US2699847A - Quartz-to-metal seal - Google Patents

Description

Jan. 18, 1955 E. H. NELSQN ET AL QUARTZ-TO-METAL SEAL Filed Sept. 1, 1949 m on DLe MW hm r Om T/ O Jfp fi m% v A V r WWW T T m E b United States Patetltf) QUARTZ-TO-METAL SEAL Evan Herbert Nelson, Harrow Weald, and Ernest Benjamin Power, Kenton, England, assignors to General Electric Company, a corporation of New York Application September 1, 1949, Serial No. 113,644

Claims priority, application Great Britain September 1, 1947 1 Claims. (Cl. 189-36.5)

This invention relates to seal-bodies of the type comprising at least one conductor hermetically sealed through a quartz body and adapted for sealing into apertures in quartz envelopes, for example the envelopes of electric discharge devices such as high pressure metal vapor electric discharge lamps, to provide an hermetically sealed conductive connection between the interior and exterior of the envelope, and is an improvement in or modification of the invention described in our copending application Serial No. 46,916, filed August 30, 1948, now Patent No. 2,659,964, dated November 24, 1953, assigned to the assignee of this application and of which this application isa continuation-in-part. The copending application is hereinafter referred to as the parent application. Here and hereinafter it will be understood that the term quartz includes any other vitreous material whose thermal expansion coeflicient is as low as that of quartz.

The parent application describes and claims a sealbody of the type specified wherein at least part of the said conductor comprises a body of metal passing through an aperture in a thin sheet of metal, which sheet is hermetically joined to the body of metal by brazing or soldering, and part of the said thin sheet is embedded in the quartz body to complete the hermetic sealing of the conductor through the quartz body.

According to the present invention, a seal-body of this kind is modified by the use of two thin sheets of metal in place of a single thin sheet, the two sheets contacting, or lying very close to each other without any quartz between them so as to be in simple abutting contact at least over the region where they are embedded in the quartz.

With this arrangement the opposing inner surfaces of the two sheets are free to move relative to each other and in this way stresses set up on cooling of the heated quartz in manufacture, or during use of the seal-body, which might lead to rupture of a single thin sheet, can be relieved by such relative movement without damage.

In the drawing accompanying and forming part of this specification species of the invention are shown in which Fig; 1 is an elevational, partly sectional view of one end of a completed seal-body embodying the invention and made by the method disclosed and claimed in our copending application referred to above; Fig. 2 is a side sectional view of the two thin sheets of metal, which are in the form of discs having a central aperture and a tapered feathered sealing edge, spaced apart to clearly show their shape; Fig. 3 is an elevational, partly sectional view of a completed seal-body also embodying the invention and made by the method disclosed and claimed in copending application Serial No. 42,823, filed August 6, 1948, now Patent No. 2,607,981, dated August 26, 1952, and assigned to the assignee of this application. Fig. 4 is a fragmentary, partly sectional view of the metal parts of the seal-body of Fig. 3 assembled for being joined together; Fig. 5 is a similar view of the metal and vitreous parts of the seal-body of Fig. 3 assembled for being joined together and Fig. 6 is a fragmentary, elevational partly sectional view of another seal-body of our invention.

Referring to Figs. 1 and 2 of the drawing, the sealbody comprises a metal rod 1, preferably tungsten, passing through apertures in two thin metal sheets in the form of annular discs 3 and 4, prefereably of molybdenum. The discs 3 and 4 are hermetically united around the rod 1 by brazing or soldering as indicated at 5 in Fig. l. The surface of each disc 3 or 4 in contact with the other disc is plane and the said plane surfaces are in simple abutting contact with each other. The composite disc made up of the two discs 3 and 4 has a feathered;

seal edge which is embedded in the quartz body 6 to complete the hermetic sealing of the conductor rod 1 through" the quartz body 6. The latter is preferably in the form of a tube having the end opposite that shown adapted to be hermetically joined to the quartz envelope of an electric discharge device, such as a high pressure mercury 1 vapor discharge lamp, with the corresponding end of the rod 1 extending into the envelope. A discharge supporting electrode, such as that shown in Fig. 3, may be mounted on the inner end of the rod 1.

Preferably both of the thin sheets or discs 3 and 4 are hermetically brazed or soldered to the body or, rod

1 of metal, but if the peripheries of the discs are completely embedded in the quartz, as is preferred and shown in Fig. 1, obviously it will suflice for only one disc 37 to be hermetically brazed or soldered to the metal body to secure the required hermetic sealing of the metal body through the quartz.

Preferably both of the contacting surfaces of the thin discs 3 and 4 are plane, so that they are everywhere substantially in simple abutting contact, but this need not necessarily be the case; thus the sheets may have the form of cups 7 and 8 with opposed flanged rims in simple abutting contact and embedded in the quartz, the hollows of the cups 7 and 8 being opposed to each other with a the rod 1 passing through apertures in their bases, as shownin Figs. 3 to 5 of the drawing.

Asin the parent application, the metals of the thin sheets in the form of discs 3 and 4 or cups 7 and 8, which is preferably the same in each case, must be capable of withstanding the temperatures involved in the embedding thereof in quartz, for which purpose the quartz 6 must in general be rendered molten, and tungsten and molybdenum are the metals best suited for this use.

Also the rod 1 must again be of a similar refractory na ture if it is also heated to the temperature of molten quartz in manufacture, for example if, as will in general be desirable for supporting purposes, molten quartz .is collapsed on to it in making the seal-body, and here also tungsten and molybdenum are the metals best suited for such use. However, in some cases the rod 1 may not be heated in manufacture, for example it may be brazed or soldered to the thin sheets after the latter have been ,embedded in the quartz body, and then a wider choice of metal is possible, consistent with the requirement that it must be capable of being brazed or soldered to at least one, sometimes both, of the thin metal sheets and i must also be suitable for the use for which the seal-body gis intended, for example a copper rod would not in general be suitable for use in a device containing a mercury vapor filling.

As in the seal-body described and claimed in the parent application, preferably the whole of the conductor rod 1 passlng through the seal-body consists of a single metal body, for example a single solid rod 1, and the quartz body 6 consists of a tube at least an appreciable length of which is collapsed onto the rod 1 to support it; prt erably the rod 1 is keyed into position by means of an indentation 9 formed in it into which quartz enters during the collapsing. The rod 1 may have to be wrapped with metal foil 10 where the quartz tube 6 is collapsed onto it to prevent the quartz cracking on cooling of the required, i. e. the side adapted to be presented to the interior of an envelope when the seal-body is sealed into the envelope, must be brazed or soldered to the metal rod 1 and preferably both cups 7 and 8 are brazed or soldered to the rod 1, as shown at 11 and 12 of the drawing. If cup 8 were not so fixed to the rod 1, the quartz attached to this cup might be removable, with the cup, from the seal-bod this may be avoided by keying the quartz to the rod 1, as shown at 9, and in any case with a U Patented Jan. 18, 19 55 seal-body in which the edges of the cup project through the quartz body, bothof'the parts ofthe quartz body into which it is divided by the cups are preferably keyed to the. rod 1 as shown in Fig. 6. It will be understood that.

the seal b'ody of 'Figr' 6:

The brazing or soldering mediumtused will'depend on the nature of' the metals-to be joined." For joining a molybdenum sheetto'a tungsten' rod; nickel-which unites-- both'with molybdenum and tungsten, may be used, but whilst nickel 'rnayin'somecasesrbe used satisfactorily wehave fo'und 'thatit often 'attacks'the thin molybdenum sheet so I as to 'l'eave gaps-between the-sheetand the tungsten conductor-yaccordingly' it is-betterto use-instead of metal a molybdenum-rich alloy of 'nickel and molybde num. Such an alloy may-readily'beproduced insitu-in" performingthe-solderingor brazing operation. However it will" beunderstood that other" soldering or brazingmediamay -be*used* and maybe -preferable;

I'n-one' method of forming the seal-body in accordance metal are-*spaced'apart, which-method is describedby way of example and shown in Figs. 3 to 50f the drawing, atungstemrod-"l" is passed through a-central aperture in each oftwo thinmoly'bdenum cup=shapeddiscs 7 and 8- (Fig. 4), the-rod 1- fitting each aperture'closely; For each cup a-ring13=-of thin molybdenum wire fittingcl'osely round the-rod 1' is then=placed round-the rod 1 'in the-corner between the-rod and asurface of the molybdenum cup and a similar ring'14 of nickel wire isplacednext to the ringlS-of molybdenum-wire.

The rod 1 is held vertically with each of the pairs ofwire- rings 15 and 14 above the correspondingmolybdenum -cups 7-'and-8" and the rings 13 and 14 are heated" until each nickel ring 14 melts and flows down-over the-associated molybdenum ring13 to form a molybdenum r-ich alloy whichsolders or brazesthe correspond in'g'nrolybdnumdisc 7 or- 8* to the tungsten rod I on cooling, the joint being shown at Hand 12 in Figs. 3, ;-and'6'; Toavoid 'oxidationthe-heating is carired out in an-electric oven: in a reducing atmosphere such as forming gas-1' 17 and'18 -arethen-fused together whilst nitrogen is passed through the tubesto avoid oxidation of the metal partsduring=the heating and-thereafter the flanges 17' and l8 and tubes-15*and 16'-are collapsed, by heating,

onto rod 1 whilst a reduced pressure is maintained within the -tub'ess- The cl'osedend of-tube-15 is, then cut away to expose the-end of; tungsten rodl and-the other tube'lti-may alscr becutio asuitable length as=required= The-electrode119 may th'en be' secured; as-bywelding, to theend of rod'l.

It is,- however, preferable if possiblev to' reverse the-- order of soldering or brazing and'sealing to reduce the possibility'of thesoldered-or brazed joints being damaged by' heatin the embeddingof the thin metalsheets. Thus in--thepreferred method of-making a seal-body in accordanee;v with the invention in which two plane contacting thin sheets are used as in the embodiment of Figs. 1.and:.2,'.parts.of the thinisheetsin the form of annular di'scs13: and 4i-with the rod 1 passing through them are firstembedded in the quartz and the rod 1 thereafter soldered or .brazedito the sheets to complete the hermetic sealingt'. Aseal-body of this kin'dmay be'manufactured exactly as described: in: the .parent copending: application SerialNo; 46,9 -l6'with reference-to Figs. 1'- to 41 ofthe drawing accompanying the copending application, the

singlesthin molybdenum disc of that seal-body being; merely replaced by two thinmolybdenum discs, which -20 with'the presentinvention in' which the places wherethe l twe -thin sheets=are brazed orsolderedto the body of' onto-the edgesof-"the molybdenum cups 7' and 8"'-and' may conveniently each be of approximately half the thickness of'the single disc ofthat seal-body.

In our copending application Serial No. 113,645 of even date herewith, and assigned to the assignee of the present application, we have described and claimed a seal-body in which one sideonlyof a single thin metal sheet is sealed to a quartz body to reduce-the possibility of the thin sheet of metal being ruptured'by stresses set up bycontraction of 'the quartz and the metal sheet while cooling; after heating in the manufacture or use. of the seal-bodyorof the-device of which the seal-body may form part. The seal bodes of the present application are similar. in that. one. side only of. each of the two metal sheets is sealed to the quartz.

What we claimas new and desire to secure by-Letters Patent of the United States is:

l. A seal-body comprising a quartz tube, a metal conductor rod extending along the interior of said tube and a pair of. thin juxtaposed metal sheets aroundsaid rod and hermetically united therewith, theouter edges of said sheets being in-simple abutting contact'with each other and hermetically united directly wtih said quartz tube.

2. A seal-body comprising aquartz-tube,a-metalt'rod* extending along'the= interiorof said tube and a pair. of thin uxtaposed metal-discs around said rod and'hermeti callyunited'therewith, the peripheries of said discs being;-

in'simple abutting contact with each other andzhermeti-z cally unlteddirectly with said quartz tube.

3. A seabbody comprising a quartz tube, a metalrod extending along the interior of said tube and. apairof thin juxtaposed metal cup-shaped discs disposed around said rodand hermetically united therewith;.said' discs opening toward-each other with their rims in sim ple abutting contactandhermetically united'directly'with.

said quartz tube.

4: A- seal-body comprising a quartz tube, a' metal rod extending" along the-interior ofsaid tube and-a pairof thin uxtaposed metal flat discs around said rod and hermetically united therewith, each of said discs-having aplane surface in simple abutting-contactwith the. corre sponding surfaceof the'other disc, theedges of said discs being embedded in said quartz tube with one side only of the edge of each disc hermetically'united directly with the quartz.

5. A seal-body comprising a quartz tube, a-metal rod extending along the interior of said tube and a pair of thin juxtaposed'metal cup-shapeddiscs around said'rod and hermetically united therewith, said discs opening-toward each'otherwiththeirrims in simpleabuttingcontact and completely embedded in said quartz tube-with.

one side only of the rim of each cup hermetically united directly with the quartz.

6. A seal-body comprising a quartz tube, a metalrod extending along'the interiorof'said tube and a, pair" of thin juxtaposed metal sheets around said rod one of which is hermetically united with said rod, the outer edges ofsaid sheets being in simple abutting contact with each other and hermetically united directly with said quartz.

7. A seal-body comprising a quartz tube, a tungsten 'rod extending through said tube, a painof' thin'juxta:

posed molybdenum sheets around said rod'and-hermetically united therewith, the outer edges of said sheets beingin' simple abutting contact witheach other and hermetically united directly on one side only withsaid quartz.

References Cited-in the file of this patent UNITED STATES PATENTS

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