A cooling time model for plastics processing operations

The cooling of a crystallizing polymer is analyzed taking into account the effect of pressure drop on the energy balance. Thermal conductivity and diffusivity of a low density polyethylene are determined at pressures between 0.1 and 150 MPa (1 and 1500 bars). Using a pressure, volume, temperature‐diagram, a complete set of material functions could be obtained. A numerical cooling model based on these material functions was established and tested experimentally. Good agreement between the model and experiment was obtained. The numerical algorithm of the model can be adapted easily to plastics processing operations, e.g., injection molding, blow molding, and extrusion.