Lubricants, Volume 12, Issue 3 (March 2024) – 39 articles

The in-pipe robot is the most commonly used technique in offshore pipelines. The use of rubber sealing discs is important for in-pipe robots to ensure that the robots are moved by fluid pressures inside offshore pipelines. This paper focuses on the measuring and modeling of the wax–oil gel-breaking process at the soft frictional area between sealing discs and the pipe wall. In this study, a detailed characterization of the gel-scraping process and in situ probing portable microscopy are performed. Two contributions are made in this study. First, a direct observation of wax–oil deposition breaking is employed to detect the minute changes at the in-pipe robot. Second, we find that a simple function is possible to describe the relationship between the wax contents and dewaxing efficiency, in which the debris material removal ratio (DRR) is discussed. Thus, the gel deposition-breaking phenomena are quite different under the influence of rubber sealing discs. This result is further confirmed by the real contact ratio measurements. It is important to research the sealing disc further and apply it more in the petroleum industry, especially in in-pipe robots for deepwater pipeline systems. Full article

The literature on the subject and the results of numerous research experiments indicate that single replacement cycles do not reflect the actual state of oil quality in the context of its degradation. Monitoring the operational quality of the oil in several successive stages allows for a more accurate diagnosis of the optimal oil change time. Therefore, it was decided to investigate the relationship between two consecutive periods of changing the operating oil in an engine. Comparative tests of seven buses included in the fleet were carried out. An important division criterion was taken into account—the operation of city and intercity buses. The HDXRF instrumental chemical analysis method was used to determine changes in the content of abrasive metals, and additives in engine oils. Additionally, the oxidation, nitration, sulfonation, and soot content were assessed using infrared spectroscopy (FTIR) based on the ASTM E2414-10 standard and kinematic viscosity at 40 °C and 100 °C using a Stabinger viscometer according to ASTM D7042. The course of these changes was analyzed in terms of their dynamics. The comparative study aimed to identify trends and sources of differences between the tested oils, as well as to demonstrate the number of exceedances of limit values for the selected parameters. Full article

The acoustic emission (AE) technique is an effective method for monitoring grinding wheels, and numerous studies have been published on applying an AE to monitor grinding wheels. However, there are few studies on the effect of the location of the AE sensor in stably acquiring the AE signals generated during deterioration in cylindrical grinding wheels. In this study, we propose a stable method for detecting the deterioration of a cubic boron nitride (cBN) grinding wheel during cylindrical grinding using AE. We compared the AE signals acquired during grinding from an AE sensor located on the hydrostatic bearing, which supports the grinding wheel shaft, with those from the tailstock spindle. Although positioning the AE sensor on the hydrostatic bearing was found to reduce the AE signal intensity, the AE signal variations were smaller at the same grinding position, and the effect of the grinding position was less than that for the tailstock spindle. Moreover, positioning an AE sensor on the hydrostatic bearing is considered to provide the characteristics of AE signals specifically focused on the changes in cBN on the grinding wheel surface allowing the surface roughness of the workpiece to be estimated during grinding. Full article

Metal machining production faces a myriad of demands encompassing ecology, automation, product control, and cost reduction. Within this framework, an exploration into employing a direct inspection of the machined area within the work zone of a given machine through a confocal chromatic sensor was undertaken. In the turning process, parameters including cutting speed (A), feed (B), depth of cut (C), workpiece length from clamping (D), and cutting edge radius (E) were designated as input variables. Roundness deviation (Rd) and tool face wear (KM) parameters were identified as output factors for assessing process performance. The experimental phase adhered to the Taguchi Orthogonal Array L27. Confirmatory tests revealed that optimizing process parameters according to the Taguchi method could enhance the turning performance of C45 steel. ANOVA results underscored the significant impact of cutting speed (A), feed (B), depth of cut (C), and workpiece length from clamping (D) on turning performance concerning Rd and KM. Furthermore, initial regression models were formulated to forecast roundness variation and tool face wear. The proposed parameters were found to not only influence the machined surface but also affect confocal sensor measurements. Consequently, we advocate for the adoption of these optimal cutting conditions in product production to bolster turning performance when machining C45 steel. Full article

This paper presents a theoretical model for calculating the carrying capacity of spherical hydrostatic bearings, including the deduction and solution of differential equations for fluid flow in the oil seal and the generation of bearing characteristic parameters. An example is used to verify the accuracy of the proposed calculation model. Additionally, the influence of dynamic pressure on the bearing capacity is investigated under various speed conditions. The results demonstrate that as the minimum width of the oil gap decreases, the maximum dynamic pressure increases non-linearly. Furthermore, the maximum dynamic pressure increases with higher rotational speeds, particularly when the width is smaller. Full article

While titanium nitride (TiN) coatings are well known for their biocompatibility and excellent mechanical properties, their wear particle and debris release in orthopedic implants remains a matter of active investigation. This study addresses the efficacy of TiN coatings on CoCrMo and Ti6Al4V alloys to enhance wear resistance and reduce ion release from prosthetic implants. Three different coating variants were utilized: one variant deposited using arc evaporation (Arc) followed by post-treatment, and two variants deposited using high-power impulse magnetron sputtering (HiPIMS) with or without post-treatment. The coatings’ performance was assessed through standard wear testing against ultra-high-molecular-weight polyethylene (UHMWPE) in bovine serum lubricant, and in the presence of abrasive PMMA bone cement particles in the lubricant. The results indicated that Arc and HiPIMS with post-treatment significantly reduced wear and eliminated detectable metal ion release, suggesting that these coatings could extend implant longevity and minimize adverse biological responses. Further long-term simulator and in vivo studies are recommended to validate these promising findings. Full article

In recent years, the trend towards larger wind turbines and higher power densities has led to increasing demands on planet gear bearings. The use of sliding bearings instead of rolling bearings in planetary bearings makes it possible to increase the power density with lower component costs and higher reliability. Therefore, the use of planet gear sliding bearings in wind turbine gearboxes has become more common. However, the flexible structure and complex load conditions from the helical tooth meshes lead to highly complex elastic structure deformation that modifies the lubricant film thickness and pressure distribution and, thus, has to be considered in the calculation of the bearing’s load-carrying capacity. This paper introduces a highly time-efficient calculation procedure that is validated with pressure measurement data from a three-stage planetary gearbox for a multi-megawatt wind energy plant. The investigations focus on three main objectives: (i) analyses of experimental and predicted results for different load cases, (ii) validation of the results of planet gear sliding bearing code, and (iii) discussion on mandatory modeling depths for the different planet stages. Results indicate the necessity of further research in this field of applications, particularly for the third-stage bearings. Full article

Textile polymer composite is made of structured fibre matrix using textile technologies in fabrication, and gains benefits from strong mechanical properties with extra light weight. However, erosion behaviours and associated wear mechanisms of the composites may be influenced by the fibre structures due to heterogeneous composition and complex architectural topologies. Understanding the erosive mechanisms of the structured composites can be important, not only for preventing surface damage and loss of mechanical strength but also for improving design and fabrication of the composites. This paper presents an experimental study of erosive wear under sand blasting on 3D woven carbon-fibre-reinforced textile composites with epoxy. The architectural topology methods of the composites include non-crimped bidirectional, tufted bidirectional, 3D layer-to-layer and 3D orthogonal textile methods. The erosion tests were conducted on four impact angles (20°, 30°, 45° and 90°) under one impact velocity at 40 m/s. The study results show that the erosive mechanism of the textile composites is different from that of the neat substrate material. The observations from this study also reveal the different erosive behaviours between the composites with different fibre structures. It concludes that architectural structures can influence the erosion of a textile composite but will not result in significant differences in the wear resistance of the composites (<20%). Full article

Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation. Full article

Efficient machinery operation relies on the performance of high-quality lubricants. Currently, mineral oils of different grades are widely employed for lubricating machine components, but their environmental impact is a concern. Biolubricants are potential alternatives to mineral oils due to environmental factors. The present study focuses on assessing the rheological characteristics of SiO₂ nanoparticle (NP)-enhanced ecofriendly biolubricants for near zero and high-temperature conditions. Pure neem oil, pure castor oil and a 50:50 blend of both oils were considered as the base oils. Nanobiolubricants with enhanced dispersion stability were prepared for varied concentrations of NPs using an ultrasonification method. Viscosity analysis was conducted using an MCR-92 rheometer, employing the Herschel Bulkley model to precisely characterize the viscosity behavior of bio-oils. Due to the fluid–solid interaction between SiO₂ NPs and bio-oils, a crossover trend was observed in the flow curves generated for different base oils enriched with SiO₂ NPs. For neem oil, a significant increase in viscosity was noted for 0.2 wt% of NPs. Using the multilayer perceptron (MLP) algorithm, an artificial neural network (ANN) model was developed to accurately predict the viscosity variations in nanobiolubricants. The accuracy of the predicted values was affirmed through experimental investigations at the considered nanoSiO₂ weight concentrations. Full article

Tribofilms, resulting from tribochemical reactions involving lubricants, additives, and metal surfaces, are pivotal in reducing friction, preventing adhesion, and minimizing wear. This study investigates the tribological characteristics of textured surfaces in boundary lubrication, emphasizing the impact of surface texturing on tribofilm formation. Untextured surfaces manifest high friction coefficients and low wear owing to the development of thick tribofilms. However, debris accumulation impedes further tribochemical reactions, necessitating more energy for sliding and resulting in higher friction coefficients. Additionally, molybdenum dialkyl dithiocarbamate-derived MoS₂ oxidation diminishes the expected lubrication effect. Textured surfaces exhibit lower friction coefficients and higher wear because the structure aids debris removal, promoting the formation of thinner tribofilms. Despite increased wear from solid-to-solid contact, textured surfaces facilitate an early fluid lubrication transition and enhance cavitation capacity, leading to reduced friction coefficients. We also consider the impact of sliding direction angles on friction coefficients, revealing that lower angles parallel to the grooves heighten friction, whereas higher angles enhance cavitation capacity. Unexpectedly, a 90° sliding direction angle increases the friction coefficients, attributed to MoS₂ distribution in the tribofilms. These results provide crucial insights for optimizing lubrication strategies and enhancing wear resistance in boundary lubrication scenarios. Full article

Different carbon-based nanomaterials (fullerenes, graphene, SWCNTs, and SWCNT-COOH) were tested as additives in a base mineral oil, SN150; rapeseed oil (RSO); and a 50/50 by volume blend of the two using an HFRR (high-frequency reciprocating rig) tester for coefficient of friction (COF) and wear scar diameter (WSD) determinations and a four-ball tester for welding point determinations. The concentrations considered for the HFRR tests were 0.1, 0.5, 1, and 2 wt.%, while the concentration considered for the welding point tests was 0.5 wt.%. The results of the welding point tests showed that the addition of different nanoparticles made it so that welding occurred at much lower pressures compared to the pure oils. This is due to the hardness of the nanoparticles, which increases the local temperature and pressure at the contact points between them and the surfaces, causing welding to occur much sooner. The results of the HFRR tests showed a possible synergistic effect between the fullerenes and SWCNT-COOH and the oil blend, which may be attributed to possible interactions that occurred at a molecular level between the nanoparticles and the different molecules of the oil blend. Full article

Carbon quantum dots (CQDs) have already demonstrated their utility as lubricant additives, and non-contact temperature sensing based on CQDs offers considerable potential for condition monitoring in mechanical, electrical, and other fields, as well as lubrication-temperature multifunctional applications in lubricants. In this paper, we have successfully synthesized and designed high-brightness carbon quantum dots/polyvinyl alcohol (PVA) temperature sensor thin film and dispersions of CQDs in a liquid paraffin lubrication system. Based on fluorescence intensity and the fluorescence intensity ratio, the carbon quantum dot/PVA film exhibited exponential temperature-dependent properties with a wide applicability range, a high goodness of fit (R² > 0.99), and high relative thermal sensitivity (relative sensitivities of 1.74% K⁻¹ and 1.39% K⁻¹ for fluorescence intensity and fluorescence intensity ratio, respectively). In addition, based on the fluorescence intensity, the CQDs exhibited a wide temperature range (20–90 °C), a high goodness of fit (R² > 0.99), and higher sensitivity (2.84% K⁻¹) in a liquid paraffin lubrication system, which reflects the temperature responsive properties of carbon quantum dots as additives in lubrication systems. These findings provide convenient and effective possibilities for the sensing and monitoring of carbon quantum dots and their multifunctional applications under lubrication systems. Full article

The aim of this research is studying the tribological performance of MoO₃, MoS₂, WS₂ and WC nanoparticles as additives of PAO4. Pure sliding tribological tests were performed at 120 °C, finding outstanding friction and wear reductions in comparison with the PAO4, with maximum friction reductions of 64% for the 0.1 wt% MoS₂ nanolubricant and greatest wear decreases for 0.1 wt% MoS₂ nanolubricant: a width reduction of 62% and a worn area decrease of 97%. Raman mapping and a roughness evaluation of the worn pins confirmed the tribofilm formation and mending as tribological mechanisms. Rolling–sliding tests were conducted with best nanolubricants performance in pure sliding, observing excellent antifriction capabilities of MoS₂ nanoparticles at low speeds, indicating that the use of nanoparticles is vital in boundary lubrication. Full article

Recently, high internal surfaces for titanium alloy pipes have been required due to the increment of various applications such as aerospace components. In this work, vertical magnetorheological polishing (VMRP) is carried out to achieve high polishing performance on the internal surface of the titanium alloy pipe. A series of comparative experiments were conducted to investigate the polishing mechanism of magnetorheological polishing (MRP) fluid and enhance the polishing performance. It is shown from the experimental results that the VMRP method under the opposite polarity arrangement improves the surface roughness from 47.85% to 83.34% by reducing unwanted vibration and noise during operation. This provides nanoscale surface polishing quality, while such a precision cannot be achieved from the previous horizontal MR polishing apparatus method. It is found that under a 2700 cycle polishing time, a polishing process combining a rough and fine polishing approach with a combination of different particle diameters results in an axial surface roughness of 0.05 μm and circumferential surface roughness of 0.038 μm, respectively. It is also identified that the axial surface roughness of 0.04 μm–0.041 μm is achieved through the combination of high- and low-speed polishing process after 1602 cycles. Full article

The solution of equilibrium positions is a critical component in the calculation of the dynamic characteristic coefficients of aerostatic bearings. The movement of the rotor in one direction leads to bidirectional variations in the air film force, resulting in low efficiency when using conventional calculation methods. It can even lead to iterative divergence if the initial value is improperly selected. This study concentrates on the orifice throttling aerostatic bearings and proposes a novel method called the bivariate interpolation method (BIM) to calculate the equilibrium position. The equilibrium equation for the rotor under the combined influence of air film forces, gravity, and external loads is established. A calculation program based on the finite difference method is developed to determine the equilibrium position. The process of solving the equilibrium position and the convergence is compared with the secant method and the search method. Furthermore, the variation trend of the equilibrium position and stiffness when the external loads changes are studied based on the BIM. Finally, the correctness of the BIM to solve the equilibrium position is proved by comparing it with the experiment results. The calculation results indicate that the BIM successfully resolves the problem of initial value selection and exhibits superior computational efficiency and accuracy. The equilibrium position initially moves away from the direction of the external load as the load increases, and then this gradually approaches the load direction. The main stiffness increases with increases in the external load, while the variation in cross stiffness depends on the direction of the external load. Full article

The traction behavior in cryogenic solid-lubricated ball bearings (CSLBBs) of liquid rocket engines (LREs) has a significant effect on the dynamic response of the bearing–rotor system. To reveal the fault mechanism of CSLBBs, a tribo-dynamic model is proposed in this paper that considers the solid-lubricated traction, six-DOF motion of the ball and contact collisions between the ball and the cage. The modified traction model uses fan-shaped and arched sections to discretize the contact area to eliminate the meshing error. The newly developed fault model, called ‘geometrical-frictional defects’, can more realistically represent solid-lubrication coating defects. The results show that the frictional excitation can significantly increase bearing vibration by increasing the traction force on the raceway. The change in the amplitude of the bearing vibration and its derivative can be used as a reference to determine the depth of defects. The width of the defect can be diagnosed by monitoring the double-pulse time interval and spectrum of the bearing vibration signal. This research may provide some theoretical guidance for the design and condition monitoring of CSLBBs. Full article

It is known that contact of rough surfaces occurs over an area much smaller than the nominal contact area, and at asperity scale, increased hardness results in experimentally observed asperity “persistence”, namely that it is hard to flatten asperities. Here, we consider Persson’s elasto-plastic solution for rough contact together with an hardness equation proposed by Swadener, George and Pharr for spherical indentation, including size effects depending on sphere radius, in particular to define a new plasticity index that defines the tendency to plastic deformation. While the classical plasticity index shows that at sufficiently small scales, there will be plastic deformations unless surfaces are extremely smooth, and with size effects, the small roughness scales the content of spectrum matter in defining the real state of asperities. In particular, what may appear as plastic at a bulk scale returns to an elastic behaviour at a small scale, as suggested by the “asperity persistence” experimental observation. Some illustrative examples are shown, but clearly, our index and elasto-plastic solution are mainly qualitative, as a realistic investigation is much more complex and still computationally too demanding. Full article

The driving and resistance torques of some rotating machinery for industrial applications are nonstationary and affect system dynamics. Under such operating conditions, coupling between torsional and lateral vibrations may become significant for drive lines supported by hydrodynamic bearings in particular design configurations. Indeed, the occurrence of fluid–structure interactions causes a reduction in the stability threshold of the journal bearings. A hypothesis based on Hopf bifurcation theory (HBT), which justifies how the coupling phenomenon develops, is validated by means of overall experimental observations and a suitable numerical model. When the pulsating driving torque induces significant angular speed oscillation, the rotor-bearing system lateral operating response becomes more complex, and bearing instability onset is detected. Such observation proves the influence of bearings in converting torsional oscillations to lateral vibrations. Particularly, during run-up and run-down tests, localized hysteresis is observed in trends of fundamental order contents. The numerical model of the hydrodynamic bearings solves the Reynolds equation in unsteady conditions to quantify the lateral vibrations amplitude in the presence of both angular speed oscillation and dynamic perturbation. The proposed approach proves the onset of torsional–lateral vibration coupling due to hydrodynamic bearings, to a certain extent. The detected hysteresis phenomena can also be explained by the onset of journal bearing instability. Full article

High-performance Al₂O₃/graphite-Al₂O₃ laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al₂O₃/graphite-Al₂O₃ laminated composites should be studied extensively under water working conditions. Here, we attempted to explore the practicability of the Al₂O₃/graphite-Al₂O₃ laminated composite as a sealing material from a tribological point of view under water lubrication conditions. The tribological properties and mechanism of friction and wear of laminated composite ceramics were investigated under dry sliding friction, water environment, and suspended particle working conditions. It was found that the Al₂O₃/graphite-Al₂O₃ laminated composite has a better friction performance under water lubrication compared to dry sliding because of the separation effects formed by a water molecule film and a transfer film. Meanwhile, the wear rate under dry contact was found to be approximately six times that under water lubrication conditions. Under the water lubrication conditions, the formation of graphite films and water-adsorbed layers improved the anti-wear properties of the laminated materials, and the friction coefficient and the wear rate were as low as 0.16 and 1.76 × 10⁻⁶ mm³/Nm, respectively. Under the suspended particle working condition, the solid particles destroyed the graphite lubricating film and abrasive wear dominated the wear mode. The Al₂O₃/graphite-Al₂O₃ laminated composite demonstrates a potential for application in dynamic sealing and sliding components. Full article

Molybdenum disulfide (MoS₂) has been used in a variety of lubrication products due to its highly tunable surface chemistry. However, the performance of MoS₂-derived tribofilms falls short when compared to other commercially available antiwear additives. The primary objective of this study is to improve the tribological performance of MoS₂ as an additive for lithium-based greases. This was achieved by functionalizing the particle with hydrophilic molecules, such as urea. Experimental results indicate that the urea-functionalized MoS₂ (U-MoS₂) leads to a notable decrease in the coefficient of friction of 22% and a substantial reduction in the wear rate of 85% compared to its unmodified state. These results are correlated with the density functional theory (DFT) calculation of U-MoS₂ to theorize two mechanisms that explain the improved performance. Urea has the capability to reside both on the surface of MoS₂ and within its interlayer spacing. Weakened van der Waals forces due to interlayer expansion and the hydrophilicity of the functionalized U-MoS₂ surface are catalysts for both friction reduction and the longevity of tribofilms on hydrophilic steel surfaces. These findings offer valuable insights into the development of a novel class of lubricant additives using functionalized hydrophilic molecules. Full article

Protecting motor bearings from electric erosion is crucial as electric vehicles evolve. To better understand how lubrication interacts with electric discharge within motor bearings during varying speeds of vehicle operation, an optical ball-on-disk tribometer was modified to investigate the influence of alternating current (AC) electric fields on film thickness, friction force under various lubrication regions, and discharge characteristics. The study revealed that in AC electric fields, as the lubrication state shifts from mixed lubrication to fluid lubrication region, the electrical characteristic of the lubricating oil film changes from resistive to capacitive, accompanied by an increase in discharge frequency. Under the elastohydrodynamic lubrication (EHL) region, an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. If the potential difference across the oil film increases to the threshold voltage, destructive discharge occurs with the emission of a significant amount of purple light. Joule heating generated by the AC electric fields also results in a reduction in the friction coefficient under the fluid lubrication region. However, due to the reduction in film thickness, the lubrication state eventually moves to mixed lubrication, leading to a substantial increase in the friction coefficient. In addition, the study also investigated the use of grease with a nanographite conductive additive. It was found that inappropriate additive amounts can lead to discharge phenomena occurring outside the contact region. Full article

Bio-lubricants are the future of lubricants as a substitute for mineral lubricants; however, bio-lubricants have drawbacks, such as poor thermal-oxidative stability. In addition, during the friction process, the temperature of the lubricant increases, so the lubricant must have good thermal conductivity to conduct heat to the environment. To combat the drawbacks of bio-lubricants, some additives have been used to improve their performance as lubricants. Composites of carboxymethyl cellulose (CMC)/MXene and Span 60 as surfactants were used as additives in CPO with different compositions. The physicochemical properties of the addition of CMC/MXene and Span 60 in CPO have changed, including kinematic viscosity, TAN, thermal conductivity, and fatty acids, which have a positive impact on lubrication performance in terms of reducing oxidation processes and increasing thermal conductivity. From fatty acid composition tests and FTIR analysis, the additives work to suppress the oxidation process. A pin-on-disk test was performed to evaluate the tribological performances of bio-lubricants. The results show that CM 10 SP (0.5% wt of CMC and MXene and 1% wt Span 60) demonstrated a significant decrease in CoF and wear rate by 49% and 74%, respectively, at a load of 50 N and a speed of 1400 rpm compared to CPO without additives. An interface layer of CMC/MXene and Span 60, separating two surfaces, could induce wear on the surface of the disk and pin. Full article

Predicting the tribological behaviour in the secondary shear zone in the metal-cutting processes is considered a significant challenge in contemporary research. This work investigated the frictional performance in the secondary shear zone of a planing process using a modified ball-on-disc open tribometer. The values of the coefficient of friction (COF) were tracked between an AISI4140 + QT disc (chip) and a cemented carbide ball (cutting tool) coated with TiAlN under three contact pressures of 0.5, 1, and 2 GPa at a range of sliding speeds starting from 0.2 m/s to 1.6 m/s. The tests were conducted under both dry and lubricated conditions using three commercial cutting fluids of CSF 35 straight oil, Vasco 6000, and Zubora 67H emulsions. Also, the MWFs were tested for their rheological properties and wettability. The tribometer results validated the same COF trend as that in the actual metal-cutting experiments, particularly at 0.5 and 1 GPa in dry conditions. Moreover, Zubora 67H emulsion is proven to be the optimal choice due to it reducing the COF between the rubbing contacts by up to 78%. Furthermore, it showed the lowest contact angle and viscosity index, revealing its ability to easily penetrate, especially at higher temperatures, within the secondary cutting zone. Full article

Gas film thickness significantly influences the performance prediction of Gas Foil Thrust Bearings (GFTB). However, the Classical Model (CM) for GFTBs exhibits inaccuracies in describing gas film thickness. In this paper, we explore the differences in the details of gas film thickness modeling and propose a Parallel Segmentation Model (PSM), which fixes the errors of the CM in describing the gas film thickness in the ramp section, and a Full-Ramp Model (FRM), to which a more realistic description of the gas film in the flat section is also added. Comparative analysis, utilizing a publicly available test dataset based on the open-source GFTB structure, establishes that the FRM surpasses the CM and PSM in accurately predicting load capacity. In-depth analysis shows that the location of the minimum gas film thickness for determining the load capacity is located at the innermost circle of the free end of the top foil, whereas the FRM is subjected to the same load with a larger film thickness at this location, which may be due to the unique geometry of the top foil of the FRM. Subsequently, employing the FRM, a parametric study explores load capacity in GFTB, considering variables such as ramp height, top foil thickness, bump foil stiffness, ramp section extent, and top foil area. The results demonstrate that GFTB load capacity exhibits a linear increase with the expansion of the top foil area. Moreover, the load capacity increases with augmented top foil thickness and bump foil stiffness, albeit at a decreasing rate. Additionally, an increase in ramp section extent initially enhances load capacity, reaching a maximum value before declining. Similarly, an increase in ramp height initially augments load capacity, attaining a maximum before subsequent diminution. Full article

To analyze the effect of static eccentricity on the air ingestion distribution and vibration damping properties of the SFD, a numerical simulation study of SFDs considering two-phase flow was carried out based on CFD using a transient solution method and dynamic mesh technique. The results show that the angle between the static eccentricity direction and the circumferential direction of the oil supply hole increases and the air ingestion area in the oil film expands. In contrast, the oil film damping decreases, and the larger the static eccentricity distance, the greater its effect on the air ingestion area in the oil film. When the circumferential angle is small, the oil film damping increases with the increase of static eccentricity distance, and when the circumferential angle is large, the oil film damping decreases with the increase of static eccentricity distance and then increases. With the increase of static eccentricity distance, the air ingestion area at both ends of the oil film increases. At the same time, studying the effect of dynamic eccentricity shows that as the dynamic eccentricity increases, the oil film damping first decreases and then increases, and the air ingestion area increases. Comparing the 1 hole, the 2 hole, and the 3 hole oil supplies, the air ingestion area is significantly larger in the 1 hole oil supply than in the 2 hole or the 3 hole oil supplies, and the oil film damping of the 1 hole oil supply is smaller than the oil film damping of the 2 hole or the 3 hole oil supplies. It can be seen from the present study that in the actual installation of the SFD, when the circumferential angle is less than 60°, the static eccentricity can be increased appropriately. When the circumferential angle is greater than 60°, the static eccentricity can be appropriately reduced. Full article

Research on polymer matrix composites with excellent tribological properties has received increasing attention in recent years. In this study, antigorite and wollastonite mineral dual-phase-reinforced polytetrafluoroethylene (PTFE) matrix composites were prepared by filling PTFE with mineral powders using ball-milling, cold-pressing, and pressureless sintering methods. The phase structure, microstructure, chemical composition, Shore hardness, and tribological behavior of the composites rubbed against steel balls under dry friction conditions were investigated. The results show that the composites have a dense structure and uniform distribution of mineral phases, with a Shore hardness of 62–68.8, an increase of 18.7–23.7% compared to pure PTFE. Compared with the addition of mono antigorite or wollastonite, the composites prepared by simultaneously filling the two minerals exhibited excellent tribological properties. The average friction coefficient and wear volume of the (10Atg + 20Wl)/PTFE composites were reduced by 44.2% and 71.4%, respectively, compared to those of pure PTFE. A dense and continuous tribofilm composed mainly of SiO₂, MgSiO₃, Mg₂SiO₄, MgO, CaO, CaMg(SiO₃)₂, and CaF₂ was formed on the worn surfaces of both the dual-phase-reinforced PTFE matrix composites and counterpart steel balls during the friction process. The reduction in friction and wear is attributed to the reinforcement effect of the minerals on the PTFE matrix as well as the complex physical and chemical reactions at the friction interface stimulated by the synergistic effects between the two minerals. The addition of wollastonite reduced the phase transition temperature of antigorite, promoting more tribochemical reaction products with good abrasion resistance and friction-reducing properties, which contributed to the excellent tribological behavior of the composites. Full article

With the advancement of industries such as high-speed railways, new energy vehicles, and wind power, bearings are frequently exposed to various electric field environments, leading to the need for lubricating oil films of bearings to withstand voltage. One of the major issues caused by the breakdown discharge process of the lubricating oil film in bearings is the generation of local instantaneous high temperatures. This temperature rise is a key factor contributing to problems such as high operating temperature of bearings, surface damage in the contact area, and degradation of lubrication performance. This research article focuses on the comprehensive influence of bearing friction and electrical factors. It establishes a heat source calculation model and a temperature field simulation model specifically for current-carrying bearings. This study analyzes both the overall temperature rise of bearings and the local temperature rise resulting from breakdown discharge. Furthermore, the accuracy of the simulation analysis is verified through experiments. The temperature field simulation and experimental results consistently indicate that electrical environmental factors can cause an increase in the overall temperature rise of a bearing. Additionally, the breakdown and discharge of the lubricating oil film generate local instantaneous high temperatures in the contact area of the bearing. Full article