JPH11297196A - Method of manufacturing cathode for discharge lamp - Google Patents

Abstract

(57) [Problem] To easily insert a chip including an emitter into a cathode body, and thereafter, the chip is sintered in an electrode without fine movement or slipping out. Provided is a method for manufacturing a cathode for a discharge lamp, in which a stable arc is obtained without irregularly disturbing a boundary region between a chip and an electrode, and the evaporation of an emitter is small. SOLUTION: A particulate barium-based electron-emitting material and tungsten powder are mixed at a desired ratio to form a mixed powder, and a primary molded body made of the mixed powder is inserted into a concave end of a cathode body such as tungsten. A method for producing a cathode for a discharge lamp, comprising squeezing the primary molded body by pressurizing and crushing the primary molded body in a state where the primary molded body is inserted into the concave portion of the cathode body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 to facilitate startability. A conventional method for manufacturing such a cathode is as follows. . First, sintering a high melting point metal of tungsten or molybdenum to be the cathode body, processing this into a desired shape,
A recess is formed at the tip. . Next, the tungsten powder and the thorium oxide powder are mixed at a desired ratio, the mixed powder is formed, and the mixed powder is sintered to obtain a chip. . Then, the cathode is completed by fitting the sintered tip into the concave portion of the cathode main body.

However, the conventional method for manufacturing a cathode of a discharge lamp has the following problems. . In the work of inserting the sintered tip into the cathode body,
If the contact surfaces of the two have irregularities, it cannot be easily performed. For this reason, before the fitting operation, it is necessary to separately perform an operation of polishing the surfaces of both surfaces smoothly in advance. At this time, the operation of smoothing the surface of the insertion hole (recess) of the cathode body is performed because the inner diameter of the insertion hole is as small as, for example, about 1 to 2 mm.
The difficulty of the work is remarkable. . As mentioned above, the contact surface between the sintered tip and the cathode body is
Although the smoothing process has been performed from the viewpoint of the insertion work,
After insertion, the two do not always adhere. And in order to perform the insertion work smoothly, the inner diameter of the insertion hole and the outer shape of the sintered chip must be delicately controlled, and after all, the insertion hole must be slightly larger than the sintered chip. Cannot perform smooth insertion work. As a result, there occurs a problem that the inserted sintered tip slightly moves in the hole, and in some cases, slips out.

On the other hand, JP-A-7-65715 discloses that
A mixed powder of a tungsten powder and a thorium oxide powder is press-molded into a chip-like form. Separately, a refractory metal powder serving as a cathode main body is also produced by press-molding so as to have a concave portion at the tip. A technology is disclosed in which, after combining them into a single body, a pressing process is further performed on the whole, followed by a sintering process.

[0005] Since the cathode manufactured by this method combines a molded body of the cathode main body and a molded chip body of the mixed powder, and then press-molds and sinters the molded body, a concave portion of the cathode main body is formed. The peripheral region and the boundary region between the mixed powder molded chip bodies are mixed irregularly, particularly 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 circumferential portion of the mixed powder molded chip body 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 is difficult to form a stable arc.

[0006]

The problem to be solved by the present invention is that the tip including the emitter can be easily inserted into the cathode main body, and the tip slightly moves or slips off after the sintering. Another object of the present invention is to provide a method of manufacturing a cathode for a discharge lamp, in which a circular arc of a sintered tip has a regular shape, a stable arc is obtained, and evaporation of an emitter is small.

[0007]

SUMMARY OF THE INVENTION A method of manufacturing a cathode for a discharge lamp according to the present invention is intended to solve the above-mentioned problem, and comprises forming a mixed powder of a powdery barium-based electron-emitting substance and tungsten powder. Is inserted into the recess at the tip of the sintered cathode body made of tungsten or molybdenum, and the primary compact is pressed and crushed in the recess, and then the primary compact is filled in the recess. And sintering the primary compact.

Further, the present invention is characterized in that after the sintering process, the sintered body of the primary molded body is swaged, and the tip portion 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 main body, and then the primary compact is pressed and crushed. It is to be sintered.

[0010] The primary molded body is prepared by pressing a mixed powder composed of an emitter powder into a mold having an inner diameter slightly smaller than that of the concave portion of the cathode main body and press-forming the same into a columnar shape. A molded body that has been subjected to heat treatment in hydrogen or an inert gas for a long time and is in such a state that it can be easily handled at the time of insertion work into the cathode main body or the like, and has a hardness of about chalk picked with tweezers. For this reason, unlike the conventional method in which the pressed compact of the mixed powder containing the emitter is formed into a sintered chip and then inserted into the concave portion of the cathode main body, the simply molded primary molded body is inserted into the concave portion of the cathode main body. The process of manufacturing a sintered chip by processing is omitted, and the manufacturing of the cathode is simplified.

Then, the inserted primary compact is crushed by the subsequent pressing and is densely filled in the concave portion of the cathode main body. Therefore, the dimensions of the primary compact are determined by the inner diameter of the concave portion of the cathode main body. Since there is no problem at smaller sizes, the insertion operation is significantly improved. In addition, the degree of adhesion between the primary molded body and the cathode body is greatly improved.

[0012] Further, for the concave portion of the cathode main body, the operation of smoothing the inner surface of the concave portion is not required. Rather, when the primary molded body is crushed in the recess without smoothing the inner surface of the recess of the cathode body, the mixture after sintering is formed so that the unevenness on the inner surface of the recess and the mixture after sintering are formed. The fine movement and the slip-out are eliminated.

[0013]

FIG. 1 shows a method of manufacturing a cathode according to the present invention. FIG. 1 (a) shows a process of manufacturing a cathode body 1, specifically, a process in which a material obtained by sintering a high melting point material such as tungsten or molybdenum is processed into a desired shape. A portion 1a to be welded with a metal foil such as a metal foil is formed. This metal foil acts to supply current and maintain vacuum tightness. The cathode main body 1 is, for example, a substantially cylindrical shape having a diameter of 4 mm and a length of 25 mm.

FIG. 1 (b) shows a step of processing a concave portion for accommodating a primary molded body to be described later in the cathode main body 1, and specifically, a portion 1a of the cathode main body 1 to which the metal foil is welded.
On the opposite end, for example, a recess 1 with 1.0 mm and length 7.0 mm
b is provided. After forming the concave portion, the substrate is washed with an organic solvent (such as acetone) in order to remove oils generated at the time of processing the concave portion. Thereby, the inside of the concave portion can be surely degreased. After finishing such a process, the cathode body 1 having the recessed portion is stored in an inert gas atmosphere until it is used in the next process. This is to prevent dust from adhering or oxidizing.

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

This mixed powder is put into, for example, an alumina crucible and fired at about 1000 ° C. to 1200 ° C. Calcination is performed in the atmosphere for about 2 hours. By this firing, carbon dioxide is decomposed and a stable emitter can be produced. On the other hand, if the temperature is too low, the calcination becomes incomplete, and if the temperature is too high, the mixed powder is melted or decomposed.

The fired mixed powder is pulverized. The pulverization is carried out by a ball mill or the like to obtain particles of several μm. This operation is performed in a place with low humidity because the emitter has a high water absorption (hygroscopicity). The particles of several μm thus formed are stored in a vacuum, in an inert gas (eg, nitrogen) atmosphere, or in a glass ampoule so as to prevent impurities from being mixed. Such a storage operation is important, and in particular, must be performed strictly so that moisture is not mixed.

Next, the tungsten powder is mixed. This mixing is performed for the purpose of stabilizing the arc discharge portion at the tip of the electrode for a long time and without deformation, 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. These powders are uniformly mixed by a ball mill or the like. The mixed powder of tungsten thus completed is stored in an inert gas (for example, nitrogen) atmosphere similarly to 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 usually 4% ~
For example, the emitter powder is weighed at a ratio of 10% by weight, and the tungsten powder is weighed at a ratio of 90% by weight, and is sufficiently mixed using a ball mill or the like. Even in such an operation, it is necessary to pay sufficient attention so that impurities, especially water, do not enter. The powder thus mixed is stored in a place without moisture or in an atmosphere of an inert gas (for example, nitrogen).

Next, a process for producing 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. The mixed powder of the emitter powder and the tungsten powder is put in a mold (not shown) and pressed. Then, heat treatment is performed at 1000 ± 100 ° C. for 10 minutes in a hydrogen atmosphere or an inert atmosphere to obtain a porosity of 30 to 50.
The hardness is about the same as that of chalk, but only with pincer tweezers. As shown in FIG. 2, the primary molded body has a columnar shape, and the diameter is slightly smaller than the diameter of the concave portion. For example, it is about 95% of the diameter of the concave portion. It should be noted that, although it is slightly brittle as compared with the one that has been heat-treated, care must be taken in handling, but a primary molded body in which only heat treatment is performed without heat treatment may be used.

Next, as shown in FIG. 3, the primary molded body is inserted into the above-described concave portion at the tip of the cathode main body. It should be noted that also in this step, care must be taken not to mix moisture and the like. Thereafter, as shown in FIG. 4, the primary molded body is pressed under pressure in the recess. Thereby, the primary molded body is crushed and spread in the concave portion, and is densely filled in the concave portion. This press is performed to increase the density of the mixed powder and to strengthen the bonding with the concave portions, and the pressure is, for example, about 8 tons / cm ² . Although it depends on the size of the molded body, the primary molded body may be formed into a plurality of pieces, inserted into the concave portion, pressed, and filled.

Then, in a state where the primary compact is pressed and densely filled in the cathode body, the primary compact is sintered. Such sintering is performed, for example, at a high temperature of 1500 ° C. for about 15 minutes under 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. In addition, examples of the heating method include heating by an arc, high-frequency heating, heating by an electric furnace, and an arc image furnace.

The heated electrode is then swaged to a sintered mixed powder compact. This swaging process is performed under a high-temperature heating state of, for example, 1500 ° C.
The swage pressure is 8 to 10 ton / cm ² , and the pressure is held at a rate of 1 second / time for about 0.1 second / time. And about 1
00 pressurizations are performed. The heating method in this case is also performed in an inert gas by an arc heating, high-frequency heating, heating by an electric furnace, an arc image furnace, or the like, similarly to the above-described sintering. By such a swaging process, the density of the tip portion of the sintered mixed powder compact, which is the emitter-containing portion (that is, the arc emission portion) at the tip portion of the electrode, can be increased.

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

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

The electrode manufactured by the above method can be widely applied to a discharge lamp having a rated power of 50 W to a rating of 2000 W. The size of a sintered body formed by embedding a primary compact at the tip of the electrode is as follows. , 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 compact in this way take various values. Increases in relation to 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 and the like.

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

[0029]

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

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

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

[Brief description of the 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 where a primary molded body is inserted into a cathode main body according to the present invention.

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cathode main body 1a Part to which metal foil is welded 1b Concave part provided in cathode main body 2 Primary molded body

Claims (2)

[Claims] 1. A method for manufacturing a cathode for a discharge lamp, comprising: forming a primary compact obtained by molding a mixed powder of a powdery barium-based electron-emitting substance and tungsten powder into a sintered cathode body made of tungsten or molybdenum. The primary molded body is pressed in the concave part to crush it, and thereafter, the primary molded body is sintered in a state where the primary molded body is filled in the concave part. A method for manufacturing a cathode for a lamp. (2) After the sintering process,
Swaged the sintered body and increased the density of the tip
The cathode for a discharge lamp according to claim 1, wherein
Production method.