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. Keywords: radial lip seal, finite element analysis, surface roughness, elastic deformation, elastomers.

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.

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.

Rotary shaft seals prevent the exchange of fluid at shaft passages. Their function and service life depend decisively on the temperature in the contact area between the sealing edge and the shaft. Since the temperature depends on both the generation of frictional heat in the contact area and the heat transfer to the surrounding sealing system, the design of the sealing system is crucial. Within the scope of this work, multiphase conjugate heat-transfer analyses were performed considering different assembly situations. The computed results were presented and contrasted to experimental data. This resulted in a valid model for predicting the temperature in the sealing system, which provided insight into the influence of the sealing surroundings on the contact temperature.