Hydrodynamic Segregation, Entrainment and Rejection of Oil in Emulsion Lubrication Problems

Emulsions are widely used as metal rolling and ironing lubricants, but their application is still an art in that no widely accepted and robust models of emulsion lubrication exist. Of particular confusion to date is the mechanism through which oil particles penetrate an inlet zone and serve as a lubricant. This paper addresses hydrodynamic behavior of emulsions and addresses topics such as droplet segregation in the inlet zone and the forces acting upon individual droplets in a worst case analysis of entrainment. In segregation, a phenomenon first noted in Poiseuille tube flows, neutrally buoyant particles will cross flow streamlines to an equilibrium position a finite distance from the edge of the flow. This paper includes an analysis of segregation using the empirical results obtained elsewhere, and describes the relevance of segregation to metal forming inlet zones. If a droplet does penetrate the inlet zone to a point near the edge of contact, and it has not adhered to a roll or strip surface, hydrodynamic forces will determine whether or not the particle will become entrained. This paper analyzes the forces involved using a foil bearing analogy. The situations under which a droplet is entrained or rejected are described, and the important parameters to achieve entrainment are discussed.