Micro-mechanical characterization of a tribological stressed elastomer surfaces with respect to Radial-Shaft-Seals

The radial shaft seal (RSS) is a widely used machine element to seal lubricants against the environment. For this purpose, the RSS, the shaft surface, and the sealed fluid as well as the operating conditions form a tribological system - the radial-shaft-sealing system. In terms of sustainability and cost efficiency, high expectations are set on the reliability and service life of such sealing systems. Therefore, downtimes due to maintenance or even leakages must be avoided. In particular, the complex interactions between the sealed lubricant and the RSS have a major influence on the long-term reliability and lifetime of a sealing system. It is therefore essential to ensure lubricant-elastomer compatibility under dynamic tribological stress. This can be achieved by dynamic compatibility tests. The post-test analysis of the seal is an essential process to determine the seal condition and therefore how the lubricant affects the seal under tribological stress. Besides other characteristics of the seal, it is of great importance to consider the near-surface material condition. While the seal wear, radial load and interference are measurable continuous values, the seal material condition rating, e.g. softening, hardening and hard deposits is a categorial value based on visual-haptic feedback of the material by seal experts with years of practical experience. Due to the importance of the seal material condition for the reliability of the sealing-system a new tactile seal material characterization method was developed by Freudenberg – “the micro-mechanical seal characterization”. This presentation introduces the new characterization method and its application for the post-test seal analysis. Therefore, the measurement procedure and accuracy will be discussed as well as the characteristic values. Furthermore, it will be shown how those values allow a precise evaluation of the seal material condition regarding hardening, softening and hard deposits.