Discharge lamp and manufacturing method of electrode for discharge lamp

Abstract

The present invention provides a discharge lamp and a method for manufacturing an electrode for the discharge lamp, which constitutes an electrode capable of obtaining a desired heat dissipation effect. In the electrode (30) of the discharge lamp (10), a structure having two heat dissipation functions, namely a coating (44) and a heat dissipation structure (40) composed of grooves (42), is formed on the side (34S) of the main body (34).

Description

Technical Field

[0001] This invention relates to discharge lamps such as short-arc discharge lamps, and particularly to heat dissipation of electrodes. Background Technology

[0002] During the illumination of the discharge lamp, the front end of the electrode becomes very hot, causing the electrode material, such as tungsten, to melt, evaporate, and the discharge tube to blacken, resulting in a decrease in lamp illumination. To prevent the electrode, including the front end of the electrode, from overheating, a threaded or uneven groove is used to increase the surface area of ​​the side of the electrode body. On top of this groove, powder of tungsten or metal oxide is sintered to form a heat dissipation layer (see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2000-306546

[0004] Regarding the grooves formed on the electrode surface, the shape of the grooves (the depth, spacing, etc.) is determined with the aim of increasing the electrode surface area, but the heat dissipation performance, i.e., the emissivity, will also vary depending on the shape of the grooves. On the other hand, the emissivity of the heat dissipation layer also varies depending on the raw materials such as sintered metal oxides. Even if a heat dissipation layer is formed on the groove without considering its relationship with the groove, it may not be possible to further improve the heat dissipation performance, and in some cases, it may even reduce the heat dissipation effect. Summary of the Invention

[0005] Therefore, it is desirable to construct electrodes that can achieve the desired heat dissipation effect.

[0006] As one aspect of the present invention, a discharge lamp includes: a discharge tube; and a pair of electrodes disposed opposite each other within the discharge tube, wherein at least one electrode has a heat dissipation structure on at least one side of its electrode body portion having an emissivity higher than that of the electrode substrate surface. Furthermore, a coating is formed on the heat dissipation structure, which further increases the emissivity of the side portion of the electrode body portion where the heat dissipation structure is provided.

[0007] Furthermore, by considering the characteristics of the electrode raw materials, the heat dissipation structure, and the reflectivity of the coating, the heat dissipation effect of the side portion of the electrode body, resulting from the heat dissipation function of both the heat dissipation structure and the coating, can be maximized. This is related to maximizing the emissivity of the side portion of the electrode body based on these two heat dissipation functions.

[0008] On the side portion of the electrode body, where the heat dissipation structure and coating are layered, a heat dissipation effect that cannot be obtained by simply forming grooves to increase the coating area and improve the heat dissipation performance of the coating can be achieved.

[0009] As a heat dissipation structure, various structures such as grooves, concave and convex shapes, and coatings can be used. For example, it can be composed of grooves along the circumference or axial direction of the electrode body, and the emissivity of the coating is greater than that of the groove.

[0010] The coating can be made of raw materials with high emissivity, and can be selected based on the electrode raw materials and operating temperature. The coating can be made of raw materials containing at least metals and / or ceramics. It can also be made of a coating containing at least a metal of the same type as the electrode raw materials. If improved heat dissipation is desired, it can be configured, for example, to be made of at least zirconium and / or tantalum, and may also contain electrode raw materials such as tungsten or molybdenum.

[0011] When the heat dissipation structure is composed of grooves along the direction surrounding the electrode body, the emissivity of the heat dissipation structure and the coating combined can be 0.8 or higher when expressed by the following formula.

[0012] ε=1 / (1+(L / S)×(1 / ε0-1))

[0013] Where L represents the axial length of the groove formation area, and S represents the total cross-sectional length. ε0 represents the emissivity of the coating. Furthermore, L / S is set to 0.9 or less.

[0014] Various structures can be applied to the coating thickness, the shape of the groove, etc. For example, it can be configured such that the distance from the electrode's central axis to the coating surface is shorter than the distance from the electrode's central axis to the side of the electrode body without a heat dissipation structure.

[0015] Alternatively, an uncoated heat dissipation structure can be provided on the tapered surface of the tapered portion at the front end of the electrode. Alternatively, an uncoated heat dissipation structure can be provided on the side of the electrode body closer to the electrode support rod than the heat dissipation structure. The uncoated heat dissipation structure can be applied to a location separate from the heat dissipation structure.

[0016] Another aspect of the present invention is a method for manufacturing an electrode for a discharge lamp, characterized in that an electrode having a front-end tapered portion and a columnar main body portion is formed, a groove along the circumference of the electrode is formed on the side of the main body portion, and a coating with an emissivity greater than that of the groove is formed on the groove by coating.

[0017] According to the present invention, it is possible to construct an electrode that can achieve the desired heat dissipation effect. Attached Figure Description

[0018] Figure 1 This is a top view of the discharge lamp according to the first embodiment.

[0019] Figure 2 This is a schematic top view of the electrode according to the first embodiment.

[0020] Figure 3 This is a graph showing the relationship between the shape of the groove and the emissivity of the coating.

[0021] Figure 4 This is a diagram showing the shape of the groove.

[0022] Figure 5 This is a schematic top view of the electrodes of the discharge lamp in the second embodiment.

[0023] Label Explanation

[0024] 10: Discharge lamp; 30: Electrode; 40: Heat dissipation structure; 42: Groove; 44: Coating; 50: Heat dissipation structure (uncoated heat dissipation structure). Detailed Implementation

[0025] The short-arc discharge lamp 10 is a large discharge lamp capable of emitting high-brightness light. It has a roughly spherical discharge tube (light-emitting tube) 12 made of transparent quartz glass, and a pair of tungsten electrodes 20 and 30 are arranged opposite each other (coaxially) inside the discharge tube 12. On both sides of the discharge tube 12, quartz glass sealing tubes 13A and 13B are connected to the discharge tube 12 and integrally formed. The discharge space DS inside the discharge tube 12 is filled with mercury and rare gases such as halogens and argon.

[0026] The cathode electrode 20 is supported by an electrode support rod 17A. Sealed within the sealing tube 13A are components including a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A connected to an external power source, and a metal foil 16A connecting the electrode support rod 17A and the lead rod 15A. Similarly, the anode electrode 30 is sealed with mounting components including a glass tube (not shown) through which the electrode support rod 17B is inserted, a metal foil 16B, and a lead rod 15B. Furthermore, lamp holders 19A and 19B are respectively installed at the ends of the sealing tubes 13A and 13B.

[0027] When a voltage is applied to a pair of electrodes 20 and 30, an electric arc discharge is generated between electrodes 20 and 30, radiating light towards the outside of the discharge tube 12. Here, a power of 1 kW or more is supplied. The light radiated from the discharge tube 12 is guided in a predetermined direction by a reflector (not shown).

[0028] Figure 2 This is a schematic top view of electrode (anode) 30. Electrode (cathode) 20 may also have the same construction.

[0029] The electrode 30 has a conical portion (hereinafter referred to as the front-end conical portion) 32, which has an electrode front end face 32T; and a columnar portion (hereinafter referred to as the main body portion) 34, which is connected to the electrode support rod 17B. Here, the electrode 30 is integrally formed, but the front-end conical portion 32 and the main body portion 34 can also be formed by bonding the electrode 30 through diffusion bonding such as SPS. Alternatively, bonding can be performed via an intermediate component. The electrode 30 is made of tungsten, for example.

[0030] A heat dissipation structure 40 is provided on the side 34S of the main body 34 (see reference). Figure 2 (The diagonal portion). Compared to the substrate surface 34T of the main body 34 (i.e., the surface without a specially designed heat dissipation structure), the heat dissipation structure 40 has a higher emissivity and improves heat dissipation. For example... Figure 2 As shown in the enlarged view, the heat dissipation structure 40 is a structure formed by creating grooves 42 along the circumferential direction (around the electrode axis) at predetermined intervals. The grooves 42 can be formed, for example, by laser or cutting.

[0031] Furthermore, a coating 44 is formed on the side 34S of the main body 34 where the heat dissipation structure 40 (slot 42) is provided. Here, the coating 44 uses a component with a higher emissivity than the slot 42. For example, the coating 44 is composed of zirconium nitride or zirconium carbide, or a zirconium compound. Alternatively, it may contain tantalum-based raw materials such as tantalum nitride or ceramic-based raw materials such as alumina. In addition, the coating 44 may also contain the same metal as the electrode 30, i.e., tungsten or molybdenum. Furthermore, depending on the operating temperature, a metal system such as titanium or its oxide, or an alloy system with added nickel or chromium, may be selected.

[0032] A portion having both heat dissipation functions, namely the coating 44 and the heat dissipation structure 40 formed by the groove 42 (hereinafter referred to as the heat dissipation function portion J), is formed on a part of the side surface 34S of the main body portion 34. This is not, as in the past, where the groove was formed to increase the electrode surface area and thus dissipate more heat, and the groove was intended as an auxiliary heat dissipation structure. Instead, the combination of the heat dissipation function of the groove 42 and the heat dissipation function of the coating 44 is configured to maximize the heat dissipation function in this heat dissipation function portion J.

[0033] This maximizes heat dissipation (emissivity) and suppresses electrode temperature rise. Because the coating 44 is formed in the groove 42, the contact area is larger compared to coating on the electrode substrate surface 34T, thus improving coating adhesion.

[0034] Furthermore, since the heat dissipation unit J is located on the side 34S of the main body 34, it is possible to suppress the heat dissipation unit J from being exposed to electric arcs or flares. Therefore, even if the temperature of the electrode 30 rises due to the lamp being lit, it is possible to suppress paint peeling and thinning. 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 paint peels off and thins.

[0035] In particular, such as Figure 2 As shown, the height of the top 42P of the groove 42 covered by the coating 44, that is, the distance from the electrode axis C to the top 42P (layer surface), is closer to the electrode center side than the side 34S of the main body 34. By positioning the top 42P of the groove 42 in a position that is recessed from the side 34S of the main body 34, it is possible to effectively suppress coating peeling and thinning caused by electric arcs or flashes.

[0036] In this embodiment, by applying the formula for the emissivity of the combination of the groove 42 and the coating 44, the shape of the groove 42 and the heat dissipation (emissivity) of the coating 44 can be appropriately combined to effectively improve the heat dissipation (emissivity) of the main body 34. This will be described in detail below.

[0037] Figure 3 It is a graph showing the relationship between the shape of the groove 42 and the emissivity of the coating 44. Figure 4 This is a diagram showing the shape of the groove.

[0038] The emissivity ε of the grooved surface can be approximated by the following equation (1).

[0039] ε=1 / (1+(L / S)×(1 / ε0-1))…(1)

[0040] Where L represents the axial length (along the side 34S) of the groove-forming region, and S represents the total length (total cross-sectional length) along the groove in the groove sectional view (refer to...). Figure 4 ).

[0041] The L / S value is related to the groove spacing and the number of grooves, i.e., the groove depth (slope length) within the groove formation area. The smaller the L / S value, the greater the groove depth and the larger the spacing; the closer the L / S value is to 1, the shallower the grooves and the fewer the spacing. On the other hand, ε0 represents the inherent emissivity of the material.

[0042] By replacing the material's inherent emissivity ε0 with the emissivity of coating 44 (here, denoted as ε), 涂层 The emissivity ε of the heat dissipation functional unit J is derived (here, denoted as ε). 槽+涂层 Since the coating 44 is very thin compared to the size (depth) of the groove 42, its thickness can be ignored.

[0043] exist Figure 3 The figure shows the emissivity ε of coating 44. 涂层 The emissivity ε of the heat dissipation function J derived from the combination of L / S with slot 42 槽+涂层 For example, the emissivity ε of coating 44 涂层 When the emissivity ε of the heat dissipation unit J is 0.8 and a slot 42 with an L / S value of 0.35 is formed, the emissivity ε of the heat dissipation unit J is... 槽+涂层 It is 0.92. Additionally, the emissivity ε of coating 44 is... 涂层 When the emissivity ε of the heat dissipation functional unit is 0.5 and a slot 42 with an L / S value of 0.2 is formed, the emissivity ε of the heat dissipation functional unit is... 槽+涂层 It is 0.83.

[0044] Here, according to the emissivity ε of the heat dissipation functional part J. 槽+涂层 The emissivity ε of L / S and coating 44 is determined by a factor greater than 0.8. 涂层 However, in order to prevent the groove 42 from having the same uneven shape as the rough surface, the L / S ratio of the circumferential groove 42 is set to 0.9 or less. 0.8 is determined, for example, based on the emissivity of tungsten, which is the electrode raw material, being 0.4.

[0045] The emissivity ε of the portion having both heat dissipation functions, slot 42 and coating 44, is derived by using the above equation (1). 槽+涂层 This allows for the free selection of the composition of the coating 44 and the shape of the groove 42 to achieve the desired emissivity. For example, a composition and shape with higher heat dissipation can be used to effectively (synergistically) increase the emissivity of the main body 34. In particular, by setting the emissivity of the coating 44 to be higher than that of the groove 42, a heat dissipation function section J can be constructed, where the heat dissipation function of the coating 44 is primary and the heat dissipation function of the groove 42 is secondary.

[0046] For example, when using a coating 44 with high emissivity, the range of L / S values ​​greater than 0.8 is wide, and the shapes of the grooves 42 that can be selected become more numerous. This allows for optimized combinations, so even if L / S is increased (i.e., the grooves 42 are made shallower), high emissivity can be maintained. Furthermore, when the grooves 42 are shallow, it is easier to apply (adhere) the coating 44 to the corners of the grooves 42.

[0047] Based on the L / S value of groove 42, sometimes if the coating 44 is not properly selected, only an emissivity not significantly different from that of the coating 44 can be obtained, thus failing to achieve sufficient heat dissipation. However, by referring to... Figure 3 The table, even when faced with various groove shapes (L / S values), can display the emissivity ε. 槽+涂层 It remains at a high level.

[0048] Compared to the main body 34 which has this heat dissipation function part J, a heat dissipation structure (uncoated heat dissipation structure) 50 is provided on the tapered side (surface) 32S of the front tapered part 32, where only a groove is formed and no coating is formed on it.

[0049] During lamp illumination, the conical side 32S is exposed to electric arcs or flashes. Therefore, if a coating is provided, paint peeling may occur. However, since no such coating is provided, contamination of the discharge tube 12 by paint components can be suppressed. In addition, by determining L / S in a way that increases the emissivity of the groove 42, the overall heat dissipation of the electrode 30 can be further improved.

[0050] On the other hand, a side portion 33 formed by the electrode substrate surface is provided between the heat dissipation structure 40 and the heat dissipation structure 50, and the heat dissipation structures 40 and 50 are not adjacent but separated from each other. By providing such a side portion 33, it is possible to suppress the movement of electric arcs or flashes towards the heat dissipation functional part with the coating during lamp illumination. Moreover, the boundary portion 33P between the front end tapered portion 32 and the main body portion 34 has rounded corners, thus protecting the coating 44 from abnormal discharge and overheating caused by abnormal discharge.

[0051] The electrode 30 of such a discharge lamp can be manufactured as follows: First, an electrode having a tapered front end and a cylindrical main body is formed, and a circumferential groove is formed on the side of the main body by laser processing or cutting. Then, a coating is formed on the groove by coating. At this time, the emissivity of the coating is set to be higher than that of the groove, thereby forming a heat dissipation functional part with high emissivity. In addition to spraying, known methods such as vapor deposition, sputtering, and CVD can also be used for coating, as long as uniform coating can be achieved. The coated coating can also be sintered by a furnace (heating device) or laser.

[0052] Next, use Figure 5 The discharge lamp of the second embodiment will be described. In the second embodiment, a heat dissipation functional part with a coating layer superimposed on a heat dissipation structure formed by grooves is formed on the front end tapered part and the main body part. On the other hand, a heat dissipation structure with grooves is provided only on the electrode support rod side.

[0053] Figure 5 This is a schematic top view of the electrodes of the discharge lamp according to the second embodiment. The anode 30' has a front-end tapered portion 32 and a main body portion 34. A heat dissipation functional portion J, on which a coating 44' is formed on a heat dissipation structure 40' consisting of grooves, is continuously formed from the middle of the main body portion 34 to the front-end tapered portion 32. On the other hand, a heat dissipation structure 50' consisting only of circumferential grooves (without a coating) is provided on the side 34S of the main body portion 34 at a position closer to the electrode support rod 17B than the heat dissipation functional portion J.

[0054] Sometimes, due to factors such as low lamp output or small electrode size, it is possible to prevent the coating 44' formed on the front-end tapered portion 32 from peeling off or disappearing due to electric arcs or flashes. Therefore, by forming the coating 44' on the front-end tapered portion 32 together with the main body portion 34, heat dissipation can be improved. In addition, similar to the first embodiment, an area of ​​the electrode substrate surface may be provided between the heat dissipation structure 40' and the heat dissipation structure 50' where the coating 44' is formed.

[0055] In the first and second embodiments, the heat dissipation structure is formed by grooves along the circumferential direction, but it can also be formed by grooves along the electrode axis. Alternatively, a heat dissipation structure other than grooves can be used. For example, a pear-skin rough surface formed by sandblasting or a blackening inhibitor can be used as the heat dissipation structure. If the primary purpose is to suppress blackening, a blackening inhibitor can be used; if improving heat dissipation is desired, grooves can be formed. If low cost is desired, a pear-skin rough surface can be used. The heat dissipation structure can be determined based on the electrode shape, electrode raw material, ease of machining, etc.

[0056] In addition, to prevent the coating formed on the heat dissipation structure from peeling off, the heat dissipation structure can be constructed by using coatings made of different raw materials. That is, it is possible to overlap the coating (heat dissipation structure).

Claims

1. A discharge lamp characterized by comprising: a discharge vessel; and a pair of electrodes disposed in opposition in the discharge vessel, in at least one electrode, at least a side surface of an electrode main body portion has a heat dissipation structure having a higher emissivity than an electrode base material surface, a coating layer is formed on the heat dissipation structure, the coating layer further increases the emissivity of the side surface portion of the electrode main body portion on which the heat dissipation structure is provided, and an uncoated heat dissipation structure, which is not covered with the coating layer, is provided on a tapered surface of a tip-side tapered portion of the electrode or a side surface of the electrode main body portion, and an exposed side surface portion composed of the electrode base material surface is provided between the heat dissipation structure and the uncoated heat dissipation structure.

2. The discharge lamp according to claim 1, characterized in that: the heat dissipation structure is composed of a groove in a circumferential direction of the electrode main body portion or an electrode axial direction, the coating layer has an emissivity greater than that of the groove.

3. The discharge lamp according to claim 1 or 2, characterized in that: the heat dissipation structure is composed of a groove in a circumferential direction of the electrode main body portion, the composition of the coating layer and the shape of the groove are such that the emissivity of the heat dissipation structure and the coating layer combined is 0.8 or greater when represented by the following formula: ε = 1 / (1 + (L / S) x (1 / ε0 - 1)) where L represents an axial length of a groove formation region, S represents a total cross-sectional length, ε0 represents an emissivity of the coating layer, and L / S is set to 0.9 or less.

4. The discharge lamp according to claim 2, characterized in that: a distance from an electrode center axis to a top of the groove is shorter than a distance from the electrode center axis to a side surface of the electrode main body portion on which the heat dissipation structure is not provided.

5. The discharge lamp according to claim 1, characterized in that: a second coating layer different from a raw material of the coating layer is formed in superposition on the coating layer.

6. The discharge lamp according to claim 1, characterized in that: the exposed side surface portion is a boundary portion between the tip-side tapered portion and the electrode main body portion, and the boundary portion has a rounded corner.

7. The discharge lamp according to claim 1, characterized in that: the uncoated heat dissipation structure is separate from the heat dissipation structure.

8. The discharge lamp according to claim 1 or 2, characterized in that: the coating layer contains at least a metal and / or a ceramic.

9. The discharge lamp according to claim 1 or 2, characterized in that: the coating layer is composed of a coating layer containing at least a metal of the same kind as a raw material of the electrode.

10. The discharge lamp according to claim 1 or 2, characterized in that: the coating layer contains at least zirconium and / or tantalum.

11. A method of manufacturing an electrode for a discharge lamp, characterized by comprising: ​ An electrode having a front end side tapered portion and a columnar main body portion is formed, grooves along the circumference of the electrode are formed in the side surface of the main body portion and the front end side tapered portion, a coating layer having a larger emissivity than that of the grooves is formed by coating on the grooves of the side surface of the main body portion or on the grooves of the front end side tapered portion and the grooves of the side surface of the main body portion near the front end side tapered portion, and an exposed side surface portion composed of the surface of the electrode substrate is provided between the grooves on which the coating layer is formed and the grooves on which the coating layer is not formed.

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