Lubricants

17 pages, 4864 KiB

Open AccessArticle

Lubrication Analysis of a Mechanical Seal Considering the Mixed Lubricant State of Gas and Liquid During External Power Shutdown of a Reactor Cooling Pump

by Youngjun Park, Gwanghee Hong, Sanghyun Jun, Jeongmook Choi, Taegyu Kim, Minsoo Kang and Gunhee Jang

Lubricants 2024, 12(12), 406; https://doi.org/10.3390/lubricants12120406 - 21 Nov 2024

Abstract

We proposed a method to calculate the pressure, opening force, and leakage rate in a mechanical seal under the mixed lubricant state of a gas and liquid for the mechanical seal in a reactor cooling pump (RCP) during external power loss. We calculated [...] Read more.

We proposed a method to calculate the pressure, opening force, and leakage rate in a mechanical seal under the mixed lubricant state of a gas and liquid for the mechanical seal in a reactor cooling pump (RCP) during external power loss. We calculated the pressure by solving the nonlinear finite element equation composed of the linear Reynolds equation of an incompressible liquid lubricant and the nonlinear Reynolds equation of a compressible gas lubricant using the Newton–Raphson method. In addition, we calculated the temperature distribution by solving the two-dimensional energy equation utilizing the finite element method. Additionally, we included the turbulence effect in the incompressible liquid lubricant and the turbulence and slip effects in the compressible gas lubricant. The accuracy of the developed program was validated by comparing the simulated opening force and leakage rate of both the mechanical seal with the liquid lubricant and the mechanical seal with the gas lubricant with prior research. Our analysis shows that in high-temperature environments, the increase in the gas region at the lubrication surface leads to a decrease in pressure and opening force and an increase in the leakage rate. Conversely, as the outer pressure increases, the gas region decreases, resulting in an increase in pressure, opening force, and leakage rate. Full article

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26 pages, 1379 KiB

Open AccessArticle

Parametric Optimization of Surface Textures in Oil-Lubricated Long-Life Aircraft Valves

by Pei Li, Qingxiang Pei, Zhe Liu, Sihai Luo, Liucheng Zhou, Junning Li and Leilei Chen

Lubricants 2024, 12(12), 405; https://doi.org/10.3390/lubricants12120405 - 21 Nov 2024

Abstract

The oil-lubricated long-life aircraft valve is one of the most important components to ensure the safety of the entire aircraft system, and it needs to operate millions of times during the whole service life, significantly necessitating techniques to enhance its tribological performance. To [...] Read more.

The oil-lubricated long-life aircraft valve is one of the most important components to ensure the safety of the entire aircraft system, and it needs to operate millions of times during the whole service life, significantly necessitating techniques to enhance its tribological performance. To this end, five different surface textures, i.e., spherical cap, ellipsoidal cap, tree-frog, grass-lip and nepenthes textures were introduced to the pin’s surface of an aircraft valve to improve the valve’s tribological performance. By numerically solving the Reynolds equation with the Jakobsson–Floberg–Olsson cavitation boundary conditions, the effect of the five textures on the tribological performance was simulated. To optimize the geometric parameters of the five textures for a better tribological performance, the Analytic Hierarchy Process was introduced to derive a coupled tribological parameter, which accounts for three classical tribological parameters, including load bearing capacity, friction and friction coefficient. The five textures with optimal values of geometric parameters were also compared to one another using the Analytic Hierarchy Process, and this finally led to a suggestion of the best surface texture for the aircraft valve. The parametric optimization approach proposed in this work can be widely applied for the parametric optimization of surface textures in other applications. Full article

(This article belongs to the Special Issue Applied Tribology: Rotordynamics)

14 pages, 14695 KiB

Open AccessArticle

Identification and Regulation of Cold Rolling Interface State Based on a Novel Modified Forward Slip Model

by Yanli Xin, Zhiying Gao, Yong Zang and Xiaoyong Wang

Lubricants 2024, 12(12), 404; https://doi.org/10.3390/lubricants12120404 - 21 Nov 2024

Abstract

With the development of rolled steel strips towards higher strength and thinner thickness, negative forward slip has been frequently observed during the process of cold rolling, and this phenomenon closely related to interface is believed to seriously influence rolling stability. However, the existing [...] Read more.

With the development of rolled steel strips towards higher strength and thinner thickness, negative forward slip has been frequently observed during the process of cold rolling, and this phenomenon closely related to interface is believed to seriously influence rolling stability. However, the existing classic forward slip models are limited to calculating positive forward slip values and cannot reflect negative forward slip effects. Therefore, in this paper, based on BLAND-FORD forward slip theory, a novel modified forward slip model capable of predicting negative forward slip is established and verified, in which the corresponding flattened curve is characterized and a compensation coefficient related to actual tension and coil number is supplemented. Then, a dimensionless sensitivity factor is defined to compare and analyze the influences of various parameters on forward slip through the modified model, in order to pick a more effective and reasonable regulation approach. Finally, an idea of keeping stable forward slip through dynamic tension regulation is suggested and applied in the actual rolling process, and it is drawn that this strategy can be used to avoid fluctuations of process parameters and suppress mill chatter. As a result, the presented modified forward slip model can identify both positive and negative forward slips and is helpful in regulating the interface state and improving the stability of the rolling process. Full article

(This article belongs to the Special Issue Intelligent Rolling Dynamics: Enhancing Friction and Lubrication in Plate and Strip Mills)

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14 pages, 7699 KiB

Open AccessArticle

Investigation of Tribological Performance of Ti:WS₂/PFPE Composite Lubricating System Under Proton Radiation

by Jian Liu, Zhen Yan, Junying Hao and Weimin Liu

Lubricants 2024, 12(12), 403; https://doi.org/10.3390/lubricants12120403 - 21 Nov 2024

Abstract

The tribological performance of PFPE oil and the Ti:WS₂/PFPE composite lubricating system with different oil amounts was investigated under a proton radiation (PR) irradiation environment. After PR irradiation, PFPE molecules occurred during cross-linking and a polymerization reaction and formed a volatile [...] Read more.

The tribological performance of PFPE oil and the Ti:WS₂/PFPE composite lubricating system with different oil amounts was investigated under a proton radiation (PR) irradiation environment. After PR irradiation, PFPE molecules occurred during cross-linking and a polymerization reaction and formed a volatile small molecular compound, which deteriorates the tribological performance of the Ti:WS₂/PFPE system. The tribological properties of the Ti:WS₂/PFPE system rely strongly on oil amount. For an unirradiated Ti:WS₂/PFPE system, the amorphous layer of transfer film near the sliding contact area was converted into a well-defined crystalline WS₂ layer with a (002) plane induced by the friction process. After PR irradiation, the transfer film became thicker and showed a wholly amorphous structure due to the difficulty in preventing the entrance of O and showed no reorientation with induced friction. Full article

(This article belongs to the Special Issue Space Tribology)

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20 pages, 12180 KiB

Open AccessArticle

Computer Vision-Based Research on the Mechanism of Stick–Slip Vibration Suppression and Wear Reduction in Water-Lubricated Rubber Bearing by Surface Texture

by Anbang Zhu, Ao Ji, Longyang Sheng, Dequan Zhu, Quan Zheng, Xincong Zhou, Jun Wang and Fuming Kuang

Lubricants 2024, 12(11), 402; https://doi.org/10.3390/lubricants12110402 - 20 Nov 2024

Abstract

Water-lubricated rubber bearings are a critical component of the propulsion systems in underwater vehicles. Particularly under conditions of low speed and high load, friction-induced vibration and wear often occur. Surface texturing technology has been proven to improve lubrication performance and reduce friction and [...] Read more.

Water-lubricated rubber bearings are a critical component of the propulsion systems in underwater vehicles. Particularly under conditions of low speed and high load, friction-induced vibration and wear often occur. Surface texturing technology has been proven to improve lubrication performance and reduce friction and wear; however, research on how different texture parameters affect friction-induced vibration and wear mechanisms remains insufficient. In this study, various texture patterns with different area ratios and aspect ratios were designed on the surface of water-lubricated rubber bearings. By combining these designs with an in situ observation system based on computer vision technology, the effects of texture parameters on bearing friction, vibration, and wear were thoroughly investigated. The experimental results show that surface textures play a critical role in improving hydrodynamic effects and stabilizing the lubrication film at the friction interface. Specifically, textures with a high area ratio (15%) and aspect ratio (3:1) exhibited the best vibration suppression effect, primarily due to the reduction in actual contact area. However, excessively high area ratios may lead to increased surface wear. This study concludes that a reasonable selection of texture area and aspect ratios can significantly reduce frictional force fluctuations and vibration amplitude, minimize surface wear, and extend bearing life. Full article

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29 pages, 4541 KiB

Open AccessArticle

Impact of Soot on Internal Combustion Engine Lubrication—Oil Condition Monitoring, Tribological Properties, and Surface Chemistry

by Adam Agocs, Marcella Frauscher, Andjelka Ristic and Nicole Dörr

Lubricants 2024, 12(11), 401; https://doi.org/10.3390/lubricants12110401 - 20 Nov 2024

Abstract

In the study at hand, a systemic investigation regarding the tribochemical effects of crankcase soot is presented. Sooted oils were generated via an engine dynamometer test. Both conventional as well as advanced oil condition monitoring methods indicated a mild degradation of additives. The [...] Read more.

In the study at hand, a systemic investigation regarding the tribochemical effects of crankcase soot is presented. Sooted oils were generated via an engine dynamometer test. Both conventional as well as advanced oil condition monitoring methods indicated a mild degradation of additives. The wear volume was greatly increased with the sooted oils in model tribometer tests, despite the high residual zinc dialkyl dithiophosphate (ZDDP) antiwear (AW) levels. Once the soot was removed via ultracentrifugation, the wear volume returned to levels comparable to the fresh oil. Surface investigations revealed that ZDDP tribofilms could not form in the sooted oils, as only a thin sulfide layer was present on the metal surfaces. Meanwhile, typical tribofilms were observable with centrifuged oils. The results indicated that a tribocorrosive mechanism is most likely responsible for the elevated wear in the sooted oils, where only the iron sulfide base layer of ZDDP films is formed, which is then rapidly removed by the soot particles in an abrasive manner. Full article

(This article belongs to the Special Issue Recent Advances in Automotive Powertrain Lubrication)

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23 pages, 10749 KiB

Open AccessArticle

Impact of Biosynthesized CeO₂ Nanoparticle Concentration on the Tribological, Rheological, and Thermal Performance of Lubricating Oil

by Siraj Azam and Sang-Shin Park

Lubricants 2024, 12(11), 400; https://doi.org/10.3390/lubricants12110400 - 20 Nov 2024

Abstract

This study presents an approach to enhance the performance of lubricating oils through the environmentally friendly synthesis of cerium oxide (CeO₂) nanoparticles using Moringa oleifera leaf extract. These biosynthesized nanoparticles were thoroughly characterized for their structural and thermal stability by utilizing [...] Read more.

This study presents an approach to enhance the performance of lubricating oils through the environmentally friendly synthesis of cerium oxide (CeO₂) nanoparticles using Moringa oleifera leaf extract. These biosynthesized nanoparticles were thoroughly characterized for their structural and thermal stability by utilizing X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The CeO₂ nanolubricants, prepared at various concentrations, displayed significant improvements in viscosity, stability, and thermal conductivity. Specifically, the 0.15 wt% concentration achieved the best performance, reducing viscosity to 9.79 pascal-second (Pa·s) at 80 °C while exhibiting excellent dispersion and minimal sedimentation over time. The thermal conductivity tests revealed a notable 43% increase in heat transfer efficiency at higher nanoparticle concentrations. Tribological tests conducted using a tribometer demonstrated significant improvements in the lubrication properties. The nanolubricant with a 0.15 wt% concentration of CeO₂ nanoparticles achieved the lowest friction coefficient, showing an approximate 26% reduction compared to the base oil, along with a notable decrease in wear rate. This study demonstrates the potential of biosynthesized CeO₂ nanoparticles as effective, sustainable additives in lubricating oils, providing improved thermal, rheological, and tribological properties and marking a significant step toward eco-friendly lubrication solutions. Full article

(This article belongs to the Special Issue Thermophysical and Tribological Characterization of Additivated Lubricants with Nanoparticles)

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15 pages, 5443 KiB

Open AccessArticle

Carbonaceous Decomposition Products at High Temperatures and Their Interfacial Role in the Friction Behaviour of Composite Brake Material

by Piyush Chandra Verma, Pranesh Aswath, Giovanni Straffelini and Stefano Gialanella

Lubricants 2024, 12(11), 399; https://doi.org/10.3390/lubricants12110399 - 20 Nov 2024

Abstract

This study aims to investigate the outcomes of carbonaceous products, derived from the decomposition of the components of vehicular brake materials, under high-temperature wear tests. Pin-on-disc (PoD) wear tests were conducted by using cast iron discs against pins made of commercially available low-steel [...] Read more.

This study aims to investigate the outcomes of carbonaceous products, derived from the decomposition of the components of vehicular brake materials, under high-temperature wear tests. Pin-on-disc (PoD) wear tests were conducted by using cast iron discs against pins made of commercially available low-steel friction material. Tests were carried out at different temperatures: 155 °C, 200 °C, 250 °C, and 300 °C. The characterization of the sliding plateaus on worn pin surfaces was based on X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. It was noted that at temperatures above 200 °C, the thermal degradation of the inorganic resin, used as a material binder, occurs. An interesting observation was recorded at 300 °C; the brake pin material’s friction curve showed higher stability despite having an excessive wear rate. However, the brake pin’s specific wear coefficient was higher at this temperature than was observed in the other friction tests. A detailed study of the friction plateaus on the worn-out pins at 300 °C revealed that the decomposed carbon resin product, i.e., the distorted graphite, was widespread over the surface of the pin. Lubricant stabilization can be expected, as established by the observed values of the coefficient of friction (CoF), retaining values within the 0.4–0.6 range, even at high temperatures. Other friction material components may have contributed to the formation of this ubiquitous carbonaceous interface film. Full article

(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)

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14 pages, 7007 KiB

Open AccessArticle

Transformation from D0₂₂ to L1₂ in Al₃Ti by Fe Addition for Enhanced Wear Resistance

by Guijiang Diao, Junfeng Yuan, Anqiang He, Dong Zhang, Aakash Kumar, Ranran Fang, Anatoliy Vorobyev, Wengang Chen and Dongyang Li

Lubricants 2024, 12(11), 398; https://doi.org/10.3390/lubricants12110398 - 19 Nov 2024

Abstract

The addition of third elements may help transform brittle D0₂₂-structured lightweight Al₃Ti to a relatively ductile L1₂-structured (Al, M)₃Ti (where M represents the third elements), thus increasing the ductility at the expense of hardness. Such [...] Read more.

The addition of third elements may help transform brittle D0₂₂-structured lightweight Al₃Ti to a relatively ductile L1₂-structured (Al, M)₃Ti (where M represents the third elements), thus increasing the ductility at the expense of hardness. Such a transformation could benefit the wear resistance of the alloy due to improved toughness if a proper balance between the hardness and ductility is achieved. In this work, a D0₂₂-predominant Al₃Ti alloy (S-Al₃Ti) and an L1₂-predominant (Al, Fe)₃Ti alloy (S-Al₆₇Ti₂₅Fe₈) were fabricated by arc melting. Change in wear resistance, corresponding to a D0₂₂-to-L1₂ transformation, caused by the addition of Fe as a representative third element, was investigated and compared with the wear resistance of a commercial Al-matrix composite reinforced by 30 wt.% SiC particles (S-Al/SiC_p) as a reference material. It was observed that wear of the S-Al₃Ti resulted from abrasion involving synergistic oxidation, leading to a larger volume loss. In contrast, the softer S-Al₆₇Ti₂₅Fe₈ showed enhanced wear resistance, benefiting from improved toughness with reasonable hardness. During the wear testing, both the alloys exhibited better performance than S-Al/SiC_p, a well-known lightweight composite. This study highlights that D0₂₂-to-L1₂ transformation enhances wear resistance due to increased toughness which can be adjusted using the addition of a third element. Full article

(This article belongs to the Special Issue Friction and Wear of Alloys)

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14 pages, 12314 KiB

Open AccessArticle

Lubrication Characteristics of a Warhead-Type Irregular Symmetric Texture on the Stator Rubber Surfaces of Screw Pumps

by Xinfu Liu, Yi Sun, Chunhua Liu, Xiangzhi Shi, Xinglong Niu, Gang Zheng, Wei Wei, Songbo Wei and Shouzhi Huang

Lubricants 2024, 12(11), 397; https://doi.org/10.3390/lubricants12110397 - 19 Nov 2024

Abstract

A theoretical model for the micro-texture on the inner wall of the stator rubber in screw pumps was developed. The finite element analysis method was employed. The pressure and streamline distributions for warhead-type, concentric circle-type, and multilayer rectangular-type textured surfaces were calculated. The [...] Read more.

A theoretical model for the micro-texture on the inner wall of the stator rubber in screw pumps was developed. The finite element analysis method was employed. The pressure and streamline distributions for warhead-type, concentric circle-type, and multilayer rectangular-type textured surfaces were calculated. The effects of textured morphology, groove depth, groove width, and other parameters on the lubrication field were systematically investigated and analyzed. A nanosecond laser was employed to process the textured rubber surface of the stator in the screw pump. Subsequently, a micro-texture friction performance test was conducted on the rubber surface of the stator in actual complex well fluids from shale oil wells. Given the results of the simulation analysis and experimental tests, the lubrication characteristics of textured rubber surfaces with varying texture morphologies, rotational speeds, and mating loads were revealed. Furthermore, it indicated that the irregular symmetric warhead-type micro-texture exhibited excellent dynamic pressure lubrication performance compared with concentric circle-type and multilayer rectangular-type textures. The irregular symmetry enhanced the dynamic pressure lubrication effect, enhanced the additional net load-bearing capacity of the oil film surface, and reduced friction. As the groove depth increased, the volume and number of vortices within the groove also increased. The fluid kinetic energy was transformed into vortex energy, leading to a reduction in wall stress on the surface of the oil film, thereby affecting its bearing capacity. Initially, the maximum pressure on the wall surface of the oil film increased and then decreased. The optimal dynamic pressure lubrication effect was achieved with a warhead-type texture size of 3 mm, a groove width of 0.2 mm, and a groove depth of 0.1 mm. Well-designed texture morphology and depth parameters significantly enhanced the oil film-bearing capacity of the stator rubber surface, improving the dynamic pressure lubrication effect, and consequently extending the service life of the stator–rotor interface in the screw pump. Full article

(This article belongs to the Special Issue Tribology of Textured Surfaces)

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14 pages, 49185 KiB

Open AccessArticle

Investigating Influence of Mo Elements on Friction and Wear Performance of Nickel Alloy Matrix Composites in Air from 25 to 800 °C

by Jinming Zhen, Yunxiang Han, Lin Yuan, Zhengfeng Jia and Ran Zhang

Lubricants 2024, 12(11), 396; https://doi.org/10.3390/lubricants12110396 - 18 Nov 2024

Abstract

Rapid developments in aerospace and nuclear industries pushed forward the search for high-performance self-lubricating materials with low friction and wear characteristics under severe environment. In this paper, we investigated the influence of the Mo element on the tribological performance of nickel alloy matrix [...] Read more.

Rapid developments in aerospace and nuclear industries pushed forward the search for high-performance self-lubricating materials with low friction and wear characteristics under severe environment. In this paper, we investigated the influence of the Mo element on the tribological performance of nickel alloy matrix composites from room temperature to 800 °C under atmospheric conditions. The results demonstrated that composites exhibited excellent lubricating (with low friction coefficients of 0.19–0.37) and wear resistance properties (with low wear rates of 2.5–28.1 × 10⁻⁵ mm³/Nm), especially at a content of elemental Mo of 8 wt. % and 12 wt. %. The presence of soft metal Ag on the sliding surface as solid lubricant resulted in low friction and wear rate in a temperature range from 25 to 400 °C, while at elevated temperatures (600 and 800 °C), the effective lubricant contributed to the formation of a glazed layer rich in NiCr₂O₄, BaF₂/CaF₂, and Ag₂MoO₄. SEM, EDS, and the Raman spectrum indicated that abrasive and fatigue wear were the main wear mechanisms for the studied composites during sliding against the Si₃N₄ ceramic ball. The obtained results provide an insightful suggestion for future designing and fabricating solid lubricant composites with low friction and wear properties. Full article

(This article belongs to the Special Issue Tribology in Manufacturing Engineering)

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17 pages, 14618 KiB

Open AccessArticle

Analysis of the Influencing Factors of Aerostatic Bearings on Pneumatic Hammering

by Yifei Li, Weiping Huang and Ran Sang

Lubricants 2024, 12(11), 395; https://doi.org/10.3390/lubricants12110395 - 16 Nov 2024

Abstract

In this study, in order to reveal the influence mechanism of bearing parameters on pneumatic hammering, an aerostatic bearing with a multi-orifice-type restrictor is analyzed. Firstly, the flow field is investigated, and the vortex-induced excitation is discussed in both the frequency and time [...] Read more.

In this study, in order to reveal the influence mechanism of bearing parameters on pneumatic hammering, an aerostatic bearing with a multi-orifice-type restrictor is analyzed. Firstly, the flow field is investigated, and the vortex-induced excitation is discussed in both the frequency and time domains. Then, the frequency-related displacement impedance is analyzed, and the effects of vortex-induced excitation on pneumatic hammering are discussed. Experiments are also conducted for verification. Moreover, the influence of damping on pneumatic hammering is identified. The results show that with larger damping, the risk of pneumatic hammering can be reduced. Finally, the impacts of design parameters on the damping are discussed in detail using an approximate model. Design optimization is considered to achieve the maximum damping, i.e., the minimum risk of pneumatic hammering. The results show that both the air supply pressure and the pocket volume should be minimized. The analysis process provides a reference for the design of bearings to reduce pneumatic hammering. Full article

(This article belongs to the Special Issue Gas Lubricated Bearings)

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22 pages, 15270 KiB

Open AccessArticle

Modeling Inertia-Driven Oil Transport Inside the Three-Piece Oil Control Ring of Internal Combustion Engines

by Tsung-Yu Yang, Mo Li and Tian Tian

Lubricants 2024, 12(11), 394; https://doi.org/10.3390/lubricants12110394 - 16 Nov 2024

Abstract

The three-piece oil control ring (TPOCR), traditionally used in light-duty gasoline engines, is becoming a viable option for heavy-duty gas and hydrogen engines due to its ability to control lubricating oil consumption (LOC) under throttled conditions. Understanding the distribution of oil inside the [...] Read more.

The three-piece oil control ring (TPOCR), traditionally used in light-duty gasoline engines, is becoming a viable option for heavy-duty gas and hydrogen engines due to its ability to control lubricating oil consumption (LOC) under throttled conditions. Understanding the distribution of oil inside the TPOCR groove, as well as the effects of rail gap and drain hole positions, is critical for optimizing TPOCR and groove designs. In this work, a one-dimensional oil distribution model was developed to simulate inertia-driven oil transport in the TPOCR groove. A novel approach was proposed by first dividing the TPOCR into units composed of a pair of expander pitches. Then, the relationship between the oil outflow rate of the unit and its oil mass was established with the help of three-dimensional two-phase computational fluid dynamics (CFD) simulations. This relationship was then used to model one-dimensional oil transport along the circumference of the TPOCR groove. Incorporating the boundary conditions at the rail gaps and drain holes, this simple model can complete computations for 10,000 cycles within a few seconds, allowing for quick the evaluation of transient behavior and design iterations. Studies on low-load conditions show that the model, with reasonable adjustment for the boundary conditions, can match the oil distribution patterns observed in visualization experiments. This is the first step toward studying oil transport in the TPOCR groove before involving the effects of gas flows. Full article

(This article belongs to the Special Issue Tackling Emissions from the Internal Combustion Engine: Advances in Piston/Bore Tribology)

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22 pages, 7710 KiB

Open AccessArticle

Investigation of the Effect of Al₂O₃ Nanoparticle-Added MQL Lubricant on Sustainable and Clean Manufacturing

by Fuat Kara

Lubricants 2024, 12(11), 393; https://doi.org/10.3390/lubricants12110393 - 15 Nov 2024

Abstract

In this study, in order to improve the characteristics of the vegetable-based cutting fluids used in the MQL technique and increase the machining performance of MQL and its positive effects on sustainable manufacturing, the effects of the MQL method with nano-Al₂O [...] Read more.

In this study, in order to improve the characteristics of the vegetable-based cutting fluids used in the MQL technique and increase the machining performance of MQL and its positive effects on sustainable manufacturing, the effects of the MQL method with nano-Al₂O₃ additives on surface roughness (Ra) and cutting temperature (Ctt) were examined through turning experiments carried out by adding nano-Al₂O₃ to the vegetable-based cutting fluid. For this purpose, machining tests were carried out on hot work tool steel alloyed with Cr-Ni-Mo that has a delivery hardness of 45 HRC. In hard machining experiments, three techniques for cooling and lubricating (dry cutting, MQL, and nano-MQL), three cutting speeds (V) (100, 130, 160 m/min), three feed rates (f) (0.10, 0.125, and 0.15 mm/rev), and two different ceramic cutting tools (uncoated and TiN-coated with PVD methods) were used as control factors. For Ra, the nano-MQL method provided an average of 21.49% improvement compared to other cooling methods. For Ctt, this rate increased to 26.7%. In crater wear areas, the nano-MQL method again exhibited the lowest wear values, decreasing performance by approximately 50%. The results of this research showed that the tests conducted using the cooling of nano-MQL approach produced the best results for all output metrics (Ra, Ctt, and crater wear). Full article

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15 pages, 5813 KiB

Open AccessArticle

Effect of Pressure on the Microstructure and Wear Performance of Cr-Mn-Mo Alloyed Steel Prepared by Squeeze Casting

by Yuan Zhuang, Yujiang Hao, Lei Guo and Xinhao Wu

Lubricants 2024, 12(11), 392; https://doi.org/10.3390/lubricants12110392 - 14 Nov 2024

Abstract

In this study, the effects of applied pressure (0, 90, 120, and 150 MPa) during solidification on the microstructure, mechanical properties, and impact–abrasive wear resistance of Cr-Mn-Mo steel prepared by squeeze casting were systematically investigated. The results demonstrated that the materials produced under [...] Read more.

In this study, the effects of applied pressure (0, 90, 120, and 150 MPa) during solidification on the microstructure, mechanical properties, and impact–abrasive wear resistance of Cr-Mn-Mo steel prepared by squeeze casting were systematically investigated. The results demonstrated that the materials produced under pressure showed smaller grains compared to those of the samples fabricated without pressure. Compared to the unpressurized sample, the grain diameter of the sample prepared at 120 MPa decreased by 37.7%, the length of the primary arm shortened by 40.7%, and the spacing of the secondary arm contracted by 14.1%. Furthermore, the impact toughness results indicated that the samples prepared without pressure exhibited brittle fracture characteristics, whereas quasi-destructive fractures predominated in the samples prepared at 120 MPa. Simultaneously, three-point bending strength exhibited a gradual increase with increasing pressure, reaching a maximum value of 855.5 MPa when prepared under 150 MPa. Additionally, the impact–abrasive wear resistance of Cr-Mn-Mo alloyed steel produced by squeeze casting was significantly enhanced compared to the samples produced without pressure. The samples without external pressure exhibited a combination of abrasive and adhesive wear, whereas the wear characteristics of the samples prepared under pressure includes grooves, cutting marks, flaking pits, and accumulating ridges. Full article

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26 pages, 14835 KiB

Open AccessArticle

Mechanical and Tribological Properties of (AlCrNbSiTiMo)N High-Entropy Alloy Films Prepared Using Single Multiple-Element Powder Hot-Pressed Sintered Target and Their Practical Application in Nickel-Based Alloy Milling

by Jeng-Haur Horng, Wen-Hsien Kao, Wei-Chen Lin and Ren-Hao Chang

Lubricants 2024, 12(11), 391; https://doi.org/10.3390/lubricants12110391 - 14 Nov 2024

Abstract

(AlCrNbSiTiMo)N high-entropy alloy films with different nitrogen contents were deposited on tungsten carbide substrates using a radio-frequency magnetron sputtering system. Two different types of targets were used in the sputtering process: a hot-pressing sintered AlCrNbSiTi target fabricated using a single powder containing multiple [...] Read more.

(AlCrNbSiTiMo)N high-entropy alloy films with different nitrogen contents were deposited on tungsten carbide substrates using a radio-frequency magnetron sputtering system. Two different types of targets were used in the sputtering process: a hot-pressing sintered AlCrNbSiTi target fabricated using a single powder containing multiple elements and a vacuum arc melting Mo target. The deposited films were denoted as R_N0, R_N33, R_N43, R_N50, and R_N56, where R_N indicates the nitrogen flow ratio relative to the total nitrogen and argon flow rate (R_N = (N₂/(N₂ + Ar)) × 100%). The as-sputtered films were vacuum annealed, with the resulting films denoted as HR_N0, HR_N33, HR_N43, HR_N50, and HR_N56, respectively. The effects of the nitrogen content on the composition, microstructure, mechanical properties, and tribological properties of the films, in both as-sputtered and annealed states, underwent thorough analysis. The R_N0 and R_N33 films displayed non-crystalline structures. However, with an increase in nitrogen content, the R_N43, R_N50, and R_N56 films transitioned to FCC structures. Among the as-deposited films, the R_N43 film exhibited the best mechanical and tribological properties. All of the annealed films, except for the HR_N0 film, displayed an FCC structure. In addition, they all formed an MoO₃ solid lubricating phase, which reduced the coefficient of friction and improved the anti-wear performance. The heat treatment HR_N43 film displayed the supreme hardness, H/E ratio, and adhesion strength. It also demonstrated excellent thermal stability and the best wear resistance. As a result, in milling tests on Inconel 718, the R_N43-coated tool demonstrated a significantly lower flank wear and notch wear, indicating an improved machining performance and extended tool life. Thus, the application of the R_N43 film in aerospace manufacturing can effectively reduce the tool replacement cost. Full article

(This article belongs to the Special Issue Recent Advances in Tribological Properties of Machine Tools)

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17 pages, 9296 KiB

Open AccessArticle

Influence of Oil Injection Lubrication Parameters of High-Speed Internal Meshing Gear Based on the Computational Fluid Dynamics

by Peixun Tang, Zhengminqing Li, Xiangying Hou, Letian Li, Rongsheng Xi and Yiyan Chen

Lubricants 2024, 12(11), 390; https://doi.org/10.3390/lubricants12110390 - 13 Nov 2024

Abstract

High-speed gears are crucial transmission components found in airplanes and other systems, and they are maintained primarily through oil injection. However, due to their high operating speeds and the influence of oil injection settings, gear surface lubrication efficacy is frequently insufficient, compromising the [...] Read more.

High-speed gears are crucial transmission components found in airplanes and other systems, and they are maintained primarily through oil injection. However, due to their high operating speeds and the influence of oil injection settings, gear surface lubrication efficacy is frequently insufficient, compromising the transmission system’s precision, durability, and safety. Currently, the parameter choices for oil injection in high-speed gears mostly rely on empirical judgment, which results in significant time and resource expenses. This study focuses on one pair of internal meshing gears within a specific aircraft gearbox, establishing an oil injection lubrication model for high-speed internal meshing gears using the computational fluid dynamics (CFD) approach. This research provides insights and references for optimizing oil injection parameters and improving lubrication efficiency in high-speed internal meshing gear systems by examining the dynamic characteristics of internal meshing wind resistance in addition to the effects of injection tube position, angle, and speed on lubrication performance. Full article

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25 pages, 6251 KiB

Open AccessArticle

Effect of Variation in Viscosity on Static and Dynamic Characteristics of Rough Porous Journal Bearings with Micropolar Fluid Squeeze Film Lubrication

by Neminath Bhujappa Naduvinamani and Bhagyashri Kotreppa Koppa

Lubricants 2024, 12(11), 389; https://doi.org/10.3390/lubricants12110389 - 13 Nov 2024

Abstract

In the present study, an effort was made to determine the effects of a porous matrix with different viscosities on the dynamic and static behaviors of rough short journal bearings taking into account the action of a squeezing film under varying loads without [...] Read more.

In the present study, an effort was made to determine the effects of a porous matrix with different viscosities on the dynamic and static behaviors of rough short journal bearings taking into account the action of a squeezing film under varying loads without journal rotation. The micropolar fluid was regarded as a lubricant that contained microstructure additives in both the porous region and the film region. By applying Darcy’s law for micropolar fluids through a porous matrix and stochastic theory related to uneven surfaces, a standardized Reynolds-type equation was extrapolated. Two scenarios with a stable and an alternating applied load were analyzed. The impacts of variations in viscosity, the porous medium, and roughness on a short journal bearing were examined. We inspected the dynamic and static behaviors of the journal bearing. We found that the velocity of the journal center with a micropolar fluid decreased when there was a cyclic load, and the impact of variations in the viscosity and porous matrix diminished the load capacity and pressure in the squeeze film and increased the velocity of the journal center. Full article

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17 pages, 16140 KiB

Open AccessArticle

An Investigation on the High-Temperature Stability and Tribological Properties of Impregnated Graphite

by Juying Zhao, Qi Xin, Yunshuang Pang, Xiao Ning, Lingcheng Kong, Guangyang Hu, Ying Liu, Haosheng Chen and Yongjian Li

Lubricants 2024, 12(11), 388; https://doi.org/10.3390/lubricants12110388 - 13 Nov 2024

Abstract

Impregnated graphite is a common material for friction pairs in aeroengine seals, especially at high temperatures. For the convenience of the application of graphite materials in aeroengines, an SRV-4 tribometer and a synchronous thermal analyzer are employed to study the tribological properties and [...] Read more.

Impregnated graphite is a common material for friction pairs in aeroengine seals, especially at high temperatures. For the convenience of the application of graphite materials in aeroengines, an SRV-4 tribometer and a synchronous thermal analyzer are employed to study the tribological properties and thermal stability of pure, resin-impregnated, metal-impregnated, and phosphate-impregnated graphite against stainless steel from room temperature to 500 °C. The results indicate that impregnations can improve the wear resistance and thermal stability of graphite at high temperatures. Compared with other impregnated graphite materials, the resin-impregnated graphite shows a good friction coefficient and poor wear rate and thermal stability over 300 °C, due to the degradation and oxidation of the resin-and-graphite matrix. The metal- and phosphate-impregnated graphite materials exhibit excellent wear resistance and thermal stability under 500 °C as a result of the protection of the impregnations, while the average friction coefficient of the metal-impregnated graphite is much greater than the phosphate-impregnated graphite, and even reaches 2.14-fold at 300 °C. The wear rates for the graphite impregnated with resin, metal, and phosphate are 235 × 10⁻⁷, 7 × 10⁻⁷, and 16 × 10⁻⁷ mm³N⁻¹m⁻¹ at 500 °C, respectively. Considering all aspects, the phosphate-impregnated graphite exhibits excellent tribological properties and thermal stability. Full article

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