CoRotating TwinScrew Extruders Hanser （共转双挤出机汉斯）.pdfVIP

Klemens Kohlgrüber Co-Rotating Twin-Screw Extruders Fundamentals, Technology, and Applications Sample Chapter 3: Rheological Properties of Polymer Melts ISBNs HANSER 978-1-56990-422-0 1-56990-422-7 Hanser Publishers, Munich • Hanser Publications, Cincinnati 3 Rheological Properties of Polymer Melts JENS HEPPERLE 3.1 Introduction and Motivation As pellets are frequently used in plastics processing as starting materials, polymers pass initially through the following aggregate conditions in the extruder: solid solid/liquid liquid. While for liquid polymers one-dimensional modeling has been available since the 1970s in the form of a dimensionless description of the pressure build-up for filled and partially filled zones in the twin-screw extruder (see Chapter 7) and we have since succeeded in producing a three-dimensional description of the speed, pressure and temperature fields of filled screw elements (see Chapter 8), it was only in recent years that models of the actual plastification process and the melting behavior (in other words the transition from solid to solid/liquid and to liquid) were developed. This is due to the fact that plastification in the extruder is a very complex process, dominated by viscous energy dissipation. In this process, friction and plastic deformation of the individual granules on the walls (of the housing and the screws) and between individual granules produces heat which causes melting. On the other hand, the quantity of heat introduced through the housing wall by thermal conduction is usually quite small in practice ([1], [2]). Since homogenous melts are covered in a later account of pressure build-up and power inp