Base Oil and Its Blends with ZDDP and Their Effect on Tribocharging, Braking Torque and Electrical Double Layers in a Friction Junction

Author： Gajewski Juliusz Głogowski Marek

Publisher： Springer Publishing Company

ISSN： 1023-8883

Source： Tribology Letters, Vol.38, Iss.2, 2010-05, pp. : 179-185

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Abstract

The paper presents the results of experiments on tribocharging of a blend of mineral-base oil and different zinc dialkyldithiophosphate (ZDDP) contents in a friction junction. A friction junction is constituted by a rotating shaft, a film of pure base oil, or its blend with the ZDDP, and a rotary lip seal, which is the interfacial system as a whole. Experiments were carried out on the specially built experimental facility to be a simplified model of an engine’s crankcase (or sump) in whose interior an earthed metal shaft rotated at given angular velocities. Electric potential of a stiffening ring of a lip seal, which is a measure of tribocharging, was measured directly with an electrometer. The stiffening ring’s potential is induced by charge in the film of pure base oil or the ZDDP-oil blend and is a function of the oil temperature for different angular shaft velocities and the ZDDP contents. The potential is presented in the form of some characteristics. Also the effects of an external DC electric field on the braking torque of the rotating steel shaft were examined for a range of oil temperatures, angular velocities, and ZDDP contents, and here the torque is presented for one temperature and different DC voltages of both polarities. An analysis of the research results obtained permitted us to show how the ZDDP content in a blend with the base oil tested, angular velocity, and oil temperature could affect tribocharging in the interfacial systems: the rotating shaft-oil and oil-lip seal, as well as the whole oil film in between and both electrical double layers (EDLs) at the surfaces of a shaft and of a lip of a rotary lip seal in the friction junction.