Theoretical study of operating limits for the calendering process

The velocity and pressure field forms within the gap of a calender is numerically calculated. The numerical calculations are based on a decoupled calculation method for the free surface of the bank. The transport equations for mass and momentum are solved numerically. The position of the free surface of the bank is determined by shifting it until it matches a stream line. Parameters are the gap height, the circumferential speed of the rolls, the speed ratio, the feed mass flow into the gap and the rheological behaviour of the polymer. All process parameters are subject to boundaries due to the requirements to the quality of the calendered sheet regarding surface appearance, air bubble inclusions or mixing of the polymer. The calendering process itself requires limited operating windows for the variation of the process parameters in order to meet the product quality requirements. These operating windows are discussed and graphically plotted.