Lubrication Science最新文献

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.

The accuracy and efficiency of the wheel-rail adhesion model are important to the wheel-rail rolling contact issues. The purpose of this study is to develop a simplified non-Hertzian wheel-rail adhesion model under interfacial contaminations to predict the wheel-rail adhesion coefficient. Firstly, a non-Hertzian full elasto-hydrodynamic lubrication (EHL) model was developed and applied to determine the wheel-rail contact pressure and film thickness under interfacial contaminations. Then, the empirical formula of central film thickness available to non-Hertzian wheel-rail normal contact relating to train speeds, axle loads and material parameters were proposed based on a large number of non-Hertzian full EHL simulation for smooth surface under interfacial contaminations using linear regression. The empirical non-Hertzian central film thickness formula and minimum film thickness formula for wheel-rail contact obtained in this paper show certain differences from the formulas based on Hertzian contact. Using the proposed non-Hertzian central film thickness formula, a simplified non-Hertzian wheel-rail contact adhesion model was developed, and the adhesion coefficient was obtained at different speeds and compared with the field test data. The numerical results showed good agreement with field test data.

As one of the liquid metals, Ga–In–Sn liquid metals can function as an advanced lubricant with high conductivity in a tribology system. It has already revealed advancements in several applications, such as coolants and electromechanical relays. However, Ga–In–Sn liquid metal shows poor lubrication performance on industrial metallic materials, which limits its application in engineering. In this study, the electrochemical boronising strategy was applied to improve the lubrication effect of Ga–In–Sn liquid metal on steel friction pairs. Electrochemical boronising treatment was performed to the base material AISI 52100, and a boronised layer with a thickness of around 64 μm was generated. Tribology tests were carried out on both boronised and original samples with the lubrication of Ga–In–Sn liquid metal (68.5 wt% Ga, 21.5 wt% In and 10 wt% Sn). Results show that the wear resistance of the tribo-system reveals great improvement: The coefficient of friction decreases by 59% and the wear rate drops 85% compared to the steel/steel friction pair. EDS and XPS results show that a tribofilm consisted of Fe/Ga was in situ–generated on the wear scar of the boronised sample, which results in the synergy effect between the boronised layer and the Ga–In–Sn liquid metal. Therefore, we provided a robust strategy to enhance the lubrication performance of Ga–In–Sn liquid metal on a steel friction pair by using electrochemical boronising treatment, which could broaden the application field of Ga–In–Sn liquid metals.

The scuffing load capacity of gear is closely related to the meshing temperature rise of tooth surface. The key to predict the temperature rise is to establish an accurate meshing temperature rise model. In the paper, a tribo-dynamic model of helical gear is established through coupling of tooth surface lubrication parameters, and the influence of temperature rise on ambient temperature during meshing process is considered. Then, the effects of oil supply temperature, input speed and torque on tooth surface temperature rise, film thickness, friction excitation and gear dynamic characteristics are discussed. The results show that the temperature rise of the gear is higher during the engaging-in and engaging-out regions. Meanwhile, there is local high temperature at the end of the contact line due to the end effect. The vibration of gear along the off-line-of-action direction is mainly determined by friction excitation. With the increase of oil supply temperature, input speed and torque, the risk of scuffing failure increases and the influence of oil supply temperature and input load is more significant. The conclusions of this paper may provide some valuable suggestions for the anti-gluing failure design of gear in engineering.

This study investigates the impact of oil additives on the performance of hydrodynamic journal bearings using hazelnut oil. Various additives, including titanium dioxide, hexagonal boron nitride and graphite, are mixed with hazelnut oil in specific concentrations. Experimental tests are conducted in boundary and mixed lubrication regimes using a specialised rig to simulate bearing operating conditions. The friction performance of these oil-additive combinations is evaluated in terms of bearing load, rotating speed and oil temperature. The findings contribute to understanding hazelnut oil as a potential lubricant and optimising its formulation for specific applications, promoting environmentally friendly lubricants and sustainability.

In order to investigate the impact of micro-textured surfaces with varying surface density on coating properties, the bionic leaf vein micro-texture with different surface densities were prepared on the substrate surface by laser processing. Bi₂S₃ soft coatings were deposited on the textured surfaces by electrohydrodynamic atomization. The influence of textured surface density on the adhesion and tribological properties of the coatings was analysed and discussed by scratch tests and friction wear tests. The results showed a significant increase in the friction coefficient as the surface density increased. However, after reaching a certain point, the friction coefficient tended to decrease. The coatings deposited on the lower surface density (13.9%, 14.5%) have better tribological performance compared with the higher surface density (35.6%, 36.2%). Meanwhile, the adhesion of coatings on the textured substrate enhanced compared with coatings deposited on the polished substrate. A reasonable textured surface density can effectively improve the adhesion and tribological properties of the coating.

Considering the rapid liquid transport characteristics of bionic dragonfly wings, an experimental investigation into the stability and drag reduction properties of an air film on various textured surfaces is being conducted. The study examines the impact of different wetting gradient textures on the stability and drag reduction properties of air film. Experimental results demonstrate an enhanced fluid transport efficiency, resulting in a maximum drag reduction of 9.1%, attributed to the size effect of the multi-scale structure of bionic dragonfly wings. Surfaces featuring wetting gradients exhibit increased stability of the air film within the texture and the ability to trap air bubbles. Based on a near-wall flow two-phase flow theory model, the simulation considers the morphological changes of the air film at structured interfaces and their influence on near-wall flow characteristics. The results indicate that the drag reduction effect arise from the slippage effect between the internal vortex in the air film inside the texture and the flow field near the wall surface. The synergistic effect of near-wall flow fields among multiple texture layers is evident. This interplay across different regions contributes to the sustained drag reduction within the near wall area.

Regarding its wide range of applications in different industries, such as oil and gas, and for manufacturing equipment used to control pollution and recycle industrial wastes, Inconel 686 turning process is highly important. The alloy is highly resistant to high temperatures and corrosion, and thus it can preserve its properties at high temperatures. Due to its low heat transfer coefficient and work hardening during operation, Inconel 686 is considered a difficult-to-cut material, and hence, turning Inconel 686 is challenged with major limitations regarding input parameter level and cutting fluid and issues such as reduced surface quality. The input parameter level and cutting fluid limitations might severely harm the environment and humans, decrease the machining efficiency and keep cleaner production goals out of reach. Novel cooling methods such as cryo-MQL can contribute to achieving cleaner production goals. Cooling methods improve the machining performance and prohibit any damage to the surface integrity. In this study, cryo-MQL, along with carbide-coated tools and biodegradable vegetable oil, was adopted. The efficiency and success rate of cryo-MQL were evaluated by comparing the results with those of MQL and wet methods. A wide range of output parameters, such as residual stresses, cutting zone temperature, cutting forces, tool wear, surface smoothness, surface defects and micro-hardness, were assessed by changing the cutting speed and feed rate. The results indicated that cryo-MQL could reduce the cutting forces, tool wear rate, cutting zone temperature and residual stresses while improving the surface quality. Moreover, environmental concerns were completely dealt with. Due to the increased possibility of higher input parameter levels, the time and cost of the cutting process were significantly reduced.

The high tensile strength and high resistance of nickel-based superalloy 686 against high temperatures and corrosion rates have made it a widely used in important applications such as the aerospace industry, high pollution- and corrosion-resistance equipment manufacturing and petrochemical industry. Therefore, the machining of this advanced alloy with its unique properties is extremely important and can be challenging. Significant increase in input parameters levels, reduction of machining costs, improvement of surface and subsurface properties and clean production are among the issues that should be considered in dealing with Inconel 686 turning operations. Simultaneous application of advanced tools such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) and optimised minimum quantity lubrication (MQL) method and evaluating the results obtained with a wide range of output parameters related to machining process performance and tribological properties can be proposed as an innovation and a solution to this problem in this article. This study analyses several output parameters with different speeds and feeds to evaluate the effect of cutting insert type on machining process performance and tribological properties. The output parameters include tool wear, residual stress, cutting zone temperature, surface smoothness, machining forces and workpiece surface defects. The results indicated that using the optimised MQL method reduces the size of lubricant droplets and increases the surface covered by cooling. With these changes, the performance of the machining process and the parameters related to the surface integrity increase significantly. Among the parameters associated with the performance of the machining process, the PCD tool reduces the cutting zone temperature by 23%, the tool wear by 19% and the machining forces by 18% compared to the PCBN tool. In the parameters related to surface integrity, this method reduces the residual stress by 19% and the surface roughness by 9% compared to the PCBN tool. From the production index perspective, the PCD tool can significantly increase the cutting speed and feed rate, reducing production time and costs.

The prediction of churning power loss has been a difficult problem in the analysis of spur gears. Thus, an analytical prediction model based on the redefinition of churning power loss and energy transformation is proposed to estimate the churning power of spur gears. Churning power loss is defined as the combination of the power loss due to the drag on the end face, the power loss due to the tangential flow, the power loss due to the acceleration of lubricants in the tooth space, and the power loss due to the centrifugal force. Several comparisons of prediction and experimental results are made and good agreement of those is obtained. Finally, the components of churning power loss under different gears and work conditions are analyzed, and the influences of each part on churning power loss are obtained.