How do the temperature, angular velocity and electric fields affect mechanical and electrokinetic phenomena in a friction junction?

•The system consists of two interfaces: shaft–oil film and oil film–lip seal.•The internal electric field exists naturally between the shaft and the lip seal in the oil film.•There are some irregularities in the exponential decrease of the torque with an increasing temperature.

In the friction junction, that is in a rotating metal shaft–base oil–rotary lip seal system, dynamic phenomena occur which are of mechanical and electrical nature. During the shaft׳s rotation the components of an oil film – a gap between the surfaces of a shaft and a lip of a rotary lip seal – are caused to move about within the film under the action of a centrifugal force. The relative movement of different particles and molecules in turn brings about tribocharging and results in establishing an electric field within the gap. The field and so acting the Coulomb force also affect the distribution of charged species as does the van der Waals attractive force. To analyze the effect of the above factors as well as the temperature of oil in the gap measurements of the shaft׳s braking torque and the voltage between the rotating metal shaft and a stiffening ring of a lip seal for different ranges of the base oil׳s temperatures and of the shaft׳s angular velocities are performed. In the experiments the synthetic PAG (polyalkylene glycol) and PAO (polyalphaolefin) base oils and a fluorocarbon rotary lip seal are used.