Particle behavior in two-phased lubrication

Emulsions and slurries are commonly encountered in tribology problems. The dispersed phase in the mixture plays an important role in lubrication or wear, but the mechanisms of particle capture by two surfaces have never been well understood, While no similar models have been proposed for slurries, emulsions researchers have attributed lubrication mechanisms to a 'plate out' theory through which oil separates from the emulsion and coats the exposed metal surfaces, Observations of particle behavior by Nakahara et al. (ASME J. Tribol., 110 (1988) 344-353) cast doubt on this theory; particles very close to the tooling were rejected and played no part in the lubrication process. Further, the behavior of a particle depended greatly on its size, This paper offers a potential explanation for this behavior through a computational fluid dynamics model of a rigid particle in an inlet zone. A particle in such a flow field is found to cross streamlines to an equilibrium position a certain distance from the tooling or workpiece. This segregation location is related to the particle size with the same trends of particle penetration as observed by Nakahara et al. The theory applies to emulsion lubrication, slurry lubrication and wear involving solid particles suspended in a liquid. (C) 1997 Elsevier Science S.A.