Measurement of Boundary Lubricant Viscosity at Metal-Deformation Pressures (3000 Atmospheres, 20 Tons/Sq In.)

In many metalworking operations, such as rolling and wire drawing, the average pressure acting between the workpiece and the tool will be of the order of the yield stress of the metal, usually 20–50 tons/sq in. The lubricant temperature may also rise by 60 deg C or more. Any consideration of hydrodynamic lubrication in these operations should thus take account of the large viscosity changes which may occur under such pressures and temperatures. In addition, it is probable that the rate of shear will be important [1], but this will not be considered in this paper. Local pressures of the same order are developed in typical boundary-lubrication apparatus using a hemispherical slider on a flat surface under kilogram loads [2]. Information on the pressure and temperature coefficients of viscosity for lubricants is therefore important also in studies of boundary lubrication and elastohydrodynamic lubrication [3], especially in the presence of boundary additives [4]. This paper describes a simple apparatus for viscosity measurement at temperatures up to 70 deg C and pressures up to 20 tons/sq in. (3000 atmospheres) or with future modifications up to 45 tons/sq in., together with some results for fluids with and without boundary additives.