Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1998-06-23
2001-01-30
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S567000
Reexamination Certificate
active
06181065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-pressure discharge lamp, and more particularly to a metal-halide discharge lamp having a ceramic discharge vessel, and especially to an arrangement to provide for long-term sealed passage of an electrical lead-through or feed-through from the exterior into the interior of the discharge vessel.
BACKGROUND
Discharge lamps, and particularly high-power metal-halide discharge lamps, present problems in connection with reliable long-term seal of an electrical lead-through into a ceramic discharge vessel. Ceramic plugs are customarily used. There are many proposals for solutions to the problems. A pin or a tubular element of a metal, such as tungsten or molybdenum, is used as the electrical conductor. The plug may be of ceramic, and the pin or tube is melt-sealed by means of a glass melt or a melt ceramic into the plug. Alternatively, the lead-through may be directly sintered to the plug. The connection between the ceramic and the metal is not a secure bond however, so that the seal has a limited lifetime. It has also been proposed to use a cermet, which is a combination material formed of ceramic and metal, as the material for the plug—see U.S. Pat. No. 5,404,078, Bunk et al., and U.S. Pat. No. 5,592,049, Heider et al.
Plugs have been tested which comprise a plurality of layers of cermet with different relationships of metal to ceramic to provide for better matching of thermal coefficients of expansion. European EP 0 650 184 A1, Nagayama, to which U.S.-designated PCT/JP93/00959 corresponds, discloses a non-conductive cermet plug having axially arranged layers. This seal is very complex and uses a lead-through which has a thread, an outer metal disk or flange, and a metal or glass melt.
U.S. Pat. No. 4,602,956, Partlow et al., discloses a metal-halide discharge lamp having a ceramic discharge vessel. The electrode is carried in a lead-through which is formed as a disk of electrically conductive cermet. The electrode is sintered into the cermet. Additionally, the lead-through is surrounded by a ring-shaped stopper or plug of cermet which is connected with the ceramic discharge vessel, typically of aluminum oxide, by a glass melt. The glass melt, however, is corroded by aggressive components of the fill in the discharge lamps, particularly by the halides therein, so that the lifetime of such a lamp is rather short. Embedding the electrode in the cermet lead-through, additionally, leads to stresses which eventually may lead to fissures and cracks in the cermet. The diameter of the disk lead-through is quite large. The lead-through is electrically conductive and, thus, the discharge arc can flash back or arc back to the lead-through which would quickly lead to blackening of the discharge vessel.
U.S. Pat. No. 4,155,758, Evans, describes a special arrangement for a metal-halide lamp having a ceramic discharge vessel without an outer surrounding envelope. The lead-through is formed as a pin of electrically conductive cermet. The electrode is sintered into the cermet. The cermet pin in turn is sintered into a plug of aluminum oxide, and this plug is connected to the vessel by a glass melt. This arrangement also has the disadvantages above mentioned.
U.S. Pat. No. 5,424,609, Geven et al., describes a metal-halide discharge lamp which requires an extremely long-drawn capillary tube of aluminum oxide as an inner plug element. A pin-like metallic lead-through is connected by a glass melt at the outer end in a melting zone. It is important that the melting zone is at a sufficiently low temperature. The lead-through pin can be made of two parts, in which the part facing the discharge can be made of an electrically conductive cermet, which contains carbide, silicide or a nitride. The sealing technology results in a large overall length of the discharge vessel, it is expensive to make and, also, uses the corrosion-susceptible glass melt. The gap between the capillary tube and the lead-through results in a comparatively large dead volume in which a substantial portion of the fill in the lamp may condense, so that a large quantity of fill is necessary. The aggressive fill has intensive contact with the corrosion-susceptible components in the sealing region.
SUMMARY OF THE INVENTION
It is an object to provide a high-pressure discharge lamp having a ceramic discharge vessel, typically retaining a fill which includes a halide, which has a long lifetime, and in which electrical conductors leading from the outside into the inside of the ceramic discharge vessel are sealingly retained without use of glass or ceramic melts. The sealing regions including the sealing means used therein are required to be vacuum-tight, resistant to high temperatures, and to corrosive attack by the fill of the lamp.
Briefly, the closing and sealing means for tubular end portions of the discharge vessel include a lead-through or feed-through which comprises a cermet structure, in which the cermet has a metal content which is so high that it can be welded like a metal. The cermet structure is directly sintered into the sealing or closing means or arrangement; and the sealing or closing arrangement or sealing or closing means, in turn, is directly sintered to the respective end portion of the discharge vessel.
Use of a cermet as at least a part of the feed-through permits a tight bond connection without use of a glass melt. This cermet structure is directly sintered to the surrounding sealing means or sealing arrangement. This direct sinterconnection does not join any simply metallic partner so that a high vacuum tight bond can be formed, which is a definite requirement for a long lifetime—reliably more than 10,000 hours of operation.
The connection partners which are directly sintered both shrink during sintering. This permits a better matching of the at least partly cermet feed-through to the sealing means or sealing arrangements which, likewise, shrink. The thermal coefficients of expansion of the respective partners—feed-through and sealing means—are closer together than when the feed-through itself is metallic. This reduces stresses upon temperature change which results when the lamp is turned ON and OFF.
The cermet partner or cermet structure of the feed-through may be formed as a pin, or as a capillary tube. In either case, the mass of this structure is very small. In case of a pin, the outer diameter of the cermet structure is small; in case of a capillary tube, the wall thickness of the tube can be made small. Thus, absolute differences in expansion upon changes in temperature, and temperature loading due to temperature changes, will be small. The end face which is directed towards the discharge is relatively small, so that back-arcing can be readily avoided.
The cermet structure is connected to the electrode, and particularly to an electrode shaft, directly or indirectly, over an additional structural element by welding. Stresses in this region are also largely avoided since the electrode shaft is not sintered in the feed-through.
The present invention is specifically directed to a high-pressure discharge lamp having a ceramic discharge vessel, which is typically of aluminum oxide, but may be aluminum nitride or aluminum oxinitride, and which is formed as a metal-halide or sodium high-pressure lamp. Customarily, the discharge vessel is surrounded by an outer envelope. The discharge vessel has two ends which are closed by closing and sealing means. These closing and sealing means may be unitary or multi-part plugs or stoppers, or may be formed directly on the vessel by suitably shaped integral ends of the discharge vessel itself.
At least one end of the discharge vessel has a construction which includes a central bore of the sealing means through which an electrical feed-through passes vacuum tightly. An electrode or, rather, an electrode shaft, is secured to the feed-through, the electrode extending into the interior of the discharge vessel. The feed-through includes a cermet structure, the metal content of which is so high that it can be welded just like a
Huettinger Roland
Lang Dieter
Tiedt Rita
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Gerike Matthew J.
Patel Nimeshkumar D.
Patent-Treuhand-Gesellschaft F. Elektrische Gluehlampen mbH
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