US2936357A

US2936357A - Manufacture of metal sheathed cable and the like

Info

Publication number: US2936357A
Application number: US424361A
Authority: US
Inventors: Thomas J Crawford
Original assignee: Individual
Current assignee: Intercole Bolling Corp
Priority date: 1954-04-20
Filing date: 1954-04-20
Publication date: 1960-05-10
Anticipated expiration: 1977-05-10

Description

IN V EN TOR.

HTTOQNE'YJI May 10, 1960 T. J. CRAWFORD MANUFACTURE OF METAL SHEATHEZD CABLE AND THE LIKE Filed April 20, 1954 6 Sheets-Sheet 1 si W a AP- WM in rum .DIWHMIU. fi m-L- i; I l

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May 10, 1960 T. .1. CRAWFORD 2,936,357

MANUFACTURE OF METAL SHEATHED CABLE AND THE LIKE Filed April 20, .954

6 Sheets-Sheet 2 e X 9 AVE/2A6: FLUX DL'N5/Ty Q 2 g AT LONG/TUD/NAL. M Q man/w: or COIL. 5 E w GE I R 53 L INEAL DlfiTANCE P INVENTOR.

y 1960 T. J. CRAWFORD 2,936,357

MANUFACTURE OF METAL SHEATHED CABLE AND THE LIKE Filed April 20, 1954 6 Sheets-Sheet 3 oemaugwhb/d QTTOZZNEYJ May 10, 1960 T. J. CRAWFORD MANUFACTURE OF METAL SHEATHED CABLE AND THE LIKE Filed April 20, 1954 6 Sheets-Sheet 4 INVENTOR. THO/M5 J. 672/] W/URD y 9 T. J. CRAWFORD 2,936,357

MANUFACTURE OF METAL SHEATI- IED CABLE AND THE LIKE Filed April 20, 1954 6 Sheets-Sheet 5 IN V EN TOR.

May 10, 1960 T. J. CRAWFORD 2,936,357

MANUFACTURE OF METAL SHEATHED CABLE AND THE; LIKE 6 Sheets- Sheet 6 Filed April 20, 1954 IN V EN TOR. T/M/f/IJ J. CfiAW/WAD United States Patent MANUFACTURE OF METAL SHEATHED CABLE AND THE LIKE Thomas J. Crawford, Berkley, Mich.

Application April 20, 1954, Serial No. 424,361

6 Claims. (Cl. 219-85) This invention relates as indicated to metal sheathed cable and the like, and more particularly tov electric cable having a closely fitting impervious outer metal sheath, preferably of aluminum. The invention is also concerned with a novel method and apparatus for producing the same.

Metal sheathed cable has, of course, long been known and has ordinarily been produced either by extruding lead about the cable or by forming a tubular metal blank about the cable and then closing the seam eithermechanically or by welding opposed upstanding seamedges of the blank. It is usually important that the sheath should be completely impervious and also that it should be light in weight. This latter is important for the reason that cable of this nature is suspended from towers of crosscountry transmission lines and the like, often in very large spans. turally high when utilizing lead sheathed cable.

When metals other than lead are employed as the sheathing material for lengths of cable in excess of about 500 feet, it has been necessary to weld a longitudinally extending seam without damage to the cable contained within the tubular blank and then to draw down the sheath into closely fitting engagement with the cable. Serious problems have been encountered due to the formation of a sharp internal bead along the. line of the welded seam which tends to cut into the cable and also due to the fact that the usual welded seam has had undesirable metallurgical characteristics whichmay cause it to fail as a result of excessive flexing in use. Indeed, the usual drawing or sizing operation above referred to likewise work-hardens the metal sheath and makes the handling of the resultant product more difiicult.

It is accordingly a principal object of this invention to provide novel metal sheathed cable and the like in which such sheath may be of unusually small thickness and light weight. w i

A further object is to provide such metal sheathed Handling and shipping costs are also nacable in which the sheath closely fits the enclosed cable I but is nevertheless highly flexible and without the disadvantages resulting from Work-hardening when employing prior art methods. 7

Another object is to provide'novel aluminum sheathed electric cable in which the sheath closely fits the enclosed cable but does not have a sharp longitudinally extending internal bead bearing thereagainst.

A still further object is to provide such aluminum sheathed cable which is fully impervious to moisture and readily flexible in use.

Another object is to provide metal sheathed cable in which the sheath is unusually thin and light but which nevertheless maintains its strength and corrosion resistance.

Still another object is to provide a novel method an apparatus for production of metal sheathed cable of the type indicated.

Other-objectsof the invention will appear'as the description proceeds.

2,936,357. Patented May 10, 1960 Fig. 1 is a side elevational view of tubular blank forming apparatus embodying the principles of my invention;

Fig. 2 is a top plan view of such mechanism;

Fig. 3 is a side elevational View of the tube welding apparatus and tube advancing means constituting a continuation of the apparatus of Fig. 1;

Fig. 4 is a top plan view of the Fig. 3 mechanism;

Fig. 5 is an end elevational view of the Figs. 1 and 2 apparatus viewed from the right-hand end of the latter as illustrated;

Fig. 6 is an end view of a metal sheathed cable in accordance with my invention; a

Fig. 7 is an end view of similar cable including insulating tape beneath the welded seam;

Fig. 8 is an end view of metal sheathed three conductor power cable in accordance with my invention;

Fig. 9 illustrates the manner of wrapping one of the three inner cables comprising the Fig. 8 assembly;

Fig. 10 is a semi-diagrammatic illustration of the proper adjustment of the rolls of the last roll assembly of Fig. 1;

Fig. 11 diagrammatically illustrates the form of the resultant cable and welded sheath at the squeeze rolls following the welding unit;

Fig. 12 corresponds to Fig. 10 but shows the eifect of setting the finned roll too deeply;

Fig. 13 corresponds to Fig. 11 showing the efiect on the cable and welded sheath resulting from such misadjustrnent of the finned roll;

Fig. 14 is a diagrammatic showing of a squeeze roll cluster especially adapted for use when welding relatively soft metals such as zinc;

Fig. 15 is a diagrammatic view of the welding operation showing the location of such cluster;

Fig. 16 is an enlarged view of an optional form of one of the spacer rolls of the Fig. 1 apparatus; and

Fig. 17 is a combined .graph and diagram to assist in explaining the relationship of the inductor field to the point of welding.

Reference may be had to my prior application Serial No. 205,511, filed January 11, 1951, entitled High Frequency Induction Tube Welding, now Patent No. 2,687 464, and to my prior application Serial No. 320,201, filed November 13, 1952, entitled Welded Tubing, now Patent No. 2,817,364, for a detailed description of the process whereby I am enabled to produce welded metal tubing, and more especially welded aluminum tubing, of high quality and at high rates of production. Such welding process is utilized and adapted in accordance with the present invention in the manufacture of metal sheathed cable.

Referring now more particularly to said drawing and especially Figs. 1, 2 and 5 thereof, the forming mechanism there illustrated is adapted to receive a continuous length of electrical cable C and a metal strip S and to form the latter into a tubular blank closely conforming to such cable. In the embodiment illustrated, such mechanism comprises a box-type main frame 1 having a lower deck 2 at its right-hand end and a narrower upper deck 3 extending longitudinally therefrom. A plurality of roll assemblies are mounted on such upper deck adapted progressively to form such strip into a tubular blank of desired conformation and dimensions. Adjustable edge scarfing tools 4 and 5 are mounted on a small box frame 6 at the right-hand end of upper deck 2 of main frame 1 in association with shoes 7 and 8 and rollers 9 and 10 which serve to guide the two side edges of strip S as the latter enters the machine. The first roll stand 11 is likewise mounted on lower deck 2 and in cludes a power driven under-roll 12 and a grooved upper roll 13. Strip S is adapted to be tightly gripped between such driven roll 12 and the end portions of roll 13 to advance such strip into the machine, the central relieved portion or groove 14 of roll 13 being dimensioned to receive and position cable C passing thereunder.

The machine may be powered by an electric motor 15, such as for example a 15 horsepower 1150 rpm. base speed DC. motor powered by a variable voltage generator and provided with a tachometer generator 16 for speed regulation. Such motor is connected by means of drive belt 17 to pulley 18 on main drive shaft 19 journalled within the lower portion of main frame 1 and extending longitudinally thereof. Roll 12 is driven from shaft 19 by means of belt 20 and a worm gear speed reduction unit 21. The rolls of the remaining roll assemblies described below are all mounted for rotation about vertical axes and are driven by means of upwardly extending universal drive shafts such as 22 and 23 in turn driven from main drive shaft 19 by means of worm gear units such as 24.

The first forming unit comprises

roll assemblies

25 and 26 including forming

rolls

27, 28, and 29, 30 adapted progressively to form the strip with the side edges turned upwardly in 90 arcs. Top idler rolls 31 and 32 are carried by a vertically adjustable cantilever support 33, such idler rolls being grooved to receive the cable to hold the latter pressed firmly against the strip but also being contoured to cooperate with the

rolls

27, 28, 29 and 30 on vertical axes thus to form the side edge portions of the strip. Such vertical rolls are mounted for adjustment toward and away from each other as are also the rolls of the succeeding roll assemblies.

The next three

roll assemblies

34, 35, and 36 are provide with pairs of rolls 37, 38, and 39, 40, and 41, 42 respectively, affording progressively narrowing passes adapted to shape the strip into a tubular blank B closely embracing the inner core formed by cable C. As best shown in Fig. 1, the rolls of these units are contoured to shape and turn the sides of the strip in arcs greater than 90 so that idler rolls bearing on the cable are not required in this region.

The next three

roll assemblies

43, 44 and 45 comprise rolls 46, 47, and 48, 49, and 50, 51 defining a series of substantially closed passes. Supported by upstanding posts are three bridge members 52, 53 and 54 pivotally mounted at one end and adapted to be secured in selected vertically adjusted position by adjusting

means

55, 56 and 57 controlling the raising and lowering of the other ends of such members. Bridges 53 and 54 support upper idler rolls 58 and 59 respectively which are shaped to enter the now relatively narrow seam between the two opposed edges of the tubular blank where they serve the dual purpose of holding down the cable as such edges are forced toward each other by the laterally disposed squeeze rolls and also of guiding such seam to assist in ensuring that the blank continues in its travel with the seam properly oriented. The side forming rolls crowd the seam edges in against

upper rolls

58 and 59. The fins of the upper rolls are, of course, progressively narrower and in cooperation with the associated side forming rolls perform the final accurate forming and truing operations.

Upper finned roll 60 carried by bridge 52 above the final side forming roll assembly 45 has a considerably narrower fin 61 (see Figs. 10 and 12) which is adapted to extend between the now closely opposed rolls and 51 and enter the seam of the tubular blank B to bear against and slightly depress the inner cable C-in this region. This action serves to prevent the cable from being pinched between the approaching seam edges of the blank but the extent to which the cable is thus locally compressed must be nicely calculated in view of its effect upon the subsequent welding operation, as more particularly explained below.

Now referring more particularly to Figs. 3 and 4 of the drawing which of course represent continuations of Figs. 1 and 2 respectively, the apparatus there illustrated comprises an extension 62 of main frame 1 carrying an adjustable stand 63 for seam guide 64 and a second adjustable stand 65 carrying a squeeze roll assembly including rolls 66, 67 and 68. The exact construction of such seam guide and squeeze roll assemblies is not a part of the present invention, and reference with regard thereto may be had to my prior applications above referred to for certain preferred embodiments of the same. Following the squeeze rolls, a scarfing tool 69 may be carried by a stand 70 adjusted to engage the bead formed at the weded seam of the tubular sheath T. This in turn is followed by a pair of power driven

roll assemblies

71 and 72 comprising

rolls

73, 74, and 75, 76 respectively, adapted to grip the tube to assist in advancing the same through the machine and also, if desired, to perform a slight final sizing operation. Interposed between the seam guide assembly and the squeeze roll assembly is a high frequency water cooled induction coil 77 which serves in the manner explained in detail in my aforesaid applications to bring the seam edges to welding temperature at the point where such edges are brought together through action of the rolls.

Operation Certain aspects of my invention will best be appreciated and understood in connection with an explanation of the method of manufacture of my new metal sheathed cable. The metal strip S will be drawn from a coil of the same (not shown) mounted on a suitable supply reel and will be threaded into and inched through the machine preparatory to initiation of high speed automatic operation of the same. Such metal strip may, for example, be thin gauge aluminum of relatively soft temper so that the resultant metal sheathed cable may have the required flexibility. Scarfing tools 4 and 5 are adjusted to shave the edges of the strip to clean and true the same in preparation for the welding operation. The strip next passes beneath a felt Wiper W carried by roll stand 11 and preferably backed by a plastic doctor blade, such wiper and blade of course being grooved to permit passage of the cable C Which is introduced longitudinally centrally of the strip. Such wiper and blade serve to clean the surface of the strip of any particles resulting from the edge scarfing operation.

The cable will likewise be drawn from a supply coil (not shown) and may be of a variety of types as discussed in more detail below. In one common form, it will comprise a large number of individual copper strands 78 individually wrapped in insulating paper 79, with the assembly twisted in a long lead helix and itself further wrapped in insulating paper 80. Cable of this type is in wide commercial use.

Grooved roller 13 cooperates with lower roller 12 to grip and advance the metal strip with the cable properly centered thereon. At the second pass comprising rolls 27 and 28 with upper grooved and contoured roll 31, slight edge forming of the strip takes place and at the third pass comprising rolls 29, 30 and 32, such edge forming amounts to approximately The upturned side edge portions of the strip are, of course, still laterally spaced from the cable by an amount equal to the operative contoured end portions of

upper rolls

31 and 32.

The fourth, fifth and sixth passes comprised of

roll assemblies

34, 35 and 36 progressively narrow to complete the forming of the strip into a tubular blank gener-ally conforming to the inner cable C but with an upwardly disposed open seam.

Iustprior to roll assembly 43, a length of insulating tape may be introduced into the tubular blank from. a supply 81 thereof, such tape underlying the seam defined by the opposed edges of the blank as the latter are now brought progressively closer together through the action of the succeeding forming rolls. Upper roll 59 bears upon the cable with such tape 81 (if such be employed) therebeneath. When the work reaches roll assembly 45, the upper finned roll 60 will be adjusted as shown in Fig. so that the fin 61 is not only interposed between the seam edges of the blank B but also bears againstthe inner cable, slightly to indent and compress the latter in the region of the seam. The cable material is somewhat resiliently deformable and gradually recovers as the work travels toward the squeeze rolls 66, 67 and 68. Seam guide 64 performs the functionof finally positioning the seam and ensuring that the edges thereof are sufficiently spaced apart to prevent arcing thereacross as such edges approach each other through the action of such squeeze roll assembly. The seam edges will be brought together in welding engagement slightly in advance of such latter assembly, the high frequency current induced in such blank by means of inductor coil 77 encircling the seam being caused to flow. to such opposed seam edges for maximum concentration at the point of juncture thereof. Such point of juncture will be located beyond the effective limits of the inductor field to obtain such desired concentration.

As shown in Fig. 11 of the drawing, if finned roller 60 was properly adjusted to compress the cable to exactly the right degree, such cable will thereafter recover to substantially completely fill the tubular blank at the point of welding illustrated in Fig. 11 to prevent the formation of a large or sharp internal bead. Instead, a considerable proportion of the molten or plastic weld metal will be extruded outwardly under action of the squeeze roll assembly to form an external head 82 and only a relatively low and smooth internal head 83 will be produced. This is, of course, the result of the inner cable backing up the seam at the point of welding without, however,

tending to protrude into the seam where it might be.

pinched. Not only is the formation of a sharp internal bead prevented, but it has been found that the paper wrapping of the cable is not even scorched since the small amount of plastic or molten weld metal internally of the blank is spread into a thin smooth layer which immediately dissipates its heat content. Now referring more specifically to Figs. 12 and 13 of the drawing, Fig. 12 shows roll 60 improperly adjusted so that fin 61 compresses the cable to too great an extent. The cable accordingly does not spring back sufliciently by the time it reaches the squeeze roll assembly completely to fill the blank at the point of welding, and as a result a relatively narrow sharp internal bead 84 may be produced tending both locally to scorch the cable and also to afford a sharp irregular edge likely to cut into and damage the cable when the latter is flexed in use. i

The scarfing tool 69 will ordinarily then be utilized to trim away the externalbead 82, and the final two roll stands 71 and 72 which are driven to assist in advancing the strip and cable through the machine may also be ad-f justed slightly to size the finished tubing T from about /z% to about 1% of its diameter to obtain exact specification dimensions and also, although less important, to cause the sheath to fit the cable even more closely. My new apparatus and method are, however, designed to avoid the necessity of any substantial sizing of the sheath subsequent to the welding operation since it is desired that the characteristics of the original metal strip be retained. The small amount of sizing indicated above is insufiicient materially to alter the characteristics of such striptsuch as its soft temper and ductility, so thatbending stresses in use will remain at a minimum value. This is important not only with aluminum but also in the case of other sheathing metals such as copper, zinc, magnesium and even lead. Due to the fact that substantial cold working of the sheath material is avoided, the original soft temper of such material may be retained, and the fact that an extremely narrow welded seam is produced by my method of welding ensures that substantially the entire periphery of the sheath will be of uniform ductility. This is very different from prior art practice where a metal sheath has been welded loosely about an inner cable and then drawn down to fit. Such prior methods have also involved welding procedures producing very much wider welded seams than those obtainable by my process. My process and machine are capable of producing aluminum sheathed 1 inch telephone cable at a rate of from about 60 to about 100 feet per minute and even higher rates of production are possible although the physical handling of the component materials then becomes somewhat more of a problem.

Fig. 6 illustrates a typical metal sheathed cable produced in accordance with my invention, the copper strands 78'of the cable being individually wrapped in paper insulation 79 and then the entire cable wrapped with insulating paper St). The outer welded tube T has but a narrow weld seam 85. Fig. 7 illustrates the same cable but with the employment of the insulating tape 81 (which may, for example, be of fish paper, a fibrous hard paper frequently used for insulating purposes). Such tape 81 may have an adhesive coating of the type of the well-known friction tape or pressure-sensitive in the manner of Scotch tape for adhering to the cable and thereby ensuring that it is not subsequently shifted in position.

Figs. 8 and 9 illustrate three-way conductor cable provided with a metal sheath in accordance with my invention. Strands of yarn 86 are introduced during the forming operation to fill the peripheral indentations defined by the three cables which are twisted together in a long lead helix. Such cables comprise a plurality of individually paper wrapped copper strands 78 enclosed by an outer static shield of copper foil. Foil static shields are conventional in the art but I have somewhat modified the same in view of the peculiar problems encountered. When employing my welding process it is important that there should not exist closed circuits within the blank subject to the localized field of the inductor as the blank passes therethrough, and l accordingly modify the foil wrapping of the individual cables comprising the three-way cable in the manner illustrated in Fig. 9. Such wrapping comprises overlapping layers or strips of thin copper foil 87 and insulating paper 88 helically wound so that each turn of the foil is spaced from the preceding turn. While each of the three inner cables of Fig. 8 will ordinarily be individually wrapped in this manner, the entire assembly of the three cables and interposed yarn may be wrapped in this fashion instead, taking the place of the paper wrapping '80 of Figs. 6 and 7. When using such copper foil static shield, it is necessary that the same should contact the metal outer sheath T to be grounded thereby. Cables of this type are ordinarily employed in high voltage power transmission. In three-way cable of the type just described, it is important to employ the longitudinally extending strip of insulating tape 81 beneath the seam to prevent electrical bridging of such seam during performance of the welding operation. While threeway cable is relatively common it will be appreciated that any number suc. as two, three, four, five, etc., may be employed, as desired. I Referring now more particularly to Figs. 14 and 15 of the drawing, a modified form of squeeze roll assembly is there illustrated for bringing the seam edges together at the point of welding P. I have found that when welding relatively soft materials such as zinc, for example, it becomes rather difficult satisfactorily to apply the proper pressure at the weld point with the usual squeeze roll arrangement as shown in Fig. 11, this for the reason that such rolls are somewhat spaced at either side of the seam, and with thin gauge metal there is a tendency to buckle. Under such circumstances, I prefer-to employ a relatively small diameter pressure roll 89 which bears upon the upper side of the tube blank B and is accordingly provided with a small central groove 90 adapted to receive the external weld head. This roll 89 adequately supports the metal of the blank closely adjacent the seam to prevent buckling under the pressure exerted by the lateral squeeze rolls 91 and 92.

As best shown in Fig. 15, the upper roll =89 bears against the upper surface of the tube-blank B and in cooperation with the rolls 91 and 92 (not shown in this figure) causes the seam edges to be brought together at the point of welding P slightly in advance of the center line of such rolls. The tapering seam guide 64 assists in causing the seam edges to approach one another at the proper angle. Roll 89 may be of ceramic material but it is also possible to employ a conductive roll inasmuch as the point of welding is in advance of the region of roll contact and in my method of Welding, the induced current flow is effectively concentrated on the opposed faces of the seam edges where they meet at such point 'of welding and there is no appreciable tendency of such induced current to flow across the welded seam at a point beyond such point of initial welding. The area of roll contact with the tube is reduced by the employment of a relatively small size roll 89 and this is also of some benefit in bn'nging the roll still further from the effective field of the inductor. A suitable squeeze roll cluster supporting stand is disclosed in my prior application Serial No. 205,511, filed January 11, 1951, such roll mounting means being capable of inversion so as to support the rolls of the cluster in the manner shown in Fig. 14 hereof.

When a supply of tape 81 is to be introduced into the tube blank to lie beneath the progressively closing seam, it will generally be desirable that upper roll 59 be provided with a peripheral groove 93 as shown in Fig. 16, such groove being adapted to receive tape 81 and to guide the same during its entry into the tube blank so as to keep the tape centered relative to the seam.

Fig. 17 is a combined graph and diagram to assist in explaining certain basic features of my method of Welding. As previously indicated, the initial point of juncture of the seam edges should lie an appreciable distance beyond the effective limit of the inductor field in the direction of travel of the tube blank. In Fig. 17, the extent and concentration of such field relative to the inductor coil is graphically and diagrammatically indicated. "in accordance with recognized electrical engineering principles, such effective limit of the inductor field may be defined as being reached at the cross-sectional plane normal to the tube blank axis beyond the inductor where the average density Within the area of the tube blank of the longitudinal components of flux has declined to a value l/ e times the value of the average flux density within the area of the tube blank at the center of the inductor coil (where e is the base of the Napierian logarithmic system). The density of the field drops off rather abruptly so that if the point of welding P is located an appreciable distance therebeyond, the direct effect of the inductor field will be relatively inconsequential at such point and beyond the latter. As a result, no appreciable current is induced to flow in the tube across the welded seam and the current which is induced in the blank Within the effective limits of the field flows circumferentially around the underside thereof and extends along the seam edges to the point of juncture, thereby providing two fairly closely spaced oppositely flowing parallel high frequency currents which consequently are subject to the proximity effect and the skin effect to a high degree, especially in the immediate region of the point of seam edge juncture. At such point the induced current is substantially entirely concentrated at the opposed faces of the seam edges, raising the same to welding temperature without; however, having any substantial heating effect on the remainder of the blank.

While this application is particularly concerned with the provision of metal sheathed cable, it will be appreciated that other core materials may be utilized in a similar manner. Thus, a plurality or bundle of small copper or steel tubes, such as hydraulic or pneumatic conduit, may be enclosed within an outer closely embracing metal sheath to provide a multi-channel conduit. Clusters of concentric cables may similarly comprise the core. In fact, a variety of fillers may be utilized as desired, including plastic or rubber tubes for example, to serve as liners, or hard-facing alloys of well-known composition for the production of arc welding electrodes. Plastic tubing of silicone rubber, neoprene, polyvinyl chloride, cellulose esters, and nylon may be snugly sheathed with metal such as aluminum in accordance with my invention. Other types of plastic tubing are also commercially available.

It will be seen from the foregoing that I have provided novel apparatus and method for the manufacture of metal sheathed cable and the like, and more particularly such apparatus arranged for the introduction of insulating tape or the like into the outer tubular blank and apparatus eifective partially to compress the inner core in a local region beneath the seam to the proper extent to obtain the desired degree of back-up to the seam without danger of pinching, scorching or cutting the inner core material during the welding operation. Novel electrical cable has been provided of such light weight and tensile strength that it may be suspended in much longer spans than formerly. It is also completely weatherproof without danger of pin holes in the welded seam. As a result of my invention, it is easily feasible to provide flexible aluminum sheathed cable comprising a flexible core (the cable), and a snugly fitting aluminum sheath having a very narrow longitudinally extending cast weld seam, the aluminum having a ductility as expressed in percentage elongation of a 2 inch gauge length before tensile failure equal to at least two-thirds of the ductility obtainable from the same material in the fully annealed state. In other words, by my novel method it is possible to employ aluminum strip material having the desired metallurgical properties and to perform the seam welding operation without substantially altering such properties, the cast weld seam being extremely narrow, as above indicated, and generally of less width than 20% of the tube wall thickness. This is, of course, in considerable contrast to the properties of tubular sheathing produced by extrusion methods, and like advantages are obtained, in varying degrees, by employment of my method utilizing other metal strip materials even including lead and zinc. In the production of metal sheathed electrical cable, the various non-ferrous metals and especially aluminum or aluminum alloy will ordinarily be employed. In certain'embodiments of the invention, however, such as the hard-facing weld rod above referred to, the tubular sheath may generally be of steel and of relatively small diameter.

A variety of metals may be employed in the manufacture of the metal sheath by my method including steel, stainless steel, copper, brass, aluminum, zinc, silicon bronze, and the other non-ferrous metals and alloys. While the tube wall thickness may be substantial or very thin, it is usually preferred when sheathing cable in an aluminum tubular sheath in accordance with my invention that the wall thickness be on the order of .050 inch in the case of a one inch diameter tube. When using extruded lead sheathing in the past it has been customary to employ a wall thickness on the order of 0.10 inch in the case of a one inch diameter tube to obtain adequate protection.

When using tape 81 for insertion beneath the seam, such tape may be of insulating paper, glass fiber, or other non-conductive material. Seam guide 64 should ordinarily enter the seam only sufficiently properly to space the opposed seam edges although it may in some cases press lightly on the tape and cable or other core.

It is generally preferred that the frequency of the welding current be sufficiently high that effective current penetration (the depth at which the current density has declined to a value l/e times the current density at the surface, where e is the base of the Napierian logarithm) will be no'more than about one-thousandths of an inch below the surface of the work. Arcing or other passage of current across the gap between the seam edges should be avoided except at the actual point of initial contact of such edges where they are brought together by the squeeze rolls. The high frequency current may ordinarily have a frequency of between 9,600 and 500,000 cycles but much higher (radio) frequencies may be utilized.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such may be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method of producing aluminum sheathed cable which comprises advancing such cable longitudinally, progressively forming a tubular sheet metal aluminum blank thereabout having an open longitudinally extending seam, continuously advancing such cable and blank in unison together, introducing a strip of insulating tape into such blank beneath such seam, temporarily compressing such cable in the region beneath such seam, generating a high-frequency alternating magnetic field, passing such tubular blank and cable through such field, and bringing the opposed seam edges together at a point beyond the effective limits of such field after passage therethrough, such point being spaced a suflicient distance beyond such limits in the direction of travel of such blank that the induced voltage across the spaced seam edges will be substantially lower immediately prior to such point than within such region, thereby causing a high-frequency induced current to flow generally circumferentially of such blank within such field and along the opposed seam edges to such point of juncture thereof, the combined result of the skin effect and proximity effect being thus to concentrate such current along such seam edges to an increasing degree toward such point of juncture where an extremely high current density is obtained, such high current density being effective to heat the seam edges to fusion temperature and to interfuse the same, the welded tube thus formed closely fitting and encasing the cable, the aforesaid compression of the cable being sufficient to avoid pinching thereof by the approaching seam edges and said cable being sufliciently elastic to return to substantially uncompressed form when the point of welding is reached thereby to prevent formation of a sharp internal weld head.

2. The method of producing metal sheathed cable which comprises advancing such cable longitudinally, progressively forming a tubular sheet metal blank thereabout having an open longitudinally extending seam, continuously advancing such cable and blank in unison together, introducing a strip of insulating tape into such blank beneath such seam, temporarily compressing such cable in the region beneath such seam, generating a highfrequency alternating magnetic field, passing such .tubular blank and cable through such field, and bringing the opposed seam edges together at a point beyond the effective limits of such field after passage therethrough, such point being spaced a sutficient distance beyond such limits in the direction of travel of such blank that the induced voltage across the spaced seam edges will be substantially lower immediately prior to such point than within such region, thereby causing a high-frequency induced current to flow generally circumferentially of 15 such blank within such field and along the opposed seani edges to such point of juncture thereof, the combined result of the skin eflect and proximity effect being thus to concentrate such current along such seam edges to an increasing degree toward such point of juncture where an extremely high current density is obtained, such high current density being eifective to heat the seam edges to fusion temperature and to interfuse the same, the welded tube thus formed closely fitting and encasing the cable, the aforesaid compression of the cable being sufficient to avoid pinching thereof by the approaching seam edges and said cable being suificiently elastic to return to substantially uncompressed form when the point of welding is reached thereby to prevent formation of a sharp internal weld head.

3. The method of claim 2, including the additional step of sizing the finished article to reduce the outer diameter of the welded sheath an amount less than 1% thereof to cause the same to fit the cable yet more snugly and to work the cast weld metal of the narrow welded seam disproportionately to bring the same more nearly into physical identity with the body of such sheath, such slight sizing operation being ineffective greatly to work harden such body.

4. The method of producing metal sheathed cable which comprises advancing such cable longitudinally, progressively forming a tubular sheet metal blank thereabout having an open longitudinally extending seam, continuously advancing such cable and blank in unison together, temporarily compressing such cable by resilient deformation of the same in the region underlying such seam to avoid pinching of such cable as such seam is closed, shortly thereafter bringing such seam edges together with such blank now snugly enclosing and fitting such cable, and welding such seam with the latter closely backed up by such cable to spread inwardly intruded molten metal into a thin fiat layer.

5. The method of producing metal sheathed cable which comprises advancing such cable longitudinally, progressively forming a tubular sheet metal blank thereabout having an open longitudinally extending seam, continuously advancing such cable and blank in unison together, temporarily compressing such cable by resilient deformation of the same in the region underlying such seam to avoid pinching of such cable as such seam is closed, shortly thereafter bringing such seam edges together with such blank now snugly enclosing and fitting such cable, and welding such seam by development of highly localized welding temperatureat such seam edges to produce a very narrow welded seam with the latter closely backed up by such cable to spread inwardly intruded molten metal into a thin fiat layer.

6. The method of producing a metal sheathed elongated resiliently deformable article which comprises advancing such article longitudinally, progressively forming a tubular sheet metal blank thereabout having an open longitudinally extending seam, applying heat resistant material to such article in the region of such seam, applying pressure to such article to deform and compress the same in such region to prevent pinching between the seam edges, closing such seam, and welding such closed seam with the latter backed up by such material as a result of the recovery of such deformed article.

References Cited in the file of this patent UNITED STATES PATENTS 1,578,286 Harmatta Mar. 30, 1926 1,948,616 Fischer Feb. 27, 1934 2,029,044 Westlinning Ian. 28, 1936 2,052,380 Chapman Aug. 25, 1936 2,139,211 Sessions Dec. 6, 1938 4 (Other references on following page) 11 12 UNITED STATES PATENTS 2,697,772 Kinghorn Deb. '21, 1954 2,723,882 B ett N 15, 1 2,139,771 Riemenschneider Dec. 13, 1938 am W 955 2,146,430 Hazen Feb. 7, 1939 FOREIGN PATENTS 2,290,333 Johnson July 21, 1942 5 377,655 Great Britain Jan. 21, 1931 2,447,168 Dean et a1. Aug. 17, 1948 661,5 0 Great Britain Nov. 21, 1951 2,582,963 Cachat Jan. 22, 1952 2,591,794 Ebel Apr. 8, 1952 9THER REFERENCES 97,7 9 carpenter 21, 1954 C ft: Alumlnum Sheathed Cables, Wire and Wire Products, July 1953, pages 682-87 and 725.