CA1139350A - Xenon arc lamp with compressive ceramic to metal seals - Google Patents
Xenon arc lamp with compressive ceramic to metal sealsInfo
- Publication number
- CA1139350A CA1139350A CA000398188A CA398188A CA1139350A CA 1139350 A CA1139350 A CA 1139350A CA 000398188 A CA000398188 A CA 000398188A CA 398188 A CA398188 A CA 398188A CA 1139350 A CA1139350 A CA 1139350A
- Authority
- CA
- Canada
- Prior art keywords
- window
- lamp
- metallic
- sealing member
- edge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An arc lamp comprising a metallic envelope member and a window, an outer surface of the window being a portion of the exterior of an enclosure for containing a gas at higher than atmospheric pressure. Sealing means for pro-viding a hermetic seal between the metallic envelope member and the window. The sealing means comprising an annular seal-ing member disposed between the metallic envelope and the window. The sealing member being in contact with the window only where a first edge of the sealing member abuts a peripheral portion of the outer surface of the window, the window being spaced apart from the metallic envelope member. A second edge of the sealing member abutting an inwardly projecting flange portion of the metallic envelope member.
An arc lamp comprising a metallic envelope member and a window, an outer surface of the window being a portion of the exterior of an enclosure for containing a gas at higher than atmospheric pressure. Sealing means for pro-viding a hermetic seal between the metallic envelope member and the window. The sealing means comprising an annular seal-ing member disposed between the metallic envelope and the window. The sealing member being in contact with the window only where a first edge of the sealing member abuts a peripheral portion of the outer surface of the window, the window being spaced apart from the metallic envelope member. A second edge of the sealing member abutting an inwardly projecting flange portion of the metallic envelope member.
Description
1~L3~.r~
This application is a division of Canadian Applica-tion 296,702 filed February 10, 1978.
Background of the Invention This invention relates to high pressure gaseous discharge devices and in particular to improvements in the envelope structure and window seal for high pressure arc lamps.
In any arc lamp, various portions of the lamp structure will be at different potentials corresponding to one or another electrode. It is necessary, therefore, to provide insulation between these portions in order to maintain their mutual electrical isolation. Prior art high pressure arc lamps, for example, as described in our U.S. patents 3,876,908 (April 8, 1975); 3,852,629 [December 3, 1974); and 3,808,496 (April 30, 1974) employ ceramic cylinders separating the lamp envelope into anode and cathode portions with a circumferential surface of the insulator as part of the lamp envelope exterior. It will be apparent that as a consequence of this construction, the lamp design, operation and usage are subject to a num~er of critical specifications.
One such critical specification is related to the internal pressure and temperature to which the ceramic and the ceramic to metal bonds are subject. Ceramic cylinders or rings so employed are primarily under tensile stresses due to the high pressure gas filling of the lamp which tends to push apart the anode and cathode portions of the lamp envelope. The brazed metal to ceramic bonds of these prior art lamps are likewise under tensile or shear stress. Due to the properties of the brazing alloys and the metallic members, the stresses within the joint 5~
must be maintained within safe tolerances. These stresses are thermally dependent and thus place limits on the lamp operation and associated cooling system.
Another critical consideration is the ambient environment wherein the lamp will be operated. Moisture dirt, grease, fingerprints and the like can seriously degrade the insulation characteristics of the ceramic, especially for high voltage starting conditions. Moreover, the exposed ceramic is subject to impact which can initiate a fracture thereof.
It will be clear also that failure of the ceramic or the metal-ceramic seals of a high pressure lamp can be hazardous to personnel or equipment nearby.
Another prior art arc lamp, described in our U.S.
patent 3,715,~13 (February 6, 1973), employed a ceramic cylinder with a recessed plane surface for accepting a metal disk which in turn supported the anode structure. The out-side surface of the ceramic was brazed to the inner surface of the envelope neck. Thus, the metal ring exerted compres-sive and shear stresses at one end of the ceramic due to the internal gas pressure while a brazement of the outer circum-ferential wall of the ceramic to the inner cylindrical surface of the envelope neck resulted in shear stresses due to the internal gas pressure.
An arc lamp is also characterized by an optical window which must withstand a very great pressure differen-tial between the interior and exterior of the lamp. Prior art window seals in such lamps have normally employed a window disc of sapphire, metallized around its circumference and then brazed to one leg of a U-shaped metal flange, which was subsequently brazed into the window-cathode 1~3~0 portion assembly, as shown for example in said U.S. patent 3,852,629. This window sealing technique resulted in an improved seal but one which is not as good as the seal to be hereinafter described with respect to this invention.
It is an object of this invention to produce a safer and more rugged lamp capable of both higher performance and production at reduced manufacturing cost.
Accordingly, the present invention provides an arc lamp comprising a metallic envelope member and a window, an outer surface of said window being a portion of the exterior of an enclosure for containing a gas at higher than atmospheric pressure, sealing means for providing a hermetic seal between said metallic envelope member and said window, said sealing means comprising an annular sealing member disposed between said metallic envelope and said window, said sealing member being in contact with said window only where a first edge of said sealing member abuts a peripheral portion of the outer surface of said window, said window being spaced apart from said metallic envelope member, a second edge of said sealing member abutting an inwardly projecting flange portion of said metallic envelope member.
3rief Description of the Drawings FIG. 1 is a section of an embodiment of the high pressure arc lamp.
FIG. 2 is a detail of an alternate embodiment of the main body seal.
FIG. 3 is a detail of an alternate embodiment of the window seal.
-~3~;~50 Detailed Description of the Embodiments FIG. 1 is illustrative of a high pressure sealed beam short arc lamp of the present embodiment. One elec-trode shown as cathode 10 is mounted in the forward part of the lamp adjacent to window 11. Cathode 10 is supported by metal struts 12 which are centrally attached to cathode 10. A getter 13 is provided to remove contaminants from the gas filling of the lamp. The struts 12 are attached to metal ring 14 adjacent the outer ends of the struts.
Reflector 16 is suspended from ring 14. The exterior of the forward portion of the lamp is a cylindrical shell 18 made of a high strength metallic alloy, such as stain-less steel.
Window 11, preferably of sapphire, is face brazed with a knife edge braze process to annular sealing ring 21, the latter preferably of Kovar*.
Although the window 11 remains subject to the same bending moment across its plane surface (face) as in prior art lamps, the outer peripheral region or rim of the window, together with the window to metal bond, is compressively loaded, with consequent reduction of tensile stresses.
Since the ultimate yield strength for sapphire in compres-sion far exceeds that in tension, this seal has been found to withstand much higher internal pressures than the prior art peripheral seals for equal thickness sapphire windows.
Whereas the prior art peripheral seals have been tested to seal failure at 1200 psi, the compressive window seal of the present invention has not been observed to fail at 1900 psi. It is conjectured that exposure of the circumferential surface 19 of the window to internal gas pressure of the lamp results in a compressive stress across . _ .
;~39 ~0 the diameters of the window, resulting in the higher observed resistance to fracture. It is also noted that the braze bond between the window 11 and the sealing ring 21 is in compression due to the high internal gas pressure. Thus higher pressures may be achieved, or alternatively, a thinner sapphire window may be employed to maintain the same structural integrity as characterized by the prior art.
A second electrode, here anode 22, is supported in the rear of the lamp. Surrounding and attached to anode 22 is a high strength metal alloy shell 28. Rear and front shells comprising the lamp envelope are connected by attaching metal shells 18 and 28 to an insulating ring 25 of high strength ceramic. Sealing rings 29 of, for example, Kovar*, are used to seal the ceramic ring 25 to anode shell 28 and cathode shell 18, thereby forming a hermetic envelope.
The cathode shell 18 and the anode shell 28 are mutually configured to place ceramic ring 25 in compression and to shield ceramic ring 25 from contamination and impact. This is accomplished by forming on cathode shell 18 an inward projecting flange 30, and by forming on anode shell 28 an outward projecting flange 32. These flanges overlap each other to intercept a common radial region defined from center line 34; and it is this common radial region, which is occupied by ceramic ring 25. The internal pressure thus tends to hold the envelope together. The exterior overlap of cathode shell 18 over the ceramic ring 25 tends to thus protect the ceramic ring 25 from contamination, which could promote short circuits, and from impacts, which could damage it. Should the ceramic ring 25 fail, fragments are li~ewise prevented from causing damage to nearby personnel or appara-tus. Moreover should the ceramic insulator ring 25 or its seals fail, the cathode and anode shells 18 and 28 are 1~3~ 50 prevented from separating by the flanges 30 and 32.
The ratio of compressive strength to tensile strength for a typical ceramic as employed here is in excess of 10:1;
therefore the ceramic insulator can withstand much higher compressive stresses arising from the high pressure gas filling of the lamp than would be the case were the ceramic to be tensile loaded.
It will be observed that preparation of ceramic ring 25 for brazing requires only grinding of the end plane surfaces rather than the more elaborate requirements for preparation of radial surfaces for brazing. Similarly, only plane surfaces (of flanges 30 and 32) need be prepared for brazing rather than circumferential surfaces of shells 18 and 28. The seals are knife-edge brazements which are subject to substantially purely compressive stresses.
FIG. 2 is an alternate seal wherein two coaxial rings 29' and 29" are employed in place of the single ring 29.
Similarly, dual sealing rings are illustrated in FIG. 3 for an alternate arrangement to seal the window 11 to the assem-bly ring 14.
Assembly of the lamp of FIG. 1 is accomplished by first performing the brazing operations required to seal cathode shell 18 to anode shell 28. The assembly ring 14 supporting the window 11 and the cathode 10 is brazed to the cathode shell 18 as the last braze. The lamp is then filled to high pressure through port 36, preferably with xenon, and the port 36 is then sealed off.
Since changes could be made in particular details of the embodiment of the invention disclosed herein with-out departing from the scope of the invention, it is intended that the above description and accompanying drawings be interpreted as illustrative only and not as limiting.
This application is a division of Canadian Applica-tion 296,702 filed February 10, 1978.
Background of the Invention This invention relates to high pressure gaseous discharge devices and in particular to improvements in the envelope structure and window seal for high pressure arc lamps.
In any arc lamp, various portions of the lamp structure will be at different potentials corresponding to one or another electrode. It is necessary, therefore, to provide insulation between these portions in order to maintain their mutual electrical isolation. Prior art high pressure arc lamps, for example, as described in our U.S. patents 3,876,908 (April 8, 1975); 3,852,629 [December 3, 1974); and 3,808,496 (April 30, 1974) employ ceramic cylinders separating the lamp envelope into anode and cathode portions with a circumferential surface of the insulator as part of the lamp envelope exterior. It will be apparent that as a consequence of this construction, the lamp design, operation and usage are subject to a num~er of critical specifications.
One such critical specification is related to the internal pressure and temperature to which the ceramic and the ceramic to metal bonds are subject. Ceramic cylinders or rings so employed are primarily under tensile stresses due to the high pressure gas filling of the lamp which tends to push apart the anode and cathode portions of the lamp envelope. The brazed metal to ceramic bonds of these prior art lamps are likewise under tensile or shear stress. Due to the properties of the brazing alloys and the metallic members, the stresses within the joint 5~
must be maintained within safe tolerances. These stresses are thermally dependent and thus place limits on the lamp operation and associated cooling system.
Another critical consideration is the ambient environment wherein the lamp will be operated. Moisture dirt, grease, fingerprints and the like can seriously degrade the insulation characteristics of the ceramic, especially for high voltage starting conditions. Moreover, the exposed ceramic is subject to impact which can initiate a fracture thereof.
It will be clear also that failure of the ceramic or the metal-ceramic seals of a high pressure lamp can be hazardous to personnel or equipment nearby.
Another prior art arc lamp, described in our U.S.
patent 3,715,~13 (February 6, 1973), employed a ceramic cylinder with a recessed plane surface for accepting a metal disk which in turn supported the anode structure. The out-side surface of the ceramic was brazed to the inner surface of the envelope neck. Thus, the metal ring exerted compres-sive and shear stresses at one end of the ceramic due to the internal gas pressure while a brazement of the outer circum-ferential wall of the ceramic to the inner cylindrical surface of the envelope neck resulted in shear stresses due to the internal gas pressure.
An arc lamp is also characterized by an optical window which must withstand a very great pressure differen-tial between the interior and exterior of the lamp. Prior art window seals in such lamps have normally employed a window disc of sapphire, metallized around its circumference and then brazed to one leg of a U-shaped metal flange, which was subsequently brazed into the window-cathode 1~3~0 portion assembly, as shown for example in said U.S. patent 3,852,629. This window sealing technique resulted in an improved seal but one which is not as good as the seal to be hereinafter described with respect to this invention.
It is an object of this invention to produce a safer and more rugged lamp capable of both higher performance and production at reduced manufacturing cost.
Accordingly, the present invention provides an arc lamp comprising a metallic envelope member and a window, an outer surface of said window being a portion of the exterior of an enclosure for containing a gas at higher than atmospheric pressure, sealing means for providing a hermetic seal between said metallic envelope member and said window, said sealing means comprising an annular sealing member disposed between said metallic envelope and said window, said sealing member being in contact with said window only where a first edge of said sealing member abuts a peripheral portion of the outer surface of said window, said window being spaced apart from said metallic envelope member, a second edge of said sealing member abutting an inwardly projecting flange portion of said metallic envelope member.
3rief Description of the Drawings FIG. 1 is a section of an embodiment of the high pressure arc lamp.
FIG. 2 is a detail of an alternate embodiment of the main body seal.
FIG. 3 is a detail of an alternate embodiment of the window seal.
-~3~;~50 Detailed Description of the Embodiments FIG. 1 is illustrative of a high pressure sealed beam short arc lamp of the present embodiment. One elec-trode shown as cathode 10 is mounted in the forward part of the lamp adjacent to window 11. Cathode 10 is supported by metal struts 12 which are centrally attached to cathode 10. A getter 13 is provided to remove contaminants from the gas filling of the lamp. The struts 12 are attached to metal ring 14 adjacent the outer ends of the struts.
Reflector 16 is suspended from ring 14. The exterior of the forward portion of the lamp is a cylindrical shell 18 made of a high strength metallic alloy, such as stain-less steel.
Window 11, preferably of sapphire, is face brazed with a knife edge braze process to annular sealing ring 21, the latter preferably of Kovar*.
Although the window 11 remains subject to the same bending moment across its plane surface (face) as in prior art lamps, the outer peripheral region or rim of the window, together with the window to metal bond, is compressively loaded, with consequent reduction of tensile stresses.
Since the ultimate yield strength for sapphire in compres-sion far exceeds that in tension, this seal has been found to withstand much higher internal pressures than the prior art peripheral seals for equal thickness sapphire windows.
Whereas the prior art peripheral seals have been tested to seal failure at 1200 psi, the compressive window seal of the present invention has not been observed to fail at 1900 psi. It is conjectured that exposure of the circumferential surface 19 of the window to internal gas pressure of the lamp results in a compressive stress across . _ .
;~39 ~0 the diameters of the window, resulting in the higher observed resistance to fracture. It is also noted that the braze bond between the window 11 and the sealing ring 21 is in compression due to the high internal gas pressure. Thus higher pressures may be achieved, or alternatively, a thinner sapphire window may be employed to maintain the same structural integrity as characterized by the prior art.
A second electrode, here anode 22, is supported in the rear of the lamp. Surrounding and attached to anode 22 is a high strength metal alloy shell 28. Rear and front shells comprising the lamp envelope are connected by attaching metal shells 18 and 28 to an insulating ring 25 of high strength ceramic. Sealing rings 29 of, for example, Kovar*, are used to seal the ceramic ring 25 to anode shell 28 and cathode shell 18, thereby forming a hermetic envelope.
The cathode shell 18 and the anode shell 28 are mutually configured to place ceramic ring 25 in compression and to shield ceramic ring 25 from contamination and impact. This is accomplished by forming on cathode shell 18 an inward projecting flange 30, and by forming on anode shell 28 an outward projecting flange 32. These flanges overlap each other to intercept a common radial region defined from center line 34; and it is this common radial region, which is occupied by ceramic ring 25. The internal pressure thus tends to hold the envelope together. The exterior overlap of cathode shell 18 over the ceramic ring 25 tends to thus protect the ceramic ring 25 from contamination, which could promote short circuits, and from impacts, which could damage it. Should the ceramic ring 25 fail, fragments are li~ewise prevented from causing damage to nearby personnel or appara-tus. Moreover should the ceramic insulator ring 25 or its seals fail, the cathode and anode shells 18 and 28 are 1~3~ 50 prevented from separating by the flanges 30 and 32.
The ratio of compressive strength to tensile strength for a typical ceramic as employed here is in excess of 10:1;
therefore the ceramic insulator can withstand much higher compressive stresses arising from the high pressure gas filling of the lamp than would be the case were the ceramic to be tensile loaded.
It will be observed that preparation of ceramic ring 25 for brazing requires only grinding of the end plane surfaces rather than the more elaborate requirements for preparation of radial surfaces for brazing. Similarly, only plane surfaces (of flanges 30 and 32) need be prepared for brazing rather than circumferential surfaces of shells 18 and 28. The seals are knife-edge brazements which are subject to substantially purely compressive stresses.
FIG. 2 is an alternate seal wherein two coaxial rings 29' and 29" are employed in place of the single ring 29.
Similarly, dual sealing rings are illustrated in FIG. 3 for an alternate arrangement to seal the window 11 to the assem-bly ring 14.
Assembly of the lamp of FIG. 1 is accomplished by first performing the brazing operations required to seal cathode shell 18 to anode shell 28. The assembly ring 14 supporting the window 11 and the cathode 10 is brazed to the cathode shell 18 as the last braze. The lamp is then filled to high pressure through port 36, preferably with xenon, and the port 36 is then sealed off.
Since changes could be made in particular details of the embodiment of the invention disclosed herein with-out departing from the scope of the invention, it is intended that the above description and accompanying drawings be interpreted as illustrative only and not as limiting.
Claims (7)
1. An arc lamp comprising a metallic envelope member and a window, an outer surface of said window being a portion of the exterior of an enclosure for containing a gas at higher than atmospheric pressure, sealing means for providing a hermetic seal between said metallic en-velope member and said window, said sealing means com-prising:
an annular sealing member disposed between said metallic envelope and said window, said sealing member being in contact with said window only where a first edge of said sealing member abuts a peripheral portion of the outer surface of said window, said window being spaced apart from said metallic envelope member, a second edge of said sealing member abutting an inwardly projecting flange portion of said metallic envelope member.
an annular sealing member disposed between said metallic envelope and said window, said sealing member being in contact with said window only where a first edge of said sealing member abuts a peripheral portion of the outer surface of said window, said window being spaced apart from said metallic envelope member, a second edge of said sealing member abutting an inwardly projecting flange portion of said metallic envelope member.
2. A lamp as claimed in claim 1, wherein said peri-pheral portion of the outer edge of said window is metallized, and wherein said first edge of said annular sealing member is brazed thereto.
3. A lamp as claimed in claim 2 wherein said second edge of said annular sealing member is brazed to said inward-ly projecting flange portion of said metallic envelope member.
4. A lamp as claimed in any one of claims 1 to 3 wherein the outer surface of said window is generally cir-cular.
5. A lamp as claimed in any one of claims 1 to 3 wherein said annular sealing member is metallic.
6. A lamp as claimed in any one of claims 1 to 3 wherein there are two of said annular sealing members brazed to said peripheral portion of said window and brazed to said inwardly projecting flange portion of said metallic envel-ope member, said two sealing members being radially spaced from each other.
7. A lamp as claimed in any one of claims 1 to 3 wherein said annular sealing member is made of an alloy of nickel, cobalt and iron, known by the Registered Trade Mark Kovar.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000398188A CA1139350A (en) | 1977-02-11 | 1982-03-11 | Xenon arc lamp with compressive ceramic to metal seals |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US76785477A | 1977-02-11 | 1977-02-11 | |
| US767,854 | 1977-02-11 | ||
| CA000296702A CA1136690A (en) | 1977-02-11 | 1978-02-10 | Xenon arc lamp with compressive ceramic to metal seals |
| CA000398188A CA1139350A (en) | 1977-02-11 | 1982-03-11 | Xenon arc lamp with compressive ceramic to metal seals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1139350A true CA1139350A (en) | 1983-01-11 |
Family
ID=27165498
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398188A Expired CA1139350A (en) | 1977-02-11 | 1982-03-11 | Xenon arc lamp with compressive ceramic to metal seals |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1139350A (en) |
-
1982
- 1982-03-11 CA CA000398188A patent/CA1139350A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |