Lubricants

22 pages, 3343 KiB

Open AccessReview

Physiochemical Processes to Reduce Friction and Wear Under Selective Transfer Conditions—A Review

by Filip Ilie, Constantin-Daniel Cotici and Alina Juganaru

Lubricants 2025, 13(3), 135; https://doi.org/10.3390/lubricants13030135 - 20 Mar 2025

Viewed by 247

A selective transfer is realized safely if the material pair and the lubricant are adequate, in the presence of a relative motion and an energy favoring the transfer. The paper highlights the mechanism of achieving the selective transfer phenomenon and analyzes the physiochemical [...] Read more.

A selective transfer is realized safely if the material pair and the lubricant are adequate, in the presence of a relative motion and an energy favoring the transfer. The paper highlights the mechanism of achieving the selective transfer phenomenon and analyzes the physiochemical aspects that take place in a suitably lubricated friction pair (here, bronze/steel lubricated with glycerin) that favor friction by reducing the friction force and implicitly reducing the wear in the selective transfer conditions. In addition, the paper seeks to highlight the effect that the servowitte layer (film) that appears on the friction pair surfaces following the selective dissolution of the superficial layer in the contact area has on the factors that influence the friction and wear process through the implications on the friction coefficient and the wear itself. Full article

(This article belongs to the Special Issue Tribology of Nanocomposites 2024)

► Show Figures

Figure 1

18 pages, 3912 KiB

Open AccessArticle

Research on the Static Thermal Degradation Law of Lubricating Grease for Wind Power Bearings

by Heng Tian, Yan Liu, Yuqing Fan, Gaofeng Wang and Zhiwei Wang

Lubricants 2025, 13(3), 134; https://doi.org/10.3390/lubricants13030134 - 20 Mar 2025

Viewed by 262

Abstract

This research addresses the issue of lubricant performance degradation in the main shaft bearings of wind turbines. Through multi-temperature accelerated aging tests, the static thermal degradation patterns were elucidated, and an aging model was developed. Initially, 176 samples were prepared at temperatures of [...] Read more.

This research addresses the issue of lubricant performance degradation in the main shaft bearings of wind turbines. Through multi-temperature accelerated aging tests, the static thermal degradation patterns were elucidated, and an aging model was developed. Initially, 176 samples were prepared at temperatures of 80 °C, 100 °C, 120 °C, and 140 °C using the static thermal degradation method, with 44 samples at each temperature point. Subsequently, key parameters such as the quality change rate, penetration, oil separation rate, and evaporation amount of the lubricant were systematically measured. Ultimately, the mathematical aging model of the lubricant was derived by fitting the aging kinetics model. The results indicate that as aging time and temperature increase, the degradation characteristics of the lubricant, such as quality change rate, penetration, oil separation rate, and evaporation amount, exhibit discernible patterns. The mathematical aging model was successfully fitted, with the maximum deviation generally within 20% of the error margin, meeting the established criteria. This research provides a theoretical foundation for the establishment of a lubricant condition monitoring system in wind farms. Predicting the performance inflection point of the lubricant can effectively prevent unplanned bearing shutdowns resulting from lubrication failures, thereby offering significant engineering value in enhancing the operational reliability of wind turbine units. Full article

► Show Figures

Figure 1

14 pages, 4011 KiB

Open AccessArticle

Experimental Analysis of a Turbocharger: Influence of Oil Supply Temperature and Pressure on the Bifurcation Phenomenon in Subsynchronous Frequencies

by Márk Pesthy, Máté Boros and Csaba Tóth-Nagy

Lubricants 2025, 13(3), 133; https://doi.org/10.3390/lubricants13030133 - 19 Mar 2025

Viewed by 211

Abstract

This study presents an experimental analysis of a turbocharger equipped with a semi-floating bearing system, with a particular focus on the bifurcation phenomenon within the subsynchronous vibration spectrum. A predefined design of experiments (DoE) methodology was employed to determine the measurement domains to [...] Read more.

This study presents an experimental analysis of a turbocharger equipped with a semi-floating bearing system, with a particular focus on the bifurcation phenomenon within the subsynchronous vibration spectrum. A predefined design of experiments (DoE) methodology was employed to determine the measurement domains to be analyzed, where the primary input parameters included the lubricant supply temperature and pressure values. The bifurcation phenomenon in relation to the physical parameters of the system is observed via vibration and displacement sensors in two directions, enabling the collection of subsynchronous frequency data for further insights into the influence of lubricant parameters on the rotor system. While the nonlinear effect of oil temperature is well studied in the literature. However, the combined effect of oil supply temperature and pressure was not yet examined, which was the focus of the present study. This paper aims to investigate its coupled effects on the bifurcation phenomenon associated with both lubricant temperature and pressure. The occurrence of the introduced phenomenon is further examined to enhance the understanding of the uncharted behavior of turbocharger rotors and other rotor-bearing-based machinery. Full article

(This article belongs to the Special Issue Friction–Vibration Interactions)

► Show Figures

Figure 1

14 pages, 5760 KiB

Open AccessArticle

Effect of Nozzle Geometry on Erosion Characteristics in Abrasive Water Jet: Experimental and Numerical Analysis

by Xuhong Chen, Haihong Pan and Lin Chen

Lubricants 2025, 13(3), 132; https://doi.org/10.3390/lubricants13030132 - 19 Mar 2025

Viewed by 271

Abstract

In the field of abrasive-water-jet polishing technology, the influence of nozzle geometry on nozzle wear and internal-structure erosion in abrasive-water-jet polishing technology is studied, and the nozzle design is optimized through experiments and a numerical simulation to improve the stability and efficiency of [...] Read more.

In the field of abrasive-water-jet polishing technology, the influence of nozzle geometry on nozzle wear and internal-structure erosion in abrasive-water-jet polishing technology is studied, and the nozzle design is optimized through experiments and a numerical simulation to improve the stability and efficiency of the abrasive jet. The mathematical model between the cross-sectional area of the nozzle and the dimensionless length of the nozzle is established, as well as the variation in the static pressure of the nozzle and the length of the nozzle. Through Fluent simulation, it is found that when the nozzle length is 12 mm, the abrasive-phase acceleration is sufficient and the erosion intensity is minimal. After 480 h of erosion experiments, the erosion profile of nozzle cavity was detected. The results show that the erosion strength of the 12 mm nozzle is the least, followed by the 6 mm nozzle, and the 18 mm nozzle is the strongest, which is consistent with the simulation results. Full article

► Show Figures

Figure 1

14 pages, 2323 KiB

Open AccessArticle

Effects of Gait Patterns on the Viscoelastic Squeeze-Film Lubrication of Hip Replacements

by Xianjiu Lu, Manyu Liang, Qingen Meng and Zhongmin Jin

Lubricants 2025, 13(3), 131; https://doi.org/10.3390/lubricants13030131 - 18 Mar 2025

Viewed by 236

Abstract

The present study investigated the influence of various gait patterns on the viscoelastic squeeze-film lubrication characteristics of UHMWPE-based artificial hip replacements. Different gait loads (slow walking, normal walking, slow running) measured by Bergmann et al. were adopted in the present lubrication simulation. A [...] Read more.

The present study investigated the influence of various gait patterns on the viscoelastic squeeze-film lubrication characteristics of UHMWPE-based artificial hip replacements. Different gait loads (slow walking, normal walking, slow running) measured by Bergmann et al. were adopted in the present lubrication simulation. A comprehensive squeeze-film lubrication model for UHMWPE hip replacement was developed and numerically solved to determine the spatial distributions of film thickness and pressure profiles. The results showed that physiological loads had a negligible impact on the minimum film thicknesses during the stand phases. However, they significantly enhanced the minimum film thicknesses in both the elastic (1.16–1.31 times) and viscoelastic models (1.43–2.85 times) during the swing phases when compared to constant loads. This improvement was notably more pronounced in the viscoelastic model than in the elastic model. The slow-running gait, characterized by its higher frequency, demonstrated a more pronounced enhancement in squeeze-film lubrication of UHMWPE artificial hip joints compared to both normal-walking and slow-walking gaits. Specifically, the minimum film thicknesses during slow running were found to be 1.15 to 1.35 times greater than those observed during normal walking and 1.33 to 1.66 times greater than those during slow walking, highlighting the superior lubrication performance in the slow running case. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

► Show Figures

Figure 1

32 pages, 14630 KiB

Open AccessArticle

Wear Prediction and Chaos Identification of Rigid Flexible Coupling Multi-Link Mechanisms with Clearance

by Yonghao Jia, Kai Meng, Shuai Jiang and Jing Kang

Lubricants 2025, 13(3), 130; https://doi.org/10.3390/lubricants13030130 - 18 Mar 2025

Viewed by 356

Abstract

Traditional revolute clearance joints assume that the shape of the contact surface of the joint is regular and ignores the effects of wear, which reduces the prediction accuracy of dynamics models. To accurately describe the collision behavior of the motion pair, an Archard [...] Read more.

Traditional revolute clearance joints assume that the shape of the contact surface of the joint is regular and ignores the effects of wear, which reduces the prediction accuracy of dynamics models. To accurately describe the collision behavior of the motion pair, an Archard formula was applied to construct a wear clearance model. Based on the absolute node coordinate method, multi-body dynamics modeling, wear prediction, and chaotic identification analysis methods for a flexible multi-link mechanism with clearance considering wear effects were proposed. The research results indicate that wear exacerbates the irregularity of the clearance surface contours, leading to increased instability in the dynamic response and the reduced motion accuracy of the mechanism. Compared with clearance size, driving speed has a more significant impact on the chaotic behavior of the system. For high-speed conditions, maintaining the clearance size within approximately 0.1 mm is beneficial for system stability, although this requirement poses challenges for cost control in manufacturing. This study provides a theoretical foundation for wear prediction and stability optimization of high-precision multi-link mechanisms. Full article

► Show Figures

Figure 1

17 pages, 16553 KiB

Open AccessArticle

Analysis and Experimental Study of Contact Stress in Bolted Connections of Pitch Bearings

by Jiuju Zhang, Wanxin Luo, Tao Chen, Xichao Yan, Jiaqi Zhang, Meng Zhu and Hongwei Zhang

Lubricants 2025, 13(3), 129; https://doi.org/10.3390/lubricants13030129 - 17 Mar 2025

Viewed by 319

Abstract

In wind turbine systems, bolted connections in pitch bearings are subjected to working loads that reduce bolt preload. This reduction can lead to issues such as bolt loosening and eccentric loading, which in turn results in the nonuniform distribution of contact stress across [...] Read more.

In wind turbine systems, bolted connections in pitch bearings are subjected to working loads that reduce bolt preload. This reduction can lead to issues such as bolt loosening and eccentric loading, which in turn results in the nonuniform distribution of contact stress across joint surfaces. These issues can compromise structural integrity and reduce fatigue life. However, the study of contact stress mainly focuses on theoretical research, lacking relatively large, complex structures. Also, the stress testing methods for contact surfaces of bolted connections are limited in practical engineering. In this paper, a localized bolt connection model using the finite element method according to pitch bearings in wind turbine systems was established. The contact stress distribution patterns of bolt specimens under varying preloads were investigated. Comparative numerical simulation and experimental analysis using thin-film pressure sensors were conducted. Furthermore, the effect of bolt assembly in different tightening processes on the contours of contact stress was analyzed to identify the optimal tightening sequence. The experimental results demonstrate a positive correlation between preload and maximum contact stress, with stress distribution exhibiting symmetry around the bolt hole and decreasing radially outward. Thin-film pressure sensors can be used for contact stress detection. Furthermore, the diagonal tightening method can achieve a more uniform contact stress distribution compared to other methods, such as sequential and alternate tightening. The findings provide valuable insights for optimizing the contact stress distribution and tightening processes in bolted joint assemblies. Full article

► Show Figures

Figure 1

12 pages, 1776 KiB

Open AccessArticle

Experimental Investigation of the Characteristics and Tribological Effectiveness of Pongamia pinnata Lubricant Oil Blended with Nanoadditives

by S. Nithya Poornima and V. Shantha

Lubricants 2025, 13(3), 128; https://doi.org/10.3390/lubricants13030128 - 17 Mar 2025

Cited by 1 | Viewed by 318

Abstract

The amalgamation of nanomaterials with bio-lubricants presents a promising approach to enhance the performance and efficiency of mechanical systems. To address the overuse of conventional lubricants, a viable strategy involves harnessing the potential of naturally available lubricants to operate effectively under extreme operating [...] Read more.

The amalgamation of nanomaterials with bio-lubricants presents a promising approach to enhance the performance and efficiency of mechanical systems. To address the overuse of conventional lubricants, a viable strategy involves harnessing the potential of naturally available lubricants to operate effectively under extreme operating conditions, such as high loads and high-temperature and high-friction environments. The incorporation of nanomaterials, with their high surface area, extended thermal conductivity, and enhanced load-carrying capacity, offers an effective means of producing alternatives to traditional lubricants. This study aimed to investigate the impact of incorporating nanomaterials in small percentages of 2%, 4%, and 6% into bio-lubricants to reduce friction and improve their tribological performance. A systematic analysis of the effects of nanomaterials on lubrication parameters, such as shear rate, shear stress, torque, and viscosity, was performed. The experimental results indicate that the incorporation of nanomaterials into bio-lubricants aligns their parameters closely with those of commercial lubricants, suggesting their potential as a viable alternative in the lubricant industry. Full article

(This article belongs to the Special Issue Thermophysical and Tribological Characterization of Additivated Lubricants with Nanoparticles)

► Show Figures

Figure 1

26 pages, 12576 KiB

Open AccessArticle

Rotor Dynamic Characteristics Supported by Multi-Pad Bump Foil Gas Bearings

by Lei Zhao, Hongyang Hu, Changlin Li and Jingquan Zhao

Lubricants 2025, 13(3), 127; https://doi.org/10.3390/lubricants13030127 - 16 Mar 2025

Viewed by 253

Abstract

Bump foil gas bearings (BFGBs) play an important role in high-speed turbomachinery. However, most studies on the dynamic characteristics of BFGBs focus on a one-pad structure composed of a bump foil and a top foil. This paper considers the multi-pad foil structure in [...] Read more.

Bump foil gas bearings (BFGBs) play an important role in high-speed turbomachinery. However, most studies on the dynamic characteristics of BFGBs focus on a one-pad structure composed of a bump foil and a top foil. This paper considers the multi-pad foil structure in BFGBs by developing the finite element model of bump and top foils and introducing nonlinear contact constraints between bearing components. In addition, a transient dynamic model of a rotor and multi-pad bump foil gas bearing (MP-BFGB) system is established through sufficient considerations of coupling effects among rotor, gas film, and foil structures. Nonlinear rotor dynamic responses, including stability and vibration characteristics, are obtained through integrating the transient state variables in the time domain. The results show that the rotor stability can be enhanced by increasing the number of top foil pads, which, however, tends to reduce the bearing load capacity and gas film stiffness. In addition, rotor sub-synchronous vibrations are more prone to appear under greater gas film stiffness. Full article

(This article belongs to the Special Issue Gas Lubricated Bearings)

► Show Figures

Figure 1

19 pages, 6177 KiB

Open AccessArticle

Influence of Engine Oils on Pre-Ignition Tendency in a Hydrogen–Kerosene Dual-Fuel Engine

by Christian Reitmayr, Peter Hofmann and Paul Howarth

Lubricants 2025, 13(3), 126; https://doi.org/10.3390/lubricants13030126 - 16 Mar 2025

Viewed by 418

Abstract

Reducing CO₂ emissions is an increasingly important goal in general aviation. The dual-fuel hydrogen–kerosene combustion process has proven to be a suitable technology for use in small aircraft. This robust and reliable technology significantly reduces CO₂ emissions due to the carbon-free [...] Read more.

Reducing CO₂ emissions is an increasingly important goal in general aviation. The dual-fuel hydrogen–kerosene combustion process has proven to be a suitable technology for use in small aircraft. This robust and reliable technology significantly reduces CO₂ emissions due to the carbon-free combustion of hydrogen during operation, while pure kerosene or sustainable aviation fuel (SAF) can be used in safety-critical situations or in the event of fuel supply issues. Previous studies have demonstrated the potential of this technology in terms of emissions, performance, and efficiency, while also highlighting challenges related to abnormal combustion phenomena, such as knocking and pre-ignition, which limit the maximum achievable hydrogen energy share. However, the causes of such phenomena—especially regarding the role of lubricating oils—have not yet been sufficiently investigated in hydrogen engines, making this a crucial area for further development. In this paper, investigations at the TU Wien, Institute of Powertrain and Automotive Technology, concerning the role of different engine oils in influencing pre-ignition tendencies in a hydrogen–kerosene dual-fuel engine are described. A specialized test procedure was developed to account for the unique combustion characteristics of the dual-fuel process, along with a detailed purge procedure to minimize oil carryover. Multiple engine oils with varying compositions were tested to evaluate their influence on pre-ignition tendencies, with a particular focus on additives containing calcium, magnesium, and molybdenum, known for their roles in detergent and anti-wear properties. Additionally, the study addressed the contribution of particles to pre-ignition occurrences. The results indicate that calcium and magnesium exhibit no notable impact on pre-ignition behavior; however, the addition of molybdenum results in a pronounced reduction in pre-ignition events, which could enable a higher hydrogen energy share and thus decrease CO₂ emissions in the context of hydrogen dual-fuel aviation applications. Full article

► Show Figures

Figure 1

17 pages, 10259 KiB

Open AccessArticle

Tribocorrosion Behavior of Medium-Entropy Super Austenitic Stainless Steel in Acidic Environments

by Chia-Chi Liu, Shih-Yen Huang, Yu-Ren Chu, Tzu-Hsien Yang, Hung-Wei Yen, I-Chung Cheng, Peng-Wei Chu and Yueh-Lien Lee

Lubricants 2025, 13(3), 125; https://doi.org/10.3390/lubricants13030125 - 16 Mar 2025

Viewed by 1054

Abstract

Although extensive studies have examined the tribocorrosion behavior of stainless steels, the performance of medium-entropy austenitic super stainless steels (MEASS) under severe combined corrosion and mechanical wear conditions has not been fully established. This study systematically compares the tribocorrosion behavior of a newly [...] Read more.

Although extensive studies have examined the tribocorrosion behavior of stainless steels, the performance of medium-entropy austenitic super stainless steels (MEASS) under severe combined corrosion and mechanical wear conditions has not been fully established. This study systematically compares the tribocorrosion behavior of a newly developed MEASS with conventional S31254 super austenitic stainless steel (SASS) in a 1 M H₂SO₄ solution, aiming to explore innovative material designs for enhanced performance under these demanding conditions. Electrochemical tests were conducted under both open-circuit potential (OCP) and cathodic potential, with and without sliding wear, to assess the corrosion, wear, and synergistic effects influencing the tribocorrosion performance. Worn surface morphologies and hardness were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and hardness measurements, respectively. The experimental results revealed that MEASS exhibits a superior repassivation capability compared to S31254, with a 34.3% lower total material loss after 24 h of tribocorrosion test, primarily attributed to enhanced strain hardening and improved wear resistance. These findings emphasize the strong potential of MEASS for use in corrosive environments, particularly in chemical processing industries, where high resistance to wear and corrosion is critically required. Full article

(This article belongs to the Special Issue Tribology of Metals and Alloys)

► Show Figures

Figure 1

17 pages, 12733 KiB

Open AccessArticle

Effects of Contact Characteristics on Dynamic Response of Planar Mechanical Systems with Lubricated Revolute Joint

by Xu Peng, Haoran Zhu, Yang Guo, Xuze Wu and Yu Chen

Lubricants 2025, 13(3), 124; https://doi.org/10.3390/lubricants13030124 - 14 Mar 2025

Viewed by 327

Abstract

In this study, a dynamic response model that incorporates lubricated clearance is developed to examine the evolution of contact and friction in a mechanical system. The dynamic model of a lubricated clearance joint is established by considering the contact, friction, and hydrodynamics. The [...] Read more.

In this study, a dynamic response model that incorporates lubricated clearance is developed to examine the evolution of contact and friction in a mechanical system. The dynamic model of a lubricated clearance joint is established by considering the contact, friction, and hydrodynamics. The expression of contact force in normal and tangential directions is developed using elastic contact theory. The lubrication characteristics of a revolute joint are obtained using hydrodynamic theory, which is introduced into the simulation model. This case study is conducted to investigate the effects of design parameters on the dynamic stability of a mechanical system with a lubricated clearance joint. The results elucidate the relationship between lubrication characteristics and vibration response, offering valuable insights for the optimization of mechanical systems. Full article

► Show Figures

Figure 1

23 pages, 6630 KiB

Open AccessArticle

Investigation into the Dynamic Parameter Characterization of Water-Lubricated Bearings Under Vibration Coupling

by Hongtao Zhu, Yong Jin, Qilin Liu, Wu Ouyang and Tao He

Lubricants 2025, 13(3), 123; https://doi.org/10.3390/lubricants13030123 - 14 Mar 2025

Viewed by 308

Abstract

This study aims to investigate the dynamic behavior of water-lubricated stern bearings during service. A transient rotor dynamics numerical model is developed to research the effects of operating conditions and critical structural parameters on the variation patterns of the dynamic characteristic coefficients and [...] Read more.

This study aims to investigate the dynamic behavior of water-lubricated stern bearings during service. A transient rotor dynamics numerical model is developed to research the effects of operating conditions and critical structural parameters on the variation patterns of the dynamic characteristic coefficients and journal orbit of WLBs. The main stiffness and damping formulas for dimensionless bearings are fitted based on numerical results. Additionally, the accuracy of the model calculations is experimentally verified on a water-lubricated bearing test rig. The results demonstrate that the variation trends of the main stiffness and main damping coefficients in the horizontal and vertical directions of the bearings are proportional to the external load and inversely proportional to the rotational speed. Under eccentric excitation, the dynamic characteristic coefficients of the bearings change periodically with time as an approximately sinusoidal function. With the increase in the bearing length-to-diameter ratio or the decrease in the radial clearance-to-radius ratio, the main stiffness and the main damping coefficients in the horizontal direction increase, while the main stiffness coefficient in the vertical direction decreases. This study provides theoretical support for modeling the transient transverse vibration of a propulsion shaft system. Full article

(This article belongs to the Special Issue Friction–Vibration Interactions)

► Show Figures

Figure 1

18 pages, 14556 KiB

Open AccessArticle

Novel Water-Based Biolubricants Using Choline Ionic Liquids

by Paloma Mostaza, María-Dolores Avilés, Pablo M. Martínez-Rubio, María-Dolores Bermúdez and Francisco J. Carrión-Vilches

Lubricants 2025, 13(3), 122; https://doi.org/10.3390/lubricants13030122 - 12 Mar 2025

Viewed by 396

Abstract

Ionic liquid molecules exhibit a variety of properties that are well suited for use as lubricants or additives for lubricants, since they form tribolayers that reduce friction and wear. As additives in the design of new water-based biolubricants, ionic liquids present the advantages [...] Read more.

Ionic liquid molecules exhibit a variety of properties that are well suited for use as lubricants or additives for lubricants, since they form tribolayers that reduce friction and wear. As additives in the design of new water-based biolubricants, ionic liquids present the advantages of polar nature to use in aqueous lubrication, whilst being biocompatible and with null toxicity, opening up the opportunity to develop novel biolubricants. Choline is a cation present in numerous ionic liquids and is widely recognized for its water solubility, biodegradability, low toxicity, and role as a green solvent in different applications. This work presents the comparative studies of several water-based biolubricants and thin-layer films on stainless steel using a low proportion of Choline-based ionic liquids. The results of friction and wear using water-based biolubricants with 1 wt% of different Choline-based ionic liquids showed good tribological performance. In addition, Choline Lysinate, an amino-acid ionic liquid which is biocompatible, nontoxic, and biodegradable, presented excellent performance and was used as a precursor of thin-layer films on stainless steel showing outstanding behavior in pin-on-disc configuration and sapphire/stainless-steel contacts. Subsequent X-ray photoelectron spectroscopy confirmed the presence of a tribolayer containing the amino acid compound on the metallic surface. Full article

(This article belongs to the Special Issue Advances in Ionic Liquids as New Lubricant Materials)

► Show Figures

Graphical abstract

20 pages, 8744 KiB

Open AccessArticle

Influence of Circumferential Convergent Wedge Pocket on the Segmented Annular Seal’s Static and Dynamic Characteristics

by Shuang Wang, Dan Sun, Zemin Yang, Wenfeng Xu and Huan Zhao

Lubricants 2025, 13(3), 121; https://doi.org/10.3390/lubricants13030121 - 12 Mar 2025

Viewed by 366

Abstract

Aiming at the problem of abnormal wear caused by the poor dynamic characteristics of aeroengine segmented annular seals, according to the hydrodynamic lubrication theory, based on the conventional structure featuring the Rayleigh step profile rectangular pocket (RP), novel structures with the circumferential linear [...] Read more.

Aiming at the problem of abnormal wear caused by the poor dynamic characteristics of aeroengine segmented annular seals, according to the hydrodynamic lubrication theory, based on the conventional structure featuring the Rayleigh step profile rectangular pocket (RP), novel structures with the circumferential linear convergent pocket (CLCP) and the circumferential parabolic convergent pocket (CPCP) were proposed. A model was developed to analyze both the static and dynamic characteristics of three types of segmented annular seals, utilizing the local differential quadrature (LDQ) method. Once the accuracy of the solution model was confirmed, the effects of working conditions and design features on both static and dynamic characteristics were analyzed. Results indicate that the circumferential wedge convergent pockets can effectively improve the dynamic characteristics of the seal system. Under different rotational speeds, compared with the RP seal, the CLCP seal’s stiffness coefficient and damping coefficient increases by an average of 60.76% and 65.27%, respectively. As the rotational speed increases, the RP seal damping ratio decreases, and the seal system transitions from an overdamped state to an underdamped state, resulting in reduced stability. Nevertheless, under different rotational speeds and pressure ratios, the CLCP and the CPCP seals are both in an overdamped state. Taking into account the static and dynamic characteristics, the CLCP seal is the optimal structure in this study. Full article

► Show Figures

Figure 1

16 pages, 16986 KiB

Open AccessArticle

Dynamic Analysis of Dual Parallel Spring-Supported Tilting Pad Journal Bearing

by Yingze Jin, Zhicai Wang and Xuefei Zhao

Lubricants 2025, 13(3), 120; https://doi.org/10.3390/lubricants13030120 - 12 Mar 2025

Viewed by 393

Abstract

The elastic-supported tilting pad journal bearing brings new momentum and opportunities for improving the lubrication performance and dynamic stability of high-speed bearing–rotor systems. The objective of this study is to investigate the dynamic and lubrication characteristics of a dual parallel spring-supported tilting pad [...] Read more.

The elastic-supported tilting pad journal bearing brings new momentum and opportunities for improving the lubrication performance and dynamic stability of high-speed bearing–rotor systems. The objective of this study is to investigate the dynamic and lubrication characteristics of a dual parallel spring-supported tilting pad journal bearing (DPSTPJB) system under unbalanced journal excitation. Considering the tilting angle and radial displacement of the pads, a 10-DOF dynamic model of the four-pad DPSTPJB system is established, accounting for the effects of unbalanced load, nonlinear fluid film force, and parallel spring force/moment. Numerical solutions are obtained for the dynamic responses of the journal and pads as well as the minimum film thickness and maximum film pressure. The effects of spring stiffness, stiffness ratio, and included angle on journal vibration, minimum film thickness, and maximum film pressure are revealed. The results show that the parallel spring parameters have a positive effect on the optimization of bearing performance with an optimal stiffness ratio that minimizes journal vibration and optimizes fluid film thickness and pressure. This research provides a theoretical basis for the optimization design and application of the DPSTPJB. Full article

(This article belongs to the Special Issue Friction–Vibration Interactions)

► Show Figures

Figure 1

37 pages, 30036 KiB

Open AccessReview

Lubrication and Drag Reduction for Polymer-Coated Interfaces

by Qiang Yang, Xiang Ben, Jingkai Lin, Yuhao Zhang, Li Xiang, Zhiyong Wei and Yajing Kan

Lubricants 2025, 13(3), 119; https://doi.org/10.3390/lubricants13030119 - 12 Mar 2025

Viewed by 674

Abstract

Lubrication is a well-established strategy for reducing interfacial frictional energy dissipation and preventing surface wear. Various lubricants have been developed, including mineral oil materials, vegetable oil materials, polymer-based materials, and solid lubrication materials. Among these, polymer-based lubrication materials have gained significant interest due [...] Read more.

Lubrication is a well-established strategy for reducing interfacial frictional energy dissipation and preventing surface wear. Various lubricants have been developed, including mineral oil materials, vegetable oil materials, polymer-based materials, and solid lubrication materials. Among these, polymer-based lubrication materials have gained significant interest due to their versatility, leading to the development of tailored strategies to meet diverse application demands. In load-bearing scenarios, polymer-based materials enhance interfacial hydration, exhibiting exceptional frictional properties, including extremely low friction coefficients, high load-bearing capacity, and superior wear resistance. In contrast, in non-load-bearing scenarios, polymer-based coatings improve interfacial hydrophobicity, promoting boundary slip and reducing frictional resistance at the solid–liquid interface (SLI), making them an important strategy for drag reduction. Despite substantial advancements in polymer-based lubrication and drag reduction (PBLDR), the underlying microscopic mechanisms remain incompletely understood. Therefore, this review aims to provide a comprehensive analysis of the fundamental principles governing PBLDR. The main topics covered will include the following: (1) the fundamentals of the surface forces and hydrodynamic force, (2) the mechanisms underlying hydration lubrication, (3) joint lubrication and polymer brush lubrication, (4) the friction tuning and interfacial drag reduction via polymer coating design, and (5) the potential and limitations of polymer-based materials. By summarizing recent advancements in PBLDR, this work will provide valuable contributions to future research and applications in related fields. Full article

(This article belongs to the Special Issue Superlubricity Mechanisms and Applications)

► Show Figures

Figure 1

15 pages, 4820 KiB

Open AccessArticle

Study on the Time-Varying Stiffness Characteristics of Four-Point Contact Ball Bearings

by Runlin Chen, Jiakai Li, Yimo Wang, Rushen Deng, Weihao Chen and Wenhui Li

Lubricants 2025, 13(3), 118; https://doi.org/10.3390/lubricants13030118 - 10 Mar 2025

Viewed by 436

Abstract

This paper takes a four-point contact ball bearing of a wind turbine as the research object, analyzes the force and deformation relationship under the combined action of axial load and radial load, obtains the load distribution of rolling elements, and establishes a time-varying [...] Read more.

This paper takes a four-point contact ball bearing of a wind turbine as the research object, analyzes the force and deformation relationship under the combined action of axial load and radial load, obtains the load distribution of rolling elements, and establishes a time-varying stiffness model of four-point contact ball bearings without clearance. The stiffness variation law of the case bearing in one rolling period is analyzed, and the time-varying characteristics of stiffness are characterized by the average stiffness and stiffness amplitude variation rate. The influence laws of the number of rolling elements, initial contact angle, axial load, and radial load on the time-varying characteristics of bearing stiffness are analyzed. The results show that within one rolling period, the average value of axial stiffness is about 2.21 times that of radial stiffness, and the amplitude variation rates of radial stiffness and axial stiffness are 0.0047% and 0.002%, respectively. The time-varying characteristics of both are not obvious. The influence of the number of rolling elements on the two stiffnesses is almost linear, while the influence of axial load on stiffness is small; the initial contact angle is positively correlated with axial stiffness and negatively correlated with radial stiffness. With the increase in radial load, the two stiffnesses also increase. Finally, the stiffness test of four-point contact ball bearings was carried out, and the error between the test value and the theoretical value was less than 15%, which preliminarily verified the correctness of the stiffness model. Full article

► Show Figures

Figure 1

25 pages, 7169 KiB

Open AccessArticle

Investigate on the Fluid Dynamics and Heat Transfer Behavior in an Automobile Gearbox Based on the LBM-LES Model

by Gaoan Zheng, Pu Xu and Lin Li

Lubricants 2025, 13(3), 117; https://doi.org/10.3390/lubricants13030117 - 10 Mar 2025

Cited by 6 | Viewed by 738

Abstract

With the rapid development of the new energy vehicle market, the demand for efficient, low-noise, low-energy consumption, high-strength, and durable gear transmission systems is continuously increasing. Therefore, it has become imperative to conduct in-depth research into the fluid heat transfer and lubrication dynamics [...] Read more.

With the rapid development of the new energy vehicle market, the demand for efficient, low-noise, low-energy consumption, high-strength, and durable gear transmission systems is continuously increasing. Therefore, it has become imperative to conduct in-depth research into the fluid heat transfer and lubrication dynamics within gearboxes. In gear systems, the interaction between fluids and solids leads to complex nonlinear heat transfer characteristics between gears and lubricants, making the development and resolution of gearbox thermodynamic models highly challenging. This paper proposes a gear lubrication heat transfer dynamics model based on LBM-LES coupling to study the dynamic laws and heat transfer characteristics of the gear lubrication process. The research results indicate that the interaction between gears and the intense shear effects caused by high speeds generate vortices, which are particularly pronounced on larger gears. The fluid mixing effect in these high vortex regions is better, achieving a more uniform heat dissipation effect. Furthermore, the flow characteristics of the lubricant are closely related to speed and temperature. Under high-temperature conditions (such as 100 °C), the diffusion range of the lubricant increases, forming a wider oil film, but its viscosity significantly decreases, leading to greater stirring losses. By optimizing the selection of lubricants and stirring parameters, the efficiency and reliability of the gear transmission system can be further improved, extending its service life. This study provides a comprehensive analytical framework for the thermodynamic characteristics of multi-stage transmission systems, clarifying the heat transfer mechanisms within the gearbox and offering new insights and theoretical foundations for future research and engineering applications in this field. Full article

► Show Figures

Figure 1

24 pages, 35679 KiB

Open AccessArticle

Rolling Bearing Dynamics Simulation Information-Assisted Fault Diagnosis with Multi-Adversarial Domain Transfer Learning

by Zhe Li, Zhidan Zhong, Zhihui Zhang, Wentao Mao and Weiqi Zhang

Lubricants 2025, 13(3), 116; https://doi.org/10.3390/lubricants13030116 - 7 Mar 2025

Viewed by 656

Abstract

To address the issues of negative transfer and reduced stability in transfer learning models for rolling bearing fault diagnosis under variable working conditions, an unsupervised multi-adversarial transfer learning fault diagnosis algorithm based on bearing dynamics simulation data is proposed. Firstly, the algorithm constructs [...] Read more.

To address the issues of negative transfer and reduced stability in transfer learning models for rolling bearing fault diagnosis under variable working conditions, an unsupervised multi-adversarial transfer learning fault diagnosis algorithm based on bearing dynamics simulation data is proposed. Firstly, the algorithm constructs both a global domain classifier and a subdomain classifier. In the subdomain classifier, the simulated vibration signal, which contains rich bearing fault label information, is generated by constructing dynamic equations to replace the label prediction of target domain data, thereby achieving alignment of marginal and conditional distributions. Simultaneously, an improved loss function with embedded maximum mean discrepancy is designed to reduce the feature distribution gap between source and target domain data. Finally, a weight allocation mechanism for source domain and simulation domain samples is developed to promote positive transfer and suppress negative transfer. Experiments were conducted using the Paderborn University dataset and the Huazhong University of Science and Technology dataset, achieving accuracy rates of 89.457% and 96.436%, respectively. The results show that, in comparison with existing unsupervised cross-domain fault diagnosis methods, the proposed method demonstrates significant improvements in diagnostic accuracy and stability, demonstrating its superiority in rolling bearing fault diagnosis under variable operational conditions. Full article

(This article belongs to the Special Issue New Horizons in Machine Learning Applications for Tribology)

► Show Figures

Figure 1

13 pages, 3205 KiB

Open AccessArticle

Heat Generation During Guided Bone Drilling: Bone Trephine Versus Pilot Drill

by Gábor Pintér, Gábor Braunitzer, Eszter Nagy, Kristóf Boa, József Piffkó and Mark Adam Antal

Lubricants 2025, 13(3), 115; https://doi.org/10.3390/lubricants13030115 - 7 Mar 2025

Viewed by 476

Abstract

In the last decade, the use of surgical guides in dentistry has expanded to include endodontic surgery, yet most studies have focused on accuracy rather than potential heat generation. This in vitro study evaluated heat generation during bone drilling with custom-made bone trephines, [...] Read more.

In the last decade, the use of surgical guides in dentistry has expanded to include endodontic surgery, yet most studies have focused on accuracy rather than potential heat generation. This in vitro study evaluated heat generation during bone drilling with custom-made bone trephines, both with and without static surgical guides, and compared the results to those of 2 mm pilot drills. Drilling was performed on porcine rib bone specimens under controlled conditions, with heat generation measured using an infrared thermometer. None of the groups exceeded the critical temperature of 47 °C; although, the guided trephine group recorded the highest peak temperature (7.9 °C above baseline). Significant differences in heat increments were observed among the groups. Post hoc analyses revealed that the guided pilot drill produced significantly lower heat increments compared to the trephine groups, particularly during the penetration of the second cortical layer and at peak temperatures (p < 0.05). The use of a surgical guide did not limit the cooling and lubricating effects of irrigation in the trephine groups. Regression analyses confirmed a strong relationship between drilling time and temperature increase, with guided trephines showing a steeper temperature rise compared to pilot drills. These findings emphasize the importance of proper irrigation, sharp instruments, reduced drilling speeds, and careful technique to minimize heat generation during guided bone drilling procedures. Full article

► Show Figures

Figure 1

19 pages, 9858 KiB

Open AccessArticle

Enhanced Tribological Performance of Melamine Long-Chain Alcohol Esters in High-Temperature Boundary Lubrication

by Jingchun Zhang, Wenjing Hu and Jiusheng Li

Lubricants 2025, 13(3), 114; https://doi.org/10.3390/lubricants13030114 - 6 Mar 2025

Viewed by 465

Abstract

The requirement to improve energy efficiency is constantly driving the development of high-performance and eco-friendly friction modifiers (FMs). Herein, two innovative sulfur- and phosphorus-free melamine long-chain alcohol esters (Dodec-EG-CC and Dodec-CC) are reported as novel organic friction modifiers (OFMs). Over a wide temperature [...] Read more.

The requirement to improve energy efficiency is constantly driving the development of high-performance and eco-friendly friction modifiers (FMs). Herein, two innovative sulfur- and phosphorus-free melamine long-chain alcohol esters (Dodec-EG-CC and Dodec-CC) are reported as novel organic friction modifiers (OFMs). Over a wide temperature range of 100 °C to 200 °C, the synthesized melamine long-chain alcohol esters, which have exceptional thermal stability, dramatically lessen wear and friction of PAO4 base oil. Dodec-EG-CC particularly reduces friction by up to 50% and wear rate by approximately 92% within this temperature range. Detailed studies of the tribological properties at elevated temperatures demonstrate that the synergistic effect of the melamine structural unit coupled with ester groups significantly enhances adsorption properties of additives on metal surfaces, improving adsorption strength and lubricating film stability. The adsorption of additives on the metal surfaces is further confirmed by surface analysis and adsorption energy calculation, which serve as a key parameter for characterizing the binding strength between molecules and surfaces. These findings demonstrate the potential of the designed triazine-based derivatives, especially Dodec-EG-CC, as OFMs in effectively reducing friction losses in motor vehicle engines. This highlights their significant potential for industrial applications in improving energy efficiency and extending engine lifespan. These in-depth studies not only provide valuable insights for the molecular structure design of OFMs, but also advances the development of sustainable lubrication technologies. Full article

(This article belongs to the Special Issue Novel Lubricant Additives in 2025)

► Show Figures

Figure 1

23 pages, 16312 KiB

Open AccessArticle

Comparative Study of Friction Models in High-Speed Machining of Titanium Alloys

by Fan Yi, Ruoxi Zhong, Wenjie Zhu, Run Zhou, Li Guo and Ying Wang

Lubricants 2025, 13(3), 113; https://doi.org/10.3390/lubricants13030113 - 6 Mar 2025

Viewed by 493

Abstract

Friction has a significant impact on chip formation, so modeling it accurately is crucial in numerical cutting simulations. However, there is still controversy regarding the application scope and effectiveness of various friction models. A two-dimensional orthogonal cutting thermomechanical coupled finite element model is [...] Read more.

Friction has a significant impact on chip formation, so modeling it accurately is crucial in numerical cutting simulations. However, there is still controversy regarding the application scope and effectiveness of various friction models. A two-dimensional orthogonal cutting thermomechanical coupled finite element model is established. Critical strain values, recrystallization temperature, and recrystallization flow stress are introduced, and a power-law-modified softening coefficient is used to modify the standard Johnson–Cook constitutive model to simulate material mechanical properties. Zorev’s friction model, velocity-dependent friction model, and temperature-dependent friction model are separately employed to describe the friction behavior between the tool and workpiece. The contact and friction characteristics between the workpiece and tool, material damage, and temperature field are evaluated. Predicted cutting forces are compared and analyzed with experimental values. The friction coefficient can adjust the contact length between the tool and chip, the high-temperature range on the tool surface, and the fluctuation of temperature throughout the entire cutting process. The friction coefficient is more sensitive to sliding velocity, and the temperature distribution is more sensitive to the friction model than to different working conditions. Whether by modifying the friction coefficient or maximum friction shear stress, and regardless of whether adding parameters affected by velocity or temperature changes the fluctuation range, period, and local peaks of the cutting force prediction curve, improving the accuracy of predictions within certain working condition ranges to some extent. However, the overall trend of error fluctuations obtained from these friction models is similar, and the accuracy of predictions from these friction models tends to become more inaccurate with increasing cutting thickness. Full article

► Show Figures

Figure 1

38 pages, 5392 KiB

Open AccessReview

Additive Manufacturing of Advanced Structural Ceramics for Tribological Applications: Principles, Techniques, Microstructure and Properties

by Wei-Jian Miao, Shu-Qi Wang, Zi-Heng Wang, Fan-Bin Wu, Yun-Zhuo Zhang, Jia-Hu Ouyang, Ya-Ming Wang and Yong-Chun Zou

Lubricants 2025, 13(3), 112; https://doi.org/10.3390/lubricants13030112 - 5 Mar 2025

Cited by 2 | Viewed by 1198

Abstract

Additive manufacturing technology has the advantages of precise manufacturing, high levels of customization, and large-scale molding; it can achieve the design of complex geometric structures and structural/functional integrated components, which is difficult to realize using traditional manufacturing technology, especially for different tribological applications. [...] Read more.

Additive manufacturing technology has the advantages of precise manufacturing, high levels of customization, and large-scale molding; it can achieve the design of complex geometric structures and structural/functional integrated components, which is difficult to realize using traditional manufacturing technology, especially for different tribological applications. Ceramic materials are widely used in industries such as high-end manufacturing in aviation, aerospace, energy, and biomedicine due to their excellent wear resistance, high temperature stability, and hardness. The tribological properties of ceramic parts determine their versatility and durability during the application process. The rise of additive manufacturing technology in the field of ceramics has opened up the possibility of creating ceramics with excellent friction and wear properties and overcoming the limitations of traditional manufacturing processes. Although several studies on 3D printing of wear-resistant/self-lubricating metal- or polymer-based parts have been published, there has until now been no comprehensive review of additive manufacturing of advanced structural ceramics and composites for the purpose of reducing friction and enhancing wear-resistant properties. This article discusses the currently used ceramic additive manufacturing technology and processes, the ceramic materials used in the field of tribology, and how the combination of these two can improve the tribological properties of ceramic components from the perspective of micro- and macrostructures. Finally, specific tribological applications of additively manufactured ceramics in various industrial and biomedical fields are also introduced. Full article

► Show Figures

Figure 1

17 pages, 10957 KiB

Open AccessArticle

Effect of Loads on Tribological Performance of Rubber Seals at Floating Wind Power in Deep Sea

by Guibin Tan, Cheng Zhou, Jiantao Liang, Guangjing Huang, Zhixing Wang and Xing Huang

Lubricants 2025, 13(3), 111; https://doi.org/10.3390/lubricants13030111 - 3 Mar 2025

Viewed by 574

Abstract

The main shaft seal of offshore wind power equipment is one of the key components of wind power systems. However, wear issues between the seals and the main shaft caused by the intrusion of particulate matter in the environment have become a key [...] Read more.

The main shaft seal of offshore wind power equipment is one of the key components of wind power systems. However, wear issues between the seals and the main shaft caused by the intrusion of particulate matter in the environment have become a key factor affecting the service life of the equipment. To improve the surface performance of the main shaft, this study used laser cladding technology to prepare an Fe55 coating on the surface of QT-500 components. Through the wear experiments on HNBR seal pairs with the main shaft under different load conditions, this study thoroughly investigated the impact of the coating on frictional coefficients, wear mechanisms, and the wear morphology of metal surfaces. The experimental results show that the average hardness of the Fe55 coating is 533 HV, which is about 2.3 times the hardness of the substrate, and as the loading force increases, the wear form of the QT-500 metal changes from being dominated by pits to being dominated by furrows. In contrast, the wear form of the Fe55 coating is more inclined to furrows, and no pit formation is observed, indicating that the coating has improved the wear resistance of the surface. The frictional coefficient of the HNBR pair with the metal decreases with increasing load, and the frictional coefficient of the coating is lower than that of the substrate. As the loading increases, the wear morphology of the rubber surface transitions from furrows to pits, and the wear mechanism becomes abrasive wear. Full article

(This article belongs to the Special Issue Marine Tribology)

► Show Figures

Figure 1

23 pages, 10156 KiB

Open AccessArticle

An Analytical Model for Aerostatic Thrust Bearings Based on the Average Pressure of the Area Surrounded by Orifice

by Jian Zheng, Jianwei Wu, Huan Liu, Jiyao Wang and Pengyue Zhao

Lubricants 2025, 13(3), 110; https://doi.org/10.3390/lubricants13030110 - 3 Mar 2025

Viewed by 557

Abstract

Aerostatic thrust bearings are widely used in advanced equipment such as lithography machines due to their excellent lubrication performance. In this study, computational fluid dynamics (CFD) was employed for the analysis of errors in the calculation of static characteristics of bearings based on [...] Read more.

Aerostatic thrust bearings are widely used in advanced equipment such as lithography machines due to their excellent lubrication performance. In this study, computational fluid dynamics (CFD) was employed for the analysis of errors in the calculation of static characteristics of bearings based on the pressure behind the orifice. We put forth an analytical model for calculating the static characteristics of bearings utilizing the average pressure (P_dAVE) within the area surrounded by orifice. By analyzing the influence of various structural parameters, film thickness, and gas supply pressure on P_dAVE in aerostatic bearings, we derived an approximate expression for the average pressure coefficient, which was subsequently verified through experiments. The findings demonstrate that the analytical model for aerostatic bearings, formulated using P_dAVE, can accurately predict the static characteristics of the bearings. The working range corresponding to the optimal stiffness of the bearings is entirely consistent, and the prediction error of the bearing capacity within the optimal working range is less than 5%. This provides a more precise and effective performance prediction model for rectangular aerostatic thrust bearings in engineering design. Full article

(This article belongs to the Special Issue Gas Lubricated Bearings)

► Show Figures

Figure 1

13 pages, 3107 KiB

Open AccessArticle

Static Characteristics of a Micro Bidirectional Rotating Thrust Bearing with Novel Herringbone Grooves

by Tianming Ren and Ming Feng

Lubricants 2025, 13(3), 109; https://doi.org/10.3390/lubricants13030109 - 2 Mar 2025

Viewed by 601

Abstract

Bidirectional rotating thrust bearings are critical components for the development of bidirectional equipment. This paper presents the design and numerical study of an oil-lubricated bidirectional rotating thrust bearing with novel herringbone grooves, which consists of three groups of spiral grooves. The lubrication mechanism [...] Read more.

Bidirectional rotating thrust bearings are critical components for the development of bidirectional equipment. This paper presents the design and numerical study of an oil-lubricated bidirectional rotating thrust bearing with novel herringbone grooves, which consists of three groups of spiral grooves. The lubrication mechanism of the novel herringbone grooves is revealed. The static characteristics of the thrust bearing are numerically investigated by solving the Reynolds equation applying the finite element method. The influences of the radial width, depth, angle, circumferential width ratio, and number of the groove on the bearing performance are analyzed. The results show that there exists an optimal combination of groove radial widths that ensures equal load capacities in both rotation directions while achieving their maximum values. Furthermore, optimal values for the depth, angle, circumferential width ratio, number of the grooves can also enhance the bearing’s load capacity, maximum film pressure, and energy efficiency. Additionally, it is found that groove radial width has the most significant influence on the bearing performance difference under different rotation directions, followed by the effects from the angle, number, circumferential width ratio, and depth of the groove. The conclusions obtained can provide a valuable reference for the research and application of bidirectional thrust bearings. Full article

► Show Figures

Figure 1

21 pages, 10268 KiB

Open AccessArticle

Tribological Performance Comparison of Lubricating Greases for Electric Vehicle Bearings

by Deepika Shekhawat, Ayush Jain, Nitesh Vashishtha, Arendra Pal Singh and Rahul Kumar

Lubricants 2025, 13(3), 108; https://doi.org/10.3390/lubricants13030108 - 1 Mar 2025

Viewed by 1164

Abstract

EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage [...] Read more.

EV motors and machine elements operate at higher speeds, generate significant heat and noise (vibration), and subject lubricants (bearings) to multiple degrading factors, requiring thermal stability, wear protection, mitigating wear mechanisms like pitting and scuffing, and low electrical conductivity to prevent arcing damage to bearings. This study evaluates the tribological performance of four types of greases—PUEs, PUPao, PUEth (polyurea-based), and LiPAO (lithium–calcium complex-based)—to determine their suitability for electric motor bearings. Key performance metrics include tribological properties, electrical resistivity, leakage, bearing noise, and wear behavior. A four-ball wear test ranks the greases by scar diameter as PUPao < PUEs < PUEth < LiPAO, while the coefficient of friction is observed in the range of 0.15–0.18, with LiPAO exhibiting the lowest friction. Electrical resistivity tests reveal that PUEs grease has the lowest resistivity. Electrical leakage tests, conducted with a voltage differential across bearings, assess pitting damage, with PUEth and LiPAO showing evidence of surface pitting. Optical microscopy and scanning electron microscopy analysis is carried out to examine the pitting. In bearing noise tests, PUEs demonstrates the lowest noise levels, whereas LiPAO produces the highest. Visual and microscopic examination of the greases further characterizes their lubricating properties. Based on overall performance, the greases are ranked in suitability for electric motor applications as PUEs > PUPao > PUEth > LiPAO. The findings highlight the critical need for selecting appropriate grease formulations to ensure optimal bearing performance under varying operational conditions. Full article

(This article belongs to the Special Issue Tribology of Electric Vehicles)

► Show Figures

Figure 1

25 pages, 17290 KiB

Open AccessArticle

Research on Debris Characteristics and Wear Mechanism of Gear Material 18CrNiMo7-6 Used in Mining Reducer Under Dust-Contaminated Lubrication

by Xinyu Pang, Yixiang He, Xun Chen, Jiapeng Zhao, Xiting Luo and Kaibo Lv

Lubricants 2025, 13(3), 107; https://doi.org/10.3390/lubricants13030107 - 28 Feb 2025

Viewed by 456

Abstract

The lubrication of mining reducer is subjected to the contamination of coal rock dust, and this contamination has extremely serious influence on the wear life of reducers. This paper examines the effects of coal dust and rock dust contamination on the wear of [...] Read more.

The lubrication of mining reducer is subjected to the contamination of coal rock dust, and this contamination has extremely serious influence on the wear life of reducers. This paper examines the effects of coal dust and rock dust contamination on the wear of mine gearboxes, especially the wear mechanisms and particle characteristics under lubrication conditions of coal dust and rock dust mixtures of different particle sizes and contents. In the paper, 18CrNiMo7-6 alloy steel was used as the reducer gear material to simulate the actual working conditions, and friction and wear tests were conducted by CFT-1 comprehensive tester to analyze the wear particle characteristics under different contamination conditions. In the experiment, 80-mesh and 200-mesh coal dust and silica particles were used (80-mesh pore size is about 180 μm; 200-mesh pore size is about 75 μm), and different mass fractions of contaminant mixtures were set. The results show that under 80-mesh coal dust contamination, punctate pits, scratches and green halos appeared on the surface of wear particles, and the corrosion and abrasive effects were enhanced when the concentration increased, while 200-mesh coal dust contamination was characterized by black pits and green halos, and the abrasive effect was not obvious. Silica contamination showed significant cutting effects with red oxide wear particles. The synergistic effect of the two contaminants accelerated the wear of the material, and the wear particles were characterized by delamination, flaking and black pits. The study shows that the concentration and type of contaminants have a significant effect on the wear performance of the reducer. Full article

► Show Figures

Figure 1

15 pages, 4740 KiB

Open AccessArticle

MoS₂ Additives in Lithium Grease for Electrified Systems

by Mohsen Tajedini, M. Humaun Kabir, Rouzhina Azhdari, Reza Bahrami, Hung-Jue Sue and Hong Liang

Lubricants 2025, 13(3), 106; https://doi.org/10.3390/lubricants13030106 - 28 Feb 2025

Viewed by 673

Abstract

This study investigates the effectiveness of micron- and nano-sized molybdenum disulfide (MoS₂) particles as additives in lithium (Li) grease under electrified conditions. By systematically applying electric current and high temperatures as experimental parameters, we evaluated the frictional and wear performance of [...] Read more.

This study investigates the effectiveness of micron- and nano-sized molybdenum disulfide (MoS₂) particles as additives in lithium (Li) grease under electrified conditions. By systematically applying electric current and high temperatures as experimental parameters, we evaluated the frictional and wear performance of the grease formulations. Our results showed that micron MoS₂ (M-MoS₂) particles outperform their nano counterparts in reducing friction in the range of room temperature to 40 °C. Meanwhile, at 80 °C, nano-sized MoS₂ (N-MoS₂) particles provide better surface protection. The superior performance of M-MoS₂ is attributed to their particle size, which improves the ability to form a more stable and robust lubricating film under the given electrical conditions. In terms of wear, both MoS₂-added greases showed substantial improvements, with a 93% reduction in wear at 40 °C and an 85% at 80 °C under an applied 3 A current. Surface characterization revealed that M-MoS₂ resulted in a smoother surface with less severe pitting and melted pools compared to the base grease. EDX analysis showed the existence of oxygen, molybdenum, and sulfur in M-MoS₂, indicating the presence and stability of MoS₂ on the wear track. These findings suggest that MoS₂ additives have great potential for improving the efficiency and durability of lubricants in electrically and thermally demanding applications. Full article

(This article belongs to the Special Issue Tribology of Electric Vehicles)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Lubricants, Volume 13, Issue 3 (March 2025) – 41 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI