Postdie extrusion of plastic pipe

In continuous plastic pipe extrusion, melt emerges from an annular die and is then freely drawn down into a sizing sleeve. Here, we investigate this extensional flow with and without internally applied air pressure. For the case without internal air pressure, an analytic solution is derived. For the case with internal air pressure, a numerical solution is presented, where differential equations for the melt cone shape are derived from aforce balance. Design curves are then constructed from the solutions to these models. These curves are helpful in predicting pipe-extrusion operating conditions for the postdie region.