Electric lamp and discharge devices – With gas or vapor – Having particular electrode structure
Reexamination Certificate
1998-09-08
2001-04-03
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having particular electrode structure
C313S633000, C313S491000
Reexamination Certificate
active
06211615
ABSTRACT:
TECHNICAL FIELD
This invention relates to an electrode component for discharge lamps. More particularly, it relates to electrode components formed from high temperature resistant metals or carbides of such metals. Still more particularly, it relates to such electrode components produced by metal powder injection moulding. This can concern, in particular, electrodes for high-pressure discharge lamps such as are used, for example, for photooptical purposes. However, on the other hand the invention can also be used for individual parts of electrodes, or also for frame parts holding the electrode, for example shaft parts for electrodes. Said parts are subsumed below under the term of components for electrodes.
PRIOR ART
In lamp construction, electrodes and components for electrodes are normally manufactured from a high-melting metal such as tungsten or molybdenum or also tantalum. In this case, the electrode is virtually always solid, that is to say it has been produced using powder metallurgy and shaped with the aid of rolling, hammering and drawing processes. Because of the high costs, the application of a sintered body has so far been unable to become established.
Solid electrodes have the disadvantage that complicated electrode shapes such as, for example, would be required for optimum thermal shaping cannot be produced with such known electrode structures, or can be produced only with a great deal of metal cutting effort, and therefore with a high level of extra consumption (up to more than 50% waste).
For specific purposes, known electrodes are also assembled from two components.
They are frequently denoted as combination electrodes or insert electrodes. The document “Elektrodenwerkstoffe auf der Basis hochschmelzender Metalle” (“Electrode materials based on high-melting metals”), publisher VEB Narva, Berlin, 1976, pages 183 to 189 has already disclosed electrodes which comprise two components. Examples described there are anodes in FIG. 55
a
and cathodes in FIGS. 56
c, d
, for xenon short-arc lamps in each case. Said electrodes comprise a conventional sintered body (radiator) made from tungsten, which serves as a heat-balancing element. On the discharge side, a solid insert made from hammered tungsten is fastened in a cavity of the radiator. Said insert is doped with an emitter, which is frequently radioactive. A supply lead in the form of a tungsten pin is sintered into a bore in the radiator by means of a filament.
A similar technique is also described in DE-A 196 26 624. However, the insert is dispensed with in the latter instance. The production of such bipartite electrodes is very time-consuming and has so far not been capable of automation.
Such electrodes are therefore also scarcely used, because the complicated processing of the heat-balancing element, specifically the production of a receptacle for inserting an insert, is uneconomical and laborious.
Electrodes with an emitter additive (mostly oxides of thorium, the alkaline earth metals or the rare earth metals, in particular lanthanum) are required for special applications. However, the known production methods described above each require a very high degree of mechanical processing. With increasing emitter content, however, the property of deformability required for processing becomes limited. Consequently, it has so far not been desired to set the emitter content relatively high (approximately 3-5%). Instead of this, it has so far been necessary to make do with complicated structures in order nevertheless to realize a high emitter content. For example, it is known to use a filament pushed onto the electrode, an emitter-containing paste being inserted into the cavities between the individual turns of the filament.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an electrode component which eliminates the disadvantages discussed above.
Another object of the invention is the provision of a method of making complicated shapes of electrode components.
Moreover, it is yet another object of the invention to improve the microstructural stability of an electrode in the thermally highly loaded region at the tip of the electrode is to be improved.
Finally, there is the aim of a higher loadability with regard to the current intensity, as well as a better thermal loadability and also a higher luminous density. Conventional techniques can no longer provide improvement here, and this is to be seen as disadvantageous chiefly in the case of high-power lamp types of over 300 W. It is also desired to improve the arc instability and to increase the service life.
These objects are achieved, in one aspect of the invention, by the provision of an electrode component for discharge lamps, produced from high-temperature resistant metal, in particular from tungsten, molybdenum, tantalum, rhenium or alloys and also carbides of said materials, characterized in that the electrode component is produced using the metal powder injection moulding method.
According to the invention, the electrode components are produced by a metal powder injection moulding method. This technique, better known under the English acronym of MIM (Metal Injection Moulding) has been known per se for a long time. However, it has never been used in lamp construction.
A brief overview of the metal powder injection moulding method (MIM) is to be found in the article “Metallspritzgu&bgr;—wirtschaftlich für komplizierte Bauteile” (“Metal injection moulding—economical for complicated components”) in: Metallhandwerk & Technik 1994, pages 118 to 120, as well as in the advertising brochure entitled “Metal Injection Molding” of the European Powder Metallurgy Association, Shrewsbury (UK). A good overview is also to be found in the article entitled “Overview of Powder Injection Molding” by P. J. Vervoort et al., in: Advanced Performance Materials 3, pages 121-151 (1996).
The metal powder injection moulding method (see, for example, U.S. Pat. No. 4,765,950 and U.S. Pat. No. 4,113,480) combines the freedom of shaping in the known plastic injection moulding with the wide-ranging materials possibilities of powder metallurgy. This renders possible the direct production of components of very complicated shape in near net shaping while avoiding metal-cutting finishing. Moreover, it is now possible to automate the production method.
The cycle of the method can be summarized briefly as follows: a suitable metal powder is mixed with so much plastic (the so-called binder) that said mixture, which is present as a granulate, assumes the flow properties of the plastic and can be further processed in a fashion similar to plastic injection moulding by inserting it into an injection mould having the contour of the desired future component. In order then to obtain a metal component, the green body is removed from the injection mould; the binder is subsequently removed from the so-called green body by heat or by solvents. This operation is denoted as dewaxing. After that, the component is sintered in accordance with classic powder metallurgy to form a component of very high density (at least 90% by volume, preferably 95% and more). The residual porosity of at most 10% or 5% is preferably to be present as closed pores.
It is important in the metal powder injection moulding method to avoid chemical reactions between the organic binder (see, for example, U.S. Pat. No. 5,033,939) and the actual material, as well as to remove the binder in a careful and gentle way from the injection-moulded body (see, for example, U.S. Pat. No. 4,534,936).
The sintering activity of the metal powder used must also be sufficiently high in order to achieve a high sinter density. Consequently, very fine metal powders with low mean grain sizes (below 20 &mgr;m, preferably below 2 &mgr;m) are used.
According to the invention, electrode components for discharge lamps are produced from high-temperature resistant metal. Particularly suitable are tungsten, molybdenum, tantalum, rhenium, or alloys thereof, but also carbides of said metals, in particular tantalum carbide (TaC).
To date, the further dev
Altmann Bernhard
Gahn Alfred
Illig Dietmar
Schade Peter
McNeill William H.
Patel Nimeshkumar D.
Patent-Truehand-Gesellshaft fuer Elektrische Gluelampen mbH
Williams Joseph
LandOfFree
Powder metal electrode component for discharge lamps does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Powder metal electrode component for discharge lamps, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Powder metal electrode component for discharge lamps will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472407