US3349832A - Method of forming sheathed conductor - Google Patents

Description

METHOD OF FORMING SHEATHED CONDUCTOR 3 Sheets Sheet 1 Filed Dec. 16, 1964 INVENTOR. GEORGE J. CROWDES GEORGE H. HUNT ATTORNEYS IINIIIIE Oct. 31, 1967 G. J. CROWDES ET AL 3,349,332

METHOD OF FORMING SHEATHED CONDUCTOR 5 Sheets-Sheet 2 Filed Deg. 16, 1964 INVENTOR.

GEORGE J. CROWDES BY GEORGE H. HUNT I I m mm ma num;

ATTORNEYS G.J.CROWDES ET AL 3,349,832 METHOD OF FORMING SHEATHED CONDUCTOR Oct. 31, 1967 5 Sheets-Sheet 3 Filed Dec. 16, 1964 INVENTOR. GEORGE J. CROWDES BY GEORGE H. HUNT m MEW ATTORNEYS United States Patent Filed Dec. 16, 1964, Ser. No. 422,060 8 Claims. (Cl. 164-86) This application is a continuation-in-part of application Ser. No. 386,530, filed July 31, 1964 and now abandoned.

This invention relates to electrical conductors and in particular to a method of forming alkali and alkaline earth metal conductors especially conductors made from sodium, lithium and calcium, and their alloys.

Although this invention could be used to form any alkali and alkaline earth metal or alloy conductor, sodium and its alloys are preferred and, therefore, the description herein is directed to the formation of sodium conductors.

Electrical conductors made from sodium have been previously suggested, for example, in the French patent to Betts, 361,102 (1905). Conductors made from sodium have been used at least experimentally in this country by Dr. H. H. Dow in which case molten sodium was poured into lengths of steel pipe which were later joined together to form a single long conductor. In that case particular difiiculty was encountered in joining the pipe sections as an interface of oxidized sodium at a joint was found to cause considerably increased resistance in the conduct-or.

The principal characteristics of sodium which recommend it for use in electrical conductors are its low cost, availability and low density; moveover, the conductivity of sodium is only slightly less than copper. Other properties which must be considered in forming a conductor from sodium include its high reactivity which makes imperative that the sodium conductor be protected from exposure to the atmosphere. The loW tensile strength of sodium, moreover, limits the length of conductor which can be used without support, its high thermal coefficient of expansion makes sodium somewhat incompatible with conventional cable sheathing materials.

It is, therefore, a purpose of this invention to provide a continuous method for forming a sheathed sodium conductor.

It is a further object of this invention to provide a strengthened sodium conductor which can be used in long unsupported lengths.

Still another purpose of the present invention is to provide a sheathed sodium conductor Which compensates for the difference in the thermal coefiicient of expansion between the sodium core and the sheathing mate-rial.

These and other objects are accomplished by continuously forming a tape of sheathing material int-o a tube by successively bending the longitudinal edges of the tape until they are in abutting relationship to each other, and welding or otherwise joining the seam formed thereby. Liquid sodium is then injected into the tube along a path aligned with the axis of the tube at a point beyond that where the seam is joined. Difiiculties due to differences between the coefiicients of thermal expansion of sodium and the sheathing material are avoided by forming the tube of sheathing material with an oval cross-section. With this construction, the sheath is able to compensate for changes in the volume of the sodium within it by changing its shape to a flatter or rounder cross-section whereby the sheathing material and sodium core remain in intimate contact with each other regardless of temperature and formation of voids which increase resistance are prevented.

Because of the high reactivity of the sodium, as a further protective measure, the liquid sodium is usually introduced to the tube under an inert gas atmosphere. The molten sodium solidifies quickly in the formed tube without external cooling and the conductor formed thereby can, as a precautionary but not an essential step, be put through a die to insure uniform and continuous contact between the sheathing material and the sodium core. Other post-hardening steps can include corrugation of the tube to increase fiexibilityy.

Where strengthened conductors are desired, a central high tensile strength core is provided which is intro duced to the tube along its longitudinal axis during formation and is preferably held in place in the center of the tube while the liquid sodium is introduced. This can be accomplished, for example, by passing the core through a locating aperture in the structure associated with the sodium inlet conduit. Alternatively the central core can include clips at intervals along its length having a central aperture receiving the core and at least three points which touch the inside of the formed tube. Such a core in preferably of material such as steel or other high tensile strength material which is non-reactive with sodium.

An alternative construction where strength is desired consists of a composite cable in which sodium conductors formed according to the present invention and high tensile strength strands or cables are intermingled in much the same way that steel and aluminum conductors are presently used.

The tube forming step of the present invention can be performed by passing the sheathing material initially in the form of a tape through a series of rollers which 0perate in pairs to define a path for the tape causing the tape to assume an increasingly arcuate shape, i.e., circular cross-section. Final closure of the tube can likewise be accomplished using rollers or by passing the partially formed tube between a pair of carbon blocks having arcuate confronting surfaces which urge the edges of the tape together forming the tube. A pair of transverse rollers can cooperate with the carbon blocks to determine the final cross-section of the tube.

The seam is preferably joined by Welding under an inert gas atmosphere. To assure a continuous and uniform seam, it is imperative that the welding be conducted as close as possible to the tube closure step.

The liquid sodium is introduced to the tube through a conduit which enters the line of tube formation just prior to the tube closure step and extends into the tube beyond the welding point along a path parallel to the axis of the tube which is preferably vertical. Inert gas can be introduced through a parallel conduit extending into the tube to a point just above the outlet of the liquid sodium conduit. It is normally not necessary to heat the sodium conduit within the tube forming area since the welding operation introduces suificient heat to the tube to maintain the sodium above its melting point, 97.5 C. What provision may be necessary for heating the conduit outside of the tube forming area will depend on the length of the conduit and the ambient temperatures encountered.

The sheathing material used can be any metal or alloy which is relatively inert to the atmosphere or other environment in which the conductor may be placed. Aluminum and copper are the chiefly suitable sheathing materials used. Lead, which may alloy with the sodium, is suitable where the formation of such alloy at the interface between the lead sheath and the sodium is not objectionable.

As a further description of the present invention, reference is made to the attached drawings of which:

FIGURE 1 is a somewhat schematic perspective view of an apparatus suitable for carrying out the method of the present invention;

FIGURE 2 is an elevation of a portion of the apparatus shown in FIGURE 1; I

FIGURE 3 is a sectional view taken along line 3-3 in FIGURE 2;

FIGURE 4 is a sectional view taken along line 4-4 in FIGURE 2;

FIGURE 5 is a sectional view taken along line 5-5 in FIGURE 2;

FIGURE 6 is an enlarged elevation partially cut away of a portion of the apparatus shown in FIGURE 1;

FIGURE 7 is an enlarged elevation partially cut away of an alternate construction for part of the apparatus shown in FIGURE 6;

FIGURE 8 is a sectional view taken along line 88 in FIGURE 7;

FIGURE 9 is a partially cut away view of a cable showing another alternate construction according to the present invention;

FIGURE 10 is a sectional view of the cable shown in FIGURE 9 taken at the point where the sheath is welded; and

FIGURE 11 is a sectional view of a composite conductor using sodium conductors formed according to the 'present invention.

Referring to FIGURE 1, sheathing material initially in the form of a tape 12 and a steel rope 14 are passed downwardly through an initial tube former 16, a final tube closure device and a welding unit 22 which are disposed in that order along a vertical path. Intermediate initial tube former 16 and final tube closure device 20, a molten sodium injection unit 26 extends laterally into the partially formed tube and extends axially downward to a point beyond welding unit 22. The completed conductor 21 is then passed to a post-formation operation 24.

Referring more particularly to FIGURE 2, initial tube former 16 consists of a series of horizontally adjacent rotatable pairs of cooperating rolls in which the various pairs of rolls are vertically aligned with one another and mounted with their axes horizontal and parallel to each other. One set of vertically aligned rolls of the series of horizontally aligned, cooperating pairs are denoted in sequence by the reference numerals 28, 29 and 30, respectively, while the other set of vertically aligned rolls of the series of pairs are denoted in sequence by the reference numerals 31, 32 and 33, respectively.

The first pair of cooperating rolls in the series, i.e., upperroll 28 and upper roll 31 (see FIGURE 3) are essentially cylindrical in construction and are mounted afiixed to axles 34 and 37, respectively, which are aligned in a horizontal plane such that the cylindrical surfaces of rolls 28 and 31 are in rolling contact.

The middle pair of rolls in the series, that is, rolls 29 and 32 (see FIGURE 4) are similarly mounted afiixed to axles 35 and 38, respectively, which are also aligned in a horizontal plane. Roll 29 of the pair is generally oblate while roll 32 is generally cylindrical.

In the case of the lower pair of rolls in the series lower roll 30 is generally oblate and lower roll 33 is generally cylindrical (see FIGURE 5). Rolls 30 and 33 are mounted on a pair of axles 36 and 39, respectively, which are aligned in a horizontal plane.

Associated with each pair of cooperating rolls in tube former 16 are a pair of stands 40 (see FIGURE 3 for example) receiving opposite ends of the pair of axles on which each such pair of cooperating rolls are affixed. Each stand 40 includes a pair of adjustable journals for holding the axles of the roll pair associated with it in proper alignment relative to one another. Stands 40 are mounted on a common vertical base 42.

Along one side of base 42 each axle 37, 38 and 39 extends outwardly through. its associated stand 40 and carries a bevel gear 44. On the same side of base 42 there is positioned a drive shaft 46 mounted in a vertical position in journals 48 aflixed to the base 42. Drive shaft 46 extends alongside the series of cooperating roll palrs and carries a series of bevel gears 50 affixed to it which are positioned to engage bevel gears 44 aflixed to the ends of axles 37-39, inclusive, providing a common drive for inner rolls 3133, inclusive. It will be noted that rolls 2830, inclusive, are idlers.

A motor 52 is mounted on base 42 and has its output connected to shaft 54 to drive each of rolls 31-33, inclusive, in the same direction such that a tape positioned to be received by the roll pairs between their cooperating surfaces will be carried progressively from roll pair 28, 31 to roll pair 29, 32 to roll pairs 30, 33, thence to tube closing device 20 (see FIGURE 1).

As pointed out above, tube former 16 essentially intended to take a flat tape 12 of copper, aluminum or other suitable metallic sheating material and to fold such tape 12 longitudinally into a tube 18. To this end each of the rolls 28-33, inclusive, are circumferentially grooved with the grooves registering in cooperating pairs. When tape 12 is to be folded into a tube 18 enclosing a stranded steel rope 14, as in FIGURE 1, idler rolls 28, 29 and 30 are provided with circumferential grooves 56, 57 and 58 sized to receive steel rope 14 permitting rope 14 to pass rolls 28, 29 and 30 received in such grooves 56, 57 and 58.

Associated driven rolls 31, 32 and 33 are provided with circumferential grooves 59, 60 and 61. Groove 59 of roll 31 of the upper roll pair is essentially flat bottomed and sized to receive tape 12 such that as tape 12 and steel rope 14 pass between rolls 28 and 31 the under surface of rope 14 is positioned centrally of and immediately above the upper surface of tape 12. Groove 60 in roll 32 of the middle pair of cooperating rolls in tube former 16 is provided with a curved, concave bottom such that as tape 12 passes between rolls 32 and 29 a slight transverse curl is imparted to tape 12 by the cooperating action of oblate roller 29 which is received in groove 60. Again groove 57 holds steel rope 14 centrally positioned immediately over tape 12. Groove 61 in roll 33 is similar to groove 60 but is provided with a deeper curved, convex bottom to impart a sharper transverse curl to tape 12. Again groove 58 in roller 30 retains steel rope 14 centrally over tape 13, the longitudinal edges of which at that point are curved upwardly such that the crosssection of tape 12 is almost semicircular.

The partially formed tube 18 is then passed to final tube closure device 20. One such device, shown in FIG- URE l and in copending Wakefield application consists of a pair of carbon blocks 70 having confronting concave parti-elliptical surfaces which are spring biased to exert suflicient pressure against the sides of partially formed tube 18 to hold the edges of tape 12 passing between them in abutting relationship. Carbon blocks 70 are slidably retained in rectangular housings 72 disposed on either side of the axis of tube formation and held adjusta'bly in place by a pair of threaded bolts 74 which are journalled in support columns 75. Columns 75 are attached to a rectangular base 76 by a pair of screws 77. The final crosssection of the tube is determined by a pair of narrow rollers 78 and 79 (not shown) which extend perpendicular to and equidistant from the axis of tube formation, one on each side of carbon blocks 70. Rollers 78 and 79 are journalled in a pair of rectangular blocks 80 which are mounted to rotate on bolts 74. By rotation of blocks 80 the displacement of rollers 78 and 79 from the axis of tube formation can be varied while rollers 78 and 79 are kept equidistant from that axis. Blocks 80', after proper adjustment, are held stationary by four bolts 82, one each passing through a tapped block 84 attached to the lower portion of each side of each support column 75- by a pair of screws 86.

The seam of tube 21 is welded in an arc welding unit,

preferably under an argon atmosphere. Since this unit is of conventional construction, it is shown generally in FIGURE 1. To insure a uniform seam it is important that the welding take place as close as possible to tube closure device 20.

Intermediate tube former 1'6 and final closure device 20 a liquid sodium injection unit extends into partially formed tube 18 and along its axis to a point below that where the seam is welded. In cases where the sodium conductor includes a central strength member, such as steel rope 14 as shown in FIGURE 1, the molten sodium injection unit can also serve to locate rope 14 centrally within tube 21. The molten sodium injection unit shown in FIGURES l and 6 includes a series of elliptical, horizontal plates 90, 91 and 92 displaced from each other along the axis of tube formation with plate 90 above plate 91 and with plate 92 below plate 91. Plates 90, 91 and 92 are rigidly held in place with respect to each other by four tie rods 94 which are secured to each of plates 90, 91 and 92 by a pair of hex nuts 96. A molten sodium conduit 98 extends from outside the tube formation area through vertically aligned apertures in each of plates 90, 91 and 92 to a point within tube 21 below welding unit 22, plates 90 and 91 being above welding point 22 and plate 92 being below unit 22, which first tube closure device 20 is positioned intermediate plates 90 and 91. A second conduit 100 extends from outside the tube forming area through plates 90 and 91 terminating at plate 91. Conduit 100 is used for the introduction of an inert gas in the area above the point of sodium injection. The circumferences of plate 90, 91 and 92 are sized to coincide with the inside diameter of the formed tube and thus olfer no obstruction to the tube formation. Plate 90 also includes an arm 102 which extends out of the partially formed tube where it is attached to a suitable support column 104.

An alternate sodium injection unit is shown in FIGURE 7. In FIGURE 7, the same apparatus, as shown in FIG- URES 1-6, can be used and the same reference numerals are employed, except that the sodium injection apparatus is replaced by a device which includes a collar 110 which surrounds a rope 14 above closure device 20 and extends along the length of tube 18 to a point below welding unit 22. A pair of elliptical, annular plates 112 and 114 are attached to the outside of collar 110', displaced from each other, at the portion of collar 110 below Welding unit 22. The peripheries of plates 112 and 114 are sized to coincide with the inside dimensions of tube 21 and thus operate to hold collar 110 with contained rope 14 in the center of tube 21. Collar 110 further includes an annular passage 116 which extend-s from the end of collar 110 below welding unit 22 up almost to the upper end of collar 110 at which end it communicates with a conduit 118 for introduction of molten sodium to annular passage 116 and through passage 116 to tube 21. A second conduit 120 extends into the partially formed tube and downwardly along a path aligned with its axis, terminating in plate 112. This conduit is used for introducing an inert gas into the formed tube above the point of sodium injection.

FIGURE 8 is an exaggerated cross-section of the conductor formed according to the present invention. As will be seen the conductor includes, as an external sheath, tube 21 with solidified sodium 122 and centrally located wire rope 14 within tube 21. In actual practice the elliptical cross-section of the tube is not as severe as that shown in FIGURE 8.

The method of the present invention is carried out using the apparatus shown in FIGURES 18 by continuously passing tape 12 and steel rope 14 in sequence through tube former 16, final tube closure device 20 and welding unit 22 while continuously introducing molten sodium through conduit 98 or 118 and inert gas through conduit 100 or 120. No external cooling is necessary to atfect solidification of the sodium since its melting point is 975 C., and the liquid sodium need only be raised to .such temperature or a few degrees higher for casting in tube 18. However, if space is limited conventional cooling means can be employed. Post-formation operation 24 can include passing the conductor through a drawing die or corrugation to insure continuous contact between the sheath and the sodium. It may also include a tractor type device to draw the finished conductor through the entire apparatus.

It will be apparent 'from the preceding description of the apparatus that indefinite lengths of sodium conductor can be formed in accordance with the present invention with the advantage that the liquid sodium can be introduced into a closed sheath while shielded from the atmosphere by a blanket of inert gas. The slightly elliptical cross-section imparted to the sheath, i.e., tube 21, permits the sheath to expand or contract in total enclosed Volume, i.e., by becoming less or more elliptical in crosssection to accommodate the same expansion or contraction of the sodium conductor as its temperature is either raised or lowered. Alternatively a tube of circular crosssection can be employed in which case as the liquid sodi um cools and contracts the tube will assume a somewhat elliptical cross-section. The use of a circular cross-section tube for a sheath as the molten sodium is injected into the tube has the limitation that, if the temperaure of the sodium wihin the ube is raised to a temperature higher than that at which it was cast, rupture of the sheath is possible. The employment of a cormgator to impart a corrugation to the tube in which the sodium is cast, either at a point where the sodium is still liquid or at a point at which it is solid, also permits expansion and contraction of the tube to accommodate expansion and contraction of the sodium. In the event the tube formation of a tube of elliptical cross-section at the point of sodium injection is therefore necessary.

An alternate cable construction is shown in FIGURES 9 and 10. In this case wire clips are affixed to steel rope 14 as rope 14 passes from tube former 16 to final tube closure device 20. Three such clips are shown in FIGURE 9 displaced from each other center of the clip. The outer extremity of each fin er coincides with the inside wall dimension of tube 21, and the portion of the clip between adjacent fingers grips rope 14 holding rope 14 in the center of tube 21. Thus the use of devices such as plates 90, 91 and 92 to hold rope 14 centered in tube 21 are unnecessary. The wire clips are left in the conductor and offer little or no resistance to electrical currents. As shown in FIGURE 10 when wire clips 130 are used, sodium and inert gas injection can be accomplished by extending a pair of conduits along paths aligned with the axis of tube 21, each conduit being located in the arcuate interval between adjacent fingers which are therefore secured strand 200 is enclosed by six strands 201 helically applied about strand 200. Strand 200 is an alumoweld strand while strands 201 are sodium strands sheathed in aluminum tube in accordance with the preceding description except neither rope 14 nor its equivalent is used. Other suitable combinations for use as composlte cables willalso be suggested to those skilled in the art.

Numerous variations of the apparatus described above can be used without changing the essential nature of the present invention. For example, other means of tube closure are presently available such as rollers and it is not intended to limit the present invention to the structure shown in the appended drawing. As a further variation of the present invention it is also possible to form and Weld two tubes in tandem, one within the other, filling the space between with molten sodium.

Moreover, While the preceding description has had reference to sodium as a pure metal, it will be noted that binary alloys of sodium and potassium containing small amounts of potassium are highly suitable when a lower melting point sodium conductor is desired. Sodium and potassium form a low melting (12.5 C.) eutectic at 22.7% sodium by weight. The reduction from the melting point of pure sodium (975 C.) by even small amounts of potassium is thus quite pronounced. Similarly, binary alloys of sodium and lithium containing only small amounts of lithium (up to 3% by weight) show a striking increase in melting point (162 C. M.P. at 3% by weight of lithium). Hence such alloys are highly suitable where a higher melting sodium conductor is desired.

In the case of lithium conductors small amounts of either sodium or potassium are effective to lower the melting point of the lithium. In the case of calcium conductors lithium binary alloys and lithium sodium ternary alloys can be used.

We claim:

1. The method of forming a conductor having a core of a conductor material selected from the group consisting of alkali metals, alkaline earth metals and their alloys and a metallic sheath about said core, which process includes drawing an indefinite length of metallic sheathing material initially in the form of a tape along a given path and acting upon said tape to form said tape into a tube by successively bending the longitudinal edges of said tape until they are in abutting relationship to each other; sealing the seam formed thereby; passing a steel rope parallel to said tape and sufficiently close to said tape to be included within said tube; filling the closed tube with said conductor material introduced in molten condition through conduit means extending along a path aligned with the axis of the tube forming path to a point along said axis beyond the point of sealing said seam and locating said steel rope centrally within said tube by means associated with said conduit means.

2. The method according to claim 1 wherein the conductor material is sodium.

3. The method according to claim 1 in which the conductor material is sodium and the sheathing material is selected from the .group consisting of aluminum, copper and their alloys.

4. The method of forming a conductor having a core of a conductor material selected from the group consisting of alkali metals, alkaline earth metals and their alloys and a metallic sheath about said core, which process includes drawing an indefinite length of metallic sheathing material initially in the form of a tape along a given path and acting upon said tape to form said tape into a tube by successively bending the longitudinal edges of said tape until they are in abutting relationship to each other; sealing the seam formed thereby; passing a steel rope parallel to said tape and sufficiently close to said tape to be included within said tube, locating said rope centrally within said tube by passing said steel rope through a sleeve which extends along the axis of said tube forming path from a point which at the longitudinal edges are not in abutting relationship with each other to a point beyond the point of sealing said seam; and filling the closed tube with said conductor material introduced in molten condition through an annular groove in said sleeve which extends from the end of said sleeve which extends beyond the point of sealing said seam to a point closely adjacent the other end of said sleeve and means for introducing the molten conductor material to said annular groove in said sleeve.

5. The method of claim 4 wherein the conductor material is sodium.

6. The method according to claim 4 wherein the conductor material is sodium and the sheathing material is selected from the groupconsisting of copper, aluminum and their alloys.

7. The method of claim 1 wherein said filling of the closed tube is conducted under an inert atmosphere.

8. The method of claim 4 wherein said filling of the closed tube is conducted under an inert atmosphere.

References Cited UNITED STATES PATENTS 833,290 10/1906 Betts. 2,055,980 9/ 1936 Liebmann 22-2001 2,185,429 1/ 1940 Burby.

FOREIGN PATENTS 669,002 7/ 1929' France. 973,315 9/1950 France.

25,203 12/ 1901 Switzerland.

OTHER REFERENCES Transactions of the Electro-Chemical Society, A 4000, Ampere Sodium Conductor, September 1932, pp. 151- 160. (Copy in Group 160.)

I. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner.

Claims (1)

1. THE METHOD OF FORMING A CONDUCTOR HAVING A CORE OF A CONDUCTOR MATERIAL SELECTED FROM THE GROUP CONSISTING A ALKALI METALS, ALKALINE EARTH METALS AND THEIR ALLOYS AND A METALLIC SHEATH ABOUT SAID CORE, WHICH PROCESS INCLUDES DRAWING AN INDEFINITE LENGTH OF METALLIC SHEATHING MATERIAL INITIALLY IN THE FORM OF A TAPE ALONG A GIVEN PATH AND ACTING UPON SAID TAPE TO FORM SAID TAPE INTO A TUBE BY SUCCESSIVELY BENDING THE LONGITUDINAL EDGES OF EACH TAPE UNTIL THEY ARE IN ABUTTING RELATIONSHIP TO EACH OTHER; SEALING THE SEAM FORMED THEREBY; PASSING

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