GB2045002A

GB2045002A - Vacuum type circuit breaker contact and method for producing the same

Info

Publication number: GB2045002A
Application number: GB8005954A
Authority: GB
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1979-02-23
Filing date: 1980-02-21
Publication date: 1980-10-22
Also published as: GB2045002B; DE3006275C2; JPS6059691B2; DE3006275A1; JPS55113225A

Abstract

This invention relates to a vacuum type breaker contact comprising a sintered body of a "predetermined" metal such as Copper and Chromium as the main component, said sintered body being impregnated with an additive such as Bismuth or Tellurium or Antimony having a low melting point, a high vapour pressure and a small limit of solubility to the main component. The amount of additive is preferably varied gradually or stepwise in the direction of the thickness of the sintered body to be more than 0.5% at the contact surface and less than 0.5% at a surface suitable for soldering to a support.

Description

SPECIFICATION Vacuum type circuit breaker contact and method for producing the same This invention relates to a vacuum type circuit breaker contact having the ability to interrupt a high-electric current, the chopping current of which is small, and this invention further relates to a method for producing said contact.

Generally, the necessary properties required by a vacuum type circuit breaker contact are as follows: (1) high-electric current can be interrupted; (2) chopping current is small; (3) contact resistance is low; (4) welding force is small; (5) dielectric strength is high; and (6) waste is little.

However, it is difficult for contacts used in practice to satisfy all of the above mentioned properties.

Thus, the conventionally used contacts satisfy particularly important properties required depending on their uses, but some other properties are sacrificed.

For example, heretofore, a Cu-Bi contact has been usually used as a circuit breaker contact. However, according to our experience, the Cu-Bi contact containing Bi in an amount of not more than 0.5% by weight has the disadvantage that the chopping current is large, and a Cu-Bi contact containing Bi in an amount of not less than 0.5% by weight has the disadvantage that solderability is poor. Thus, these contacts are not satisfactory for practical use.

Other contacts comprising other alloys also have, more or less, almost the same tendencies a mentioned above with regard to the Cu-Bi contact.

Sometimes, Cr is used as the main component. In place of Bi, other metals such as Te, Sb and the like can be used. These metals satisfy the three conditions that the melting point is as low as that of Bi; that they have a low limit of solid solubilityto the main component; and that the vapour pressure is high. However, in any case, these metals also have the disadvantages as mentioned above with regard to Bi.

With a view to mitigating the above disadvantages the present invention provides a vacuum type circuit breaker comprising a sintered body of a predetermined metal as the main component, said sintered body being impregnated with an additive having a low melting point, a high vapour pressure and a small limit of solubility to the main component.

In accordance with a second aspect of the present invention, there is provided a method for producing a vacuum type circuit breaker contact, with comprises the steps of mixing a predetermined metal; sintering said mixture containing the predetermined metal as the main component; impregnating said sintered body with an additive having a low meltin point, a high vapour pressure and a small limit of solubility to said main component; and cutting said sintered body impregnated with said additive at a predetermined position.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the relation between various properties and Bi content varying in the thickness direction of a Cu-Cr sintered body impregnated with Bi.

Figure 2 shows an amount of chopping current of an Ag-WC contact and the contact comprising a Cu-Cr sintered body impregnated with Bi.

This invention provides a vacuum type circuit breaker contact having the ability to interrupt a high-electric current, the chopping current of which is small, and this invention further provides a method for producing said contact.

The present invention is illustrated hereinafter, taking Cu as the main component and Bi as an additive for example.

A first important feature of this embodiment is that the Bi content of the contact is varied slope-like or step-wise in accordance with the direction of thickness of the contact.

A second important feature of this embodiment is that the Bi content of contact surface facing the counterpart contact is made not less than the limit of solubility to the main component, i.e. 0.5% by weight. If the Bi content is not less than 0.5%, Bi precipitates alone at the grain boundary of Cu and consequently the chopping current is significantly reduced.

A third important feature of this embodiment is that the Bi content of the contact surface which does not face the counterpart contact but is soldered to a conductive bar, is made not more than the limit of solubility to the main component, i.e. 0.5%. If the Bi content is not more than 0.5%, Bi does not precipitate as a simple substance at the grain boundary of Cu and consequently solderability is improved.

The above mentioned features may also be embodied by impregnating a Cu-Cr contact Bi.

It is impossible to embody the above mentioned features by the conventional melting method. For example, when Bi is melted with Cu or Cr at the same time in a mixture, it is impossible to vary the Bi content in accordance with the direction of thickness of contact since Bi is uniformly dispersed throughout the contact.

Thus, the contact is obtained by impregnating a Cu sintered body with Bi, wherein the Bicontentofthe contact surface facing the counterpart contact is made not less than 0.5% by weight and the Bi content of the contact surface to be soldered with a conductive bar is made not more than 0.5% by weight. In Figure 1, if the Bi content is not more than 0.5% by weight, Cu and Bi make a Cu-Bi alloy, and if the Bi content is not less than 0.5% by weight, not only Cu-Bi alloy is formed but also Bi precipitates as a simple substance.

Example The method for producing a vacuum type breaker contact in accordance with this invention is described hereinafter.

A sintered body comprising 75% by weight of Cu and 25% by weight of Cr was prepared in accordance with powder metallurgy techniques. A predermined amount of Bi powder was then placed on the above sintered body, and was heated at a predetermined temperature (e.g. 1000 C) higherthanthe melting point of Bi (271"C). The aboe mentioned Cu-Cr sintered body had a density ratio of not less than 95% to the theoretical density. This means that at least 95% of the Cu-Cr sintered body is filled with Cu and Cr. Internal spaces lie scattered, and Bi penetrates and impregnates the Cu-Cr sintered body.

Bi content in the above Cu-Cr sintered body measured along the direction of thickness of the sintered body is shown in Figure 1. As clearly seen from Figure 1, if the impregnated surface is subjected to 2 mm cutting, a part, the Bi content of which is 1 - 2% by weight, is exposed. This part makes a satisfactory contact surface to be face to a counterpart contact, and the chopping current of this part is sufficientiy low, sometimes 1 A or less. On the other hand, as can be seen from Figure 1, solderability is improved by soldering the zone having satisfactory solderability.

Figure 2 shows the chopping current properties of the contact obtained by subjecting the above Biimpregnated Cu-Crsintered body to cutting. As clearly seen from Figure 2, the chopping current of the above prepared contact of this invention is equivalent to that of an Ag-WC contact, the chopping current of which is considered to be the lowest among the various conventional contacts. Thus, the chopping current properties of the contact of this invention are excellent, and besides, the manufacturing cost of the contact of this invention is much lower than that of an Ag-WC contact.

In addition to these properties, the contact of this invention was proved to be excellent with regard to other properties such as solderability, welding force, contact resistance, arc time at the time of interrupting and the like.

The present invention has been explained particularly with regard to Cu-Bi contact, but substantially the same effect could be achieved with regard to other contacts obtained by using Cr as the main component and using Te or Sb as an additive in place of Bi.

Claims

1. A vacuum type circuit breaker contact comprising a sintered body of a predetermined metal as the main component, said sintered body being impregnated with an additive having a low melting point, a high vapour pressure and a small [imit of solubility to the main component.

2. A vacuum type circuit breaker contact according to Claim 1, wherein said main component is Cu and Cr.

3. A vacuum type circuit breaker contact according to Claim 1, wherein said additive is selected from the group consisting of Bi, Te and Sb.

4. A vacuum type circuit breaker contact according to Claim 1, wherein the amount of the additive impregnated varies gradually or stepwise in the direction of the thickness ofthesintered body.

5. A vacuum type circuit breaker contact according to Claim 2 or 3, wherein the amount of the additive impregnated on the contact surface facing the counterpart contact is not less than the limit of solubility to the main component and the amount of the additive impregnated on the contact surface to be soldered to a conductive bar is not more than the limit of solubility to the main component.

6. A method for producing a vacuum type circuit breaker contact, which comprises the steps of mixing a predetermined metal; sintering said mixture containing the predetermined metal as the main component; impregnating said sintered body with an additive having a low melting point, a high vapour pressure and a small limit of solubility to said main component, and cutting said sintered body impregnated with said additive at a predetermined position.

7. Avacuum type circuit breaker contact constructed substantially as herein described with reference to the foregoing Example.