Numerical Modelling of the Contact between Lithographic Printing Press Rollers by Soft EHL Theory

Abstract

The contact behaviour in a coating roller or printing press roller nip is investigated in this paper by using soft elastohydrodynamic lubrication (EHL) theory. Film thickness, roller deformation and pressure profiles are evaluated for a range of possible dimensionless speed, load, elastomer thickness, Poisson's ratio and fluid inlet positions. To achieve the simultaneous iterative solution of the describing equations, the Reynolds equation is transformed into a form of boundary integral equation which is solved by Simpson's rule and surface distortion is obtained by a boundary element method. The numerical scheme proved to be very effective for such layered soft EHL problems. Results show that relatively thick fluid films exist in the nip because of the large deformation of the elastomer under normal working conditions. The dimensionless speed parameter has more influence on film formation at a fully flooded condition than any of the other parameters. Because the layer is easily deformable, film thickness may increase when load increases. The shape and thickness of the film and pressure profile are also controlled by the degree of starvation. At severely starved fluid supply, speed and load parameters have the most significant effect on the minimum film thickness. Larger Poisson's ratios produce a little smaller film thicknesses and larger surface displacements than the small values, and small elastomer thickness gives small indentation and large pressures in the nip.