Handling of molten Poly(ethylene terephthalate) cylinders for preforms compression molding machines

This thesis describes the research done on the handling of molten Poly(ethylene terephthalate) (PET) cylinders - from now on "gobs" - for preform compression molding, which is a cutting-edge technology in the beverage field. SACMI, a world leading company in manufacturing advanced packaging plants, holds a strong background in compression molding technologies. A new way of handling gobs was investigated, i.e. the pneumatic transport through a swirl flow generated by a particular pipe design. It was developed both with Computational Fluid Dynamic simulations and extensive field tests on a prototypal compression molding machine. The very promising results led SACMI to patent the swirl flow pipe design. A new testing machine was designed and assembled to further develop the tests. The ultimate validation will be on a new compression molding machine prototype. Simultaneously, improved CFD simulations were started to increase pipe efficiency. Moreover, simulations could reduce costs and testing time of new pipe design for different preforms. By comparing the simulation video with a real field test one, a part of the process simulation was validated. Gob adhesiveness to pipe inner walls increased after many gobs passed through the pipe. The cause could be the deposition of a very thin layer of PET oligomers on the pipe wall. Cyclic oligomers, which are dissolved in PET melt, vaporize and then condense on the pipe walls which are colder than the gob. FTIR analyses supported this conclusion. Finally, the effect of metal temperature on gob adhesiveness for short time contact, typical of the preform compression molding technology, was studied and an innovative kind of experiment was designed. A tests campaign was hence performed and led to the description of a new phenomenon for which a theoretical explanation was proposed. These results give a valuable contribution on this topic to the scientific community.