The Research On Key Theory For Polymer Multi-layer Co-extrusion Blow Precision Molding

To meet the high-tech development, plastic products will continue to develop in the direction of precision molding. However, due to the coupling effect of fluctuations between process parameters and polymer viscoelastic properties parameters will produce fluctuations in die swell, which makes the production of plastics products with the precise size or complex shape to be still a technical challenge in engineering.The key technologies of currently implementing multi-layer co-extrusion precision blow molding process is the strictly constant control of molding process parameters, which eliminates the fluctuations of parison die swell and implements polymer precision molding. But because our country lack the research on online detection device of high precision plastic products dimensions and wall thickness, so that it can not meet the high precision molding requirements of superior quality precision plastic extrusion blow molding products. Therefore, in connection with the key scientific issues on precise controlling of products dimensions under the environment of no high-precision closed loop control system, the research on critical dimensions precision control theory is implemented which is great theoretical and engineering application value for speeding up China's technological breakthrough of polymer precision molding equipment. On the basis of the die swell mechanism of multi-layer co-extrusion blow molding parison and breaking through with the penetration of high-precision closed loop control system thinking, Innovative research ideas was put forward in which parison die swell is eliminated through the slip flow of gas-assisted molding,so that products dimensions is precisely controlled, the precise size controlling problems of superior quality precision molding products are solved under the backgrounds of lack of high precision online detection device research,this paper established critical precision molding theory of gas assisted multi-layer co-extrusion blow molding in order to lay the science heoretical fundation of our precision molding equipment and technology breakthroughs for Polymer multilayer composite products. The major achievements are as follows: (1) On the basis of polymer multi-layer co-extrusion blow molding characters and polymer rheological theory, reasonable assumptions were put forward; the fully three-dimensional unsteady viscoelastic non-isothermal theoretical model was established to describe the molding process. Meanwhile, the corresponding stabled finite element numerical algorithm was established.(2) Through influencing comparative analysis of process parameters and polymer rheological parameters on polymer multilayer co-extrusion blow molding parison die swell,the scientific hypothesis of secondary flow induced parison die swell was proposed, parison die swell is proportional to the secondary flow intensity of die exit(3) The theoretical premise of precise controlling products dimensions for multi-layer co-extrusion blow molding is to eliminate the secondary flow of molding process under the environment of no high-precision closed loop control system, and extrusion flow from the shear flow with the uneven distribution of molding flow velocity into the plunger flow with the uniform distribution of molding flow velocity is technical prerequisite for the elimination of secondary flow, innovative gas-assisted multi-layer blow molding process is the key technologies for the realization of molding flow from the shear flow with the uneven distribution of molding flow velocity into the plunger flow with the uniform distribution of molding flow velocity.(4) Gas-assisted multi-layer coextrusion parison precision molding mechanism is that gas-assisted multi-layer coextrusion parison precision molding process make molding flow from the shear flow with the uneven distribution of molding flow velocity into the plunger flow with the uniform distribution of molding flow velocity by mean of air cushion non-adhesive Full slipping effect which make the shear strain rate of molding flow tend to zero, result that the second normal stress difference which driven secondary flow tends to zero, make eventually secondary flow disappearance at die exit,therefore, the parison molding die swell is eliminated, and a gas-assisted multi-layer co-extruded parison precision molding is achieved.(5) A set of numerical simulation method is established in which parison molding process and parison inflation process are integrated together(6) The Influencing rules of process parameters and polymer rheological parameters on the traditional and gas-assist multi-layer coextrusion parison molding process was studied, its impact mechanism was revealed;(7) Numerical simulation and experimental results of gas-assisted multi-layer coextrus parison precision molding process match, the conclusion of research shows that the theoretical model and numerical algorithm are reliable.