Oil Film Thickness Research Articles

Modelling and theoretical research on transient lubrication and wear coupling behavior of main bearing during start-up of low-speed diesel engine

This study endeavors to establish a transient mixed lubrication model for time-varying wear of main bearings under dynamic loading conditions during the startup process. This model accounts for variations in oil film thickness attributable to deformation, wear profiles, and journal misalignment throughout the operational cycle. The evolution of main bearing lubrication characteristics during the startup process was analyzed, as well as the evolution of wear profiles and their effects on lubricating properties under different numbers of startups. The results indicate that as the number of startup cycles increases, the wear rate gradually levels off. With increasing startup times, there is a decrease in contact pressure and a slight reduction in oil film pressure, resulting in enhanced lubricating performance. Furthermore, the influence of startup duration on wear is significantly greater than that of radial clearance.

Study on oil film spreading characteristics on the jet lubricating tooth surface of aviation herringbone gear

Purpose During the oil lubrication process of aviation herringbone gears, lubricating oil is injected into and spreads around the tooth surface. Its spreading characteristics directly affect the lubrication state and transmission efficiency of gears. This study aims to investigate the effect of changing the injection parameters and gear operating conditions on the oil film deposition during injection lubrication. Design/methodology/approach The computational fluid dynamics method was used to establish the computational domain for the simulation and optimization using an orthogonal test. The oil film spreading and thickness of the tooth surface were calculated with the change in gear speed, fuel injection distance and fuel injection speed. Optimized oil injection lubrication parameters were obtained, and design ideas were provided for the oil injection lubrication analysis of aviation herringbone gears. Findings Under different operating conditions, such as varying the injection speed, gear rotational speed and injection distance, there were differences in the distribution of the lubricating oil film formed on the tooth surface. The thickness of the oil film decreases as the distance from the injection port increases. The thickness of the oil film deposition can be increased by increasing the injection velocity and reducing the gear rotation speed. The injection distance had a relatively small effect on the spreading thickness of the deposited oil film, affecting only the dynamic spreading process of oil film deposition. Furthermore, the simulation results are compared with the analytical calculation results, and finally the experimental verification is carried out. Originality/value Oil spray lubrication characteristics are important for achieving precise gear lubrication designs in the aerospace field. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2023-0250/

Study on the wear performance of 304 stainless steel aerospace joint bearings

In order to investigate the influence of surface micro-texture on the oil film carrying capacity, a theoretical model of dynamic pressure lubrication is constructed based on CFD, and dynamic pressure lubrication simulation and friction and wear experimental research are used to analyse the influence of speed and load on the friction behaviour of the bearing pair, and the wear performance of the specimen is evaluated by means of the surface morphology and friction coefficient. The results show that the carrying capacity of the oil film on the textured surface is relatively large compared with that of the non-textured surface, showing regular fluctuations, and that the pressure values of turbulent flow are greater than those of laminar flow. As the rotational speed increases, the cavitation effect becomes more and more obvious, and the carrying capacity of the oil film increases. The smaller the thickness of the surface oil film, the higher the load carrying capacity and the lower the degree of wear; The surfaces of the textured specimens showed the best friction reduction and anti-wear properties, followed by the smooth surfaces and the worst rough surfaces. With the increase of rotational speed, the friction coefficient tends to decrease. When the rotational speed is 0.4 m s−1, the wear of the textured surface is reduced. With the increase of load, the thickness of the formed oil film decreases, the friction coefficient decreases, and the anti-friction effect of the textured surface increases. This indicates that the surface texure treatment of 304 stainless steel, and the selection of appropriate working condition parameters can effectively reduce wear during the friction process, and improve the wear resistance of bearings.

Addressing thermal challenges in hydrodynamic bearings: A contemporary review of strategies and technologies

Hydrodynamic bearings are integral components in various industrial sectors, including aerospace, defense technologies, and power generation units etc. Advancements in modern technology have driven the evolution of bearings to withstand the high temperatures, increased speeds, and additional load demands of contemporary operations. Some of the prime consequences of high temperatures include thermal deformation, misalignment, viscosity degradation, reduced oil film thickness, reduced load carrying capacity and premature failure due to bearing seizure. Researchers have rigorously addressed the persistent thermal challenges posed to hydrodynamic bearings, achieving significant advancements over the years. Key developments include innovative bearing pad designs, optimal materials, coating technologies, advanced computational software, novel lubrication methods, and efficient monitoring techniques. The introduction of materials with tailored properties such as high heat conductivity, high strength, and low-friction coatings has greatly enhanced bearing performance. Additionally, advanced computational software like ANSYS CFX, Fluent, and COMSOL, adaptive lubrication methods, and real-time temperature sensors have significantly improved the performance of critical systems, including hydro power plants. This review paper summarizes significant developments and investigations carried out to mitigate thermal effects in hydrodynamic bearings, and hence provides a comprehensive in depth details of the subject matter. Even though there has been a lot of progress in the field of hydrodynamic bearings, continuous research is important to tackle issues related to sustainability, industry-specific obstacles, developing technologies, and dynamic operating conditions.

A study on the temperature rise characteristics of high-speed ball bearings under starvation lubrication

Purpose This paper aims to study the problem of starvation lubrication of high-speed ball bearings due to temperature rise during operation and to avoid thermal failure of bearing lubrication. Design/methodology/approach Under the quasi-statics model of grease lubrication, both the oil film dragging force and the rolling friction between the balls and raceways collectively counteract the gyroscopic torque. Initially, the static model for grease lubrication is solved, followed by calculating the generated heat using the local heat generation method and ultimately the multinodal thermal network model is solved, and the solved results of the quasi-statics are updated by the temperatures of the grease nodes based on the relationship of the grease temperature and viscosity, as well as the relationship of the viscosity and the film thickness. Findings By comparing the numerical calculation results of bearings under different working conditions, the influence of starvation lubrication on the oil film thickness, oil film drag force and rolling friction of bearings is discussed, and it is found that the numerical calculation results of the outer ring temperature of bearings under the starvation lubrication due to the consideration of temperature rise are closer to the experimental values. Originality/value This study reveals the dynamic characteristics of bearings under starvation lubrication, which is more practical and engineering guiding significance for the design of bearings, and introduces a new method and basis for the calculation of temperature rise of rolling bearings. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2024-0208/

Can Microcavitated Slippery Surfaces Outperform Micropillared and Untextured?

Surface features' morphology is crucial in designing lubricant-infused slippery surfaces (LIS). Microcavities were hypothesized to provide lower physical pinning, reduced droplet normal adhesion, and superior lubricant retention as compared to micropillars and untextured surfaces. Micropillars and microcavities (h = 10 ± 3 μm, d = 8 ± 1 μm, p = 17 ± 3 μm, rw = 1.4 ± 0.2) were replicated on polydimethylsiloxane from Lotus leaf and were coated with 1000 cSt silicone oil films (530 nm-27 μm thick). Water wetting, water-oil thermodynamic stability, droplet's normal adhesion and oil shear drainage properties were investigated to evaluate the relative performance of microcavitated, micropillared and untextured LIS. For ≤7 μm thick oil films, cavitated and untextured LIS displayed superior slippery properties than micropillared LIS (16 ± 1°, 7 ± 1°, 30 ± 4° slide-off angles respectively). Also, normal adhesion is of the order: cavities < untextured < pillars, and smaller than their dry counterparts. Furthermore, the oil retention efficiency under the action of centrifugal forces and continuous shear flow of water is of the order: pillars > cavities > untextured. Thus, it can be concluded that microcavitated LIS can outperform micropillared and untextured LIS.

Application Study of Acoustic Reflectivity Based on Phased Array Ultrasonics in Evaluating Lubricating Oil Film Thickness

Bearings play a key role in rolling mills, and the uniformity of their lubricant film directly affects the degree of wear of bearings and the safety of equipment. Due to long-term stress, the lubricant film inside the bearing is not uniformly distributed, resulting in uneven wear between the journal and the shaft tile, which increases the potential safety hazards in production. Traditional disassembly inspection methods are complex and time-consuming. Ultrasonic nondestructive testing technology, which has the advantages of nondestructive and adaptable, has become an effective means of assessing the thickness of the oil film in bearings. In this study, an experimental platform for calibrating the lubricant film thickness in bearings was constructed for the first time, and the acoustic characteristics of different thicknesses of the oil film were measured using ultrasonic detection equipment to verify the accuracy of the simulation process. The experimental results show that after discrete Fourier transform processing, the main features of the frequency channels of the reflected acoustic signals of different thicknesses of the oil film are consistent with the finite element simulation results, and the errors of the oil film thicknesses calculated from the reflection coefficients are within 10% of the set thicknesses, and the measurement ranges cover from 5 μm to 250 μm. Therefore, the above method can realize the accurate measurement of the thicknesses of the oil film in bearings.

Thermal–Elastohydrodynamic Lubrication Characteristics of the Flow Distribution Pair of Balanced Double-Row Axial Piston Pumps

A theoretical model for the calculation of thermal elastohydrodynamic lubrication performance of the flow distribution pair of piston pumps is established, which is composed of the oil film pressure governing equation and energy equation, and solved by means of numerical solution and simulation. We carry out quantitative analysis of the influence of various parameters on the thermal elastohydrodynamic lubrication characteristics of the flow distribution pair. The results indicate that both the oil film thickness and the cylinder tilt angle of the flow distribution pair vary in a periodic manner. The increase in the rotational speed of the cylinder block will increase the film thickness of the oil film and reduce the fluctuation, and the inclination angle of the cylinder block and its fluctuation amplitude will decrease. An increase in working pressure will lead to a decrease in the average oil film thickness, an increase in fluctuations, and an elevation in both the tilt angle of the cylinder block and its fluctuation amplitude. The increase in the rotational speed of the cylinder block and the increase in the working pressure will lead to the increase in the viscous friction dissipation of the flow distribution pair, the increase in the oil film temperature and the increase in the leakage. The reduction in the sealing belt will lead to the reduction in oil film friction torque and leakage.

High-accuracy ultrasonic measurement of oil film thickness in sliding bearings considering surface thin coating

Focusing on the difficulty and inaccuracy of separating reflected waves from overlapping echoes caused by coating when measuring the oil film thickness of coated sliding bearings using ultrasonic. This paper proposes a pseudo reflection coefficient (PRC) constructed using the overall reflected wave and reference wave. And a robust PRC model is constructed to simultaneously calculate the oil film and coating thickness. Acoustic simulations verify the accuracy of the method and reveal that the PRC model has better stability. Application experiments are conducted on an actual aviation fuel gear pump. The good consistency between theory and experiment has demonstrated the effectiveness of the method. In addition, the elastic deformation of the bearing is derived based on the minimum oil film thickness.

An Optimization Approach for Enhancing Energy Efficiency, Reducing CO2 Emission, and Improving Lubrication Reliability in Roller Bearings using ABC Algorithm

Friction and energy waste pose significant challenges in various industrial processes. Lubrication plays a crucial role in reducing friction and optimizing energy consumption. This study focuses on analyzing, simulating and calculation the oil film thickness, friction levels, energy losses, and CO2 emissions. The objective is to optimize lubrication conditions to enhance performance, improve energy consumption, and maximize lubrication efficiency for rolling bearings in a centrifugal fan. The simulation utilizes ANSYS CFX software, MATLAB programming. The optimal oil viscosity grade is determined based on two objectives by using artificial bee colony algorithm (ABC): minimizing energy consumption (thus reducing CO2 emission) and achieving the optimal oil film thickness and viscosity ratio. The findings reveal that, under the current lubrication conditions and normal fan operation, energy losses due to oil friction amount to 36.3 MWh per year, with CO2 emissions resulting from power losses reaching 18,750 kilograms per year. By transitioning to the optimized oil grade, energy savings of 1.08 MWh per year and a corresponding reduction of 557 kilograms in CO2 emissions per year can be achieved.

A simultaneous ultrasonic measurement method for lubrication film thickness and coating wear depth with thermal effect

Lubrication film thickness and coating wear depth are two important parameters indicating tribological condition in tribological elements. In this paper, a new ultrasonic model was proposed to measure the lubricant film thickness and the coating wear depth simultaneously. A ratio coefficient, which was constructed by dividing the echo signal reflected from the oil film layer to that reflected from the pad-coating interface, was established, and the amplitude and phase of this ratio coefficient were used to measure the film thickness and wear depth, respectively. A pre-calibration test was conducted to help eliminate the effect of the temperature and a dynamic calibration test rig was built to construct series known oil film thickness and wear depth under various temperature. The calibration tests demonstrated that the proposed ultrasonic method could measure the lubricant film thickness and coating wear depth simultaneously under varying temperature. This paper can provide an effective means to observe the evolution characteristics between lubrication and wear.

Partial abrasion modeling and variable load characteristics analysis for high-speed load sensing electro-hydrostatic actuator pump of aircraft

The load-sensing electro-hydrostatic actuator (LS-EHA) allows to reduce the thermal output and enhance the dynamic characteristics of the more electric aircraft (MEA). In addition, the forecasting of the LS-EHA is crucial for its efficient functioning. This study proposes a novel model for the analysis of overturning and wear characterization of the slipper, while focusing on the partial abrasion. The transient thermoelastic hydrodynamic (TEHD) lubricating analysis of the slipper pair is solved by an analytical model along with the finite difference method. In the proposed partial abrasion model, the non-uniformity of the oil film thickness and the partial abrasion contour for the slipper bottom surface are considered through the discrete friction area approach in order to reach a higher precision. Afterward, the overturning behavior characteristics of the slipper and the variation law in its overturning behavior under different rotation speeds, load delivery pressures, and swashplate angles are analyzed. The obtained results demonstrate that the lubricating oil film field is unevenly distributed, and the overturning behavior of the slipper has certain variable load characteristics. Finally, the effectiveness and precision of the proposed partial abrasion model are validated through comparative simulation experiments and analysis.

Experimental Performance Evaluation of a Lightweight Additively Manufactured Hydrodynamic Thrust Bearing

In this paper, a lightweight additively manufactured (AM) fixed geometry hydrodynamic thrust bearing fabricated via laser powder bed fusion (LPBF) is experimentally compared to a traditionally manufactured cast aluminum alloy thrust bearing of similar design. The purpose of this study is to evaluate how weight-saving design features in the AM bearing affect active critical hydrodynamic performance parameters to better understand in-service viability. Under various static operating conditions, performance parameters such as hydrodynamic pressure distribution, minimum oil film thickness (MOFT), bearing temperature and increase in oil temperature are measured. Compared to the traditionally manufactured bearing, the AM bearing showed an average increase in minimum oil film thickness of 53%, an average increase in trailing edge hydrodynamic pressure of 116%, while exhibiting an average decrease in bearing temperature of 1%. Experimental results are compared to numerical simulation showing reasonably good agreement.

Measurement of slip length and friction reduction: An experimental study about boundary slip using omniphobic and 2D coatings

There is an intrinsic link between boundary slip and superlubricity. However, due to limitations in experimental techniques, the slip length cannot be precisely measured, leaving the mechanism of boundary slip controversial. This paper aims to accurately measure the slip length at the solid-liquid interface under oil-lubricated elastohydrodynamic lubrication (EHL) conditions using experimental methods, and to explore the friction reduction due to boundary slip. The study reveals that both omniphobic (lotus leaf essence) coatings and two-dimensional (2D) material (MoS2) coatings facilitate boundary slip. The slip length measurement method proposed in this study builds a bridge between oil film thickness and slip length, successfully addressing a key issue in boundary slip research. The findings confirm the significant friction reduction due to boundary slip, representing a major advancement in reducing friction in oil-lubricated EHL contacts through boundary slip. Future research should focus on searching for coating materials with a slip length on the micrometer scale so that superlubricity could be achieved.

A novel time-varying mesh stiffness model for orthogonal face gear drives considering EHL

PurposeThis study aims to research the time-varying mesh stiffness (TVMS) model for orthogonal face gear drives considering elastohydrodynamic lubrication (EHL) and provide a theoretical basis for understanding the dynamic characteristics of face gear drives.Design/methodology/approachConsidering EHL, a novel model is proposed to calculate the TVMS of orthogonal face gears using the deformation compatibility condition. First, the tooth surface equations of orthogonal face gears are derived according to the tooth surface generation principle. Then, the oil film thickness on the tooth surface of face gears is obtained by solving the governing equations of EHL. Furthermore, the proposed model is used to calculate the TVMS of face gears along the mesh cycle and is verified. Finally, the effects of module, tooth number of shaper cutter and pressure angle on mesh stiffness are analyzed.FindingsThe results indicate that when the contact ratio is greater than 1 and less than or equal to 2, the TVMS of face gears exhibits a phenomenon of double-single tooth alternating meshing where sudden changes occur. As the module increases, the overall mesh stiffness of face gears increases, and the magnitude of the sudden change at the moment of single-double tooth alternating meshing gradually increases. As the tooth number of shaper cutter and pressure angle increase, so does the TVMS of face gears. When the effect of oil film is considered, the calculated TVMS of face gears slightly increases overall and the increase in average oil film thickness leads to a rise in the TVMS. This study provides a theoretical basis for understanding the dynamic characteristics of face gear drives.Originality/valueThis study’s originality and value lie in its comprehensive approach, which includes conducting analysis based on loaded tooth contact, considering the influence of elastohydrodynamic lubrication, proposing a novel analytical–finite–element model, calculating TVMS of face gears, verifying the proposed model and analyzing the effects of typical structural parameters and oil film thickness.

Bi-level optimization and integrated multiple-criteria decision making under uncertainty for structural design of insulated bearings

To address the premature failure of insulated bearings, this article proposes a design method for the structure of bearings to prolong their service life. First, a bi-level optimization model is established to determine the structural parameters of bearings considering their insulating and mechanical properties. Upper-level problems include bearing voltage ratio, porosity of insulating coatings, minimum thickness of oil film and Hertz contact area. Lower-level problems include fatigue life of bearings and adhesion of insulating coatings. Second, a non-dominated sorting genetic algorithm-III based on space decomposition and penalty-based boundary intersection (NSGA-III-SD-PBI) is designed to solve the optimization model. Third, the integrated multiple-criteria decision-making (MCDM) using the fuzzy best–worst method (BWM) and fuzzy technique for order preference by similarity to an ideal solution (TOPSIS) is developed to determine the best structural parameters of bearings. A case study demonstrates the effectiveness and superiority of the proposed method, with fatigue life increased by 20%.

Full-size experimental investigations on planetary gear journal bearings in high-power wind turbines

Abstract To satisfy the large-scale and high-power demands of wind turbines, planetary gear journal bearings (PGJBs) have been applied in large wind turbine gearboxes (WTGs), as an alternative to traditional rolling bearings, due to their higher reliability and smaller size. To simulate the actual lubrication behaviors of PGJBs and investigate their hydrodynamic performance, a full-size test rig for PGJBs was built in this paper. A multi-parameter detection system coupled with the ultrasonic testing method was developed. Four ultrasonic piezoelectric elements, eight thermistors, two pressure transducers, and one torque sensor were used to obtain the film thickness, oil temperature, oil pressure, and friction torque data of the test PGJB. The rated condition experiment was conducted to investigate the variation of measured lubrication performance with the operating time. Three-dimensional predictions of oil film pressure, temperature, and thickness were presented to analyze the steady-state lubrication characteristic at the rated condition. Moreover, a series of steady-state experiments were also carried out to simulate the normal operations of the test PGJB at different conditions. And the measured results were verified by the numerical predictions. The influence of rotational speed, input load, oil supply temperature, and oil supply flow on the hydrodynamic performance of the test PGJB were explored.

Analysis and Prospects of Lubrication and Friction Characteristics in Cold Strip Rolling: A Review

Lubrication and friction are the core processes in cold strip rolling, which are the key links to realizing the stable production of high‐quality strips, reflecting country advanced level in rolling technology. This review investigates the crucial properties of lubrication and friction in cold strip rolling by analyzing the mechanism, characterization methods, and influencing factors. The lubricant forms an oil film on the surface of rolls and strips based on the lubrication dynamics and tribology theory, changing the asperity contact state in the loaded roll gap, leading to changes in friction characteristics. Oil film thickness and coefficient of friction (COF) are crucial parameters for characterizing and judging the characteristics of lubrication and friction, theoretical calculations have become the core analytical method, and the study of the measurement method is still a great challenge. Parameters like rolling speed and oil viscosity affect the lubricant distribution and asperity contact in the loaded roll gap, changing the lubrication and friction state. The influence of parameters is strongly linked to the experimental or rolling environment. Prospective research trends on lubrication and friction in cold strip rolling are presented based on the status of research on lubrication and friction characterization.

Study on the wear characteristics of cylindrical needle bearings on the crankshaft of RV decelerator

PurposeThe purpose of this study is to systematically analyze the wear of cylindrical needle bearings in rotary vector reducers under temperature rise and identify the influencing factors.Design/methodology/approachBased on the dynamic characteristics of the RV-20E reducer, the time-varying contact force of the cylindrical needle bearing and the entrainment speed of the inner and outer raceways were calculated. A mixed elastohydrodynamic lubrication model of the needle bearing, considering friction and temperature rise, was established using a dynamic rough tooth surface model. The model solved for the oil film thickness, contact stress and wear conditions of the bearing raceway contact area. The effects of the number of rolling needles, the diameter of rolling needles and surface strength on the wear characteristics were analyzed.FindingsThe results of this study show that the oil film thickness, oil film pressure and surface scratches of cylindrical needle bearings exhibit an uneven, patchy distribution under the combined effects of friction and temperature rise. When the radius of the rolling needle is less than 1.44 mm, inner ring wear is less than outer ring wear. Conversely, when the radius exceeds 1.44 mm, inner ring wear is greater. The optimal rolling needle radius is 1.6 mm. Increasing the number of rolling needles and enhancing the yield strength of the contact surface significantly extend bearing life.Originality/valueThis study provides valuable recommendations for optimizing bearing structural parameters and material characteristics in the design of rotary vector reducers.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2024-0242/

The mechanism of small wear particles entrainment in friction under boundary lubrication

When the lubricating oil flowing between the contact surfaces contains simulated wear particles, it is considered that there is a high possibility for the particles to enter between the contact surfaces if the particles are present on the disk side in a friction test between a fixed ball and a rotating disk. For particles with a diameter of 0.8 μm, it has been previously shown that the entrainment frequency changes with the outside oil film thickness, but the effect of the disk material on the amount of particle deposition and the visualization of particle movement direction due to vortices generated between the contact surfaces had not been performed. In this study, by using SiO2 disks and sapphire disks with different Hamaker constants, the effect on the amount of particle deposition in front of the contact surfaces was experimentally clarified by changing the van der Waals forces acting between the particles and the disks. Additionally, assuming that vortices generated in the oil film between the contact surfaces move the particles to the disk surface side, the flow direction of the lubricating oil was visualized using Navier-Stokes simulation.