Nature of contact between polymer and mold in injection molding. Part I: Influence of a non-perfect thermal contact

In injection molding, the pressure in the cavity usually reaches the atmosp heric pressure before the ejection, therefore the thermal contact between p olymer and mold is modified. This paper aims to evaluate the nature of the thermal contact between the polymer and the mold during the holding and coo ling phase. An experimental plate mold has been designed to study this phen omenon. Thermal sensors facing each other and pressure sensors have been se t in the mold. An inverse method is used to determine the heat flux density crossing the polymer mold interface, and the mold surface temperature. The n. a second inverse algorithm allows to determine the temperature profile a t the end of the filling and the time evolution of the thermal contact resi stance (TCR). Finally, the polymer temperature distribution in the thicknes s is determined between the thermal sensors. The results of this study show that the TCR between the polymer and the mold is not negligible and not co nstant with time. The polymer temperature at the surface can be 20 degrees C higher than the mold surface temperature. Moreover, asymmetric air gaps h ave been observed when cavity pressure becomes equal to atmospheric pressur e, therefore asymmetric temperature profile in the thickness are generated.