Discharge lamp electrode manufacturing method, discharge lamp electrode manufacturing device, and short arc discharge lamp

Abstract

A method for manufacturing an electrode for a discharge lamp that can increase the surface area in a high-temperature environment such as a discharge lamp is provided. [Solution] The electrode's outer shape is processed (Step S1). Next, the electrode surface is irradiated with laser light to melt and solidify the electrode surface, forming random fine irregularities with an average roughness of Ra 10 μm or less (Step S2). Helium is converted into plasma in a plasma irradiation device, and He ions are irradiated onto the electrode surface to form bubbles and holes (Step S3).

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode for a discharge lamp, and more particularly to an improvement in heat dissipation efficiency. [Background technology]

[0002] Conventionally, a method for increasing the surface area has been known as a method for cooling electrodes in discharge lamps. Patent Document 1 discloses a method for increasing the surface area by forming V-grooves on the surface using laser processing. Patent Document 2 also discloses a technology for forming a fluffy structure by irradiating a metal with plasma. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7337532 [Patent Document 2] Japanese Patent Application Publication No. 2023-077977 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the increase in surface area by laser processing in Patent Document 1 forms V-shaped grooves, which means there is a physical limit to how much finer the structure can be made. Furthermore, Patent Document 2 requires several hours of plasma irradiation to form a W fluff structure of about several μm, and when applied to the electrodes of a discharge lamp, the W fluff structure itself disappears when the lamp is lit due to temperatures exceeding 1000°C.

[0005] Thus, there has been no conventional method for increasing the surface area of ​​a discharge lamp electrode by miniaturizing the surface thereof.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a manufacturing method for a discharge lamp that can increase the surface area in a high-temperature environment such as a discharge lamp. [Means for solving the problem]

[0007] (1) A method for manufacturing an electrode for a discharge lamp according to the present invention includes the steps of preparing an electrode for a discharge lamp having a predetermined shape, forming a fine irregularity on the surface of the metal electrode with a mean roughness Ra of 10 μm or less, and subjecting the electrode with the fine irregularity formed thereon to an arc discharge environment where helium gas is turned into plasma and helium ions are irradiated onto the electrode surface, thereby forming open pores with a diameter of 0.5 to 5 μm and random shapes and orientations on the surface of the fine irregularity.

[0008] This makes it possible to provide an electrode in which open pores having a diameter of 0.5 to 5 μm are formed in the fine concave-convex shape.

[0009] (2) In the method for manufacturing an electrode for a discharge lamp according to the present invention, in the fine concave-convex forming step, a laser is irradiated onto the surface of the metal electrode to melt and solidify the electrode surface, thereby forming fine concave-convex structures having random shapes and positions and an average roughness Ra of 10 μm or less. Therefore, it is possible to provide an electrode having the fine concave-convex structure formed thereon by laser irradiation.

[0010] (3) The discharge lamp electrode according to the present invention is made of a high-melting-point metal, has a finely textured surface with an average roughness Ra of 10 μm or less, and has numerous open pores with random shapes and orientations formed in the finely textured surface. Therefore, an electrode with a high heat dissipation effect can be provided.

[0011] (4) In the discharge lamp electrode according to the present invention, the minute concave-convex portions are randomly shaped and arranged at random positions, thereby providing an electrode with a high heat dissipation effect.

[0012] (5) In the discharge lamp electrode according to the present invention, the open pores have a diameter of 0.5 to 5 μm, which makes it possible to provide an electrode with a high heat dissipation effect.

[0013] (6) In the discharge lamp electrode according to the present invention, the open pores have a diameter of 1 to 2 μm, and therefore it is possible to provide an electrode in which the open pores are unlikely to disappear even when used at high temperatures.

[0014] (7) In the discharge lamp electrode according to the present invention, the average diameter of the open pores is smaller at the tip of the electrode than at the base of the electrode, so that an electrode that can adapt to temperature distribution can be provided. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an outline of the manufacturing process of the present invention. [Figure 2] 1 is an electron microscope photograph of the electrode surface after laser irradiation. [Figure 3] 1 is a schematic diagram of an electrode manufacturing apparatus 1 according to the present invention. [Figure 4] 4 is a view seen from the direction of the arrow α in FIG. 3. [Figure 5] 1 is an electron microscope photograph of the surface of Sample 7. [Figure 6] Electron microscope photographs showing the state of FIG. 5 at a further 10 times magnification (before and after heat treatment). [Figure 7] These electron microscope photographs show the state after heat treatment with only bubble holes processed, the state where the bubble holes have almost disappeared due to high heat treatment, and the state where the bubble holes have been maintained due to high heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0016] The manufacturing process of the discharge lamp electrode according to the present invention will be described with reference to FIG.

[0017] (1.1 Outer shape processing process) (Figure 3 Step S1) A pure tungsten round bar is machined to the shape of the anode. This process is the same as in the conventional process. This completes the outer shape machining process, and an electrode for a discharge lamp with a determined shape is prepared.

[0018] (1.2 Random Crown Structure Formation Process) (Figure 3 Step S2) The surface of the anode is irradiated with laser light to melt and solidify the W surface, forming irregular unevenness in the horizontal and vertical directions, resulting in the formation of random fine unevenness with an average roughness Ra of 10 μm or less (hereinafter referred to as a random crown structure), as shown in Figure 2.

[0019] In this embodiment, a fiber laser marker TF450 (manufactured by Gravotech Co., Ltd.) was used for the laser processing, and the fine irregularities were formed under the following conditions.

[0020] Laser power: 80% (40 W) of the maximum power of the device, 50 W; Repetition rate: 80 kHz, Pulse width: 100 ns, Wavelength: 1064 nm, Laser diameter: approx. 60 μm, Scan speed: 150mm / s, The distance between two adjacent lines is approximately 0.01 mm. Ambient temperature: room temperature, Ambient gas: Nitrogen, Pressure: atmospheric pressure.

[0021] In this specification, the average roughness Ra refers to the arithmetic mean roughness, which represents the average of the absolute values ​​of Z(x) over a reference length in JIS B 0601. The maximum roughness Rz refers to a measurement parameter according to JIS B 0601-2001, which is obtained by extracting a portion of a roughness curve measured with a roughness meter over a reference length and summing the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv).

[0022] In this embodiment, the average roughness Ra was measured by a stylus roughness measurement method using a surface roughness measuring instrument SURFTEST SJ-310 (manufactured by Mitutoyo Corporation).

[0023] 2A and 2B show electron microscope images (hereinafter referred to as SEM images) of the surface shape observed with a TM3030 electron microscope (Hitachi High-Technologies Corporation). As can be seen, random irregularities with an average roughness Ra of 10 μm or less are formed on the electrode surface.

[0024] (1.3 Bubble-hole structure formation process) (Figure 3 Step S3) The formation of the bubble-hole structure will be explained using Figure 3.

[0025] In this process, a bubble-hole structure is formed on the electrode surface on which the random crown structure has been formed. In this embodiment, the bubble-hole structure is formed by generating helium (He) plasma in the plasma irradiation device 1 and irradiating the electrode surface on which the contour processing process has been completed in step S1 with He ions.

[0026] The plasma irradiation apparatus 1 that performs the bubble-hole forming process will be described with reference to Figures 3 and 4. The plasma electrode manufacturing apparatus 1 includes a vacuum vessel 2, a cathode 3, an anode 4, an observation window 9, a power supply 40, a bipolar power supply 41, and a resistor 42. Note that Figure 3 shows the plasma irradiation apparatus 100 as viewed from above (in the direction of gravity), and Figure 4 is a schematic view as viewed from the direction of arrow α in Figure 3.

[0027] The vacuum vessel 2 is cylindrical, 402 mm high and 165 mm in diameter. Inside the vacuum vessel 2, He gas is converted into plasma in an arc discharge environment, and He ions are irradiated, thereby forming a bubble-hole structure on the electrode surface.

[0028] A sample 7 with a random crown structure formed on its surface is set in the vacuum state 2.

[0029] The sample 7 had a diameter of 2 mm and a length of 23 mm, and the discharge voltage was 38.5 V and the discharge current was 33.5 A. The sample was placed at the center of the cathode 3 and the anode 4 in the X direction and on the axis of the cathode 3 and the anode 4 in the Z direction.

[0030] Two electrodes (anode 4 (tungsten) with a diameter of 20 mm and cathode 3 (tungsten doped with 2 wt % thoria) with a diameter of 2 mm) are inserted into the vacuum vessel 2 through horizontal ports.

[0031] As shown in Figure 4, He gas is introduced as the working gas from the bottom of the vacuum vessel 2, and the He gas is exhausted from the top of the vacuum vessel 2. This keeps the gas pressure inside the vacuum vessel 2 constant. The gas flow rate is adjusted by a gas flow meter (not shown). In this embodiment, an air-cooled dry vacuum pump NeoDry15E (manufactured by Kashiyama Kogyo Co., Ltd.) is used to exhaust the gas. A gas pressure meter GM-2201 (manufactured by ULVAC, Inc.) is used to measure the gas pressure inside the device.

[0032] An observation window 9 is provided on the side of the vacuum vessel 2. The observation window 9 is a glass window made of synthetic quartz. Through the observation window 9, the temperature of each part of the electrode can be measured with a radiation thermometer.

[0033] The process up to irradiation in the plasma irradiation device 1 is as follows.

[0034] 1) Evacuate the gas pressure inside the device to 1 Pa or less.

[0035] 2) Fill the chamber with He gas to a gas pressure of 30 kPa.

[0036] 3) Set the distance between the two electrodes to about 10 mm.

[0037] 4) A high voltage pulse is applied to cause an arc discharge.

[0038] 5) Once the arc is stable and the anode is red hot, increase the distance between the electrodes to 25 mm and evacuate until the gas pressure reaches 5 kPa.

[0039] 6) The gas flow rate is set to 1 L / min, a voltage of about -12 V is applied to the sample 7, which is the object to be processed, and the sample 7 is inserted between the electrodes. Once the sample 7 is inserted, a bias voltage of -120 V is applied.

[0040] This starts irradiation, forming an arc region 11 between the cathode 3 and the anode 4.

[0041] In this embodiment, the temperature of the sample 7 is 1700 degrees Celsius, and the irradiation time is 15 minutes. 22 m 2 / s The temperature of Sample 7 was measured using a radiation thermometer IR-AH (manufactured by Chino Corporation) with the emissivity set to 0.43 before the fine structure was formed on the W surface.

[0042] The He plasma irradiation conditions are not limited to these, and may be set to a temperature of 1600 to 2300 degrees Celsius, an ion flux of 10 22 m 2 / s is sufficient.

[0043] The temperature of the sample 7 can be adjusted by changing the number of He ions (particle flux) per unit time and unit area, the bias voltage, the position of the sample, etc. Increasing the bias voltage increases the number of He ions with high ion incident energy, which in turn increases the temperature of the sample 7. In addition, the temperature of the sample 7 can be increased by bringing the sample 7 closer to the He plasma.

[0044] As a result, a bubble-hole structure is formed on the random crown structure, as shown in FIG. 5A. FIG. 5B is a 10x magnified photograph of FIG. 5A. A further 5x magnified photograph of FIG. 5B is shown in FIG. 6A. As is clear from FIG. 6A, open pores (e.g., pores 61a, 61b, and 61c) with diameters of 0.5 to 5 μm are formed on the random crown structure. The inventors hypothesized that helium penetrates the interior of the tungsten, forming bubbles, which then grow in size and reach the tungsten surface, forming bubble-holes.

[0045] (1.4 Heat resistance of completed electrodes) The sample 7 with the bubble-hole structure formed was placed in a vacuum heat treatment furnace at a vacuum of 1×10 ?2 The sample was heated to 1300°C at a rate of 10°C / min under a pressure of 0.1 Pa or less, and held at 1300°C for 1 hour, after which it was allowed to cool naturally in a vacuum. Sample 7 was then removed and observed under an electron microscope.

[0046] Figures 6A and 6B show SEM images before and after heat treatment, respectively. As can be seen, there is almost no change in the structure before and after heat treatment at 1300°C, demonstrating high heat resistance. For comparison, Figure 7 shows an SEM image of the electrode surface after bubble and hole processing without laser irradiation processing.

[0047] (1.5 Spectral emissivity) The spectral reflectance of Sample 7, which had a random crown structure before heat treatment and a random crown structure with a bubble-hole structure formed on it, was measured using a SolidSpec-3700 ultraviolet-visible-near-infrared spectrophotometer (Shimadzu Corporation). The emissivity in the wavelength range of 0.24 to 2.25 μm was 0.74, approximately double that of the sample with only the outer diameter formed in step S1.

[0048] In this embodiment, both the random crown structure and the bubble hole structure are three-dimensional structures with random sizes and orientations. Therefore, they can efficiently radiate heat in all directions over a wide wavelength range. Furthermore, the bubble hole structure has bubble holes, which are roughly hemispherical open pores, on its surface. These bubble holes are smaller than the microstructure formed in the base material and have a random three-dimensional structure with a size of 0.5 to 5 μm, which is about the same as the wavelength of the electromagnetic waves to be radiated. Therefore, they are heat-resistant and can efficiently radiate heat in all directions over a wide wavelength range.

[0049] 2.1 Other Embodiments The inventors have noticed the following problem with the openings in the electrodes: Since such electrodes are used in discharge lamps, they are used in high-temperature environments. Therefore, there is a risk that the open pores with a diameter of 1 μm or less will disappear in areas that become hot.

[0050] An example is shown in Figure 7B, which is an SEM image of the electrode surface after heat treatment at 2000 degrees Celsius for 1 hour.

[0051] To solve this problem, the diameter of the bubble holes formed can be changed depending on the temperature environment used, for example, by making the diameter of the bubble holes near the tip of the electrode 1 μm or more. Figure C shows an SEM image of open holes with a diameter of about 1 to 2 μm.

[0052] Thus, the diameter of the open pores is preferably in the range of 0.5 to 5 μm, more preferably 1 to 4 μm, and even more preferably 1 to 2 μm.

[0053] In this embodiment, the diameter of the open pores was calculated by image processing of the image obtained by SEM observation of the bubble-hole formation area. Specifically, the diameter of each open pore in the image was measured, and the average value was used as the open pore diameter of the bubble-hole formation area. To calculate a statistically significant average value, SEM observation was performed at multiple locations, and the total number of measured open pores was set to 400 or more.

[0054] (2.2 Other embodiments) In this embodiment, the bubble-hole structure is formed after the random crown structure is formed, but a powder sintered layer may be used instead of the random crown structure. Even in this case, a finely textured portion with an average roughness Ra of 10 μm or less is formed on the electrode surface, and by performing the bubble-hole processing on top of that, an electrode with high heat dissipation effect can be provided.

[0055] In this embodiment, the structure before the formation of the bubble-hole structure is described as being an irregular random crown structure or a powder sintered layer. However, a finely textured structure with a certain periodicity may be used instead of such a random structure. For example, etching techniques using pattern masks or molds, such as those disclosed in Japanese Patent Laid-Open No. 2015-26631, or nanoimprinting techniques, can be used. For example, this can be applied when the directionality of thermal radiation is important and a regular structure is desired. Electron beams and sandblasting can also be used.

[0056] The average diameter of the bubble holes may also be varied depending on the location of the electrode. For example, the temperature at the tip is higher, so the average diameter may be made larger, and the temperature is lower towards the rear end, so the average diameter may be made smaller. The difference in average diameter may be gradually increased towards the base of the electrode, or may be in multiple stages. Such multiple stages may be two or three stages.

[0057] The random crown structure of this embodiment allows for easier heat conduction from the electrode body surface to the sintered layer surface than when a powder sintered layer is used, resulting in higher heat dissipation power. This is because when sintering tungsten powder with a particle size of several microns, the powder is sintered in layers in the thickness direction, leaving small gaps between the powder particles. This can make it difficult for heat to be conducted from the electrode body surface to the sintered layer surface, resulting in lower heat dissipation power.

[0058] Furthermore, the plasma irradiation device 1 can generate plasma even at gas pressures close to atmospheric pressure, and does not require a magnetic field or turbomolecular pump, making it possible to generate high-density plasma with a simple device. This allows for the formation of a heat dissipation structure at low cost and in a short time. [Explanation of symbols]

[0059] 1. Plasma irradiation device 2...Vacuum container 3...Cathode 4...Anode 7. Sample 9. Observation window 11. Arc region 40...Power supply 41. Bipolar power supply 42 Resistor

Claims

1. providing an electrode for a discharge lamp having a determined shape; a fine concavo-convex forming step of forming fine concavo-convex portions on the surface of the metal electrode having an average roughness Ra of 10 μm or less; forming open pores having a diameter of 0.5 to 5 μm and random shapes and orientations on the surface of the fine irregularities by converting helium gas into plasma in an arc discharge environment and irradiating the electrode surface with helium ions; A method for manufacturing an electrode for a discharge lamp comprising the steps of:

2. 2. The method for manufacturing a discharge lamp electrode according to claim 1, In the fine irregularity forming step, a laser is irradiated onto the surface of the metal electrode to melt and solidify the surface of the electrode, thereby forming irregularities having random shapes and positions and an average roughness Ra of 10 μm or less; A method for manufacturing an electrode for a discharge lamp, comprising:

3. An electrode for a discharge lamp made of a high-melting point metal and having a fine concave-convex portion on the surface with an average roughness Ra of 10 μm or less, a large number of open pores having random shapes and directions are formed in the fine concave-convex portion; An electrode for a discharge lamp, characterized by:

4. 4. The discharge lamp electrode according to claim 3, the fine concave-convex portions have random shapes and randomly arranged positions; An electrode for a discharge lamp, characterized by:

5. 4. The discharge lamp electrode according to claim 3, the open pores have a diameter of 0.5 to 5 μm; An electrode for a discharge lamp, characterized by:

6. 6. The discharge lamp electrode according to claim 5, the open pores have a diameter of 1 to 2 μm; An electrode for a discharge lamp, characterized by:

7. 6. The discharge lamp electrode according to claim 5, the average diameter of the open pores is smaller at the tip of the electrode than at a portion closer to the base than the tip of the electrode; An electrode for a discharge lamp, characterized by:

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