Lubricants

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 (registering DOI) - 31 Aug 2024

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

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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 (registering DOI) - 31 Aug 2024

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

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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 (registering DOI) - 31 Aug 2024

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

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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

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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)

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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 (registering DOI) - 29 Aug 2024

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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)

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15 pages, 5453 KiB

Open AccessReview

Changes in Surface Topography and Light Load Hardness in Thrust Bearings as a Reason for 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 159

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)

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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 325

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)

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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 361

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)

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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 344

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)

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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 513

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

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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 293

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

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16 pages, 17436 KiB

Open AccessArticle

Friction and Wear in Hot Stamping: The Role of Tool and Workpiece Temperature and Tool Steel Composition

by Leonardo Pelcastre

Lubricants 2024, 12(9), 297; https://doi.org/10.3390/lubricants12090297 - 23 Aug 2024

Viewed by 325

Abstract

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and [...] Read more.

Hot stamping is a forming process widely used in the manufacturing of structural components in automobiles. It is a versatile process that enables the fabrication of complex-shaped components with high strength. It also facilitates the manufacturing of components that incorporate high-strength sections and high-ductility sections, by controlling the cooling rate. The process is versatile in terms of the microstructures and mechanical properties that can be obtained. This versatility, however, puts high demands on the materials pertaining their stability, wear resistance, costs, etc. This study has focused on understanding the effect of temperature on the tribological response of different tool materials when these are exposed to high temperatures. The results show that friction significantly stabilises with increased temperature for most tool steels. One tool steel behaves more unstably at high temperature, and this is attributed to the presence of Cr₇C₃, MoO₃, and VO and severe wear on the workpiece material. The most severe wear on the workpiece is caused by a partially melted interdiffusion layer, which facilitates the detachment of the Al-Si coating and subsequent transfer onto the tool; this effect is maximised at the highest temperatures of the workpiece. An important finding is that friction and material transfer severity decrease as the workpiece temperature decreases, and friction is stabilised as tool temperature increases without minimising wear or the average friction coefficient. Full article

(This article belongs to the Special Issue Friction, Wear and Lubrication of Tool Steels in Metal Forming and Machining)

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

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