US2549249A - Method of drawing filled tantalum tubes - Google Patents

Description

April 17, 1951 D. S. SEABURY ET AL METHOD OF DRAWING FILLED TANTALUM TUBES Filed Jan. 22; 1947 2 Sheets-Sheet l APatented Apr. 17, 1951 UNITED STATES PATENT OFFICE METHOD F DRAWING FILLED TANTALUM TUBE Application January 22, 1947, SerialNo. 723,616

3 Claims.

This invention relates to drawing tubes through dies to reduce the diameter of the tubes and elongate the same, and more particularly to an improved method of and apparatus for drawing tubes of tantalum or other metal or alloys that present similar drawing difculties.

Although not limited thereto, the invention is particularly applicable to the production of cathodes for use in concentrated arc discharge lamps, such as disclosed and claimed in a copending application of W. D. Buckingham and C. R. Deibert, Serial No. 668,092, led May 8, 1946, now Patent No. 2,453,118, issued November 9, 1948. In one embodiment of the invention disclosed in the aforesaid application, the cath ode structure comprises a short length of metal tubing of small diameter, within which is packed a core of active material, such as zirconium oxide, that forms on its exposed end surface an active layer or film which is the cathode proper of the Concentrated arc discharge lamp. It has been found desirable to employ a tube of tantalum as the outer cathode pencil or holder. Tantalum tubing can be drawn down and hardens slowly during the drawing process, but'when it was drawn through the dies to reduce the tubing to a small diameter suitable for the electrode struc tures of such lamps, it quickly fouled and injured the dies, and the heretofore known drawing operations proved to be too expensive and slow and also impracticable in other respects.

An object of the invention is to obviate the disadvantages of prior methods of drawing downV tubes of tantalurn and like materials, and kto enable the same to be drawn to small diameters at an increased speed andwithout undue injury to the reducing clies employed.

Another object is to draw down a tube of tan talum or like material in manner suitable to form the holder or cathode pencil for thecore of active material of an electrode structure.

These and other objects and advantages of the invention will be apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

Figs. 1 and 2 are top and side views, respectively, of a bell jar within which the tantalum tubes are cleaned and coated in a vacuum prior to a drawingr operation, a portion of the bell jar cover being broken away to show the interior thereof;

Figs. 3 and 4 are top and side views, respectively, of a draw bench for drawing down a tube of tantalum or like metal after the tube has been cleaned and coated by the apparatus of Figs. 1 and 2;

Fig. 5 is an enlarged sectional View taken along the line 5-5 of Fig. 3 showing details of one of the wire drawing dies and support means therefor;

(Cl. .Z9-155.42)

Fig. 6 is a fragmentary view, partly in section, showing details of supporting structure for one of the wire drawing dies employed; and

Fig. 7 is an enlarged sectional View, taken along the line 'I-'I of Fig. 6, showing means for clamping the end of a tube during a drawing operation.

Referring to Figs. l and 2 there is shown a bell jar IU of glass which rests on a circular base plate ll composed of cast iron or other suitable material, the base plate being secured, as by brackets I4, to atable or other support I5. Secured to and passing through the base plate I! is a tube I8 which opens into the bell jar, and by means of which the bell jar may beevacuated, tube I6 comprising a line from a vacuum pump, not shown, which is capable of producing a high vacuum within the bell jar. A circular cover plate I7 is mounted as by machine screws I8, above the open end of a vacuum line I', the plate being spaced from the opening to enable exhaustion of air and gasses from the interior of the bell jar, while preventing foreign, material from entering the vacuum line. The vacuum line I6 passes through the base plate II with a Suniciently tight fit to prevent substantial loss of vacuum at this point.

Mounted on, but electrically insulated by bushw ings from, the base plate II and projecting upwardly within the bell jar are two posts 29, 2| of copper or other suitable metal, which `posts have slotted ends for receiving and holding a tube: 22 of tantalum or the like which is to be treated. Clamping screws 23, Fig.- 2, are provided to hold firmly the ends of the rod 2|. Two electrical terminals 24, 25 are supported by metal connecting studs 26 that are electrically insulated by bushings and pass through the base plate II, thereby to make electrical connections through lugs 29 and 29 to an external sourceof heating current supply. Secured to terminals 24 and 25, respectively, are conducting brackets 3E] and 3| which, in conjunction with two threaded terminal posts 32 and 33, serve to support two heating wires and 36. rl'he heating wires preferably, although not necessarily, are composed of tantalum, and in the embodiment disclosed each comprises a .030 inch diameter wire. The terminal posts 32 and 33 are mounted in studs 3l, 38, Fig. 2, which pass through the base plate I I and make electrical connections through lugs 39, 4i! to the source of heating current supply, these elements being electrically insulated from the base plate I I. Terminal post 32 is elec trically connected, by means of a stranded conductor 4I, to the tube-supporting post 2|, and terminal post 33 is electrically connected, through a strap 42, to the supporting post 2E). The foregoing arrangement enables separate cont-rol of the heating circuits whereby the tanta-lum tube 22 and wires 35, 36 may be heated either inde- 3 pendently or conjointly during the treatment of the tantalum tube as hereinafter explained.

Initially, aV tantalum rod is cut into short lengths and centrally drilled to produce a hollow rod or tubing` For small size concentrated arc lamp cathodeswsuch as for use in a 2-watt Y lamp, a 1/4 inch tantalum rod is kcut into lengths of 1% inches and these are centrally drilled tol provide short pieces of tubing. The outer diameter of each piece is then reduced by a swaging lmachine, in a series of swaging steps, in known clamped at its ends in the slotted portions of the supporting posts and 2l. vOn the tantalum heating wires and 36 are hung small tin *copper straps 35. The bell jar cover is replaced and its lower circular edge sealed at 41 with a vacuum sealing compound, various of which compounds are commercially obtainable; one of'these designated'in the trade as Apiezon Q often is used.

lThe vacuum system represented by the tube I6V then is turned on and the bell jar is exhausted until a high degree of vacuum is obtained within. Heating current is then caused to ilow in a series circuit through the tantalum tube 22 and the heating wires 35 and 36. This circuit within the bell jar, as seen from Fig. l, is the terminal 2li, bracket 35, heating wire 35, terminal post 32, conductor 4i, supporting post 2l, tantalum tube 22, supporting post 2li, strap d2, post l 33, heating wire V3E, bracket 3l and terminal'25.

The flow of heating current is continued until there is very little or no indication of gases being L liberatedrfrom the tantalurn tube. VBy this time the small copperstrips on the heatingwires 35 and 36 will have melted down and have formed Vsmall copper beads or balls, as indicated at a in Fig. l. The tantalum tube again is degassed vcopper has been built up thereon. This tubing is then llled and packed with zirconium oxide or other cathode material suitable for the purpose, and the ends of the tubing are closed in and sealed in any suitable manner, as by the use of a jig, so that the core of zirconium oxide will not be affected by the subsequent steps of treating and drawing the tubing. The copper-coated tantalum tube with its iilling of cathode material may be drawn through the reducing dies without fouling or injuring the dies and the tubes maybe drawn down expeditiously to a very small diameter and to a great length.

The draw bench shown in Figsl 3 and 4 com prises an 'iron framework generally designated at which is sup-ported by legs 5! at a convenient working height. Mounted in the framework is a driving sprocket 53 and a driven sprockby applying the heating c-urrent to the terminal thoroughly degassed, the heating current is disconnected therefrom, and while `the tantalum tube is still very warm, as cherry red, the heating Acircuit is connected rst across terminals 24, 32 v and subsequently across terminals 25,733 so ,as to heat the wires 35 and 35 successively and hence theV small copper balls 45a thereon. The copper balls are heated to nearly white heat and are thus evaporated oliD the wires 35, 35, a high vacuum being maintained within the bell jar during this entire period. lThe evaporated copper condenses on the outer surface of the coolerV tantalum tube 22 and forms a thin copper Vcoating thereon, the heating current being discontinued at this time. During these operations cooling water is passedthrough a tube VI2 which is in Vcontact with the base plate i l, so thatthe sealing compound 4'! will not soften and cause a leak into the bell jar. The vacuum is then broken .and the coated tube removed, care being taken clearance for the tube 22.

rotated manually through the medium of a crank The various links of Si! and crank handle 6|. the chain 55 may be engaged by a hook member 63 having secured thereto a jaw chuck 54 which receives and grips one end of the copper-plated tantalum tube 2 2 for drawing the tube throughl drawing dies such as the die 65, Figf. 5. These dies, which preferably are composed of a material such as a tungsten-carbon-cobalt alloy, commonly designated in the trade as Carboloy,ror aluminum bronze, are mounted in a die block; 6 6 and the die block is secured, as by a set screw El, in a die holder 68 which is secured, as by screws; to a supporting plate member Vlll. The latter member is bifurcated at 10a to provide The plate 'l0 is clamped against an end 50a of the iron framework support' 50 this end 0f the framework havving a block I2 that receives and holds a threaded by a hand Wheel 15 which is internally threaded' to engage the stud i3. The lower portion of the clamp member 74 is hingedly mounted by ears 19 and a pin 'I8 which passes through the ears and through an ear which depends Vfrom VYthe block member i2.

The tantalum tube is drawn down on the draw bench in a series of drawingsteps through successively .smaller dies. For example, in the first operation on the draw bench the 61/2 inch copper-coated tube, one end of which is gripped by the jaw chuck 54, is drawn through a starting die and is elongated thereby to a length of 7 inches or ,more The second drawing die, which is slightly smaller than the rst, further elongates the tantalum tube approximately 1 inch, and the successively smaller dies employed Veach progressively increases the length and decreases the diameter of thetantalum tube. In ldrawing down electrode tubing for use in a small size lamp, and starting with a copper-coated tube having an outside diameter of approximately .155 inch, the rst drawing die used will be a .1443 inch die and the last die used will be .0142 inch. Prior to each die-drawing operation, the pulling end of the tube 22 is swaged down slightly to enable the end to be passed through the drawing die a sufficient distance so that it can be seized by the jaw chuck 64 or by the other drawing mechanism hereinafter described. Beeswax or other suitable lubricant also is applied to the drawing dies to reduce to some extent the friction during the drawing operations.

When the tube 22 has been drawn out to a considerable length, for example, feet, it is too long to be handled by the jaw chuck 64 and hook member 63. The die 68, without the plate 10, is then lowered and clamped in the position shown in Fig. 6, and the drawing is effected by a pulley 85 which is keyed at 86, Fig. 7, to a shaft 81 driven by the sprocket 515. Within the pulley is a screw-threaded bore and pin 88, the pin having an inner end 89 that clamps the pulling end of the tube 22 which has been passed through a hole 90 in the pulley. The outer end of the clamping pin has either a square or hexagonal hole 9| therein for receiving a tool for rotating the pin until it tightly clamps the end of the tube against an internal shoulder 93 of the pulley, and thus enables the pulley to exert the high pulling force required to draw down the tubing` to a small diameter. In drawing down the tubing to produce a diameter of .0142 inch, approximately drawing operations are employed whereby the original 61/2 inch tube is drawn out to form about feet of electrode tubing. Such a length of tubing will provide cathodes for approximately 1000 2-watt lamps. After the drawing operations are completed the tubing is cleaned of any remaining copper in a nitric acid bath.

Not only do the drawing operations above described enable the tube of material, such as tantalum, to be drawn down expeditiously without undue injury to the drawing dies, but the drawing operations compress and tightly pack the zirconium oxide core within the tubing which results in substantially improved operating characteristics of the lamp in which the electrode is used.

As above set forth, the methods of drawing down tantalum tubing or the like is especially useful in the production of cathodes for concentrated arc lamps, but it will be obvious to those versed in the art that the method advantageously may be employed wherever it is desired to draw down tubes of tantalum or like refractory material to produce tubing of smaller diameter and greater length, and the invention therefore is not limited except as indicated by the scope of the appended claims.

What is claimed is:

1. A method of drawing a tube of tantalum or other refractory metal adapted for use in an electrode structure in a concentrated arc discharge lamp, which comprises passing heating current through the tube in a high vacuum to remove occluded gases and impurities therefrom, passing heating current through a conductor in said vacuum in such manner as to heat a quantity of copper until thecopper evap- Orates and condenses on the outside of the tube to form a coating thereon, filling said tube with a core of an electrode-forming material,` sealing the ends of the cored tube, electroplating the coated tube with a further coating of copper, drawing the coated tube through successively smaller drawing dies to reduce the diameter and increase the-length of the tube, and subsequently removing the copper coating that remains on said tube after the drawing operations.

2. A method of drawing a tube of tantalum or other refractory metal adapted for use as an electrode structure in an electrical discharge device, which comprises electrically heating a length of such tubing in a rareed atmosphere to remove occluded gases and impurities therefrom, electrically heating in said rarefied atmosphere a ductile metal that has the property of adhering to the metal of the tube and is considerably softer than the metal of the tube in such manner that the softer metal evaporates and condenses on the outer surface of the tube to form a coating thereon, electroplating the coated surface of the tube with a further coating of a ductile metal that has the property of adhering thereto and is considerably softer than the metal of the tube, filling said tube with a core of electrode-forming material, thereafter drawing the coated and :lled tube through successively smaller drawing dies to reduce the diameter and increase the length of said tube, and subsequently removing the coating of softer metal that remains on said tube after the drawing operations.

3. A method of drawing a tube of tantalum or other refractory metal adapted for use as an electrode structure in an electrical discharge device, which comprises electrically heating a length of such tubing in a rarefied atmosphere to remove occluded gases and impurities therefrom, electrically heating in said rareed atmosphere a quantity of copper in such manner that the copper evaporates and condenses on the outer surface of the tube to form a coating thereon, electroplating the coated surface of the tube with a further coating of copper, filling said tube with a core of electrode-forming material, thereafter drawing the coated and lled tube through successively smaller drawing dies to reduce the diameter and increase the length of said tube, and subsequently removing the coating of copper that remains on said tube after the drawing operations.

DONALD S. SEABURY.. WILLIAM D. BUCKINGHAM. CLARENCE R. DEIBERT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 395,963 Edison Jan. 8, 1889 930,723 Von Bolton Aug. 10, 1909 936,403 Von Bolton Oct. 12, 1909 982,751 Thowless Jan. 24, 1911 1,010,866 Coolidge Dec. 5, 1911 1,163,329 Edison Dec. 7, 1915 1,601,931 Van Arkel i Oct. 5, 1926 1,948,485 Anselin Feb. 27, 1934 2,333,534 Lang Nov. 2, 1943

Claims (1)

1. A METHOD OF DRAWING A TUBE OF TANTALUM OR OTHER REFRACTORY METAL ADAPTED FOR USE IN AN ELECTRODE STRUCTURE IN A CONCENTRATED ARC DISCHARGE LAMP, WHICH COMPRISES PASSING HEATING CURRENT THROUGH THE TUBE IN A HIGH VACUUM TO REMOVE OCCLUDED GASES AND IMPURITIES THEREFROM, PASSING HEATING CURRENT THROUGH A CONDUCTOR IN SAID VACUUM IN SUCH MANNER AS TO HEAT A QUANTITY OF COPPER UNTIL THE COPPER EVAPORATES AND CONDENSES ON THE OUTSIDE OF THE TUBE TO FORM A COATING THEREON, FILLING SAID TUBE WITH

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