Improved heat transfer for cycle time reduction in extrusion blow molding

This study investigated the effect of the cooling channel design and turbulence of the coolant on the cycle time in extrusion blow molding. An aluminum mold using four different cooling channels to cool four equal sides of a square polypropylene bottle was used as the coolant flow rate varied. Other processing conditions were the melt temperature and the coolant temperature. In addition, to enhance the turbulence of the coolant, spiral baffles and wire gauze were inserted in the cooling channels.;Results from this study are compared to results from a similar study carried out by Toshiaki Kakemura for his thesis (1997) at the University of Massachusetts Lowell. In his study, Toshiaki performed experiments at the same processing conditions, but without the spiral baffles and the wire gauze in the cooling channels.;The results indicate a reduction in cooling time up to 50% with flow rate. In addition, the largest time reduction is seen in the channel with the highest coolant turbulence. This reduction was higher than that observed by Toshiaki without the cooling aids in the channels. The Reynolds number at which the change in the heat transfer from convection to conduction occurred was also seen to be lower indicating greater cooling efficiency for channels with higher coolant turbulence. Also, results obtained show the highest heat transfer rate in the high Nusselt number region.