CA1246654A

CA1246654A - End seal for ceramic arc discharge tubes

Info

Publication number: CA1246654A
Application number: CA000461520A
Authority: CA
Inventors: George A. Fryburg; Francis B. Makar, Jr.
Original assignee: GTE Products Corp
Current assignee: Osram Sylvania Inc
Priority date: 1983-09-02
Filing date: 1984-08-22
Publication date: 1988-12-13
Also published as: EP0136564A2; JPS6059352U; EP0136564A3

Abstract

ABSTRACT:

Sealing means for arc discharge tubes employ chamfers formed in the arc tube which mate with frusto-conical portions on sealing disks. Self-centering is thus provided as well as the elimination of one wire stop positioner for holding the sealing disks.

Description

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D-24,209 END SEAL FOR CERAMIC ARC DISCH~RG~. TUBES

TECHNICAL FIELD-This invention relates to ceramic arc discharge tubes, sucA
a~ of alumina or yttria; and more particularly to end seal~
thereof.
BACKGROUND ART
Cer~ain arc discharge device6~ such a6 high pressure sodium lamps, employ ceramic discharge tube~O These tubes generally comprise an elongated, tubular body of, for example, poly cry~talline alumina, which have electrode~ sealed into the ends thereof. The electrodes are mounted in di~ks o the ~ame material as the arc tube. The di~ks have an out~id~ diameter sized to fit within the inside diameter of the body with enough clearance to allow for the presence of a sealing material, such as a high temperature frit. The positioning of the electrode along the longitudin~l axi~ of the device is usually accomplished by means of a wire 6top which i~ secured to the electrode. A similar wire stop i6 used to position the disk ~nd hold it in the proper positio~ with the body for ~ealing.
There are many problems with this type of seal. The disk itself can cock during the sealing operation which provide~ a poor seal and a~ off-center electrode. Two wire stops are used to support the disk and t~e electrode. Further, e~en though extremely tight ~olerances are maintained on the arc tube inside diameter and the disk out6ide diameter, there i~ no co~venient way to center the disk in order to provide the proper seal annulu~. Thi~ annulu~ is critical for seal integrity.
DISCLOSUR~ OF T~E_INVENTION:
It i~, therefore, an ob3ect of this inven~ion to ob~iate the disadvantages o~ the prior art.
It is anot~er objec~ of the inventio~ to improve arc tube seals.
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- 2 -Yet another object of the invention is the provision of an arc tube seal that is self-centering.
According to the present invention there is provided a hermetically sealed ceramic arc tube comprising an elongated, substantially cylindrical, tubular body having an outside diameter, an inside diameter, and opposed ends, said inside diameter widening to a maximum diameter greater than said inside diameter and less than said outside diameter adjacent each of said opposed ends to form a chamfex, and a sealing disc sealed into each of said ends, said sealing disc having a frusto-conical portion formed to mate with said chamfer and a circumferential flange formed to mate with said body, said circumferential flange having a diameter equal to said outside diameter.
The described embodiments of this invention provide a seal that is self-centering and self-positioning. One of the wire stops is eliminated and the disk will not cock during sealing. Further, the proper seal annulus is maintained.
BRIEF DESCRIPTION OF THE DRAWINGS:
FIG. 1 is an exploded, sectional elevational view of an embodiment of the invention;
FIG. 2 is a similax view of an alternate embodiment;
and FIG. 3 is a similar view of yet another embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION:
, For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.
Referring now to the drawings with greater particular-ity, there is shown in ~IG. 1 a ceramic arc tube 10 compris-ing a body 1~ which is elongated, substantially cylindrical and tubular. Body 1~ has an outside diameter 14 and an inside diameter 16.

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~-2~,20g Adjacent the ends 18 and 20 the inside dia~eter 16 ~idens to form an intermediate diameter Z2 which i6 greater than diameter 16 but less than diameter 14, thus forming a chamEer ~4 ~ sealing disk 26, which includes a frusto-conical portio~
2~ formed to mate with chamfer 24 is sealed into each end o body 12 by means of a sealing material 30 ~hich forms a sealing annulu~.
An electrode 32, which can be a conventional electrode for a high pressure sodium lamp, is sealed into a centrally located aperture in di~k 26. A wire stop 34 can hold electrode 32 in position during sealing.
I~ the alternate embodiment of YIG. 2~ the sealing disk 36 i8 provided with a circumferential rim or flange 38 which seals 15 additionally to the outermos~ plane~ 40 and 42 o~E end~ 18 and 20, respectively.
In the al~ernate embodiment shown in FI~. 3, the body 12 ha~ an insert 44 sealed into each end, and ~he i~serts 44 are provided wi~h chamfer~ 46. Thus it will be seen ~ha~ body 1 in ~I~. 3 ha~ a first in~ide diameter 16 for a substantal por~ion of it6 length and a seco~d inside diameter 4B whicb i8 les6 than the diameter 16. The widest point of chamfer~ 46 i~
at diame~er 50, which is al~o le~s than diameter 16 although greater than diameter 48.
The sealing disk~ 52 have a frusto-conical portion 54 for mating with chamfers 46 and also have the circum~erential flange 56.
There i~ thus provided a sealing me~ns for arc discharge devices such a~ high pressure sodium lamps which avoid the disad~antages of the prior art.
While there haYe been shown what are at present considared to be preferred embodimen~ o~ the invention, ;t will be apparent to those ~killed in the art ~hat variou6 change~ and modifications can be made herein withou~ depar~ing from the scvpe of the invention a6 defined ~y the appended ~lai~.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A hermetically sealed ceramic arc tube compris-ing:
an elongated, substantially cylindrical, tubular body having an outside diameter, an inside diameter, and opposed ends, said inside diameter widening to a maximum diameter greater than said inside diameter and less than said outside diameter adjacent each of said opposed ends to form a chamfer, and a sealing disc sealed into each of said ends, said sealing disc having a frusto-conical portion formed to mate with said chamfer and a circumferential flange formed to mate with said body, said circumferential flange having a diameter equal to said outside diameter.

2. The ceramic arc tube of claim 1 wherein said sealing disc has a central longitudinal aperture therein which mounts an electrode.

3. A hermetically sealed ceramic arc tube compris-ing:
an elongated, substantially cylindrical, tubular body having an outside diameter, first, second and third inside diameters, and opposed ends, said first inside diameter being constant for a substantial portion of the length of said body, said second inside diameter being formed adjacent said ends and being less than said first inside diameter, said third inside diameter being greater than said second diameter and less than said first diameter and cooperating with said second diameter to form a chamfer, and a sealing disc sealed into each of said ends, said seal-ing disc having a frusto-conical portion formed to mate with said chamfer and a circumferential flange formed to mate with said body, said circumferential flange having a diameter equal to said outside diameter.

4. The ceramic arc tube of claim 3 wherein said sealing disc has a central longitudinal aperture therein which mounts an electrode.