Research On Injection Molding Performance Of Special-shaped PET Preforms

Polyethylene terephthalate(PET)bottles are excellent in performance and reasonable in price.They are widely used in beverage packaging.People are paying more and more attention to the molding cycle of their preforms—the preforms.The cooling time of the preform occupies more than 70% of its molding cycle.Shortening the cooling time of the preform is an important way to improve production efficiency.By analyzing the forming process of the preform,increasing the heat conduction area of the preform can improve the cooling efficiency of the preform.This paper proposes and studies PET preforms with special-shaped structures.Based on conventional inverted conical preforms,the preforms with special-shaped structures are designed to increase the heat conduction area of the preforms during the pressure-holding cooling process and ensure that the performance of the formed bottles is satisfied.At the same time,the cooling time of the preform can be effectively shortened.Under the condition that the volume of the preform remains unchanged and the stretch ratio is in a reasonable range,two design schemes for the preform with special-shaped structure are given.The finite element analysis of the forming process of the special-shaped structure preform and the conventional inverted conical preform was carried out using Moldflow software,which proved the rationality of the design scheme of the special-shaped structure preform: under the same process conditions,the special-shaped structure has an effect on the volume of the preform The shrinkage rate and warpage deformation have little effect,but can significantly improve the cooling efficiency of the preform.Experiments are carried out to verify the feasibility of the preform with special-shaped structure and the correctness of the simulation results.This paper focuses on the ejection temperature of the preform and the performance of the bottle blow-molded from the preform with the special-shaped structure.The experimental results show that the ejection temperature of the fold-line preform and the inner-circle-external fold-shaped preform are respectively24.9% and 19.1% lower than the ejection temperature of the basic preform,and under the same heating conditions,the heating temperature of the special-shaped preform is higher.What’s more,the bottle blow-molded from the special-shaped preform has some visible stripes,and the other properties of the bottle are slightly worse than that of the bottle blow-molded from the basic preform,but still meet the requirements of use.A three-level three-factor orthogonal test was carried out with the wave crest angle,the number of wave crests and the fillet of the profiled preform as the influencing factors,and the volume shrinkage rate,axial warpage deformation and the time to reach the ejection temperature during ejection In order to investigate the indicators.It is found that the crest angle and the number of crests are the key factors that affect the time for the preform to reach the ejection temperature,and the optimal combination of structural parameters for the profiled structure preform is that the crest angle is 100° and the number of crests is 18,the fillet size is1 mm.Finally,combining the cooling performance of the special-shaped structure preform and the performance of the formed bottle,an optimization suggestion for the special-shaped structure preform is given,which can effectively reduce the thickness difference of the special-shaped structure preform under the condition of ensuring a good cooling effect.