Showing papers in "Tribology Transactions in 2007"

Optimization of Partially Textured Parallel Thrust Bearings with Square-Shaped Micro-Dimples

Abstract: In this study we attempt to find the optimum geometrical parameters of square-shaped micro-dimples imposed on parallel flat bearing surfaces, which give the best tribological performance, including the load capacity and the friction coefficient. An analytical solution of the Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of the number of dimples as well as the dimple length, and the height ratios for a constant dimpled length, it is used to get the optimum value of the parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remains nearly constant.

Grease Degradation in R0F Bearing Tests

Abstract: This paper is the second in a series that examines grease lubrication mechanisms and failure in rolling element bearings. The aim of the work was to understand the grease condition changes during use and the relationship to lubrication performance and failure. R0F bearing tests were carried out with two lithium hydroxystearate greases and the effects of the temperature, the speed, and the additive package on lubrication life was studied. Post-test, one pair of bearings (fail and non-fail) was dismantled and grease distribution and condition assessed. IR spectroscopy was then used to determine the lubricant composition and the oxidation level of the grease remaining on the shields, the inner raceway, and the cage pockets. The additive package increased the grease life by 100-700% depending on the test condition. Most of the grease remaining in the bearing was found on the shields, with only trace amounts in the cage pockets or close to the rolling track. The IR analysis showed that the composition of the s...

Stability Analysis of a High-Speed Automotive Turbocharger

Abstract: Automotive turbochargers are known to have operation into the linear unstable region. The operation in the nonlinear limit cycle has been tolerated on most applications to date. The need for a quieter, smoother operation and reduced emissions has prompted new evaluations of the rotor-bearing design for these systems. In this research, a commercial rotordynamics computer program is used to evaluate the stability and transient response of a high-speed automotive turbocharger. Various models with varying bearing designs and properties have been solved to obtain the linear stability threshold speeds and also the nonlinear transient response. The predicted whirl speed map shows two modes of instability and is very similar to the limited test results in the literature. The calculation process is discussed in detail and the results of the current research will be compared to the literature. An experimental research project is currently in progress at Virginia Tech and those results will be documented in a future...

Performance of Friction Modifiers on ZDDP-Generated Surfaces

Abstract: Most modern engine oils contain a friction modifier additive to reduce boundary friction and thus contribute to improved fuel economy. Considerable research work has been carried out to measure the effectiveness of friction modifiers, both in base oil and in fully formulated engine oils. Most of this work has studied the behavior of friction modifiers on rubbing ferrous surfaces. However, engine oils generally also contain the antiwear additive zinc dialkyldithiophosphate (ZDDP) and it is well known that this additive reacts rapidly with rubbed ferrous surfaces to form a thick iron and zinc phosphate-based coating. Thus, to be effective, a friction modifier additive has to form a friction-reducing film not on a ferrous surface but on a zinc phosphate one. In the current study, the friction-reducing properties of friction modifiers on steel surfaces have been compared with their performance on surfaces having a ZDDP reaction film coating. It has been found that additives that are effective in reducing fric...

Formation Mechanism of a Low Friction ZDDP Tribofilm on Iron Oxide

Abstract: In a previous study, an iron oxide layer (mixture of Fe 3 O 4 and FeO) formed by water-vapor treatment on a steel plate resulted in an anomalous low friction (μ < 0.06) when slid against a steel cylinder in a lubricant containing ZDDP. This value is about a half of a steel/steel friction contact under the same condition. The formation of a tribofilm containing zinc and sulfur has been identified on the iron oxide. In this study, the formation mechanism of such tribofilm is discussed. The adsorption characteristics of ZDDP on the iron oxide and steel are investigated experimentally. The adsorption layer on the iron oxide analyzed by XPS is rich in zinc but contains almost no sulfur, while the one on steel includes phosphorous and oxygen, and probably phosphates. The adsorption plays a significant role in increasing the zinc content in the tribofilm on the iron oxide, while other mechanisms such as mechanical mixing are necessary to incorporate sulfur in the tribofilm.

Oil/Thickener Interactions and Rheology of Lubricating Greases

Abstract: The present communication concerns the effect of base oil/thickener interaction on the flow properties of lubricating greases. The flow properties of paraffinic and naphthenic lithium greases in th...

Thermal Management Techniques for Oil-Free Turbomachinery Systems

Abstract: Tests were performed to evaluate three different methods of utilizing air to provide thermal management control for compliant journal foil air bearings. The effectiveness of the methods was based on bearing bulk temperature and axial thermal gradient reductions during air delivery. The first method utilized direct impingement of air on the inner surface of a hollow test journal during operation. The second, less indirect method achieved heat removal by blowing air inside the test journal parallel to the shaft axis to simulate air flowing axially through a hollow shaft. The third method emulated the most common approach to removing heat by forcing air axially through the bearing's support structure. Internal bearing temperatures were measured with three type K thermocouples embedded in the bearing that measured general internal temperatures and axial thermal gradients. Testing was performed in a 1 atm, 260°C ambient environment with the bearing operating at 60 krpm, and supporting a load of 222 N. Air volu...

Effect of Lubrication on Friction and Torque-Tension Relationship in Threaded Fasteners

Abstract: In this research, three types of lubricants are investigated for their effects on the friction and torque-tension relationships in threaded fastener applications. Investigated lubricants included oils, greases, and solid film lubricants that were applied to the threads of the fastener and the nut, and the turning bolt underhead surface as well as the joint surface in contact with the bolt head. The oils tested were mineral oils with different viscosities, i.e. 21cst, 115cst, 1000cst respectively at 40°C. Three types of grease were tested; namely, regular grade, pure nickel special, and heavy metal free grease. For the solid lubricants, an olefinic type, an olefinic base with a polytetrafluoroethylene additive, and an olefinic base with an inorganic additive (Molybdenum disulfide), were applied. Class 8.8 M12 fasteners with both fine and coarse threads were used. The experiments were carried out using a Laboratory Fastener Testing System which measures the input torque, the fastener tension, the thread fri...

Deterministic Modeling of Honed Cylinder Liner Friction

Abstract: An experimental apparatus and an analytical model have been developed to investigate and determine the lubrication condition and frictional losses at the interface between a piston ring and a honed cylinder liner (PRCL). The experimental apparatus was used to measure the friction at the PRCL interface under various conditions. The analytical model developed to corroborate with experimental results includes the effects of boundary and mixed lubrication conditions using a fully deterministic approach. The procedure for analyzing the honed profile and generating a numerical equivalent for use in the mixed lubrication model is discussed. A comparison of measured and generated surfaces indicates that the model is capable of reproducing a honed cylinder liner surface profile with good accuracy. A comparison of experimental and analytical friction results shows good agreement. The model is used to analyze the effects of a cross-hatch angle on frictional behavior at the piston ring/cylinder liner contact.

Numerical Study of the Sensitivity of Tilting-Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances: Dynamic Analysis

Abstract: The bearing selection for rotating machinery is based on predictions obtained for nominal dimensions. Very often the experienced performance is different than that expected. In this paper the authors theoretically analyze the possible effects of deviations from the nominal parameters of tilting-pad journal bearings on their operating characteristics. Using an example of five-pad tilting-pad journal bearings, the effects of realistic variations of pad and bearing clearances, pivot angular position, and pad angular extent have been evaluated theoretically for bearings with different diameters and L/D ratios. The characteristics analyzed in this study include operating temperatures, friction loss, minimum film thickness, and pressure.

Highly crosslinked polyethylenes in hip replacements : Improved wear performance or paradox?

Abstract: The lubrication and wear of artificial joints are important issues for their longevity Bone loss caused by the biological response (osteolysis) to the wear debris leads to implant loosening and eventual failure of the device Various studies have shown that the size, shape, and the number of particles are important factors in the osteolytic response to wear debris It has been demonstrated that both submicron-size particles and long fibrils can stimulate macrophage responses This paper examines the clinical and laboratory data on highly crosslinked polyethylene (XLPE) regarding implant wear and particulate debris In simulator studies, total hip replacements have shown greatly reduced wear with XLPE cups compared with conventional polyethylene (PE) and short-term clinical studies of XLPE have now also shown reduced levels of wear However, simulator studies have also demonstrated that adverse wear conditions can partially or completely negate the wear advantage of XLPE Additionally, it has been shown t

The Role of Hydrogen Atmosphere on the Tribological Behavior of Non-Hydrogenated DLC Coatings against Aluminum

Abstract: Diamond-like carbon (DLC) coatings are promising candidates as tool coatings for dry machining of aluminum alloys as aluminum has a lower tendency to adhere to the DLC surface when compared to other hard coatings in ambient conditions. This study investigated the tribological behavior of non-hydrogenated DLC coatings against a 319 Al alloy in various environments including ambient air (47% RH), vacuum (6.65 × 10 − 4 Pa), inert gases (Ar, He, and N 2 ) and a mixture of 60% He-40% H 2 . Unlike the results from the other test conditions, significantly low coefficient of friction (COF) values, ranging between 0.01–0.02, were observed in the 60% He-40% H 2 mixture after a brief period with a high COF of 0.70. The formation of a carbonaceous tribolayer on the counterface and the passivation of the sliding surfaces by the chemisorption of hydrogen were suggested as mechanisms that might have been responsible for the very low COF behavior of the non-hydrogenated DLC coatings in the 60% He-40% H 2 mixture.

Investigation of Tribo-Chemistry by Means of Stable Isotopic Tracers, Part 2: Lubrication Mechanism of Friction Modifiers on Diamond-Like Carbon

Abstract: A solution of glycerol monooleate (GMO) in polyalphaolefin (PAO) considerably reduced the friction between the steel and the diamond-like carbon (DLC) under boundary conditions. The combination of the material-oil-additive is of importance. Model additives composed of a stable isotope ( 2 H or 13 C) were employed to trace the additive molecule by time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that the additive interacted with DLC surfaces in the form of an ester. Inclusion of PAO in the boundary film on DLC was found by TOF-SIMS analysis.The utility of the isotopic tracer technique in tribo-chemistry was demonstrated in this study.

Equivalent Stiffness and Damping Investigation of a Hydrostatic Journal Bearing

Abstract: The aim of this research is to study the dynamic characteristics of a hydrostatic journal bearing, with four hydrostatic bearing flat pads fed by diaphragm restrictors and supporting a rotor. We assumed that the fluid flow is incompressible, laminar, isothermal, and steady-state. Linear modeling was performed using a numerical method in order to investigate the effects of the film thickness, the recess pressure, and the geometric configuration on the equivalent stiffness and damping of a hydrostatic journal bearing. In the first step, the variation of equivalent stiffness and damping is studied according to the pressure ratio for different geometric configurations of a hydrostatic bearing at the point of operation. In the second step, the variation of the equivalent stiffness and damping is studied according to the ratio of the film thickness for different geometric configurations of a hydrostatic bearing when one moves away from the point of operation. The results show that the hydrostatic journal bearin...

Friction and Wear Characteristics Due to Stick-Slip under Fretting Conditions

Abstract: Friction and wear characteristics between two steel surfaces under fretting conditions are investigated experimentally The fretting damage caused by low-amplitude oscillatory sliding can be classified into three regimes of gross-slip, mixed-slip, and partial-slip due to the stick-slip phenomenon One of the most important characteristics of fretting wear is the transition from gross-slip to mixed-slip Several criteria have been introduced for a quantitative determination of the transition between mixed-slip and gross-slip However, the transition criteria have some problems in determining the regimes because parameters are difficult to calculate or depend on the system To introduce new transition criteria in this study, the phase difference between friction force and relative displacement is used to determine the transition and predict the fretting wear It is found that the phase difference with a range of 0° to 90° can predict the onset of fretting conditions

Alkylated Naphthalenes as High-Performance Synthetic Lubricating Fluids

Abstract: Alkylated naphthalene is a unique class of synthetic fluids with outstanding thermo-oxidative and hydrolytic stability, low volatility, and good solubility characteristics. This paper discusses the flexibility of this technology to achieve a balance of physical and chemical properties. In particular, fluid properties including thermo-oxidative stability, viscosity, aniline point, and volatility are related to chemical variations. Also, new elastohydrodynamic (EHD) film thickness and pressure-viscosity coefficient data show the good performance of this family of fluids as compared to synthetic esters. Presented at the STLE/ASME International Joint Tribology Conference in San Antonio, Texas October 23-25, 2006 Review led by Lois Gschwender

Thermo-Elasto-Hydro-Dynamic Modeling of Hydrostatic Seals in Reactor Coolant Pumps

Abstract: EDF, the French energy company, has experienced some failures of mechanical seals in reactor coolant pumps in operation in recent years. So, a thermo-elasto-hydro-dynamic model of the first seal has been developed. The present model is a steady two-dimensional approach to characterize the seal behavior in normal operating conditions. The coupling between structure thermo-elastic deformations and the fluid flow is taken into account through influence coefficient matrices. Numerical results are successfully compared to operational results of the leak-flow rate. The effects of heat transfers, of mechanical deformation, and of thermo-mechanical deformation are compared. The influence of pressure drop and the injection temperature is described. The influence of the coning angle of the faceplates is underlined. The elastomeric secondary O-rings are also proven to be influential. The internal friction (between each element of the seal) and the external friction (between the seal ring and the surrounding stationa...

Determination of Turboprop Reduction Gearbox System Fatigue Life and Reliability

Abstract: Two computational models to determine the fatigue life and reliability of a commercial turboprop gearbox are compared with each other and with field data. These models are (1) Monte Carlo simulation of randomly selected lives of individual bearings and gears comprising the system and (2) two-parameter Weibull distribution function for bearings and gears comprising the system using strict-series system reliability to combine the calculated individual component lives in the gearbox. The Monte Carlo simulation included the virtual testing of 744,450 gearboxes. Two sets of field data were obtained from 64 gearboxes that were first-run to removal for cause, were refurbished and placed back in service, and then were second-run until removal for cause. A series of equations were empirically developed from the Monte Carlo simulation to determine the statistical variation in predicted life and Weibull slope as a function of the number of gearboxes failed. The resultant L(sub 10) life from the field data was 5,627 hr. From strict-series system reliability, the predicted L(sub 10) life was 774 hr. From the Monte Carlo simulation, the median value for the L(sub 10) gearbox lives equaled 757 hr. Half of the gearbox L(sub 10) lives will be less than this value and the other half more. The resultant L(sub 10) life of the second-run (refurbished) gearboxes was 1,334 hr. The apparent load-life exponent p for the roller bearings is 5.2. Were the bearing lives to be recalculated with a load-life exponent p equal to 5.2, the predicted L(sub 10) life of the gearbox would be equal to the actual life obtained in the field. The component failure distribution of the gearbox from the Monte Carlo simulation was nearly identical to that using the strict-series system reliability analysis, proving the compatibility of these methods.

Experimental Identification of Bearing Dynamic Force Coefficients in A Flexible Rotor—Further Developments

Abstract: Bearing force coefficients are a necessary component in the analysis of linear stability and response of rotating dynamic systems. Often, these bearing parameters are predicted using limited or restrictive flow models, or operating conditions in the actual machine differ largely from the assumed conditions during the analysis. In these instances, the identification of actual support properties represents a means to verify the rotordynamic predictions. The current work presents an identification procedure that is suitable for implementation in the field and that relies on measurements of rotor synchronous response to calibrated imbalance. The method is extended to the typical case when the displacement measurements occur away from the bearing locations in flexible rotor systems. Measurements and identification are performed on a test rotor supported on a pair of identical two-lobe fluid film bearings and for increasing values of imbalance over a speed range from 1,000 to 4,000 rpm. Identification using inc...

Study of Surface Films of the ZDDP and the MoDTC with Crystalline and Amorphous Overbased Calcium Sulfonates by XPS

Abstract: The role of amorphous or crystalline overbased detergent and sulfur containing AW/EP additives on the surface films created in a tribometer was investigated. In the crystalline overbased sulfonate containing samples the weld point was higher than for the equivalent blend using an amorphous overbased sulfonate. The calcium carbonate core of the overbased sulfonates was deduced to be present in the surface film when combined with either ZDDP or MoDTC. For samples containing ZDDP the crystalline overbased sulfonate, reduced the phosphate film thickness, while for the MoDTC it reduced the MoS2 film thickness. In both cases significantly more carbon, likely as calcium carbonate (which acts to improve the EP/AW properties of the lubricant), was present when using the crystalline overbased calcium sulfonate compared to the amorphous overbased calcium sulfonate.

Valvetrain Friction and Wear Performance with Fresh and Used Low-Phosphorous Engine Oils

Abstract: Continued legislative pressure to reduce automotive exhaust emissions requires an automotive catalyst to operate at its peak efficiency up to 120,000 miles. Catalyst life is shortened by the poisoning of active sites by glazing caused by the deposition of phosphorous. The primary source of phosphorous is zinc dialkyldithiophosphate, an antiwear and antioxidant additive in engine oil. Therefore, the reduction of the phosphorous level in engine oils raises concern for increased wear of engine components. In an engine equipped with a direct acting mechanical bucket-type valvetrain, high contact stress coupled with sliding action at the cam and tappet contact makes it particularly vulnerable to wear. Motored single cam lobe valvetrain experiments were conducted to evaluate the wear protection capability of several 0.05 wt% P containing engine oils while the oil is fresh. The wear protection capability of vehicle drain samples was also evaluated to ensure adequate protection up to the point of oil change. It w...

Re-Evaluation of Basic Dynamic Load Rating and Life Formula for a Ball Screw

Abstract: The existing method of calculation for the basic dynamic load rating for a ball screw mentioned in the ISO standard is based on the method used for the angular contact ball bearing, and thus it does not align with the one used for the linear bearing. The unit for the rating life; i.e., the unit running life (URL) is defined in terms of 10 6 rev. As a result of this, the effect of the linear stroke of the nut or screw shaft, the lead, the number of starts, and the number of circulating ball circuits and their turns are not clearly reflected in the load rating formula. In this paper, the basic dynamic load rating and the life formula for the ball screw based on the method used for the linear bearing; i.e., in terms of a unit URL = 100 km is proposed and some representative calculation results for a ball screw are discussed. The results are summarized as follows: (1) Basic dynamic load rating Ca for standard stroke corresponding to the nut raceway length is defined along with a stroke factor to generalize th...

Reexamination of Ball-Race Conformity Effects on Ball Bearing Life

Abstract: The analysis in this report considers the life of the ball set as well as the respective lives of the races to reassess the effect of ball-race conformity on ball bearing life. The related changes in ball bearing life are incorporated in life factors that can be used to modify the bearing predicted life using the Lundberg-Palmgren equations and the ANSI/ABMA and ISO Standards. Two simple algebraic relationships were established to calculate life factors LF(sub c) to determine the effect of inner- and outer-race conformity combinations on bearing L(sub 10) life for deepgroove and angular-contact ball bearings, respectively. Depending on the bearing type and series as well as conformity combinations, the calculated life for deep-groove ball bearings can be over 40 percent less than that calculated by the Lundberg-Palmgren equations. For angular-contact ball bearings, the life can vary between +16 and -39 percent from that calculated by the Lundberg-Palmgren equations. Comparing the two ball bearing types, the life factors LF(sub c) for the deep-groove bearings can be as much as 40 percent lower than that for angular-contact ball bearings.

Thermal Analysis of Elliptic Bore Journal Bearing

Abstract: An irregular bore journal bearing of elliptic shape is analyzed numerically for various performance parameters considering the adiabatic temperature rise in the lubricant conjunction. The temperature contours are plotted to study the behavior of isotherms due to the presence of bore ellipticity. The ratio of thermal to isothermal value of all parameters are investigated for a range of non-circularity value with various eccentricity ratios. A numerical solution of the Reynolds equation and energy equation is carried out by setting an appropriate convergence criteria for pressure and temperature. Review led by Gordon Kirk

Journal Bearing “Morton Effect” Cause of Cyclic Vibration in Compressors

Abstract: A tilting pad bearing supporting an integrally geared compressor in an air separation service had gradually developed symptoms of very consistent cycling of high synchronous vibration levels. The vibration envelope increased and decreased over a roughly six-minute period. There was a difference in the phasing of vibration increase at one end of the rotor versus the other such that the two ends were not in phase but not 180 degrees out of phase either. Intensive site testing determined that no rotor critical speeds were close to the running speed of the pinion or of the bull gear shaft. However, it was observed with infrared thermography that the temperatures of the bearing pedestals were also cyclic with the same period as the vibration, as were the bearing pad and exit oil temperatures. The temperature cycle peaks were not in phase with each other or with the vibration. Various process parameters were changed on an experimental basis, indicating that the main parametric influence was bearing oil inlet te...

Utilizing the TEOST MHT® to Evaluate Fundamental Oxidation Processes in Low-Phosphorus Engine Oils

Abstract: The thermo-oxidation engine oil simulation test (TEOST)® MHT protocol was used to generate information on deposits and the formation of polar volatile organic compounds. Fourier transform IR (FTIR) spectroscopy was then used to analyze the level of oxidation in recovered TEOST® used oil as well as in the collected volatiles. Data was generated comparing different antioxidant systems in molybdenum-containing and molybdenum-free low-phosphorus engine oil formulations. The results show a surprising difference in deposits, volatiles, and carbonyl oxidation based on the presence or absence of molybdenum and also based on the type of antioxidant system selected. The amount of volatiles produced in the TEOST® is related to well-established oxidation mechanisms and also explains specific oxidation processes sometimes seen in Sequence III engines. A mathematical definition of antioxidant effectiveness or “robustness” is proposed that combines TEOST® deposits and volatiles measurements with FTIR carbonyl oxidation ...

Hydrodynamic and Thermal Behavior of Journal Bearings using Upwind Petrov-Galerkin FEM

Abstract: A novel approach to modeling plain journal bearings is presented. The journal is assumed to be cut open at the oil supply groove and modeled in Cartesian coordinates. The streamline upwind Petrov-Galerkin (SUPG) finite element method is used to develop the three-dimensional model. The model is validated using Boncompain, Costa, and Dowson's experimental data and compared to Khonsari's analytical method. The maximum deviation from the measured temperatures is 10 per cent for Costa's data and the predictions of 51.2°C from the model are 0.3°C lower than Dowson's experimentally measured peak temperature. The model shows rapid convergence, stabilizing in only three iterations. The cavitation interface thermal boundary conditions need not be specified. Side leakage predictions are within 2.8 percent of the measured value whereas Martin's analytical method achieves an accuracy of 11.2 percent.

Measurements of Elasticity in Multigrade Motor Oil at Elevated Pressure

Abstract: It has been recognized for about 50 years that the addition of polymer to motor oil will result in shear-dependent viscosity at relatively low shear stress. This shear-thinning can be shown to reduce the elastohydrodynamic film thickness and there has been an expectation of a reduced film in hydrodynamic lubrication as well. The expected associated increase in the journal bearing wear, however, has not been observed. The load-supporting benefit of the elastic properties contributed by the polymer has been used as an explanation for the success of the polymer blended oils in this application. The available measurements of elasticity in the form of normal stress differences have been inconclusive regarding their contribution to load support. These measurements have all been at atmospheric pressure, however, and at a very high shear rate. The oil in the load-carrying region of a bearing is at elevated pressure and the elevated pressure may enhance the elasticity. A new experimental technique for the measurem...

Corrosive Wear of Bronze Propeller Shaft Sleeve (Part 1; Investigation of the Sleeve Used and Fundamental Corrosive Wear Test)

Abstract: As propeller shaft diameters of ferries become larger in conjunction with higher vessel speed and equipping with CPPs (controllable pitch propellers), the life duration of a stern tube bearing under seawater lubrication has a tendency to be reduced. The wear of the propeller shaft sleeve is typically greater than that of the rubber bearings, with triangularly shaped craters appearing on the sleeve surface. In this paper, we describe the investigation of a used sleeve sample taken from an actual vessel, as well as the wear characteristics of various bronze alloys examined by conducting corrosive wear testing under sliding conditions equivalent to actual ferry service. The results indicated that corrosive wear was the main cause of sleeve wear and, based on comparisons between the amount of wear in seawater and in distilled water, the influence of corrosion on sleeve wear was found to be substantial. Also, the craters are considered to be formed by erosion corrosion. In a follow-up report, cathodic protecti...

A New Approach to Analyze the Hydrodynamic Flow in Sealing Aids—PTFE-Lip Seals with Spiral Grooves

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 presents a project that aims to analyze and optimize the function and design of these grooves. A test rig developed at the Institute of Machine 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 an investigation of 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.