An Experimental Study to Show the Behavior of Electrical Contact Resistance and Coefficient of Friction at Low Current Sliding Electrical Interfaces

Abstract

Electrical contact resistance (ECR) and coefficient of friction (COF) are the two parameters that characterize the performance of sliding electrical contacts. Due to geometrical minuteness of the electrical and mechanical phenomena occurring at the sliding interface, it has been extremely difficult to develop widely applicable theoretical models and analytical correlations. Consequently, experimental studies gain importance as the contact manufacturers have to depend on the available experimental data. The scope of present work is limited to light duty sliding contacts, which are commonly used in various radio-electronic devices and control and automated systems. Experimental studies conducted on oxygen-free high conductivity (OFHC) Cu contacts are presented in this paper. Effect of normal force, surface roughness, initial run-in, sliding speed, and liquid lubricants on ECR and COF is studied. Experiments are conducted with the help of indigenously developed test setup, consisting of a reciprocating pin-on-flat sliding arrangement. All contacts showed a decrease in ECR with increase in normal force. At small speeds (¡U 1.0 mm/s), both ECR and COF are found to be independent of sliding speed. A significant decrease in ECR and COF is observed with progressive sliding during the initial cycles. Roughness of the flat sample is found to have significant effect on ECR and COF, especially during initial sliding cycles. Contacts exhibited an inverse relationship between ECR and COF in the mild wear regime (0.2 < COF ¡U 0.4). Liquid lubricants having low viscosity exhibited reasonably low values of ECR and COF for prolonged sliding duration. Presence of wear debris at the sliding zone is found to have significant effect on both ECR and COF. Wear of the sliding surfaces is analyzed using scanning electron microscopy (SEM) and correlated with the observed behavior of ECR and COF.