Fretting of Electrical Contacts

Abstract

Fretting can cause the contact resistance of electrical components to become unstable. Fretting originates in vibration, mechanical shock, thermal fluctuations, and magnetic forces to which conductors are subjected. Gold is a preferred contact material because it is inert and therefore has a contact resistance which remains nearly constant during fretting. However, insulating oxide films appear at the interface of base metal contacts and gold-coated base metal contacts when the gold wears out. Platinum group metal contacts catalyze the formation of frictional polymers from organic materials, such as air pollutants, in their vicinity. Thus, fretting corrosion and friction polymerization can increase contact resistance and thereby cause electrical failure. This paper describes a new research apparatus for studying the fretting of electrical contacts, in which a stepping motor causes small oscillatory movements of a slide table. One specimen is mounted on the table, and the stationary contact is loaded against it in the force range of 5 to 500 g. Contact resistance is determined at 1.6-μm intervals along the wear track by a data acquisition system computer. Examples of the use of this equipment to model fretting of electrical contacts are given.