JPH0215964B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an airborne electrical contact member suitable for use in large current circuit breakers such as no-fuse breakers. Generally, the requirements for electrical contacts include high welding resistance and abrasion resistance, long switching life, and low contact resistance. Silver-oxide contacts have been known to meet these electrical contact requirements. There are two methods for obtaining this silver-oxide contact: powder metallurgy and internal oxidation. The internal oxidation method is an application of the phenomenon that, when an alloy is heated to high temperature in an atmosphere with sufficient oxygen supply, only the added metals of the alloy are selectively oxidized before the base of the alloy is oxidized. This method is mainly known as a method for manufacturing Ag-CdO-based contact members, and is described in "Sintered Electrical Contact Terminology" published by JPMA (Japan Powder Metallurgy Association) in January 1976, page 3, page 209. It is explained as follows. “This is mainly a method of manufacturing Ag-CdO contact parts,
First, an alloy of Ag and Cd is produced by melting, processed into wire or plate material, and formed into the desired contact shape.Then, this alloy is oxidized in an oxidizing atmosphere (around 750℃ in O ₂ gas). be. ” At around this temperature, O ₂ diffuses into Ag,
Ag is not oxidized, only Cd is selectively oxidized, and the alloy is
Ag-Cd becomes Ag-CdO. In other words, this alloy is a dispersion-strengthened alloy in which oxides are finely dispersed, but since this oxidation occurs from the surface, a concentration gradient occurs toward the surface, resulting in the concentration of cadmium oxide (CdO) increasing closer to the surface. There is a tendency for the number of cases to increase. A method for uniformly distributing CdO in Ag is also already known from Japanese Patent Application Laid-Open No. 135584/1984. To homogenize this oxide, the alloy is made into fine particles in advance, and the additives in Ag are oxidized in an oxidizing atmosphere as described above.
It hardens particles and forms them into a predetermined contact shape.
It can be said that this is also a type of contact member made by internal oxidation. However, this method has the drawback of high manufacturing costs because it requires two steps: first turning the alloy into particles, and then compacting the oxidized particles. The present invention is an internal oxidation method (hereinafter referred to simply as an internal oxidation method) in which a member is formed into a predetermined contact shape and then oxidized, which is inexpensive to manufacture.
To provide a contact member in which the oxide is dispersed in the Ag to a sufficient extent that it can be used as an air contact, and the contact performance is improved by using the combination and amount of metal oxide added to the Ag. be. In addition, it is already known that, in addition to the above-mentioned Cd, Sn, In, etc. are included as oxide metals added to Ag for silver-oxide based contact members made by the internal oxidation method (for example, in JP-A No. Publication No. 50-28691). The reason why this silver-oxide contact is relatively often used as an air contact is that it has excellent welding resistance and arc wear resistance when turning on and off current, and the contact remains stable even after the contact is opened and closed many times. This is because it maintains a good balance of excellent properties as a contact, such as little increase in resistance and high conductivity. However, recently, there has been a demand for smaller size, improved performance, and improved reliability of switching equipment, and contacts that have welding resistance and insulation resistance are particularly important. This can cause damage to electrical equipment if the contacts do not open when they should open and instead become firmly welded and cannot be disconnected, or if the dielectric strength voltage deteriorates after disconnection.
This is because it can lead to electric shock and other major secondary disasters. Insulation resistance is the resistance of the inner surface of the insulation case of circuit breakers and switches to arc energy generated between contacts.
This refers to the degree to which the dielectric strength voltage between contacts or between contacts and case decreases due to adhesion of evaporative material, carbonization, etc. This insulation resistance characteristic is largely due to the evaporation material scattered by the arc, although it is not unrelated to the evaporation and wearability of the contact material by the arc. On the other hand, contact wear is often caused by melting due to arc heat or joule heat generated by contact resistance, and the arc wear resistance and insulation resistance of contacts are not necessarily in a parallel relationship. Conventionally, in high-current circuit breakers such as no-use breakers, the arc space that occurs when the contacts open and close is large, and the extinction chamber (space that absorbs the arc) is large.
However, due to the reduction of the arc space due to the miniaturization of equipment, the simplification or omission of the extinguishing chamber, and the decrease in heat resistance due to the use of cheap molding materials, thermal deterioration due to arcing has been prevented. This has recently become a major problem, as the insulation properties of the inner wall of the mold deteriorate. For this reason, it has become important for contacts to have low arc energy due to interruption, low evaporation, and excellent insulation properties. Furthermore, it is already known that adding tin and indium to a silver-cadmium alloy and causing internal oxidation can improve contact performance, but this does not necessarily meet the target contact performance, especially insulation resistance. It was not enough and did not reach the required level. The present invention has been made in view of the above points, and it is a silver-oxide type contact made by an internal oxidation method, in which the tin content in the conventional silver-cadmium-tin-indium alloy is specifically adjusted to a predetermined amount. Therefore, it is possible to provide an electrical contact with excellent practicality, which does not increase contact resistance and further improves insulation resistance without reducing welding resistance. The present invention will be described in detail below. The contact material of the present invention contains cadmium (Cd) in an amount of 1 to 6% by weight.
An alloy containing 7.3 to 10% by weight of tin (Sn), 2 to 5% by weight of indium (In), and the remainder being silver (Ag) is melted and processed into a wire or plate material to form the desired contact shape. It is obtained by internal oxidation in an oxidizing atmosphere. In the present invention, the lower limit of the amount of cadmium is set at 1% by weight because the welding resistance effect is small if the content is less than this, so the upper limit of the amount of cadmium is set at 6% by weight.
The reason for this is that, although the welding resistance is excellent above this value, it is difficult to apply the internal oxidation method and the desired alloy cannot be obtained. The lower limit of indium was set at 2% by weight because if it is less than this, internal oxidation becomes difficult due to the combination with tin-cadmium, and if it exceeds 5% by weight, internal oxidation becomes impossible, and as a result, the welding resistance deteriorates. This is based on the fact that it actually declines. The lower limit of tin was set at 7.3% by weight because if the content is lower than this, there is no decrease in welding resistance, but it is not effective in improving insulation properties.
The reason for the weight percentage is that if it exceeds this range, the workability of the alloy will decrease, cracks will occur during internal oxidation, internal oxidation will become difficult, and variations in welding resistance will become noticeable. Next, examples of the present invention will be described together with comparative examples. A to J in Tables 1 and 2 are examples of the present invention, and K to T are comparative examples. These samples were manufactured by melting an alloy having the composition shown in the table (all weight percentages), processing this into a plate material, shaping it into the desired contact shape, and then heating it in an oxidizing atmosphere at a temperature of 720°C. , Sn, Cd, and In in the alloy were internally oxidized to prepare a sample with a structure in which oxides of SnO ₂ , CdO, and In ₂ O ₃ were finely dispersed in silver, and a contact welding test and a breaking test were conducted. Table 1 shows the welding test results. The welding test conditions were as follows: Voltage AC220V, 60Hz, current 2300A, power factor 0.8 circuit was applied with contact size 5 x 6 x 1.5mm, contact pressure 1Kg, several seconds after 1 cycle of electricity was applied. The welding force was measured. The results of the test were repeated five times on the same sample, and it is desirable that the welding force be as small as possible. Table 2 shows the wear amount and insulation properties of the contacts after the circuit breaker breaking test, and the breaking test conditions are voltage
The amount of wear on the contacts and the insulation characteristics inside the arc shot were measured after breaking a circuit with AC220V, 60Hz, current 3000A, and power factor 0.8 with contact dimensions 5 x 5 x 1.5 mm and contact pressure 2 kg. , shows the test results conducted once on the same sample. The insulation properties here refer to the characteristics of each arc chute 2 to 8 and iron piece 1 shown in the figure after testing under the conditions and method described above using a breaker mechanism and arc extinguishing device (arc chute).
"1-2" in Table 2 refers to the insulation resistance between
is the insulation resistance between the arc chute 2 and the iron piece 1, “1
-8'' is the insulation resistance between the iron piece 1 and the arc chute 8. This is JIS earth leakage breaker C8371−1974
The settings are based on the insulation resistance test described in . It is desirable that the insulation resistance between the arc shoots after this interruption test is high, that is, the dielectric strength voltage is high. From this test result, even if the amount of contact material wear is small, it does not necessarily mean that the insulation resistance (withstand voltage) is high, and although the cause is not clear, there is a proportional relationship between the amount of contact material wear and the withstand voltage. do not have. As is clear from Tables 1 and 2, it is clear that the contact member according to the present invention has excellent performance in a well-balanced manner in terms of welding resistance, wear amount, and insulation resistance properties in the large current region, and is small in size. It can be used in comparatively large current circuit breakers and switches such as low-cost no-fuse breakers, and can improve insulation properties without increasing welding resistance or wear resistance. It is.

【table】

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the positional relationship between a breaker mechanism and an arc chute when measuring insulation resistance. A: Fixed contact, B: Movable contact, 1: Iron piece, 2,
3, 4, 5, 6, 7, 8: Arc shoot.

Claims (1)

[Claims] 1. In a silver-oxide contact member obtained by melting an alloy, processing it into a wire or plate material to form a desired contact shape, and then internally oxidizing it in an oxidizing atmosphere, 1 to 6% by weight of cadmium and tin 7.3~10
An aerial electrical contact member for a large current interrupting switch, characterized in that it contains 2 to 5% by weight of indium.