螺杆圆周展开面的流场与混合效果分析
摘要
聚合物是一种应用广泛的材料。它是由成百成千个原子组成的一种大分子，由一种或两种，有时由更多种的小分子一个接一个地连接成链状或网状结构而形成的。在聚合物加工中，大约80％都要经过螺杆挤出这一重要加工工艺。在任何一个聚合物加工企业或研究单位，挤出机都是最基本的装置之一。随着挤出科学与工程的发展，挤出机除了完成传统的加工工艺，如固体输送、增压、熔融、排气、脱湿、熔体输送、混合均化、泵送之外。更多的过程，如交联、发泡、接枝、甚至聚合反应等都愈来愈多地在螺杆挤出机上进行。由于挤出工艺装备可集多种化工单元过程于一体，以连续操作代替间歇操作，大大提高了生产效率并降低了能耗，同时节约占地，自动化程度高，减少污染，改善劳动条件。因此，挤出加工工艺广泛用于聚合物加工。
橡胶挤出机问世100多年来，在技术上最大的突破是由挤出机的机外塑化转变为机内塑化，从而将热喂料挤出机演变为冷喂料挤出机。采用冷喂料挤出机挤出，可把橡胶加工过程分为混炼工艺和成型工艺，可以经济地制造出多种制品。但关键问题是如何使冷喂料挤出均匀加热，如何保证挤出质量，提高挤出效率。20世纪70年代中期出现的销钉机筒冷喂料挤出机，可以说是冷喂料挤出技术的一次重大突破，大大促进了冷喂料挤出机性能的提高及其向大型化方向的发展。因此销钉机筒冷喂料挤出装置的研究就成了近30年来橡胶加工技术的研究焦点。
由于橡胶加工过程的复杂性，建立的理论和计算方法有很大的局限性，主要依赖于经验的方法处理加工中的问题。随着人们对传递现象的深入理解和实践经验的积累，加上计算机技术的迅速发展，现在可以利用数学模型和模拟技术解决聚合物加工问题。计算机模拟可以形象、直观地显示实际加工、成型过程，预测设备性能，优选结构和操作参数，从而使注射、挤出、压延、混合、脱挥等操作实现优化。只有通过相关的计算机模拟，才能满足聚合物加工高质量和高产量的要求。从经验分析发展到计算机模拟，这是橡胶加工过程研究方法上的变革。
由于销钉机筒挤出机穿过机筒固定有大量的销钉，且销钉插入到螺杆的根部，在销钉截面处，螺棱上开有环形槽，使其物料在挤出过程的流动十分复杂，求解复杂流道流体流场的解析解几乎是不可能，目前，只能通过有限元法获得数值解。作者在单螺杆挤出简化分析模型的基础上，采用GAMBIT软件进行前处理，首先建立几何模型，其次划分网格，网格的类型为TGrid，将销钉所在的区域做成动态区域，螺杆展
\
开面的其它区域做成静态区域，然后添加边界条件，最后把动静区域的网格合并，动
态区域与静态区域之间定义成分界面。进行完前处理后，应用FLUENT软件导入
GAMBIT的前处理结果，使用层流模型，采用滑移网格技术，进行数值计算，可得
到以下各种模型的流场分布:不同的销钉个数、不同的销钉排间距、不同的螺槽宽度
以及不同的拖曳速度。通过有限元(F LUENT)计算，可知物料在销钉的作用下作横向
运动、分流运动、旋转运动。销钉的存在，改变了流动通道的几何形状，使流层厚度
减小，产生延伸流动。所以销钉结构对物料的流动状况有显著影响。在挤出机螺杆表
面附近，存在着很大的速度梯度，这是高剪切率的层流区。从流场分析的结果来看，
螺槽越窄，则速度梯度越大，速度值大小的变化越频繁。从这一点来看，在设计螺槽
时候，宽度不宜过大。销钉的排间距越小，则速度梯度值就越大，速度值大小的变化
越频繁，从而剪切率就会高，有利于混合均化。改变上表面的拖曳速度后，流场分布
没有明显变化，所以说改变流速的大小不会影响流场的分布。本简化模型认为物料的
前进运动是由于机筒内表面的拖曳作用，但实际上，物料的前进运动是在螺杆转动时，
螺棱的推进作用所导致的。因此，其结果与实际情况有一定误差，但用来分析研究结
构对流场的影响，仍具有重要意义。本文所处理的流场类型适用于层流状态。
混合均化是一个广泛而重要的物理现象，传统上，不同的混合过程，用不同的混
合理论来处理。本文忽略剪切对非牛顿流体粘度的影响，基于高粘度非牛顿流体的流
动进行研究，从考虑体积形变所消耗的能量来考虑，通过基于流场分析的混合均化效
果计算方法，对不同结构螺杆圆周展开面的混合效果进行了计算与评价。通过数值分
析我们发现:减小销钉的排间距、螺槽宽度，增多销钉数目，增大拖曳速度，都会改
善混合效果。就中90销钉挤出机而言，每排以6一8枚销钉为宜:螺槽宽度以54mm左右
为宜;销钉的排间距以48一72Inln为宜;拖曳速度(转速)越高越好。能促使物料界面更
新以及产生较大剪切作用的结构，将有利于混合均化效果的强化。销钉机筒的优良挤
出效果得益于销钉与螺棱切槽对物料的剪切、延展、拉伸、变向作用。
Polymer is a kind of material that is applied in a broad area. It is a kind of big molecule, which is composed of many small molecules. The polymer has a structure of chain or reticulation. About 80% polymer process needs extrusion. The extruder is a kind of important equipment. Along with the development of science and engineering, more reactions have been processed in the extruder. Many chemical cells can be incorporated through extruder. The intermittent operation can be replaced by the continuous operation through extruder. The production efficiency can be increased and the energy can be reduced. Because the automation degree of extruder is higher, it can reduce pollution, improve work conditions. So extrusion technique has been applied in polymer process.
Since rubber extruder came out 100 years ago, the cold feed extruder has replaced hot feed extruder, which is a technical breakthrough. For cold feed extruder, the rubber process can be divided into mixing technique and molding technique. A lot of products can be manufactured by the cold feed extruder economically. The key is how to heat up the cold feed extruder equably and improve extrusion efficiency. The pin barrel extruder appeared about in the 1970, which is a breakthrough of cold feed extruder. It improves cold feed extruder performance. So, the pin barrel extruder has been the research focus of rubber process technique in recent 30 years.
Because of the complexity of rubber process, there is localization in the theory and computation method of rubber process, which relies on experiential method. Along with the deep comprehension, accumulated practice and the rapid development of computer, now the problem of polymer process can be settled by simulation technique. The computer can display process course, forecast the equipment performance, optimize the parameters of structure and operation. So the operation of injection, extrusion, extension and mixing can be optimized. Only by computer simulation, can the request of high quality and high output for the polymer process be satisfied. From experience analysis to computer simulation, it is a transformation of rubber process research method.
Because many pins are fixed in the barrel, the material flows complexly in the channels. It is impossible to solve the complex flow accurately now. Only by finite element
method, can the numerical value be got.
Based on the simplified model of the single screw, the soft ware GAMBIT was adopted to process the models in advance. First, geometrical models were constructed. Second, the meshes were plotted. The area around pins was plotted as sliding meshes, and other area were plotted as actionless meshes. Last, the boundary conditions were set up and the two kinds of meshes were incorporated. After that the results of GAMBIT were processed by the finite element soft ware FLUENT. The flow distributions of every kind of model were got: different numbers of pins, different width of grooves, different daggling velocities. It can be seen through the analysis of FLUENT that the material goes through landscape orientation movement, diffluent movement and circumrotating movement under the influence of the pins. Because the existence of the pins, the geometrical figure of flow channels were changed. The flow layers were attenuated. The extension flow came into being. So we can say that the structure of pins can affect the flow of material notably. It can be seen from the analysis results of FLUENT that the velocity grads are higher on the condition that the channels of screw are narrower and the row distance of pins is smaller. Higher velocity grads are in favor of mixing. If the daggling velocity changes, the flow distribution changes a little. In this simplified model, it was considered that the movement of material was in virtue of the daggling effect of the inner barrel. But in fact, it is the ridges of screw that push the material forward. There are differences between this model and facts. But the results still play an important role in analyzing flow distributio
橡胶挤出机问世100多年来，在技术上最大的突破是由挤出机的机外塑化转变为机内塑化，从而将热喂料挤出机演变为冷喂料挤出机。采用冷喂料挤出机挤出，可把橡胶加工过程分为混炼工艺和成型工艺，可以经济地制造出多种制品。但关键问题是如何使冷喂料挤出均匀加热，如何保证挤出质量，提高挤出效率。20世纪70年代中期出现的销钉机筒冷喂料挤出机，可以说是冷喂料挤出技术的一次重大突破，大大促进了冷喂料挤出机性能的提高及其向大型化方向的发展。因此销钉机筒冷喂料挤出装置的研究就成了近30年来橡胶加工技术的研究焦点。
由于橡胶加工过程的复杂性，建立的理论和计算方法有很大的局限性，主要依赖于经验的方法处理加工中的问题。随着人们对传递现象的深入理解和实践经验的积累，加上计算机技术的迅速发展，现在可以利用数学模型和模拟技术解决聚合物加工问题。计算机模拟可以形象、直观地显示实际加工、成型过程，预测设备性能，优选结构和操作参数，从而使注射、挤出、压延、混合、脱挥等操作实现优化。只有通过相关的计算机模拟，才能满足聚合物加工高质量和高产量的要求。从经验分析发展到计算机模拟，这是橡胶加工过程研究方法上的变革。
由于销钉机筒挤出机穿过机筒固定有大量的销钉，且销钉插入到螺杆的根部，在销钉截面处，螺棱上开有环形槽，使其物料在挤出过程的流动十分复杂，求解复杂流道流体流场的解析解几乎是不可能，目前，只能通过有限元法获得数值解。作者在单螺杆挤出简化分析模型的基础上，采用GAMBIT软件进行前处理，首先建立几何模型，其次划分网格，网格的类型为TGrid，将销钉所在的区域做成动态区域，螺杆展
\
开面的其它区域做成静态区域，然后添加边界条件，最后把动静区域的网格合并，动
态区域与静态区域之间定义成分界面。进行完前处理后，应用FLUENT软件导入
GAMBIT的前处理结果，使用层流模型，采用滑移网格技术，进行数值计算，可得
到以下各种模型的流场分布:不同的销钉个数、不同的销钉排间距、不同的螺槽宽度
以及不同的拖曳速度。通过有限元(F LUENT)计算，可知物料在销钉的作用下作横向
运动、分流运动、旋转运动。销钉的存在，改变了流动通道的几何形状，使流层厚度
减小，产生延伸流动。所以销钉结构对物料的流动状况有显著影响。在挤出机螺杆表
面附近，存在着很大的速度梯度，这是高剪切率的层流区。从流场分析的结果来看，
螺槽越窄，则速度梯度越大，速度值大小的变化越频繁。从这一点来看，在设计螺槽
时候，宽度不宜过大。销钉的排间距越小，则速度梯度值就越大，速度值大小的变化
越频繁，从而剪切率就会高，有利于混合均化。改变上表面的拖曳速度后，流场分布
没有明显变化，所以说改变流速的大小不会影响流场的分布。本简化模型认为物料的
前进运动是由于机筒内表面的拖曳作用，但实际上，物料的前进运动是在螺杆转动时，
螺棱的推进作用所导致的。因此，其结果与实际情况有一定误差，但用来分析研究结
构对流场的影响，仍具有重要意义。本文所处理的流场类型适用于层流状态。
混合均化是一个广泛而重要的物理现象，传统上，不同的混合过程，用不同的混
合理论来处理。本文忽略剪切对非牛顿流体粘度的影响，基于高粘度非牛顿流体的流
动进行研究，从考虑体积形变所消耗的能量来考虑，通过基于流场分析的混合均化效
果计算方法，对不同结构螺杆圆周展开面的混合效果进行了计算与评价。通过数值分
析我们发现:减小销钉的排间距、螺槽宽度，增多销钉数目，增大拖曳速度，都会改
善混合效果。就中90销钉挤出机而言，每排以6一8枚销钉为宜:螺槽宽度以54mm左右
为宜;销钉的排间距以48一72Inln为宜;拖曳速度(转速)越高越好。能促使物料界面更
新以及产生较大剪切作用的结构，将有利于混合均化效果的强化。销钉机筒的优良挤
出效果得益于销钉与螺棱切槽对物料的剪切、延展、拉伸、变向作用。
Polymer is a kind of material that is applied in a broad area. It is a kind of big molecule, which is composed of many small molecules. The polymer has a structure of chain or reticulation. About 80% polymer process needs extrusion. The extruder is a kind of important equipment. Along with the development of science and engineering, more reactions have been processed in the extruder. Many chemical cells can be incorporated through extruder. The intermittent operation can be replaced by the continuous operation through extruder. The production efficiency can be increased and the energy can be reduced. Because the automation degree of extruder is higher, it can reduce pollution, improve work conditions. So extrusion technique has been applied in polymer process.
Since rubber extruder came out 100 years ago, the cold feed extruder has replaced hot feed extruder, which is a technical breakthrough. For cold feed extruder, the rubber process can be divided into mixing technique and molding technique. A lot of products can be manufactured by the cold feed extruder economically. The key is how to heat up the cold feed extruder equably and improve extrusion efficiency. The pin barrel extruder appeared about in the 1970, which is a breakthrough of cold feed extruder. It improves cold feed extruder performance. So, the pin barrel extruder has been the research focus of rubber process technique in recent 30 years.
Because of the complexity of rubber process, there is localization in the theory and computation method of rubber process, which relies on experiential method. Along with the deep comprehension, accumulated practice and the rapid development of computer, now the problem of polymer process can be settled by simulation technique. The computer can display process course, forecast the equipment performance, optimize the parameters of structure and operation. So the operation of injection, extrusion, extension and mixing can be optimized. Only by computer simulation, can the request of high quality and high output for the polymer process be satisfied. From experience analysis to computer simulation, it is a transformation of rubber process research method.
Because many pins are fixed in the barrel, the material flows complexly in the channels. It is impossible to solve the complex flow accurately now. Only by finite element
method, can the numerical value be got.
Based on the simplified model of the single screw, the soft ware GAMBIT was adopted to process the models in advance. First, geometrical models were constructed. Second, the meshes were plotted. The area around pins was plotted as sliding meshes, and other area were plotted as actionless meshes. Last, the boundary conditions were set up and the two kinds of meshes were incorporated. After that the results of GAMBIT were processed by the finite element soft ware FLUENT. The flow distributions of every kind of model were got: different numbers of pins, different width of grooves, different daggling velocities. It can be seen through the analysis of FLUENT that the material goes through landscape orientation movement, diffluent movement and circumrotating movement under the influence of the pins. Because the existence of the pins, the geometrical figure of flow channels were changed. The flow layers were attenuated. The extension flow came into being. So we can say that the structure of pins can affect the flow of material notably. It can be seen from the analysis results of FLUENT that the velocity grads are higher on the condition that the channels of screw are narrower and the row distance of pins is smaller. Higher velocity grads are in favor of mixing. If the daggling velocity changes, the flow distribution changes a little. In this simplified model, it was considered that the movement of material was in virtue of the daggling effect of the inner barrel. But in fact, it is the ridges of screw that push the material forward. There are differences between this model and facts. But the results still play an important role in analyzing flow distributio
引文
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