Reducing the Contact Resistance of Tarnish Layers on Silver by Means of an Oscillating Tangential Motion

An apparatus simulating the conditions in a relay contact was employed to investigate the reduction in the resistance of a layer of tarnish when subjected to a mechanical load. This entailed subjecting a thick layer of silver sulfide (Ag2S) tarnish on silver to an oscillating friction load from a hard gold stud and registering the effect of the following four parameters on the contact resistance: contact force, number of frictional movements, excursion and frequency. As the number of frictional movements increased, with the remaining three parameters being maintained at constant values, the contact resistance decreased to a basically constant value. The contact force and/or excursion determined both the magnitude of this value and the number of frictional movements required to reach this value. The effect of the frequency in the investigated range of 30 Hz to 750 Hz was insignificant. The investigations showed that in the case of excursions which were in the range of the contact area diameter, the reduction in the contact resistance was dependent not only on the sum of the excursions (excursion · number of frictional movements), but also on the amount of the excursion. The processes are interpreted in conjunction with visual inspection of the areas subjected to frictional treatment.