JP4898978B2 - Electrical contact material - Google Patents

Abstract

Provided is an electrical contact material excellent in welding resistance, wear-out resistance, and temperature performance. The electrical contact material (31) includes more than 30% by mass and 55% by mass or less of tungsten carbide and 2% by mass or more and 5% by mass or less of graphite, the remainder including silver and an unavoidable impurity, the electrical contact material (31): having a relative density of 98.0% or more; an oxygen content of 450 ppm or less; an electrical conductivity of 45% IACS or more; and a transverse rupture strength of 350 MPa or more.

Description

  The present invention generally relates to an electrical contact material, and more particularly to an electrical contact material made of a silver-tungsten carbide-graphite (Ag-WC-Gr) -based material and used for a circuit breaker (breaker) or the like. It is.

  An electrical contact material made of a silver-tungsten carbide-based material containing a certain amount or more of tungsten carbide as a heat-resistant non-oxide has been conventionally used for a breaker having a rated current value of 200 A or more. To this electrical contact material, graphite is added in order to prevent oxidation of tungsten carbide under high heat at the time of interruption to suppress temperature rise (temperature performance) and to improve welding resistance.

  For example, Japanese Patent Application Laid-Open No. 58-11753 (hereinafter referred to as Patent Document 1) discloses 5-70% by weight of carbides of Group IVa, Va, and VIa group metals such as tungsten carbide and 1-11 of graphite. 5% to 60% by weight of iron group metal, 0.1 to 30% by weight of group IVa, Va, VIa, and VIIa metal nitride, the balance being silver, and carbide and nitride in the iron group metal And electrical contact materials dispersed in silver are disclosed.

  Japanese Patent Application Laid-Open No. 58-11754 (hereinafter referred to as Patent Document 2) discloses 5-70% by weight of carbides of group IVa, Va, and VIa metals such as tungsten carbide and 1-11 of graphite. 5% to 60% by weight of iron group metal, 0.1 to 5% by weight of metals of groups IVa, Va, VIa, and VIIa, with the balance being silver, carbides and metals of groups IVa, Va, VIa, and VIIa Is disclosed as a solid solution or dispersion in iron group metals and silver.

Japanese Patent Laid-Open No. 58-11753 JP 58-11754 A

  The electrical contact material described above is manufactured not by a melting method but by a powder metallurgy method because of poor wettability between a heat-resistant non-oxide such as tungsten carbide and silver. In the powder metallurgy method, a starting material powder is compression-molded to form a compact, and this compact is sintered. In the sintered body thus obtained, there are gaps (pores) between the bonded powder particles.

  For this reason, since the obtained electrical contact material has a low relative density and is not densified, the electrical conductivity is low. Thereby, in the breaker comprised using this electrical contact material, the heat | fever which generate | occur | produces at a contact at the time of interruption | blocking increases. Therefore, there is a problem that the obtained electrical contact material is inferior in welding resistance, wear resistance, and temperature performance.

  In order to solve such a problem, in the electrical contact material manufacturing methods described in Patent Document 1 and Patent Document 2, the relative density is improved by repressurizing the sintered body. However, the relative density obtained with this method is less than 95%. For this reason, the electrical conductivity of an electrical contact material will become low. Thereby, the welding resistance, wear resistance, and temperature performance of the electrical contact material become insufficient. In order to solve this problem, it is necessary to increase the contact area of the electrical contact material.

  Therefore, an object of the present invention is to provide an electrical contact material excellent in welding resistance, wear resistance, and temperature performance.

  The electrical contact material according to the present invention contains tungsten carbide more than 30 mass% and 55 mass% or less, graphite 2 mass% or more and 5 mass% or less, the remainder contains silver and inevitable impurities, and the relative density is 98. 0% or more, oxygen content is 450 ppm or less, conductivity is 45% IACS or more, and bending strength is 350 MPa or more.

  In the electrical contact material of the present invention, it is preferable that the average particle diameter of tungsten carbide is 0.5 μm or more and 5 μm or less.

  In the electrical contact material of the present invention, it is preferable that the average particle diameter of graphite is 1 μm or more and 50 μm or less.

  According to the present invention, the relative density is 98.0% or more, the oxygen content is 450 ppm or less, the conductivity is 45% IACS or more, and the bending strength is 350 MPa or more. It is possible to provide an excellent electrical contact material.

It is a side view which shows the arrangement | positioning relationship in the closed state of the fixed side contact member and movable side contact member which comprise the breaker in which the electrical contact material as one embodiment of this invention was integrated. It is a side view which shows the arrangement | positioning relationship in the open state of the stationary side contact member and movable side contact member which comprise the breaker in which the electrical contact material as one embodiment of this invention was integrated.

  First, the configuration of a breaker incorporating an electrical contact material as one embodiment of the present invention will be described.

  As shown in FIGS. 1 and 2, the breaker 10 can contact the fixed contact member 30 and the fixed contact member 30, or can be separated from the fixed contact member 30. The movable-side contact member 20 is disposed so as to be movable repeatedly. The stationary contact member 30 is composed of a joined body of an electrical contact material 31 and a base metal 32. The movable contact member 20 is composed of a joined body of an electrical contact material 21 and a base metal 22. The electrical contact material 31 according to the embodiment of the present invention is used for a part of the stationary contact member 30 of the breaker 10. The electrical contact material 31 shown in FIGS. 1 and 2 is an example of the “electrical contact material” according to the present invention.

  In the stationary contact member 30, the electrical contact material 31 and the base metal 32 are joined to each other via the brazing material 4 with the upper surface of the joint portion 32 a formed integrally on the base metal 32 side as the joint surface. Yes. In the movable contact member 20, the electrical contact material 21 and the base metal 22 are joined to each other via the brazing material 4 with the upper surface of the joint portion formed integrally on the base metal 22 side as the joint surface. .

  Since the movable contact member 20 and the fixed contact member 30 are configured in this way, the electric contact of the movable contact member 20 with respect to the electric contact material 31 of the fixed contact member 30 as shown in FIG. When a current exceeding the allowable current value of the breaker 10 flows for a predetermined time from a state in which the material 21 is in contact (closed state), a built-in contact trip device (not shown) is activated, and FIG. As shown in the figure, the electric contact member 21 of the movable contact member 20 is instantaneously separated from the electric contact member 31 of the fixed contact member 30 in the direction of the arrow Q, and the current is cut off. . As shown in FIGS. 1 and 2, the end side of the base metal 32 on which the electrical contact material 31 is not provided is connected to the primary side (power supply side) terminal of the breaker 10 among the fixed side contact members 30. In addition, of the movable contact member 20, the end portion of the base metal 22 on which the electrical contact material 21 is not provided is connected to the secondary side (load side) terminal of the breaker 10.

  In the above embodiment, the movable-side electrical contact material 21 incorporated in the breaker 10 is made of a silver-tungsten carbide (Ag-WC) -based material, and the fixed-side electrical contact material 31 is the electrical contact material of the present invention. As a material of silver-tungsten carbide-graphite (Ag-WC-Gr), tungsten carbide (WC) is more than 30% by mass and 55% by mass or less, and graphite (Gr) is 2% by mass to 5% by mass. And the balance contains silver (Ag) and inevitable impurities, the relative density is 98.0% or more, the oxygen content is 450 ppm or less, the conductivity is 45% IACS or more, and the bending strength is 350 MPa or more.

  In the electrical contact material of the present invention, first, tungsten carbide as a heat-resistant non-oxide which is a refractory is contained in an amount of more than 30% by mass and 55% by mass or less, so that arc resistance, welding resistance, wear resistance are reduced. The advantage of improving the property over a certain level is obtained. When the content of tungsten carbide is 30% by mass or less, not only the above advantages cannot be obtained, but the bending strength may be less than 350 MPa. When the content of tungsten carbide exceeds 55% by mass, the electrical conductivity is lowered, so that the material does not function as a contact for a breaker, an electromagnetic switch or the like. Specifically, if the content of tungsten carbide exceeds 55% by mass, the conductivity may be less than 45% IACS. The content of tungsten carbide is preferably 40% by mass or more and 50% by mass or less.

  Further, in the electrical contact material of the present invention, graphite is contained in an amount of 2% by mass or more and 5% by mass or less, thereby preventing oxidation of tungsten carbide as a heat-resistant non-oxide under high heat at the time of interruption, and welding resistance. The advantage of improving can be obtained. If the content of graphite is less than 2% by mass, the above advantages cannot be obtained. If the graphite content exceeds 5% by mass, the material cannot be molded. The graphite content is preferably 2% by mass or more and 4% by mass or less.

  Furthermore, in the electrical contact material of the present invention, the balance contains silver and unavoidable impurities. However, in order to ensure the electrical conductivity of the contact, it is preferable that the silver content is 40% by mass or more and 68% by mass or less. When the silver content is less than 40% by mass, the electrical conductivity is lowered, and the material is not suitable for electrical contact materials for breakers, electromagnetic switches, and the like. When the silver content exceeds 68% by mass, the content of tungsten carbide as a heat-resistant non-oxide, which is a refractory, becomes small, so that arc resistance, welding resistance, and wear resistance are improved to a certain extent. I can't. The silver content is preferably 45% by mass or more and 60% by mass or less.

  In the electrical contact material of the present invention, the balance is iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), molybdenum (Mo), copper (Cu), tantalum (Ta), vanadium (V). , Magnesium (Mg), zinc (Zn), tin (Sn), and at least one element or carbide selected from the group consisting of these carbides and the like in a range of 0% by mass to 3% by mass It may be. When the content of the element or carbide exceeds 3% by mass, the conductivity may be less than 45% IACS. The content of the element or carbide is preferably 1% by mass or less.

  In the electrical contact material of the present invention, when the relative density is 98.0% or more, excellent welding resistance and wear resistance can be obtained. If the relative density is less than 98.0%, the electric conductivity may be less than 45% IACS, so that the electrical contact material is inferior in welding resistance and wear resistance. The relative density is preferably 99.0% or more and 100% or less.

  In the electrical contact material of the present invention, since the oxygen content is 450 ppm or less, excellent wear resistance can be obtained. When the oxygen content exceeds 450 ppm, oxygen remaining in the electrical contact material is suddenly released at the time of interruption, and there is a possibility that contact consumption increases. Specifically, when the oxygen content exceeds 450 ppm, oxygen present in the material becomes a gas due to high heat of several thousand degrees generated during the short-circuit test, so that a part of the base material of the electrical contact material is scattered. This increases the rate at which the electrical contact material is consumed. The oxygen content is preferably 350 ppm or less. In the overload test, since the contact load is small, the rate at which the electrical contact material is consumed is hardly affected by the oxygen content. However, the oxygen content is preferably 120 ppm or more for reasons of difficulty in production. Here, “difficulty in production” means that no matter how small the oxygen content is, 120 ppm is a production limit.

  In the electrical contact material of the present invention, since the electrical conductivity is 45% IACS or higher, excellent welding resistance, wear resistance, and temperature performance can be obtained. When the electrical conductivity is less than 45% IACS, the welding resistance, wear resistance, and temperature performance deteriorate. However, the conductivity is preferably 65% IACS or less for reasons of difficulty in manufacturing. Here, “manufacturing difficulty” means that 65% IACS is a manufacturing limit no matter how much the conductivity is increased.

  Since the impact is large in the short-circuit test for large current applications, the bending strength of the electrical contact material of the present invention is 350 MPa or more in order to withstand the impact. When the bending strength is less than 350 MPa, the electrical contact material breaks due to insufficient mechanical strength of the material in a short-circuit test with a large contact load. The bending strength is preferably 380 MPa or more. In the overload test, since the contact load is small, it is hardly affected by the bending strength. However, the bending strength is preferably 580 MPa or less because of difficulty in production. Here, “difficulty in production” means that no matter how much the bending strength is increased, 580 MPa is a production limit.

  In the electrical contact material of the present invention, the average particle size of tungsten carbide is preferably 0.5 μm or more and 5 μm or less. If the average particle size of tungsten carbide is less than 0.5 μm, the material cannot be molded. If the average particle size of tungsten carbide exceeds 5 μm, the strength varies depending on the location of the electrical contact material. When low strength parts are connected, the electrical contact material is selectively consumed after the short circuit test. As a result, arc resistance, welding resistance, and wear resistance may be deteriorated.

  In the electrical contact material of the present invention, the average particle size of graphite is preferably 1 μm or more and 50 μm or less. If the average particle size of graphite is less than 1 μm, the material cannot be molded. Further, when the average particle diameter of graphite exceeds 50 μm, the strength varies depending on the location of the electrical contact material. When low strength parts are connected, the electrical contact material is selectively consumed after the short circuit test. As a result, arc resistance, welding resistance, and wear resistance may be deteriorated.

  The electrical contact material made of the silver-tungsten carbide-graphite (Ag-WC-Gr) material of the present invention is manufactured as follows.

  (Preparation of powder)

  The average particle size of the prepared silver (Ag) powder is 0.5 μm to 10 μm, the average particle size of the tungsten carbide (WC) powder is 0.5 μm to 5 μm, and the average particle size of the graphite (Gr) powder is 1 μm or more. 50 μm or less. When the average particle size of each powder is less than the lower limit, the powder is agglomerated and each particle cannot be uniformly dispersed, so that the area of silver eluted on the surface of the electrical contact material increases. As a result, the welding performance of the electrical contact material may be deteriorated. When the average particle diameter of each powder exceeds the upper limit value, the inter-particle distance increases in the powder and each particle cannot be finely dispersed, so that the area of silver eluted on the surface of the electrical contact material increases. As a result, the welding performance of the electrical contact material may be deteriorated. Preferably, the average particle diameter of silver (Ag) powder is 1 μm or more and 5 μm or less, the average particle diameter of tungsten carbide (WC) powder is 1 μm or more and 3 μm or less, and the average particle diameter of graphite (Gr) powder is 3 μm or more and 10 μm or less. .

  The purity of each of the silver (Ag) powder, tungsten carbide (WC) powder, and graphite (Gr) powder is preferably 99.5% or more. If the purity of each powder is less than 99.5%, impurities such as oxygen (O) and carbon (C) existing at the grain boundaries of the powder increase, and the electrical conductivity of the electrical contact material may be lowered.

  (Mixing process)

  Next, the silver powder, the tungsten carbide powder, and the graphite powder are mixed in a vacuum of 80 Pa to 150 Pa, for example, for 30 minutes to 60 minutes, for example, in a dry ball mill according to a predetermined composition. Thus, by mixing raw material powder in a vacuum, fine raw material powder can be mixed uniformly and each particle can be disperse | distributed uniformly. Thereby, mechanical strength, such as the bending strength of an electrical contact material, can be raised and the tolerance with respect to a short circuit test with a large contact load can be improved. If the pressure of the mixed atmosphere is less than 80 Pa, the cost for creating a high vacuum may increase. When the pressure of the mixed atmosphere exceeds 150 Pa, the degree of vacuum becomes insufficient, and there is a possibility that the particles of the raw material powder having a large specific gravity difference cannot be uniformly dispersed. If the mixing time is less than 30 minutes, the mixing becomes insufficient, and the particles of the raw material powder may not be uniformly dispersed. When the mixing time exceeds 60 minutes, productivity may be deteriorated.

  (Compression molding process)

  Thereafter, a compression molded body is formed by applying a pressure of, for example, 250 MPa or more and 350 MPa or less to the mixed powder. This step is performed so that an electrical contact material having a higher relative density can be obtained by a coining step and an extrusion step, which are subsequent steps. If the pressing pressure is less than 250 MPa, the amount of deformation in the coining process becomes large, so there is a possibility that it is not possible to press the relative density to 93% or more in a single coining process. When the press pressure exceeds 350 MPa, the relative density of the press body exceeds 85%, so that the gap in the press body becomes small. As a result, the internal reduction of the material becomes insufficient in the subsequent sintering step, and oxygen may remain.

  (Sintering process)

  The obtained compression molded body is sintered, for example, by holding it in a reducing gas atmosphere such as hydrogen gas at a temperature of 1000 ° C. or higher and 1100 ° C. or lower, for example, for 1 hour or more and 2 hours or less. . By sintering the compression molded body in a reducing gas atmosphere in this manner, the amount of oxygen as an impurity adsorbed inside the electrical contact material can be reduced. If the sintering temperature is less than 1000 ° C., the sintering is not completed. When the sintering temperature exceeds 1100 ° C., a large amount of gas is generated and the material may foam. If the sintering time is less than 1 hour, the sintering is not completed. If the sintering time exceeds 2 hours, the productivity may deteriorate.

  (Coining process)

  The obtained sintered body is subjected to coining under a pressure of, for example, 1000 MPa to 1200 MPa so that the relative density is, for example, 93% to 99%. This step is performed in order to obtain an electric contact material having a higher relative density by an extrusion step which is a subsequent step. In addition, this step is performed in order to reduce the amount of oxygen as an impurity that enters the material during preheating in the extrusion step. If the coining pressure is less than 1000 MPa, the relative density of the material may be about 90%. If the coining pressure exceeds 1200 MPa, the durability of the mold used may be deteriorated. If the relative density after the coining process is less than 93%, the amount of oxygen as an impurity entering the material during preheating in the extrusion process may increase. If the relative density after the coining step exceeds 99%, even if the pressure is increased beyond this, the relative density is not improved by the spring back, and the productivity may be deteriorated.

  (Extrusion process)

  For example, the coined sintered body is, for example, 1 hour or more in a reducing gas atmosphere such as hydrogen gas or an inert gas atmosphere such as nitrogen gas at a temperature of 850 ° C. or more and 920 ° C. or less. After preheating by holding for 2 hours or less, an extrusion pressure of 180 GPa or more and 250 GPa or less is applied to extrude into a predetermined shape.

  As described above, the electrical contact material made of the silver-tungsten carbide-graphite (Ag-WC-Gr) material of the present invention is manufactured.

  According to the manufacturing method combining conventional pressing and sintering, it is difficult to increase the relative density. Moreover, in the conventional manufacturing method, the old powder grain boundary in the raw material powder in which many impurities such as oxygen and carbon are present is easily maintained even after sintering. For this reason, impurities such as oxygen and carbon remain concentrated at the grain boundaries of the sintered electrical contact material. This remaining impurity reduces the electrical conductivity and bending strength of the material.

  On the other hand, by extruding the coined sintered body as described above, the relative density can be increased, the old powder grain boundaries are extended, and the high purity silver particles are in contact with each other. However, the influence of the old powder grain boundary in the raw material powder is extremely small. As a result, a relative density of 98% or more can be obtained, and the amount of impurities remaining at the grain boundary can be reduced, so that the electrical conductivity and the bending strength of the electrical contact material are improved.

  If the preheating temperature is less than 850 ° C., the deformation resistance of the extruded material is increased, so that extrusion may not be possible. If the preheating temperature exceeds 920 ° C., the temperature during extrusion exceeds the melting point of silver, so that the surface of the extruded material may be foamed. If the preheating time is less than 1 hour, the inside of the material is not heated, so that the deformation resistance increases and there is a possibility that the material cannot be extruded. If the preheating time exceeds 2 hours, the material is heated sufficiently uniformly, so that the productivity may be deteriorated.

  When the extrusion pressure is less than 180 GPa, the relative density of the extruded material may be lowered. If the extrusion pressure exceeds 250 GPa, the extrusion die may be damaged.

  In addition, in the manufacturing method of the electrical contact material of patent document 1 and patent document 2, the relative density is improved by repressurizing a sintered compact. However, as described above, impurities such as oxygen and carbon remain concentrated at the grain boundaries of the sintered electrical contact material. There is a problem that the remaining impurities reduce the conductivity and bending strength of the material. Moreover, when pressurizing a sintered compact again, you must restrain the outer peripheral direction of a sintered compact without gap. For this reason, it is necessary to set the sintered bodies one by one in the mold and pressurize them. As a result, there is a problem that the production cost becomes high.

  On the other hand, in order to manufacture an electrical contact material from the above-described silver-tungsten carbide-graphite (Ag-WC-Gr) -based material of the present invention, an extrusion method is employed. For this reason, an electrical contact material having a relative density of 98% or more can be produced by a method with high mass productivity. As a result, the production cost can be reduced.

  In summary, in the electrical contact material of the present invention, high conductivity can be obtained in a material containing 10% by mass or more and 30% by mass or less of tungsten carbide as a refractory. Thereby, since heat generation at the time of interruption can be reduced, welding resistance, wear resistance, and temperature performance can be improved. Further, since the electric contact material of the present invention has a higher bending strength than the conventional electric contact material, it is possible to reduce contact breakdown in a short-circuit test with a large contact load.

  Hereinafter, comparative experiments by Examples and Comparative Examples conducted for confirming the effects of the above-described embodiment will be described.

  [Example]

  In this example, as an example corresponding to the above-described embodiment, a fixed-side electrical contact material 31 according to Examples 1 to 15 below was manufactured. In addition, as a comparative example using a conventional manufacturing method, a stationary-side electrical contact material 31 according to the following comparative examples 1 to 4 was produced. An interruption test by an overload test and a short-circuit test was conducted using each of the breakers for a large current with a rated current value of 125 A configured by incorporating each of these electrical contact materials 31. The movable-side electrical contact material 21 was made of a material containing 50% by mass of silver and the balance being tungsten carbide.

  The average particle diameter of the graphite (Gr) powder, the content of graphite (Gr) in the prepared electrical contact material 31, tungsten carbide used to produce the electrical contact material 31 in the examples and comparative examples of the present invention The following table shows the average particle diameter of the (WC) powder, the content of tungsten carbide (WC) in the produced electrical contact material 31, the relative density, the oxygen content, the electrical conductivity, and the bending strength of the electrical contact material 31. The consumption rate of the electrical contact material 31 after the overload test, the consumption rate of the electrical contact material 31 after the short circuit test, and the evaluation results for the temperature test are also shown in Table 1. Numerical values underlined indicate that they are outside the scope of the present invention.

  In addition, the relative density, oxygen content, electrical conductivity, and bending strength of the electrical contact material 31, the method of the interruption test by the overload test and the short circuit test of the breaker for high current, the consumption after these interruption tests The evaluation of the rate and the method and evaluation of the temperature test will be described later.

  (Examples 1 to 15)

  In Examples 1 to 15, the electrical contact material 31 of a silver-tungsten carbide-graphite (Ag-WC-Gr) -based material containing graphite (Gr) and tungsten carbide (WC) with the contents shown in Table 1 is as follows. It was made.

  The graphite (Gr) powder and tungsten carbide (WC) powder having the average particle size shown in Table 1 and the silver (Ag) powder having an average particle size of 3 μm are set to have the Gr content and WC content shown in Table 1. Were mixed in a vacuum (100 Pa) for 45 minutes using a dry ball mill. By applying a pressure of 300 MPa to the obtained mixed powder with a press, a disk-shaped compression molded body having a thickness of 300 mm and an outer diameter of 80 mm was formed. This compression-molded body was sintered by being held in hydrogen gas having a reducing gas atmosphere at a temperature of 1050 ° C. for 1.5 hours. This sintered body was coined under a pressure of 1100 MPa so that the true density was 97% or more. The coined sintered body is preheated by holding in a reducing gas atmosphere of hydrogen gas at a temperature of 900 ° C. for 1.5 hours, and then applied with an extrusion pressure of 220 GPa so that the cross section is 10 mm square. Extrusion processing was performed to obtain a rod-shaped body. The obtained rod-shaped body was cut into a thickness of 1 mm to produce an electrical contact material 31.

  (Comparative Example 1)

  In Comparative Example 1, an electrical contact material 31 of a silver-tungsten carbide-graphite (Ag-WC-Gr) -based material containing graphite (Gr) and tungsten carbide (WC) with the contents shown in Table 1 is as follows. Produced.

  The graphite (Gr) powder and tungsten carbide (WC) powder having the average particle size shown in Table 1 and the silver (Ag) powder having an average particle size of 3 μm are set to have the Gr content and WC content shown in Table 1. Were manually mixed in the atmosphere for 30 minutes. A plate-like compression-molded body having a planar shape of 10 mm square and a thickness of 1 mm was formed by applying a pressure of 300 MPa to the obtained mixed powder with a press. This compression-molded body was sintered by holding it in a vacuum at a temperature of 900 ° C. for 1 hour. This sintered body was coined under a pressure of 500 MPa so that the true density was 97% or more. Thus, the electrical contact material 31 was obtained.

  (Comparative Example 2)

  In Comparative Example 2, except that the step of coining the sintered body is not performed, the same average particle size as in Example 1 as shown in Table 1 according to the same steps as in Examples 1 to 15 above. An electrical contact material 31 made of a silver-tungsten carbide-graphite (Ag-WC-Gr) material containing graphite (Gr) and tungsten carbide (WC) in content was produced.

  (Comparative Example 3)

  In Comparative Example 3, the same procedure as in Examples 1 to 15 above was followed, except that the compression molded body was sintered by holding it in nitrogen gas at a temperature of 950 ° C., which is a protective gas atmosphere, for 1 hour. As shown in Table 1, the silver-graphite-tungsten carbide (Ag-Gr-WC) -based electrical contact material containing graphite (Gr) and tungsten carbide (WC) with the same average particle size and content as in Example 1 31 was produced.

  (Comparative Example 4)

  Comparative Example 4 is the same as Example 1 as shown in Table 1 according to the same steps as in Examples 1 to 15 except that silver powder, graphite powder and tungsten carbide powder were mixed in the atmosphere. An electrical contact material 31 of silver-graphite-tungsten carbide (Ag-Gr-WC) based material containing graphite (Gr) and tungsten carbide (WC) with an average particle size and content was produced.

  (Relative density)

  The relative density [%] of the produced electrical contact material was calculated by dividing the weight of the electrical contact material by the volume of the electrical contact material (calculated value obtained by product of vertical dimension × horizontal dimension × thickness dimension). The density was calculated by dividing by the theoretical density of each material.

  (Oxygen content)

  The oxygen content [ppm] remaining in the produced electrical contact material was measured by an infrared absorption method using an oxygen analyzer (model BMGA520) manufactured by Horiba, Ltd.

  (conductivity)

  The electrical conductivity [% IACS] was measured with a sigma tester (manufactured by FOERSTER INSTRUMENTS, product number: SIGMATEST D) using a sample of an electrical contact material having a cross section of 10 mm square.

  (Drag strength)

  A sample for a bending test having a size of 5 mm × 2 mm × 30 mm was produced from the same material as the produced electrical contact material. Using this sample, the bending strength [MPa] was measured under the conditions of a distance between supporting points of 15 mm and a head speed of 1 mm / min.

  (High current breaker interruption test (overload test))

  In the overload test, a breaking current of 600 A was set at a load voltage of 220V. As a test method, CO duty (test to set a breaker in a circuit through which a cutoff current of 600 A at a load voltage of 220 V flows, and forcibly turn on the switch in the switch OFF state to instantaneously cut off the current) 50 times It was. And the consumption rate of the electrical contact material 31 after an overload test was computed by the following formula | equation. In Table 1, as the evaluation of the consumption rate, “◎” when the calculated consumption rate is 5% or less, “◯” when it is 10% or less, and “×” when it exceeds 10%.

  (Consumption rate of electrical contact material) = [[(thickness of electrical contact material before test) − (thickness of electrical contact material after test)] / (thickness of electrical contact material before test)] × 100 (%) ... (Formula 1)

  (High current breaker interruption test (short circuit test))

  In the short circuit test, a breaking current of 5000 A was set at a load voltage of 220V. As test methods, set the breaker to a circuit where a 5000 A cutoff current flows at a load voltage of 220 V and set the breaker in the O OFF state (the test that causes the cutoff current to flow when the breaker switch is ON and cut off the current) and the CO duty The test for forcibly turning on the switch and cutting off the current instantaneously) was performed according to the following procedure. That is, in this short circuit test, one O duty and three CO duties were performed in this order as operation duties. And the consumption rate of the electrical contact material 31 after a short circuit test was computed by said (Formula 1). In Table 1, as the evaluation of the consumption rate, “◎” is shown when the calculated consumption rate is 10% or less, “◯” when it is 40% or less, and “x” when it exceeds 40%.

  (Welding test of breaker for high current)

  In the welding test, a breaking current of 5000 A was set at a load voltage of 265V. As test methods, set the breaker to a circuit where a 5000 A cutoff current flows at a load voltage of 265 V, and set the breaker in the O OFF state (a test in which a cutoff current flows when the breaker switch is ON and the current is cut off) The test for forcibly turning on the switch and cutting off the current instantaneously) was performed according to the following procedure. That is, in this welding test, one O duty and five CO duties were performed in this order as operation duties. And the welding condition of the electrical contact material 31 during a welding test or after a welding test was evaluated. In Table 1, as an evaluation of the welding condition, “◎” when the contacts are not welded at all, “○” when the breaker is easily removed by ON / OFF of the breaker (“light”), easy welding by ON / OFF of the breaker When it does not come off (heavy welding), it is indicated by “x”.

  (Temperature test)

  The rated current was passed after the overload test and the interruption test, and the temperature of the breaker terminal when the temperature stabilized was measured. Table 1 shows “◎” when the temperature rise is less than 75K, “◯” when it is 75K or more and less than 80K, and “X” when it is 80K or more.

  From Table 1, in the large current breaker having a rated current value of 125 A using the electrical contact material 31 of a silver-tungsten carbide-graphite (Ag-WC-Gr) series material, tungsten carbide exceeds 55 mass% and 55 mass %, Graphite is contained in an amount of 2% by mass to 5% by mass, the remainder contains silver and inevitable impurities, the relative density is 98.0% or more, the oxygen content is 450ppm or less, the conductivity is 45% IACS or more, By configuring the electrical contact material 31 (Examples 1 to 15) so that the folding force is 350 MPa or more, not only the consumption rate after the overload test but also the consumption amount after the short circuit test can be reduced. It can be seen that the welding after the interruption test by the short-circuit test can be prevented, and that the temperature rise after the overload test and after the interruption test can be suppressed.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

  For example, in the above embodiments and examples, an example in which the electrical contact material 31 of the present invention is applied to the stationary contact member 30 of the breaker 10 has been described. However, the present invention is not limited to this example, and the breaker is not limited thereto. The electric contact material of the present invention may be used for any of the ten movable side contact members 20 or the fixed side contact member 30. The electrical contact material of the present invention is preferably incorporated in the breaker 10 having a rated current value of about 100 A to 1600 A, and more preferably incorporated in the breaker 10 having a rated current value of 100 A or more and less than 800 A.

  In the above-described embodiment and examples, an example in which the electrical contact material 31 of the present invention is used for the breaker 10 as an example of a switch is shown, but the present invention is not limited to this example. The electrical contact material of the present invention may be used for a switch (switch device) other than a breaker such as an electromagnetic switch.

  The electrical contact material of the present invention is used by being incorporated in a breaker for high current having a rated current value of 100A to 1600A.

  10: Breaker, 21, 31: Electrical contact material.

Claims (3)

  Tungsten carbide exceeds 30 mass% and 55 mass% or less, graphite contains 2 mass% or more and 5 mass% or less, the balance contains silver and inevitable impurities, the relative density is 98.0% or more, and the oxygen content is 450 ppm or less. Electrical contact material (31) having a conductivity of 45% IACS or more and a bending strength of 350 MPa or more.   The electrical contact material (31) according to claim 1, wherein the tungsten carbide has an average particle size of 0.5 µm or more and 5 µm or less.   The electrical contact material (31) according to claim 1, wherein the average particle size of the graphite is 1 µm or more and 50 µm or less.

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