Starved Lubrication Conditions Research Articles

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.

Molybdenum Disilicide (MoSi2) and Ferrophosphorus Particles (FemPn) Improve the Anti-Seizure Properties of Copper-Tin-Bismuth Composites under Conformal and Nonconformal Contacts

Seizure is a severe accident that can abruptly stop or even damage running equipment. Improving the anti-seizure properties of friction pair materials is also crucial as lubricating and wear resistance. While the tribological performances of molybdenum disilicide (MoSi2) and ferrophosphorus (FemPn) particle-doped copper-tin-bismuth (Cu-Sn-Bi) composites have been investigated in previous studies, the specific effects of MoSi2 and FemPn particles on the anti-seizure property of Cu-Sn-Bi materials remain unclear. This study explores the seizure resistance of Cu-Sn-Bi composites containing MoSi2 and/or FemPn under conformal and nonconformal contact conditions. The materials were prepared using powder sintering technology, and the metallographic structures of four types of self-lubricating copper composites were observed. Seizure resistance under starved lubrication conditions was investigated, and the worn surfaces under different contact types were discussed and analyzed. The results indicate that the addition of MoSi2 and/or FemPn particles effectively refines the grain size, and these particles exhibit different distribution trends after powder sintering. The MoSi2 and FemPn particles improved the maximum seizure load of copper-based composite samples by 66.67% and 84.62%, respectively. The seizure forms under different contact types were also discussed.

Dynamic performance analysis of ball bearings with multi-factor coupling excitation

Skidding behavior and unstable cage whirling of bearings are key factors limiting the service performance of a spindle-bearing system. This study proposes an improved dynamic model of ball bearings focusing on structure deformations and poor lubrication conditions. The ring deformations induced by the radial preload for the spindle-bearing-pedestal mechanical system are first discussed, and the asperity contact and starved lubrication conditions on the traction effect are further considered. Then, the cage flexibility induced by the centrifugal effect is determined by the lumped mass method, and cage clearance deformations are analyzed. On this basis, the dynamic equations are derived by investigating the motions and stress states among the bearing components, and the calculations are compared with experimental data to verify their accuracy and reliability. Finally, the regulatory mechanism of bearing skidding and cage motion stability from the perspective of bearing preload and structural parameters is revealed. The results show that although surface roughness and starved lubrication weaken the lubrication conditions of the ball-race, the traction effect is enhanced to reduce bearing skidding. Compared with the curvature radius of inner race, the groove diameter decreases the cage guiding effect, and ensures cage motion stability by suppressing the collision behavior of the ball-pocket. The system preload is more effective for improving the bearing service performance, which can optimize the collision force of the ball-pocket and increase the cage guiding effect.

Effect of bearing size on film thickness in grease-lubricated axially loaded deep groove ball bearings

Estimating the film thickness in a grease lubricated bearing in the post-churning phase is complex because of the prevalent starved lubrication conditions. In our earlier work, we showed that the relative film thickness (hg/hff) in an axially loaded 6209 deep groove ball bearing (DGBB) depends on the product of viscosity, load and linear speed (ηbu). In this article, we present the results of experiments performed using bearings of different sizes – 6204, 6206, 6209 – and show that the relative film thickness maintains a power-law relationship with ηbu, independent of the bearing size.

Laser Melting and Surface Texture Technology: Effect on Friction Properties

This paper discusses the role of laser surface texturing and laser melting technology in enhancing surface lubrication and wear resistance under starved lubrication conditions. The aim is to enhance the wear resistance of laser surface texturing and to explore the role of surface texturing in enhancing lubrication. This paper observes the microstructure of the melting zone, transition zone and matrix of the base material Cr12MoV after laser melting and condensing, detects and analyses the metallographic composition, and tests the micro-hardness. The effects of laser surface texturing technology and laser melting technology on the coefficient of friction under different friction and wear environments were comparatively investigated. The laser melting zone consists of martensite with fine grain size and a large amount of residual austenite. After laser melting, the hardness reaches 1.4 times the hardness of the matrix. The laser surface texture increases lubrication significantly at low rpm. The fully fusion-coagulated treatment is wear-resistant in a variety of different frictional wear environments.

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Electric vehicle (EV) transmissions operate at high speeds. High-speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. The high mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATFs. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matching the lubricant and hardware characteristics for optimal performance. In the present communication, we demonstrate the effects of different lubricants and surface finishing technologies on the tribology of high-speed gears using tribological tests and advanced thermal elastohydrodynamic (TEHD) simulations. The important roles of lubricity additives and surface finish optimization are highlighted in conjunction with a move towards ultralow viscosity EV transmission fluids.

Influence of micro-texture radial depth variations on the tribological and vibration characteristics of rolling bearings under starved lubrication

Surface micro-texturing involves creating microscopic pits or textures, serving as lubricant reservoirs to enhance lubrication distribution, potentially reducing friction and wear. This study specifically delves into the influence of varied depth patterns of pits on the operational performance of textured rolling bearings under severe lubrication conditions. Five distinct patterns with a fixed pit diameter (250 µm) and different depth variations (concave, decreasing, increasing, convex, and horizontal) were introduced on the shaft rings of cylindrical roller thrust bearings using the laser marking method. Wear tests were conducted under starved lubrication condition. Wear loss and signal analysis highlight the profound effect of depth variations, whereby bearings with shallow pits near the outer side of their working surfaces exhibit longer lubrication times, improved tribological performance, and enhanced vibration characteristics. Notably, the convex pattern stands out for providing comprehensive and favorable tribological and vibration properties. This research contributes valuable insights for the optimal design of micro-textures for rolling bearings, paving the way for enhanced efficiency and reliability in mechanical systems.

Effects and optimization of bionic texture parameters on the tribological behavior of line contacts under starved lubrication conditions

PurposeGears are prone to instantaneous failure when operating under extreme conditions, affecting the machinery’s service life. With numerous types of gear meshing and complex operating conditions, this study focuses on the gear–rack mechanism. This study aims to analyze the effects and optimization of biomimetic texture parameters on the line contact tribological behavior of gear–rack mechanisms under starvation lubrication conditions.Design/methodology/approachInspired by the microstructure of shark skin surface, a diamond-shaped biomimetic texture was designed to improve the tribological performance of gear–rack mechanism under starved lubrication conditions. The line contact meshing process of gear–rack mechanisms under lubrication-deficient conditions was simulated by using a block-on-ring test. Using the response surface method, this paper analyzed the effects of bionic texture parameters (width, depth and spacing) on the tribological performance (friction coefficient and wear amount) of tested samples under line contact and starved lubrication conditions.FindingsThe experimental results show an optimal proportional relationship between the texture parameters, which made the tribological performance of the tested samples the best. The texture parameters were optimized by using the main objective function method, and the preferred combination of parameters was a width of 69 µm, depth of 24 µm and spacing of 1,162 µm.Originality/valueThe research results have practical guiding significance for designing line contact motion pairs surface texture and provide a theoretical basis for optimizing line contact motion pairs tribological performance under extreme working conditions.

Vibration-based identification of lubrication starved bearing using spectral centroid indicator combined with minimum entropy deconvolution

For bearings under starved lubrication conditions, direct contacts occur between metallic surfaces, leading to random impulses in vibration response. This paper proposes a vibration-based scheme for starved lubrication identification. Minimum entropy deconvolution (MED) is utilized to enhance the weak random impulses caused by lubricant starvation. Moreover, a starved lubrication feature (SLF) based on the spectral centroid indicator is constructed to diagnose starved lubrication. The efficacy is verified by a comparative study conducted on a bearing test bench. Bearing vibration signals under two lubrication conditions are collected at different rotating speeds. The kurtosis of raw signals under starved lubrication is less than 4, but increases to above 7 after MED. For evaluation of lubrication conditions classification, the Davies-Bouldin index (DBI) of SLF is 0.042, significantly better than that of traditional characteristics (RMS DBI = 0.484, kurtosis DBI = 0.559). The results indicate that the SLF can identify starved lubrication conditions under different speeds.

Polymeric Coatings With Superior Tribological Performance for Lightweight Materials in HFO-1234yf Refrigerant

As global warming concerns continue to rise, research has shifted toward developing more climate-friendly refrigerants for air-conditioning and refrigeration compressors, with HFO-1234yf being a prominent candidate. In line with the need for lightweight engineering in electric vehicles, advanced composite coatings are necessary to improve the surface properties of parts and system components made from light metals such as magnesium and aluminum, which typically have poor tribological performance. This study investigates the tribological performance of advanced polymeric coatings (aromatic thermosetting copolyester [ATSP]-, polytetrafluoroethylene [PTFE]-, and polyether ether ketone [PEEK]-based) on lightweight aluminum alloy substrates in the presence of HFO-1234yf refrigerant and polyalkylene glycol (PAG) lubricant under starved lubrication conditions. Using a high-pressure tribometer, scuffing pressure, friction, and wear experiments were conducted, with all three coatings exhibiting excellent tribological performance compared to the bare substrate. Notably, PEEK and ATSP coatings demonstrated superior performance with high load-to-failure, low coefficient of friction, and negligible wear. Results also showed ATSP to have superior durability against a broad range of stress levels, while PEEK coating partially wears out at higher stress levels. These findings provide valuable insights for developing robust coatings on lightweight materials for high-stress applications.

A textured surface with oil inflow and outflow function designed for starved lubrication

This study presents a surface, referred as ‘pocket-textured surface’, which combines traditional surface texture with the oil storage pocket that can improve the tribological performance of line contact under extremely starved lubrication conditions. The pocket-textured surface has up to 48% lower friction coefficient than the untextured surface with the same little lubricant supply. Tribological experiments were carried out to explore the tribological behavior of pocket-textured surfaces with different ratios of texture hole depth and oil pocket depth under different loads and sliding speeds. In addition, a high-speed camera observed the lubricant inflow and outflow, and Ansys simulation calculated the deformations and pressures of the pocket-textured surface.

Effect of compound pit textures on the friction and wear of thrust cylindrical roller bearings under starved lubrication

PurposeThis study aims to investigate the effect of compound pit textures on the tribological properties of thrust cylindrical roller bearings (TCRBs) using several parameters, such as compound type, pit diameter, pit depth and pit area density.Design/methodology/approachThe surface texture parameters of the shaft washer (WS) raceway include pit diameter (D; 100, 300 and 500 µm), pit depth (H; 10 and 20 µm) and pit area density (S; 10%, 13% and 18%). Pits were produced on the WS of the TCRBs using laser marking equipment. The friction and wear performances of compound pit-textured TCRBs under starved lubrication conditions are studied using a friction and wear test rig. The influence mechanisms of the compound pit texture on the friction and wear properties of TCRBs are discussed through real tests and discussions.FindingsCompared with nontextured bearings, the average coefficient of friction (ACOFs) and wear loss of TCRBs with single/compound pit textures are reduced when rotating under starved lubrication. D has the greatest effect on the COFs curve. When D = 300 µm, H = 10 µm and S = 10%, the ACOF and wear loss are the lowest, that is, 0.0207 and 3.38 mg, respectively. Under the same lubrication conditions, compared with the nontextured bearing group, the COF and wear loss are reduced by 41.4 and 59.6%, respectively.Originality/valueThis study provides a useful reference for the raceways of textured TCRBs.

Preparation and Modification of Porous Polyetheretherketone (PEEK) Cage Material Based on Fused Deposition Modeling (FDM).

To address the problems of the difficult processing and internal microstructure disorder of porous bearing cages, Polyetheretherketone (PEEK) porous self-lubricating bearing cage material was prepared based on a fused deposition molding (FDM) process, and the porous samples were heat-treated on this basis, the research was carried out around the synergistic design of the material preparation, microstructure, and tribological properties. The results show that the pore size of the PEEK porous material prepared by the FDM process meets the requirements of the porous bearing cage; the samples with higher porosity also have higher oil content, and all the samples show high oil retention. Under dry friction conditions, the higher the porosity of the porous material, the larger the friction coefficient, and the friction coefficients of each sample after heat treatment show the same pattern; under starved lubrication conditions, the friction coefficient of the porous PEEK material decreased significantly compared to the compact PEEK material, showing a better self-lubrication effect, and the porous samples reached the best self-lubrication effect after heat treatment. The optimal process parameters were 60% mass fraction of NaCl, 40% mass fraction of PEEK, and the applied heat treatment process.

LUBRICATING PROPERTIES OF POLYESTER OILS AND R404A REFRIGERANT MIXTURES UNDER STARVED LUBRICATION CONDITIONS

There has been a dynamic shift towards the use of ecological refrigerants in the refrigeration industry. Until recently, R404A was a quite commonly used HFC refrigerant for commercial refrigeration equipment, in both small and large systems resulting in the need to select appropriate compressor lubricants. In refrigeration compressors, the amount of oil in friction pairs in certain situations may be insufficient. In that event, starved lubrication conditions or lubrication only by refrigerant may occur. The article contains a methodical selection of test parameters for polyester oils allowing one to assess the lubricating properties of the mixtures of oils for refrigeration compressors and refrigerants under the conditions of poor lubrication. The article also includes the results of wear tests which allow one to evaluate the lubricating properties of oil-refrigerant mixtures under starved lubrication conditions for R404A refrigerant and polyester oils.

Tribological Investigation of Textured Surfaces in Starved Lubrication Conditions

The present work investigates the friction reduction capability of two types of micro-textures (grooves and dimples) created on steel surfaces using a vertical milling machine. The wear studies were conducted using a pin-on-disc tribometer, with the results indicating a better friction reduction capacity in the case of the dimple texture as compared to the grooved texture. The microscopic images of the pin surface revealed deep furrows and significant damage on the pin surfaces of the groove-textured disc. An optimization of the textured surfaces was performed using an artificial neural network (ANN) model, predicting the influence of the surface texture as a function of the load, depth of cut and distance between the micro-textures.

Mixtures of Lubricants and Ecological Refrigerants under Starved Lubrication Conditions.

The presented results show that the presence of refrigerant significantly deteriorates the lubricating properties of compressor oil under starved lubrication conditions (with a small amount of oil). The change can be 40-120% compared to the properties of the oil alone. Additionally, in the group of oils that are substitutes (operational alternatives) compatible with a given refrigerant, the effect of the refrigerant on the lubricating properties varies. The differences can be as much as 25%. In order to evaluate and properly select compressor oils for the refrigerant, the lubricating properties should be tested in a mixture with the refrigerant under conditions similar to actual operation. Such an evaluation of lubricating properties is made possible by the author's method of testing the wear of the block-on-ring friction node. The obtained rankings of lubricating properties for oils (due to the wear volume) can provide good guidelines for the suitable selection of a lubricant for refrigeration compressors (especially for new, environmentally friendly refrigerants, such as R452A). The research was carried out for mixtures of zeotropic refrigerants (R404A, R452A) with polyester oils (POE) and natural refrigerant (R600a) with mineral oils (MO). In each group of refrigerants, different mechanisms of oil-refrigerant mixture formation occur. Each refrigerant was tested with three different compressor oils recommended for each other for alternative uses in refrigeration systems.

Tribological performances of CuSn10Bi3 alloy containing MoSi2 and ferrophosphorus under starved lubrication

The effects of molybdenum disilicide (MoSi2) and ferrophosphorus (FemPn) particles on the tribological properties of copper-tin bismuth (CuSn10Bi3) bimetallic bearing materials were studied in this paper. The samples of CuSn10Bi3 containing MoSi2 and/or FemPn were prepared by powder sintering technology and the metallographic structure of four kinds of self-lubricating copper alloy composite materials after sintering was observed. The tribological properties of the copper alloy composites under starved lubrication conditions were investigated and its worn surfaces and wear debris were discussed and analysed. The results show that the addition of MoSi2 and/or FemPn particles can effectively refine the grain size, optimise the grain boundary morphology, and improve the mechanical properties of the alloys. Under extreme working conditions, the hard particles reinforced copper-based alloy samples have better wear resistance and anti-seizure resistance.

Measuring Film Thickness in Starved Grease-Lubricated Ball Bearings: An Improved Electrical Capacitance Method

Presented in this article is a new method to measure the film thickness in a rolling bearing running under starved conditions, such as in grease-lubricated bearings, using the electrical capacitance method. The method was used to study the impact of speed on film thickness. Results show that fully flooded conditions prevail at lower speeds where the film thickness increases with increasing speed. At higher speeds, where grease-lubricated bearings run under starved lubrication conditions, this increase is less pronounced. At even higher speeds, the film thickness becomes almost independent of the speed.

Significance of g-C3N4 nanosheets for enhancing tribological performance of epoxy subjected to starved lubrication

It is of great interest to realize controllable tribo-designs of a large variety of motion components operating under starved lubrication conditions. In this work, g-C3N4 nanosheets were prepared and uniformly dispersed into pure epoxy (EP) matrix. Especially for sliding with only 5 μL oil supply. In comparison to neat EP, friction coefficient and wear rate are reduced by up to 27% and 83% with addition of only 1% g-C3N4. Research illustrates a small amount of two-dimensional g-C3N4 nanosheets promote the growth of robust tribofilm on oil starved interface. The carbonous top layer of tribofilm benefits the boundary lubrication effect of the sliding pair, whereas the beneath layer confers a high load-bearing ability to tribofilm. It is anticipated that this work will pave a route for designing new polymer nanocomposites serving under oil starved conditions.

Investigations for vibration and friction torque behaviors of thrust ball bearing with self-driven textured guiding surface

In order to improve the starved lubrication condition of rolling bearings, three kinds of textures, namely dimple, groove texture, and gradient groove texture, were developed on the guiding surface of thrust ball bearings in this study. The results show that gradient groove texture has the one-way self-driving function of liquid droplets. The root mean square (RMS) value of vibration acceleration of gradient groove textured bearing (GGB) decreased by 49.1% and the kurtosis decreased by 24.6% compared with non-textured bearing (NB) due to the directional spreading effect of gradient groove textures on oil. The frequency domain analysis showed that the textures mainly suppressed the medium and high-frequency energy of bearing vibration, and the GGB was reduced the most with 65.3% and 48%, respectively. In addition, whether the grease is sufficiently sheared has a large impact on the oil guiding effect, and the friction torque of GGB could decrease by 10.5% compared with NB in the sufficiently sheared condition. Therefore, the gradient groove texture with oil self-driven effect on the guiding surface of rolling bearing can effectively improve the lubrication condition of the bearing and thus reduce the bearing vibration and friction torque, which has a promising application prospect.