Rheometer-independent description of the wall slip behaviour of rubber compounds

根据胶料成分和工艺参数的不同，橡胶胶料有增加壁滑等流动异常的趋势。因此，由于基本的分析和数值计算方法假定壁面粘附性，因此流变性材料测量和所得到的材料参数容易产生误差。除了通过壁面滑移效应对挤出过程和挤出物质量的影响外，在流动模拟和工具设计中没有考虑壁面滑移也会导致误差。这些问题通常只在生产操作期间被检测到，并导致耗时和成本密集的修正。本研究项目的目的是开发一种不依赖于流变仪的方法来描述橡胶化合物的壁滑移行为。为此，使用高压毛细管流变仪(HKR)、Contifeed(实验室挤出机螺杆直径为20 mm和HKR的组合)以及在线挤出流变仪对不同螺杆直径(32 mm和60 mm)的挤出机进行了广泛的流变学研究。在研究项目中考察了三个基本假设。首先，橡胶化合物的壁滑移行为取决于所用流变仪的大小(测试通道的几何形状)。其次，Gleissle(I，II)的镜像关系在壁滑移条件下对非填充和填充橡胶体系都是有效的。此外，挤压过程中的剪切历史对壁面滑移行为也有影响。通过使用橡胶过程分析仪(RPA)，可以确定橡胶化合物在壁面粘合边界条件下的流动行为，因为RPA被认为是无壁滑的，因为试验室的设计具有啮合侧翼。对于粘壁材料，根据Gleissle和Cox-Merz规则的镜像关系已经被多次证明。对于填充的弹性体，这些方法的有效性有限是由于壁滑移效应。考虑到线性粘弹性范围和非等温效应的修正，常规流变仪和RPA之间的测量值的偏差可以归因于壁面滑移效应，并且可以修正。给出了一种与材料和几何形状无关的有效的修正墙体滑移效应的方法。由于挤压过程，滑移效应的明显程度与HKR测量结果不同，因此建立了影响变量与滑移行为之间的关联，并将其组合在地图中。

Depending on the compound ingredients and the processing parameters, rubber compounds have an increased tendency to flow anomalies such as wall slip. As a result, rheological material measurements and the resulting material parameters are subject to errors, since the underlying analytical and numerical calculation approaches assume wall adhesion. Besides the influence on the extrusion process and thus the extrudate quality through wall slip effects, the non-consideration of wall slip in the context of flow simulations and the design of tools leads to errors. These are often only detected during production operation and result in time-consuming and cost-intensive corrections. The aim of this research project is to develop a methodology for the rheometer-independent description of the wall slip behaviour of rubber compounds. For this purpose, extensive rheological investigations of EPDM rubber compounds are carried out using high-pressure capillary rheometer (HKR), the Contifeed (combination of laboratory extruder with a screw diameter of 20 mm and HKR) as well as online extrusion rheometers on extruders with different screw diameters (32 mm, 60 mm). Three basic hypotheses are investigated in the research project. First, the wall slip behavior of rubber compounds depends on the size (geometry of the test channel) of the used rheometer. Secondly, the mirror relations according to Gleissle (I, II) are valid for both unfilled and filled rubber systems under wall-slip conditions. In addition, the wall slip behavior is influenced by the shear history in the extrusion process. By using the Rubber Process Analyzer (RPA), it is possible to determine the flow behavior of rubber compounds under the boundary condition of wall adhesion, since the RPA is considered to be wall-slip-free due to the test chamber design with the engagement flanks. For wall-adhering materials, the mirror relations according to Gleissle and the Cox-Merz rule have already been proven many times. The limited validity of these for filled elastomers is due to wall-slip effects. Considering the linear viscoelastic range and the correction of non-isothermal effects, deviations in the measured values between conventional rheometers and the RPA can be attributed to wall slip effects and can be corrected. A description is given of a procedure for correcting wall slip effects which is valid independent of the material and geometry. Due to the extrusion process, slip effects are apparent to a different extent than in HKR measurements, therefore correlations between the influencing variables and the slip behavior are established and combined in a map.