JP2529560B2 - Silver-base metal oxide contact material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a completely new "in-particle vicinity oxidation" which is completely different from the "internal oxidation method" and the "powder metallurgy method" which are conventional manufacturing methods of silver-metal oxide contacts. The present invention relates to a silver-base metal oxide contact material obtained by a so-called "sintering method" and a manufacturing method thereof.

[Prior art and its problems]

Conventionally, various materials have been used as electrical contact materials, in particular Ag-CdO contact materials are widely used, and contact materials in which 10% CdO is appropriately dispersed in Ag are resistant to welding, arc resistance and resistance. It is widely used in small to large current regions such as various switches, contactors and breakers because of its excellent contact characteristics such as wear resistance and contact stability. Recently,
With the pollution problem of Cd pointed out, research on materials not containing Cd was also conducted, and Ag, La, Sb, Sn, Zn, Pb, In,
Contact materials containing oxides of base metals such as Te were developed one after another in connection with the manufacturing method.

As a method of manufacturing such a silver-base metal oxide contact material, there are an internal oxidation method and a powder metallurgy method, but at present, most of the mass production products use the internal oxidation method.

Internal oxidation method is based on Ag and base metal as solute metal (eg Cd,
Sb, Sn, etc.) is made into a molten alloy, and this is processed into a desired molded body.
This is a method of heating at a temperature of 0 ° C or higher to selectively oxidize only the solute metal by oxygen outside the alloy system, subject to the compositional conditions that at least plastic working and internal oxidation are possible. .

In this internal oxidation method, oxygen is forcibly supplied from the outside, and oxygen that diffuses in the silver matrix oxidizes the solute metal in the solid state for a long time.Therefore, the concentration gradient of the solute metal inside the alloy causes the diffusion of oxygen. Opposite the direction, it occurs in the thickness direction. This is extremely inconvenient in terms of contact characteristics,
This is an unavoidable phenomenon in principle due to the mechanism of oxidation.

In particular, in the case of the double-sided internal oxidation method in which the material is oxidized from both sides, it is well known that concentration unevenness is concentrated in the central part and a thin layer of oxide is formed there (Japanese Patent Publication No.
60-16505), the thickness of the dilute layer varies depending on the type and concentration of the solute metal, the oxygen partial pressure, the internal oxidation temperature, etc., but reaches 0.1 to 0.3 mm, significantly impairing the contact characteristics.

In this method, oxygen is diffused from the outside over the entire contact thickness. Therefore, the thicker the thickness, the longer the oxidation takes, and the more difficult it is to determine the end point of the oxidation. It also has drawbacks such as high production and quality control.

On the other hand, the powder metallurgy method, which is also called a sintering method, is a generic term for those that perform sintering after molding silver powder and base metal oxide powder, or internally oxidize silver powder and base metal powder. To belong, (1) mechanically mix Ag pieces and base metal oxide powder,
Mixed sintering method of molding and sintering (2) Unoxidized manufactured by atomizing method and arc method
Sintering internal oxidation method to sinter Ag alloy powder and oxidize it internally (3) Crush the Ag alloy plate or wire produced by the melting method, and internally oxidize these pieces, and then sinter One-side internal oxidative sintering method (4) There is an internal oxidative crushing sintering method, etc. in which Ag alloy is melted, processed into a plate or wire, and then internally oxidized, and this Ag-metal oxide body is crushed and sintered. However, except for (1), all the other methods still utilize internal oxidation.

In the case of (1), it is a typical powder metallurgy method, and if large-scale equipment necessary for melting is not required and necessary oxides can be procured, various oxides can be obtained without restrictions on alloying and internal oxidation. Although there is an advantage that can be used, because it is not possible to omit the mechanical mixing step of Ag powder and oxide powder in manufacturing, as long as it is manufactured in the gravity zone, it is not possible to eliminate the difference in specific gravity of the powder. It is difficult to do, uniform mixing is difficult due to the influence of grain size and grain shape, segregation in composition is likely to occur, and it is difficult to obtain a uniform sintered density. .

In the case of (2), the drawbacks of the internal oxidation method are inherited as they are, and in the case of (3), it takes time and labor, and although the crushed pieces are small pieces, the size of the particles is about 0.5 mm. As in the case of the internal oxidation method, a thin layer of the oxide formed therein remains after sintering and exhibits unfavorable contact characteristics.

Further, in the case of (4), the Ag alloy is melted, cast, forged, or formed into a plate by a plastic working to form a plate or wire, and a very complicated process of completely internal oxidizing and then pulverizing is taken, so that the cost is high. In addition, mechanical crushing has processing limits, and the size of the powder is only about 0.1 mm, it is not only difficult to make it into a fine powder, but also impurities are easily mixed during crushing, which is good for various characteristics. With unforeseen effects,
Although the dilute layer at the time of internal oxidation is also crushed, it mixes as coarse particles, and it also affects the internal structure after sintering to make it non-uniform, causing abnormal wear and the like.

On the other hand, looking at trends in the use of contact points, the rationalization in each industrial field and automation of mechanical devices have recently made remarkable progress, but with this trend, devices tend to become larger and more complex. On the other hand, the control system of these devices is rather required to be smaller, more frequent in operation, and larger in capacity. The contact surface is heated by the arc heat and Joule heat associated with opening and closing to a high temperature that melts locally during operation, and the temperature drops to room temperature during rest, which means that high-temperature and low-temperature thermal cycles are repeated. Become. When a contact with a thin oxide layer inside, which is the fate of the manufacturing method utilizing internal oxidation, is encountered in such a situation, it is repeatedly expanded and contracted frequently, and the vicinity of the boundary of the oxide thin layer is encountered. A complex stress is intensively applied to the contacts, causing arcuate curved deformation to make the surface of the contact concave, and microcracks and cracks at each stress concentration site, eventually leading to chipped wear. I will go.

Also, when the contact continues to wear normally, and a thin layer of oxide appears on the contact surface, the welding resistance sharply decreases,
It may lead to abnormal wear or welding, resulting in a serious accident.

Furthermore, in the case of a contact made by a normal double-sided internal oxidation method, the life cannot fully consume the contact thickness because the thin layer exists in the center of the contact, and the life may be halved. .

[Problems to be solved by the invention]

The present invention utilizes the conventional internal oxidation for the purpose of eliminating the formation of the oxide thin layer that deteriorates the contact characteristics as described above, preventing abnormal wear and extending the contact life, and improving the reliability thereof. Unlike the manufacturing method, the oxygen supply source does not depend on the outside at the time of sintering, and it is not a method of simply sintering base metal oxide powder and silver powder like the conventional powder metallurgy method. The present invention has developed a method in which the oxygen contained in the composite particles themselves can oxidize the powder particles and / or oxidize other particles near the particles, that is, oxidize and sinter near the particles.

As described above, the present invention is excellent in the uniform dispersion of oxides that influence the contact characteristics due to the new oxidation mechanism that should be called the “in-particle near-field oxidative sintering method” (or interparticle oxysintering). The purpose is to supply contact material.

[Detailed Description of the Invention]

According to the present invention, the powder itself has an oxygen supply source, so that oxygen required for oxidation is supplied from offshore outside the solid phase as in the conventional method, and the adverse effect of diffusing oxygen in a long diffusion step in the solid phase is eliminated. This is based on the idea of supplying oxygen from the powder itself in the immediate vicinity of the oxide to be excluded.

In addition, the free energy of formation of metal oxides decreases with increasing temperature, the metal is more activated at high temperatures, and higher-order oxides are easily generated. At higher temperatures, the larger the oxygen pressure, the more the amount of oxygen dissolved in silver. Is focused on the fact that it increases.

Many studies have been conducted on the amount of dissolved oxygen in simple substance of silver (eg, HHPodgurski & FNDavis: Trans.AIME230.731 ~
5 (1964), et al.), And there are studies of phase diagrams at high temperatures, but little is known about the behavior of oxygen in a silver-base metal alloy system such as the present invention.

In the present invention, by analogy with the behavior of oxygen in a simple substance of silver, a silver-base metal alloy is considered to be reacted with oxygen in a highly active state, that is, in a molten state and in a state having as large a surface area as possible, By blowing oxygen or an oxidizing gas to this melt at a high temperature, silver-base metal alloy droplets are generated, and the base metal is forcibly oxidized in the process until it solidifies, that is, in the melt or semi-molten state. However, by generating a stable oxide and metastable high-order oxide, or by occluding oxygen, the particles after solidification are dispersed in a high-temperature oxidizing atmosphere for as long as possible and blown off in the same manner. By continuing oxidation and / or storage of oxygen, oxygen is as rich as possible in the peripheral portion of the particle, that is, stable base metal oxide is formed with respect to the base metal in that portion. When compared to the atomic ratio of oxygen / base metal in the case of the presence of oxygen, a stoichiometrically excess amount of oxygen is provided, and the inner part of the particle is in an oxygen-lean state, and in some cases there is no oxygen binding to the base metal. Such a state, that is, a base metal in a state where there is no oxygen inside the silver-based alloy particles,
Stoichiometrically oxygen-deficient base metal oxides and base metal oxides, including metastable higher oxides, and / or free oxygen, and stoichiometrically oxygen excess as much as possible. In other words, it has succeeded in producing composite particles having an oxidizing function in the vicinity of particles.

This composite particle has a size of submicron order to several tens of microns, but when viewed microscopically with respect to these particles, the oxygen concentration distribution is non-uniform, and Ag, base metal, and oxygen-deficient state as described above. And base metal oxides, including metastable oxides with excess oxygen, and / or free oxygen, etc., and in the process of making the contact material in the next process, existing free oxygen and / or metastable Oxygen generated by decomposition of higher oxides, base metal present in the composite particles in an unoxidized state, base metal oxide in the state of oxygen deficiency or the base metal in other particles present in the vicinity of the composite particles, By using oxygen-deficient base metal oxides as a source of oxygen to oxidize, produce composite particles that also have an oxidizing effect on silver alloy powder containing unoxidized base metal elements. Successful bets, in which paved the way for the particles in the vicinity oxidation use.

In order to generate a composite particle having a portion having as much oxygen as stoichiometrically as described above with respect to the base metal element which is a component of the composite particle, the oxygen serving as the oxygen supply source is an alloy. Not only the base metal element as a component, but also the concentration and pressure of the oxidizing gas to be injected, the melt temperature, the size of the droplets and the flight-in-flight oxidation time, the oxidation temperature, the flying oxidation time of the solidified particles, the atmospheric gas concentration and temperature, etc. It can be considered as various conditions at the time of producing the composite particles, but in the present invention, the temperature maintained at an appropriate temperature for producing composite fine particles by injecting oxygen or an oxidizing gas into a silver-based alloy melt containing a base metal. Oxygen or an oxidizing gas is blown to the molten metal to form droplets, which are then allowed to fly in a high-temperature oxidizing atmosphere for several times until they solidify as fine particles. g, a base metal, a base metal oxide including an oxide in an oxygen-deficient state, and / or free oxygen, and obtains composite particles capable of exhibiting an oxidizing effect in the vicinity of particles during heating and sintering.

In the near-particle oxidization process, these composite particles have a non-uniform distribution of oxygen even if they are microscopic as described above.
After powder compaction at a temperature of about 400 to 850 ° C for about 2 to 8 hours, and in some cases by heat sintering using a hot press, the oxygen in the oxygen-rich part is transferred to the oxygen lean part in the grain or in the vicinity of the grain. By migrating and oxidizing the base metal element and the base metal oxide in the state of oxygen deficiency, a uniform oxide dispersion is realized, and at the same time, facing the diffusion of oxygen, the base metal with a micro diffusion process is involved. Since the transfer is carried out within the particles or between the particles, it is considered to be useful for improving the interparticle sintering strength.

 Hereinafter, the features of the present invention will be described with reference to examples.

Examples In the accompanying drawings, the drawings are schematic illustrations of an apparatus suitable for producing composite particles used in the present invention.

A silver-base metal alloy having the composition shown in Table 1 is melted in an electric furnace (not shown), and the molten metal 10 is placed in the holding furnace 1. The holding furnace is provided with a heating element 11 on the periphery and an opening 2 at the bottom to keep the molten metal at an appropriate temperature.
Drop it from the hole 2. The molten metal that falls is supplied with oxygen or an oxidizing gas from the atomizing nozzle 3 at an appropriate nozzle pressure, for example, 50.
It is sprayed at -100 kgf / cm ² to form droplets, and the droplets are flown in a high temperature oxidizing atmosphere in the main chamber 5 at a temperature of, for example, about 600 ° C. until the droplets solidify as fine particles.

The molten metal temperature and the types of injection gas are as shown in Table 1.

The particles that have been solidified by flying in the main chamber 5 are further designed as needed, especially when the particles are relatively large, they are designed to drop while drifting in a high temperature oxidizing atmosphere in order to continue the oxidation after solidification. It drifts in the sub-chamber 6 provided with the spiral-shaped oxidation tunnel, drops into the collecting hopper 8, and is collected. The main chamber 5 and the sub-chamber 6 are for adjusting the flight distance to secure the time during which the sprayed droplets generate heat due to the reaction with oxygen or stay in a state where they can sufficiently combine with oxygen while being heated. The secondary injection nozzle 4 of is arranged at an appropriate position.

The yield, particle size distribution and granular shape of the composite particles thus produced are summarized in Table 2.

In the case of the composite particles obtained as described above, or in the case of the compounded powder in which the unoxidized powder particles are supplementarily added to the composite particles (first
Examples 8 and 9 in the table) together with them, after mixing,
It was molded into 50φ × 100 at a pressure of 2.5 t / cm ² , and the molded material was heated in the air at 800 ° C. for 3 to 6 hours to oxidize and sinter the vicinity of the particles to obtain a billet. 800 ° C
Hot extruding with a uniform increase in the sintering density, a plate with a thickness of 7 mm, and an Ag plate being hot-pressed on one side of the plate,
An Ag layer for brazing was formed.

Next, the material was cold-rolled to form a plate with a thickness of 2 mm, which was punched into a disk with a diameter of 6 mm, and then 6
A contact material was obtained by performing stabilization treatment at 50 ° C. for 5 hours.

Regarding the contact characteristics of the above contact materials, the contact resistance and welding resistance were checked using an ASTM contact tester (AC 200V, 60A).
Furthermore, it was mounted on a commercially available switch and tested using an actual device (220 V
A, wear time 0.1 sec, power factor 0.35) were evaluated for wear resistance, and those are shown in Table 3.

Regarding the components of the composite particles, especially the base metal element, the first is Sb, Sn, In, Mn, and Pb, which are elements that generate high-order oxides.
Cd, Zn, Te, La, Fe, Ni, Co, which are elements that make it difficult to form higher-order oxides and trace elements, are included in the second group, and the first group is added to the second group as needed. By using the elements added in duplicate, excellent contact characteristics as shown in Table 3 could be obtained.

As described above, the present invention does not require an oxygen supply source only to the outside unlike the conventional internal oxidation method, does not oxidize by being controlled by the diffusion mechanism of oxygen atoms from the outside, and the powder itself is Since it produces composite particles composed of silver, a base metal, a base metal oxide and / or free oxygen having an oxidizing function, and mainly supplies oxygen mainly in the contact manufacturing process using this to oxidize the vicinity of particles. ,
Oxidation does not take a long time, a non-uniform oxide layer that causes internal stress does not occur at the contact, and sinterability is a micro diffusion process that opposes the diffusion of oxygen between particles. The movement of the base metal due to increases the bond between particles, and in addition, the effect is further enhanced by the auxiliary mixing of the unoxidized powder particles, so that the sinterability is further excellent,
Since it exerts the binding force to withstand the tensile and compressive stresses caused by the expansion and contraction due to the heat cycle of heating and cooling as mentioned above, the above-mentioned lacking consumption phenomenon is suppressed, and of course, in the center of the contact, of course, the conventional oxide is used. Not only does it have no thin layer, but also because it has excellent uniform dispersibility of oxides, it does not have the risk of sudden deterioration of welding resistance or abnormal wear as described above, and it has a long life and also has a contact material composition. Since there is no restriction on the concentration by the conventional method (internal oxidation), the range of selection can be widened, and it is possible to easily select the component concentration according to the application, which has various effects.

In addition, in terms of productivity, the long time required for conventional internal oxidation is not necessary, and the processes such as forging, cutting, rolling, and annealing of the ingot are not necessary, so man-hours can be saved and economical production is possible. Become.

[Brief description of drawings]

The drawings are schematic illustrations of an apparatus suitable for producing the composite particles used in the present invention. In the figure, 1 ... Holding furnace, 2 ... Drop opening, 3 ... Spraying nozzle, 4 ... Secondary injection nozzle, 5 ... Main chamber, 6 ... Sub chamber, 7, 8 ... Collection Hopper for. 9: recovery hopper, 10: molten metal, 11: heating element

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Claims (6)

(57) [Claims] 1. A silver-base metal oxide contact material comprising silver-base metal oxide-based composite particles, the base metal oxide including oxide in a stoichiometrically oxygen-deficient state inside the composite particles. And / or a silver-base metal oxide contact material consisting of silver, including a base metal not bound to oxygen, a base metal, a base metal oxide and / or free oxygen, obtained by oxidizing the base metal. 2. The contact material according to claim 1, wherein the base metal is at least one selected from the group consisting of Sb, Sn, In, Mn and Pb. 3. The base metal is at least one selected from Sb, Sn, In, Mn and Pb, and Cd, Zn, Te, La, Fe, Ni and Co.
The contact material according to claim (1), which is a mixture with at least one selected from the group consisting of: 4. A liquid of a silver-based alloy containing a base metal is jetted with oxygen or an oxidizing gas to form droplets, and the droplets are flown in a high temperature oxidizing atmosphere until the droplets solidify as fine particles, A silver-base metal oxide contact material comprising silver-base metal oxide-based composite particles, characterized by being allowed to drift as fine particles in a high-temperature oxidizing atmosphere even after solidification. Is composed of silver, a base metal, a base metal oxide and / or free oxygen including a base metal oxide including an oxygen-deficient oxide and / or a base metal that is not bound to oxygen, and is obtained by oxidizing a base metal. Silver-
Method for manufacturing base metal oxide contact material. 5. The method according to claim 4, wherein the base metal is at least one selected from the group consisting of Sb, Sn, In, Mn and Pb. 6. The base metal is at least one selected from Sb, Sn, In, Mn and Pb, and Cd, Zn, Te, La, Fe, Ni and Co.
The production method according to claim (4), which is a mixture of at least one selected from the group consisting of: