Discharge lamp and manufacturing method of electrode for discharge lamp

Abstract

To construct an electrode capable of obtaining a desire heat radiation effect.SOLUTION: In an electrode 30 of a discharge lamp 10, a construction (hereinbelow, the side surface part is referred to as a heat radiation function part J) having a heat radiation structure 40 constructed from a groove 42 and a coating layer 44 containing a metal that is similar to a component of the electrode as two heat radiation function is to a side surface 34S of a body part 34. In the case where the heat radiation structure is constructed by the groove along a periphery of the electrode body part, an emissivity obtained by matching the heat radiation structure and the coating layer can be set to 0.8 or more when it is expressed by the following formula: ε=1 / (1+(L / S)×(1 / ε0-1)), where L indicates a shaft direction length of a formation region of the groove, S indicates a total cross sectional length, ε0 indicates the emissivity, of the coating layer, and L / S is fixed to 0.9 or less.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 electrodes.

Background Art

[0002] During operation 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, the surface area of the side surface of the electrode body is increased with screw-shaped or uneven grooves, and a powder such as tungsten or a metal oxide is sintered on the grooves to form a heat dissipation layer (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding the grooves formed on the electrode surface, the groove shape (such as its depth and pitch) is determined for the purpose of expanding the electrode surface area, but the heat dissipation performance, that is, the emissivity also varies depending on the groove shape. On the other hand, the emissivity of the heat dissipation layer also differs depending on the material such as the metal oxide to be sintered. Even if a heat dissipation layer is formed on the groove without considering the relationship with the groove, the heat dissipation performance cannot be further improved, and in some cases, the heat dissipation effect may be reduced.

[0005] Therefore, it is required to configure an electrode capable of obtaining a desired heat dissipation effect.

Means for Solving the Problems

[0006] A discharge lamp according to one aspect of the present invention includes a discharge tube and a pair of electrodes disposed opposite to each other within the discharge tube. At least one of the electrodes has a heat dissipation structure with a higher emissivity than the surface of the electrode substrate at least on the side surface of the electrode body portion. A coating layer is formed on the heat dissipation structure to further increase the emissivity of the side surface portion of the electrode body portion provided with the heat dissipation structure. The heat dissipation structure is constituted by grooves along the circumference of the electrode body portion. The coating layer contains a metal having the same component as the electrode, and the combined emissivity of the heat dissipation structure and the coating layer is 0.8 or more when represented by the following formula. ε = 1 / (1 + (L / S) × (1 / ε 0 -1)) However, L represents the axial length of the groove formation region, and S represents the total cross-sectional length. ε 0 represents the emissivity of the coating layer. Also, L / S is determined to be 0.9 or less.

[0007] For example, in the electrode, an exposed side surface portion composed of the surface of the electrode substrate is provided.

[0008] For example, the boundary portion between the tapered portion at the tip side and the body portion of the electrode is rounded.

[0009] A method for manufacturing an electrode for a discharge lamp according to another aspect of the present invention forms an electrode having a columnar body portion and a tapered portion at the tip side, forms a side surface portion with the surface of the electrode substrate exposed and grooves along the circumferential direction of the electrode on the side surface of the body portion, and forms a coating layer having an emissivity greater than that of the grooves on the grooves by coating.

[0010] For example, a discharge lamp according to one aspect of the present invention includes a discharge tube and a pair of electrodes disposed opposite to each other within the discharge tube. At least one of the electrodes has a heat dissipation structure with a higher emissivity than the surface of the electrode substrate at least on the side surface of the electrode body portion. And a coating layer is formed on the heat dissipation structure to further increase the emissivity of the side surface portion of the electrode body portion provided with the heat dissipation structure.

[0011] The heat dissipation effect of the side surface portion of the electrode body due to the heat dissipation function of the heat dissipation structure and the heat dissipation function of the coating layer can function most effectively based on the electrode material, the characteristics of the heat dissipation structure, the reflectivity of the coating layer, etc. This leads to maximizing the emissivity of the side surface portion of the electrode body based on the two heat dissipation functions.

[0012] In the side surface portion of the electrode body where such a heat dissipation structure and coating layer are layered, a heat dissipation effect that cannot be obtained by the heat dissipation effect due to groove formation for expanding the coating area to simply enhance the heat dissipation performance of the coating layer can be obtained.

[0013] As the heat dissipation structure, various configurations such as grooves, uneven shapes, and coating layers are applicable. For example, it is composed of grooves along the circumferential direction or the electrode axis direction of the electrode body, and the emissivity of the coating layer is configured to be larger than the emissivity of the grooves.

[0014] As the coating layer, it can be composed of a material with a relatively high emissivity and can be selected based on the electrode material, operating temperature, etc. The coating layer can be composed of a material containing at least metal and / or ceramic. It may be configured to be composed of a coating layer containing at least the same type of metal as the electrode material. Considering the improvement of heat dissipation performance, for example, it can be configured to be composed of at least zirconium and / or tantalum, etc., and it is also possible to include the material of the electrode such as tungsten or molybdenum.

[0015] When the heat dissipation structure is composed of grooves along the circumference of the electrode body, the emissivity of the combined heat dissipation structure and coating layer can be made to be 0.8 or more when expressed by the following formula. ε = 1 / (1 + (L / S) × (1 / ε 0 - 1)) However, L represents the axial length of the groove formation region, S represents the total cross-sectional length. ε 0indicates the emissivity of the coating layer. Also, L / S is defined to be 0.9 or less.

[0016] Various configurations can be applied to the thickness of the coating layer, the shape of the groove, etc. For example, it can be configured such that the distance from the electrode central axis to the layer surface of the coating layer is shorter than the distance from the electrode central axis on the side surface of the electrode body portion without the heat dissipation structure.

[0017] A non - coating heat dissipation structure not covered by the coating layer may be provided on the tapered surface of the tapered portion on the tip side of the electrode. Alternatively, on the side surface of the electrode body portion, a non - coating heat dissipation structure not covered by the coating layer may be provided on the side closer to the electrode support rod than the heat dissipation structure. The non - coating heat dissipation structure can be applied to a location away from the heat dissipation structure.

[0018] A method for manufacturing a discharge lamp, which is another aspect of the present invention, is characterized by molding an electrode having a columnar body portion and a tip - side tapered portion, forming a groove along the circumferential direction of the electrode on the side surface of the body portion, and forming a coating layer having an emissivity greater than that of the groove on the groove by coating.

Advantages of the Invention

[0019] According to the present invention, an electrode capable of obtaining a desired heat dissipation effect can be configured.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

BEST MODE FOR CARRYING OUT THE INVENTION

[0021] The short arc type discharge lamp 10 is a large discharge lamp capable of outputting high-intensity light, and includes a substantially spherical discharge tube (light-emitting tube) 12 made of transparent quartz glass. Inside the discharge tube 12, a pair of tungsten 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, mercury and rare gases such as halogen and argon gas are enclosed.

[0022] 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, mount components 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.

[0023] 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).

[0024] Figure 2 is a schematic plan view of the electrode (anode) 30. Note that the electrode (cathode) 20 can have the same structure.

[0025] The electrode 30 has an electrode tip surface 32T and is composed of a tapered portion (hereinafter referred to as the tip-side tapered portion) 32 and a columnar portion (hereinafter referred to as the body portion) 34 connected to the electrode support rod 17B. Here, the electrode 30 is integrally formed, but it is also possible to form the electrode 30 by joining the tip-side tapered 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.

[0026] A heat dissipation structure 40 is provided on the side surface 34S of the body portion 34 (see the hatched portion in Fig. 2). The heat dissipation structure 40 has a higher emissivity than the base surface 34T of the body portion 34, that is, the surface where no special heat dissipation structure is adopted, and has a function of enhancing heat dissipation. As shown in the enlarged portion of Fig. 2, the heat dissipation structure 40 has a configuration in which grooves 42 are formed at a predetermined pitch along the circumferential direction (around the electrode axis) here. The grooves 42 can be formed by, for example, laser or cutting.

[0027] And a coating layer 44 is formed on the side surface 34S of the body portion 34 provided with this heat dissipation structure 40 (grooves 42). Here, a component having a higher emissivity than the grooves 42 is used for the coating layer 44. For example, the coating layer 44 is composed of zirconium nitride or zirconium carbide, a zirconium compound. Alternatively, it contains tantalum-based materials such as tantalum nitride and ceramic-based materials such as alumina. Also, the coating layer 44 may contain the same metal as the electrode 30, that is, tungsten or molybdenum. In addition, it can be selected based on the use temperature, such as metal-based materials such as titanium and its oxides, and alloy-based materials added with nickel or chromium.

[0028] A heat dissipation structure 40 composed of grooves 42 and a portion having two heat dissipation functions of a coating layer 44 (hereinafter, this side surface portion is referred to as a heat dissipation function portion J) are formed on a part of the side surface 34S of the body portion 34. This is not to form grooves for the purpose of increasing the electrode surface area in order to increase the amount of heat dissipated as in the prior art and provide the grooves as an auxiliary heat dissipation structure, but the combination of the heat dissipation function by the grooves 42 and the heat dissipation function by the coating layer 44 is configured by a combination that maximally enhances the heat dissipation function in the heat dissipation function portion J.

[0029] Thereby, the heat dissipation property (emissivity) is maximally enhanced, and the rise in the electrode temperature can be suppressed. Since the coating layer 44 is formed on the grooves 42, the contact area becomes larger compared to the coating on the electrode base surface 34T, and the adhesion of the coating can be enhanced.

[0030] Also, since the heat dissipation function portion J is provided on the side surface 34S of the body portion 34, it is suppressed from being exposed to arcs and flares. Therefore, it is possible to suppress the coating from peeling off and thinning even with respect to the rise in the temperature of the electrode 30 due to lamp lighting. Further, since the grooves 42 have a heat dissipation function, even if the coating peels off and thins, it is possible to maintain a certain degree of heat dissipation property.

[0031] In particular, as shown in FIG. 2, the height of the top 42P of the groove 42 covered with the coating layer 44, that is, the distance from the electrode axis C to the top 42P (layer surface) is located closer to the electrode center side than the side surface 34S of the body portion 34. Since the top 42P of the groove 42 is located in a position recessed from the side surface 34S of the body portion 34, it is possible to effectively suppress the peeling and thinning of the coating due to arcs and flares.

[0032] In this embodiment, by applying the calculation formula of the emissivity combining the grooves 42 and the coating layer 44, the shape of the grooves 42 and the heat dissipation property (emissivity) of the coating layer 44 can be appropriately combined to effectively enhance the heat dissipation property (emissivity) of the body portion 34. This will be described in detail below.

[0033] 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.

[0034] The emissivity ε of the surface formed with the groove can be approximately expressed by the following formula (1). ε = 1 / (1 + (L / S) × (1 / ε 0 - 1)) ···(1) However, L represents the axial direction (along the side surface 34S) length of the groove formation region, and S represents the total length (total cross-sectional length) along the groove in the groove cross-sectional view (see FIG. 4).

[0035] The value of L / S is related to the groove pitch and the number of grooves, that is, the groove depth (slant length) in the groove formation range. The smaller the value of L / S, the greater the groove depth and the number of pitches. The closer the value of L / S approaches 1, the shallower the groove and the fewer the number of pitches. On the other hand, ε 0 represents the emissivity inherent in the material.

[0036] The emissivity ε 0 inherent in the material is replaced with the emissivity of the coating layer 44 (herein represented by εcoat) to derive the emissivity ε of the heat dissipation functional part J (herein represented by εgroove + coat). However, since the coating layer 44 is very thin compared to the size (depth) of the groove 42, its thickness can be ignored.

[0037] FIG. 3 shows the emissivity εgroove + coat of the heat dissipation functional part J derived from the combination of the emissivity εcoat of the coating layer 44 and L / S of the groove 42. For example, when the groove 42 with the emissivity εcoat of the coating layer 44 being 0.8 and the L / S value being 0.35 is formed, the emissivity εgroove + coat of the heat dissipation functional part J is 0.92. Also, when the groove 42 with the emissivity εcoat of the coating layer 44 being 0.5 and the value of L / S being 0.2 is formed, the emissivity εgroove + coat of the heat dissipation functional part is 0.83.

[0038] Here, the L / S and the emissivity εcoat of the coating layer 44 are determined such that the emissivity εgroove+coat of the heat radiation functional 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 the same uneven shape as the rough surface. 0.8 is determined based on, for example, the emissivity 0.4 of tungsten which is an electrode material.

[0039] By deriving the emissivity εgroove+coat of the part having the two heat radiation functions of the groove 42 and the coating layer 44 using the above formula (1), the component of the coating layer 44 and the shape of the groove 42 can be freely selected so as to have a desired emissivity. For example, a component and shape with higher heat radiation performance can be adopted, and the emissivity of the body part 34 can be effectively (cooperatively) increased. In particular, by setting the emissivity of the coating layer 44 higher than the emissivity of the groove 42, a heat radiation functional part J can be configured in which the heat radiation function of the coating layer 44 is the main one and the heat radiation function of the groove 42 is the subordinate one.

[0040] For example, when a coating layer 44 with a high emissivity is used, the values of L / S that satisfy 0.8 or more are wide, and the shapes of the groove 42 that can be selected increase. Since the combination can be optimized, even if the L / S is increased, that is, even if the groove 42 is formed shallowly, a high emissivity can be maintained. Also, when the groove 42 is shallow, it becomes easy to apply (attach) the coating layer 44 to the bottom of the groove 42.

[0041] Depending on the value of the L / S of the groove 42, if the selection of the coating layer 44 is incorrect, only an emissivity that is not much different from the emissivity of the coating layer 44 can be obtained, and a sufficient heat radiation effect cannot be obtained. However, by referring to the table in FIG. 3, the emissivity εgroove+coat can be maintained high for various groove shapes (values of L / S).

[0042] For the body portion 34 provided with such a heat dissipation functional portion J, on the tapered side surface (front surface) 32S of the tip-side tapered portion 32, only grooves are formed, and a heat dissipation structure (non-coating heat dissipation structure) 50 in which a coating layer is not formed thereon is provided.

[0043] During lamp lighting, since the tapered side surface 32S is exposed to arcs and flares, if a coating layer is provided, there is a possibility of coating peeling off, etc. However, since such a coating layer is not provided, it is possible to suppress the inside of the discharge tube 12 from being contaminated with the components of the coating. Further, by determining the L / S so that the emissivity of the groove 42 becomes high, the heat dissipation performance of the entire electrode 30 can be further enhanced.

[0044] On the other hand, between the heat dissipation structure 40 and the heat dissipation structure 50, a side surface portion 33 made of an electrode base surface is provided and is separated from each other without being adjacent. By providing such a side surface portion 33, it is possible to suppress the movement of arcs and flares to the heat dissipation functional portion having a coating layer during lamp lighting. And since the boundary portion 33P between the tip-side tapered portion 32 and the body portion 34 is rounded, the coating layer 44 can be protected from the occurrence of abnormal discharge and overheating due to abnormal discharge.

[0045] Such an electrode 30 of a discharge lamp can be manufactured as follows. First, an electrode having a columnar body portion and a tip-side tapered portion is formed, and grooves along the circumferential direction are formed on the side surface of the body portion by processing such as laser or cutting. Then, a coating layer is formed on the groove by coating. At this time, by setting the emissivity of the coating layer higher than the emissivity of the groove, a heat dissipation functional portion having a high emissivity can be configured. Note that for coating, known means such as spraying, vapor deposition, sputtering, and CVD may be adopted as long as it can be applied uniformly. The applied coating may be sintered by a furnace (heating device) or a laser.

[0046] Next, with reference to FIG. 5, a discharge lamp according to the second embodiment will be described. In the second embodiment, a heat radiation functional part in which a coating layer is stacked on a heat radiation structure composed of grooves is formed in the tip-side tapered part and the body part, while a heat radiation structure having only grooves is provided on the electrode support rod side.

[0047] FIG. 5 is a schematic plan view of an electrode of a discharge lamp according to the second embodiment. The anode 30' includes a tip-side tapered part 32 and a body 34. A heat radiation functional part J in which a coating layer 44' is formed on a heat radiation structure 40' composed of grooves is continuously formed across the tip-side tapered part 32 from the middle of the body part 34. On the other hand, on the side surface 34S of the body part 34, on the electrode support rod 17B side rather than the heat radiation functional part J, a heat radiation structure 50' (non-coated heat radiation structure) composed only of grooves along the circumferential direction is provided.

[0048] For example, due to reasons such as low lamp output or small electrode size, in some cases, it is possible to suppress the coating layer 44' formed on the tip-side tapered part 32 from being peeled off or disappearing due to an arc or flare. Therefore, by forming the coating layer 44' also on the tip-side tapered part 32 together with the body part 34, the heat dissipation performance can be improved. Similar to the first embodiment, an electrode base surface region may be provided between the heat radiation structure 40' formed with the coating layer 44' and the heat radiation structure 50'.

[0049] In the first and second embodiments, the heat radiation structure is constituted by grooves along the circumferential direction, but it may also be constituted by grooves along the electrode axial direction. Further, a heat radiation structure other than grooves may be adopted. For example, a matte surface by sandblasting or the like, or a blackening suppression body can be configured as the heat radiation structure. If the main purpose is blackening suppression, a blackening suppression body may be adopted, and if improvement in heat dissipation performance is required, grooves may be configured. If low cost is required, a matte surface can be adopted. The heat radiation structure may be determined according to the electrode shape, electrode material, ease of processing such as cutting, and the like.

[0050] In addition, in order to prevent peeling of the coating layer formed on the heat dissipation structure, it is also possible to configure coating layers made of different materials as the heat dissipation structure. That is, a coating layer can be stacked on the coating layer (heat dissipation structure).

Explanation of Signs

[0051] 10 Discharge lamp 30 Electrode 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, 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 circumference of the electrode body portion, the coating layer contains a metal having the same composition as the electrode; A discharge lamp characterized in that the combined emissivity of the heat dissipation structure 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.

2. 2. The discharge lamp according to claim 1, wherein the electrode has an exposed side portion that is made of an electrode base surface.

3. 3. The discharge lamp according to claim 1, wherein a boundary between the tip end taper portion of the electrode and the body portion is rounded.

4. An electrode having a cylindrical body and a tapered tip is formed. A side surface of the body portion is formed with a side surface portion where the electrode base surface is exposed and a groove is formed along the electrode circumferential direction, A coating layer having an emissivity greater than the emissivity of the groove is formed on the groove by coating.

2. A method for manufacturing an electrode for a discharge lamp comprising the steps of:

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