Analysing and modelling the melting behavior of planetary roller extruders

挤出和复合是塑料制品生产过程中的基本步骤。由于质量要求的提高和通过工艺优化降低成本的趋势，复合工艺显得尤为重要。这一工艺步骤的主要目标是添加剂与聚合物基质的最佳混合。在这种情况下，行星辊挤出机是一种非常适合这些任务的机械概念。这是因为材料具有良好的均匀和分散能力，材料的剪切率低，停留时间分布窄。描述单螺杆和双螺杆挤出机过程行为的模型已经在科学和工程文献中讨论了几年。对于行星辊式挤出机，首次提出了工艺模型。然而，这些模型忽略了熔融过程，因此仅适用于熔体输送。本研究项目的目的是分析行星辊式挤出机的熔融行为，并首次开发描述熔融过程的物理数学模型。在已成功模拟熔体输送行星辊挤出机输送机理的基础上，对描述单螺杆和双螺杆挤出机熔融过程的方法进行了调整，以适应行星辊挤出机的条件。调整后的模型将使计算行星辊式挤出机作为熔融挤出机运行时的压力、填充度、熔融度、温度和功率消耗沿挤出机长度方向成为可能。由于课题的复杂性，在头两年只观察到了未填充的聚合物颗粒的熔融行为。有了这个简化的系统，就创建了建模的基本原理。首先建立了一套实验装置，利用死止点实验对熔化行为进行了分析。实验表明，弥散熔融模型适用于描述熔融过程。该模型适用于行星辊式挤出机，并集成到仿真工具SimPla中。首先，用SimPla进行的模拟和实验之间的比较显示出很好的一致性。在要求的研究项目中，应将熔融模型扩展到粉状和填充材料，以便在项目结束时，可以获得行星辊式挤出机的综合工艺模型。

Extrusion and compounding are fundamental steps in the production process of plastic products. Due to increased quality requirements and the trend to cost reduction by process optimization, the compounding process is outstandingly important. The major aim of this process step is the optimal mixing of additives with the polymer matrix. In this context, the planetary roller extruder is a machine concept that is well suited for these tasks. Reasons for this are the excellent homogenization and dispersion abilities t with a low shearing of the material as well as a narrow residence time distribution.Models that describe the process behavior of single and twin screw extruders have been discussed in the scientific and engineering literature for several years. For planetary roller extruders, first process models were published. However, these models neglect the melting process and thus they are only applicable for melt transportation.The aim of this research project is the analysis of the melting behavior of planetary roller extruders and the first time development of physical mathematical models, which describe the melting processes. Based on the successes in modeling the transport mechanism of melt fed planetary roller extruders, the approaches that are used to describe the melting process of single and twin screw extruder are adjusted to the conditions in the planetary roller extruder. The adjusted models shall make it possible to calculate the pressure, filling degree, melting degree, temperature and power consumption along the extruder length for planetary roller extruders that run as melting extruders.Because of the complexity of the topic, in the first two years only the melting behavior of unfilled polymer pellets was observed. With this simplified system the fundamentals of the modeling were created. At first an experimental setup, which enabled the analyses of melting behavior with dead stop experiments, was build. The following experiments showed, that a disperse melting model is suitable for describing the melting. This model was adapted for the planetary roller extruder and integrated in the simulation tool SimPla. First comparisons between simulations done with SimPla and experiments showed a good agreement. In the requested research project, the melting model shall be extended for powder shaped and filled materials, so that at the end of the project, a comprehensive process model for planetary roller extruders will be available.