The influence of thickener type on grease lubrication was examined by comparing six greases formulated with the same base oil (PAO10) and NLGI grade. Friction curve, traction curve, and film thickness were measured in rolling/sliding point contacts over a broad range of entrainment speeds and temperatures. Under mixed lubrication conditions, clear differences in friction behavior were observed among the greases, particularly at low speeds and higher temperatures. In this regime, several greases showed lower friction coefficients than both the base oil and their corresponding bled oils. With increasing entrainment speed, the friction and traction responses of the greases progressively approached those of the base oil. In addition, temperature markedly affects the frictional behavior of greases compared to the base oil and bled oils. Film thickness measurements further showed that both greases and bled oils produced thicker films than the base oil, with the extent depending on thickener morphology and oil release behavior. The results indicate that thickener-related effects play an important role in grease lubrication and should be considered when assessing performance across different lubrication regimes.

Carbon dots (CDs) have gained more attention as lubricating nanomaterials. When faced with practical applications, the compatibility between CDs and commercial additives needs to be considered. Simultaneously, some traditional organometallic additives need to reduced their dosage due to the increasingly stringent environmental protection regulations. Herein, the liquid-like carbon dots (LCDs) with fewer steps and larger potential yield were obtained. When used as additives with molybdenum dithiocarbomate (MoDTC) or zinc dialkyldithiophosphate (ZDDP) in lithium grease, they work hand in hand to improve the lubricating properties. Notably, ZDDP exhibits better synergistic effects than MoDTC, attributing to the greater grease film forming performance, good dispersibility in grease and tendency to combination with carbon core of LCDs. This study is conducive to promoting the application of fully formulated additives for CDs and reducing the use of organometallic additives.

A limited supply of lubricant can minimize energy dissipation and waste, enabling lean lubrication. However, insufficient lubricant supply can lead to a critical issue known as starved lubrication, emphasizing the need to address this concern under limited lubricant supply (LLS) condition. In this study, a ball-on-disc lubricating film test rig, with a circular contact, was employed. The impact of zinc dialkyl dithiophosphate (ZDDP) interfacial adsorption on the lubrication characteristics under LLS condition was investigated by introducing ZDDP as an anti-wear additive. A dichromatic interference intensity modulation (DIIM) approach was utilized to reveal the evolution of the lubricant film at various lubricant supply stages under LLS. Three distinct lubricant supply stages were identified: the fully flooded stage, the transition stage from fully flooded to starved lubrication, and the starved lubrication stage. The mechanism of ZDDP interfacial adsorption during different lubricant supply stages was evaluated by analyzing variations in oil reservoir morphology, lubricant film thickness, and friction coefficient. The results indicate that, under LLS conditions, changes in the oil reservoir directly influence the transition between lubricant supply stages. The adsorption effect of ZDDP was found to promote lubricant entrainment and improve the lubricant supply in the inlet area during the second and third lubricant supply stages, thereby enhancing the anti-collapse capacity of the lubricant film. Additionally, in the LLS condition, the improved anti-friction effect of ZDDP is attributed to the synergistic impact of enhanced lubricant entrainment and increased shear resistance.

Lubricants are used in modern industrial applications to enhance energy efficiency and reduce material damage by minimizing friction and preventing wear in both sliding and rolling contacts. Zinc dialkyldithiophosphate (ZDDP), the most extensively used anti-wear additive in engine oils, has been the subject of extensive research over the past few decades. Studies have shown that ZDDP undergoes tribochemical reactions to form a robust phosphate glass-based tribofilm on friction surfaces, effectively preventing direct contact between two surfaces. Although significant progress has been achieved toward understanding the drivers of tribofilm growth, tribofilm formation has been considered to follow a stress-promoted thermal activation model. However, an ongoing debate, as well as extended discussion, persists regarding the precise nature of the underlying mechanism involved in the overall tribofilm formation process. To systematically investigate the key factors influencing tribofilm growth, we developed a non-Newtonian point-contact thermal elastohydrodynamic lubrication (EHL) model incorporating the Ghanbarzadeh tribofilm growth model under the assumption of smooth contact surfaces. The pressure is computed using the multigrid method, elastic deformation is determined using the multigrid integration method, and temperature field is analyzed using the sequential column sweeping technique. This model provides a detailed and comprehensive examination of how various influencing factors, such as temperature, pressure, shear stress, and slide-roll ratio, collectively affect and determine the distribution characteristics of the tribofilm thickness. Furthermore, the influencing mechanisms and underlying interactions of these factors are thoroughly explored and interpreted from the perspective of temperature variation. The results demonstrate that temperature is a critical driving factor for tribofilm growth. Even under EHL conditions, as the temperature increases, the increase in the solid surface temperature becomes more pronounced, resulting in a significant increase in the tribofilm thickness, which exhibits an exponential growth trend. Additionally, by comparing three lubricants with different friction properties, we observed that shear stress significantly promotes tribofilm growth. Specifically, lubricants with high EHL friction, characterized by their higher pressure-viscosity coefficients, generate greater shear forces, resulting in thicker tribofilms than those with low EHL friction. This finding validated the stress-promoted thermal activation model. Moreover, both the pressure and the slide-roll ratio significantly influence the thickness of the tribofilm. An increase in either parameter promotes tribofilm formation. Specifically, when the slide-roll ratio is relatively low, the influence of pressure on the thickness of the tribofilm is minimal and can almost be considered negligible. In contrast, as the slide-roll ratio increases to higher levels, the effect of pressure on the tribofilm thickness becomes increasingly significant and much more pronounced. In particular, when the slide-roll ratio is high, a significant increase in pressure causes a marked and considerable increase in the thickness of the tribofilm. This phenomenon can primarily be attributed to the combined and notable effects of the pressure and slide-roll ratio on the temperature of the contact surfaces. These changes in the temperature directly and significantly contribute to the variations observed in the tribofilm thickness. Consequently, the role of pressure in enhancing and promoting the tribofilm growth should not be underestimated and should be carefully considered. Under EHL conditions, the tribofilm formation process is primarily controlled and influenced by key factors such as shear stress, pressure, and temperature within the contact region, which is consistent with the well-established stress-promoted thermal activation model. Furthermore, in the context of EHL, a more accurate and comprehensive representation of the various factors that affect the growth of the tribofilm can be achieved by considering the variations in temperature within the contact region and thereby generating the distribution of the tribofilm.

[Objective]The temperature significantly influences the elastic modulus of polymer gears,which consequently affects their elastohydrodynamic lubrication performance.It is therefore imperative to investigate the impact of temperature on the lubrication characteristics of polymer gears.[Methods]A thermal elastohydrodynamic lubrication(TEHL)model for steel-POM gear pairs was developed,incorporating temperature-dependent variations in the elastic modulus of polyformaldehyde(POM)gears.The multigrid technique and the column scanning method were employed to systematically analyze and discuss the TEHL performance of steel-POM gear pairs under diverse operating temperatures.[Results]The results show that the friction coefficient of the steel-POM gear decreases forward of the pitch point and increases afterward of the pitch point.The maximum temperature of the oil film of the steel-POM gear is near the polymer gear.The inlet viscosity has a great influence on the oil film thickness,and the elastic modulus is the major factor for the oil film pressure.The oil film temperature is greatly determined by the environmental viscosity,and the oil film pressure caused by the elastic modulus has little effect.As the operating temperature increases,the friction coefficient decreases.

The aging of lubricants is a primary factor contributing to rolling bearing failures. The rolling stability test simulated the aging behavior of grease under shear and high-temperature circumstances. An investigation was conducted on how mechanical-thermal aging impacts the chemical and physical structures of polyurea grease, as well as how changes in thickener microstructure affect rheological and tribological properties. The results show that under shear and high temperature, structural changes in urea lead to a transformation of the thickener morphologies from the growth of entangled ribbon fiber to a large-diameter rod structure, with a significant decrease in the degree of entanglement. When a certain proportion of fibrous and rod structures coexist, the grease has good oil separation capacity, the structural stabilities of grease become weak, and the deformation resistance decreases. During this phase, the polyurea grease has the best tribological performance.

ABSTRACT This article presents the preparation of environmentally friendly water‐soluble lubricant additives. Adipic acid (AA), sebacic acid (SA) and dodecanedioic acid (DA) were individually subjected to esterification reactions with polyethylene glycol 1500 (PEG1500) to prepare a class of water‐soluble polyether esters (AAPEE1500, SAPEE1500 and DAPEE1500) (referred to as XAPEE1500s) that exhibit excellent water solubility and do not contain environmentally harmful elements. First, the molecular structure characterisation and functional group analysis of these additives will be conducted using an infrared spectrometer and a nuclear magnetic resonance spectrometer. Subsequently, the frictional properties of the additives in the base liquid (deionised water) will be investigated using an SRV‐V tribometer, Falex pin‐on‐disc tribometer and screw torque tester. The surface morphology of wear scars will be characterised and analysed using scanning electron microscopy (SEM) and a non‐contact 3D profilometer. Finally, the lubrication mechanism of the DAPEE1500 additive will be analysed using X‐ray photoelectron spectroscopy (XPS). The results indicate that the optimal lubrication performance is achieved when the added mass fraction of DAPEE1500 is at 3%. Compared with 0.5 wt% DAPEE1500, the average friction coefficient of 3 wt% DAPEE1500 decreased from 0.285 to 0.122, and the wear volume decreased from 25.52 × 10 −5 μm 3 to 10.96 × 10 −5 μm 3 . The lubrication mechanism of polyether ester is the result of the combined action of its polar ester functional groups and long carboxylic acid chains in the structure. These polar functional groups can form a relatively firm adsorption film on the friction surface, while the long carboxylic acid chains act as a brush‐like isolating layer, thus demonstrating superior anti‐wear and anti‐friction performance.

Three types of alcoholic amine proton-type ionic liquids (PILs) with varying alkyl chain lengths were successfully synthesized and utilized as lubricating additives for water-ethylene glycol (WEG) through a straightforward process. Additionally, Long-chain PIL was combined with Cu nanoparticles (Cu NPs) as a lubrication additive for WEG. It was observed that both the long-chain PIL and Cu NPs were effectively dispersed in WEG. In addition, the tribological properties and lubrication mechanisms of PILs and Cu NPs were investigated and discussed. The experimental results demonstrated that the long-chain PILs showed more significant friction reduction and anti- wear effects as water-based lubricant additives than the short-chain PILs. Meanwhile, the lubrication performance of PIL and Cu NPs mixed lubricant additive was superior to that of pure WEG and WEG containing a single additive, and it showed excellent friction reduction, anti-wear, and extreme pressure properties. The outstanding tribological properties of PILs and Cu NPs can be attributed to the synergistic effect between them, as further

The poor compatibility with nonpolar lubricant still hinders the application of carbon dots (CDs) in lubrication. In addition, research proves that the existence of ionic structure and active groups on CDs are conducive to their lubricity. In order to obtain the ionic structures and good oil compatibility synchronously, a kind of ionic nitrogen-doped CDs (NCDs) was synthesized via the alkylation of nitrogen in NCDs and anion exchange. The new material could exhibit good tribological performance as poly alpha olefins (PAO4) additives with low addition. Moreover, an ionic liquid, [N44HH][DEHP], with the same anion was chosen as a comparison to investigate the role of NCD cations. The surface analyses demonstrate that NCD cations and phosphate ester anions adsorb on the friction interface to play a synergistic lubrication role during the friction process, which could generate a superior carbon-based tribofilm.

The roller end/rib contact of tapered roller bearings significantly affects lubricating condition and power loss. To improve the lubrication performance of the inner ring rib and the large end of the roller in tapered roller bearings used in railway coaches, based on the structural analysis of the inner rib and the large end of the roller and considering spin–slide effects between the rib and the large end of the roller, a thermal elastohydrodynamic lubrication model with a Carreau rheological model was established in a tapered roller bearing. Two kinds of rib structures were provided: the tapered rib and spherical rib. Under different conditions, variations in the friction coefficient versus the ratio of curvature radius of the large end of the roller to that of the rib were compared, and the film thickness and film temperature varied with the rotational speed and the effect of load was compared between the two rib structures. Results showed that spinning motion has little effect on the lubrication at the contact point between the inner ring rib and the large end of the tapered roller. There exists an optimal ratio of the curvature radius between the large end of the roller and the spherical or tapered rib; moreover, the friction coefficient corresponding to this optimal ratio value is the smallest. With the increase in the inner ring speed, both film thickness and temperature increase for the two rib structures. Different from the spherical rib, the difference between the minimum and the central film thickness is almost unchangeable, and the tapered rib shows a slight temperature rise. As the load increases, the difference between the minimum and the central film thickness becomes larger, and the temperature in the contact zone gradually increases for the two ribs. Different from the tapered rib, the lower frictional coefficient and lower minimum film thickness are generated for the spherical rib because of higher film temperature.

Based on the cam-roller pair of an internal combustion engine, a mathematical model of transient thermal elastohydrodynamic lubrication under finite line-contact and the corresponding numerical solver have been established. Under an actual load spectrum and other working parameters from an industry partner, the detailed lubrication performance of the cam-roller pair has been obtained in a cam rotation cycle. Particularly, the influences of the roller convexity, the roller tilting and the skidding between cam and roller on the contact pair lubrication are presented. The lubrication performance of the cam-roller pair depends on the roller convexity markedly, and an optimal roller convexity can effectively reduce the probability of the lubrication film rupture and improve the uniformity of pressure distribution in the contact zone. The roller tilting can worsen the lubrication of the contact zone, and increase the possibility of lubrication failure. If the tilting is taken into consideration at the beginning of the roller convexity design, its negative effect can be effectively alleviated to a certain extent. The skidding results in noticeable increase in temperature and friction coefficient, which can deteriorate the contact zone lubrication. The results provide some theoretical data basis for the lubrication design of cam-roller pairs.

格莱圈由聚四氟乙烯(PTFE)矩形滑环和丁腈橡胶(NBR)O形圈组成.为了研究不同因素对于格莱圈密封材料摩擦磨损性能的影响,利用UMT-3多功能摩擦磨损试验机,通过改变往复频率、粗糙度、润滑状态研究格莱圈材料与45钢配副时的摩擦磨损性能,利用SEM对试块试验前后表面形貌进行观测,并对摩擦磨损机制进行分析.试验结果表明:在干摩擦和滴油润滑条件下PTFE材料相比NBR材料具有更为优异的摩擦磨损性能;NBR材料表面粗糙度过高或过低都会导致摩擦因数升高,表面粗糙度对具有自润滑性能的PTFE材料的摩擦因数影响不大;高往复频率会使NBR材料摩擦因数降低,过高或过低的往复频率都会使PTFE材料摩擦因数降低;NBR材料的磨损形式以磨粒磨损和黏着磨损为主,PTFE材料以黏着磨损和疲劳磨损为主.

为研究水污染对润滑油性能的影响,通过点接触光干涉试验得到充分供油、轻微乏油及严重乏油3种润滑状态下的油膜光干涉图和膜厚形状曲线,研究游离水对接触区油润滑润滑性能的影响.结果 表明:在充分供油条件下,游离水对点接触润滑油膜厚度的影响不大,主要影响中心膜厚;在乏油润滑状态下,游离水对点接触润滑油膜厚度有增益效果;但3种润滑状态下,游离水都会使气穴区边界变得模糊不清,提高了油润滑的弹流润滑性能.

To investigate thermal failure of dynamic oil film in cylindrical roller bearings(CRBs), based on the temperature field of CRBs, non-Newtonian dynamic thermal elastohydrodynamic (TEHL) lubricating performance in cylindrical roller bearings was conducted. A single surface bump was coupled with longitudinal waviness on the roller surface, and a dynamic non-Newtonian finite line contact TEHL model was established considering the boundary temperature of the bearing assembly. Effects of the roller boundary temperature, the surface bump amplitude, the rotational speed, and the viscosity-pressure coefficient on thermal failure were analyzed. Comparison of lubricating performance between Newtonian and non-Newtonian fluid was made as well. Results show that, when the roller boundary temperature increases, the pressure and the oil temperature become larger, and the film thickness and frictional coefficient decrease obviously for roller to outer race contact. As the surface amplitude is large enough, or the rotational speed is low enough, phenomenon of partial contact between the roller and the outer ring may be generated due to high boundary temperature of solids. In addition, when the rotational speed is very low, the temperature of the roller surface reaches the first critical temperature of the adsorbed film, so thermal film failure may occur for roller to outer race lubrication.

To overcome the mandatory requirement of nozzle conductivity in the conventional electrohydrodynamic (EHD) jet printing, this paper proposed a self-induced electric-field-driven jet printing for fabricating ultrafine silver grids. In this method, only a copper foil is mounted on an insulating glass nozzle to serve as an extraction electrode for producing an electric field with substrate by electrostatic induction, which not only saves the fabrication cost of conduction treatment, but also reduces the amount of residual charges to improve printing stability. The simulation and experimental results have confirmed printing ability and optimised the printing parameters. Based on the optimised parameters and high viscosity silver paste, silver grids with line width (300 nm–7 μm) and aspect-ratio (0.39–1) have been printed successfully. Finally, silver grids with line width of 3.5 μm and a pitch of 90 μm were successfully fabricated with excellent performance of transmittance (T = 92%) and sheet resistance (Rs = 1.3429 Ω sq−1).

为了研究格莱圈的往复密封性能,基于ANSYS Workbench建立格莱圈的有限元模型,并对格莱圈进行往复动态分析,分析压缩率、 流体压力和滑环圆角半径对格莱圈最大接触压力和最大Von Mises应力的影响.数值模拟结果表明:在同一压缩率下O形圈与滑环之间的接触压力要大于O形圈与缸体之间的接触压力;随着介质压力的增加,滑环-活塞杆接触对与其余接触对之间的接触压力差值越明显;当滑环空气侧圆角半径小于流体侧圆角半径时,内外冲程所受到的压力差要明显大于空气侧圆角半径大于流体侧圆角半径时的压力差,因此当空气侧圆角半径大于流体侧圆角半径时,可延长格莱圈的使用寿命.

为了研究表面粗糙度及热效应对非牛顿混合润滑的影响,基于平均流量模型,考虑表面粗糙度以及热效应,建立线接触非牛顿混合润滑模型.研究表面粗糙度对膜厚、 膜厚比、 平均摩擦因数、 载荷比以及温度分布的影响,并与等温解进行比较.结果表明:随着表面粗糙度的增大,油膜温度逐渐升高,尤其是出口区与入口区的温升最为显著,且油膜温升越大,载荷比及平均摩擦因数越大,膜厚比越小;与等温解相比,热解的膜厚比及平均摩擦因数小,载荷比大;等温与热条件相比,中心膜厚与最小膜厚随表面粗糙度的变化趋势差异显著,说明热效应对混合润滑的影响不可忽略.

目的 为了提高圆柱滚子轴承的润滑性能,研究滚子与外图表面纹理及硬弹比对圆柱滚子轴承混合润滑的影响.方法 基于平均流量模型、非牛顿效应、热效应和粗糙峰的弹塑性变形,建立了圆柱滚子轴承有限长线接触热混合润滑模型.研究了表面纹理及硬弹比对膜厚、膜厚比、载荷比、平均摩擦系数及最高温度的影响.结果 随着表面纹理参数的增大,油膜厚度逐渐减小,粗糙峰接触压力、平均摩擦系数和载荷比逐渐增,最高温度先减小后增大,最小膜厚先增大后减小.但表面纹理参数小于1/3时,对最小膜厚的影响非常小.表面硬度引起的完全塑性变形、弹塑性和塑性变形、完全弹塑性变形对润滑状态的影响不同.在硬弹比处于0.01～0.03时,粗糙峰同时发生弹塑性和塑性变形,油膜厚度、最小膜厚、载荷比、平均摩擦系数、粗糙峰接触压力及最高温度不随表面硬度而变化.当硬弹比小于0.01时,粗糙峰产生完全塑性变形;当硬弹比大于0.03时,粗糙峰发生完全弹塑性变形.这两种情况的载荷比、平均摩擦系数、粗糙峰接触压力及最高温度均随着表面硬弹比的增大而增大.在不同工况下,表面硬度与表面纹理参数对圆柱滚子轴承润滑状态的影响存在差异.在表面纹理参数小于1/3时,表面硬度的影响占主导地位;在表面纹理参数大于1.0时,表面纹理参数的影响占据主导地位.结论 表面纹理参数等于1.0时,润滑状态最好;硬弹比处于0.01～0.03时,综合润滑性能最好.在不同条件下,表面纹理参数与表面硬度对润滑影响的程度不同.因此,圆柱滚子轴承混合润滑中,存在最佳的表面纹理参数和表面硬弹比.

为研究滚动直线导轨的润滑性能,对LG-45型滚动直线导轨进行了运动分析,建立了导轨副的弹流润滑模型,并对其润滑性能进行了研究,分析了不同接触角、滚珠直径、曲率比、润滑油参数下的油膜厚度,同时讨论了滚珠直径、接触角对导轨副润滑状态的影响.结果 表明,在接触角增大时,油膜厚度减小;在滚珠直径增大时,油膜厚度增大;在曲率比增大时,油膜厚度增大,但增加的趋势减小;在相同工况下,润滑油黏度和黏压系数较大时,膜厚较大.在文中研究工况条件下,滚珠直径和接触角变化时不会改变导轨副的润滑状态.