Discharge lamp and method of manufacturing electrode for discharge lamp

Abstract

To provide an electrode capable of bringing about a desired heat dissipation effect.SOLUTION: In an electrode 30 of a discharge lamp 10, a constitution (hereinafter, this side surface part is referred to as a heat dissipation function part J), which comprises two heat dissipation functions, that is, a heat dissipation structure 40 composed of a groove 42 and a coating layer 44, is formed for a side surface 34S of a body part 34.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a discharge lamp, such as a short arc type discharge lamp, and in particular to heat dissipation of electrodes. [Background technology]

[0002] When a discharge lamp is turned on, the electrode tip becomes very hot, causing the electrode material such as tungsten to melt and evaporate, blackening the discharge tube and reducing the illuminance of the lamp. To prevent overheating of the electrode, including the electrode tip, the surface area is increased by forming threaded or uneven grooves on the side of the electrode body, and tungsten powder or metal oxide is sintered on top of the groove to form a heat dissipation layer (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-306546 A Summary of the Invention [Problem to be solved by the invention]

[0004] The groove shape (shallowness, pitch, etc.) of the grooves formed on the electrode surface is determined with the aim of expanding the electrode surface area, but the heat dissipation performance, i.e., the emissivity, also changes depending on the groove shape. Meanwhile, the emissivity of the heat dissipation layer also differs depending on the material, such as the metal oxide, that is sintered, so if a heat dissipation layer is formed in the grooves without considering the relationship with the grooves, it is not possible to improve the heat dissipation performance, and in some cases, it may even reduce the heat dissipation effect.

[0005] Therefore, it is necessary to configure electrodes that can achieve a desired heat dissipation effect. [Means for solving the problem]

[0006] A discharge lamp according to one aspect of the present invention comprises a discharge tube and a pair of electrodes disposed opposite each other within the discharge tube, at least one of the electrodes being provided with a heat dissipation structure having a higher emissivity than the electrode base surface at least on a side surface of the electrode body, and a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body on which the heat dissipation structure is provided.

[0007] This allows the heat dissipation effect of the side part of the electrode body, which is due to the heat dissipation function of the heat dissipation structure and the heat dissipation function of the coating layer, to work most effectively based on the electrode material, the characteristics of the heat dissipation structure, the reflectance of the coating layer, etc. This leads to the highest emissivity of the side part of the electrode body based on the two heat dissipation functions.

[0008] In the side portion of the electrode body, in which such a heat dissipation structure and coating layer are layered, a heat dissipation effect can be obtained that cannot be obtained by simply forming grooves to expand the coating area in order to improve the heat dissipation performance of the coating layer.

[0009] As the heat dissipation structure, various configurations such as grooves, uneven shapes, and coating layers can be applied. For example, the heat dissipation structure is configured with a groove along the circumferential direction or the electrode axial direction of the electrode body, and the emissivity of the coating layer is configured to be greater than the emissivity of the groove.

[0010] The coating layer can be made of a material with a relatively high emissivity, and can be selected based on the electrode material, the operating temperature, and the like. The coating layer can be made of a material containing at least a metal and / or ceramic. It may be made of a coating layer containing at least the same type of metal as the electrode material. In consideration of improving heat dissipation performance, it can be made of at least zirconium and / or tantalum, for example, and can also contain the electrode material, such as tungsten or molybdenum.

[0011] When the heat dissipation structure is formed of a groove along the circumference of the electrode body, the combined emissivity of the heat dissipation structure and coating layer can be made to be 0.8 or greater when expressed by the following formula. ε=1 / (1+(L / S)×(1 / ε0-1)) Here, L is the axial length of the groove formation region, S is the total cross-sectional length, ε0 is the emissivity of the coating layer, and L / S is set to 0.9 or less.

[0012] Various configurations can be applied to the thickness of the coating layer, the shape of the groove, etc. For example, the distance from the central axis of the electrode to the layer surface of the coating layer can be configured to be shorter than the distance from the central axis of the electrode to the side surface of the electrode body that is not provided with a heat dissipation structure.

[0013] A non-coated heat dissipation structure that is not covered by a coating layer may be provided on the tapered surface of the tip end tapered portion of the electrode. Alternatively, a non-coated heat dissipation structure that is not covered by a coating layer may be provided on the side surface of the body portion of the electrode, closer to the electrode support rod than the heat dissipation structure. The non-coated heat dissipation structure can be applied to a location away from the heat dissipation structure.

[0014] A method for manufacturing a discharge lamp according to another aspect of the present invention includes forming an electrode having a columnar body and a tapered portion on the tip side, forming a groove on the side surface of the body along the circumferential direction of the electrode, and forming a coating layer on the groove by application, the coating layer having an emissivity higher than that of the groove. Effect of the Invention

[0015] According to the present invention, it is possible to configure an electrode capable of obtaining a desired heat dissipation effect. [Brief description of the drawings]

[0016] [Figure 1] 1 is a plan view of a discharge lamp according to a first embodiment. [Diagram 2]FIG. 2 is a schematic plan view of an electrode according to the first embodiment. [Diagram 3] FIG. 13 is a table showing the correlation between groove shape and emissivity of a coating layer. [Figure 4] FIG. 4 is a diagram showing the shape of the groove. [Diagram 5] FIG. 4 is a schematic plan view of an electrode of a discharge lamp according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The short arc type discharge lamp 10 is a large-sized discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (light emitting tube) 12 made of transparent quartz glass, and a pair of tungsten electrodes 20, 30 are arranged facing each other (coaxially) within the discharge tube 12. On both sides of the discharge tube 12, sealing tubes 13A, 13B made of quartz glass are connected to the discharge tube 12 and formed integrally with it. Mercury and rare gases such as halogen and argon gas are sealed in a discharge space DS within the discharge tube 12.

[0018] The cathode electrode 20 is supported by an electrode support rod 17A. Sealed in the sealed tube 13A are a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A that connects to an external power source, and a metal foil 16A that connects the electrode support rod 17A and the lead rod 15A. Similarly, the anode electrode 30 is sealed with mounting parts such as a glass tube (not shown) through which the electrode support rod 17B is inserted, a metal foil 16B, and a lead rod 15B. Furthermore, caps 19A and 19B are attached to the ends of the sealed tubes 13A and 13B, respectively.

[0019] 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).

[0020] 2 is a schematic plan view of the electrode (anode) 30. The electrode (cathode) 20 can also have a similar structure.

[0021] The electrode 30 has an electrode tip surface 32T and is composed of a tapered portion (hereinafter referred to as a tip taper portion) 32 and a columnar portion (hereinafter referred to as a body portion) 34 connected to the electrode support rod 17B. Here, the electrode 30 is integrally formed, but it is also possible to form the electrode 30 by joining the tip taper portion 32 and the body portion 34 by diffusion bonding such as SPS. It is also possible to join them via an intermediate member. The electrode 30 is composed of, for example, tungsten.

[0022] A heat dissipation structure 40 is provided on the side surface 34S of the body portion 34 (see the shaded area in FIG. 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 purposely employ a special heat dissipation structure, and functions to enhance heat dissipation. As shown in the enlarged portion of FIG. 2, 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 a laser or cutting.

[0023] 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 is made of a component having a higher emissivity than the groove 42. For example, the coating layer 44 is made of zirconium nitride, zirconium carbide, or a zirconium compound. Alternatively, the coating layer 44 includes a tantalum-based material such as tantalum nitride, or a ceramic-based material such as alumina. The coating layer 44 may also contain the same metal as the electrode 30, that is, tungsten or molybdenum. Other materials may be selected based on the operating temperature, such as metals such as titanium, oxides thereof, and alloys to which nickel or chromium is added.

[0024] A portion equipped with two heat dissipation functions, heat dissipation structure 40 composed of grooves 42 and coating layer 44 (hereinafter, this side portion is referred to as heat dissipation function part J), is formed on a part of side surface 34S of body part 34. This is not like the conventional method in which grooves are formed for the purpose of expanding the electrode surface area to increase the amount of heat dissipated and the grooves are provided as auxiliary heat dissipation structures, but rather, a combination of the heat dissipation function of grooves 42 and the heat dissipation function of coating layer 44 is configured to maximize the heat dissipation function in heat dissipation function part J.

[0025] This maximizes heat dissipation (emissivity) and suppresses the rise in electrode temperature. Since the coating layer 44 is formed on the grooves 42, the contact area is larger than that of a coating on the electrode base surface 34T, and the adhesion of the coating can be improved.

[0026] In addition, since the heat dissipation function part J is provided on the side surface 34S of the body part 34, exposure to arcs and flares is suppressed. Therefore, even if the temperature of the electrode 30 rises due to lighting the lamp, the coating can be prevented from peeling off and becoming thinner. In addition, since the groove 42 has a heat dissipation function, it is possible to maintain a certain degree of heat dissipation even if the coating peels off and becomes thinner.

[0027] 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 or thinning of the coating due to arcing or flaring can be effectively suppressed.

[0028] In this embodiment, by applying a formula for calculating the emissivity of the grooves 42 and the coating layer 44 in combination, it is possible to effectively increase the heat dissipation (emissivity) of the body portion 34 by appropriately combining the shape of the grooves 42 and the heat dissipation (emissivity) of the coating layer 44. This will be described in detail below.

[0029] Fig. 3 is a diagram showing a table of the correlation between the shape of the groove 42 and the emissivity of the coating layer 44. Fig. 4 is a diagram showing the shape of the groove.

[0030] 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) Here, L indicates the axial length (along the side surface 34S) of the region where the groove is formed, and S indicates the total length (total cross-sectional length) along the groove in a cross-sectional view of the groove (see FIG. 4).

[0031] The value of L / S is related to the groove pitch and number of grooves, i.e., the groove depth (slope length) in the groove formation area. The smaller the value of L / S, the greater the groove depth and number of pitches, and the closer the value of L / S is to 1, the shallower the grooves and the fewer the number of pitches. On the other hand, ε0 represents the emissivity specific to the material.

[0032] The emissivity ε of the heat dissipation function part J is derived (here, expressed as εgroove+coat) by replacing the emissivity ε0 specific to the material with the emissivity of the coating layer 44 (here, expressed as εcoat). However, since the coating layer 44 is very thin compared to the size (depth) of the groove 42, its thickness can be ignored.

[0033] 3 shows the emissivity εgroove+coat of the heat dissipation function part J, which is derived from a combination of the emissivity εcoat of the coating layer 44 and the L / S of the groove 42. For example, when the emissivity εcoat of the coating layer 44 is 0.8 and the groove 42 has an L / S value of 0.35, the emissivity εgroove+coat of the heat dissipation function part J is 0.92. In addition, when the emissivity εcoat of the coating layer 44 is 0.5 and the groove 42 has an L / S value of 0.2, the emissivity εgroove+coat of the heat dissipation function part is 0.83.

[0034] Here, the L / S and the emissivity εcoat of the coating layer 44 are determined so that the emissivity εgroove+coat of the heat dissipation function part J is 0.8 or more. However, the L / S of the groove 42 along the circumferential direction is determined to be 0.9 or less so that the groove 42 does not have an uneven shape similar to a rough surface. 0.8 is determined based on the emissivity of 0.4 of tungsten, which is the electrode material, for example.

[0035] By deriving the emissivity εgroove+coat of the portion having the two heat dissipation functions of the groove 42 and the coating layer 44 using the above formula (1), it becomes possible to freely select the components of the coating layer 44 and the shape of the groove 42 so as to obtain a desired emissivity. For example, it is possible to adopt a component and shape with higher heat dissipation properties to effectively (collaboratively) increase the emissivity of the body portion 34. In particular, by setting the emissivity of the coating layer 44 higher than that of the groove 42, it is possible to configure a heat dissipation function portion J in which the heat dissipation function of the coating layer 44 is the main function and the heat dissipation function of the groove 42 is the secondary function.

[0036] For example, when a coating layer 44 with high emissivity is used, the L / S value that satisfies 0.8 or more is broad, and a large number of shapes of grooves 42 can be selected. Because the combination can be optimized, a high emissivity can be maintained even if the L / S is large, that is, even if the grooves 42 are formed shallow. Furthermore, when the grooves 42 are shallow, it becomes easy to apply (attach) the coating layer 44 to the back of the grooves 42.

[0037] Depending on the L / S value of the groove 42, if the coating layer 44 is selected incorrectly, the emissivity obtained will be little different from that of the coating layer 44, and a sufficient heat dissipation effect will not be obtained. However, by referring to the table in Fig. 3, it is possible to maintain a high emissivity εgroove+coat for various groove shapes (L / S values).

[0038] 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 a groove is formed and no coating layer is formed thereon.

[0039] While the lamp is lit, the tapered side surface 32S is exposed to arcs and flares, and if a coating layer were provided, there is a possibility that the coating would peel off, but since no such coating layer is provided, it is possible to prevent the inside of the discharge tube 12 from becoming dirty with coating components. Also, by determining the L / S so that the emissivity of the groove 42 is high, the heat dissipation properties of the entire electrode 30 can be further improved.

[0040] Meanwhile, a side portion 33 made of the electrode base surface is provided between the heat dissipation structures 40 and 50, and they are separated from each other without being adjacent to each other. By providing such a side portion 33, it is possible to prevent arcs and flares from moving to the heat dissipation function part having the coating layer while the lamp is lit. In addition, since the boundary portion 33P between the tip side tapered portion 32 and the body portion 34 is rounded, it is possible to protect the coating layer 44 from the occurrence of abnormal discharge and overheating due to abnormal discharge.

[0041] The electrode 30 of such a discharge lamp can be manufactured as follows. First, an electrode having a columnar body and a tapered tip is formed, and a groove is formed along the circumferential direction on the side of the body by processing such as laser or cutting. A coating layer is then formed on the groove by application. At this time, by setting the emissivity of the coating layer higher than that of the groove, a heat dissipation function part with high emissivity can be formed. In addition to spraying, known means such as deposition, sputtering, and CVD can be used for application, as long as the coating can be applied uniformly. The applied coating may be sintered in a furnace (heating device) or by laser.

[0042] Next, a discharge lamp according to a second embodiment will be described with reference to Fig. 5. In the second embodiment, a heat dissipation function part in which a coating layer is laid on a heat dissipation structure composed of grooves is formed on the tapered part on the tip side and the body part, while a heat dissipation structure in which only grooves are formed is provided on the electrode support rod side.

[0043] 5 is a schematic plan view of an electrode of a discharge lamp according to the second embodiment. The anode 30' includes a tip tapered portion 32 and a body portion 34. A heat dissipation function portion J, in which a coating layer 44' is formed on a heat dissipation structure 40' consisting of grooves, is formed continuously from the middle of the body portion 34 across the tip tapered portion 32. Meanwhile, a heat dissipation structure 50' (non-coated heat dissipation structure) consisting only of grooves along the circumferential direction is provided on the side surface 34S of the body portion 34, closer to the electrode support rod 17B than the heat dissipation function portion J.

[0044] For example, due to reasons such as low lamp output and small electrode size, it may be possible to prevent the coating layer 44' formed on the tip taper portion 32 from peeling off or disappearing due to arcing, flare, etc. Therefore, by forming a coating layer 44' on the tip taper portion 32 as well as the body portion 34, it is possible to improve heat dissipation. As in the first embodiment, an electrode bare surface area may be provided between the heat dissipation structure 40' on which the coating layer 44' is formed and the heat dissipation structure 50'.

[0045] In the first and second embodiments, the heat dissipation structure is configured by grooves along the circumferential direction, but it may be configured by grooves along the electrode axial direction. Also, a heat dissipation structure other than grooves may be adopted. For example, a matte rough surface obtained by sandblasting or a blackening suppressor may be configured as the heat dissipation structure. If the main purpose is to suppress blackening, a blackening suppressor may be adopted, and if improved heat dissipation is required, a groove may be configured. If low cost is required, a matte rough surface can be adopted. The heat dissipation structure may be determined according to the electrode shape, electrode material, ease of processing such as cutting, etc.

[0046] In addition, in order to prevent the coating layer formed on the heat dissipation structure from peeling off, it is also possible to configure a coating layer made of a different material as the heat dissipation structure. In other words, a coating layer can be layered on top of a coating layer (heat dissipation structure). [Explanation of symbols]

[0047] 10. Discharge Lamp 30 electrodes 40 Heat dissipation structure 42 Groove 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, A discharge lamp characterized in that at least one of the electrodes has an exposed side portion consisting of an electrode base surface, and at least the side of the electrode body has a heat dissipation structure having a higher emissivity than the electrode base surface, and a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body on which the heat dissipation structure is provided.

2. The heat dissipation structure is formed of a groove along the circumferential direction or the electrode axial direction of the electrode body portion, 2. The discharge lamp of claim 1, wherein the emissivity of the coating layer is greater than the emissivity of the groove.

3. The heat dissipation structure is formed of a groove along the circumferential direction of the electrode body portion, 3. The discharge lamp according to claim 1, wherein the components of the coating layer and the shape of the grooves are such that the combined emissivity ε of the heat dissipation structure and the coating layer is 0.8 or more when the combined emissivity ε is expressed by the following formula: ε=1 / (1+(L / S)×(1 / ε 0 -1)) Here, L is the axial length of the groove formation region, S is the total cross-sectional length, ε 0 is the emissivity of the coating layer, and L / S is set to 0.9 or less.

4. A discharge tube; A pair of electrodes disposed opposite each other within the discharge tube, At least one of the electrodes is provided with a heat dissipation structure having a higher emissivity than the surface of the electrode substrate at least on a side surface of the electrode body, and a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body on which the heat dissipation structure is provided; The heat dissipation structure is formed of a groove along the circumferential direction or the electrode axial direction of the electrode body portion, A discharge lamp characterized in that the distance from the central axis of the electrode to the top of said groove is shorter than the distance from the central axis of the electrode to a side surface of the electrode body not provided with said heat dissipation structure.

5. A discharge tube; A pair of electrodes disposed opposite each other within the discharge tube, At least one of the electrodes is provided with a heat dissipation structure having a higher emissivity than the surface of the electrode substrate at least on a side surface of the electrode body, and a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body on which the heat dissipation structure is provided; a non-coated heat dissipation structure that is not covered by the coating layer on a tapered surface of a tip side tapered portion of the electrode; The discharge lamp according to claim 1, wherein the non-coated heat dissipation structure is spaced from the heat dissipation structure.

6. A discharge tube; A pair of electrodes disposed opposite each other within the discharge tube, At least one of the electrodes is provided with a heat dissipation structure having a higher emissivity than the surface of the electrode substrate at least on a side surface of the electrode body, and a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side portion of the electrode body on which the heat dissipation structure is provided; A discharge lamp comprising a non-coated heat dissipation structure, which is not covered by a coating layer, on the side surface of the body portion of the electrode, closer to the electrode support rod than the heat dissipation structure.

7. 2. The discharge lamp according to claim 1, further comprising a second coating layer made of a material different from that of the coating layer, the second coating layer being formed on the coating layer.

8. 8. A discharge lamp according to claim 1, wherein the coating layer comprises at least a metal and / or a ceramic.

9. 9. The discharge lamp according to claim 1, wherein the coating layer is made of a coating layer containing at least the same type of metal as the electrode material.

10. 10. A discharge lamp according to any one of the preceding claims, characterized in that the coating layer contains at least zirconium and / or tantalum.

11. An electrode having a cylindrical body and a tapered tip is formed. A groove is formed on the side surface of the body portion along the circumferential direction of the electrode. A method for manufacturing an electrode for a discharge lamp, comprising applying a coating layer having an emissivity higher than that of the groove on the groove by coating, the method comprising the steps of: a method for manufacturing an electrode for a discharge lamp, comprising determining a component of the coating layer and a shape of the groove so that a combined emissivity ε of the groove and the coating layer is 0.8 or more when expressed by the following formula: ε=1 / (1+(L / S)×(1 / ε 0 -1)) Here, L represents the axial length of the groove forming region, and S represents the total cross-sectional length. 0 indicates the emissivity of the coating layer, and L / S is set to 0.9 or less.

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