同向旋转双螺杆挤出机中的聚合物共混胶(上)

鉴于聚合物组合的形态结构可使聚合物共混胶的性能测定达到准确无误的程度，为此，挤出机设计需要采用模型，以能计算熔体输送段中挤出机螺杆长度上的估算形态发展，由于观测到的最明显的形态变化出现于熔融段，本文就着重描述了挤出机这一段中的共混胶熔融过程中形态的形成和发展。文中对PP和PA6共混胶的熔融流变性、界面张力、熔融形态进行了描述，并对熔融过程中开始时的固体含量、固体温度平均熔体温度及熔体温度的发展熔融过程的模拟、熔融度、粘度比、单位挤出量恒定时的速度影响、挤出机规格影响、螺杆顶部的熔融度、挤出量恒定时螺杆速度的影响、恒速下挤出量的影响、粘度比的影响、微滴分散与聚结等作了较为详尽的计算与讨论，从而为研究熔融过程、形态发展以及为理论模型和形态发展对比提供了数据基础。     

同向旋转双螺杆挤出机中的聚合物共混胶(下)

鉴于聚合物组合的形态结构可使聚合物共混胶的性能测定达到准确无误的程度，为此，挤出机设计需要采用模型，以能计算熔体输送段中挤出机螺杆长度上的估算形态发展。由于观测到的最明显的形态变化出现于熔融段，本文就着重描述了挤出机这一段中的共混胶熔融过程中形态的形成和发展。文中对PP和PA6共混胶的熔融流变性、界面张力、熔融形态进行了描述，并对熔融过程中开始时的固体含量、固体温度平均熔体温度及溶体温度的发展熔融过程的模拟、熔融度、粘度比、单位挤出恒定时的速度影响、挤出机规格影响、螺杆顶部的熔融度、挤出量恒定时螺杆速度的影响、恒速下挤出量的影响、粘度比的影响、微滴分散与聚结等作了较为详尽的计算与讨论。从而为研究熔融过程、形态发展以及为理论模型和形态发展对比提供了数据基础。     

单螺杆挤出固体输送段非塞流的三层模型法

依据单螺杆挤出机固体输送段的非塞流现象，把固体塞分成上、中、下三层，通过应力—速度方程，推导出产量与压力降的三次方程；详细讨论了摩擦系数对最大产量的影响，并深入地分析了单螺杆挤出机固体输送段产量与末端压力的关系，通过这些分析计算，三层模型法能很好地预示单螺杆挤出机固体输送段的压力与产量，该方法不仅简单明晰而且精度高，是一个可使用的方法     

单螺杆挤出过程固体输送段的数值模拟

介绍了挤出成型过程数值模拟的现状及现有通用计算流体力学(CFD)软件在模拟聚合物流动时存在的缺陷，指出自主开发CFD程序的必要性。针对单螺杆挤出过程固体输送段的数值模拟方法，讨论了传统塞流固体输送理论的缺陷，介绍了非塞流固体输送理论的优越性及相关的有限元计算方法。并针对有限元方法的复杂性，介绍了简化的三层模型方法。计算结果表明：非塞流固体输送理论的三层模型法与有限元法计算结果接近，且优于塞流固体输送理论，而三层模型法计算方法简单，便于其在工程计算中的应用。     

离心式挤出机工作原理及其固体输送压力影响因素的研究

离心式挤出机是一种新型的塑料加工机械,具有节能特点。详细地介绍了离心式挤出机的结构及工作原理。根据离心式挤出机的固体输送机理建立固体输送压力分布的数值模型,并研究分析了转鼓结构(半径、锥角)、转鼓内壁与聚合物之间的摩擦因数、以及转鼓转速对固体输送压力分布的影响。     

振动力场作用下的单螺杆挤出机固体输送理论

在单螺杆挤出机中,通过螺杆的轴向振动将振动力场引入聚合物固体输送过程,提出振动力场强化固体输送过程的新概念.以螺槽中运动的物料为对象建立了振动力场强化固体输送过程的数学模型,并获得了物料沿螺槽方向输送的压力（密度）、速度的近似解析解.传统固体输送过程就是当螺杆轴向振动的振幅为零时的特例,此时的压力降与Darnell and Mol 理论一致,但不同的是物料速度及密度沿螺槽方向是变化的,从而修正了Darnell and Mol 固体输送理论.螺杆的轴向振动提高了固体输送平均压力,缩短了固体输送的长度,增加了固体输送角.透明料筒全程可视化实验挤出机证明了螺杆轴向振动确实缩短了物料固体压实输送所需的螺槽长度.     

基于离散单元法一字排列三螺杆挤出机固体输送段输送机理分析

利用离散单元法对计量加料下一字排列三螺杆挤出机固体输送段进行模拟。分析了聚合物颗粒在一字排列三螺杆挤出机正位移输送和摩擦拖曳输送2种输送机理下的输送情况,计算出一字排列三螺杆挤出机的输送特性参数,并与双螺杆挤出机进行对比分析。结果表明,由于三螺杆挤出机啮合区的增加,提高了颗粒在挤出机螺槽内的填充率。一字排列三螺杆挤出机在填充程度、质量流速率等方面均优于双螺杆挤出机,并且输送产量大约为双螺杆挤出机的1.3倍,在聚合物加工行业具有较好的工程应用前景。     

同向啮合双螺杆挤出过程固体输送可视化研究

借助可视化同向啮合双螺杆实验挤出机和特殊的实验方法，作者进行了大量固体输送实验研究，弄清了在这种双螺杆挤出过程中固体输送存在的两种输送机理和临界充满度，有三个子输送区，进而建立了具有三个子输送区的固体输送理论模型。     

单螺杆挤出机固体输送机理研究的发展与趋势

介绍了国内外单螺杆塑料挤出机固体输送理论研究的发展，指出对固体输送段中固体颗粒体系密度和磨擦系数的研究是固体输送理论的两个研究热点，因为它们为更好地预测固体输送段的压力、产量提供数据，并指导团体输送段的设计及工艺操作。还提出了将固体输送与熔融过程作为一连续过程来研究的思路。     

聚合物多元醇分散相的电镜研究

本文应用JEM—200CX电子显微镜及其扫描系统对聚合物多元醇分散相进行了系统的研究.比较了制样方法;概述了分散相固体微粒(<1μ)的组成和形态结构;证实了聚合物多元醇是聚醚多元醇液体及其与乙烯基共聚物、均聚物和接枝共聚物的复合体-接枝体固体微粒组成稳定的粘稠乳状分散液体系;其分散相微粒的组成和形态结构与工艺条件密切相关;应用数理统计测定了分散相固体微粒的粒度大小及其分布。     

Prediction of polymer pellet conveying behavior in microinjection molding machine

The higher requirements in dosage accuracy and material strength for products with micro features have made the solid conveying process in microinjection molding machines very important. Problems such as starve feeding and process instability will adversely affect quality more in microinjection molding than bigger parts. Studies have been carried out on the conveying of discrete solid polymer pellets in the plasticizing unit of microinjection molding machines using a newly developed discrete element modeling method to simulate polymer particle movements in the screw channel. The model takes into consideration the influences of adhesion and gravity. The effect of inclination of the conveying screw on the speed of solid conveying is investigated with both simulation and experimental approaches. The results of simulations agree with the results of experiments qualitatively. POLYM. ENG. SCI. 46:1608–1612, 2006. © 2006 Society of Plastics Engineers     

同向双螺杆熔融段螺杆组合对共混物相态变化的影响

研究了双螺杆熔融段不同螺杆组合对模型聚合物共混体系HDPE/PS相态变化的影响。发现错列角为正向30°及正向60°的捏合块具有较好的输送能力,但不利于物料的熔融和混合;90°错列角捏合块对共混物具有很好的熔融和混合效果,其混合性能甚至优于反向30°捏合块,接近反向60°捏合块;及向螺纹元件对共混物相态变化影响显著。     

同向双螺杆熔体输送段捏合盘错列角对不相容体系共混物相态结构的影响

对啮合同向双螺杆挤出机,将捏合盘置于熔体输送段,通过改变捏合盘错列角,研究双螺杆挤出过程熔体输送段捏合盘错列角对不相容体系共混物相态结构的影响。应用差示扫描量热仪对两相共混体系HDPE/PS的热性能进行了实验研究,结果表明:螺杆构型对共混物的相容性影响不大。同时采用扫描电子显微镜考察了HDPE/PS共混物在熔体输送段末端位置和机头末端所取试样的相态结构,研究表明:置于熔体输送段捏合盘元件错列角对共混物分散相的相畴尺寸有一定影响。     

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.     

双转子连续混炼机固体物料输送过程研究

对双转子连续混炼机转子喂料段固体物料的输送过程进行了理论分析,提出了描述此过程的物理模型。运用该物理模型,得出了计算连续混炼机固体输送速率的公式,并由此提出双转子连续混炼机的产量与喂料量成正比以及与转子转速无关的结论。     

Analytical expressions for transient melting of polymer pellet sliding against adiabatic wall

The melting of polymer caused by friction before the solid plug is formed is an important phenomenon in the plastic injection process. To analyze the melting process caused by solid particles sliding against the bellow, a method that can simulate behavior of each particle during the calculation should be used. Particle element numerical method is hence adopted in the analysis for this research to take into consideration the behavior of each particle, where the melting of pellets caused by friction against flight and screw are assumed as friction against adiabatic walls. In this paper, analytical expressions of the transient melting process for spherical polymer pellets sliding against adiabatic wall are derived, which is essential for the numerical simulation of melting process in solid conveying section by particle element method.     

A Computer Model for Single-Screw Plasticating Extrusion

A fully predictive computer model has been developed for a single-screw plasticating extrusion (with conventional screws). The model takes into account five zones of the extruder (hopper, solids conveying, delay zone, melting zone, melt conveying) and the die, and describes an operation of the extruder-die system, making it possible to predict a mass flow rate of the polymer, pressure and temperature profiles along the screw channel and in the die, solid bed profile, and power consumption. Moreover, mixing degree, temperature fluctuation and viscoelastic properties of the polymer are estimated. The simulation parameters are the material and rheological properties of the polymer, the screw, hopper and die geometry, and the operating conditions (screw speed and barrel temperature profile). Such a comprehensive approach to the modeling of extrusion creates the possibility of optimizing the process, for example, from the point of view of the quality of extrusion. The model has been verified experimentally for a low-density polyethylene on a 45 mm diameter single-screw extruder.     

Modeling of the conveying of solid polymer in the feeding zone of intermeshing co-rotating twin screw extruders

In this paper, a model for the conveying of solid polymer in the feeding zone of intermeshing co-rotating twin screw extruders is proposed. The theoretical model uses an approach that is similar to that commonly used in single screw extruders; however, it takes into account the particular geometry of the screw channel, the partially filled channel, and the special configuration of the two self-wiping screws. The model thus considers two conveying mechanisms: the first one in the channel, which is analyzed in terms of polymer-metal friction, and the second one, which is mainly an axial transport in the intermeshing zone. The theoretical predictions of the model are compared with the experimental results obtained on a laboratory extruder with a polymer in powder form, and satisfactory agreement is observed. The model enables the prediction of the evolution of the filling of the screws towards the geometry and the operating conditions. This is an important key to analyzing the thermal aspects in this zone, which can lead to a prediction of the melting capacity of the extruder. Indeed, the filling of the feeding zone defines the heat transport that occurs between the hot barrel and the solid polymer.