The role of relatively humidity in friction and wear behaviors of carbon sliding against copper with electric current

Abstract

During the train operation, the pantograph/catenary system is subjected to an extremely harsh service environment. Relative humidity has a great influence on the current-carrying tribological behaviors of carbon strips. The identification and understanding of the wear mechanism are extremely important in wet and dry conditions. This study was carried out to investigate the humidity effect on the service properties of carbon sample rubbing against copper (Cu) with and without electric current using a home-made wear tester, and the humidity ranging from 10% RH to 80% RH. The results indicate that the sliding wear behavior of the friction interface is drastically affected by the intervention of water vapor and electric current. The coefficient of friction (COF) without current is obviously lower than current-carrying sliding when the humidity is constant. However, the increased humidity led to a decreasing trend. After the current increases to 10 A, all the COF values are closed to each other ultimately. These phenomena mainly result from the formation and destruction of water lubrication film. Furthermore, the tribo-pairs worn surface appears the most sensitive to the current effect under dry conditions. The reverse transfer of Cu and carbon is greater on account of the current agglomeration effect, and the oxidation degree is more severe. The wear mechanisms of carbon are mainly material transfer accompanying with oxidation erosion. However, the wear degradation is weakened under water lubrication and uniform current distribution which improves the conductive quality. This is the coupling effect of humidity environment, current and heat concentration. This experiment provides technical support for the operation of an electric locomotive under an extremely harsh service environment.