Abstract
This paper highlights for the first time a full comprehension of the deformation procedure during the injection stretch blow moulding (ISBM) process of poly(ethylene terephthalate) (PET) containers, namely thin-walled rigid bottles. The processes required to form PET bottles are complicated and extensive; any development in understanding the nature of material deformation can potentially improve the bottle optimisation process. Removing the bottle mould and performing free-stretch-blow (FSB) experiments revealed insight into the bottle forming characteristics at various preform temperatures and blowing rates. Process outputs cavity pressure and stretch-rod force were recorded using at instrumented stretch-rod and preform surface strain mapping was determined using a combination of a unique patterning procedure and high speed stereoscopic digital image correlation. The unprecedented experimental analysis reveals that the deformation behaviour varies considerably with contrasting process input parameters. Investigation into the effect on deformation mode, strain rate and final bottle shape provide a basis for full understanding of the process optimisation and therefore how the process inputs may aid development of the preferred optimised container.
Highlights
(ethylene terephthalate) (PET) is the dominant material for the manufacture of thin-walled containers
The manufacturing process that has been developed to form the containers is the injection stretch blow moulding (ISBM) process; where injection moulded poly(ethylene terephthalate) (PET) preforms are reheated above the glass transition temperature Tg using infrared radiation, placed into a suitable mould and formed using a combination of linear stretching and air pressure inflation [2]
The pressure inflation occurs in two stages; pre-blow (6-10 bar) to form the majority of the bottle shape and final blow (>25 bar) to form the final bottle shape and bottle details
Summary
(ethylene terephthalate) (PET) is the dominant material for the manufacture of thin-walled containers. The pressure inflation occurs in two stages; pre-blow (6-10 bar) to form the majority of the bottle shape and final blow (>25 bar) to form the final bottle shape and bottle details. This manufacturing process is complex with variables such as magnitude of pressure, air flow, preform temperature and stretch-rod velocity all influencing the final bottle thickness and mechanical properties. As a result the process is a ‘black art’ and can rely heavily on previous knowledge and operator experience. This in turn can be costly in terms of raw material, mould material, energy and setup time. A more scientific approach into the effect of process conditions on PET bottles during the ISBM formation must be developed
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