Rotational molding cycle time reduction through surface enhanced molds: Part A--theoretical study

Rotational molding has been regarded as a plastic molding method with great potential. The process offers virtually stress-free products having no weld lines or material wastage, and utilizes relatively inexpensive molds. Yet its widespread growth is hindered due to long production cycle times, which are limited by the time required to heat up and cool down the mold and the product. To address this issue, efforts have been made to enhance heat transfer to and from molds, ultimately reducing cycle times. The application of extended and rough surfaces to molds is investigated here. The aim of this study is to predict reductions in cycle time due to the enhancement of mold surfaces (i.e. roughness-enhanced and pin-enhanced molds). By utilizing a combination of heat transfer correlations, numerical analysis, and an existing rotational molding process simulation, cycle time predictions were made. The average predicted cycle time reductions were ∼21 and 32% for the roughness-enhanced and pin-enhanced molds considered, under a variety of conditions.