MODELING OF DISPERSED MELTING MECHANISM OF PVC POWDERS IN CALENDER GAPS IN AN INTERMESHING COUNTER-ROTATING TWIN-SCREW EXTRUDER

摘要

Our experimental studies on unplasticized PVC (uPVC) melting process by ultrasound in-line monitoring method suggest that calendering effect between two screws dominates the melting process in an intermeshing counter-rotating twin-screw extruder. In this paper, a dispersed melting model in calender gaps is proposed to predict the melting length of PVC powders in terms of the number of calender gaps. Effects of screw geometries (channel depth, calender gap clearance) and processing conditions (screw speed, leakage flow) on melting length are discussed for both filled Newtonian and non-Newtonian fluid models. The calculated results are compared with experimental observations by "screw pulling out" method and ultrasound in-line monitoring method.