Improved Lubricant Film Strength Under Extreme Load Conditions

A lubricating grease additive comprising PAEK particles with a particle size D50 of up to 20 µm, wherein the PAEK particles are dispersed in a lubricating grease to improve tribological properties, particularly coefficient of friction, wear, and lubrication life, in non-metallic surface contacts.

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In the quest for sustainable lubrication solutions, the present research explored the potential of five organic compounds as additives in castor oil (CO) to improve its lubricating properties. The compounds tested were curcumin, eugenol, 1,3-Diphenyl-2-propanone, 1,3-Diphenyl-2-propenone, and 1,3-Diphenyl-1,3-propanedione. The main results showed that each additive enhanced at least one characteristic of CO. Most of the additives lowered the density of the castor oil but increased the viscosity by up to 20%. Curcumin and eugenol were particularly effective in creating thicker lubricant films and higher film thickness ratios. Eugenol and 1,3-Diphenyl-2-propanone significantly reduced the friction coefficient by up to 25%. Wear rate and wear mechanisms were significantly reduced with all the additives, achieving a reduction in wear rate of up to 50% (CO+curcumin). All the additives, except the 1,3-Diphenyl-1,3-propanedione, enhanced the oxidation onset temperature up to 8 C. The influence of chemical structure was also addressed. The optimal additive combination for a specific applica... Read More

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Abstract The bearing cage played a pivotal role in affecting the lubricant redistribution and lubrication states. In this study, a cage unit is incorporated into an optical ball-on-disc apparatus for the purpose of a quantitative study of cage-induced lubrication phenomena. It is found that the presence of the lubricant layer on the ball surface, shaped by the cage, affects the inlet lubricant supply of contact between the ball and the glass disc. Thereafter, the oil reservoirs surrounding the contact area and the film thickness were measured. The results showed that the lubricant reservoirs and inlet lubricant supplement were significantly improved with the employment of the cages. In addition, the lubrication state transformed from starved to fully flooded, effectively enhancing the lubrication state. Moreover, the lubricant on the steel ball surface moved from the side bands to the central rolling track, indicating that the lubricant redistribution was the main reason for the lubricating enhancement. Notably, the groove modification on the inner surface of the cage pocket facilita... Read More

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Abstract Journal bearing operation particularly in regard to marine applications is significantly affected by the performance of the most critical operational factors. Specifically, the lubricating oil film within journal bearing is so often than not subject to hazardous deterioration and ultimate failure in real operating conditions. Considering such fact, the current study is intended to carry out a literature survey regarding the efforts towards enhanced journal bearing performance based on proper selection of geometrical design for journal bearing. The aggregated data were thoroughly analyzed and assessed utilizing experimental, theoretical as well as numerical means. The outcomes derived from the conducted review represent firm grounds for carrying out extensive modifications into journal bearing design for marine applications. Further, such data will possibly be employed in future research investigations to extend the capability of journal bearing and its functions to attain the most possible enhanced performance in actual operating conditions. Apparently, the vast majority of ... Read More

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Solid lubricants are those materials that are used to lubricate mainly in dry circumstances. Its main role is similar to that of oils and greases, which is used to create a continuous and adherent lubricant film on the tribological pair surfaces for minimising friction and wear [1]. These coatings are typically employed in situations where liquid lubricants cannot be used or do not offer expected lubrication, such as in high or cryogenic temperatures, high vacuum, ultrahigh-radiation, reactive environments and in extreme contact pressure conditions [2]. Different types of solid lubricants, including graphite, have been extensively used since the middle of the 20th century [3]. From 1950 onwards, development in aeronautics industries emphasised the research and development of advanced solid lubricants. They can be classed based on their crystalline structure, features, properties, or functions, among other things. Different types of solid lubricant coating are shown in Fig. 1 [1].

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An anti-wear and anti-friction lubricating oil additive comprising malic acid, fatty alcohol, malic acid ester, and maleic acid ester, wherein the additive generates graphite-like carbon structures in situ at the friction contact interface to reduce friction coefficient and wear. The additive can be formulated with malic acid (0.5-20 wt%), fatty alcohol (5-50 wt%), malic acid ester (0.1-80 wt%), and maleic acid ester (0.2-50 wt%). The additive can be prepared by ultrasonication or stirring with a lubricating oil base oil.

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Grease composition with excellent extreme pressure (EP) properties, comprising a compound with a phosphate ester moiety in its molecular structure, for use in applications requiring wear resistance such as bearings, gears, and industrial machinery.

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Abstract Nonrenewable energy has produced abundant waste during tribological applications because a large portion of energy has been consumed to overcome friction and wear. Solid lubricants have recently aroused significant interest due to their defined friction and wear properties. Despite enormous efforts on solid lubricants, their important contributions to coatings, bulk materials, oil/grease, and super-lubricity have not yet been fully evaluated. This paper discusses in detail the present status of solid lubricants as effective reinforcements in tribology. It begins with the introduction of various descriptions and advanced structures of solid lubricants. Afterwards, it discussed their applications on improving friction properties in coatings and bulk materials. Additionally, lubrication mechanisms of solid lubricants in oil/grease are highlighted, followed by the detailed discussion of super-lubricity for solid lubricants. Finally, this review concludes final outlooks on the main challenges and future directions in this key area.

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The development of environmentally friendly and cost-effective lubricating materials to reduce friction and wear at macroscale is crucial for reducing fuel consumption and exhaust emissions, thereby enhancing sustainability. Deep eutectic...

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The influence of tuned surface wettability on the oil film building in a hydrodynamically lubricated contact under limited lubricant supply was investigated in this study. The thickness of the oil film was measured for three surface wettability combinations, OD & OS, AFD & OS, and AFD & AFS. The results indicate that the AFD & AFS combination maintains the largest oil film thickness. This enhanced performance is owing to the oil's non-wetting behavior on the AFD & AFS surfaces, which promote more lubricant supply at the slider inlet. Moreover, the oil accumulates at the inlet in the form of convex reservoir so that positive Laplace pressure is generated, which effectively bears part of the load and the film thickness increases.

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Rapid advances in modern industrial tribo-systems under high temperatures and heavy loads generate a growing demand for lubricating materials used in extreme environmental conditions. Metal-based lubricant coatings with excellent mechanical properties and thermal stability are widely used on core parts to reduce friction in harsh environments. This paper reviews the progress on modulating the frictional properties of coatings by designing the components and preparation techniques to prolong the lifetime of metal-based lubrication coatings. The impacts of the microstructural changes on the mechanical performances, including hardness, plasticity, interfacial adhesion, and environmental stability, were essential for the deformation and crack propagation of the coatings. Their performances and lubrication mechanisms were concerned under heavy loads, in a wide range of temperatures, and in corrosive marine environments. Finally, the study concluded the basic requirements of metal-based coatings for extreme environments at this stage. The research challenges and potential problems of metal... Read More

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Abstract A renewed interest in elastohydrodynamic lubrication (EHL) phenomena at high speeds, for which thermal effects strongly influence both traction and film thickness, has grown out of the challenges presented by high-speed geared transmissions in electric vehicles. This study uses a new ball-on-disc set-up employing the well-known ultra-thin-film interferometry technique to simultaneously measure EHL film thickness and traction at entrainment speeds up to 20 m/s and slide-roll ratios up to 100%. The effect of fluid composition is examined for Group I, II and III mineral oils, for two polyalphaolefins in Group IV, and for the traction fluid Santotrac 50. The effect of viscosity in the range 4180 mPa.s is investigated by varying bulk fluid temperature. At high speeds, both film thickness and traction are considerably lower than predicted by conventional EHL theory. The contact is seen to be fully-flooded for all conditions tested. The widely-used thermal EHL correction of Gupta is shown to overcorrect for the film thickness reduction even at modest SRRs. Finally, the influence o... Read More

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Lubrication technology plays a key role in solving tribological problems in engineered structural systems, and this technology has become a focus of research in order to enhance the efficiency and lifetime of the system. This review integrates the mechanism and the effect of many factors, such as surface charge, surface morphology, temperature, humidity, acidity, and fluid properties, on the lubrication performance enhancement by triboelectricity-controlled fluid attached to the coupled surface. Additionally, this review discusses methods for improving the lubrication performance of solid-liquid surfaces. Finally puts forward some future prospects on the lubrication performance enhancement by triboelectricity-controlled fluid attached to the coupled surface.

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Understanding the relevance and significance of the various replenishment mechanisms in grease-lubricated bearings is very important in choosing the appropriate lubrication strategy. This study shows that the lubricant film thickness in the ball-ring contacts of a deep groove ball bearing may increase by 10%25% due to vibrations. The possible mechanisms behind this film thickness increase are discussed. Of the proposed contact replenishment mechanisms, the micro-lateral motion of the contact edge across the tracks caused by in-operation vibrations appears crucial. Results show that in the starved contacts, vibration plays a vital role in determining the film thickness.

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Solid-liquid composite lubrication coatings provide highly reliable and long-lasting solutions to friction, wear, and lubrication problems in extremely harsh environments. Herein, a novel type of solid-liquid composite lubrication coating with a high load-bearing capacity and long service life was constructed by introducing epoxy resin containing lubricating oil into inherent defects of thermally sprayed ceramic coatings. Compared with conventional ceramic coatings, the hybrid coatings exhibited an 80.5 % reduction in the coefficient of friction to 0.15 and a decrease in the specific wear rate from 2.69 104 mm3N1m1 to 3.86 108 mm3N1m1. The low friction and wear of the composite coating were mainly attributed to the formation of a well-covered lubrication film consisting of PFPE, epoxy resin, Al2O3, and ZrO2 during the friction of the composite coating. This paper presented a novel approach to preparing new solid-liquid composite lubricating coatings that using unavoidable defects in thermal sprayed ceramic coatings to introduce a lubricating phase.

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Solid lubricants are crucial for industries operating at temperatures beyond 300 C, where liquid lubricants encounter limitations. Diamond-like carbon (DLC) films, known for exceptional solid lubrication and mechanical properties, need higher thermal stability for effective use in high-temperature applications. This study focuses on developing DLC films with the required thermal stability and solid lubricating properties. Hydrogen-free and hydrogenated DLC films were deposited utilizing deep oscillation magnetron sputtering (DOMS). Thermal characterizations revealed both films surpassed 500 C in thermal stability, rendering them suitable for high-temperature tribological applications. However, the hydrogenated DLC film exhibited superior solid lubricating properties, achieving an ultra-low friction coefficient below 0.05 at elevated temperatures, along with enhanced wear resistance, while effectively protecting its counterpart up to 500 C.

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This manuscript developed a novel DLCsupramolecular gel (HTG) composite lubrication system to achieve long-life outstanding lubrication under extreme contact stress while avoiding sealing challenges relying on the unique thixotropic properties of the gel. DLCHTG exhibited ultra-low wear and excellent friction reduction performance under a maximum contact stress of 2.24 GPa. DLC films with designed double transition layers possess high interfacial bond strength and mechanical properties, providing the basis for high wear resistance. The establishment of a robust tribofilm and the confinment effect of HTG on wear debris dominate the achievement of ultra-low wear. This ultra-low wear sliding extends the service life of the lubrication system with the broad implications for mechanical engineering, transportation, and wind power generation.

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Abstract The reduction of frictional power losses in power transmitting gears takes a crucial role in the design of energy- and resource-efficient drivetrains. Water-containing lubricants like glycerol and polyalkylene glycols have shown great potential in achieving friction within the superlubricity regime with coefficients of friction lower than 0.01 under elastohydrodynamic lubrication. Additionally, a bio-based production of the base stocks can lead to the development of green lubricants. However, one challenge associated with the application of water-containing lubricants to gearboxes is the evaporation of water and its impact on the lubricant properties. In this study, the influence of water evaporation on elastohydrodynamic friction and film thickness was investigated for three water-containing polyalkylene glycols. Two nominal water contents of 20 wt% and 40 wt% and two viscosities were considered. The results show that the friction increases continuously with higher evaporated water content, while the overall friction level remains low in nearly water-free states. A similar ... Read More

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Abstract Today, mineral or synthetic oils that are made out of fossil raw materials, are the most common lubricants in gear drive applications. Most of them are non-biodegradable and may pose a risk to the environment. An important step to minimize the risk and the ecological footprint is the use of biodegradable and eco-friendly lubricants. Former research shows the potential of water-based lubricants in gear applications. Therefore, an oil-free, water-based lubricant, was developed for this study. The base lubricant contains plant-based thickeners to generate an appropriate viscosity for a sufficient lubricant film thickness in the tooth contact. In experimental investigations, the sliding wear and scuffing performance has been examined under variation of the added polymers and additives. The scuffing tests A/8.3/RT are performed acc. to DIN ISO 14635-1. The wear tests procedure is based on DGMK 377-01. In both scuffing tests with the sample the failure load stage = 8 was achieved. For case-carburized gears a medium to high amount of wear can be detected. Additional tests with ... Read More

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Water-lubricated bearings are widely used in propulsion shafting of large marine equipment, such as ships. When a water-lubricated stern bearing operates in harsh environments involving a low speed and heavy load for extended periods, there is a serious impact on the friction and wear performance of the bearing. In this study, a full pair of bearings made of a special polymer material was used as the research object in a sediment environment and was subjected to low-speed heavy-duty durability tests. At different temperatures, specific pressures, and speed conditions, the friction coefficient and wear were measured and linearly extrapolated. The results show that under harsh working conditions such as low speed and heavy load sediment, and the loading pressure is greater. It is difficult to form a complete water film between the friction pairs. A loading pressure of 0.2 MPa is beneficial to the long-term operation of the bearing under harsh working conditions. Moreover, the bearing damage is not serious, resulting in a reduction in bearing wear and an extension of operation life.

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Eco-friendly lubricant research continues to increase since it has a comparative performance to commercial mineral lubricants to overcome the effects of environmental impact. However, the efficiency of these green lubricants depends on specific applications. In this study, we analyzed the friction and wear performance of a castor/sesame oil mixture as an eco-friendly lubricant and its comparison to a commercial mineral lubricant tested in a metallic system employed in bearing elements. For this purpose, AISI 8620 steel against ISO 100Cr6 was used as tribological pair. The friction and wear tests were carried out through a Tribometer of ball-on-disk configuration under boundary lubricating conditions, whereas the worn surfaces were investigated by using optical and electron microscopy. The physical properties and the rheological properties of the lubricants were also determined. The friction and wear performance between the eco-friendly lubricant and mineral oil were similar so that the CLE were comparable. The CLE values in terms of friction and wear ranged from 86% to 99.4%, respect... Read More

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Although lubrication is necessary for the satisfactory operation of rolling bearings, the effect of lubricant on the fatigue life of the bearing has not been sufficiently studied. In recent times, the theory of elastohydrodynamic (EHD) lubrication [1] has been used to explain the different effects of lubricants. According to this theory, the thickness of the lubricating layer separating the moving elements of the bearing is determined by the viscosity-pressure dependence of the lubricant. The contact of surface micron irregularities does not occur if it is possible to maintain a sufficient thickness of the lubricating layer - in this case, the long-term durability of the bearing is ensured. If the film thickness is reduced to a level where surface irregularities are encountered, the fatigue life rapidly decreases with increasing contact frequency. In any case, a comprehensive calculation methodology is needed that would allow to take into account the influence of lubricant on the fatigue life of bearing units.

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Eco-friendly lubricants have drawn a lot of interest in the lubrication industry as a way of promoting global sustainability in response to the growing environmental pollution danger posed by the use of petroleum-based lubricants. As a result of these, developing lubricants with organic additives stands as a promising technique in solving the environmental challenges caused by non-degradable materials. This research investigates the effect of bio-based water hyacinth (Eichhornia crassipes) (EC) carboxylmethyl cellulose (CMC) polymer in different base lubricants as well as under different volumetric blend to determine their compatibility effect on lowering friction and wear using base rapeseed oil (BRO) and mineral oil (MO) as a base lubricant sample. High frequency reciprocating rig tribo-tester machine was used in the experiment, followed by substrate surface analysis via energy dispersive x-ray spectroscopy. The additives were evaluated for their potential to improve tribology in terms of friction, surface roughness and wear reduction, load-carrying capacity, and mechanism of repai... Read More

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Abstract The current work investigates the influence of real lubricant densitypressure behavior on the dynamic response of elastohydrodynamic lubricated conjunctions. Such a response is often based on a nonrealistic universal equation of state, despite longstanding evidence of its lack of support by measurements. A finite element framework is employed to investigate the damping and stiffness characteristics of line contact elastohydrodynamic (EHD) lubricating films, subject to a harmonic loading. Both the equivalent stiffness and damping coefficients of lubricating films are found to increase with the base applied external load and its amplitude of oscillation. They decrease however with increasing mean entrainment speed and load oscillation frequency. That is, they both increase as lubricant films get thinner. By comparison with the real densitypressure response of a highly compressible silicon oil, the universal equation of state is shown to underestimate the lubricant films stiffness and damping characteristics. The relative deviations in equivalent damping and stiffness coeffi... Read More

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Abstract: We have an increasing global need for bio lubricants that are safe for human and environmental use, easily biodegradable, and non-polluting. The friction and wear qualities of cotton seed blended lubricant as well as castor blended lubricant are compared and contrasted in this research using a Pin on disc wear testing Tribometer. In this research, we will look at the study's results and analyse their significance. Blended lubricants were created by combining cotton seed & castor based biodiesel with the basic lubricant SAE20W40 at volumetric ratios of 5, 10, 15, & 20%. Cotton seed and castor blended bio lubricants were tested for friction and wear at sliding velocities of 2.5 metres per second while subjected to weights of 50 N, 100 N, and 150 N. Wear might be slowed by as much as 15 percent by mixing in cotton seed biodiesel with the base oil, as has been shown. When this threshold is passed, wear increases at an ever-increasing pace. Castor oil blended lubricant performed best in wear tests when coupled with a base lubricant at a 5 and 10 percent castor oil blende... Read More

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Lubricant composition for steel bearings that suppresses wear and corrosion under severe conditions, comprising an inorganic sodium salt with a spontaneous potential of 0.04 V or more, zinc alkyldithiophosphate, and a synthetic hydrocarbon oil, preferably polyalphaolefin (PAO) oil. The composition is particularly effective in preventing premature flaking and wear on bearing surfaces when used in high-speed, high-load applications.

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Limited lubricant supply (LLS) with tuned dosage is an emerging approach to reduce friction and energy consumption. However, LLS can cause severe starvation when the oil supply is insufficient. Therefore, how to effectively replenish oil to the lubricated contact in LLS operation is very important. Using a custom-made optical slider bearing test rig, this work experimentally revealed some characteristics of LLS lubrication in a cylinder-on-disc contact, and proposed two wettability gradient patterns, namely stripe wettability and interlaced wettability, to regulate the lubricant supply to improve the lubricating properties of LLS. The effect of these two wettability patterns was evaluated experimentally according to the lubricating film thickness. The interferograms of the bearing contact under LLS show that the two patterns can augment the oil replenishment through unidirectional lubricant transport by the unbalanced interfacial force via the wettability gradient. Moreover, the interlaced wettability pattern is more effective due to the discontinuous distribution of lubricant from i... Read More

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This reprint features 12 research articles that contribute to the research on lubricated bearings. The articles focus on the latest steps in understanding bearing operating behavior, its interaction with lubricants, and its role as a component in the drive train. In addition to the description of novel modeling approaches, a variety of experimental data are presented to provide interesting identification results as well as validation data for the research and engineering community.

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A brief overview of the properties of lubricating oils and greases is given, and how those properties correlate with bearing performance by film thickness. The tribological performance of a rolling bearing is significantly dependent upon the state of lubrication during operation. The treatment of lubricants begins with an overview of some of the most important physical properties that enable oils and greases to function as lubricants. Next, the different types of oils and greases and their nominal compositions are explored. Finally, an overview is provided on how lubricant films are generated in rolling bearings and how application conditions such as load, temperature, speed, and material type affect film thickness.

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The paper aims to reveal the lubrication bearing mechanism of double-film bearing under different conditions. Modified lubrication models of double-film bearing with laminar/turbulent effect, cavitation and other conditions are established. The function reflection relations between lubrication behavior and structural parameters, working condition parameters are illuminated. The regulations of influences of coupling factors (eccentricity ratio, speed, length-diameter ratio, misaligned angle and operating models) on lubrication characteristics are explored. The lubrication mechanism of double-liquid film interface is elucidated. The variation rules of bearing performance are summarized. The research is important to the optimal design (load-carrying capacity enhancement & friction-reduction) of the double-film bearing.

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Lubricants play a very important role in multiple industries in minimizing wear and friction between two moving parts. Most lubricants are produced from petroleum oil which is poorly biodegradable and toxic in nature. Hence these lubricants are highly undesirable due to environmental hazards and the health and safety of the operator. Bio-Lubricants like Castor Oil have found a potential scope in research and are being used in various applications as a substitute for these chemical lubricants. This paper examines the Tribological Properties of developed Bio-Lubricants, prepared using Castor Oil and Neem Oil in a mixing ratio of 20%. Wear and Friction analysis has been carried out using Pin on Disc apparatus at varying loads, which has shown that the blend of Castor Oil as a base with 20% Neem Oil has promising properties, with around 70% reduction in wear rate at specific loads, hence showcasing a tremendous capacity for being used in maintenance applications. An overall reduction in wear and coefficient of friction was observed in the developed mixture, making it a potential environm... Read More

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The traditional water-lubricated bearings are difficult to form effective lubricating film under extreme low-speed and heavy-duty conditions, resulting in the low-load, high-resistance, high-vibration and high-noise shortcomings. The deep-physical mechanisms are not clear. The paper investigates the mixed lubrication performances and critical characteristics for water-lubricated bearings under extreme conditions. A novel multi-field coupling lubrication model is proposed. The functional mapping relationships among lubrication performances, the critical characteristics and the influencing factors are developed. The rotor dynamic models considering surface micro-topography are built. The variation mechanisms of the dynamic behaviors are revealed. The theoretical analysis is consistent with experiment, which proves the model and algorithms correctness. The academic value of the paper is expected to achieve a novel breakthrough in formation of effective hydrodynamic film under extreme severe conditions for such bearings.

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In recent years, the demand for friction reduction in oil lubrication systems has become increasingly important due to the need to improve fuel economy and achieve carbon neutrality. Ester-based lubricants are known to show low friction and environmentally friendly, and they have high viscosity indexes. In the present paper, first, in situ reflectance spectroscopy was used to clarify the behavior of the oil-film thickness increase during sliding. The results showed that as the number of ester bonds increased from 1 to 4, the ester oil film thickened and the friction coefficient decreased from 0.10 to 0.06. In addition, oleic-acid-type lubricants were found to have superior ability to form a thicker oil film than the isostearic acid type.

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The lubrication system plays an important role in the reliability of moving links for spacecrafts while lubrication failure has emerged as one of the challenges in developing advanced spacecrafts with long life and high reliability. However, the process and mechanism of lubrication in space are still unclear due to a complex environment. In this study, the lubrication behavior under various pressure loads was studied by analyzing the lubricant conformation changes and energy transfer through molecular dynamics simulations. Results indicated that a "one-step" or "two-step" adjustment in the polymer conformations occurred, and the film exhibited different motion modes and temperature fields under different pressure loads. This work studied polymer thin film lubricant via energy transfer and molecular motion at a molecular level and gave a fundamental understanding on the lubrication behavior and lubrication failure of polymer thin film in space, providing theoretical guidance in developing advanced space lubrication technology.

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Lubricants, including oil and grease, are used in various mechanical elements to reduce the friction generated in rubbing parts and prevent surface damage, such as wear, seizure, and peeling. This chapter describes the fundamentals from a lubrication perspective that should be known in order to prevent fretting wear. Unlike normal wear, fretting wear occurs when two surfaces facing each other oscillate minutely. Therefore, understanding the lubrication mechanism in such nonsteady states can lead to the prevention of fretting wear. According to the literature, oil and grease lubrication adopt completely different approaches for preventing fretting wear. Here, we first describe the mechanism of oil film formation under minute oscillation in oil lubrication and then explain the approach used for reducing fretting wear in grease lubrication in comparison with that used in oil lubrication.

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In most all tribological systems, the main goal is to reduce friction and control wear between the contacting solid surfaces. This chapter introduces and discusses two typical methods, which are frequently applied to enhance tribological properties of engineering machinery, namely, lubrication and surface engineering techniques. The principle of lubrication is to introduce a substance, called lubricant, between the contacting surfaces to minimize friction and wear. The chapter reviews various aspects involved in fluid film lubrication such as fluid flow, Reynold's equation, Stribeck curve, and different types of fluid lubrication. A detailed description of the gas film, grease, and solid film lubrication techniques is also addressed. Different surface engineering techniques are discussed including surface coatings, surface treatment, and surface texturing with an overview of the typical applications of each technique.

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This study provides a review of recent progress on designs, properties, and mechanisms of surface texturing and solid lubricants. Firstly, the design and processing of surface texture, the type of solid lubricants and the preparation method of texture combined with lubricants are mentioned in design strategy, respectively. Then, effects of surface texture and solid lubricants on tribological properties are analyzed, including antifriction, wear-resistance and other beneficial effects. Next, the synergistic effect mechanisms of surface texture and solid lubricants are discussed, focusing on the effect of texture on the surface/interface of lubricating coating and the lubrication effect of solid lubricants by texturing. Finally, this review looks forward to the problems and future development of texture and lubricants.

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Lubrication is a technique of using a lubricant to reduce friction & wear.There are four major lubrication regimes i.e., boundary, mixed, elasto-hydrodynamic & hydrodynamic.Most of the industrial machines & equipment's moving surfaces in contact, works in the mixed lubrication regime.Almost the entire major breakdown related to surface pitting & wear resulted from high friction occurs in this regime only.A lot of study & research is required in this field for improving the tribological performance of the surfaces in contact.Hardness of the base material always plays an important role in the performance of the tribological pair in all lubrication regimes especially in mixed lubrication.Therefore, authors consider the tribo pair of brass & EN31 as base material for conducting the study of the effect on various tribological parameters in mixed lubrication regime with VG-46 lubricant.Authors have also focused themselves to investigate the effect of the hardness of the base material (EN31) on the friction & wear parameters for the above mentioned tribo pair & lubricant in mixed lubricatio... Read More

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Enhancing the mechanical strength while promoting the free migration of liquid lubricants within a solid-liquid composite coating is a pressing issue. In this study, inspired by the sweat glands stimuli-responsive behavior, a lubricating coating was prepared by template-assisted method. The distribution of liquid lubricant was regulated by surfactant as template, which prevented the weakening of substrate mechanical strength from phase separation. The designed coating demonstrated a friction coefficient of 0.018 and a wear rate of 4.93 107 mm3N1m1. Subsequently, the evolution of the oil film structure at the friction interface was characterized in-situ and the impact of oil distribution status on seepage mechanism was also elucidated. With exceptional lubrication and wear resistance, the prepared composite coating holds great potential for applications in engineering.

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Lubrication is a crucial factor in improving the tribological performance of various components and thus, the overall working performance of an internal combustion engine. This paper addresses the lubrication performance of different lubricants, which are commercially available and used in automobile engines. The experiments are conducted on a four-ball tester for evaluating the tribological performance of selected lubricants, namely SAE20W-50, SAE15W-40, and SAE10W-30. The tests are designed according to ASTM D4172, and the friction and wear performance of the lubricants are characterized for better lubrication performance. The lubricant SAE15W-40 has shown excellent lubrication performance with lower friction coefficient and wear scar diameter among all the tested lubricants.

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The degradation of the lubricant is not possible as they are non-biodegradable and are toxic to nature. Around the globe, various studies are going on while concentrating on bio-based lubricant which could be environment friendly. In this analysis, friction and wear of the Mahua oil-based lubricant have been carried out at different loads. The mahua oil was treated with trimethylolpropane for improving lubrication characteristics and then blended with synthetic oil in the ratio 4%, 8%, and 12% by volume. The proper mixing of the blends was done with help of ultrasonicator. The loads assigned were 20, 80, and 140 N. The tribological analysis at various loads was assessed using a pin on disc tribometer. The sliding velocity of the disc on every load applied has been 0.4 m/s. The lubricating framework that existed during the experiment constituted boundary lubrication. Improvement in frictional behaviour and anti-wear characteristics was shown by 4% and 8% blends of Mahua oil at all the applied loads. The 12% blend shows maximum friction and wear. The worn surface images were better obt... Read More

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Although the lubrication systems for internal combustion engines have been designed to prevent engine wear and friction, their configuration does not contemplate the maximum use of each load of lubricant; because of this limitation, lubricant consumption is currently an environmental and economic problem. In this work, the performance of lubrication systems to form the tribological film that prevents wear is simulated and optimized, through the mass balance of the lubricant precursors contained in the oil and the implementation of optimal control techniques. Optimization results indicate that regulating the flow of lubricant passing through the engine prevents excessive degradation of lubricant precursors, maximizing the life of each lube oil charge, giving the possibility to increase the sustainability of internal combustion engines.

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Solid lubricants are described as solid materials of intentionally introduced or in situ formed on contact surfaces in relative motion for the purpose of lowering friction and wear and providing protection from damage. Solid lubricants and advanced self-lubricating materials are widely used in modern industries, especially in aerospace, aviation, automotive, metallurgy, materials forming, and machining industries, and have attracted great interest in lubrication applications under very severe circumstances such as elevated temperatures, heavy loads, ultrahigh vacuum, extreme radiation, strong oxidation, and chemical reactivity environments. Many efforts have been made to develop self-lubricating composites by a variety of material preparation techniques, which include powder metallurgy, physical/chemical vapor depositions, thermal spraying, electrodeposition, laser cladding, and additive manufacturing. Although several reviews on the development of high-temperature solid lubricants have been published, most of them only focus on a type of material, a specific process, or application.... Read More

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Bonded MoS2 film lubricants are widely used in industry as solid lubricants. It has excellent lubrication properties, but it also has characteristics that require careful consideration. As is well known, its friction and wear are greatly affected by the environmental atmosphere and its wear life depends on the pre-treatment of the substrate. It was found that in many cases the wear life could not be correctly estimated by a specific wear rate and could be explained by the fatigue life, especially under high loading conditions. The atmosphere dependent wear life can also be explained by the fatigue life.

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A process for depositing a composite coating on a mechanical part bore using cold spray technology. The coating is formed by mixing metal or polymer particles, ceramic hard particles, and solid lubricant particles, and then cold spraying the mixture onto the bore. The resulting coating exhibits tribological properties suitable for mixed or boundary lubrication conditions, enabling it to replace traditional bearings in mechanical components.

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High-temperature lubrication is widely used in modern industrial fields such as aviation, aerospace, nuclear, metallurgy and metal processing. The service temperature of corresponding mechanical equipment is getting higher and higher, and the problems of high-temperature lubrication and wear failure are becoming more and more prominent.This article reviews the latest research progress of binary and ternary oxide coatings with high-temperature solid lubricant application potential, discusses the structure, chemical and electrical properties of these oxides and their tribology, and focuses on the main types of solid lubricating materials. The correlation of performance and its lubrication mechanism are analyzed.This review also discusses the industrial applications of these coatings and predicts that lubricating coatings might develop in the direction of self-lubricating and self-healing smart lubricating materials.

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Considerable research has been conducted in the past decade and a half regarding the bio-lubricants potential to replace mineral-based lubricants as mainstream lubricants such as engine oil, hydraulic oil, compressor oil, and metalworking oil. This study studied several bio-lubricants (rapeseed oil, palm olein, and soybean oil) and a mineral-based lubricant, SAE40. The bio-lubricants have better physiochemical, tribological characteristics and environmental friendly nature, and are promising to replace mineral-based lubricants. In this study, a journal bearing test rig (JBTR) was developed in order to investigate the effect of journal speed on the temperature of oil film with time. Additionally, the load-carrying capacity of bio-oils was tested against the mineral-based lubricant SAE40 by adding a load on the journal. For all three speeds, i.e., 1000, 1500, and 2000 rpm, the bio-lubricants recorded minimum temperature. At 1000 rpm, rapeseed oil recorded a 9.2% lower temperature than SAE40. Similarly, at 2000 rpm, rapeseed oil recorded a minimum temperature that was 2.5% lower than SA... Read More

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Abstract Type of lubricant used for fluid film bearings is one of the most important factors to consider. Bearing characteristics have to maintain steady throughout a wide range of conditions. However, viscosity, which is one of the primary lubricant properties, highly deviates depending on environmental and operational conditions. Macro-molecular micro-structure of lubricants is strongly correlated to temperature and shear rate, leading to a shear thinning behaviour. This work aims in studying a pad bearing lubricated by a shear thinning oil in hydrodynamic region. Hydrodynamic wedge was modelled for a small fixed pad bearing of 8.5 mm inner radius, 14.5 mm outer radius, 40 angle and 50 m inlet outlet film thickness difference. Variety of cases were studied for several runner rotational velocities and minimum film thickness. Lubricant was modelled as a carreau fluid. Load carrying capacity, power losses, friction coefficient, mass flow rate, temperature and viscosity were evaluated. From the aspect of load carrying capacity, this specific pad bearing is optimally operating for r... Read More

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Understanding the complex nature of wear behavior of materials at high-temperature is of fundamental importance for several engineering applications, including metal processing (cutting, forming, forging), internal combustion engines, etc. At high temperatures (up to 1000 C), the material removal is majorly governed by the changes in surface reactivity and wear mechanisms. The use of lubricants to minimize friction, wear and flash temperature to prevent seizing is a common approach in engine tribology. However, the degradation of conventional liquid-based lubricants at temperatures beyond 300 C, in addition to its harmful effects on human and environmental health, is deeply concerning. Solid lubricants are a group of compounds exploiting the benefit of wear diminishing mechanisms over a wide range of operating temperatures. The materials incorporated with solid lubricants are herein called 'self-lubricating' materials. Moreover, the possibility to omit the use of conventional liquid-based lubricants is perceived. The objective of the present paper is to review the current state-of-... Read More

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Abstract High torque and friction factors are major challenges while drilling. Providing lubrication helps in reducing torque and drag and increasing rate of penetration (ROP) in water-based fluids and produced water. The lubricants are inert hence, they do not react with other fluid additives or cuttings and will not affect fluid rheology. All Lubricants in the oil and gas industry are in liquid form and usually used to reduce torque and decrease coefficients of friction, they came in different chemical compositions a toxic lubricant mineral oil and non-toxic vegetable lubricants, and they have many papers talk about how they function as lubricants, but with a new generation of solids lubricants, it will be changing the whole industry. Powdered encapsulated lubricant additive comprises a liquid lubricant blended with an inert solid substrate. The solid lubricant additive compositions thus, obtained are advantageously employed in drilling fluids. Fatty acid solid lubricant is one of the aforementioned powdered lubricants. It is a dry form encapsulated lubricant composed of micronized... Read More

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