Modelling of forward roll coating flows with a deformable roll: Application to non-Newtonian industrial coating formulations

This paper describes the development of a model of the application nip of a forward roll coater and its use to investigate the hydrodynamics of non-Newtonian industrial coating formulations. The focus of the work is on the simulation of the roll deformation and its relationship with the hydrodynamics in the nip. The free surface movement of the fluid domain is included in the model, and is coupled to the deformation of the elastomer-covered roll for the case of a negative gap. An iterative approach is used, whereby the free surface movement is adjusted according to the normal velocity component along the boundary. The governing equations are solved with the finite element method and adaptive re-meshing of the domain between iterations. The elastomer deformation is modeled using a two-dimensional approach, where the elastomer/liquid interface is updated using the force balance at the surface. The solid and fluid problems are solved in a de-coupled manner, in which each problem is solved separately and alternately until final overall convergence is obtained. A comparison with recently obtained data shows a close match between experiment and simulation. Finally, the methodology is applied to investigate the effect on the pressure profile of the properties of non-Newtonian Kaolin-latex coating formulations and roll speeds typical of those in the industry. The results show that the proposed model can help gain insight into the mechanisms that govern this type of coating process.