JPH0470380B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electrical contact material used in switching equipment for electric circuits, and particularly to an electrical contact material made of a silver-carbide-graphite-based sintered alloy, and a method for manufacturing the same. [Prior Art] Electrical contact materials made of silver-graphite sintered alloys have the advantage of excellent welding resistance while maintaining low contact resistance, but have the disadvantage of poor wear resistance. In order to improve this wear resistance, an attempt was made to add a carbide with a high melting point, but when manufactured using the commonly used powder mixing method and sintering method, the graphite particles agglomerated. Since the particles become large and several are connected, a fine and uniform dispersion state cannot be obtained, and small pores remain in the sintered alloy, so the graphite reacts with oxygen in the atmosphere due to the arc heat when the contacts are opened and closed. It becomes CO gas and evaporates and decreases. This resulted in the formation of pores and cracks inside the alloy, conversely increasing wear and tear, and had the drawback of worsening arc breakage if the CO gasification reaction progressed more than necessary. Furthermore, as the number of times the contact is opened and closed increases, there is a shortage of graphite in the alloy, causing decomposition and oxidation of carbides, resulting in an increase in contact resistance. Furthermore, if the dispersion of graphite or carbide in the alloy is non-uniform, silver segregation may occur, which may lead to welding. [Problems to be Solved by the Invention] The present invention provides a silver-carbide-graphite electrical contact that maintains low contact resistance, has excellent welding resistance and abrasion resistance, and has good arc breakage. The purpose is to provide materials. [Means for Solving the Problems] The electrical contact material of the present invention is an alloy made by powder metallurgy, and contains at least 97 to 50% by weight of silver and a carbide of a metal of Group A, A, or A of the Periodic Table of the Elements. It consists of a sintered alloy containing 3 to 50% by weight of type 1 graphite and 0.1 to 10% by weight based on the total amount of silver and carbide, and all graphite particles in the sintered alloy have a size of It is characterized by having a diameter of 3 μm or less, being independently and uniformly dispersed, and having substantially no pores. This electrical contact material contains 97 to 50% by weight of silver powder, 3 to 50% by weight of at least one type of carbide powder of a metal of Group A, A, or A of the Periodic Table of the Elements, and based on the total amount of the silver powder and carbide powder. 0.1 to 10% by weight of graphite powder is mixed, mechanical alloying is used to reduce the size of all graphite particles to 3 μm or less, and each particle is independently and uniformly dispersed. The resulting mixed powder is pressure-molded and reduced. It can be manufactured by sintering in a neutral atmosphere or in a vacuum and then pressurizing again to substantially eliminate pores. [Operation] Mechanical alloying is generally a method of alloying powder at the same time as pulverization and mixing, and although a powder mixing device such as a ball mill is used, in normal powder mixing, the ball: powder volume While the ratio is about 1:1, mechanical alloying has a ratio of 5:1.
Mechanical alloying differs from ordinary powder mixing methods, which aim only at pulverizing and mixing powders, in that the degree and amount of powder is small, and in mechanical alloying, no lubricant is used. In the present invention, by utilizing such mechanical alloying, a mixed powder in which carbide powder and graphite powder are embedded in silver powder in an inlaid manner can be obtained. By alloying, they all have a size of 3 μm or less, and each can be independently and uniformly dispersed in silver. This mixed powder is pressure-molded, sintered, and re-pressed to produce electrical contact materials.
The graphite particles are small, less than 3 μm, and are independently and uniformly dispersed in the alloy. These fine and uniformly dispersed graphite particles minimize the reaction of oxygen in the atmosphere to form CO gas due to arc heat during contact opening/closing, and furthermore, repressurization virtually eliminates pores. Since this reaction does not spread to the inside of the sintered alloy, wear resistance is greatly improved and arc breakage is also improved. Therefore, since graphite shortage does not occur, carbide oxidation is less likely to occur, and contact resistance is maintained low. Furthermore, since carbide and graphite are uniformly dispersed, welding due to silver segregation is also eliminated. Proportion of carbide in total amount of silver and carbide 3-50
The reason why it is set at % by weight is that if it exceeds 50% by weight, the contact resistance will increase, and if it is less than 3% by weight, the abrasion resistance will be insufficient. The reason why the amount of graphite is set to 0.1 to 10% by weight based on the total amount of silver and carbide is that if it exceeds 10% by weight, no improvement in wear resistance will be seen and arc breakage will deteriorate, so if it is less than 0.1% by weight. This is because the welding resistance and contact resistance deteriorate, and the preferable range is 1 to 5.
Weight%. Furthermore, if the size of the graphite particles in the alloy exceeds 3 μm, the CO gasification reaction due to oxidation of the graphite will easily occur, the arc will not cut easily, the amount of consumption will increase, and the alloy will be impractical. [Example] Silver powder (average particle size: 3 μm), carbide powder (average particle size: 3 μm), and graphite powder (average particle size: 15 μm) in the proportions shown in Table 1.
were mixed and mechanically alloyed using a ball mill for 100 hours without using a lubricant and at a ball:powder volume ratio of 5:1. However, sample No. 1 was not mechanically alloyed, but was wet mixed using a ball mill under normal conditions. The obtained mixed powder
Embossing was carried out at a pressure of 2 ton/cm ² , and the molded body was sintered at a temperature of 900°C in a hydrogen atmosphere. Next, sample no.
Except for No. 1, the sintered bodies were repressurized at a pressure of 3 tons/cm ² to produce alloys with zero porosity. Table 1 also shows the size of graphite (Gr diameter) in the obtained alloy. The compositions (% by weight) shown in Table 1 are values indicating the proportion of each powder in the total amount of raw material powder used.

[Table] Sample No. 1 is a comparative example. Due to the normal mixing method, the graphite powder as a raw material is crushed but coagulated at the same time, so the size of the graphite particles obtained is at most 60 μm. The properties of the manufactured alloy as an electrical contact material were tested. The test was conducted using an ASTM contact testing machine, and a sample with dimensions of 5 x 5 x 1.5 x R was brazed to a special jig, thoroughly pickled, and then opened and closed 20,000 times through AC 220 V, 100 A, and a current of pf 0.75. We investigated each characteristic after The results are shown in Table 2.

〔Effect of the invention〕

According to the present invention, there is provided an electrical contact material made of a silver-carbide-graphite-based sintered alloy that maintains low contact resistance, has excellent welding resistance and wear resistance, and has good arc breakage. can do.

Claims (1)

[Scope of Claims] 1 97 to 50% by weight of silver, a of the periodic table of elements,
At least one carbide of group a metal 3 to 50
% by weight, and based on the total amount of silver and carbide.
It consists of a sintered alloy containing 0.1 to 10% by weight of graphite, and all graphite particles in the sintered alloy have a size of 3 μm or less, are independently and uniformly dispersed, and are substantially empty. An electrical contact material characterized by the absence of pores. 2 Silver powder 97-50% by weight, periodic table of elements a,
At least one type of carbide powder of a, group a metal3~
50% by weight and 0.1 to 10% by weight of graphite powder based on the total amount of the silver powder and carbide powder,
All graphite particles are made to have a size of 3 μm or less by mechanical alloying, and each particle is independently and uniformly dispersed. The resulting mixed powder is pressure-molded, sintered in a reducing atmosphere or in a vacuum, and then reprocessed. A method for producing an electrical contact material, the method comprising substantially eliminating pores by pressing the material.