Lubrication Science最新文献

In this study, we employed high-throughput all-atom molecular dynamics simulations to calculate the adsorption properties of various carbon chain lengths and branching forms of phosphate ester anions on metal surfaces. Two layers of high-throughput concurrent parallel algorithms were applied in the calculations. The results indicate that both chain length and branching forms influence the magnitude of the adsorption free energy. Longer carbon chains result in larger adsorption free energy, while more complex branching forms lead to smaller adsorption free energy. The analysis suggests that chain length and branching complexity have dual effects. As the carbon chain length increases, on the one hand, more adsorption sites between the molecule and the metal substrate are created, thereby increasing the adsorption free energy. On the other hand, more chemical bonds exist between adsorption sites, enhancing the pulling forces between atoms and reducing the adsorption effect. Furthermore, we employed a machine learning approach to establish a quantitative relationship between descriptors of phosphate ester anions and adsorption free energy. This work offers a universal high-throughput computational approach and machine learning prediction strategy for the molecular dynamics calculations of the adsorption properties of organic molecules on metal surfaces.

In recent years, stringent policies on low-sulfur fuel oil (LSFO) usage in the shipping industry have raised concerns regarding the reliability of two-stroke marine engines. This study conducts a longitudinal investigation of the main engine on a wood-pulp carrier fuelled with LSFO, aiming to underlying causes of cylinder wear and develop solutions. Throughout an operation period of roughly 2500 h, drain oil was sampled with the following characteristics evaluated: viscosity, basicity, moisture contents, ferrography and compound containment, as well as the concentration of trace elements, seeking to monitor the wear and lubrication status of a two-stroke marine engine. The comparative analysis of representative lubricant samples revealed that the severity of cylinder wear intensifies with engine operation when using LSFO, transitioning from rubbing wear to fatigue, cutting and sliding wear, with the corrosion-induced wear being prevalent even during the early stage of the engine lifecycle. Meanwhile, intermittent replacement of high alkalinity cylinder oil has been proven an effective solution for improving cleanliness, mitigating cylinder wear and lubricant degradation. Viscosity and basicity with high sensitivity can serve as control parameters to determine the necessity of oil replacement. To prevent the generation of severe corrosive wear, intervals for oil replacement are advised to exceed no more than 500 h.

As an oil-based superlubricity material on steel surfaces, 1,3-diketone fluid is promising for the friction reduction of mechanical devices. However, the unsaturation of its molecular structure would potentially cause the oxidation problem in industrial applications. In this study, the oxidation mechanism of diketone fluid 1-(4-ethyl phenyl) nonane-1,3-dione (EPND) was discovered through the accelerated oxidation experiment in an oven. By doping butylated hydroxytoluene (BHT) anti-oxidation additive at an optimal concentration of 0.5%, both the oxidation onset temperature (OOT) and oxidation induction time (OIT) of EPND could be enhanced to a comparable level of 4121 commercial oil, which is a fully-formulated lubricant with a similar viscosity to EPND. Moreover, the friction test verified that the incorporated BHT additive induced negligible influence on the superlubricity performance of EPND. The result of this study is helpful for improving the weakness of the diketone superlubricity system and promotes a further step in its practical applications.

When the hydrostatic thrust bearing is machining parts, the machined parts are easily disturbed by external factors and deviate from the centre of the workbench so that the hydrostatic thrust bearing is in the state of eccentric load. In order to explore the lubrication characteristics of hydrostatic thrust bearings under eccentric load conditions, the hydrostatic thrust bearing with 12 tilting oil pads is taken as the research object in this paper. Based on the tribology principle and lubrication theory, the flow equation, load capacity equation and oil film thickness equation of double rectangular oil cavity are derived from the working and structural parameters of hydrostatic thrust bearing. The matching relationship between load and oil film thickness is obtained. The effects of rotational speed, load, and offset distance on the oil film pressure field and temperature field are studied. The experimental platform of hydrostatic thrust bearing is built to verify the correctness of the simulation method of the oil film temperature field and pressure field.

Characterisation of eco-friendly biodegradable lubricant is a significant investigation in the replacement of the toxic mineral/synthetic oil that creates a negative impact on health. In this study, the nanoparticle titanium dioxide (TiO₂) was synthesised by the coprecipitate method and dispersed in the palm oil blended with Moringa oleifera seed oil (enriched palm oil-EPO) to prepare a biodegradable lubricant. Structural and compositional analysis of TiO₂ nanoparticles was carried out using scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy analysis (FTIR). The biodegradable lubricant nature of TiO₂ dispersed at different volume fractions in EPO was investigated by varying viscosity and density with temperature (30°C–60°C), and the Brownian motion of the particle in the oil was studied through the diffusion constant, diffusion time and Brownian velocity. The biodegradable lubricant nature of TiO₂ has been analysed using machine learning (ML) techniques that categorise the lubricant nature of the blended oil.

Full-ceramic bearings possess numerous exceptional attributes, such as enhanced rigidity and superior resistance to wear. Nevertheless, full-ceramic bearings consistently encounter elevated temperatures for extended periods of high-speed operation, which easily affect the processing performance of the equipment. Lubrication viscosity has a significant effect on bearing heat generation, so it is meaningful to approach the effect of lubrication viscosity with respect to the dynamics of full-ceramic bearings. Full-ceramic angular contact ball bearings are treated as research objects to analyse their optimal working condition in this article. A coupled fluid–solid simulation model is constructed for analysis of the fluid and solid in the bearing cavity. First, at the conditions of different lubricant viscosity, the oil volume distribution, temperature field distribution in the bearing cavity is analysed. Then, the vibration characteristics of the inner ring is examined by constructing a dynamic model of the inner ring. Meanwhile, temperature and vibration variation of full-ceramic bearings are verified through experiments under different rotational speeds. The results show that the lubricant volume distribution inside the bearing cavity is nonuniformly distributed, which the lubricant is mainly located in the outer ring groove position. Moreover, elevating the lubricant viscosity within a certain range promotes the enhancement of bearing lubrication properties. The maximum error of the bearing temperature between the simulation results and the experiment is 7.592%. Ultimately, the simulation analysis is validated through experiments, and it provides a theoretical foundation for selecting optimal parameters for the oil–air lubrication of full-ceramic bearing.

A thermal elastohydrodynamic lubrication model is combined with a wear model under mixed lubrication to investigate the lubrication performance and wear characteristics of double-circular-arc spiral bevel gears for nutation drive. Moreover, the effects of operating conditions on the characteristic parameters of the film are analysed under the mixed lubrication point-contact conditions. Furthermore, the characteristics of gears in terms of friction coefficient and wear depth are discussed. According to the results, the performance of lubrication and wear during the mutual meshing of the convex tooth surface of the external bevel gear and the concave tooth surface of the inner bevel gear is better than that during the mutual meshing of the other pair of tooth surfaces. The minimum film thickness of the whole meshing process occurs near the inner of the bevel gear due to the joint action of the load and the end edge effect. Moreover, an increase in torque at a certain rotational speed is favourable to the lubrication performance of the meshing process. The wear depth in the double-circular-arc spiral bevel gears' meshing process is heavily influenced by the roughness of the tooth surface.

Harmonic gears are widely used in precise space technology, robotic, medical equipment and other fields, while the magnitude of surface topography changes due to wear is usually comparable to or larger than the original surface roughness and elastic deformation, leading to severe transmission failures. This paper reports a numerical approach to simulate the lubrication status considering wear evolution based on mixed elastohydrodynamic lubrication (EHL) and Archard models, in which the Reynolds equation is solved with finite difference method and surface deformation is calculated by the discrete convolution-fast Fourier transform (DC-FFT) algorithm. The interfacial pressure and film thickness distributions are validated by comparison with available results from literature. The harmonic gear lubrication and wear performances are calculated, including effects of machined surface, velocity, load, wear time and material properties, and the results suggest that avoiding long-term and high-torque working with a large wear coefficient can effectively prevent surface wear failure, which is beneficial for increasing the harmonic gears' lifespan.

A strategy involving the use the rare-earth compound LaF₃ with good lubrication and stability properties as a filler in the preparation of Cu-based composites was proposed to solve the problem of poor wear resistance in Pb-free Cu-Bi materials. The influence and regulatory mechanism of LaF₃ content on the mechanical and tribological properties of these composites were studied. The results indicate that LaF₃ has a good refining effect on Cu alloy grains, and LaF₃ and Bi are distributed in a network along the grain boundaries of the Cu alloy in the material. As the LaF₃ content increases, the mechanical properties and friction coefficient of the composite gradually decrease, and the wear rate first declines and then increases. The wear resistance of Cu-Bi composite containing LaF₃ mainly depends on the mechanical support provided by the matrix. When the LaF₃ content is higher than 6%, the composite strength is extremely low, and the increase in lubricant content at the friction interface does not play a decisive role in the material wear behaviour. The material wear rate increases with the increase in LaF₃ content. Therefore, using 6% LaF₃ is recommended to improve the wear resistance of the material and maintain a balance among its mechanical properties, antifriction and wear resistance.

ZnO nanoparticle surface-modified by diisooctyl phosphate (P204) was prepared by liquid-phase in situ surface modification technique with zinc acetate as the raw material, P204 as the modifier and anhydrous ethanol as the solvent. The morphology and microstructure of the P204-ZnO nanoparticle were characterised by transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectrometry. Its thermal stability was evaluated by thermogravimetric analysis; and its tribological properties as the additive in alkylnaphthalene were evaluated with an SRV-5 friction and wear tester in reciprocal sliding mode. The results show that the as-prepared P204-ZnO nanoparticle has an average particle size of about 4 nm and a P204 content of about 42% (mass fraction); and the surface modifier is grafted onto the surface of ZnO nanoparticle by physical adsorption. With a mass fraction of 0.5% in alkylnaphthalene base oil, P204-ZnO nano-additive can mildly reduce the friction coefficient and drastically reduce the wear rate of the steel–steel sliding pair. This is due to the formation of the composite tribofilm via the adsorption and deposition of the nano-additive on rubbed steel surfaces as well as the tribochemical reactions of the modifier P204 yielding phosphate and of steel substrate yielding iron oxides. The as-formed composite tribofilm with a thickness of about 20 nm, consisting of phosphate and iron oxides as the binder as well as deposited ZnO nanoparticle as the filling phase, is responsible for the excellent friction-reducing and antiwear abilities of P204-ZnO nano-additive for the steel sliding contact.