Thermal treatment unit for the manufacture of pet containers

A continuous-feed thermal treatment unit for the manufacture of containers made of polyethyleneterephthalate (PET) and capable of withstanding, during use and without appreciable deformation, relatively severe thermal conditions encountered during processes filling the containers with a hot liquid or pasteurizing their contents, said unit comprising:

• a) heating means for heating both the body and neck of each container, the body having preliminarily undergone bidirectional stretching and being heated to a temperature of 160.degree. to 240.degree. C. to produce contractive recovery followed by increased crystallization, and the neck being heated under temperature and time conditions suitable for producing spherulitic crystallization of the PET in the neck;
• b) cooling means for lowering the temperature of both the neck and body of each container, wherein the neck is cooled relatively slowly to ensure the crystallization thereof;
• c) wherein the heating means comprises:
• 1) means (27, 44) for heating the bodies of the containers positioned facing the bodies in proximity thereto along a path of conveyance thereof, extending continuously over approximately the height thereof, and configured to emit, in the direction of the bodies, medium-wavelength infrared radiation having a wavelength equal to or greater than 2 .mu.m, said body-heating means comprising first heating means (27) for producing the contractive recovery and second heating means (44) for increasing the crystallization of the body;
• and
• 2) means (47) for heating the necks of the containers positioned opposite the necks along the path of conveyance and configured to emit, in the direction of the necks, short-wavelength infrared radiation having a wavelength to equal to or less than 2 .mu.m, said neck-heating means being cooperable with internal heating mandrels (18) individually inserted inside the necks for supporting the containers during the conveyance thereof, said neck-heating means being positioned following the first heating means in the direction of conveyance and alongside the second heating means;
• and
• d) means (9, 10, 15) for modifying the spacing distance between adjacent containers such that a substantially large spacing distance (P) is provided along the length of the first heating means whereat said bodies have a substantially large transverse dimension, and a reduced spacing distance (p) is provided along the length of the second heating means and neck-heating means whereat the heated bodies have contracted and have reduced transverse and longitudinal dimensions.