Analysis of the effects of internal heating and cooling during the rotational molding of plastics

Abstract

Abstract In rotational molding, shortening the cycle time is one of the most important requirements for increasing production rates and reducing product cost. A characteristic feature of the process is that the mold and plastic powder are heated from room temperature to the melting temperature of the plastic and then back to room temperature. In addition, in the vast majority of cases the heat input and subsequent heat extraction occur at the outside surface. In order to improve the heat transfer, this paper considers the effects of internal heating and cooling. A mathematical model has been developed in which an internal heating term can be incorporated. The experiments with rotomolding powders show that the predictions made by the model are accurate. In particular, it is found that the introduction of internal heating is very effective in shortening the cycle time and that the introduction of internal cooling in rotational molding provides a more uniform structure and less likelihood of warpage.