Effect of Lubricant on Degradation Process of Au-Plated Slip-Ring and Ag-Pd Brush System for Small Electric Power

The authors have been investigating degradation process of Au plated slip ring and Ag-Pd brush system. In almost all cases the lifetime of the sliding system ends, when Au plating layer is worn out, the ring surface is oxidized to be black in color and contact resistance becomes very high. However, the lifetime is greatly changed case by case, while it is very short without lubricant. Even with lubricant the lifetime is varied from about 1000 hours to almost 7000 hours in the past experiments. It is an important issue where such variation comes from. In this paper the effect of lubricant on degradation process of contact resistance is focused on. In the past tests the lubricant is supplied only once before the test. In this test the lubricant is regularly supplied almost every 900 operation hours. The followings can be made clear. Just after the supply of the lubricant the contact resistance fall down just for a short time, but it comes back to the similar value before the supply. However the operation more than 8000 hours is realized. In addition the contact voltage drop increase gradually until 2600 hours and after that it stays almost constant around 70 mV. It probably means that the Au plating layer is gradually worn out at the stage of increasing voltage drop, while the Ni base plating layer is totally exposed at the stage of constant voltage drop. The reason of long operation seems to be that the lubricant not only decreases wear but also suppresses oxidation of the Ni layer.