Lubrication mechanisms of hot-dipped tin separable electrical contacts

Degradation phenomena occurring during the lifetime of tinned separable electrical contacts remain a factor of loss of reliability that can be minimised. In a previous paper, friction, wear and electrical properties of hot-dipped tin coatings on bronze substrates have been analysed with various techniques in order to show the improvement due to a well-suited fluorinated lubricant layer. Contacts were of the sphere on plane type obtained from strips of tinned CuSn4 (as received for the flats, and formed by stamping for the dimples). Macroscopic friction cycles simulating insertion and withdrawal of separable contacts were performed as well as fretting cycles. Efficiency of the lubricant was strongly related to the film thickness in the case of macroscopic friction of dimple on flat contacts. For a sufficient film thickness different behaviours were observed for different molecules. Here the particularity of lubrication mechanisms of hot-dipped tin contacts is analysed. The evolution of static contact resistance values before friction and during the friction tests correlated to the wear behaviour shows the influence of some of the lubricant properties such as viscosity and chain structure.