US3502932A - Incandescent lamp and method of manufacture - Google Patents

Description

, I. BERLEC Mar ch 24, 1916 INQANDESCENT LAIIP AND METHOD OF MANUFACTURE med Oct. 2. 19s? lnventov Ivan BeT'Lec by M l-hsA t t-ore United States Patent O 3,502,932 INCANDESCENT LAMP AND METHOD OF MANUFACTURE Ivan Berlec, Wicklifie, Ohio, assignor to' General Electric Company, a corporation of New York Filed Oct. 2, 1967, Ser. No. 672,276

Int. Cl. H01k 1/28 I US. Cl. 313315 2 Claims ABSTRACT OF THE DISCLOSURE In the manufacture of quartz incandescent lamps having integral end portions of the tungsten filament hermetically sealed through the quartz envelope, refractory metal leadin wires or pins are first secured to terminal end portions of the filament which is then inserted into the quartz envelope with an end portion of the filament confined within an open end portion of the envelope and the associated lead-in wire extending to the exterior, the said open end portion of the envelope is then heated above its softening point and the said end portion of the filament is also heated while maintaining an inert gas atmosphere around the filament to outgas the surface thereof, and said end of the envelope is then compressed to form a hermetic seal with the said end portion of the filament while simultaneously embedding, although not hermetically sealing, the inner end of the lead-in wire and the terminal portion of the filament which is connected thereto, thereby anchoring the lead-in 'wire in the seal and providing a nonincandescible current supply conductor which also serves as a heatsink for the said terminal portion of the filament which is not hermetically sealed.

BACKGROUND OF THE INVENTION Field of the invention The invention relates generally to electric incandescent lamps and more particularly to tungsten filament incandescent lamps having envelopes of essentially fused silica or quartz glass. Still more particularly, the invention relates to the construction and manufacture of a hermetic seal and current supply connection to the filament.

DESCRIPTION OF THE PRIOR ART Although not necessarily limited thereto, the invention has particular application to, and will be described with reference to, incandescent lamps of the halogen regenerative cycle type wherein a tungsten filament is hermetically sealed in a compact envelope of fused silica which is heated to a relatively high temperature during operation, and which contains an inert gas filling together with a small quantity of a halogen, particularly iodine or bromine or compounds thereof. During operation of the lamp, tungsten vaporized from the filament and normally deposited as a dark film on the envelope walls, reacts with the halogen to form a compound which migrates back to the vicinity of the filament where it is broken down to release the tungsten which is redeposited on the filament, and to also release the halogen which is then free to repeat the cyclic reaction.

In view of the very low coefiicient of expansion of fused silica or quartz, the provision of a hermetic seal of the current lead-in conductors requires the use of a molybdenum foil of small dimensional tolerances in order to obtain a tight hermetic seal in the quartz and to provide the necessary current carrying capacity. In some cases, the foil is a separate piece of ribbon having a lead wire welded to each end thereof, one wire extending to the exterior of the lamp envelope and the other to the interior where it is connected to one end of the filament. In other cases,

3,502,932 Patented Mar. 24, 1970 the foil is a rolled portion of a molybdenum wire. In either case, the foil is a relatively costly part of the lamp. Such foil type structures are used in lamps of the double-ended type wherein a tubular quartz envelope contains an axially extending filament and has pinch seals at respective ends thereof in which are hermetically sealed a foil and lead wires connected to respective ends of the filament. Such seals are also used in lamps of the single-ended type wherein the quartz envelope has a pinch seal at one end thereof through which are sealed both of the foil type lead-in structures at respective ends of the filament.

A construction and manufacture of lamps wherein the foil is eliminated is disclosed and claimed in applications Ser. No. 601,930 to R. C. Millikan, now Patent No. 3,448,320, and Ser. No. 601,927 to R. C. Millikan and L. A. Osburg, now Patent No. 3,448,322, both filed Dec. 15, 1966, and the disclosures of which are incorporated herein by reference. In accordance therewith, seals are made directly between portions of the incandescent filament and the quartz envelope by keeping the diameter of the tungsten filament wire at a value less than 0.004 inch, by outgassing the filament wire prior to and during scaling to preclude the presence of any adsorbed gas and by continuously flushing the filament and the quartz during scaling to preclude the presence of any molecular or gaseous impurities evolved from either during heating to be interposed between the quartz and the clean oxide-free tungsten filament in the final seal. After the quartz has been collapsed or shrunk directly over end portions of the filament, the terminals or lead-in wires are attached externally by a brazing technique.

It may be here noted that in some cases in the past, the ends of the coiled tungsten filament in tubular lamps have been pulled out to form straightened leg portions which extended into the pinch seals at respective ends of the quartz lamp envelope where they were welded to foil portions of lead-in conductors. In such cases, the said foil portions constituted the usual hermetic: seal with the quartz. Therefore, no attempt was made in such cases to hermetically seal the embedded portion of the filament, nor was a hermetic seal obtained inasmuch as the filament wire was usually of too large a diameter and, moreover, no particular precautions were taken to insure a hermetic seal in accordance with the disclosure of the aforesaid copending applications of Millikan, and Millikan et al. Actually, the straightened filament leg structure was employed in some cases to provide an internal fuse elfect, as in Patent 3,211,942 to E. H. Wiley, or in some cases simply as an economy measure whereby the usual relatively heavy inner lead-in wire could be eliminated because the coiled filament was otherwise adequately supported.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved construction and method of assembly of the direct filament seal which will retain the advantages associated with elimination of the foil but which will also eliminate the problem of attaching the lead-in conductors externally to the sealed-in filament.

In accordance with the invention, the objects are achieved by preliminarily forming an assembly of the filament with lead-in conductors of refractory metal and of materially greater cross sectional area than the filament connected electrically andphysically to respective terminal end portions of the filament. The filament is then disposed in the quartz envelope which has a portion thereof softened and compressed and hermetically sealed directly to an end portion of the filament andalso compressed about, although not hermetically sealed to, the interconnected terminal end portion of the filament and the associated inner end of the lead-in conductor, so that the said terminal end portion of the filament which extends beyond the hermetically sealed portion thereof serves, together with the lead-in conductor, as a current supply member, and the lead-in conductor serves as a heat sink to prevent destructive overheating of the said terminal end portion of the filament upon flow of current therethrough.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the drawing is an elevation of an electric incandescent lamp comprising the invention;

FIG. 2 is an elevation, partly in section and on an enlarged scale, illustrating the assembly and manufacture of a lamp in accordance with a preferred embodiment of the invention;

FIG. 3 is a fragmentary elevation, at a still more greatly enlarged scale, of one end of the lamp and having a slight modification of the lead-in conductor; and

FIG. 4 is an elevation of a light source wherein the lamp unit of FIG. 1 is enclosed in an outer bulb.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, the lamp illustrated therein is of the tubular double-ended type comprising a cylindrical envelope 1 of essentially fused silica which may be a vitreous quartz or a material sometimes referred to as 96% silica glass or Vycor, and which has a pinch seal portion 2 at each end thereof. The envelope 1 contains a tungsten wire filament herein illustrated as a helically coiled-coil 3 extending axially of the envelope. The ends of the coiled filament 3 are stretched out to form end legs 4 of quite open pitch which extend into and are hermetically sealed in the respective pinch seals 2. The stretched out turns should be sufficiently apart so that softened quartz can readily be compressed between them, but need not be straightened out. Some springiness is beneficial to accommodate the thermal expansion.

The extremities or terminal end portions 5 of the legs 4 are electrically and physically connected, preferably by welding, to inner end portions of respective lead-in conductors 6 which are, together with terminal portions 5 of the filament, also embedded in the pinch seals 2 although not hermetically sealed therein because of their relatively large size and diiferent coefficient of expansion than that of quartz.

The lead-in conductors -6 are of refractory metal, preferably molybdenum, having a melt-ing point above the softening point of the quartz envelope and having a materially greater cross section-a1 area than the filament wire. Other refractory metals which might be used for the lead-in wires include tungsten, tantalum and platinum or alloys thereof. The said lead wires 6 may be of simple pinlike form although, if desired, the inner ends may be somewhat flattened as shown .at 7 in FIG. 3, for ease of welding and to provide a lateral deformation which may be used to more securely anchor the lead wire in the seal. The said end 7 is not flattened to a degree even approaching the extremely thin dimensions required to form a hermetic seal with the quartz. The hermetic seal is formed between the quartz and the embedded portion of tungsten filament leg 4 located between the inner end wall 8 (FIG. 3) of the pinch seal and the edge 9 of the lead-in wire 6.

The terminal end portion 5 of the tungsten filament wire which is connected to lead wire 6 and which is therefore not hermetically sea-led in the pinch seal 2 due to the relatively large size of the associated lead wire 6, is nevertheless protected 'from destructive overheating by virtue of the heat sink effect of the lead wire 6 which extends exteriorly of the pinch seal 2 as a nonincand-escible current supply terminal for the incandescible filament 3.

'By way of specific example, the tungsten filament wire size of not greater than 0.004 inch diameter is compatible with the manufacture of a lamp of 100-watt size for operation at about 120 volts and which has a tungsten filament wire of about 0.0025 inch diameter. In such a lamp of the form shown in FIG. 1, the main coiled-coil body portion of the filament 3 may be about inch long. The quartz envelope 1 may be of approximately inch outside diameter, and may be filled with an inert gas such as nitrogen, argon, krypton or xenon or mixtures thereof, and a small quantity of halogen such as iodine or a bromine compound such as hydrogen bromide or a hydrocarbon compound of bromine.

The lamp filament and envelope may be assembled and sealed together on equipment similar to that, for example, shown in Patent 2,855,265 to Foote et a1. As shown in FIG. 2, the envelope 1 may be supported in this case by a quartz exhaust tube 10 which extends laterally from the midpoint thereof and is, in turn, supported in a chuck member 11 which is mounted for vertical adjustment and for rotation about its axis, and is connected to a supply of inert gas.

The previously prepared assembly of filament 3 and rigid molybdenum lead wires 6 is threaded into the envelope 1 and is supported by a cap member 12 which has an axial bore in which the upper lead wire 6 is received and held by a screw 13. The cap 12 has a reduced lower end portion 14 which fits the interior of the envelope 1 so that the cap 12 rests on the upper end of the envelope and effectively closes it off. The lower lead wire 6 is pulled down to slightly stretch the coiled filament 3 and to insert the said lower lead wire 6 in an axial bore 15 in a chuck 16 and is held therein in any suitable manner, for example by the lateral end portion of a spring-loaded finger member 17 which is located in a cavity in the chuck 16 in a position to be retracted from or permitted to press against the lead wire 6 in cavity 15, all as more fully explained in the aforesaid Patent 2,855,265.

A flow of inert gas, such as argon, is then started through the chuck 11, exhaust tube 10 and lamp envelope 1 to purge the envelope of air and-provide a protective nonoxidizing atmosphere about the metallic filament 3 and lead wires 6, the gas escaping through the slight space between the lower end of envelope 1 and upper surface of chuck 16. The-argon gas line may be at a pressure of about 3 /2 pounds per square inch, for example, in making a lamp of the l00watt size referred to above. The lower end of the envelope 1 is then intensely heated by a pair of burners (not shown) to a temperature above the softening point of the quartz envelope. The lower end or leg portion 4 of the filament is heated to white heat (between about 17502200 C.) by radiation and conduction and convection of heat from the intensely hot envelope which also highly heats the gas flowing through the envelope, so that the said filament leg is kept clean and free of oxide and adsorbed gases.

The plastic lower end of the envelope 1 is then pinched by a suitable pair of jaws (not shown) to flatten it and hermetically seal therein the lower filament leg 4 and to also embed therein the inner (upper) end of the lower lead wire 6 and the attached extremity or terminal end 5 of the filament leg. The pinch seal 2 may be a simple flattened area or, as indicated in FIGS. 1 and 3, it may be of known I-shaped cross section. Immediately upon pinching of the envelope, a flow of nitrogen gas may be started through a passage 18 in chuck 16 and directed at the exposed end of lower lead 6 to protect it from oxidizing.

The envelope 1 and the chuck 11 are then raised, the cap 12 is removed, the envelope 1 and chuck 11 are rotated 180 degrees to invert the envelope while continuing the flow of argon gas therethrough. The assembly is then lowered, the then lowermost lead wire 6 is engaged in chuck 16, and the fusing and pinch sealing operation is repeated.

Subsequently, the envelope 1 may be exhausted, and the final fill gas and halogen added in known manner through the exhaust tube 10 which is then tipped off or sealed as shown in FIG. 1. In the particular l00-watt lamp described hereinbefore, the gas filling may be krypton at a pressure between about 2000 and 5000 torr with about 5-20% nitrogen added to avoid arcing across the filament when lighted, and a small amount of iodine may be added as described and claimed in Patent 2,883,571 to Fridrich and Wiley.

The lamp shown in FIG. 1 may be provided with bases at respective ends thereof, for example as shown in Patent 3,001,096 to F. A. Mosby.

However, the lamp of FIG. 1 may also be mounted within an outer bulb in place of the simple filament of conventional incandescent lamps to provide a lamp of exceptionally high efiiciency and maintenance of light output for a long, useful life. Such a lamp is shown in FIG. 4 where, by way of example, the lamp unit 1 of FIG. 1 has its lead wires 6 secured to respectively long and short rigid lead wires 20 and 21 which have portions thereof hermetically sealed in the pressed seal portion 22 of a glass stem 23 which has its lower flared end sealed to a glass bulb 24 which may be evacuated and filled with inert gas, such as nitrogen, through a conventional exhaust tube 25. The enclosure of the lamp unit 1 in the outer bulb 24 has the additional advantage that the presence of the nonoxidizing gas filling in bulb 24 avoids the necessity of taking any precautions to avoid oxidation of the lead wires 6 and terminal end portions 5 of the filament 3. It will be understood that in the finished lamp the bulb 24 is provided with a base (not shown) such as the conventional screw base for insertion in a conventional socket.

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

1. An incandescent electric lamp comprising a hermetically sealed envelope of essentially fused silica, an incandescible filament of tungsten wire of a diameter not greater than about 0.004 inch supported within said envelope and having a unitary integral seal portion at each end thereof with a clean elemental tungsten surface extending into and hermetically sealed directly to and terminating within a compressed seal portion of the envelope, a refractory metal lead-in conductor of materially greater cross-sectional area than the filament wire and having an inner end electrically and physically connected directly to a terminal portion of each said end portion of the filament which is firmly embedded together with said inner end of the conductor directly in the seal portion of the envelope without being hermetically sealed therein and which extends as a current conductor beyond the hermetically sealed portion thereof,

said seal portions at the ends of the filament being the sole hermetic seals for respective ends of the filament and associated lead-in conductors, said lead-in conductor serving as a heat sink for the filament terminal portion connected thereto and emerging exteriorly of said compressed seal portion of the envelope as a nonincandescible current supply terminal.

2. In the manufacture of an incandescent lamp comprising a hermetically sealed envelope of essentially fused silica and an incandescible filament of tungsten wire of a diameter not greater than about 0.004 inch supported within said envelope and having a portion at each end thereof hermetically sealed directly to and within a com pressed seal portion of the envelope, the method which comprises preliminarily connecting a terminal portion at each end of said filament electrically and physically di rectly to the inner ends of respective refractory metal lead-in conductors of materially greater cross-sectional area than. the filament wire, disposing the filament within the envelope with an extended end thereof confined within an open end portion of the envelope along with the associated inner end of the lead-in conductor which also extends exteriorly of the envelope, heating the said end portion of the envelope above the softening point thereof and simultaneously heating the confined extended end of the filament while maintaining an inert gas atmosphere around the filament to outgas the surface thereof and maintain it free of oxide, and compressing the said end portion of the envelope to form a hermetic seal solely with the heated extended end of the filament and to embed and anchor therein the inner end portion of the lead-in conductor along with the associated terminal portion of the filament which is connected thereto.

References Cited UNITED STATES PATENTS 2,276,218 3/1942 Lemmens 313-318 X 2,855,265 10/1958 Foote et al. 316-31 3,270,238 8/1966 Mosby 313-315 X JAMES W. LAWRENCE, Primary Examiner R. F. HOSSFELD, Assistant Examiner US. Cl. X.R.

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