间断副螺棱强化单螺杆挤出过程混合性能模拟

建立了带有间断副螺棱的新型单螺杆计量段螺槽展开物理模型及数学模型。借助流体动力学软件Ployflow,采用网格叠加技术,对熔体在新型单螺杆及普通单螺杆挤出机计量段展开螺槽内的流动情况分别进行了数值模拟。运用粒子示踪技术及统计学方法以停留时间分布、分离尺度及累计混合指数为指标来表征螺杆的混合性能。结果表明,相比于普通单螺杆,新型单螺杆不仅可以减小熔体物料分离尺度,提高混合指数,还可以加宽停留时间分布概率密度曲线,获得更好的混合分散效果。     

强化单螺杆挤出机内层流混合的方法

综述了单螺杆挤出机内聚合物熔体层流混合机理的研究进展，对提高混合的措施进行了分析总结，指出了进一步强化混合效果的方法。     

单螺杆挤出机中三维流动有限体积数值模拟

Based on the vortex-velocity method,the dimensionless control equations of three-dimensional flow in single screw extruder were developed,and a new simulation method for the flow of non-Newtonian fluids was presented.A staggered grid arrangement was used,in which the dependent variables were located at different mesh points in the computational domain.The discretization scheme was second-order accurate,resulting from the use of central differencing.The simulation concerned the incompressible fluid obeying power law and the application of the finite volume method to the geometrical configuration of channel with aspect ratio up to 13.The distributions of velocities and stresses were investigated for different longitudinal pressure gradients.It was found that the distributions of velocities and stresses agreed well with the result of the two-dimensional approximation over 84% width scope owing to the large aspect ratio of the cross-section of the channel.The output decreased linearly with the increase of the longitudinal pressure gradients as observed in dimensionless forms.In addition,the center of the recirculating region in the channel cross-section drifted upward with the increase of longitudinal pressure gradients,which had positive influence on mixing performance.     

往复式单螺杆销钉挤出机停留时间分布研究

使用Polyflow软件对往复式单螺杆销钉挤出机(Buss机)三类典型螺纹元件的停留时间分布(RTD)进行了三维动态模拟,分析了工艺条件和物料特性对RTD的影响。根据Buss机的螺杆组合构型,应用卷积技术求得了物料沿整根螺杆的RTD曲线,探讨了物料在Buss机内的RTD规律与工艺条件变化的相关性。     

单螺杆挤出机中非牛顿流体层流混合停留时间表征

基于有限差分数值模拟技术,提出了计算非牛顿流体在单螺杆挤出机内停留时间分布的半解析方法,得到了不同操作参数下的停留时间分布,该分布可用来表征聚合物熔体在加工过程中的混合情况.结果表明：半解析方法能够反映由流体的非牛顿性所导致的耦合流场及压力反流对混合的影响,能更真实地反映聚合物熔体在单螺杆挤出机内的混合程度.     

单螺杆挤出机的混合及应用

本文分析了单螺杆挤出机的分散和分布混合能力,得出了单螺杆挤出机的适用混合类型。对比了Maddock、Pineapple、Twente以及CTM混合元件的性能。加装混合元件以后,单螺杆挤出机的分布混合效果得到很大提高;但在分散混合上,除颜料与聚烯烃外,效果尚不理想。     

单螺杆挤出机中聚合物熔体停留时间分布预测

基于有限差分数值模拟技术 ,提出了预测聚合物熔体在单螺杆挤出机内停留时间分布半解析模拟方法 ,得到了不同操作参数下的停留时间及其函数的分布曲线。结果表明 ,无因次挤出流量越小 ,聚合物熔体在单螺杆挤出机内的停留时间就越长 ,而且分布越宽。所提出的方法能够反映耦合流场及压力反流对停留时间分布的影响 ,能更真实地反映聚合物熔体在单螺杆挤出机内的停留时间分布     

螺棱梯形底角和凹槽半径对反应挤出机流场的影响

利用Polyflow计算机软件,在相同温度的条件下,通过最大剪切速率、最大剪切应力、最大混合指数和累计停留时间这4个指标,研究螺杆螺棱截面形状为梯形时其梯形底角角度和凹槽半径两个变量对聚乙烯在单螺杆反应挤出机中流场的影响。结果表明,当螺杆螺棱截面梯形底角角度为60°时,螺杆提供的最大剪切速率、最大剪切应力、最大混合指数均较底角为30°和45°的高,粒子累积停留时间则居中;在底角为60°的梯形螺棱上开半径为1.5 mm的半圆凹槽时,该结构所提供的最大剪切速率、最大剪切应力和最大混合指数均较不开槽(凹槽半径0 mm)和凹槽半径为2 mm的高,粒子累积停留时间相对最短。当螺杆螺棱截面梯形底角角度为60°且凹槽半径为1.5 mm时,可使物料获得的剪切效果最好且使其在流道中的停留时间最短,从而为大规模生产加工节约了时间。     

间断副螺棱结构对挤出机内混沌混合影响的数值模拟

建立了混沌单螺杆挤出机计量段展开螺槽的物理模型及数学模型,根据流体符合Carreau定律,借助Ployflow软件,采用网格叠加技术,对聚合物熔体在插有间断结构副螺棱螺槽内的流动进行了数值模拟分析,从统计学的角度结合粒子示踪技术以停留时间分布、分离尺度、混合效率及累计混合指数为指标来表征螺杆的混合性能。结果表明,当副螺棱间断次数多且高度略低于螺槽高时混沌单螺杆混合性能更好。     

往复式单螺杆销钉挤出机典型螺纹元件混合性能研究

使用Polyflow有限元软件对往复式单螺杆销钉挤出机（简称Buss机）的三类典型螺纹元件内物料流动和混合过程进行了数值模拟。流场分析中使用了网格重叠技术。在得到流场速度分布后,基于粒子轨迹跟踪技术计算了物料微元在螺纹元件内的流动轨迹,并分析了Buss机螺纹元件内物料的动态混合过程。以分布混合指数和分隔比例为指标定量地对比了螺纹元件的分布和分散混合性能,在此基础上分析了加工条件、物料特性及销钉布置对Buss机混合性能的影响。数值模拟结果与前人研究有较好的吻合性。     

挤出机螺杆直槽式屏障混炼元件的优化设计

研究挤出机螺杆直槽式屏障混炼元件的优化设计问题。根据粘性流体流动基本方程。以单位产量能耗最小为优化目标,建立简化的挤出机螺杆直槽式屏障混炼元件优化设计的数学模型，并应用复合形法求解，确定剪切长度、剪切问隙、屏障长度和屏障槽数等主要几何参数。本研究优化结果均在文献所建议的最佳取值范围内。     

单螺杆挤出机混合装置与混合机理研究的新进展

由于单螺杆的简单、低成本等众多优点，对单螺杆挤出机不断加强研究。近年由于CRD混合结构的推出，其在混合效果方面获得一定的新进展。本文概述了单螺杆挤出机混合装置的历史发展过程，从其混合功能的机理演变，提出拉伸混合应作为适用与高效的混合研究发展方向。     

Residence time in a single screw free helix extruder using a new solution to the biharmonic equation

A new analytical solution for the biharmonic equation was developed for single screw extrusion cross-channel fluid mechanical flow. This analysis led to a quantitative model for residence time distribution when combined with the historic solutions of the drag and pressure flow in the rectangular channel in the single-screw extruder. The focus of the theoretical and experimental investigation here was to examine how closely the new analytical solution correlated with experimental residence time data for a free-helix extruder. This new extrusion device was operated as both a conventional extruder and a more positive displacement device by using only helix rotation as the pump. The Moffatt eddies that occur in the quiescent corners of the rectangular channel with screw rotation were found to have a strong effect on the residence time of the extruder. Because there were no quiescent corners for the free-helix flow there was essentially no residence time tail for this mode of extruder displacement. The theoretical results for a sheet of dye spanning the screw channel width and dye “blobs” were compared with experimental results for both modes of operation. In all cases, the experiments and the theory predictions were essentially consistent.     

挤出过程停留时间分布影响因素之间的交互作用

应用全析因设计方法,研究了捏合块角度、比产率(喂料速率/螺杆转速)和螺杆转速对双螺杆挤出机机筒不同位置的延迟时间和平均停留时间的影响,考察了各因素之间的交互作用。结果表明,在所选取的操作条件下,螺杆转速对延迟时间和平均停留时间的影响最大,捏合块角度与比产率的影响程度相近。3因素两两交互作用对延迟时间的影响程度由大到小依次为捏合块角度与比产率、螺杆转速与比产率、捏合块角度与螺杆转速;对平均停留时间的影响由大到小依次为比产率与螺杆转速、捏合块角度与比产率、捏合块角度与螺杆转速。3因素3阶交互作用对平均停留时间的影响比较显著。     

齿形盘元件的局部停留时间分布

采用自制荧光检测装置在线测量含齿形盘元件（TME）的双螺杆挤出机的部分停留时间分布（PRTD），利用去卷积方法计算TME的局部停留时间分布（LRTD），并将PRTD转换成停留体积分布（RVD）和停留转数分布（RRD）。研究表明，直齿的LRTD曲线形状比斜齿更宽，其混合能力更强；喂料速率（Q）和螺杆转速（N）的提高均使LRTD曲线向短时间方向移动。等流量转速比（Q／N）的RRD和RVD曲线重合；提高Q／N，使RRD向低转数的方向移动，而RVD向高体积方向移动。对于特定螺杆构型，不同螺杆转速和喂料速率下的RVD曲线仅是体积坐标方向的平移，RVD曲线形状主要取决于螺杆构型。     

Modelling of polymer fluid flow and residence time distribution in twin screw extruder using fictitious domain method

Abstract

The flow behaviour of a polymer melt in the conveying region of an intermeshing corotating twin screw extruder was studied using the combination of mixed finite element and fictitious domain method. The model was a combination of the governing equations of continuity and momentum with Carreau rheological model in a three-dimensional Cartesian coordinate system. The equations were solved by the use of a mixed Galerkin finite element technique. The Picard’s iterative procedure was used to handle the non-linear nature of the derived equations. The particle tracking technique was used to obtain residence time distribution and analyse distributive mixing in conveying region. The shear rate distribution was investigated as a criterion for dispersive mixing. The applicability of this model was verified by the comparison of experimentally measured pressure and simulation results for high density polyethylene melt. This comparison shows that there is a good adequacy between experimental data and model predictions.     

Flow behavior in a corotating twin‐screw extruder of pure polymers and blends: Characterization by fluorescence monitoring technique

The objective of this work was to investigate the flow behavior of pure polymers and blends, especially miscible polymer/polymer systems, in a corotating twin‐screw extruder (TSE) using an online fluorescence monitoring device. An immiscible blend was also studied for the sake of comparison. The fluorescence signal was obtained by using synthesized fluorescence tracers added to the melt at very low concentrations. These tracers consisted of two styrene‐maleic anhydride copolymers (SMA) labeled with anthracene. The investigated blends were SMA8 (8 wt % of MA in SMA)/polystyrene (PS), SMA14 (14 wt % of MA in SMA)/styrene acrylonitrile copolymer (SAN), and poly(methyl methacrylate) (PMMA)/ethyl acrylate‐methyl methacrylate copolymer (PMMAEA). The residence time distribution (RTD), the mean residence time (t ), the dimensionless variance (σ_θ²), the Peclet number (Pe) and the fluorescence peak intensity distribution of pure polymers and binary polymer systems were investigated and interpreted in terms of polymers rheological properties. It was observed that polymers presenting higher viscosity or higher pressure showed longer residence time. A difference in behavior was also observed for the RTD of miscible and immiscible blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

新型螺杆元件对LDPE-g-MAH反应挤出的影响

改变同向双螺杆挤出机主反应区的螺杆元件,研究该螺杆元件对低密度聚乙烯(LDPE)熔融接枝马来酸酐(MAH)的接枝产物和接枝率的影响。傅里叶变换红外光谱分析证实,部分MAH成功接枝到LDPE分子链上。对挤出沿程4个在线取样位置的试样做了对比分析,结果表明具有高剪切性能的捏合盘元件的沿程试样接枝率最大,熔体流动速率最小;具有高分布混合性能的齿形盘元件的沿程试样接枝率较大,熔体流动速率较小;具有回混作用的非啮合多过程元件能够迅速提高该元件所在区域的接枝率。     

Laboratory modular instrumented single screw extruder for optimisation of polymer processing

Abstract

A laboratory fully modular instrumented single screw extruder designed to gather information on the development along its axis of temperature, mixing, chemical conversion and/or morphology development of a given material is presented. Some of its capabilities are utilised to study the effect of operating conditions and of screw geometry, including conventional versus barrier profiles, on the evolution of the plasticating sequence of a low density polyethylene. Melting of an immiscible polymer blend (polyamide 6/polypropylene) is also investigated and a specific melting mechanism is proposed.