| In wire coating, polymer melt is extruded through an annular die and then drawn onto a wire, with a vacuum applied to the inner annular surface. In pipe extrusion, the annular extrudate is pressed into a sizing sleeve, sometimes using a positive pressure applied to the inner annular surface. For both flows, there is an annular free boundary flow between the die and a radial constraint. The similarity between these two flows suggests that these could be modeled similarly. These flows also resemble tubular film blowing, for which solutions exist. Here, the available literature on wire coating and pipe extrusion is reviewed. Analytic and numerical models are developed for these flows. These models include solutions for non-Newtonian fluids, specifically power-law and upper convected Maxwell fluids. Solutions are presented in ways most helpful to practitioners saddled with designing process equipment and predicting operating parameters. Specifically, for wire coating, ways of avoiding melt tearing and ovality are investigated. For plastic pipe extrusion, the problem of sizing sleeve placement is addressed. |
