Simon Feldmeth

Zusammenfassung

Grease-lubricated sealing systems have an increased risk of starved lubrication. For this work, the lubricity of 23 greases in a rotary shaft sealing system was evaluated with a new test and evaluation method. The lubricity was then correlated with rheological and other grease properties. These grease properties are either available by the data sheet or can be measured with low effort. The results of the correlation allow a preselection of greases which are expected to lubricate rotary shaft seals well. This can support manufacturers and users in considering the lubrication of the sealing system early in the development process.

Zusammenfassung

This contribution presents an elastohydrodynamic lubrication (EHL) model for pneumatic spool valves. For an accurate estimation of the transient friction of this tribological sealing system, the surface topography of the cylindrical sealing counterfaces of the valve housings are measured and analyzed with an optical surface measurement instrument. Based on the surface topography data, tribological properties and flow factors of the system are derived. It has been found that the consideration of the surface topography has a significant influence on the simulation results of the EHL model, lowering the calculated friction force by up to 20 %.

Zusammenfassung

Ausfälle von Elastomer-Radial-Wellendichtungen sind häufig auf die Überhitzung des Kontaktbereichs zwischen Radial-Wellendichtring (RWDR) und Welle zurück zu führen. Hohe Temperaturen im Kontaktbereich entstehen meist durch erhöhte Reibleistung und/ oder durch eine schlechte Wärmeabfuhr aus dem Kontaktbereich. Im Rahmen dieses Projekts wurden unterschiedliche Einflussfaktoren auf die Wärmeentstehung und die Wärmeabfuhr untersucht. Untersucht wurde dazu der Einfluss von Dichtringen mit Zusatzelementen, wie Schutzlippen und Vliesen, der Einfluss von unterschiedlichen Ölen, sowie wasserbasierten Fluiden, der Einfluss von Wellenbeschichtungen, der Einfluss der Wellengestaltung und der Einfluss der konstruktiven Gestaltung des Dichtungsumfelds. Zu allen zuvor genannten Themen wurden Versuche auf Reibmomentprüfständen durchgeführt. Zusätzlich zu den Prüfstandsversuchen wurden für die Wellengestaltung und die konstruktive Gestaltung des Dichtungsumfelds Simulationen durchgeführt. Die Übereinstimmung zwischen der Simulation und den Versuchen ist gut. Anhand der Versuchs- und Simulationsergebnisse wurden die wichtigsten Einflüsse auf die Temperatur im Kontaktbereich ermittelt. Diese Einflüsse wurden in ein Berechnungstool für die Kontakttemperatur integriert. Dadurch konnte ein praxistaugliches Berechnungstool für die Kontakttemperatur entwickelt werden, welches die häufigsten Einsatzbedingungen von Radialwellendichtungen berücksichtigt. Das Berechnungstool wurde um eine Datenbank mit allen im Projekt untersuchten Schmierstoffen ergänzt. Zusätzlich wurde das Berechnungstool um Anwender- und Warnhinweise ergänzt, um die Konstruktive Gestaltung des Dichtungs-Umfelds im Berechnungstool sinnvoll berücksichtigen zu können. Zusätzlich wurde ein Katalog mit Optimierungsmaßnahmen erstellt. Damit werden Handwerkszeuge geschaffen, um die Überhitzung von Radial-Wellendichtungen zu vermeiden. Das Ziel des Forschungsvorhabens ist erreicht worden.

Zusammenfassung

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.

Zusammenfassung

In a joint research project within the ZIM programme, sustainable high performance TPUs (thermo-plastic polyurethane) for hydraulic rod seal rings were developed by replacing conventional raw materials with regenerative biogenic structural components. Hydraulic rod seal rings were manufactured from these biogenic materials and time-accelerated tested to analyse their extrusion and wear behaviour. This paper shows the developed test methods as well as the results obtained with these. In all tests, various TPU prototypes were used in combination with the hydraulic fluids intended for this purpose (water-based, rapidly biodegradable). The prototype seal rings manufactured of the new developed regenerative TPU compounds were comparable to non-regenerative TPU compounds regarding their functional behaviour.

Zusammenfassung

The so called “tear-in” tests were developed to evaluate a correlation between the tear-in of a grease dam in a tribological system and the lubricity of the grease. They were carried out with a rheometer as equivalent system and 23 greases. The grease sample was sheared in the gap between a rotating and a stationary plate with a linearly increasing shear rate. The motion of the grease within this gap was observed optically with a high-speed camera. In addition, the shear stress was measured and evaluated. The results of the tear-in tests correlate well with functional tests using a rotary shaft sealing system.

Zusammenfassung

The thermal behaviour of rotary shaft seals is affected by the fluid which has to be sealed. The fluid lubricates the sealing contact and determines the frictional heat generated there. Additionally, the fluid influences the heat transfer to the environment. Both aspects were experimentally analysed by measuring the friction torque and the temperature on the air side near the sealing contact during test runs with 16 different lubricants. The measurement results show that the fluid affects the heat generation much more than the heat transfer. In general, the friction torque is higher for more viscous fluids. However, several exceptions restrict this finding.

Zusammenfassung

In this paper, the influence of dynamic eccentricity and low operating temperatures on the pumping rate of elastomeric rotary shaft seals is analysed experimentally. For this purpose, function tests and pumping rate measurements were carried out at different dynamic eccentricities up to 0.3 mm (0.6 mm TIR) and oil sump temperatures between +40 and -20 °C with rotary shaft seals made of nitrile rubber (NBR) and fluoro rubber (FKM) in combination with synthetic polyalphaolefin oil FVA PAO1. The function tests and the pumping rate measurements show the application limits of the rotary shaft seals under the combination of dynamic eccentricity and low oil sump temperature

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

Elastomeric radial lip seals are complex tribological systems. Their sealing performance is essentially determined by the back pumping capability of the system. During the dynamic operation, radial lip seals can actively pump leaking fluid back to the fluid side. For the assessment of the pumping capability and the leak-tightness of the sealing system, the pumping rate can be used. The pumping rate measures the pumped fluid volume per time or distance. In this paper, the influence of low operating temperatures on the pumping rate of elastomeric radial lip seals is analysed experimentally. For this purpose, the pumping rate was measured at different oil sump temperatures betweenþinspace+40 and --20 °C. The experimental analyses were performed with radial lip seals made of nitrile rubber (NBR) and fluoro rubber (FKM) in combination with mineral and synthetic (polyglycol and polyalphaolefin) oils.

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

The radial load of a radial lip seal indicates how strongly the sealing lip is pressed on the shaft. The radial load significantly affects the function of the seal. The German standard DIN 3761-9 describes the measurement of the radial load according to the split-shaft method but leaves room for interpretation. During the revision of the standard, a parameter study was conducted at the University of Stuttgart. This study analyses the influence of the measurement device, the mandrels and the measuring procedure on the results. Based on the study results, recommendations are derived and summarized in a best-practice guideline, which should enable an appropriate and reproducible measurement of the radial load. Die Radialkraft eines Radial-Wellendichtrings (RWDR) gibt an, wie stark dessen Dichtlippe an die Welle angedrückt wird. Die Radialkraft beeinflusst das Funktionsverhalten des RWDR maßgeblich. Die DIN 3761-9 beschreibt die Messung der Radialkraft nach dem Zwei-Backen-Verfahren, lässt dabei aber Interpretationsspielraum. Im Rahmen der Normüberarbeitung wurde am Institut für Maschinenelemente (IMA) der Universität Stuttgart in einer Parameterstudie untersucht, welchen Einfluss die Eigenschaften des Messgeräts, die Ausführung der Messbacken und die Gestaltung des Messvorgangs auf das Messergebnis haben. Basierend auf den Studienergebnissen werden Empfehlungen abgeleitet und in einem Best-Practice-Leitfaden zusammengefasst, der eine zielgerichtete und reproduzierbare Messung der Radialkraft ermöglichen soll.

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.

Zusammenfassung

Bei der Abdichtung von Schmierfetten tritt häufig Mangelschmierung des Dichtsystems auf. Die Entstehung und Möglichkeiten zur Vermeidung dieser Mangelschmierung wurden im Projekt Fettmangel untersucht. Dazu wurde zunächst eine Prüf- und Bewertungsmethodik entwickelt, mit der 23 Schmierfette hinsichtlich ihrer Schmierfähigkeit von Radial-Wellendichtsystemen untersucht wurden. Dieselben Schmierfette wurden in einer ausführlichen rheologischen Charakterisierung ausführlich analysiert. Hierzu wurden teilweise neue Prüfverfahren entwickelt oder bestehende Prüfverfahren erweitert. Die dabei beobachteten Korrelationen mit der Mangelschmierung aus den Prüfläufen am Dichtsystem ermöglichen es, die Schmierfähigkeit der Fette im Dichtsystem anhand schnell messbarer rheologischer Kenngrößen vorherzusagen. Zusätzlich wurde der Einfluss der Betriebsbedingung auf die Mangelschmierung bei schlecht schmierenden Fetten untersucht. Als zentraler Einflussfaktor wurde im untersuchten Bereich die Temperatur identifiziert. Abschließend wurde untersucht, ob geometrische Strukturen auf dem Dichtring oder der Welle die Schmierung des Dichtsystems beeinflussen können. Die untersuchten Strukturen zeigten dabei ein Potential zur Reduzierung des Mangelschmierungsrisikos. Im Forschungsprojekt wurden dadurch Möglichkeiten entwickelt, Mangelschmierung in kurzen Prüfläufen zu identifizieren, durch kurze einfache und schnelle Messungen an häufig verfügbaren Rheometern vorherzusagen, mittels einer geeigneten Fettauswahl zu verhindern oder durch eine Anpassung der Betriebsbedingungen oder des Dichtsystems gezielt zu verringern.

Zusammenfassung

Elastomeric radial lip seals are complex tribological systems. Their sealing performance is essentially determined by the back pumping capability of the system. During the dynamic operation, radial lip seals can actively pump leaking fluid back to the fluid side. For the assessment of the pumping capability and the leak-tightness of the sealing system, the pumping rate can be used. The pumping rate measures the pumped fluid volume per time or distance. In this paper, the influence of low operating temperatures on the pumping rate of elastomeric radial lip seals is analysed experimentally. For this purpose, the pumping rate was measured at different oil sump temperatures between +40 °C and 20 °C. The experimental analyses were performed with radial lip seals made of nitrile rubber (NBR) and fluoro rubber (FKM) in combination with mineral and synthetic (polyglycol and polyalphaolefin) oils.

Zusammenfassung

Static and dynamic eccentricity between the radial lip seal and the rotating shaft are the result of imprecise production and assembly. In this work, the influence of static and dynamic eccentricity on the pumping rate are analysed experimentally. The experimental analyses were performed with radial lip seals made of nitrile rubber (NBR) and fluoro rubber (FKM) in combination with mineral and synthetic (polyglycol and polyalphaolefin) oils.

Zusammenfassung

For the FKM research project "Lack of grease - Preventing starved lubrication of grease-sealing rotary shaft seals”, a large number of lubricating greases are characterized rheologically in detail. This paper presents a procedure for the time-effective measurement of the shear viscosity of a large number of lubricating greases at several shear rates and temperatures. The measurement is based upon DIN 51810 1. The critical factor here is the influence of previous measurements at lower shear rates. For the determination of the flow curve according to DIN 51810 2, a procedure of tempering the sample is determined and the influence of temperature on the flow behaviour investigated.

Zusammenfassung

Lip seals made of PTFE compound are used due to their high thermal and chemical stability for the sealing of shaft interfaces in housings. For a better dynamic leak-tightness hydrodynamic sealing aids are manufactured on the sealing lip. Thus a PTFE lip seal is capable of back-pumping fluid from the air to the fluid side. The pumping rate serves as an important parameter for the dynamic leaktightness of seals with a unidirectional sealing aid design. The correlation of pumping rate and dynamic leak-tightness for bi-directional sealing aid designs is deficient. A new hydrodynamic parameter is introduced to assess the dynamic leak-tightness of a sealing aid design. The so called pressure drag is the force resulting from the integral of the hydrodynamic pressure over the surface of the sealing aid. A hypothesis is proposed, stating that in order to guarantee a dynamically leak-tight shaft seal, two conditions should be satisfied. First, the pumping rate should be greater than zero. Second, the axial pressure drag should be directed entirely towards the fluid side. The hypothesis is verified on different types of unidirectional and bi-directional sealing aid design. In conclusion the axial pressure drag is shown to be a suitable performance parameter for the sealing aid design.

Zusammenfassung

Lip seals made of PTFE compound show very high thermal and chemical stability. Dynamic sealing aids are often added on the sealing lip in the contact zone with the shaft to guarantee dynamic leak-tightness. The dynamic behaviour of different sealing aids can be analysed by simulating the fluid-structure-interaction of PTFE lip seal, shaft and lubricant in the sealing contact. This paper introduces a multiscale simulation approach for the analysis of the static and dynamic leak-tightness of PTFE lip seals with a novel sealing aid design. The multiscale approach consists of a macroscale, mesoscale and microscale. A nonlinear structural finite element analysis of the mounting of the seal on the shaft is introduced on the macroscale. The material law is elastic plastic with a combined hardening rule. The contact stress and contact geometry obtained by the finiteelement analysis are used as an input for an elastohydrodynamic lubrication (EHL) analysis on the meso- and microscale. In the elastohydrodynamic lubrication analysis the hydrodynamic pressure and the hydrodynamic gap height between the seal and the shaft are simulated. Furthermore, characteristic performance quantities of the sealing system such as the pumping rate and friction torque are calculated. Experimental measurements are also presented in order to validate the simulation results. Thus, the potential of the validated multiscale analysis method for the topological optimisation of the lip seal design is shown.