Modelling of the coextrusion process

Model investigations of the coextrusion process were carried out with a model extrusion head extruding two- or three-layer extrudates. Flow profiles during coextrusion in the head die were recorded by taking pictures. The velocity profiles and their changes along the path of flow in the die were determined with particular attention given to flow instability at the die inlet. The length of the hydrodynamic inlet section varies with the total Reynolds number. A relationship was given which describes the location of the boundary surface during the coextrusion of polypropylene and various grades of PE-LD with different melt flow rate indexes. The principle was given for designing some geometrical elements of the flow channels in the head in the region where the streams of coextruded materials become joined.