Design and manufacturing of radial shafts seals mating surfaces using manufacturing processes with geometrically defined cutting edges - Diregeo

• Applicants: Professor Dr.-Ing. Andreas Schubert; Professor Dr.-Ing. Stefan Thielen
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering ; Engineering Design, Machine Elements, Product Development
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 430170022

For the sealing of shaft feedthroughs in pressure-free areas or sections with minor pressure difference typically radial shafts seals (RSS) are applied. The specific design of RSSs leads to an axial carriage of the lubricant due to the shaft rotation, always directed in the direction of the oil storage. However, the surface microstructure of the shaft counter-surfaces (SCS) can result in a carriage effect as well. Plunge grinding is typically considered as default process for finish machining of SCS, as typically hardened steels are applied. From an economical point of view, there are several disadvantages such as high investment, reduced flexibility, and due to comparably long spark-out times reduced economic efficiency. The substitution of grinding by hard turning provides significant potential for cost reduction. However, a holistic understanding of the interactions between the process parameters, the surface microstructure, and the functional properties of the SCS is still lacking. The end user information concerning the required surface specific values as well as information on the selection of tools and cutting parameters are limited. In the first funding period, an in-depth understanding of the relationships between the process parameters in hard turning, the resulting surface microstructure of the SCS, and its functional properties in the sealing system was obtained by means of machining experiments and bench tests as well as computer-aided process and EHD simulations. As a result, it was possible to determine the influence of the conveying cross section and twist angle of the machined SCS on the functional properties of the sealing contact. The subsequent experiments with a special machining method (start-stop turning) showed that start-stop turned SCS also have a conveying effect despite the lack of a twist structure due to deviations at the surface structure as a result of elastic-plastic material behaviour. An adjustment of the dwell value to an integer multiple of one led to a reduction of these effects. However, the comparatively large contact length of the sealing lip due to the lack of twist (zero twist) resulted in an increase of the frictional torque. In a second funding period, therefore, the aim consists in a reduction of friction and RSS wear by modifying the turning process. In this context, the influence of deterministic microstructures generated by an ultrasonic vibration superimposed two-stage hard turning process on the hydrodynamic operation properties of the RSS is to be investigated. The overall objective of the research project is to gain an in-depth understanding of the interactions in the sealing contact between the microstructure geometry, the fluid, and the RSS.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Oliver Koch