Frank Bauer

Abstract

This article examines the generation of micro lead during cylindrical plunge grinding of sealing counterfaces for rotary shaft seals. Micro lead can cause fluid leakage through the sealing contact, impacting sealing performance. Preliminary investigations indicate that dressing parameters influence micro lead formation. This publication presents new insights into this phenomenon, aiming to enhance industrial sealing reliability by optimizing sealing counterfaces for demanding applications, such as E-powertrains with high sliding speeds and temperatures. The presented findings underscore the value of using specifically optimized grinding and dressing parameters for the manufacturing of sealing counterfaces.

Abstract

Surface structures of the sealing counterface are called “lead structures” when they have the capability to pump oil rotation dependent through the sealing contact of a rotary shaft seal systems. This feature is called “pumping effect”. The structures interrupt the equilibrium state of the sealing system, which may cause dry run or leakage as failure result. Especially for higher circumferential velocities the pumping effect increases and therefore cannot be neglected. To assess the functional influence of lead structures on the sealing system, one can measure the pumping rate of the sealing counterface experimentally. The higher the pumping capability of a sealing counterface, the more likely the sealing system will fail. In this paper, the development a new pumping rate evaluation method with the help of a continuously measuring scale, which allows to visualize the course of the pumping rate over time, is described. With this knowledge it is possible to determine the end of the running-in phase of the rotary shaft seal and to determine the minimum duration of the pumping rate tests. The pumping rate evaluation method is demonstrated with different shaft counterfaces to validate the stability of the new method.

Abstract

Tactile measuring instruments were used for a long time to measure surface characteristics of sealing counterfaces and are still state of the art today throughout the industry. The data measured are roughness profiles mostly in the axial direction of the shaft. Rapid developments in computer hardware and software have improved optical measurement technology, advancing its application in the analysis of sealing counterfaces. The measurement data are topographies that represent partial areas of the shaft with high resolution in both the axial and circumferential direction. These characteristics are especially useful for the analysis of shaft lead. Lead describes all types of structural features on the shaft surface that axially pump oil in sealing contact during operation. Their pumping effect influences the sealing mechanism depending on the direction of rotation of the shaft and can result in leakage. Lead structures appear in various forms and sizes – micro and macro lead, which are superimposed on the shaft surface. Optical measurements enable the detection of the superimposed structures with a single measurement run. Specially developed segmentation algorithms can be used to separate micro and macro lead and then identify flow channel-like structures as individual elements in surface topographies. The statistical analysis of the segmentation results offers an objective characterization of the sealing counterface. This article presents the benefits of utilizing optical measurement techniques in conjunction with innovative structure-based analysis approaches for lead on shaft counterfaces. The outcome can improve the reliability of sealing systems and associated products.

Abstract

The Back-Structured Shaft Seal (B3S) 1 was developed to achieve an optimal balance between static and dynamic tightness, thermal and chemical resistance, as well as high reliability and durability for PTFE shaft seals. Structures on the back of the sleeve create an active pumping mechanism in the sealing contact. This paper sums up the results of a stamped version in comparison to the laser engraved version. The stamping process causes significant alterations to the material properties of the seal. All prototypes underwent both static and dynamic tests which demonstrate that the B3S principle can be successfully implemented in a stamped version. However, the design of the structures must take additional influencing factors into account.

Abstract

Rotary shaft seals are commonly used to seal machines with rotating shafts and prevent the leakage of fluids into the environment. Failures of elastomeric rotary shaft seals are often the result of overheating in the contact area between the sealing edge and the shaft. High temperatures in this contact area occur due to high frictional power and/or inadequate heat dissipation. The surrounding of the seal has a significant impact on the temperatures occurring in the contact area. Especially rolling-element bearings near the seal strongly influence the contact temperature. The frictional heat generated in the bearings results in an increase in the temperature of the fluid near the seal, consequently raising the contact temperature. Tapered roller bearings pump oil. Depending on the installation situation, this can lead to a higher or lower fluid level next to the seal. Tests are conducted on a high-speed friction torque test bench. This investigation involves four different bearing arrangements, as well as a reference variant without bearings. In these test runs, both the frictional torque and the temperature near the contact area are examined. In addition to the experiments on the test bench, Conjugate Heat Transfer (CHT) simulations are conducted with the same installation conditions. The simulated temperatures are compared with the measured temperatures. In most cases, the correlation is good. However, for one bearing arrangement, the correlation is significantly worse. These differences are investigated further.

Abstract

The use of additive manufacturing, particularly 3D printing, for the production of seal rings is a promising way to speed up the development cycle of new products. In addition, this technology enables the rapid optimization and investigation of seal profiles. In order to guarantee the required sealing function, the sealing material must meet specific requirements. In this study, a comprehensive analysis is performed focusing on the evaluation of elastic 3D printable materials to gain an understanding of the general properties and behaviour of these materials. A liquid crystal display printer was used for all tests. The first prototypes of additive manufactured rod seals for a pneumatic application were tested.

Abstract

Rotary shaft seals are an established standard for sealing rotating shafts 1. The geometry has been optimized over decades and adapted to the material properties to ensure an optimum sealing capability 2. With the widespread availability of 3D printing technologies, there is a growing interest in printable seals for replacement parts or prototypes. This means that failed parts can be replaced as quickly as possible and the development process can be significantly accelerated. However, geometries established for conventional production cannot be implemented as 3D printed variants without accepting severe functional restrictions. A seal that can be successfully 3D printed must therefore be specially adapted. The following findings provide an overview of the latest research and development in the field of 3Dprinted rotary shaft seals.

Abstract

Rotary shaft seals are used to seal shaft passages and prevent the exchange of fluids. The performance and service life of rotary shaft seals is strongly dependent on the temperature in the contact area between the sealing edge and the rotating shaft. Multiphase conjugate heat-transfer analyses covering different assembly scenarios, for example additional bearings or different shaft geometries, were performed in the software Ansys CFX 2021 R2. A model for predicting the maximum temperature in the sealing contact and for determining the heat dissipation from the sealing contact to the surrounding geometry was developed. This model provides the ability to predict the influence of the design of the surrounding sealing system on the contact temperature. Thus, the surrounding geometry of rotary shaft seals can be optimally designed to reduce the contact temperature between the sealing ring and the shaft as much as possible in order to achieve a longer service life.

Abstract

Rotary shaft seals are used to seal rotating machine parts. In most cases one single sealing lip (main lip) contacts the shaft and separates the fluid on one side from the environment on the other side. To prevent the entry of other fluids and or particles, seals with additional protection lips are used (two lips), especially in heavily contaminated environments. When the protection lip contacts the shaft, a vacuum can form between the main lip and the protection lip, leading to increased contact pressure and friction. The increased frictional torque generates more heat and leads to overheating in the contact area between the lip and the shaft. Test runs conducted on a friction torque test bench with various seal configurations confirm that the two lips influence each other. Higher frictional torques and contact temperatures occur, when the volume between the lips isn't vented. This shows the importance of venting.

Abstract

Hydraulic oils differ in their chemical composition and viscosity substantially. Their influence on the wear of rod seals is neither fully understood nor can be predicted precisely. The primary objective of this study was to evaluate the influence of various oils and their wetting properties on the wear of rod seals. In an empirical study, the wear of 30 commercially available polyurethane U-cups was investigated with 15 different oils using a recently built test rig. The wear of rod seals increased with lower viscosity and higher polarity of the oil. Both oil properties are combined in a new parameter which helps to assess the lubricity of oil and the wear of rod seals.

Abstract

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.

Abstract

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 %.

Abstract

Increased wear on radial lip seal systems is observed when sealing modern lubricants, such as polyglycols and esters. This can impair the function of the sealing system and ultimately lead to leakage. This work, carried out within the AiF research project “Welleneinlauf” (wear of counter faces) 1, shows methods to identify and predict excessive wear of radial lip sealing systems based on their wetting properties and pumping rate. The knowledge gained will support users by providing faster and more cost-effective testing methods early in the design process, thus enables a significant increase in the service life of radial lip sealing systems.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

Plunge grinding is considered to produce lead free surfaces for the usage with rotary shaft seals. The term “lead” summarizes all surface structures, which create a rotation dependent pumping effect. Since lead influences the complex tribological system “rotary shaft seal”, it is essential that the process “plunge grinding” manufactures surfaces without lead. A kinematic simulation model of the manufacturing process “plunge grinding” was developed to understand and visualize the complex interactions between the manufacturing parameters and the macro lead parameters on the surface. Additionally, an approach for the stochastic influence on the surface is also presented to investigate parameters for lead free surfaces. The model has been validated by the measurement of plunge ground parts with the same manufacturing parameters.

Abstract

Lead, especially micro lead, on ground shaft sealing surfaces has been an ongoing issue in sealing technology for many years. Now that suitable lead measuring methods have finally been developed, the scientific focus has shifted from the measurement of lead and its influence on the sealing function to the formation of lead. Experimental investigations have been carried out to analyse the influence of the process parameters on the formation of micro lead during external cylindrical plunge grinding. The results show that micro lead occurs using industrial common parameters. The influence of the grinding tool specification, the dressing and the grinding parameters on the micro lead structures are described and discussed.

Abstract

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

Abstract

The influence of the dwell time and properties of oil on the breakaway friction of a U-cup rod seal was analysed. A logarithmic correlation between the breakaway friction force and the dwell time (in a range from 30 to 104 seconds) was found. We used oils from various viscosity classes (ISO VG 32 …460) and chemical compositions (mineral oil, silicone oil, perfluoropolyether, polyglycol). An almost linear correlation between the dynamic viscosity and the breakaway friction was found. Among viscosity and dwell time, further properties of oil must have a remarkable influence on the breakaway friction of rod seals. Using ellipsometry, we showed that even a film thickness of approximately 8 nanometres can be squeezed out of the sealing gap during dwell time.

Abstract

Various operating conditions can cause sealing systems to be insufficiently supplied with oil, resulting in starved lubrication. This paper deals with the experimental investigation of starved lubrication operating conditions. For this purpose, the test rig configuration used is introduced. The influence of starved lubrication on 3 different sealing systems was investigated. In addition to a standard elastomeric rotary shaft seal, a multi-lip initially grease-filled elastomeric rotary shaft seal and a PTFE sleeve with circumferential grooves were employed. The results show that the standard rotary shaft seal is unsuitable for the investigated starved lubrication conditions. The other two sealing systems performed better in comparison and are suitable for operation with a starved oil supply, at least for short durations.

Abstract

Modern lubricants (e.g. polyglycols, esters) cause problems when sealed with rotary shaft seals. The wear of rotary shaft seals strongly depends on the wetting properties of the respective friction partners. The paper shows, how the susceptibility to wear of rotary shaft sealing systems can be estimated by a combined consideration of the wetting properties of the sealing components, the lubricants viscosity and the pumping rate of the sealing system. Investigations were carried out using polished steel counter faces made from eight different alloys, together with FKM rotary shaft seals and eleven chemically different lubricants (mineral oils, polyglycols, poly-α-olefins, esters and silicone oils).

Abstract

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.

Abstract

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

Abstract

Elastomeric rotary shaft seals are a common seal type for various industrial applications. They are comparably cheap and easy to use and offer an overall good performance. But the wear behavior of these sealing systems is not fully understood and not predictable so far. If a lip seal fails, it causes high maintenance costs and environmental damage. In this article, various tribological conditions are considered. For this purpose, the sealing systems are tested with multiple operating conditions relevant to practice. Three test series are conducted with rotary shaft seals BAUM5X7 75FKM585 on plunge ground shafts. The tests are carried out with two different circumferential velocities of the shaft (4.2 and 10 m/s), three different oil sump temperatures (40, 80, and 120 °C), two different lubricant types (FVA 3 and PG 3), and five different test durations (between 100 and 625 h). For a complete acquisition of the system condition, all shaft surfaces are measured in 2D and 3D before and after the test runs and the wear of the sealing edges is evaluated with a recently developed laser line triangulation method on the complete circumference of the sealing rings. Results show large amounts of wear, depending significantly on the operating conditions. A strong correlation of the wear effects in the tribocontact area of the sealing system becomes evident. This article helps to understand and avoid critical operating conditions concerning abrasive wear.

Abstract

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

Abstract

The seal failure of an elastomer rotary shaft seal is often caused due to lead on the shaft counterface. In sealing technology, the term ‘lead’ includes all structures on sealing counterfaces that are capable of transporting fluid in axial direction through the sealing contact and thus disrupting the sealing mechanism. Lead structures are created during the manufacturing process of the shaft surface or throughout the handling. They occur in various shapes and sizes. Depending on the characteristics of the lead structures, several specialized measurement and evaluation methods exist which have to be applied in combination. However, not all types of lead can be covered with the methods known so far. State of the art are frequency-based and model-based analysis methods, which are only able to detect periodic lead structures. Aperiodic and stochastically distributed lead structures cannot be detected due to the functional principle. This article provides an approach for a structure-based evaluation of macroscopic lead structures based on optical topography measurement data. This allows to detect all known types of macroscopic lead on the shaft surface and in future to measure microscopic and macroscopic lead with a single measurement procedure.

Abstract

Elastomeric rotary shaft seals are a common seal type for automotive and industrial applications. The wear mechanism of these sealing systems is not fully understood and not predictable so far. If a lip seal fails, it causes high maintenance costs and environmental damage. In order to investigate the wear mechanism, an empirical test series is conducted with shaft seals on plunge ground shafts. Various tribological conditions are considered, including operating conditions relevant to practice. For a complete acquisition of the system condition, all shaft surfaces are measured 2- and 3-dimensional before and after the test runs. The wear of the sealing edges is evaluated with a recently developed laser line triangulation method on the complete circumference of the sealing rings. Results show large amounts of wear, depending significantly on the operating conditions. We discuss the wear mechanisms and the correlations of wear effects in the tribo contact area of the sealing system.

Abstract

Modern lubricants (e.g. polyglycols, esters) cause problems when sealed with radial lip seals. The wear of radial lip seals strongly depends on the wetting properties of the respective friction partners. The paper shows, how these wetting characteristics correlate to the wear measured on both, the radial lip seal and the shaft countersurface. Investigations were carried out using polished 100Cr6 steel counter faces and FKM radial lip seals, together with ten chemically different lubricants (two mineral oils, four polyglycols, two poly-α-olefins, one ester and one silicone oil). The results show why some radial lip sealing systems are able to maintain their function over the expected service life and others fail prematurely.

Abstract

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.

Abstract

The function of radial sealing systems depends significantly on the shaft counterface. External cylindrical plunge grinding is considered the standard for the manufacturing of suitable shaft counterfaces. It creates a stochastic surface texture with many anisotropic groove-like grinding structures, oriented in the circumferential direction of the shaft. The structures are created by the grain engagement into the workpiece during the grinding process. This surface characteristic exhibits optimal properties for hydrodynamic lubrication between the seal and the shaft. Although there is no axial relative movement between grinding wheel and workpiece in plunge grinding, under unfavorable conditions grinding structures can be produced that deviate from the circumferential direction. These structures then transport fluid through the sealing during rotation. Structures, that cause fluid transportation because of inclined orientation to the circumferential direction, are referred to as micro lead. Especially for high rotational speeds, e.g. in electric powertrains, micro lead causes high pumping effects and therefore leakage and following failure of products. This publication presents findings on the influence of the dressing parameters on the formation of micro lead during external cylindrical plunge grinding. The experimental investigations show that especially negative dressing speed ratios lead to the formation of micro lead structures.

Abstract

Elastomere Radial-Wellendichtungen werden in fast jedem antriebstechnischen Aggregat eingesetzt. Ohne Abdichtung der Wellendurchtrittstelle ist ein Betrieb unmöglich. Obwohl die Dichtringe millionenfach eingesetzt werden, kommt es immer wieder zum Systemschaden „Leckage“. Die Dichtringe zeigen als tribologischen Primärschaden beispielsweise Verhärtung, Risse oder exzessiven Verschleiß. Eine Berechnung der Lebensdauer ist für RWDR nach wie vor nicht möglich, daher sind Prüfläufe das einzige Werkzeug zur sicheren Auslegung von Dichtsystemen. Die Forschungsvorhaben der Projektreihe 696 haben zum Ziel, KmU und anderen Unternehmen einen Leitfaden zur systematischen Prüfung von Dichtsystemen zur Verfügung zu stellen. Wichtigstes Werkzeug dafür ist der vollständige Gesamtschadenskatalog. Das Wissen aus 696 I bis IV zum Thema Schadenanalyse, einstufigen und wechselnden Belastungen sowie zur Validierung der Ergebnisse unter industriellen Einsatzbedingungen wird in diesem Gesamtbericht zusammengeführt. Die Unternehmen können mit dem Leitfaden Schadensfälle analysieren und angepasste Kollektive für tribometrische Versuche erstellen. Damit können Dichtsysteme untersucht und optimiert werden. Leckage und Imageverlust können sicher vermieden werden. Die Erkenntnisse sind digitalisiert und stehen für den Wissenstransfer zur Verfügung. In der Projektreihe 696 wurden 278 Prüfläufe mit einer kumulierte Versuchslaufzeit von 108.117,4 h (= 12,3 Jahre) und einem kumulierten Laufweg von fast 2 Millionen km individuell ausgewertet. Das Ziel des Forschungsvorhabens wurde erreicht.

Abstract

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.

Abstract

Radial lip seals are used in various sizes and designs to seal shaft interfaces. In contrast to other sealing systems, elastomeric radial lip seals have a back-pumping capability. Fluid is pumped under the sealing edge from the air side to the fluid side. The simplest method for measuring the back-pumping rate is the converse installation of the radial lip seal. This paper describes the current state of the art in back-pumping rate measurement. It shows the advantages over other methods and the limitations of the method. For the converse installation, there was always the assumption of hydrodynamic lubrication. This means there would be only minimal initial run in effects and no further wear. Current research work however, question this assumption. To analyze the wear formation during back-pumping rate measurements, various long-term tests were carried out. The resulting wear is compared with identical tests in normal installation.

Abstract

A key factor influencing the friction of rod seals is a thin oil film, which is dragged into the sealing gap at outstroke and instroke. Accurate determination of oil film thickness in the sealing gap of rod seals is a challenging task since it is only in the range of a few nanometers. A novel measurement procedure to analyze the friction of common reciprocating sealing systems in direct relation to the shear rate and film thickness is introduced in this paper. Results from a first empirical study with film thicknesses in the range of a few nanometers and shear rates up to γ˙=107 s−1 were used to compare the friction of practically relevant polyurethane U-cups. The U-cups differ in their geometry and surface roughness. It is seen that even at such thin films, the measured friction of those seals can be approximated by Newtonian fluid friction (speed, film thickness, viscosity, contact area). In general, the novel measurement procedure is useful in a scientific and technical context, since it offers a new perspective on tribological mechanisms at thin film lubrication conditions.

Abstract

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.

Abstract

In the event of damage to sealing systems, expert knowledge in dealing with these problems is often not available to many industrial users. The development engineer is faced with the question of improving the product to meet the new requirements. The aim of this publication is to provide a proven guide for dealing with problematic sealing systems.

Abstract

Conclusions on the lubrication conditions in the sealing gap of rod seals can be drawn by measuring the oil film thickness on the rod after outstroke, for which ellipsometry is used in this paper. A commercially available U-cup rod seal made of polyurethane and a polished, hard-chrome-plated hydraulic rod were used. The film thickness was measured at various rod speeds (5–800 mms^(−1)), operating pressures (up to 25 MPa) and oil viscosities (ISO VG 15 - 460). Discrepancies between the inverse theory of hydrodynamic lubrication (IHL) and empirically measured film thickness are discussed in this paper. An approximation equation to calculate the film thickness of the analyzed sealing system based on the presented measurement data is provided.

Abstract

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

Abstract

Radial lip seals are a common seal type for drive units in various industrial applications. Environmentally friendly operation strategies require these drive units to be driven on demand in short time duty. The sealing systems have to deal with fast changing oil sump temperatures. This cannot be reproduced on usual test rigs. Firstly, a test rig with advanced heating and cooling capacities was developed. Then, comprehensive test series were carried out. As expected, test results show, different constant temperature levels lead to a significant change of wear. Furthermore, fast changing temperatures are adding additional tribological stress to the sealing system.

Abstract

The function of a radial shaft seal is based on interactions between the sealing edge and the shaft counterface. To better understand these mechanisms, a look inside the sealing contact was taken. The procedure and the testing facility are presented in this article. In addition, a research methodology was developed to systematically analyze the fluid flow and the distortion of the sealing surface of shaft seals. The results of the test procedure are documented in an evaluation matrix that allows the comparison of sealing systems with different worn sealing edges. For example, the tests show an influence of the rotation direction of the shaft during running-in on the formation of leakage channels or oil collecting chambers within the sealing contact.

Abstract

Dieses Lehr- und Grundlagenbuch gliedert das Thema Tribologie von Grund auf neu. Die Begriffe werden einheitlich definiert und eindeutig verwendet. Es zeigt die Komplexität auf, weckt das Interesse für die Tribologie und bringt Klarheit in die Wechselwirkungen zwischen Festkörper und Schmierstoffe.

Abstract

Erhöhter Verschleiß am Radial-Wellendichtsystem ist ein häufig auftretendes Problem bei der Abdichtung moderner Schmierstoffe wie Poly-α-Olefinen, Polyglykolen und Estern. Im Forschungsprojekt "Welleneinlauf" wurden in diesem Zusammenhang Stoff- und Benetzungskenngrößen untersucht und identifiziert, mit deren Hilfe übermäßiger Verschleiß am Dichtsystem vorhergesagt werden kann. Ungeeignete Materialkombinationen der Dichtungskomponenten können so frühzeitig erkannt und vermieden werden. Das senkt Kosten und spart Zeit bei der aufwendigen Validierung von Dichtsystemen durch Prüfstandsuntersuchungen. Auf Grundlage der durchgeführten Analysen und Prüfstandsuntersuchungen wurde ein Korrelationsmodell erarbeitet, das zur Abschätzung des Verschleißverhaltens von Radial-Wellendichtsystemen genutzt werden kann. Dieses erfordert ausschließlich Stoff- und Benetzungskenngrößen aus genormten Mess- und Berechnungsverfahren. Einige Stoffgrößen können vom Anwender bereits aus Datenblättern oder als Anhaltswerte aus Tabellenwerken übernommen werden. Zentraler Punkt zur Bestimmung der Benetzungskenngrößen ist die meist unbekannte Oberflächenspannung, die nach DIN 55660, mit ergänzenden Hinweisen aus diesem Forschungsprojekt. bestimmt werden kann. Insbesondere bei der Verwendung modernerer Schmierstoffe wie Estern oder Polyglykolen anstelle von Mineralölen ergeben sich Schwierigkeiten, wie ein erhöhtes Leckage- und Verschleißrisiko. Bislang sind diese Schwierigkeiten nur mit zeit- und kostenintensiven Vor- und Prüfstandsuntersuchungen auszuräumen. Im abgeschlossenen Forschungsprojekt konnte gezeigt werden, dass verglichen mit den aktuell genutzten Prüfstandsuntersuchungen, zeit- und kostengünstigere Förderwertuntersuchungen zur Identifikation verschleißanfälliger Radial-Wellendichtsysteme genutzt werden können. Die erzielten Forschungsergebnisse zeigen einen grundlegenden Zusammenhang zwischen den Benetzungseigenschaften der beteiligten Dichtungskomponenten und dem Verschleiß des Dichtsystems. Die gewonnenen Erkenntnisse bilden eine wichtige Grundlage für die Anpassung und Weiterentwicklung von Radial-Wellendichtsystemen. Durch die gezielte Manipulation der Benetzungseigenschaften einzelner Dichtungskomponenten kann zukünftig der Einsatzbereich von Radial-Wellendichtungen erheblich gesteigert, Verschleiß reduziert und deren Lebensdauer erhöht werden.

Abstract

Das Tribosystem Radialwellendichtung bestehend aus Dichtelement und Welle sind die Hauptteile dieses Fachbuches. Es wird umfassend, basierend auf neuesten wissenschaftlichen Erkenntnissen der Aufbau und die Funktionsweise beschrieben. Etliche Beispiele mit Schadensbildern zeigen die verschiedenen Schadenskategorien und beschreiben deren Ursachen.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

Dieses Lehr- und Grundlagenbuch gliedert das Thema Tribologie von Grund auf neu. Die Begriffe werden einheitlich definiert und eindeutig verwendet. Es zeigt die Komplexität auf, weckt das Interesse für die Tribologie und bringt Klarheit in die Wechselwirkungen zwischen Festkörper und Schmierstoffe.

Abstract

Grease-lubricated sealing systems show starved lubrication much more frequently than oil lubricated sealing systems. Different greases provide different lubricity to the sealing system. A test and evaluation method was developed that allows to assess the lubricity of different greases and to compare them with each other. The test and evaluation method consists of a test run and a subsequent analysis of the test components. The test run comprises a 24-hour speed collective and is performed on a test rig using real sealing system components. For the evaluation method, eight criteria are analysed, which are rated suitable for evaluating starved lubrication. The criteria include parameters measured during the test run, such as friction torque and temperature, as well as parameters inspected in the subsequent examination of all test components. All criteria are assessed and combined to an overall score, that allows to directly compare different greases with each other. The test and evaluation method developed reveals significant differences between 23 greases examined. Thus, the lubricity of greases in sealing systems can be analysed and compared much more quickly than in the past. Thanks to the rapid testing and focused evaluation of the relevant criteria, greases can be tested much more cost- and resource-efficiently than before.

Abstract

Diese Arbeit gibt Einblicke in das tribologische Verhalten fettgeschmierter Kontakte in pneumatischen Schieberventilen. Aufgrund des stark nicht-newtonschen Fließverhaltend des Fettes wurden verschiedene rheologische Messungen durchgeführt, um die beiden Materialmodelle nach Herschel-Bulkley und Palacios-Palacios zu parametrieren. Diese beiden Materialmodelle wurden in eine EHD Simulation des Dichtkontakts integriert und für zwei Temperaturen qualitativ verglichen. Für das Dichtsystem ist die Reibkraft nahezu unabhängig von der Wahl des Materialmodells. Außerdem konnten mit einer newtonschen Näherung des Fließverhaltens qualitativ vergleichbare Reibkräfte mit etwa 10% Abweichung gegenüber den nicht-newtonschen Modellen erzielt werden.

Abstract

Radial lip seals are a common seal type for various industrial applications. In retarder breaking systems for commercial vehicles, radial lip seals are exposed to very fast changing oil sump temperatures. Due to increasing demands, the elastomer seals are increasingly failing premature in such applications. It is assumed that this is caused in particular by the very high temperature gradients, that result from the fact that a lot of braking power is dissipated within a short time. This is the case, for example, when braking while driving downhill with heavy loads. Since the temperature gradient is of minor importance in many applications, there are no publications regarding the specific influence of high temperature gradients on the function of radial shaft seals. Therefore, a test rig with advanced heating and cooling capacities is developed. A comprehensive test series is carried out, with the main focus on the influence of high temperature gradients on the wear behavior of the seals. Test results show, that different temperature levels lead to a significant change of the wear behavior. Additionally, fast changing temperatures are adding additional tribological stress to the sealing system.

Abstract

Modern lubricants, such as polyglycols and esters, can cause problems when sealed with radial lip seals. Alongside chemical incompatibility with the elastomer, increased wear can impair the function of the sealing system and ultimately lead to leakage. Wear of the counterface is characterized by a characteristic abrasion that has the shape of a tangential circumferential groove. This wear is referred to as ``wear track''. Current research in the field of sealing technology shows that the wear of radial lip seals strongly depends on the wetting properties of the respective friction partners in addition to hydrodynamic influences. The wear sensitivity of the counterface is determined by the surface hardness (e.g. Vickers hardness HV) and the grain size of the microstructure (DIN EN ISO 643). The tendency to wear can thus ultimately be specified as the product of the lubrication condition and wear sensitivity. In this paper, the wear of different radial lip sealing systems is compared with hydrodynamic and wetting characteristics measured on the basis of the resulting wear track. For this purpose, wear investigations were carried out on five steel materials in combination with radial lip seals made of FKM and nine chemically different lubricants (two mineral oils, three polyglycols, two poly-a-olefins, one esters and one silicone oil). In addition, the relevant parameters (surface tension, dynamic viscosity, density, hardness) of the involved friction partners were determined as a function of temperature. Increased wear was observed especially in tests with polyglycol- and ester-based lubricants. In combination with the investigated steel materials, these lubricants show adhesion work that is less than or equal to the cohesive work in the lubricants themselves. This leads to incomplete wetting thus to a lubrication condition in the sealing gap which promotes abrasive wear and can have a negative influence on service life.

Abstract

The oil film generation of a U-cup rod seal and the oil film thickness on the rod after outstroke were analyzed analytically, numerically, and experimentally. The analyzed sealing system consists of an unmodified, commercially available U-cup, a polished rod, and mineral oil. The inverse theory of hydrodynamic lubrication (IHL) and an elastohydrodynamic lubrication (EHL) model—both based on the Reynolds equation for thin lubricating films—were utilized to simulate the oil film generation. In the EHL analysis, physical parameters and numerical EHL parameters were varied. Both the analytical and numerical results for the varied parameters show that the film thickness follows a square-root function (i.e., with a function exponent of 0.5) with respect to the product of dynamic viscosity and rod speed, also referred to as the duty parameter. In comparison to the analytical and numerical results, the film thickness obtained via ellipsometry measurements is a function of the duty parameter with an exponent of approximately 0.85. Possible causes for the discrepancy between theory and experiments are discussed. A potential remedy for the modeling gap is proposed.

Abstract

Das Tribosystem Radialwellendichtung bestehend aus Dichtelement und Welle sind die Hauptteile dieses Fachbuches. Es wird umfassend, basierend auf neuesten wissenschaftlichen Erkenntnissen der Aufbau und die Funktionsweise beschrieben. Etliche Beispiele mit Schadensbildern zeigen die verschiedenen Schadenskategorien und beschreiben deren Ursachen.

Abstract

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.

Abstract

The duty parameter diagram is a common tool to compare and analyse the lubrication and friction condition of different radial shaft sealing systems. In addition, it also allows an evaluation of the suitability of differently manufactured sealing counterfaces. This paper deals with the influences of different shaft surface structures on the formation of a lubricating film and a sealing gap. For this purpose, friction torque measurements were carried out, starting from very low sliding speeds of about 0.0042 m/s (corresponds to 1 rpm at a shaft diameter of 80 mm) up to 10.5 m/s. The aim is to cover the mixed friction area in addition to the liquid friction area and thus determine the position of the transition point between both friction states.

Abstract

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.

Abstract

Development of a redox flow battery (RFB) goes hand in hand with sealing technology. Mechanical variations on different RFB components affect the sealing performance. The clamping force generated by through-bolt-joints to assimilate compression, which must provide enough contact stress on the elastomeric seals and flanges over a stacked design to seal off leakage paths. Tolerances must be set according to norms or a well-defined compression range. Most mechanical variations are due to geometrical irregularities from manufacturing. The seal and other components also undergo time-dependent deformations due to stress relaxation and swell. Experiments and mathematical analysis determine initial RFB design conditions.

Abstract

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.

Abstract

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.

Abstract

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.

Abstract

The shaft is an important part of the sealing system. In standard sealing counterfaces are hardened and grinded. This process is useful to reduce wear on the shafts used. Hardening is complex and expensive, so most companies try to avoid this process by using soft (not hardened) shafts. Soft shafts often show imperfections caused by the grinding process. Those imperfections causes leakage on the sealing system or even a breakdown of the entire sealing system. The latest research on these imperfect shafts shows different kinds of imperfections. Typical imperfections are called grinding burn or grinding chatter marks. The soft shafts are manufactured by a grinding process with different parameters. Afterwards the shafts were analysed concerning the imperfections. Detected imperfections are analysed qualitatively and quantitatively with different measurement and analysis methods. Those imperfections and measurement results will be showed. In the next steps functional tests will be performed. This functional tests include measurements of the pumping rate and the friction torque. The results will be correlated with the lubrication condition in the sealing contact. In a further step the wear behavior of the sealing edge, in contact with different imperfections on the countershaft positioned in the sealing contact, will be ratet. In this paper the research results will be showed and summarized.

Abstract

Die Oberflächentopografie der Dichtungsgegenlauffläche hat einen wesentlichen Einfluss auf die Fluidförderung im Dichtsystem Radial-Wellendichtung. Daher ist die funktionsgerechte Beschreibung dieser besonders wichtig. Die Charakterisierung erfolgt anhand von 3D-Kennwerten der DIN EN ISO 25178. The topography of shaft counterfaces has a significant influence on the pumping rate of radial lip seals. Therefore, it is important to describe its functional properties as good as possible. The characterization based on 3D parameters of the ISO 25178.

Abstract

This paper shows and explains which visual failure analysis methods are meaningful and how they can be useful to analyse dynamic sealing systems. While most people think a scanning electron microscope (SEM) image of a sealing edge is always necessary, the presentation helps to judge which method is better suitable. This leads to an adjusted effort while costs and primarily time is saved. The result is a perfect analysis and the knowledge about the tribological function 1 or the failure mechanism 2, 3.

Abstract

Mit einem 8-Zellen-Dauerlaufprüfstand hat sich der Fachbereich Dichtungstechnik am Institut für Maschinenelemente der Uni Stuttgart der Herausforderung gestellt, die Wechselwirkungen in komplexen tribologischen Systemen und deren Auswirkung auf die Dichtfunktion realitätsnah zu untersuchen.

Abstract

The minimum of the friction torque can be achieved if the cross sections of the convolutions are big enough to pump out the oil beneath the lip.

Abstract

Elastomeric lip seals are frequent and reliable machine components. However, their range ofapplication is limited. Ifthese limits are reached, the seals are often replaced by PTFE sleevetype seals with spiral grooves (PTFE lip seals). The basic geometries and types ofgrooves have an empiric origin. An exact analysis and with it the knowledge of their function does not exist. This paper presents a project that aims to analyze and optimize the function and design ofthese grooves. A test rig developed at the Institute ofMachine Components at the University of Stuttgart visualizes the flow in PTFE lip seals and between hydrodynamic sealing aids of elastomeric lip seals. The flow is observed and recorded through a glass hollow shaft, which allows investigating the behavior in all directions and areas of the lip. This knowledge is essential to develop new geometries and to verify complex fluid dynamic analysis.

Abstract

Elastomeric lip seals are used to seal rotating shafts in all areas of mechanical and automotive engineering. The Elastomeric lip seal is a frequent and reliable sealing system in millions of cases. Based on its good static sealing and the active dynamic sealing mechanism it is accepted by the market. However, limits are set to its area of application. The load on the lip seal during its use, for example at high ambient temperatures and high shaft speeds leads to high temperatures at the seal edge. Also the high specific friction work leads to overheating. This degrades the elastomer and the fluid. Elastomeric lip seals are ageing very fast under such high-loads. An even bigger problem is the comparative low chemical resistance. For these reasons Elastomeric lip seals are being substituted more and more by sleeve type lip seals made of Polytetrafluorethylene (PTFE) compounds. The PTFE lip seals can be used in a temperature range up to 260 °C and at higher circumferential speeds. Due to their good tribological attributes they can also be used at sparsely oiled sealing areas or for the sealing of poorly lubing fluids. Its universal chemical resistance is another major advantage. In comparison to an Elastomeric lip seal the plain PTFE lip seal does not have an inward pumping mechanism. Therefore the PTFE lip seal with spiral groove was developed. The spiral groove is connected, analogue to a thread with several convolutions, to the shaft. Thereby it generates an adjusted pump effect on the oil beneath the lip depending on the direction of rotation. The static sealing has to be stated critically due to the fact that fluids can leak through the continuous spiral groove at standstill of the shaft. The precise functions of the dynamic and the static seal mechanism are not well understood up to now. Therefore today’s products were largely developed by empiric procession. Nevertheless, the understanding of the flow is necessary to be able to develop and improve new seals. This work aimed to analyse and optimise the function and design of the groove- geometry. Therefore the state-of-the-art of market-available PTFE lip seals was investi- gated. The following behaviours and methods were analysed and used: Geometry Radial Force Friction Torque Oil pumping rate Air pumping rate Leak tightness, wear and development of oil coal in long-time tests Static leak tightness Flow in the convolutions due to visual analysis through a glass hollow shaft Finite Element Analysis Computational Fluid Dynamic Analysis With these methods the penetration behaviour, the hydrodynamic flow and the back pumping mechanisms were investigated and exemplarily described for three groove types. The mechanisms in different groove types can now be understood, compared, and optimised. In addition, the influence of entered particles or of an oxidation deposit from degraded oil can be analysed. Furthermore, this knowledge serves the verification of Computational Fluid Dynamic simulations. Results for the dynamical function are: The oil is forwarded circumferentially in the convolutions around the shaft and therefore pumped back. No axial flow takes place. The transport of the oil takes also place on the contacting areas, even if the convolutions are not filled. è The geometries of the different spiral grooves are working well if the shaft rotates. Results for the statical function are: All PTFE lip seals leak if the oil level reaches the shaft, and therefore the lip. The oil flows through the open entry into the groove, around the shaft and even above the oil level. It leaks out at the air side. è The geometries of the different spiral grooves do not work sufficiently if the oil level reaches the lip seal at standstill of the shaft. With this knowledge, the groove geometry was optimized in this dissertation. The contacting area has to be small, and the walls of the groove have to be rampant. Therefore the oil can be hold in this area by cohesion forces and the oil does not flow in the convolution. The lip seal was innovatively extended with a closed ring at the oil side. This ring closes the open entry of the spiral groove and thus avoids the inflow of oil. The radial force and the pressure distribution were optimised with the help of finite element analysis. They were adjusted with newly-created add-ons. With these optimisations a new, statically leak tight lip seal for the use in all fields of mechanical engineering was developed. It can seal all fluids at temperatures up to 260 °C. This innovative lip seal prevents choosing a wrong seal, optimises the storage and ensures an optimal function at all operating conditions. The costs are comparable to highgrade Fluorelastomeric lip seals.

Abstract

Elastomeric lip seals are frequent and reliable machine components. However, their range of application is limited. If these limits are reached, the seals are often replaced by PTFE sleeve-type seals with spiral grooves (PTFE lip seals). The basic geometries and types of grooves have an empirical origin. An exact analysis and with it the knowledge of their function does not exist. This paper is a sequel to a presentation at 2005 Annual Meeting which is published in Tribology Transactions, Volume 50 Issue 3, 2007. Within this project the flow in different groove geometries was visually analyzed. Furthermore the friction torque, the pumping rates and the long time behavior regarding leakage, wear and soiling by degraded lubricants were analyzed. The knowledge and understanding of the behavior of PTFE lip seals is now available. With this knowledge it is possible to push the limits of PTFE lip seals and to use them in other fields of applications – applications with overflowed shafts.

Abstract

Seit etwa zwei Jahrzehnten werden PTFE-Manschettendichtungen mit Spiralrille als Kurbelwellenabdichtung erfolgreich eingesetzt. Die Dichtstelle ist hier nur bespritzt. Probleme durch zu hohe Temperaturen oder chemische Unverträglichkeiten, wie sie bei Elastomer-Radialwellendichtringen häufig auftreten, gibt es aufgrund der überlegenen Werkstoffeigenschaften nicht. Sie sind jedoch an teilüberfluteten Dichtstellen bei Wellenstillstand undicht. Warum war bisher unklar.

Abstract

Gelangen Radial-Wellendichtringe aus Elastomer an ihre Einsatzgrenzen werden bei bespritzten Dichtstellen z.B. Manschettendichtungen mit Spiralrille aus PTFE-Compounds eingesetzt. Diese sind chemisch universell und thermisch bis über 200°C beständig. Die Spiralrille fördert in die Dichtfläche eingedrungenes abzudichtendes Fluid in den abzudichtenden Raum zurück. Wie der Dichtvorgang abläuft ist unbekannt. Die Geometrie der Spiralrille wird auf Grund mangelnder spezifischer Kenntnisse durch Versuch und Irrtum entwickelt. Dies ist Unbefriedigend. Insbesondere klein- und mittelständische Unternehmen (KMU) benötigen dafür unbedingt eine zielführende Handlungsanleitung. Äußerst wünschenswert für KMU's wäre auch, solche Dichtringe bei überfluteten Dichtstellen zuverlässig einsetzen zu können. Ziel dieses Projektes war zu klären, wie die Spiralrille funktioniert und wie sie dem zufolge günstig zu gestalten ist. Dieses Ziel wurde erreicht. Als zusätzliches Ergebnis wurden Gestaltungsvorschläge für zuverlässige Dichtringe bei dauerhaft überfluteter Dichtstelle abgeleitet. Am Markt erhältliche Dichtringe wurden mittels Materialschnitten im eingebauten Zustand detailliert vermessen. Radialkräfte, Reibmomente, Förderwerte von Luft und Öl sowie die statische Dichtheit wurden ermittelt. In Dauerläufen über 500 und 1000 Stunden wurde die dynamische Dichtheit, der Verschleiß der Dichtringe und der Wellen sowie die Bildung von Ölkohle untersucht. Aufwändige Strömungsanalysen (statisch und dynamisch) durch eine Glashohlwelle hindurch führten zu entscheidenden Erkenntnissen. Radiale und axiale Strömungen in der Dichtzone wurden visualisiert und damit einer Analyse zugänglich gemacht. Zwischenergebnisse führten zu von Herstellerfirmen im Arbeitskreis weiter entwickelten Dichtringen die ebenfalls untersucht wurden. Die Ergebnisse waren positiv. Alle Dichtringe verschlissen im Vergleich zu früheren Untersuchungen vor 10 Jahren kaum. Im dynamischen Betrieb waren, bis auf zwei, alle Dichtungen dicht. Bei teilweiser oder vollständiger Überflutung sind alle Dichtungen statisch undicht. Wie die Spiralrille zusammen mit ihrem Umfeld wirkt und wie sie demzufolge zu gestalten ist wurde ermittelt und beschrieben. Darauf basierend wurden Gestaltungsvorschläge für eine Optimierung der Spiralrille und für eine wirksame statische Abdichtung erarbeitet. Die optimierten Dichtringe können zumindest an teilüberfluteten Dichtstellen funktionssicher eingesetzt werden. Weitere Untersuchungen zu überfluteten Dichtstellen stehen noch aus. Die Ergebnisse wurden bei zwei themenbezogenen Tagungen und in einem Buchbeitrag vorgestellt (siehe Abschlussbericht Quellen 27-29). Das Forschungsvorhaben (AiF-Nr. 13353N) wurde aus Haushaltsmitteln des BMWi über die Arbeitsgemeinschaft industrieller Forschungsvereinigungen „Otto von Guericke“ e.V. (AiF) gefördert. Das Ziel des Forschungsvorhabens wurde erreicht. Weit darüber hinausgehende praxisrelevante Erkenntnisse wurden abgeleitet.

Abstract

Elastomer-RWDR sind ein häufig eingesetztes und zuverlässiges Maschinenelement. Gelangen diese an ihre Einsatzgrenzen (Temperatur, Drehzahl, Chemikalienbeständigkeit), können sie in einigen Spezialfällen (drehrichtungsabhängig, nicht überflutete Dichtstellen) durch PTFE-Manschettendichtungen mit Spiralrille ersetzt werden. Die Grundgeometrien und –arten dieser Spiralrillen sind weitgehend empirisch entstanden. Eine genaue Analyse, und damit ein fundiertes Verständnis der Funktionsweise gab es bisher nicht. In dieser Veröffentlichung wird die Funktionsweise der Spiralrillen im statischen und dynamischen Betriebszustand vorgestellt. Hierzu wird neben den herkömmlichen Untersuchungsverfahren eine visuelle Methode zur Beobachtung der Strömung unter der Dichtlippe eingesetzt.

Abstract

The development of seals is often based on empiric knowledge. Especially the hydrodynamic flow and the “back pumping mechanisms” in sealing aids of elastomeric lip seals and in the spiral grooves of PTFE lip seals are not well understood up to now. Nevertheless, this understanding of the flow is indispensable to be able to develop and improve new seals. For this purpose, it is necessary to be able to visualise and analyse the hydrodynamic flow in and beneath the sealing aids. A method was developed and a test rig was built at the Institute of Machine Components at the University of Stuttgart to visualise the flow. The flow under the sealing interface can be observed and recorded through a glass hollow shaft and a prism by a zoom lens and a digital camera. This knowledge helps to analyse and understand the mechanisms. Furthermore, it is the base for optimisations of the geometry of the sealing aids and for fluid mechanic simulations, which can avoid expensive prototypes.

Abstract

Elastomeric lip seals are frequent and reliable machine components. However their range of application is limited. If these limits are reached, the seals are often replaced by PTFE sleeve-type seals with spiral grooves (PTFE lip seals). The basic geometries and types of grooves have an empiric origin. Exact analysis and with it the knowledge of their function does not exist. This paper presents a project, which aims to analyze and optimize the function and design of these grooves. A new method and test rig developed at the Institute of Machine Components/ University of Stuttgart visualizes the flow in PTFE lip seals and between hydrodynamic sealing aids of elastomeric lip seals. The flow is observed and recorded through a glass hollow shaft, which allows investigating the behavior in all directions and areas of the lip. This knowledge is essential to develop new geometries and to verify complex fluid dynamic analysis.