Lubrication Science最新文献

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.

In order to ensure the reliability of drilling tractor in the downhole operation, three high-temperature and high-pressure sealing mechanisms are designed in this paper to balance the pressure difference between the inside and outside of the drilling tractor, namely the triangular, the U-shaped and the right-angle combined sealing structure. In this paper, three models of combined sealing structures are established, the contact stress of different contact surfaces of the three combined sealing structures is analysed by simulation method, and their sealing performance is studied and compared. By comprehensively comparing the effects of pre-compression ratio, working medium pressure and reciprocating motion on the sealing effect of the three combined sealing structures, the optimal combined sealing structure of the drilling tractor is selected as the U-shaped combined sealing structure. The research results of this paper can provide reference and theoretical basis for the design and selection of the combined sealing structure.

The lubricating greases employed in this study were formulated with polyalphaolefin (PAO) 100 as the base oil and 12-lithium hydroxystearate as the thickener. The sol–gel method was used to produce the LaF₃ nanoadditives. The oleic acid-treated LaF₃ (i.e., OA-LaF₃) and carboxylic acid-treated MWCNTs (i.e., COOH-MWCNTs) were blended in the formulated grease samples and used as nanoadditives. The detailed microstructural and chemical properties of chemically treated nanoadditives were investigated using HR-TEM, XRD, FTIR and XPS analyses. Using a four-ball tester, the effect of different concentrations of nanoadditives on the tribo-performance of greases was investigated. Tribo-test results revealed the role of nanoadditives in PAO-based grease lubrication performance. COOH-MWCNTs and OA-LaF₃ nanoadditives outperformed PAO grease in terms of physicochemical and tribo-performance for steel-steel tribo-pair. The improved tribo-performance is attributed to the formation of tribo-film on the contact interfaces via nanoadditives. The development of tribo-film was confirmed by XPS analysis of worn surfaces.

Currently, substantial adhesion wear frequently occurs in Zr alloy cold rolling, which not only affects the quality of product's surface, but shortens the mould's service life. In this paper, water-based lubricant was prepared by using ZnO as additive and hydroxyethyl cellulose (HEC) as dispersant. The tribological test results showed the friction coefficient decreased by a maximum of 84.6%, and the friction surface was smooth and flat, with essentially no wear. By analysing the friction area, it was found after ZnO entered the friction interface, HEC carried a hydrated molecular layer to form a stable lubrication film at the interface. This film worked with nanoparticles to reduce friction and wear, and is expected to prolong the service life of rolling dies.

The marine stern bearing provides supporting force by lubricating film to minimise the contact friction with the propeller shaft. A model considers local wear and asperity contact is proposed to investigate the mixed lubrication of bearing with misalignment. The finite difference method and over-relaxation iteration method are employed to solve the average Reynolds equation. The lubrication behaviour includes hydrodynamic pressure, film thickness, contact force and friction coefficient were calculated. The influence of sliding speed, local wear, contact roughness, misalignment angle, elastic deformation and eccentricity ratio is discussed in detail. The critical speed from mixed lubrication to fluid lubrication is obtained by employing the Stribeck curve. Moreover, the dimensionless average hydrodynamic pressure, film thickness and the peak value of contact force are compared.