Jeremias Grün

Zusammenfassung

Although rotary shaft seals have been used successfully in many industrial applications for decades, their tribological behavior is still not completely understood. In-depth knowledge of the structural mechanics is essential for the design and optimization of such sealing systems. High complexity results from the multiscale interactions in the tribological system rotary shaft seal. Large macroscopic deformations occur due to the hyperelastic material behavior of elastomers coupled with microscopic tangential distortions of the sealing edge surface in the contact area. This paper includes both numerical and experimental studies on the tribological behavior of rotary shaft seals. A multiscale finite element model provides the simulation of the macroscopic deformations and the microscopic displacements. A test rig equipped with a hollow glass shaft enables in situ visual contact analyses, qualitative determinations of pressure distributions and quantitative measurements of elastomer surface distortions. The optical phenomenon of frustrated total internal reflection enables qualitative evaluations of the pressure distribution. Particle image velocimetry (PIV) is employed to quantify the tangential distortions. The test rig enables the measurement of the friction torque with the same configuration. The results of the numerical and experimental investigations for the radial load, friction torque and tangential distortions are compared and discussed. This serves to validate the simulation methods and the correlation of the measured parameters. This finally results in a solid and validated basis for further tribological investigations of rotary shaft seals.

Zusammenfassung

The primary task of rotary shaft seals is to prevent an unwanted fluid transfer between two areas. In shaft passages of gearboxes, for example, rotary shaft seals avoid the leakage of transmission oil to ambient air. This means the flow in the lubricant film in the sealing gap between the sealing edge and the shaft surface consists of at least two phases. Taking the phenomenon of cavitation into account, the flow consists of three phases. This study aims to provide an in-depth understanding of the multiphase flow in the lubricant film of rotary shaft seals. As experimental studies of the flow processes on a microscale have proven to be quite difficult, a simulation-based approach is applied. Computational fluid dynamics (CFD) serves to compute the transient multiphase flows in the lubricant film in the sealing gap. The computational domain is a three-dimensional microscale model of the lubricant film. The results show the transient hydrodynamic pressure buildup and the dynamic phase interactions during operation. This study provides far-reaching insights into the multiphase flow processes in the lubricant film in the sealing gap and simulation-based evidence of the lubrication and sealing mechanism of rotary shaft seals

Zusammenfassung

Bei einer Vielzahl von Forschungsprojekten konnten mutmaßlich schädliche Einflüsse auf Radial- Wellendichtungen durch das Auftreten von Leckage nicht gezeigt werden. Eine quantitative Bewertung oder gar die Ermittlung von Grenzwerten ist nicht möglich. Das Fluidpumpvermögen eines Dichtsystems lässt sich über den Förderwert quantifizieren. Der Systemförderwert setzt sich dabei aus dem Förderwertanteil des Radial-Wellendichtrings und dem der Dichtungsgegenlauffläche zusammen. Häufig haben handelsübliche Radial-Wellendichtringe ein so starkes Fluidpumpvermögen, dass schädliche Einflüsse kompensiert werde können. Ziel des gesamten Projektes ist daher die Entwicklung eines Referenz-Radial-Wellendichtrings, dessen Fluidpumpvermögen gering aber gleichzeitig stabil ist. Dadurch soll der Einfluss auf den Systemförderwert minimiert werden. Ziel dieser Vorstudie ist ein schneller Erkenntnisgewinn und Wissenstransfer für das Gesamtprojekt. Das Fluidpumpvermögen wird in diesem Projekt durch gezielte geometrische Veränderungen der Querschnittsgeometrie beeinflusst. Dazu wurden Radial-Wellendichtringe aus zwei unterschiedlichen Materialien mit insgesamt sieben unterschiedlich abgestochene fluidseitigen Flankenwinkeln untersucht. In Geometrieanalysen konnte zunächst nachgewiesen werden, dass die vorgegeben geometrischen Parameter umsetz- und herstellbar sind. Daraufhin konnte in Radialkraftanalysen ein Zusammenhang zwischen der Geometrie der Dichtringe und der Radialkraft festgestellt werden. In Förderwertuntersuchungen konnte mit keinem der untersuchten Dichtringe Förderneutralität erreicht werden. Ferner konnte keine direkte Korrelation zwischen dem variierten fluidseitigen Flankenwinkel und dem Förderwert festgestellt werden. Erklärungen hierfür liefern Strömungsanalysen und Simulationen. Zusammenfassend lässt sich daraus schließen, dass für die Entwicklung eines förderneutralen Referenz- Radial-Wellendichtrings weitere geometrische Parameter betrachtet werden müssen. Das Ziel des Forschungsvorhabens wurde erreicht

Zusammenfassung

The lubricant flow in the sealing gap significantly affects the sealing behavior of rotary shaft seals. Computational fluid dynamics (CFD) are applied here to analyze these fluid flows. A decisive input parameter is the sealing gap height respectively the lubricant film thickness. The film thickness is estimated on the basis of several analytical elastohydrodynamic lubrication (EHL) equations. The results for sealing characteristics such as the pumping rate and the friction torque derived from the numerical analyses are compared and discussed with the results obtained from test rig studies. This allows the validity of the applied methods to be verified.

Zusammenfassung

The sealing behaviour of elastomeric radial lip seals is essentially affected by the sealing mechanism in the contact area between the sealing edge and the shaft surface. The relative motion between radial lip seal and shaft deforms the sealing edge tangentially in the circumferential direction. This mechanical deformation is considered essential for the sealing mechanism. In this study, a numerical approach is employed to simulate this deformation. A three-dimensional multiscale model serves this purpose. The radial lip seal geometry is described on the macro-scale. On the micro-scale, an artificial rough surface with a stochastic roughness distribution is applied to an ideal sealing edge surface. A new meshing algorithm is used to discretise different sealing edge surfaces and automatically generates structured hexahedral meshes of the sealing edges. Mesh transitions connect the resulting finely meshed sealing edge to the coarsely meshed global macro-scale mesh of the radial lip seal. The paper introduces the modelling method used to simulate the deformation of radial lip seals. Results are presented and discussed with reference to the sealing behaviour. This contributes to a better understanding of the sealing mechanism of radial lip seals.

Zusammenfassung

The lubrication and sealing mechanism of elastomeric radial lip seals are significantly influenced by local deformations in the contact area between the sealing edge and the shaft. These microscopic mechanical effects cannot be completely analysed in visual observations. This paper presents a methodology for the numerical analysis of the radial compression and the tangential distortion of the sealing edge surface during operation. The finite element analysis is used for this purpose. The modelling of a three-dimensional multiscale model is described in detail. Results are presented and discussed with reference to the possible sealing behaviour

Zusammenfassung

In this paper a numerical approach is applied to analyse the influence of wear on the lubrication and sealing mechanism of radial lip seals. A three-dimensional multi-scale mechanical model is presented. This allows to simulate the macroscopic deformation of the entire radial lip seal and the microscopic deformations in the contact area between the sealing edge and the shaft surface. Furthermore, different wear band widths and surface roughness of sealing edges can be analysed efficiently. In the context of this paper, measurement results of radial lip seals in different wear states out of test runs are applied. The simulation results of the different sealing edges are compared. This allows drawing conclusions about the influence of wear on the performance of radial lip seals. This leads to a better understanding of the potential failure mechanisms of radial lip seals.