Rheology spiral flow

Rheology is a complex subject, and in the formulated colorant industry two simplified approaches have served well in the majority of cases. These are the single-point method, melt flow, and the molding simulation test, spiral flow. 

S.Z. Gebrehiwot, Manufacturing and rheological analysis of spiral flow test piece. Degree Thesis, ARCADA, 2014... 

The analysis of mould filling requires rheological and thermal data for the plastic, and the mould dimensions. Polymer manufacturers usually provide shear flow curves at a range of temperatures these can be approximated by a power law relationship over a limited range of shear strain rates. In the days before computer analysis, flow lengths of short shots were determined in spiral test cavities, as a function of the injection pressure. However, the geometry of this constant cross section mould differs so much from most other moulds that the flow lengths in the two types of mould do not correlate well. 

Multilayer spiral dies are becoming more common but are hmited to rheological compatible polsrmers in the layers much as with the feed block method in flat dies. This is due to the long flow distances required for layer uniformity in the multilayer spiral dies, which makes them more prone to generate interfacial instabilities. 

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