JP2937620B2 - Manufacturing method of contact alloy for vacuum valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a contact alloy for a vacuum valve, and more particularly to a method for producing a contact alloy for a vacuum valve capable of reducing the frequency of restriking and improving the breaking performance.

[0002]

2. Description of the Related Art The characteristics required for vacuum valve contacts are as follows.
It has resistance to welding, withstand voltage and high breaking. However, these three requirements require conflicting physical properties, making it difficult to make them ideally compatible. Therefore, the priority requirement of the circuit to be applied is first, and the other requirements are slightly sacrificed. The current situation is to respond.

[0003] For example, conventionally, in a high-voltage, large-capacity vacuum circuit breaker, a welding-preventive component (Bi, Te, Pb, etc.) contains 5 parts.
It is known that a Cu alloy containing not more than% by weight (hereinafter, referred to as wt%) is provided as an electrode contact (Japanese Patent Publication No. Sho 4).
No. 1-12131).

[0004] However, in recent years, with respect to demand for high voltage, withstand voltage is not sufficient. In other words, the vacuum circuit breaker has features that are superior to other circuit breakers, such as small size, light weight, and maintenance-free environmental harmony. In addition to the application to circuits of higher voltages, the demand for opening and closing special circuits such as capacitor circuits is also rapidly increasing, so that higher voltage resistance is required. One of the important factors hindering the achievement is a re-ignition phenomenon and a re-arc phenomenon.

[0005] Although the re-ignition phenomenon is regarded as important from the viewpoint of improving the reliability of products, not only its prevention technique but also its direct cause has not been clarified yet.

[0006] With the increase in the withstand voltage, the contact material is required to have a higher withstand voltage and a characteristic in which a re-ignition phenomenon occurs less frequently. In order to achieve high withstand voltage and no restriking of the contact material, it is necessary to minimize the amount of the fragile anti-welding component itself which becomes a defect in pressure resistance as much as possible or to avoid excessive concentration. It is desirable to minimize the number of pinholes and the like and to increase the strength of the contact alloy itself. From these viewpoints, the aforementioned Cu
-Bi alloys are not satisfactory.

[0007] Further, although other conventional contact materials such as Cu-W contacts or Cu-WC contacts are considerably excellent in withstand voltage, this sintered contact alloy is not suitable for manufacturing because of its production method. However, there is a drawback that the re-ignition phenomenon is liable to occur because of the tendency for the residual to occur and the active emission of thermoelectrons.

On the other hand, in a field requiring a high withstand voltage and a large current interruption, a Cu—Cr alloy is used. Cu-
The Cr alloy has the advantage that the vapor pressure difference between the constituent elements is smaller than other contact materials, so that uniform performance can be expected. Depending on the usage, the feature is a contact alloy that can be fully utilized. .

This Cu-Cr-based contact alloy is generally manufactured as follows. For example, Japanese Patent Publication No. 59-3076
According to Japanese Patent Publication No. 1 (1993), Cr powder and a small amount of Cu powder are mixed, the mixed powder is filled in a die, press-molded with a small pressure, and the molded body is taken out from the die. This is a method of forming a Cr skeleton by vacuum sintering and finally infiltrating Cu.

[0010] Recently, a method has been disclosed in which a Cr powder is poured into a mold, Cu pellets are placed thereon, and the whole is degassed, and then infiltration is performed under reduced pressure. (See JP-A-59-25903).

Further, a method of obtaining a Cu—Cr alloy by mixing the final target values of Cu and Cr from the beginning and subjecting the obtained compact to solid-phase sintering at or below the melting point of Cu is also carried out. Have been done.

[0012]

However, these alloys are generally manufactured by the powder metallurgy technique as described above, and their raw material powder management, sintering technology, and infiltration technology involved in restriking occur. Because it ’s not well established,
It is not yet satisfactory in terms of the frequency of restriking and the breaking performance.

An object of the present invention is to provide a method of manufacturing a contact alloy for a vacuum valve, which can significantly reduce the frequency of restriking and improve the breaking performance.

[0014]

Means and Functions for Solving the Problems The present inventor has provided:
As a result of studying the selection of raw material Cr, sintering conditions, infiltration conditions, and the like for this manufacturing method in order to reduce the frequency of occurrence of restriking of the contact alloy for vacuum valves and to stabilize the cutoff characteristics, the present invention was completed. Was completed.

The method for producing a contact alloy for a vacuum valve according to the present invention comprises the steps of: starting material Cr powder as an arc-resistant material, a Cr compact, mixed powder of Cr and Cu as a conductive material, surface of a compact of Cr and Cu 2 × 10 ⁻⁷ Torr at approximately 800 ° C.
a first step in which a high-vapor-pressure material having a higher vapor pressure than r is applied as a protective layer to a thickness of 0.05 to 5 μm or covered or alloyed, and a contaminated atmosphere being heated by the high-vapor-pressure material A second step of obtaining a Cr sintered body or a Cr-Cu sintered body from the material with a protective layer obtained in the first step while protecting from the first step, and part or all of the period of the second step. With the progress of sintering of Cr or Cr-Cu,
Cr skeleton, Cr-Cu skeleton, and Cr-Cu alloy are controlled while controlling the sintering temperature, time, heating / cooling rate, and atmosphere evaporation amount so that the remaining high vapor pressure material becomes 0.25 wt% or less. By providing the third step, the frequency of occurrence of restriking is reduced and the breaking performance is improved. Next, an example of the raw material Cr used in the method for producing a contact alloy for a vacuum valve of the present invention will be described.

At present, the refining method of metal Cr supplied industrially is Cr Cr such as FeCr ₂ O ₄ or MgCr ₂ O _4.
Reduction of ore with other metals such as Al or Si
(Reduction method) and a method of dissolving the Cr ore to separate undissolved non-metallic impurities, and electrically dispersing this as an electrolytic solution to obtain metallic Cr (electrolytic method). .

However, the Cr obtained by the former reduction method
Means that the gas amount (oxygen, nitrogen) is about 1000 ppm,
several thousand ppm to 100 of impurities such as l, Si and Fe
It contains about 00 ppm. On the other hand, Cr in the latter electrolytic method has a gas amount (oxygen, nitrogen) of 1000 ppm.
It is remarkably large at 1 to 10000 ppm and relatively low in impurities such as Al, for example, generally contains about 100 ppm or less.

In the present invention, the Cr-C mixed powder obtained by adding carbon powder to Cr powder obtained by pulverizing Cr obtained by the above-mentioned reduction method or electrolytic method, if necessary Atmosphere, especially above 800 ° C and 140
The heat treatment is performed at least once at a temperature of 0 ° C. or less.
Thus, degassed Cr powder can be obtained.

If the temperature is less than 800 ° C., the degassing efficiency of the Cr—C mixture and the compact is inferior, and the effect of reducing restriking is small. At 1400 ° C. or higher, the effect is significant, and is particularly effective for degassing efficiency.
It is not advisable to evaporate violently, resulting in a large loss of materials and a large contamination of the furnace. By performing the heat treatment before the powdering step in this way, it is possible to more advantageously reduce restriking than to perform the heat treatment after forming the Cr powder. In order to further enhance the performance of the vacuum valve, it is effective not only to perform the step before processing the metal Cr aggregate, but also to superimpose the heat treatment in the subsequent step if necessary.

With respect to the adjustment of the degassed Cr powder, the degassed Cr powder obtained by pulverizing the degassed Cr mass obtained by the heat treatment is made to be a degassed Cr powder having a predetermined particle size without being stained. The particle size of the degassed Cr powder is limited by contact manufacturing technology such as contact characteristics as a vacuum valve and sintering. The average particle size of the degassed Cr powder is preferably from 5 to 250 μm. Degassing Cr
If the average particle size of the powder is less than 5 μm, undesired pores are likely to be formed in the skeleton or / and the contact material after sintering or / and infiltration, and a large amount of corresponding gas tends to remain. Contact characteristics as a valve (for example,
This is unfavorable for restriking characteristics).

When the particle size of the degassed Cr powder exceeds 250 μm, remarkable variations are observed in all of the welding resistance, the withstand voltage characteristics, and the cutoff characteristics. Segregation also appears in the contact material, which is not preferable from the viewpoint of vacuum valve reliability.

On the other hand, it is desirable that the oxygen and nitrogen gas in the degassed Cr powder be suppressed to 200 ppm or less, respectively. These gases are composed of the total amount of the gas contained in Cr and the adsorbed gas. Since the gas contained in the former has been minimized in the heat treatment step of the raw material Cr, it is particularly important to reduce the amount of adsorbed gas in the latter step. That is, it is an important point that the pulverization is performed without soiling, and the condition during the pulverization is that the Cr powder does not generate excessive heat due to the pulverization energy and oxidation does not proceed. Therefore, intense pulverization that generates large frictional heat should be avoided. Pulverization in a non-oxidizing atmosphere is also effective. Especially when the Cr particle size is 100
In the case of μm or less, it is necessary to give due consideration to such points.

When the gas amount is 200 ppm or more, even if a Cu-Cr alloy is formed by using Cr powder, the gas amount in the alloy is maintained at a preferable low level (for example, 200 ppm or less, preferably 100 ppm or less). It is difficult. That is, at the heat treatment temperature selected when sintering and / or infiltrating the vacuum valve contact, it is somewhat insufficient to advance the purification of Cr. When the gas amount (in this case, oxygen) in the Cu-Cr alloy is 200 ppm or more, the occurrence of restriking may occur frequently.

Regarding the molding, the Cr-C mixed powder Cu-
8 tons / cm ^{2 of} Cr mixture A compact is formed under the following external pressure or the pressure of the weight of the Cr powder. The molding pressure at the time of obtaining a compact is a factor that determines the amount of Cr in the Cu—Cr alloy, and is important especially in the production by the infiltration method (in the case of the second invention). Therefore, here, a process in the case of the infiltration method will be described.

The amount of the degassed Cr powder in the Cu (or / and Ag) -Cr alloy can be selected within a range of 20 to 80 wt%. The molding pressure for this is 8 ton / cm ² Less than,
Preferably 7.5 tons / cm ² Below, more preferably 7
Ton / cm ² It is as follows. This is 8 tons / cm ² If the pressure exceeds, the amount of Cr after infiltration exceeds 80 wt%,
It is excluded to leave the gist of the present invention. 80wt
% Can be dealt with by using pure Cr as a skeleton. However, to secure an alloy with a low Cr amount of about 20%, pure C must be used as a skeleton.
It is not possible to select r, and when obtaining a Cr-C mixed powder in
This is achieved by employing a Cr + C + Cu mixed powder containing an appropriate amount of The molding pressure at this time is 8 tons / cm ² depending on the amount of the Cr powder to be mixed. The following pressures can be freely selected: The molding pressure is 8 tons / cm ² Exceeding the ratio is not preferred because cracks may occur in the molded article during heating.

Regarding the sintering, the solid phase sintering method is a simple process because the degassed Cr powder, Cu and / or Ag, which are conductive components, and the final component are mixed. Therefore, the process in the case of the infiltration method is shown here.

The compact obtained as described above is placed in a heating furnace together with a sintering vessel and sintered. The sintering atmosphere needs to be a non-oxidizing atmosphere, for example, in a vacuum or in hydrogen. Of these atmospheres, the filled Cr
In order to remove oxygen and nitrogen occluded in powder, pressed compacts and containers, etc., vacuum (1 × 10 ⁻⁵ T)
orr) atmosphere is preferred.

The sintering temperature and the sintering time to be applied affect the density of the skeleton, that is, the porosity of the skeleton. For example, in order to make the relationship between the Cr skeleton and the amount of Cu infiltrated into the voids close to 50:50 by weight, the porosity is preferably set to 40 to 50%. Sintering temperature 800 to 1050 ° C, preferably 900 to 950 ° C, sintering time 0.25 to 2 hours,
Preferably, the range is 0.1 to 1 hour. The above conditions are appropriately selected according to the ratio of Cr to Cu.

The infiltration material Cu and / or Ag is placed on the upper surface and / or lower surface of the obtained skeleton, and the whole is heated, for example, in a vacuum (1 × 10 ^-4 to 1 × 10 ^-6 Torr). Then, Cu and / or Ag are infiltrated into the skeleton void.

The temperature during infiltration is a temperature higher than the melting point of Cu and / or Ag. 1100 to 1300 for Cu
In the case of ° C and Ag, the temperature is preferably in the range of 1000 to 1100 ° C. The infiltration time is set to a time sufficient to completely impregnate these melts into the voids in the skeleton.

In the above-mentioned infiltration step, a layer of infiltrated metal is formed on at least a part of the surface of the skeleton at the time of warming, so that the obtained contact alloy has a silver brazing property (when brazing the conductive rods). ) Can be excellent. Describing the alloy composition ratio, each component of the finally obtained contact alloy preferably has the following range (however,
A trace amount of the anti-welding component is omitted). Cu and / or Ag: 80 to 20% by weight Cr: 20 to 80% by weight

When the Cr content in the alloy is more than 80%, Joule welding occurs frequently, which is not preferable for the surface roughness deeply related to restriking, but also at a voltage of 7.2 KV.
In this case, it is difficult to block 40 KA. Conversely, the amount of Cr is 2
If it is less than 0%, for example, when the voltage is cut off at 40 KV, the arc resistance cannot be maintained, and large arc consumption occurs, which is not preferable.

In the above composition range, the amount of Cr which forms a solid solution in the Cu and / or Ag phase, which is a highly conductive component, is 0.01 to 0.35 wt%, thereby stabilizing the conductivity characteristics. It is preferable in making it.

Next, the processing atmosphere will be described. The processing in each of the above steps is preferably performed in a non-oxidizing atmosphere, specifically, in an inert gas such as an argon gas, H ₂ gas, or N ₂ gas. Or in a vacuum.

[0035]

EXAMPLES Examples of the present invention will be described below based on specific embodiments. First, the configuration of a vacuum valve (vacuum circuit breaker) applicable to the alloy obtained by the method of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 1 denotes a shut-off chamber. The shut-off chamber 1 is formed of an insulating container 2 made of an insulating material in a substantially cylindrical shape, and a metallic material provided at both ends thereof through sealing fittings 3a and 3b. And the lids 4a and 4b are airtight. A pair of electrodes 7, 8 attached to opposing ends of the conductive rods 5, 6 are disposed in the shut-off chamber 1, and an upper electrode 7 is provided.
Is a fixed electrode, and the lower electrode 8 is a movable electrode. A bellows 9 is attached to the electrode rod 6 of the movable electrode 8, and the movable electrode 8 is held while keeping the inside of the shut-off chamber 1 vacuum-tight.
Can be moved in the axial direction. A metal arc shield 10 is provided above the bellows 9 to prevent the bellows 9 from being covered with the arc vapor. Also,
Numeral 11 denotes a metallic arc shield provided in the shut-off chamber 1 so as to cover the electrodes 7 and 8;
Is prevented from being covered with arc vapor. further,
The electrode 8 is fixed to the conductive rod 6 by a brazing portion 12 or is crimp-connected by caulking as shown in an enlarged manner in FIG. The contact 13 a is fixed to the electrode 8 by brazing 14. In addition, 13b in FIG. 1 is a fixed side contact. The contact alloy manufactured in the present embodiment is suitable for forming both or one of the contacts 13a and 13b as described above. Next, the operation of the present invention will be described based on the above steps.

With regard to the control of impurities in the Cr powder, the present inventors made detailed observations on the total amount of gas released during the process of heating the contact material and the form of release.
There is an important correlation between these factors and the occurrence of restriking,
In particular, for each of the raw materials constituting the contact material, it has been found that the re-ignition phenomenon can be effectively suppressed by controlling the release of these gases, in particular, the release of the gas suddenly generated near the melting point. That is, as the contact material is heated, most of the adsorbed gas is degassed below the melting point and a solid-dissolved gas is released in the vicinity of the melting point. For a short period of time (for example, on the order of several milliseconds), a pulse-like burst of gas is emitted (several times to hundreds of times).

Although these sudden gases contain a small amount of C ₂ H ₂ , CH _4, etc., these sudden gases are contained in the contact material because they are mainly composed of oxygen such as CO, CO ₂ , O _2. It is considered to be released by decomposition of the oxides.

According to the study of the present inventors, contact materials in which re-ignition occurs frequently emit a large amount of sudden gas.
Therefore, according to the above findings, it is considered that the occurrence of the re-ignition phenomenon can be reduced by holding the contact material at a temperature equal to or higher than its melting point and releasing the burst gas in advance.

However, the contact material for the vacuum circuit breaker is C
In order to contain a considerable amount of u and decompose and remove these oxides, for example, a temperature of about 1200 ° C. or more is required at a degree of vacuum of 10 ⁻³ to 10 ⁻⁴ Torr. Applying the above-described heat treatment to a contact material containing a highly conductive material such as Ag or a welding prevention material such as Bi or Te may cause fluctuations in components and cause inconvenience in the management of contact characteristics.

For example, when heating Cu, 400-
At around 550 ° C, it emits several kinds of gases extremely violently.
Some of these released gases combine with Cr and the like in the process of raising the temperature to form relatively stable compounds, some of which decompose during the melting operation, while others remain and remain in a sudden gas. Contributes to

Even if Cu having a purity of 99.9999% is used as a raw material, such a sudden release of gas is still recognized when the oxidation or gas adsorption is allowed to proceed.

The above observations show that, in the contact material including the anti-weld material, the impurities which cause the sudden gas are preliminarily determined by individually heat-treating the highly conductive material such as Cu and the anti-weld component such as Bi. This suggests the necessity of elimination, and in the process of manufacturing or heat-treating the contact alloy, the contact alloy, which is in direct contact with the liquid phase of the contact alloy, which is partially or entirely in a liquid state, is released from the crucible, boat, plate, etc. Suggests the need to control the pollution they receive.

In response to the former finding, the present inventors have found that heat treatment of the constituent elements individually to reduce the sudden gas
It is recognized that it is effective to some extent and the probability of restriking tends to decrease accordingly.

In response to the latter finding, the present inventors have determined that the material of the crucible or the like in contact with the liquid phase and the physical and chemical state of the surface affect the form of sudden gas release, and are also related to the reignition probability. In addition, it was recognized that the former is indispensable for reliably and efficiently improving the effect of reducing sudden gas emission by controlling the contact elements at the component element level.

Although a few findings on the re-ignition are effective in reducing the re-ignition, the improvement is still required in order to further reduce the re-ignition and increase the breaking capacity. There is a need to recognize the necessity and to develop other measures to effectively exert the above-mentioned knowledge and technology effects.

For example, by superimposing the above two or three findings,
The production of a -Cr alloy has a greater synergy than when used alone, thus indicating the necessity of comprehensively managing a series of processes. In particular, it is necessary to fully understand the raw material technology and the cooling technology. That is, it is considered that the contents (impurities) and states (surface oxidation, presence / absence of inclusions) of the raw materials Cr, Cu, and the like are important as one of the causes of the sudden gas described above.

Foreign substances such as oxides, which have an oxide form from the beginning and are simply mixed into the raw material powder, are removed by a sedimentation method using a difference in specific gravity from the raw material powder, or a difference in particle size is used. However, foreign substances such as the oxides can be collected in one place by mainly removing them by sieving in advance, or by performing an infiltration step when infiltrating a highly conductive material into the skeleton from one direction. Providing these operations also showed good results in reducing the occurrence of restriking.

However, the problem is impurities present as a solid solution or precipitated in the raw material. It was considered that these could not be removed by sieving, specific gravity difference or infiltration process, and accounted for one factor of potential restrike. However, it is still recognized that the occurrence of the re-ignition phenomenon tends to be further reduced by thoroughly examining the raw material powder (Cr powder) and selecting a raw material powder having less impurities as one means of solving the problem. Was.

As described above, although the selection of the raw material powder having a small amount of impurities (mainly oxides in this case) is effective for reducing the re-ignition phenomenon, there is still room for improvement if strict experiments are carried out. The present inventors have confirmed that

That is, a lot in which impurities in the Cr powder are substantially not recognized is selected, and this is used as a Cr raw material. Similarly, a lot of Cu that has been thoroughly examined is used as a raw material to prepare a Cu—Cr alloy. Despite the production, there were obtained alloys with precipitates and alloys without precipitates.Comparing the frequency of restriking, the alloys with the former were used. It was found that more occurred in the vacuum valve.

Such precipitates are formed by (a) certain elements which were initially dissolved in Cr powder and (b) sintered or /
And impurities generated later by the reaction with the atmosphere during infiltration. Therefore, in order to further improve the re-ignition characteristics, (a) besides impurities such as oxides simply mixed in the raw material, (b) certain elements particularly solid-solved in the raw material (solid solution state) Microscopically cannot be detected and confirmed microscopically), indicating that it is necessary to pay attention also to the presence of oxides generated by the reaction with oxygen supplied from the inside of the raw material or from the atmosphere. It was considered.

Based on such knowledge, the present inventors first made a specific treatment on the raw material Cr before pulverizing the raw material Cr, that is, the raw material Cr was previously heated to 1300 ° C. to a temperature just below the melting point. After the heat treatment in the range, the technology of pulverizing this was put to practical use. Cr-Cu using the Cr powder thus obtained
The contacts contributed to the suppression of restriking. However, this technique has a great effect on suppressing the occurrence of restriking,
To give Cr a high temperature treatment just below the melting point,
Improvements have been required, such as a large loss of material due to remarkable evaporation of r, and a large contamination of the production equipment system.

However, the fact that a great effect has been obtained by the above-mentioned heat treatment in the temperature range of 1300 ° C. to just below the melting point is based on the fact that the above consideration is an important guideline for suppressing restriking from the material side. It does not change.

As another technique, a Cr-C mixed powder obtained by adding carbon having the same particle size to Cr powder pulverized to a predetermined particle size is cooled to a lower temperature, that is, 800 to
A heat treatment in a heating range in a temperature range of 1400 ° C. is given, and the resulting powder is pulverized to a predetermined particle size.
A technique for producing an r-Cu alloy, that is, a Cr powder preferable for suppressing restriking by adding a process of adding carbon powder has also been developed.
However, this technique is also highly effective in suppressing restriking, but since the required amount of C (carbon) depends on the degree of contamination of the crushed Cr, a large amount of C is added in the actual process. I have to help. Therefore, the suppression effect varies, and more than necessary C remains undesirably, because the withstand voltage characteristic is remarkably reduced.

As described above, even if a raw material satisfying the predetermined conditions is selected by the examination of the raw material, it has not yet been possible to obtain a sufficient restrike suppression technique. It suggests the need to control impurities. That is, even if the selected Cr having predetermined conditions is used, the surface or / and the inside of the Cr is unfavorably suppressed in restriking in the next step of sintering and / or infiltration. It is suggested that it changes.

Therefore, in the present invention, as a means for preventing or delaying the change of Cr to an undesired state as described above, a protective layer having the above conditions is formed on the surface of Cr in the first step, By the action of this protective layer, Cr
A Cr sintered body and a Cr-Cu sintered body are obtained while protecting the surface from a contaminated atmosphere during sintering (second step), and the final target composition is controlled while controlling the evaporation amount as the sintering progresses. This is to obtain Cr, Cr-Cu, skeleton, and Cr-Cu alloy having the following (third step).

Particularly, the point of the present invention is that the protective layer is made of Cr.
While it is present on the surface and Cr-Cu surface, the inside is protected. However, if this protective layer evaporates and scatters due to a rise in temperature, the surface is exposed to a contaminated atmosphere and the effect of the protective layer is reduced. Halve. However, as the protective layer evaporates and scatters, on the other hand, the sintering of Cr and Cr-Cu to some extent begins, and the area of direct contact with the contaminated atmosphere is reduced, and this area is further reduced by further sintering. Finally, by the time the evaporation of the protective layer is completed, there is no direct contact area, and the effect of the protective layer applied to the Cr surface in the first step on other functions is negligibly low.

In the first step, the high vapor pressure material selected as the protective layer is 2 × 10 ⁻⁷ To at 800 ° C.
It must have a higher vapor pressure than rr. The reason is,
If the protective layer is formed of a material lower than this value, a large amount of the protective layer remains on the surface of Cr even after predetermined sintering or / infiltration heating, which has an adverse effect on contact resistance characteristics and welding resistance characteristics.

However, the vapor pressure is 1 × 1 at 800 ° C.
0 ² In the case of a material having a higher vapor pressure than Torr, on the contrary, at the very early stage of the sintering process, the protective layer evaporates and scatters, and when the protective layer is substantially required, the protective layer is eliminated. Not preferred. In this case, Cr receives contamination from the atmosphere during the heating, which causes a re-ignition phenomenon.

Further, in the first step, the thickness of the protective layer to be provided on the surface of Cr needs to be in the range of 0.05 to 5 μm. The reason is that when the thickness is less than 0.05 μm, Cr cannot be sufficiently protected from the contaminant atmosphere during heating, and as a result, the effect of suppressing re-ignition is small. On the other hand, when the thickness is more than 5 μm, sufficient protection can be obtained, but not only the high vapor pressure material adheres to the inside of the furnace, the furnace wall and other parts during processing, but also the failure of the furnace increases. These protective layers which are not completely removed from the Cr surface during the predetermined sintering and / or melting step and slightly remain undesirably cause a decrease in withstand voltage characteristics and a decrease in contact resistance characteristics.

As described above, in the present invention, mainly C
r, a protective layer is adhered or covered or alloyed under predetermined conditions, and Cr is in the form of Cr powder,
A Cr compact, a mixed powder of Cr and Cu, or a compact of Cr and Cu can be applied without any problem. In addition, the protective layer on Cr is sufficiently present in the early and middle stages of the heat treatment requiring a protective action, and evaporates and scatters at the end of the heat treatment when the protection is not required with the progress of sintering.
The purpose is to select the material of the protective layer (high-vapor-pressure material A) and its thickness according to the temperature, time and atmosphere of the heat treatment so as to remain at most 0.01% by weight.

In the third step, the amount of the remaining high vapor pressure material A needs to be 0.25% by weight or less. The reason is that if the value is larger than this value, the contact resistance value varies due to the influence of the remaining high vapor pressure material A, and the withstand voltage characteristic also deteriorates. In order to strictly control the restriking characteristic, it is preferable to limit it to 0.01 wt% or less. Next, a method for manufacturing the contact alloy according to the present embodiment will be described.

A metal Cr plate obtained by dissolving high-carbon ferrochrome in sulfuric acid and electrolyzing or reducing the same was pulverized by a crusher into particles having a size of about 0.5 to 2 mm to obtain coarse granular Cr. The coarse granular Cr was further pulverized by a pulverizer, and a Cr powder having an average particle size of 1 to 250 μm was collected by a vibrating sieve to obtain a raw Cr powder. Carbon powder having substantially the same particle size as the raw material Cr powder is used in an amount of 50 to 30,000 with respect to the amount of the raw material Cr powder.
The mixture was sufficiently mixed by a mixer in an amount of ppm to obtain a Cr-C mixed powder. Next, the Cr-C mixed powder was applied to a briquette machine at 8 ton / cm ^2. Hardened with the following molding pressure Cr-C
A molded article was obtained. Further, the Cr-C compact is heated to 800 ° C. or more (140 ° C.) in a vacuum (in a non-oxidizing gas such as hydrogen if necessary).
Degas Cr by heating at a temperature of 0 ° C or less)
A lump (degassed Cr briquette) was obtained. And degas C
The lumps are again refined in a non-oxidizing atmosphere, if necessary, preferably in a non-oxidizing atmosphere such as N ₂ gas by a pulverizer.
Degassed Cr powder.

A part of the Cr powder thus obtained was transferred to a quartz tube having one end closed, and a predetermined amount of Cr was transferred. At the same time, Bi was selected as the high vapor pressure material A, and 0.5% of the Cr amount was selected. Bi
Then, while the inside of the quartz tube was evacuated from the other end opening of the quartz tube by vacuum, the other end was melted and closed.

In this way, the whole quartz container in which predetermined amounts of Cr and Bi are vacuum-sealed, for example, at least 300 to 10
The material was heated to about 00 ° C., and the high vapor pressure material A was uniformly evaporated on the Cr surface (first step).

The quartz tube is broken, and the extracted Cr powder (Bi-sheath) is used as it is as a raw material of the Cr powder and the Cr compact (Cr sample 1), or a predetermined amount of Mixing highly conductive material consisting of Cu and / or Ag
r and Cu (Cr sample 2) and Cr and Ag (Cr sample 3) are used as raw materials for mixed powders and compacts.

The control of the thickness of the skin of the high vapor pressure material A on the Cr surface can be easily changed, for example, by changing the ratio of the amount of Cr and the amount of Bi sealed in the quartz tube. Further, in the case where the selected high vapor pressure material A is Ga whose vapor pressure is higher than Bi, 200 ° C. lower than 300 ° C. in the case of Bi above.
However, the coating temperature can be varied depending on the material selected and the thickness to be coated so that 200 ° C. to 800 ° C. is a suitable range.

On the other hand, as described above, B
In addition to the method of obtaining a Cr powder covering i, the method of attaching a protective layer to the surface of the Cr powder includes, for example, electroplating, electroless plating, ion plating, sputtering (Cr samples 4 to 7), and the like. Obtained easily. Evaluation method (1) Current characteristics

The superiority or inferiority of the large current interrupting property can be evaluated by the magnitude of the current when the interruption is successful, that is, the maximum value of the current, and the larger this value is, the more excellent the large current interrupting property is. 6. After cleaning the contact surface by baking, voltage aging, etc. to make the conditions constant,
The maximum value of the current at the cutoff limit was measured while increasing the current by 1 KA at 2 KV and 50 Hz, and the magnification with respect to a predetermined standard value was calculated as the interruption magnification. (2) Restriking characteristics

A disk-shaped contact piece having a diameter of 30 mm and a thickness of 5 mm was mounted on a demountable vacuum valve, and the pressure was 6 KV ×
The frequency of occurrence of restriking when the circuit of 500 A was interrupted 20,000 times was measured and indicated by the variation width (maximum and minimum) of two circuit breakers (six valves). When mounting the contacts, only baking heating (450 ° C., 30 minutes) was performed, and the use of brazing material and the accompanying heating were not performed. (3) Contact resistance characteristics

The contact resistance characteristic is such that a flat electrode having a surface roughness of 5 μm and a diameter of 50 mm is opposed to a convex electrode having a curvature radius of 100R having the same surface roughness, and both electrodes are opened and closed with a degree of vacuum of 10 ^−5. It is mounted in a detachable vacuum vessel evacuated to Torr or less, and opens and closes a load of 1.0 kg and a current of 100 A. Then, a contact resistance is obtained from a potential drop when an AC current of 10 A is applied between both electrodes. In addition,
The contact resistance value is a value including a resistance or a contact resistance of a wiring member, a switch, or the like forming the measurement circuit as a circuit constant.

The value of the contact resistance includes the resistance of the shaft of the detachable vacuum switchgear itself of 1.8 to 2.5 μΩ and the resistance of the coil for generating the magnetic field of 5.2 to 6.0 μΩ, with the remainder being the rest. This is the contact point value (resistance of the contact alloy, the same contact resistance).

[0074]

[Table 1]

[0075]

[Table 2] Examples 1-3, Comparative Examples 1-2

A Cr powder (Cr sample 2) under the conditions described above was prepared. (Cr sample 2) was prepared by mixing about 10% of Cu with Cr in a Cr powder in advance with Cr in a quartz tube at about 0.3% with respect to the amount of the (Cr + Cu) powder.
Bi was encapsulated (the amount of Bi evaporates by half in the subsequent Cu infiltration step), and Bi was attached to the (Cr + Cu) surface (Cr sample 2).

The above (Cr sample 2) was heated at about 1000 ° C. in a vacuum.
For 1 hour to form a Cr skeleton having a porosity of about 45 to 50% by volume.
To infiltrate Cu to prepare a Cu-50% Cr alloy (% by weight). The obtained Cu-50% Cr alloy contains about 0.1 to 0.15% of Bi. If it is necessary to further reduce the value of Bi, (Cr + C
u) It can be easily changed by adjusting the amount of Bi to be enclosed together with the powder.

An alloy in which no Bi was encapsulated was a comparative example.
Comparative Example 4 described below, in which a large amount was sealed. It should be noted that such a large amount of Bi-containing alloy can be obtained by not only supplying Bi by enclosing Bi in a quartz tube but also using a Cu-Bi alloy instead of pure Cu instead of pure Cu. Are also supplied from That is, in Examples 1 to 3 and Comparative Example 2, (Cr + C
u) and the amount of Bi to be encapsulated is gradually changed, and the processing temperature is appropriately selected from about 300 ° C.
The thickness of i was adjusted to a value between 16 μm and 0.05 μm (Comparative Example-2, Examples 1-3) to form a protective layer.
Cu was infiltrated at 150 ° C. to form a contact. The Cr
-Bi remaining contained in the Cu alloy is 0.06
〜0.2 wt%, corresponding to the thickness of the protective layer.

In Comparative Example 1 where no protective layer was present,
Due to the influence of trace gas components (mostly oxygen) in the atmosphere during the temperature rise process during skeleton fabrication, the contact resistance increases and varies greatly.
The presence of r ₂ O ₃ was seen. Accordingly, the frequency of restriking was high and the variation width between samples was large. This suppression was observed in samples having a protective layer thickness of 4-5 μm (Example-1) to 0.05-0.1 μm (Example-3). However, in the case where the thickness of the protective layer is 13 to μm (Comparative Example-2), the occurrence of restriking due to selective and intensive evaporation of the protective layer component (Bi in this case) is rather observed, and conversely. Restriking tends to occur frequently, which is not preferable. As a result, the thickness of the protective layer is preferably in the range of 5 μm to 0.05 μm from the viewpoint of both the frequency of restriking and the contact resistance characteristics,
When the thickness is less than 5 μm, the control is difficult and causes variation, so the lower limit control amount is set to 0.05 μm. Examples 4 to 7

In Examples 1 to 3 and Comparative Example 2, as the raw material Cr used for manufacturing the contact, a Cr (Cu + Cu) powder in which a small amount of Cu was previously mixed with Cr was used as Cr sample-2.
However, the material Cr can be used without limitation.

That is, as shown in (Cr sample-1),
In the case of using only Cr (Example-6) and the one in which only Cr was formed (Example-5), a small amount of Cu was not mixed in advance with Cr as in (Cr sample-3), but A
g (Example-7) also showed favorable values in both the frequency of restriking and the contact resistance characteristics. Therefore, the raw material Cr may be not only a mixture of Cr and Cu but also a molded one, or even only Cr. Examples 8 to 15 and Comparative Examples 3 to 4

In Examples 1 to 7 and Comparative Example 2,
The high vapor pressure elements used for the protective layer are all exemplified by Bi, but the effect of the present invention is not limited to Bi as the protective layer, and other elements having similar vapor pressure exert their effects. did.

That is, the previously used (Cr sample 2) was adopted as a Cr raw material powder, and the (Cr + Cu) surface was coated with N
i, Sn, Ag, In, Ga, Mn, Pb, Sb, Z
After covering the respective materials of n and Se, a skeleton of (Cr + Cu) powder was formed in the same manner, and Cu was infiltrated to obtain a Cr-Cu alloy.

When the same evaluation was carried out,
In the contacts having each of the elements n to Zn as the skin cover layer, the reignition occurrence frequency and the contact resistance characteristics were all within preferable ranges (Examples 8 to 15).

On the other hand, in the contact where Ni is selected as the protective layer, the Ni of the protective layer has a tendency to remain on the entire surface or a part of the surface even after the skeleton is made of (Cr + Cu) powder or after infiltration. As a result, a region where the contact resistance was extremely high was partially observed (Comparative Example 3).

On the other hand, in the contact where Se is selected as the protective layer, Se is evaporated and removed at a very early stage of the heating process when the skeleton is made of (Cr + Cu) powder, thereby preventing contamination from the heating atmosphere. Not only can not play a role, not only can not obtain a signal, high-quality skeleton that is partially or entirely contaminated surface, in the Cu infiltration process, voids in the Cr-Cu alloy The consequences were: At this contact point, a value that was not much different from that of Comparative Example-1 in which re-ignition occurred frequently and no protective layer was present at all from the beginning was shown (Comparative Example-4). For the same reason, the contact resistance characteristics are also unfavorable.

Therefore, a material suitable for the protective layer from these tendencies is a vapor pressure of Sn (5 × 10 ^{−6 at} 800 ° C.).
Preferably, the material is between Torr) and the vapor pressure of Zn. Example-16

In all of Examples 1 to 15 and Comparative Examples 1 to 4 described above, the method of manufacturing the contacts is such that after the Cr skeleton is formed, Cu is heated and melted to a temperature higher than the melting point of Cu, and the Cu skeleton is filled in the voids of the Cr skeleton. The effect of the protective layer of the present invention is not limited to this infiltration method, and the effect of the raw material Cr for producing a contact by a solid phase sintering method is shown.
It can also be applied as a powder.

That is, in Example-16, after mixing (Cr sample 2) and an approximately equivalent amount of Cu powder, 4 tons / cm ² In hydrogen with a dew point of -70 ° C or less, 1030 ° C ×
Sintering for 3 hours and re-pressing were performed, and this was repeated as many times as necessary. As a result, as shown in the table, the same effect as in the other examples was obtained. Examples 17 to 20

In Examples 1 to 16 and Comparative Examples 1 to 4 described above, the used Cr powder was mixed with Cr and Bi in a quartz tube.
And Cr was attached to the surface of Cr using the difference in vapor pressure (Cr samples 1, 2, and 3).

However, the raw material Cr powder is not limited thereto, and the protective layer may be provided on the Cr surface by electroplating, electroless plating, ion plating, sputtering (Cr
Samples 4 to 7) can be used similarly (Examples 17 to 20). Examples 21 to 24, Comparative Example 5

The protective layer provided on the surface of each raw material Cr powder
The amount of the protective layer component finally remaining in the alloy by evaporating and scattering in the heating process received during the sintering or infiltration process at the time of manufacturing the contact is determined. The amount that remains also affects the contact characteristics. For example, after sintering or infiltration is completed, it remains in the alloy.

At the contact point when the amount of the protective layer component was 7.2% by weight, re-ignition frequently occurred and the contact resistance value also varied (Comparative Example-5). Considering restriking characteristics and contact resistance characteristics, the amount of the remaining protective layer component is 0.25
There is no problem if it is less than wt% (Examples 21 and 22). Therefore, the alloy targeted by the present invention is preferably one in which the amount of the protective layer component in the alloy after sintering or infiltration remains at 0.25 wt% or less. The raw material Cr is a Cr-Ti alloy, Cr-Z
Similar effects can be obtained for the r alloy (Examples 23 to 23).
24) The present invention is not limited to the above embodiment.

The Cr used in the above Examples and Comparative Examples was previously deposited on the surface in the first step by vapor deposition, plating, sputtering, or the like. Instead of attaching, Cr
If a material to be a protective layer is placed in the vicinity of the powder, the same process as previously applied is performed in the heating process during the sintering. This behavior is also included in the definition of the first step described in the present invention. That is, the formation of the protective layer and the progress of sintering are performed during sintering. Even in this case, the second and third steps are similarly essential steps.

In the alloy for a vacuum valve obtained in this example, not only the occurrence rate of restriking was reduced but also the variation in the occurrence rate of each vacuum valve was reduced while maintaining the contact resistance characteristics stably. It should be noted that the technology of the present invention is not limited to Cu-Cr binary alloys, but also to Cu-C
It is clear that a similar effect is exhibited in the r-based alloy.

[0096]

As will be understood from the results of the above embodiments, the method for producing a contact alloy for a vacuum valve according to the present invention is as follows.
The contact alloy obtained is extremely excellent in that the contact resistance characteristics are stable, the frequency of occurrence of restriking is significantly reduced, and the breaking performance is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a vacuum valve to which a contact alloy manufactured by an embodiment of a method for manufacturing a contact alloy for a vacuum valve according to the present invention is applied.

FIG. 2 is an enlarged sectional view of a contact portion in FIG.

[Explanation of symbols]

 13a: movable side contact, 13b: fixed side contact.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01H 33/66 H01H 33/66 B (72) Inventor Kadan 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Yokohama Business In-house (72) Inventor Yoshiko Majima 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Corporation Yokohama Office (58) Field surveyed (Int.Cl. ⁶ , DB name) B22F 3/10 B22F 1/02 B22F 3 / 26 C22C 1/04 H01H 11/04 H01H 33/66

Claims (6)

(57) [Claims] 1. A raw material Cr powder as an arc-resistant material, a Cr compact, a mixed powder of Cr and Cu as a conductive material, Cr and Cu
2 × at approximately 800 ° C. on part or all of the surface of
A first step in which a high vapor pressure material having a vapor pressure higher than 10 ^-7 Torr is applied, covered, or alloyed by a thickness of 0.05 to 5 μm as a protective layer, and heating is performed by the high vapor pressure material; From the material with a protective layer obtained in the first step, while protecting from the contamination atmosphere of
u in a second step of obtaining a sintered body, and with the progress of sintering of Cr or Cr—Cu during part or all of the period of the second step, the remaining high vapor pressure material is reduced to 0.25 wt. % While controlling the sintering temperature, time, heating / cooling rate, and atmosphere evaporation amount so that the sintering temperature is less than or equal to%.
A method for producing a contact alloy for a vacuum valve, comprising a third step of obtaining a skeleton and a Cr-Cu alloy. 2. In the third step, Cr, Cr—Cu skeleton, Cr—C, while controlling the amount of evaporation so that the amount of the remaining high vapor pressure material becomes 0.01% by weight or less.
The method for producing a contact alloy for a vacuum valve according to claim 1, wherein a u alloy is obtained. 3. The method according to claim 1, wherein after the third step, Cu remains in the residual vacant space in the Cr skeleton or the Cr—Cu skeleton.
3. A method for producing a contact alloy for a vacuum valve according to claim 1, wherein a Cr-Cu alloy is obtained by infiltrating the alloy. 4. The method for producing a contact alloy for a vacuum valve according to claim 1, wherein a part or all of the conductive material made of Cu is Ag. 5. The method of manufacturing a contact alloy for a vacuum valve according to claim 1, wherein a part or all of the arc-resistant material made of Cr is one of Ti and Zr. Method. 6. The high vapor pressure material is Ga, Ag, I
6. An element selected from the group consisting of n, Bi, Cu, Pb, Sb, Te, and Zn.
A method for producing a contact alloy for a vacuum valve according to any one of the above.