DYNAMIC MODELING OF THE PREFORM REHEATING STAGE IN INJECTION BLOW MOLDING

The reheating stage of the injection-stretch blow moulding process is critical in the manipulation of the final part thickness distribution, degree of crystallinity and permeability (particularly in the case of PET ). Optimization of the duration of the reheating stage is importa nt so as to obtain the fastest possible reheat rate, yet ensuring that the preform surface does not burn. A numerical modelling approach wou ld be useful in screening process conditions, in the light of a minimu m of experimental data, so as to obtain an indication of the optimal p rocessing situation. A transient two-dimensional model is employed bas ed on Fourier's law of heat conduction within a solid domain. The oute r preform boundary is subjected to radiative heat transfer, whereas th e inner boundary is assumed to be adiabatic. Single layer as well as m ultilayer material domains are considered. Transient surface temperatu re responses are presented for various processing situations, such as the heater setting, preform-heater distance and preform thickness. One -dimensional nodal temperature distributions are also presented for a single layer and a multilayer material preform. The two-dimensional tr ansient nodal temperature distribution is presented for a preform subj ect to a heating gradient along its length. A comparison with availabl e experimental results is also presented.