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Serge Monteix (V.2)
Abstract
A study of the infra-red heating of polymer preforms and of their blowing
Serge Monteix - 2 february 2001.
The injection stretch-blow moulding process of thermoplastic P.E.T. bottles requires an heating step before forming in order to heat the P.E.T. preforms from the ambient temperature to a temperature about 100°C. Thus short wave infrared heating is used.
Both experimental and numerical study are conducted in order to model the 3D temperature distribution and particularly throughout the preform thickness, versus electric power of halogens lamps, reflector and the cooling fan influence. A numerical software called «PLASTIRAD» has been developed using a non- orthogonal control-volume method.
In order to optimise CPU time to model heating of rotating preforms, we developed unidirectional radiative heat transfer model. This model is based on preform heat flux irradiance using view factor computation, and using the Beer Lambert's law. Then P.E.T absorption has been described, measuring transmittance and reflectance from amorphous preform, relative to a cold layer without diffusion.
Spatial and temporal temperature measurements have been carried out, on P.E.T. sheets and preforms surfaces. Its yields to characterise interactions between P.E.T. preforms and halogen lamps inside a laboratory heating device, developed on the basis of industrial machines.
Finally comparisons between numerical and experimental temperature provide the main influence of the radiative heat transfer transmission and the inversion temperature phenomenon throughout the preform thickness, with calculated errors less than 10%.
Key-words :
infrared heating, halogen lamps, semitransparents materials, infrared camera,
control volume method, view factor, polyethylene terephtalate.
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