a certain amount of interstitial spacing is also known. Several methods and devices for producing such conductors, and various conductors or cables so produced, are found in U.S. Pat. Nos. 3,383,704; 3,444,684; 4,175,212; 4,436,954; 4,048,794; 2,978,860; 3,083,817; 3,130,536; 3,164,670; and 3,234,722.
U.S. Pat. Nos. 3,383,704 and 3,444,684 teach a method and apparatus for forming a multistrand conductor having a core of substantially circular cross section and a plurality of layer wires, each of which is of substantially circular cross section and each of which has a slightly flattened region along its length. This flat region is limited in width to that width which can be achieved by deforming the individual wire strands without causing the conductor to have the above discussed undesirable characteristics.
U.S. Pat. No. 4,175,212 teaches a conductor constructed so as to minimize a change in the length of the conductor as it is put under load and its temperature increases. The conductor is described as having a modified trapezoidal shaped wire strand composition, but the method of forming these strands and the advantages of using such a construction is limited to a description of a method of fabricating the stranded conductor lay such that expansion of tee individual wire strands does not detrimentally affect the length of the multiple strand conductor.
U.S. Pat. No. 4,436,954 teaches a steel-cored aluminum conductor used mainly for electric power conduction. The steel core of the conductor is a stranded cable. An aluminum mantle surrounding the core consists generally of cable-like staples. The advantages of the product of this patent rests in its use of an intermediate layer of material between the steel core and the aluminum wires or staples stranded thereon. This intermediate layer minimizes the effect of the interaction, both chemically and mechanically, of the dissimilar metals used to form the conductor. Though the outer aluminum wires are described as being trapezoidally shaped, they are roughly formed by the action of a drawing stone, which the conductor is drawn through between the application of each layer of the conductor.
As described above, forming a compacted conductor is taught in U.S. Pat. No. 3,760,093. In this process, the stranded conductor is drawn through a compacting die between the application of each layer of wires as they are stranded onto the conductor. The result is that as each layer is deformed, metal from the individual round wires flows into the interstices and a more compact conductor results. The disadvantages of this process are the lack of uniformity of the physical properties of the individual wires and the weak spots created by the resulting indentions in the wire strands.
U.S. Pat. No. 4,048,794 teaches the use of layers of shaped conductors in submarine anchorage cables. In this process, layers of wire having a Z-shaped cross section are utilized in the outer layers of a stranded cable. These wires are positioned such that the Z-shaped cross sections interlock. The purpose of such a configuration is to produce a layer or layers of interlocking wires that effectively seal the cable and prevent the introduction of sea water into the inner portions of said cable. No claim is made nor is the construction of such a cable intended to reduce the diameter of the cable.
U.S. Pat. No. 3,164,670 also teaches the use of swaging or crushing a layered cable to reduce the interstitial spacing. This patent teaches that from a practical point of view there is a limit to the size of the conductor that can be satisfactorily compacted using either a roll swaging or a drawing die type compacting operation. This patent teaches the compacting of the inner or core portions of the conductor followed by an application of preformed trapezoidal conductors, which it calls keystone shaped wires, stranded about the core. These trapezoidal shaped conductors are coated with insulating enamel. An alternative to the insulating enamel is the use of insulating polyester film tapes. The inventors purpose is stated as designing a conductor, as described above, so that the required degree of flexibility and minimum diameter of the cable cross section can be obtained without sacrificing dimensional accuracy. The method of constructing the cable herein is similar to methods referenced above in that the core is compacted after it is stranded to minimize the interstitial spacing. After the central layers have been compacted, trapezoidal shaped wires are applied to the outside of the cable. Again, the disadvantages of a cable so compacted are present in the core.
U.S. Pat. Nos. 3,083,817 and 2,978,860 deal with the manufacture of wire ropes. In these patents, a layer of wires smaller in diameter than the central or core wire are applied directly to the core wire, then a layer of wires having a diameter equal to the diameter of the core wire is stranded on top of the smaller wires. These conductors are then passed through a suitable drawing die and a compact product is obtained. The difference between the method taught herein and those methods described above is that the interstitial spacing is filled with the wires having a smaller diameter, and does not require the larger diameter wires to flow into the interstitial spaces. One teaching of this patent is a core or king wire, nine smaller wires surrounding it, and six wires of the same diameter as the core or king wire surrounding the ten. When the cable so conformed is passed through a drawing die, the natural result is the core or king wire acquiring a six sided configuration, and the nine smaller wires and the six wires having the same diameter as the king wire acquiring a five sided configuration. This construction is taught to make a steel wire rope that will have the five sided or keystone configuration wires around its outer layer. The advantages to this construction are mainly in the uniformity of its cross section and the lack of any tendency of these flat multi-sided wires to want to roll between the layers of wires which constitute the rope.
U.S. Pat. No. 3,130,536 also teaches the construction of wire rope. As above, the wire rope is constructed by utilizing wires of smaller diameter to fill the interstitial spacing such that when the cable is subjected to a compressing or a compacting operation less deformation of the larger wires is required and the interstitial spacing is filled with the swaged smaller diameter wires.
U.S. Pat. No. 3,234,722 teaches another method of cable fabrication. This patent teaches compacting six wires which surround a central core wire, then the application of alternating large and small wires in the next layer. When this layer is compacted the result is a conductor with an outer layer which more nearly properly fits over the seven strand core. The advantage stated in this patent is that upon compacting this outer layer of alternating size conductors there is a minimum amount of nicking and sharp edges protruding from this layer of wire since it now is a better geometrical fit than would be the case if twelve wires of a larger diameter were used instead of the six large and six smaller wires.
It should be readily seen that stranded conductors formed of shaped wires is not unknown in the industry. It should be evident from a reading of the above references that compacted electrical conductors are used and accepted in the industry and are desirable. It should also be evident from a reading of the above references that there are disadvantages associated with forming compacted conductors by the methods described.
Attempts have been made to overcome problems associated with compacting stranded conductors. One solution to the problems is to preform the wires into a shape that more efficiently utilizes the space they occupy in the stranded conductor prior to the stranding or assembly of the conductor. A trapezoidally shaped wire substantially fills the interstitial spaces and results in a more compact conductor. Typically, such a wire is formed during the drawing operation by drawing a round wire through a die having the trapezoidal shape. One disadvantage of this method is the tremendous decrease in speeds at which round wires can be drawn through such dies, when compared to speeds at which round wires are normally drawn. Another disadvantage is the expense of producing drawing dies having a trapezoidal geometry.
Reforming or reshaping a wire after it has been drawn but before it is collected at the end of the drawing machine eliminates many of the disadvantages described above. By utilizing a separate forming means, the speed at which a round wire can be reshaped is no longer a function of how fast such a wire can be drawn through an irregularly shaped hole in a drawing die, but rather how fast the forming means can accomplish its task.
One such forming means for reforming a round wire into one having a desired cross section comprises a first and second wheel, the wheels being singly, individually and rotatably mounted respectively on a first and second axle, the axis of said first axle being parallel to the axis of said second axle, and the axis of both axles positioned at right angles to the axis of movement of said round wire, and each wheel having a groove machined into its periphery, said groove forming a portion of the reshaped cross sectional configuration desired of said reshaped wire, and the periphery of said first wheel being tangent to the periphery of said second wheel at a point, said point being substantially aligned with the axis of movement of said reshaped wire.
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