Numerical Simulation of Extrusion Characteristics for Co-rotating Tri-Screw Extruder

The flow of polyethylene melt in new tri-screw extruder was simulated using the finite element method (FEM). A special study of flow in central region was performed by analysis of the velocity, pressure, and resident time distribution (RTD). The extrusion characteristics of tri-screw extruder, namely the abilities of material conveying, mixing, and power consumption, were compared with those of twin screw extruder. The results showed that there was circumfluence in central region but no stagnation in it. Tri-screw extruder had better operative abilities and high productivity ratio than twin screw extruder in the aspect of material conveying and mixing.     

新型偏心三螺杆挤出机流体混合特性分析

在传统的三螺杆挤出机的基础上,设计了一种新型偏心三螺杆挤出机。该三螺杆挤出机中具有螺杆几何结构偏心、螺槽构型呈梯度变化特殊以及较高的面积利用系数等特征。利用有限元法对聚丙烯（PP）熔体在新型偏心三螺杆挤出机中流动和混合规律进行三维数值模拟,给出偏心三螺杆挤出机中压力和速度分布规律,计算了3种偏心螺杆挤出流场的停留时间分布、分布指数、分离尺度、最大剪切应力等混合表征参数。结果表明,螺杆偏心距不仅决定了螺杆端面形状,也改变了螺槽梯度的变化程度。随着螺槽梯度的逐渐减小,挤出机内粒子团聚效应逐渐降低、物料剪切作用逐渐增强。在3种新型偏心三螺杆挤出机中,偏心距e=3 mm的新型偏心螺杆挤出机的混合性能相对较好。     

双螺杆挤出机的进展及其应用

着重介绍日本新型双螺杆挤出机的最新研制和开发的机型,评述新型双螺杆挤出机的特点,特别是新近开发的SCR双螺杆挤出机、BIVOLAV双螺杆挤出机、HTM双螺杆挤出机、TEX双螺杆挤出机、高剪切型双螺杆挤出机、格子形叶的双螺杆挤出机、新AP型双螺杆挤出机的结构、性能及其应用,提出今后双螺杆挤出机发展前景及方向。     

Flow field analysis of the kneading disc region in a co-rotating twin screw extruder

Co-rotating, intermeshing twin screw extruders are widely used in polymer compounding and blending. Among the different modules of the co-rotating twin screw extruder, the kneading discs are the dominant ones in determining mixing efficiency. The major difficulty in solving the flow problem in the kneading disc region arises from the complex geometry and the time-dependent flow boundaries as the discs rotate. In this work, a fluid dynamics analysis package—FIDAP—using the finite element method was employed to simulate the flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-30 co-rotating twin screw extruder. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries to represent a complete mixing cycle. The flow field was characterized in terms of velocity profiles, pressure distributions, shear stresses generated and a parameter λ quantifying the elongational flow components. The last two parameters are the most important ones in analyzing mixing efficiency. The influence of design variables (stagger angle, right or left handed configuration) and processing conditions (rpm, axial pressure gradient) on the flow characteristics was analyzed.     

Analysis and experimental evaluation of twin screw extruders

Twin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co- and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix.     

The grafting of maleic anhydride on high density polyethylene in an extruder

The grafting of maleic anhydride (MAH) on high density polyethylene in a counter-rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non-linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.     

Continuous polymerization of ω‐lauryl lactam in an intermeshing corotating twin‐screw extruder

This article describes the synthesis of poly(ω‐lauryl lactam) by a reactive extrusion process. Anionic ring‐opening polymerization was performed in an intermeshing corotating twin‐screw extruder. We investigated the evolution of conversion of ω‐lauryl lactam as a function of reaction time, screw speeds, different feed rates, and different screw configurations along the screw axis in a twin‐screw extruder. For comparison with continuous polymerization in a twin‐screw extruder, we studied polymerization in an internal mixer, which was considered a batch reactor. We found the final conversion of ω‐lauryl lactam made in a twin‐screw extruder was higher than in an internal mixer. Higher molecular weights are found at lower screw speeds and feed rates. Melt viscosities and mechanical properties of the polymers were measured. Residence time, molecular weights, and shear mixing have the main effect on the mechanical properties of products. The twin‐screw extruder performance was interpreted in terms of commercial software. It was found that twin‐screw extruder reaction rate was higher than those in the batch reactor and increased locally with screw speed and feed rate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1605–1620, 2005     

Advanced compounding: Extrusion of polypropylene nanocomposites using the melt pump

A melt pump was assembled into the compounding line to ensure both sufficient time for diffusion process of polymer chains into the silicate gallery and sufficient mechanical shear energy for exfoliation of clay layers. The melt pump in front of the open co‐rotating twin‐screw extruder controls the throughput rate and the residence time, whereas the screw speed and screw geometry in the extruder determine the mechanical shear energy applied on the compound. Due to melt pump employment, the melt in metering zone can be accumulated, which results in higher mixing efficiency. It was found that using the melt pump leads to up to two times higher residence time and, consequently, higher level of material reinforcement as investigated by extensional rheology. Different melt pump adjustments, screw geometries, and screw speeds were tested and their effect on processing characteristics and material reinforcement was investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

锥形双螺杆挤出过程菠萝型混合元件三维流场分析（Ⅱ）

利用ANSYS有限元软件对啮合异向锥形双螺杆挤出机中的新型螺杆元件——菠萝型混合元件进行了三维流场的模拟计算，对其速度场、压力场、粘度场以及剪切速率、剪切应力进行了分析，绘制出更为直观的展开图。同时，将其和常规螺纹元件进行了比较。     

新型混炼技术应用研究

聚合物改性对混炼设备的性能提出了更高要求。介绍了自主研制的5种新型混炼设备：同向平行双螺杆挤出机、串联式磨盘螺杆挤出机、往复式销钉螺杆挤出机、新型销钉式冷嗖料橡胶混炼挤出机的性能特点、适用范围、结构机理等。并对几种设备的混炼效果作了重点介绍。     

啮合同向双螺杆挤出过程轴向循环流道三维流场分析—轴向循环流场分析（Ⅱ）

介绍了作者在啮合同向双螺杆某一轴向位置设置一非啮合段（且该段其中一根螺杆是反向螺纹元件）,从而将轴向循环流动的概念引入到啮合同向双螺杆挤出过程中,并利用ANSYS有限元分析软件对啮合同向双螺杆挤出过程轴向循环流道中的非牛顿流体等温流动进行了三维模拟分析。在得出速度场和压力场的基础上,还对剪切速率、剪切应力及剪切粘度进行了模拟,并将各模拟结果与未引入轴向循环流的啮合同双螺杆挤出过程常规螺纹元件流道的模拟结果进行了比较。     

新型锥形双螺杆混合元件三维流场分析

利用ANSYS有限元分析软件对带有混合块的新型锥形双螺杆的混合段流场进行了三维模拟分析，通过速度场求出流量，并求出剪切速率，剪切应力及回流量来衡量混合效果，找出了混合块几何条件（间隙，错列角）及操作条件（转速，压差等）对挤出机混合效果的影响。     

反应性挤出的新进展

简要介绍了双螺杆反应型挤出机在处理带漆膜的热塑性塑料、交联橡胶以及热固性塑料等废弃聚合物方面的应用。利用挤出机高剪切、可注水的功能实施体型高分子的分解，从而制得性能优良的再生塑料。此外利用这类设备还可用于插层法纳米复合材料的制备。     

Non-Newtonian and non-isothermal analysis of flow during polymerization of methyl methacrylate in a model twin screw extruder. Part II

The flow analysis network (FAN) method was modified to analyze the flow during polymerization of methyl methacrylate (MMA) in a model counter-rotating nonintermeshing screw extruder. The shear viscosity of the reactive mixture in the twin screw extruder was considered as a mixture of polymer and monomer. Thus, the reaction viscosity of the mixture of polymer and monomer was taken to be an explicit function dependent on the shear rate, temperature, conversion, and molecular weight. A new flow path method was developed to calculate the residence time distribution, which related to the degree of conversion. The numerical prediction of the velocity, temperature, viscosity, and pressure profiles during reaction in the model twin screw extruder is described.     

Temporal distributions: The basis for the development of mixing indexes for scale‐up of polymer processing equipment

New and better mixing criteria are needed to assess dispersive and distributive mixing efficiency in polymer processing equipment. Such criteria can serve the purpose of process optimization and machine scale‐up. In this work, the history of flow strength and shear stresses experienced by a number of particles in a twin‐flight, single‐screw extruder serve as the basis to produce temporal distributions of these parameters. In turn, the temporal distributions can be used for developing new mixing indexes for process optimization and scale‐up. Using models for dispersion kinetics and experimental data, calculations of agglomerate size distribution and average agglomerate size can be used as a dispersive mixing criterion.     

含能材料锥形双螺杆安全混合径向间隙的研究

以锥形双螺杆挤出机挤出段、过渡体和挤出机头为研究对象,基于Polyflow非等温稳态和瞬态的有限元模拟,对不同径向间隙下流场中各场量分布情况和变化曲线进行分析,研究含能材料在挤出段、过渡体和挤出机头流道中的安全和混合问题。从安全和混合效果两方面考虑,建立了综合评价方法,优选径向间隙。结果表明,最大剪切速率、最高剪切应力和最高黏性耗散热均在挤出段流道入口附近,最高压力在挤出段流道出口处,最高温度在机头处;锥形双螺杆的混合效果随着间隙的增加而增加;在径向间隙为0.5 mm时,流道的安全性能最差,径向间隙为1 mm时,流道的安全性能最好。     

Microstructure and rheologic development of polypropylene/nano‐CaCO3 composites along twin‐screw extruder

Polypropylene/nano‐calcium carbonate (PP/nano‐CaCO₃) composites were prepared by using an intermeshing, co‐rotating twin‐screw extruder. Two different screw configurations, denoted by screws A and B, respectively, were employed. The former provided high dispersive mixing and the later provided high dispersive and distributive mixing. Effect of mixing type on microstructure and rheologic development of nanocomposites was investigated by taking samples from four locations along screws A and B. Transmission electron microscopy results show that in the sample at the exit of extruder, the percentage of nano‐CaCO₃ particles with the equivalent diameter lower than 100 nm along screws A and B is 66.5 and 79.0%. respectively. Moreover, for screw B, the number‐averaged diameter at four sampling locations is smaller than that for screw A. This means that the distributive mixing, provided by screw B, favors the size decrease of nano‐CaCO₃ in the PP matrix. In addition, rheologic results show that the decrease of complex viscosity for the nanocomposites is deeply related to turbine mixing elements, which provides distributive mixing. The online melt shear viscosity of the nanocomposite at the exit of extruder prepared by screw B is lower than that of pure PP. This is related to the dispersion of nano‐CaCO₃ in PP matrix. Finally, the relationship between rheologic properties and microstructure was analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

啮合异向双螺杆挤出过程停留时间分布实验研究

通过对啮合异向双螺杆挤出过程常规螺纹元件螺杆组合及引入轴向循环段的螺杆组合停留时间的实验研究，分析了轴向循环段的引入对啮合异向双螺杆挤出过程停留时间及其分布的影响。     

新型锥形双螺杆——混炼型锥形双螺杆的研制

介绍了锥形双螺杆的一个新概念,即混炼型锥形双螺杆。炼型锥形双螺杆保留了常规锥形双螺杆加料量大和正位移输送的特点,解决了常规锥形双螺杆混合效果及挤出压力波动等问题,使其不但能够加工PVC,而且也能够加工其它物料,拓宽了锥形双螺杆挤出机的加工应用范围。     

同向啮合双螺杆挤出机捏合块流道三维流场分析

利用ANSYS有限元分析软件对啮合同向双螺杆挤出机的捏合块流场部分进行了三维模拟分析。通过速度场求出流量 ,并求出拉伸速率、剪切速率及剪切应力来衡量混合效果。得到了机筒表面和啮合区的压力分布 ,找出了捏合盘几何条件 (间隙、错列角 )及操作条件 (转速、压差等 )对挤出机混合效果的影响。