High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Vacuum
Reexamination Certificate
2001-09-13
2004-07-20
Donovan, Lincoln (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Vacuum
C218S123000, C218S130000
Reexamination Certificate
active
06765167
ABSTRACT:
BACKGROUND OF OF THE INVENTION
1. Field of the Invention
The present invention relates to a new electric contact member used in a vacuum circuit breaker, vacuum switch or the like, a manufacturing method thereof, and a vacuum valve and vacuum circuit breaker made thereof.
2. Description of the Prior Art
The electrode in a vacuum valve installed in a vacuum circuit breaker or the like comprises a pair of electrodes on the fixed and movable sides. The electrodes on the fixed and movable sides consist of an electric contact and electrode rod connected thereto, and the back of the electric contact is often reinforced by a stainless steel plate.
Cr—Cu composite metal is often used to manufacture the electric contact member for large current and high voltage breaking.
The electric contact is manufactured by machining an electric contact material into a specified form, wherein the electric contact material is produced in the so-called method of powder metallurgy consisting of a first step of forming metal powder of various components or a mixture thereof into a simple structure (disk form, for example) at a specified composition and a second step of sintering it. The electric contact is provided with three or more slots for giving driving force to the produced arc so that arc will move to the circumference of the electrode without allowing arc to stay at one particular point, and these slots are formed in a vane-like separate shape. The center of the electric contact is provided with a concave to ensure that arc does not occur to remain at the center of the electric contact.
The above-mentioned electric contact is exposed directly to arc since it is used to turn on or off high voltage and current. The electric contact is required to provide a high breaking capacity, high dielectric strength and high welding resistance. It is difficult to meet all these requirements. In the products offered on the market, emphasis is generally placed on especially important characteristics according to a particular application at the sacrifice of other characteristics to some extent.
A large electric conductivity is essential to ensure large breaking capacity in the Cr—Cu composite metal, for example. This requirement can be met by the composition with an increased amount of Cu. However, this involves an decrease in the amount of Cr which increases dielectric strength, with the result that both dielectric strength and welding resistance are decreased.
Amid ever increasing amounts of voltage in power distribution business, a vacuum circuit breaker or vacuum switch is required to ensure compatibility of a large current breaking capacity with dielectric strength and welding resistance. For example, when the Cr—Cu composite metal is used to manufacture an electric contact, dielectric strength and welding resistance can be improved by increasing the amount of Cr. Increase in the amount of Cr, however, reduces conductivity and breaking capacity, making it difficult to ensure compatibility of a large current breaking capacity with dielectric strength and welding resistance in the prior art.
Japanese patent laid-Open publication NO. 235825/2000 discloses an electrode member with fire proof metal powder having the form of a flat plate. This is produced by spray-coating of the composite metal between highly conductive metal and fire proof metal onto the contact point face. Spray coating method, however, involves spray coating gas and atmosphere, so the obtained spray coated film contains a large amount of gas. Gas is discharged by arc heating at the time of current breaking, and arc is kept there through this gas, possibly causing current breaking to be disabled. Further, the size and form of fire proof metal powder on the spayed film is difficult to control, and tend to be irregular, with the result that breaking performances are unstable. In addition, formation of sprayed film requires much time, raising problems with productivity and costs.
SUMMARY OF THE INZENTION
The object of the present invention is to provide an electric contact member characterized by excellent current breaking capacity as well as a high degree of dielectric strength and welding resistance, and the method for manufacturing this electric contact member at a low production cost with high productivity.
In an effort to attain the above object, the inventors of the present application have invented a material texture which allows a large area to be occupied by the dielectric strength component on the contact point face where current breaking is performed. Namely, in the case of Cr—Cu electric contact, Cr particles are formed in a flat plate and the flat surfaces of Cr particles are oriented to be parallel to the contact point face in the Cu matrix. This structure allows many Cr particles to be exposed on the contact point face while reducing the amount of Cr and maintaining high conductivity, whereby high dielectric strength can be ensured. Further, the strength of the Cr particles perpendicular to the flat surface is reduced because of weak chemical bond between Cr particles and Cu matrix, and welding resistance is improved.
The following describes the summary of the present invention:
The electric contact member according to the present invention has a texture wherein fire proof metal powder having the form of a flat plate is diffused in the matrix comprising a highly conductive metal, and the electric contact member further characterized in that the flat surface of the fire proof metal powder is oriented in one direction and the surface in parallel with the flat surface of the fire proof metal powder is used as a contact point face.
The fire proof metal powder having the form of a flat plate according to the present invention is characterized in that the maximum length of the flat surface divided by the minimum dimension of the surface perpendicular thereto is within the range from 3 to 30.
The electric contact member according to the present invention is characterized in that 90 wt % or more of the fire proof metal powder having the form of a flat plate has the flat surface oriented with respect to the contact point face within the range from +40 to −40 degrees, and 75 wt % or more has the flat surface oriented with respect to the contact point face within the range from +20 to −20 degrees.
The above-mentioned fire proof metal powder according to the present invention comprises one of Cr, W, Mo, Ta, Nb, Be, Hf, Ir, Pt, Zr, Ti, Te, Si, Rh and Ru, a mixture comprising two or more of them or a compound thereof, and highly conductive metal comprises Cu, Ag, Au or an alloy mainly consisting of them.
The above-mentioned fire proof metal powder contains 50 to 2000 ppm of oxygen, 50 to 3000 ppm of aluminum and 100 to 2500 ppm of silicon.
The electric contact member according to the present invention comprises 15 to 40 wt % of the above-mentioned fire proof metal powder and 60 to 85 wt % of the conductive metal.
The electric contact member according to the present invention is characterized in that the percentage of the area occupied by the above-mentioned fire proof metal powder is 30 to 50% on the contact point face, and the percentage of the area occupied by the fire proof metal powder is 14 to 25% on the surface perpendicular to the contact point face.
The electric contact member according to the present invention contains 2500 ppm or less of oxygen, wherein the tensile strength in the direction perpendicular to the contact point face is 150 MPa or less, and the specific resistance is 5.5 &mgr;&OHgr;.cm or less.
The method for manufacturing an electric contact member according to the present invention characterized in that
a powder mixture consisting of the above-mentioned fire proof metal powder and highly conductive metal powder is pressure-molded at a pressure of 120 to 500 MPa to create a molded product;
this molded product is sintered under vacuum or in inert atmosphere at the melting point equal to or less than that of said highly conductive metal powder; and
a contact point face is created in parallel to the pre
Baba Noboru
Goto Yoshitomo
Kikuchi Shigeru
Kobayashi Masato
Sato Takashi
Donovan Lincoln
Fishman M.
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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