Lubrication Conditions Research Articles

Study on the Effect of Starved Lubrication on the Dynamic Characteristics of Locally Failed Roller Bearings

When the lubricant is not enough to maintain the ideal lubrication state of the bearing, the deep groove ball bearing will enter the starved lubrication state, which leads to the change of the vibration response of the deep groove ball bearing with localized defects. Previous bearing dynamics models mainly consider the lubrication state as an ideal lubrication condition, which may not reveal the effect of starved lubrication on the vibration characteristics of defective bearings. In this paper, the internal interaction of the system under starved condition is taken into account, and a dynamic model of defective deep groove ball bearings with insufficient lubricant is established to investigate the effects of different starved lubrication degrees on the contact force, friction force, cage speed, and system vibration characteristics. The results show that the lubricant insufficiency significantly changes the contact force inside the bearing, and the increase in friction caused by the increase in the degree of starved lubrication leads to the suppression of the degree of bearing slipping. The root mean square (RMS) value of the time-domain signal and the outer ring fault frequency both increase with the increase of the starved degree. The results of the study are helpful for fault diagnosis and condition monitoring of related equipment.

Effect of Shot‐Peening Process and Nanoparticle‐Added Lubricant on the Tribological Performance of Aluminium‐Based Sliding Bearing Material

ABSTRACTIn this study, it is aimed to increase the wear and fatigue performance of aluminium‐based sliding bearing material by using silver nanoparticles (AgNPs) added lubricant and shot‐peening process. The main purpose is to minimise the wear of the bearing material by penetrating AgNPs added lubricants into the rough surfaces formed by shot peening. Almen intensity, coverage and shot size parameters in the shot‐peening process were analysed in terms of hardness, surface roughness and fatigue strength. The shot‐peened aluminium bronze was subjected to wear experiments under dry, pure water and AgNPs added lubricant conditions. The wear test results were analysed in terms of friction coefficient, wear volume and surface roughness parameters, and the interaction of lubricant and shot‐peening parameters was evaluated. According to the results of the shot‐peening experiments, the Almen intensity was the most effective parameter in terms of hardness and surface roughness (91.62%). It was concluded that the hardness value was 8% higher at high Almen (12–14A) intensity compared with low Almen intensities, and the shot‐peening process could increase the fatigue strength by ~21 times. According to the wear tests, the most effective parameters were 4–6 Almen intensity and AgNP‐added lubricant.

Wear Characteristics of Textured Floating Oil Seal Surfaces: A Simulation and Experimental Study

This study aimed to analyze the effects of surface texture on the wear amount of floating oil seals and how these effects are related to the texture parameters. To achieve this, a finite element model was constructed to simulate the frictional behavior of seal discs under both textured and non-textured conditions. The study focused on a specific set of texture parameters. The texture depth was held constant, while the area density and diameter of the textures were varied. Three different area densities were considered: 10%, 20%, and 30%. Similarly, three different texture diameters were included in the study: 100, 200, and 300 μm. For each combination of area density and diameter, three different texture depths were evaluated: 50, 100, and 150 μm. The results show that compared with the non-texture, the wear loss of the texture is significantly reduced, and the wear loss is reduced by 56.8%. As the texture depth increases, the corresponding increase in wear remains relatively small. In contrast, increasing the texture diameter and area density leads to a more significant increase in wear, indicating that these two parameters have a more significant effect on the wear behavior of the seal. Under the condition of dry friction, the average friction coefficient analysis shows that the texture area density is 30%, the texture diameter is 200 μm, and the minimum value is about 0.602. Under the lubrication condition, the lowest average friction coefficient is about 0.147, the texture area density is 20%, and the texture diameter is 300 μm.

Tribological behavior and mechanism of Ti3SiC2/Cu composites in a wide temperature range under lubrication condition

Preparation of Ti3SiC2/Cu composites using Spark Plasma Sintering (SPS) process. The friction and wear behavior of Ti3SiC2/Cu-45# steel tribo-pair under lubrication conditions was investigated in a wide temperatures range. The results demonstrated that the influence of temperature on the tribological properties of the Ti3SiC2/Cu-45# steel tribo-pair under lubrication condition was characterized by a continuous transition from a lubricant to an oxide film. At 200 ℃, mobility of the lubricant increased and the friction interface was in the boundary lubrication state. As the temperature increased, the base oil in the lubricant rapidly evaporated, causing to solidification of the lubricant, and the friction interface formed the friction oxide film. The mechanisms of friction and wear were primarily abrasive wear and tribo-oxidation wear.

Visualising the lubrication condition in hydrodynamic journal bearings using impedance measurement

Visualising the lubrication condition in hydrodynamic journal bearings using impedance measurement

Superlubricity in solid lubricated sliding and rolling contacts

Superlubricity, or near zero friction is a highly desired lubrication state for a wide range of practical applications. Although such application scenarios often involve complex contact geometries, solid lubricant technologies, including previous efforts on achieving superlubricity, are almost entirely in linear sliding test conditions. This report demonstrates an experimental pathway to yield superlubricity in rolling-sliding contact conditions using solid-lubricant materials. Ti3C2X based solid lubricant was tested under complex sliding-rolling conditions at engineering-significant contact pressures. The material's compression and inter-layer shearing result in material reconstruction to pose superlubricity. High-resolution transmission electron microscopy analysis, complemented by multi-scan Raman spectroscopy showed the formation of a robust amorphous tribolayer. This demonstration is expected to not only advance the applied aspects in the development of oil-free solid lubricants but also push the boundaries of fundamental understanding of materials’ structure-property relations across physical states.

Machining and Sustainability Performance Comparison for the Milling Process of Al6082 Alloy Under Various Minimum Quantity Lubrication Conditions

Machining and Sustainability Performance Comparison for the Milling Process of Al6082 Alloy Under Various Minimum Quantity Lubrication Conditions

Lubrication condition monitoring of journal bearings in diesel engine based on thermoelectricity

There is still a lack of effective lubrication condition monitoring methods in the field of diesel engines. The paper proposes a novel thermoelectric approach to divide the lubrication state of bearings. First, the generation mechanism of thermoelectric potential on bearings is clarified. Then, both experimental and simulation studies are done, and a strong correlation between lubrication and thermoelectric potential is shown. The film thickness and temperature are further confirmed as significant factors influencing thermoelectric potential. Generally, the thermoelectric potential increases with temperature. However, a small film thickness ratio (when the film thickness ratio is less than 4) will suppress the thermoelectric potential. Three typical lubrication states of bearings are distinguished through thermoelectric potential and supported by the Stribeck curve results. Moreover, the significant influence of lubrication on the bearing is confirmed through the analysis of surface morphology and composition.

Influence of Lubrication Cycle Parameters on Hydrodynamic Linear Guides through Simultaneous Monitoring of Oil Film Pressure and Floating Heights

Hydrodynamic linear guides in machine tools offer a high load capacity and excellent damping characteristics, improving stability, precision, and vibration reduction. This study builds on previous research where floating heights were verified with a simulation model limited to measured floating heights. Advancements include incorporating pressure sensors into a fixed steel rail, enabling simultaneous measurement of oil film pressure and floating heights for a comprehensive understanding of lubrication conditions within the lubrication gap. The experimental results explore the effects of different lubrication methods, providing valuable insights into cavitation and lubrication adequacy. The results demonstrate the feasibility of utilizing pressure sensors to measure oil film pressure within the lubrication gap, providing a nuanced understanding of lubrication dynamics. By measuring both floating heights and pressure measurement, distinctions between hydrodynamic lubrication, mixed friction regions, and instances of lubricant deficiency become readily discernible. The variations in real-time oil film pressure and floating heights help to optimize the lubrication cycle for hydrodynamic linear guides, enhancing system performance and longevity.

Optimum texture shape under different lubrication conditions applied to the start-up phase of journal bearings

This paper presents a parameterized model to optimize the texture units using an improved particle swarm optimization. The texture units are optimized under three lubrication states: boundary lubrication, mixed lubrication, and hydrodynamic lubrication, by utilizing the Stribeck curve. The optimal texture units can be applied to journal bearings and thrust bearings in different operating conditions to achieve maximum load-carrying capacity. The paper applies the optimal textures under the three lubrication states to the start-up stage of journal bearings to examine the lubrication performance and dynamic characteristics of the textured journal bearing system. The results demonstrate that compared to the untextured journal-bearing system, the introduction of optimal textures improves the tribological performance of the journal-bearing system, and the optimal textured units under hydrodynamic lubrication have the best friction reduction effect. Furthermore, it is found that the introduction of textures has no significant effect on the dynamic characteristics of the journal bearings.

Investigation of the tribological behaviors for 4H–SiC substrate under different lubrication conditions

Lubrication conditions are an important factor affecting both the machining efficiency and quality of 4H–SiC. To investigate the tribological behaviors under different lubrication conditions, a series of scratching experiments are conducted under different loads and environments. The X-ray photoelectron spectroscopy (XPS) surveys and atomistic simulations are used to explain the different tribological behaviors. Both experimental and simulation results show that liquid lubrication can significantly reduce the coefficient of friction (COF) and minimize structural damage. Compared to pure water, the H2O2 solution is more conducive to the oxidation of SiC atoms and the modification of tribological behaviors. However, the difference in tribological behaviors between H2O2 solution and pure water diminishes as the load increases. The XPS surveys show that the liquids lead to higher-order oxidized species of SiC atoms, such as Si4C4-xO2 and Si-Ox-Cy, which are also observed in the simulation results. It is shown that the oxidized species can reduce the direct bonding between SiC and diamond indenter, which is an important reason for the lower COFs in the liquids. Since the liquids can reduce the direct bonding and mechanical interaction between 4H–SiC and diamond, the material removal rate is much lower under lubrication conditions.

The role of manufacturing-induced texture on the tribological performance of cold work tool steels

Manufacturing operations produce surface characteristics that, although stochastic, can significantly affect functionality, especially in forming tools, impacting contact and lubrication conditions during operation. This study investigates the influence of stochastic microtextures resulting from milling on the tribological performance of cold work tool steels with two different carbon contents (0.8 and 2 wt%). Different surface textures were observed resulting from the different C contents, with 3D roughness parameters indicating rougher surfaces for the 2.0% wt. C steel. Tribological behavior was assessed using the strip drawing test to analyze friction, wear coefficients, and wear mechanisms. Surface analysis before and after testing was executed employing SEM, EDX, and CLSM, with CLSM also used to determine 3D roughness parameters of the worn tracks. Post-test macrographic analyses and 2D roughness measurements were conducted on the pulled sheets. Tribological test data revealed lower friction and wear coefficients for the 2.0 wt% C tool steel, with susceptibility to abrasion wear, while the 0.8 wt% C tool exhibited a higher tendency towards adhesion wear. Post-test analysis suggested smoother surfaces for the 2.0 wt% C steel compared to the 0.8 wt% C steel. Macrographic analysis showed no visible wear marks on sheets tested with the 2.0 wt% C steel, contrasting with wear grooves visible on sheets pulled against the 0.8 wt% C steel. Additionally, 2D roughness measurements indicated higher roughness after pulling against the 0.8 wt% C tool compared to the 2.0 wt. C tool. Overall, the study demonstrates that manufacturing-induced textures without the need of post-manufacturing texturing influence the tribological performance of the evaluated steels, opening an avenue to be explored to improve the tribological performance of forming tools.

Simulation-based research on enhancing lubricity: investigating wettability and textured surfaces in alkane lubricants under boundary lubrication conditions.

Changing the wettability and surface texturing have a significant impact on lubrication. In this study, the researchers used the molecular dynamics (MD) method to investigate how adjusting the interaction between alkanes and the wall affects oil film morphology and frictional properties under boundary lubrication. The findings revealed that the bearing capacity was influenced by both the morphology of the oil film and the strength of solid-liquid adsorption. In cases where the walls had weak wettability, the alkanes formed clusters to effectively separate the walls, while in cases where the walls had strong wettability, the oil film spread and formed a strong adsorption film. The super oleophilic textured surface could enhance the oil film adsorption capacity and replenish the oil film to the friction area in time, and the super oleophobic smooth surface could further reduce the friction coefficient. Therefore, a composite surface consisting of a super oleophilic textured surface and a super oleophobic smooth surface can be designed to enhance the bearing capacity of the oil film and reduce friction.

The effects of medium and friction pair on the tribological behavior of Mo-doped DLC films

Diamond-like carbon (DLC) films are widely used to improve the tribological properties of key components in internal combustion engines. However, their performance can be significantly affected by the service environment, which may impact engine reliability. This study investigates the impact of various media and friction pairs on the tribological behavior of molybdenum-doped DLC (Mo-DLC) films. The results demonstrate that Mo-DLC films exhibit excellent tribological properties across different media, showcasing their adaptability to various conditions. The lubrication mechanism varies with media viscosity: in methanol, Mo-DLC films operate under boundary lubrication conditions, leading to a relatively high wear rate of approximately 5.2 × 10−8 mm3/N·m. Conversely, in diesel and polyalphaolefin-based oil (PAO), where fluid dynamic lubrication occurs, wear rates are significantly lower, at 4.4 × 10−8 mm3/N·m and 3.1 × 10−8 mm3/N·m, respectively. In addition, the friction pair significantly influences the tribological performance of the Mo-DLC film. When paired with D-GCr15 in methanol, Mo-DLC films exhibit a low friction coefficient of 0.09 and a wear rate of 1.6 × 10−8 mm3/N·m, respectively. However, when coupled with N-GCr15, the increased surface roughness extends the running-in period and raises the friction coefficient in methanol. These findings offer valuable theoretical insights and practical guidance for optimizing DLC films in internal combustion engines.

Influence of pore structures on friction and wear properties of iron-based oil-containing composites under dry and self-lubricated sliding conditions

This study successfully prepares iron-based oil-containing materials with connected porous structures using TiH2 and nylon 66 short fibers as pore-forming agents. The dehydrogenation of TiH2 can produce large pore cavities and the nylon 66 short fiber with a highly regular shape has a unique advantage in pore channel production. Compared to the iron-based specimen without the pore-forming agent, the oil content of the iron-based specimen with the two pore-forming agents increases by 33.86 %. The tribologica23ee3l properties of the iron-based oil-containing materials under dry and self-lubricated sliding conditions are evaluated using the MM-200 ring-block sliding tribometer and the HDM-20 end-face friction and wear tester, respectively. Special emphasis is given to the effect of pore structures on wear patterns. The results showed that the material's surface is subjected to significant shear failure under dry sliding conditions, leading to the closure of pores due to plastic deformation during the initial sliding. The connected pore structure is a non-dense region, allowing shear damage to occur in the deeper subsurface of the matrix and increasing the material's wear rate. Under self-lubricated conditions, the connected pore structure facilitates the rapid release of lubricating oil, improves the initial lubrication state, and delays pore closure. As compared with dry friction, the wear rate can be reduced by two orders of magnitude under self-lubricating conditions. At a sliding speed of 0.46 m/s, an appropriate load (about 900 N) can enhance the material's ability to continuously and rapidly supply oil.

Effect of Grease Composition on Impact-Sliding Wear

Impact-sliding experiments were performed by using four self-made lithium-based greases, namely Yangtze Grease 1, Yangtze Grease 2, Yangtze Grease 3, and Yangtze Grease 4. The influence of base oil viscosity, thickener content, and morphology of thickener fiber clusters on the lubricating state were visually explored, combined with field-emission microscopy and two-light interference technology. The grease film distribution at the middle section was measured using Dichromatic Interference Intensity Modulation (DIIM) software. All experiments were executed in a completely flooded environment. The results show that among the components of grease, the base oil’s viscosity has the greatest impact on the anti-wear performance of the grease. As the viscosity of the base oil increases, the grease exhibits better anti-wear performance. The grease film thickness under the condition of high-viscosity base oil is about 10 times higher than that under the condition of low-viscosity base oil. Secondly, the content of thickener in the grease needs to be controlled within a reasonable range. The experiments indicate that the effect of thickener content on the grease’s film-forming properties becomes more pronounced at higher speeds. From the experiment using YG 4, it can be seen that a higher thickener content under high-speed conditions increases the thickness of the lubricating grease film by about 10 times. The dimensions of the thickener fibers and the density of their entanglement structure significantly influence the rheological properties and load-bearing capacity of the grease. Larger fiber sizes and higher entanglement densities result in reduced grease fluidity and recovery but enhance its load-bearing capabilities. In order to obtain the best anti-wear performance during impact-sliding motion, the size of the thickener fiber and the density of the entanglement structure need to be controlled within an appropriate range.

Wear Performance Evaluation of Polymer Overlays on Engine Bearings.

Modern engine bearing materials encounter the challenge of functioning under conditions of mixed lubrication, low viscosity oils, downsizing, start-stop engines, potentially leading to metal-to-metal contact and, subsequently, premature bearing failure. In this work, two types of polymer overlays were applied to the bearing surface to compensate for extreme conditions, such as excessive loads and mixed lubrication. Two different polymer overlays, created through a curing process on a conventional engine bearing surface with an approximate thickness of 13 µm, were investigated for their friction and wear resistances under a 30 N load using a pin-on-disc setup. The results indicate that the newly developed polymer overlay (NDP, PAI-based coating) surface has a coefficient of friction (COF) of 0.155 and a wear volume loss of 0.010 cm3. In contrast, the currently used polymer overlay (CPO) in this field shows higher values with a COF of 0.378 and a wear volume loss of 0.024 cm3, which is significantly greater than that of the NDP. It was found that, in addition to accurately selecting the ratios of solid lubricants, polymer resins, and wear-resistant hard particle additives (metal powders, metal oxides, carbides, etc.) within the polymer coating, the effective presence of a transfer film providing low friction on the counter surface also played a crucial role.

Thermal Characteristics of Oil Film in Critical Lubrication State of Heavy Hydrostatic Bearing

Background: Lubrication failure has always been a concern in the research of heavy hydrostatic bearings. A preliminary study found that under a certain working condition, the heavy hydrostatic bearing will appear in the condition of zero local flow of oil film, which is called a critical lubrication state. It produces a significant thermal accumulation effect and affects the lubrication performance of the bearing. Objective: This paper takes Q1-205 double rectangular cavity hydrostatic thrust bearing as the research object and adopts the research method combining theoretical analysis, simulation, and experimental test to analyze the temperature rise and characteristics of the bearing when it is in critical lubrication state under different working conditions. Methods: The finite volume method is used to simulate the critical lubrication state under the condition of common load and rotating speed, and the corresponding operating parameters of the critical lubrication of heavy static support are obtained. Results: It is found that when the oil film is in the critical lubrication state, the low temperature zone is concentrated at the bearing position of the oil film, while the high temperature zone is concentrated at the counter-current side sealing edge Conclusion: The oil film's local temperature rise is intensified, and the heat accumulation phenomenon is serious because the heat cannot be taken away in time.

Nonlinear Dynamics and Meshing State Transition Analysis of Spalling Defect Gears with Multi-Lubrication Conditions

The purpose of this paper is to analyze the dynamic characteristics and the meshing state transition characteristics of spalling defect gears under various lubrication conditions. The time-varying geometric parameters, motion parameters and load distribution of the gears in the state of positive meshing and reverse impact are analyzed. The time-varying meshing stiffness considering the time-varying friction coefficient under elastohydrodynamic lubrication (EHL), mixed lubrication and boundary lubrication are calculated, and the spalling defect is introduced in the stiffness calculation process. The equivalent lubrication model of the gear is established, the switching condition of the lubrication state is derived, and the distribution of the lubrication state in the torque-speed plane is discussed. The multimeshing state dynamic model of the spalling defect gear is established, and the evolution characteristics of the coexistence response and the transition of the meshing state under different lubrication conditions are simulated by using the attraction domain, phase trajectory, meshing force and bifurcation diagram. The results show that the phase trajectory of the gear with the spalling defect is deformed compared with that of the healthy gear. The change of lubrication state has little effect on the phase trajectory and attraction domain of the gear with spalling defect, but has a great influence on the meshing force. At the spalling boundary, the meshing force is changed abruptly, and the worse the lubrication state, the more obvious the mutation. Due to the influence of spalling on tooth stiffness, it will also affect the meshing force in the nonspalling area.

Exploring the Impact of HFO-1234YF Refrigerant on the Tribological Properties of Advanced Polymeric Coatings

Abstract The global focus has shifted toward mitigating the impact of global warming, particularly in the air-conditioning and refrigeration sectors, where there is a strong emphasis on the use of environmentally friendly refrigerants. One such refrigerant that has gained increased usage is HFO-1234yf. The increasing use of HFO-1234yf as a refrigerant in automobile air-conditioning compressors presents new challenges in terms of material compatibility. In this research, we investigate the impact of HFO-1234yf in automobile compressor applications by comparing the tribological results of the same materials in air. We conducted tribological experiments under starved lubrication conditions using polyetheretherketone (PEEK)/polytetrafluoroethylene (PTFE) and aromatic thermosetting co-polyesters (ATSP)/PTFE-coated aluminum alloy samples. We found that the ATSP/PTFE coatings perform exceptionally well irrespective of the atmosphere, while the presence of HFO-1234yf refrigerant adversely affects the tribological performance of the PEEK/PTFE coatings, citing the lack of a stable tribofilm formation. These findings offer valuable insights for the development of materials and lubricants that are compatible with HFO-1234yf refrigerant applications.