In this thesis the melting behaviour in single screw extruders in depedence on temperature, screw tip pressure and screw speed was investigated. For that purpose the screw was pulled out of the cylinder after chilling down under the melting temperature of the polymer. The solidified material was cut in 1 D-distances and was taken off the screw. This made it possible to observe the flow behaviour and the melt pool formation during the extrusion process. Subsequently a balance of energy was prepared to determine the influence of the different types of energy on the melt behaviour, on the one hand the mechanical drive power and on the other hand the external heating of the extruder.