Lubrication Mechanism Research Articles

Calculation and Lubrication Characteristics of Cylindrical Roller Bearing Oil Film with Consideration of Thermal Effects

Aiming at the problem of how the thermal characteristics of cylindrical roller bearings affect the lubrication characteristics of bearings under actual working conditions, the influence of parameters such as speed and load on the lubrication characteristics of cylindrical roller bearings under thermal effects is analyzed. The numerical calculation method combining the quasi-static model of cylindrical roller bearing and the thermal elastohydrodynamic lubrication model is adopted. The effects of rotational speed, load and thermal effect on the lubrication performance of the bearing and the lubrication state under certain oil supply conditions were analyzed via numerical model calculation. The oil film thickness was measured via an immersion ultrasonic method to verify the correctness of the model. The results show that the larger the bearing speed, the larger the central film thickness and the minimum film thickness. At the same time, the thermal effect on the film thickness is more obvious; the greater the load, the greater the maximum oil film pressure. The film thickness gradient in the inlet region is greatly reduced, but the thermal effect has no obvious effect on the overall film thickness. In addition, there is a critical value of effective lubrication film thickness for each set of operating parameters. When the actual film thickness is equal to the critical value, the bearing lubrication state is at its best; the numerical simulation results are compared with the experimental values. Under the calculation conditions, the maximum error at the measuring point is within 10%, which meets the error requirements and provides a theoretical basis for revealing the bearing lubrication mechanism.

Lanthanide complexes functionalized carbon dot nanocomposites as lubricant additives for improving tribological performance

A novel nanocomposite, CDs-La-EDTA, was synthesized by bonding carbon dots to the functional sites of rare earth complexes, and its tribological characteristics were evaluated as lubricant additives. The results showed that the mean friction coefficient and the wear scar diameter of lubricating oil containing 0.15 wt% CDs-La-EDTA were reduced by 14% and 22%, respectively, compared with those of the base oil. Furthermore, the dual lubrication mechanism of the nanocomposite was proposed. The rolling or sliding effect of rare earth nanofibrous rods and the mending effect of carbon dot particles contributed to excellent lubrication performance.

Sliding wear of MAX phase composites Ti3SiC2–TiC and Ti3AlC2–Ti2AlC at 400 °C and the influence of counterface material (steel, Al2O3, and Si3N4) on wear behaviour

This study explores the feasibility of employing MAX phase composite as impregnated solid lubricants and/or as bulk material for advanced high temperature tribological applications. The development of microstructure of Ti-based MAX phase composites Ti3SiC2–TiC and Ti3AlC2–Ti2AlC fabricated by spark plasma sintering and their dry sliding tribological properties against bearing steel, Si3N4, and Al2O3 counterfaces were investigated using a ball on disc tribometer at 400 °C. An orientation relationship between the Ti3SiC2 matrix and TiC particle was established wherein Ti3SiC2/TiC interphase is a coherent boundary from which Ti3SiC2 grows epitaxially from TiC. Against steel, the MAX phase composites – in stark contrast to Si3N4 and Al2O3 – exhibited a negative wear behaviour due to the excessive wear and subsequent sintering of the transferred Fe particles at the sliding interface. Intrinsic lubrication mechanisms involving tribo-oxidation, tribochemical reaction, and mechanochemical reaction played a vital role in the friction and wear properties. The friction and wear properties of the Ti3AlC2–Ti2AlC MAX phase composite was superior to the Ti3SiC2–TiC composite owing to better oxidation kinetics governing the oxide growth and their retention. Evidently, the wear of the MAX phase is expected to proceed upon extensive deformation incorporating a range of microscale micromechanisms.

Study on the cooling and lubrication mechanism of magnetic field-assisted Fe3O4@CNTs nanofluid in micro-textured tool cutting

To address the challenge of insufficient lubricity and thermal conductivity of conventional lubricating fluids and single type of nanofluids during cutting, a new nanofluid (Fe3O4@CNTs nanofluid) was prepared in this paper, and the coupling effect of Fe3O4@CNTs nanofluid and micro-texture on the cutting performance of TiC ceramic tools under the action of magnetic field was revealed for the first time. The micro-texture (TTC) was prepared on the rake face of the tool by laser processing technique, and the non-textured tool (TC) was used as a control group. The conventional Fe3O4 nanofluid (F-0.5) and Fe3O4@CNTs composite nanofluid (FC-0.5) and with a volume fraction of 0.5 vol% were prepared by co-precipitation method. For facilitating the penetration of the nanofluid into the tool/chip contact area, an external magnetic field was applied during machining operations. The cutting test of titanium alloy was performed, and the influence of various magnetic field strengths on the friction properties of micro-textured tool/chip interface under the lubrication condition of Fe3O4@CNTs nanofluid was studied. Simulation analysis of the flow characteristics of nanofluid in micro-texture under the action of magnetic field was performed to provide theoretical support for the subsequent results. The results of the cutting tests showed that the cutting forces and tool wear of TTC + FC-0.5 were alleviated in the presence of magnetic field, and the cutting performance was further improved with the increasing of magnetic field from 300 Gs to 1200 Gs. Under the highest magnetic field strength (1200 Gs), TTC + FC-0.5 has 36.9 % lower cutting force and 28.15 % lower surface roughness than TC + F-0.5. Additionally, the penetration and lubrication mechanisms of Fe3O4@CNTs nanofluid on micro-textured tool/chip contact interface under the influence of applied magnetic field was exposed.

On the Elastohydrodynamic Film-Forming Properties of Metalworking Fluids and Oil-in-Water Emulsions

Oil-in-water (O/W) emulsions are water-based lubricants and used as fire-resistant hydraulic fluids and metalworking fluids (MWFs) in industry. The (elasto-)hydrodynamic film-forming properties of O/W emulsions have been studied extensively in literature. Typical elastohydrodynamic lubrication (EHL) behaviors are revealed at low rolling speeds followed by a starved EHL regime at elevated speeds. These emulsions are self-prepared and mostly stable only for a limited time ranging from hours to several days. By contrast, the film-forming behavior of water-miscible commercial MWFs (long-term stable O/W emulsions) has rarely been reported. This restricts the understanding of the lubrication status of many tribological interfaces in manufacturing processes, e.g., the chip-tool contact in cutting. In this work, the (elasto-)hydrodynamic film-forming property of two commercial MWFs is investigated by measuring the film thickness on two ball-on-disc test rigs using different optical interferometry techniques. For comparison, two self-prepared simple O/W emulsions with known formulation have also been investigated. Experimental results from the two test rigs agree well and show that the two self-prepared emulsions have typical EHL behaviors as reported in literature. However, for the two commercial MWFs, there is almost no (elasto-)hydrodynamic film-forming ability over the whole range of speeds used in this study. This could be explained by the cleaning and re-emulsification effects of the MWFs. The lubrication mechanism of the two MWFs is mainly boundary lubrication rather than hydrodynamic lubrication.Graphical

The Effect of Rectangular Grooves on the Lubrication Mechanism in an Inclined Slider Bearing

This research aims to study the effect of rectangular grooves on the lubrication mechanism in an inclined slider bearing. Reynolds' equation was used in the theory part to calculate the pressure gradient in a one-dimensional fluid film. The tilted sliding bearing compared the practical results, where the researcher manufactured and developed the device by adding pressure sensors along with the pad. These sensors will give accurate readings because they will read the pressure directly from the bottom of the pads without manometer tubes. Four pads were manufactured, one without grooves and three with rectangular grooves, varying slot widths (3, 5, 8mm), and a depth of 2mm. This study examined various variables: sliding velocities, pad inclination values, and oil temperatures. The conclusions indicated that the flat model is significantly superior to the groove’s models. One significant finding for grooved models is that as the inclination increases, the maximum load capacity approaches the pad's center, allowing grooved models to be used in applications requiring less load and weight. The maximum load-carrying capacity of flat and grooved models was in the film ratio (K) = 2–2.5. In contrast, the load capacity of the flat model was greater than that of the groove model by percentages of 0.5%, 4.27%, and 14.66%, respectively. Moreover, the flat model's coefficient of friction is lower than the coefficient of friction of the groove models, with percentages of 0.38%, 4.63%, and 17.37%, respectively.

Copper phosphate nanosheets as high-performance oil-based nanoadditives: Tribological properties and lubrication mechanism

Geometric variables and surface chemistry of nanomaterials as lubricant additives both affect the details on the interacting frictional surface. Herein, copper phosphate nanosheets (CPNs) were synthesized by a simple and facile method, which exhibited extraordinary tribological properties as the novel lubricating oil nanoadditives. Compared with the base oil, the friction coefficient (COF) has been reduced by 77% by CPNs at a concentration of 20 wt%, which could also protect the titanium alloy surface from any measurable wear. But as the CPNs content increased to 25 wt%, the shear jamming caused by hydrogen bonding between crystal water in CPNs may interfere with lubrication. Besides, it is significantly effective in preventing the adhesions of titanium alloy on the surface of counterface at a suitable concentration. The extraordinary tribological performance is contributed to the nanosheets of copper phosphate but not the nanoparticles. Moreover, in the presence of CPNs, the tribo-film containing CPNs is formed during sliding contact, but this tribo-film can’t hold for a long time without CPNs, indicating that CPNs can well retain the tribo-film. However, the dominant factor for friction reduction and antiwear is not this tribo-film but the solid-liquid interface lubrication between nanosheets and lubricating oil. The Stribeck curves were used to explain how CPNs play a role in boundary lubrication and mixed lubrication.

A dynamic approach of frictional heating and thermal pressurization in landslides

Frictional heating and thermal pressurization mechanisms have been demonstrated by many researchers as vital lubrication mechanisms in landslides. However, in the previous model, plastic deformation is ignored while velocity profiles are assumed in the shear zone, which could lead to infinite growth of temperature when the landslide body keeps traveling on the sliding surface. This research aims to reveal the importance of plastic deformation in the thermo-poro-mechanical model and better understand the thermal effects in landslides. To achieve this aim, we established the plastic deformation process according to the assumed velocity profile. We proposed a dynamic thermo-poro-mechanical model by considering plastic deformation. A simplified numerical simulation and a sensitivity analysis were performed through the proposed dynamic model. Simulated results showed different and unique evolutions of temperature and excess pore pressure. While high values of temperature and excess pore pressure are still found at the top of the shear zone, thermal effects decrease dramatically at the bottom of the shear zone. Moreover, the sensitivity analysis indicates a much larger temperature and excess pore pressure at the rear of the landslide.

Physicochemical and tribological comparison of bio- and halogen-based ionic liquid lubricants

The friction and wear behavior of bio-based trihexyltetradecylphosphonium saccharinate [P6,6,6,14][Sacc] and halogen-based trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) amide [P6,6,6,14][NTF2] ionic liquids (ILs) were studied to understand their lubrication mechanisms at steel sliding interfaces. The physicochemical and tribological properties of the ILs were characterized over a wide temperature range (10–120 ℃) to reflect the conditions present in wind turbine applications. Friction increased with increasing temperature for both ILs. At any temperature, [P6,6,6,14][Sacc] had significantly higher viscosity that provided thicker lubricant films and, in turn, better friction and wear protection than the halogen-based [P6,6,6,14][NTF2]. [P6,6,6,14][Sacc] also had lower density, comparable thermal stability, more favorable wettability, and better corrosion performance than [P6,6,6,14][NTF2]. Simulations showed that the cohesion interaction energy was stronger for [P-Sacc] due to its smaller anion-cation distance. The higher viscosity and stronger cohesion of [P6,6,6,14][Sacc] than [P6,6,6,14][NTF2] contributed to the ability of the bio-based IL to form an effective adsorption film that reduced friction and wear across a range of temperatures.

Effect of Sliding Velocity on UHMWPE and VEXLPE Friction Against CoCr in Multidirectional, Serum Lubricated Conditions

Abstract The recently introduced four-station friction RandomPOD device was utilized in multidirectional, circular translation pin-on-disk (CTPOD) tests. The effect of sliding velocity on friction with orthopaedic bearing materials was studied. The tests included UHMWPE and VEXLPE pins against polished CoCr disks in serum lubrication at 37 °C. In the constant velocity tests, the sliding velocities used were from 5 to 50 mm/s at intervals of 5 mm/s. The test length with each velocity was 24 h. In the constant acceleration tests, the velocity steadily increased from 0 to 50 mm/s in 24 h. In all tests, the sample size was 4. No strong effect of velocity on friction was observed. This indicated a boundary lubrication mechanism. With sliding velocities above 10 mm/s, VEXLPE showed significantly lower friction than UHMWPE. The finding was in agreement with earlier dynamic RandomPOD tests. Clinically, the use of VEXLPE may result in lower frictional heating.

Lubrication Performance and Mechanism of Electrostatically Charged Alcohol Aqueous Solvents with Aluminum–Steel Contact

Alcohol aqueous solvents were prepared by individually adding n-propanol, isopropanol, 1,2-propanediol, and glycerol to deionized water for use as lubricants for the electrostatic minimum quantity lubrication (EMQL) machining of aluminum alloys. The tribological characteristics of those formulated alcohol solvents under EMQL were assessed using a four-ball configuration with an aluminum–steel contact, and their static chemisorption on the aluminum surfaces was investigated. It was found that the negatively charged alcohol lubricants (with charging voltages of −5 kV) resulted in 31% and 15% reductions in the coefficient of friction (COF) and wear scar diameter (WSD), respectively, in comparison with those generated using neutral alcohol lubricants. During the EMQL, static charges could help dissociate the alcohol molecules, generating more negative ions, which accelerated the chemisorption of those alcohol molecules on the aluminum surfaces and thereby yielded a relatively homogeneous-reacted film consisting of more carbon and oxygen. This lubricating film improved the interfacial lubrication, thus producing a better tribological performance for the aluminum alloys. The results achieved from this study will offer a new way to develop high-performance lubrication technologies for machining aluminum alloys.

The Current Situation and Future Direction of Nanoparticles Lubricant Additives in China

Nanoparticles as lubricant additives demonstrate powerful friction reduction and antiwear properties and are potential alternatives to traditional additives in line with green and environmentally friendly requirements. However, the vast majority of currently available research focuses on the tribological properties of various nanoparticles in base oils at laboratory, which has a large gap with their application in engineering. To cope with the rapid economic and industrial development in China, there is a need to improve the tribological properties of nanoparticles. This paper highlights the current status and development trend of nanoparticles as lubricant additives in China. The factors influencing the tribological properties of nanoparticles, such as their composition, particle size and morphology, as well as the base stocks and their combination with other additives, are summarized. Furthermore, the research progress in the lubrication mechanism of nanoparticles is discussed, and the issues concerning the application of nanoparticles as lubricant additives as well as their future directions are discussed. This review is expected to provide an impetus to guide the design of high-performance, fully formulated lubricant systems containing nanoparticles as the lubricant additive.

Development of lubrication film and influence on friction in a total knee replacement during a gait cycle

The presented study dealt with the experimental analysis of friction and lubrication mechanism observed with fluorescent microscopy in total knee replacement represented by CoCrMo wheel and PMMA plate. Model synovial fluid with marked constituents was used as test lubricant. The experiments investigated three main parameters. Slide-roll-ratio (SRR) showed the greatest influence on lubrication film formation. Friction coefficient was mostly influenced by axial load; its increase led to a decrease in friction. Relative speed was manifested for SRR 1.25 and higher where its increase caused a decrease in friction. The complex experiment showed a development of friction coefficient and lubrication film along the whole gait cycle. The results of this experiment correspond with the initial results concerning the influences of parameters.

Polyaniline Nanoparticles: A Novel Additive for Augmenting Thermal Conductivity and Tribo-Properties of Mineral Oil and Commercial Engine Oil

The present work demonstrates the novel composition of nanoparticles (NPs) of polyaniline (PANI) solo and, in combination with particles of polytetrafluoroethylene (PTFE) ~230 nm, as a powerful additive (antiwear-AWA and extreme-pressure additive EPA) in lubricating oils. The concentration of PANI NPs varied from 1–4 wt.% in a base oil and commercial 5W30 engine oil. The tribo-performance was evaluated on a four-ball tester. The PANI-based oils significantly enhanced the load-bearing ability, and 3 wt.% of PANI NPs led to enhancement in EP properties by 220% in a base oil and 58% in engine oil. Additionally, hybrid combinations of NPs of PTFE with PANI in base oil were prepared by mixing in a ratio of 3:1 and 2:1 and were explored for possible tribo-synergism in EP properties. The hybrid nano-oils led to the highest reported ~ 535% enhancement in the load-carrying capacity of mineral oil. The lubrication mechanisms for enhanced tribo performance were linked with studies on a scanning electron microscope, an energy-dispersive X-ray analyzer, and with the use of Raman spectroscopy.

Local Responses to Genital Arousal — Mechanisms of Lubrication

Local Responses to Genital Arousal — Mechanisms of Lubrication

In-situ measurement of the meniscus at the entry and exit of grease and oil lubricated rolling bearing contacts

The lubricant inlet meniscus in a rolling element bearing acts as a reservoir that feeds the elastohydrodynamic contact, resulting in a sufficiently thick film to avoid wear. A shortening and/or thinning of the inlet meniscus towards the contact centre is an indicator of bearing starvation and impaired lubricant performance. This work introduces an ultrasonic method to measure meniscus dimensions. Using in situ ultrasonic sensors on a full-scale cylindrical roller bearing test rig, we show that ultrasonic waves can cause oil films to resonate, and that the resonant frequency is directly related to the film thickness. Using a benchtop rig we validate the relationship between resonant frequency and film thickness. This allows for the measurement of meniscus thickness and length in situ during bearing operation. Menisci were measured at both the inlet and outlet of rolling bearing line contacts while lubricated with different viscosity oils and grease. All lubricants used showed they could be monitored using this approach. The implication of this paper is that it is possible to measure a critically important lubrication mechanism during operation without major component modifications.

Lubrication Performance and Mechanism of Water-Based TiO2 Nanolubricants in Micro Deep Drawing of Pure Titanium Foils

Micro deep drawing (MDD) is a fundamental process in microforming which has wide applications in micro electromechanical system (MEMS) and biological engineering. Titanium possesses excellent mechanical properties and biocompatibility, which makes it a preferred material in micromanufacturing. In this study, eco-friendly and low-cost water-based TiO2 nanolubricants were developed and applied in the MDD with 40 μm-thick pure titanium foils. The lubricants consisting of TiO2 nanoparticles (NPs), 10 wt% glycerol, 0.1 wt% sodium dodecyl-benzene sulfonate (SDBS) and balanced water were synthesised in a facile process. The MDD with 40 μm-thick pure titanium was carried out using the lubricants with varying concentrations of 0.5, 1.0 and 2.0 wt%. The results show that the formability of micro cups could be significantly improved when the nanolubricants are applied. Especially, the use of 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and the wrinkles by up to 24.2%, 12.55% and 4.82%, respectively. The lubrication mechanisms including the ball bearing and mending effects of NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructure observation.

Effect of Contact Conformity on Grease Lubrication

This work focused on the experimental study of grease lubrication mechanisms around contacts in radial ball bearing 6314. The main objective of this work was to show the influence of conformities and their impact on grease lubrication in ball bearings. For the experiments, a tribometer of ball-on-ring configuration was used and fluorescence microscopy was chosen as the observation method. The results showed that, under starvation conditions, a conformity of 0.52 at velocities around 2 m/s produces a 50% thicker lubricating film than a conformity of 0.58. The available amount of lubricant around the contact area for conformity 0.52 was approximately three times less than that for conformity 0.58, and the same ratio was observed for the amount of lubricant on the rolling track. Experiments show that a realistic tribometer geometry allows a more accurate experimental study of the lubrication mechanisms of greases in ball bearings.

Lubrication Mechanism of Surface‐Attached Hydrogel Layers in Sliding Contact

AbstractSwollen, surface‐attached hydrogel layers in sliding contact exhibit unusual friction properties. To study this phenomenon, hydrogel layers covalently bonded to solid substrates are generated by CH insertion crosslinking. Brief UV irradiation of thin layers of photoreactive prepolymers leads to simultaneous crosslinking of the polymer chains and attachment of the network to the substrate. As the surface‐attached hydrogel layers can only swell perpendicular to the surface, and the polymer subchains on the two sides of the friction pair cannot interpenetrate for entropic reasons, adhesion in such friction pairs is negligible. In this work, the tribological behavior of surface‐attached hydrogel pairs is investigated as a function of load and sliding velocity. It is observed that for very thin films, the indentation and accordingly the friction is a strong function of the film thickness and the role of the chain confinement on the lubrication of surface‐attached hydrogels is discussed. A model for the friction mechanism of such systems is developed.

A Review of Nanomaterials with Different Dimensions as Lubricant Additives.

Lubricant additives can effectively enhance the performance and environmental adaptability of lubricants and reduce the energy loss and machine wear caused by friction. Nanomaterials, as important additive materials, have an essential role in the research and development of new lubricants, whose lubrication performances and mechanisms are not only related to their physical and chemical properties, but also influenced by the geometric shape. In this paper, the friction reduction and antiwear performances of nanomaterials as lubricant additives are first reviewed according to the classification of the dimensions, and their lubrication mechanisms and influence rules are revealed. Second, the recent research progress of composite nanomaterials as lubrication additives is introduced, focusing on their synergistic mechanism to improve the lubrication performance further. Finally, we briefly discuss the challenges faced by nanoadditives and provide an outlook on future research. The review expects to provide new ideas for the selection and development of lubricant additives to expand the application of nanoadditives.