Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1999-05-28
2001-01-16
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S625000, C252S570000, C585S006300
Reexamination Certificate
active
06175188
ABSTRACT:
TECHNICAL FIELD
The invention relates to a sealing body which is used for a discharge lamp. Description of related art In a discharge lamp in which there is a pair of electrodes opposite one another, recently a functional gradient material has been increasingly used as a sealing arrangement. In a sealing body of this functional gradient material one side is rich in a dielectric component and in the direction to the other side the proportion of electrically conductive component increases continuously or incrementally.
In a functional gradient material in which as the dielectric component silicon dioxide is used and as the electrically conductive component molybdenum is used, the silicon dioxide end has a coefficient of thermal expansion which is roughly equal to the coefficient of thermal expansion of the silicon dioxide which forms the arc tube, while the molybdenum end has the property that its coefficient of thermal expansion approaches the coefficient of thermal expansion of the tungsten or molybdenum which forms the upholding parts of the electrodes. These properties are suitable for the sealing body of a discharge lamp.
FIG. 7
is a schematic cross section of a discharge lamp in which a functionally gradient material is used. In the figure reference number
1
labels a discharge lamp with an arc tube
2
and side tube
3
consisting of a dielectric component (for example, silica glass). In arc tube
2
there is a pair of electrodes, i.e. a cathode
5
and an anode
6
opposite one another. The two electrodes are located on the tips of the upholding parts of the electrodes
7
which are inserted as far as the electrically conductive areas of the sealing bodies
4
and which are shrink-fitted. Outer leads
8
are connected to the sealing bodies
4
. There are also cases in which the outer leads
8
are made in one piece with the upholding parts of the electrodes
7
and this one-part arrangement is penetrated by the sealing bodies
4
and is thus shrink-fitted.
The sealing bodies
4
consist of a dielectric component (for example, of silicon dioxide) and an electrically conductive component (for example, molybdenum). One side of the sealing body
4
(the side towards the arc tube) is rich in the dielectric component and is insulating, while the other side (the side away from the arc tube) is rich in the electrically conductive component and is electrically conductive.
The end face
9
on the side of the dielectric component is adjacent to the discharge space of the arc tube
2
of the discharge lamp
1
. The side tube
3
formed on the two ends of the arc tube
2
is hermetically sealed (welded) in the areas of the sealing body
4
which are rich in the dielectric component.
The outside of the side tube is heated with a flame torch for this sealing of the side tube
3
with the sealing bodies
4
in the negative pressure state of the inside of the arc tube. In this way the side tube contracts. In this way sealing is effected. In doing so it is necessary to carry out heating until the outer peripheries of the sealing bodies and the inner periphery of the side tube are welded to one another enough to weld the side tube
3
and the sealing bodies
4
tightly to one another and to execute secure sealing. If however heating is done in this way it is impossible to prevent the silica glass which forms the arc tube from hanging from the face ends of the sealing bodies on the side of the emission space and thus hanging sites
10
from forming. In a discharge lamp with these hanging sites, depending on the amount and shape of the hanging silica glass, variations of the sustaining voltage occur during sealing.
DISCLOSURE OF THE INVENTION
Therefore the object of the invention is to reduce variations of the intensity of the sustaining voltage when the discharge lamp is sealed and therefore to devise a sealing arrangement of a discharge lamp which always has the desired intensity of the sustaining voltage.
As a result of extensive research the inventors have ascertained that variations of the intensity of the sustaining voltage by this sealing arrangement are largely influenced by the amount of the above described drooping and that it is advantageous if the amount of this hanging, i.e. the size of the aperture of the sites which are to be sealed and which are already closed by hanging, is kept constant.
If however formation of the hanging sites
10
progresses, the viscosity of the silica glass is extremely low, by which the progression is accelerated. It is therefore difficult to control the amount of hanging by controlling the arcing process with the torch. In this case the expression “aperture of the sites to be sealed” is defined as the width labelled with reference letter A in FIG.
7
.
It was further ascertained that it is advantageous if areas of the sealing bodies on the side of the emission space which are rich in the dielectric component are tilted. Due to this arrangement the glass which forms the arc tube and which hangs down when the discharge lamp is sealed by melting flows slowly along the obliquely running surfaces.
Therefore constant hanging and constant openings of the sites to be sealed can be easily achieved and thus variations of the intensity of the sustaining voltage reduced.
As claimed in the invention a sealing body described below for a discharge lamp is given:
In a roughly cylindrical sealing body for a discharge lamp which consists of a functionally gradient material in which one side is rich in dielectric component and the other side is rich in electrically conductive component, and which is sealed by a side tube which is connected to the arc tube of the discharge lamp and by its areas which are rich in a dielectric component, the invention is characterized in that in this sealing body the upholding parts of the electrodes with tips provided with electrodes are shrink-fitted, and that furthermore on the outer peripheral surfaces of the areas of the sealing bodies which are rich in dielectric component, surfaces are formed which run obliquely with respect to the center axis of the above described discharge lamp so that the maximum width of the end faces of the sealing bodies on the side of the discharge space becomes smaller than the maximum width in one direction perpendicular to the axis of the sealing bodies and becomes greater than the diameter of the upholding parts of the electrodes.
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Patent Abstracts of Japan, vol. 1996, No. 08, Aug. 30, 1996, & JP 08 096750 A (Toshiba Lighting & Amp; Technol Corp.), Apr. 12, 1996, English Abstract.
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Komiya Masanobu
Morimoto Yukihiro
Tagawa Yukiharu
Nixon & Peabody LLP
Patel Ashok
Safran David S.
Ushiodenki Kabushiki Kaisha
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