Discharge lamp and method of manufacturing electrodes for discharge lamp

Abstract

To improve heat resistance and durability of an electrode surface while enhancing heat radiation property in a discharge lamp.SOLUTION: On an electrode 30 of a discharge lamp 10, a coating layer 44 is formed on a heat radiation structure 40 configured by grooves 42. The coating layer 44 is irradiated with laser to form a mixed layer 43 where an electrode material and a coating component are mixed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to discharge lamps such as short arc discharge lamps, and more particularly to heat dissipation of electrodes. [Background technology]

[0002] When a discharge lamp is lit, the electrode tip becomes very hot, causing electrode materials such as tungsten to melt and evaporate, blackening the discharge tube and reducing the lamp's illuminance.To prevent overheating of the electrode, including the electrode tip, a screw-shaped groove is made on the side of the electrode body to increase the surface area, and tungsten powder is sintered on top of the groove to form a heat dissipation layer (see Patent Document 1).

[0003] Furthermore, a method is known in which a metal oxide heat dissipation layer is formed on the uneven surface of an electrode to improve the adhesion of the heat dissipation layer on the electrode surface (see Patent Document 2). In this method, an uneven surface with a surface roughness of Rmax 10 μm or more is formed on the electrode surface, and oxide powder containing titanium oxide or chromium oxide is mixed in a solvent, applied to the electrode surface, and sintered to form a porous heat dissipation layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-306546 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-105059 Summary of the Invention [Problem to be solved by the invention]

[0005] Even if the roughness of the electrode surface is adjusted, there is a limit to how much adhesion between the electrode surface and the heat dissipation layer can be improved, and the heat dissipation layer may peel off due to the high temperatures during lamp operation, which may result in the heat dissipation performance not being maintained and the electrode surface not being adequately protected.

[0006] Therefore, it is necessary to improve the heat dissipation performance while also improving the heat resistance and durability of the heat dissipation layer to adequately protect the electrode surface. [Means for solving the problem]

[0007] A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes arranged opposite each other within the discharge tube. At least one of the electrodes comprises, at least on the side surface of the electrode body, a coating layer and a portion where the coating component of the coating layer and the electrode material are mixed (herein referred to as a mixed layer). The term "comprises a mixed layer" is defined here not only when the mixed layer is layered on the side surface of the electrode body, but also when the mixed portion is partially scattered.

[0008] The degree of mixing of the electrode material and the coating component in the mixed layer (mixed portion) can be broadly defined as long as the coating component and the electrode material are mixed together. On the other hand, from the viewpoint of adequately protecting the electrode surface, it is possible to provide a mixed portion in which the electrode material is the main component as the mixed layer.

[0009] The mixed layer on the side surface of the electrode body can be formed in various ways, for example, it can be configured to be included as part of the coating layer. Furthermore, when a heat dissipation structure with a higher emissivity than the electrode substrate surface is provided, it is possible to form a coating layer on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body where the heat dissipation structure is provided, and the mixed layer. The heat dissipation structure can also be formed in various ways, for example, it can be formed as a groove along the circumferential direction or the electrode axial direction of the electrode body.

[0010] The coating layer may be configured to contain various components, for example, the coating layer may contain at least zirconium and / or tantalum, or may contain the same type of metal as the electrode material.

[0011] Another aspect of the present invention is a method for manufacturing a discharge lamp electrode, which includes forming an electrode having a cylindrical body and a tapered tip, forming a coating layer on the surface of the electrode, and then irradiating the coating layer with a laser. The laser irradiation can adjust the optical output or focal position. For example, the focal position can be adjusted by shifting it toward or away from the electrode base surface. [Effects of the Invention]

[0012] According to the present invention, the heat dissipation property can be improved, while the heat resistance and durability of the coating layer can be improved, and the electrode surface can be sufficiently protected. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic plan view of a discharge lamp according to a first embodiment. [Figure 2] FIG. 2 is a schematic plan view of the electrode of the first embodiment. [Figure 3] FIG. 2 is a diagram schematically illustrating the shape of a groove. [Figure 4] FIG. 4 is a schematic plan view of an electrode of a discharge lamp according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The short arc type discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (light emitting tube) 12 made of transparent quartz glass, within which a pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially). On both sides of the discharge tube 12, sealed tubes 13A, 13B made of quartz glass are connected to and integrally formed with the discharge tube 12. Mercury and a rare gas such as halogen or argon gas are sealed in a discharge space DS within the discharge tube 12.

[0015] Electrode 20, which serves as the cathode, is supported by electrode support rod 17A. Sealed in sealed tube 13A are a glass tube (not shown) through which electrode support rod 17A is inserted, lead rod 15A that connects to an external power supply, and metal foil 16A that connects electrode support rod 17A to lead rod 15A. Similarly, for electrode 30, which serves as the anode, are sealed with mounting parts such as a glass tube (not shown) through which electrode support rod 17B is inserted, metal foil 16B, and lead rod 15B. Furthermore, bases 19A and 19B are attached to the ends of sealed tubes 13A and 13B, respectively.

[0016] When a voltage is applied to the pair of electrodes 20, 30, an arc discharge occurs between the electrodes 20, 30, and light is emitted toward the outside of the discharge tube 12. Here, a power of 1 kW or more is input. The light emitted from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

[0017] 2 is a schematic plan view of the electrode (anode) 30. The electrode (cathode) 20 can also have a similar structure.

[0018] The electrode 30 has an electrode tip surface 32T and is composed of a tapered portion (hereinafter referred to as the tip tapered portion) 32 and a columnar portion (hereinafter referred to as the body portion) 34 connected to the electrode support rod 17B. Here, the electrode 30 is composed of an integral body, but it is also possible to form the electrode 30 by joining a member having the tip tapered portion 32 and a member having the body portion 34 by solid-state bonding such as diffusion bonding. It is also possible to join them via an intermediate member. The electrode 30 is composed of tungsten, molybdenum, or an alloy of these, and here it is composed of tungsten.

[0019] A heat dissipation structure 40 is provided on the side surface 34S of the body portion 34 (see the shaded area in Figure 2). The heat dissipation structure 40 has a higher emissivity than the bare surface 34T of the body portion 34, i.e., a surface that does not have a special heat dissipation structure, and functions to enhance heat dissipation. As shown in the enlarged portion of the side surface 34S in Figure 2 (see symbol L1), the heat dissipation structure 40 here is configured with grooves 42 formed at a predetermined pitch along the circumferential direction (around the electrode axis). The grooves 42 can be formed, for example, by laser or cutting.

[0020] Furthermore, a coating layer 44 is formed on the side surface 34S of the body portion 34 on which the heat dissipation structure 40 (groove 42) is provided. The coating layer 44 contains zirconium nitride, zirconium carbide, or a zirconium compound. It may also contain the same metal as the electrode 30, i.e., tungsten or molybdenum. The coating layer 44 may contain a tantalum-based material such as tantalum nitride, a ceramic material such as zirconia, or a mixture of these.

[0021] 2, the height of the apex 42P of the groove 42 covered with the coating layer 44, i.e., the distance from the electrode axis C to the apex 42P (layer surface), is located closer to the electrode center than the side surface 34S of the body portion 34. By positioning the apex 42P of the groove 42 recessed from the side surface 34S of the body portion 34, peeling and thinning of the coating due to arcing and flaring can be effectively prevented.

[0022] The coating layer 44 functions to further enhance the heat dissipation function of the heat dissipation structure 40 (grooves 42), and here has a higher emissivity than the grooves 42. A portion equipped with two heat dissipation functions, the heat dissipation structure 40 consisting of the grooves 42 and the coating layer 44 (hereinafter, this side portion will be referred to as heat dissipation function portion J), is formed on a part of the side surface 34S of the body portion 34. The emissivity ε of the surface on which the grooves are formed can be approximately expressed by the following equation (1): ε=1 / (1+(L / S)×(1 / ε0-1)) ···(1) where L is the axial length (along the side surface 34S) of the groove formation area, and S is the total length along the groove in the cross-sectional view of the groove (total cross-sectional length) (see Figure 3). The emissivity ε of the surface on which the grooves are formed is derived by replacing the material-specific emissivity ε0 with the emissivity of the coating layer 44. However, because the coating layer 44 is very thin compared to the size (depth) of the grooves, its thickness can be ignored.

[0023] By applying the above formula (1) that derives the combined emissivity of the grooves 42 and the coating layer 44, it is possible to appropriately combine the shape of the grooves 42 and the heat dissipation property (emissivity) of the coating layer 44, thereby effectively (collaboratively) improving the heat dissipation property (emissivity) of the body portion 34. In particular, by setting the emissivity of the coating layer 44 higher than that of the grooves 42, it is possible to configure a heat dissipation function portion J in which the heat dissipation function of the coating layer 44 is primary and the heat dissipation function of the grooves 42 is secondary.

[0024] For the body portion 34 provided with such a heat dissipation function portion J, a heat dissipation structure (non-coated heat dissipation structure) 50 is provided on the tapered side surface (surface) 32S of the tip side tapered portion 32, in which only grooves are formed and no coating layer is formed thereon.

[0025] In this embodiment, not only is a coating layer 44 formed on the heat dissipation structure 40, but a portion of the coating layer 44 exists as a mixed portion 43, where the electrode material and the coating components are mixed. However, in FIG. 2, a portion of the mixed portion is indicated by the reference numeral 43, and mixed portions exist in places other than the portion indicated by the reference numeral 43 in FIG. 2. The mixed portion 43 has a thickness on the order of μm and is irregularly formed between the coating layers 44. Furthermore, a relatively large amount of the mixed portion 43 is formed near the electrode substrate surface 34T of the heat dissipation structure 40, i.e., near the tops 42P of the grooves 42. Hereinafter, this mixed portion 43 will be referred to as a mixed layer.

[0026] As shown in the enlarged portion of Figure 2 (see symbol L2), in the mixed layer 43, part of the electrode material of the heat dissipation structure 40 and part of the coating layer 44 are mixed together, and the coating component is supported by the electrode material. In the mixed layer 43, the electrode material is the dominant component (at%), so that the coating component is surrounded by the electrode material. The part of the electrode material that contains a large amount of tungsten is indicated by symbol C1, and the part of the electrode material that contains a large amount of zirconium is indicated by symbol C2.

[0027] In the mixed layer 43, the coating components are integrated with the base material (tungsten) of the electrode material, but are not yet alloyed. The partial formation of this mixed layer 43 increases mechanical strength and durability, and can suppress peeling of the coating layer 44. The heat dissipation properties of the coating layer 44 are maintained, and the coating layer will not peel off and roughen the electrode surface, so the electrode surface can be protected.

[0028] Furthermore, because the main component of mixed layer 43 is the electrode material, the coating component does not melt more than necessary, and the heat dissipation function from side surface 34S can be fully exerted. On the other hand, because mixed layer 43 is formed near tops 42P of grooves 42, which have low heat capacity, peeling and thinning of the coating can be suppressed. Furthermore, if the coating component contains the same component as the electrode material, mixed layer 43 becomes stronger.

[0029] The electrodes 30 of such a discharge lamp can be manufactured as follows.

[0030] First, an electrode with a cylindrical body and a tapered tip is formed, and a groove is formed along the circumferential direction on the side of the body using a laser or cutting process. Next, a coating layer is formed on the groove by coating. At this time, by setting the emissivity of the coating layer higher than that of the groove, a heat dissipation function with high emissivity can be created. Note that methods that can be used to apply the coating uniformly, such as spraying, vapor deposition, sputtering, and CVD, can be used.

[0031] The grooves formed in the coating layer are then partially irradiated with a laser, melting part of the coating layer and part of the electrode surface to form a mixed layer. The temperature at which the laser melts is lower than the sintering temperature. The laser irradiation location and irradiation time can be adjusted to achieve the desired location and thickness. Furthermore, under natural cooling, the molten tungsten cools and solidifies into a spherical shape, firmly adhering. On the other hand, the irradiation time and cooling period during laser irradiation can also be controlled. This prevents the molten tungsten from becoming spherical when it cools and solidifies.

[0032] The laser light intensity is adjusted to achieve an appropriate melting of the coating layer (avoiding excessive melting). The output setting of the device may be controlled, or the focal position may be controlled. For example, by shifting the focal position away from (moving away from) the electrode substrate surface, the laser light intensity can be reduced and a mixed layer can be formed on the top side of the groove 42. The same can be achieved by shifting the focal position toward the electrode substrate surface.

[0033] After the mixed layer is formed, it may be sintered in a furnace, etc. When the laser irradiation is performed in the atmosphere, the surface may be oxidized and removed in a furnace.

[0034] Next, a discharge lamp according to a second embodiment will be described with reference to Fig. 4. In the second embodiment, a heat dissipation function part in which a coating layer is laid on a heat dissipation structure consisting of grooves is formed on the tapered part at the tip end and the body part, while a heat dissipation structure in which only grooves are formed is provided on the electrode support rod side.

[0035] 4 is a schematic plan view of an electrode of a discharge lamp according to the second embodiment. The anode 30' includes a tip-side tapered portion 32 and a body portion 34. A heat-dissipating function portion J, in which a coating layer 44' is formed on a heat-dissipating structure 40' consisting of grooves, is formed continuously from the middle of the body portion 34 to the tip-side tapered portion 32. Meanwhile, a heat-dissipating structure 50' (non-coated heat-dissipating structure) consisting only of circumferential grooves is provided on the side surface 34S of the body portion 34, closer to the electrode support rod 17B than the heat-dissipating function portion J.

[0036] In the above-described embodiment, the mixed layer is included in part of the coating layer, but the mixed layer may be formed in a planar shape along the circumferential direction of the electrode. Furthermore, the coating layer and the mixed layer may be separated. For example, the region closer to the electrode tip surface, which becomes relatively hot, may be made of a highly heat-resistant mixed layer, and the region closer to the electrode support rod, which becomes cooler than the electrode tip surface, may be made of a coating layer.

[0037] In the first and second embodiments, the heat dissipation structure is formed by grooves along the circumferential direction. However, grooves along the electrode axis direction may also be used. Heat dissipation structures other than grooves may also be used. For example, the heat dissipation structure may be formed by a matte finish produced by sandblasting or a blackening suppressor. If the primary purpose is to suppress blackening, a blackening suppressor is used, and if improved heat dissipation is desired, grooves are used. A matte finish may be used if low cost is desired. The heat dissipation structure may be determined based on factors such as lamp output, electrode shape, electrode material, and ease of machining (e.g., cutting). The heat dissipation structure may also be formed by coating layers made of different materials. That is, a coating layer may be layered on top of a coating layer (heat dissipation structure). In this case, the mixed layer may be a mixture of part of the electrode material, part of the coating layer (first layer), and part of the coating layer (second layer). [Explanation of symbols]

[0038] 10. Discharge lamp 30 electrodes 40 Heat dissipation structure 42 Groove 43 Mixed layer 44 coating layer 50 Heat dissipation structure (non-coated heat dissipation structure)

Claims

1. A discharge tube; a pair of electrodes disposed opposite each other within the discharge tube; At least one of the electrodes has a coating layer and a mixed portion in which a coating component of the coating layer and the electrode material are mixed together at least on a side surface of the electrode body portion, the coating layer and the mixed portion are formed on a groove formed in the circumferential direction or the electrode axial direction of the electrode body portion, A discharge lamp characterized in that the mixed portion is formed more in the vicinity of the top of the groove than in the vicinity of the bottom.

2. A discharge lamp as described in claim 1, characterized in that the groove has a heat dissipation structure with a higher emissivity than the electrode base surface.

3. 2. The discharge lamp according to claim 1, wherein the groove is formed along the circumferential direction of the electrode body portion.

4. 4. The discharge lamp according to claim 1, wherein the coating layer contains the same type of metal as the material of the electrodes.

5. 5. The discharge lamp according to claim 1, wherein the coating layer contains at least zirconium and / or tantalum.

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