A torque-based analysis of the reverse roll coating process

In a laboratory film coater operated at industrial speed, the torque exerted by the metering rod was used to investigate the hydrodynamics in the metering nip flow. CFD simulations were also performed taking into account the deformation of the roll cover to depict the elastohydrodynamics of the metering nip flow. From the experiments, it was found that the torque increases with transfer speed, load and viscosity. When runnability problems such as spitting were observed, the torque signal decreased. Torque measurements could also predict excessive friction between rod and roll, which may damage the elastic cover. The numerical simulations showed trends similar to the experiments. Regions of positive and negative torque values demonstrated how the fluid interacts with the rod, a phenomenon apparently related to the occurrence of secondary flows in the metering nip. Finally, the numerical results also showed that the minimum nip gap becomes constant at high loads.