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，胶料发生壁面滑移等流动异常的倾向增加。因此，流变材料测量和由此产生的材料参数受到误差的影响，因为潜在的分析和数值计算方法假设了壁粘附性。除了壁面滑移效应对挤压过程和挤压质量的影响外，在流动模拟和工具设计中不考虑壁面滑移也会导致误差。这些问题通常只在生产过程中被检测到，并且导致耗时且成本高的纠正。本研究项目的目的是开发一种不依赖流变仪描述橡胶化合物的壁滑移行为的方法。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）以及在线挤出流变仪对不同螺杆直径（32 mm, 60 mm）的挤出机进行了EPDM橡胶化合物的广泛流变学研究。本研究项目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尺寸（测试通道的几何形状）。其次，根据Gleissle （I， II）的镜像关系在壁滑条件下对未填充和填充橡胶体系都有效。此外，挤压过程中的剪切历史对壁滑移行为也有影响。使用橡胶过程分析仪（Rubber Process Analyzer， RPA），可以确定橡胶化合物在壁面粘附的边界条件下的流动行为，因为RPA被认为是无壁面滑移的，因为测试室设计有接合的侧翼。对于粘壁材料，格莱斯定律和考克斯-默兹定律的镜像关系已经被多次证明。这些对填充弹性体的有限有效性是由于壁滑效应。考虑到线性粘弹性范围和非等温效应的校正，常规流变仪与RPA之间的测量值偏差可归因于壁面滑移效应，并可进行校正。给出了一种不受材料和几何形状影响的壁滑移校正方法。由于挤压过程，滑移效应明显程度不同于HKR测量，因此建立了影响变量与滑移行为之间的相关性，并将其组合在图中。

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.