Discharge lamp

Abstract

To provide a discharge lamp having an electrode structure provided with a body unit with enhanced heat radiation effect.SOLUTION: A discharge lamp 10 includes an electrode (a cathode) 20 in which a tip portion 22 and a body portion 24 are joined via an insert material 25. The tip portion 22 of the electrode 20 contains an emitter material, and the body portion 24 contains a high melting point metal different from the emitter material. In the body portion 24, a grain size is different in a direction perpendicular to an electrode axis C and in a direction along the electrode axis C. The grain size in the vicinity of an electrode outer surface 24S is larger than the grain size in the vicinity of the electrode axis C. The grain size in the vicinity of a junction face GM is larger than the grain size in the vicinity of a central portion F along the electrode axis C.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a discharge lamp such as a short arc discharge lamp, and particularly to heat dissipation of an electrode.

Background Art

[0002] During lighting of a discharge lamp, the tip of the electrode becomes hot, and electrode materials such as tungsten melt and evaporate, causing the discharge tube to blacken and resulting in a decrease in lamp illuminance. To prevent overheating of the electrode including the tip of the electrode, a discharge lamp provided with an electrode composed of a tungsten alloy (tungsten part) containing an emitter material such as thorium and a high melting point metal (high melting point metal part) mainly composed of tungsten or molybdenum has been proposed (see Patent Document 1).

[0003] In this case, an electrode having a tip-integrated structure is configured, in which a tapered portion including the tip surface of the electrode is a tungsten part and the body portion is a high melting point metal part. Alternatively, an electrode having a surrounding-integrated structure is configured in which a high melting point metal part is provided so as to surround the tungsten part. These electrodes are formed by 3D printing.

[0004] In 3D printing, a high melting point metal powder having a crystal grain size larger than that of the tungsten part is laid on the tungsten part and irradiated with a laser. By making the crystal grain size of the high melting point metal part larger than that of the tungsten part, heat of the tungsten part is dissipated from the high melting point metal part.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0010] to

[0014] ,

[0030] to

[0038] ,

[0108] to

[0115] , etc.).

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above electrode structure formed by 3D printing, the heat transfer effect by the high melting point metal part is limited. That is, in the case of an electrode having a surrounding integrated structure, since the ratio occupied by the tungsten part of the body part is relatively large, the heat transfer to the high melting point metal part on the outer surface side of the electrode is inhibited by the tungsten part having a large number of grain boundaries which are heat transfer inhibiting factors.

[0007] Also, in the case of an electrode having a tip integrated structure, the crystal grain size of the high melting point metal part constituting the body part does not differ inside the body part. Therefore, the heat dissipation effect to the side surface of the electrode having a larger surface area compared to the side end part of the electrode support rod is suppressed.

[0008] Therefore, there is a demand for a discharge lamp having an electrode structure provided with a body part with a higher heat dissipation effect.

Means for Solving the Problem

[0009] The discharge lamp of the present invention includes a discharge tube and a pair of electrodes disposed opposite to each other inside the discharge tube, and at least one of the electrodes is configured as an electrode in which a body part including a columnar part configured as a single member and a tip part including a tapered part are joined.

[0010] Here, "configured as a single member" means being configured as a single piece based on a defined material, and is different from a member formed by joining members of different materials integrally (for example, a tip integrated structure, a surrounding integrated structure).

[0011] A heat dissipation structure can be provided on the outer surface of the electrode of the body part. Further, the electrode can be configured as an electrode structure in which the body part and the tip part are joined via an insert material.

[0012] In the present invention, in the body part, the crystal grain size (crystal grain size) near the outer surface of the electrode is larger than the crystal grain size near the electrode axis. Regarding the crystal grain size, it can be represented by a measured value based on a standard. For example, it can be represented by an average grain size according to the cutting method of JISG0551.

[0013] In the body portion, it is possible to change the crystal grain size from near the electrode axis toward the vicinity of the outer surface of the electrode in a direction perpendicular to the electrode axis. For example, it can be configured such that the crystal grain size increases as it moves away radially from near the electrode axis.

[0014] Also, it is possible to change the crystal grain size in the direction of the electrode axis. For example, the body portion can be configured such that the crystal grain size near the outer surface of the electrode is larger than the crystal grain size near the electrode axis on the tip side rather than the central portion along the electrode axis direction of the body portion.

[0015] Alternatively, the body portion can be configured such that the crystal grain size near the joint surface of the body portion is larger than the crystal grain size at the center of the electrode along the electrode axis direction.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a discharge lamp having an electrode structure with a body portion having a higher heat dissipation effect.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0018] Hereinafter, the discharge lamp according to the present embodiment will be described with reference to the drawings.

[0019] FIG. 1 is a schematic plan view of the discharge lamp according to the present embodiment.

[0020] 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. Inside the discharge tube 12, a pair of electrodes 20 and 30 are arranged opposite (coaxial) to each other. On both sides of the discharge tube 12, sealing tubes 13A and 13B made of quartz glass are connected to the discharge tube 12 and integrally formed. In the discharge space DS inside the discharge tube 12, a rare gas such as mercury and argon gas is enclosed.

[0021] The electrode 20, which is the cathode, is supported by an electrode support rod 17A. In the sealing tube 13A, a glass tube (not shown) through which the electrode support rod 17A is inserted, a lead rod 15A connected to an external power source, a metal foil 16A connecting the electrode support rod 17A and the lead rod 15A, etc. are sealed. Similarly, for the electrode 30, which is the anode, 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 are sealed. Also, caps 19A and 19B are respectively attached to the ends of the sealing tubes 13A and 13B.

[0022] When a voltage is applied to the pair of electrodes 20 and 30, an arc discharge occurs between the electrodes 20 and 30, and light is radiated toward the outside of the discharge tube 12. Here, power of 1 kW or more is input. The light radiated from the discharge tube 12 is guided in a predetermined direction by a reflecting mirror (not shown).

[0023] FIG. 2 is a schematic plan view of the electrode (cathode) 20. Note that the electrode (anode) 30 can also have a similar electrode structure.

[0024] The electrode 20 has an electrode tip surface 22T, and includes a tapered portion (hereinafter referred to as the tip portion) 22 and a columnar portion (hereinafter referred to as the body portion) 24 connected to the electrode support rod 17A. Here, the tip portion 22 and the body portion 24 are joined via an insert material (intermediate member) 25 by a solid-phase joining such as diffusion bonding. Note that the tip portion 22 and the body portion 24 may be joined without using the insert material 25.

[0025] The tip portion 22 contains an emitter and tungsten. For example, the tip portion 22 is made of tungsten containing thorium (thoriated tungsten). The body portion 24 is a metal different from the emitter material and contains a high melting point metal. For example, the body portion 24 is made of pure tungsten or an alloy containing additives such as molybdenum and potassium. The insert material 25 is made of a material with high ductility and is made of a rhenium-tungsten alloy here.

[0026] On the side surface of the body portion 24, that is, on the outer surface 24S of the electrode, a heat dissipation structure 40 is provided on the surface portion with a constant diameter. The heat dissipation structure 40 has a higher emissivity compared to the base surface of the body portion 24, that is, the surface where a special heat dissipation structure is not deliberately adopted, and has a function of enhancing heat dissipation.

[0027] The heat dissipation structure 40 is constituted by, for example, an uneven structure formed with grooves along the circumferential direction (around the electrode axis) at a predetermined pitch, or a coating layer, etc. Note that the heat dissipation structure 40 is disclosed in, for example, Japanese Patent Laid-Open No. 2023-48876, etc., and detailed description is omitted.

[0028] In the electrode (cathode) 20 of the present embodiment, the crystal grain size (crystallite size) differs depending on the location inside the body portion 24. This will be described in detail below. The crystal grain size of the body portion 24 represents the size of the average crystal grain size measured according to the cutting method of JIS G05A1. However, the crystal grain size may also be measured by other measurement methods.

[0029] In a cross-section along the direction perpendicular to the electrode axis C (refer to the symbol M in Figure 2), the crystal grain size of the location near the outer surface 24S of the electrode (refer to the symbol A3) is larger than the crystal grain size of the location on the electrode axis C (refer to the symbol A1).

[0030] Also, in cross-section M, as the distance from the electrode axis C increases (as approaching the outer electrode surface 24S), the crystal grain size of the body portion 24 gradually (continuously) increases. That is, in cross-section M, the crystal grain size increases in the order of the locations represented by reference signs A1, A2, and A3. And such a difference in crystal grain size occurs at least on the electrode tip surface 22T side from the central portion (see reference sign F) along the electrode axis C of the body portion 24.

[0031] On the other hand, the crystal grain size of the body portion 24 varies not only in the direction perpendicular to the electrode axis C but also in the direction along the electrode axis C. Specifically, the crystal grain size near the joint surface GM of the body portion 24 (see reference sign A4) is larger than the crystal grain size at the central portion F along the electrode axis C of the body portion 24.

[0032] Thus, by providing an electrode structure with different crystal grain sizes inside the body portion 24 configured as a single member, the heat dissipation effect (heat conduction) can be further enhanced.

[0033] First, since the crystal grain size near the outer electrode surface 24S is larger than the crystal grain size near the electrode axis C, the grain boundaries near the outer electrode surface 24S are reduced. Grain boundaries existing between crystals in polycrystals impede heat transfer, but the reduction in the number of grain boundaries enhances the heat dissipation property from the outer electrode surface 24S.

[0034] Also, as approaching from near the electrode axis C to near the outer electrode surface 24S, the crystal grain size gradually increases without a sudden change in the crystal grain size. Therefore, heat transfer becomes smooth. And since the heat dissipation structure 40 is formed on the outer electrode surface 24S, the heat transferred to the outer electrode surface 24 is effectively released to the outside of the electrode.

[0035] Furthermore, such a difference in crystal grain size along the direction perpendicular to the electrode axis C occurs on the electrode tip surface 22T side from the central portion F along the electrode axis C, that is, on the bright spot side of the arc discharge. Since the crystal grain size is large on the electrode tip surface 22T side that becomes high temperature during lamp lighting, heat can be effectively dissipated.

[0036] Also, the crystal grain size near the joint surface GM of the body portion 24 is larger than the crystal grain size of the central portion F along the electrode axis C. This makes it easier to transfer the heat on the electrode tip side to the electrode support rod 17A side.

[0037] As described above, in the discharge lamp 10 of this embodiment, the electrode (cathode) 20 that joins the tip portion 22 and the body portion 24 via the insert material 25 is provided. The tip portion 22 of the electrode 20 contains an emitter material, and the body portion 24 contains a high melting point metal different from the emitter material. And in the body portion 24, regarding the direction perpendicular to the electrode axis C and the direction along the electrode axis C, the crystal grain sizes are different. The crystal grain size near the outer surface 24S of the electrode is larger than the crystal grain size near the electrode axis C, and the crystal grain size near the joint surface GM is larger than the crystal grain size near the central portion F along the electrode axis C.

[0038] Such an electrode (cathode) 20 can be manufactured, for example, by the following manufacturing method.

[0039] First, a material for the tip portion, a material for the body portion, and a material for the insert material are joined by solid-phase bonding such as SPS to form an electrode material. The electrode is formed into a predetermined shape by a known method. Then, a heat treatment is performed for a predetermined time so that the difference in crystal grain size described above occurs. For example, the heat treatment is performed at 1200°C to 2500°C for 1 to 5 hours.

Example

[0040] Hereinafter, the electrode (cathode) of the discharge lamp of this example will be described.

[0041] The electrode of the first example corresponds to the electrode of the discharge lamp of this embodiment described above in terms of shape and the like. The tip portion is made of Tritan, and the body portion is made of potassium-doped tungsten. Also, the insert material is made of rhenium-tungsten. An electrode with an outer diameter of 20 mm for the constant-diameter portion of the body portion was manufactured according to the manufacturing method described above. At this time, the heat treatment within the above temperature range and heating time was performed in a vacuum treatment furnace.

[0042] After manufacturing the electrode, in accordance with the cutting method of JIS G0551, the crystal grain size of the body portion was measured using a digital microscope. Specifically, the crystal grain size (average grain size due to the cutting method) at the locations corresponding to reference signs A1 to A4 in Fig. 2 was measured.

[0043] As a measurement result, the crystal grain size at the location corresponding to reference sign A1 on the electrode axis C (hereinafter, the central location) was 0.027 mm, the crystal grain size at the location corresponding to reference sign A2, which was 3 mm away from the central location along the direction perpendicular to the electrode axis C, was 0.053 mm, and the crystal grain size at the location corresponding to reference sign A3, which was 9 mm away from the central location along the direction perpendicular to the electrode axis C, was 0.070 mm. Also, the crystal grain size at the location corresponding to reference sign A4 near the joint surface was 0.028 mm.

[0044] The electrode of the second embodiment also corresponds to the electrode of the discharge lamp of the present embodiment described above with respect to the shape and the like. However, the joint surface with the body portion is formed at a position closer to the electrode tip side. The tip portion is made of Tritan, the body portion is made of potassium-doped tungsten, and the insert material is made of rhenium-tungsten. An electrode with an outer diameter of 25 mm for the constant-diameter portion of the body portion was manufactured according to the same manufacturing method as in Example 1. At this time, heat treatment within the above-described temperature range and heating time was performed in a vacuum treatment furnace.

[0045] As a measurement result, the crystal grain size at the central location on the electrode axis C was 0.035 mm, the crystal grain size at the location corresponding to reference sign A2, which was 3 mm away from the central location along the direction perpendicular to the electrode axis C, was 0.045 mm, and the crystal grain size at the location corresponding to reference sign A3, which was 9 mm away from the central location along the direction perpendicular to the electrode axis C, was 0.097 mm. Also, the crystal grain size at the location corresponding to reference sign A4 near the joint surface was 0.038 mm.

Explanation of Reference Signs

[0046] 10 Discharge lamp 20 Electrode (cathode) 22 Tip portion 24 Body portion

Claims

1. A discharge tube and a pair of electrodes arranged to face each other inside the discharge tube, wherein at least one of the electrodes is an electrode in which a body portion including a columnar portion configured as a single member and a tip portion including a tapered portion are joined, and in the body portion, a crystal grain size near the outer surface of the electrode is larger than a crystal grain size near the electrode axis, characterized by a discharge lamp.

2. The discharge lamp according to claim 1, characterized in that in the body portion, the crystal grain size increases as the distance from the vicinity of the electrode axis in the radial direction increases.

3. The discharge lamp according to claim 1, characterized in that in the tip portion side rather than the central portion along the electrode axis direction of the body portion, the crystal grain size near the outer surface of the electrode is larger than the crystal grain size near the electrode axis.

4. The discharge lamp according to claim 1, characterized in that the crystal grain size near the joint surface of the body portion is larger than the crystal grain size at the central portion of the electrode along the electrode axis direction.

5. The discharge lamp according to claim 1, characterized in that a heat dissipation structure is provided on the outer surface of the electrode of the body portion.

6. The discharge lamp according to any one of claims 1 to 5, characterized in that the electrode is an electrode in which the body portion and the tip portion are joined via an insert material.

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