双轴向拉伸吹塑成型技术原理和实验研究

Theoretical and Experimental Study on Biaxial Stretch Blow Molding Technology

针对传统拉伸吹塑工艺生产出的聚对苯二甲酸乙二酯(PET)瓶具有底部积料严重、材料拉伸不充分等缺点,提出双轴向拉伸吹塑方法。在双轴向拉伸吹塑中,模具的底模中心设置一根下杆,下杆在吹塑过程中上升到一定高度并停留一段时间,使底部材料能够充分拉伸,然后下杆卸载,上杆继续下降至底模位置,瓶坯在高气压下进一步成型为瓶子。通过实验和运用仿真软件Polyflow,对质量85 g体积4 500 mL的PET瓶分别在双轴向拉伸吹塑工艺和现有拉伸吹塑工艺下成型进行对比,发现双轴向拉伸吹塑能明显降低瓶底的厚度和质量。通过对比两种工艺在底部开始发生大幅度变形时刻的温度分布,数据表明在双轴向拉伸吹塑工艺中瓶底部分在接触模具之前保持高温状态的时间更长。分别对下杆停留时间、下杆上升延迟时间和下杆上升高度三项重要影响参数进行实验研究,三个参数均能显著降低瓶底质量,而且下杆上升高度会影响瓶整体材料分布。

The polyethylene terephthalate( PET) bottle produced by the traditional stretch blow molding process had the disadvantages of serious bottom material accumulation and insufficient material stretching,and a biaxial stretch blow molding method was proposed. In biaxial stretch blow molding,a lower rod was arranged in the center of the bottom mold,and the lower rod rised to a certain height during the blowmolding process and stayed for a period of time. Therefore,the bottom material could be fully stretched,and then the lower rod was unloaded,and the upper rod descended to the bottom mold position,and the preform was further molded into a bottle at a high pressure. Through experiments and using the simulation software Polyflow,the PET bottles with a mass of 85 g and a volume of 4 500 mL were compared under the biaxial stretch blowmolding process and the existing stretch blow molding process. The results showthat the biaxial stretch blow molding could significantly reduce the thickness and quality of the bottom. Comparing the temperature distribution at which the two processes begin to undergo large deformations at the bottom,the data indicates that the bottom of the bottle remains in a high temperature state for a longer period of time before contacting the mold in the biaxial stretch blow molding process. The three important influence parameters of the lower rod dwell time,the lower rod rise delay time and the lower rod rise height are studied experimentally. All three parameters can significantly reduce the quality of the bottom of the bottle,and the rise height of the lower rod will affect the overall material distribution of the bottle.