Analytical Model for the Throughput and DrivePower Calculation in the Melting Section of Single Screw Plasticizing Units considering Wall-Slippage

摘要

A two-part article presents a process model developed at the KTP for describing the pressure/throughput and drive power behaviour of wall-slipping polymers in the melting section of single-screw plasticizing units. After a new model for describing the flow behaviour in the melt film was developed in the first part of the paper, this second part now covers the adaptation of an existing process model for pure melt conveyance to allow for the processes that take place in the melt pool, and the extension of the model to include the drive power calculation. Following this, the two individual models are then coupled through the assumption of a constant pressure gradient in the conveying direction. Using the overall model that is generated, the pressure/throughput and power behaviour during melting are investigated on the basis of the influencing di-mensionless variables. This requires the geometry of the solid bed and the solid bed velocity to be specified as input variables. Apart from this, the other material parameters that need to be defined are the viscosity of the polymer melt, the critical shear stress, a material-specific parameter for describing the slipping-velocity-dependent shear stress and the operating point of the process that is taken as a basis.