This paper introduces a new type of RSS measurement device aimed at unifying seal ring analysis. The impact of clamping the RSS in the measuring device on the sealing edge is demonstrated through FE simulation, microscopic images, and nanoindentation. And based on this, an automation solution for tactile detection of the wear characteristics and measurement of material changes at the sealing edge using Nanoindentation is presented. Measuring device The measuring device for this new analysis of tribologically damaged RSSs according to DE 10 2022 001 802 A1 allows the sealing lip to be turned towards the air side. This exposes the sealing edge in axial direction. Figure 1 illustrates the process and the design of the corresponding eversion device. Eversion is achieved by applying a consistent load through a threaded cover (3). The RSS is supported on a movable disc (4) to prevent twisting of the sealing lip during the everting process. Optimal eversion results in a minimally curved wear profile along the entire perimeter of the sealing lip. The level of optimum eversion depends on the RSS’s geometry and the elastomer’s properties. RSS-adapted spacer rings dictate the eversion degree and contact surface, ensuring reproducibility independent of the examiner. Aus Wissenschaft und Forschung 22 Tribologie + Schmierungstechnik · 70. Jahrgang · 4-5/ 2023 DOI 10.24053/ TuS-2023-0019 Motivation and state of the art Lubricants play a key role in ensuring the functionality and longevity of industrial gearboxes. A well-coordinated sealing system is critical for a durable and stable tribosystem. Chemical incompatibilities between seals and lubricants account for approximately 40 % of long-term failures due to leaks according to the current state of the art. To ensure the functionality and stability of a tribological sealing system, dynamic sealing ring tests are often carried out during the development of new lubricants and elastomers. A subsequent analysis of the radial shaft seals provides insights into chemical and physical interactions of elastomer and lubricant at the sealing edge, thereby assessing the compatibility with the applied lubricant. According to the current state of the art, an RSS analysis can be divided into a metrological and an optical analysis. Experienced seal experts perform the optical analysis. The damage characteristics that indicate chemical changes of the elastomer, loss of rebound resilience, or insufficient lubrication in the sealing gap (hardening, softening, deposition, excessive wear) are crucial. The tester in question handles the radial shaft seals (RSSs), stretches and compresses the sealing edge during the optical analysis. This can directly affect the subjective perception and outcome of the optical analysis. The quality of the seal analysis data is essential to robustly model correlations between changes at the sealing edge and the tested tribosystem using statistical analysis methods. Nanoindentation presents a promising measurement technique to quantify relevant damage characteristics from the optical analysis, such as hardening and softening [1]. Due to the rotational symmetry of the RSS and the lack of standardisation, handling remains a challenge for accessible and time-efficient analysis. Measurement device and automation solution for analysing tribologically damaged radial shaft seals Katrin Alt, Felix Bernhardt, Klaus Ganz, Alexander Hüttinger, Markus Wöppermann* Dieser Beitrag wurde im Rahmen der 64. Tribologie-Fachtagung 2023 der Gesellschaft für Tribologie (GfT) eingereicht. A new measurement device is introduced for analysing worn radial shaft seals (RSSs). This device enables unified and reproducible analysis and allows an automated nanoindentation for reliably detecting material changes at the seal edge. Keywords elastomer compatibility, rotary shaft seal, sealing, dynamic test, nanoindentation, automation, µ-Mechanical characterization, tribologically damaged radial shaft seal, everted sealing lip, measurement device Abstract *M.Sc. Katrin Alt B.Sc. Felix Bernhardt Dipl.-Ing. Klaus Ganz, Dipl.-Ing. Alexander Hüttinger Dr.-Ing. Markus Wöppermann SEW-EURODRIVE GmbH & Co KG Ernst-Blickle-Straße 42 in 76646 Bruchsal TuS_4_2023.qxp_TuS_4_2023 20.09.23 09: 16 Seite 22 Mechanical and optical effect of the measuring device The eversion process causes compression of the sealing edge. The average diameter of the sealing edge of five RSSs (38 x 52 x 7 72 NBR 902) in the non-everted state without spring is 36.7 mm. After everting without a spring and a resting period of 24 h, the average diameter is 35.5 mm, which corresponds to a change of 3.3 %. Indentation measurements on the everted sealing edge, depending on the resting time, show a significant impact on the elastomer’s stiffness. After 18 h of rest, constant stiffness values within their respective range of dispersion are measured, necessitating an 18 h relaxation period defined for subsequent measurements in the testing device. To analyse the deformation of the sealing lip during the everting process, an FE simulation of the everting process is carried out. The material parameter is estimated according to Battermann and Köhler [2]. Figure 2 illustrates the required force and displacement of the sealing edge in the y-direction during the eversion process. For condition 1-5, the deformation and elastic strain of the sealing lip is shown. During the transition from condition 2 to 3, the force decreases abruptly, the sealing lip slips noticeably, and the force required for complete eversion is significantly lower than at the start of the process. After relief (5), the elastic strain in the sealing lip area fully retracts, leading to the conclusion that the proportion of reversible deformation in the sealing lip prevails during eversion and reverting. Microscope images of tribologically damaged sealing edges, captured at the same position before and after eversion (except b2), are shown below (Figure 3). The extent of the crack formation cannot be discerned on either image of the non-everted RSS. Sealing edge Figure 3a is found to be slightly hardened with microcracks. Everting the sealing edge causes a displacement of the Aus Wissenschaft und Forschung 23 Tribologie + Schmierungstechnik · 70. Jahrgang · 4-5/ 2023 DOI 10.24053/ TuS-2023-0019 Figure 1: Principle and measuring device for everting an RSS Figure 2: FE simulation of the force and displacement of the sealing lip during the everting process with material parameters according to [2] TuS_4_2023.qxp_TuS_4_2023 20.09.23 09: 16 Seite 23 new automation possibilities for measuring tribologically damaged RSSs. An automated solution for metrological analysis of RSSs is being developed in collaboration with LNP. This uses an LNP 3 measurement device with motorized linear and rotary axes, holding an eight-device interchangeable plate (Figure 4). The accompanying software package facilitates an automated workflow for tactile wear profile capture, wear width calculation and indentation measurement on the everted sealing edges. Within a few hours, this fully automated process captures, documents and illustrates damage features like hardening, softening, deposition, wear width and grooving of eight tribologically damaged RSSs with n measuring points per sealing edge. Figure 5 shows an exemplary evaluation of an FKM (severe wear, grooves) and NBR (minimal wear) RSS, measured automatically. The polar diagram illustrates the calculated wear widths at 20 measuring points each. The middle Aus Wissenschaft und Forschung 24 Tribologie + Schmierungstechnik · 70. Jahrgang · 4-5/ 2023 DOI 10.24053/ TuS-2023-0019 slightly hardened microcracks, rendering them visible. An optical analysis of sealing edge Figure 3b reveals severe crack and blister formation. For the everted sealing, an inconsistent stress state around the tribologically damaged sealing edge has been detected for the first time. Around the perimeter, the sealing edge can be divided into areas with cracks in softened material and blisters (Figure b1) and areas with stress cracks in the highly hardened elastomer (Figure b2). This indicates an inhomogeneous material state of the worn sealing edge, which can lead to the application of uniform deformation, resulting in localized areas with negative and positive stresses visible at the micro level. Automated solution Everting the sealing edge allows access to the entire perimeter of the sealing edge from a single plane, enabling Figure 3: Microscope images (40x magnification) of tribologically damaged sealing edges - non-everted and everted Figure 4: LNP measurement machine for nanoindentation and tactile analysis of eight RSSs TuS_4_2023.qxp_TuS_4_2023 20.09.23 09: 16 Seite 24 diagram shows the profile at the measuring points M1 and M2, allowing assessment of the wear condition. Notably, the previously optically detected grooving at M1 is clearly captured. LNP’s developed algorithm for wear width calculation yields 1.091 mm for M1 and 0.289 mm for M2. Summary The introduction of a new measurement device with everted sealing lips has enabled axial access to the worn sealing edge, enhancing existing analysis of tribologically damaged RSSs. Compared to non-everted RSSs, cracks on hardened sealing edges were able to be identified and documented. The accessible analysis of the entire sealing edge, with defined support and deformation, enables automated mechanical wear feature measurement (e.g., wear width and groove formation) and elastomer material change assessment (e.g., hardening and softening) by using nanoindentation. The clamping in the measuring device is primarily used for the comparative analysis of RSSs and does not purport to be able to precisely determine the physical material data of the elastomers. The everting device and the automation solution significantly help to unify the RSS analysis and enhance the reproducibility and measurement reliability of seal analysis data across different testing labs. Literature [1] Wilbs, C., Adler, M., Frölich, D., Bellon, A., Schuster, N., Menzel, J., Bopp, E.: µ-Mechanical characterization of tribologically stressed elastomer surfaces with respect to radial shaft sealing systems. GfT 2023. [2] Battermann, W., Köhler, R.: Elastomere Federung, elastische Lagerungen. Wilhelm Ernst und Sohn, 1982. Aus Wissenschaft und Forschung 25 Tribologie + Schmierungstechnik · 70. Jahrgang · 4-5/ 2023 DOI 10.24053/ TuS-2023-0019 Figure 5: Example of the evaluation of two tribologically damaged RSSs that were measured automatically (see Figure 4) TuS_4_2023.qxp_TuS_4_2023 20.09.23 09: 16 Seite 25