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Changes in Surface Topography and Light Load Hardness in Thrust Bearings as a Reason of Tribo-Electric Loads
Friction and Wear in Hot Stamping: The Role of Tool and Workpiece Temperature and Tool Steel Composition
The Improvement of CrN Coatings Wear Resistance by Adjusting the Cycle Number of Electrochemical
Effect of Grease Composition on Impact-Sliding Wear

Journal Description

Lubricants

Lubricants is an international, peer-reviewed, open access journal on tribology published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Engineering, Mechanical) / CiteScore - Q2 (Mechanical Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 16.7 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the first half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 3.1 (2023); 5-Year Impact Factor: 3.1 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2075-4442

Latest Articles

17 pages, 5260 KiB

Open AccessArticle

Lubrication, Friction and Wear Characteristics of Textured Surface Slipper Pairs in Axial Piston Pumps

by Bin Bian, Zhiqiang Zhang, Lin Li, Qun Chao, Hao Yuan and Zhiqi Liu

Lubricants 2024, 12(11), 370; https://doi.org/10.3390/lubricants12110370 - 25 Oct 2024

The study investigates the impact of textured surface parameters and pump operating parameters on the friction performance of slipper pairs in axial piston pumps. The orthogonal experimental scheme was developed, and the influence of several factors was explored, such as rotational speed, area [...] Read more.

The study investigates the impact of textured surface parameters and pump operating parameters on the friction performance of slipper pairs in axial piston pumps. The orthogonal experimental scheme was developed, and the influence of several factors was explored, such as rotational speed, area ratio, micro-pit shape, diameter, depth-to-diameter ratio and film thickness. Optimal dimension combinations of the micro-pit were identified by numerical simulation and standard pin–disk friction experiment. In the pin–disk friction pair test, the friction coefficient of the textured surface compared to the smooth surface showed a maximum average friction reduction rate of 26.974%. Under various pump pressures (4, 8, 12 MPa) and pump displacements (10, 20, 35 L/min), the friction reduction rates of the textured surface slipper pairs (texture diameter 500 µm, depth 250 µm, area ratio 20%) ranged from 0.78% to 18.13%. The study underscores the importance of surface texture in enhancing the operational efficiency and reliability of axial piston pumps, offering valuable insights for the design and maintenance of hydraulic pumps. Full article

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21 pages, 7422 KiB

Open AccessArticle

Leakage Characteristics and Experimental Research of Staggered Labyrinth Sealing

by Na Wang, Yongbing Cao, Zhencong Sun, Shixin Tang and Seung-Bok Choi

Lubricants 2024, 12(11), 369; https://doi.org/10.3390/lubricants12110369 - 24 Oct 2024

The staggered labyrinth seal is widely used in aerospace, transportation, mining, and other fields due to its advantages of adapting to high speed, reliable sealing performance, and low or even frictionless friction between dynamic and static rotors. The traditional calculation method of labyrinth [...] Read more.

The staggered labyrinth seal is widely used in aerospace, transportation, mining, and other fields due to its advantages of adapting to high speed, reliable sealing performance, and low or even frictionless friction between dynamic and static rotors. The traditional calculation method of labyrinth seal leakage mostly focuses on the fact that the internal medium is an ideal gas and only considers a single effect, which cannot accurately describe the leakage of liquid medium lubricating oil in the labyrinth seal. Therefore, this study focuses on the leakage characteristics of labyrinth seals, and it proposes a leakage calculation method based on liquid medium in view of the shortcomings of existing calculation methods under liquid medium conditions. By considering the thermodynamic and frictional effects of the staggered labyrinth sealing, the resistance loss and thermodynamic effect of the lubricating oil in the sealing cavity were analyzed. The flow field analysis was used to reveal the leakage law of lubricating oil under different conditions, and the factors such as total inlet pressure, spindle speed, and sealing clearance were considered. Finally, the leakage characteristics of the staggered labyrinth seal and the accuracy of the calculation method of the leakage of the staggered labyrinth seal under multiple effects were revealed through experimental verification. This study provides useful guidance for the performance optimization of labyrinth seals in practical applications. Full article

(This article belongs to the Special Issue Thermal Hydrodynamic Lubrication)

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14 pages, 5001 KiB

Open AccessArticle

Wear and Friction Characteristics of In Situ TiC-Reinforced Ti₃SiC₂-Ti₅Si₃ Composites Against 100Cr6 Steel Counterpart

by Abdessabour Benamor, Hiba Benamor, Youcef Hadji, Maharshi Dey, Nabil Chiker, Adel Haddad, Riad Badji, Arnaud Tricoteaux, Jean-Pierre Erauw, Merouane Salhi and Mohamed Hadji

Lubricants 2024, 12(11), 368; https://doi.org/10.3390/lubricants12110368 - 24 Oct 2024

In this study, the dry sliding characteristics of a Ti₃SiC₂/Ti₅Si₃ matrix reinforced with different TiC contents against a 100Cr6 steel ball were investigated. The composites were fabricated using the spark plasma sintering method with Ti, SiC, [...] Read more.

In this study, the dry sliding characteristics of a Ti₃SiC₂/Ti₅Si₃ matrix reinforced with different TiC contents against a 100Cr6 steel ball were investigated. The composites were fabricated using the spark plasma sintering method with Ti, SiC, and C powders. SEM revealed that the composites possessed damage tolerance behavior, where grain pull-out, buckling, delamination, and diffuse microcracking were observed. In comparison, the unreinforced composite showed severe adhesive wear and tribo-oxidative wear mechanisms. The integration of the TiC phase in the Ti₃SiC₂/Ti₅Si₃ matrix enhanced the wear resistance by at least one order of magnitude. A new wear regime was observed in the TiC-reinforced composites, classified as mild wear, where tribo-oxidation and third-body abrasion were dominant, with ferrous deposits on the sliding surfaces. Full article

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12 pages, 7176 KiB

Open AccessArticle

Abrasive Wear Characteristics of 30MnB5 Steel for High-Speed Plough Tip of Agricultural Machinery in Southern Xinjiang Region

by Xiaorui Han, Qiang Yao, Mingjian Li, Zhanhong Guo, Pengwei Fan, Ling Zhou and Youqiang Zhang

Lubricants 2024, 12(11), 367; https://doi.org/10.3390/lubricants12110367 - 24 Oct 2024

The high-speed plough tip is the core soil-touching component in southern Xinjiang field cultivation, but the interaction of the plough tip with the soil results in severe wear of the tip. The friction behaviour of sand and soil on plough tips was investigated [...] Read more.

The high-speed plough tip is the core soil-touching component in southern Xinjiang field cultivation, but the interaction of the plough tip with the soil results in severe wear of the tip. The friction behaviour of sand and soil on plough tips was investigated with a homemade rotary abrasive wear tester in a one-factor multilevel test with three parameters: moisture content, velocity/rotational speed and friction distance. The objective was to study the friction behaviour of the sand soil and plough tip and analyse and characterise the wear amount, wear thickness and compressive stress distribution, three-dimensional wear morphology and microscopic wear morphology of the plough tips. The results show that with increasing speed, the wear amount changes more gently; with increasing soil water content, the soil adhesion force and lubricating water film increase so that the wear amount follows a second-order parabolic law; and with increasing friction distance, the wear amount gradually increases, and the wear rate also shows an upward trend when the plough tip is in the abrasive wear stage. The tip makes contact with the firmer soil with higher surface compressive stresses, causing the most wear. As the friction distance increases, sand particles become embedded in the contact surfaces, creating a groove effect along with spalling pits caused by fatigue wear. During the whole wear period, the groove effect is always accompanied by spalling pits appearing repeatedly. The analysis of the wear micromorphology of the plough tip shows that the number of flaking pits gradually decreases in the direction of soil movement, and the form of damage changes from impact wear to plough groove scratches. Abrasive wear interacts with corrosive wear to exacerbate plough tip wear. Full article

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16 pages, 5310 KiB

Open AccessArticle

Investigations on Spin Power Losses Generated in a Planetary Gear Set Using Thermal Network Method

by Marie Winger, Yann Marchesse, Thomas Touret, Christophe Changenet, Fabrice Ville and Patrice Gédin

Lubricants 2024, 12(11), 366; https://doi.org/10.3390/lubricants12110366 - 24 Oct 2024

This paper introduces an experimental approach to study the distribution of power losses in an oil jet-lubricated planetary gear set, with the aim of increasing the efficiency of these gearboxes. A thermal model is developed to estimate power losses associated with temperature distribution. [...] Read more.

This paper introduces an experimental approach to study the distribution of power losses in an oil jet-lubricated planetary gear set, with the aim of increasing the efficiency of these gearboxes. A thermal model is developed to estimate power losses associated with temperature distribution. This model is applied to analyze experimental data collected from a dedicated test setup. Different configurations are studied to progressively validate the thermal network. In this paper, only a configuration composed of a rotating ring gear and a fixed planet carrier is studied. This configuration enables the validation of a thermal network developed from a basic configuration where power loss sources are not numerous. The study reveals that, for this configuration, load-independent power losses are primarily attributed to hydrodynamic losses in the bearings, while the gear windage effects are of second order. The power losses are then compared to those generated by the same planetary gear set but using a rotating planet carrier. The comparison shows that the configuration composed of the rotating ring gear and fixed planet carrier produces less power loss than the other configuration. Full article

(This article belongs to the Special Issue Modeling and Prediction of Wear in Gears)

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17 pages, 3497 KiB

Open AccessArticle

Physics-Informed Neural Networks for the Reynolds Equation with Transient Cavitation Modeling

by Faras Brumand-Poor, Florian Barlog, Nils Plückhahn, Matteo Thebelt, Niklas Bauer and Katharina Schmitz

Lubricants 2024, 12(11), 365; https://doi.org/10.3390/lubricants12110365 - 23 Oct 2024

Gaining insight into tribological systems is crucial for optimizing efficiency and prolonging operational lifespans in technical systems. Experimental investigations are time-consuming and costly, especially for reciprocating seals in fluid power systems. Elastohydrodynamic lubrication (EHL) simulations offer an alternative but demand significant computational resources. [...] Read more.

Gaining insight into tribological systems is crucial for optimizing efficiency and prolonging operational lifespans in technical systems. Experimental investigations are time-consuming and costly, especially for reciprocating seals in fluid power systems. Elastohydrodynamic lubrication (EHL) simulations offer an alternative but demand significant computational resources. Physics-informed neural networks (PINNs) provide a promising solution using physics-based approaches to solve partial differential equations. While PINNs have successfully modeled hydrodynamics with stationary cavitation, they have yet to address transient cavitation with dynamic geometry changes. This contribution applies a PINN framework to predict pressure build-up and transient cavitation in sealing contacts with dynamic geometry changes. The results demonstrate the potential of PINNs for modeling tribological systems and highlight their significance in enhancing computational efficiency. Full article

(This article belongs to the Special Issue Intelligent Algorithms for Triboinformatics)

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23 pages, 4143 KiB

Open AccessArticle

End-to-End Intelligent Fault Diagnosis of Transmission Bearings in Electric Vehicles Based on CNN

by Yong Chen, Guangxin Li, Anhe Li and Bolin He

Lubricants 2024, 12(11), 364; https://doi.org/10.3390/lubricants12110364 - 23 Oct 2024

Environmental noise and transmission components can cause significant interference in vibration signals, rendering the extraction of bearing fault features challenging in service scenarios. Traditional fault diagnosis methods rely heavily on professional domain knowledge, prior models, and signal preprocessing methods. The accuracy of fault [...] Read more.

Environmental noise and transmission components can cause significant interference in vibration signals, rendering the extraction of bearing fault features challenging in service scenarios. Traditional fault diagnosis methods rely heavily on professional domain knowledge, prior models, and signal preprocessing methods. The accuracy of fault diagnosis depends on the quality of the fault-sensitive features extracted by vibration signal preprocessing methods. An improved convolutional neural network (CNN) end-to-end intelligent fault diagnosis model based on raw vibration data (RVDCNN) is proposed. The time-domain vibration signal of the transmission bearing is converted into a continuous two-dimensional numerical matrix, and a two-dimensional CNN model is constructed through network structure optimization. The original time-domain vibration signal numerical matrix of the bearing is trained and tested to extract and learn abstract fault features of different fault types, and then the fault classification of the bearing is achieved. To verify the generalizability of the RVDCNN intelligent fault diagnosis model, it is applied to the recognition of rolling bearings in the two-speed mechanical automatic transmission of electric vehicles, achieving recognition accuracy of 99.11% for seven types of bearings. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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13 pages, 5714 KiB

Open AccessArticle

Fabrication and Tribology Properties of PTFE-Coated Cemented Carbide Under Dry Friction Conditions

by Shoujun Wang, Wenlong Song, Lei An, Zixiang Xia and Shengdong Zhang

Lubricants 2024, 12(11), 363; https://doi.org/10.3390/lubricants12110363 - 23 Oct 2024

PTFE coatings were deposited on YT15 carbide substrates using spray technology. A series of examinations were conducted, including the use of surface and cross-section micrographs to analyze the structural integrity of the coatings. The surface roughness, the adhesion force between the PTFE coatings [...] Read more.

PTFE coatings were deposited on YT15 carbide substrates using spray technology. A series of examinations were conducted, including the use of surface and cross-section micrographs to analyze the structural integrity of the coatings. The surface roughness, the adhesion force between the PTFE coatings and the carbide substrate, and the micro-hardness of the coated carbide were also evaluated. Additionally, the friction and wear behaviors were assessed through dry sliding friction tests against WC/Co balls. The test results indicated that while the PTFE-coated carbide exhibited a rougher surface and reduced micro-hardness, it also demonstrated a significant reduction in surface friction and adhesive wear. These findings suggest that the PTFE coatings enhance the overall wear resistance of the carbides. The lower surface hardness and shear strength of the coatings influenced the friction performance, leading to specific wear failure mechanisms, such as abrasion wear, coating delamination, and flaking. Overall, the deposition of PTFE coatings on carbide substrates presents a promising strategy to enhance their friction and wear performance. This approach not only improves the durability of carbide materials but also offers potential applications in industries where reduced friction and wear are critical for performance. Full article

(This article belongs to the Special Issue Tribological Properties of Sprayed Coatings)

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15 pages, 8729 KiB

Open AccessArticle

Power Losses of Oil-Bath-Lubricated Ball Bearings—A Focus on Churning Losses

by Florian de Cadier de Veauce, Yann Marchesse, Thomas Touret, Christophe Changenet, Fabrice Ville, Luc Amar and Charlotte Fossier

Lubricants 2024, 12(11), 362; https://doi.org/10.3390/lubricants12110362 - 23 Oct 2024

This study investigates the power losses of rolling element bearings (REBs) lubricated using an oil bath. Experimental tests conducted on two different deep-groove ball bearings (DGBBs) provide valuable insights into the behaviour of DGBBs under different oil levels, generating essential data for developing [...] Read more.

This study investigates the power losses of rolling element bearings (REBs) lubricated using an oil bath. Experimental tests conducted on two different deep-groove ball bearings (DGBBs) provide valuable insights into the behaviour of DGBBs under different oil levels, generating essential data for developing accurate models of power losses. Observations of the oil bath dynamics reveal the formation of an oil ring at high oil levels, as observed for planetary gear trains, leading to modifications in the oil flow behaviour. The experiments demonstrate that oil bath lubrication generates power losses comparable to injection lubrication when the oil level is low. However, as the oil level increases, so do the power losses due to increased drag within the bearing. This study presents a comprehensive model for calculating drag losses. The proposed drag power loss model accounts for variations in oil level and significantly improves loss predictions. A comparison of existing models with the experimental results shows good agreement for both bearings, demonstrating the effectiveness of the developed model in accounting for oil bath height in loss calculations. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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12 pages, 3950 KiB

Open AccessArticle

Tribological Behavior and Cold-Rolling Lubrication Performance of Water-Based Nanolubricants with Varying Concentrations of Nano-TiO₂ Additives

by Linan Ma, Luhu Ma, Junjie Lian, Chen Wang, Xiaoguang Ma and Jingwei Zhao

Lubricants 2024, 12(11), 361; https://doi.org/10.3390/lubricants12110361 - 22 Oct 2024

This study aimed to investigate the effect of water-based nanolubricants containing varying concentrations (1.0–9.0 wt.%) of TiO₂ nanoparticles on the friction and wear of titanium foil surfaces. Water-based nanolubricants containing TiO₂ nanoparticles of varying concentrations were prepared and applied in friction [...] Read more.

This study aimed to investigate the effect of water-based nanolubricants containing varying concentrations (1.0–9.0 wt.%) of TiO₂ nanoparticles on the friction and wear of titanium foil surfaces. Water-based nanolubricants containing TiO₂ nanoparticles of varying concentrations were prepared and applied in friction and wear experiments and micro-rolling experiments to evaluate their performance regarding friction and wear properties. The findings indicated that the best results were achieved with a 3.0 wt.% TiO₂ nano-additive lubricant that significantly improved the tribological properties, with reductions in the COF and wear of 82.9% and 42.7%, respectively, compared to the dry conditions without any lubricant. In addition, nanolubricants contribute to a reduction in rolling forces and an improvement in the surface quality of titanium foils after rolling. In conclusion, nanolubricants exhibit superior lubricating properties compared to conventional O/W lubricants, which is attributed to the combined effect of the rolling effect, polishing effect, mending effect and tribo-film effect of the nanoparticles. Full article

(This article belongs to the Special Issue Advances in Water-Based Nanolubricants)

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16 pages, 10702 KiB

Open AccessArticle

Difference in High-Temperature Tribological Performance of Oxide/Ag-MoS₂-Based Composites

by Yufei Wang, Xibo Shao, Jianyu Liu, Xinyue Hu, Xuhui He and Guanyu Deng

Lubricants 2024, 12(10), 360; https://doi.org/10.3390/lubricants12100360 - 21 Oct 2024

MoS₂ has excellent vacuum lubricating performance. However, it is prone to be oxidized in a high-temperature atmospheric environment, leading to the deterioration of its lubricating performance and even serious space accidents. The high-temperature lubricating performance of MoS₂-based solid lubricating materials [...] Read more.

MoS₂ has excellent vacuum lubricating performance. However, it is prone to be oxidized in a high-temperature atmospheric environment, leading to the deterioration of its lubricating performance and even serious space accidents. The high-temperature lubricating performance of MoS₂-based solid lubricating materials can be improved to some extent by the co-compounding of appropriate oxides and Ag. The tribological properties of several common nano-oxides (ZnO, TiO₂, Al₂O₃, and ZrO₂) composited with metal Ag of MoS₂-based composites were compared at 450 °C. The results showed that the comprehensive tribological performance of MoS₂-TiO₂-Ag was the best, an the average friction coefficient of about 0.26, and a wear rate of about 1.2 × 10⁻⁵ mm³/Nm, which was 18% and 43% lower than that of MoS₂-Ag, respectively. The excellent tribological properties of MoS₂-TiO₂-Ag composites were attributed to three aspects: Firstly, with the help of the oxidation resistance of TiO₂ to MoS₂ to some extent and its high ionic potential, its oxidation resistance was improved and its shear strength was reduced to provide low friction. Secondly, relying on the low shear strength and good film-forming tendency of soft metal Ag on the sliding surface, a low shear tribo-film was easily formed on the friction interface, which was helpful for the synergistic lubrication of Ag, MoS₂, and TiO₂.Thirdly, through the matching of hard TiO₂ and soft Ag, the wear resistance and bearing capacity of the composites were improved to some extent. The research results can provide some reference for the selection and design of MoS₂-based high-temperature lubricating materials and the enhancement of their tribological properties. Full article

(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)

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32 pages, 3090 KiB

Open AccessReview

Nanofluid Minimum Quantity Lubrication (NMQL): Overview of Nanoparticle Toxicity and Safer-Design Guidelines

by José V. Abellán-Nebot, Oscar Andreu-Sánchez, Carlos Fito-López and Rosa Mondragón

Lubricants 2024, 12(10), 359; https://doi.org/10.3390/lubricants12100359 - 21 Oct 2024

Minimum Quantity Lubrication (MQL) has received much attention from the research community as a potential lubricating system to reduce environmental hazards and health issues that can be commonly found in flood cooling/lubricating systems based on metalworking fluids. The addition of nanoparticles in MQL [...] Read more.

Minimum Quantity Lubrication (MQL) has received much attention from the research community as a potential lubricating system to reduce environmental hazards and health issues that can be commonly found in flood cooling/lubricating systems based on metalworking fluids. The addition of nanoparticles in MQL systems (NMQL) has led to improved machining performance, increasing the cooling capability and reducing friction and tool wear, and some researchers have proved the applicability of this type of system for difficult-to-cut materials. However, the mist generated by MQL systems due to both the MQL system itself and the machining operation may pose an additional hazard to operators which is being overlooked by the research community. These hazards become more severe when using nanoparticles, but unfortunately very few works have paid attention to nanoparticle toxicity as applied in MQL systems, and this issue should be clearly understood before encouraging its implementation in industry. Furthermore, current legislation does not help since regulation of permissible exposure limits when dealing with nanoparticles is still ongoing in most cases. In this work, the toxicity of nanoparticles applied in MQL systems is analyzed, and recent research on studies of nanoparticle toxicity both in vitro and in vivo is presented. A relative comparison of toxicity is provided for those nanoparticles that have been reported in the literature as potential additives for MQL. The review is focused on analyzing the main factors of toxicity of nanoparticles which are identified as size, shape, surface properties, agglomeration and solubility. This review presents guidelines for safer nanolubricant formulations, guiding practitioners towards proper NMQL implementations in industry. Furthermore, current occupational exposure limits and recommendations are provided for all the nanoparticles potentially used in MQL systems, which is of interest in terms of work safety. Full article

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13 pages, 4564 KiB

Open AccessArticle

Moringa Oil and Carbon Phases of Different Shapes as Additives for Lubrication

by Nadiège Nomède-Martyr, Philippe Bilas, Grégory Mathieu, Yves Bercion, Henry Joseph and Philippe Thomas

Lubricants 2024, 12(10), 358; https://doi.org/10.3390/lubricants12100358 - 19 Oct 2024

Vegetable oils in the lubricant field are largely studied. Their efficiency depends on their viscosity parameters and their fatty acid composition. The actions of moringa oil used as a lubricant base and as a lubricant additive have been shown in this work. Graphite, [...] Read more.

Vegetable oils in the lubricant field are largely studied. Their efficiency depends on their viscosity parameters and their fatty acid composition. The actions of moringa oil used as a lubricant base and as a lubricant additive have been shown in this work. Graphite, carbon nanofibers, and carbon nanodots are carbon phases of different shapes used as solid additives. The tribological performances of lubricant blends composed of between 0.5 and 1 wt.% of particles have been evaluated using a ball-on-plane tribometer under an ambient atmosphere. No additional surfactant was used. The positive and important actions of a small amount of moringa oil added in the lubricant formulas are demonstrated. The results obtained allow us to point out the influence of the type and shape of particles. Physicochemical investigations allow us to propose a synergistic effect between the particles and moringa oil as additives in dodecane. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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18 pages, 4698 KiB

Open AccessArticle

Study on Atomization Mechanism of Oil Injection Lubrication for Rolling Bearing Based on Stratified Method

by Feng Wei, Hongbin Liu and Yongyan Liu

Lubricants 2024, 12(10), 357; https://doi.org/10.3390/lubricants12100357 - 18 Oct 2024

The atomization mechanism of lubrication fluid in rolling bearings under high-speed airflow between the rings was investigated. A simulation model of gas–liquid two-phase flow in angular contact ball bearings was developed, and the jet lubrication process between the bearing rings was simulated using [...] Read more.

The atomization mechanism of lubrication fluid in rolling bearings under high-speed airflow between the rings was investigated. A simulation model of gas–liquid two-phase flow in angular contact ball bearings was developed, and the jet lubrication process between the bearing rings was simulated using FLUENT computational fluid dynamics software (Ansys 19.2). The complex motion boundary conditions of the rolling elements were addressed through a layered approach. We can obtain more accurate boundary layer flow field changes and statistics of the diameter of oil particles in lubricating oil atomization, which lays the foundation for analyzing the law of influence on lubricating oil atomization. The results show that as the number of boundary layer layers increases, the influence of the boundary layer flow field on the lubricating oil is more obvious. The oil particle size is excessively flat, and the concentration of large particles of oil appears to decrease. As the speed increases, the amount of oil in the cavity decreases, but the oil droplets are also fragmented, which intensifies the atomization and reduces the particle diameter. This reduces the Sauter Mean Diameter (SMD), which is not conducive to the lubrication of the bearing. Under different injection pressures, when the injection pressure is large, it is beneficial to the lubrication of the bearing. Full article

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22 pages, 6478 KiB

Open AccessArticle

Effect of Thermal Load Caused by Tread Braking on Crack Propagation in Railway Wheels on Long Downhill Ramps

by Jinyu Zhang, Xun Chen, Gongquan Tao and Zefeng Wen

Lubricants 2024, 12(10), 356; https://doi.org/10.3390/lubricants12100356 - 17 Oct 2024

To investigate the propagation behavior of thermal cracks on the wheel tread under the conditions of long downhill ramps, a three-dimensional finite element model of a 1/16 wheel, including an initial thermal crack, was developed using the finite element software ANSYS 17.0. The [...] Read more.

To investigate the propagation behavior of thermal cracks on the wheel tread under the conditions of long downhill ramps, a three-dimensional finite element model of a 1/16 wheel, including an initial thermal crack, was developed using the finite element software ANSYS 17.0. The loading scenarios considered include mechanical wheel–rail loads, both with and without the superposition of thermal wheel–brake shoe friction loads. The virtual crack closure method (VCCM) is employed to analyze the variations in stress intensity factors (SIFs) for Modes I, II, and III (K_I, K_II, and K_III) at the 0°, mid, and 90° positions along the crack tip. The simulation results show that temperature is a critical factor for the propagation of thermal cracks. Among the SIFs, K_II (Mode II) is larger than K_I (Mode I) and K_III (Mode III). Specifically, the thermal load on the wheel tread during braking contributes up to 23.83% to K_II when the wheel tread reaches the martensitic phase transition temperature due to brake failure. These results are consistent with the observed radial propagation of thermal cracks in wheel treads under operational conditions. Full article

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20 pages, 6428 KiB

Open AccessArticle

Dynamic Models of Mechanical Seals for Turbomachinery Application

by Renat Badykov, Sergei Falaleev, Maxim Benedyuk and Dmitriy Diligenskiy

Lubricants 2024, 12(10), 355; https://doi.org/10.3390/lubricants12100355 - 16 Oct 2024

One of the primary causes of mechanical face seal failure is rotor vibration. Traditional dynamic seal models often cannot fully explain failure mechanisms. The dynamic models of seals proposed in this paper, including those developed by the authors, are valuable for predicting seal [...] Read more.

One of the primary causes of mechanical face seal failure is rotor vibration. Traditional dynamic seal models often cannot fully explain failure mechanisms. The dynamic models of seals proposed in this paper, including those developed by the authors, are valuable for predicting seal dynamics during operation in specific turbomachinery and for explaining the causes of seal failure. The single-mass dynamic model is suitable for analyzing the dynamics of contact mechanical face seals and simply designed dry gas seals. The two-mass dynamic model is used to investigate the operational dynamics processes of classical dry gas seals under complex loading conditions. The three-mass dynamic model is used to study various complex types of mechanical face seals. This model can determine the normal operating condition range and explain leakage mechanisms in the presence of excessive rotor vibrations. Full article

(This article belongs to the Special Issue Gas Lubrication and Dry Gas Seal)

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17 pages, 4963 KiB

Open AccessArticle

Predictive Model for Scuffing Temperature Field Rise of Spiral Bevel Gears under Different Machining Conditions

by Zhi-Jie Cai, Xi-Qing Zheng, Hui-Qing Lan, Liu-Na Wang, Si-Wei Yang and Rui Shen

Lubricants 2024, 12(10), 354; https://doi.org/10.3390/lubricants12100354 - 14 Oct 2024

Spiral bevel gears are extensively employed in mechanical transmissions; however, they are prone to adhesive wear when operating under high-speed and heavy-load conditions. Research indicates that the tooth surface roughness of gears significantly influences the friction and wear of the meshing gears. The [...] Read more.

Spiral bevel gears are extensively employed in mechanical transmissions; however, they are prone to adhesive wear when operating under high-speed and heavy-load conditions. Research indicates that the tooth surface roughness of gears significantly influences the friction and wear of the meshing gears. The present study delves into the origins of tooth surface roughness through the integration of the W-M function and fractal theory. Utilizing an involute helical gear with surface roughness for tooth cutting, a three-dimensional model is established with roughened tooth surfaces. This paper introduces an approach to developing three-dimensional gear models with roughness and applies the finite element method to perform thermodynamic analysis on gears exhibiting diverse levels of surface roughness. The thermal analysis of gears with varying degrees of roughness was conducted using the finite element method. Comparative analysis of the results under specific operating conditions elucidated the impact of roughness on tooth surface temperature rise. In order to validate the simulation model, an experimental test platform for spiral bevel gears of identical size was established. This model integrates tooth surface roughness with thermodynamic analysis, allowing for the rapid assessment of tooth surface temperature rise under different machining conditions, and reducing the cost of validating predicted tooth surface load-carrying capacity. Full article

(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)

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19 pages, 19105 KiB

Open AccessArticle

Investigation of Tribological Properties of Inconel 601 under Environmentally Friendly MQL and Nano-Fluid MQL with Pack Boronizing

by Gonca Uslu, Mehmet Erdi Korkmaz, Rajab Hussein Rajab Elkilani, Munish Kumar Gupta and Govind Vashishtha

Lubricants 2024, 12(10), 353; https://doi.org/10.3390/lubricants12100353 - 14 Oct 2024

Friction and high temperatures greatly affect the hardness and processing efficiency of superalloys. Therefore, it is important to provide a coating on their surfaces with a hard layer. In this study, pack boronizing was applied on Inconel 601 to improve its microstructure and [...] Read more.

Friction and high temperatures greatly affect the hardness and processing efficiency of superalloys. Therefore, it is important to provide a coating on their surfaces with a hard layer. In this study, pack boronizing was applied on Inconel 601 to improve its microstructure and tribological properties. In this regard, tribological tests were performed under MQL, nano-MQL1 (MQL + CuO), and nano-MQL2 (MQL + TiO₂) environments. The research results showed that the lowest wear depth, friction force, coefficient of friction (CoF), and volume loss values were obtained in pack-boronized Inconel 601 in a nano-MQL2 environment. In the nano-MQL2 environment, the wear depth decreased by 17.81% (from 57.922 µm to 47.605 µm) with package-boronized Inconel 601 compared to as-received Inconel 601 at a 45 N load. Pack-boronized Inconel 601 experienced an average reduction of 30.23%, 41.60%, and 52.32% in friction force when switching from dry to MQL, nano-MQL1, and nano-MQL2 environments, respectively. It was also observed that the coefficient of friction (CoF) and volume loss values decreased with pack boronizing in an MQL/nano-MQL environment. In a nano-MQL2 environment at 15 N load, volume losses for as-received and boron-coated Inconel 601 were determined as 0.288 mm³ and 0.249 mm³, respectively (13.54% decrease). The findings of this study demonstrate that pack boronizing and MQL and nano-MQL techniques enhance the tribological characteristics of Inconel 601 alloys. Full article

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16 pages, 7493 KiB

Open AccessArticle

On Lubrication Regime Changes during Forward Extrusion, Forging, and Drawing

by Man-Soo Joun, Yun Heo, Nam-Hyeon Kim and Nam-Yun Kim

Lubricants 2024, 12(10), 352; https://doi.org/10.3390/lubricants12100352 - 14 Oct 2024

The tribological phenomena concerning the lubrication regime change (LRC) during bulk metal forming are comprehensively studied. A multi-step cold forward extrusion process shows the evolution of LRC and reveals the shortcomings of the traditional Coulomb friction law. The previous works of the specific [...] Read more.

The tribological phenomena concerning the lubrication regime change (LRC) during bulk metal forming are comprehensively studied. A multi-step cold forward extrusion process shows the evolution of LRC and reveals the shortcomings of the traditional Coulomb friction law. The previous works of the specific author’s research group on friction are reviewed, focusing on the LRC during bulk metal forming. Various LRC phenomena from various examples are revealed. It has been found that the drawing and forward extrusion processes are vulnerable to LRC because of significant sliding motion at the material–die interface, and that when the strain hardening of the material is slight, the influence of friction increases, and as a result, the influence of LRC increases excessively. The new findings also include the impact of LRC on the macroscopic phenomena of the process and the reason for the sharp increase in friction coefficient via LRC, which is validated by the work of Wilson. This paper aims to make engineers and researchers think much of the tribology with lubricant in bulk metal forming with a focus on the dependence of tribological phenomena on the state of the lubricants and the irrationality of traditional friction law, especially in the forging of materials with a low strain hardening capability. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)

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12 pages, 1852 KiB

Open AccessArticle

Mixed Friction in Fully Lubricated Elastohydrodynamic Contacts—Theory or Reality

by Dirk Bartel

Lubricants 2024, 12(10), 351; https://doi.org/10.3390/lubricants12100351 - 14 Oct 2024

Mixed friction in liquid-lubricated tribosystems is characterized by the simultaneous presence of liquid and solid friction. Liquid friction results from the shearing of the lubricant, and solid friction from deformation and adhesion. Elastic hysteresis and plastic deformation of the solids cause energy losses [...] Read more.

Mixed friction in liquid-lubricated tribosystems is characterized by the simultaneous presence of liquid and solid friction. Liquid friction results from the shearing of the lubricant, and solid friction from deformation and adhesion. Elastic hysteresis and plastic deformation of the solids cause energy losses during deformation and the separation of molecular bonds between the solids causes energy losses during adhesion. The classic conception of mixed friction presupposes direct contact between rough solids for solid friction to exist. However, if hysteresis losses are fully accepted as a cause for solid friction, every fully lubricated elastohydrodynamic contact would ultimately be a mixed friction contact since the elastic deformations of the solids also cause a loss of energy induced by hysteresis. Thus, the classic conception of mixed friction should be expanded since mixed friction can occur even when solids do not have any direct contact. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

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