Automated Optimization of Spiral Shearing and Mixing Elements for Single-screw Extruders

在各种挤出生产线中加工聚合物的过程中，越来越多地使用具有带槽进料段的单螺杆挤出机。这是因为它们的恒定输送特性不受挤出模头的影响。由于这些高速挤出机的高特定产量，在螺杆末端应用混合单元，以确保熔体的热均匀性和材料均匀性。这里的一个巨大挑战是在考虑相互作用的不同要求的情况下设计这些混合单元。因此，对混合元件进行纯实验评估非常耗时且成本高。此外，实验装置不允许详细了解混合过程。在这种情况下，混合单元代表了一个黑匣子，它对过程中的任何变化或对所处理材料特性的修改做出不可估量的响应。计算流体动力学模拟是混合单元纯实验设计的替代方案。遗憾的是，现有的混合质量的预测方法有很大的缺陷，这使得虚拟设计是不可能的。这一事实已在文献中以及在自己的初步研究中得到证实。近年来，在申请人的研究所对现有技术进行了进一步的研究，因此，新的和验证的模拟模型，现在可以允许一个整体的看法，在混合过程中的分布和分散的混合能力。本研究项目的目的是提供一个工具，自动优化混合几何方面的分布和分散的在有利的时间范围内实现混合性能。除了混合性能外，流动和热性能（如压降、停留时间和熔体温度）也将影响优化。在一个特定的实验设置中的优化工具的广泛验证期间，将在不同的条件下验证仿真工具的有效性。该实验装置还能够对混合单元内的混合质量进行局部评估。最后，这种新的方法将比较传统的替代品和它的优点和缺点将工作。

During the processing of polymers in various extrusion lines, more and more single-screw extruders with a grooved feed section are being used. This is due to their constant conveying characteristics which aren’t being influenced by the extrusion die. Because of the highly specific throughputs of these high-speed extruders, mixing units are applied at the end of the screw to ensure thermal and material homogeneity of the melt. A great challenge here is the design of these mixing units under consideration of varying requirements, which are interacting with each other. Therefore, a pure experimental evaluation of mixing elements is very time-consuming and cost-intensive. Also, the experimental setup does not allow a detailed insight into the mixing processes. In that case, the mixing unit represents a black-box which responds incalculably to any changes in the process or to modifications to the processed material properties. The computational fluid dynamics simulation is an alternative to the pure experimental design of mixing units. Regrettably, the existing methods for the prediction of the mixing quality have substantial shortcomings, which make the virtual design impossible. This fact has been verified in the literature as well as in own preliminary studies. In recent years, further research has been carried out at the applicant's research institute on the current state of the art, so that new and verified simulation models are now available that allow a holistic view of the mixing process in terms of distributive and dispersive mixing capability.The objective of this research project is to provide a tool which automatically optimizes a mixing geometry in regard to the distributive and dispersive mixing performance within a profitable time frame. Beside the mixing performance, flow and thermal properties such as pressure drop, residence time and melt temperature will be influencing the optimization as well. During an extensive validation of the optimization tool within a particular experimental setup, the validity of the simulation tool will be verified under different conditions. This experimental setup additionally enables a local evaluation of the mixing quality inside the mixing unit. Finally, this new approach will be compared to conventional alternatives and its advantages and disadvantages will be worked out.