Reliability of electrically conducting knife-edge bearings of switches

Abstract

Knife-edge bearings are used as electrically conducting elements between the movable and fixed part of the current path in many kinds of switches, e.g., microswitches and snapaction rocker switches. The contact resistance of such bearings may rise to unacceptably high values and may d i m i i h the reliability of the device.Experimental investigations showed that fretting corrosion is the cause of occassionally observed increase and fluctuation of the electrical resistance of nonbouncing knife-edge bearings. In the case of bouncing knife-edge bearings erosion and oxidation-caused by the arc during the repeatedly opening and closing bearing contacts (notch-cut)diminishes the reliability of the bearings.Precautions have been specified in order to improve the reliability of knife-edge bearings in the current path of switches.A detailed description of the results of the investigations, a synopsis of the fundamentals (of fretting corrosion, dynamics of knife-edge bearings, friction, bouncing), and an indication of important correlations facilitate the understanding of the phenomenon occuring in electrically conducting knife-edge bearings.