Behaviour of fibre brushes under transient atmospheric conditions

Voltage drop and friction measurements were made on fibre brushes working under transient atmospheric conditions. These transient conditions correspond to the introduction of ball-bearing greases or of water into the chamber containing the experimental set-up under a dry nitrogen atmosphere. It is shown that vapours from a particular grease have a contaminating effect on the sliding contacts. When the same grease is heated up to 100 °C and when the disc on which the brushes are rubbing is gold plated, very low frequency oscillations in the cathodic voltage drop are observed. This phenomenon is interpreted by assuming that the surface film resistance and the surface temperature are dependent on each other. In addition, a short and simplified linear stability study of sliding contacts is given. It is shown that the behaviour of brushes in an atmosphere having a variable relative humidity strongly depends on the surface material ( i.e. gold or copper) of the disc. The major conclusion emerging from the results presented is that, under certain circumstances, water vapour may play the role of an adsorption inhibitor for organic molecules whereas, in other cases, it may act as a lubricant.