JPH11306970A - Manufacture of cathode for discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a sintered body from coming off from a hole in a metallic base body, breaking, cracking by hitting the hole peripheral part on the base body end face and the sintered body while heating the metallic base body and the sintered body under a condition in which the sintered body made of an electron discharging substance and high melting point metal is arranged in the hole formed from the tip of the metallic base body to the inside of a cathode. SOLUTION: On the end face on the cathode tip side of a metallic base body 11 made of high melting point metal, a hole 12, into which a sintered body 1 is inserted, is bored in a recess form. Under this condition, the peripheral part of the hole 12 and the sintered body 1 are hit by means of a hammer H and the like while the sintered body 1 is heated at a high temperature. Consequently, a degree of machining of the metallic base body 11 is increased, and the metallic body 11 is shrunk in the axial direction with ease in the vicinity of the hole 12 and the inside diameter of the hole 12 is reduced. The sintered body 1 is also shrunk in the axial direction, and at the same time, expanded in the radial direction. Therefore, a clearance between the hole 12 and the sintered body 1 is eliminated, so that the inside wall of the hole 12 and the bottom part and the side part of the sintered body 1 are brought into tight contact mutually and fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a cathode for a discharge lamp used for, for example, the photochemical industry and semiconductor exposure.

[0002]

2. Description of the Related Art An electron-emitting substance (hereinafter referred to as "emitter") is added to a cathode of a discharge lamp in order to obtain a large amount of electron emission. Among the cathodes, there is generally known a cathode having a structure in which an emitter and a sintered body made of a high melting point metal are embedded at a tip portion of the cathode in order to maintain stability of arc discharge.

[0003] A cathode having a structure in which a sintered body is embedded is provided with a concave hole at the tip of a metal base, and an emitter or a pellet made of a high melting point metal is inserted thereinto, and the pellet is fixed by caulking or shrink fitting. It is manufactured by fixing or embedding and then cutting it into a desired cathode shape. Examples of the pellets include a press-formed product obtained by pressing a mixed powder of a powdered emitter and a powder of a high melting point metal (for example, tungsten) in a mold, and a calcined product obtained by temporarily sintering the press-formed product. A sintered body obtained by sintering the pre-sintered body at a higher temperature is used.

When a pellet of a sintered body is used among the above, the sintered body is inserted into a hole of the metal base to form a locking portion for locking the sintered body at a thick portion of the metal base. A technique of caulking and fixing is used.

FIG. 7 shows a method for fixing a sintered body by the above-described caulking. As shown in the figure, in a state where the sintered body 1 is inserted into the concave hole 12 of the metal base 11, the thick part of the metal base 11 is hit with a punch P having a pointed tip, so that the locking part 13 is pressed. Let it form. The locking portion 13 is formed such that the thick portion of the metal base 11 has the hole 1.
2 is formed so as to protrude toward the center of the sintered body 1.
Can be locked.

FIG. 8 shows a state in which the locking portion 13 is formed as described above, and is a view as seen from the opening side of the metal base 11. In the figure, the portion indicated by the mark x is hit with the punch P. Specifically, the cross-marked portion is a portion separated from the inner peripheral edge of the hole 12 by about 1 mm when the inner diameter of the hole 12 is about 1.5 mmφ and the outer diameter of the metal base 11 is about 10 mm.

According to the above method, the hole 1 in the metal base 11 is
Since there is a clearance required for insertion between the inner wall 2 and the sintered body 1, there is a clearance on the side surface of the sintered body 1 even when the cathode is finally used. Therefore,
The adhesion (fit-in) between the metal base 11 and the sintered body 1 is very poor, and if the locking portion 13 is insufficient, the sintered body 1 may fall out of the hole 12 when the metal base 11 is carried around. is there. Further, when cutting the tip portion of the cathode, that is, the metal base 11 near the sintered body 1 in order to process the cathode into the final shape, the sintered body 1 is loose and cracked or chipped inside the hole 12. The problem described above occurs.

In addition, when thermal or electrical enjoyment is provided between the metal substrate and the sintered body, the clearance portion serves as a barrier, and physical properties such as thermal conductivity and electrical conductivity at the tip of the cathode are reduced. Even if the clearance is so small that it is local and does not fall out of the sintered body, the adhesion between the sintered body and the metal substrate is poor, so that heat and electricity are transferred at the boundary between the two members. Is not performed smoothly, and thermal conductivity and electrical conductivity are reduced.

When the thermal conductivity between the sintered body and the metal substrate is reduced, the heat generated by the arc discharge is generated on the rear end side (ie, on the rear side).
There is a problem that the sintered body is overheated and evaporated without being diffused to the metal substrate side). When the sintered body evaporates in this manner, the inner wall of the arc tube is stained and the amount of lamp light is reduced, and the tip of the cathode is worn, so that arc discharge becomes unstable and the lamp life is shortened.

Further, as described above, if the adhesion (fit-in) between the metal substrate and the sintered body is poor, the electric conductivity also becomes poor, and the power supply to the sintered body is not performed smoothly, resulting in arc discharge. It also causes the problem of flickering.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a sintered body can be formed into a cathode without falling out of a hole in a metal substrate, and without cracking or chipping. It is an object of the present invention to provide a method of manufacturing a cathode capable of generating an arc by using the same.

[0012]

According to another aspect of the present invention, there is provided a method of manufacturing a cathode for a discharge lamp, comprising: a hole formed from the tip to the inside of a metal base of the cathode; In a state in which the sintered body made of is disposed, the metal base and the sintered body are heated and the hole peripheral portion of the end face of the metal base and the sintered body are hit.

[0013]

Next, an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of a sintered body 1 including a metal substrate 11 and an emitter of a cathode 22 as viewed from the side. A hole 12 is formed in a concave shape on the end surface of the substantially cylindrical metal base 11 made of a high melting point metal on the cathode tip side, and the sintered body 1 is formed in the hole 12.
Is inserted. In this state, the metal base 11 and the sintered body 1 are heated to a high temperature, for example, 1400 ° C., and the metal base 11 using a hammer H or the like.
And the sintered body 1 is hit.

By hitting the metal base 11 and the sintered body 1 while heating to a high temperature, the working degree of the cathode base 11 is increased, and the metal base 11 is easily contracted in the axial direction near the hole 12, whereby The inner diameter of the hole 12 becomes smaller. Further, the sintered body 1 is also reduced in the axial direction and is simultaneously increased in the radial direction. As a result, the clearance between the hole 12 and the sintered body 1 is eliminated, and the inner wall of the hole 12 and the bottom and the side of the sintered body 1 are fixed in close contact.

Further, since the metal base 11 is hit from the end face on the tip side of the cathode, the degree of diameter reduction of the inner diameter of the hole 12 is large on the opening side. Does not fall off, and the sintered body 1 does not wobble inside the hole 12. Therefore, there is no problem that the sintered body 1 is cracked or chipped during cutting.

As described above, since the sintered body can be buried by improving the adhesion (fit-in) between the metal base and the sintered body, the heat generated at the boundary between the metal base and the sintered body can be reduced. Barriers to energy enjoyment are also reduced, and thermal and electrical conductivity can be improved.

[Embodiment] A first embodiment of the present invention will be described. FIG. 1 shows a metal base 11 and a sintered body 1 of a cathode. As the metal base 11, a cylindrical tungsten rod having an outer diameter φ of 10 mm was cut into a length L of 40 mm and used. A concave hole 12 having an inner diameter d of 1.0 to 1.5 mm and a length of 1 to 5 to 8 mm is provided at one end of the cut bar at a position corresponding to the tip of the cathode. Was cut to connect the metal foil.

Next, the sintered body 1 containing thorium oxide (ThO ₂ ) as an emitter was inserted into the hole 12 provided in the metal base 11. In the first embodiment, the sintered body 1
Is, for example, an outer diameter φ ₁ = 1.20 mm and a length L 1 = 7.0.
mm, but usually the outer diameter φ _{1 of the} sintered body ₁
Is formed so as to have a clearance of about 0.05 mm with respect to the inner diameter d of the hole 12.

As the emitter, an alkaline earth metal (Sr, Ba, Ca, etc.) or an oxide thereof, thorium oxide, or a composite oxide of an alkaline earth metal and another metal is used. A substance exhibiting desired characteristics is appropriately selected and used.

Further, when the sintered body 1 is inserted into the hole 12, for example, a sintered body containing a low melting point emitter, a sintered body containing a high melting point emitter, or the same material as the metal base 11 is sintered. A plurality of sintered bodies such as a sintered body may be appropriately combined and put. In this case, depending on the combination of the sintered bodies 1, they may be inserted one by one into the holes 12, or ones that are combined together may be inserted.

Subsequently, the metal substrate 11 and the sintered body 1 are put into a heat-resistant container into which gas can flow, and hydrogen, an inert gas, or a mixed gas thereof is flowed therein, and about 1400
Heat to a temperature of ° C. Then, the periphery of the hole of the metal base 11 and the sintered body 1 are hit from the top of the metal base 11 using a hammer H having an outer diameter φ ₂ = 2 mm. The means for heating the metal base 11 includes high frequency or arc heating. This step is, for example, 981 MPa
(10 tonf / cm ² ) at a rate of 30 times / minute for about 1 minute.

In the above-mentioned process, the optimum heating temperature differs depending on the emitter. For example, when an emitter of thorium oxide is used, 1000 ° C. to 2500 ° C., and when a barium-based emitter among alkaline earth metals is used, 1000 ° C.
A temperature of １1400 ° C. is optimal.

FIG. 3 is a cross-sectional view of the metal base 11 and the sintered body 1 in a state of being hit with a hammer. As shown in the figure, the metal substrate 11 has a thick portion on the opening surface of the hole 12 which is uniformly crushed in the center direction of the hole 12 so that the inner diameter becomes small, and the sintered body 1 is also hit from the opening surface. As a result, the sintered body 1 is fixed because the clearance between the metal base 11 and the sintered body 1 is eliminated because the metal body 11 is reduced in the axial direction and simultaneously expanded in the radial direction. Then, since a large impact force is applied to the metal base 11 and the sintered body 1, the adhesion (fit-in) between the two members is improved. Further, in the tapping step, since the material is heated to a high temperature, the degree of processing is increased, and the metal base 11 and the sintered body 1 can be easily crushed without breaking.

Finally, a cutting process is performed to obtain a desired shape of the cathode 22. Here, the desired cathode shape means that the tip of the metal base 11 is a truncated cone. FIG. 4 shows the tip of the cathode 22 completed in this manner.

FIG. 5 is a diagram showing a second embodiment of the present invention. In the cathode 22 in which the metal base 11 is made of tungsten and the sintered body 1 containing thorium oxide as an emitter is embedded, an inner wall of the hole 12 of the metal base 11
2 tungsten carbide (W ₂ C) between the sintered body 1
This is a cathode in which the layer 14 (hereinafter, also referred to as a “carbonized layer”) is interposed except for the arc emission portion of the cathode. As a method of forming the carbonized layer 14, for example, there is a method of carbonizing other parts of the sintered body 1 except for the arc discharge part. As a carbonization method, specifically, the sintered body 1 is placed in a heat-resistant container into which gas can flow, and benzene (C ₆
While flowing H ₆ ), a high temperature, e.g.
There are a method of heating to 00 ° C. and a method of directly applying carbon (C) to the sintered body 1 and heating to a high temperature, for example, 1000 ° C. to 1400 ° C.

The carbonized layer 14 traps oxygen of thorium oxide diffused during the arc discharge operation and efficiently supplies thorium (Th) atoms to the arc discharge portion at the tip of the cathode. On the other hand, the carbonized layer 14
Is formed up to the arc-emitting portion at the tip of the cathode, the arc-emitting portion is exposed to a very high temperature (approximately 2500 ° C.), which may cause a problem that the carbonized layer 14 melts during the arc discharge operation. . However, according to the present invention, there is no gap between the metal base 11 and the sintered body 1,
Since the peripheral portion of the hole 12 of the metal base 11 can also be made high in density, the carbonized layer 1 is not exposed to the outer surface even during the arc discharge of the cathode 22, so that the carbonized layer 14 is melted. Since it does not occur, the emitter can be efficiently supplied to the tip of the cathode.

In the first and second embodiments described above, the cross-sectional shape of the hole 12 is circular, but the present invention can be implemented with any shape of the cross-sectional shape of the hole 12. Therefore, it is sufficient that the shape of the sintered body 1 inserted into the hole 12 is also formed into a shape suitable for the hole 12. Further, even when the pellets inserted into the metal base 11 are a pressed compact or a pre-sintered body, the present invention may be applied after the metal base 11 and the pellets are sintered, and the pellets are shrink-fitted and fixed. This is preferable because the density of the inside of the hole 12 can be further increased. Further, the present invention may be carried out after press-fitting and sintering the mixed powder of the emitter and the high melting point metal into the hole 12 of the metal base 11, and sintering.

FIG. 6 shows an example of a discharge lamp using the cathode according to the present invention. In the arc tube 21, a cathode 22 and an anode 23 are arranged to face each other. The cathode 22 and the anode 23 are hermetically sealed at the rear end of the arc tube.
Mercury is sealed as a light emitting substance, and xenon and argon are sealed as a lighting gas. The discharge lamp according to the present invention is, for example, a high-pressure mercury lamp rated at 30 V, 35 A, and 1000 W.

[0029]

The effect of the method for manufacturing a cathode for a discharge lamp according to the present invention is that a sintered body made of an electron-emitting substance and a high melting point metal is inserted into a hole provided at the top of a metal substrate on the tip side of the cathode. In this state, while heating both the metal base and the sintered body, by hitting the periphery of the hole of the metal base and the sintered body, the metal base can be easily processed without cracking, The clearance between the hole and the sintered body can be eliminated, and the sintered body can be fixed in close contact, so that the sintered body does not fall out of the hole,
Since the sintered body does not fluctuate inside the hole, the sintered body does not crack or chip when cutting.

Furthermore, since the adhesion between the metal substrate and the sintered body (adhesion) is good, barriers for enjoying energy such as heat generated at the boundary between the metal substrate and the sintered body are reduced, and the thermal conductivity and the thermal conductivity are improved. Electric conductivity can be improved. Therefore, even if the sintered body is exposed to a high temperature, since the heat is quickly diffused to the rear end side, the sintered body does not overheat and evaporate, and a stable arc discharge is obtained. It does not stain the inner wall of the arc tube. Further, since the electric conductivity is improved, the power supply to the sintered body is performed smoothly, and the flicker of the arc discharge does not occur. As a result, stable arc discharge can be maintained, and the lamp life can be extended.

[Brief description of the drawings]

FIG. 1 is a diagram showing a metal substrate and a sintered body.

FIG. 2 is a view showing a method for manufacturing a cathode according to the present invention.

FIG. 3 is a view showing a base metal and a sintered body.

FIG. 4 is a sectional view of a cathode according to the first embodiment of the present invention.

FIG. 5 is a sectional view of a cathode according to a second embodiment of the present invention.

FIG. 6 is an example of a lamp using the cathode according to the present invention.

FIG. 7 is a view showing a conventional method for manufacturing a cathode.

FIG. 8 is a view of the metal base as viewed from the opening side of the hole.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sintered body 11 Base metal 12 Hole 13 Locking part 14 Carbonized layer 21 Arc tube 22 Cathode 23 Anode

Claims (1)

[Claims] 1. A method for manufacturing a cathode for a discharge lamp, wherein a sintered body made of an electron-emitting substance and a high melting point metal is arranged in a hole formed from the tip to the inside of a metal base of the cathode, A method for producing a cathode for a discharge lamp, comprising: hitting a peripheral portion of a hole at an end face of the metal base and the sintered body while heating the metal base and the sintered body.