US2876377A - Ribbon seal and method of fabrication - Google Patents

Description

March 3, 19 T. c. RETZER ET AL 2,

RIBBON SEAL. AND METHOD OF FABRICATION FiledSept. 1, 1955 14 .30 25 IJZ INVENTOM 44 48 Z4 44 7? c. Ear-2E2 Z4 44 flUUE/VEX 7 2,876,377 Patented Mar. 3, 1959 RIBBON SEAL AND METHOD OF FABRICATION Theodore C. Retzer, Cedar Grove, and Robert A. Gingras,

Preakuess, N. J., assignors to Westinghouse Electric 1 Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 1, 1955, Serial No. 531,883 6 Claims. Cl. 313-184 This invention relates to seals and, more particularly to ribbon-type seals for .high pressure gaseous discharge lamps, such as a quartz short are mercury lamp, and to .the method of protecting and maintaining the ribbon conductor in a desired preselected position within the stem portion of the lamp envelope during the sealing operation.

Seals capable of withstanding the high operating currents, temperatures, and pressures of mercury or xenon discharge lamps are generally fabricated by embedding an extremely thin leading-in ribbon conductor of refractory material, such as molybdenum, in a tubular quartz arm or stem tube which forms part of the lamp envelope. In order to'facilitate electrical connection with the electrode and-an external power supply connector strips of substantially greater thickness are usually attached to eachend'of the main ribbon conductor thereby forming'a ribbon leading-in conductor assembly.

Heretofore, the ribbon assembly was either inserted into the tubular stem portion of the lamp envelope or, if extremely high current carrying capacity was required, a plurality of ribbon assemblies were affixed to the outer surface of a quartz 'retaining body which was, then inserted into the stem tube. In either type of seal, after the ribbon assembly was inserted into the stem tube the end of the "tube was sealed to permit evacuation of the envelope whereupon the stem tube was rotated in a high temperature fire until the quartz became plastic and was drawn into intimate contact with the ribbon conductor assembly to form a hermetic seal. Moreover, in order to effect a more perfect bond between the quartz and the metal ribbon conductor it has been found'advantageous to gradually reduce the thickness of the ribbon extremities by a chemical etching process to form an extremely thin edge, or, as it is commonly referred to in the art, a feather edge. Due to the complexity of the type of seal required for high currents its use in the lower Wattage lamps is not practical from an economic standpoint. Hence, where relatively low current carrying capacity is required, as in the case of short are lamps of under 500 watts capacity, the ribbon conductor assembly is generally sealed directly into the tubular stem portion of the lamp envelope. It has been found, however, that when the main ribbon conductor, particularly one that has a feather edge, has been sealed in the stem tube in this manner the ribbon tends to become deformed or the edges become damaged when the stem tube is rotated during the sealing operation by virtue of the fact that the inner walls of the tube are considerably closer to the edges of the ribbon than to the flat surfaces thereof. This type of sealing assembly and method of fabrication has resulted in a large percentage of seals that leak, thereby causing high shrinkage in production or deleteriously affecting the useful life of the'lamp.

It is the principal objectof the invention, therefore, to avoid and overcome the foregoing and other difiiculties and objections to the prior art by providing a seal for 2 short are gaseous discharge lamps in which the' thin ribbon conductor is not deleteriously deformed or the feather edgesv thereof damaged as a result of the operations required to make the seal.

A further object is to provide a ribbon leading-in conductor and electrode supporting assembly which will permit the electrode and ribbon conductors to be properly positioned within the lamp envelope and;maintained in such position until the sealing operation has been completed.

Another object of the invention is to reduce'manufacturing costs and improve the performance of short are gaseous discharge lamps by providing a simple economic means of fabricating uniform ribbon-type seals of high quality. I

A still further object is to provide a method of fabricating and sealing a leading-in conductor and electrode supporting assembly within the stem portionof a short are gaseous discharge lamp without deforming the ribbon conductor or damaging the feather edge thereof.

The aforesaid objects of theinvention, and .other objects which will become apparent to those skilled: in the art asthe description proceeds, are achieved by enclosing the main ribbon conductor and a portion of the electrode in quartz members to form a laminous .core of substantially cylindrical configuration having such dimensions that'it makes a snug fit with the 'stemtube portion of thelamp envelope into which it is to be sealed. Specifically, the main ribbon conductor and electrode supporting assembly is so constructed that the. ribbon portion thereof may be interposed between the two halves of a bisected quartz rod'which halves are held in the proper position for insertion into the stem tube and are of substantially greater diameter than the width of the ribbon conductor so that the ribbon is totally enclosed and protected during the sealing operation.

For a better understanding of the invention reference should be had to the accompanying drawings, in which like numerals of reference indicate similar parts through out the several views, wherein:

Fig. 1 is a front elevational view of a quartz. short are gaseous discharge lamp employing the seal of this invention and showing the envelope and two stem portions with the completedseal therein as it would appear if viewed from the side and top, respectively;

Fig. 2 is an enlarged cross-sectional view taken along the line IIII of Fig. 1 in the direction of the arrows, showing the mainribbon conductor hermetically sealed within the stem portion of the completed lamp;

Fig. 3 is an enlarged cross-sectional view of the stem portion of the lamp envelope taken along the line III'IIl of Fig. 1, in the direction of the arrows, showingthe electrode with its metal foil Wrapping hermetically sealed within the stem of the; completed lamp;

Fig. 4 is a perspective view of the ribbon leading-in conductor and electrode supporting assembly just prior tofits insertion into the stem tube portion of the lamp envelope; v

Fig.1 5 is an exploded side view of the ribbon portion of the assembly showing the various. components and their relation to each other prior to their jointure to form one electrical unit;

Fig. 6 is a fragmentary cross-sectional view of a short are lamp at onestage of its fabrication showing the.

alongthe line VII-VII of Fig. 6, in thedirection' of' the arrows, "showing the relationship between the ribbon applicable to the manufacture of other types of high.

pressure-gaseous discharge lamps, the invention isusually employed in conjunction with the manufacture of short arc mercury discharge lamps and hence has-been so illus- H ribbon conductor and electrode supporting assembly of this-invention. As iswell known, short are lamps in general consist of an envelope of vitreous lighttransmitting materialhaving a high" melting point, such as quartz, and having a substantially spherical bulb portion a 12 and two oppositely disposed arms or stem tube portions 14of substantially equal length extending outwardly therefrom. Sealed within each of the stem tube portions 14 is a main ribbon conductor 26 one end of which is electrically connected to an elongated electrode 19 and the-other end of which is connected to a pair of terminal strips 32. A portion of each of the electrodes 19 is sealed in the stem portion 14 so'that the electrodes 19 are positioned in a predetermined spaced relation within the spherical bulb portion 12, which encloses a' suitable ionizable. medium such as mercury vapor or xenon gas. The electrodesl9 are preferably fabricatedfrom tungsten and may have tungsten coils 18 afiixed to their inner end portions which coils 18 may contain a small amount of efficient-electron emitting material, such as thorium, to facilitate starting of thearc discharge, as is well known in the art. The essence of this invention resides in the fabricationof the ribbon leading-in conductor and electrode supporting assembly and the manner in which it is positioned and sealed .within the stern portion 14 of. the lamp envelope. and these are hereinafter more fully described.

.As illustrated in the exploded view of the ribbon portion of the assembly shown in Fig. 5, a main ribbon conductor 2.6 of thin refractory material, such as molybdenum ribbon approximately 5.5 mm. wide and .0012" thick, is interposed between two relatively long terminal strips 32 of a suitable refractory metal which serve as external electrical connectors for the lamp 10. In order to facilitateconnection with a source of electrical power it has been found desirable to fabricate the terminal strips 32 from moly ribbon having a substantially greater thickness than the main ribbon conductor 26, as for example .00 To insure a strong electrical junction between the ribbon conductor 26: and terminal strips 32 during thelife of the lamp 10. it has been found advantageous toplace thin narrow. strips 44 of. a suitable metal foil (see Fig. 5), such as'nickel or platinum of approximately .0Ol,'.' -thickness, between the conductor 26 and each of the strips 32 to serve as a brazing agent. A more perfect bond between the quartz and edges of the main ribbon conductor 26 may be obtained and the overall quality and..-strength of the finishedseal improved by fabricating the ribbon conductor 26 from a molybdenum ribbon M4" wide. and approximately..0016 thickwhich ribbon is subsequently chemically etched until its maximum thickness is no greater than approximately .0012" and its outer edge ti are gradually reduced to extremely thin sections to form a wellknown feather edge. Although the current carrying capacity of a ribbon of these di.- mensions is limited to approximately. l0 amperes, increased current carrying capacity, as for example up to approximately 30 amperes, may be obtained by appropriately increasing the ribbon dimensions and forcecooling the, exposed portions of the moly terminal strips 32 to prevent the deleterious effect of oxidation which would yup-at the-highambient temperature conditions generated by a lamp of such wattage.

-- Superimposed over each of the terminal strips 32 and overlapping the end of the ribben conductor 26 are two retaining tabs 30 which may be fabricated from relatively short sections of resilient metal ribbon, such as molybdenum .004" thick. The end portions of the retaining tabs 30 which extend beyond the edge of the ribbon conductor 26 are bent at right angles to the plane containing the ribbon conductor 26 to form a pair of oppositely disposed end panels. In order to prevent cracks from occurring in the region of the juncture of the retaining tabs 30 and terminal strips 32 with the relatively thin main ribbon conductor 26 as a result of the ledge or sharp edges left exposed, a pair of protective strips or flaps 28 of refractory material, such as molybdenum .0006" in thickness, are provided and positioned so as to overlap the aforesaid connected members and form a sheath over the juncture formed therebetween. .The protective flaps 28 also insure a good electrical connection between the members by obviating a high resistance juncture which could cause the ribbon to burn through and lead to subsequent lampj failure and serve to shield the electrical connection between the main ribbon conductor 26 and terminal strips 32 from any strains which may arise as a result of the unequal expansion and contraction of the quartz and metal portions of the seal during the normal operation of the lamp 10.

The other end of the main ribbon conductor 26 is interposed between the ends of a pair of connector strips 22 of refractory metal,'such as molybdenum, which serves to connect the ribbon conductor 26-to the electrode 19. To facilitate electrical connection with the electrode 19 the connector strips 22 may be of substantially greater thickness than the ribbon conductor 26, as for example .004". A firm bond between said conduct0r26 and strips 22 may be obtained by inserting therebetween .two strips 44 of suitable metal foil to act as a brazing agent (see Fig. 5).- A pair of protective flaps 24 may be provided to' present a substantially smooth curved sealing surface overthe ledge formed by the juncture of the relatively thin ribbon conductor 26 with the connector strips 22 and to protect the electrical connection therebetween from excess strains during the heating and cooling of the completed seal. After the main ribbon conductor 26, terminal strips 32,-retaining tabs 30, connector strips 22, metal foil strips 44, and protective flaps 24 and 28 have been assembled as heretofore described, they are electrically joined together, such as by welding, to form the ribbon conductor member of the leading-in conductor and electrode supporting assembly which member is then ready for connection with theother-parts of the assembly as hereinafter described. 1 I

An elongated electrode 19 having a coil 18 of refractory 1 metal attached to its inner end portion is inserted into thereof up tothe coil 18 may be encased in a wrapping of refractory metal foil 16, such as molybdenum ribbon .0006 thick, to prevent cracks from occurring in the completed seal when the electrode 19 becomes heated and expands during the operation of the lamp 10. The

. free end portions of the connector strips 22 which extend beyond the end of the main conductor 26 are bent outwardly to form a V-shaped pocket into which the foil encased electrode tip 20 is inserted and electrically connected. .The terminal strips 32 are connected to a positioning tab. 42 by a rod 38 of refractory metal suchas molybdenum. For addedstrength the positioning tab 42 may consist of a pair of metal ribbons of unequal length welded together and affixed to each side of the rod 38. A pair of positioning clips 40, such as of arcuate retrovert'edmolybdenum strips for example, are attached to opposite sides of an intermediate portion of the rod 38 to .serve as compre ssible members to insure accurate positioning of the electrode and ribbon conductor assembly within the stem tube14. A pair of plano-cylindrical quartz rods 36 are formed by bisecting a quartz cylinder of the same diameter as the aforementioned quartz tube 34,'as for example A"; The rods 36 are inserted between the edges of the retaining tabs 30 and the quartz tubing 34'with their plane surfaces facing inwardly and are resiliently 'held in this position so that the main ribbon conductor 26 and its lapping end connections together with the'electrode tip 20 are totally enclosed to form a composite laminous'core member of substantially cylindrical configuration having one end of the electrode 19 and the terminal strips 32' and the associated electrode positioning elements attached thereto protruding from opposite ends thereof.

The cylindrical core member formed as hereinbefore described is then inserted into the tubular stem portion 1 4 of "the lamp envelope, as shown in Fig. 4. The core member and electrode supporting assembly are inserted into the tubular stem portion 14 until the positioning clips 40 'are forced into intimate contact with the inner surfaces of'the tubular portion 14 and upon further penetration are c'ompressed inwardly to frictionally engage the inner surfaces of the tube 14. This enables the assembly to be'a'ccurately positioned'within the stem tube portion 14 so that the electrodes 19 can be oriented in the desired preselected position within the spherical bulb portion 12. After the electrodes 19 are properly positioned, the positioning tab'42 is sealed in the tube portion 14 to anchor the inserted core member and associated elements in their respective positions and to seal off the envelope for evacuation by heating the end of the stem tube portion 14 to plasticity and forming an air tight seal 45 around the tab 42, as shown in Fig. 6. At this stage of the fabrication of the seal the main ribbon conductor 26 is interposed between the plane surfaces of the rods 36 of semi-hemispherical cross-section which rods 36 are, in turn, {completely enclosed by the walls of the tubular stern portion 14, as shown in Fig. 7.

-The spherical bulb portion 12 and tubular stem portions 14 of the lamp envelope are now evacuated through an exhausttubulation 15 having a constriction 13 formed th'erein'adjacent to the spherical bulb portion 12. After the envelope has been evacuated to the desired pressure, as for example .001 mm. of mercury, the exhaust tubulation' 15 is sealed off at a point beyond the constriction 13 by suitable sealing fires (not shown). The outer end portion of the stem tube 14 is then held and rotated, as in a rotatable chuck for example (not shown), while a high temperature flame (also not shown) is directed to the region of the stern portion 14 adjacent to the outermost edge of the semi-cylindrical rods 36, as viewed in Fig. 6 until the quartz becomes plastic and the wall portion of thefstern 14 thereat is forced inwardly by atmospheric pressure and fuses with the rods 36 to form' a solid mass. The tubular stem portion 14 is constantly rotated and the high temperature sealing fires progressively advanced inwardly toward the spherical bulb portion 12, as viewed in Fig. 6, until the neck portion of the envelope between the tube portion 14 and spherical portion 12 is reached. The

main ribbon conductor 26 and outer end portion of the electrode 19 are thus sealed'in a solid cylinder of fused quartz,as shown in Figs. 2 and 3, Due to the vacuum within'the envelope the quartz tube 34, semi-cylindrical rods 36, and'the walls of the stem tube 14 are drawn into' intimate contact with the metal portions of the core memberwhen the quartz is in a plastic state. This permits a uniform high strength seal to be formed and the use of the quartz tube 34 and semi-cylindrical rods 36 as core members prevenfthe main conductor 26 from being deleteriously deformed or damaged during the sealing operation.

After the seal has been completed as hereinbefore described, the tip (not shown); previously formed on the exhaust tube 15 is broken and the envelope filled with a predetermined amount of mercury or suitable ionizable gas, such as xenon, and the exhausttube 15 tipped-off by suitable fires at the constriction 13 to form a seal tip 11. The outer end portion of the stem 14 beyond the region of the seal is then cut off by a wet cutting wheel 46, as shown in Fig. 6, care being exercised to prevent cutting of theterminal strips 32. After'the cutting operation has been completed 'the terminal strips 32 are severed at a point adjacent to the end of the rod 38 thereby com pleting the fabrication of the'larnp.

It will be recognized from the foregoing that a simple but most effective means of protecting a ribbon conductor andits edges from deformation and damage during the sealing operation necessary to embed it within the stem tube portion of a gaseous discharge lamp has been provided. Moreover, this is accomplished by providing a quartz tube and a pair' of semi-cylindrical rods resiliently held in an abutting relation tototally enclose the main ribbon portion and end portion of the electrode and form a cylindrical core member to protect the ribbon assembly and maintain the electrode in the proper position during sealing.

Although a preferred embodiment of the invention has been illustrated,it will'be understood that other modifications may be made without departing from the spirit and scope of the appended claims.

We claim:

1. A gaseous discharge lamp comprising an envelope having a bulb .portionand outwardly extending fused sternportions, an ionizable medium enclosed within said envelope, and ribbon leading-in conductor and electrode assemblies sealed through each of said stern portions, each of said assemblies comprising a main ribbon conductor of thin refractory material-having its outer end portion interposed between and fastened to a plurality of paired metallic strips arranged in overlapping relation therewith, at least one pair of said strips extending longitudinally of said main conductor to serve as external connectors and another pair of said strips adapted to serve'as retaining members, an elongated electrode having an end adapted for connectionwith said main conductor, a wrapping of metal foil'around said electrode end, and asecondplurality of paired and overlapping metal strips'joining the said foil enwrapped end of said electrode with the end of said main conductor opposite the first said plurality of strips, said assemblies being centrally embedded andhermetically sealed within said fused stem portions and longitudinally positioned therein so that the end sections of the said longitudinally-extending strips protrude fromthe stems-and the free ends of the electrodes project into the bulb portion of the envelope in predetermined spaced apart relation.

2. A short arc gaseous discharge lamp comprising a light-transmitting envelope having a spherical bulb portion with two oppositely disposed arms extending outwardly therefrom,'an' ionizable medium enclosed within saidenvelope, and ribbon leading-in conductor and electrode assemblies sealed through each of said arms, each of said assemblies comprising a main ribbon conductor having its outer end portioninterposed between and fastened to three pairs of refractory metal strips arranged in smooth sealing surface, an elongated electrode having one end shaped to form a flat wedge-shaped tip, a wrapping of metal foil around said flattened end portion and 'adjacent body portion of said'electrode, anda second group of paired refractory metal strips comprising an inner pair of strips of substantially greater thickness than said main conductor attached to the end of said main conductor opposite the first said group of strips and connected to the said foil enwrapped end of the electrdoe in enveloping relation therewith, and an outer pair of strips proportioned and disposed to cover the juncture between the main conductor and said inner pair of strips, said main ribbon conductonhaving extremely thin tapered edges and said assemblies being centrally embedded and hermetically sealed within each of said arms and of sufficient length that the end sections of the said longitudinally-extending strips protrude from the arms and the free ends of the electrodes project into the spherical bulb portion of the envelope in opposite and predetermined spaced apart relation. I

3. An electrically-conductive ribbon type seal for a gaseous discharge lamp having an envelope with a bulb portion and a fused tubular stem portion comprising a main leading-in conductor of refractory metal ribbon having extremely thin tapered edges, an elongated electrode having a flattened end portion adapted for connection with said main conductor, a wrapping of metal foil around said flattened end portion and adjacent body portion of said electrode, a pair of metal connector strips fastened to one end of said main conductor and the flattened foilenwrapped end of said electrode, said main conductor and electrode ends being interposed between said connector strips in overlapping relation therewith, the other end of said main conductor being interposed between and connected to a plurality of paired metal strips arranged in overlapping relation, at least one pair of said strips extending longitudinally of said main conductor to serve as external connectors and another pair of said strips being adapted to serve as retaining members, and thin metal flaps covering the junctures between said strips and main conductor to provide a smooth sealing surface, said connector and longitudinally-extending strips being substantially greater in thickness than said main conductor, and said conjoined main ribbon conductor, strips and foil enwrapped portion of said electrode being centrally embedded and hermetically sealed within said fused stern portion and of suflicient length that the said longitudinallyextending strips protrude from the end of said stem portion and the free end of the electrode projects into the bulb portion of the envelope in predetermined spaced apart relation with the walls thereof.

4. A ribbon leading-in conductor and electrode assembly for sealing into the tubular stem portion of a gaseous discharge lamp comprising a main ribbon conductor of refractory metal, an elongated electrode having a fiattened end portion and an enlarged opposite end portion, a wrapping of metal foil around the flattened end portion and intermediate body portion of said electrode adjoining said enlarged end portion, a section of vitreous tubing carried by the foil-enwrapped intermediate portion of said electrode, said tubing being seated against the enlarged portion of said electrode and of such length that the flattened end portion of the electrode protrudes therefrom, means connecting one end of said main ribbon conductor with the said protruding electrode end portion, the other end of said main conductor being interposed between and connected to a plurality of metal strips adapted to provide a longitudinally extending terminal and a pairof oppositely disposed retaining members, a pair of matching lano-cylindrical vitreous rods longitudinally inserted between said retaining members and the edge surfaces of said tubing, said rods being positioned so that their plane surfaces face inwardly toward each other, to totally enclose and protect said main rib- 8 r bon conductor and form a'composite laminous core mem ber of substantially cylindrical configuration adapted to be received by said tubular stem portion.

5. A ribbon leading-in conductor and electrode supporting assembly for sealing into the tubular quartz arm of a short are lamp comprising a main ribbon conductor of molybdenum having extremely thin tapered edges, an elongated electrode having a flattened end portion and a coil mounted at its opposite end portion, a wrapping of metal foil around the flattened end portion and intermediate body portion of said electrode adjoining said coil, 2. section of heavy-Wall quartz tubing surrounding oppositely disposed and transversely projecting resilient end panels, a pair of matching plano-cylindrical quartz rods longitudinally inserted between said end panels and the edge surfaces of said tubing, said rods having substantially the same outer curvature as said tubing and being positioned so that their plane surfaces face inwardly toward each other to totally enclose and protect said main ribbon conductor and form a composite laminous core member of substantially uniform cylindrical configuration adapted to be received by the tubular arm of said lamp, and means attached to said terminal strips for longitudinally positioning said core member within said arm including compressible members operable to frictionally engage the inner wall surfaces of said arm and maintain said member in its assembled position during the sealing-in operation.

6. The method of fabricating and sealing a ribbon leading-in conductor and electrode assembly within the tubular stem portion of a gaseous discharge lamp envelope comprising, providing an elongated electrode having an enlarged body portion and a flattened end portion, wrapping-said flattened end portion and adjacent part of said electrode adjoining the said enlarged body portion in metal foil, inserting the foil-enwrapped portion of the electrode into a section of vitreous tubing of such length that the flattened end portion of the electrode protudes therefrom when said tubing is seated against the said enlarged body portion, seating said tubing against said enlarged body portion, connecting the protruding flattened end portion of said electrode with a refractory metal ribbon, aflixing a plurality of metal strips to the end of said ribbon opposite said electrode to provide a longitudinally extending terminal connector and a pair of oppositely disposed transverse members, placing a pair of matching plano-cylindrical vitreous rodsbetween said transverse members and the edge surfaces of said tubing to enclose said metal ribbon and adjoining portions of said electrode and metal strips and thus form a composite laminous core member of substantially uniform cylindrical configuration, attaching an elongated positioning member having intermediate compressible extensions to the free end portion of said terminal connector, inserting said electrode and conjoined core member into the tubular stem portion until said extensions frictionally engage the inner wall surfaces of said stern, orienting said core member and electrode in predetermined longitudinal relation with said stem portionby means of said positioning member, sealing the end of said stem portion over said positioning member,

evacuating said .envelope and progressively heating the section of said stem occupied by said core member until the tube walls collapse and fuse with the vitreous tubing and rod portions of said core member to hermetically seal the refractory metal ribbon and foil enwrapped section of the electrode in said stem portion, and thereafter separately severing said stern and terminal connector at difierent points remote from the fused outer end portion of said stem.

References Cited in the file of this patent UNITED STATES PATENTS Kettlewell Mar. 30, 1948 Wiener Dec. 29, 1953 Freeman Feb. 23, 1954 Unglert Apr. 13, 1954 Hodge Mar. 29, 1955

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