JPS5948947B2 - electrical contact materials - Google Patents

Description

[Detailed description of the invention] The present invention relates to silver or copper-carbide contact materials.

Silver or copper-carbide contact materials combine the excellent conductivity of silver or copper and the high hardness of carbide.
It is used in air circuit breakers such as no-fuse breakers, and as a contact material for various electrical devices.

Among these, materials using WC as the carbide have excellent arc resistance and welding resistance, and therefore occupy a position as the central material for these devices.

However, these circuit breakers and switches are becoming smaller in size and higher in performance, and as a result, the load on contact materials is increasing, and improvements in contact performance are desired.

That is, as equipment becomes smaller, the size of the contact point tends to become smaller and the contact force tends to decrease.

These tend to cause wear and welding when the current is cut off, as well as temperature rise when switching on and off at the rated current, and improvements in these characteristics are desired.

As is well known, WC has the drawback that the current is turned on and off many times, causing the WC to oxidize and further react with silver or copper to form a low melting point glass, which is an insulator, impeding electrical conductivity and causing a rise in temperature. This characteristic is becoming more important as the trend toward

On the other hand, MO□C oxidizes and evaporates when the current is turned on and off many times, so although it has excellent current conductivity, it has poor wear resistance and welding resistance, so it is rarely used.

If wear resistance and welding resistance comparable to WC are added to this, the temperature rise during opening and closing, which is a drawback of contacts, can be prevented, and the development of higher performance contacts is expected.

The present invention has been made in view of the above points, and aims to provide a material that improves the performance of silver or copper-carbide contact materials, especially the temperature rise characteristics, and further reduces the cost of expensive WC. be.

The present invention focuses on the physical properties of carbides, including W and M.

By dispersing hexagonal monocarbide consisting of a solid solution in silver or steel, we have discovered a material that exhibits excellent temperature rise characteristics and exhibits welding resistance and wear resistance comparable to WC.

The following features of the present invention will be described.

Hexagonal monocarbide consisting of W and Mo is
It has physical properties and hardness similar to WC, and oxidation properties similar to MO2C.

It is clear from the following examples that this carbide has excellent contact characteristics, and the reason is thought to be as follows.

Originally, the purpose of dispersing WC powder in an edible conductive metal such as Ag or Cu was to (1) prevent melting due to arc discharge due to the high melting point of WC, and (2) provide excellent deformation resistance at high temperatures. , (3) reducing mechanical wear due to opening and closing of contacts, etc.

Naturally, a hard material should fully satisfy this property, but since a considerable impact is applied when the contact opens and closes, even more toughness is required, and a high Young's modulus is preferable because it helps prevent deformation.

For these reasons, many contacts contain WC as a main component.

However, when used as a contact, the alloy surface is exposed to arc heat, so WC is WO2, WO2, 7□,
It becomes oxides such as WO3.

This W oxide does not volatilize unless it is heated to a high temperature of 1100° C. or higher.

This is because the surface temperature of a contact with a small current capacity does not rise much, so as the number of times the contact is used increases, a large amount of oxide remains on the surface and forms a film.

Furthermore, as mentioned above, this oxide reacts with copper and silver to form a stronger glass with a lower melting point.

To solve the above problems, low current contacts are required to have good volatility of the oxide formed on the surface.

Only Mo oxide satisfies this requirement.

The reason for this is that Mo oxide volatilizes from 600° C., and the amount of volatilization is more than 100 times that of W oxide.

Therefore, it seems that the problem can be easily solved by using Mo carbide, but unlike WC, MoC does not exist at room temperature.

For this reason, previous researchers have attempted experiments using MO2C.

However, as shown in Table 1, MO2C does not satisfy the characteristics of WC.

That is, compared to WC, MO2C is 70% harder, has more than twice the electrical resistance, and has a thermal conductivity of 1710 or less.

If MO2C is used, the resistance is large and the thermal diffusivity is poor, so the temperature of the contact surface will rise abnormally.

Moreover, the hardness is low, and the oxide quickly volatilizes and is consumed.

In other words, Mo2C is compared with W2C,
Its characteristics are completely different from WC.

In order for MO carbide to satisfy characteristics similar to WC, its crystal form must be a simple hexagonal crystal like WC.

The monocarbide (MoC) of

In order to stabilize MoC at room temperature, it is preferable to use hexagonal monocarbide ((MOW)C) consisting of a solid solution of Mo and W.

This (MoW)C was discovered by W. Dawihl in 1950.

This (MoW)C was developed as a raw material for cemented carbide, but it is not very stable during sintering, so it is not used much.

However, when dispersed in Ag or Cu, the sintering temperature is 1100-1400°C, (MoW
) C is a relatively stable temperature, so it is also a material suitable for such alloys.

As shown above, (with particle size of 20μ or less in Ag or Cu)
Contact alloys containing dispersed Mob) C particles have physical properties similar to those of WC, so they have excellent heat resistance and strength under arcs. It seems to have excellent weldability.

Furthermore, unlike WC, (MoW)C evaporates oxides, making it difficult to form a film on the contact surface, which is thought to provide excellent temperature rise characteristics.

The amount of these carbides varies depending on the equipment used, but is preferably 20 to 80% by weight.

Those with a large content are suitable for large currents, and those with a small content are suitable for medium currents.

Basically, the contact performance is provided by this constituent material.

However, since silver or copper and these carbides do not form a solid solution with each other, blisters or cavities occur during normal sintering.

As a result of various studies regarding sintering stability, it was found that addition of iron group elements is preferable.

The effective range of this iron group element is 10% by weight or less.

W and M. The hexagonal monocarbide consisting of carbon (
Although C) tends to precipitate, it is thought that the iron group elements prevent this decomposition.

If the iron group element content increases, it becomes difficult to fully exhibit the characteristics of the carbide, so a content of 10% by weight or less is appropriate.

Next, in order to further clarify the characteristics of the electrical contact material of the present invention, typical examples of specific electrical contacts will be described.

Each powder was blended in the proportions shown in Table 2, and mixed in a wet ball mill for 30 hours.

This powder is molded, and the molded body is heated to 1150°C in a hydrogen gas atmosphere.
Sinter at °C.

The sintered state of the obtained sintered body was as shown in Table 3.

These alloys were cut into predetermined shapes, brazed to a Cu alloy, and three types of performance evaluations were performed under the conditions shown in Table 3.

The conductivity test results are shown in Figure 1.

The alloy of the present invention exhibits a voltage drop value that is approximately half that of the conventional material (H).

Figures 2 and 3 show the results of observing the back surface of the contact using a scanning electron microscope after the test.

FIG. 2 shows the invention material, and FIG. 3 shows the comparative material.

It is recognized that a low melting point glass phase is not formed in the material of the present invention.

The welding test results are shown in Table 4.

The alloy of the present invention had a welding force comparable to that of the conventional material (H), while the conventional material (I) exhibited strong welding strength of 2 kg or more.

Table 5 shows the consumption amount after the cutoff test.

The amount of wear of the material of the present invention was comparable to that of the conventional material (H), and no difference was observed in terms of the amount of arc generation.

Further, each powder was blended in the proportions shown in Table 6, and mixed in a wet ball mill for 30 hours.

This powder is molded, and the molded body is heated to 1300 in a hydrogen gas atmosphere.
Sintered at °C.

These alloys were cut into predetermined shapes, brazed to Cu joints, and subjected to the electrical conductivity test, welding test, and interruption test shown in Table 3.

The conductivity test was conducted 1000 times and the voltage drop was measured.

The results are shown in Table 7.

The voltage drop value of the alloy of the present invention is about 60% compared to the comparative material.

Furthermore, the welding force and the amount of wear were also low.

As described above, the alloy of the present invention is superior to conventional materials in terms of temperature rise, welding resistance, and abrasion resistance, and is also of low cost, so it is of high industrial value.

[Brief explanation of drawings]

Figure 1 shows the current conduction test results in Examples, Figure 2 is a scanning electron micrograph of the contact surface of the inventive material after the test shown in the Example, and Figure 3 is the same as Figure 2 for the comparative material. It is a diagram.

Claims (1)

[Claims] 1. Carbide is composed of a solid solution of tungsten, morphine, and carbon, and the crystal structure of this solid solution is hexagonal monocarbide, containing 20 to 80% by weight of at least one of these carbides, and a binder phase. A silver- or copper-carbide-based electrical contact material characterized in that the material is composed of silver or copper and has improved oxidation resistance. 2 Carbide is composed of a solid solution of tungsten, molybdenum, and carbon, and the crystal structure of this solid solution is hexagonal monocarbide, containing 20 to 80% by weight of at least one of these carbides, and the binder phase is silver or copper. A silver or copper-carbide electrical contact material comprising an iron group element, having an iron group element content of 10% by weight or less, and having improved oxidation resistance.