Lubrication Conditions Research Articles

Study on oil film spreading characteristics on the jet lubricating tooth surface of aviation herringbone gear

Purpose During the oil lubrication process of aviation herringbone gears, lubricating oil is injected into and spreads around the tooth surface. Its spreading characteristics directly affect the lubrication state and transmission efficiency of gears. This study aims to investigate the effect of changing the injection parameters and gear operating conditions on the oil film deposition during injection lubrication. Design/methodology/approach The computational fluid dynamics method was used to establish the computational domain for the simulation and optimization using an orthogonal test. The oil film spreading and thickness of the tooth surface were calculated with the change in gear speed, fuel injection distance and fuel injection speed. Optimized oil injection lubrication parameters were obtained, and design ideas were provided for the oil injection lubrication analysis of aviation herringbone gears. Findings Under different operating conditions, such as varying the injection speed, gear rotational speed and injection distance, there were differences in the distribution of the lubricating oil film formed on the tooth surface. The thickness of the oil film decreases as the distance from the injection port increases. The thickness of the oil film deposition can be increased by increasing the injection velocity and reducing the gear rotation speed. The injection distance had a relatively small effect on the spreading thickness of the deposited oil film, affecting only the dynamic spreading process of oil film deposition. Furthermore, the simulation results are compared with the analytical calculation results, and finally the experimental verification is carried out. Originality/value Oil spray lubrication characteristics are important for achieving precise gear lubrication designs in the aerospace field. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2023-0250/

Melt Characteristics of a Deposited Layer on Rail Surface under Different Contact Models for Electromagnetic Launching

Understanding the melting of the deposited layer is crucial for the armature’s melting process and sliding electrical contact performance. This study first establishes contact models for both the boundary lubrication state (BLS) and squeezed-film lubrication state (SFLS). A three-dimensional magnetic diffusion model is then constructed to simulate interface current distribution in these contact states. It is discovered that the maximum current density on the surface of the armature shows a decreasing trend as the thickness of the deposited layer grows. Then, a calculation model for the deposited layer’s melting thickness under BLS is developed. For SFLS, Reynolds and energy equations are used to construct models for liquid film thickness and the deposited layer’s melting thickness. The results indicate that the deposited layer’s melting thickness under BLS is significantly greater than that under SFLS. Specifically, the melting thickness decreases with launching displacement in BLS and increases under SFLS. In SFLS, the deposited layer’s melting can suppress armature melting, though it remains nearly equivalent to that observed with polished rail. These findings provide a foundation for deposited layer control technology, which is essential for enhancing sliding electric contact performance and launching efficiency.

Mechanism of Wheel-Rail Adhesion Recovery during Large Sliding processes under Water Lubrication condition

The challenge of low adhesion between the wheel and rail constrains the advancement of train braking technologies, resulting in sliding during braking, increased braking distances, and even operational safety incidents. Low adhesion arises from the contamination of the rail surface by a third body, such as water or oil, significantly reducing adhesion. However, experimental studies have found that wheel-rail adhesion coefficient under water lubrication conditions possesses a recovery capability: In scenarios characterized by low adhesion in water lubrication conditions, a secondary rise in adhesion occurs when substantial wheel-rail sliding is present. This paper focuses on numerically modeling the unique phenomenon of adhesion recovery during large-sliding processes under water lubrication conditions. Considering the notable differences in frictional heating during wheel sliding, as opposed to pure rolling conditions, we construct a wheel-rail contact model under mixed lubrication conditions that incorporates the solid-liquid coupled heat transfer effect. This model achieves stable solutions for the wheel-rail contact relationship and the temperature at the wheel-rail interface. The impacts of velocity, axle load, water temperature, and slide ratio on the adhesion recovery phenomenon are discussed, revealing the underlying mechanism of adhesion recovery during large sliding processes. Finally, brake adhesion tests under water lubrication conditions are conducted on a scaled test rig to validate the proposed theoretical model.

Enhanced Tribological Performance of UHMWPE Composites Reinforced with Wollastonite: biocompatibility and Wear Behavior

Abstract Ultra-high molecular weight polyethylene (UHMWPE) is often limited by poor tribological properties in artificial joints, leading to high wear rates compared to metals and ceramics. This study explores the use of wollastonite, a natural mineral, as a filler to enhance the tribological performance of UHMWPE composites. X-ray diffraction (XRD) analysis revealed that wollastonite content and particle size inversely affected the crystallinity of the composite due to heterogeneous nucleation and stress concentration. The incorporation of wollastonite significantly improved the tribological performance, with wear rate reductions of 71%, 69.81%, and 50.73% under dry friction, normal saline (NS) lubricant, and new-born calf serum (NBCS) lubricant conditions, respectively. The wear mechanisms in the composite were predominantly slight fatigue and abrasive wear, contrasting with the extrusion deformation and severe fatigue wear observed in neat UHMWPE. Additionally, simulated body fluid (SBF) immersion tests demonstrated the composite's ability to form a surface apatite- like deposition. These findings suggest that wollastonite reinforcement effectively enhances both mechanical and tribological properties of UHMWPE.

Dynamic Modeling of Angular Contact Ball Bearing with Local Defects under EHL Considering Impact Force

In order to analyze the operating status of angular contact ball bearings(ACBBs) with local defects in more detail, a dynamic model of ACBB with local defects considering impact force under elastohydrodynamic lubrication conditions is proposed. Firstly, an elastohydrodynamic lubrication model for defective bearings considering spin is established, the film thickness and film stiffness of the defective bearings are calculated, and then time-varying displacement excitation model and time-varying stiffness model for local defects in angular contact ball bearings is presented. Based on this, an instantaneous impact force function related to defect size and bearing speed is established. Secondly, based on Hertz contact theory and impact force function, a dynamic calculation method for ACBBs with local defects on the outer ring is proposed. Finally, the vibration characteristics of ball bearings with faults are investigated, and the influence of different parameters on the dynamic response of the bearings is analyzed. The calculation results show that under lubrication conditions, the impact force on the vibration of the bearing is significantly weakened. With the increase of defect size and load, the frequency of bearing fault characteristics remain unchanged, but its amplitude increases. As the bearing speed increases, the characteristic frequency and amplitude of bearing faults increase.

Investigation on the performances of thrust ball bearing with a novel oil self-transportation biomimetic composite guiding surface

Improving the lubrication condition of oil-starved rolling bearings is a proven method to improve their reliability and service life. In this study, a composite surface texture was designed inspired by the microscopic structure of cactus spine, pitcher plant and blood clam. Superhydrophobic surface coating technology was also employed. An oil self-transportation biomimetic composite surface was developed on the guiding surface of a thrust ball bearing. Experimental results show that the biomimetic composite surface effectively drives oil for high-speed directional transport. The biomimetic composite guiding surface bearing demonstrated excellent best vibration and friction torque performance. Compared to conventional bearing, it has an overall vibration performance improvement of 37.4 %, as well as a significant reduction in friction torque of 43.3 % and wear of 72.2 %. We conclude that oil self-transportation biomimetic composite surfaces on rolling bearings can significantly improve the lubrication condition.

A Biomimetic Adhesive Disc for Robotic Adhesion Sliding Inspired by the Net-Winged Midge Larva.

Net-winged midge larvae (Blephariceridae) are known for their remarkable ability to adhere to and crawl on the slippery surfaces of rocks in fast-flowing and turbulent alpine streams, waterfalls, and rivers. This remarkable performance can be attributed to the larvae's powerful ventral suckers. In this article, we first develop a theoretical model of the piston-driven sucker that considers the lubricated state of the contact area. We then implement a piston-driven robotic sucker featuring a V-shaped notch to explore the adhesion-sliding mechanism. Each biomimetic larval sucker has the unique feature of an anterior-facing V-shaped notch on its soft disc rim; it slides along the shear direction while the entire disc surface maintains powerful adhesion on the benthic substrate, just like the biological counterpart. We found that this biomimetic sucker can reversibly transit between "high friction" (4.26 ± 0.34 kPa) and "low friction" (0.41 ± 0.02 kPa) states due to the piston movement, resulting in a frictional enhancement of up to 93.9%. We also elucidate the frictional anisotropy (forward/backward force ratio: 0.81) caused by the V-shaped notch. To demonstrate the robotic application of this adhesion-sliding mechanism, we designed an underwater crawling robot Adhesion Sliding Robot-1 (ASR-1) equipped with two biomimetic ventral suckers. This robot can successfully crawl on a variety of substrates such as curved surfaces, sidewalls, and overhangs and against turbulent water currents with a flow speed of 2.4 m/s. In addition, we implemented a fixed-wing aircraft Adhesion Sliding Robot-2 (ASR-2) featuring midge larva-inspired suckers, enabling transit from rapid water surface gliding to adhesion sliding in an aquatic environment. This adhesion-sliding mechanism inspired by net-winged midge larvae may pave the way for future robots with long-term observation, monitoring, and tracking capabilities in a wide variety of aerial and aquatic environments.

Periodic dual-mixing method for fast and robust solving of ultra-thin fluid-structure interaction problems

This study proposes the periodic dual-mixing method (PDMM) that can rapidly and robustly solve ultra-thin fluid-structure interaction (UTFSI) problems, especially in severe mixed lubrication. The dual mixing denotes a two-step process: the first step is to mix the historical inputs and outputs separately according to optimal mixing weights; the obtained results are mixed with dynamic damping factors in the second step to predict the deformation of the next iteration. Meanwhile, the residual is injected into the predicted deformation periodically. The comparison study is carried out with the popular IQN-ILS method in general FSI, which shows the PDMM is 5.3 times faster and 5 times more robust. Furthermore, the advantages of the PDMM are more significant under harsh mixed lubrication conditions.

High-speed grinding: from mechanism to machine tool

AbstractHigh-speed grinding (HSG) is an advanced technology for precision machining of difficult-to-cut materials in aerospace and other fields, which could solve surface burns, defects and improve surface integrity by increasing the linear speed of the grinding wheel. The advantages of HSG have been preliminarily confirmed and the equipment has been built for experimental research, which can achieve a high grinding speed of more than 300 m/s. However, it is not yet widely used in manufacturing due to the insufficient understanding on material removal mechanism and characteristics of HSG machine tool. To fill this gap, this paper provides a comprehensive overview of HSG technologies. A new direction for adding auxiliary process in HSG is proposed. Firstly, the combined influence law of strain hardening, strain rate intensification, and thermal softening effects on material removal mechanism was revealed, and models of material removal strain rate, grinding force and grinding temperature were summarized. Secondly, the constitutive models under high strain rate boundaries were summarized by considering various properties of material and grinding parameters. Thirdly, the change law of material removal mechanism of HSG was revealed when the thermodynamic boundary conditions changed, by introducing lubrication conditions such as minimum quantity lubrication (MQL), nano-lubricant minimum quantity lubrication (NMQL) and cryogenic air (CA). Finally, the mechanical and dynamic characteristics of the key components of HSG machine tool were summarized, including main body, grinding wheel, spindle and dynamic balance system. Based on the content summarized in this paper, the prospect of HSG is put forward. This study establishes a solid foundation for future developments in the field and points to promising directions for further exploration.

An Optimization Approach for Enhancing Energy Efficiency, Reducing CO2 Emission, and Improving Lubrication Reliability in Roller Bearings using ABC Algorithm

Friction and energy waste pose significant challenges in various industrial processes. Lubrication plays a crucial role in reducing friction and optimizing energy consumption. This study focuses on analyzing, simulating and calculation the oil film thickness, friction levels, energy losses, and CO2 emissions. The objective is to optimize lubrication conditions to enhance performance, improve energy consumption, and maximize lubrication efficiency for rolling bearings in a centrifugal fan. The simulation utilizes ANSYS CFX software, MATLAB programming. The optimal oil viscosity grade is determined based on two objectives by using artificial bee colony algorithm (ABC): minimizing energy consumption (thus reducing CO2 emission) and achieving the optimal oil film thickness and viscosity ratio. The findings reveal that, under the current lubrication conditions and normal fan operation, energy losses due to oil friction amount to 36.3 MWh per year, with CO2 emissions resulting from power losses reaching 18,750 kilograms per year. By transitioning to the optimized oil grade, energy savings of 1.08 MWh per year and a corresponding reduction of 557 kilograms in CO2 emissions per year can be achieved.

Measurement of slip length and friction reduction: An experimental study about boundary slip using omniphobic and 2D coatings

There is an intrinsic link between boundary slip and superlubricity. However, due to limitations in experimental techniques, the slip length cannot be precisely measured, leaving the mechanism of boundary slip controversial. This paper aims to accurately measure the slip length at the solid-liquid interface under oil-lubricated elastohydrodynamic lubrication (EHL) conditions using experimental methods, and to explore the friction reduction due to boundary slip. The study reveals that both omniphobic (lotus leaf essence) coatings and two-dimensional (2D) material (MoS2) coatings facilitate boundary slip. The slip length measurement method proposed in this study builds a bridge between oil film thickness and slip length, successfully addressing a key issue in boundary slip research. The findings confirm the significant friction reduction due to boundary slip, representing a major advancement in reducing friction in oil-lubricated EHL contacts through boundary slip. Future research should focus on searching for coating materials with a slip length on the micrometer scale so that superlubricity could be achieved.

Investigating lubricant behavior in a partially flooded tapered roller bearing: Validation of a multiphase CFD solver for aerated oil sump via particle image velocimetry studies and high-speed camera acquisitions

In the recent years, the efficacy of utilizing sapphire outer rings as a viable tool for experimentally observing oil flows within rolling bearings has been demonstrated. However, in previous studies, such approach was applied under fully-flooded lubrication conditions exclusively. This paper presents the outcomes of observations and measurements conducted under oil-bath lubrication conditions of a vertical-axis Tapered Roller Bearing (TRB). The experimental work encompasses four operational speeds ranging from 1000 min−1 to 2500 min−1, and two oil levels, i.e. 10% and 100% of the bearing width. Pictures were captured using an High-Speed Camera (HSC) for a qualitative inspection. Particle Image Velocimetry (PIV) measurements were conducted for a quantitative assessment of the oil velocity fields. The findings reveal specific lubricant flows, highlight aeration, and show particular vorticity patterns that intensify with increasing speed. These experimentally obtained results align with Computational Fluid Dynamics (CFD) simulations conducted using a specially developed model in OpenFOAM®, leveraging a solver that accounts for aeration.

Homogenization Heat Treatment and Tribological Properties of In Situ Alloyed NiTiCu by Laser Powder‐Bed Fusion

In situ alloying by additive manufacturing (AM) of premixed powders has been recognized as a promising low‐cost method for creating complex parts for biomedical implants, in which homogenization heat treatment is a critical concern in this technology. Also, as promising implant materials, their tribological properties under dry and lubrication conditions are significantly concerned with evaluating the functionalities of 3D printing. This work preliminarily addresses these two concerns with the laser powder‐bed fusion (LPBF) 3D‐printed nickel titanium copper (NiTiCu) alloy using three homogenization heat treatments and ball‐on‐disc wear tests under dry and NaCl‐lubricated conditions. It is found that to achieve sufficiently good microstructural homogeneity with low porosity, a temperature of 800 °C and a duration of 5 h is needed. Despite the promising outcome, analysis of the results revealed that all heat treatments led to the formation of a secondary phase identified as Ti2(Ni,Cu), which induced two‐step phase transformations. Thus, further studies on the optimization of the postprocessing techniques are required. The heat‐treated alloy resulting in the most favorable properties is selected for tribological testing. AM and the addition of Cu are observed to enhance the wear resistance of the alloy under lubrication conditions.

Analysis and Prospects of Lubrication and Friction Characteristics in Cold Strip Rolling: A Review

Lubrication and friction are the core processes in cold strip rolling, which are the key links to realizing the stable production of high‐quality strips, reflecting country advanced level in rolling technology. This review investigates the crucial properties of lubrication and friction in cold strip rolling by analyzing the mechanism, characterization methods, and influencing factors. The lubricant forms an oil film on the surface of rolls and strips based on the lubrication dynamics and tribology theory, changing the asperity contact state in the loaded roll gap, leading to changes in friction characteristics. Oil film thickness and coefficient of friction (COF) are crucial parameters for characterizing and judging the characteristics of lubrication and friction, theoretical calculations have become the core analytical method, and the study of the measurement method is still a great challenge. Parameters like rolling speed and oil viscosity affect the lubricant distribution and asperity contact in the loaded roll gap, changing the lubrication and friction state. The influence of parameters is strongly linked to the experimental or rolling environment. Prospective research trends on lubrication and friction in cold strip rolling are presented based on the status of research on lubrication and friction characterization.

Effect of stick and slip zones on fatigue life of a slewing ball bearing

Prediction of fatigue life of slewing ball bearings is challenging due to the influence of large deformations and adverse lubrication conditions. The present study presents an elegant simulation model that considers the flexibility of the supporting elements of the slewing bearing along with stick/slip zones at the raceway-ball contact interface. Using the stresses predicted by the simulation model, relative fatigue life using stick/slip condition versus no-friction condition is computed. A sensitivity study of the ball contact force, ball contact angle, coefficient of friction and raceway conformity is also performed. The present study also evaluates the results in comparison with full-sliding assumptions. The final results show that the stick/slip zone determination at the contact interface is beneficial for accurate determination of fatigue life of slewing bearings.

Film Thickness in Grease-Lubricated Deep Groove Ball Bearings—A Master Curve

Film thickness in a grease-lubricated bearing is a critical bearing operation parameter, yet there are no models available to predict it. Our recent articles demonstrated that the relative film thickness ( h g / h ff ) can be predicted using the base oil viscosity ( η ), half contact width (b), and linear speed (u) for any axially loaded deep groove ball bearing. In this article, we extend this study to include radial loads and combined—axial and radial—loads. Radial load application causes an additional replenishment in the unloaded zone, introducing a new length variable z r and surface tension σ . A universal power-law relationship between the relative film thickness in a deep groove ball bearing and the nondimensional number ( η bu ) / ( z r σ ) for all loading and grease lubrication conditions is presented for use in predicting film thickness.

Exploring the influence of ultrasonic peening treatment at ambient and cryogenic conditions on the surface characteristics and fatigue life of austenitic stainless steel 304L

This study investigates the impact of Ultrasonic Peening Treatment (UPT) at room temperature (Troom) and cryogenic temperature (Tcryo) on phase transformation, surface morphology, and fatigue life of stainless steel 304L samples. Finite element simulations were developed to analyze the effects of different material models and the pin's vertical velocity on residual stress, martensite volume fraction (ξ), and surface deformation. The numerical results of residual stress and ξ were consistent with experimental measurements obtained via X-ray diffraction. Significant compressive residual stress and martensite volume fraction were induced in the subsurface of the specimens following UPT at both temperatures. Various UPT process parameters, including static load, the pin's horizontal velocity, the number of treatments, and lubrication conditions, were experimentally explored for their effects on surface morphology and hardness. Indentation hardness revealed values of 621 HV for samples treated at Tcryo and 489 HV for those treated at Troom, compared to 286 HV for untreated specimens. Furthermore, UPT reduced surface roughness by approximately 88 % for a mechanically polished surface and over 93 % for a rough surface. Investigating conditions leading to potential damage and defects during the process was also undertaken. Fractography of the fracture surfaces and fatigue analysis revealed that the fatigue life of UPT-treated samples at Troom and Tcryo increased by 63 % and 45 %, respectively, compared to untreated specimens.

An ionic liquid crystal functionalized nanocellulose lubricant additives

Cellulose, one of nature's most abundant, clean, and sustainable resources, has often shown unsatisfactory results when used as bio-lubricant additives. Herein, nanocellulose (NC) from amorphous waste natural poplar was extracted using deep eutectic solvent encapsulation treatment and chlorine bleaching process. Subsequently, 1-hexadecyl-3-methylimidazolium bromide was integrated onto NC using a one-step hydrothermal treatment (high-temperature and high-pressure environment) to obtain ionic liquid crystal (ILC) functionalized products (named as ILC-NC). After ball-milling process and solid phase separation step, ILC-NC exhibits excellent dispersion stability and lubrication properties in the liquid phase (including water and vegetable oil). Based on the polar and colloidal activity properties of ILC, it can form an ordered molecular layer on NC surface and form a lubricating film-like structure, making NC smoother and sliding well. Compared to ILC/NC aqueous dispersion, ILC-NC reduces the coefficient of friction and wear rate on steel disk surface by 68.75 % and 74.07 %, respectively. The minimum coefficient of friction was further reduced to 0.032 as dispersing ILC-NC in sunflower oil, showing a reduction of 0.134 (77.91 %) compared to pure sunflower oil. Finally, the lubrication theoretical model calculation reveals the lubrication state of ILC-NC on the steel disk surface and proposes the lubrication mechanism.

Application of the Gradient-Boosting with Regression Trees to Predict the Coefficient of Friction on Drawbead in Sheet Metal Forming.

Correct design of the sheet metal forming process requires knowledge of the friction phenomenon occurring in various areas of the drawpiece. Additionally, the friction at the drawbead is decisive to ensure that the sheet flows in the desired direction. This article presents the results of experimental tests enabling the determination of the coefficient of friction at the drawbead and using a specially designed tribometer. The test material was a DC04 carbon steel sheet. The tests were carried out for different orientations of the samples in relation to the sheet rolling direction, different drawbead heights, different lubrication conditions and different average roughnesses of the countersamples. According to the aim of this work, the Features Importance analysis, conducted using the Gradient-Boosted Regression Trees algorithm, was used to find the influence of several parameter features on the coefficient of friction. The advantage of gradient-boosted decision trees is their ability to analyze complex relationships in the data and protect against overfitting. Another advantage is that there is no need for prior data processing. According to the best of the authors' knowledge, the effectiveness of gradient-boosted decision trees in analyzing the friction occurring in the drawbead in sheet metal forming has not been previously studied. To improve the accuracy of the model, five MinLeafs were applied to the regression tree, together with 500 ensembles utilized for learning the previously learned nodes, noting that the MinLeaf indicates the minimum number of leaf node observations. The least-squares-boosting technique, often known as LSBoost, is used to train a group of regression trees. Features Importance analysis has shown that the friction conditions (dry friction of lubricated conditions) had the most significant influence on the coefficient of friction, at 56.98%, followed by the drawbead height, at 23.41%, and the sample width, at 11.95%. The average surface roughness of rollers and sample orientation have the smallest impact on the value of the coefficient of friction at 6.09% and 1.57%, respectively. The dispersion and deviation observed for the testing dataset from the experimental data indicate the model's ability to predict the values of the coefficient of friction at a coefficient of determination of R2 = 0.972 and a mean-squared error of MSE = 0.000048. It was qualitatively found that in order to ensure the optimal (the lowest) coefficient of friction, it is necessary to control the friction conditions (use of lubricant) and the drawbead height.

Influence of triangular texture composite MAO coating on the tribological properties of aluminum alloys

To compensate for the poor friction and wear performance of aluminum alloys, in this study, four triangular textures with different area occupancy rate (5.16 %, 9.17 %, 20.63 % and 28.07 %) were prepared on the surface of aluminum alloys by laser texture technology, subsequently micro-arc oxidation (MAO) coatings were prepared using MAO technique. The treated samples were characterised by X-ray diffraction, micro-morphological analysis, optical profiler and energy dispersive spectroscopy. The tribological performance under oil lubrication conditions was tested by using a pin-disc contact rotational friction wear tester. The results showed that the sharp corners at the edges of the texture caused current concentration, which resulted in more intense sparking and accelerated MAO growth, thus creating more pores and roughening the surface of the coating. In terms of tribological performance, the triangular texture with 9.17 % area occupancy rate showed the best tribological performance before MAO coating, compared with the substrate, the average friction coefficient decreased by 64.11 %; and after the MAO coating was applied, the triangular texture composite MAO coating with 9.17 % area occupancy rate still had the best tribological performance, and its average friction coefficient further decreased compared with that of the smooth MAO coating by 33.07 %. The analysis suggests that the texture can store abrasive particles to prevent the MAO coatings from being worn through, leading to coating failure, while the hard MAO coatings can resist contact stresses well enough to prevent the texture from being flattened, leading to the failure of the function of storing abrasive debris. Therefore, the integration between texture and MAO coating can greatly enhance the anti-wear properties of aluminum alloys.