Melt rheology and rheometry
Two main groups of material property data are needed to analyse and simulate Fow in
the injection moulding process:
Properties of resistance to Fow under stress (
expressed by shear stress
. shear strain rate data;
Properties of static compressibility and thermal expansion:
expressed using PVT
These notes deal with the ±rst group:
rheological properties and their measurement
Rheometric methods have to be simple and analysable, so they provide a clear
introduction to the analysis of melt Fow in injection moulding and a warning about
After completing this section you should be able to…
Demonstrate an understanding of the theoretical basis and practical application
of a Capillary Rheometer and a Cone and Plate rheometer.
Manipulate power-law, Cross, Cross-Arrhenius and Cross-WL² constitutive
equations for polymer melts, and use them to represent data.
Assess whether Bagley or Rabinowitsch corrections are needed in calculations for
polymer melt Fow in channels (e.g. rheometer capillaries, mould runners and
gates), and apply them if necessary.
Demonstrate understanding and make appropriate use of the following
apparent viscosity, Bagley correction, consistency, Cross model,
degradation, die, extensional Fow, extensional viscosity, Fow curve, melt, melt
slip, M²I, newtonian viscosity, power-law Fow, pseudoplasticity, Rabinowitsch
correction, reference viscosity, reference shear rate, jetting, rheometer (capillary,
cone-plate), shear rate (= shear strain rate), temperature coe³cient of viscosity,
viscometer = rheometer, zero-shear viscosity.
a widely-used industrial test which provides a single-point ‘index’ of
Polymer Processing Technology
19 October 2009