Autor: Peter Bajer

Abstract Radial shaft seals (RSS) made of elastomer are used for sealing rotating shafts in various applications such as industrial gears, crankshafts and wheel bearings. The prediction of the RSS operation behavior, especially to evaluate product reliability and life time, is of great interest for customers as well as for the manufacturer. Up to now, predictions are based on a variety of time and money consuming tests. Therefore calculation methods, which can help to reduce these experimental efforts, are very attractive. In contrast to metals, elastomers exhibit a nonlinear stress-strain behavior with a pronounced dependence on temperature, time and speed of load. Furthermore, a RSS is exposed to multiple loads in operation. Beside thermal and chemical loads due to addictive containing lubricants, additional mechanical loads in terms of static and dynamic eccentricities may occur between RSS and shaft. But even at constant rotational speeds, a non-steady state of the RSS system is present with complex mutual interactions between the system parameters. If a run-in seal ring shows a certain contact pressure, which affects the friction loss, the initial stae will be changed continuously by temperature, aging, dynamic loads and mainly by wear. In addition ti the behavior of the elastomer, the narrow contact width (around 100 μm in the new condition) and the asymmetric distribution of the contact pressure require sophisticated RSS calculation methods. For a realistic prediction of the behavior of RSS systems, all influencing factors as well as their mutual interactions habe to be taken into account in the simulation. Within the scope of this work, a FE based, integrated calculation approach was developed, which makes the transient parameters of the sealing system accessible on a macroscopic scale and thus allows the calculation of the dynamic operation behavior for the first time. The integrated calculation takes into account the mutual interactions of temperature dependent hyperelastic and viscoelastic elastomer properties, of friction-, wear- and temperature behavior as well as of time dependent load spectra. The load spectra are a combination of shaft speed, oil temperature and static or dynamic shaft deflection in radial directions. The quantities which can be evaluated over operation time are e.g. the wear during shaft deflections, the friction losses, the distortion of the sealing edge in circumferential direction due to rotation of the shaft and the ability of the sealing lip to follow shaft vibrations. Experiments are presented to determine the input parameters and to validate the calculation approach and they are carried out for an exemplary friction couple of elastomer, oil and shaft. The input parameters which are necessary for the calculation can be divided into parameters of the RSS system, which depend on the friction couple and into machanical and thermal material properties. By means of experimental validation, the calculation results of the investigated friction combination are evaluated qualitatively and the limitations of the calculation are discussed.