US2816398A

US2816398A - Apparatus for manufacture of a quartzto-metal foil press seal

Info

Publication number: US2816398A
Application number: US272985A
Authority: US
Inventors: Donald L Pearson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-02-23
Filing date: 1952-02-23
Publication date: 1957-12-17
Anticipated expiration: 1974-12-17
Also published as: GB725695A; BE517821A; FR63277E; DE1018548B; FR1068795A; FR64156E; FR63733E

Description

Dec. 17, 1957 L. PEARSON 2,816,398

APPARA S FOR MANUFACTURE OF A QUARTZ-TO-ME F0 PRESS SEAL Filed 1952 InveWkOT': DonaLd L.Pea1"son,

His A k lrornea.

United APPARATUS FOR MANUFACTURE OF A QUARTZ- TO-METAL FDIL PRESS SEAL Application February 23, 1952, Serial No. 272,985

2 Claims. (Cl. 49--2) The present invention relates to gaseous electric discharge devices, and more particularly to the manufacture of quartz-to-metal seals for mercury vapor discharge lamps having tubular quartz envelopes.

A commercial form of such lamps comprises an electric lead-in wire of refractory metal, such as a tungsten or molybdenum wire, a section of which between its ends is flattened by rolling, for example, to a foil-like shape thin enough to make a mechanically strong, high tem perature resistant, fused gas-tight seal with quartz. Such lead-in wires are disclosed and claimed in the copending application Serial No. 244,818, filed September 1, 1951, now Patent Number 2,667,595, of Edward B. Noel and Paul A. Dell, which application is assigned to the assignee of the present application. The quartz is hermetically united with the wire by pressing a quartz tube portion in a hot softened condition between a pair of opposed jaws which are moved in a direction perpendicular to the plane of the foil-like section to press the quartz onto the said section.

As disclosed in the co-pending application Serial No. 267,297, filed January 19, 1952, of Ernest Benjamin Power, which application is assigned to the assignee of the present application, a difficulty encountered in the manufacture of seals in which the conductor includes a foillike section is the splitting of the thin foil-like section of the lead-in wire when the hot plastic quartz is squeezed onto it by the opposed jaws. I have observed that in most instances the foil sections split by being pulled apart by the flow of quartz in a direction parallel to the axis of the quartz tube.

Another difficulty I have observed in the manufacture of quartz envelopes suitable for high pressure mercury vapor discharge lamps and incorporating such seals is the occurrence of cavities at the inner end of the press seal and opening into the lamp envelope. These cavities are thin, wedge-shaped openings between the pressed quartz walls of the tube and are objectionable because mercury vapor condenses therein during operation of the lamp. The condensed mercury remains in the cavities with the result that the quantity of mercury available in the envelope during operation of the lamp is less than the predetermined measured small amount of mercury provided therein during manufacture of the lamp to obtain the desired operating mercury vapor pressure. Consequently, the operating voltage and the light output of the lamp, both of which are dependent on the mercury vapor pressure in the envelope, are less than that for which the lamp is designed. Such lamps, wherein condensation of mercury takes place in the seal cavities, are commercially unacceptable and must be rejected, which of course increases the over-all manufacturing cost of lamps of this type.

The principal object of this invention is to provide apparatus for the manufacture of pressed seals of the above type wherein these difficulties are eliminated. Another object of the invention is to provide quartz-to-metal pressedseals having smooth surfaces free from cavities.

tats atent "ice Other objects and advantages of the invention will appear from the following description,

In accordance with the invention the operative faces of the opposed pressing jaws each have a transverse groove which overlies the foil-like section and raised lands which overlie the ends of the said section and which perform the dual function of minimizing flow of the hot plastic quartz longitudinally of the quartz tube when the latter is pressed onto the lead-in wire and insure that both the top and bottom of the press seal are completely closed thereby eliminating not only the cavities at the inner end of the seal but also those at the outer end. Further, the jaws are provided with flanges extending longitudinally of the quartz tube to prevent the lateral flow of the hot plastic quartz which frequently causes a bowing of the foil sections which are torn apart under the pressure squeezing the plastic quartz onto the foil section.

In the drawing accompanying and forming part of this specification an embodiment of the invention is shown by way of example in which, Fig. 1 is a fragmentary perspective view of the parts of a seal assembly, a jig for holding said assembly and the ends of a pair of pinching jaws mounted in opposing positions with respect to the seal assembly and shown in their open position; Fig. 2 is a fragmentary perspective view on an enlarged scale of the assembly of Fig. 1 after the pressed seal has been made by the pinching jaws shown in Fig. 1; Fig. 3 is an elevational view on a reduced scale of a lamp stem made in accordance with and embodying the invention; Fig. 4 shows the stem of Fig. 3 mounted in the end of a lamp envelope.

Referring to Fig. 1 of the drawing the seal assembly comprises a pair of molybdenum lead-in wires 1 and 2 having a flattened section 3 and 4-, respectively. The wires are supported by a cylindrical jig 5 having a tapered end 6 with a flat top surface 7 provided with apertures 8 and 9 for receiving and gripping the ends 10and 11 (Fig. 2) of the wires to hold the wires 1 and 2 upright on the jig 5'. The Wires 1 and 2 are mounted on the jig 5 with their flattened sections 3 and 4 in a common plane and at the same level above the top surface 7 of the jig 5.

The seal assembly also includes a quartz tube 12 provided with a tubulation 13 by which the tube 12 may be held around the wires 1 and 2 with its end supported approximately /2 mm. above the top surface 7 of the jig 5. During the heating and pressing of the end of the quartz tube around the wires an inert gas, such as nitrogen, under a pressure slightly above atmospheric is passed into the tube 12 through the said tubulation 13. The opposite end of the tube 12 is closed during sealing by a stopper (not shown) so that the inert gas flows out of the tube 12 through the /2 mm. opening between the lower end of the tube 12 and the top surface 7 of the jig 5. The wires 1 and 2 are thus surrounded by the inert gas during the heating and pressing of the end of the quartz tube 12 to prevent oxidation of the wires.

A pair of pressing jaws 14 and 15 are mounted in opposing positions with respect to the seal assembly mounted on jig 7. Said jaws 14 and 15 are arranged to approach the assembly together at right angles to the common plane of the flat sections 3 and 4 of the wires 1 and 2 as indicated by the arrows. Pressing the end of the quartz tube 12 onto the wires 1 and 2 is accomplished in two pressing movements of the jaws 1.4 and 15. The first pressing movement flattens but does not close the end of the tube 12 after the said end has been heated to its softening temperture by an oxy-hydrogen flame. The jaws are then retracted from the tube 12 and the flattened tube end is reheated to its softening temperature by reapplication of the flame. Thereupon the jaws 14 and 15 are again advanced and forced against the tube until the motion thereof is stopped by the pressed quartz.

The operative faces 16 of the jaws l4 and 15 are identical in structure and are each provided with a groove 17 between two raised

lands

18 and 19 placed so as to overlie the ends of the flat foil sections 3 and 4 of the wires 1 and 2. The grooves 17 determine the two major plane surfaces of the press: the foil sections 3 and 4 are hermetically united with the press between and parallel to these plane surfaces. The

lands

18 and 19 restrict flow of the hot plastic quartz in the region of said sections 3 and 4 longitudinally of the assembly when the sides of the quartz tube are pressed onto the wires 1 and 2 by jaws 1 3 and The tendency of the compressed quartz to. pull the foil sections 3 and 4 apart and thus rupture the lead-in wires 1 and 2 is thus minimized The top surface of each of the jaws is concave and the upper land 19 is curved to follow the contour of said surface and conform to a curved concave end to the interior of tube 12. A pair of arcuate grooves 21 are impressed on the quartz by the opposed said lands 19 to. completely close the end of the tube 12 leaving no cavities between the walls at the sealed end of the tube.

The contour of the inner surface of the sealed end of the tube 12 is rounded and smooth and completely free from mercury trapping cavities. The juncture between the seal press and the tube 12 is thus necked and presents a solid surface to the interior of the tube 12.

The lands 18 at the bottom of the jaws 14 and 15 are straight and transverse to the longitudinal axis of the tube 12 and lead-in wire assembly. These lauds 18 in the operative faces 16 completely close the outer end of the tube 12 and press the quartz around the portions 10 and 11 of the lead-in wires extending outwardly of the tube 12 from the foil sections 3 and 4 to provide good mechanical support for said wire portions 10 and 11. The end surface of the press is thus a solid surface also free from cavities.

Flow of the hot plastic quartz laterally of the seal assembly during sealing frequently causes the foil sections 3 and 4 to become bowed and torn when pressing jaws having flat operative faces are used. The pressing jaws 14 and 15 of the present invention minimize such lateral flow of the quartz by confining the quartz, when being pressed in a plastic condition, between a pair of flanges 22, one on each of the jaws 14 and 15 and extending longitudinally of the tube and lead-in wire assembly. The flanges 22 are in opposed positions with respect to the seal assembly when the jaws 14 and 15 are in their closed position, are each in the form of an extension of one side of the jaw, extend beyond the operative face 16 of the jaw, across one end of the groove 17 and overlap a cut-out portion 23 of a side of the opposing jaw. The width of the pressing jaws 14 and 15 of the present invention is correlated with the diameter of the quartz tube 12 so that the flanges 22 are spaced apart a proper distance to effectively minimize lateral flow of the plastic quartz when the quartz is compressed by the jaws 14 and 15. For example, when the outer diameter of the tube 12 is 10 mm. the flanges 22 are spaced apart a distance of 1.5 mm. when the jaws are closed.

As shown in Pig. 1 of the drawing the surfaces defining the groove 17 slope upwardly and slightly outwardly from the bottom surface of the groove to facilitate sep aration of the operative faces 16 of the jaws 14 and 15 from the quartz seal press after the latter has been made.

After the seal press has been made at one end of the quartz tube 12 the position of the tube may be reversed and a similar seal press made at the opposite end of the tube 12 in the manner described above. Usually only one lead-in wire having attached to its inner end a main discharge supporting electrode, such as the electrode 24 mounted on lead-in wire 2, is mounted on the jig S and included in the seal at the opposite end of the tube but, of course, two lead-in Wires such as those shown in the drawing may be used, when desired. The electrode is made up of a tungsten slip-over wire coil about a thorium insert. The end 25 of the lead-in wire 1 4 serves as an auxiliary electrode in the completed lamp.

After seals have been made at both ends of the tube 12 the other usual steps in the manufacture of high pressure discharge lamps are performed, such as exhausting the tube 12 and then introducing therein a starting gas and a predetermined measured small amount of mercury to provide a desired high vapor pressure and an unsaturated vapor atmosphere on a predetermined power input, such as a power input of watts or more. When the lamp has been otherwise completed the tubulation 13 is sealed off at the end thereof united with the tube 12 and the excess is removed.

It will be understood, of course, that the invention is useful for the manufacture of quartz-to-metal seals having lead-in wires made up of two end wires, such as tungsten wires, Welded to the ends of a metal foil strip, such as a strip of molybdenum foil.

The quartz-to-metal seals of the present invention may also be made in the form of reentrant stems for low pressure mercury vapor electric discharge lamps having envelopes which transmit ultra-violet radiation of 2537 A. wave length, which consist of quartz or hard glass having a low coeflicient of expansion and in which the mercury vapor is at. a pressure in the neighborhood of about 10 microns during operation and is highly emissive of radi ation of 2,5 37 A. wave length.

When the, seals are made in the form of stems for such low pressure lamps a, flared quartz stem tube is mounted on the jig 5 and about the inleads 1 and 2 in place of the quartz tube 12 and the portion of the inleads 1 and 2 extending upward from the flattened portions 3 and 4 therefore are longer so as to extend slightly beyond the end of the flare as shown in Fig. 3 in which the stem is shown at 26. The electrode 24 is omitted from the end of wire 2, of course.

The stem tube 26 is held in the same position on the jig 5 as the tube 12 by any suitable means and the seal press is made at the end thereof opposite the flared end in the same manner as described above.

After the wires 1 and 2 have been scaled into the stem tube 26 the stem is provided with an exhaust tubulation 27- the inner end of which is slightly bent and united by fusion with the wall of the tube 26. The tubulation 27 communicates with the interior of the lamp envelope 28, Fig. 4, through an opening 29 blown through the wall of the stern tube 26 adjacent the seal after the end of tubulation 28 has been attached thereto. The stem 26 is then complete and its flared end 30 is fused to quartz envelope 28 with the usual filamentary electrode 31 provided with an alkaline earth oxide coating attached to the ends of sections 10 and 11 of wires 1 and 2, Fig. 4.

The tubular envelope. 28 provided with a stem. at each end may be exhausted of air and; filled with a starting gas at a few mm. pressure through the exhaust tubulation 27 and the usual small amount of, mercury may also be introduced into the envelope 28 through the tubulation. 27 before the latter is sealed off from, the exhaust system.

What I claim as, new and desire to secure by Letters Patent of the United States is:

1. In apparatus for making a quartz-to-metal seal of the type comprising a quartz press at the end of a quartz tubev and. a metal conductor extending through said press into said tube and having a foil center section hermetically united withv said press, a pair of, jaws provided with operative, faces, in opposing spaced positions to receive therebetween a quartz tube mounted around the conductor, the operative face of each of, said jaws having a wide groove extending thereacross transversely to said conductor bounded by transverse lands spaced apart a distance such that, the. groove overlies the foil section of the: conductor and the lands are in opposing positions with respect to. the ends of the foil section to minimize flow of the hot plastic quartz longitudinally of the foilsection tending topull apart the foil section when pressed:

onto the conductor by the jaws, the land in each operative face next to the tubular portion of the tube being in the form of an arc to close the tubular portion with a concave rounded end having a press providing a solid wall free from cavities, each of said jaws having a forwardly projecting flange along one of its sides, said flanges being in opposed positions with respect to said tube and overlapping a side of the opposing jaw when said jaws are in a closed position to minimize flow of the hot plastic quartz laterally of the conductor during sealing.

2. In apparatus for making a quartz-to-metal seal of the type comprising a quartz press and a metal conductor having a foil center section, a pair of jaws provided with operative faces in opposing spaced positions to receive therebetween a quartz tube mounted around the conductor, the operative face of each of said jaws having a wide groove extending thereacross transversely to said conductor bounded by transverse lands spaced apart a distance such that the groove overlies the foil section of the conductor and the lands are in opposing positions with respect to the ends of the foil section to minimize flow of the hot plastic quartz longitudinally of the foil section tending to pull apart the foil section when pressed onto the conductor by the jaws, each of said jaws having a forwardly projecting flange along one of its sides at an end of the groove, said flanges being in opposed positions with respect to said tube and overlapping a side of the opposing jaw when said jaws are in a closed position to minimize flow of the hot plastic quartz laterally of the conductor during sealing.

References Cited in the file of this patent UNITED STATES PATENTS 1,659,613 Phelps et a1. Feb. 21, 1928 1,933,323 Fagan Oct. 31, 1933 1,969,525 Ronci Aug. 7, 1934 2,020,729 Knoeppel Nov. 12, 1935 2,069,079 Rudd Jan. 26, 1937 2,143,690 Flaws Jan. 10, 1939 2,251,062 Lindwurm et al. July 29, 1941 2,334,604 Bunger Nov. 16, 1943 2,632,033 Kreift Mar. 17, 1953 FOREIGN PATENTS 476,488 Great Britain Dec. 6, 1937 481,940 Great Britain Mar. 16, 1938 489,626 Great Britain July 28, 1938