An annular rotating-die technique in extrusion process: effect of mandrel rotating speed on entrance pressure drop and flow properties of molten HDPE

An annular rotating-die system proposed in this work was specifically designed and constructed so the mandrel could rotate in stationary barrel during extrusion. Effect of mandrel rotating speeds on flow properties and entrance pressure drop of melt HDPE with and without mandrel rotation was monitored in real-time in a single screw extruder. Experimental results showed that the entrance pressure drop decreased steadily with the increase of mandrel rotating speed from 0 to 70 rpm by an average of 45 %. Flow properties of melt HDPE were in accordance with pseudoplastic non-Newtonian behavior. In general, it was found that, at the same wall shear rate, wall shear stress detected in annular rotating-die (mandrel rotation) was lower than that found from normal annular die. The wall shear stress tended to decrease with the increasing mandrel rotating speed from 0 to 70 rpm by an average of 43 %. Possible explanations for the reduction in die entrance pressure drop and flow properties magnitudes for melt HDPE due to mandrel rotating effect were given in connection with the flow pattern of melt HDPE in the annular rotating-die.