Wear of contact elements in electromechanical switches

Abstract

The main purpose of this paper is to investigate friction, wear and contact conductivity behaviour in lubricated sliding contacts of electromechanical switches (EMS), in the course of long-term use (upto 1.5 × 10 5 cycles). The investigation with various lubricants has been carried out using a specially designed laboratory device with the cylinder-on-flat contact configuration, which simulates operating conditions of a typical EMS. Lubrication of contacts is shown to stabilize friction and most of lubricants maintain the boundary lubrication condition even after 150 000 sliding cycles. At the same time, contact resistance increases with time simultaneously with its instability, which can lead to a significant distortion of the transmitted signal. The influence of the state of the working surfaces and the lubricating layer properties on the performance of contact is analysed. Also, the peculiarities of the cylinder contact surface formation, its variation during operation and its effect on contact conductivity is considered. It's shown that if the contact element has a more isotropic and smooth surface a much better tribological performance will be imparted to the contact and, to a certain degree, conductivity improves. The boundary lubricating layer behaviour is studied and it has been found that the formation of polymer-like substances occurs under multiple reciprocating motion. Such modification of the lubricating layer increases the load-carrying capacity, provides a more reliable screening of the surfaces and simultaneously impairs contact conductivity. The methods of EMS serviceability improvement are discussed.