JPS588529B2 - Method for manufacturing electrode alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a low-melting-point, high-vapor-pressure element that has copper as its main component and is capable of forming a solid solution of 1% by weight or less in copper. Based on the above, the method for producing an alloy for electrodes containing up to 25% by weight, particularly low melting point alloys such as lead and bismuth suitable for use as electrodes for vacuum breaker,
The present invention relates to a method for manufacturing a copper alloy electrode material containing a large amount of high vapor pressure elements.

Electrical properties that the electrode material for a vacuum breaker should have include welding resistance, pressure resistance, breaking properties, and low cutting properties.

Conventional electrode materials for vacuum circuit breakers are generally made of copper alloy as a main component and have other additive elements to maintain pressure resistance and welding resistance.

In the prior art, it is known that adding iron group elements such as cobalt and iron is effective in increasing the voltage resistance characteristics of the former (Japanese Patent Publication No. 48-40384).

On the other hand, in order to satisfy the latter welding resistance property, it is known that alloys containing small amounts of lead or bismuth, which are low-melting elements that do not dissolve in copper, are effective (Japanese Patent Publication No. 41-1
No. 2131).

It is also known that adding lead-bismuth not only improves welding resistance, but also that low cutting current characteristics can be obtained, especially when lead and bismuth are contained in large amounts.

However, if these low melting point elements are contained in large amounts, they may seep out during electrode soldering, degassing, or during shutoff, or they may evaporate and adhere to the inner wall of the vacuum valve. There was a problem in that the pressure resistance suddenly deteriorated.

Therefore, in the past, it was difficult to maintain low cutting current characteristics by containing such large amounts of lead, bismuth, etc.

In order to eliminate these drawbacks, it is recommended that the low melting point element, which is not normally dissolved in copper, be uniformly dispersed not only in the grain boundaries of copper but also throughout the entire matrix, and that it be made into fine spherules. Conceivable.

That is, it is sufficient to use some method to confine the elements present in large amounts at the grain boundaries within the crystal grains and prevent them from seeping out and evaporating.

However, it has been difficult to achieve sufficient improvement by considering conventional agglomeration methods, methods of adding a third element, or general heat treatment.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and is an electrode that reduces seepage and evaporation of low melting point and high vapor pressure elements contained in large amounts, and has large current cutoff characteristics and stable low cutting characteristics. The purpose is to provide alloys for

The present invention has copper as its main component, and contains a low melting point, high vapor pressure element that can dissolve in copper in a solid state of 1% by weight or less, from above the solid solubility limit of the element in copper to 25% by weight or less. In the method for producing an alloy for electrodes, the method includes at least a crystal refining processing step in which processing strain is applied after melting and solidification of the alloy, and a spheroidizing annealing step in which the alloy subjected to the processing step is annealed at a temperature at which it recrystallizes. The above objective was achieved by including the test one or more times.

In the same manufacturing method for electrode alloys, after the alloy is melted and solidified, there is a primary spheroidizing annealing process in which copper dendrites undergo secondary recrystallization below the melting point of the alloy, and crystal refinement in which processing strain is applied. The above object is also achieved by including the processing step and the secondary spheroidizing annealing step of annealing at a temperature at which the alloy recrystallizes again at least once.

The principle of the present invention will be explained below.

If the copper alloy contains trace amounts of lead, bismuth, etc., there will be no adverse effects due to evaporation or seepage during soldering or degassing during vacuum valve assembly.

On the other hand, if the above elements are contained in a weight coefficient of about 3 or more,
The elements adhere to the inner wall of the vacuum valve due to evaporation or staining, resulting in deterioration of the pressure resistance characteristics and often making it impossible to shut off.

On the other hand, it is known that copper alloys containing a large amount of the above-mentioned elements have excellent low cutting properties, so it has been desired to take appropriate measures to prevent evaporation and seepage. .

As a result of studying this seepage phenomenon, the present inventors confirmed that this seepage is mostly lead, bismuth, etc. present in the grain boundaries of copper.

In other words, the above elements do not form compounds with copper,
Almost no solid solution.

Therefore, regardless of the amount of content, it usually exists in a continuous line at the copper grain boundaries.

When this is heated to a temperature higher than the melting point of the added element, only the added element begins to melt, and at the same time the contained gas expands.
This acts as a driving force, causing the element to seep out through the grain boundaries of the copper, causing seepage and evaporation.

Therefore, the higher the heating temperature, the greater the gas expansion.
The amount of stain will also be large.

In addition, lead, bismuth, etc. in ordinary cast ingots containing 3% by weight or more of lead, bismuth, etc. are continuously connected to the gaps between copper dendrites, but this is a state in which staining easily occurs. It becomes.

The present inventors attempted to improve the silk weave by discontinuously dividing and spheroidizing the lead and bismuth that are continuous at the grain boundaries, or by confining them within the crystal grains.
We have discovered an effective method to prevent seepage.

In other words, if a normal casting ingot is heated to just below the melting point of the alloy, the copper dendrite in the casting will be 2.
Collapse or grain growth occurs due to the next recrystallization phenomenon.

This can be inferred from conventional knowledge.

In view of this phenomenon, the present invention investigated the following points and discovered a method for preventing seepage.

That is, (1) the heating causes copper dendrite collapse, and lead and bismuth are separated from a continuous shape into spherical shapes and become discontinuous.

(2) Some lead and bismuth are trapped within the steel grains due to grain growth.

(3) The effects of (1) and (2) above increase the elongation of the alloy itself, making it possible to refine the recrystallization by some forging (for example, in a cast ingot of copper-7 weight-lead alloy, The elongation is 2 to 4 inches, but the elongation becomes 8 to 10% by operating (1) and (2)) As described in (1)
In order to achieve (3), as shown in Figure 1, there are two main steps: primary spheroidizing annealing (desirably a mixture just below the melting point) to increase spheroidization and elongation, and forging. Three steps are required: a crystal refining process and a secondary spheroidizing annealing process (preferably at a temperature just below the melting point) for final further recrystallization and spheroidization.

In the secondary annealing, lead, bismuth, etc. are refined, and at the same time, 70 to 80% of the lead and bismuth content is confined within the steel grains, which can significantly prevent conventional oozing. It becomes like this.

Therefore, in the vacuum valve using the electrode alloy of the present invention, it is possible to cut off a large current while exhibiting low cutting characteristics.

Although it is possible to prevent staining to some extent by conventional spheroidizing annealing alone, lead, screws, etc. Because the mass itself was roughly spherical, there were many drawbacks, such as the cutting current value varying depending on the position of the arc at the time of cutting.

This force ζIn the present invention, at the same time as preventing seepage, lead,
By finely distributing bismuth or the like, stable low cutting characteristics can be obtained, which improves the reliability of the vacuum valve.

In addition, a series of experiments have shown that when melting an electrode alloy, if the lead or bismuth content exceeds 25% by weight, liquid phase separation occurs, making it difficult to melt, and also significantly deteriorating the pressure resistance characteristics of the valve electrode. It has been revealed that

Furthermore, if the content is large as mentioned above, problems such as serious contamination of various exhaust equipment surfaces in the electrode manufacturing process will occur, so the maximum content of low melting point, high vapor pressure elements is 25% by weight. % or less.

According to a series of cutting current characteristic tests, it has been found that the effect does not change if the content of this low melting point, high vapor pressure element is 7% by weight or more. The alloy is suitable for practical use.

Note that the primary spheroidization step in the above description can be omitted when the cooling rate is slow, for example, when solidification is performed in a crucible without being cast into a mold.

Examples will be described below.

Example 1 Oxygen-free copper (OFC) and degassing purified lead (JIS Class 1) were used as raw materials for a copper-7 wt% lead alloy.
A graphite crucible was placed on the outside under a pressure of ×105 torr, and an alumina crucible of 60φ was placed on the inside for high-frequency melting.

The amount dissolved was 2.5 kg including copper and lead.

In addition, to prevent lead loss due to evaporation under high-temperature vacuum conditions,
After confirming that the copper had melted, the vacuum atmosphere was replaced with an argon gas atmosphere of 10 to 50 torr, and then the copper was added and solidified in the crucible.

The ingots melted using this method are not processed directly,
Primary spheroidizing annealing was performed by heating at 5×10 5 torr and 900° C. for one hour.

Figure 2a (400x magnification) shows the tissue as solidified;
FIG. 2b (400x magnification) shows the structure of the first spheroidizing annealing.

In Fig. 2a, lead is continuously connected along the grain boundaries, but in Fig. 2b, it becomes almost spheroidal and is partially confined within the crystal grains.

Furthermore, the ingot material after the heat treatment was subjected to cold tap forging.

The degree of processing at this time is approximately 50%.

This ingot was heated again at 5×10 5 torr and 900° C. for 1 hour to perform secondary spheroidizing annealing.

The structure after heating is as shown in Figure 2C (magnification: 400x), in which the crystal grains have grown large, lead is distributed in a fine spherical shape, and the matrix is present both inside and outside the copper grain boundaries. It can be seen that they are evenly distributed over the entire area.

Furthermore, the lead analysis value after the collection process was maintained at approximately 7% by weight, so there was no problem.

Electrodes were cut out from the ingot after the various treatments described above, and assembled into a vacuum valve to simulate the heat treatment (welding temperature 850 to 900°C) in the valve manufacturing process.
When heating was performed at 900° C. for 1 hour and the state of lead oozing was examined, almost no lead oozing was observed.

Next, when we measured the cutting current of the vacuum valve at 6.5kV and 15A test current, the average was 4.6A, which was less than half that of copper alone, and even in repeated tests, the fluctuation range was very small and the cutting current was stable. It showed cutting characteristics.

Example 2 Copper-4wt% lead-
A 3% by weight bismuth alloy was prepared.

The purity of the bismuth used was 99.9%.

Next, as an ingot, 5 × 105 torr, 850
It was heated at ℃ for 1 hour to perform primary spheroidizing annealing.

In this result, the same tissue change as in Example 1 occurred,
It was found that the lead-bismuth alloy was fragmented and spheroidized.

Furthermore, the above ingot was subjected to cold tap forging to a degree of processing of 50%, and then 1
Second spheroidizing annealing was performed by heating for a certain period of time.

The distribution of lead and bismuth at this time is also fine and spherically dispersed, just as in Example 1 when lead is added.

Next, after processing it into an electrode shape in the same way, we simulated the degree of soldering and heated it at 5 x 105 torr and 850 to 900°C, and investigated the seepage of the lead-bismuth alloy. There is very little contamination on the inner wall and electrode surface, which is extremely good. Ta.

Furthermore, when we conducted a cutting current test using the same method, we found that
The average current was 4.1 A, and compared to Example 1, it had excellent low cutting characteristics.

Example 3 In this example, the first
The subsequent spheroidizing annealing step was omitted, direct processing was added, and spheroidizing annealing was subsequently performed.

That is, samples containing 0.7% by weight, 3% by weight, and 7% by weight of lead were each forged by swaging with a working degree of 75%, and then forged at 925°C in a vacuum of 5 x 105 torr for 3 hours. When the structure of the sample which had been subjected to spheroidizing annealing was examined, it was as shown in Fig. 3 a-i.

The magnification of FIG. 3 is 100x.

In this example, as well as in Example 1 and Example 2,
Lead was dispersed within the copper crystal grains, and the same effects as in Examples 1 and 2 were obtained.

In the above embodiments, lead and bismuth were used as low melting point, high vapor pressure elements, but lead is particularly effective.

On the other hand, the present invention is also applicable to electrode alloys in which other elements such as tellurium, selenium, cadmium thallium, etc. are used.

Note that the method of the present invention is also effective in combination with silver and a similar element that does not form a solid solution with silver.

In addition to the crucible-solidified material, the present invention can also be fully applied to all-type casting materials.

In addition to tap forging, it is also possible to use rolling, wire drawing, etc. as a method of increasing the elongation of the material itself simultaneously with spheroidization through primary spheroidizing annealing to obtain a processed structure.

In addition, the first and second spheroidizing annealing temperatures have the greatest effect when they are just below the melting point, but the slight effect is 300
It occurs from around ℃, so it is from 300℃ to 950℃.
It is possible to appropriately select the temperature within the range of °C.

As explained above, the present invention has copper as its main component, and contains a low melting point, high vapor pressure element that can form a solid solution of 1% by weight or less in copper at a temperature higher than the solid solubility limit of the element in copper. In the method for producing an alloy for electrodes containing up to 25% by weight, after melting and solidifying the alloy, at least a crystal refining process in which processing strain is applied and a spheroidizing annealing process in which the alloy is annealed at a temperature at which it recrystallizes. Included at least once.

In the same manufacturing method for electrode alloys, if necessary, after melting and solidifying the alloy, a primary spheroidizing annealing process is performed, in which the alloy is annealed at a temperature at which it recrystallizes, and a crystal refining process in which processing strain is applied. , and a second spheroidizing annealing step of annealing at a temperature at which the alloy recrystallizes, at least once.

Therefore, it prevents the seepage of low melting point, high vapor pressure elements,
It has the excellent effect of realizing an electrode alloy for a large current cutoff vacuum valve that has stable and low cutting characteristics.

[Brief explanation of the drawing]

Fig. 1 is a process diagram showing an example of the method for manufacturing an electrode alloy according to the present invention, and Fig. 2 shows the structure of a copper-7% by weight lead electrode alloy manufactured by the manufacturing method shown in Fig. 1. . FIG. 3, a micrograph at a magnification of 400 times, shows copper-0.7 produced by another manufacturing process of the electrode alloy according to the present invention.
1 is a micrograph at 100x magnification showing silk weave of wt% lead electrode alloy, copper-3wt% lead electrode alloy, and copper-7wt% lead electrode alloy.

Claims (1)

[Scope of Claims] 1. A substance containing copper as a main component and having a low melting point such that it can form a solid solution with copper in an amount of 1% by weight or less. The high vapor pressure element is
In the method for producing an alloy for electrodes containing up to 5% by weight, the alloy is melted and solidified, and then the alloy is melted and solidified, followed by a crystal refining processing step in which processing strain is applied, and spheroidizing annealing in which the alloy that has undergone the processing step is annealed at a temperature at which it recrystallizes. 1. A method for producing an electrode alloy, the method comprising the steps of: at least once. 2. The method for producing an electrode alloy according to claim 1, wherein the low point, high vapor pressure element is lead. 3. The method for producing an electrode alloy according to claim 1, wherein the low melting point, high vapor pressure element is bismuth. 4. The method for producing an electrode alloy according to claim 1, wherein the low melting point, high vapor pressure element is a Button bismuth alloy. 5. An electrode whose main component is copper, and which contains a low melting point, high vapor pressure element that can form a solid solution of 1% by weight or less in copper, from the solid solubility limit of the element in copper to 25% by weight or less. In the method for producing an alloy for use, after melting and solidifying the alloy, a primary spheroidizing annealing step of annealing at a humidity where the alloy recrystallizes;
A method for producing an electrode alloy, comprising at least one crystal refining process in which processing strain is applied, and a secondary spheroidizing annealing process in which the alloy is annealed at a humidity that recrystallizes the alloy. 6. The method for producing an electrode alloy according to claim 5, wherein the low melting point, high vapor pressure element is lead. 7. The method for producing an electrode alloy according to claim 5, wherein the low melting point, high vapor pressure element is bismuth. 8. The method for producing an electrode alloy according to claim 5, wherein the low melting point, high vapor pressure element is a lead-bismuth alloy.