Lubrication Science最新文献

The results of a research on the tribological behaviour of lithium grease with the addition of graphene nanoparticles are presented in current work. Using a four-ball tribometer, the wear and friction coefficient of lithium grease and blended grease samples with graphene additions were assessed. The significance of graphene in enhancing the tribological properties of grease materials is evident from experimental results. In the experimental investigation, a considerable decrease in wear and friction co-efficient values was also noted. One weight percent addition of graphene to base grease decreases friction by 23.73% and wear scar width by 19.51%.

This paper firstly reports the size effect of typical micro- and nano- calcium carbonate additives on the friction properties of calcium sulfonate grease. The rheological and tribological performance of calcium sulfonate grease with typical micro- and nano- calcium carbonate additives were investigated at 30 or 80°C by Rheometer and Optimol SRV-V tester. To its surprise, calcium sulfonate grease with 5% calcium carbonate microparticles behave remarkable lubrication performance than calcium sulfonate grease with 5% calcium carbonate nanoparticles under boundary lubrication condition according to the rheological analysis and tribological evaluation. The enhancement in excellence tribological performance can be attributed to the synergistic effect between calcium carbonate microparticles and calcium carbonate in thickener of calcium sulfonate grease. The thin film composed of CaCO₃ and CaO on the worn surface generated by solid particles is conducive to reducing friction and wear.

A numerical method is proposed to evaluate the effect of non-Gaussian roughness on point contact elastohydrodynamic lubrication (EHL). A mixed EHL model of point contact, considering non-Gaussian roughness, is developed. The oil film pressure in the model was controlled by the Reynolds equation of average flow, and the contact pressure of asperity was obtained by the rough surface micro-contact model. The influence of non-Gaussian roughness parameters on contact pressure distribution, film thickness profile and the ratio of asperity pressure to contact load (asperity load ratio) are investigated based on the mixed EHL model. The results show that the asperity pressure increases as root mean square (RMS) roughness increases, skewness and kurtosis. The film thickness also increases with RMS roughness and skewness, but is not sensitive to kurtosis.

Thermodynamics has historically been used to derive characteristic material properties. In this study, fundamental thermodynamics is applied to grease. First-principle formulations of existing material properties—heat capacity and storage modulus—and new properties—thermal strain and stress coefficients, chemical resistance and thermo-chemical decay coefficient—are derived, some of which are experimentally determined. A new group of Maxwell relations is introduced by replacing the classical compression work $��\mathrm{PdV}�$ with the grease shearing work $��\text{Vτdγ}�$. The physical interpretations and implications of these properties on grease behaviour and performance are presented. Experimental measurements of the derived properties are performed in accordance with the theoretical formulations. Six different grease types are studied. Obtained results are shown to conform with anticipated, observed and established grease behaviours. The proposed properties can be used in grease performance and degradation analyses, as well as grease selection for lubrication applications.

This study investigated tribofilm layers formed under boundary lubrication using a polysulfide additive on S45C and SUS304 steel surfaces. In the tribotests, the friction coefficient of the SUS304 disc fluctuated and increased more gradually in comparison to that of the S45C disc. The tribofilm on the S45C disc comprised the outermost and inner layers of FeS₂ (pyrite) and FeS (troilite), respectively. Notably, all the tribofilm layers on the SUS304 disc surface contained pyrite. The tribofilm on the SUS304 disc was weakly crystalline in the outermost layer and thinner than that on the S45C disc. The poor formation of the tribofilm on the SUS304 disc was potentially caused by the unstable friction coefficient and scuffing.

The elastohydrodynamic lubrication (EHL) model of angular contact ball bearings (ACBB) with local defects under spin condition is established. The local defect surface profile is characterised. On this basis, the modified quasi-static model of ACBB with local defects is proposed. Then, the comprehensive stiffness model of ACBB with local defect under EHL is built, and the influence of different factors on the mechanical characteristics of ACBB with local defect is investigated. The results show that with the increase of the local defect size, the equivalent contact stiffness of the defect area decreases, and the contact load in non-defect area increases. Considering EHL, the contact deformation of bearing decreases, the contact load and equivalent comprehensive stiffness increases obviously. The axial contact angle of the defect area largely determines the equivalent comprehensive stiffness of the roller at the defect.

In this paper, a tribo-dynamic model of a helical gear is established. For the lubrication sub-model, a finite line thermal elastohydrodynamic lubrication model of helical gear is adopted. The lateral vibration, axial vibration of gear and torsional vibration of the gear shaft are considered in the dynamic sub-model. Results show that the tribological parameters of helical gear under the tribo-dynamic model deviate significantly from that of the quasi-static model, especially in the engaging-in region of tooth pair. The friction excitation mainly affects the vibration along the off-line-of-action direction of the gears. The influence of operating conditions on the tribological and dynamic properties of a helical gear pair is significant, especially in the case related to the characteristic frequency of gears.

Lubricants are of paramount importance in protecting metallic contact surfaces and reducing friction. The viscosity of lubricating oil can be engineered by introducing long linear polymers, such as poly(lauryl methacrylate) (PLMA). In particular, the formation of adsorption films by using polymers with hydroxy or amino side groups has attracted much attention in recent years. In this study, copolymers with controlled structure were synthesised by SARA ATRP, which can be used in large scale production. A comparison of friction and wear under boundary lubrication was conducted using both statistical and block copolymers with low Ð. Friction test results using a reciprocating sliding machine (SRV) showed that the block copolymers were less likely to desorb from the metal surface than the statistical copolymers. In addition, the wear evaluation after the SRV test showed that the block copolymer had less wear and less wear debris.

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.

The present study evaluates the combined use of micro-textures and ‘wettability gradient’ on the thermohydrodynamic performance of inclined slider bearings. Mass conserving Elrod cavitation model with slip boundary condition has been used to investigate the dimensionless static performance parameters at different convergence ratios and sliding speeds. The most effective location of the wettability gradient and textures has been considered in the present work. It has been observed that with the increase in sliding speed, the load carrying capacity, friction force and volumetric inflow rate of the slip-textured bearings were improved. The improvements were more pronounced at smaller convergence ratios. Moreover, the slip-textured bearings exhibited significant improvement in the average pressure and temperature of the lubricant. However, at higher sliding speeds, a substantial increase in friction force and average lubricant temperature was noticed. The square textured slip bearing exhibited maximum improvements towards various performance parameters of the three considered texture shapes.