Lubrication Failure Research Articles

Impact of oil supply conditions on water lubrication assisted with minimal secondary lubricating medium

Abstract Previous research has revealed that introducing a secondary lubricating medium can temporarily enhance water-lubricated bearing performance, thereby reducing the risk of lubrication failure under challenging conditions. This study aims to identify the optimal injection point for the secondary lubricating medium and evaluates oil supply rate effects. Experiments are conducted using a block-on-ring test rig, complemented by CFD simulations to elucidate the underlying mechanisms. Three oil supply settings, upstream, inlet and outlet of the contact region, are compared. Results shows that upstream oil supply led to a lower critical speed at which the added oil loses any effect compared to the inlet oil supply and outlet oil supply. The effect of oil supply rates on friction reduction varies among the oil supply settings and ring rotational speeds. In conclusion, the most effective oil supply setting positions the injector at the outlet of the contact region, outperforming placement at the entrance of the contact region.

Topology optimization of AISI 4140 steel with surface texture filled by multi-solid lubricants for enhancing tribological properties

Wind power gears will be excessively worn due to lubrication failure during operation. Herein, the tribological properties of rubbing pairs are improved by filling solid lubricants into surface texture. In texture design, three types of topological textures (Circle (C), Hexagon (H) and Circle/Hexagon (CH)) were obtained by cell topology optimization, and then three cases with 20%, 30%, and 40% density were designed for each texture. Next, SnAgCu and TiC were deposited in texture of AISI 4140 steel (AS) to obtain 9 kinds of self-lubricating surfaces. Among them, AS with 30% CH density (AS-CH30) exhibits excellent mechanical and tribological properties. Compared with AS-C and AS-H, the maximum equivalent stress of AS-CH was decreased by 10.86% and 5.37%, respectively. Friction coefficient and wear rate of AS-CH30 were 79.68% and 78% lower than those of AS. The excellent tribological performances of AS-CH30 can be attributed to the synergistic effect of topological surface and solid lubricants. Topological surface can not only reduce fluctuation of equivalent stress, but also promote the stored lubricants to be easily transferred at the contact interface to form a 200 nm lubricating film containing solid lubricants (mainly), oxides and wear debris.

Fluorinated graphite reinforced polytetrafluoroethylene/poly(butylene terephthalate) composites as friction materials for deep‐sea applications

AbstractThe application of polymer composites is one of the most effective methods for preventing lubrication failure in deep‐sea engineering. In this study, fluorinated graphite (FGr) microsheets were incorporated into polytetrafluoroethylene (PTFE) microparticle‐filled poly(butylene terephthalate) (PBT) composites. The tribological performance in the simulated deep‐sea environment at elevated seawater pressure equivalent to 3000 m ocean depth was investigated. The results showed that FGr enhances the flexural and compressive strengths, thermal stability, and seawater resistance of the PTFE/PBT composite. The wear rate was decreased to 96% at the critical FGr content of 4% by improving the transfer onto the metallic counterfaces, preventing direct contact and shear between friction couples. Moreover, the seawater pressure impedes composite transfer, leading to a 29% increase in the wear rate.

Dual in-situ observation of tribochemical and morphological evolution of single-layer WS2 and multi-layer WS2/C coatings

The outstanding tribological performance of transition metal dichalcogenides (TMDs) is attributed to their unique sandwich microstructure and low interlayer shear stress. This advantageous structure allows TMDs to demonstrate exceptional friction reduction properties. Furthermore, the incorporation of TMDs and amorphous carbon (a-C) in multi-layer structures shows excellent potential for further enhancing tribological and anti-oxidation properties. Amorphous carbon, known for its high ductility, chemical inertness, and excellent wear resistance, significantly contributes to the overall performance of these multi-layer coatings. To gain an in-depth understanding of the tribological mechanism and evolution of TMDs’ multi-layer coatings, a dual in-situ analysis was carried out using a tribometer equipped with a 3D laser microscope and a Raman spectrometer. This innovative approach allowed for a comprehensive evolution of the tribological, topographical, and tribochemical characteristics of both single-layer WS2 and multi-layer WS2/C coatings in real time. The findings from the dual in-situ tribotest revealed distinct failure characteristics between the single-layer WS2 coating and the multi-layer WS2/C coating. The single-layer WS2 coating predominantly experienced failure due to mechanical removal, whereas a combination of mechanical removal and tribochemistry primarily influenced the failure of the multi-layer WS2/C coating. The tribological evolution process of these two coatings can be classified into four stages on the basis of their tribological behavior: the running-in stage, stable friction stage, re-deposition stage, and lubrication failure stage. Each stage represents a distinct phase in the tribological behavior of the coatings and contributes to our understanding of their behavior during sliding.

Blackening failure of poly-α-olefin impregnated porous polymide due to the splitting of lubrication oil catalyzed by iron

Lubrication failure accompanying with blackening phenomenon significantly reduces the long-running operational reliability of porous polymide (PPI) lubricated with poly-α-olefin (PAO) oil. Here, the effects of lubrication condition and counter-surface chemistry on the blackening failure of PAO impregnated PPI were studied through the comparison of the tribological tests against GCr15 steel ball and Al2O3 ceramic ball with and without PAO oil lubrication. Black products were found to be formed on the PAO impregnated PPI surface slid against steel ball or Al2O3 ball added with iron nano-particles, but be absent under the conditions without iron or PAO oil. Further analysis indicated that the iron-catalyzed splitting of PAO oil into small molecule alkanes and following the formation of black organic matter should be mainly responsible for the blackening phenomenon. Molecular dynamic (MD) simulations demonstrated that the iron facilitated the separation of hydrogen atom and the following broken of C-C bonds in PAO molecules, final resulting in the splitting of PAO oil.

Stochastic uncertain lubrication in gear transmission subjected to tribodynamic loading

A stochastic uncertain tribodynamic model is established for a spur gear pair for the first time. The stochastic uncertainty of pinion rotation speed propagated to lubrication performance is investigated. The probability density function of the minimum lubricant film thickness hmin evolves over time periodically at interval of an engagement process. Correspondence between abrupt increase in meshing force and amplification of hmin uncertainty is found. Robust and reliable lubrication performance can be achieved by suppressing the hmin uncertainty and decreasing the lubrication failure probability. This can be done by increasing lubricant viscosity, and decreasing input torque and uncertainty level of input rotation speed. This work lays a solid foundation for robust and reliability based optimization for tribodynamic gear system.

Investigation of hydrodynamic lubricant film breakdown between the journal and bearing in a high-speed coolant pump of electric vehicles

The high-speed coolant pump is essential for electric vehicle thermal management, ensuring optimal module temperatures. The pump impeller and bearing are combined into a rotor and then fit on a fixed shaft with a clearance, aiming to generate a complete lubricant film between the stationary journal and rotating bearing during pump operations. However, during the pump durability test under off-design conditions, severe wear occurred on both the journal and bearing. A novel simulation method based on computational fluid dynamics and dynamic mesh is developed to investigate the lubrication failure. User-defined functions are programmed to articulate the simultaneous rotation and whirl of the bearing, and the effects of temperature and cavitation are considered. Both the pump and bearing simulations closely align with experimental results. When the radial force of the pump rotor is steady, the bearing only rotates without whirling, and the bearing load capacity can counteract the maximum radial force of the rotor. However, the rotor experiences fluctuating radial forces over time, primarily attributed to elevated pressure levels at the volute tongue caused by the rotor–stator interaction. This phenomenon results in the bearing to rotate and whirl simultaneously. The load capacity generated by the backward whirl of the bearing is greater than that of the forward whirl. Nevertheless, the bearing whirl initiates a decline in the extremum values of lubricant film pressure. Subsequently, both load capacity and minimum film thickness exhibit a continuous decrease, eventually culminating in the breakdown of the complete lubricant film and resulting in contact wear failure. These new findings contribute to proposing measures to reduce wear under unsteady excitations.

Tribological properties of graphene-reinforced polyurethane bearing material

For water-lubricated stern tube bearing in ships, bearing material with low friction can prevent severe damage on the shaft surface when lubrication failure occurs, and hence improve operation reliability of the whole propeller system. In this work, 0.25–5 wt% of solid lubricant graphene platelets were blended with commonly used bearing matrix thermoplastic polyurethane (TPU) via melting injection, and tribological performance of TPU composites were investigated at a set of applied loads and sliding speeds which mimics the actual operating conditions. Graphene inclusion at a low content (< 0.5 wt%) reduced friction and wear compared to neat TPU, while maintaining mechanical properties. Graphene-induced tribofilm is formed and it is believed to offer low shear strength at the sliding surfaces while also regulating the size of wear particles. Since more platelets are exfoliated due to the greater extent of surface damage under high loads, it presents a pressure-dependent anti-friction ability. Higher concentration of graphene led to further friction reduction but deteriorated both the strength and ductility of materials due to the agglomeration. Results from Raman spectroscopies show that graphene-reinforced TPU composites underwent no chemical changes but mechanical deformation during rubbing, and this resulted in wear particles and tribofilm, containing graphene platelets with modified structure.

One-step preparation of high performance Ni-MoS2 self-lubricating coatings via jet electrodeposition on additive manufactured aluminum alloy

Composite coatings with solid lubricants can improve the tribological performance of aluminum alloy parts prepared by Laser Powder Bed Fusion (LPBF). In this study, Ni-MoS2 self-lubricating composite coatings were one-step prepared on additive manufactured aluminum alloy surface via jet electrodeposition. The properties and lubrication performance of the coatings prepared using composite electrolyte with different MoS2 particle diameters and concentrations were investigated. The lubrication mechanism of the composite coating was discussed. The results showed that 0.8 μm MoS2 had less agglomeration than 80 nm, resulting in a uniform surface. The lubrication performance of the composite coating was affected by MoS2 particles content and coating hardness. With the increase of MoS2 concentration in the composite electrolyte, the friction coefficient and wear rate decreased, and achieved the best lubrication performance of 0.12 friction coefficient and 0.11 mg/m wear rate when MoS2 composite electrolyte is 5 g/l and MoS2 is 0.8 μm. However, the addition of soft MoS2 decreased the coating hardness, lower hardness will cause lubrication failure.

Friction and wear behavior of molybdenum-disulfide doped hydrogen-free diamond-like carbon films sliding against Al2O3 balls at elevated temperature

Diamond-like carbon (DLC) films quickly experience lubrication failure due to oxidation and mechanical degradation when used above 300 °C, which limits their application. Molybdenum disulfide (MoS2) doping is considered as a feasible method to improve high-temperature properties of DLC films. However, the effect of MoS2 doping on the high-temperature friction behavior of MoS2-DLC composite films and its mechanism remain unclear. Here, MoS2-DLC composite films with different contents of MoS2 were synthesized by a superimposed deposition system consisting of high-power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). The MoS2 content in the films was controlled by varying the number of MoS2 pellets in the graphite-MoS2 (C–MoS2) mosaic target. The effect of MoS2 doping content on the structure and mechanical properties of MoS2-DLC films was analyzed. In addition, the friction and wear behavior and mechanism of MoS2-DLC composite films sliding against Al2O3 balls at 25–450 °C were studied. The results indicated that MoS2 was successfully incorporated into DLC matrix, and the content of Mo in the films ranged from 0 to 6.15 at. %. The as-deposited MoS2-DLC composite films exhibited a dense and featureless structure. The doping of MoS2 improved the adhesion strength and released the internal stress of MoS2-DLC composite films, but reduced the hardness and elastic modulus of the films. In particular, MoS2-DLC composite films with 3.78–6.15 at. % Mo maintained excellent anti-friction and anti-wear performances in the temperature range of 25–450 °C. Abrasive wear and fatigue wear occurred in the friction test of the films at different temperatures. However, the friction mechanism of the films varied with the temperature of friction test. At 25 °C, MoS2-DLC composite films showed excellent lubrication and anti-wear abilities due to the carbon suspension bond was passivated by H2O molecules. At 250 °C, MoS2 phase precipitated on the surface of the films, resulting in low friction. At 350 °C, MoS2-xOx solid solution was generated on the surface of the wear track to maintain lower friction and wear. Interestingly, MoS2-DLC composite films with high Mo content still achieved relatively low coefficient of friction and wear rate up to 450 °C due to the continuous availability of MoS2-xOx generated on the surface of wear track.

Why do hybrid nanoparticles perform better in improving heat transfer performance of lubricating oil during lubrication process: An experiment and molecular dynamics simulation

Lubricants are indispensable ingredients for alleviating friction and wear in mechanical components especially in automobile. However, due to its poor heat transfer capabilities, traditional lubricants are denatured under extreme working conditions, leading to lubrication failure during the friction process. Therefore, this study elaborately put forward to a novel MoS2/h-BN hybrid nanoparticle as efficient nano-additive for engine oil. The results of experiments and molecular dynamics simulation jointly show that compared with mono nanoparticles, hybrid nano-lubricants (NL) thermal conductivity was significantly improved than that of base oil owing to the synergistic effect. The corresponding mechanism for the improving heat transfer performance was suitably proposed based on the Mean Square Displacement (MSD) and Radial Distribution Function (RDF) results at the microscopic atomic level.

A novel self-powered triboelectric sensor for early waring of lubrication failure

In tribology, maintaining good lubrication of friction pairs is an important technical means to reduce wear and failure, which is very important but difficult to monitor the lubrication state of friction pairs. In this paper, when measuring the thickness and shape of the lubricating oil film by the ball-disk elastohydrodynamic oil film measuring instrument, a current amplifier is integrated to measure the electrical signal generated during the friction process. By monitoring the change of lubricating oil film, the change of ball-disk friction force, and the change of triboelectric signal during the friction process in real time, the relationship between the tribological behavior and the triboelectric behavior of the friction pair is explored. The experimental results show that under the conditions of limited oil supply, different rotational speeds and different lubricating oil viscosities, the time of the discharge phenomenon of the steel ball corresponds one-to-one with the time when the friction pair starts to wear under oil-scarce lubrication. The discharge occurs due to the electric charge breaking through the air in the micro-gap of the wear scar. The results demonstrate that the formation of the oil-depleted state has an important influence on the triboelectric process. Based on the relationship between the two, the state of the lubricating oil can be reflected in real time by using the triboelectric signal, which provides a reliable method for the real-time monitoring of the lubrication state.

Numerical investigations on the lubrication characteristics of involute harmonic gears

PurposeHarmonic gears always work under different operating conditions and may usually break down due to lubrication failures, while its lubrication mechanism is still not clearly understood. This paper aims to present a lubrication model comprehensively considering the influence of contact geometry, lubrication properties and three-dimensional (3D) real surface roughness to analyze the lubrication performance under different conditions.Design/methodology/approachBased on the discrete convolution-fast Fourier transformation with duplicated padding and quasi-system numerical methods, the lubrication model for harmonic gears is developed, which is verified by comparing results with available lubrication data.FindingsThe effects of meshing process, working conditions and 3D roughness on the lubrication characteristics are discussed. From the calculated cases, the increase in rotational speed and decrease of applied torque may increase the film thickness, enhancing the lubrication performance of harmonic gears. It is also observed that proper surface roughness can be used for lubrication design.Originality/valueThe research results can provide theoretical guidance for improving lubrication performance and reducing friction/wear of the harmonic gear interfaces. This study can be promoted to various engineering scenarios of harmonic gears, such as industrial robots, space-driven agencies and precision measuring instruments.

Coupling analysis of timing gear dynamics and three-dimensional mixed lubrication under multi-branch shafting of marine diesel engine

Timing gears are the fundamental transmission components of marine diesel engines, and their operational reliability and efficiency are significantly impacted by their health status. The performance of timing gears is influenced by external excitations from the branch drive shaft and load input, as well as internal excitations caused by time-varying meshing stiffness and transmission errors. Therefore, it exhibits pronounced nonlinear characteristics as a result of the coupling effect between variable dynamic loading and micro-mixed lubrication induced by surface roughness and shaft vibration. The timing gear of a specific marine 20 V diesel engine is selected as the subject of investigation in this study, taking into account the impact of various types of internal and external comprehensive excitation. The three-dimensional (3D) mixed lubrication state analysis model, influenced by the coupling dynamic effect, was expanded based on the dynamic load and speed fluctuation in conjunction with the 3D line contact mixed lubrication model. The results demonstrate that the accuracy of the model can be validated through vibration testing, simulation testing, and empirical formulas for elastohydrodynamic lubrication (EHL). Additionally, the meshing process results in significant rough peak contact between the shaved surface and the ground surface, leading to potential lubrication failure. By implementing an optimization scheme that incorporates shock absorbers, the maximum contact area ratio of the four actual machining surfaces is reduced to only 16.06 %. This effectively mitigates the issue of severe rough peak contact, enhances the lubrication condition of gear pairs, and offers theoretical guidance for tribological optimization design in marine diesel engine timing gears.

Analysis of flow diffusion of secondary lubricant in water-lubricated bearings

To reduce the lubrication failure of water-lubricated bearings under short-term harsh conditions, preliminary experiments have shown that temporarily supplying a small amount of lubricating oil into a bearing as a secondary lubricant can improve the load capacity of the water film therein. However, the physical flow and diffusion state of this secondary lubricant (oil) in water are unclear. Therefore, a mixed lubrication model and a volume-of-fluid model are incorporated to study the diffusion behavior of a small amount of lubricating oil in a water-lubricated bearing. The results show that there is a backflow effect in the local area inside the bearing, where the fluid velocity is in the opposite direction to the linear velocity of the shaft. This backflow effect intensifies with increasing eccentricity ratio, which enlarges the oil-free zone in the middle part of the bearing. In the convergence area at the water inlet end of the bearing, the water supply pressure and backflow effect prevent the lubricating oil from escaping. Increasing the shaft speed has a positive effect on the diffusion of the oil and the load capacity of the fluid. To enhance the assisted lubrication effect of the oil, the oil injection port should be set in the loading zone to avoid the backflow zone. This research provides some fundamental data for reducing the friction and wear of water-lubricated bearings under harsh conditions.

Structural selection of liquid hydrogen lubricated herringbone spiral-grooved thrust bearing considering viscous dissipative heat

Spiral-grooved thrust bearing (SGTB) is one of the important kinds of supporting component in high-speed rotating devices. The high shearing rate of SGTB can produce a large amount of viscous dissipative heat, which causes a temperature rise. Dynamic pressure effect induces pressure variation in the herringbone SGTB (HSGTB). When liquid hydrogen (LH2) is used as a lubricant, cavitation caused by lower pressure and higher temperature can result in lubrication failure. Especially, the cavitation of LH2 is more prone to occur because of its small temperature difference between the triple point and critical point, and the smaller supercooling degree. The influence of thermal properties on the phase transition process of LH2 is more significant. In this paper, the thermal and mechanical performance of three different structures of LH2 lubricated SGTB is compared by considering viscous dissipative heat. Herringbone SGTB is proposed for better performance and feasibility of its application in LH2 lubrication. The static performances of HSGTB such as load capacity, friction torque, cavitation rate, average temperature, and heat flux have been evaluated numerically by introducing the cryogenic cavitation model. The orthogonal sampling method and range analysis are used to optimize the HSGTB structure. Compared with the original HSGTB, cavitation rate and temperature rise are significantly suppressed in the optimized HSGTB. In addition, the load capacity is also improved effectively at high rotational speed, which is expected to be applied to high-speed centrifugal pumps.

Investigation on the lubrication component and mechanism for a biolubricant isolated from the agro-waste resource of Codonopsis pilosula

Waste plant resource provides a new sustainable feedstock for the biolubricant, and purification of the effective components in biomass oil is vital to improve the performance of biolubricant. In this work, the crude extract of the aerial part of Codonopsis pilosula was divided into four different parts by petroleum ether, ethyl acetate, n-butanol and water, respectively. Their thermal stability, lubricating performances and mechanisms have been systematically investigated. In the four extracts, the petroleum ether extract displays the best thermal stability and lubricating performance over the entire test conditions, and other three extracts are confronted with lubrication failure at high loads and elevated temperatures. Triterpenoid saponin, typical for n-butanol extract exhibit the best lubricity at room temperature, followed by the fatty acid derivatives as phosphatidylcholine; flavonoid, and sugar exhibit poor lubricity. At high temperature, only the petroleum ether extract retains the good lubricity.

Probing the role of sp2-C in high-temperature tribology of a-C films by a comparative study of ta-C film and a-C film

The high-temperature tribological properties of ta-C and a-C films are comparatively studied. The ta-C film shows friction coefficients of around 0.10 at 450 °C and 500 °C, but the a-C film shows high friction coefficients above 0.5 at 450 °C. Surprisingly, the lubrication failure of the a-C film at 450 °C is not due to the failure (wear-out) of the film. Furthermore, the graphitization degree of the wear track of a-C film at 450 °C is higher than those of ta-C films at 450 °C and 500 °C. The underlying frictional mechanism is clarified, and the role of sp2-C atoms at the rubbing surfaces is highlighted. The higher sp2-C content is, the more water needs to achieve sufficient passivation.

Analysis of the auto lube system electric grease pump against the unscheduled breakdown of the dump truck unit brand k type HD 1500-7

A lubrication failure resulted in damage to the HD 1500-7 dump truck unit auto lube system, making the system ineffective and leading to lubrication failure on the frame components. Because the damaged HD 1500-7 dump truck unit is inoperable when it occurs, this damage may have an impact on its production. The goal of this study was to ascertain whether maintenance performance on the Dump Truck Brand K type HD 1500-7 unit was impacted by lubrication failure in the auto lube system. Additionally, learn how to assess the Auto lube system on the Dump Truck Brand K type HD 1500-7 and how much electricity the Grease Pump Auto lube system Dump Truck unit Brand K type HD 1500-7 uses. Using a quantitative approach, discover what is causing the HD 1500-7 dump truck unit and the auto lube system to malfunction. The analysis of the Dump Truck HD 1500-7 unit's maintenance performed from February to April 2022 revealed that the average MTBF value is 352.9 hours, the average MTTR value is 5.388 hours, and the average PA value is 96.38%. The oil-powered reciprocating pump produces 537.81 Watts of power. At a grease pressure of 2500 psi, the displacement (grease) pump requires 163.29 Watts from the reciprocating (oil) pump to operate, compared to 58.67 Watts at a grease pressure of 1500 psi. The standard working pressure for the displacement (grease) pump is 2500 psi, whereas the standard working pressure for the reciprocating (oil) pump is 400 psi. The working pressure on the oil and grease does not achieve the standard pressure, an error arises and results in lubrication failure in the frame components, and this might have an impact on the HD 1500-7 unit's maintenance performance

Lubrication failure analysis of camshaft bearings in V6 diesel engine

This contribution investigates the lubrication characteristics and failure causes of camshaft bearings belong to a V6 diesel engine. Numerical simulation based on the theory of elastohydrodynamic lubrication and flexible multibody dynamics is performed to analyse the lubrication characteristics of camshaft bearings. The results reveal that lubrication performance of different bearings of camshaft shows great differences. For a certain bearing, the mixed lubrication state and elastohydrodynamic lubrication state alternately occur in one engine cycle. The duration of mixed lubrication varies greatly in different bearings. For the bearing closest to the timing drive gear, the total pressure is dominated by the asperity contact pressure, and the predicted safety factors of the asperity contact pressure, hydrodynamic pressure and oil film thickness are less than 1, which means that this bearing will have lubrication failure.