Lubrication Science最新文献

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.

Nanoparticle incorporation plays an active feature in heat transfer, ultimately enhancing the tribological process under boundary conditions of heat stress. Nanoparticles like zinc oxide (ZnO) and multiwall carbon nanotubes (MWCNT) are well known to significantly affect the cooling and lubrication applications, resulting in improved heat transfer and kinematic viscosity. The present work investigates the tribological performance of ZnO/MWCNTs hybrids as lubricant additive in the paraffinic type of mineral base oil of Group I (SN150) engine oil. The chemical composition of the modified and unmodified oil was examined by an inductively coupled plasma-optical emission spectrometer (ICP-OES), energy dispersive x-ray fluorescence (EDXRF) spectrometer, and Fourier-transform infrared spectroscopy (FTIR). A ring-on-disk tribotester was performed to investigate the tribological behaviour through the linear reciprocating mechanism alloy-steel contacts. The worn steel alloy surfaces morphology and chemical compositions were examined by scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDX), and 3D optical profilometer. Different ZnO/MWCNTs nanomaterial volumetric concentrations were examined in order to determine the most effective performance. According to the tribological results, ZnO/MWCNTs hybrid nanomaterials in the engine oil were found to have significantly higher friction temperature and antiwear capability than the base oil. A volumetric concentration of 3.00 wt% ZnO/MWCNTs nanomaterials to SN150 engine oil imparted excellent wear protection to the steel sample than the pure SN150 base oil. Based on the statistical analysis, the modified oil anti-wear performance was enhanced by reducing the wear loss by 80.5% and friction temperature by 55.8°C compared with the oil base.

The friction and anti-wear behaviours of hexagonal boron nitride (h-BN) nanoparticles as a lithium lubricating grease additive are being investigated under sliding conditions. The grease with 3 wt% 60 nm h-BN particles and the grease with 1 wt% 500 nm h-BN particles lead to 22.34% and 20.18% reductions in the wear scar diameter, respectively, although the friction coefficients slightly decrease. The boric acid H₃BO₃ with layer-crystal structure produces during the friction process, and the synergistic effect of h-BN nanoparticles and H₃BO₃ makes friction reduction and wear-resistant enhancement. Furthermore, the 60 nm h-BN particles filled in the asperity valleys of the friction surface make a rolling effect and establish a protective film, while the 500 nm h-BN particles shield the asperity contact between friction pairs and make a polishing effect as well.

The objective of this paper is to study the parameters that affect the remaining useful life of lubricant (RULL). Fourier-transform infrared spectroscopy (FTIR) of gear oil is used to observe the contamination in the oil. Coefficient of friction (COF) has been found out using pin on disc tribometer using gear oil, and simultaneously, wear debris has been collected. Particles distribution and elemental analysis of wear debris were observed by emission scanning electron microscopy (FESEM) Field with energy dispersive x-ray (EDX) respectively. Oxidation, sulfation, soot and water content in lubricant increase with time and decrease the RULL. ANOVA is applied to find out the most influential parameter for wear debris and found a load on gears is the dominating factor for wear. This method is the potential to monitor the root causes of contamination and change in lubricant properties and may help to detect the other early signs of failure.

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.

This paper presents the design and numerical optimization of oil-lubricated spiral grooved thrust bearing (SGTB) for its application at high speed and axial loading conditions. A numerical model is developed using nonlinear incompressible Reynold's equation and is solved using the finite volume method (FVM) to determine the static characteristics over the bearing surface. Further, the influence of groove parameters such as spiral angle, groove angle, film thickness ratio, number of grooves and speed on the static characteristics of the bearing has been investigated. The result shows that the designed oil-lubricated SGTB can operate at high-speed conditions and withstand high axial load. Further, the characteristic data sets acquired from the numerical analysis are trained using an artificial neural network (ANN), and their performance is evaluated through the computation of the regression coefficient. Then adaptive neuro-fuzzy interface system (ANFIS) surface plot is obtained to determine the optimum bearing parameters.