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Heat transfer simulation in thermoplastics processing is crucial to predict the quality of parts in terms of geometry and mechanical properties. The results accuracy depends on the knowledge of thermo-physical properties, crystallization kinetics and boundary conditions, which have to be determined in representative process conditions. In this work, we focus on the impact of high cooling rate on heat transfer and crystallization at the surface of a thermoplastic part. For this purpose, a home-made device named “Lagardère apparatus” is presented. It can reproduce cooling rate encountered in injection moulding by the sudden contact between a cold surface and a molten polymer. The first objective of this paper is the direct measurement of the thermal contact resistance used to model the imperfect contact between the polymer and the mould. The mould surface temperature and the heat flux at the interface were provided by a heat flux sensor. The specificity of this methodology was to obtain the polymer surface temperature with an optical fibre associated with a photodetector. A particular attention was made to avoid the invasiveness of the sensors on heat transfer. The second objective of the paper is the crystallization study at the surface of the polypropylene part. The experimental heat flux was compared with computed ones for which crystallization kinetics comes from Fast Scanning Calorimetry measurement and a standard model commonly used in the literature. It seemed that a very fast crystallization occurred at the surface of the part with a lower released enthalpy compared to the bulk. [ABSTRACT FROM AUTHOR]

Abstract: The control and optimization of heat transfer during the forming of thermoplastic parts is of primary importance since they impact on the quality of final parts. The modelling of this transfer requires accurate knowledge of the polymer thermo-physical properties, and also of the parameters describing the crystallization, this latter data being very sensitive to the thermal history for semi-crystalline polymers. The experimental determination of these parameters requires the use of many instruments, which is time consuming. To address this issue, a home-built instrumented mould was designed to measure and identify several properties from a single experiment. Specific volume, transverse thermal conductivity in amorphous and solid states can be estimated as a function of the temperature. Parameters of a crystallization kinetics model are identified with a non invasive procedure. Our methodology is illustrated on a well-known semi-crystalline thermoplastic. Identified parameters are compared with literature results. [Copyright &y& Elsevier]