JPH0715127B2 - Method for manufacturing electrode material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for producing an electrode material composed of an infiltration type composite metal used as an electrode of a vacuum interrupter, for example.

B. Outline of the Invention By using copper or a copper alloy as an infiltrant, and infiltrating the infiltrant into a porous infiltrated base material obtained by sintering a metal powder having a melting point higher than that of the infiltrant. When manufacturing an infiltration type composite metal, pre-pressurize the metal powder in the range of 10% to 30% of the molding pressure in advance before obtaining the infiltration base material, and then preform at the specified molding pressure. It is intended to improve the moldability and the electric conductivity and the strength by forming the.

C. Prior Art Mo-Cr-Cu, which is an infiltration type composite metal material disclosed in Japanese Patent Laid-Open No. 59-27418 as an electrode material for a vacuum interrupter
Composite metals are Cu-Bi composite metals and Cu-
It is known that the material has excellent welding resistance as compared with W composite metal and the like, and is also excellent in electrical characteristics such as current blocking ability and dielectric strength.

An example of a conventional manufacturing method for manufacturing this Mo-Cr-Cu composite metal is shown in FIG.

In FIG. 3, a container 1 made of alumina ceramics, which does not react with copper and is stable even at high temperature, is filled with a mixed powder 2 of molybdenum and chromium having a melting point higher than that of copper, and a copper lump 3 is placed on the mixed powder 2 to form alumina. A ceramic lid 4 is covered, and these are heated at a temperature not higher than the melting point of copper in a non-oxidizing atmosphere to first form a porous sintered body of molybdenum and chromium in the container 1 and then degassing treatment. While heating these in a non-oxidizing atmosphere at a temperature not lower than the melting point of copper and not higher than the melting points of molybdenum and chromium, the copper ingot 3 is infiltrated into the porous sintered body to form a Mo-Cr-Cu composite metal. It was manufactured.

These heat treatments in a non-oxidizing atmosphere are usually performed in a vacuum furnace in many cases.

D. Problems to be Solved by the Invention If the temperature raising rate or temperature lowering rate is increased during the heat treatment operation in the vacuum furnace, the alumina ceramics container may be destroyed by thermal stress. When a crack or the like occurs in the container as described above, the mixed powder of molybdenum and chromium spills out of the container or copper flows out, and as a result, the interior of the vacuum furnace is likely to be damaged by these.

In addition, since the Mo-Cr-Cu composite metal ingot is in close contact with the entire inner wall of the container, it is difficult to extract the ingot from the container and the container is often damaged.

Furthermore, when the copper remaining without being infiltrated during the infiltration work is joined to the container, especially when copper is joined to the inner peripheral surface of the container, Mo-Cr-Cu
It is almost difficult to extract the composite metal ingot from the container, and even if it is possible to extract it, a chip is often formed on the inner peripheral surface of the container. If you use a container with such a chip again, part of the Mo-Cr-Cu composite metal ingot fills the chip in the container, so you can take out the ingot unless you break the container. It becomes impossible.

In any case, the conventional method is a very simple method in that the infiltration type electrode material is formed in the container, but when it is taken into consideration including the removal from the container and damage to the container. The productivity was not always good.

E. Means for Solving the Problems In order to improve the performance as an electrode and the productivity, the inventors of the present invention used a metal powder to obtain a porous sintered body as an infiltration base material. Was pressure-molded to form a temporary molded body of the infiltrated base material, which was then sintered to try to infiltrate the infiltrated material. Note that the vacuum interrupter uses the electrodes in vacuum, so the following points were noted.

(1) To form a temporary compact by pressurizing only the metal powder without using any binder that may pollute the inside of the vacuum furnace and the vacuum interrupter.

(2) Since the preformed body is sintered and becomes porous before the infiltration material such as copper or copper alloy is infiltrated, it has a predetermined void inside which the infiltration material can be infiltrated. Pressure molding should be done at the lowest possible pressure to ensure the desired conductivity.

(3) However, considering the work of taking out the temporary molded body from the molding machine die and placing the infiltrant, at least the molded temporary molded body is pressure-molded to a strength that can be handled by hand. To be.

(4) Cracks do not occur in the temporary molded product after pressing.

The experimental conditions were molybdenum powder and chromium powder each having a particle size of −100 mesh (149 μm or less) in a weight ratio of Mo: Cr.
= 3: 1 was mechanically mixed, and about 100 g was loaded into a mold with an inner diameter of 60 mm and held under pressure for 1 minute to obtain a temporary molded body with a diameter of 600 mm and a thickness of about 10 mm. .

As a result, it was found that when the pressure was 400 kg / cm ² or less, the mold collapsed during hand-holding work, and it was found that a pressure of 500 kg / cm ² or more was required.

Therefore, based on the above results, about 11
Place a copper ingot on a temporary compact pressed with a pressure of 00 kg / cm ² , place it in a vacuum furnace, sinter the temporary compact, and then infiltrate the copper ingot into the infiltrated base material. The surface of the obtained electrode material was cut and the conductivity thereof was measured. There were a total of 5 measurement points on the surface of the disk, the center and the peripheral part, but it was found that the conductivity (IACS%) varied, and the conductivity in the central part tended to be lower than in the peripheral side. It was

In this way, if the electrode is made of a material whose conductivity in the central part is low and conductivity in the peripheral part tends to be high, an arc is likely to occur in the peripheral part with high conductivity when the current is interrupted, and the current interrupting performance is It is one of the causes of adverse effects. That is, if the arc generation is biased to the outer periphery of the electrode, the electrode area is not effectively used when the current is cut off, which causes local heating of the electrode to roughen the electrode surface and cause re-ignition. is there. Further, in a vacuum interrupter that applies a vertical magnetic field, the magnetic field effect immediately after arcing is weakened, and the current interruption performance deteriorates.

Since the present inventors have formed a temporary molded body of metal powder by suddenly applying a pressing force, the metal powder in the center of the mold is crushed and systematically densified. It was speculated that copper might be difficult to infiltrate into the central part of the infiltrated base material.

Therefore, after applying a low pressure pre-pressurization in two steps,
Attempts were made to improve the variation in conductivity by molding the preform with high pressure.

The experimental conditions were such that the preliminary pressure was maintained for 30 seconds, then the predetermined molding pressure was maintained for 60 seconds, and the other conditions were the same as described above, and the results shown in Table 1 were obtained.

The following facts were revealed from this experiment.

(1) 400k, which is a pressing force that makes it impossible to hold the temporary molded body by hand
When pre-pressurizing at a pressure of g / cm ² or less, and then pressurizing and molding and pressing, the conductivity is improved and the conductivity in the central part of the electrode is relatively higher than that in the peripheral part.

(2) If the preliminary pressure exceeds 30% of the molding pressure,
The effect of pre-pressurization disappears and cracks occur.

Although not described, the preliminary pressure is 10% of the molding pressure.
In the following cases, there is no effect of pre-pressurization, the molding pressure should be 5000 kg / cm ² or less, and the pre-pressurizing holding time should be 30 to 50% of the molding pressurizing holding time. I also understood that.

The present invention has been made based on the above results, and at least one kind of metal powder having a melting point higher than that of the infiltrant is pressure-molded to form a temporary molded body and the temporary molded body is baked. When the electrode material is manufactured by infiltrating the infiltrant into the infiltrate base material and then infiltrating the infiltrate base material, the metal powder is prepared at a low pressure within the range of 10% to 30% of the molding pressure. After pressurizing, the pressing force is increased to form the temporary molded body at a molding pressure of 500 kg / cm ² or more.

The holding time for pre-pressurization is 30% of the holding time for molding pressure.
It is good to set the range from 50% to 50%. As the metal powder, a metal having a melting point higher than that of copper, which is an infiltrant, may be used. For example, any combination of molybdenum and chromium, tungsten, iron, cobalt, niobium, and stainless copper may be used. The maximum particle size is -60.
Similar results are obtained up to the mesh (about 230 μm or less).

F. Action When the metal powder is pressed to form a temporary compact, the air at the grain boundaries is released uniformly and the air at the grain boundaries is released uniformly because the pressure is pre-pressurized at a low pressure and then increased. Stress distribution during pressure contact is effectively performed. As a result, the metal powder in the central portion is not particularly crushed and densified even when pressed under high pressure, and the variation in conductivity is improved.

G. Example First, -100 mesh molybdenum and chromium powders were mixed with each other mechanically and uniformly in a mixer with a weight ratio of Mo: Cr = 3: 1.

Then, a mold with a shape larger than the desired electrode shape (inner diameter
60 mm) is prepared, this mold is mounted on a pressure molding machine, and about 100 g of the above-mentioned mixed powder of molybdenum and chromium is filled in the mold. After that, the pressure molding machine is operated to hold the mixed powder under a pre-pressurization pressure of 300 kg / cm ² for about 30 seconds as shown in Fig. 1, and subsequently the applied pressure is 1100 kg / c.
It is raised to m ² and molded and pressed for about 60 seconds to form a temporary molded body.

As shown in FIG. 2, one or more tentatively formed bodies thus obtained are placed in a container 11 made of alumina ceramics or the like with a space between them, and the tentatively formed bodies 12 are molded into a disc shape or the like. Place the copper ingot 13 placed on it, and then cover 14 made of the same material as the container 11.
Then, the container 11 is placed in a vacuum furnace. And 5
Maintaining a temperature of about 1000 ° C (below the melting point of copper) for about 60 minutes in a vacuum of about 1.333 mPa (5 × 10 ^-5 mmHg) for about 60 minutes, degassing the preform 12, and molybdenum particles and chromium particles. And are diffusion-bonded to obtain a porous infiltration matrix.

Thereafter, the temperature (about 1100 ° C.) that is higher than the melting point of copper and lower than the melting point of the metal powder is maintained for about 30 minutes, and the amount of the copper ingot 13 is infiltrated into the void portion of the infiltration matrix. The amount of the copper ingot 13 needs to correspond to the void volume of the infiltration base material, but if it is too large, it may spread over the entire bottom surface of the container 11.

The infiltration work, the degassing process, and the sintering process may be performed in a specific oxidizing atmosphere such as hydrogen gas, argon gas, or nitrogen gas other than the vacuum atmosphere.

When the surface of the electrode material thus obtained was cut and the conductivity was examined, the central part was 49% (IACS) and the peripheral part was 48% at maximum, and the above-mentioned experimental results could be confirmed.

Also, this electrode material is processed into an electrode with an outer diameter of 50 mm and a thickness of 4 mm,
As a result of a built-in test in a vacuum interrupter, the same current interruption performance as the conventional one was obtained. In particular, the result was obtained that the withstand voltage characteristic was improved by about 10%.

H. Effect of the Invention According to the method for producing an electrode material of the present invention, the preformed body is pre-pressurized at a low pressure in the range of 10% to 30% of the molding pressure, and then molded and pressed at a high pressure. Therefore, the air existing in the metal powder during the pre-pressurization is uniformly released, and the stress is effectively dispersed when the powders are in pressure contact with each other. As a result, the powder in the center of the mold is not crushed and compacted during molding and pressurization, and the variation in conductivity is improved, and the copper electrical conductivity between the edge of the electrode and the center is improved. The difference between can be reduced.

Moreover, since the strength is improved, the withstand voltage characteristics can be improved as a whole.For example, when it is used as the electrode material of a vacuum interrupter for switching capacitors, the contact surface is not roughened by the applied current when the current is applied, and the re-ignition probability is high. Can be significantly reduced. As a result, the distance between the electrodes can be reduced, the opening / closing speed of the electrodes can be reduced, and the vacuum interrupter and its operating device itself can be miniaturized.

In addition, handling by solidifying the metal powder is possible, and since this metal powder can be molded into any shape, it is possible to minimize the machining cost to the electrode shape after infiltration, and compared with the conventional method. Productivity could be improved by 1.5 to 2 times.

[Brief description of drawings]

FIG. 1 is a diagram of a pressure operation in a manufacturing method according to the present invention, FIG. 2 is a conceptual drawing showing an example of an infiltration operation thereof, and FIG. 3 is a conceptual drawing showing an example of a conventional manufacturing method. Is. In the figure, 11 is a container, 12 is a temporary infiltration mother, 13 is a copper ingot, and 14 is a lid.

Front page continuation (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01H 11/04 D 8936-5G 33/66 B 8121-5G

Claims (2)

[Claims] 1. At least one metal powder having a melting point higher than that of the infiltrant is pressure-molded to form a temporary molded body, and the temporary molded body is sintered to form an infiltrated base material. When further infiltrating the infiltrant into this infiltrate base material to produce the electrode material, the metal powder is prepressurized to a low pressure within the range of 10% to 30% of the molding pressure, and then the applied pressure is increased. 500 kg / cm ²
A method for manufacturing an electrode material, wherein the temporary molded body is formed under the above molding pressure. 2. The method for producing an electrode material according to claim 1, wherein the holding time of the pre-pressurization is set in the range of 30% to 50% of the holding time of the molding pressure.