Studies On Electrical Contact Resistance And Coefficient Of Friction Across Sliding Electrical Contacts

Abstract

Simultaneous measurement of electrical contact resistance (ECR) and coefficient of friction (COF) at the sliding interface is essential to assess the performance of selected material contact pairs for the transfer of current from stationary member to moving member (or vice-versa). Low and stable values of ECR and COF are desirable during the intended operating life of the contact members. These parameters may change with respect to time as a consequence of change in the surface properties of contact members due to their relative movement. Hence experimental investigations have been conducted to study the variation of ECR and COF while different riders sliding on copper and brass flat samples in different environments. As a part of the experimental investigation, a reciprocating sliding setup is designed and developed to study the variation of ECR and COF in terms of normal force, sliding speed, current and environment. The details of the experimental setup are described along with its construction and operation. The sample preparation, instrumentation, data acquisition and presentation are explained in detail. The variations of ECR and COF at different normal forces, currents and sliding speeds by moving OFHC copper, brass, silver, Ag10Cu and Ag20Cu riders on OFHC copper and brass flat samples in vacuum, argon, nitrogen and air are studied in detail. Studies are also conducted to evaluate the performance of metallic contacts under lubricated condition using general purpose lubricating oils of different viscosity. Metallic contacts show a decrease in ECR with increase in normal force at all sliding speeds in all media. Sliding metallic contacts show a significant decrease in both ECR and COF during the initial sliding cycles at constant normal force in all media. Surface roughness of flat sample is found to have a significant effect on both ECR and COF in all media. Wear of rider is found to be significant as compared to wear of flat samples. Metallic contacts show an inverse relationship between ECR and COF in all media under mild wear regime (0.2< COF≤ 0.4). ECR and COF of sliding metallic contacts are independent of current (≤ 4A) in mild wear regime in all media. Reasonably low values of ECR and COF are observed for prolonged duration with lubricants having low viscosity. The presence of wear fragments at the sliding zone is found to have significant effect on both ECR and COF in all media. Low values of ECR are observed while copper rider sliding on brass sample as compared to silver rider under same operating conditions. Significant amount of metal transfer is observed with silver based riders sliding on copper and brass flat samples in different media. The present investigations are useful in understanding the contact behaviour of copper and brass flat samples for similar and dissimilar riders sliding on them in various environments.