JP2775261B2 - Manufacturing method of cathode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high-melting-point metal powder sintered body cathode used for a microwave electron tube or the like.

[Prior art] Conventionally, in the production of this kind of sintered compact cathode, press molding of a high melting point metal powder or a mixture of a high melting point metal powder and an electron emitting substance can be performed, and the pressed molded body can be machined. In order to obtain the hardness, it is pre-sintered at about 1200 ° C. for about 15 minutes in a reducing atmosphere or vacuum, and machined into a cylinder having a predetermined size in the pre-sintered state, and then as shown in FIG. Then, the pre-sintered body 1 machined into a cylindrical shape is placed on the stage 4 of a furnace, and is placed in a reducing atmosphere or
The method of main sintering at 2000 ° C. for about 1 hour has been adopted. In addition,
When only the high melting point metal powder is sintered, an electron emitting material is impregnated after the main sintering.

[Problems to be solved by the invention]

In the conventional manufacturing method as described above, at the time of main sintering, more heat escapes in the portion of the pre-sintered body 1 that is in contact with the stage 4 of the furnace than in other portions, and the true sintering is performed in this portion. There has been a problem that the degree of circularity deteriorates or the shrinkage ratio differs between the upper and lower portions, resulting in large deformation.

The present invention has been made to solve the above problems, and has as its object to provide a method that does not cause deformation during main sintering.

[Means for solving the problem]

The present invention, in the hollow of the cylindrical temporary sintered body, in the case of the present invention,
Insert a round bar made of high melting point metal whose thermal expansion outside diameter is slightly larger than the contracted inner diameter of the pre-sintered body, so that the pre-sintered body does not directly contact the stage of the furnace for main sintering. The main sintering is performed by disposing a round bar.

[Action]

When the main sintering is performed as described above, the escape of heat from each part becomes uniform, and when the hollow part of the sintered body contracts, the hollow inner wall of the sintered body adheres to the round bar. Good roundness is maintained, and there is no dimensional difference between the upper and lower portions.

〔Example〕

FIG. 1 shows an example of a method for holding a temporarily sintered body during the main sintering in the present invention.

Tungsten powder and about 10% of thorium oxide, an electron-emitting substance, are mixed and press-molded. The molybdenum round bar 2 is inserted into the hollow of the machined temporary sintered body 1 and the molybdenum round bar 2 is inserted into the molybdenum base 3.
The stage 3 is placed on a stage 4 of a hydrogen furnace, and the pre-sintered body 1 is arranged so as not to directly contact the stage 4 of the hydrogen furnace, and the main sintering is performed at about 2000 ° C. for about 1 hour.

The coefficient of thermal expansion during sintering of the molybdenum round bar 2 is about 1.
The coefficient of thermal expansion during sintering of the pre-sintered body 1 is about 1.1% at 2000 ° C. Also, considering that the shrinkage rate of the pre-sintered body 1 after sintering is about 2%, the outer diameter of the molybdenum round bar is
It is set so as to have a gap of about 0.4 mm between the inner wall of the temporary sintered body 1.

During sintering, the inner wall of the pre-sintered body 1 comes into close contact with the outer periphery of the round bar 2 made of molybdenum, so that there is no difference in shrinkage between the upper and lower portions and the roundness is not deteriorated at all.

Because the coefficient of thermal expansion of molybdenum is larger than that of a sintered body,
After cooling, a gap of about 0.05 mm is formed between the hollow inner wall of the cylindrical sintered body and the surface of the round bar 2 made of molybdenum, and the sintered body can be easily removed from the round bar 2.

When impregnating with an electron-emitting substance after the main sintering, press-forming only tungsten powder, molding, pre-sintering, machining, and main-sintering, then applying a mixture of oxides mainly composed of barium oxide Then, it is melted and impregnated at about 1500 ° C. in a hydrogen furnace. At this time, surplus electron-emitting material adhering to the surface of the sintered body is removed after cooling.

In the case of the temporary sintered body 1 machined into a cylindrical shape having an outer diameter of about 8 mm, an inner diameter of about 5 mm, and a height of about 8 mm, the outer diameter of the molybdenum round bar 2 is set between the inner wall of the temporary sintered body 1 Good results were obtained when the gap was about 0.2 mm.

FIG. 2 shows the measured values of the difference between the roundness and the inner diameter of the example of the cathode according to the method of the present invention from the reference value, and FIG. 3 shows the corresponding measured values of the cathode according to the conventional method.

According to the conventional method, the roundness is particularly poor in the lower part in contact with the stage 4 of the furnace, and there is a large difference in the inner diameter between the upper and lower parts. You can see that it is done.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a cylindrical cathode having good circularity in all portions and uniform dimensions in all portions, and has a large effect of contributing to the improvement of the characteristics of the electron tube. .

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a method of holding a pre-sintered body at the time of main sintering in the present invention, and FIG. FIG. 3 is a graph showing actual measured values of the difference, FIG. 3 is a graph showing actual measured values corresponding to the actual measured values of FIG. 2 of the cathode according to the conventional method, and FIG. FIG. 4 is an explanatory diagram showing an example of a holding method of FIG. DESCRIPTION OF SYMBOLS 1 ... Temporary sinter, 2 ... Molybdenum round bar, 3 ... Molybdenum base, 4 ... Furnace stage In the figure, the same code | symbol shows the same or corresponding part.

Claims (2)

(57) [Claims] 1. A high-melting metal powder and an electron-emitting substance are mixed and press-molded, and the pressed body is calcined in a reducing atmosphere or vacuum to a hardness that can withstand machining at a temperature lower than the main sintering temperature. In the method for manufacturing a cathode, the pre-sintered body is machined into a desired cylindrical shape and then main-sintered in a reducing atmosphere or in a vacuum. At this time, insert a round bar made of a high melting point metal whose outer diameter is slightly larger than the contracted inner diameter of the pre-sintered body, and the pre-sintered body is subjected to main sintering. A method for producing a cathode, comprising arranging the round bar so as not to make direct contact and performing main sintering. 2. A high-melting metal powder is press-formed, and the press-formed body is pre-sintered in a reducing atmosphere or vacuum at a temperature lower than the main sintering temperature to a hardness that can withstand machining. The body is machined into a desired cylindrical shape, main-sintered in a reducing atmosphere or vacuum, and a method for producing a cathode in which the main sintered body is impregnated with an electron-emitting substance. At the time of the main sintering, a round bar made of a high melting point metal having a thermally expanded outer diameter slightly larger than the contracted inner diameter of the temporary sintered body is inserted into the hollow. A method for producing a cathode, comprising arranging the round bar so as not to directly contact a stage of a furnace for performing the sintering.