Theoretical analysis of film casting process with a pinning device under a transient state

In previous reports, we proposed the model describing the catenary of the steady state of film casting in consideration of gravity or the electrostatic power of a pinning device. In this report, the model of the steady state was developed, and the perturbation transient solution around the steady state, the frequency response transfer function and the analysis of stability were calculated. The stability criterion of Nyquist, well known for control engineering, was used to determine stability. A new analytical model of film casting process that had been developed to judge stability by turbulence had an excellent practicality. Through an analysis of the film casting in transient states, it was found that (1) the stability limit grew wider when the electrostatic force was stronger, the chill roll radius was longer, and the vertical distance from the die exit to the landing point was longer, and (2) a thickness variation of about 10% occurred in response to a stepwise change in the extrusion viscosity by 1%.