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The oil film lubrication performance of a large hydrostatic turntable operating at the model of constant surface cutting speed is studied. Firstly, the rotary speed equation which is bound by the constant surface cutting speed is established. According to the fluid lubrication theory, the gap flow equation, the oil film temperature rise equation and the double‐rectangular‐cavity oil pad bearing capacity equation are derived. Further, a prediction model of oil film lubrication performance in the operating mode is established. The change rules of temperature, pressure and other performance indexes of the film with time are obtained by numerical simulation. And, the above laws are verified by design experiments. It is found that the cutting speed, feed rate leaves a significant impact on the law of variations of oil film performance with time. According to the conclusions, it will be beneficial to improve the bearing capacity of the hydrostatic turntable and further improve the machining accuracy by using cutting parameters reasonably to control the speed within a certain range. [ABSTRACT FROM AUTHOR]

Regular lard (RL) was chemically modified into isopropyl‐branched lard (BL). The isopropyl group was introduced into the triglyceride structure via a reaction of carbon–carbon double with isopropyl bromide in presence of ethylaluminum sesquichloride. The reaction was confirmed with gas chromatography–mass spectroscopy, nuclear magnetic resonance, infrared spectroscopy. The physical, tribological and chemical properties of the RL, BL and their blendings in polyalphaolefin (PAO) and high‐oleic sunflower oil (HOSuO) were investigated. The BL exhibited better solubility both in HOSuO and PAO than RL. Compared to RL, BL exhibited higher density, viscosity, improved oxidative stability and cold flow properties both as a neat material and blendings in HOSuO or PAO. However, BL displayed lower viscosity index (197 vs. 162) compared to RL. Both RL and BL displayed similar lubricity as HOSuO and showed potential such as a good lubricity additive in PAO even in small amounts (~10 wt%). This study reveals introducing alkyl branching into lard can lead to improved physico‐chemical properties and lubrication performance. [ABSTRACT FROM AUTHOR]

The distribution of lubricant flow field inside the two‐stage transmission reducer is very complicated during splash lubrication, which is difficult to be visually simulated and analysed using traditional finite element methods (FEM). There are many problems in model processing, algorithm selection, mesh division, and computational workload. Through sufficient investigation and experimental validation based on literature, the moving particle semi‐implicit (MPS) method is proposed to study the splash lubrication characteristics of a rail vehicle reducer. Through this method, the visual simulation calculation of multiple working conditions of reducer with complex structure is realised, and the unreasonable structure of the gearbox body is optimised. The model of oil supply demand in the Hertz contact zone of gear transmission is established, and the time‐domain variation law of oil particles number in the contact zone and oil supply state are analysed. It is found that the optimised reducer model can meet the demand of oil supply under the four typical working conditions of the rail vehicle. The higher the initial oil volume is, the more sufficient the oil supply is. Compared with the working temperature conditions of 20 and 80 °C, the lubrication effect is better at 40 and 60 °C. By analysing the power loss proportion of each gear, it is found that the sum of power loss of gear 1 and gear 2 is dominant under different working conditions, reaching 76%–99.5% of the total churning power losses. [ABSTRACT FROM AUTHOR]

In this study, plastic oil (PO) as a potential lubricant was investigated. The base PO was incorporated with graphene nanoplatelets (GNP) and hexagonal boron nitride (hBN) nano additives in varying concentrations to form nano lubricants. Their viscosity, tribological, acidic/basic nature, thermal degradation and dispersion stability properties were investigated. It was observed that 1.5 wt% GNP and 1.0 wt% hBN added separately to the base PO, provided the lowest coefficient of friction (COF) and wear volume. Based on these lowest COF and wear volume insights, three nano lubricant mixtures were formulated by incorporating both GNP and hBN at different combinations using base PO. Positive synergistic behaviour was observed for COF (49%–60% reduced) and wear volume (90%–97% reduced) for two combination mixtures compared to the base PO. These improvements in the mixture were due to the polishing, mending mechanisms and tribofilm that protected the interacting surfaces. [ABSTRACT FROM AUTHOR]

Porous materials are widely used in friction pairs. The transient squeezing flow of the lubricant significantly affects the lubrication quality. The study found that the lubricant penetrates into the porous matrix in the contact area and exudes upward to the entrance of the contact area. The maximum stress occurs at the subsurface of the contact zone, and the maximum pressure occurs at the contact centre. In the early loading stage, the lubricant exudates, resulting in a higher liquid‐phase load. With the prolongation of the time, the average stress decreases and then increases gradually, whilst the average pressure has the opposite change. In the late loading stage, the load is completely borne by the solid phase. Increasing the load will increases the seepage velocity of the lubricant, which enhance the pumping effect of the friction interface. The findings can help for better understanding of the self‐lubrication mechanism of the porous materials. [ABSTRACT FROM AUTHOR]

In the actual working condition, due to the manufacturing errors, improper installation, load, thermal deformation or other factors can cause the journal surface to produce the form and position errors. The mathematical models are developed that takes into account the form and position errors, the lubrication performance of four‐recess capillary restrictor hybrid journal bearings with different journal tilt angles and cylindricities is studied, and the effect of eccentricity on the oil film lubrication performance is analysed. The results show that the dimensionless oil film pressure and loading capacity increase as the journal tilt angle and eccentricity increase considering journal tilt, and the friction coefficient tends to increase and then decrease. Compared with journal alignment, the oil film thickness distorts, the oil film pressure peak shifts to the edge of bearing, and the horizontal tilt has a greater impact on bearing when the journal is tilted. The oil film pressure distribution has no significant change considering cylindricity errors, while the oil film pressure value increases, the loading capacity increases and the coefficient of friction decreases as the cylindricity and eccentricity increase. The research shows that the presence of a certain cylindricity error contributes to the lubrication performance of four‐recess capillary restrictor hybrid journal bearings. [ABSTRACT FROM AUTHOR]

The friction and wear reducing properties of ammonium thiomolybdate as a water‐soluble lubricant additive were evaluated using a pin‐on‐disck tribometer on a steel‐steel contact. The tribological performance of aqueous solutions of thiomolybdate prepared at concentrations between 0.1 and 0.3 wt% Mo were evaluated at the same load (10 N), entrainment speed, sliding distance and temperature. Although there is a reduction of friction and wear compared with pure water, a significant difference is observed, depending on the additive concentration. SEM/EDAX and Raman spectroscopy analyses of the wear tracks of specimens tested at concentrations below 0.3 wt% Mo reveal the formation of FeS which is responsible for gradually reducing the coefficient of friction from values between 0.30 and 0.5 down to ~0.11. At 0.3 wt% Mo, the analyses indicated the formation of a MoS2 which keeps the coefficient of friction in ~0.05, the lowest recorded value. [ABSTRACT FROM AUTHOR]

Polyol‐ester lubricants have been used and developed for aviation gas turbine engines for many decades. The newest MIL‐PRF‐23699 lubricant class, called enhanced ester (EE), provides the best combination of thermal stability, load carrying capability, boundary lubrication and compatibility with fluoroelastomer O‐rings. Two candidate EE Class formulations and one high thermal stability class formulation conforming to MIL‐PRF‐23699G were evaluated for oil degradation with up to 3000 h of bearing operation. Lubricant degradation was studied using VIM VAR M50 bearings with M50 and silicon nitride balls under two operating conditions using two bearing test rigs. Oil degradation in terms of oxidation time, total acid number and viscosity was studied as a function of time with varying results for the three lubricants. [ABSTRACT FROM AUTHOR]

In the present work, a comparison between traditional oil‐in‐water (O/W) based lubricant and nano‐TiO2 additive water‐based lubricants was made to explore the lubrication effects during rolling of ferritic stainless steel (FSS) strips. The results show that marked reduction in rolling force and improvement in the surface quality can be achieved by utilisation of water‐based nanolubricant, which can be attributed to the synergism of rolling effect, mending effect, polishing effect and protection film. An optimal concentration of 3.0 wt% TiO2 nanoparticles is found to exhibit excellent lubrication effects with sufficient nanoparticles at real contact regions without aggregation, leading to 10% reduction in the surface roughness during rolling of FSS strips. [ABSTRACT FROM AUTHOR]

We investigate flow and slip behaviour of Santotrac 50 molecules under high shear in Couette cell by means of Molecular Dynamic simulation to understand reduced friction force. Molecular chain stretches and oriented to shear direction, and move. Slip starts on metal surface at 2 × 108 s−1, and increases with shear rate. Slip length keeps scale at nanometre. Molecular conformation and occurrence of slip both indicate a reduced shear stress. Furthermore, when changing wettability, slip length increases in power law and thus decreases shear stress greatly. Occurrence of low‐density region near surface can explain slip. And thus, we extended apparent slip model, which divided lubricant into liquid layers with different viscosities, to elucidate the relationship between molecule distribution inner layer and slip on surface influenced by shear velocity and wettability. Above all, our research sheds light on flow and slip behaviour of complex fluid and can be applied in improving lubrication property. [ABSTRACT FROM AUTHOR]

Research was focused on understanding the degradation kinetics of cold rolling oil used in the rolling mill at Tata Steel. Aged rolling oil leads to various surface defects. Ageing phenomenon is influenced through thermo‐mechanical behaviour, oxidation, hydrolysis and presence of iron fines. Ageing of cold rolling oil in presence of iron fines was systematically performed at various temperature followed by thermo‐mechanical wear tests. With variation in intensity of ageing, change in physico‐chemical parameters and fatty acid distribution (FAD) within triglycerides could be observed. The impact of the controlled ageing on performance parameters like lubrication, evaporation kinetics and oxidative stability were also studied. Thermo‐oxidative ageing depletes antioxidant concentration within the rolling oil resulting in rapid oxidation of unsaturated fats. This leads to rapid build‐up of high molecular weight ingredients resulting in formation of fatty acid soaps or scum. The resultant scum negatively impacts the boundary lubrication and evaporation kinetics of rolling oil. [ABSTRACT FROM AUTHOR]

This study had investigated the main degradation mechanism of a roll in hot rolling process, to reduce the wear and oxidation, a type of low‐melting glass fabricated by the fuse‐polymerisation method was tested as a hot metal forming lubricant by a ball‐on‐disc tribometer at high temperature. The results revealed that the roll degrades mainly due to the cracks initiated at the interface of carbides/matrix on the roll surface, then propagate along the interface, and being sheared off when the cracks confluence in the subsurface. The high‐speed steel (HSS) starts to be oxidised at 500°C, and grows heavily with increasing temperature. The recommended lubricant presented a desired lubrication behaviour for hot rolling process that generating a higher friction coefficient at low temperature and a lower one at high temperature. The friction coefficient, wear rate, and oxidation of HSS roll was reduced materially, which meets the requirements of hot rolling lubricant well. [ABSTRACT FROM AUTHOR]

An UHMWPE‐based multiscale composite containing graphene oxide, nanodiamonds, and short carbon fibres has shown excellent performance under distilled water lubrication. However, it is crucial to evaluate its tribological performance under conditions which more accurately represent the final application. In this study, the tribological performance of the developed UHMWPE‐based multiscale composite is evaluated and compared with neat UHMWPE under different lubricating conditions: no lubricant (dry), in seawater (SW) and in an environmentally acceptable lubricant (EAL). While neat UHMWPE displays a lower friction and wear in dry conditions, the multiscale composite performs better under SW and EAL lubrication. A maximum reduction in friction coefficient of 77% and specific wear rate of 88% are obtained in SW. Under EAL lubricated conditions, the multiscale composite has a maximum reduction in specific wear rate of up to 75%. [ABSTRACT FROM AUTHOR]

This study aims at the characterisation of physicochemical properties and tribological behaviour of quaternary phosphonium based ionic liquids (QPILs) P44414Sac and P44414Ace at ambient temperature and elevated temperature. The kinematic viscosity, viscosity index (VI), thermal stability, corrosivity and tribological properties of the ionic liquids (ILs) were systematically investigated. The copper strip corrosion test results revealed that the two green ILs are non‐corrosive because of their halogen‐free characteristic. Tribological data demonstrated that the present ILs exhibited extremely superior friction‐reducing and anti‐wear properties to conventional IL lubricant 1‐Butyl‐3‐methylimidazolium hexafluorophosphate (L‐P104), 1‐n‐Octyl‐3‐methyl imidazolium hexafluorophosphate (L‐P108) and commercially available synthetic oil PAO10. Electrical contact resistance (ECR) and surface analysis of the worn‐out steel disc surfaces revealed that the synergistic effect of a polarity induced physical adsorption layer and a tribo‐chemical reaction film formed a boundary film to protect steel‐steel contact between rubbing surfaces. [ABSTRACT FROM AUTHOR]

The tribological properties of Pb‐free FeS/Cu–Bi (FCB) self‐lubricating composites were optimised with the Taguchi method. The effects of lubricant content and ball milling time on the anti‐friction and wear resistance of FCB composites were investigated. Then the evolution of the friction interface was observed through interrupted microscopy measurement to reveal its synergistic lubrication mechanism. The results showed that the primary and secondary factors that affected the anti‐friction and wear resistance of the FCB composites were FeS content, Bi content and ball milling time. The synergistic lubrication mechanism of FCB composites was that FeS could prevent the crack from extending with the continuous Bi mesh and could prevent the matrix with Bi debris from peeling off, which was conducive to the formation of a lubricant‐rich tribofilm at the friction interface to improve the tribological properties of the composites. [ABSTRACT FROM AUTHOR]

This paper reported the tribological behaviours of Cu nanoparticles as lubricant additives. Cu nanoparticles were prepared by an innovative technology called mass‐produced nanoparticles (MPNP). A SRV‐IV friction and wear tester was used to investigate the influence of load on the tribological performance of 0.1 ~ 2 wt% Cu nanoparticles. The results indicated adding 0.1 wt% Cu nanoparticles into PAO6 base oil and 10 W/40 CH‐4 commercial lubricant, reduce the average friction coefficient by 38% and 3%, and decrease the wear rate by 96% and 66% under 300 N, respectively, compared to the lubricants without nanoparticles. The excellent antiwear and antifriction effect could be attributed to the rolling effect caused by the ideal spherical shape and good dispersibility of the prepared Cu nanoparticles and form deposition film on the surface of the friction pair. Therefore, the Cu nanoparticles prepared by MPNP show excellent tribological performance and possess broad prospects in the fields of lubricant additives. [ABSTRACT FROM AUTHOR]

In mixed lubrication, material wear is inevitably caused due to solid contact. Simultaneously, the surface morphology after wear will affects the lubrication performance. To understand this coupling process, virtual surface reconstruction technology and mixed lubrication sliding wear model were applied to predict the evolution of wear characteristics and lubrication characteristics during wear in this study. The effects of the roughness root mean square (RMS), roughness direction and wavelength ratio on the contact area ratio, the contact load ratio, accumulated wear, film thickness and the friction coefficient were analysed. The results indicated that the contact area ratio and the contact load ratio and the friction coefficient decreased and average film thickness increased with the increase in the number of the wear cycles. In addition, a surface with low‐roughness RMS, longitudinal roughness texture and high‐wavelength ratio is suitable for improving lubrication performance and reducing wear. [ABSTRACT FROM AUTHOR]

Calculating the flow of a film of lubricant between rough surfaces by solving the Reynolds equation requires a very fine mesh to capture the details of the topography and is thus very time consuming. In the present paper, a multiscale method is proposed. The domain is divided into an appropriate number of subdomains on which deterministic simulations are performed. The results of this microscale solution are coupled at the macroscale by employing a macromesh on which a mass flow balance is implemented. This method has already been successfully applied to liquid lubrication and is extended to gas lubrication. A significant reduction in computation time is obtained compared to a fully deterministic solution. The calculation of the load is also accurate. [ABSTRACT FROM AUTHOR]

Free surface lubrication of rotating cylinders by Newtonian liquid jets was investigated at different impingement positions, jet‐ and circumferential velocities. The interaction between impinging round laminar jet and rotating surface was characterised by high‐speed imaging. Compared to flat surface impingement, the liquid deposition mechanism is more complex and often accompanied by phenomena such as splashing, jet deflection and formation of radial surface stripes. Liquid splashing initially develops in direct deposition regime due to hydraulic jump‐induced droplet shedding, transitioning to lamella instability splash at higher Reynolds numbers. The critical Reynolds number for splash onset is of same order of magnitude as for flat surface impingement and fairly constant at low relative jet impingement angles, but increases exponentially when angle approaches 90°. Liquid film width and thickness were both determined proportional to the square root of the jet/surface velocity ratio, with respective power law models in good agreement with measured values. [ABSTRACT FROM AUTHOR]

This study proposes a tribo‐dynamic model for point contacts under lubrication, focusing on the excitations caused by surface movement, defect and load impact. Surface movement and load impact can cause changes in contact force, resulting in acceleration and dynamic displacement, which may affect the flow of the lubricant. The traditional lubrication model is usually steady or transient, and load balance is used to correct the normal height, ignoring a series of influences such as the mass, stiffness and damping. It requires repeated corrections to obtain a balanced position, which is very time‐consuming. By combining tribology and dynamics, dynamic excitation is introduced in the contact process in this study. After determining the initial value, the normal height can be directly obtained from the dynamic equation. Besides, a comparison between the tribo‐dynamic model and the steady‐state model is presented. It is found that the film thickness and pressure distribution calculated by the two models are almost the same at medium and low speeds, while the calculation results of the two models are different at high speed or under load impact, which emphasises the importance of considering the dynamic behaviour in the study of contacts. [ABSTRACT FROM AUTHOR]

In this investigation, a self‐assembly method was used to fabricate black phosphorus (BP)/MoS2 composites as water‐based lubrication additives. The tribological behaviours of the lubrication additives for GCr15 steel ball/TC4 titanium alloy disk contact under different mass ratios, loads and rotational speeds were also investigated. The experimental results showed that 0.01 wt.% BP and 0.04 wt.% MoS2 as water‐based lubrication additive have the best the synergistic lubrication effect. Compared with pure water, coefficient of friction (COF) and wear rate of the lubrication additive at the test conditions of 8 N and 150 r/min were reduced by 32.6% and 68.8%, respectively. As the loads increased, the COFs and wear rates of all the lubricants including pure water, BP as water‐based lubrication additive (BP‐WL), MoS2 as water‐based lubrication additive (MS‐WL) and BP/MoS2 composites as water‐based lubrication additive (BM‐WL) were all reduced. As the rational speeds increased from 100 to 250 r/min, all the lubricants were firstly decreased and then increased. Based on tribological tests and wear surface analysis, the lubrication mechanism of BM‐WL is proposed. The interlaminar shear and the adsorption of BP/MoS2 composites on the wear surface of the friction pairs are the key to reducing COFs sand wear rates. In addition, the tribo‐chemical reaction films consists of FeO/Fe2O3, Al2O3 and TiO2 were formed during the friction process, which can effectively protect the surface of the titanium alloy/steel contact from wear. [ABSTRACT FROM AUTHOR]

In this study, a vapour‐assisted drag reduction mechanism of texture surface with elevated temperature is explored. The computational fluid dynamics simulation is performed to understand the vapour membrane generated by the coupled effect of elevated temperature and surface texture. Simulation results indicated that elevated temperature may help generate the vapour membrane which can isolate the liquid water from the solid surface, thereby reducing friction. Meanwhile the introduction of surface micro‐texture has dramatic positive effect in vapour volume fraction, vapour thickness and the average velocity of outflow. It was found that introducing the micro‐texture to the elevated surface has dramatic positive effect in reducing frictional drag, the groove formed by the micro‐texture can store vapour and form a vapour vortex inside, which may have a certain driving effect on the fluid. [ABSTRACT FROM AUTHOR]

Thrust bearings are widely used in many rotary industrial applications. In this work, a thrust bearing surface under the mixed lubrication regime is analysed and then optimised with aim for use in an injection moulded polymer bearing. A model which couples the mechanical deformation, boundary lubrication and solid contact is developed to investigate the behaviour of the thrust bearing under the load balance condition. This model provides the predictions of important quantities such as load carrying capacity from fluid and solid contact, minimum film thickness and contact pressure. More important, the large‐scale surface geometry is optimised using a quadratic geometry and this large‐scale surface is superimposed with the small‐scale roughness from measured surface to form an optimised surface. This large‐scale geometry might be controlled in the injection moulding process of polymer thrust bearings, whereas it is more difficult to control the roughness. The fluid load carrying capacity for the optimised surface has more than doubled compared to the fluid load carrying capacity for the measured surface. [ABSTRACT FROM AUTHOR]

The present work addresses the use of synergistic blends of two different types of nanomaterials (spherical particles and lamellar sheets) as additives for coconut oil‐based grease formulation to provide the energy‐efficient and sustainable alternative to conventional grease. The spherical SiO2 nanoparticles are separately blended with 2D lamellar sheets of MoS2 and graphene oxide (GO) in variable ratio and probed their synergistic effects for enhancement of physicochemical and lubrication properties. The SiO2 nanoparticles, MoS2, and GO nanosheets are prepared by modified sol–gel, hydrothermal reduction, and Hummer's methods, respectively. The 0.05 wt% nanomaterials blends of MoS2/SiO2 (30:70) and GO/SiO2 (50:50) as optimised doses furnished the maximum reduction in the friction and wear. The combination of rolling friction and low shear properties using the synergistic blend of the spherical nanoparticles (SiO2) and nanosheets (MoS2 and GO) showed significant improvement in tribological properties. The optimised blends of nanoadditives, that is, MoS2/SiO2 and GO/SiO2 conserved the energy by 20% and 19%, respectively. These findings suggest that the use of synergistic blends of variable nanomaterials to vegetable oil‐based lubricants can pave a direction for new generation lubricant formulation, where environmental sustainability and energy conservation are on prime importance. [ABSTRACT FROM AUTHOR]

Citric acid‐synthesised Eu‐doped WO3 (WO3:Eu3+) and Mn3B7O13Cl nanoparticles were characterised by X‐ray diffraction and transmission electron microscopy. The tribological properties of the Eu doped WO3 and Mn3B7O13Cl prepared as anti‐wear additives for enhanced lubrication were studied using a four‐ball tester. The experiment results indicated that Eu doped WO3 nanoparticle reinforce Mn3B7O13Cl has excellent load‐carrying capacity, wear‐resistance and friction‐reducing properties in water‐based lubricant, optimum concentration of WO3:Eu3+‐Mn3B7O13Cl was 0.5 wt%. The wear scar diameter decreased from 0.62 to 0.37 mm and the coefficient of friction was reduced from 0.083 to 0.065, which reductions are attributed to the nanotribofilms composed of B2O3, WO3, Fe2O3 and Eu2O, which prevented direct contact between metals. Hot rolling experiments of laminated Cu‐Fe composite sheet were carried out to study the effect of nano‐WO3:Eu3+‐Mn3B7O13Cl on surface qualities including topography of rolled strips. Results show that the surface topography becomes smooth with the addition of nanoparticles into water‐based lubricant, which is mainly attributed to the nanoparticles increase the viscosity of water‐based lubricant and the oil film to avoid the direct contact tribopair during hot rolling, thus reducing the friction coefficient and roll wear. [ABSTRACT FROM AUTHOR]

Thrust bearings are machine elements designed to support axial loads in rotating machinery. The hydrodynamic lubrication analysis of such bearings has been a major subject for many studies over the years, leading to important conclusions for design parameters that affect their optimal operating conditions. Furthermore, the last few years, the influence of the industry 4.0 concept has brought new tools that can revolutionise bearings' design. The aim of this study is to combine numerical analysis and machine learning techniques in order to identify optimal thrust bearing's hydrodynamic designs. For this purpose, the Reynolds equations are solved using the finite difference technique on a 2‐D grid of a tilting pivoted bearing's pad. The bearing pressure distribution; load carrying capacity and friction are calculated for multiple operating conditions. The data produced are used as input for the training of regression models that predict the behaviour of the thrust bearing for a wide range of loads and rotating speeds. Simple and multi‐variable, linear, polynomial and SVM regression models are compared for their accuracy to predicting the bearing's operating conditions. The major findings related with three different lubricants, a monograde SAE 30, a multi‐grade SAE 10W40 and a bio‐lubricant AWS 100 that are compared and their optimal operating conditions are suggested in terms of minimum friction force and maximum load carrying capacity for the bearing pad. AWS 100 is found to be the most suitable lubricant that provides the bearing with low operating friction and high load carrying capacity in all studied cases. [ABSTRACT FROM AUTHOR]

As the progress of the high‐speed performance requirement for porous gas journal bearings continuing, the aerodynamic effect, which plays a key role in the state of lubrication, causes the porous gas journal bearings being gradually to be used as hybrid bearings. This paper firstly presents a theoretical analysis on the lubrication mechanism of the hybrid bearings. The gas flow in the porous and clearance is modelled by using the mass continuity equation. Two experimental test rigs are designed to systematically test the static and dynamic characteristics of the hybrid bearings. The numerical results are corroborated by the experimental data. Results show that there is optimal clearance for hybrid bearings to obtain maximum load capacity. The load capacity of the hybrid bearings is increased by the aerodynamic effect to be higher than that of pure aerostatic bearings especially at higher rotational speed and larger eccentric ratio. However, due to the occurrence of the aerodynamic effect, the hybrid bearings show clear cross‐coupling dynamic coefficients, which may lead to bearing instability. It is interesting to note that the direct dynamic stiffness and damping coefficients are both influenced by the aerodynamic and aerostatic effects. Higher rotational speed and external supply pressure will result in higher direct dynamic coefficients. [ABSTRACT FROM AUTHOR]

The aim of the work is to improve tribological properties of an ATF oil by means of additives. Two ionic liquids (IL) and one IL with 0.1 wt.% graphene were chosen as candidates. The ILs were selected because of their promising surface interactions and proven synergy with anti‐wear additives. However, little is known about the addition of ILs to fully formulated lubricants, especially in the low temperature range. Therefore, static and sliding friction as well as wear were measured in an application‐relevant temperature range of −30 to 100°C using a rotating ball‐on‐3‐plate test. The best additive for ATF oil for material pairing 100Cr6/polyether ether ketone was 5 wt.% [P66614][TMPP][G] (halogen‐free) and for 100Cr6/sintered iron 3 wt.% [P66614][BTA]. The additives lead to a wear reduction of more than 50%. Furthermore, it could be observed that the selected ILs have different effects on the friction behaviour at the temperatures investigated. [ABSTRACT FROM AUTHOR]

Nozzle clogging in roll gap lubrication (RGL) is a pain area for hot strip steel rolling. Nozzle clogging severely affects lubrication affecting rolled surface quality causing prominent hot rolling defects like banding and peel‐off phenomenon in work roll. Uneven coefficient of friction leads to variable or poor lubrication, which raises the chances of cobble and tail chewing in coils, lowers roll force reductions ultimately increasing the power consumption of the mill. The present work focuses on a holistic approach where causes leading to nozzle clogging have been identified and eliminated in a stepwise manner. Gas chromatography has been employed for the first time to get an understanding about the specific carbon chains contributing towards pulp generation. Optimising the distance between mixer and spray header and using indigenously modified spray header improves the lubrication during hot rolling. roll force reduction upto 15%–16% could be achieved. [ABSTRACT FROM AUTHOR]

A type of compound texture combining micro‐dimple and variable‐depth groove was designed to improve sealing performance and reduce wear of the plunger couple in diesel engine. The simulation results indicate that moderate oil film thickness can be produced by compound texture to settle the lack of lubrication of groove mode. Meanwhile, higher hydrodynamic pressure is produced to improve sealing performance of a plunger couple, tackling the problem of relatively high leakage of micro‐dimple mode. The compound texture was fabricated on the plunger surface by laser surface texturing (LST) and the test results confirmed the improvement of lubrication and sealing performance. The basic tribological test result shows that that the deepest wear depth and average roughness were reduced by 72.4% and 22.6%, respectively. Meanwhile, the engine bench test result shows that the amount of fuel leakage was reduced by 73.1% as well. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of oil‐air lubrication on contact temperature and sliding tribological properties. On the basis of heat transfer theory, a numerical simulation model of forced convection was established. Experiments were conducted using the tribology machine. Results show that in oil‐air lubrication, forced convection can significantly reduce the temperature at the contact position. Nonlinear decline and decrease in the descent rate of contact temperature were observed with the increase in convective heat transfer coefficient. The convective heat transfer between friction pairs increased with air supply velocity, whereas the sliding friction coefficient initially decreased and then increased. The friction flash temperature reached its lowest value with proper heat dissipation capacity. With the increase in ambient temperatures of the friction pairs, the sliding friction coefficient decreased, whereas the friction flash temperature increased. Influenced by the oil‐air lubrication heat dissipation in the test, the wear mechanism of point contact sliding friction was abrasive wear. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the influence of cavitation effect caused by surface texture on the lubrication performance of friction pairs. In order to verify and research the cavitation phenomenon induced by surface texture, cavitation images are collected by visual experimental apparatus. The results show that the surface texture will induce the cavitation of the lubricating oil under certain speed and load conditions, gas bubbles will be generated at the outlet of the dimples, and the cavitation will affect the lubrication performance of the friction pair. When the texture depth is close to the oil film thickness, it has the best effect in terms of inducing cavitation and promoting lubrication. And it is found in the experiments when area density of texture is 8% and the square dimples are arranged at inlet area of the sample, the best effect of the surface texture can be obtained. [ABSTRACT FROM AUTHOR]

The exfoliation for few layers of graphene was prospective for scale output due to low cost and processable advantages. However, the massive production had some obstacles such as high pollution with organics and harmful elements and use of rare metal. Herein, we developed a facile and eco‐friendly expansion‐reduction exfoliation method to prepare graphene from graphene oxide (GO) with aid of oxalic acid(H2C2O4). The as‐exfoliated graphene nanosheets possessed a 10‐layered thickness and large lateral size of approximately 0.5 μm. As a prospective application, the as‐exfoliated graphene nanosheets were conducted as additive in the grease for the sake of antifriction and antiwear. The results showed that the friction reduction and wear resistant properties were improved by 35.8% and 32.8%, respectively. The friction reducing mechanism of graphene in grease was proposed due to forming a protective film. [ABSTRACT FROM AUTHOR]

Real‐time measurement of the lubrication state is one of the critical problems in studying the lubrication state and its transformation characteristics. Based on the experimental results, shrinkage resistance principle and Greenwood's contact theory, a mathematical model for cylinder liner‐piston ring that can be used to measure the resistance of film thickness ratio is established. On this foundation, the correspondence between the film thickness ratio and the contact resistance for cylinder liner‐piston ring was presented and the technical possibility to characterise the real‐time lubrication state was provided. An experimental study for determining the lubrication state of cylinder liner‐piston ring based on resistance measurement method was conducted on a reciprocating friction and wear tester to verify the applicability of resistance measurement method in cylinder liner‐piston ring friction pair. Results show that the contact resistance method is reliable and practicable to determine the lubrication state of cylinder liner‐piston ring friction pair. [ABSTRACT FROM AUTHOR]

In current researches on the lubrication of engine piston ring, some were based on a hypothesis that the piston ring is on a flooded lubrication status. Although some others belong to the starved lubrication analysis, the one‐dimensional model, a certain form of starved lubrication status or simplified manner were used. In this paper, on the basis of the equations about the lubricating oil flow‐rate and control volume, a flow model of lubricating oil in the piston ring‐cylinder liner conjunction is established, and the influence of the situation of supplied lubricating oil film at the piston ring inlet on the two‐dimensional starved lubrication characteristics of piston ring for a four‐stroke engine is studied. The results indicate that the lubrication condition at the piston ring inlet has significant impact on the lubrication characteristics of piston ring. When the supplied lubricating oil at the piston ring inlet increases, the minimum film thickness of piston ring will increase, meanwhile the maximum film pressure, asperity contact force, friction force and power loss will decrease. If the film thickness at the piston ring inlet is smaller, the increase of the supplied film thickness can improve obviously the lubrication characteristics of piston ring. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic characteristics of an oil film under vibration, the dynamic model of an involute gear system was established based on the dynamics theory. The vibration and lubrication characteristics of the gear system were analysed in detail. Furthermore, based on the numerical solution of lubrication, a model of oil film stiffness was established. The dynamic characteristics of the oil film were verified by calculating the oil film stiffness. It was found that both oil film pressure and thickness manifested certain dynamic characteristics under vibration. Moreover, the intensities of oscillation amplitude and frequency were different under different loads and rotating speeds. The oil film stiffness gradually decreased and increased, respectively, with the increasing rotating speed and load. Therefore, for a heavy‐duty high‐speed gear system, the coupling effect of vibration and lubrication should be considered. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) nanoparticles are widely used as oil additives for obtaining low friction and wear. In this article, MoS2 nanosheets with ultrathin shape and structure defects were prepared by a facile solvothermal method with the aid of polyethylene glycol (PEG 200). The products were analysed by X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR). Results indicated that PEG 200 played a crucial role as the shape controller in the formation of different MoS2 structures. Interestingly, the prepared MoS2 perform excellent in improving the friction‐reducing and antiwear properties of oils. More importantly, the lubricating behaviour of the obtained MoS2 nanosheets as oil additives was still effective in the harsh condition of heavy load and high temperature. Further, the excellent lubrication performance of the prepared MoS2 was discussed based on the exfoliation into individually ultrathin nanosheets and nanosized debris, and the formation of MoS2‐based tribofilm inside the wear tracks. [ABSTRACT FROM AUTHOR]

Aiming at the asymmetric helical gear injection lubrication, simulation models for coast flank and drive flank injections were established by computational fluid dynamics (CFD). Firstly, the two oil injection methods of the asymmetric helical gear were explained. Then, a mathematical calculation model suitable for gear injection lubrication analysis was established. Finally, the model is simulated by CFD software. The oil volume fraction and pressure at the meshing point during the gear meshing process of the two injection models are obtained. The effects of gear speeds and spray velocities on the oil volume fraction and pressure are analysed. By comparing the two oil injection methods, when the spray velocity is more than 2.7 times the pitch line velocity, better lubrication is obtained by the drive flank injection method. When the spray velocity is less than 2.7 times the pitch line velocity, the coast flank injection method can achieve better lubrication. [ABSTRACT FROM AUTHOR]

Thickener as an important ingredient affects the performance characteristics of lubricating grease. Here, seven lithium complex greases (LCGs) were prepared by saponification of 12‐OH stearic acid and low molecular weight dibasic acids (including adipic acid, sebacic acid, phthalic acid, dodecanedioic acid, and the combination of sebacic acid and phthalic acid in different molar ratios) with LiOH, using polyalphaolefin (PAO 40) as base oil. Physical properties and lubrication function of as‐prepared LCGs were evaluated in detail, and the friction mechanism was explored via analysis on the morphologies and composition of worn surfaces. Results illustrate that the saponification of mixed 12‐OH stearic acid and sebacic acid with LiOH provides good thickener for improving the physico‐chemical performance of LCG, while the thickener prepared by 12‐OH stearic acid and adipic acid with LiOH enhances lubrication function of LCG, mainly depending on synergy of grease film and tribo‐chemical reaction film. [ABSTRACT FROM AUTHOR]

The connecting rod big end bearings are under dynamic lubrication during working cycle, and in most of the time, the con rod is subjected to compressive stress. The conventional method of performing an EHL analysis on a bearing involves development of complex mathematical equations and simplification of actual physical model. This paper presents a methodology to model and simulate the elastohydrodynamic lubrication and wear study of connecting rod big end bearings of off‐highway application engine using the application of computational fluid dynamics (CFD) and computational structural dynamics (CSD) approaches. The pressure field for a full journal bearing operating under laminar flow regime with various eccentricities was obtained by CFD, and fluid pressure distribution and deformation in the bearing liner due to pressure were evaluated using FSI approach. Relevant parameters of lubrication characteristics were analyzed to optimize the eccentricity value. The maximum bearing load value of 21 kN was noticed at TDC position for the optimum eccentricity. The load distribution indicated critical points in the bearing, and the data obtained from bearing load and sliding velocity of journal were used in Archard's wear relation to determine the wear depth along the bearing width. The simulated wear results were compared with three‐cylinder off‐highway application engine con rod big end bearings, which ran for 1000 hours at full load condition, and satisfactory agreement was observed between experiment and simulation values. [ABSTRACT FROM AUTHOR]

The lubrication performance of adsorbed triblock copolymers polypropylene oxide‐polyethylene oxide‐polypropylene oxide (PPO–PEO–PPO) with phosphate ester films at different temperature on the Si surface was investigated using a pin‐on‐disc tribometer. The results revealed that the molecular architecture of the triblock copolymer and the temperature had a significant influence on the tribological behaviour. The triblock copolymer with a higher weight percentage of PPO exhibited a better lubrication performance both below and above the cloud point. However, when the temperature is above the cloud point, the adsorbed PPO–PEO–PPO film showed worse lubricity than that below the cloud point. The addition of phosphate ester to the triblock copolymer solution resulted in the decrease of the coefficient of friction and the improvement of the anti‐wear property. Moreover, with the added phosphate ester, the tribological performance became insensitive to the temperature. [ABSTRACT FROM AUTHOR]

Nanolubricants, thanks to their ability to reduce friction and wear, are increasingly studied in the transport and automotive sectors. These systems are generally produced with a two‐step procedure by dispersing nanoparticles into base oils. Very recently, one‐step methods have received increasing attention for the production of highly stable nanosuspensions at lower cost. Degradation‐decomposition of the base oil can however occur during the synthesis affecting the final performances. In this work, copper‐based nanolubricants were produced using a new procedure that preserves the base oil from the degradation induced by the synthesis and allows producing highly stable nanolubricant. The produced fluid showed a monodisperse distribution of nanometric particles and a good stability up to at least 60 days from its production. The as‐produced nanolubricants showed notable performance reducing the friction coefficient even up to 32.7% for Cu concentration of 0.01 vol% at 80°C. [ABSTRACT FROM AUTHOR]

In this work, a tribological performance analysis is numerically conducted for a surface‐textured ring‐deformed liner conjunction. In the analysis, three different distribution patterns of surface texture are designed and machined on the surface of ring. To evaluate the frictional properties of the textured rings under mixed lubrication regime, a transient lubrication model considering the oil film thermal effect is developed. Meanwhile, to evaluate the oil film consumption and the transition of lubrication condition in an engine cycle, an oil transport model is built to determine the boundary positions of lubrication zone. Based on the models, the oil consumption, MOFT (minimum oil film thickness), friction force, power loss, and FMEP (friction mean effective pressure) value of the textured ring are studied under different oil supplies. The frictional characteristics of the rings with various distribution patterns of surface texture are also analyzed and compared. The results show that the edge‐textured ring can improve the tribological performance significantly, and the improvement varies with the oil supply. [ABSTRACT FROM AUTHOR]

Internal gears with small tooth number difference are widely used as core component in robotics, medical, and other fields. The clearance between the entire meshing teeth is much smaller compared with other gear transmissions, indicating that the entire tooth profile can significantly affect the mixed elastohydrodynamic lubrication (EHL) state of a certain meshing point. Thereby, available lubrication analysis is limited with the assumption of effective radius at each meshing point. In the present study, the entire tooth profile with gear flank modification is studied to improve lubricating characteristics. A mixed EHL model for predicting the film, pressure, power loss, and subsurface stress is presented with consideration of the entire tooth geometry. We find that the tooth geometry away from the meshing location shows a remarkable influence on the film and pressure distribution as well as power loss of tooth rubbing interface, which is commonly unrecognised in previous study. Optimization of modification parameters is observed under different operating conditions, highlighting the critical role of entire tooth geometry in mixed EHL behaviour for internal gears with small tooth number difference. [ABSTRACT FROM AUTHOR]

The Mn3B7O13Cl nanoparticle (~30 nm) has been prepared by sol‐gel method and characterised by powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The tribological properties of prepared Mn3B7O13Cl nanoparticle and the common nano‐Cu and nano‐Fe nanoparticles as antiwear additives with various concentrations in polyalphaolefin (PAO) base oil have been investigated. PB values of nano‐Mn3B7O13Cl added oil are superior to base oil, nano‐Cu and nano‐Fe added oil with the same content, and it reaches the value of 637 N. The wear scar diameter is 0.52 mm when the concentration is only 0.2 wt.%. And meanwhile, Mn3B7O13Cl nanoparticle as efficient antiwear lubricant and commercial oil was measured in the sliding wear between tantalum strip and 52100 bearing steel ball by MFT‐3000 friction and wear tester at an optimised additive concentration (0.2 wt.%). Coefficient of friction of tantalum strips is reduced by 41.5% compared with that of the commercial oil. Surface morphology studies and X‐ray photoelectron spectroscopy (XPS) analysis have revealed that the prominent tribological behaviour of Mn3B7O13Cl was caused by the formation of ~ 30‐nm tribofilm made of adsorbed boron and tribosintered nano‐Mn3B7O13Cl. Therefore, Mn3B7O13Cl nanoparticle has a potential to develop as friction‐reducing and antiwear lubricant in the sliding wear between tantalum strips and steel ball to avoid the severe wear. [ABSTRACT FROM AUTHOR]

In this paper, the angular contact ball bearings under low‐speed and heavy‐load conditions is studied with a coupled numerical method of mixed elastohydrodynamic lubrication (EHL) and quasi‐dynamic analysis. Compared with the quasi‐dynamic analysis without consideration of the mixed lubrication characteristics, the present coupled method reveals a smaller minimum film thickness and a larger frictional coefficient in ball‐race contact interface, leading to increases in the normal contact load, slide‐to‐roll ratio, and relative sliding velocity. Effects of operation condition (eg, rotational speed) and structural parameter (eg, inner raceway curvature coefficient and initial contact angle) on the contact and lubrication performances are discussed. The results show that a larger inner raceway curvature coefficient results in a smaller average film thickness and film thickness ratio, a larger frictional coefficient, and maximum contact pressure, while the increase in the initial contact angle has an opposite effect on these parameters. [ABSTRACT FROM AUTHOR]

In this paper, to solve the problem that di‐n‐hexadecyldithiophosphate (DDP)‐modified Cu nanoparticles initially used as oil‐based lubricant additive cannot be directly used in water‐based lubricants, we adopt a water‐in‐oil reverse micro‐emulsion method to incorporate hydrophobic Cu nanoparticles into silica spheres for obtaining water‐dispersible Cu@SiO2 nanoparticles. The effects of reaction conditions on the morphology and microstructure of Cu@SiO2 nanoparticles were investigated. Furthermore, the tribological properties of the as‐prepared Cu@SiO2 nanoparticles as a lubricant additive in distilled water were investigated with a UMT‐2MT tribometer. Results indicate that the as‐prepared Cu@SiO2 nanoparticles exhibit good dispersion stability and antioxidant ability in distilled water. Besides, Cu@SiO2 nanoparticles can significantly improve the tribological properties of distilled water, which is attributed to the formation of a protective and lubricious film consisting of Cu, FeS and SiO2 on the rubbed steel surface. [ABSTRACT FROM AUTHOR]

An elastohydrodynamic model of ferrofluid‐lubricated involute spur gears was established, and transient thermal elastohydrodynamic lubrication (EHL) analysis was conducted using multigrid method and multigrid integral method. The transient lubricant film thickness, pressure, and friction coefficient characteristics of the spur gears were compared under different carrier fluid ferrofluids. Ester‐based H01 ferrofluid was selected to further examine the lubricant film elastohydrodynamic characteristics of the involute spur gears under different loads and speeds. The results indicated that the film thickness and the inlet area pressure were the largest when hydrocarbon‐based E02 ferrofluid was used for lubrication and were the smallest when ester‐based ferrofluid H01 was used for lubrication. When ester‐based H01 ferrofluid was used, the film thickness, the inlet area pressure, and the second pressure peak increased with the increase of speed, and the second pressure peak shifted toward the inlet area. The friction coefficient and the maximum temperature gradually decreased with the increase of speed, and the second pressure peak, the friction coefficient, and the maximum temperature gradually increased with the increase of load, while the film thickness gradually decreased. [ABSTRACT FROM AUTHOR]

In this work, a series choline monocarboxylate ionic liquids ([Ch][MA] ILs) were synthesized. The physicochemical properties and lubricating efficiency of the ILs on copper and aluminum discs were systematically investigated. At the same time, their ecotoxicity was explored on aquatic organisms. In comparison with 1‐butyl‐3‐methyl imidazolium tetrafluoroborate (L‐B104), which is a kind of traditional IL, [Ch][MA] ILs exhibited excellent lubricating properties and low toxicities, thus can be considered as environmentally friendly lubricants in tribology. [ABSTRACT FROM AUTHOR]

Many researches were conducted in the past in order to maximise the efficiency of gearboxes, and for many of the sources of power loss, very effective models and tools are already available and can significantly help to optimise the design. Nevertheless, for the load‐independent power losses of gears only in the recent years some progress has been made. Concerning these losses, numerical simulations can help the designers in optimising the internal shape of the casing, thus ensuring the proper lubrication of all the components and reducing the undesired splashing losses. The amount of lubricant plays a fundamental role: A reduction of the lubricant can be critical from the point of view of adequate lubrication and of failures of the system due to wear, scuffing, and pitting but, on the other side, an excessive amount of lubricant leads to additional power dissipation and could even determine an overheating of the system. Another possibility to improve efficiency could be represented by the reduction of the pressure inside the housing: in this paper, the effect of the static pressure on the load‐independent power losses both for complete‐ and dip‐lubrication has been deeply studied. The numerical results, validated by experimental data, show that a reduction up to 15% of the churning losses can be achieved without reducing the amount of lubricant, that is, without increasing the risk of failures related to lubrication. Based on the results obtained, the reduction of the pressure of the housing proves to be a way to improve the efficiency, provided the related engineering issues are also addressed. [ABSTRACT FROM AUTHOR]