Lubrication Science最新文献

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.

The study investigated the potential of waste plastic oil (PO) as an alternative to petroleum-based lubricants, specifically mineral oil. The rheological properties, dispersion stability, friction, and wear performance of PO were examined and compared with mineral oil. Results showed that PO demonstrated similar lubrication performance to mineral oil. To enhance the lubrication performance of PO, the study incorporated various concentrations of nano CuO solid lubricant additives, resulting in the formation of CuO nano lubricants. These lubricants showed an improvement in friction and wear by 20% and 44% compared with PO. Furthermore, the CuO solid lubricant additives were functionalized and incorporated in the same concentrations into PO, resulting in the formation of functionalized nano lubricants, which further lowered the friction and wear by 28% and 91% compared with PO. The novelty of the paper is that a simple chemical functionalization process that not only helped in improving its dispersion stability of additives in the PO, but also enhanced the wear performance. The mechanisms behind the enhancement of friction and wear performance were discussed. Based on these findings, it can be concluded that incorporating functionalized nano additives in PO improve friction and wear performance in mechanical components, promoting wider utilisation of PO.

Functionally graded coating (FGC) has played a pivotal role in numerous engineering applications owing to its exceptional properties. This work proposes a novel elastohydrodynamic lubrication (EHL) model with FGC, in which the elastic deformation and stress are computed using influence coefficients (ICs) and discrete convolution-fast Fourier transform (DC-FFT) algorithm. Comparisons are made with homogeneous EHL solutions and finite element analysis (FEA) to validate its accuracy. The study systematically explores how coating elastic modulus, coating thickness and substrate elastic modulus influence contact and lubrication behaviours. The developed model is expected to establish a theoretical framework for FGC material design, enhancing the performance of friction pairs.

In order to investigate the anti-friction and anti-wear performance of different crystal forms nano MoS₂ in paraffin oil. Freeze-drying method combined with hydrothermal was used to prepare different crystal forms nano MoS₂ and their microstructures were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anti-friction and anti-wear performance of MoS₂ nanoparticles as lubricat additives under different working conditions was investigated by the ball-and-disk friction and wear testing machine and the mechanism of friction and wear reduction was investigated. The results showed that the thickness of the floral sheet MoS₂ flakes was about 10 nm and the particle size of the spherical MoS₂ was about 90 nm. When the addition concentration was 3 wt%, the friction coefficient of the floral sheet MoS₂ in paraffin oil was lower at 0.094, which was 29.3% lower than that of the pure paraffin oil, the width of the abrasion marks was 24.2% lower than that of the pure paraffin oil and the wear rate was 71.6% lower than that of the pure paraffin oil; The friction coefficient of the spherical MoS₂ with 2.5 wt% addition was 0.082, which was 38.3% lower than the friction coefficient of pure paraffin oil, 24.1% lower than that of paraffin oil in terms of wear scar width and 81.9% lower than that of paraffin oil in terms of wear rate.

In numerical studies of grease lubrication, thermal effect is often neglected and surface plastic deformation is almost not considered. This paper has developed a deterministic thermal plasto-elastohydrodynamic lubrication (PEHL) model for grease-lubricated rolling bearing. The influence of tangent modulus, rheological index and texture orientation on lubrication characteristics and temperature rise is analysed. The results show that increasing the rheological index of grease and decreasing the wavelength factor are obviously positive for improving lubrication behaviour. Since surface plastic deformation in the EHL state is at nanoscale, film thickness, friction coefficient and temperature rise of solid surfaces decline slightly with the decrease of tangent modulus.

The coefficient of friction of low carbon chromium alloy steel with military grade lubricant was high, resulting in increased heat generation and temperature rise of the lubricant in the aircraft power transmission units such as engine gearbox, accessory gearbox and so on. To address this, the current research proposes the addition of TiO₂ nanoparticles to MIL grade lubricant as an additive to enhance the tribological performance. In this experimental study, TiO₂ nanolubricant was prepared using various surfactants for better suspension of TiO₂ nanoparticles, and properties were evaluated for both base lubricant and nanolubricant. The tribological experiments were conducted using a four ball tester, a shear stability tester and a reichert tester. In a four ball test, TiO₂ nanolubricant resulted in a 27.3% reduction in wear scar diameter by the addition of TiO₂ nanoparticles to the base lubricant. In a shear stability test, TiO₂ nanolubricant showed 80% better shear stability than the base lubricant. In the reichert test, the coefficient of friction was reduced by 13% with the TiO₂ nanolubricant. The experimental findings demonstrated that the TiO₂ nanoparticles, as an additive to a military grade lubricant, have superior tribological properties for aerospace applications.