JPH0636657A - Contact material for vacuum circuit breaker and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a contact material for use in a vacuum circuit breaker, having a low chopping current value and excellent in current cutoff characteristics and weld resitance by forming the material out of an Ag-Cr sintered alloy of specific composition. CONSTITUTION:Ag-Cr mixed powders 19 comprising 30-50wt.% Ag and the rest Cr and having a 1000 or less mesh are packed in a capsule 18 made of a metal such as soft steel, and a lid 21 having a metallic pipe 20 attached thereto is joined to the upper portion of the metallic capsule 18. The powders are put in an electric furnace and heated and the inside of the capsule 18 is evacuated through the pipe 20 and then the pipe 20 is sealed. Then the powders are put in the high-pressure container 22 of a hot hydrostatic press and sintered at temperatures between 500 and 800 deg.C and at pressures between 700 and 2000kgf/cm<2> for 15 to 60 minutes so as to manufacture an Ag-Cr sintered alloy, which is then formed into a contact for use in a vacuum circuit breaker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact material for a vacuum circuit breaker having a low breaking current characteristic and a good current breaking characteristic, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, an oil-filled circuit breaker has been widely used as a circuit breaker for medium voltage (3.6 to 36 kV).
Currently, vacuum circuit breakers are mainly used because of their small size, light weight, long life, nonflammability, and labor saving in maintenance. FIG. 3 is a schematic cross-sectional view showing a configuration of a main part of the vacuum circuit breaker for explaining the vacuum circuit breaker. In FIG. 3, a fixed current-carrying rod 2 and a movable current-carrying rod 3 are arranged in an insulating cylinder 1 made of ceramics or the like so as to have the same central axis. 5 are joined by brazing. Furthermore, in the insulating cylinder 1,
An arc shield 6 for preventing the metal vapor generated from the contacts from adhering to the surface of the insulating cylinder 1 when the current is cut off is attached to the fixed conducting rod 2 side, and the fixed contact 4 is attached to the movable conducting rod 3 side.
And a bellows 7 for opening and closing the movable contact 5. The arc shield 6 is fixed to the inner surface of the lid 8 of the insulating cylinder 1, and similarly, the bellows 7 is fixed to the inner surface of the lid 9 of the insulating cylinder 1.

The vacuum circuit breaker thus constructed is usually assembled in a vacuum heat treatment furnace, and the inside of the insulating cylinder 1 is always maintained at a vacuum degree of 1 × 10 ^-4 torr.
The fixed contact 4 and the movable contact 5, which are in contact with each other when energized, are separated by the expansion and contraction movement of the bellows 7 integrated with the movable energization rod 3 in response to a signal from the outside to interrupt the current. You can

Fixed contact 4 and movable contact 5 used here
Are required to have the following characteristics for a vacuum circuit breaker. Excellent current blocking characteristics. Excellent in arc resistance and welding resistance. The breaking current value is low.

Excellent withstand voltage characteristics. The vapor pressure of the material components is low. Easy manufacturing method and excellent machinability. Be inexpensive. On the other hand, it is very difficult to satisfy all these characteristics because the above items include characteristics that are contradictory to each other, but until now, it has been used as a contact of a vacuum circuit breaker. As the materials that have been used, Cu-Bi system, C
There are various alloys such as u-Te series, Cu-Cr series, and Ag-WC-Co series.

[0006]

Of these alloy systems,
The Cu-Bi alloy and the Cu-Te alloy have the characteristics that when the content of the low melting point component in the alloy is increased, the welding resistance is improved and the breaking current value is lowered, but on the other hand, the low melting point component is large. If this happens, the current cutoff characteristics will deteriorate. Cu-C
The r-alloy is relatively excellent in both current blocking characteristics and welding resistance, but has the drawback of high breaking current value. Although the Ag-WC-Co alloy has an advantage that the breaking current value is lower than that of other alloy systems, it has a problem that the current breaking characteristic is insufficient and the workability is poor.

The present invention has been made in view of the above points, and an object thereof is a contact material for a vacuum circuit breaker which has a low breaking current value and can maintain a good balance between current breaking characteristics and welding resistance. And to provide a manufacturing method thereof.

[0008]

In order to solve the above-mentioned problems, the contact material for a vacuum circuit breaker of the present invention has a weight ratio of 30.
Ag-C containing ~ 50% Ag, balance Cr
r alloy. This contact material is produced by baking Ag and Cr powders by hot isostatic pressing.

[0009]

The contact material of Ag-Cr alloy of the present invention containing 30 to 50% by weight of Ag and the balance of Cr has high vapor pressure and electric conductivity, and has good current interruption characteristics.
g and Cr, which has a low vapor pressure and good welding resistance and a getter action, are combined, and a mixed powder of Ag and Cr is produced by hot isostatic pressing under optimum conditions. A vacuum circuit breaker that can be obtained as a densified sintered body and that incorporates contacts made of this material is
Both a low breaking current value and a good current interruption characteristic can be given.

[0010]

EXAMPLES The present invention will be described below based on examples. INDUSTRIAL APPLICABILITY The present invention is used as a contact alloy having a low breaking current characteristic and a good current breaking characteristic for use in a vacuum circuit breaker, and has a high vapor pressure and a high electric conductivity.
And an alloy consisting of Cr, which has a low vapor pressure and is excellent in welding resistance and also has a getter action, was made based on the idea of the present inventors that it is suitable for the purpose.

In making an alloy of Ag and Cr,
Since Ag and Cr have no mutual solubility, an alloy having a desired composition cannot be obtained by a usual melting method.
Therefore, the present inventors initially tried to manufacture an alloy by using the powder metallurgy method. That is, powders of Ag and Cr having a grain size of 1000 mesh or less were well mixed in a ball mill, a molded body was obtained using a mold, and this was sintered in vacuum. However, Ag and Cr have poor wettability with each other,
It was impossible to obtain a true density alloy body, no matter how the mixing ratio and sintering conditions were changed. It was found that voids existed in the alloy after sintering, and this could not provide good current breaking characteristics and low breaking current characteristics even when used as contacts of a vacuum circuit breaker.

[0012] Therefore, the present inventors can expect a synergistic effect of high temperature and high pressure to produce an Ag-Cr alloy having a desired composition in a completely dense state without pores. Isostatic press [HIP (Hot I
abbreviated as “somatic Pressing”] is the most effective way to achieve the present invention.

HIP is a known technology, but a brief overview of the device is given here. FIG. 1 is a schematic sectional view showing the structure of this device. In FIG. 1, the basics of this apparatus are a high-pressure vessel 10, a heat insulating structure 11 and a heater 1 therein.
2, the whole is housed in the outer structure 13, and the object to be processed 14 is placed on a table placed on the lid 15 of the high-pressure container 10 and heated under pressure in a gas atmosphere of high temperature and high pressure. To do. The pressurizing method is usually Ar as a pressure medium.
Alternatively, an inert gas 16 such as N ₂ is used, and the gas compressor 1
The pressure in the high-pressure container 10 can be increased to 1000 Kgf / cm ² or more by means of 7, and at the same time, the heater 12 in the high-pressure container 10 can be heated to further increase the pressure by expanding the gas filled therein.

A characteristic of such HIP processing is that gas pressure is used, so that isotropic pressure can be applied to the object to be processed 14 having an arbitrary shape. Therefore, the powder or the object to be processed 14 obtained by molding the powder is vacuum-enclosed in a metal capsule or the like and subjected to the HIP process, whereby a high-density sintered body having fine particles and a theoretical density can be obtained. Further, the HIP process can also sinter the alloy powder, which is not possible by a normal sintering method.

2 (a), 2 (b) and 2 (c) are schematic diagrams showing the process of HIPing the Ag--Cr alloy of the present invention. First, a metal capsule 18 made of mild steel, stainless steel, copper or the like is filled with Ag—Cr powder 19 mixed at a predetermined ratio. Here, Ag-C
In order to confirm the proper composition of r alloy, the Cr content should be 4
The experiment was carried out with the content changed in the range of 0 to 80% by weight, which will be described later. afterwards,
A lid 21 to which a metal pipe 20 is attached is joined to the upper portion of the metal capsule 18 [Fig. 2 (a)].

Next, the metal capsule 1 with the lid 21 joined thereto
8 is charged into an electric furnace (not shown) and heated to about 100 ° C., vacuum deaeration is performed through the metal pipe 20 by an exhaust device (not shown), and sealed with a part of the metal pipe 20. [FIG.2 (b)]. At this time, A
It is also possible to adopt a method in which a mixed powder of g and Cr is molded in a mold and the molded body is sealed in the metal capsule 18.

After the metal capsule 18 is sealed, it is sealed with HI.
It is loaded in the high-pressure container 22 of the P treatment apparatus, and the temperature is 500 to 800 ° C. and the pressure is 700 to 2000 Kgf / cm in an Ar atmosphere.
The range is set to ² and the treatment is performed for 15 to 60 minutes. The temperature is set to 500 to 800 ° C., because at a temperature of 500 ° C. or lower, the metal capsule 18 is not softened and cannot be pressed.
This is because the metal capsule 18 reacts with the Ag-Cr mixed powder 19 that is the content at a temperature of 00 ° C or higher,
As to the pressure and the holding time at this time, if the ratio is within the above range in relation to the temperature, it will be separately tested that a dense alloy can be obtained without generating voids regardless of the ratio of Ag and Cr. I'm confirming. The arrow indicates that the pressure acts isotropically. [FIG.2 (c)].

The Ag--Cr alloy thus obtained was machined into a contact having a diameter of 25 mm and a thickness of 4 mm, and a vacuum circuit breaker shown in FIG.
Interruption test under conditions of 7.2KV / 12.5KA,
When the current was applied to 10 A, the breaking current value was measured. The results are shown in Table 1. As mentioned above in Table 1,
Each alloy produced by changing the mixing ratio of Ag and Cr powder,
For comparison, Cr-Cu tested under similar conditions
The system alloys and Cr-Cu-Bi system contact alloys are also shown. The alloy compositions shown in Table 1 all represent% by weight, ◯ indicates that the characteristics are good, and x indicates that the characteristics are poor.

[0019]

[Table 1] From the results shown in Table 1, the following will become clear. That is, although the Ag-Cr alloy according to the present invention has variations, the breaking current value tends to decrease as the Ag content increases. Usually, a vacuum circuit breaker of 7.2 KV / 12.5 KA class is required to have a breaking current value of 2 A or less. Therefore, the breaking current value is satisfied by including 30% of Ag. However, when Ag is 30% or less, the barrier performance is deteriorated, and when Ag is 60% or more, the welding resistance is deteriorated. Therefore, it is most effective to set the Ag content to 30 to 50%, and the alloy composition can be determined within this range. Ag content is 30
The Ag-Cr alloy of the present invention consisting of -50% and the balance Cr has a lower breaking current value than the Cr-50% Cu alloy which is the conventional contact for vacuum circuit breaker, and Cr-55% Cu-2.
Although the breaking current value is higher than that of the 0% Bi alloy, it has an advantage in that it has an excellent breaking performance.

[0020]

The conventional vacuum circuit breaker contact has a reciprocal relation between the breaking current value and the current breaking characteristic, and it was not possible to obtain one satisfying both of them, but the Ag of the present invention is 30 to 50%.
The contact of Ag-Cr alloy containing is as described in the embodiment.
By utilizing the advantages of Ag and Cr as contact materials, the composition ratio of Ag and Cr is set to the optimum range. In making it, a mixed powder of Ag and Cr is pressed by hot isostatic pressing. Since it was produced by sintering and the hot isostatic pressing conditions were set to be optimal, it was obtained as a completely dense sintered body, and as a result, there were no pores, and as a result, A vacuum circuit breaker incorporating this contact can exhibit good characteristics in both the breaking current value and the current breaking characteristic.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the main configuration of a hot isostatic pressing apparatus.

FIG. 2 shows a procedure of hot isostatic pressing used for producing an Ag—Cr alloy of the present invention, (a) shows a state in which a powder is filled in a capsule, (b) shows a state in which it is sealed in a vacuum,
(C) is a schematic diagram showing the state of storing in a high-pressure container and performing high-temperature high-pressure processing

FIG. 3 is a schematic cross-sectional view showing the configuration of the main part of a vacuum circuit breaker.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulation cylinder 2 Fixed energizing rod 3 Movable energizing rod 4 Fixed contact 5 Moving contact 6 Arc shield 7 Bellows 8 Lid 9 Lid 10 High pressure container 11 Heat insulation structure 12 Heater 13 Outer structure 14 Object to be treated 15 Lid 16 Inert gas 17 Gas compressor 18 Metal capsule 19 Ag-Cr mixed powder 20 Metal pipe 21 Lid 22 High pressure container

Claims (3)

[Claims] 1. A contact material for a vacuum circuit breaker, which is an Ag--Cr alloy containing 30 to 50% by weight of Ag and the balance being Cr. 2. The method for producing a contact material for a vacuum circuit breaker according to claim 1, wherein the powder of Ag and Cr is sintered by hot isostatic pressing. 3. The hot isostatic press has a temperature of 500 to 800.
15 to 60 at ℃ and pressure of 700 to 2000 kgf / cm ² .
The method for producing a contact material for a vacuum circuit breaker according to claim 2, wherein the method is performed by holding for a minute.