JP2004281153A - Cathode for discharge lamp and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide cathode structure having high productivity, reducing a cost, and to provide its manufacturing method. <P>SOLUTION: In this cathode structure porous wolfram or molybdenum impregnated with a barium compound is coaxially arranged in a central axis of an electrode substrate made of wolfram or molybdenum. In this manufacturing method of the cathode, an impregnated rod impregnated with the barium compound is sheathed with a wolfram tube or a molybdenum tube, the sheathed impregnated rod is aged in a high temperature heating state, and then the outer shape is worked. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge lamp cathode and a method of manufacturing the same, and more particularly, to a discharge lamp cathode having a long lamp life and capable of being formed at low cost, and a method of manufacturing the same.
[0002]
[Prior art]
Conventional discharge lamp cathodes are broadly classified into cathodes using thoria as an emitter material and cathodes using a barium compound as an emitter material. FIG. 4 is an explanatory view of a triplet tungsten cathode as an example of a cathode using thoria as an emitter material, and FIG. 5 is an illustration of an impregnated cathode impregnated with barium / calcium aluminate as an example of a cathode using a barium compound as an emitter material. FIG. 6 and FIG. 6 are explanatory views of the cathode structure in which the emitter material is localized only at the tip of the cathode.
[0003]
The triplet tungsten cathode 6 shown in FIG. 4 is formed through the following manufacturing steps. First, a thorium nitrate solution and tungsten trioxide are slurried, and through processes such as thermal decomposition, reduction, molding, firing, and swaging, a dense tungsten rod-like substrate containing about 1 to 5% of thorium dioxide is obtained. Form. Thereafter, the rod-shaped base material is cut in accordance with the dimensions of the electrode, and is formed into a sharp tip shape (tip angle: about 20 °) by polishing or the like. The triplet tungsten cathode 6 formed in this manner is relatively inexpensive because many cathodes can be formed from one base material.
[0004]
However, when such a triplet tungsten cathode 6 is mounted on a discharge lamp, the maximum cathode temperature reaches 3000 to 3500 ° C. When operated at a high temperature exceeding 3000 ° C. for a long time, the shape of the cathode tip deteriorates. In addition, the cathode drop (potential drop near the cathode) is relatively large, and the collision of sealing gas ions generated by ionization causes an increase in the cathode temperature and spatter of the cathode base material, which promotes deterioration of the cathode tip shape. Had disadvantages.
[0005]
Due to the above characteristics, the triplet tungsten cathode 6 is inexpensive, but in the case of a 150 W discharge lamp, the tip shape deteriorates in about 1700 hours, and the life of the cathode, that is, the discharge lamp is reduced. This is because the deterioration of the shape of the cathode tip lowers the luminance and the stability of the light output of the discharge lamp.
[0006]
On the other hand, as shown in FIG. 5, as a cathode using a barium-based compound as an emitter material, there is an impregnated cathode 7 in which porous tungsten is impregnated with barium calcium aluminate. This involves pressing, molding, sintering, or forming and removing copper from tungsten powder, and forming the resulting tungsten into porous tungsten with a porosity of about 20% and a tip angle of about 80 °. It is impregnated with calcium. 8 is a molybdenum lead.
[0007]
The impregnated cathode 7 has a higher thermionic emission characteristic and a γ action (secondary electron emission due to ion collision) as compared with a triplet tungsten cathode, and the cathode drop is relatively eased. For this reason, the maximum temperature of the cathode is suppressed to 3000 ° C. or less, and spatter by gas ions is reduced. Therefore, in the impregnated cathode 7, the tip shape is less deteriorated as compared with the triplet tungsten cathode 6, and the lamp life time is about 2500 hours in a 150 W high pressure arc lamp.
[0008]
However, the life of the arc lamp using the impregnated cathode 7 is due to a decrease in luminance due to the evaporation of barium calcium aluminate adhering to the glass tube wall and lowering the light transmittance. There was a problem that the service life was not maximized. Further, since the cathode base material is a porous body, there is a problem that it is difficult to sharpen the tip of the cathode as in the case of the triplet tungsten cathode 6, and the luminescent spot tends to fluctuate.
[0009]
In order to solve such a problem, Japanese Patent Application Laid-Open No. 2000-156198 (Patent Document 1) discloses that an emitter material is localized only at the tip of a cathode to reduce the amount of evaporation of the emitter material and stabilize a bright spot. Is disclosed. As shown in FIG. 6, a press-formed body 9 containing an emitter mixed, pressed and fired with barium tungstate as an emitter material, pressed into a tungsten press fired body 10, and then hot-pressed or A cathode having a structure densified by swaging or the like is disclosed. However, such a complicated cathode structure has a problem that a manufacturing process is complicated, mass productivity is poor, and a manufacturing cost is increased.
[0010]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-156198
[Problems to be solved by the invention]
As described above, a conventional tungsten cathode using thoria as an emitter material is excellent in mass productivity and can be reduced in cost, but has the disadvantage that the tip shape is easily deteriorated and the life is short. Was. In addition, in the impregnated cathode impregnated with barium calcium aluminate, the tip shape is less deteriorated and the life is longer than that of the thoriated tungsten cathode. There is a problem that the life as is short. Furthermore, since the impregnated cathode is a porous body, it is difficult to sharpen the tip, and there has been a problem that the luminescent spot tends to fluctuate. Further, among cathodes using a barium compound as an emitter material, a cathode having a structure in which the emitter material is localized only at the tip can achieve low evaporation and stabilization of a bright spot, but since the cathode structure is complicated, There has been a problem that a large number of manufacturing steps are required and the cost is high. SUMMARY OF THE INVENTION It is an object of the present invention to provide a cathode structure and a method for manufacturing the same, which can solve the above-mentioned problems, and in particular can extend the life of the discharge lamp and reduce the cost of the cathode.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a discharge lamp cathode according to the first aspect of the present invention is configured such that porous tungsten or porous molybdenum impregnated with barium calcium aluminate is coaxially arranged at the center of an electrode substrate made of tungsten or molybdenum. The configuration is as follows.
[0013]
Further, the method for producing a cathode for a discharge lamp according to the second invention of the present application includes a step of forming an impregnating rod in which barium / calcium aluminate is impregnated into a porous body made of tungsten or molybdenum; After enclosing in a molybdenum tube, it is swaged to form a cathode bar in which porous tungsten or porous molybdenum impregnated with barium calcium aluminate is coaxially arranged, and the cathode bar is externally processed. And a process. In particular, by configuring the swaging process to be performed in a temperature range of 1400 ° C. or more and 1750 ° C. or less, the barium / calcium aluminate becomes a liquid phase, swaging becomes possible, and the impregnated rod and the tube are integrated. This is convenient for external processing.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing a cathode structure according to an embodiment of the present invention. This is a structure in which a porous body 1 made of porous tungsten impregnated with barium calcium aluminate is arranged and formed on the center axis of an electrode substrate 2 made of a dense tungsten tube. In the structure of the present invention, since barium / calcium aluminate, which is an emitter material, is localized on the central axis of the electrode substrate 2, unnecessary evaporation of barium / calcium aluminate is eliminated, and the amount of evaporation can be reduced. That is, dirt on the lamp tube wall is reduced, the tip shape deterioration which is a characteristic of the barium-based cathode is small, and the long life is fully exhibited, and the life of the discharge lamp can be further extended. Furthermore, since the localization of barium calcium aluminate concentrates the bright spot on the tip of the cathode, the bright spot fluctuation is small and the light output can be stabilized.
[0015]
It is preferable that the diameter of the porous body 1, which is the localized area of barium calcium aluminate, be 0.2 mm or more and 1.0 mm or less. This is because the bright spot diameter must be at least 0.2 mm or more, and if the diameter of the porous body 1 is less than 0.2 mm, a sufficient bright spot cannot be obtained. The diameter of the porous body 1 is set according to the output of the discharge lamp, and the diameter of the porous body 1 is preferably increased as the output increases. However, practically, when the diameter exceeds 1.0 mm, the concentration of the bright spot on the cathode tip is reduced, and the variation of the bright spot is not significantly different from that of the conventional impregnated cathode. Therefore, it is preferable that the diameter of the porous body 1 be 1.0 mm or less.
[0016]
The porosity is desirably 1 vol% or more and 25 vol% or less. If it is less than 1 vol%, the characteristics of the discharge lamp become unstable due to insufficient supply of barium calcium aluminate as an emitter material, and if it exceeds 25 vol%, the shape of the cathode tip deteriorates and the evaporation amount of barium calcium aluminate increases, This is to shorten the lamp life.
[0017]
FIG. 2 is a view showing a manufacturing process of the cathode of the present invention. First, a porous tungsten rod is impregnated with barium calcium aluminate (BaO: CaO: Al ₂ O ₃ = 6: 1: 2) at 1750 ° C. in a reducing atmosphere to form an impregnated rod 3 (step A). . Subsequently, as shown in FIG. 3, the impregnating rod 3 is sheathed so as to be coaxially arranged on the central axis of the tube 4 made of tungsten (step B). Here, the diameter of the impregnating rod 3 and the inner and outer diameters of the tube 4 are determined according to the amount of swaging in the next step. Further, both ends are sealed by using a sealing member 5 in order to prevent the barium calcium aluminate from being scattered by the heating during the swaging.
[0018]
The next step is swaging (step C). The processing temperature at this time must be 1400 ° C. or higher, which is the melting point of barium calcium aluminate. This is because barium / calcium aluminate in a solid phase having a melting point or lower has no ductility like a metal, so that swaging does not proceed. However, if the processing temperature exceeds 1750 ° C., the barium / calcium aluminate deteriorates, so it is desirable to set the processing temperature to 1400 ° C. to 1750 ° C. Then, by the swaging, the porous tungsten structure of the impregnating rod 3 and the structure of the sheathed tungsten tube 4 are integrated, and a cathode bar in which the porous body 1 is coaxially arranged on the cathode base 2 is obtained.
[0019]
Further, since the porous tungsten of the impregnating rod 3 is densified by the swaging, the pore size becomes smaller than before the swaging, and the number of pores per unit volume increases. This contributes to efficient activation of barium / calcium aluminate, which is an emitter material, and is therefore advantageous in terms of the electron emission characteristics of the cathode.
[0020]
Finally, the cathode rod is subjected to external processing such as outer diameter processing, cutting, and tip processing, and a discharge lamp cathode in which the porous body 1 is coaxially arranged on the central axis of the cathode base 2 made of tungsten. (Step D). The diameter of the porous body 1 can be adjusted according to the amount of swaging.
[0021]
As described above, in the embodiment of the present invention, an example is shown in which a porous tungsten rod is impregnated with barium calcium aluminate and sheathed with a tube made of tungsten, but a porous molybdenum rod may be used instead of the porous tungsten rod. Alternatively, a tube made of molybdenum may be used instead of tungsten. Further, the composition ratio of barium calcium aluminate was described as BaO: CaO: Al ₂ O ₃ = 6: 1: 2, but is not limited thereto, and is not limited to 4: 1: 1 or 5: 1: 2. Or, 4: 2: 2 has the same effect.
[0022]
【The invention's effect】
As described above, according to the present invention, barium / calcium aluminate as an emitter material can be localized only near the tip of the center axis of the electrode substrate. As a result, excess evaporation of barium calcium aluminate is eliminated, and the amount of evaporation can be reduced. That is, the characteristics of the barium-based cathode, which is a long-life cathode with little deterioration in the shape of the cathode tip, can be sufficiently exhibited, and the life of the lamp can be further extended. In addition, since the localization of barium calcium aluminate at the tip of the cathode concentrates the bright spot on the tip of the cathode, the variation of the bright spot is reduced, and the light output of the lamp can be stabilized.
[0023]
Further, according to the production method of the present invention, a cathode rod material in which a porous tungsten rod or a porous molybdenum rod impregnated with barium calcium aluminate is arranged and formed coaxially on the central axis of the electrode substrate can be produced at low cost. This rod can adjust the localization state of barium calcium aluminate on the central axis according to the amount of swaging. Further, if outer diameter processing, cutting and tip processing are performed in accordance with the electrode dimensions, cathodes having the same characteristics can be continuously manufactured, and the structure and process of individually manufacturing cathodes by pressing or the like are eliminated.
[0024]
In particular, by setting the temperature during swaging to 1400 to 1750 ° C., the barium / calcium aluminate becomes a liquid phase without deterioration, and is excellent in swaging workability, radiation characteristics of the cathode, and outer shape workability. Material can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a sectional structure of a discharge lamp cathode according to an embodiment of the present invention.
FIG. 2 is a diagram showing a manufacturing process of the present invention.
FIG. 3 is a view showing a method of manufacturing a tungsten sheath in a manufacturing process of the present invention.
FIG. 4 is a view showing a triplet tungsten cathode which is one of the conventional discharge lamp cathodes.
FIG. 5 is a diagram showing an impregnated cathode impregnated with barium calcium aluminate, which is one of the conventional discharge lamp cathodes.
FIG. 6 is a diagram showing an example of a cathode in which an emitter material is localized only at the tip of the cathode which is one of the conventional cathodes for a discharge lamp.
[Explanation of symbols]
1: Porous body 2: Electrode substrate 3: Impregnated rod 4: Tube 5: Sealing material 6: Triated tungsten cathode 7: Impregnated cathode 8: Molybdenum lead 9: Press molded body with emitter 10: Tungsten pressed fired body 11 : Metal substrate

Claims (3)

A cathode for a discharge lamp, wherein porous tungsten or porous molybdenum impregnated with barium calcium aluminate is coaxially arranged at the center of an electrode base made of tungsten or molybdenum. A step of forming an impregnating rod in which a porous body made of tungsten or molybdenum is impregnated with barium / calcium aluminate, and enclosing the impregnated rod in a tungsten tube or a molybdenum tube, followed by swaging to obtain a barium / calcium aluminate A step of forming a cathode rod in which porous tungsten or porous molybdenum impregnated with a cathode is disposed coaxially, and a step of externally processing the cathode rod. 3. The method of claim 2, wherein the swaging is performed in a temperature range of 1400 ° C. to 1750 ° C. in which the barium calcium aluminate is in a liquid phase. 4.

Images