Effect of enhancing fins on the heating/cooling efficiency of rotational molding and the molded product qualities

Rotational molding has become one of the most important polymer processing methods for producing hollow plastic articles. However, the long cycle time required by the rotational molding process has confounded the overall success of this technology. Molds with extended surfaces (fins) have the potential to enhance heat transfer by increasing surface area. This report aims to examine the effects of enhanced fins on the heating/cooling efficiency of rotational molding and on molded product qualities. Rotational molding experiments were carried out in a laboratory-scale uniaxial machine, which is capable of measuring internal air temperature in the cycle. Three types of fins, including pin, rectangular and triangular fins, were used to mold the parts. Cycle-time reductions by the fins were measured. Characterization of molded part properties was also performed after molding. It was found that the mold surfaces with pin fins exhibited the highest heating and cooling efficiency. The use of fins in rotational molding can be better justified under conditions for which the convective heat transfer is small. In addition, molds with extended surfaces produce parts with less shrinkage but with greater warpage. The internal surface quality and tensile strengths of molded parts were not affected by these fins. It was shown that the heating/cooling efficiency can be increased by the fins, and this increase provides significant advantages in terms of reduced cycle time.