Experimental study of melting in an intermeshing counter-rotating twin screw extruder

An experimental study, is presented of the melting mechanism in a starve fed closely intermeshing counter-rotating twin screw extruder of a modular Leistritz design. Polypropylene and low density polyethylene as well as different screw configurations of thick flighted and thin flighted elements were investigated, at various operating conditions. A Screw Pulling-out Technique was used to characterize polymer behavior along the screw axis. In particular the solid conveying, melting positions, the extent of starved character along the screw, and the fully filled regions were observed. Polymer samples were stripped off from each screw which was removed from the machine to investigate melting mechanism. Generally, it was concluded that the melt mechanism consists of pellets being dragged into the calendering gap where they are melted due to calendering action. In the case of thick flighted screws, the molten polymer is expelled from the gap and pushes against the pellet bed which is continuously dragged into the gap.