US2504521A - Quartz-to-metal seal - Google Patents

Description

(fig x r April 1950 A. GREHNER 2,

QUARTZ-TO-METAL SEAL Filed ma 1, 1948 T ig. 4.

2/ [Z 20 g r 1 z d Inventor': ALFFfiECl Gveiner,

Patented Apr. 18, 1950 UNITED ST PATENT? ouAnrz-r iji rhn Alfred Greiner; Cleveland Heights,.0hio,' assignor tolGeneral Electric Company, a corporation of N ew York Application May 1, 1948, Serial No. 24,523

12'Claims.

My invention relates to'quartz-to-metal seals for high pressure discharge devices, such as high pressure mercury vapor discharge lamps.

Lamps of this 'kind are high intensity light sources and'may-operate with-a power-consumption in the order of several kilowatts and-a vapor pressure of many atmospheres; One type of such lamp'comprises a spherical quartz envelope having seals in the form of protruding stems supporting theelectrodes and including leading iii-conductors in the form of multiple-molybdenum' foils connected in parallel to carry the heavy discharge current and fusedinto the quartz body of-the stem. The foils are extremely thin andtherefore require careful and skilled handling in making the stem.

An object of my invention is .toprovide a quartzto-metal seal in the form of"a stem which is of simple structure. Another object of my invention'is to provide-a method: of making such a stem. A further object of my invention" is to provide a method of making a quartzto-metal seal. Other objects and advantages of the in vention'will appear from the following description of species thereof-taken in conjunction with the accompanying drawing in which Fig. 1 is an elevational view, partly in section, of a lamp having stems embodying my invention; Fig. 2 is an exploded view ofthe metal parts of the stem shown in'section in Fig. 1; Fig. 3'is a sectional elevational View of vitreous tube constituting part of the stem; Fig. 4-is a similar view of another quartz tube also constituting part of the stem; and Fig; 5 isa similar view of the stemelements of Figs. 2 to 4 assembled for fusion together.

Theda-mp shown' in Fig. 1 of'the drawing is of the high vapor pressure electric discharge type having a. spherical quartz envelope I provided with quartz-'to-metal seals in "the form of alignedstems 2 and 3'protruding. from diametrically opposed portions thereof. Thestems-Z and 3-are identical in structure-and have lead-in conductors including tungsten" rods 4 and 5 extendingthrough quartz stem tubes and carrying electrodes G and l at their inner ends. Rods 4 and 5 are exposed at their outer ends for connection to the terminals of a power source for the lamp.

The electrodes 6' and l are closely spaced in the center of the quartz envelope I Which'com tains an ionizablegaseous atmosphere includ-- ing-a startinggas, sucl1'asarg0n', and mercury in an amount sufficient to produce-on the power? input for which the-'lanipis-designedanun-* saturated vapor atmosphere" having a: pressure 2. of the order of atmospheres; A vapor pressure of.- the order of 300 pounds per square inch-or mat mospheres'maybe produced in'such a lamp hav ing a-power consumption-of about 10 kilowatts.--

In order to carry such large currents-,the-tungr sten rods 4 and 5 must be of such large diameter. that quartz cannot be fused directly'thereto-ytw make a fused joint-which will-be'gasP-tight'underr the conditions of-operation.

To provide such a joint I utilize thimblesd -of refractory metal, suchas molybdenum or tung sten, positioned in the stemrtubesand around thesrods 4 and 5. The thimbles fl are hermetically=- united with the rods; ,4 and 5: andha-ve-afeather ed'sealing edge 8; The quartz of the. stems-.zand 3 is fused to both the: inner and-outer: surfaces of the edge- 9, as described below, to make amechanically strong and ,temperature-resl stantf quartz-to-meta'lseal. The quartz parts: of -the stems surrounding the thimblesand the-rods;provide good support therefor tohold the electrode'si 6 and l in proper position inthe'envelope-l As best-shown in Figs. 2' and"5. the outer sur face of the'thimble' 8 back from the portion-.to" which the quartzis fusedand theportion.of tlzle -v rod 4 extending'from'the thimble 8'to.ward th e electrode 6 are sheathed with molybdenum'foilii! which acts as a cushion between-the quartz tube and the parts of the rod and the thlmble covered by the foil. Thisfoil. covering; thethicla ness of which is greatly'exaggerated in the, draw;- ing, prevents the quartz-from adhering-to thesethick-metal parts during-fabrication of thestem. and avoids cracking of the' quartz when' these metal parts-expand and contract in respons'ertochanges in temperature.

A metal spacer H inside the thimblea serves-r the-same purpose by preventing the qua-rtz .;from. going -so far into the thimble duringfabrication:

that it would fuse-not only to the inner surface of the feathered sealing edge 9 of the thimblec-w but also toother thicker portions ofthevinner surface of the. thimb'lei' Thusy'the' only portiontofthe conductor, cluding the rod 4 and the metai thimblegat to which the'uuartzds"hermeticalfy fusd'is'the' afl nular; tapered; feathered-sealing.- edge 9: whiclrs is-of'suchthin wall section that the-quartz; ad heres to-b'oth the" innerandouter surfaces-thaw of without cracking duringfabricatiomandwusev ofthe' stem. v

In making the stem; the thimble 8 is; cut-and. ground" to shape: from: bar-or flat-molybdeninrr stock; As best showrrin-Fig; 2 of the drawing-git has-adomed=shaped closed end having an opening I2 for the rod 4. A specific embodiment of a thimble which has given good results has its annular side .wall '7 of an inch in depth with an inner diameter of of an inch and tapers from the closed end to the feathered sealing edge 9 which is between 0.0006 to 0.001 of an inch in thickness at its end. About inch back from the end of the edge 9 the wall thickness is between .0016 and .002 of an inch. I have demonstrated that these upper limits are critical; the quartz will break away from the metal surface or crack and the seal will leak if the upper limit is exceeded.

The flanged spacer II inside the thimble 8 is also made of molybdenum. It is of an inch long, the cylindrical part thereof is of an inch in outside diameter and the flange part I3 slightly less than of an inch in diameter so that there is small clearance between it and the inner surface of the annular thimble wall. The tungsten .5.

rod 4 passing through the opening I2 in the thimble 8 and through the spacer II is approxi mately $4 of an inch in diameter and the openings in the spacer II and in thimble 8 are made just large enough to accommodate the rod 4. The spacer I I holds the rod and the thimble in alignment during the brazing operation by which these three members are joined together after they are assembled as shown in Figs. 1 and 5.

I prefer to use platinum as the brazing material to bond the three metal members together. This metal withstands the high temperatures existing thereat during fabrication and use of the stem and forms a hermetic joint between the tungsten rod 4 and the molybdenum thimble 8.

After the rod 4, the thimble 8, and the spacer I I have been joined together they are thoroughly cleaned and the metal sheath I is applied. The sheath consists of two sheets of molybdenum foil approximately .0006 of an inch thick wrapped around the parts of the rod 4 and the thimble 8 to be covered. One of the sheets is shaped in the form of a collar I0 wrapped around the domed end of the thimble 8, the part of the rod emerging from the closed end of the thimble and the part of the annular wall of the thimble adjacent the domed bottom. The foil collar I0 covers the brazed joint between the rod and the thimble and extends to within of an inch of the feathered edge 9 of the thimble 8. The collar I0 is preferably shaped from a foil strip approximately of an inch wide and 2% inches long. One long edge of the strip is serrated to a depth of approximately of an inch with a distance of an inch between serrations which overlap when the strip is wrapped around the thimble and the rod to form the collar. The tab is welded to the surface of the strip after the collar is formed. In Fig. 2 the collar is shown removed from the thimble for purposes of illustration.

The foil sheet In wrapped around the rod 4 may overlap the end of the collar slightly and is made of a sheet approximately 1%; inches wide and 1% inches long.

This assembly of the metal members is insorted in the two quartz tubes I4 and I5 shown separately in Figs. 3 and 4, respectively. The complete assembly before fusing the various elements of the stem together is shown in Fig. 5.

The quartz tube I4 surrounding the thimble 8 and the outer end of the rod 4 is made up of three overlapping coaxial tubes l6, l1, and I8, the tube I8 of smallest diameter being of an inch in outside diameter, 6 inches long and 1 g of an inch thick, the tube of largest diameter I8 being of an inch in outer diameter, of an inch in inner diameter and 2 inches long, and the intermediate tube I! being slightly larger than of an inch in outer diameter and of an inch thick. The ends of the tubes I6, ,II, and I8 are fused together as shown in Fig. 3. The tubes I1 and I8 form a longitudinally extending annular recess opening into the interior of the tube I4 and which accommodates the feathered edge 9 of the thimble 8 with the said edge 9 touching or in close proximity to the fused joint between the tubes I1 and I8 and the flange I3 on the spacer II resting against the fused joint between the tubes I6 and I! as shown in Fig. 5.

The quartz tube I5 surrounding the inner end of the rod 4 has a thick wall portion I9 approximately 3% inches long which surrounds the rod 4 in the completed stem and a thinner wall portion 20 approximately 5 inches long. The thicker wall portion I9 has an outer diameter of of an inch, an inner diameter slightly greater than inch to accommodate the rod 4 and the sheath ID, a flare 2| about 11% of an inch in diameter at the end thereof to be inserted in the end tube I8 of the quartz tube I4 and a bulge or bulbous portion 22 of about %3- of an inch outside diameter at the end joining the thin wall portion 20 thereof.

In the assembly including all the elements shown in Fig. 5 the portion I8 of the tube I4 overlaps the end of portion I9 of tube I5 with the flare 2| on the latter making a close mechanical fit with the inner surface of the tube portion I8. The two quartz tubes I4 and I5 then form a chamber for the metal parts. In completing the stem a non-oxidizing gas, such as nitrogen or forming gas which is a mixture of hydrogen and nitrogen, is first caused to flow into the chamber through the open end of each of the tubes I4 and I5. This gas fills the chamber to prevent oxidation of the metal parts therein during heating of the quartz parts. It flows out of the chamber between flare 2| and tube portion I8. The flare 2| prevents too rapid escape of the gas from the chamber formed by the tubes I4 and I5 before these are fused together.

With the gas flowing as described above, heating flames are applied to the tube portion I8 surrounding flare 2I and overlapping the tube por-- tion I9. During this heating step and before the overlap of tube I8 collapses onto the flare 2| to seal the opening between them, the stream of gas passing between the flare 2| and the inner surface of tube portion I8 prevents products of combustion from the heating flame entering the chamber and affecting the metal parts. When the heated quartz becomes plastic and closes the space between the flare 2| and the tube portion I8, the pressure of the gas in the chamber is immediately reduced to only slightly above atmospheric pressure to avoid blowing out the plastic quartz as the overlapping portions of the tubes I4 and I5 are being fused together.

After the tubes I4 and I5 have been spliced together in the above manner the assembly is allowed to cool to room temperature with the gas still flowing through the chamber. The chamber is then exhausted to a high vacuum and, while the vacuum is maintained, the metal parts are heated by a high frequency oscillator to remove any gas which may have formed on these parts during the splicing of the tubes I4 and I5. The assembly is again allowed to cool until it may be sealed off from the vacuum sysest th he sinister n. a hi hl ei st andide-e. As sh wn d tted lines a nd Q 1 l 5, oth ends. of the chamber formed y he. uarts tubes .4 and ar a e aheetins were s then p ied a h Juneure o l 8 surr und-iris the feathered sealing edge 9 of the thirnble 8 to soften and lla sethe e t bes simu ee cusly n ot des f-t e ed e 9- f h himb and to m k a u ed bermetie Jointv t en th u r a d th hiiab e, Peri-as h s h a i tep w s be xerci ed- 9 hea both f theSC u s H n "i at heser at o t their reasin no. tions collapse simultaneously back from their juncture and. contact with the inner and uter-- surfases c t i athe c sc l n e If wells collapse at different rates, the thin wall ofthe thimble will either be split if the nner tube l eclla scs nt e a e therefist, or will wrinkle if the outer tube i8 doessoii t.

The oil sheath on the outside of the thimble 8 the flange I33 0n the spacer H prevent the tubes If! and H; from fusing with the thicker portion o he t in l llbetween the quartz and the thimble edge 9 is approgzi nately of inch long on the outside and about ofan inch long on the inside of the thimble wall measured back from the end edge a so that the seal has an overall length o aoproi ma e y e nch s and i of large ea- ;t-he hermetic seal has been formed the quartz tubing surrounding the foil covered portion of the thimble and the tungsten rod is heated, starting from the thi nble, to collapse the quantz onto the sheath 10 to give good mechanical support to the metal par-ts of the stern. Due to the sheath 10 the quartz does not adhere to the rod 4 or the covered portion of the thimble. The assembly is again allowed to cool and the surplus quartz tubing is severed and removed at about the maximum diameter of the bulge 22 and at a point approximately inch from the opposite end of the rod 4 to complete the stem. One end of the rod 4 is thus exposed for connection to a power source when mounted in a lamp and the other end, which is the inner or electrode end of the rod, extends an appreciable distance beyond .the remaining part of the bulge and into the lamp envelope when the remaining bulge part, which constitutes a sealing flange for fusion with the quartz envelope of the lamp, is joined to the lamp envelope as shown in Fig. l.

The cathode 5 of the high pressure lamp is constituted by the inner end of rod 4 which is shaped in the form of a wedge and preferably impregnated with material having high elec tron emissivity characteristics, such as thorium. The anode l is constituted by a block of tungsten welded to the end of rod 5. In making the lamp, electrodes 5 and l are inserted into the quartz envelope 1 through diametrically opposed openings and the flanges on the stems are fused into said openings to close them and to support the electrodes in proper spaced apart positions in lamp. The lamp is completed by steps well known in the art, including evacuation and introduction of the gas filling and mercury.

In the co-pending application of Leo R. Peters, Serial No. 24,522, of even filing date herewith and assigned to the assignee of the present .application, themethod of brazing the tungsten and molybdenum parts of the conductor together and the article produced by the method are disclosed and claimed.

The hermetic seal d I la m as w and d si e o tee s 3 Letters ten r e was sates s Th meth d o maki a stem f e m ws el which ompr s um n f a es be w th a l d n ll 'e isn i a l l's e? s op nin n its inte qr ins a mate! o ductor n lud ng a we a d a himb can a od and h me all un ther w t an thirnble having a feathered sealing egg?- covering th or on of a d red nd wa d from the closed end of the thimble and said thirnble, other than the feathered sealing edge ofthe latter, with a metal foil, positioning said conductor in said tube with the feathered seal: ing edge in said recess, positioning a second vitreous tube around the foil-covered portion of, the, rod and fusing it to said first-named tube to form a composite tube, reducing the pressure in said composite tube below atmospheric, heating the wall of the recess on both sides ofsaid edge o. c llapse. s id wall n b t of i s e multaneously to fuse said wall to said edge without deforming. the latter and then heating the portion of the composite tube surrounding the foil covered portion of said thimble and said 110. 1 collapse said portion onto said metal foil so that said composite tube tightly fits said thimble and said rod and provides mechanical support for said conductor in said composite tube.

2,. The method ofmaking a mechanically strong. electrically conducting gas-tight seal for i h capacity. high pressure dischar e. quartz lamps which comprises hermetically joining a molybdenum thimble having a feathered sealing edge around a tungsten rod passing through the thimble, forming a quartz tube with a longitudinally extending annular recess opening into its interior, positioning the thimble in said tube with its feathered edge in said recess and the rod .ex-

tending along the tube and exposed beyond one end thereof, positioning a second quartz tube around the exposed .end of the rod and telescoped within said first-named tube, filling said tubes with a non-oxidizing atmosphere. fusing the telescoped .tube portions together to form a chamber.

evacuating the said chamber, heating the wall of the recess on both sides .of the feathered edge of the thimble to collapse said wall onto both of said sides simultaneously to fuse said wall to said edge without deforming the latter and then heating the wall of said chamber surrounding the remainder of said thimble and said rod to collapse said wall so that it tightly fits said thimble and said .rod to provide mechanical support therefor.

3. A high-pressure-resistant stem tor electric devices comprising an elongated vitreous stem tube, a lead-in conductor extending along said tube and beyond each of its ends and a thimble wholly within said tube and hermetically joined to and disposed around said conductor'wlth its closed end'toward the inner end of the conductor. said thirnble having a feathered sealing edge embedded =in and making a-fused joint with the wall of the stem tube said tube tightly fitting the .exterior of said thimble and at least the portion of said conductor extending outward from' the closed end of the thimble'to provide mechanical support therefor.

1. A high-pressureresistant stem for electric devices comprising an elongated vitreous stem tube. a lead-in conductor extending along said tube and beyond each of itsend's'and a thimbl'e wholly within said tube and hermetically joined (6 to and disposed around said conductor with its closed end toward the inner end of the conductor and with the ends of the conductor extending beyond the thimble ends, said thimble having a feathered sealing edge embedded in and making a fused joint with the wall of the stem tube, said tube tightly fitting the portions of said conductor extending from said thimble and said thimble to provide mechanical support therefor.

5. A high-pressure-resistant stem for electric devices comprising a vitreous stem tube, a leadin conductor extending along said tube and a thimble wholly within said tube and hermetically joined to and disposed around said conductor with its closed end toward the inner end of the conductor, aid'thimble having a feathered sealing edge embedded in and making a fused joint with the wall of the stem tube, said stem tube wall extending into said thimble, and a cylindrical member around said conductor and butting against the tube wall in said thimble and the closed end of the thimble to reinforce the latter.

6. Ahigh-pressure-resistant stem for electric devices comprising a vitreous stem tube, a leadwall closely surrounding said conductor and said thimble to provide mechanical support therefor,

and a loose metalfoil covering portions of said conductor and said thimble to prevent said tube adhering to said portions.

-7. A high-pressure-resistant stem of high capacity for electric discharge quartz devices comprising an elongated quartz stem tube, a tungsten rod extending along said tube and beyond its ends and a molybdenum thimble wholly within said tube and hermetically joined to and disposed around said rod with its closed end toward the inner end of the rod, said thimble having a feathered sealing edge embedded in and making a fused joint with the wall of the stem tube said tube tightly fitting the exterior of said thimble and at least the portion of said rod extending fro'mt-he closed end of the thimble to provide mechanical support therefor.

8. A high-pressure-resistant stem of high capacity for electric discharge quartz devices comprising an elongated quartz stem tube, a tungsten rod extending along said tube and beyond its ends and a molybdenum thimble wholly within said tube and hermetically joined to and disposed around said rod with its closed end toward the inner end of the rod, said thimble having a feathered sealing edge embedded in and making a fused joint with the wall of the stem tube, and a molybdenum foil sheath extending'from the fused joint and covering th exterior of said thimble and the portion of said rod extending inward of the stem tube from the closed end of the thimble, said stem tube tightly fitting the sheathed portions of said thimble and said rod to provide mechanical supp rt therefor.

9. In a high pressure resistant stem for electric devices, a conductor rod, 2. metal thimble around said rod and a cylindrical metal spacer also around said rod and butting against the inner surface of the thimble, said rod and said thimble being rigidly bonded together with a gastight joint therebetween.

10. In a high pressure resistant stem for electrio devices, a. tungsten rod, a molybdenum thimble around said rod and a molybdenum spacer also around said rod and butting against the inner surface of the thimble, said rod and said thimble being rigidly bonded together with a gas-tight joint therebet'weeri.

11. A high-pressure-resistant stem of high capacity for electric discharge quartz devices comprising an elongated quartz stem tube having a flared end for fusion with the envelope of said device, a tungsten rod extending along said tube and beyond each of its ends and a molybdenum thimble wholly within said tube and 'hermetically joined to and disposed around said rod with its closed end toward the flared end of the stem tube and with the ends of the rod extending beyond the ends of the thimble, said thimble having a feathered sealing edge embedded in and making a fused hermetic joint with the wall of the stem tube, a molybdenum foil collar around said thimble and extending from the fused joint to the said rod and a molybdenum foil sheatharound said rod and extending from said thimble to adjacent the flared end of said stem tube, said stem tube tightly fitting the sheathed portion of said thimble and both ends of said rod to provide mechanical support for said rod and said thimble in said stem tube.

12. A high-pressure-resistant stem of high capacity for electric discharge quartz devices com prising an elongated quartz stem tube having a flared end for fusion with the envelope of said device, a tungsten rod extending along said tube and beyond each of its ends and a molybdenum thimble wholly within said tube and hermetically joined to and disposed around said rod with its closed end toward the flared end of the stem tube and with the ends of the rod extending beyond the ends of the thimble, a molybdenum spacer' around said rod and in said thimble and butting against said rod and said thimble, said thimble having a feathered sealing edge embedded in and making a fused hermetic joint with the wall of the stem tube, a molybdenum foil collar around said thimble and extending from the fused joint to the said rod and a molybdenum foil sheath around said rod and extending from said thimble to adjacent the flared end of said stem tube, said stem tube tightly fitting the sheathed portion of said thimble and both ends of said rod to provide mechanical support for said rod and said thimble in said stem tube.

ALFRED GREINER.

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

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