Numerical study of transient instabilities in reverse-roller coating flows

A semi-implicit Taylor-Galerkin/pressure-correction algorithm of a transient finite element form is applied to analyse the flow instabilities that commonly arise during reverse-roller coating A mathematical model is derived to describe the solvent coating applied to the underside of the sheet, assuming that the lacquer is a Newtonian fluid and considering the flow between application roller and foil. Here, we have investigated the effects of temporal instabilities, caused by adjustment of nip-gap width and foil-position, extending our previous steady-state analysis. Foil shifting is found to have a significant influence upon pressure and lift on the foil, drag on the roller, and free coating profiles. This would result in process instabilities, such as chatter and flow-lines. In contrast, nip-gap adjustment has no influence on the coating finish.