Effect of Rotating Speed on Surface Damage of Rolling Current-Carrying Pairs in a Water Environment

The effect of rotating speed on the current-carrying properties and surface damage of pure copper rolling pairs were investigated in a water environment. With the increasing of rotation speed from 30 r/min to 480 r/min, the friction coefficient decreased from 1.06 to 0.49 in water environment, which was much higher than that of dry current-carrying friction. And the underwater contact resistance increased from 0.57 Ω to 6.4 Ω, which was higher than that in dry rolling. The possible mechanisms were as follows. At low speeds, the water mainly exhibited capillary action, resulting in a high coefficient of friction and significant flaking on the surface of the material. While at high speeds, water exhibited partial lubrication effect, the coefficient of friction decreased and pitting occurred on the surface because of the pressurization effect. The evolution of the damage characters was based on the competition of the lubrication and pressurization of water, and the critical rotation speed of such transition was 200~240 r/min. Electrochemical oxidation happened on the current-carrying friction surface, but the atomic ratio of O to Cu was lower at lower speed due to the severe peeling, and therefore the contact resistance was lower.