Polymer-mould interface heat transfer coefficient measurements for polymer processing

Reliable process and product design for plastics through simulation requires reliable heat transfer properties data. The thermal contact resistance of interfaces can have a significant influence in simulation predictions, in particular for micro-moulding, yet the availability of data is limited. Furthermore, the formation of air gaps at the polymer-wall interface due to shrinkage of the polymer on cooling are not adequately modelled in process simulations. To address these issues, an instrument has been developed for measuring the thermal contact resistance of interfaces relevant to polymer processing, in particular for injection moulding. It has been used to quantify the thermal resistance of the polymer-mould interface and also that of air gaps introduced between the mould surface and the polymer, thereby representing the interfaces occurring in injection moulding. Heat transfer coefficients (HTC) across a polymer-steel interface were measured to be of the order of 7000 W/(m2 K). The thermal contact resistance of the polymer-air-steel interface were in reasonable agreement with predictions assuming heat transfer across an air gap based on thermal conduction through air.