HYDRODYNAMIC SEGREGATION, ENTRAINMENT AND REJECTION OF OIL IN EMULSION LUBRICATION PROBLEMS

Emulsions are widely used as metal rolling and ironing Ilrbricants, bu t their application is still an art in that no widely accepted and rob ust models of emulsion lubrication exist. Of particular confusion to d ate is the mechanism through which oil particles penetrate an inlet zo ne and serve as a lubricant. This paper addresses hydrodynamic behavio r 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 crossflow 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 adh ered to a roll or strip surface, hydrodynamic forces will determine wh ether or not the particle will become entrained. This paper analyzes t he forces involved using a foil bearing analogy. The situations under which a droplet is entrained or rejected are described, and the import ant parameters to achieve entrainment are discussed.