Analysis of the preform blowing stage when obtaining a polymeric product using the extrusion blow molding method

Abstract

It was shown that the process of blowing a polymer preform has two characteristic stages. We obtained analytical dependences that link geometric parameters (diameter, wall thickness) of a molded polymeric preform and parameters of the finished molded product to technological parameters of the process of extrusion blow molding of a polymeric product (tangential drawing rate, polymer melt viscosity, internal blowing pressure, tangential drawing factor, molding time). The illustrations of modeling different technological modes are presented. Basic calculations were carried out for the modes of internal blowing pressure from 1 kPa to 3 kPa for a polymeric preform made of high density polyethylene at a temperature of 200 °С, with effective viscosity 8,300 Pa·s, an average diameter of a polymeric preform of 0.05 m, and a thickness of its wall of 5·10 –3 m. In this case, stage 1 is characterized by moderate modes of deformation and is limited to tangential drawing factor k=2.5. Stage 2 has an intensive character of deformation, which can lead to defects of the molded product. It was shown that one of the ways for preventing defects is to reduce internal pressure when blowing a polymeric preform. In this case, the main factor that limits the rate of blowing a polymeric preform due to an increase in internal blowing pressure is the maximal dimensional diameter of the molded product.