Electric lamp and discharge devices – With gas or vapor – Having particular electrode structure
Patent
1997-02-24
1999-02-23
Patidar, Jay M.
Electric lamp and discharge devices
With gas or vapor
Having particular electrode structure
313326, 313632, 313311, 313346R, 313346DC, H01J 1704, H01J 6104
Patent
active
058748059
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrode structures. The invention has particular, although not exclusive, relevance to electrode structures for use in sealed arc lamps which incorporate an ionizable gas (for example xenon), to enable an arc to be established between two electrode structures in the lamp.
2. Description of the Related Art
As a result of the high temperatures involved in the formation of an arc, sealed arc lamps generally use tungsten electrodes. Such electrodes often contain small amounts of additional elements in order to modify the properties of the electrodes. For example by the addition of thorium oxide, the work function of the electrode may be reduced thus promoting arc ignition in the lamp. Normally the electrode is machined by diamond grinding from a solid tungsten rod or bar, the surface of the electrode often being profiled so as to increase the effective surface area of the electrode thereby facilitating radiative cooling of the electrode. However, this machining is expensive and, in the case where thorium oxide has been added to reduce the work function, is a hazardous procedure.
It is an object of the present invention to provide an electrode structure wherein these problems are at least alleviated, and in which the effective surface area of the electrode structure may be increased over that which has previously been possible.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of forming a structure comprising inserting a high melting point material rod into a press tool, pressing a block of powder around said rod, sintering the structure to create a fused integral structure, and forming the structure into the required shape.
Where the structure is an electrode, the powder will suitably be electrically conductive. The electrically conductive powder suitably comprises tungsten or a tungsten containing mixture.
The forming of the structure into the required shape may be produced by the shape of the press tool. Alternatively or additionally, the forming may be performed by machining prior to sintering while the powder is friable.
According to a second aspect of the present invention there is provided an electrode structure comprising a high melting point material rod, part of which forms the arc seat of the electrode, the rod being at least partially surrounded by a sintered electrically conductive powder block.
In a preferred embodiment the powder is impregnated with a heat conductive material. Suitable heat conductive materials are copper, silver or braze alloys.
BRIEF DESCRIPTION OF THE DRAWINGS
A number of embodiments of electrode structures in accordance with the invention will now be described by way of example only, with reference to the accompanying figures in which:
FIG. 1 illustrates schematically a stage in the formation of an electrode structure in accordance with a first embodiment of the invention;
FIG. 2 illustrates schematically a stage in the formation of an electrode structure in accordance with a second embodiment of the invention;
FIG. 3 illustrates schematically a further stage in the formation of the electrode structure of FIG. 2;
FIG. 4 ilustrates an adaptation of the electrode structure of FIG. 2; and
FIG. 5 is a schematic illustration of an arc lamp incorporating an electrode structure in accordance with an embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring firstly to FIG. 1, the electrode structure incorporates a tungsten rod 1. Around the rod 1 there is provided a block 3 of tungsten powder.
The rod 1 is dimensioned to have a sufficient diameter to provide the arc seating. In the example shown the diameter of the rod is 3.2 mm, with the diameter of the tungsten block being 7.95 mm.
The electrode structure is formed by inserting the rod 1 into a press tool (not shown) and pressing the block 3 of tungsten powder around the rod 1. The structure is then sintered at a high temperature, typically between 1000.degree. and
REFERENCES:
patent: 3248591 (1966-04-01), Arndt
patent: 3849690 (1974-11-01), Cosco et al.
patent: 3911309 (1975-10-01), Kummel et al.
patent: 3916241 (1975-10-01), Pollard
patent: 4097762 (1978-06-01), Hilton et al.
patent: 4229873 (1980-10-01), Bykhovsky et al.
patent: 4275123 (1981-06-01), Buxbaum et al.
patent: 4487589 (1984-12-01), Mishra et al.
patent: 4574219 (1986-03-01), Davenport et al.
patent: 5422539 (1995-06-01), Chodora
Abstract of Japanese Patent Publication No. JP 58 034556, published Mar. 1, 1983, from Patent Abstract of Japan, vol. 7, No. 115, 1 page (1983).
Digital Projection Limited
Patidar Jay M.
LandOfFree
Electrode structure including a rod comprising refractory metal does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrode structure including a rod comprising refractory metal , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrode structure including a rod comprising refractory metal will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-310123