新型非对称同向双螺杆挤出机内混沌混合表征

提出了全新的同向自洁双螺杆非对称造型新概念。给出了转速比为2∶1的2根螺杆的端面造型和运动关系并建立了数学模型。以符合Carreav定律的流体为加工对象,采用Polyflow软件的叠加网格技术,分别对新型非对称双螺杆和传统双螺杆端面内的周期性二维流动和混合进行数值模拟研究。采用粒子追踪技术,对混合过程进行了动力学行为表征,证实了新型非对称螺杆内混沌混合的存在。通过统计学分析,得出累积分散准数和拉伸长度,分析了新型非对称双螺杆和传统双螺杆的混合行为差异。     

一种新型差速同向双螺杆挤出机

同向双螺杆挤出机是重要的配混加工设备,尤其在高分子材料制备过程中起到关键作用。为引入混沌混合和拉伸场,本文提出了一种新型差速同向双螺杆的新概念。介绍了具有自洁功能的差速双螺杆几何学。针对螺杆转速比为2:1的螺杆结构进行了一系列研究。在螺纹元件全充满状态下,有限元数值模拟研究揭示了流体的输运和混炼过程。借助机筒剖分结构及全透明机筒,开展了加工过中非充满及充满情况下静态及动态可视化研究,探索新型螺杆的熔融机理和输送过程的非对称效应。选择了纳米碳酸钙填充LLDPE体系及不相容PP/TPU共混体系,进一步进行材料制备研究,对比了差速双螺杆与传统同向双螺杆混炼能力。     

非对称同向双螺杆挤出机加工PP/HDPE/POE共混复合材料的研究

首先分别采用两种不同的同向双螺杆挤出机(新型非对称同向双螺杆挤出机以及传统双螺杆挤出机),制备了聚丙烯/高密度聚乙烯(PP/HDPE)共混复合材料,通过试样力学性能以及微观结构形貌对其加工过程进行了表征。然后采用新型非对称同向双螺杆挤出机进一步制备出了PP/聚烯烃弹性体(POE)、PP/HDPE/POE共混复合材料,分析了HDPE及POE用量对复合材料力学性能的影响,并采用扫描电子显微镜(SEM)观察了共混复合材料的表面微观结构形貌。结果表明:新型非对称同向双螺杆挤出机具备更好的分布、分散混合能力,所加工共混复合材料的分散相颗粒粒径分布更加集中,粒径也更小;HDPE和POE对PP有良好的协同增韧作用,当PP、HDPE、POE的质量比为68:17:15时,PP/HDPE/POE共混体系的综合性能最佳。     

非对称同向双螺杆端面造型对混合行为影响数值模拟

提出了同向自洁型双螺杆挤出机端面非对称造型的新概念。以符合Carreau定律的纯黏性流体为加工对象,建立相应的数学模型。采用Polyflow软件,基于叠加网格技术,对两种螺杆造型端面内的周期性流动和混合情况进行数值模拟。将粒子示踪技术及分离尺度相结合,研究了流场内分布混合能力;将分散准数与剪切速率相结合,表征了流场的分散混合能力。当两组螺杆单位时间转过的总圈数一致时,螺杆转速比为2∶3的组合混合能力稍优于转速比为2∶1的组合。     

差速双螺杆混炼机非对称流场引发混沌混合特性

差速双螺杆混炼机具有转子几何结构和转速的非对称性,将产生非对称流场,是诱发混沌混合的源驱动力。基于网格叠加技术,采用有限元法对三种差速双螺杆混炼机端面流体流动进行数值模拟。利用Poincaré映射、平均对数线拉伸率、粒子束分布指数、平均混合效率和位移频谱曲线等研究了差速双螺杆混炼机非对称流场诱发的混沌混合特性。结果表明,随着差速比的增大,差速双螺杆混炼机流体的位移频谱成分愈加丰富,增大了流体从一根转子流向另一根转子的概率,强化了非对称流场的混沌混合。     

新型偏心双螺杆挤出机流域混合特性

基于非对称流场的混沌混合理论,设计了一种新型的偏心双螺杆挤出机。通过对比传统普通螺杆元件与新型偏心螺杆元件,偏心距不仅决定了螺杆的端面形状,也改变了螺槽形状,使同一导程内的2个独立的C型室螺槽形成一个ω型室螺槽。利用Polyflow软件分别对传统双螺杆挤出机与3种不同偏心距螺杆元件的新型双螺杆挤出机进行模拟仿真,分析了压力场、速度场与混合指数分布规律,计算了4种双螺杆挤出机流场的停留时间分布、分离尺度、最大剪切应力等混合表征系数。结果表明,与传统双螺杆挤出机相比,偏心双螺杆挤出机压力分布不均匀,正负压压力值增大,因此,压力差增大,使熔体回流速度增大,混合效果更佳;拉伸流区域增大,混合能力增强;熔体在流体域内的总体停留时间缩短,混合效果更佳;分离尺度数值下降较快,混合效率较高;偏心螺杆元件对流体的剪切应力增大,分散混合能力增强。     

自洁型非对称同向双螺杆挤出机混合分析

设计了自洁型非对称同向双螺杆,并采用实验研究及数值模拟方法分析其混合特性。采用活性纳米CaCO3（nano CaCO3）填充线形低密度聚乙烯(PE LLD)的体系进行实验研究,在挤出量一定的前提下分别在自洁型非对称同向双螺杆挤出机以及普通同向双螺杆挤出机上造粒,通过扫描电子显微镜观察产品中nano CaCO3分布情况。结果表明,非对称双螺杆挤出PE LLD/nano CaCO3复合材料中nano CaCO3分布较为均匀,粒径尺寸更小,具有明显的增韧效果,这与数值模拟结果一致。     

非对称差速三螺杆挤出机混合机理分析

设计了非对称差速三螺杆挤出机端面造型，并且，对比其与常规三螺杆、非对称双螺杆挤出机内流体混合行为。对流场中速度矢量场和压力场进行分析，同时，比较分布混合性能中停留时间、分离尺度和混合效率，分散混合性能中最大剪切应力、对数拉伸率和混合指数。结果表明，与常规三螺杆相比，非对称差速三螺杆能有效地避免常规三螺杆中心区回流较大的问题，正向输送能力更强，并且，啮合区两侧压差更大，有利于物料压延。流域内粒子停留时间分布区间集中，分离尺度显著降低，有利于物料分布混合。同时，能提供较强的拉伸作用，使流域内粒子受到更好的拉伸和折叠，从而使其具有较好的混沌混合能力，有利于物料分散混合。     

差速双螺杆挤出机二维端面流场及混合模拟

介绍了差速双螺杆挤出机的特点,应用Polyflow软件对差速双螺杆挤出机端面进行了二维流场及混合模拟。并且将差速比4∶1、5∶1以及异向同速双螺杆的端面流场及混合效果进行了对比分析。模拟结果显示:差速双螺杆的切面混合效果好于同速双螺杆,且随差速比增大而略有改善;而差速比4∶1的剪切速率和拉伸速率大于5∶1的。由此可见,设计挤出机时要综合考虑混合和塑化两方面效果选择差速比。     

同向非对称双螺杆挤出PP/PA6形态演变

借助于自主研制转速比为2的剖分式同向非对称双螺杆挤出机,对PP/PA6共混体系的混合过程进行了沿程取样研究,并比较不同螺杆截面对形态演变过程的影响,利用等价平均粒径分析分散相的粒径。粒径统计分析发现,单头和双头螺杆螺槽内分散相的形态有所不同,且单头螺杆的分散混合能力高于双头螺杆,而在熔融后期螺杆端部,分散相平均粒径值有所下降。     

The behaviour of an intermeshing twin screw extruder with catalyst immobilised screws as a three-phase reactor

The characteristics of an intermeshing co-rotating twin screw extruder were investigated as a three-phase reactor using a model reaction. The kinetics of the reaction and base line data were obtained using a high pressure stirred tank reactor. The feasibility of immobilisation of palladium on the surface of the screws as the catalyst was also studied. The behaviour of the extruder in batch and continuous mode and with slurry and non-slurry solutions was investigated. The results confirmed the superiority of the intermeshing co-rotating twin screw extruder as a novel three-phase reactor compared to the stirred tank reactor as a traditional three-phase reactor. The residence time distribution measurements indicated that the behaviour of the extruder approached perfect plug flow reactor with increasing viscosity of reaction solution.     

啮合同向双螺杆挤出机中组合螺杆性能的数值研究（Ⅱ）混合特性分析

采用有限元软件POLYFLOW,对组合式啮合同向双螺杆挤出机ZSK60中不同构型的组合螺杆进行了混合分析。通过计算螺杆转过不同角度时的拟稳态流场,采用粒子示踪分析(PTA)方法,对组合螺杆中聚合物熔体的动态混合过程进行了可视化模拟;在此基础上通过对大量粒子运动轨迹的统计处理,分别采用停留时间分布、分布混合指数、分离尺度等累积混合指数表征了组合螺杆的轴向混合性能、分布混合性能以及分散混合性能。此外还研究了不同工艺条件下组合螺杆的混合特性。并将部分数值模拟结果与前人实验研究进行了对比。     

啮合同向双螺杆挤出机新型混炼元件性能及应用

就全啮合同双向螺杆挤出机中的混合过程进行了分析讨论，分析了普通螺纹元件和捏合盘元件的混合特性和泵送特性，针对这些元件存在的问题讨论了新型混炼元件的特点（包括典型分散性混炼元件和典型分布性混炼元元件），并作了深入的对比讨论，就上述元件在聚合物改性加工，共混和填充过程中典型的应用示例进行了分析讨论。     

自洁型同向双螺杆几何设计及间隙修正原理探讨

从工程应用的角度论述自洁型同向双螺杆的几何设计原理,从两根螺杆最基本的相对运动关系和几何关系出发,推导出可用于工程设计的同向双螺杆元件外廓几何形状的数学表达式。讨论设计中所涉及的间隙修正问题,并给出解决这一问题的数学方法。这些工作为后续的设计计算软件开发打下了良好的基础。     

A mass transfer model for a twin-screw extruder

A mass transfer model was developed to represent the desorption of a volatile species from a molten polymer in an extruder consisting of co-rotating twin screws in a figure-eight bore. The melt undergoes a series of alternating exposure and mixing processes while being transported axially through the device. The model relates the ratio of entrance to exit concentrations of the volatile species to the dimensions of the screws, the rate of their rotation, the rate of polymer flow, and the diffusion coefficient of the volatile species in the polymer. Experimental data, obtained with a halocarbon-polybutene system in a twin-screw extruder, were compared with predictions of the model. For the observed performance, the model predicts a process screw length about 14 percent below the actual screw length in the experimental extruder.     

Compatibilizing Effect of Halloysite Nanotubes on Polyetherimide/Silicone Rubber Blend Based Nanocomposites

The present study deals with the preparation of nanocomposites comprising of polyetherimide (PEI) and silicone rubber reinforced with both unmodified and modified halloysite nanotubes (HNTs) by melt blending process with the aid of co-rotating twin screws extruder. The developed nanocomposites have been characterized by various sophisticated analytical instrument viz. TGA, DMA, SEM,TEM, FTIR and UTM. There is remarkable enhancement in various properties of the developed nanocomposites due to incorporation of modified HNTs. This can be attributed to fairly good dispersion of the HNTs in the polymer matrix resulting in reductions of filler-filler interaction.     

啮合同向双螺杆挤出过程停留时间分布实验研究

通过对啮合同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同向双螺杆挤出过程停留时间及其分布的影响。     

Co-rotating twin screw compounding studies of PVC formulations

A 50 mm twin screw extruder was used to study the melting profiles of various PVC formulations. Melt temperature and degree of flux are measured axially along various mixing paddle arrangements. The viscous work is correlated with the rheology of the PVC mass and effective shear rate of the intermeshing co-rotating screws. The results of this investigation are used to develop a conceptual model of compounding PVC formulations. The radial mixing patterns in paddle segments down the barrel length are analyzed by introduction of trace quantities of pigment added to the dry blend. The resulting residence time distributions coupled with localized shear rate distributions give a numerical evaluation of shear strain required to flux PVC particles into a continuous fluid mass. By proper agitator design, compounding of PVC formulations can be accomplished with minimal thermal history.     

Solid transportation in the feeding zone of intermeshing co-rotating twin-screw extruders

A mathematical model was proposed for the characteristics of solid transportation in the feeding zone of an intermeshing co-rotating twin screw extruder. The model was based on the observations made from a “transparent” extruder. The analysis considered optimal solid conveyed with maximum throughput rate, i.e., when the upper and lower intermeshing zones, and the two sides of the screws were all partially filled with solid resin to an extent that a slight increase in the solid filling would immediately cause blocking of the solid transportation. Because of these starve-fed characteristics, the conventional approach for analysing solid feeding used in single-screw extruders was inadequate for twin-screw extruders. This paper also suggests a solution for the mathematical expressions describing the stress and velocity fields in the solid feeding zone of a twin-screw extruder. Finally, the predicted values are compared with our experimental findings.