Power-law numerical solution for post-die extrusion of plastic pipe

Abstract

In a continuous plastic-pipe extrusion, melt emerges from an annular die and is then drawn freely into a sizing sleeve. Here, we investigate this extensional flow when a pressure difference is applied across the melt cone. A numerical solution to a power-law fluid is presented. Differential equations for the melt-cone shape are derived from a force balance on the melt cone. Design curves are then constructed from the solutions to these equations. These curves are helpful in predicting the pipe-extrusion operating conditions. The model is also used to predict an operating envelope for sizing-sleeve placement. Examples demonstrate how to use these results. We also compare it to an earlier analytical solution that excludes a pressure difference across the melt cone.

Acknowledgments

The authors wish to thank Rachel M. Clark for her assistance in constructing this manuscript. Professor S. A. Klein provided valuable assistance regarding the ees software. Helpful discussions with Dr. John Slattery and Mr. Fan Ding are also greatly appreciated.