Matthias Baumann

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

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

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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).

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.