Lubricants

15 pages, 5013 KiB

Open AccessArticle

The Influence of a Lubricant Medium on the Development of Fretting Wear in an Interference Fit Connection

by Dalibor Barta, Sławomir Kowalski, Ján Dižo and Aleš Dittrich

Lubricants 2024, 12(9), 327; https://doi.org/10.3390/lubricants12090327 - 23 Sep 2024

Viewed by 309

Fretting wear is a phenomenon occurring in many engineering objects, including push fit connections. In view of a large number of factors conducive to wear development, it is difficult to describe the mechanism of wear initiation and development. Therefore, various methods are sought [...] Read more.

Fretting wear is a phenomenon occurring in many engineering objects, including push fit connections. In view of a large number of factors conducive to wear development, it is difficult to describe the mechanism of wear initiation and development. Therefore, various methods are sought to limit wear development. The use of a lubricant may be one of those ways. The aim of this article is to present the results of testing the influence of a lubricant medium on the development of fretting wear in interference fit connections. As a lubricant medium, MoS₂ and Whitmore greases were used. For that purpose, wear tests were first conducted on the shaft/sleeve tribological kinematic pair, and then observations and laboratory measurements were performed. The observations demonstrated the presence of fretting wear traces on all tested samples, irrespective of the tribological kinematic pair being tested. The main kind of damage consisted of material build-ups which, during operation, become oxidised and, while moving along the connection, caused local abrasion and micropits. The best results in restricting the development of fretting wear were achieved with Whitmore grease. Full article

► Show Figures

Figure 1

15 pages, 11180 KiB

Open AccessArticle

Numerical Study on Characteristics of Lead-Bismuth Lubricated Hydrodynamic Bearing Considering Non-Condensable Gas

by Kefeng Lyu, Yuanyuan Zhang, Xudan Ma and Zude Cheng

Lubricants 2024, 12(9), 326; https://doi.org/10.3390/lubricants12090326 - 23 Sep 2024

Viewed by 319

Abstract

Lead-Bismuth Eutectic (LBE) is an interesting candidate as a coolant for Generation IV nuclear power plants. Lead-bismuth lubricated radial guide bearing is the key component of the mechanical pump in a lead-bismuth coolant system. In this paper, the transient calculation model of multiphase [...] Read more.

Lead-Bismuth Eutectic (LBE) is an interesting candidate as a coolant for Generation IV nuclear power plants. Lead-bismuth lubricated radial guide bearing is the key component of the mechanical pump in a lead-bismuth coolant system. In this paper, the transient calculation model of multiphase lubrication flow field of journal bearing is established by using Singhal full cavitation model and structured dynamic grid technique. Due to the saturated vapors of LBE being very low, the effects of different Non-Condensable Gas (NCG) contents on the characteristics of lead-bismuth lubricated journal bearing systems were analyzed. The results show that the NCG content has an obvious influence on the working state of the bearing. With the increase in NCG content, the bearing load capacity decreases. Under the same load, with the increase in NCG content, the eccentricity of the static equilibrium position will be larger, which will increase the risk of bearing contact with the bearing bush. Moreover, the increase of NCG content will lead to the increase of tangential oil film force work, which is helpful to improve rotor stability. Full article

► Show Figures

Figure 1

18 pages, 14791 KiB

Open AccessArticle

Effect of Substrate Bias on the Structure and Tribological Performance of (AlTiVCrNb)C_xN_y Coatings Deposited via Graphite Co-Sputtering

by Haichao Cai, Pengge Guo, Yujun Xue, Lulu Pei, Yinghao Zhang and Jun Ye

Lubricants 2024, 12(9), 325; https://doi.org/10.3390/lubricants12090325 - 23 Sep 2024

Viewed by 362

Abstract

In the existing literature, there are few studies on the effect of deposition bias on the tribological properties of carbon-doped high-entropy alloy coatings. In order to further study the effect of the deposition bias on the properties of coatings, (AlTiVCrNb)C_xN_y [...] Read more.

In the existing literature, there are few studies on the effect of deposition bias on the tribological properties of carbon-doped high-entropy alloy coatings. In order to further study the effect of the deposition bias on the properties of coatings, (AlTiVCrNb)C_xN_y coatings were deposited via unbalanced RF magnetron sputtering. The microstructure and tribological properties of carbon-doped high-entropy alloy ceramic coatings under different deposition biases were studied. The composition, morphology, crystal structure, and chemical morphology of each element of the coating were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The hardness, elastic modulus, friction, and wear properties of the coating were further characterized using a nanoindentation instrument, reciprocating sliding friction, a wear tester, and a white light interferometer. The coating density reached the optimal level when the deposition bias value was 90 V. The hardness and elastic modulus of the (AlTiVCrNb)C_xN_y coating increased first and then decreased with an increase in deposition bias, and the maximum hardness was 23.98 GPa. When the deposition bias was 90 V, the coating formed a good-quality carbon transfer film on the surface of the counterbody due to sp2 clusters during the friction and wear process. The average friction coefficient and wear rate of the (AlTiVCrNb)C_xN_y coating were the lowest, 0.185 and 1.6 × 10⁻⁷ mm³/N·m, respectively. The microstructure, mechanical properties, and tribological performance of the (AlTiVCrNb)C_xN_y coating were greatly affected by the change in deposition bias, and an (AlTiVCrNb)C_xN_y coating with excellent structure and friction properties could be prepared using graphite co-sputtering. Full article

► Show Figures

Figure 1

16 pages, 8886 KiB

Open AccessReview

Applications of Phyllosilicates Mineral Powder as Anti-Wear Lubricating Materials in Lubricating Oil and Grease: A Review

by Nan Jiang and Feng Nan

Lubricants 2024, 12(9), 324; https://doi.org/10.3390/lubricants12090324 - 20 Sep 2024

Viewed by 352

Abstract

Wear caused by friction is one of the main causes of most mechanical component failures. The application of powders as anti-wear lubricating materials has achieved great advances, which are of great significance in reducing friction and wear. This review focuses on the applications [...] Read more.

Wear caused by friction is one of the main causes of most mechanical component failures. The application of powders as anti-wear lubricating materials has achieved great advances, which are of great significance in reducing friction and wear. This review focuses on the applications of phyllosilicates mineral powders as anti-wear lubricating materials in lubricating oil. The tribological behaviors of phyllosilicates mineral powders and the combination of phyllosilicates mineral powders with other materials as lubricant additives are provided. Moreover, the fundamental mechanism are systematically reviewed and concluded based on tribology data and surface, and interface analysis. Finally, current unsolved issues and suggestions for future research on phyllosilicates mineral powders as lubricant additives are proposed. Full article

(This article belongs to the Special Issue Anti-wear Lubricating Materials)

► Show Figures

Graphical abstract

24 pages, 6766 KiB

Open AccessArticle

Environmentally Acceptable Lubricants for Stern Tube Application: Shear Stability and Friction Factor

by Marek Večeř, Petr Stavárek, Simona Krčková, Ladislav Zelenka and Sergio Armada

Lubricants 2024, 12(9), 323; https://doi.org/10.3390/lubricants12090323 - 20 Sep 2024

Viewed by 302

Abstract

Stern tube lubricants are essential in maritime operations, safeguarding ship propeller shafts from wear and corrosion while ensuring efficient propulsion. Their role in reducing friction and maintaining system integrity is critical. With growing environmental concerns, the adoption of environmentally acceptable lubricants (EALs) for [...] Read more.

Stern tube lubricants are essential in maritime operations, safeguarding ship propeller shafts from wear and corrosion while ensuring efficient propulsion. Their role in reducing friction and maintaining system integrity is critical. With growing environmental concerns, the adoption of environmentally acceptable lubricants (EALs) for stern tubes has gained importance, balancing operational performance with environmental protection. This study investigates the rheological and tribological properties of EALs formulated for ship propeller stern tube applications. The primary focus is on comparing these EALs with conventional mineral oils to assess their suitability in marine environments. EALs are increasingly favored due to their biodegradability and reduced environmental impact. Key parameters such as shear stability, friction factor, and temperature dependency were evaluated using a range of experimental methods including rotational viscometry and tribological analysis. The results indicate that the newly formulated EALs based on synthetic esters exhibit the highest viscosity index, a higher range of shear stability, and lower friction factors, compared to commercially available mineral oils, especially under varying operational conditions. These findings contribute to the ongoing efforts to promote eco-friendly lubricants in maritime industries, aligning with global environmental protection initiatives. Full article

(This article belongs to the Special Issue Recent Advances in Green Lubricants)

► Show Figures

Figure 1

15 pages, 1662 KiB

Open AccessCommunication

A Fully Implicit Coupled Scheme for Mixed Elastohydrodynamic Problems on Co-Allocated Grids

by Sören Wettmarshausen and Hubert Schwarze

Lubricants 2024, 12(9), 322; https://doi.org/10.3390/lubricants12090322 - 19 Sep 2024

Viewed by 314

Abstract

In the modeling of elastohydrodynamic lubrication problems considering mixed friction, strongly coupled dependencies occur due to piezo-viscous effects and asperities, which can make a numerical solution exceptionally difficult. A fully implicit coupled scheme for solving mixed elastohydrodynamic lubrication problems is presented. Our scheme [...] Read more.

In the modeling of elastohydrodynamic lubrication problems considering mixed friction, strongly coupled dependencies occur due to piezo-viscous effects and asperities, which can make a numerical solution exceptionally difficult. A fully implicit coupled scheme for solving mixed elastohydrodynamic lubrication problems is presented. Our scheme uses finite-volume discretization and co-allocated grids for hydrodynamic pressure and elastic deformation. To provide strong coupling between pressure and deformation even in the highly loaded zone, a correction term that adds numerical diffusion is used. The resulting linear equation system of this scheme can be efficiently solved by Krylov subspace methods. This results in an improved accuracy and computational efficiency compared to the existing methods. This approach was validated and has been shown to be accurate. Full article

(This article belongs to the Special Issue Advances in Mixed Lubrication)

► Show Figures

Graphical abstract

25 pages, 1732 KiB

Open AccessReview

A Review of Wear in Additive Manufacturing: Wear Mechanism, Materials, and Process

by Xiangjun Jiang, Juntao Lu, Na Zhao, Zhen Chen and Zhiming Zhao

Lubricants 2024, 12(9), 321; https://doi.org/10.3390/lubricants12090321 - 17 Sep 2024

Viewed by 855

Abstract

In fields such as industrial engineering and healthcare, additive manufacturing technology is a focal point for researchers. Wear represents a significant challenge for additive manufacturing technology, increasingly emerging as a research hotspot in recent years. This review categorizes and summarizes wear issues in [...] Read more.

In fields such as industrial engineering and healthcare, additive manufacturing technology is a focal point for researchers. Wear represents a significant challenge for additive manufacturing technology, increasingly emerging as a research hotspot in recent years. This review categorizes and summarizes wear issues in additive manufacturing technology, providing a comprehensive overview of wear mechanisms, materials, and the effects of additive manufacturing processes on wear. Research indicates that different wear mechanisms result in varying wear characteristics. The inherent properties of the materials significantly influence wear during the manufacturing process. Modifying material compositions and optimizing microstructures can enhance the wear properties of additive manufacturing products. Additionally, the study of additive manufacturing technology in repair and maintenance is a current and anticipated research hotspot for the coming decades. In the research of additive manufacturing processes, the effective regulation of process parameters and their post-processing play a positive role in enhancing the wear characteristics of products produced via additive manufacturing. Lastly, the challenges and recent advancements concerning wear issues in the field of additive manufacturing technology research are summarized. Full article

(This article belongs to the Special Issue Wear in Additive Manufacturing)

► Show Figures

Figure 1

18 pages, 10290 KiB

Open AccessArticle

Assessment of Hydraulic Oil Properties during Operation of a Mini Loader

by Diego Andrés Duque-Sarmiento and Daysi Alexandra Baño-Morales

Lubricants 2024, 12(9), 320; https://doi.org/10.3390/lubricants12090320 - 17 Sep 2024

Viewed by 563

Abstract

This study employs a rigorous methodology to assess the condition of the hydraulic oil in a recently introduced mini skid-steer loader. The assessment is conducted through laboratory analysis, which adheres to a range of international standards. The objective is to provide accurate insights [...] Read more.

This study employs a rigorous methodology to assess the condition of the hydraulic oil in a recently introduced mini skid-steer loader. The assessment is conducted through laboratory analysis, which adheres to a range of international standards. The objective is to provide accurate insights into the viscosity, particle count, and characterisation of the oil, along with thermographic data. The friction of oil is evaluated at specific time points: 0, 10, 100, 125, and 150 h of operation. This examination offers a comprehensive insight into the alterations in oil characteristics during a pivotal period when machine components are undergoing initial consolidation and abrasion to attain the factory-defined performance thresholds. The principal aim of this research is to provide valuable insights into the wear of oil and hydraulic system components through an in-depth analysis of a range of variables. Moreover, the investigation aims to ascertain the impact of this factor on the temperature elevation of system components and accessories to formulate enhanced technical guidelines for implementation. The main results indicate the presence of particles in the oil, resulting in a cleanliness code of 23/21/13, which exceeds the permissible threshold of 20/18/15 specified in ISO 11171. In addition, hydraulic oil shows a viscosity instability of more than 10% due to moisture absorption, leading to wear of mechanical components composed of iron, nickel, copper, zinc, and silicon. This deterioration is corroborated by thermographic evaluations, which reveal a considerable temperature increase in components such as cylinders and system accessories. Full article

► Show Figures

Figure 1

19 pages, 14430 KiB

Open AccessArticle

The Preparation of MoS₂/Metal Nanocomposites Functionalized with N-Oleoylethanolamine: Application as Lubricant Additives

by Yaping Xing, Zhiguo Liu, Weiye Zhang, Zhengfeng Jia, Weifang Han, Jinming Zhen and Ran Zhang

Lubricants 2024, 12(9), 319; https://doi.org/10.3390/lubricants12090319 - 14 Sep 2024

Viewed by 604

Abstract

In this study, MoS₂ nanosheets have been prepared and treated ultrasonically with silver ammonia solutions. The MoS₂/Ag precursor was reduced using dopamine (DA) as reducing and linking agent at room temperature, and it was subjected to a hydrothermal treatment to [...] Read more.

In this study, MoS₂ nanosheets have been prepared and treated ultrasonically with silver ammonia solutions. The MoS₂/Ag precursor was reduced using dopamine (DA) as reducing and linking agent at room temperature, and it was subjected to a hydrothermal treatment to produce MoS₂/Ag nanocomposites (denoted as MoAg). The MoAg samples were functionalized with N-oleoylethanolamine to improve dispersion in the base oil component of additives. Use of the functionalized MoAg (denoted as Fc-MoAg) as a lubricant additive for steel balls resulted in effective friction reduction and anti-wear. This work avoids ion exchange during exfoliation, and the Ag⁺ has been reduced to nano-silver particles by dopamine to enlarge the layer spaces of MoS₂. Taking the case of lubrication with base oil containing Fc-Mo_0.6Ag₁₅, the wear scar diameters and coefficients of friction of the steel balls were 0.428 and 0.098 mm, respectively, which were about three-fifths base oil. In addition, MoS₂/Cu and MoS₂/Ni nanocomposites were synthesized and the tribological properties associated with steel/steel balls assessed. The results demonstrate that all MoS₂/metal composites exhibit enhanced tribological behavior in the steel/steel pair tests. Both nanocomposite synergy and the tribofilm containing sulfide, oxide, carbide, and other compounds play important roles in achieving reduced friction and improved anti-wear. The friction and wear properties of base oil containing Fc-MoAg and commercial additives were evaluated using a four-ball wear tester with steel/steel, steel/zirconia and zirconia/zirconia pairs. The base oil containing Fc-MoAg delivered smaller coefficients of friction (COFs) and/or scarring groove depths than those observed with the use of pure base oil and base oil containing commercial additives. Full article

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

► Show Figures

Figure 1

12 pages, 2255 KiB

Open AccessArticle

Vibration Friction Investigation on the NCS of Joints of the CNC Machine Tools Considering Friction Factor

by Yunnan Teng, Xiangpu Liu and Liyang Xie

Lubricants 2024, 12(9), 318; https://doi.org/10.3390/lubricants12090318 - 14 Sep 2024

Viewed by 438

Abstract

Machine tool vibrations play a significant role in hindering productivity during machining. The growing vibrations accelerate tool wear and chipping, cause a poor wave surface finish, and may damage the spindle bearing. Some research showed that tribological properties such as friction factors can [...] Read more.

Machine tool vibrations play a significant role in hindering productivity during machining. The growing vibrations accelerate tool wear and chipping, cause a poor wave surface finish, and may damage the spindle bearing. Some research showed that tribological properties such as friction factors can have obvious influences on the topography of rough surfaces and the nonlinear dynamic characteristics of machine tool systems. Therefore, studying the vibration friction dynamic characteristics on the normal contact stiffness (NCS) of joints of CNC machine tools is absolutely necessary for improving the machining accuracy and precision of the whole system. The study results of NCS of joints of the CNC and the friction coefficient are discussed in this paper. The model of NCS based on fractal parameters was obtained. The models of deformations of the rough surfaces and contact surfaces were deduced. The results showed that the NCS based on the calculation method considering the elastic–plastic deformation of the asperity is much higher in precision than the methods considering only elastic or plastic deformation separately. The observations this paper described suggest that in the CNC machine tools system, higher D and G and higher friction coefficients lead to higher normal contact stresses (NCSs). Full article

► Show Figures

Figure 1

19 pages, 9051 KiB

Open AccessArticle

Dynamic Modeling and Behavior of Cylindrical Roller Bearings Considering Roller Skew and the Influence of Eccentric Load

by Yang Yang, Jiayu Wang, Meiling Wang and Baogang Wen

Lubricants 2024, 12(9), 317; https://doi.org/10.3390/lubricants12090317 - 14 Sep 2024

Viewed by 357

Abstract

At high speeds, skew and skid may frequently occur for the rollers in cylindrical roller bearings, especially when under eccentric load, as the uneven load distribution along the generatrix of the roller further aggravates this phenomenon. In this paper, a dynamic model of [...] Read more.

At high speeds, skew and skid may frequently occur for the rollers in cylindrical roller bearings, especially when under eccentric load, as the uneven load distribution along the generatrix of the roller further aggravates this phenomenon. In this paper, a dynamic model of a cylindrical roller bearing was established, taking into account roller skewing and interactions with the cage. Firstly, the interaction between the roller and the raceway was calculated by slicing the roller along its generatrix. Furthermore, the computation of the interaction between the roller and the cage is based on elastic theory, taking into account pocket clearance. Subsequently, the dynamic equations for both rollers and cage were derived. Based on this foundation, an investigation was conducted to reveal how rotational speed, radial loads, and moment loads affect roller slipping, skewing characteristics, and interactions with the cage under uneven load conditions. The findings indicate a direct proportionality between roller slipping and bearing speed while exhibiting an inverse relationship with load magnitude. Additionally, it was observed that both bearing speed and load have a direct influence on roller skewing angle. Moreover, normal interaction force between the roller and cage demonstrates a direct proportionality to bearing speed while inversely correlating with load magnitude. Full article

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

► Show Figures

Figure 1

35 pages, 11086 KiB

Open AccessArticle

Research on the Correlation between Mechanical Seal Face Vibration and Stationary Ring Dynamic Behavior Characteristics

by Yunfeng Song, Hua Li, Wang Xiao, Shuangxi Li and Qingfeng Wang

Lubricants 2024, 12(9), 316; https://doi.org/10.3390/lubricants12090316 - 12 Sep 2024

Viewed by 419

Abstract

To address the lack of reliable measurement methods for identifying wear mechanisms and predicting the state of mechanical seal tribo-parts, this study proposes a method for characterizing tribological behavior based on measuring face vibration acceleration. It aims to uncover the source mechanism of [...] Read more.

To address the lack of reliable measurement methods for identifying wear mechanisms and predicting the state of mechanical seal tribo-parts, this study proposes a method for characterizing tribological behavior based on measuring face vibration acceleration. It aims to uncover the source mechanism of mechanical seal face vibration acceleration influenced by tribology and dynamic behavior. This research delves into the dynamic behavior characteristics and vibration acceleration of the mechanical seal stationary ring. We explored the variation pattern of face vibration acceleration root mean square (RMS) with rotation speed, sealing medium pressure, and face surface roughness. The results indicate that under constant medium pressure, an increase in rotation speed leads to a decrease in acceleration RMS and an increase in face temperature. Similarly, under constant rotation speed, an increase in medium pressure results in nonlinear changes in acceleration RMS, forming an “M” shape, along with an increase in face temperature. Furthermore, under conditions of constant medium pressure and rotation speed, an increase in the surface roughness of the rotating ring face corresponds to an increase in acceleration RMS and face temperature. Upon starting the mechanical seal, both acceleration RMS and temperature initially increase before decreasing, a trend consistent with the Stribeck curve. Full article

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

► Show Figures

Figure 1

26 pages, 14958 KiB

Open AccessArticle

Study on Temperature Field Distribution of a High-Speed Double-Helical Gear Pair with Oil Injection Lubrication

by Xiaozhou Hu, Yangmei Yuan and Jie Chen

Lubricants 2024, 12(9), 315; https://doi.org/10.3390/lubricants12090315 - 9 Sep 2024

Viewed by 525

Abstract

The temperature field distribution of high-speed double-helical gears under oil injection lubrication is investigated by obtaining heat flux density and convective heat transfer coefficients through theoretical calculations and CFD (computational fluid dynamics) simulations. Based on the CFD method, fluid simulations are performed to [...] Read more.

The temperature field distribution of high-speed double-helical gears under oil injection lubrication is investigated by obtaining heat flux density and convective heat transfer coefficients through theoretical calculations and CFD (computational fluid dynamics) simulations. Based on the CFD method, fluid simulations are performed to obtain the distribution of lubricating oil on the surface of the double-helical gears, the velocity streamline diagram of the lubricating oil, and the convective heat transfer coefficients of different surfaces of the gears. The friction heat flux density is calculated using Hertzian contact theory and theoretical formula of heat generation. The double-helical gears’ steady-state temperature field simulation uses this heat flux density as a boundary condition. The correctness of the calculation method is verified through experiments. The study shows that increasing the jet velocity allows the jet to reach the tooth surface more effectively, improving the cooling effect and reducing the maximum gear temperature. However, the relationship between the jet velocity and the minimum gear temperature is non-linear. Within a certain range, increasing the jet diameter makes the jet wider, and the area covered by the lubricating oil becomes larger as the jet spreads around the gear teeth, enhancing the cooling effect. An increase in gear speed leads to an increase in frictional heat flux density; moreover, the high-velocity airflow generated by the increased speed reduces the amount of lubricant entering the mesh zone, which in turn causes the maximum temperature of the gears to continue to rise. Full article

► Show Figures

Figure 1

11 pages, 9625 KiB

Open AccessArticle

Running-In of DLC–Third Body or Transfer Film Formation

by Joachim Faller and Matthias Scherge

Lubricants 2024, 12(9), 314; https://doi.org/10.3390/lubricants12090314 - 4 Sep 2024

Viewed by 625

Abstract

Amorphous carbon coatings are widely used due to their beneficial friction and wear characteristics. A detailed understanding of their behavior during running-in, apart from model tribosystems, has yet to be obtained. Multiple analytical methods were used to detect the physical and chemical changes [...] Read more.

Amorphous carbon coatings are widely used due to their beneficial friction and wear characteristics. A detailed understanding of their behavior during running-in, apart from model tribosystems, has yet to be obtained. Multiple analytical methods were used to detect the physical and chemical changes in a ta-C coating and its thermally sprayed, metallic counterpart after a running-in procedure with pin-on-disk experiments. Both coatings exhibited changes in their surface and near-surface chemistry. The mechanisms in and on the metallic coating were identified to be a mixture of the third-body type, with the formation of gradients in the microstructure and chemistry and an additional carbon-rich tribofilm formation on top. The ta-C coating’s changes in chemistry with sp² enrichment and lubricant element inclusions proved to be too complex to allocate them to tribofilm or third-body formation. Full article

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

► Show Figures

Figure 1

16 pages, 3838 KiB

Open AccessArticle

The Generation and Evolution of High-Order Wheel Polygonal Wear from the Effects of Wheelset Rotation

by Yahong Dong and Shuqian Cao

Lubricants 2024, 12(9), 313; https://doi.org/10.3390/lubricants12090313 - 4 Sep 2024

Viewed by 566

Abstract

Polygonal wear affects driving safety and drastically shortens a wheel’s life. This work establishes a wheel–rail coupled system’s rotor dynamics model and a wheel polygonal wear model, taking into account the wheelset’s flexibility, the effect of the wheelset rotation, and the initial wheel [...] Read more.

Polygonal wear affects driving safety and drastically shortens a wheel’s life. This work establishes a wheel–rail coupled system’s rotor dynamics model and a wheel polygonal wear model, taking into account the wheelset’s flexibility, the effect of the wheelset rotation, and the initial wheel polygon. The energy approach is applied to study the stability of the self-excited vibration of a wheel–rail coupled system. The wheel polygonal wear generation and evolution mechanism is revealed, along with the impact of vehicle and rail characteristics on a wheel’s high-order polygon. The findings demonstrate that wheel polygonal wear must occur in order for the wheel–rail system to experience self-excited vibration, which is brought on by a feedback mechanism dominated by creepage velocity. Additionally, the Hopf bifurcation characteristic is displayed by the wheel–rail system’s self-excited vibration. Wheel polygonal wear is characterized by “fixed frequency and integer division”, and the wheelset flexibility largely determines the fixed frequency of high-order polygonal wear, which is mostly unaffected by the suspension characteristics of the vehicle. By decreasing the tire load, increasing the wheelset’s damping, and choosing a variable running speed, the progression of polygonal wear on wheels can be prevented. Future investigations on the suppression of wheel polygonal wear evolution can be guided by the results. Full article

► Show Figures

Figure 1

40 pages, 6373 KiB

Open AccessReview

Research on Polymer Wear under Water Conditions: A Review

by Shuyuan Song, Zehan Zhu, Shaonan Du, Yunlong Li and Changfu Liu

Lubricants 2024, 12(9), 312; https://doi.org/10.3390/lubricants12090312 - 4 Sep 2024

Viewed by 731

Abstract

Polymeric materials are widely used in aerospace, biomedical, marine, and agricultural applications due to their viscoelasticity and corrosion resistance. Polymeric materials fail due to wear during their service life, so studying their wear behavior is essential to control and predict their service life. [...] Read more.

Polymeric materials are widely used in aerospace, biomedical, marine, and agricultural applications due to their viscoelasticity and corrosion resistance. Polymeric materials fail due to wear during their service life, so studying their wear behavior is essential to control and predict their service life. This paper summarizes the progress of water lubrication research as well as experimental studies on the wear of polymeric materials under aqueous conditions. The effects of lubrication conditions, material formulation ratios, load, sliding speed, impact angle, abrasive particles, and temperature factors on the wear behavior of commonly used polymeric materials ideal for water lubrication (NBR, SBR, NR, EP, polyethylene, and their composites, etc.) are summarized in terms of the three most frequently occurring forms of wear, namely, two-body wet sliding wear, two-body erosive wear, and three-body wet abrasive particle wear. The results show that the mechanical properties, such as hardness, can be effectively changed by altering the formulation ratios of the materials, and the hardness and hydrophilicity of the formulations can further affect the wear and lubrication. In general, the coefficient of friction and the wear rate decrease with the increase in hardness, and the increase in temperature leads to the localized lubrication failure and the aging of the materials, which in turn leads to the intensification of wear. Among the working condition factors, load and sliding speeds are the most important factors affecting the wear, and the wear rate increases with the increase in the load and sliding speed; in contrast, the three-body wet abrasive wear is more obviously affected by the load. In the study of the impact angle effect, the overall trend of the erosion wear rate with the increase in the angle shows the first rise and then fall, the maximum value is mostly concentrated in the 45–60° between. Usually, the increase in the abrasive particle size can make the wear rate increase. Overall, the three-body wet abrasive wear of the rubber material wear rate shows first an increase and then a decrease. The research in this paper provides theoretical support and reference ideas for the tribological study of polymer materials in the water environment and puts forward the outlook for future water lubrication and material improvement of the research directions and applications. Full article

(This article belongs to the Special Issue Advanced Polymeric and Colloidal Lubricants)

► Show Figures

Graphical abstract

14 pages, 4353 KiB

Open AccessArticle

Premature Damage in Bearing Steel in Relation with Residual Stresses and Hydrogen Trapping

by Maximilian Baur, Iyas Khader, Dominik Kürten, Thomas Schieß, Andreas Kailer and Martin Dienwiebel

Lubricants 2024, 12(9), 311; https://doi.org/10.3390/lubricants12090311 - 3 Sep 2024

Viewed by 551

Abstract

In this study, premature damage in cylindrical roller bearings made of 100Cr6 (SAE 52100) was investigated. For this purpose, full bearing tests were carried out using two different lubricant formulations with similar viscosities. Published research has pointed out the occurrence of tribo-chemical reactions [...] Read more.

In this study, premature damage in cylindrical roller bearings made of 100Cr6 (SAE 52100) was investigated. For this purpose, full bearing tests were carried out using two different lubricant formulations with similar viscosities. Published research has pointed out the occurrence of tribo-chemical reactions that cause lubricant degradation and the release of hydrogen in tribo-contact. Hydrogen content measurements were conducted on tested samples, and these measurements showed dependence on the lubricant formulations. Hydrogen diffusion and trapping were identified as significant factors influencing premature damage. The measurement of trapping energies was conducted by thermal desorption spectroscopy, whereas residual stresses, which influence hydrogen diffusion and accumulation, were measured using X-ray diffraction. The measured trapping energies indicated that rolling contact caused the creation and release of hydrogen traps. Over-rolling resulted in changes in residual stress profiles in the materials, demonstrated by changes in stress gradients. These can be directly linked to subsurface hydrogen accumulation. Hence, it was possible to determine that the location of the microstructural damage (WEC) was correlated with the residual stress profiles and the subsurface von Mises stress peaks. Full article

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

► Show Figures

Figure 1

18 pages, 36375 KiB

Open AccessTechnical Note

Short-Term Influence of Water Ingress on Wear in Pitch Bearings of Wind Turbines

by Matthias Stammler, Henry Ellerbrok, Rihard Pasaribu and Ulf Rieper

Lubricants 2024, 12(9), 310; https://doi.org/10.3390/lubricants12090310 - 2 Sep 2024

Viewed by 758

Abstract

The pitch bearings of wind turbines are slowly oscillating, grease-lubricated slewing bearings. They facilitate the pitching movements of blades which control aerodynamic loads. These bearings have diameters of several meters, their blade-side sealings can face the environment, bending moment loads can cause radial [...] Read more.

The pitch bearings of wind turbines are slowly oscillating, grease-lubricated slewing bearings. They facilitate the pitching movements of blades which control aerodynamic loads. These bearings have diameters of several meters, their blade-side sealings can face the environment, bending moment loads can cause radial deformation of the bearing rings, and their highly variable operating temperatures can facilitate condensation of water inside them. All of this makes water ingress into the lubricant possible. There is limited public knowledge with regards to the maximum water content for safe operation in this application. This work presents the results of a series of scaled wind turbine time series tests with both ‘dry’ (no water contamination) and ‘wet’ (10 mass % demineralized water added) greases. A set of four commercially available greases were tested. The time series were scaled from wind turbine operation and represented a 13.7 h worst-case scenario of operation with small oscillation amplitudes and no longer lubrication runs in between. Three of the greases showed reduced friction and no or limited raceway damage in the wet condition, whereas one showed increased friction and raceway damages. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

► Show Figures

Figure 1

14 pages, 5497 KiB

Open AccessArticle

Galling-Free Forging of Titanium Using Carbon-Supersaturated SiC Coating Dies

by Tatsuhiko Aizawa and Tatsuya Fukuda

Lubricants 2024, 12(9), 309; https://doi.org/10.3390/lubricants12090309 - 1 Sep 2024

Viewed by 530

Abstract

The thermal chemical vapor deposition (CVD) process was utilized to fabricate 6H-structured SiC coating dies with carbon control. The carbon-rich clusters along the SiC grain boundaries acted as a pinning site to suppress irregular crystal growth and to homogenize the fine-grained structure. These [...] Read more.

The thermal chemical vapor deposition (CVD) process was utilized to fabricate 6H-structured SiC coating dies with carbon control. The carbon-rich clusters along the SiC grain boundaries acted as a pinning site to suppress irregular crystal growth and to homogenize the fine-grained structure. These massive carbon-supersaturated (MCSed) SiC dies with a thickness of 4 mm were utilized for upsetting pure titanium bars in dry and cold conditions. Under a stress gradient from the contact interface to the depth of the SiC coating, the carbon solute isolated from these carbon clusters diffused through the grain boundaries and formed free carbon agglomerates on the contact interface to the pure titanium bars. These in situ-formed free carbon agglomerates acted as a solid lubricant to sustain the friction coefficient at 0.09 at the hot spots on the contact interface and to protect the dies and bars from severe adhesive wearing. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

► Show Figures

Figure 1

14 pages, 10346 KiB

Open AccessArticle

Biomass-Derived Carbons as Friction Reducing Additives for Lubricants: Tribological Properties of Biochars and Activated Carbons Obtained from Sugar Cane Bagasse

by Audrey Molza, Philippe Bilas, Nadiège Nomède-Martyr, Thierry Césaire, Christelle Yacou, Sarra Gaspard and Philippe Thomas

Lubricants 2024, 12(9), 308; https://doi.org/10.3390/lubricants12090308 - 31 Aug 2024

Viewed by 557

Abstract

Activated carbons are commonly used for adsorption/depollution applications, but only a few studies are related to their lubricating properties. In order to investigate a new family of friction reducers, the tribological properties of biochars and derived activated carbons obtained from sugar cane bagasse [...] Read more.

Activated carbons are commonly used for adsorption/depollution applications, but only a few studies are related to their lubricating properties. In order to investigate a new family of friction reducers, the tribological properties of biochars and derived activated carbons obtained from sugar cane bagasse are investigated. Activated carbons are obtained from either a physical (steam water) or chemical (with phosphoric acid) activation process. The tribological tests show that the activated carbons present very low friction coefficients, close to 0.08. The correlation of textural and tribological investigations shows that the specific surface area of the compounds as well as the microporous and mesoporous domain extensions are key parameters to optimize the friction reduction properties of activated carbons. The friction properties of the compounds are improved if the mesoporous domain extension is above 40% of the total porous volume. This study shows that local biomass waste valorization is possible and that sugar cane bagasse-derived activated carbons appear as interesting new friction reduction additives for lubricants. Full article

► Show Figures

Figure 1

11 pages, 3687 KiB

Open AccessArticle

Evaluation of a Commercial MoS₂ Dry Film Lubricant for Space Applications

by Duval A. Johnson, Marcello Gori, Azhar Vellore, Andrew J. Clough, Scott D. Sitzman, Jeffrey R. Lince and Ashlie Martini

Lubricants 2024, 12(9), 307; https://doi.org/10.3390/lubricants12090307 - 31 Aug 2024

Viewed by 693

Abstract

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding [...] Read more.

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding friction in air and dry gaseous nitrogen atmospheres at ambient temperatures with both linear reciprocating and rotary unidirectional tribo-tests. Measurements are performed for Microseal 200-1 applied on substrates and surface treatments commonly used in aerospace components, particularly stainless steel and a titanium alloy. Our findings indicate that the friction of stainless steel balls sliding on Microseal 200-1-coated disks is significantly influenced by the environment as well as the disk substrate material. The average friction coefficient ranges from 0.12 to 0.48 in air and from 0.04 to 0.41 in dry gaseous nitrogen, and the amount of friction is consistently much higher for the Microseal 200-1 on the stainless steel than on the titanium alloy. Microscopy and surface analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence, of the coatings on stainless steel substrates reveals that the coatings are sparse and relatively thin, likely a key factor contributing to their high friction. This insight underscores the substrate dependence of this widely used coating and highlights the importance of detailed tribological testing in accurately assessing the tribological performance of commercial dry film lubricants, a key step towards improving the reliability and effectiveness of actuating mechanisms for space applications. Full article

► Show Figures

Graphical abstract

14 pages, 15274 KiB

Open AccessArticle

Microstructure, Mechanical and Tribological Properties of Cu40Zn-Ti₃AlC₂ Composites by Powder Metallurgy

by Fangdian Peng, Shidong Zhou, Tao Yang, Liwei Wu, Jianbo Wu, Puyou Ying, Ping Zhang, Changhong Lin, Yabo Fu, Zhibiao Tu, Tianle Wang, Xin Zhang, Nikolai Myshkin and Vladimir Levchenko

Lubricants 2024, 12(9), 306; https://doi.org/10.3390/lubricants12090306 - 31 Aug 2024

Viewed by 612

Abstract

The exploration of unleaded free-cutting Cu40Zn brass with excellent mechanical and tribological properties has always drawn the attention of researchers. Due to its attractive properties combining metals and ceramics, Ti₃AlC₂ was added to Cu40Zn brass using high-energy milling and hot-pressing [...] Read more.

The exploration of unleaded free-cutting Cu40Zn brass with excellent mechanical and tribological properties has always drawn the attention of researchers. Due to its attractive properties combining metals and ceramics, Ti₃AlC₂ was added to Cu40Zn brass using high-energy milling and hot-pressing sintering. The effects of Ti₃AlC₂ on the microstructure, mechanical and tribological properties of Cu40Zn-Ti₃AlC₂ composites were studied. The results showed that Ti₃AlC₂ could suppress the formation of ZnO by adsorbing oxygen impurity and promote the formation of the β phase by releasing the β-forming element Al to the substrate. The hardness and wear resistance of Cu40Zn-Ti₃AlC₂ composites increased with increasing Ti₃AlC₂ content from 0 to 5 wt.%. The proper Ti₃AlC₂ additive was beneficial to both the strength and plasticity of the composites. The underlying mechanisms were discussed. Full article

► Show Figures

Figure 1

28 pages, 8706 KiB

Open AccessArticle

Moving beyond Flow Factors: Modeling Full Film Lubrication with Representative Surface Topography Using Heterogeneous Multiscale Methods

by Joshua Montgomery, Camille Hammersley, Mark C. T. Wilson, Michael Bryant and Gregory de Boer

Lubricants 2024, 12(9), 305; https://doi.org/10.3390/lubricants12090305 - 30 Aug 2024

Viewed by 622

Abstract

Lubrication modeling has long been dominated by the well-established Patir and Cheng flow factors method. The flow factors approach allows for accurate estimates of macroscale parameters (such as friction) in a reasonable amount of time. These methods are stochastic representations of microscale interactions [...] Read more.

Lubrication modeling has long been dominated by the well-established Patir and Cheng flow factors method. The flow factors approach allows for accurate estimates of macroscale parameters (such as friction) in a reasonable amount of time. These methods are stochastic representations of microscale interactions and are not able to predict local scale (pressure, film thickness) phenomena with a suitable degree of accuracy. This contrasts with a deterministic approach, where a numerical grid must be applied that fully defines the microscale surface topography across the contact. The mesh resolution required leads to prohibitively long execution times and lacks scalability to engineering systems, but provides accurate predictions of local scale phenomena. In this paper, heterogeneous multiscale methods (HMM) are expanded to model varying and are, therefore, more representative of surface topography within lubricated contacts. This representative topography is derived from measured data, thereby allowing the accuracy of deterministic methods to be achieved with the speed of a flow factor method. This framework is then applied to compare key performance characteristics (pressure, film thickness, etc.) when idealized, Gaussian, and measured surface topography are modeled. The variations in microscale geometry are defined by measurements from across two tilted-pad bearings, demonstrating the ability of the expanded HMM framework to model representative surface topography. A comparison with a deterministic method is included as validation, and outputs of the HMM are discussed in the context of the lubrication across multiple length scales. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

► Show Figures

Figure 1

11 pages, 2649 KiB

Open AccessArticle

Laboratory Test of a Gear Hydraulic Pump during the Application of an Environmentally Friendly Hydraulic Fluid with Constant Pressure and Temperature

by Ján Kosiba, Zdenko Tkáč, Juraj Jablonický, Gabriela Čurgaliová, Juraj Tulík and Marek Halenár

Lubricants 2024, 12(9), 304; https://doi.org/10.3390/lubricants12090304 - 29 Aug 2024

Viewed by 511

Abstract

The use of environmentally friendly hydraulic fluids is frequently influenced by the temperature reached in the hydraulic circuit. This paper presents an analysis of the effect of temperature on the lifetime of the hydraulic fluid and the hydraulic pump. The test was carried [...] Read more.

The use of environmentally friendly hydraulic fluids is frequently influenced by the temperature reached in the hydraulic circuit. This paper presents an analysis of the effect of temperature on the lifetime of the hydraulic fluid and the hydraulic pump. The test was carried out by continuous loading with a pressure of 21 MPa and a temperature of 96 °C for 100 h. A pressure valve was used for the continuous loading and the temperature was maintained using a cooler. At intervals of 25 h, the flow characteristics of the hydraulic pump were measured and oil sampling was carried out. Subsequently, a comprehensive chemical and physical analysis was carried out. In the present paper, a comprehensive analysis of the influence of eco-friendly hydraulic fluid on the operation of a gear hydraulic pump has been carried out. The study itself did not show the negative influence of the eco-friendly hydraulic fluid on the operation of the gear hydraulic pump. It can be expected that the results of the study will enable the use of eco-friendly hydraulic fluids in environmentally sensitive areas. Full article

(This article belongs to the Special Issue Recent Advances in Green Lubricants)

► Show Figures

Figure 1

15 pages, 5453 KiB

Open AccessReview

Changes in Surface Topography and Light Load Hardness in Thrust Bearings as a Reason of Tribo-Electric Loads

by Simon Graf and Oliver Koch

Lubricants 2024, 12(9), 303; https://doi.org/10.3390/lubricants12090303 - 28 Aug 2024

Viewed by 457

Abstract

The article focuses on the findings of endurance tests on thrust bearings. In addition to the mechanical load (axial load: 10 ≤ C0/P ≤ 19, lubrication gap: 0.33 µm ≤ h0 ≤ 1.23 µm), these bearings are also exposed to electrical loads (voltage: [...] Read more.

The article focuses on the findings of endurance tests on thrust bearings. In addition to the mechanical load (axial load: 10 ≤ C0/P ≤ 19, lubrication gap: 0.33 µm ≤ h0 ≤ 1.23 µm), these bearings are also exposed to electrical loads (voltage: 20 Vpp ≤ U0 ≤ 60 Vpp, frequency 5 kHz and 20 kHz), such as those generated by modern frequency converters. In a previous study, the focus was on the chemical change in the lubricant and the resulting wear particles. In contrast, this article focuses on the changes occurring in the metallic contact partners. Therefore, the changes in the surface topography are analysed using Abbott–Firestone curves. These findings show that tests with an additional electrical load lead to a significant reduction in roughness peaks. A correlation to acceleration measurements is performed. Moreover, it is shown that the electrical load possibly has an effect on the light load hardness. An increase in the occurring wear could not be detected during the test series. Also, a comparison with mechanical reference tests is made. The article finally provides an overview of different measurement values and their sensitivity to additional electrical loads in roller bearings. Full article

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

► Show Figures

Figure 1

14 pages, 4105 KiB

Open AccessArticle

Numerical Computation and Experimental Research for Dynamic Properties of Ultra-High-Speed Rotor System Supported by Helium Hydrostatic Gas Bearings

by Changlei Ke, Shun Qiu, Kongrong Li, Lianyou Xiong, Nan Peng, Xiaohua Zhang, Bin Dong and Liqiang Liu

Lubricants 2024, 12(9), 302; https://doi.org/10.3390/lubricants12090302 - 27 Aug 2024

Viewed by 576

Abstract

This study delves into the dynamic behavior of ultra-high-speed rotor systems underpinned by helium hydrostatic gas bearings, with a focus on the impact of rotational velocity on system performance. We have formulated an integrative dynamic model that harmonizes the rotor motion equation with [...] Read more.

This study delves into the dynamic behavior of ultra-high-speed rotor systems underpinned by helium hydrostatic gas bearings, with a focus on the impact of rotational velocity on system performance. We have formulated an integrative dynamic model that harmonizes the rotor motion equation with the transient Reynolds equation. This model has been meticulously resolved via the Finite Difference Method (FDM) and the Wilson-Θ technique. Our findings unveil intricate nonlinear dynamics, including 2T-periodic and multi-periodic oscillations, and underscore the pivotal role of first-order temporal fluctuations, which account for over 20% of the transient pressure at rotational speeds exceeding 95.0 krpm. Further, we have executed empirical studies to evaluate the system’s performance in practical settings. It is observed that when the ratio of low-frequency to fundamental frequency approaches 0.3 and the amplitude ratio exceeds 3, the vigilant monitoring of system stability and reliability is imperative. Collective insights from both computational simulations and experimental studies have enriched our understanding of the dynamic attributes of ultra-high-speed rotor systems. These revelations are crucial for the advancement of more efficacious and resilient rotor systems designed for high-speed applications. Full article

(This article belongs to the Special Issue Applied Tribology: Rotordynamics)

► Show Figures

Figure 1

13 pages, 18409 KiB

Open AccessArticle

A Comparison of the Tribological Properties of SiC Coatings Prepared via Atmospheric Plasma Spraying and Chemical Vapor Deposition for Carbon/Carbon Composites

by Yan Qi, Jiumei Gao, Wenping Liang, Qiang Miao, Feilong Jia, Xiangle Chang and Hao Lin

Lubricants 2024, 12(9), 301; https://doi.org/10.3390/lubricants12090301 - 26 Aug 2024

Viewed by 598

Abstract

The microstructure, mechanical performance, and tribological properties of SiC ceramic coatings prepared via atmospheric plasma spraying (APS) and chemical vapor deposition (CVD) method were compared to provide good anti-wear protection for carbon/carbon composites. The surface morphology of the APS-SiC coating was characterized as [...] Read more.

The microstructure, mechanical performance, and tribological properties of SiC ceramic coatings prepared via atmospheric plasma spraying (APS) and chemical vapor deposition (CVD) method were compared to provide good anti-wear protection for carbon/carbon composites. The surface morphology of the APS-SiC coating was characterized as having a porous structure, whilst the CVD-SiC coating presented with many pyramidal-shaped crystals constituting the surface. The APS-SiC coating consists of a dominating SiC phase and a small fraction of the Si phase, while the XRD pattern of the CVD-SiC coating mainly consists of the SiC phase. The dense crystalline microstructure of the CVD-SiC coating made it possess a higher hardness and Young’s modulus at 31.0 GPa and 275 GPa, respectively. The higher H/E and H³/E² parameters of the CVD-SiC coating implied that it exhibited better plastic resistance, which is also beneficial for anti-wear properties. The scratch test reflected the critical loads of the spallation of the APS-SiC coating and CVD-SiC coating, which were evaluated to be 25.9 N and 36.4 N, respectively. In the tribological test, the friction coefficient of the APS-SiC coating showed obvious fluctuations at high load due to damage to the SiC coating. The wear mechanism of the APS-SiC coating was dominated by abrasive wear and fatigue wear, while CVD-SiC was mainly dominated by abrasive wear. The wear rate of the CVD-SiC coating was far below that of the APS-SiC coating, suggesting the better wear-resistance of the CVD-SiC coating. Full article

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

► Show Figures

Figure 1

15 pages, 2759 KiB

Open AccessReview

Plant-Based Oils for Sustainable Lubrication Solutions—Review

by Diana Berman

Lubricants 2024, 12(9), 300; https://doi.org/10.3390/lubricants12090300 - 26 Aug 2024

Viewed by 720

Abstract

Traditional lubricants, often containing harmful chemicals and synthetic or fossil-derived oils, pose environmental risks by damaging ecosystems and threatening human health and wildlife. There is a growing demand for environmentally sustainable and cost-effective bio-based lubricants derived from renewable raw materials. These bio-based oils [...] Read more.

Traditional lubricants, often containing harmful chemicals and synthetic or fossil-derived oils, pose environmental risks by damaging ecosystems and threatening human health and wildlife. There is a growing demand for environmentally sustainable and cost-effective bio-based lubricants derived from renewable raw materials. These bio-based oils often possess natural lubricating properties, making them an attractive alternative to traditional synthetic lubricants. In addition to providing effective lubrication, they offer good biodegradability and minimal toxicity, which are essential for reducing environmental impact. However, the primary challenge lies in optimizing their performance to match or surpass that of conventional lubricants while ensuring they remain cost-effective and widely available. This paper reviews the general requirements for lubricants and explores how plant-based oils can be utilized to meet the diverse lubrication needs across various industries. Further, it highlights different approaches that can be used for further improvements in the area of plant-based lubrication through bio-inspired means, such as the use of estolides, wax esters, or erucic acid, as well as through additions of nanomaterials, such as nanoparticles, nanoclays, or two-dimensional films. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

► Show Figures

Figure 1

16 pages, 15164 KiB

Open AccessCommunication

Study on Traction Characteristics of Point Contact State under Oil–Air Lubrication

by Bing Su, Han Li, Jiongli Ren and Zeyu Gong

Lubricants 2024, 12(9), 299; https://doi.org/10.3390/lubricants12090299 - 25 Aug 2024

Viewed by 704

Abstract

Oil–air lubrication technology is commonly utilized in the lubrication design of traditional components to reduce friction between contact pairs. This study focuses on testing the point-contact friction pairs of two quantitative valves using a self-made oil–air lubrication traction force machine with a G95Cr18 [...] Read more.

Oil–air lubrication technology is commonly utilized in the lubrication design of traditional components to reduce friction between contact pairs. This study focuses on testing the point-contact friction pairs of two quantitative valves using a self-made oil–air lubrication traction force machine with a G95Cr18 disk and ball as the friction pairs. The test data are analyzed using a four-parameter exponential model. Additionally, a calculation model of the oil–air lubrication flow field is established, defining boundary conditions and conducting flow field simulation analysis. The results of the ball and disk test show that the traction coefficient increases with load and decreases with entrainment speed. Furthermore, when the air-speed is 12 m/s, the traction coefficient is lower for the oil supply of 6 mL/min than for the oil supply of 1.5 mL/min. According to CFD analysis, the volume fraction of the oil phase in the contact area increases with the increase of entrainment speed when the slip–roll ratio is 0.1. The theoretical values from the four-parameter exponential model align well with the experimental results, and the fitting accuracy is higher than 0.95. Full article

► Show Figures

Figure 1

24 pages, 3185 KiB

Open AccessArticle

Dynamic Coefficient Investigation for Supercritical Carbon Dioxide Dry Gas Seal Based on Complete Variable Perturbation Model

by Ruqi Yan, Baodui Chai, Lu Ma, Hanqing Chen and Xuexing Ding

Lubricants 2024, 12(9), 298; https://doi.org/10.3390/lubricants12090298 - 23 Aug 2024

Viewed by 440

Abstract

In this work, a new model to analyse the dynamic characteristic coefficient of the S-CO₂ dry gas seal was reported. Taking into account that the flow within the S-CO₂ dry gas seal is close to adiabatic flow, the impact of the [...] Read more.

In this work, a new model to analyse the dynamic characteristic coefficient of the S-CO₂ dry gas seal was reported. Taking into account that the flow within the S-CO₂ dry gas seal is close to adiabatic flow, the impact of the temperature change on the dynamic characteristic coefficient of the gas film cannot be ignored. To address this issue, a complete variable perturbation model (CVPM) under the adiabatic flow process was established using the frequency perturbation method while considering multiple complex effects. Then, the finite difference method was used to solve the CVPM. The gas film’s dynamic stiffness and damping coefficients were calculated and analysed for different conditions, operating parameters, and frequency ratios. From our analysis, it was demonstrated that the dynamic coefficient of the gas film exhibited frequency dependence. The turbulence coefficient perturbation had the most remarkable influence on the gas film’s dynamic coefficient, compared to the temperature, viscosity, and centrifugal inertia force perturbations. The isothermal flow, adiabatic flow, inlet pressure, and inlet temperature also affected the magnitude of the dynamic characteristic coefficient of the gas film. However, no significant impact on their tendency to vary with the frequency ratio was found. Our work provides new theoretical support for the dynamic analysis of S-CO₂ dry gas seals, which is of great importance for future applications. Full article

► Show Figures

Figure 1

Journal Menu

Journal Browser

Lubricants, Volume 12, Issue 9 (September 2024) – 31 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI