W.c. Heraeus Gmbh

Dieter Feldmer

Heinrich Wolf

Rudolf Schnabl

Intermediate material in the form of a metal strip with a contact area is provided with a projection on the bottom surface of its core area, i.e., on the surface to be joined to a contact carrier strip of copper or a copper alloy. The bottom surface of the strip facing the contact carrier strip is plated with a material which consists essentially of silver, and the melting point of the core area of the metal strip is above the melting point of silver. For the production of a semifinished product for electrical contacts, the metal strip is welded by its silver-coated bottom surface to the contact carrier strip, consisting essentially of copper. The silver from the coating on the core area of the metal strip and the copper from the contact carrier strip mix with each other and thus form an alloy which corresponds or is very close to the eutectic alloy with 28 wt. % of copper and the remainder of silver.

Welding process

To manufacture a starting material for electrical contacts, such as relay contacts, a contact sandwich in the form of a metal strip made of a material of good electrical conductivity is bonded to a contact support strip consisting essentially of copper by resistance welding. The bonding surface of the metal strip has wales or ridges running lengthwise, the crests of the ridges being tapered in cross section and being provided with a coating consisting essentially of silver. To produce an electrical contact, the ridges are pressed against a copper contact support and a high heat is produced at the crests of the ridges by a welding circuit. This results in the melting of the silver coating, which is forced between the ridges by the pressure applied through the electrodes of the welding circuit, where it forms a silver-copper alloy with a melting point close to the eutectic. The surface of the strip which is to be the working contact is disposed on the side of the strip opposite the side provided with the ridges.

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Nidderau, Germany

Dieter Feldmer