GB2067832A - Unplated Copper Leads for Gas- filled Incandescent Lamps - Google Patents

Abstract

An incandescent lamp having unplated copper inner lead wires 13, 14, for mechanically supporting and electrically connecting a filament 12 has an aluminum-zirconium getter 30 applied to the lead wires in the vicinity of the lead wire filament clamps 25, 26. Dispersion-strengthened copper wires are preferably employed. <IMAGE>

Description

SPECIFICATION Unplated Copper Leads for Gas-filled Incandescent Lamps This invention relates to gas-filled incandescent lamps and more particularly to gasfilled incandescent lamps having unplated copper inner lead wires and an aluminum and zirconium getter material applied thereto for cleansing the lamp atmosphere of deleterious gases which otherwise erode and contaminate the filament.

Incandescent lamps generally comprise an envelope having a stem sealed therein. A filament is electrically connected and mechanically supported by lead wires which are embedded in and extend through the stem to permit external electrical connection of the filament. The lead wires are required to have a high conductivity while providing sufficient rigidity to adequately support the filament. Medium and low wattage gas-filled incandescent lamps generally employ suitable fuse or copper wires from the metal base to the glass stem press, composite wires or dumet in the stem press and nickel plated copper wire from the stem press to the filament. The Dumet composite wire within the stem press consists of a nickel iron core enclosed in a copper sleeve and has substantially the same coefficient of expansion as the glass in the stem press of the lamp and enables hermetic sealing therebetween.

The inner filament lead wires, those between the stem press and the filament, are exposed to the lamp atmosphere and accordingly can directly affect the operation of the filament. Also the inner lead wires should be of a material which exhibits substantial rigidity to support the filament and high electrical conductivity. Inner lead wires have generally been nickel, nickel-plated iron, nickelplated copper or molybdenum. In particular, these metals are less susceptible to oxidation and, accordingly, do not introduce contaminants into the lamp envelope. However, nickel and nickelplated iron lead wires do adversely affect lamp operation inasmuch as the nickel migrates into the tungsten filament and embrittles it causing early lamp failure by fracture of the filament near the filament clamp.

Bare copper wires have heretofore not been used within gas-filled incandescent lamps inasmuch as, during the sealing of the lead wire within the stem press, the lead wire is subjected to a high heat and, accordingly, the copper is oxidized forming a copper oxide coating thereon.

Generally, a gas-filled lamp contains a small percentage of hydrogen or hydrogen compounds which reduces the copper oxide and forms water vapor which activates the weli-known water cycle wherein tungsten is transported from the hot filament and deposited on the cooler envelope wall. The water cycle shortens the lamp life by eroding the filament and additionally decreases the light output of the lamp by blackening the envelope wall. In the prior art, copper inner lead wires have been plated, with for instance nickel, to prevent oxidation of the copper during both lamp manufacture and operation. Small amounts of nickel oxide which are produced are less susceptible to reduction by free hydrogen gas.

However, nickel plating creates other problems within the lamp.

The present invention utilizes exposed copper lead wires within the lamp with an aluminum zirconium getter which is applied to the inner lead wires in the vicinity of the filament clamps for the sorption of gases which detrimentally affect operation of the incandescent lamp and more particularly for the sorption of water vapor. The getter material is generally comprised of aluminum and zirconium powders which are 18% and 82% by weight respectively, suspended in an amyl acetate and nitro-cellulose binder and applied to the lamp lead wires in the vicinity of the filament clamps. In one embodiment, an approximately 10 mil thickness of getter material is applied to the lead wires. Both the aluminum and the zirconium are activated by the relatively high temperatures produced by the filament.

Generally the aluminum acts as a chemical getter which forms aluminum oxide with oxygen or water vapor within the lamp atmosphere.

Zirconium is a solution getter wherein a gas impurity is adsorbed to the surface of the getter and later diffuses inward forming a solid solution within the getter material. Accordingly, the zirconium getter has an extended period of operation and is particularly good for eliminating oxygen and hydrogen from the lamp atmosphere.

The getter materials are applied to the lead wires before the stem is sealed within the lamp envelope and, accordingly, the binder materials are evaporated from the lead wires by the heat of lamp manufacture, further reducing the possibility of lamp contamination.

The aluminum-zirconium getter of the present invention enables the use of plated copper lead wires in gas-filled incandescent lamps. These getter materials also enable the use of copper lead wires which have been dispersion strengthened to rigidly withstand the press seal temperatures necessary to form hermetic seals between the lead wires and the stem press.

Accordingly, the present invention provides for the practical application of substantially rigid unplated copper lead wires within an incandescent lamp envelope and thereby eliminates the need for additional filament and lead wire supports.

The present invention will be further described by way of example only, with reference to the accompanying drawings, in which the figure illustrates an incandescent lamp in accordance with the present invention.

Referring to the Figure of the drawings, the lamp illustrated therein comprises a sealed glass bulb 11 containing a filament 12, preferably of tungsten, which is clamped by and electrically connected to the inner ends of the lead wires 1 3 and 14 which hermetically extend through the glass stem 1 5 which is also hermetically sealed to and extends inwardly from the neck portion 1 7 of the bulb 11. The hermetic envelope 11 is gas filled through an exhaust tube 18 which extends through the stem 1 5. The exhaust tube 1 8 is tipped off in an hermetic seal 19 after the appropriate lamp atmosphere such as an inert gas, usually a mixture or argon and nitrogen, in introduced into the lamp envelope 11.These fill gases inhibit tungsten evaporation and allow higher temperature operation of the filament.

For the sake of simplicity the lamp 10 is illustrated as a single filament lamp having two contacts or terminais. The lamp envelope 11 is cemented to a base 20 which is provided with an appropriate number of terminals for externally connecting the lead wires 13 and 14. More particularly, lead wire 13 is connected to the shell of the base 20 while lead wire 14 is connected to a base eyelet 21 which is insulated from the shell.

In the manufacture of the lamp 10, one of the more difficult processes is sealing the lead wires 13 and 14 through the glass stem 5. Lead wires 1 3 and 14 generally include section of composite wire such as Dumet which is sealed within the stem press 22.

The inner ends 25 and 26 of the lead wires 13 and 14 are respectively crimped or clamped around the legs 27 and 28 of the tungsten filament 12 and hold the filament 12 in structural and electrical connection between the lead wires.

The filament 12 may be a single wire, coiled, coiled-coil or triple coil filament with the lead wires 13 and 14 clamped to the uncoiled wire, or the first, second or third coiling.

At the heart of this invention is the use of improved lead wires as taught in U.S. patent 4,131,819,4,138,623 and 4,208,603. The first of these references teaches the use of lead wires having a particular stiffness; the second teaches the use of dispersion-strengthened copper for the inner and outer leads in an electric lamp; the third application suggests the use of dispersionstrengthened copper which is devoid of an exterior copper matrix metal, more commonly referred to as sheath less dispersion-strengthened copper. All the above lead wires are nickel plated in a manner well-known in the art to inhibit oxide contamination of the lamp.A combined summary of these applications teach that stiff lead wires eliminate the need for tie and support wires anchored to a glass button within a lamp; dispersion-strengthened copper is a desirable stiff lead wire which must be nickel plated to prevent contamination of the lamp atmosphere; sheath less dispersion-strengthened copper is also a stiff lead wire which additionally enables an improved bond between the nickel plating and the copper lead wire to further reduce the possibility of oxide contamination of the lamp and nickel migration into the tungsten filament.

In contrast, the present invention teaches the eiimination of the nickel plating to thereby completely avoid the problem of nickel migration and embrittlement of the tungsten filament by teaching the use of plated copper lead wire in combination with an aluminum-zirconium getter in the vicinity of the tungsten filament.

Copper oxide is formed on the unplated copper lead wires during processing and handling. This copper oxide can be reduced, by for instance hydrogen gas which may be present within the lamp envelope either as an impurity or as a fill gas, and forms water vapor within the lamp. As known in the art, water vapor attacks and erodes the tungsten filament by the well-known water cycle exemplified by the below reaction.

At the hot filament W+H20oW0x+H At the bulb wall Wox+HoW+H2O where W represents the tungsten component inasmuch as the exact types of tungsten oxides formed are not known.

The present invention provides an aluminum and zirconium getter 30 which is applied to each of the lead wires 13 and 14 in an appropriate thickness such as an approximately 10 mils thickness in the vicinity of the lead wire clamps 25 and 26. Aluminum readily forms aluminum oxide with either water vapor or free oxygen and accordingly is a practical reagent for extracting or gettering free oxygen and water vapor from the lamp atmosphere.

Zirconium on the other hand reacts with oxygen and hydrogen, not by forming an oxide coating on the surface thereof, but by a surface adsorption of the gases with a subsequent migration or absorption of the gas within the zirconium particle. Accordingly, zirconium is a long life or continuous getter which cleanses the lamp atmosphere continually during its operation.

In a preferred embodiment aluminum and zirconium metallic particles or flakes are mixed with a binder such as amyl acetate and nitrocellulose and form a getter material which is subsequently applied to lead wires in the vicinity of the filament clamps. Getter application is made before the lamp mount is sealed within the bulb envelope and, accordingly, the suspending and binder materials (amyl acetate and nitrocellulose) are sufficiently dissipated such that they do not contribute to contamination of the lamp atmosphere.

As above-described, aluminum and zirconium getter contaminants within the lamp and sufficient quantities of each should be provided to counterbalance the oxide formed on the copper lead wires 13 and 14 where they exit the stem press 22 and other possible contaminants within the lamp. The getter metal particles are mixed with approximately equal quantities of nitrocellulose binder and amyl acetate carriers and form a suspension of metal particles within a slurry which is applied to the lead wires by for instance painting or dabbing. In an amyl acetate nitrocellulose slurry, increasing the weight percentage of aluminum makes the slurry more viscous and more adherent to the lead wires.The preferred relative weight percentage of aluminum of zirconium cover a broad range, inasmuch as a larger quantity of getter material may be applied to the lead wires in order to compensate for low weight percentages. It is preferred that zirconium be the dominant material by weight and in specific embodiments weight percentages of aluminum in the range of 1525% have worked well. A further specific embodiment employs in weight percentages 18% aluminum and 82% zirconium.

Although the present invention has been described in combination with a standard gasfilled incandescent lamp, it is readily apparent that unplated copper lead wires may be used in combination with aluminum, zirconium getter in any of a number of different lamp configurations and types. More particularly, unplated copper lead wires may be used in infrared lamps or lamps which employ an arc tube in combination with an incandescent filament.

In the particular environment of a lamp unit, the present unplated copper lead wire aluminum zirconium getter combination yields surprising advantages. The present invention enables the use of stiff unplated and accordingly less expensive copper lead wires to be employed within incandescent lamps without substantially affecting the life or quality of the lamp.

Accordingly, the present invention represents an entirely new concept in incandescent lamps.

Although the invention has been described in preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred embodiment has been made by way of example only and that various changes in the details of construction may be resorted to without departing trom the true splnt and scope of the invention as hereinafter claimed.

Claims (6)

Claims

1. An incandescent lamp comprising a hermetically sealed glass envelope with a filament electrically connected and mechanically supported by a plurality of lead wires which are hermetically extending through a glass stem, one of said lead wires being of unplated copper and having an aluminium-zirconium getter applied thereto.

2. An incandescent lamp as claimed in claim 1, wherein said lead wires are of plated dispersion-strengthened copper or sheathless dispersion-strengthened copper.

3. An incandescent lamp as claimed in claim 1, or claim 2, wherein said aluminium and zirconium getter is applied in the vicinity of the lead wire clamps.

4. An incandescent lamp as claimed in any one of the preceding claims, wherein said aluminium and zirconium getter is comprised of irregularly shaped aluminium and zirconium particles having approximate relative weight percentages of 18% and 82% respectively which are combined in a nitrocellulose binder amyl acetate binder carrier.

5. An incandescent lamp as claimed in any one of the preceding claims, having an aluminium and zirconium getter wherein the getter has a thickness of approximately 25 microns.

6. An incandescent lamp as claimed in claim 1, substantially as hereinbefore described in the accompanying drawing.