JPS59111222A - Impregnated cathode member - Google Patents

Abstract

PURPOSE:To securely weld and fix a cathode base substance, a cup, and a cathode sleeve, by providing a recess on the peripheral wall of the cathode base substance and irradiating a laser beam on the cup and the cathode sleeve opposing the recess portion. CONSTITUTION:A cathode base substance 21 provided with a ring-shaped recess 21a on its peripheral wall is contained in a cup 22 made of such a metallic material having a high melting point as tantalum or molybdenum. The cup 22 is inserted in the top portion of a cathode sleeve 23 made of a tantalum or molybdenum plate rounded and welded into a cylindrical shape. A laser beam 34 generated by a YAG pulse laser beam machine is irradiated on the portion to be welded 31 opposing the recess portion 21a of the cathode base substance 21. Then, the portion to be welded 31 of the cup 22 and the cathode sleeve 23 is melted into the recess 21a to form a projection 35 there and the cathode base substance 21, the cup 22, and the cathode sleeve 23 are fixed together very strongly.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in impregnated cathode structures.

[Technical background of the invention and its problems]

An example of the structure of a conventional impregnated cathode structure will be explained with reference to FIG.

The cathode substrate (1) has an outer diameter of 1.5 mm and a thickness of 0.5 van.
It is a disk of about.

This cathode substrate (1) is made by compression molding tungsten powder with a particle size of 3 to 10 μm, and then sintering it in a reducing atmosphere.An electron emitting substance such as Ba0, 20 g of At, or CaO is reduced to the base metal at high temperature. A porous tungsten sintered body obtained by melting and impregnating in a neutral atmosphere, and generally formed to an outer diameter of 30 to 50 jB, is cut into a thin plate. After impregnating this thin plate with an electron emitting substance, it is processed by electric discharge machining or laser processing. A large number of cathode substrates (1) can be obtained from a single thin plate by cutting the cathode substrate to a desired outer diameter by processing or the like.

The cathode substrate (1) made in this way has a wall thickness of 0.02
It is attached to a cup (2) made of a high melting point metal such as tantalum or molybdenum.

The cup (2) on which the cathode substrate (1) is attached is made of tantalum;
Alternatively, it is inserted into the top of a cathode sleeve (3) made of a high melting point metal such as molybdenum and fixed by welding at a welding point σD.

The cathode supporter (4) is made of tantalum or molybdenum ribbon with a wall thickness of 0.05 mm and a width of 0.5 to 0.7 mm.Multiple pieces are attached to the bottom outer periphery of the cathode sleeve (3), with one end at the welding point α2. The other end is welded to the shoulder (51) of the cathode support ftJ (5) made of Kovar or the like at the welding point (13), thereby completing the impregnated cathode structure.

The guide tube (2) is provided to prevent electron emitting material scattered by thermal evaporation from the cathode base (1) from adhering to a heater (not shown) installed in the cathode sleeve (3).

However, such an impregnated cathode structure has problems in that poor welding occurs during the manufacturing process and the cathode substrate (1) peels off from the weld during a life test for the following reasons.

That is, since the cathode base body (1), the cup (2), and the cathode sleeve are all made of high-melting point metal, they cannot be easily welded by resistance welding, and laser welding may cause intergranular fracture.

Next, the reason for this is that in resistance welding, the melting point of the copper alloy material used as the welding electrode material is extremely lower than that of the cathode base (1), cup (2), and cathode sleeve (3) materials. This is because the welding electrode melts when a strong current is passed during welding, making it impossible to completely weld the bath weld.

The base metal (1) is made of tungsten with a melting point of 33704C, and the cup (2) and cathode sleeve are made of tantalum with a melting point of 2940°C or molybdenum with a melting point of 2617°C. It is necessary to heat the weld to a temperature above the melting point of at least one of the metals. However, the cathode substrate (1) is impregnated with an electron-emitting substance, and this electron-emitting substance has a melting point of 1800°C, so during welding, this electron-emitting substance melts and precipitates in a large amount near the welding area, causing the cup to melt. (2) It may even adhere to the sides.

When an electron tube using such an impregnated cathode structure is operated, the precipitated electron emitting material becomes a source of abnormal evaporation, causing leaks between the electrodes that make up the electron gun, resulting in deterioration of the characteristics of the cathode ray tube. There is a problem with this.

Furthermore, in laser welding, unlike the above-mentioned resistance welding, welding is possible even when the constituent material is a high melting point metal, and the precipitation of electron emitting substances is also minimal.

However, due to laser welding, the cathode base (1) and cup (2)
When the impregnated cathode structure with the welded cathode sleeve (3) and cathode sleeve (3) was assembled into an electron tube and a life test was performed, a phenomenon □ in which the cut-off voltage changed significantly was observed.When this electron tube was disassembled and investigated, it was found that the cathode base (It had fallen off from the cup (2) and the cathode sleeve with a slight force.

The reason for this is that in laser welding, the porous tungsten constituting the cathode substrate (1) is locally heated and crystal growth occurs. This was the result of grain boundaries between the part where the crystals grew and the part not affected by heat caused grain boundary sliding and fracture due to the heat cycle.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a high-quality impregnated cathode structure in which a cathode substrate, a cup, and a cathode sleeve are well welded and fixed and maintained in high quality. The purpose is

[Summary of the invention]

That is, the present invention comprises a cathode substrate impregnated with an electron-emitting substance, a cup made of a high-melting point metal to which the cathode substrate is mounted, and a cathode sleeve made of a high-melting point metal to which the cup is inserted and fixed. An impregnated cathode assembly comprising at least a cup and a cathode sleeve in which a recess is formed in the entire circumference or a part of the side wall of the cathode substrate, and the cup and cathode sleeve corresponding to the recess are irradiated with a laser beam and melted. This is an impregnated cathode structure characterized by a cathode substrate fixed by fixing the protrusion and the recess.

[Embodiments of the invention]

Next, an embodiment of the impregnated cathode structure of the present invention will be described with reference to FIGS. 2 and 3.

The cathode substrate f2 is a disk with an outer diameter of 1.5'mg and a thickness of about 0.5 mm, and the side wall (211) has four annular parts (21a
) is provided.

This cathode substrate 12υ is made by compression-molding tungsten powder with a particle size of 3 to 10 μm and then sintering it in a reducing atmosphere.The resulting substrate metal is melt-impregnated with 20g of BaOXAt, CaO, or other electron-emitting substances in a high-temperature reducing atmosphere. The resulting ○ recess (2) a) is obtained by lathing the cathode substrate 12υ or by scribing with a high-speed pulse oscillation YAG laser processing machine, and has a width of 01 to 0.25 and a body depth of 01 to
It is about 03 Hu.

The cathode substrate ■υ made in this way has a wall thickness of 0.025
It is installed in a cup (A) with an inner diameter of approximately 1.5 mm and a height of 0.5 mm, which is made of a high-melting point metal such as tantalum or molybdenum.

The cup (A) on which the cathode substrate Qυ is mounted is inserted into the top of a cylindrical cathode sleeve (E) made by rolling a 25μ thick plate of tantalum or molybdenum and welding it.

Next, we will explain how to join the cathode base 121), the cup (A), and the cathode sleeve (A).As shown in Figure 3, first attach the K cathode base (2) to the cup.Next, the cathode sleeve Insert the cup (A) on which the cathode substrate (21) is attached into the top of (A).

Next, when the welded part 01) corresponding to the concave part (21a) of the cathode base body (21) is irradiated with the laser beam (■) oscillated from the YAG pulse laser processing machine, the welded part 01) of the cup (2) and the cathode sleeve (A) is irradiated. ]) melts and forms a protruding part (to) in the recess (21a), and is very firmly attached to the cathode base Q.
]), the cup (A) and the cathode sleeve holder are fixed.

By providing the protrusions (to) at two or more points on the circumference of the cathode substrate at equal intervals, they can be securely fixed.

Next, a plurality of cathode supports (E) made of tantalum or molybdenum ribbons with a wall thickness of 0.05 mm and a width of 0.7 mm are fixed to the outer circumference of the bottom of the negative sleeve (A) at one end at the welding point (A). , the other end is a cathode support tube made of Kovar etc.
It is fixed to the shoulder (252) of (c) at the welding point (to) to complete the impregnated cathode structure.

As in this example, there is a recess (21a) on the outer periphery of the cathode substrate ◇.
The protrusions of the cup (A) and the cathode sleeve (A) are fitted into the recess (21a) by melting the cup (A) and the cathode sleeve holder that are opposite to the four parts (21a) using a laser beam. By combining them, the impregnated cathode structure has the following effects.

That is, first, since welding is performed using a laser beam, heating is performed only extremely locally, and only a very small amount of the electron emitting material impregnated into the cathode substrate is precipitated.

Therefore, no abnormal evaporated matter is generated during operation, and stable characteristics can be obtained without causing inconveniences such as leakage between electrodes. Secondly, by forming a recess in the cathode substrate, the welding area can be made larger, which is advantageous against intergranular fracture.The protrusion has a caulking effect, rather than a bulge, and can be cut during the heat cycle in a life test. It has become possible to obtain an extremely excellent impregnated cathode structure without any change in off-state characteristics.

Next, different examples of cathode assemblies used in other embodiments of the present invention will be explained with reference to FIGS. 4 to 7. First, the cathode assembly shown in FIG. This is an example in which an elongated recess (41a) is partially provided in the circumferential direction, and the cathode structure t51) shown in FIG. 5 has a side wall portion (5] +
) is an example in which a plurality of recesses (51a) are provided in the circumferential direction, and the cathode assembly shown in FIG. , the cathode assembly (7]) shown in FIG. 7 has a vertical recess (
71a), and in both cases the same effects as in the previous embodiment can be obtained.

In addition, in the above-mentioned embodiment, the cup (2) and the cathode sleeve (
We have described the case in which both of 3) are provided at the same time, but if a brazing material such as Re-Mo is brazed to the lower surface of the cathode substrate in advance to close the eyes of the cathode substrate (1) and prevent evaporation, Similar effects can be obtained even when only the cathode substrate (1) and cathode sleeve (3) are used. In addition, although the above-mentioned embodiment described an example in which the cathode sleeve was supported on the cathode support cylinder via the cathode supporter, the present invention is not limited to this, and an impregnated cathode assembly using only a slightly longer cathode sleeve may be used. But there is no need to explain that they are the same.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to securely fix the cathode substrate, the cup, and the cathode sleeve, and there is no inconvenience such as abnormal evaporated matter or leakage between electrodes, and furthermore, it is an impregnated type that does not change the cutoff characteristics. Since a cathode structure can be obtained, its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of a conventional impregnated cathode structure, and FIGS. 2 and 3 are views showing an embodiment of the impregnated cathode structure of the present invention. Partial cutaway perspective view, 3rd
The figure is an explanatory cross-sectional view of the main parts showing a method of identifying the cathode substrate, the cup, and the cathode sleeve using laser light. FIG. 1, 21.41.51.61.71... cathode substrate 2.
22... Cup 3, 23... Cathode sleeve 4
．． 24... Cathode supporter 5, 25... Cathode support cylinder I
I, 12.13.32.33--Welding point 21 a
+ 41a + 51a + 61a t 71 a・
...Concave portion 31...Welding portion 34-...Laser beam 35...Protrusion portion Agent Patent attorney Inoue-Male No. 4, No. 6, No. 1, No. 5, No. 7, No. γl 103-

Claims (2)

[Claims] (1) It comprises at least a cathode substrate impregnated with an electron emitting substance, a cup made of a high melting point metal to which the cathode substrate is attached, and a cathode sleeve made of a high melting point metal to the top of which the cup is inserted and fixed. In the impregnated cathode structure, a concave portion is formed on the entire circumference or a part of the side wall portion of the cathode substrate, and the cup and cathode are obtained by irradiating and melting the cup and cathode sleeve corresponding to the four portions with a laser beam. An impregnated cathode structure, characterized in that the cathode substrate is fixed by fixing the protrusion of the sleeve to the recess. (2) The impregnated cathode assembly according to claim 1, wherein the protruding portions are formed at a plurality of locations.