EP0448757A1 - Silver contact material - Google Patents

Abstract

Preferred silver contact materials are silver/nickel and silver/tin oxide alloys. In the case of silver/nickel, alloys of 10% and 40% by weight are used. In the case of silver/tin oxide alloys, tin oxide proportions of between 8% and 12% by weight have proved advantageous. The object of the invention is to provide a silver contact material which is easy to produce and readily deformed and for which attention does not have to be paid to the polarity. This is achieved by a silver alloy containing nickel and tin oxide alloy constituents.

Description

The invention relates to a silver contact material for producing contacts usable for direct and alternating current, in particular for producing contact wire, which is suitable for direct riveting into contact pieces (contact springs).

Silver and silver alloys are primarily used to produce high-voltage contacts, which not only have good mechanical and electrical properties, but are also economical to produce. However, pure silver is unsuitable for many applications because of its tendency to weld when switching, its further tendency to stick at high contact pressure, and finally also because of the expected material migration when switching direct current. In addition, its mechanical abrasion resistance and erosion resistance are limited. Silver alloys are therefore used to an ever increasing extent, which reduce or even completely avoid these disadvantages inherent in pure silver.

Preferred silver-nickel composites have a nickel content between 10% by weight and 40% by weight. Composites of this type exhibit high hardness and strength, good electrical and thermal conductivity and, as a high-current contact - also with good burn-off resistance - even with direct current. It is particularly worth mentioning that the erosion residues are not conductive, so that such contacts can be used with advantage in low-voltage switching devices. However, they cannot be produced in the melting path, but only by powder metallurgy by pressing and sintering a metal powder mixture and are therefore more expensive than contacts made from fine-grain silver.

Also known among these silver alloys and used with great success, in particular for switching direct currents, are silver-tin oxide alloys. Because of their high brittleness, these materials are able to compensate for the shrinkage stresses caused by the effects of arcing in the contact surface in the event of thermal or electrical overload. As a result, very good erosion resistance is achieved, especially with heavy-duty circuits.

In summary, it can be said that silver-nickel alloys with a low nickel content have a low contact resistance, but have a high tendency to sweat, while such alloys have high nickel content has a low tendency to sweat, but has a relatively high contact resistance. Silver alloys with tin oxide have a low tendency to weld and are practically weld-resistant at higher tin oxide proportions, but are subject to a relatively high contact resistance.

In order to combine the advantages of these two contact alloys or to largely avoid their disadvantages, it has become known when using these materials for switching direct current that have a contact side with silver-tin oxide in a proportion of 8% by weight to 10% by weight. % Of tin oxide and the further contact side with a silver-nickel alloy with a nickel content of about 10% by weight. The silver-tin oxide on one contact side ensures the desired switching capacity, while the silver-nickel alloy keeps the material migration within limits and, above all, ensures that no conductive burn-off residues arise. The disadvantage of such a contact material application can be seen in the fact that different contact materials must always be used, the polarity of which must be observed when using them.

Another disadvantage of using silver-tin oxide contact materials is that this material can only be used to a limited extent in the case of miniaturized contacts due to the natural hardness. Wire riveted contacts made of these materials repeatedly lead to manufacturing difficulties due to their difficult cold forming.

The aim of the invention is therefore to provide a contact material based on silver alloy, which, as mentioned above, combines the advantages of the different materials, is easy to produce and is easy to deform, and also does not have to take polarity into account.

According to the invention, this requirement is met by a silver contact material consisting of the alloy components silver, nickel and tin oxide. The invention can be implemented by a silver alloy composed of 90% by weight to 94% by weight of silver, 3% by weight to 5% by weight of nickel and 3% by weight to 5% by weight of tin oxide.

In fact, such an alloy combines the advantages of the two silver alloys discussed above, namely the good manufacturability and processability and the favorable combustion behavior with little material migration, the combustion residues being non-conductive. In addition, there is a relatively low contact resistance, and finally, the polarity of the contacts made from this contact material need not be taken into account. The material is so ductile that thin contact wires can also be easily produced, which can be used for direct riveting into corresponding contact pieces (contact springs).

Claims (2)

Silver contact material for producing contacts that can be used for direct and alternating current, in particular for producing contact wire, which is suitable for direct riveting into contact pieces (contact springs),
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through a silver alloy with alloy components of nickel and tin oxide. Silver contact material,
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by a silver alloy of 90% by weight to 94% by weight of silver, 3% by weight to 5% by weight of nickel and 3% by weight to 5% by weight of tin oxide.