Solids conveying in screw extruders part III: The delay zone

A theoretical model was developed for the newly-defined delay zone of the plasticating screw extruder. The delay zone starts at the end of the solids conveying zone, i.e. at the point where the solid plug surface contacting the barrel melts and forms a film of melt up to where the steady state melting mechanism starts to operate. The model permits the film thickness and pressure profiles in this zone to be calculated. Published results were used to support the validity of the model. The results indicate that the film thickness at the end of the delay zone is several times the flight clearance. Finally, a criteria, based on the final value of the film thickness, is suggested to calculate the length of the delay zone.