US2055948A - Electrical conductor and process of making the same - Google Patents

Description

Sept. 29, 1936. R. SELQUIST ELECTRICAL CONDUCTOR AND PROCESS OF MAKING THE SAME Filed April 8, 1935 INVENTOR Patented Sept. 29, 1936 UNITED STATES PATENT OFFICE ELECTRICAL CONDU F MAKIN CTOR AND PROCESS GTHESAME Rolf Selquist, McKeesport, Pa.,

per-weld Steel Company,

assignor to Can- Glassport, Pa., a cor- 80laims.

This invention relates to a novel article of manufacture useful as an electrical conductor which must possess considerable tensile strength. More particularly, the invention relates to a conductor of the type used for transmission lines where the spacing of the towers or other supports is suiilcient to require a conductor whose ultimate strength is high.

Certain cheap metals, of which copper is the 10 most satisfactory electrical conducting material,

have relatively high conductivity, and indeed copper is accepted as the standard among metals in this characteristic. These metals and particularly copper, however, are subject to the drawll back for use in transmission lines that the relatively low ultimate strength of the metal limits the maximum length to which the spans may be carried. For increasing the ultimate strength of such conductors, wires have been produced having a a steel core surrounded by a sheath of copper. This product, in comparison with copper wire having the same conductivity, is considerably more expensive 0n the other hand, this bimetallic product has considerably higher ultimate strength than pure copper. The latter has an ultimate strength of approximately 60,000 pounds per square inch. A good product of the bimetallic type'iust referred to has an ultimate strength which is of the order of three times that a of copper. Thus, with this bimetallic product it is possible to increase the length of span in electric transmission lines beyond what is possible with a pure copper conductor.

. One object of the present invention is to pro- .35 vide a novel article of manufacture which combines the advantageous features of an all copper conductor and the high ultimate strength oi the bimetallic product above referred to, particularly in asymmetrical cables composed of wires of 4. widely diiferent physical characteristics.

A further object of my invention is to provide an improved method of manufacturing such a product.

drawing which illustrates In the accompanying a my invention.

Fig. 1 is a view in side elevation and Fig. 2 is a view in cross section of a two-strand con ductor embodying my invention;

Fig. 3 is a view in side elevation and Fig. 4 is ,a

I view in cross section of a similar article composed of three wires: and

Fig. 5 is a diagrammatic view illustrating the stranding of composite wire for producing such; a conductor.

In accordance with my invention, I combine in a composite electrical conductor a wire of a single metal having high conductivity with a bimetallic wire having a core of higher unit strength than the metal of high conductivity and having a sheath of said metal of high conductivity. I 5 strand the composite conductor by laying the wires against each other substantially on the axis of the conductor. I prefer to use as the wire of a single metal a copper wire because of its high conductivity; and I prefer to use copper as the sheath of the bimetallic wire, the copper sheath being permanently bonded with the core. For purposes of increasing the ultimate strength of the product, the core of the bimetallic wire is preferably steel.

My improved article of manufacture is illustrated' by two embodiments, one of which consisting of two wires is shown in Figs. 1 and 2. The wire of a single metal is indicated by the numeral 6 and the bimetallic wire is indicated by the numeral 1. As above set forth, the wire 8 is preferably a copper wire and the wire I preferably comprises a core C of a metal of higher unit strength than the copper while the sheath S is of copper.

A second. embodiment of my invention is 11- lustrated in Figs. 3 and '4. The composite electrical conductor is made up, in this embodiment, of copper wires 9 and I0 and a bimetallic wire ll. Here again, the wire H preferably comprises a so core 0 of steel and a sheath S of copper permanently bonded to the core. With a threewire type of conductor it is, of course, possible to substitute a bimetallic wire for eitherthe wire 9 or the wire l0; but such a-conductor has not in general the field of usefulness that the embodiments shown have.

There is one respect at least in which the several embodiments of my invention are a distinct departure from electrical conductors heretofore 40 produced. There is a lack of balance of the metal of high unit. strength about the central axis of the conductor. It will be noted that in Fig. 2 the bimetallic wire on one side of the axis is not balanced by a similar wire on the other side of the axis of the conductor. In the same way, the bimetallic wire introduces a lack of symmetry into the embodiment shown in Fig. 4. While this introduces into the manufacture of the conductor problems peculiar tosuch asymmetrical 5 distribution of metal of high unit strength about the axis of the conductor, I have found that by modifying the customary practice in stranding the wires, these diiiiculties can be overcome.

In the production of composite conductors of this type the usual stranding practice should be modified to take care of the distinct characteristics of the bimetallic wire, including the greater rigidity or stiffness of such wire. It is customary in stranding a composite conductor to preform the several wires entering into the strand before they reach the closing die. It has been discovered that if this customary practice is followed in making my improved product, the wires do not lie close together in the strand. This is due to the'fact. that the copper wire or wires are more plastic and have less stiffness than the bimetallic wire. In overcoming thisdifllculty I accentuate the preforming action on the bimetallic wire while reducing or almost eliminating the preforming action on the copper wire or wires. 7

As illustrated diagrammatically in Fig. 5, the several wires are as usual unwound from bobbins l4, l5, etc., and passed about guides l1, l8, etc. to the closing die 20, the bobbins and guides being carried on a revolving spider (not shown) in the customary manner.

I have found that if the preforming action on the copper wire by its respective guide, in Fig. 5 the guide It, is greatly reduced or almost eliminated, the stranding operation functions smoothly and the wires lie close together in the finished conductor. Preferably, the guide cooperating with the copper wire is so formed as to eliminate any sharp bending as the wire passes about the guide. These guides are customarily rollers, and the desired purpose may be accomplished by increasing the diameter of the roller. The preforming action is also controlled to a considerable extent by the drag imposed upon the bobbin by the usual brake indicated at 2|. The bobbin from which the copper wire is unwound is -allowed to revolve with but slight braking action.

' Accordingly, the copper wire running to the closing die is practically straight.

On the other hand, the accentuation of the preforming action on the bimetallic wire may be secured by causing the bimetallic wire to make a sharper bend about its respective guide, and

furthermore by increasing the braking action on the bobbin. The result of the accentuation of the preforming action on the bimetallic wire and the reduction in the preforming action on the copper wire is to enable the closing die 20 to closely. and uniformly intertwine the wires into a uniform strand.

The term preformed" as it appears in this description of my invention and in the claims is used in the sense of forming the wire into a permanent helix before it goes into the closing die. The term preformed is not used in the claims with the intent that itshould be construed as the action of straightening a wire.

The product produced in accordance with my invention has, in addition to the advantages pointed out in the above description, further advantages which are inherent in the product. The moduli of elasticity (Youngs modulus) of the bimetallic wire and of the copper wire are such that, within the limits of strain to which such conductors would generally be sublected in service, the load applied to the conductor is distributed between the wires in proportion to the moduli of these wires. Accordingly. the bimetallic wire carries a larger proportion of the load than the copper wire or wires, thus utilizing the full strength of all of the component wires without premature over-stressing of either material. This is in contrast to composite conductors in which the wires have all the same modulus of elasticity. In such a case, the strains tend to cause equal loading in all of the component wires.

This would result in proportioning the loads, not

according to the strengths of the individual wires, but equally, which is disadvantageous.

. A further advantage inherent in my improved product is that there is no chemical dissimilarity between the wires exposed to the atmosphere. In other words, there is no tendency to establish electrogalvanic action or electrolytic deterioration within the cable, such as is apt to occur when two dissimilar metals are juxtaposed.

A further advantage lies in the freedom from vibration of the conductor when strung on long spans with high stringing tensions. The particular shapes of these conductors are such that they have little or no tendency to vibrate in winds. As is well known, such vibration is objectionable, as it subjects the conductor to excessive stresses and to chafing at points of support.

It is furthermore noteworthy that in accordance with my invention wires of radically different characteristics, particularly with respect to their unit strength, are combined into a uniform conductor. It will be apparent that this constitutes a notable contribution in the way of m a l possible the production of a conductor having the wires so stranded that the metal of high unit strength is asymmetrically distributed about the axis of the conductor.

While I have illustrated and described certain preferred embodiments which my invention may assume, it will be understood that my invention may be otherwise embodied and practiced within the scope of the following claims.

I claim:

1. In the method of stranding a composite cable comprising a wire of a single metal and a bimetallic wire having a core of higher unit strength than the metal of the first wire. the steps consisting in preforming the-bimetallic wire to a considerably greater extent than the wire of a single metal, and then intertwining the wires and passing them through a closing die.

2. In the method of stranding a composite cable comprising a wire of a single metal and a bimetallic wire having a core of higher unit strength than the metal of the first wire, the steps consisting in accentuating the preforming action on the bimetallic wire as compared to that proper for the stranding of a composite cable of similar wires while substantially reducing the preforming action on the wire of a single metal, and then intertwining the wires and passing them through a closing die.

3. A composite electrical conductor comprising a wire of a single metal having high conductivity stranded with a bimetallic wire having a core of higher unit strength than the metal of high conductivity and having a sheath permanently bonded thereto of said metal of high conductivity, the bimetallic wire being preformed to lie against the wire of a single metal and both wires being disposed in substantially equal helices about the axis of the conductor.

4. A composite electrical conductor composed of wires closed about the axis of the conductor without a central core wire, the component wires comprising a preformed bimetallic wire having a core of relatively high unit strength and an integrally united sheath of metal of relatively high conductivity, and a wire of said metal of high conductivity twisted therewith while in. substan' tially straight condition so as to be twisted to sub stantially conform to the shape of said bimetallic wire one bimetallic wire having a core of relatively high unit strength and an integrally united sheath of copper and stranding it together with at least one unpreiormed copper wire without a central core wire, and passing the stranded wires through a closing die.

7. A composite electrical conductor as claimed in claim 3 in which the wire of a single metal is a copper wire and the bimetallic wire has a sheath of copper permanently bonded to a core of steel. 8. A composite electrical conductor comprising 5 a bimetallic wire having a sheath 01' copper permanently bonded to a core 01' steel and at least one copper wire, said wires being twisted about the axis or the conductor without a central core wire, the bimetallic wire being formed into permanent helices before being stranded with the remainder of the wires, and the latter being in substantially straight condition before they are twisted about the axis of the conductor so as to be twisted to substantially conform to the shape of said bil5 metallic wire.

ROLF SELQUIBT.

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