JPS6131172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing a contact material used in vacuum shields and circuit breakers that particularly require a high withstand voltage.

[Conventional technology]

Conventionally, Cu-Bi has been mainly used as a contact material for shield breakers that require large current shielding performance (see Japanese Patent Publication No. 12131/1973).
A feature of Cu--Bi material is said to be that it is possible to suppress welding resistance to a sufficiently small value without reducing voltage resistance too much.

[Problem that the invention seeks to solve]

However, the above contact material contains more than 1% Bi, which is caused by high temperature heating during the exhaust process.
Some of it evaporates and diffuses from within the contact. This evaporated Bi is then exhausted by the exhaust pump to the outside of the vacuum chamber and disconnector, but a considerable amount of Bi still adheres to the metal shield and insulating container inside the vacuum chamber, and this causes the vacuum chamber to disconnect. This is one of the major causes of deterioration of the withstand voltage of the device. Therefore, when using a vacuum circuit breaker using such a contact in an application requiring a high withstand voltage, a long opening distance is required, which is extremely disadvantageous and uneconomical in practice.

In addition, as a contact material that can eliminate the above drawbacks,
Conventionally, as described in JP-A No. 50-55870, there was a product made by sintering 50% by weight of Cu and 50% by weight of Cr, but this conventional product had a high withstand voltage, In order to obtain large current characteristics, it was necessary to perform forging at a high temperature or re-pressing after the sintering.

The present invention has been made in view of the above-mentioned conventional situation, and is directed to the production of a contact material for vacuum shields and disconnectors that can obtain characteristics suitable for high withstand voltage and large current without the need for conventional forging processes, etc. The purpose is to provide a method.

By the way, it has been known for a long time that Cr has a high withstand pressure in vacuum. However, when Cr is used as a contact material, since Cr is a heat-resistant metal, it has strong thermionic emission characteristics, so Cr alone cannot be expected to have great shearing performance, and Cr has low thermal conductivity and high contact resistance. Therefore, it is difficult to use in a heater for large current applications because the temperature rise is excessive.

Therefore, the present inventors solved this weakness of Cr by using Cu.
An attempt was made to compensate by adding . in general
Since Cr is a material that easily oxidizes, it is difficult to manufacture such an alloy of Cu and Cr using normal manufacturing methods. Further, in order to prevent deterioration of pressure resistance performance due to the addition of Cu, Cu and Cr must be present uniformly. Conventionally, contact materials were usually made by casting, but according to the casting method, copper was mixed into
It is difficult to homogeneously disperse Cr, and
It becomes expensive.

Taking these into consideration, the present inventor has determined through various experiments that a method of sintering Cu and Cr in vacuum using a powder metallurgy method is optimal for manufacturing this contact, and that Cu is It has been found that by setting the content of Cr to 80% by weight and 35 to 20% by weight, the above-mentioned conventional casting process after sintering becomes unnecessary.

[Means for solving problems]

Therefore, the method for manufacturing a contact material for a vacuum sinter and disconnector according to the present invention involves sintering 65 to 80% by weight of Cu and 35 to 20% by weight of Cr in a vacuum using a powder metallurgy method. .

[Effect]

In this invention, a contact in which Cr is uniformly dispersed can be provided at a low cost while preventing the oxidation of Cr without performing a casting process after sintering.

〔Example〕

Here, before explaining the embodiments of the present invention, Cu
Figures 2 to 7 show the properties of contact materials obtained by varying the mixing ratio of Cr and Cr. in this case,
The contact material of each mixing ratio was adjusted to have a predetermined porosity.

FIG. 2 shows the relationship between the amount of Cu and the electrical conductivity, and it can be seen from the figure that the electrical conductivity increases as the amount of Cu increases.

Figure 4 shows the relationship between the amount of Cu and the surface hardness, and it can be seen from the figure that the hardness decreases with the amount of Cu.

Figure 3 shows the relationship between Cu content and contact resistance.
As shown in Figures 2 and 4, the characteristics of the Cu
It is interpreted that the contact resistance decreased due to the synergistic effect of increasing the electrical conductivity and decreasing the hardness, increasing the effective contact area as the amount increases.

Figure 5 shows the relationship between the withstand voltage and the amount of Cu after a current of approximately 200A is switched on and off 50,000 times.
It can be seen that it decreases with the amount of Cu, but the decrease is not so large when the amount of Cu is between 40% and 80%, and it decreases rapidly when it exceeds 80%.

Figure 6 shows the relationship between Cu amount and shearing current,
As can be seen from the figure, the severing current is almost constant between 40% and 80% Cu, and exhibits a pot-bottom type characteristic with an average of about 2.9A. The characteristics of the breaking current value of the contact according to the present invention include, for example, compared to the Cu-Bi system, the average value is considerably lower, the width of the distribution is smaller, and the value does not change much even after the current is switched on and off. be.
Note that, not only Cu-Bi type contacts, but also the cutting current values of contacts to which a small amount of low-boiling point material is added have relatively large variations depending on the number of current openings and closings.

Figure 7 shows the relationship between the amount of Cu and the welding characteristics, and this data shows that when a specified current was applied to the contact point of the model pipe with a pressure of 20 kg applied, it was possible to trip with a force of 100 kg. Indicates the maximum current value. From the same figure, it can be seen that when the Cu content is in the range of 40 to 90%, the conventional operation mechanism can be used to sufficiently remove the weld, but in other ranges, the welding force increases rapidly.

Figure 8 shows the relationship between Cr grain size and withstand voltage. From the figure, if the average grain size of Cr is 100 μm or less, a nearly constant withstand voltage can be obtained, but if it exceeds this, the equivalent withstand voltage deteriorates. It turns out that this is not desirable. Also, regarding the large current shedding ability, if the Cu content is 40% or more, there will be no practical problem.

Therefore, we obtained the following conclusion from the above experiment. i.e. 40-80% by weight Cu and 60-20% by weight
A contact material made of an alloy obtained by sintering Cr with an average particle size of 100 μm or less in a vacuum using a powder metallurgy method has excellent properties as a contact for vacuum shields and breakers for high voltage and large current. Moreover, as described later, if Cu is 65 to 80% by weight and Cr is 35 to 20% by weight, a product with a specified density can be obtained without casting after sintering, and sintering The above characteristics can be obtained with just one.

Examples of the present invention obtained from the above experimental results will be described below.

First example: Cu powder and Cr powder with an average particle size smaller than 100 μm are
Mixed at a weight ratio of 80:20, a predetermined amount of this mixed powder is filled into a mold of a desired shape, and cold compressed at a pressure of about 3 tons/cm ² . The molded product obtained in this way is placed in an atmosphere with a worst-case vacuum of about 1 Torr.
By performing sintering at 1080°C for 1 hour, a sintered body with a theoretical density ratio of 98% (porosity: 2%) was obtained.

Second example: Cu powder and Cr powder with an average particle size smaller than 100 μm
Mixed at a weight ratio of 75:25, a predetermined amount of this mixed powder is filled into a mold of a desired shape, and cold-pressed at a pressure of about 3 tons/cm ² . The molded product obtained in this way is placed in an atmosphere with a worst-case vacuum of about 1 Torr.
By performing sintering at 1100°C for 1 hour, a sintered body with a theoretical density ratio of 98% (porosity: 2%) was obtained.

Third example: Cu powder and Cr powder with an average particle size smaller than 100 μm
Mixed at a weight ratio of 65:35, a predetermined amount of this mixed powder is filled into a mold of a desired shape, and cold-pressed at a pressure of about 5 tons/cm ² . The molded product obtained in this way is placed in an atmosphere with a worst-case vacuum of about 1 Torr.
By performing sintering at 1150°C for 1 hour, a sintered body with a theoretical density ratio of 98% (porosity: 2%) was obtained. Note that when only the sintering temperature was set to 1080° C. under the conditions of this example, the porosity was 8%.

As described above, the contact materials according to the first to third embodiments are prepared by pre-mixing and molding 65 to 80% by weight of Cu and 35 to 20% by weight of Cr, and heating the mixture at 1000°C to 1200°C in an atmosphere of about 1 Torr. It was obtained by sintering at a temperature of . In order to prevent oxidation, a very high vacuum is not necessary, and a vacuum of about 1 Torr is sufficient as mentioned above, but in this case, in order to effectively release the gas adsorbed by Cu powder, Cu It is desirable to sinter in a temperature range where the metal melts.

FIG. 1 shows a microscopic photograph of the structure of a contact material obtained by the manufacturing method of the present invention. The contact material shown in Figure 1 consists of 75% Cu and 25% Cr by weight.
This shows the case of mixing and sintering at 1100℃. The porosity in this case is 2%. As is clear from the photo, Cr particles (white parts) are well dispersed in Cu.

Next, to explain the porosity of the sintered body mentioned above, the porosity of the sintered body changes depending on the mixing ratio of Cu and Cr, sintering conditions, etc., but when the amount of Cu is changed, the predetermined density In order to adjust to
As shown in the third embodiment, if the Cu amount is 65 to 80% by weight, this can be achieved by appropriately setting the sintering conditions. However, when the Cu amount is 65% or less, it becomes increasingly difficult to adjust the density to a specified level even if the sintering conditions are set appropriately.For example, when the Cu amount is 50% (the first comparison described below (see example) cannot reduce the porosity to below 12-13% by sintering alone. For this reason, in cases such as when the Cu content is 50%, in order to obtain the specified density, it is necessary to
As described in Japanese Patent No. 55870, it is necessary to perform high-temperature casting or re-pressing after sintering.

On the other hand, when the Cu amount is 65 to 80% as in the present invention, a material with a predetermined density can be obtained only by sintering.

Here, there are several conditions that affect the porosity, but if we focus only on the sintering temperature, the porosity will be smaller if sintered at a temperature that produces a liquid phase. 1st above
In the example, the porosity was 2% even when sintered at a temperature where a liquid phase did not occur due to the high proportion of Cu.
In the third embodiment, since the proportion of Cu is low, sintering is performed at a temperature at which a liquid phase is generated, and the porosity is set to 2%.

In addition, in order to clarify the effects of the present invention,
A comparative example where the amount of Cu is 65% or less is shown below.

First comparative example: Cu powder and Cr powder with an average particle size smaller than 100μm
Mixed at a weight ratio of 50:50, a predetermined amount of this mixed powder is filled into a mold of a desired shape, and cold compressed at a pressure of about 5 tons/cm ² . The molded product obtained in this way is placed in a vacuum with a worst-case vacuum of about 1 Torr.
By performing sintering at 1150°C for 1 hour, a sintered body with a theoretical density ratio of 88% (porosity 12%) was obtained.

Second comparative example: Cu powder and Cr powder with an average particle size smaller than 100 μm
Mixed at a weight ratio of 30:70, a predetermined amount of this mixed powder is filled into a mold of a desired shape, and cold compressed at a pressure of about 5 tons/cm ² . The molded product obtained in this way is placed in a vacuum with a worst case vacuum level of about 1 Torr.
By performing sintering at 1150°C for 1 hour, a sintered body with a theoretical density ratio of 80% (porosity 20%) was obtained.

〔Effect of the invention〕

As described above, according to the present invention, Cu is 65 to 80% by weight and Cr is 35 to 20% by weight, and these are sintered in a vacuum, so there is no need for conventional casting processing. This has the effect of easily obtaining a contact material for vacuum shields and disconnectors that have excellent properties for high withstand voltage and large current applications.

[Brief explanation of the drawing]

FIG. 1 is a micrograph of the structure of a contact material according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the amount of Cu and conductivity, and FIG. 3 is a diagram showing the relationship between the amount of Cu and contact resistance. Figure 4 is a diagram showing the relationship between Cu content and surface hardness, Figure 5 is a diagram showing the relationship between Cu content and withstand pressure,
Figure 6 is a diagram showing the relationship between Cu content and shearing current value, Figure 7 is a diagram showing the relationship between Cu content and welding resistance, and Figure 8 is a diagram showing the relationship between Cr average grain size and withstand voltage. FIG.

Claims (1)

[Claims] 1. A contact material for vacuum shields and breakers, characterized in that it is made by sintering 65 to 80% by weight of Cu and 35 to 20% by weight of Cr with an average particle size of 100 μm or less in vacuum using a powder metallurgy method. manufacturing method.