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(11) | EP 0 092 109 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Method for increasing the life of a tungsten filament for an incandescent lamp Verfahren zum Verlängern der Lebensdauer eines Wolframleuchtdrahtes für eine Glühlampe Méthode pour prolonger la durée de vie d'un filament en tungstène pour une lampe à incandescence |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Technical Field
[0001] This invention relates to incandescent lamps and more particularly to a method for increasing the life of tungsten filaments.
[0002] The use of tungsten filaments in incandescent lamps is well established. Also well established is the fact that tungsten filaments do not heat to a uniform temperature upon passage of an electric current therethrough. Rather, localized hot spots are generally observed. Such hot spots are the filament life-determining factor in a well-made lamp because of their higher rate of tungsten evaporation. A runaway condition thereby exists, with evaporation promoted thinning of the wire and consequent increased ohmic heating and ever higher localized temperatures.
[0003] Hot spots on a filament may arise because of nonuniform wire cross sectional area, nonuniform cross sectional shape, variations in wire surface smoothness, nonuniformly spaced turns or segments of turns in a coiled or coiled coil geometry, and other reasons. While good lamp manufacturing practice strives to reduce all such contributing factors, the presence of hot spots is nevertheless ubiquitous.
[0004] It is well known to those skilled in the art that a halogen cycle based on fluorine or its compounds differs from those based on bromine and the other halogens in that with fluorine evaporated tungsten is redeposited back onto the filament in a rate that increased with filament temperature. This is because of the relatively greater thermal stability of tungsten hexafluoride as compared to the other tungsten halides. In effect, the fluorine cycle renders the fialment much more stable because the hot spots, which are more prone to evaporation, are also significantly more effective in thermally breaking down tungsten hexafluoride and thereby depositing tungsten back onto the filament. In practice, it is found that, at hot spots, tungsten deposition occurs at a higher rate than does evaporation, and the net effect is for a fluorine-cycle lamp to continually repair its filament.
[0005] The attractiveness of the fluorine cycle in incandescent lamps is somewhat offset by the toxicity of fluorine compounds (either initially or after operation of the lamp) and the technical difficulty of providing a lamp vessel and lead wires that are resistant to fluorine attack. U.S. Patent No. 4,256,988, e.g., addresses the problems of how to protect a lamp envelope and the filament supporting structure from attack by fluorine in a tungsten- fluorine lamp. The suggested method involves coating the interior of the lamp envelope and the internal structure with fluorine resistant compounds.
[0006] While this approach is interesting, it would certainly be expensive; and, it does not solve the problems occasioned by leaving in the hands of consumers a vessel loaded with toxic fluorine or fluoride compounds.
[0007] It is, therefore, an object of the invention to obviate the disadvantages of the prior art and to enhance the life of tungsten filaments.
[0008] These objects are accomplished by the provision of a method for increasing the life of tungsten filaments employed as a light emitting element in a lamp. The method comprises the steps of forming a filament from a length of tungsten wire; placing said filament in a closed environment; providing said closed environment with a gas fill which includes tungsten hexafluoride; applying sufficient electrical energy to said filament to cause said filament to incandesce; maintaining said filament at incandescence for a sufficient period of time to substantially remove hot spots from said filament; withdrawing said electrical energy and removing said filament from said closed environment; and subsequently operatively sealing said filament in a lamp envelope having an atmosphere free of fluorine and fluorine compounds.
[0009] This process allows the use of the advantageous fluorine regenerative cycle under closely controlled manufacturing conditions while keeping the ultimate lamp delivered to the general public fluorine-free.
Best Mode for Carrying Out the Invention
[0010] For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims.
[0011] The method is accomplished by first forming a filament from a length of tungsten wire. The filament can remain as cut; or it can be formed into a coil; a coiled coil; or any other desired configuration. The filament is then placed in closed environment which can be the final lamp vessel but preferably is a separate chamber formed of monel@ or other suitable fluorine resistant material.
[0012] The closed environment is then provided with a gas fill which includes tungsten hexafluoride (WF6). Electrical energy is then applied to the filament to cause the filament to incandesce. The time and operating conditions should be sufficient to allow substantial repair of hot spots, wherever located or regardless of cause. This fluorine treatment, as noted above, renders the filament more stable.
[0013] After the treatment the filament is removed from the closed environment and subsequently is assembled into a lamp. The treated filament is effective in vacuum incandescent lamps, inert gas filled incandescent lamps such as, for example, lamps containing an argon-nitrogen fill, and tungsten-halogen lamps containing a halogen other than fluorine.
1. In a method of increasing the life of tungsten filaments employed as a light emitting
element in a lamp, the steps comprising: forming a filament from a length of tungsten
wire; placing said filament in a closed environment; providing said closed environment
with a gas fill which includes tungsten hexafluoride; applying sufficient electrical
energy to said filament to cause said filament to incandesce; maintaining said filament
at incandescence for a sufficient period of time to substantially remove hot spots
from said filament; withdrawing said electrical energy and removing said filament
from said closed environment; and subsequently operatively sealing said filament in
a lamp envelope having an atmosphere free of fluorine and fluorine compounds.
2. The method of Claim 1 wherein said gas fill includes also nitrogen.
3. The method of Claim 2 wherein said gas fill comprises up to about 50% tungsten
hexafluoride.
4. The method of Claim 1 wherein said lamp envelope is evacuated.
5. The method of Claim 1 wherein said lamp envelope contains an inert gas.
6. The method of claim 1 wherein said lamp envelope contains a halogen selected from
chlorine, bromine and iodine.
1. Verfahren zur Verlängerung der Lebensdauer von als Licht aussendendes Element in
einer Lampe dienenden Wolframräden, bestehend aus den folgenden Schritten: Bilden
eines Fadens aus einem Stück Walframdraht; Anordnen dieses Fadens in einer abgeschlossenen
Umgebung; Versehen dieser abgeschlossenen Umgebung mit einer Wolfram-Hexafluorid enthaltenden
Gasfüllung; Beaufschlagen des Fadens mit einer ausreichenden Menge elektrischer Energie,
um denselben zum Glühen zu bringen; Aufrechterhalten des Glühzustands des Fadens für
eine ausreichende Zeitspanne, um überhitzte Stellen bzw. Aufblasestellen im wesentlichen
zu entfernen; Abschalten der elektrischen Energie und Entfernen des Fadens aus der
abgeschlossenen Umgebung; und schließlich betriebsmäßiges Einsiegeln des Fadens in
eine Lampenhülle, die eine von Fluor und Fluorverbindungen freie Atmosphäre aufweist.
2. Verfahren nach Anspruch 1, bei welchem die Gasfüllung auch Stickstoff aufweist.
3. Aufweise nach Anspruch 2, bei welchem die Gasfüllung bis etwa 50% Wolfram-Hexafluorid
aufweist.
4. Verfahren nach Anspruch 1, bei welchem die Lampenhülle evakuiert ist.
5. Verfahren nach Anspruch 1, bei welchem die Lampenhülle ein inertes Gas aufweist.
6. Verfahren nach Anspruch 1, bei welchem die Lampenhülle ein aus Chlor, Brom und
Jod ausgewähltes Halogen enthält.
1. Procédé pour augmenter la durée de vie des filaments au tungstène utilisés en tant
que composant émettant de la lumière dans une lampe, comprenant les étapes suivantes:
- mise en forme d'un filament à partir d'une longueur d'un fil de tungstène;
- mise en place du dit filament dans un environnement clos;
- emplir le dit environnement clos d'un gaz de remplissage comprenant de l'hexafluorure de tungstène;
- appliquer au dit filament une quantité d'énergie électrique suffisante pour obtenir son incandescence;
- maintenir en incandescence le filament pendant un temps suffisant pour éliminer les point chauds du dit filament;
- arrêter la dite énergie électrique et ôter le dit filament du dit environnement clos; puis
- sceller pour son fonctionnement le dit filament dans une ampoule de lampe enfermant un gaz libre de fluor et de composés de ce dernier.
2. Procédé selon la revendication 1 caractérisé en ce que le dit gaz de remplissage
contient en outre de l'azote.
3. Procédé selon la revendication 2 caractérisé en ce que le gaz de remplissage contient
jusqu'à 50 % environ d'hexafluorure de tungstène.
4. Procédé selon la revendication 1 caractérisé en ce qu l'on fait le vide dans la
dite ampoule de lampe.
5. Procédé selon la revendication 1 caractérisé en ce que la dite ampoule de lampe
enferme un gaz inerte.
6. Procédé selon la revendication 1 caractérisé en ce que la dite ampoule de lampe
enferme un halogène choisi parmi le chlore, le brome et l'iode.