JPS6047011B2 - Manufacturing method of electrical contact material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an electrical contact material, particularly a composite contact material containing silver-bismuth oxide as a main component.

Conventionally, silver-cadmium oxide has been used as contacts for medium to high currents that involve discharge, and has excellent properties such as welding resistance, abrasion resistance, and contact resistance required for electrical contacts. Therefore, it is widely used.

However, this silver-cadmium oxide material has certain problems during its manufacturing process, such as melting, hot processing, and cleaning.
There is a problem that cadmium is easily discharged to the outside, which is not desirable in terms of pollution prevention measures, and also from the viewpoint of general society.
It is becoming a material that is difficult to adapt. Therefore, there has been a strong demand for the development of a new contact material that solves the problem of cadmium pollution and is comparable to silver-cadmium oxide, and in recent years, various research and development efforts have been carried out.
The inventors have already developed a silver-bismuth oxide-based composite material and have obtained the prospect that this material can replace silver-cadmium oxide, but the powder sintering method is not yet suitable for its production. As a result, there was a problem in terms of contact characteristics, such as a large amount of wear.

In other words, the usual method for manufacturing silver-oxide composite materials, taking silver cadmium monoxide as an example, is to create an ingot of silver-cadmium alloy, process this to make it close to the final contact shape, A so-called internal oxidation method in which cadmium is selectively internally oxidized by heating in an oxidizing atmosphere, and then this is used as a material to form a desired contact shape.
Mix silver powder and cadmium oxide powder homogeneously, then
This is broadly classified into the so-called sintering method, in which the material is loaded into a mold, press-molded, and then heated and sintered.

In recent years, the internal oxidation method is mostly used to manufacture small contacts due to wear resistance and other characteristics of contacts, and the sintering method is used only when large-sized contacts require an extremely long time for internal oxidation. That is the reality. However, the silver-bismuth monoxide composite material described above is a material that is extremely difficult to cold-work even if the silver-bismuth alloy is within the solid solubility limit of bismuth, that is, 5.1% by weight or less (600°C). be. Methods that allow this processing include processing methods in a heated state such as hot forging and hot extrusion. Therefore, processing to a shape that can ultimately be internally oxidized requires considerable consideration in manufacturing conditions and manufacturing equipment, and is difficult even with these methods. Bismuth alloys are difficult to process because bismuth is a brittle metal, and in silver-bismuth alloys, bismuth tends to segregate at grain boundaries, making them even more difficult to process. It's for a reason.

Several examples of silver-bismuth alloy contact materials have been seen so far. Most of them have a bismuth content of 1% by weight or less, and all of them point out that processing becomes difficult as the bismuth concentration increases. In addition, in the above materials, the desired internal oxidation is achieved by utilizing the phenomenon that bismuth precipitates at grain boundaries and using bismuth as an oxygen carrier to oxidize other alloy additive elements that oxidize slowly. is taken. However, the material targeted by the present invention has bismuth oxide as its main component, and it is desired that it be homogeneously dispersed in the silver matrix. It is clear that desired characteristics cannot be obtained.

The present invention solves the difficulties in processing silver-bismuth monoxide-based contact materials containing 1% by weight or more of bismuth, and provides a manufacturing method that can enjoy the contact characteristics obtained by internal oxidation.

Bismuth oxide, which is the object of the present invention, can be considered to be an oxide with relatively low hardness as described below among metal oxides used as additives for various contacts. Cadmium oxide...3.0 (mineral scale) copper oxide
...4.0 Bismuth oxide ...4.5 Zinc oxide ...4.5 Tin oxide ...6.5 Indium oxide ...7.0 Aluminum oxide ...・9.0 (Supervised by Samsonov, Nippon-Soviet Press, Monooxide Handbook)
Therefore, it is expected that if bismuth oxide is homogeneously dispersed in a silver matrix, a material with relatively good processability will be obtained.

As a result of various experimental studies on this point, the inventors found that
We have discovered that it is possible to homogeneously disperse bismuth oxide in a silver matrix by the method described below. First, a silver-bismuth alloy having a desired composition ratio is melted and then cast.

The mold is preferably water-cooled, and if water-cooling is not used, an iron mold having a weight of 10 to 2@2 of the casting amount is preferred. This is achieved by rapidly cooling and casting the molten metal.
This is to prevent segregation of bismuth. The ingot thus produced is immediately coarsely crushed using a rolling mill to form alloy grains. 0.7-2TG1 preferably 1.0-1.
5TfrIn(7) is preferably scaly. A rolling mill is used to make the ingot into flakes, but since the processing ability of the alloy is low, the ingot cracks during rolling and is converted into appropriate flake-like particles at any time. Next, the flaky alloy grains are subjected to internal oxidation treatment to convert the bismuth contained in the alloy into an oxide, and if other base metals are also contained,
These are also deposited as oxides in the silver base. Internal oxidation treatment is performed at 600-800℃ in an oxidizing atmosphere.
This is done by heat treatment. Next, the internally oxidized grains are again milled to a thickness of 0.7 TIr1n or less, preferably 50% or less of the particle thickness during the previous rough crushing. At this time, the oxide particles dispersed in the silver matrix by the above-mentioned oxidation treatment are crushed and made into fine particles, which greatly affects the machinability imparted to the final wire rod. 0.7Tn! The powder chips rolled to a thickness of n or less are washed, loaded into a cylindrical shape, molded, and then sintered.

The sintered cylinder built in this way is processed into a wire material by warm extrusion. The wire material produced in this way usually exhibits an elongation rate of 10 to 20% in a state containing 10 to 15% by weight of oxide in the silver matrix, which is sufficient for processing headers to make contact studs. It becomes a contact material that can be used. In order to make the above-mentioned manufacturing method of the present invention more clear, the following examples will be given and explained.

The main ingredients are silver and bismuth, and if necessary,
Other additive metals were added to give a total weight of 200 g, which was dissolved.

Melting was carried out using an alumina crucible in an argon atmosphere using a high frequency furnace. The molten metal is 15×30×
It was cast into a steel mold with dimensions of 70w1m3. The weight of the mold was approximately 4k9, and care was taken to ensure that the ingot was cooled rapidly and segregation of bismuth did not occur. The ingot thus produced was immediately rolled using a rolling mill to a thickness of 2 to 0.
7? coarsely ground into small pieces. Silver alloys containing 1% by weight or more of bismuth have almost no cold workability, so the thickness is 15T.
When the $L ingot was rolled, it naturally cracked and was crushed into scaly chips. This was heated in air at 650'C for 6C$111 to selectively oxidize bismuth and other base metal components added.
In this example, as shown in the table, tin, zinc, indium, etc. were used as base metal elements other than bismuth. Next, this was crushed and rolled again using a rolling mill so that the thickness was 50% or less of the above-mentioned small pieces. After washing this with a solvent, 2077!77! Loaded into a cylindrical shape with a diameter of 8 tons/C! Molded at a pressure of 1. Next, this molded body was heated and sintered in air at a temperature of 800° C. for 2 hours. Furthermore, this sintered body has a diameter of 20.577!77!
It was charged into a warm heating mold of
Sintered for hours. Thereafter, this sintered body was processed into a wire rod with a diameter of 3T$t by warm extrusion at 550°C. This wire was subsequently cold drawn to a diameter of 2w0n, and its mechanical strength, ie, tensile strength and elongation, were measured. For reference, the value of silver cadmium monoxide (1 weight %), which has excellent workability in this type of wire, is shown. As shown in the results in this table, according to the manufacturing method of the present invention, a material with sufficient workability can be obtained even for silver-bismuth monoxide-based contact wires, and silver-bismuth monoxide-based contacts The practical value of can be increased by 50%.

Claims (1)

[Claims] 1. Casting a molten metal of an alloy containing silver and bismuth as main components, cooling it to form an ingot, coarsely crushing the ingot into small pieces using a rolling mill, and internally oxidizing the ingot. A method for producing an electrical contact material, further comprising rolling the material into a scale-like thin piece again, forming and sintering it to form a billet, and extruding the billet to obtain a contact material. 2. The method for producing an electrical contact material according to claim 1, wherein the alloy containing silver and bismuth as main components contains at least 1% by weight of bismuth. 3 The thickness of the small pieces roughly crushed by the rolling mill is 0.7
2. The method of manufacturing an electrical contact material according to claim 1, wherein the material has a thickness of 2 mm. 4. The electrical contact material according to claim 1, characterized in that the thickness of the scale-like chips re-pulverized with a rolling mill is 50% or less of the thickness of the coarsely-pulverized small pieces. Production method.