| Die lines in plastics extrusion are annoying surface striations that can destroy extrudate aesthetics and compromise product properties. Here, the available literature on die lines is first reviewed to explore how die lines arise and how to minimize them. We find that many factors influence die line formation and there are a few ways to suppress them.; Die line metrology is then developed, where die lines are measured using a mechanical stylus profiler, and characterized qualitatively by their profiles and by visual comparison with scratch standards, or quantitatively using statistics.; Dimensional analysis of die lines is next conducted for amorphous polymers extruded from a slit. The Buckingham pi theorem is used to determine the governing dimensionless groups in die line formation. Semi-crystalline polymers and two special cases are also studied.; Film blowing experiments are carried out to study how various die defects, material properties and operating conditions affect die line formation. The empirical relations between die lines and die defects, material properties and affecting operating conditions are then explored using the dimensionless groups from dimensional analysis.; Die line formation is then simulated using a finite element analysis package (FIDAP version 8.52), the results of which are compared with film blowing experiments. Finally, new ways to suppress die lines and prospects for future studies are proposed. |
