Radial Lip Seals Research Articles

Measurement and prediction of thermal performance of automotive transmission radial lip seals

The paper reports on the use of a developed novel and specific test-rig for the assessment of performance of radial lip seals of automotive transmissions, with particular emphasis on determination of thermal performance. The test-rig can accommodate original components from a donor vehicle, thus accurately represents vehicular conditions. The specific aim is to experimentally determine the effect of shaft surface roughness parameters on the generated contact temperature. Excessive exposure to high temperatures can accelerate degradation and aging of elastomeric seals, resulting in increased wear. Corundum and CBN (Cubic Boron Nitride) ground shafts are used to ascertain the effect of surface roughness parameters in the shaft seal conjunction. An analytical thermal model is also developed in combination with temperature measurements to determine the exact temperature in the lip seal-shaft contact. It is shown that depending on the type of shaft surface grinding process some potential correlation exists between roughness parameters and generated contact temperatures. It is also shown that the contact temperature can be several degrees Celsius higher than those measured in the proximity of the seal contact.

How Wetting Properties Influence the Wear of Radial Lip Sealing Systems

AbstractIncreased 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.

An investigation of oil leakage from automotive driveshaft radial lip seals

There is an ever-increasing stringent directive for environmental protection, even for the previously rather negligible lubricant leakage from vehicular drivetrains. Leakage from transmissions and differential units are no longer permitted and can lead to excessive warranty costs. Additionally, the trend in component downsizing, including for sealing systems has indirectly altered the leakage behaviour of transmissions. To guarantee leakage-free operation, it is important to establish standardised methods of manufacturing processes, particularly for surface topography of shafts. The paper investigates the leakage from two different shaft machining processes: corundum and cubic boron nitride (CBN) grinding. The performance of passenger car transmission sealing system is ascertained with the development and use of a novel detailed representative fully instrumented test rig. A test protocol is set up to assess the performance of shafts during break-in period and correlate shaft topographic data with its measured performance. The results show that the measured oil leakage correlates well with the shaft surface skewness whilst no particular trend is observed with Ra, Rz and shaft lead angle values, which form the basis of most current standards used in industry. Overall, it was observed that shafts with negative skewness in their roughness profile produced lesser leakage. A basic analytical predictive method is also developed which corroborates with the measured data.

The sealing mechanism of radial lip seals: A numerical study of the tangential distortion of the sealing edge

The sealing behaviour of elastomeric radial lip seals is essentially affected by the sealing mechanism in the contact area between the sealing edge and the shaft surface. The relative motion between radial lip seal and shaft deforms the sealing edge tangentially in the circumferential direction. This mechanical deformation is considered essential for the sealing mechanism. In this study, a numerical approach is employed to simulate this deformation. A three-dimensional multiscale model serves this purpose. The radial lip seal geometry is described on the macro-scale. On the micro-scale, an artificial rough surface with a stochastic roughness distribution is applied to an ideal sealing edge surface. A new meshing algorithm is used to discretise different sealing edge surfaces and automatically generates structured hexahedral meshes of the sealing edges. Mesh transitions connect the resulting finely meshed sealing edge to the coarsely meshed global macro-scale mesh of the radial lip seal. The paper introduces the modelling method used to simulate the deformation of radial lip seals. Results are presented and discussed with reference to the sealing behaviour. This contributes to a better understanding of the sealing mechanism of radial lip seals. Keywords: radial lip seal, finite element analysis, surface roughness, elastic deformation, elastomers.

How to measure the radial load of radial lip seals

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.

Theoretical and experimental characterization for macro-micro friction behaviors of EPDM rubber

Friction behaviors of Ethylene Propylene Diene Monomer (EPDM) rubber ring will result in the oil leakage of radial lip seals. This research provides theoretical and experimental characterization for the friction behaviors of EPDM rubber. A friction coefficient prediction model is developed with consideration of the effect of temperature. The friction coefficient of EPDM rubber at different temperatures is studied experimentally, and its wear mechanisms throughout the temperature interval [20, 140] are revealed. Both the contact pressure and friction work density are investigated by using finite element method (FEM). Results show that the deviation between the predicted friction coefficient and experimental one is lower than 10%. The increase of temperature causes a decrease in the friction coefficient and leads to an increase of surface roughness of EPDM rubber, while it results in a reduction in the contact pressure and the friction work density.

Wear on radial lip seals: a numerical study of the influence on the sealing mechanism

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.

Influence of Alternating Temperature Levels on the Wear Behavior of Radial Lip Seals: Test Rig Design and Wear Analysis

Influence of Alternating Temperature Levels on the Wear Behavior of Radial Lip Seals: Test Rig Design and Wear Analysis

Method of calculating the contact pressure of the cuff on the shaft

The calculation of the pressure in the connection "shaft — radial lip seal" with a seal in the form of a rubber reinforced cuff is proposed. An algorithm for calculating the contact pressure is obtained taking into account the properties of the material, thickness and angle of inclination to the shaft axis of the pressing section of the cuff, the tensile force of the spring, and the geometric parameters of the free section of the cuff. Keywords: lip seal, contact pressure, axisymmetric problem. B-Mikhael@yandex.ru, ommelnikov@mail.ru

Experimental study of radial lip seals with different sleeve coatings

Lip seals are vital components. Found on a range of machines, they are used to keep oil or grease within a system and help to prevent the ingress of contaminants. This article describes research that looks at the performance of various seal–shaft combinations by testing four different sleeve coatings – tungsten carbide, chrome oxide, hard chrome and stainless steel – in conjunction with radial lip seals pressured by preloaded garter springs. To find optimum sleeve coating and seal combinations, leakage and performance are investigated using an experimental test-bench.

Diagnostic Model of Crankshaft Seals

Abstract The paper presents a research stand being a diagnostic model of radial lip seals used, among others, on crankshafts of piston combustion engines in order to identify the correctness of their operation. The possibility of determining the technical condition of lip seals on the basis of the proposed coefficient of correctness of operation has been described. The basic features of seals influencing their correctness of operation were also described, along with examples of determining the durability limits of lip seals. A modified version of the friction node of the T-02 four-ball apparatus is presented. It allows to check the correctness of sealing lips operation as well as to test the compatibility between the steel shaft, sealing lip and sealed lubricating oil. It was shown that the test results con-firmed the usefulness of the hypothesis that the quality of oil affects the durability of sealing lips and their coefficient of correctness. Additionally, attention was paid to the possibility of analyzing the pumping effect affecting the transition of the seal-shaft system from the state of partial suitability S2 to the state of full suitability S1 or to the state of unfitness S3, and because the change in the state of such a system is random, it requires a probabilistic analysis.

Measurement of the crankshaft seals friction losses in a modern passenger car diesel engine

This paper presents results of experimental investigations on the friction losses of the crankshaft radial lip seals of a modern four-cylinder diesel engine for passenger car applications. A two stage strip-test has been conducted on a motored engine test bed to obtain the friction torque of the radial lip seals. For the experimental investigations with the crankshaft seals removed from the engine, a special sealing apparatus has been designed and built. A wide range of tests have been performed covering the full speed range of the engine at lubricant temperatures of 70 ℃, 90 ℃, and 110 ℃. The results show a dependency on crankshaft speed and engine media supply temperature but also revealed the presence of constant plateaus of friction torque over engine speed.

Lubricant compatibility of FKM seals in synthetic oils

PurposeElastomer seals are used in many applications. They are exposed to lubricants and additives at elevated temperatures, as well as mechanical stresses. They can only provide good sealing function when they have resistance to those factors. There are many elastomer-lubricant compatibility tests based on DIN ISO 1817 in industry. However, they are insufficient and costly. Correlations between the tests and the applications are inadequate. The purpose of this study is investigating lubricant compatibility of fluoroelastomers (FKM) seals in polyethylene-glycol (PG)- and polyalphaolefin (PAO)- based synthetic oils and developing a methodology to predict seal service life.Design/methodology/approachA new compatibility test which is more sufficient in terms of time and cost was developed and compared with a standard test, currently used in industry. Compatibility of FKM radial lip seals with PG- and PAO-based synthetic oils with different additives was investigated chemically and dynamically. Failure mechanisms were examined.FindingsThe new method and the Freudenberg Flender Test FB 73 11 008 showed similar results concerning damages and similar tendencies regarding wear. The additive imidazole derivative was the most critical. Static tests give indications of possible chemically active additives, but alone they are insufficient to simulate the dynamic applications.Originality/valueThe paper describes a new method to investigate elastomer-lubricant compatibility and gives first results with a variety of lubricants.

Investigations of the Friction Losses of Different Engine Concepts. Part 1: A Combined Approach for Applying Subassembly-Resolved Friction Loss Analysis on a Modern Passenger-Car Diesel Engine

This work presents the application of a combined approach to investigate the friction losses in a modern four-cylinder passenger-car diesel engine. The approach connects the results from engine friction measurements using the indication method and the results from journal-bearing simulations. The utilization of the method enables a subassembly-resolved friction loss analysis that yields the losses of the piston group, crankshaft journal bearings, and valve train (including the timing drive and crankshaft seals). The engine and engine subassembly friction losses are investigated over the full speed and load range, covering more than 120 engine operation points at different engine media supply temperatures ranging from 70 to 110 ∘ C. The subsequently decreasing lubricant viscosity due to higher engine media supply temperatures allow for the identification of friction reduction potentials as well as possible risks due to an onset of mixed lubrication. Furthermore, additional strip-tests have been conducted to determine the friction losses of the crankshaft radial lip seals, the timing drive, and the crankshaft journal bearings, thus enabling a verification of the calculated journal-bearing friction losses with measurement results. For the investigated diesel engine, a friction reduction potential of up to 21% could be determined when increasing the engine media supply temperature from 70 to 110 ∘ C, at engine speeds higher than n = 1500 rpm and part load operating conditions. At low engine speeds and high load operations, the friction loss reduction potential is considerably decreased and below 8%, indicating mixed lubrication regimes at the piston group and valve train.

The effect of interference on the leakage performance of rotary lip seals

In this study, a test system is developed in order to determine the effect of interference on the lifetime of the sealing element. A set of experiments are carried out with thermoplastic polyurethane radial lip seals with three different inner diameters varied by lip surface tolerance (40, 39.80 and 39.60 mm), and EP gear oil is used as lubricant. In order to determine the lifecycle of the sealing element, mass of the leaking oil is measured. Meanwhile, in order to determine the frictional performance of the sealing element, four load cells are mounted on the cylindrical housing of the system and frictional force values are monitored by a data acquisition terminal and frictional torque values are calculated. As a result, the frictional moment values of the seals increased with the increase in interference. Moreover, the increase in interference leads to a longer service life.

Numerical Investigation of Grooved Shaft Effects on the Rotary Lip Seal Performance with Relative Lip Motion

It is generally agreed that radial lip seals are used in systems with a rotating shaft and a stationary lip. However, according to previous work, it was demonstrated that relative motion between the shaft and the lip has substantial effects on the hydrodynamic lifting load and sealing performances. Nowadays, new generations of textured shafts have emerged in order to reduce friction torque and improve reverse pumping, but no study has confirmed the effect of the relative motion between the rough lip and the shaft grooves on the rotary lip seal performances. In this work, an isothermal hydrodynamic lubrication was performed in transient conditions to investigate the effect of the relative velocity between an oblique grooved shaft and a rough lip. After confirming the validity of the current model with respect to previous works, simulations have underlined the effect of the grooved shaft with relative lip motion on the rotary lip seal performance. Indeed, by keeping the same relative velocity between surfaces, it is shown that moving the shaft with a rate higher than that of the lip surface could produce an important reverse pumping and reduce the friction torque significantly, in comparison with cases where the shaft velocity is weaker.

Investigations of blistering in the sealing zone of radial lip seals dependent on the operating factors and the power loss

The causation of damage to radial lip seals (RLS) is largely unexplained, especially with regard to blistering. Initial tests indicate a dependency of blistering on the circumferential speed and the sump temperature, whereat solely a high sump temperature does not result in blisters. It is assumed that a specific combination of operating factors leads to a tribological state in the sealing zone, which favours damage. Though, the key drivers leading to blisters are still unknown especially as influencing parameters interact. The power loss in the sealing zone is a measure for the thermal energy generated in the sealing zone. The RLS Tribometer offers the possibility to control the power loss via different operating parameters such as sump temperature, speed and line load. Consequently, it is possible to investigate the influence of one operating parameter independent from the power loss. This aims at identifying the tribological conditions leading to blistering. In this work, initial tests controlling the power loss are presented and associated with their influence on the tribological state of the sealing zone.

Effect of Shaft Surface Roughness on the Performance of Radial Lip Seals

Reduction of leakage from the shaft–radial lip seal conjunction is critical in ensuring enduring performance of entire lubrication system. This paper investigates leakage from three types of shaft surfaces, finished using different manufacturing processes. The measurement of surface topography is conducted in order to determine the pertinent roughness parameters which correspond to the observed sealing performance in real practical applications. It is found that the skewness of the surface topography correlates well with the anecdotal leakage failure rate. To quantify this association, a hydrodynamic model, accounting for shaft roughness in a deterministic manner is developed. The results from the numerical analyses confirm that the lubricant mass flow rate is reduced in the case of negatively skewed surface height distributions, when compared with the positively skewed profiles.

Numerical Investigation of the Effect of Radial Lip Seal Geometry on Sealing Performance

Sealing elements are often needed in industry and especially in machine design. With the change and development of machine technology from day to day, sealing elements show continuous development and change in parallel with these developments. Many factors influence the performance of the sealing elements such as shaft surface roughness, radial force, lip geometry etc. In addition, the radial lip seals must have a certain pre-load and interference in order to provide a good sealing. This also affects the friction torque. Researchers are developing new seal designs to reduce friction losses in mechanical systems. In the presented study, the effect of the lip seal geometry on sealing performance will be examined numerically. The numerical model created for this purpose will be verified with experimental data firstly. In the numerical model, shaft and seal will be modeled as hyper-elastic in 2D and 3D. NBR (Nitrile Butadiene Rubber) as seal material will be analyzed for the rotating shaft state at constant speed by applying a uniform radial force.

Driveline Lubricant Impacts on Dynamic Seal Test Life

ABSTRACTThe automotive market's demands for increased efficiency and improved fuel economy are driving a change to lower viscosity lubricants. However, the move to increased efficiency cannot come at the expense of hardware life and durability. Modern lubricants are being developed to provide efficiency and durability and the additive package is an important part of this design. Laboratory tests that simulate vehicle subsystem operation are an important tool to ensure that lowering the lubricant viscosity does not result in reduced hardware life. This article presents results from dynamic radial lip seal testing of a variety of driveline lubricants. In addition to overall seal failure life parameters such as seal lip and shaft wear, changes in radial load, seal failure analysis, and lubricant rheology and surface tension are discussed.