【作者】 周文彦；

【导师】 周国发；

【作者基本信息】 南昌大学 ， 化工过程机械， 2011， 硕士

【摘要】 为了满足高新技术发展,塑料制品不断向精密化方向发展。但由于聚合物黏弹特性与工艺参数波动的耦合作用,会产生离模膨胀波动,使得生产尺寸精确或形状复杂的高精度复合塑料器件在工程上仍是一项技术挑战。目前实现多层共挤吹塑精密成型技术关键是通过高精密的过程参数在线检测装置和闭环控制系统,严格控制成型过程参数恒定,以消除型坯离模膨胀的波动,实现聚合物精密成型。但由于我国高精度塑料制品外形尺寸和壁厚在线检测装置研究的缺乏,使其成型精度仍不能满足高档精密塑料制品挤吹成型的要求。为此,针对无高精度闭环控制系统环境下制品尺寸精密控制这一关键科学问题,开展多层共挤吹塑成型尺寸精密控制的关键理论研究,对于加快我国聚合物精密成型装备的技术突破具有重要的理论和工程应用价值。本文在多层复合共挤吹塑型坯离模膨胀产生机理研究的基础上,突破采用高精度闭环控制系统的贯性思维,提出了通过气辅滑移成型流动消除型坯离模膨胀以精密控制制品尺寸的创新研究思路,可在我国高精密在线检测装置研究缺乏背景下解决高档精密制品尺寸的精密控制问题。通过数值模拟,本文研究建立了聚合物气辅多层共挤吹塑成型创新工艺的精密成型关键理论,为我国聚合物多层复合制品精密成型装置和技术研究的突破奠定科学的理论基础。主要取得如下成果：(1)基于聚合物多层复合吹塑成型的特点和聚合物流变学理论,经合理假设,建立了描述其成型过程的多因素相互作用的非等温非稳态多层共挤吹塑成型的机理理论模型和与之相适应的高效稳态有限元数值算法；(2)通过过程参数和聚合物流变性能参数对聚合物多层共挤吹塑成型型坯离模膨胀影响研究结果的对比分析,提出了二次流动诱发型坯离模膨胀的科学假设,型坯离模膨胀与口模出口处向外的二次流动强度成正比。(3)无高精度闭环控制系统环境下精密控制多层复合共挤吹塑成型尺寸的理论前提是消除成型过程中的二次流动,而成型流动由速度分布不均匀的剪切挤出成型流动转化为速度均匀分布的柱塞挤出成型流动是消除二次流动的技术前提,气辅多层共挤吹塑精密成型创新工艺是实现这一转化的关键技术；(4)气辅多层共挤型坯精密成型的机理是气辅多层共挤型坯精密成型工艺通过气垫膜层的无粘着完全滑移作用,使多层共挤型坯成型流动由速度分布不均匀的剪切挤出成型流动转化为速度均匀分布的柱塞挤出成型流动,使成型流动的剪切变形速率趋于为零,导致驱动诱发型坯成型二次流动的熔体第二法向应力差趋于为零,最终使机头口模出口处的二次流动消失,从而消除了型坯成型的离模膨胀,实现了气辅多层共挤型坯精密成型；(5)研究建立了集型坯成型与吹胀于一体的多层共挤吹塑成型过程的数值模拟方法；(6)研究了过程参数与聚合物流变性能参数对传统和气辅多层共挤型坯成型过程的影响规律,揭示了其影响机理；(7)气辅多层共挤型坯精密成型过程数值模拟研究结果与实验研究结论相吻合,证明本文的理论模型和数值算法可靠更多还原

【Abstract】 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.更多还原