Lubricants

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 (registering DOI) - 3 Mar 2025

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

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

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 (registering DOI) - 28 Feb 2025

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

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

16 pages, 21443 KiB

Open AccessArticle

Investigations on the Thermal Stability and Kinetics of Biolubricants Synthesized from Different Types of Vegetable Oils

by Majher I. Sarker, Kalidas Mainali and Brajendra K. Sharma

Lubricants 2025, 13(3), 105; https://doi.org/10.3390/lubricants13030105 - 27 Feb 2025

Abstract

Petroleum-based lubricants raise environmental concerns due to their non-biodegradability and toxicity, whereas biobased lubricants underperform owing to low thermal stability. This study examined and compared three vegetable oils, along with their chemically modified versions, to better understand their suitability as biolubricants. High oleic [...] Read more.

Petroleum-based lubricants raise environmental concerns due to their non-biodegradability and toxicity, whereas biobased lubricants underperform owing to low thermal stability. This study examined and compared three vegetable oils, along with their chemically modified versions, to better understand their suitability as biolubricants. High oleic soybean oil (HOSOY), regular soybean oil (RSOY), and waste cooking oil (WCO) were subjected to chemical modification, where isopropyl groups were attached to the fatty acid chains of the oils to produce branched oils, i.e., b-HOSOY, b-RSOY, and b-WCO. The detailed kinetic study of each regular and modified sample was investigated using thermogravimetric analysis. The kinetic parameters, such as the activation energies, reaction rate, and pre-exponential factor, were generated via Friedman methods. The differential thermal gravimetric (DTG) analysis showed low volatilization at the onset temperature in each modified oil as compared with the unmodified samples under an oxidative environment. Furthermore, the comparative kinetic studies demonstrated the enhanced thermoxidative stability of the modified products relative to their unaltered counterparts. Among the tested oils, the b-RSOY showed an average activation energy of 325 kJ/mol, followed by the b-WCO: 300 kJ/mol and the b-HOSOY: 251 kJ/mol, indicating the most stable modified product under an oxidative environment. For all the samples, the pre-exponential factors were in good agreement with the activation energies, which validates that finding the pre-exponential components is crucial to the kinetic analysis. Full article

► Show Figures

Figure 1

26 pages, 1137 KiB

Open AccessArticle

Optimizing Friction Losses of Conveyor Systems Using Large-Diameter Idler Rollers

by Tiago Cousseau, Jayne O’Shea, Peter Robinson, Shawn Ryan, Stephan Hoette, Yusuf Badat, Michael Carr and Craig Wheeler

Lubricants 2025, 13(3), 104; https://doi.org/10.3390/lubricants13030104 - 26 Feb 2025

Abstract

This study investigates the influence of idler roller diameter on indentation rolling resistance and idler rotating resistance in belt conveying systems, crucial for long-distance bulk material transport. It encompasses the impact on grease-lubricated rolling bearings, grease-filled labyrinth seals, and lip seals, with the [...] Read more.

This study investigates the influence of idler roller diameter on indentation rolling resistance and idler rotating resistance in belt conveying systems, crucial for long-distance bulk material transport. It encompasses the impact on grease-lubricated rolling bearings, grease-filled labyrinth seals, and lip seals, with the aim of optimizing energy consumption. Experimental devices were used to refine predictive models, demonstrating that larger idler rollers reduce both resistances, leading to a 40% to 55% efficiency improvement. The study offers a detailed breakdown of friction losses under various operating conditions and provides valuable insights for lubricant selection and system enhancement, highlighting the significance of idler roller diameter in reducing energy costs and enhancing system performance. Full article

(This article belongs to the Special Issue Tribological Research on Transmission Systems)

► Show Figures

Figure 1

17 pages, 10802 KiB

Open AccessArticle

Low Brine Shrimp Bio-Toxicity Marine Lubricating Hydraulic Fluid with Ultra-Low Friction Coefficient and Enhanced Frictional Heat Suppression

by Wei Li, Huanyi Chen, Long Chen, Shanqin Ge, Qingzhao Cai, Genxiang Gong, Jinhong Yu, Kazuhito Nishimura, Nan Jiang and Tao Cai

Lubricants 2025, 13(3), 103; https://doi.org/10.3390/lubricants13030103 - 26 Feb 2025

Abstract

Hydraulic technology has been instrumental in the extensive application of offshore mechanical equipment, particularly in drilling platforms and ships, where high-performance hydraulic fluids are essential for safe and efficient operations. Addressing the urgent need for water-based hydraulic fluids as an alternative to traditional [...] Read more.

Hydraulic technology has been instrumental in the extensive application of offshore mechanical equipment, particularly in drilling platforms and ships, where high-performance hydraulic fluids are essential for safe and efficient operations. Addressing the urgent need for water-based hydraulic fluids as an alternative to traditional oil-based fluids, this study introduces a novel water-based hydraulic fluid fortified with phytic acid, derived from plant seeds, to achieve low biotoxicity, low coefficient of friction, and reduced frictional heat generation. The integration of phytic acid has significantly enhanced the lubricating performance, reducing the average coefficient of friction to as low as 0.013, as tested by the four-ball tester, which is the lowest value reported to date. Real-time monitoring of the temperature rise of the friction testing apparatus using an infrared thermal imager revealed a 78.6% reduction in temperature increase. Acute toxicity assays using Brine Shrimp demonstrated that the 96 h LC50 value for the water–glycol flame-resistant hydraulic fluid with added phytic acid exceeded 26,304 mg/L, indicating low toxicity. Characterization analyses elucidated the mechanisms underlying the improved tribological properties, highlighting the potential of this eco-friendly fluid for safe and efficient offshore operations. Full article

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

► Show Figures

Figure 1

30 pages, 17970 KiB

Open AccessArticle

Interaction Lubrication Mechanism Between Nano-Biochar and Traditional Oil Additives Under Various Sliding Conditions

by Weiwei Guan, Xianjun Hou, Youheng Wang, Chen Chu and Mohamed Kamal Ahmed Ali

Lubricants 2025, 13(3), 102; https://doi.org/10.3390/lubricants13030102 - 25 Feb 2025

Abstract

The development of green lubrication requires nano-lubricants to possess more environmentally friendly fabrication modes and materials with superior tribological properties. This study investigates the tribological properties of nano-biochar in PAO6 base oil and in combination with different additives. The effect of adsorption on [...] Read more.

The development of green lubrication requires nano-lubricants to possess more environmentally friendly fabrication modes and materials with superior tribological properties. This study investigates the tribological properties of nano-biochar in PAO6 base oil and in combination with different additives. The effect of adsorption on friction reduction and anti-wear performance is demonstrated by replacing the friction sub-materials in the four-ball friction test. Based on the comparison of wear region characterization, the incorporation of nano-biochar improves the friction reduction performance of detergent and dispersant base oils with a reduction in coefficient of friction (COF) by 16.7% and 19.0%, respectively, and produces a synergistic effect on the anti-wear performance. When nano-biochar is compounded with anti-wear agents and friction reducer, there is a synergistic effect on friction reduction performance, and COF decreases by 9.4% and 4.5% compared with anti-wear agents and friction reducer base oils, respectively. A method to analyze the friction reduction and anti-wear mechanism of nano-additives in complex lubrication system is proposed, which reveals in depth the interaction law and synergistic lubrication mechanism between NBC and additives in the friction process. Full article

► Show Figures

Figure 1

15 pages, 6947 KiB

Open AccessArticle

Effects of Intermetallic NiAl Particle Content on Friction and Wear of Spark Plasma-Sintered Alumina Matrix Composites

by Nay Win Khun, Mingyue Huang, Zhong Alan Li, He Zhang, Khiam Aik Khor, Jinglei Yang and Fei Duan

Lubricants 2025, 13(3), 101; https://doi.org/10.3390/lubricants13030101 - 25 Feb 2025

Abstract

The spark plasma sintering (SPS) technology was applied to develop alumina matrix composites (Al₂O₃MCs) with different nickel-aluminium (NiAl) particle contents of 5–20 wt.% to understand a correlation between their NiAl particle contents and their microstructures, fracture, hardness, friction, and [...] Read more.

The spark plasma sintering (SPS) technology was applied to develop alumina matrix composites (Al₂O₃MCs) with different nickel-aluminium (NiAl) particle contents of 5–20 wt.% to understand a correlation between their NiAl particle contents and their microstructures, fracture, hardness, friction, and wear. The incorporation of NiAl particles suppressed micrograins and micropores in the microstructures of the Al₂O₃MCs, which resulted in their improved fracture resistance. Increasing the NiAl particle content from 0 to 20 wt.% gave rise to a 23.9% decrease in the hardness of the Al₂O₃MCs. The Al₂O₃MCs had 18.2% and 13.3% decreases in their friction coefficients and 68.3% and 81.3% decreases in their specific wear rates under the normal loads of 2 and 6 N, respectively, with an increased NiAl particle content from 0 to 20 wt.% thanks to their decreased fatigue wear. The SPS Al₂O₃MCs with NiAl particles had promising tribological performance for rotating gas turbine components. Full article

(This article belongs to the Special Issue Friction and Wear of Ceramics)

► Show Figures

Graphical abstract

21 pages, 2644 KiB

Open AccessReview

Comparative Analysis of Wear Models for Accurate Wear Predictions

by Guntis Springis and Irina Boiko

Lubricants 2025, 13(3), 100; https://doi.org/10.3390/lubricants13030100 - 25 Feb 2025

Abstract

The development of innovative technologies and the employment of diverse material compositions have contributed to the enhancement of wear prediction methods. However, the accurate forecasting of service life and the identification of critical influencing factors remain challenging due to the complex interactions governing [...] Read more.

The development of innovative technologies and the employment of diverse material compositions have contributed to the enhancement of wear prediction methods. However, the accurate forecasting of service life and the identification of critical influencing factors remain challenging due to the complex interactions governing wear behaviour. Throughout history, various methodological approaches have been developed to model wear, primarily categorised into analytical calculations and experimental investigations. Analytical methods, including Archard’s equation and its variations, provide a theoretical basis for wear estimation. However, these models frequently depend on empirical coefficients derived from extensive experimentation, which restricts their predictive accuracy. Moreover, classical wear models do not fully account for material fatigue effects and 3D surface texture parameters, which are critical for solving complex engineering problems. Recent advancements have sought to address these limitations by integrating probabilistic surface modelling, fatigue-based degradation theories, and numerical simulations to enhance wear predictions. Experimental investigations remain essential for validating analytical models, as they provide empirical data necessary for parameter calibration. However, these experiments require specialised equipment and are often time-consuming and costly. The integration of modern measurement tools and numerical simulations, such as finite element analysis (FEA) and machine learning-based models, presents a promising direction for improving wear predictions. This review highlights the strengths and limitations of existing wear models and emphasises the need for further refinement of analytical approaches to incorporate fatigue wear mechanisms, real surface roughness effects, and environmental influences for more accurate and reliable wear assessments. Full article

► Show Figures

Figure 1

14 pages, 8009 KiB

Open AccessArticle

Influence of Piston Lubricant on the Distribution of Defects in Cold Chamber High Pressure Die Casting

by Jingzhou Lu, Ewan Lordan, Yijie Zhang, Zhongyun Fan and Kun Dou

Lubricants 2025, 13(3), 99; https://doi.org/10.3390/lubricants13030099 - 24 Feb 2025

Abstract

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of [...] Read more.

In the cold chamber high pressure die casting process (CC-HPDC) for light alloys, the piston lubricants play a key role in protecting the piston tip from wearing and ensure adequate seal with the shot sleeve. However, during the production process, the pouring of overheated aluminum alloy melt into the shot sleeve would lead to evaporation and burning of the lubricants once in contact with the piston tip. The burning products, however, would form gas and non-metallic inclusions in the melt which would be transported and injected into the die area and finally trapped in the castings, all of which would affect the mechanical properties of the as-cast samples and deteriorate the product quality. To further investigate this issue, a pilot scale HPDC machine is used and the lubricant burning issue is studied based on material characterization and numerical modelling. The chemical composition, size, and morphology of the burned products are observed using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In order to better explore the issue of lubricant combustion discovered in the experiment, a finite element model describing the entire HPDC process is established and the burning, motion, and trapping of the lubricant are calculated. The final distribution of the burned products such as gas and non-metallic inclusions are predicted and their influence on final solidification quality of the as-cast products under various process parameters are analyzed qualitatively. Finally, a slow shot velocity range of 0.4–0.6 m/s and an acceleration profile that ramps up to 0.3 m/s over 0–370 mm of the shot sleeve proved to be the most effective in reducing air entrainment and oxide inclusions to alleviate the burning of lubricant on final product quality. Full article

► Show Figures

Figure 1

42 pages, 12382 KiB

Open AccessReview

Development of Wear-Resistant Polymeric Materials Using Fused Deposition Modelling (FDM) Technologies: A Review

by Zhiwang Li and Li Chang

Lubricants 2025, 13(3), 98; https://doi.org/10.3390/lubricants13030098 - 22 Feb 2025

Abstract

The advancement of 3D printing technology has changed material design and fabrication across various industries. Among its many applications, the development of high-wear-resistance polymer composites, particularly using Fused Deposition Modelling (FDM), has received increasing interest from both academic and industrial sectors. This paper [...] Read more.

The advancement of 3D printing technology has changed material design and fabrication across various industries. Among its many applications, the development of high-wear-resistance polymer composites, particularly using Fused Deposition Modelling (FDM), has received increasing interest from both academic and industrial sectors. This paper provides an overview of recent advances in this field, focusing on the selection of key printing parameters (such as layer thickness, print speed, infill density, and printing temperature) and material compatibility optimisation to enhance print quality and tribological performance. The effects of various tribo-fillers, such as fibres and nanoparticles, on the tribological properties of the printed polymer composites were studied. Generally, in the case of nano-sized particles, the wear rate can be reduced by approximately 3 to 5 times when the nanoparticle content is below 5 vol.%. However, when the nanoparticle concentration exceeds 10 vol.%, wear resistance may deteriorate due to the formation of agglomerates, which disrupts the uniform dispersion of reinforcements and weakens the composite structure. Similarly, in short fibre-reinforced polymer composites, a fibre content of 10–30 vol.% has been observed to result in a 3 to 10 times reduction in wear rate. Special attention is given to the synergistic effects of combining micro- and nano-sized fillers. These advancements introduce novel strategies for designing wear-resistant polymer composites without requiring filament fabrication, making 3D printing more accessible for tribological applications. In the last part of the review, the impact of emerging AI technologies on the field is also reviewed and discussed. By identifying key research gaps and future directions, this review aims to drive further innovation in the development of durable, high-performance materials for wide industry applications in aerospace, biomedical, and industrial engineering. Full article

► Show Figures

Figure 1

16 pages, 8324 KiB

Open AccessArticle

Tribological Behavior of Anodized Aluminum Oxide (AAO) Under the Addition of PAO6 Lubrication with Nano-Alumina

by Marina C. Vasco, Rodrigo L. Villanova and Giuseppe Pintaude

Lubricants 2025, 13(3), 97; https://doi.org/10.3390/lubricants13030097 - 21 Feb 2025

Abstract

Anodizing can generate porous wear-resistant layers, which can act as reservoirs for gradually releasing lubricants. Studies on the formation of zinc dialkyl dithiophosphate (ZDDP) tribofilms in non-ferrous metals are relatively rare. Furthermore, adding nanoparticles can improve wear resistance in various applications. This investigation [...] Read more.

Anodizing can generate porous wear-resistant layers, which can act as reservoirs for gradually releasing lubricants. Studies on the formation of zinc dialkyl dithiophosphate (ZDDP) tribofilms in non-ferrous metals are relatively rare. Furthermore, adding nanoparticles can improve wear resistance in various applications. This investigation aims to correlate several anodized surfaces using H₂SO₄ (5 or 10%wt. concentration and 45 or 60 min exposition) to tribological outputs, contributing to understanding the friction behavior of non-metallic layers. Three steps were applied on anodized Alumold 500 alloy. Firstly, the scratching test, to select the layers with higher critical loads. The greatest scratch resistance was obtained with the highest H³/E² value and thickest layer. Secondly, lubricated tests with only poly-alpha-olefin oils (PAO6) were performed in a reciprocating test rig using an alumina ball as the counterpart. From that, only the best AAO condition was selected. Finally, three more lubricant compositions were tested, as follows: adding ZDDP to PAO6, alumina nanoparticles (~100 nm) to PAO6, and ZDDP + nanoparticles. The addition of nano-alumina to the PAO6 resulted in the maintenance of COF values with only PAO6 (~0.1), when the most significant drop in the surface roughness was observed along with the tests. Full article

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

► Show Figures

Figure 1

16 pages, 6195 KiB

Open AccessArticle

A Mechanics Model for Contact with Rough Surface Considering the Interaction of Micro-Asperity Bodies

by Yazhou Mao, Qingxin Hu, Yingying Yu, Shaolin Shi, Jiaming Pei, Zichen Li and Linyuan Wang

Lubricants 2025, 13(3), 96; https://doi.org/10.3390/lubricants13030096 - 20 Feb 2025

Abstract

In order to evaluate contact characteristics, a modified contact model was proposed considering the deformation characteristics of asperity bodies, and the variation rules of wear rate with fractal dimension, material property constant and debris probability were established. The results show that the actual [...] Read more.

In order to evaluate contact characteristics, a modified contact model was proposed considering the deformation characteristics of asperity bodies, and the variation rules of wear rate with fractal dimension, material property constant and debris probability were established. The results show that the actual contact area increases with an increase in load when the surface topography is constant, whereas the contact area decreases with an increase in characteristic scale coefficient if the fractal dimension or load is constant. For running-in wear, the wear rate increases with an increase in surface profile parameters under the same contact area. In addition, the wear rate increases with an increase in actual contact area when the surface profile parameter is constant. Regarding abrasive wear, the wear rate is the smallest when the fractal dimension is 1.6. The wear rate increases with an increase in contact area under the same characteristic scale coefficient, but decreases with an increase in the characteristic scale coefficient under the same contact area, and the smaller the material constant and the larger the probability constant, the higher the wear rate. The establishment of this model provides a basis for further study of the tribological properties of the contact surface. Full article

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

► Show Figures

Figure 1

25 pages, 99294 KiB

Open AccessArticle

Comparative Study on the Leakage Characteristics and Parameter Influence of Bio-Inspired Fishway Staggered Labyrinth Seals

by Zhentao Yu, Jinbo Jiang, Xuan Zhang, Mengli Zhang and Canlong Li

Lubricants 2025, 13(3), 95; https://doi.org/10.3390/lubricants13030095 - 20 Feb 2025

Abstract

Innovating seal structures and optimizing size parameters are effective ways to enhance the leakage characteristics of labyrinth seals (LSs). Inspired by the ecological fishways with high flow resistance on dam sides, a novel bio-inspired staggered labyrinth seal is proposed. The leakage characteristics of [...] Read more.

Innovating seal structures and optimizing size parameters are effective ways to enhance the leakage characteristics of labyrinth seals (LSs). Inspired by the ecological fishways with high flow resistance on dam sides, a novel bio-inspired staggered labyrinth seal is proposed. The leakage characteristics of both the curved-edged bio-inspired labyrinth seal (CELS) and the straight-edged bio-inspired labyrinth seal (SELS) at different tooth-incline angles are studied numerically and experimentally. The influence of key geometrical parameters on the leakage characteristics and flow field parameters of the CELSs are investigated, and the leakage control mechanism of bio-inspired LSs is revealed via analyzing flow field parameter distribution. The results indicate that, compared to conventional double-sided staggered straight-tooth labyrinth seals, the leakage rate reduction in CELSs is up to 30% when the incline angle is equal to 25°, outperforming that of the SELS in leakage control. This improvement is mainly attributed to the flow path bending and jet contraction effects at the tooth-tip entrance, along with the thermodynamic effects of the high-turbulence dissipation zone adjacent to the tooth top. The optimum leakage characteristics can be achieved when seal clearance h < 0.5 mm, aspect ratio δ < 0.6, and tooth thickness t < 1.5 mm. This work provides new insights into the structural design of high-resistance and low-leakage labyrinth seals. Full article

► Show Figures

Figure 1

15 pages, 5648 KiB

Open AccessArticle

The Influence of Friction Parameters and Material Type on Results in the Block-on-Ring Friction System

by Marcin Madej and Beata Leszczyńska-Madej

Lubricants 2025, 13(2), 94; https://doi.org/10.3390/lubricants13020094 - 19 Feb 2025

Abstract

The block-on-ring friction system is one of the more universal methods of measuring the tribological properties of materials, where we are able to compare the properties of different materials using a prescribed counter sample. When preparing for a test, we usually determine the [...] Read more.

The block-on-ring friction system is one of the more universal methods of measuring the tribological properties of materials, where we are able to compare the properties of different materials using a prescribed counter sample. When preparing for a test, we usually determine the parameters that appear to be optimal for testing a given material for its applications. The question remains whether and how such a choice affects the results obtained. In this paper, tests have been carried out on two commonly used plain bearing alloys, B83 and B89. The T-05 tester used for the tests allows the rotation of the counter sample to be adjusted, and, in this study, this was varied in the range of 50, 100, 150, 200 and 250 rpm. Another parameter variable in the tests was the friction distance, and two distances of 100 and 250 m were used. As the tests were carried out under technically dry friction conditions, it was possible to capture both the effect of the running-in period and the stable friction path. The tests showed that the alloys tested over the longer friction distance of 250 m responded differently to a change in parameters, with alloy B83 showing a sinusoidal variation in wear resistance with a maximum at medium speed, whereas alloy B89 is characterized by a continuous increase in wear with increasing speed. The coefficient of friction is more dependent on speed, and the basic conclusion can be drawn that increasing speed results in a lower coefficient of friction. This research has confirmed the need for the careful selection of test parameters and the difficulty of comparing results when there is even a slight difference in the test parameters used at different test centers. Full article

(This article belongs to the Special Issue Wear Mechanism Identification and State Prediction of Tribo-Parts)

► Show Figures

Figure 1

56 pages, 16932 KiB

Open AccessReview

Study of the Influence of Nanoparticle Reinforcement on the Mechanical and Tribological Performance of Aluminum Matrix Composites—A Review

by Varun Singhal, Daksh Shelly, Abhishek Saxena, Rahul Gupta, Vipin Kumar Verma and Appurva Jain

Lubricants 2025, 13(2), 93; https://doi.org/10.3390/lubricants13020093 - 19 Feb 2025

Abstract

This study investigates the influence of nano-sized reinforcements on aluminum matrix composites’ mechanical and tribological properties. Microstructural analysis revealed that introducing nanoparticles led to grain refinement, reducing the grain size from 129.7 μm to 41.3 μm with 2 wt.% TiO₂ addition. Furthermore, [...] Read more.

This study investigates the influence of nano-sized reinforcements on aluminum matrix composites’ mechanical and tribological properties. Microstructural analysis revealed that introducing nanoparticles led to grain refinement, reducing the grain size from 129.7 μm to 41.3 μm with 2 wt.% TiO₂ addition. Furthermore, ultrasonic-assisted squeeze casting of AA6061 composites reinforced with TiO₂ and Al₂O₃ resulted in a 52% decrease in grain size, demonstrating nano-reinforcements’ effectiveness in refining the matrix structure. Despite these advantages, the high surface energy of nanoparticles causes agglomeration, which can undermine composite performance. However, ultrasonic-assisted stir casting reduced agglomeration by approximately 80% compared to conventional stir casting, and cold isostatic pressing improved dispersion uniformity by 27%. The incorporation of nano-reinforcements such as SiC, Al₂O₃, and TiC significantly enhanced the material properties, with hardness increasing by ~30% and ultimate tensile strength improving by ~80% compared to pure Al. The hardness of nano-reinforced composites substantially rose from 83 HV (pure Al) to 117 HV with 1.0 vol.% CNT reinforcement. Additionally, TiC-reinforced AA7075 composites improved hardness from 94.41 HB to 277.55 HB after 10 h of milling, indicating a nearly threefold increase. The wear resistance of Al-Si alloys was notably improved, with wear rates reduced by up to 52%, while the coefficient of friction decreased by 20–40% with the incorporation of graphene and CNT reinforcements. These findings highlight the potential of nano-reinforcements in significantly improving the mechanical and tribological performance of n-AMCs, making them suitable for high-performance applications in aerospace, automotive, and structural industries. Full article

► Show Figures

Figure 1

16 pages, 4247 KiB

Open AccessArticle

Tribological Assessment of Synthetic Grease (PDPLG-2) Derived from Partially Degraded Low-Density Polyethylene Waste

by Divyeshkumar Dave, Yati Vaidya, Kamlesh Chauhan, Sushant Rawal, Ankurkumar Khimani and Sunil Chaki

Lubricants 2025, 13(2), 92; https://doi.org/10.3390/lubricants13020092 - 18 Feb 2025

Abstract

This study focuses on addressing the pressing challenge of reusing plastic in an eco-friendly manner. This research aimed to produce synthetic grease through an environmentally friendly pyrolysis technique, utilizing 69% predegraded low-density polyethylene (LDPE) combined with visible-light-working TiO₂ thin film, protein-coated TiO [...] Read more.

This study focuses on addressing the pressing challenge of reusing plastic in an eco-friendly manner. This research aimed to produce synthetic grease through an environmentally friendly pyrolysis technique, utilizing 69% predegraded low-density polyethylene (LDPE) combined with visible-light-working TiO₂ thin film, protein-coated TiO₂ NPs, and Lactobacillus plantarum bacteria in a batch reactor. The optimized conditions of temperature (500 °C) and heating time (2 h) resulted in the creation of 166 gm of partially degraded polyethylene grease 2 (PDPLG2) with National Lubricating Grease Institute (NLGI 2) grade consistency. PDPLG2 grease exhibits a wide-range dropping point of 280 °C and effectively maintains lubrication under high friction and stress loads, thereby preventing wear. Thermal analysis using TG and DSC validated the grease’s stability up to 280 °C, with minimal degradation beyond this point. Taguchi analysis using substance, sliding speed, and load as factors identified the ideal process parameters as aluminum, 1500 rpm, and 150 N, respectively. The present study revealed that sliding speed has the greatest impact, contributing 31.74% to the coefficient of friction (COF) and 11.28% to wear, followed by material and load. Comparative tribological analysis with commercially available grease (NLGI2) demonstrated that PDPLG2 grease outperforms NLGI2 grease. Overall, this innovative eco-friendly approach presents PDPLG2 as a promising alternative lubricant with improved anti-wear and friction properties, while also contributing significantly to plastic waste reduction. Full article

(This article belongs to the Special Issue Wear-Resistant Coatings and Film Materials)

► Show Figures

Figure 1

Journal Description

Lubricants

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI