Patent Grant
8053990
The invention relates generally to lamps and, more particularly, techniques to reduce the potential for thermal stresses and cracking in high intensity discharge (HID) lamps.
High-intensity discharge lamps are often formed from a ceramic tubular body or arc tube that is sealed to one or more end structures. Unfortunately, various stresses may arise from the sealing process, the interface between the joined components, and the materials used for the different components. For example, the component materials may have different mechanical and physical properties, such as different coefficients of thermal expansion (CTE), which can lead to residual stresses and sealing cracks. These potential stresses and sealing cracks are particularly problematic for high-pressure lamps.
HID lamps are typically assembled and dosed in a dry box, which includes a furnace to facilitate hot sealing with temperatures reaching about 1500 degrees centigrade or higher. Unfortunately, the dry box complicates the assembly of HID lamps due to the closed environment. In addition, the furnace typically subjects the dose materials to high temperatures, thereby limiting the operational pressure of the dose materials.
A system, in certain embodiments, includes a high intensity discharge lamp having a composite leg. The composite leg includes a plurality of leg sections coupled together in series. The plurality of leg sections includes different materials, coefficients of thermal expansion, Poisson's ratios, or elastic moduli, or a combination thereof. A method, in certain embodiments, includes enclosing a high intensity discharge within a ceramic arc envelope. The method also includes reducing thermal stresses associated with the high intensity discharge via a composite leg extending outwardly from the ceramic arc envelope. The composite leg includes a plurality of leg sections coupled together in series. The plurality of leg sections includes different materials, coefficients of thermal expansion, Poisson's ratios, or elastic moduli, or a combination thereof.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “top,” “bottom,” “above,” “below,” and variations of these terms is made for convenience, but does not require any particular orientation of the components.
The composite legs 12 and 14 may simplify the manufacturing process, reduce the potential for thermal stresses, increase the pressure capacity, increase the light output, and/or enable use of a wide variety of dosing materials. For example, in certain embodiments, an assembly process includes dosing the lamp 10 and sealing the composite legs 12 and 14 at room temperature without a dry box and/or a furnace. As a result, the illustrated lamp 10 is amenable to dosing with mercury and a high cold (e.g., room temperature) pressure of a buffer gas, such as 10 atmospheres of xenon. The composite legs 12 and 14 also may include different materials having different coefficients of thermal expansion, which gradually change (e.g., in steps) from one section to another to reduce thermal stresses during start up, operation, and shut down of the lamp 10.
In addition, the composite legs 12 and 14 may have any number of sections and different materials to provide the desired characteristics to improve performance of the lamp 10. For example, the composite legs 12 and 14 may include 2, 3, 4, 5, 6, 7, 8, 9, 10, or more different sections and/or materials. These sections of the composite leg 12 and 14 may include tubular sections that are coaxial and at least partially overlapping one another. In addition, the various tubular sections of the composite legs 12 and 14 may include one or more intermediate compliant seals (e.g., annular seals). The compliant seals have properties that are generally between those of the sections coupled together by the compliant seals. In this manner, the compliant seal provides a more gradual change in the properties from one section to another. These properties may include coefficient of thermal expansion, Poisson's ratio, elastic modulus, or a combination thereof.
As discussed in detail below, in certain embodiments, the composite legs 12 and 14 include one or more ceramic tubular sections and one or more metallic tubular sections. The one or more metallic tubular sections may include molybdenum, rhenium, molybdenum-rhenium alloy, niobium, or a combination thereof. For example, in each discussion of this alloy below, an exemplary molybdenum-rhenium alloy has about 35-55% by weight of rhenium. In certain embodiments, the molybdenum-rhenium alloy comprises about 44-48% by weight of rhenium. The molybdenum and molybdenum-rhenium alloy materials are thermochemically compatible with corrosive dose materials, such as metal halides. Moreover, the molybdenum, rhenium, molybdenum-rhenium alloy, and niobium materials enable sealing at room temperature without a dry box and furnace. For example, these materials are sufficiently ductile to enable mechanical compression via a crimping tool. The niobium may also have certain advantageous characteristics, such as high electrical conductivity.
As illustrated in
In the illustrated embodiment, the leg sections 20 and 22 are an integral part of the central hollow body 18. In other words, the hollow body 18 and leg sections 20 and 22 are a single or one-piece structure, which may be made from a suitable transparent ceramic. In alternative embodiments, the leg sections 20 and 22 are separate from the central hollow body 18, but are sealed at opposite end portions 24 and 26 of the hollow body 18. In such an embodiment, the leg sections 20 and 22 may be made of the same ceramic or a different ceramic than the hollow body 18. In the illustrated embodiment, the hollow body 18 and the leg sections 20 and 22 have a hollow tubular or cylindrical geometry, wherein the hollow body 18 has a diameter greater than the leg sections 20 and 22. The arc envelope 16 also defines an interior volume 28 to contain a dosing material 30 and electrode assemblies 32 and 34.
In certain embodiments, the lamp 10 may have a variety of different lamp configurations and types, such as a high intensity discharge (HID) or an ultra high intensity discharge (UHID) lamp. For example, certain embodiments of the lamp 10 comprise a high-pressure sodium (HPS) lamp, a ceramic metal halide (CMH) lamp, a short arc lamp, an ultra high pressure (UHP) lamp, or a projector lamp. Thus, the lamp 10 may be part of a video projector, a vehicle light, a vehicle, or a street light, among other things. As mentioned above, the lamp 10 is uniquely sealed to accommodate relatively extreme operating conditions. Externally, some embodiments of the lamp 10 are capable of operating in a vacuum, nitrogen, air, or various other gases and environments. Internally, some embodiments of the lamp 10 retain pressures exceeding 200, 300, or 400 bars and temperatures exceeding 1000, 1300, or 1400 degrees Kelvin. For example, certain configurations of the lamp 10 operate at internal pressure of 400 bars and an internal temperature at or above the dew point of mercury at 400 bars, i.e., approximately 1400 degrees Kelvin. These higher internal pressures are also particularly advantageous to short arc lamps, which are capable of producing a smaller (e.g., it gets smaller in all directions) arc as the internal lamp pressure increases. Different embodiments of the lamp 10 also hermetically retain the variety of dosing materials 30, such as a rare gas and mercury. In some embodiments, the dosing material 30 comprises a halide (e.g., bromine, iodine, etc.) or a rare earth metal halide. Certain embodiments of the dosing material also include a buffer gas, such as xenon gas.
The illustrated electrode assemblies 32 and 34 extend through and are supported by the composite legs 12 and 14. As illustrated in
The leg sections 20, 22, 36, and 38 of the composite legs 12 and 14 may include a variety of different materials with desirable characteristics for the lamp 10. For example, the leg sections 20 and 22 may be made of a ceramic, such as polycrystalline alumina (PCA), while the leg sections 36 and 38 may be made from a different ceramic, a non-ceramic material, a cermet, a metal, an alloy, or a combination thereof. For example, in one embodiment, the leg sections 36 and 38 may be made from molybdenum, or rhenium, or a molybdenum-rhenium alloy, or niobium, or a combination thereof. In the illustrated embodiment, the leg sections 36 and 38 are made from a metal or alloy that is both ductile and resistive to corrosive substances in the dosing material 30, for example, metal halides. Accordingly, the illustrated leg sections 36 and 38 of the embodiment of
In view of the ductility of the leg sections 36 and 38, the composite legs 12 and 14 are directly compressed and hermetically sealed about portions of the electrode assemblies 32 and 24. As illustrated, the leg sections 36 and 38 have compressed portions or crimps 46 and 48 disposed directly about lead wires 50 and 52 of the electrode assemblies 32 and 34. The illustrated leg sections 36 and 38 also include welds 54 and 56, such as laser welds, directly fusing the crimps 46 and 48 with the lead wires 50 and 52. These crimps 46 and 48 and associated welds 54 and 56 are performed without a dry box and/or a furnace. Therefore, the lamp 10 may be assembled, dosed, and sealed at room temperature without subjecting all of the components and the dosing material 30 to high heat associated with the furnace. As a result, the cold sealing (e.g., room temperature sealing) of the lamp 10 may enable substantially higher pressures of the dosing material 30, thereby improving light output and performance of the lamp 10. For example, the dosing material 30 may include mercury, a halide, and a buffer gas such as xenon. The composite legs 12 and 14 and unique seals provided by the compliant seals 42 and 44, the crimps 46 and 48, and the welds 54 and 56, may enable pressures as high as 10 atmospheres or even higher at room temperature. The high pressure capacity is particularly advantageous for certain buffer gases, such as xenon.
The electrode assemblies 32 and 34 along with the composite legs 12 and 14 enable precise control of an arc gap 58 to improve performance of the lamp 10. As illustrated, the electrode assemblies 32 and 34 and the composite legs 12 and 14 are all aligned lengthwise along and coaxial with the axis 40. During assembly, the electrode assemblies 32 and 34 can move along the axis 40 toward and away from one another to adjust the arc gap 58. Specifically, the electrode assemblies 32 and 34 include the lead wires 50 and 52, electrodes 60 and 62, and arc tips 64 and 66 separated from one another by the arc gap 58.
In certain embodiments, the assembly process includes moving the electrode assembly 32 lengthwise along the axis 40 within the leg section 36 until a desired position is reached within the hollow body 18. The process also may include compressing the ductile material of the leg section 36 directly about and engaging the lead wire 50 to create the crimp 46, which secures the position of the arc tip 64. The process also may include applying focused heat via a laser, an induction heating device, a welding torch, or another suitable focused heat source, to create the weld 54 between the leg section 36 and the lead wire 50. Thus, the composite leg 12 is completely sealed about the electrode assembly 32 in a room temperature environment prior to injecting the dose material 30.
Subsequently, in certain embodiments, the process may include inserting the electrode assembly 34 lengthwise along the axis 40 into the hollow body 18 through the composite leg 14. The process may include filling the arc envelope 16 with the dosing material 30 through the composite leg 14 via a processing station as discussed in further detail below. Again, the dosing material 30 is provided at room temperature without a dry box or furnace. Subsequently, the process may include compressing the leg section 38 directly about and engaging the lead wire 52 to create the crimp 48. The process may then proceed to apply focused heat to create the weld 56 directly fusing the leg section 38 to the lead wire 52. Advantageously, the process of crimping and applying focused heat does not significantly heat or shock the dosing material 30 within the arc envelope 16. Therefore, the process can result in a much greater pressure of the dosing materials 30, e.g., including a buffer gas such as xenon. In other embodiments, the process may include injecting the dosing material 30 through the composite leg 14 before insertion of the electrode assembly 34. Furthermore, the electrode assembly 34 is crimped and welded in place at a suitable position to set the desired arc gap 58 between the arc tips 64 and 66.
The illustrated electrode assemblies 32 and 34 of
In addition, the lead wires 50 and 52 have outer diameters that are smaller than inner diameters of the leg sections 36 and 38, thereby forming intermediate annular gaps 68 and 70. These annular gaps 68 and 70 may enable some expansion and contraction of the leg sections 36 and 38 relative to the lead wires 50 and 52, thereby reducing the possibility of stress on the leg sections 36 and 38. However, in some embodiments, the outer diameter of the lead wires 50 and 52 may be more closely fitting within the leg sections 36 and 38.
In the illustrated embodiment of
However, similar to the embodiment of
In the embodiment of
Similar to the embodiment of
In the embodiment of
In one embodiment, the leg sections 36, 38, 100, and 102 are all made of niobium. In another embodiment, the leg sections 36, 38, 100, and 102 are all made of molybdenum or a molybdenum-rhenium alloy. In a further embodiment, the leg sections 36 and 38 are both made of molybdenum or a molybdenum-rhenium alloy, while the leg sections 100 and 102 are both made of niobium. In another embodiment, the leg sections 36 and 38 are both made of a molybdenum-rhenium alloy, while the leg sections 100 and 102 are both made of molybdenum, or a different molybdenum-rhenium alloy, or a different metallic composition, or a cermet. Similar to the embodiment of
The assembly process for the lamp 10 of
Continuing with the assembly process, the lead assemblies 32 and 34 may be secured to the composite legs 12 and 14 either before or after sealing the leg sections 100 and 102 to the leg sections 36 and 38. In either case, the leg sections 36 and 38 may be compressed about and welded to the lead wires 50 and 52 as indicated by crimps 116 and 118 and welds 120 and 122. However, one of the legs 36 or 38 is not sealed shut about the respective lead wire 50 or 52 until the dosing material 30 is injected into the arc envelope 16. For example, the assembly process may include crimping and welding the leg section 36 about the lead wire 50, injecting the dosing material 30 into the arc envelope 16 through the open leg section 38, and then subsequently crimping and welding the leg section 38 about the lead wire 52. In this manner, the dosing material 30 is not subjected to the heat associated with a furnace. Furthermore, the focused heat applied to the leg section 38 and the lead wire 52 to create the weld 122 does not substantially increase the temperature of the dosing material 30 within the arc envelope 16.
In certain embodiments, the assembly process also cools or freezes the dosing material 30 and/or the lamp 10 as the dosing material 30 is injected into the arc envelope 16. For example, liquid nitrogen may be used to substantially cool the arc envelope 16 and the composite leg 12. Again, as discussed above with reference to
As discussed above with reference to
The leg sections 20 and 22, the leg sections 36 and 38, and the leg sections 140 and 142 may be made of the same or different materials such as a ceramic, a metal, an alloy, a cermet, or a combination thereof. In certain embodiments, the leg sections 20 and 22 are made of a transparent ceramic as part of the arc envelope 16. The leg sections 140 and 142 may be made of a ductile and/or electrically conductive material, such as a metal, an alloy, or a combination thereof. In some embodiments, the leg sections 140 and 142 are made of molybdenum, or rhenium, or a molybdenum-rhenium alloy, or niobium, or a combination thereof. The material of the leg sections 140 and 142 may be selected to provide good electrical conductivity while also enabling compression to form the crimps 152 and 154.
In one embodiment, the leg sections 140 and 142 are made of niobium, which has good electrical conductivity but poor resistance to corrosive materials such as a metal halide in the dosing material 30. Accordingly, in embodiments using niobium for the leg sections 140 and 142, the welds 156 and 158 may be located at the end portions 144 and 146 of the leg sections 140 and 142 as discussed above. In addition, protective layers may be disposed at the end portions 144 and 146 and/or along the interior of the leg sections 140 and 142. These protective coatings or layers may include molybdenum, or molybdenum-rhenium, or another suitable material resistant to attack by halides and other corrosive materials in the dosing material 30.
In addition, the leg sections 36 and 38 may be made with materials having properties (e.g., CTEs, Poisson's ratios, elastic moduli, etc.) between those of the leg sections 20 and 22 and the leg sections 140 and 142. In this manner, the composite legs 12 and 14 may have a gradual change in properties (e.g., CTEs, Poisson's ratios, elastic moduli, etc.), which may further reduce the possibility of thermal stresses arising within the legs 12 and 14. Furthermore, the compliant seals 42, 44, 148, and 150 may be selected with properties (e.g., CTEs, Poisson's ratios, elastic moduli, etc.) between the surrounding leg sections. As a result, the composite legs 12 and 14 may have a plurality (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, or more) of different materials or properties (e.g., CTEs, Poisson's ratios, elastic moduli, etc.) associated with the leg sections 20 and 22, the compliant seals 42 and 44, the leg sections 36 and 38, the compliant seals 148 and 150, and the leg sections 140 and 142. Furthermore, some embodiments of the compliant seals 42, 44, 148, and 150 may include a plurality of concentric layers of different materials with different properties (e.g., CTEs, Poisson's ratios, elastic moduli, etc.), thereby further reducing the gradients between adjacent leg sections.
In the illustrated embodiment, the leg sections 36 and 38 may be formed of a cermet, a metal, an alloy, or a combination thereof. For example, in one embodiment, the leg sections 36 and 38 are made of molybdenum, rhenium, a molybdenum-rhenium alloy, niobium, or a combination thereof. In one embodiment, the leg sections 20 and 22 are made of a transparent ceramic such as PCA, the leg sections 36 and 38 are made of a molybdenum-rhenium alloy, and the leg sections 140 and 142 are made of niobium. In addition, the electrode assemblies 32 and 34 may have a variety of material compositions as discussed in detail above.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
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