The effect of mandrel rotation on power consumption in polypropylene extrusion

Improved properties of thermoplastic pipes may be achieved by rotating the core of the extrusion die, to produce orientation in the tangential direction. It has been suggested that a further advantage of mandrel rotation is an increased output rate for a given power input. The flow of a “power law” fluid through a rotating die is analyzed, and the power consumption and throughput are investigated. Experimental results for polypropylene melt are presented, which illustrate the effect of rotation on the die characteristics. It is found that the output is increased, but the savings are minimal in view of the power which must be introduced via the rotating mandrel.