JP3402191B2 - Method of manufacturing cathode for discharge lamp - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a cathode for a discharge lamp.

[0002]

2. Description of the Related Art Generally, the cathode of a discharge lamp contains an emitter such as thorium oxide for facilitating startability. The conventional method of manufacturing such a cathode is as follows. ． First, a refractory metal of tungsten or molybdenum, which becomes the cathode body, is sintered and processed into a desired shape,
A recess is formed at the tip portion. ． Next, tungsten powder and thorium oxide powder are mixed at a desired ratio, this mixed powder is molded, and this is sintered to obtain a chip shape. ． Then, the sintered tip is fitted into the concave portion of the cathode main body to form the cathode.

However, the conventional method for manufacturing the cathode of the discharge lamp has the following problems. ． In the work of fitting the sintered tip into the cathode body,
If the contact surfaces of both are uneven, it cannot be done easily. For this reason, before the fitting work, a separate work of previously polishing the surfaces of both of them is required separately. At that time, the work of smoothing the surface of the insertion hole (recess) of the cathode body is performed because the inner diameter of the insertion hole is small, for example, about 1 to 2 mm.
The work is extremely difficult. ． As mentioned above, the contact surface between the sintered tip and the cathode body is
The smoothing process is performed from the viewpoint of the insertion work,
After insertion, the two are not always in close contact. Then, in order to perform the insertion work smoothly, the inner diameter of the insertion hole and the outer shape of the sintered tip must be delicately controlled, and in the end, the insertion hole must be slightly larger than the sintered tip. I cannot insert it smoothly. As a result, there arises a problem that the inserted sintered tip slightly moves in the hole, and in some cases, slipping out occurs.

On the other hand, Japanese Patent Laid-Open No. 7-65715 discloses that
A mixed powder of tungsten powder and thorium oxide powder is press-molded into a chip shape, and separately, a high-melting-point metal powder to be the cathode body is also press-molded so as to have a recess at the tip. There is disclosed a technique in which, after being combined into one, the whole is further subjected to a press treatment, and then a sintering treatment is performed.

In the cathode manufactured by this method, after the molded body of the cathode body and the molded chip body of the mixed powder are combined, both are press-molded and sintered, so that The boundary area between the peripheral portion and the mixed powder molding chip body is mixed irregularly during press molding,
The boundary circumferential portion of the mixed powder molded chip body after sintering does not have a smooth circumference, but is formed in an irregular state. That is, the outer peripheral circular portion of the mixed powder molded chip body, which is responsible for arc formation, has an irregular circumferential shape. For this reason, there is a problem that the arc becomes irregular at the time of lighting and it becomes difficult to form a stable arc.

[0006]

The problem to be solved by the present invention is to easily insert a chip including an emitter into a cathode main body, and after the assembly and sintering, the chip may be slightly moved or slipped out. Another object of the present invention is to provide a method for manufacturing a cathode for a discharge lamp, in which the circumference of the sintered tip has a regular shape and a stable arc can be obtained, and the evaporation of the emitter is small.

[0007]

The method for producing a cathode for a discharge lamp according to the present invention is intended to solve the above-mentioned problems, and a mixed powder of powdered barium-based electron emissive material and tungsten powder is molded. The primary molded body consisting of tungsten or molybdenum is inserted into the recessed portion of the tip of the sintered cathode body, and the primary molded body is pressed and crushed in the concave portion, and then the primary molded body is filled in the concave portion. Is characterized in that the primary compact is sintered.

Further, after the sintering treatment, the sintered body of the primary molded body is swaged, and the tip portion thereof is densified.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a primary compact formed by molding a mixed powder containing an emitter powder is inserted into a concave portion of a sintered cathode body, and then the primary compact is pressed and crushed, and then this is compacted. It is what is sintered.

This primary compact is obtained by putting mixed powder of emitter powder into a mold having an inner diameter slightly smaller than the recess of the cathode body and press-molding it into a columnar shape, or after press-molding at a temperature of around 1000 ° C. It is a molded product that has been heat-treated for a period of time in hydrogen or an inert gas and is in a state where it is easy to handle when inserting it into the cathode body, etc., and has a hardness of a choke that can be picked up with tweezers. Therefore, unlike the conventional method in which a press-molded body of a mixed powder containing an emitter is inserted into the recess of the cathode main body as a sintered chip, the primary molded body simply inserted as it is into the recess of the cathode main body, The process of manufacturing a sintered chip by processing is omitted, and the manufacturing of the cathode is simplified.

Since the inserted primary compact is crushed by the subsequent pressing by the press and densely filled in the recess of the cathode main body, the size of the primary compact is the inner diameter of the recess of the cathode main body. The insertion work is significantly improved since there is no problem with making it smaller. Moreover, the degree of adhesion between the primary molded body and the cathode body is also greatly improved.

Further, with respect to the recess of the cathode body, the work of smoothing the inner surface of the recess is unnecessary. Rather, when the primary compact is crushed in the recess without smoothing the inner surface of the recess of the cathode body, the unevenness of the inner surface of the recess and the mixture after sintering are formed so as to mesh with each other. The slight movements and missing points of the turtle will disappear.

[0013]

FIG. 1 shows a method of manufacturing a cathode according to the present invention. FIG. 1 (a) shows a process of making the cathode body 1. Specifically, a material obtained by sintering a refractory material such as tungsten or molybdenum is processed into a desired shape. A portion 1a for welding a metal foil such as is formed. This metal foil serves to supply electric current and maintain vacuum tightness. The cathode body 1 is, for example, a substantially cylindrical body having a diameter of 4 mm and a length of 25 mm.

FIG. 1 (b) shows a step of processing a recess for inserting a primary molded body described later in the cathode main body 1, specifically, a portion 1a of the cathode main body 1 for welding the metal foil.
At the opposite end, for example, 1.0 φmm, 7.0 mm long recess 1
b is provided. After forming the recesses, cleaning is performed with an organic solvent (acetone or the like) in order to remove oils generated during processing of the recesses. As a result, the inside of the recess can be surely degreased. After finishing such a step, the recessed cathode main body 1 is stored in an inert gas atmosphere until it is used in the next step. This is to prevent dust from adhering and oxidizing.

Next, the emitter forming process will be described. First, a plurality of powdery emitter materials are weighed and mixed. Specifically, 1.8 mol of BaCO ₃ and SrC
O ₃ is mixed at 0.2 mol, CaCO ₃ is mixed at 1.0 mol, and WO ₃ is mixed at 1.0 mol to obtain a mixed powder state. Further, in the present invention, as the emitter, a mixed powder (ThO) of thorium oxide and tungsten that has been conventionally used is used.
_2- W) is not used. As a result, the operating temperature during lighting can be lowered by about 1000 ° C., and therefore, evaporation, wear and deformation of tungsten can be eliminated, and the lamp can be stably lit for a long time.

The mixed powder is put in, for example, an alumina crucible and fired at about 1000 ° C to 1200 ° C. Firing is performed in the air for about 2 hours. This firing decomposes carbon dioxide to make a stable emitter. If the temperature is too low, firing will be incomplete, and if the temperature is too high, the mixed powder will melt or decompose.

The fired mixed powder is pulverized. The pulverization is performed with a ball mill or the like to form particles of several μm. This work is performed in a place with low humidity because the emitter has strong water absorption (hygroscopicity). The particles of several μm formed in this way are stored in a vacuum, in an inert gas (for example, nitrogen) atmosphere, or in a glass ampoule so that impurities are not mixed. Such storage work is important, and in particular, it is necessary to perform it strictly so as not to mix water.

Next, the tungsten powder is mixed. This mixing is performed for the purpose of stabilizing the arc emission portion of the electrode tip for a long time and without deforming, and mixes large, medium and small particles. Specifically, 70% of large particles (about 10 μm), 20% of medium particles (about 4 μm), and 10% of small particles (about 1 μm) are weighed and mixed. Then, these powders are uniformly mixed by a ball mill or the like. The mixed powder of tungsten thus completed is also stored in an inert gas (for example, nitrogen) atmosphere like the mixed powder of the emitter. If necessary, tantalum or zirconium may be added to the mixed powder of tungsten.

Next, the step of mixing the emitter powder and the tungsten powder will be described. Emitter powder is usually 4% ~
It is mixed at a ratio of 15%, and specifically, for example, the emitter powder is weighed at a ratio of 10% and the tungsten powder is weighed at a ratio of 90%, and sufficiently mixed using a ball mill or the like. Even in such work, it is necessary to take great care not to mix impurities, especially water. The powder thus mixed is stored in a moisture-free place or in an inert gas (for example, nitrogen) atmosphere.

Next, a process of forming a primary compact for inserting a mixed powder of the emitter powder and the tungsten powder into the tip hole of the cathode body will be described. A mixed powder of the emitter powder and the tungsten powder is put into a mold (not shown) and pressed. Then, heat treatment is performed at 1000 ± 100 ° C. in a hydrogen atmosphere or an inert atmosphere for 10 minutes to obtain a porosity of 30 to 50.
% Tweezers make it as hard as chalk. As shown in FIG. 2, the primary molded body has a columnar shape and its diameter is slightly smaller than the diameter of the recess. For example, it is about 95% of the recess diameter. It should be noted that although it is slightly brittle as compared with the heat-treated product, it requires careful handling, but it may be a primary molded product obtained by pressing only without heat treatment.

Next, as shown in FIG. 3, this primary molded body is inserted into the above-mentioned recessed portion of the tip of the cathode main body. Note that it is necessary to take care not to mix water in this step as well. After that, as shown in FIG. 4, the primary molded body is pressed in the recess with pressure. As a result, the primary molded body is crushed and expanded in the recess, and the recess is densely filled. This press is for increasing the density of the mixed powder and for strengthening the joint with the recess, and the pressure is, for example, about 8 ton / cm ² . Further, depending on the size of the molded body, a plurality of primary molded bodies may be molded, and the primary molded body may be inserted into the concave portion and pressed to fill.

Then, the primary compact is sintered in a state where the primary compact is pressed and densely packed in the cathode body. Such a sintering process is performed, for example, at a high temperature of 1500 ° C. for about 15 minutes in a vacuum or an inert gas atmosphere. This sintering temperature is processed at a high temperature within a range where the emitter does not evaporate, and is about 1500 ° C. for the barium-based emitter as in the present invention. The heating method includes heating with an arc, high frequency heating, heating with an electric furnace, and an arc image furnace.

The heat-treated electrode is then swaged into a sintered mixed powder compact. This swaging is performed under a high temperature heating condition of 1500 ° C., for example.
The swaging pressure is 8 to 10 tons / cm ² , and the pressing is continuously performed at intervals of 1 second / 1 time for about 0.1 second each time. And about 1
Pressurization is performed 00 times. The heating method in this case is also carried out in an inert gas, such as heating by an arc, high frequency heating, heating by an electric furnace, or an arc image furnace, as in the case of the above-mentioned sintering. By such swaging treatment, the density of the tip portion of the sintered mixed powder compact, which is the emitter-containing portion (that is, arc emission portion) in the tip portion of the electrode, can be increased.

Next, cutting is performed so that the diameter of the electrode tip is approximately the same as the outer peripheral portion of the primary molded body. That is, the cathode tip is processed so that only the sintered mixed powder compact is exposed in the discharge space.

FIG. 5 shows an example of the cathode of the present invention. In this example, the diameter of the cathode tip and the diameter of the recess into which the primary molded body is inserted are substantially the same as described above.

The electrode manufactured by the above method can be widely applied to a discharge lamp having a rated power of 50 W to a rated power of 2000 W, but the size of a sintered body formed by embedding a primary compact at the tip of the electrode is small. , Take various values as shown in FIG. The length (recess depth) L and the diameter d of the sintered body formed by embedding the primary molded body in this way take various values, but the electric current emitted from the cathode becomes larger in a large input type lamp. It increases in relation to the quantity.

The cathode manufactured by the manufacturing method of the present invention is
High pressure mercury lamp, ultra high pressure mercury lamp, xenon lamp,
Widely applicable to xenon mercury lamps.

Next, the attenuation characteristics of the illuminance with respect to the lighting time will be shown. FIG. 7 shows a discharge lamp (A) having a cathode according to the present invention and an emitter similar to BaCO ₃ : S of the present invention.
Each of the discharge lamps (B) manufactured by a conventional manufacturing method as rCO ₃ : CaCO ₃ : WO ₃ , that is, a method of sintering the mixed powder after molding into chips and then inserting it into the cathode body is lit for 2000 hours. The results of measuring the illuminance of light having a wavelength of 365 nm emitted from each lamp are shown. The vertical axis represents the illuminance maintenance ratio when the value of the illuminance in the initial stage of lighting is 100, and the horizontal axis represents the lighting time. As shown in FIG. 7, the experimental result of the present invention shows that the discharge lamp (B) is attenuated to 90% or less after being lit for 2000 hours, whereas the discharge lamp (A) according to the present invention has almost 1%.
It can be seen that the illuminance is close to 00%.

[0029]

According to the method of manufacturing a cathode for a discharge lamp according to the present invention, after the primary compact formed by molding the mixed powder containing the emitter powder is inserted into the recess of the sintered cathode body, the primary compact is inserted. By pressing, it is crushed and densely filled in the recess and then sintered, so unlike the method of inserting the mixed powder as a sintered chip into the recess of the cathode body, the primary molding of the mixed powder Since the body can be inserted into the recess of the cathode main body, the labor of manufacturing a sintered chip is omitted and the manufacturing of the cathode is simplified.

Since the primary molded body is pressed and crushed in the concave portion and densely filled, the joint between the mixed powder body and the cathode body becomes extremely strong. In addition, since the primary molded body having a diameter smaller than the inner diameter of the recess can be inserted into the recess of the cathode body, the work becomes extremely easy, and the work of smoothing the inner surface of the recess is unnecessary. Rather, by inserting the primary molded body and performing the sintering process without smoothing the inner surface of the recess of the cathode body,
Since the unevenness on the inner surface of the recess is formed so as to mesh with the mixture after sintering, fine movement of the sintered tip and slipping out of the sintered chip are eliminated.

In addition, a primary compact of the non-sintered mixed powder is inserted into the sintered cathode body, pressed and crushed in the concave portion of the cathode, and the primary compact is then sintered. The boundary region between the mixed powder body and the cathode body after binding is not disordered irregularly, and an electrode with a stable arc can be obtained.

[Brief description of drawings]

FIG. 1 shows a cathode body of the present invention.

FIG. 2 shows a mixed powder primary compact according to the present invention.

FIG. 3 shows a state in which a primary molded body is inserted into a cathode body according to the present invention.

FIG. 4 shows a state where the primary molded body is pressed and crushed in the cathode body in the present invention.

FIG. 5 shows an example of a cathode manufactured according to the present invention.

FIG. 6 shows various examples according to the rated power of the cathode manufactured according to the present invention.

FIG. 7 shows the illuminance maintenance rate of a discharge lamp using a cathode manufactured according to the present invention.

[Explanation of symbols]

1 Cathode body 1a Part for welding metal foil 1b Recess on the cathode body 2 Primary molding

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Claims (2)

(57) [Claims] 1. A method of manufacturing a cathode for a discharge lamp, comprising a step of molding a mixed powder of a powdery barium-based electron emissive material and a tungsten powder into a primary molded body, and a sintered cathode body made of tungsten or molybdenum. The electric discharge, characterized in that the primary molded body is inserted into the recessed portion, is pressed and crushed in the recessed portion, and then the primary molded body is sintered while the primary molded body is filled in the recessed portion. Manufacturing method of cathode for lamp. 2. After the sintering process, the primary composition of the mixed powder
Swaged shaped sintered body to densify the tip
The cathode for a discharge lamp according to claim 1, wherein
Production method.