Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1998-12-08
2001-07-10
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S623000, C313S624000
Reexamination Certificate
active
06259205
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a high-pressure discharge lamp comprising a ceramic discharge vessel which encloses a discharge space which contains an ionizable filling including a metal halide and which accommodates a first and a second electrode, which discharge vessel has a longitudinal axis and is provided with
a central cylindrical part which encloses the discharge space and which is provided with an end,
an end part which is provided with an outside surface and which closes the cylindrical part at the end in a gastight manner, and
a projecting plug which is connected to the end part in a gastight manner by means of a sintered connection and which encloses a feedthrough conductor to the first electrode with clearance, said plug containing a seal of a sealing ceramic through which the feedthrough conductor exits.
A lamp of this type is known from U.S. Pat. No. 5,424,609. In this description and in the claims, a ceramic dischargevessel is to be taken to mean a discharge vessel provided with a wall of a refractory material, such as monocrystalline metal oxide (for example sapphire), gastight sintered polycrystalline metal oxide (for example polycrystalline aluminium oxide; yttrium aluminium granate or yttrium oxide) and polycrystalline gastight sintered non-oxidic material (for example aluminium nitride). The gastight connection between the cylindrical part and the end part is generally formed by means of a sintered connection, because this type of connection is just as resistant to high temperatures and attack as the ceramic wall portions themselves. The sintered connection to the end part extends over a length of at least 2 mm. In practice, such a length of the sintered connection proved to be sufficient to form a strong and gastight fastening, also in the case of large-scale series production. Also the sintered connection between the wall of the end part and the projecting plug extends over a length of at least 2 mm. Each sintered connection between two parts forms a sintering seam. A discharge vessel constructed in said manner can be very reproducibly produced in series on an industrial scale. It is advantageous that the discharge vessel is composed of a limited number of prefabricated shaped parts which, as a result of their relatively simple shapes, can be manufactured very accurately and subsequently sintered to form the intended ceramic body in a single sintering process. In particular with respect to the projecting plug it is observed that due to the very small cross-section dimensions of the plug in practical circumstances, the projecting plug is preferably shaped as a cylindrical tube. Such a shape is very suitable to be manufactured with high accuracy on an industrial scale in series by way of extrusion. The resultant reproducible dimensional accuracy of the discharge vessel is very important for obtaining a good color stability of the lamp during its service life.
The known lamp has a quantity of sealing ceramic at the location of the sintering seam between the outside surface of the end part and the projecting plug. This sealing ceramic may be covered with an additional slice of ceramic material. Although the risk of leakage of the discharge vessel due to cracks in the end part and/or the projecting plug as a result of thermal stresses is substantially reduced in this manner, the construction has the drawback that at least one additional process step in the manufacturing process is required. A further drawback is that, during operation of the lamp, evaporation of the sealing
SUMMARY OF THE INVENTION
To achieve this, a lamp of the type mentioned in the opening paragraph is the location of the projecting plug, the outside surface of the end part is positioned so as to be axially remote from the discharge space with respect to the outside surface at the location of the end. The lamp in accordance with the invention has the advantage that, by means of an important simplification of the manufacturing process, it has been achieved that not only the risk of leakage of the discharge vessel has been substantially reduced, but even the risk of crack formation in the end part and/or the projecting plug due to thermal stresses. As a result thereof, a reduction of the service life of the lamp due to evaporation of sealing ceramic is precluded.
In an advantageous embodiment of the lamp in accordance with the invention, the end part is monolithic and the outside surface includes an angle A with the longitudinal axis, at the location of the projecting plug, which angle, expressed in degrees, meets the following relation
30<A<60.
This form of attachment between the end part and the projecting plug causes internal stresses to be homogeneously distributed over the end part, which has a very favorable influence on the further reduction of the risk of crack formation caused by thermal stresses. In this respect, it has been found that if the outside surface of the end part is shaped like a truncated cone provided with a foot at its base, a very robust lamp-vessel construction having favorable thermal properties is obtained. The cap may be widened with respect to the base of the cone. In another advantageous embodiment of the lamp in accordance with the invention, the end part is composed of at least two concentric tubular portions which are interconnected in a gastight manner by sintering. This embodiment has the special advantage that all prefabricated ceramic shaped parts of which the discharge vessel is composed can be formed by means of an extrusion process. The measure in accordance with the invention can be particularly advantageously applied to a lamp having a rated wattage of more than 150 W. The measure can particularly suitably be used in a metal-halide lamp.
REFERENCES:
patent: 4208605 (1980-06-01), McVey et al.
patent: 4625149 (1986-11-01), Danno et al.
patent: 4765820 (1988-08-01), Naganawa
patent: 5321335 (1994-06-01), Klung et al.
patent: 5404078 (1995-04-01), Bunk et al.
patent: 5424609 (1995-06-01), Geven et al.
patent: 5426343 (1995-06-01), Rhodes et al.
Mohan Sundararajarao
van Bakel Bernardus L. M.
Wijenberg Christoffel
Wittig Ralph D.
Halajian Dicran
Patel Nimeshkumar D.
Santiago Mariceli
U.S. Philips Corporation
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