塑料挤出吹塑的机理问题

Mechanism of Plastics Extrusion Blow Molding

挤出吹塑过程由型坯成型、型坯吹胀与制品冷却三个阶段构成。采用不同的方法对该三阶段的机理问题进行了研究。采用神经网络方法预测了受模口温度和挤出流率影响的型坯成型阶段的膨胀。利用建立起来的神经网络模型预示的膨胀与实验结果很吻合 ,且可在一定范围内 ,预示不同工艺条件下型坯的直径膨胀和壁厚膨胀 ,为型坯的直径和壁厚的在线控制提供了理论依据。基于薄膜近似和neo Hookean本构关系 ,建立了描述型坯自由吹胀的数学模型 ,并通过实验方法获得了型坯吹胀的瞬态图象。比较发现 ,理论预示的型坯轮廓分布与实验观察结果较吻合。该模型还可预示型坯的自由吹胀对材料性能、型坯尺寸和工艺条件等的依赖性。基于ANSYS有限元软件 ,对吹塑制品的三维冷却进行了模拟 ,预示了制品厚度方向任一位置的瞬态温度分布 ,并可预示成型工艺参数、制品壁厚、塑料与模具材料的热性能以及吹塑模具冷却的强度与时间等对吹塑制品冷却的影响 。

The plastics extrusion blow nolding process consists of three stages,i.e.,parison formation,parison inflation,and part cooling.In this paper,the mechanism of these three stages was studied using different methods.Neural network method was used to investigate the parison swell affected by the die temperature and extrusion flow rate.The comparison of the experimentally determined parison swell of high density polyethylene with the predicted ones using the neural network model showed very agreement between the two.The parison swell can be predicted at different processing conditions from the neural network model.A mathematical model based on the thin membrane approximation and neo\|Hookean constitutive relations was used to describe the parison free inflation.The instantaneous images of parison inflation within a mold cavity were obtained by employing a video capture technique.The theoretically predicted parison growth profiles are found to be in good agreement with the experimental measurements.Based on the ANSYS finite element software,three\|dimensional cooling of blow molded part was investigated.The transient temperature profiles at various locations across the thickness of part can be predicted.The influence of the major operating variables,part thickness,and the thermal properties of plastics and mold materials on the cooling of parts can also be predicted.