Lubrication Science最新文献

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.

Porous materials are widely used in friction pairs. The transient squeezing flow of the lubricant significantly affects the lubrication quality. The study found that the lubricant penetrates into the porous matrix in the contact area and exudes upward to the entrance of the contact area. The maximum stress occurs at the subsurface of the contact zone, and the maximum pressure occurs at the contact centre. In the early loading stage, the lubricant exudates, resulting in a higher liquid-phase load. With the prolongation of the time, the average stress decreases and then increases gradually, whilst the average pressure has the opposite change. In the late loading stage, the load is completely borne by the solid phase. Increasing the load will increases the seepage velocity of the lubricant, which enhance the pumping effect of the friction interface. The findings can help for better understanding of the self-lubrication mechanism of the porous materials.

The tribological behaviour of YG8-cemented carbide/Ti6Al4V (YG8/TC4) contacts under aqueous lubrication was investigated in this work. Three types of nano-additives including poly (N-isopropylacrylamide) (PNIPAM), graphene quantum dots (GQDs), and GQDs@PNIPAM microgels were prepared for use as water lubricant additives. Tribological tests were conducted at different concentrations of nano-additives using a ball-on-disk reciprocating tribometer. The experimental results show that GQDs@PNIPAM has the optimum lubricating performance, the average friction coefficient decreases by 28.7% and the average cutting wear volume of the TC4 disk increases by 29.5% when the concentration is 1.5 wt.%. This provides a new strategy for the cutting of titanium alloy materials, which not only reduces the friction coefficient, but also increases the cutting wear volume of the TC4 disk, thereby improving the machining efficiency.