JPS6315694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a heater for an electron tube, and particularly to a method of manufacturing a heater used for an indirectly heated cathode.

In general, the indirectly heated cathode of an electron tube has an electron emitting material 3 attached to the top of a cap-shaped sleeve 2 that houses a heater 1 inside, as shown in a simplified longitudinal cross-sectional view in FIG.
It has a structure coated with

The indirectly heated cathode configured in this way is housed in a vacuum-sealed electron tube, and by heating the heater 1 by passing an electric current through it, the sleeve 2 is heated by the radiant heat from the surface of the heater 1. Further, the electron emitting material 3 is heated to emit thermoelectrons.

The heater 1 that emits thermoelectrons also has a core wire 4 made of tungsten (hereinafter referred to as W) whose main material is coated with aluminium oxide for electrical insulation, as shown in the cross-sectional view of the main part in FIG. A layer 5 is applied and sintered, and a blackening layer 6 is formed on the surface of the layer 5 to improve heat radiation efficiency.

In the indirectly heated cathode structure configured in this way, in order to improve the heating efficiency of the cathode, the heater 1
The heat generated must be efficiently conducted to the electron emitting material 3 via the sleeve 2. However, since the sleeve 2 and the electron emitting material 3 are placed in close contact with each other, the thermal conductivity is extremely good, but since the heater 1 and the sleeve 2 are not in close contact with each other and there is a vacuum space between them, the heat conduction between them is poor. Furthermore, since the alumina layer 5 on the heater core wire 4 is white, the thermal emissivity is further reduced. For this purpose, a metal material with high thermal radiation efficiency such as W, Mo, Cr, Ta, or Ti, or a hydrogen compound such as CrO ₃ , TiO, niobium carbide, tantalum carbide, or Zr, Nb, or Ti is used on the surface of the alumina layer 5. A blackening layer 6 consisting of the following is deposited and formed.

However, it is technically extremely difficult to coat and sinter these materials to a predetermined thickness on the surface of the alumina layer 5. Among these materials, W in particular has a high melting point, and if it can be improved even in terms of coating work, it would be an extremely ideal high heat radiation material.

However, when a suspension for application is made using W powder, (1) Since the specific gravity of W powder is high, it tends to precipitate in the liquid.

(2) The W powder surface is electrically inactive, has poor adsorption with binders, and lacks electrophoretic properties.

It had drawbacks such as:

Therefore, attempts to solve these drawbacks have been proposed, such as improving the dispersion method or using a mixture of W powder with alumina, etc. However, in both cases, essentially W powder is mixed with alumina, etc. Because of its characteristics, it has not been possible to stably implement it industrially.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing an electron tube heater that can solve the above-mentioned drawbacks and form a blackened layer of stable quality industrially.

In order to achieve such an object, the method for manufacturing an electron tube heater according to the present invention includes applying alumina sintered W powder, in which fine alumina particles are sintered in advance on the surface of the W powder, to the surface of the alumina layer on the W core wire. It is made into a suspension, coated and sintered. DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an electron tube heater according to the present invention will be described in detail below with reference to the drawings.

Normally, in order to apply alumina insulator on a W core wire, a suspension containing the coating material is made and the coating is carried out by spraying, dipping (drag coating), electrodeposition, etc. For example, in the case of a thin layer, Most of the coating methods are dipping, but the stability, quality, etc. of any coating method can be determined by the suspension manufacturing method. Therefore, the present invention first mixes W powder 7 and fine alumina powder 8 well, as shown in FIG.
Sintering is performed by heat treatment in an H ₂ or N ₂ atmosphere at 1000 to 1300° C. to form alumina sintered W powder 9 . In this case, the W powder 7 has a particle size of about 1 to 3 μm, which is used as a suspension, whereas the fine alumina powder 8 has a smaller particle size, the larger the surface area is obtained, and the adhesive force to the W powder increases. Experimentally, the particle size was approximately 1/2 that of W powder. Further, there is no practical problem as long as the mixing ratio of fine alumina to W powder is in the range of 1 to 9% by weight. In this case, if the mixing ratio of fine alumina is less than 1% by weight, good effects cannot be obtained, and if it exceeds 9% by weight, alumina will sinter together during sintering, making it impractical. Furthermore, if the sintering temperature of the W powder 7 and the fine alumina powder 8 is less than 1000°C, sintering will not take place, and if the temperature exceeds 1300°C, both will melt and form a lump, which is not preferable. Therefore, the heat treatment for sintering is
A temperature range of 1000-1300°C is optimal. This will be explained in detail below using examples.

Example: An alumina insulating layer was provided on the outer periphery of a heater core wire made of W by a conventionally known method, and a blackened layer with a thickness of about 10 μm was coated on the outer periphery using a suspension described in detail below using a dipping method. to form a heater.

First, we added W powder with an average particle size of about 2.2 μm to
Approximately 5% of 0.05 μm colloidal alumina powder is added to W, mixed well and heated in a hydrogen atmosphere at approximately 1100°C for approximately 10 minutes to coat the surface of W powder 7 as shown in Figure 3. Alumina sintered W powder 9 is formed by sintering fine alumina particles 8. Then, this alumina sintered W powder 9 and the average particle size of about 2μ
A suspension was prepared by mixing 50% of alumina powder with m and alumina powder, mixing it with a nitrocellulose binder using a ketone solvent, and dispersing it in a ball mill for about 5 hours using an alumina ball mill pot. The suspension made in this way was applied to a thickness of about 10 μm by dipping, dried, and then
Sintered in _H2 at 1600 °C.

The blackened layer formed by such a method is
By pre-sintering and adhering fine alumina to the W powder, the alumina on the W powder and the alumina in the suspension can be smoothly sintered during firing after application, resulting in a strong blackened layer. It will be glued. Further, since the suspension according to the present invention has alumina on the surface side compared to the W powder suspension, the adhesion to the alumina layer is extremely good, and the life of the suspension can be further extended.

The blackened layer formed by this method was also compared with a heater made from a suspension of W powder and alumina powder in a forced test of film strength. In this case, in the forced test, approximately 200 meshes of sandpaper was attached to the vibrator, a heater was placed on it, and the weight loss due to friction with the blackening layer was measured. In other words, by placing a heater on sandpaper and applying vibrations, the amount of alumina scraped off from the blackened layer is measured, and the smaller the amount, the stronger the alumina adhesion is. It is the law.

As a result, the weight loss due to friction is about 1/2 smaller in the coating applied with the suspension of the present invention, which is shown in the characteristics, compared to the heater using the W powder alumina suspension, which is shown in the characteristics in Figure 4. This shows that the adhesion strength to the alumina insulating layer was significantly enhanced.

In addition, in the above example, the amount of colloidal alumina added to the W powder and sintered was 5%.
However, in practice, it is sufficient that the weight ratio is in the range of 1 to 9%, but considering the above-mentioned relationship with the friction weight loss, as shown in the characteristics in Figure 5, the weight loss due to vibration for about 20 minutes is The range of the amount of colloidal alumina added in which the amount of colloidal alumina is minimized, that is, the adhesive strength is maximized, is 2 to 8% by weight. Further, as shown in the characteristics, when the amount of colloidal alumina added exceeds 8% by weight, alumina begins to be liberated. Therefore, based on the above relationship, the amount of colloidal alumina added to the W powder is 2 to 8% by weight.
The range of is the optimal value.

In addition, as a result of a life test performed by mounting a heater formed by the above method on a cathode ray tube, it was found that even after 3000 hours of life, there was no exposure due to friction with the sleeve, and there were no alumina cracks or chips. It did not occur.

As explained above, in the method for manufacturing an electron tube heater according to the present invention, the adhesion and sinterability are improved by forming the black layer by coating and sintering a suspension of alumina sintered W powder. However, the mechanical adhesion strength is increased, and there is a great effect that an indirectly heated cathode heater with high quality and reliability can be provided.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a main part showing an example of a conventional indirectly heated cathode for an electron tube, FIG. 2 is a cross-sectional view of a main part showing an example of a heater, and FIG. 3 is an example of alumina sintered tungsten according to the present invention. FIG. 4 is a characteristic diagram showing the results of a forced test of the strength of the blackened layer, and FIG. 5 is a characteristic diagram showing the rubbing weight loss and the amount of free alumina with respect to the amount of colloidal alumina added. 1... Heater, 2... Sleeve, 3... Electron emitting material, 4... Heater core wire, 5... Alumina layer,
6...Blackened layer, 7...W powder, 8...Alumina powder, 9...Alumina sintered W powder.

Claims (1)

[Claims] 1. In manufacturing a heater for an electron tube, the heater includes a step of applying an alumina insulating material around a core wire mainly made of tungsten, and a step of applying an alumina insulating material around a core wire mainly made of tungsten, and a step of applying an alumina insulator to a core wire made of tungsten, and a step of applying an alumina insulating material to the tungsten powder. A suspension containing alumina calcined tungsten powder obtained by mixing and firing fine alumina particles with the following particle size and in a weight ratio of 1 to 9% with respect to the tungsten powder, and another alumina powder. A method for manufacturing an electron tube heater, comprising the steps of coating the alumina insulator on the alumina insulator, and performing heat treatment after coating to form a blackened layer. 2. The method for manufacturing an electron tube heater according to claim 1, wherein the temperature of the heat treatment is in the range of 1000 to 1300°C.