PREFORM PRODUCTION PETplanet Insider Vol. 24 No. 10/23 www.petpla.net 23 BOTTLE MAK NG 16th INTERNATIONAL TRADE SHOW FOR PLASTICS & RECYCLING, PETROCHEMICALS, PACKAGING & RUBBER INDUSTRY Platinum Sponsor www.arabplast.info International Associate India Associate Organiser 750+ Exhibitors 35+ Countries 13-15 DECEMBER, 2023 Dubai World Trade Centre, Dubai, UAE #ARABPLAST #arabplast2023 Where Plastic Meets Business Media Partners Industry Communication & Show Daily Partner Onsite Registration Partner Principal Sponsor Figure 8.8 Computer simulation of preform temperature But that is not all. As previously mentioned, one disadvantage of ISBM is that processors are not in complete control of the temperature profile of the preform. Because the melt in the neck area had a longer time to cool down compared with the melt in the gate area it is also cooler and we may find a temperature profile similar to the one in the graph as shown in Fig. 8.8. In this simulated graph a temperature gradient from the hot gate to the cooler neck can be clearly shown. Actual temperatures and differences depend on process conditions and are therefore not shown here. This heat profile will result in a relatively thin bottle base with more material toward the neck because PET will stretch first in the hotter areas. To counteract this behavior preforms are designed with thinner gate areas and/or more cooling and thicker areas toward the neck. While this may sound counterintuitive, a thicker wall in the preform neck area leads to a thinner area in the bottle neck. This is because the thicker preform area retains more heat and will then stretch more resulting in an overall thinning. For the processor there is another way of changing this temperature profile. It relies on the observation that faster injections will lead to less difference between cooler and warmer areas because the material injected first has less of a time difference spent in the cold mould than with longer injections. Overall, the temperature will be higher but the temperature gradient from hot to cold is less. This will then result in thicker bottle bases. Of course the opposite is also true, to increase material thickness in the bottle base a slower injection may be selected. Please order your copy at: info@petpla.net Stretch Blow Molding Third Edition by Ottmar Brandau € 130,00 374 pages © Copyright Elsevier 2017, 2012
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