Development of a test method for the rheological characterization of polymers under the injection molding process conditions

The reliability of numerical simulations of the injection molding process depends mainly on the rheological characteristics of polymers. The rheological characterization of a polymer for injection molding is commonly carried out by a capillary rheometer. However, in this method the measurement is carried out on a sample of unprocessed polymer, neglecting the influence of the plastication phase. This influence is demonstrated in the first part of the paper by comparing the rheological characterizations of a polycarbonate both in the virgin and processed state. To improve the accuracy of rheological data by rejecting these simplifications, a laboratory test method has been developed for the physical simulation of polymers rheology under industrial process conditions. The method is based on an in-line slit-die rheometer which has been mounted as a mold on an injection molding machine. By means of this test it is possible to relate a polymer viscosity not only to its temperature and shear rate but also to those parameters that characterize the plastication process: screw rotation speed, residence time, temperature and geometry of the system.