Effect of screw axial vibration on polymer melting process in single‐screw extruders

A model for investigating the melting process of polymer in a vibration‐induced single‐screw (VISS) extruder is presented. The key feature of this model is as follows: vibration force field is introduced into the overall course of extrusion by the axial vibration of the screw, and the velocity distribution in the polymer melt behaves strongly nonlinear and time‐dependent. To analyze this model, half‐open barrel visible experimental method and low‐density polyethylene material are adopted to investigate the effect of the vibration parameters on the melting process, which goes into further details of study and research on the melting mechanism, and thus, a novel physical melting model is derived. Combining the conservation equations of mass, movement, energy, and constitutive, analytical expressions of the melting rate, the energy consumption, the length of melting section, and the distribution of solid bed are obtained. This model enables the prediction of the processing and design parameters in the VISS extruders from which the optimum conditions for designing VISS extruder and polymer processing are obtained. The theory is supplemented by a calculation sample and experiment, which shows that the introduction of vibration force field can improve the melting capacity and decrease the power consumption of extruder greatly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3860–3876, 2006     

Theoretical and experimental study of the melting process of high‐density polyethylene for multidimensional vibration equipment

A model for investigating the melting process under a vibration force field is presented. The key parameters of this model are as follows: the rotation of the screw and heat are supplied by the vibration force field for the material phase conversion. A multidimensional vibration desk (DWZD‐500) and low‐density polyethylene material were used to investigate the effect of the vibration parameters on the melting process. A comparison of the derived model and experimental results revealed that increasing the vibration parameters increased the melting mass. This study will serve as the theoretical basis to optimize the parameters of vibration extruders' processing polymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Simulation of nonisothermal flow of melt during melting process of vibration‐induced polymer extruder

A simplified 2D melt film model was established to simulate the nonisothermal melt flow during the melting process of the vibration‐induced polymer extruder of which the screw can vibrate axially. Since polymer has time‐dependent nonlinear viscoelastic characteristic with vibration force filed (VFF), a self‐amended nonisothermal Maxwell constitutive equation that can reflect the relaxation time spectrum of polymer was adopted. Using the 2D melt film model, melt films of two kinds of thickness representing different melting stages were simulated to investigate the influence tendency of the same VFF on the different melting stage. Special flow patterns and temperature distribution of melt in the melt film between the driving wall and the solid/melt interface with various vibration force fields were systematically simulated. It is found out that within a certain range of vibration strength, the application of vibration can optimize the time‐averaged shear‐rate distribution, improve the utilization efficiency of energy, and promote melting process; and the thinner the melt film is, the more intense the nonlinear viscoelastic response becomes with the same VFF; moreover, there exists optimum vibration strength to make the melting process fastest, which is in accord with the visualization experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5825–5840, 2006     

Melting process and mechanism for vibration induced single‐screw extruder

The effect of a vibration force field on the melting process of an extruder is studied. It is shown that the mechanism for melting differs from conventional theory. Experimental studies of melting of low‐density polyethylene (LDPE) pellets in a vibration‐induced single‐screw (VISS) extruder show that melting is initiated on the inside of the barrel and the surface of screw. Models were developed that explain the melting mechanism in those regions. The melting at the surface of the screw is mainly initiated by frictional work on the pellets by the vibration and rotation of the screw. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced. The theory is supplemented by a calculation sample, which shows good agreement with experimental data obtained on a transparent barrel VISS (T‐VISS) extruder and a half‐open barrel VISS (H‐VISS) extruder with LDPE. The results of the experiment and calculation sample indicate that the introduction of vibration‐induced field can improve the melting capacity of extruder to a great extent. The present model enables the prediction of processing parameters for VISS extruders, from which the optimum operating conditions can be obtained. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2504–2514, 2007     

振动力场作用下聚合物熔体分子动力学(Ⅰ) 运动模型

引入振动力场以后,聚合物熔体分子的运动模式和状态都会发生变化。研究聚合物熔体分子在振动力场作用下的运动过程对于准确把握聚合物材料成型加工过程的各物理性能具有重要意义。本文建立了振动力场作用下聚合物熔体分子运动的珠-簧物理模型,运用统计力学方法求解该模型,得到了聚合物分子的动态松弛时间与振动频率的关系表达式,研究该式可以发现,聚合物的松弛时间是与振动频率密切相关的,当其他参数固定时,松弛时间随振动频率增加而减少。为聚合物成型加工工艺制定及成型设备研制提供了理论依据。     

Melting process of polymer under pure vibration force field（Ⅰ）Theoretical model and melting mechanism

为了能够清楚、透彻、无干扰地研究振动场对聚合物材料熔融塑化过程的影响,建立了纯振动场作用下聚合物材料熔融塑化过程的物理模型,并对其熔融机理进行了深入的分析,提出了纯振动场作用下熔融过程的连续性方程、动量方程、能量方程以及本构方程,并运用复杂的数学推导,得到了纯振动场作用下聚合物固体床下降速度与振动参数的关系表达式。从公式中可以看出,振动场的引入可以提高熔融速度。本研究将会为聚合物新型成型加工工艺的制定以及成型加工设备的设计提供必要的理论支持。     

Influence of Vibration on Density of Polymer Solid Granules in Single Screw Extruder

In an especially compaction apparatus the vibration force field is applied to the solids conveying process by the axial vibration of the piston. Through the experimental investigation of solid granule compaction, it is demonstrated that the effect of vibration field and temperature on the density of polymer solid granules is very significant. The experimental results show that the pressure exerted on the solid granules increases with the increase in the amplitude or frequency of the vibration force field, which accelerates the compaction of loosely solid granules.     

温度和振动力场对聚合物固体物料压实密度的影响

通过对聚合物固体物料的压实实验,探讨了温度和振动力场对固体物料压实密度的影响。结果表明,温度越高,固体物料越容易被压实;振动力场的引入有利于聚合物固体物料的压实,随着振动力场各参数的增大,可以加速聚合物固体物料的压实。     

纯振动场作用下聚合物的熔融塑化过程

通过建立纯振动作用下的熔融模型,排除了螺杆转动对振动的影响,推导出熔融速率与振动参数之间的关系。结果表明,振动的引入加快了熔融进程,熔融速率随着振动强度的增大而增大。同时,试验结果证明了上述模型及理论的正确性。     

纯振动场作用下聚合物熔融塑化过程（Ⅰ）理论模型及熔融机理

为了能够清楚、透彻、无干扰地研究振动场对聚合物材料熔融塑化过程的影响,建立了纯振动场作用下聚合物材料熔融塑化过程的物理模型,并对其熔融机理进行了深入的分析,提出了纯振动场作用下熔融过程的连续性方程、动量方程、能量方程以及本构方程,并运用复杂的数学推导,得到了纯振动场作用下聚合物固体床下降速度与振动参数的关系表达式。从公式中可以看出,振动场的引入可以提高熔融速度。本研究将会为聚合物新型成型加工工艺的制定以及成型加工设备的设计提供必要的理论支持。     

振动力场对高密度聚乙烯固体物料输送压力的影响

在自行设计的动态固体物料压实试验机上,对高密度聚乙烯固体物料分别做了稳态和动态压实试验,研究了振动力场对固体物料输送过程的影响。结果表明:有振动力场存在时,螺槽中固体物料的压力明显高于稳态压实时的压力;在振动力场作用下,在一定范围内,增大振幅或者提高振动频率,都能明显提高螺槽中固体物料的压力,且压力随时间增加上升得更快;振动力场的引入可以加速固体物料的压实,使螺槽中提早建立固体物料的输送压力,且使压实效果更好。     

Melting behavior of solid polymers on a metal surface at processing conditions

The melting or plasticating behavior of seven commercial polymers (high density polyethylene, low density polyethylene, polypropylene, polyoxymethylene copolymer, polystyrene, poly(methyl methacrylate), and polycarbonate (PC) was investigated using an experimental apparatus specifically designed to measure the melting rate and the viscous shear stress of a solid polymer on a steel surface under precisely controlled conditions of temperature, velocity, pressure and sample width comparable to actual processing. The melting rate (per unit polymer solid/metal contact area) was found to increase with increasing temperature for all polymers except PC, to decrease with increasing sample width and to increase less than proportionally to velocity. Pressure increased the melting rate somewhat for most of the polymers. The viscous shear stress decreased with increasing temperature for all polymers except PC, decreased with increasing sample width and increased with increasing velocity. Pressure generally increased the viscous shear stress. PC showed an unusual behavior with a maximum in the melting rate near 4200°F(215.5°C) and also a maximum in the viscous shear stress near 445°F (229.4°C). The present melting model could be examined unequivocally for the first time using our experimental results. Comparison of our experimental results with the predictions of the present melting model clearly indicates the inadequacy of the present melting model, Our experimental results will provide a basis for rational development of a reliable melting model.     

振动力场下单螺杆挤出机聚合物熔融过程模拟

采用数值模拟方法对振动诱导挤出熔融过程中振动参数的影响规律做了深入系统的研究。利用大型通用有限元软件ANSYS作为汁算机仿真平台，利用振动力场作用下聚合物依时性非线性粘弹特性和自行修正的具有松弛谱特性的Maxwell本构模型，对振动诱导挤出熔融过程在不同振动参数作用下的响应情况进行模拟分析。结果表明在一定振动参数范围内振动力场的引入有利于加速熔融进程。     

Numerical computation of the fiber diameter of melt blown nonwovens produced by the inset die

Melt blowing is used commercially as a one‐step process for converting polymer resin directly into a nonwoven mat of microfibers. The inset die is often used to produce polymeric fibers in the melt blowing process. The air jet flow field model for the dual slot inset die is established. The flow field model is solved by using the finite difference method. The numerical computation results of the air velocity distribution coincide with the experimental data. Then the air drawing model of polymers in the melt blowing process established in our previous research is solved with the aid of simulation results of the air jet flow field. The final fiber diameter of the nonwoven fabrics predicted by the air drawing model of polymers tallies with the experimental data. The results show the great potential of this research for the computer assisted design of melt blowing technology and equipment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

振动挤出对LDPE熔融结晶行为的影响

通过对低密度聚乙烯(LDPE)毛细管动态挤出物进行测试分析,探讨了振动力场对聚合物挤出物熔融结晶行为的影响.发现在LDPE熔体流动过程中叠加适当的振动力场后,LDPE挤出物的熔融始态发生明显变化,结晶度不变的同时,晶粒大小有较大降低,并认为这是振动力场对聚合物内部结构产生影响的结果.研究结果对聚合物动态成型加工新技术的深入理论研究具有十分重要的意义.     

聚合物球型螺杆电磁动态低温塑化挤出过程

为了研究振动场作用下聚合物低温塑化成型过程,研制了一套球型螺杆电磁激振挤出装置,建立了振动场作用下聚合物低温塑化成型的物理模型,深入分析了振动场作用下聚合物低温塑化机理,然后从振动耗散能、聚合物变形能、摩擦热、剪切热等方面分析了聚合物塑化的能量来源,并通过数学推导得出了能量输送密度的数学表达式。最后使用球型螺杆电磁激振实验台和低密度聚乙烯(LDPE)进行实验和理论计算,实验结果与理论计算结果符合很好,并得出结论:振动场的引入可以降低聚合物的成型温度40℃以上、可以节约单位质量物料成型能耗47%以上,同时可以提高制品力学强度。本研究将会为聚合低温成型工艺和成型设备的研究提供可靠的理论基础。     

Thermoplastic vibration welding: Review of process phenomenology and processing–structure–property interrelationships

Vibration welding offers a robust method for physically joining thermoplastics to fabricate complex hollow assemblies from simpler injection‐molded articles without using an external heat source, adhesives, or mechanical fasteners. Vibration welding involves a complex interplay of several phenomena—solid (Coulomb) friction, melting, high strain‐rate, pressure‐driven, strong (high‐strain) melt flows, solidification, and microstructure development—which ultimately govern the strength and integrity of the weld. Defects in the weld region may lead to catastrophic failure of the welded assembly. In this article, the current understanding of the processing–structure–property relationships in the context of vibration welding of thermoplastics and polymer‐matrix composites is reviewed. Experimental as well as analytical methods of investigation of the vibration welding process phenomenology are presented. The interrelationships between the microstructure in the weld region and the resulting weld strength and fatigue behavior are then discussed in the light of this phenomenological information for neat polymers, filled polymers, polymer blends, and foams. This review is also aimed at identifying the areas requiring further investigation with regard to understanding vibration welding phenomenology and weld structure–property relationships. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Effect of vibration extrusion on the structure and properties of high‐density polyethylene pipes

BACKGROUND: The axial strength of a plastic pipe is much higher than its circumferential strength due to the macromolecular orientation during extrusion. In this work, a custom‐made electromagnetic dynamic plasticating extruder was adopted to extrude high‐density polyethylene (HDPE) pipes. A vibration force field was introduced into the whole plasticating and extrusion process by axial vibration of the screw. The aim of superimposing a vibration force field was to change the crystalline structure of HDPE and improve the molecular orientation in the circumferential direction to obtain high‐circumferential‐strength pipes. RESULTS: Through vibration extrusion, the circumferential strength of HDPE pipes increased significantly, and biaxial self‐reinforcement pipes could be obtained. The maximum increase of bursting pressure and tensile yield strength was 34.2 and 5.3%, respectively. According to differential scanning calorimetry and wide‐angle X‐ray diffraction measurements, the HDPE pipes prepared by vibration extrusion had higher crystallinity, higher melting temperature, larger crystal sizes and more perfect crystals. CONCLUSION: Vibration extrusion can effectively enhance the mechanical properties of HDPE pipes, especially the circumferential strength. The improvement of mechanical properties of HDPE pipes obtained by vibration extrusion can be attributed to the higher degree of crystallinity and the improvement of the molecular orientation and of the crystalline morphology. Copyright © 2008 Society of Chemical Industry     

聚合物振动诱导单螺杆熔融塑化过程(Ⅰ)熔融机理及熔融速率

在振动诱导单螺杆挤出机中,通过螺杆的轴向振动使聚合物的熔融塑化过程在周期性的振动状态下进行,而经典熔融塑化理论无法描述处于周期性振动状态的熔融塑化过程。通过可视化和剖分料筒实验,观察了振动诱导单螺杆挤出机的熔融过程,深入分析了振动诱导熔融机理,建立了熔融过程动态物理模型,提出了振动场作用下熔融过程的质量平衡方程、动量平衡方程、能量平衡方程及本构方程,并运用复杂的数学方法求得近似解析解,最后得到了熔融速率方程和熔膜厚度方程,从公式中可以看出：熔融速率与熔膜厚度都是与振动参数相关的,且具有时间依赖性,振动场的引入可以加快熔融速率,减少熔膜厚度。理论研究与前面的实验结果符合得很好.     

Modeling of coat‐hanger die under vibrational extrusion

The distributions of the pulsatile pressure field, the pulsatile velocity field, and the pulsatile resident time of the polymeric melt in the coat‐hanger die are derived by using the pulsation of volumetric flow rate and pressure. Subsequently, formulae of the manifold radius and the slope of the manifold are deduced via volumetric flow rate pulsation. Polypropylene (PP) was employed for the experiments of the vibrational extrusion. The results indicate that the average extrusion pressure declines with frequency or amplitude decreasing; the distribution of residence time along the width of the coat‐hanger die performs uniformly during the vibrational extrusion process; the theoretical extrusion pressure well agrees with the experimental pressure; the experiments of tensile test, impact test implicate that vibration improves the mechanical properties of products; differential scanning calorimetry testing demonstrates that the melting point of PP is moved to a higher temperature value, and the endothermic enthalpy and the crystallinity are improved as well when superimposing the vibrational force field. Accordingly, the model of the coat‐hanger die under vibrational extrusion is well consistent with the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008