A new rheological measuring die to determine the influence of the flow channel surface on wall slippage

Rheological instabilities like stick slip or shark skin as well as wall slippage in thermoplastic melt flow affect significantly the surface quality of extruded products. These effects are not only influenced by the processed polymeric material but also by the flow channel surface and material. To avoid these problems it is necessary to find optimized combinations between the processed polymeric material and the die surface material. A rheological measuring die to determine the influence of the flow channel material and surface or wall slippage and rheological flow instabilities and the first results are presented in this paper. For the simple change of the test channel surfaces a measuring die with an exchangeable rectangular testing channel has been designed. This measuring die can be used in combination with a standard High Pressure Capillary Rheometer. The advantage of this die is that exchangeable inserts are placed in the main body of the measuring die. With these exchangeable inserts it is possible to assemble several channel surfaces within a very short time. Furthermore it’s not necessary to change the whole die, therefore cost savings are the result, also a wide range of different test channel surfaces can be tested. The pressure and temperature of the melt can be measured to analyze the influence of e.g. polished, roughened and coated test channels on the flow of the polymer melt. The expected results will provide an overview of several combinations of testing channel surfaces combined with different polymer melts. With these results it will be possible to improve the whole extrusion process, melt flow instabilities can be avoided. Furthermore the expected results will provide important information concerning the flow channel surface to improve the quality of extruded products.