Research on the Mechanical Wear of Gear-Shaped Parts

Topic Information

Dear Colleagues,

Gear-shaped parts are widely used in industries for the purpose of sealing, power transmission, etc. They are usually in direct contact with paired gears to perform their functionalities, and surface wear due to the interaction of micro-contact of rough sliding surfaces is one of several failure modes. Apart from the direct material loss that leads to the functional failure, the wear causes the system to change its vibration and noise characteristics and consequently accelerates the occurrence of other failure modes.

At present, contemporary wear theories make it possible to build a relatively accurate model to assess the wear state of a surface, and the wear measurement techniques are capable of displaying the surface topographies at an enlarged scale. However, the in-depth wear mechanism of gear-shaped parts bridging the manufacturing process, molecular details, and macroscale properties of materials remains unclear. A good understanding of the wear mechanism and the monitoring and evaluation method is desired for the strength enhancement of gear-shaped parts and elongation of gear-like systems.

This Topic aims to provide a premier international platform for professionals to discuss and present their most recent research on the mechanical wear of gear-shaped parts. The articles in this Topic will cover various topics, including surface modification, lubrication, and tribology; anti-friction design; wear and wear evaluation; and fault diagnosis or damage detection of gears. Submissions on other topics are also welcomed.

Prof. Dr. Qingbing Dong
Prof. Dr. Zhibo Yang
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Applied Sciences applsci	2.5	5.3	2011	18.4 Days	CHF 2400
Machines machines	2.1	3.0	2013	15.5 Days	CHF 2400
Materials materials	3.1	5.8	2008	13.9 Days	CHF 2600

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Published Papers (16 papers)

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13 pages, 4989 KiB  

Open AccessArticle

Thermoelastohydrodynamic Characteristics of Low-Temperature Helium Gas T-Groove Face Seals

by Delei Zhu, Jing Yang and Shaoxian Bai

Materials 2021, 14(11), 2873; https://doi.org/10.3390/ma14112873 - 27 May 2021

Cited by 8 | Viewed by 2749

Abstract

Thermoelastohydrodynamic lubrication behaviors of helium gas T-groove face seals are numerically simulated under conditions of low temperature and high pressure, with the consideration of real-gas properties including compressibility coefficient, viscosity, and heat capacity. It is found that helium gas T-groove face seal presents [...] Read more.

Thermoelastohydrodynamic lubrication behaviors of helium gas T-groove face seals are numerically simulated under conditions of low temperature and high pressure, with the consideration of real-gas properties including compressibility coefficient, viscosity, and heat capacity. It is found that helium gas T-groove face seal presents a sharp divergent deformation at low temperature and high pressure, which makes the opening performance weaken and the leakage rate increase. This result is obviously different from the case of high-temperature gas face seals. As the sealing temperature drops from 300 K to 150 K, the leakage rate increases about 17% and the opening force decreases about 15%. Moreover, with the growth of rotational speed, both the outlet film pressure and the sealing performance present a non-monotonic trend. Specifically, while the rotating speed of moving ring raises from 3000 to 30,000 r·min?1, the leakage rate changes more than 30%, and the opening force is reduced about 10%. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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25 pages, 57345 KiB  

Open AccessArticle

A New Approach for Modeling Mixed Lubricated Piston-Cylinder Pairs of Variable Lengths in Swash-Plate Axial Piston Pumps

by Bo Zhao, Xinqing Hu, Haifeng Li, Yonghui Liu, Baocheng Zhang and Qingbing Dong

Materials 2021, 14(19), 5836; https://doi.org/10.3390/ma14195836 - 6 Oct 2021

Cited by 10 | Viewed by 2676

Abstract

The swash-plate axial piston pump is one of the most widely used pumps due to its simplicity and compactness in structure. In such a pump, the piston-cylinder system plays a crucial role, with its lubrication characteristics greatly affecting the overall pumping performance. A [...] Read more.

The swash-plate axial piston pump is one of the most widely used pumps due to its simplicity and compactness in structure. In such a pump, the piston-cylinder system plays a crucial role, with its lubrication characteristics greatly affecting the overall pumping performance. A new numerical approach is proposed in this study for modeling mixed lubricated piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps in the framework of multibody dynamics. The approach couples the hydrodynamic mixed lubrication model of the piston-cylinder interface with the multibody dynamics model of the piston pump. The lubrication model is established with a transient average Reynolds equation considering asperity contacts and is solved with the finite element method to derive the hydrodynamic forces of the lubricated pair, while the multibody dynamics model is established with Lagrangian formalism by considering hydrodynamic forces as external forces. Results for piston-cylinder interfaces of variable lengths in swash-plate axial piston pumps are presented, and the impacts of cylinder length and the tilt angle of the swash plate on the tribological performances of the interface are discussed. The results indicate that increasing the cylinder length can improve the stability and wear resistance of the piston, but it can exacerbate the frictional power loss. Moreover, although enlarging the tilt angle of the swash plate can effectively increase pump displacement, it can easily lead to serious friction, wear, and leakage problems. Consequently, the tilt angle of the swash plate should be carefully selected in practical applications. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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13 pages, 6785 KiB  

Open AccessArticle

Fault Feature Analysis of Gear Tooth Spalling Based on Dynamic Simulation and Experiments

by Zhiguo Wan, Jie Zheng, Jie Li and Zhenfeng Man

Materials 2021, 14(20), 6053; https://doi.org/10.3390/ma14206053 - 13 Oct 2021

Cited by 9 | Viewed by 2629

Abstract

Gear dynamics analysis based on time-varying meshing stiffness (TMS) is an important means to understand the gear fault mechanism. Based on Jones bearing theory, a bearing statics model was established and introduced into a gear system. The lateral–torsion coupling vibration model of the [...] Read more.

Gear dynamics analysis based on time-varying meshing stiffness (TMS) is an important means to understand the gear fault mechanism. Based on Jones bearing theory, a bearing statics model was established and introduced into a gear system. The lateral–torsion coupling vibration model of the gear shaft was built by using a Timoshenko beam element. The lumped parameter method was used to build the dynamic model of a gear pair. The dynamic model of a spur gear system was formed by integrating the component model mentioned above. The influence of rectangular and elliptical spalling on TMS was analyzed by the potential energy method (PEM). The fault feature of tooth spalling was studied by dynamic simulation and verified by experiments. It is found that the gear system will produce a periodic shock response owing to the periodic change of the number of meshing gear teeth. Due to the contact loss and the decrease of TMS, a stronger shock response will be generated when the spalling area is engaged. In the spectrum, some sidebands will appear in the resonance region. The results can provide a theoretical guide for the health monitoring and diagnosis of gear systems. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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24 pages, 8159 KiB  

Open AccessArticle

Bearing Performance Degradation Assessment Based on SC-RMI and Student’s t-HMM

by Huiming Jiang, Jinhai Luo, Bohua Zhou, Chao Li, Zhongwei Lv, Zhibo Yang and Jin Chen

Materials 2021, 14(20), 6077; https://doi.org/10.3390/ma14206077 - 14 Oct 2021

Cited by 3 | Viewed by 1809

Abstract

Bearing performance degradation assessment (PDA), as an important part of prognostics and health management (PHM), is significant to prevent major accidents and economic losses in industry. For the data-driven PDA, the extraction and selection of features is quite important. To better integrate the [...] Read more.

Bearing performance degradation assessment (PDA), as an important part of prognostics and health management (PHM), is significant to prevent major accidents and economic losses in industry. For the data-driven PDA, the extraction and selection of features is quite important. To better integrate the degradation information, the bearing performance degradation assessment based on SC-RMI and Student’s t-HMM is proposed in this article. Firstly, spectral clustering was used as a preprocessing step to cluster features with similar degradation curves. Then, rank mutual information, which is more suitable for trendability estimation of long time series, was utilized to select the optimal feature from each cluster. The feature selection method based on these two steps is called SC-RMI for short. With the selected features, Student’s t-HMM, which is more robust to outliers, was utilized for performance degradation modeling and assessment. The verifications based on an accelerated life test and the public XJTU-SY dataset showed the superiority of the proposed method. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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16 pages, 5925 KiB  

Open AccessArticle

Wear Estimation of DLC Films Based on Energy-Dissipation Analysis: A Molecular Dynamics Study

by Zhiyuan Yin, Hong Wu, Guangan Zhang, Chenzhong Mu and Lichun Bai

Materials 2022, 15(3), 893; https://doi.org/10.3390/ma15030893 - 25 Jan 2022

Cited by 6 | Viewed by 3357

Abstract

This study employs the energy-dissipation method to analyze the tribological behaviors of diamond-like carbon (DLC) films through molecular dynamics simulation. It is found that at small load and sliding velocity, the variation trend of average friction force is only dependent on the number [...] Read more.

This study employs the energy-dissipation method to analyze the tribological behaviors of diamond-like carbon (DLC) films through molecular dynamics simulation. It is found that at small load and sliding velocity, the variation trend of average friction force is only dependent on the number of interface bonds (or contact area). However, at large load and sliding velocity, the friction mechanism is not only related to the number of interface bonds but also related to the presence of the transfer layer. The elastic–plastic deformation mainly occurs in the early sliding stage, and a part of the stored elastic potential energy is dissipated by plastic potential energy or internal frictional heat. After the sliding stabilization, over 95% of the total frictional energy is dissipated by thermal conduction, and the rest is mostly dissipated by wear. The increase in load, velocity, and temperature cause more frictional energy dissipated by elastic–plastic deformation, atomic motion, and elastic deformation instead of thermal conduction, respectively. Finally, the wear rate obtained in this work is the same order of magnitude as the experiment. Generally, this work provides an effective atomic-scale method to comprehensively analyze the microscopic wear mechanism of materials. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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17 pages, 5163 KiB  

Open AccessArticle

Gas–Liquid Mass Transfer Behavior of Upstream Pumping Mechanical Face Seals

by Shaoxian Bai, Jialin Hao, Jing Yang and Yuansen Song

Materials 2022, 15(4), 1482; https://doi.org/10.3390/ma15041482 - 16 Feb 2022

Cited by 13 | Viewed by 2789

Abstract

For gas–liquid medium isolation seals in aero-engines, the upstream pumping function of directional grooves provides an effective way to realize the design of longer service life and lower leakage rate. However, this produces a new problem for gas–liquid mass transfer in the sealing [...] Read more.

For gas–liquid medium isolation seals in aero-engines, the upstream pumping function of directional grooves provides an effective way to realize the design of longer service life and lower leakage rate. However, this produces a new problem for gas–liquid mass transfer in the sealing clearance. This study establishes an analytical model to investigate the gas–liquid mass transfer behavior and the change rule for the opening force of mechanical face seals with elliptical grooves. Compared with traditional studies, this model considers not only the gas–liquid transfer but also the cavitation effect. The results obtained show that with the increase of rotational speed, the gas medium transferred from the inner low-pressure side to the outer high-pressure side. In addition, the leakage rate of the liquid medium from the outer high-pressure side to the inner low-pressure side increased with the growth of sealing clearance, rotational speed and seal pressure. The upstream pumping effect of the gas medium with elliptical grooves not only led to a state of gas–liquid mixed lubrication in the sealing surfaces, but also significantly increased the opening capacity of the seal face. This research may provide a reasonable basis for the design of upstream pumping mechanical face seals. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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17 pages, 8448 KiB  

Open AccessArticle

A Novel Blade Vibration Monitoring Experimental System Based on Blade Tip Sensing

by Haoqi Li, Shaohua Tian and Zhibo Yang

Materials 2022, 15(19), 6987; https://doi.org/10.3390/ma15196987 - 8 Oct 2022

Cited by 9 | Viewed by 1916

Abstract

Due to its non-intrusive manner, blade tip timing (BTT) is considered a potential tool for the condition monitoring of turbomachinery. The challenge of BTT relates to significant under-sampled signal processing, which is induced by a lower number of probes. Signal processing assumes that [...] Read more.

Due to its non-intrusive manner, blade tip timing (BTT) is considered a potential tool for the condition monitoring of turbomachinery. The challenge of BTT relates to significant under-sampled signal processing, which is induced by a lower number of probes. Signal processing assumes that the ability of the hardware system can meet the requirements of the software algorithm. The abilities of the hardware, including the time resolution of the data acquisition system (DAS) and the dynamic characteristics of rigs, are compromised, particularly when the rotating speed increases. This increase in speed causes two problems for BTT: (1) the rig is less stable, due to the reduction of dynamic stiffness; (2) the time resolution of the DAS can be inadequate for identification. To promote the performance of the hardware system, here a BTT rig was designed with high dynamic performance, including a new DAS with a time resolution of 10 ns. A variety of commonly used BTT signal processing methods are used to analyze the experimental data and verify the good reliability and validity of the experimental platform. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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16 pages, 6008 KiB  

Open AccessArticle

Piston Wear Detection and Feature Selection Based on Vibration Signals Using the Improved Spare Support Vector Machine for Axial Piston Pumps

by Shiqi Xia, Yimin Xia and Jiawei Xiang

Materials 2022, 15(23), 8504; https://doi.org/10.3390/ma15238504 - 29 Nov 2022

Cited by 5 | Viewed by 2586

Abstract

A piston wear fault is a major failure mode of axial piston pumps, which may decrease their volumetric efficiency and service life. Although fault detection based on machine learning theory can achieve high accuracy, the performance mainly depends on the detection model and [...] Read more.

A piston wear fault is a major failure mode of axial piston pumps, which may decrease their volumetric efficiency and service life. Although fault detection based on machine learning theory can achieve high accuracy, the performance mainly depends on the detection model and feature selection. Feature selection in learning has recently emerged as a crucial issue. Therefore, piston wear detection and feature selection are essential and urgent. In this paper, we propose a vibration signal-based methodology using the improved spare support vector machine, which can integrate the feature selection into the piston wear detection learning process. Forty features are defined to capture the piston wear signature in the time domain, frequency domain, and time–frequency domain. The relevance and impact of sparsity in 40 features are illustrated through the single and multiple statistical feature analysis. Model performance is assessed and the sparse features are discovered. The maximum model testing and training accuracy are 97.50% and 96.60%, respectively. Spare features s₁₀, s₁₂, E_w(8), x₇, E_e(5), and E_e(4) are selected and validated. Results show that the proposed methodology is applicable for piston wear detection and feature selection, with high model accuracy and good feature sparsity. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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21 pages, 16162 KiB  

Open AccessArticle

An Improved Modeling and Numerical Analysis Method for Tooth Surface Wear of Double-Arc Harmonic Gears

by Qian Zhao, Zuoxiang Xing, Jing Yuan, Zhijun Zhang, Jun Zhu and Huiming Jiang

Materials 2022, 15(24), 8869; https://doi.org/10.3390/ma15248869 - 12 Dec 2022

Cited by 8 | Viewed by 2377

Abstract

Tooth surface wear is one of the most common failure modes of harmonic gears, especially in space drive mechanisms. Due to difficulty accurately modeling its wear failure model and the complex mechanism, its dynamic behavior and wear mechanism have not been deeply investigated, [...] Read more.

Tooth surface wear is one of the most common failure modes of harmonic gears, especially in space drive mechanisms. Due to difficulty accurately modeling its wear failure model and the complex mechanism, its dynamic behavior and wear mechanism have not been deeply investigated, and study of the double-arc tooth profile wear model is relative lacking. Therefore, an improved wear modelling and analysis method that is more in line with actual conditions for double-arc harmonic gears is here proposed. Firstly, a tooth surface wear model under mixed elastohydrodynamic lubrication (EHL) was established based on the Archard formula, which combines the Reynolds equation and double-arc tooth profile equation, and considering the meshing offset caused by elastic deformation. Then, the wear analysis method combined with mixed EHL was derived, and numerical simulation analysis of the wear characteristics in lubrication state was carried out, including wear depth calculation and wear output comparison of different tooth profiles. Furthermore, the influence of main working parameters and design parameters on the wear quantity was analyzed. The results show that wear depth for mixed EHL is significantly less than at dry contact. The double-arc tooth profile can withstand more wear cycles than the involute tooth profile, and the input torque and the number of cycles significantly affect the amount of tooth wear. This study further reveals the tooth wear mechanism for harmonic gears, and provides a theoretical basis for the structural optimization design, wear reduction, and life prolonging of harmonic gears. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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20 pages, 5644 KiB  

Open AccessArticle

Microhardness, Indentation Size Effect and Real Hardness of Plastically Deformed Austenitic Hadfield Steel

by Quanshun Luo and Matthew Kitchen

Materials 2023, 16(3), 1117; https://doi.org/10.3390/ma16031117 - 28 Jan 2023

Cited by 7 | Viewed by 3461

Abstract

Microhardness testing is a widely used method for measuring the hardness property of small-scale materials. However, pronounced indentation size effect (ISE) causes uncertainties when the method is used to estimate the real hardness. In this paper, three austenitic Hadfield steel samples of different [...] Read more.

Microhardness testing is a widely used method for measuring the hardness property of small-scale materials. However, pronounced indentation size effect (ISE) causes uncertainties when the method is used to estimate the real hardness. In this paper, three austenitic Hadfield steel samples of different plastic straining conditions were subjected to Vickers microhardness testing, using a range of loads from 10 to 1000 g. The obtained results reveal that the origin of ISE is derived from the fact, that the indentation load P and the resultant indent diagonal d do not obey Kick’s law (P = A · d²). Instead, the P and d parameters obey Meyer’s power law (P = A · dⁿ) with n < 2. The plastically strained samples showed not only significant work hardening, but also different ISE significance, as compared to the non-deformed bulk steel. After extensive assessment of several theoretical models, including the Hays-Kendall model, Li-Bradt model, Bull model and Nix-Gao model, it was found that the real hardness can be determined by Vickers microhardness indentation and subsequent analysis using the Nix-Gao model. The newly developed method was subsequently utilised in two case studies to determine the real hardness properties of sliding worn surfaces and the subsurface hardness profile. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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20 pages, 9352 KiB  

Open AccessArticle

Thermo-Hydrodynamic Effect of Gas Split Floating Ring Seal with Rayleigh Step Grooves

by Shaoxian Bai, Dongdong Chu, Chunhong Ma, Jing Yang and Shiyi Bao

Materials 2023, 16(6), 2283; https://doi.org/10.3390/ma16062283 - 12 Mar 2023

Cited by 3 | Viewed by 2029

Abstract

The force equilibrium and moment equilibrium play a significant role on the sealing performance of gas split floating ring seals. A small deflection angle may generate seriously wear on sealing surface and cause seal failure. Therefore, the thermo-hydrodynamic lubrication analysis of gas split [...] Read more.

The force equilibrium and moment equilibrium play a significant role on the sealing performance of gas split floating ring seals. A small deflection angle may generate seriously wear on sealing surface and cause seal failure. Therefore, the thermo-hydrodynamic lubrication analysis of gas split floating ring seal with Rayleigh grooves is investigated considering the deflection angle and frictional heat of surface contact, which is beneficial to grasp the hydrodynamic characteristics and rules under high-temperature and high-speed conditions. Pressure and temperature distributions of sealing rings are numerically calculated for the cases with different deflection angle, rational speed, seal pressure and ambient temperature. Then, the hydrodynamic effect and sealing performance are analyzed. The obtained results show that, the surface Rayleigh step grooves do not present obvious hydrodynamic effect when split seal ring has no deflection. While, a significant hydrodynamic effect can be obtained when the split seal ring presents a deflection angle about dozens of micro radians. Here, a 10% increase of opening force is achieved when the deflection angle reaches 80 μrad in the case of speed 30,000 r/min and seal pressure 0.2 MPa. Moreover, the hydrodynamic effect becomes obvious with increasing deflection angle as well as rotational speed. Meanwhile, the growth of rotational speed results in an obvious increase of film temperature. The increase of ambient temperature has a significant influence on the decrease of leakage rate. When the ambient temperature increases from 340 K to 540 K, the leakage rate reduces exceeding 50%, however, it does not present obvious effect on the opening force. The proposed model has the potential to provide the theoretical basis and design guidance for surface grooves of gas split floating ring seal in the future. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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18 pages, 12571 KiB  

Open AccessArticle

Thermo-Hydrodynamic Lubricating Behaviors of Upstream Liquid Face Seals with Ellipse Dimples

by Shaoxian Bai, Kaixin Li, Jing Yang, Shiyi Bao and Chunhong Ma

Materials 2023, 16(8), 3248; https://doi.org/10.3390/ma16083248 - 20 Apr 2023

Cited by 4 | Viewed by 1617

Abstract

In order to obtain the leakage characteristics of an upstream pumping face seal with inclined ellipse dimples under high-temperature and high-speed liquid lubricating conditions, a thermo-hydrodynamic lubricating model is developed. The novelty of this model is that it takes the thermo-viscosity effect and [...] Read more.

In order to obtain the leakage characteristics of an upstream pumping face seal with inclined ellipse dimples under high-temperature and high-speed liquid lubricating conditions, a thermo-hydrodynamic lubricating model is developed. The novelty of this model is that it takes the thermo-viscosity effect and cavitation effect into account. The influence of operating parameters, such as rotational speed, seal clearance, seal pressure, ambient temperature and structural parameters, such as dimple depth, inclination angle, slender ratio and dimple number on the opening force and leakage rate, is numerically calculated. The results obtained show that the thermo-viscosity effect makes the cavitation intensity decrease noticeably, leading to an increase in the upstream pumping effect of ellipse dimples. Moreover, the thermo-viscosity effect may make both the upstream pumping leakage rate and opening force increase by about 10%. It can also be found that the inclined ellipse dimples can produce an obvious upstream pumping effect and hydrodynamic effect. Based on the reasonable design of the dimple parameter, not only can the sealed medium achieve zero leakage, but the opening force can also increase by more than 50%. The proposed model has the potential to provide the theoretical basis for and guide the future designs of upstreaming liquid face seals. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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18 pages, 9361 KiB  

Open AccessArticle

Graphene Enhances the Loading Capacity and Lubrication Performance of Ionic Liquids: A Molecular Dynamics Study

by Haodong Jiang, Yaoze Wang, Zhipeng Xiong, Runhua Zhou, Linyan Yang and Lichun Bai

Materials 2023, 16(14), 4942; https://doi.org/10.3390/ma16144942 - 11 Jul 2023

Cited by 4 | Viewed by 1532

Abstract

Ionic liquid (IL) combined with graphene additives have garnered extensive attention in the field of high-performance lubricating materials. However, the ambiguous mechanism of graphene influencing the load-carrying and anti-wear capacity of ILs needs further study. In this work, friction simulation shows that adding [...] Read more.

Ionic liquid (IL) combined with graphene additives have garnered extensive attention in the field of high-performance lubricating materials. However, the ambiguous mechanism of graphene influencing the load-carrying and anti-wear capacity of ILs needs further study. In this work, friction simulation shows that adding graphene causes friction coefficient to reduce by up to 88% compared with pure ILs, but lubrication performance is lost due to the destruction of graphene under high stress. Meanwhile, multilayer graphene has better friction-reducing performance and friction durability as compared to the monolayer structure, which is attributed to the easy-shear property and the reduction in the percentage of high tensile stress sites in multilayer graphene structure. In addition, it was found that excessively thick ILs film would form a three-body abrasive wear structure with graphene, which accelerated the structural destruction of graphene and caused a decline in its tribological properties. It is believed these findings can be valuable for designing of high-performance lubricating oil for practical engineering. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)
(This article belongs to the Section Manufacturing Processes and Systems)

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20 pages, 15250 KiB  

Open AccessArticle

High-Temperature Flow Behavior and Energy Consumption of Supercritical CO₂ Sealing Film Influenced by Different Surface Grooves

by Jing Yang, Shuaiyu Wang and Shaoxian Bai

Materials 2023, 16(22), 7129; https://doi.org/10.3390/ma16227129 - 11 Nov 2023

Viewed by 973

Abstract

The Brayton cycle system, as a closed cycle working under high-temperature, high-pressure and high-speed conditions, presents significant prospects in many fields. However, the flow behavior and energy efficiency of supercritical CO₂ is severely influenced by the structures of face seals and the [...] Read more.

The Brayton cycle system, as a closed cycle working under high-temperature, high-pressure and high-speed conditions, presents significant prospects in many fields. However, the flow behavior and energy efficiency of supercritical CO₂ is severely influenced by the structures of face seals and the sealing temperature, especially when the sealing gas experiment is the supercritical transformation process. Therefore, a numerical model was established to investigate the high-temperature flow behavior and energy consumption of face seals with different surface grooves. The effects of the operation parameters and groove structure on the temperature distribution and sealing performance are further studied. The obtained results show that the supercritical effect of the gas film has a more obvious influence on the flow velocity u_θ than u_r. Moreover, it can be found that the temperature distribution, heat dissipation and leakage rate of the gas face seals present a dramatic change when the working condition exceeds the supercritical point. For the spiral groove, the change rate of heat dissipation becomes larger, from 3.6% to 8.1%, with the increase in sealing pressure from 15 to 50 MPa, when the temperature grows from 300 to 320 K. Meanwhile, the open force maintains a stable state with the increasing temperature and pressure even at the supercritical point. The proposed model could provide a theoretical basis for seal design with different grooves on the supercritical change range in the future. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)

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21 pages, 8587 KiB  

Open AccessArticle

Vaporization Phase Transition in Cryogenic Liquid Oxygen Sealing Film on Spiral Groove Faces

by Junjie Chen, Chunhong Ma, Shaoxian Bai and Jing Yang

Materials 2024, 17(6), 1443; https://doi.org/10.3390/ma17061443 - 21 Mar 2024

Viewed by 1250

Abstract

The property of vaporization phase transition in liquid oxygen face seals is a key factor affecting the stability of mechanical face seals in many fields, especially under cryogenic conditions. Here, a numerical model based on the saturated vapor pressure is established to investigate [...] Read more.

The property of vaporization phase transition in liquid oxygen face seals is a key factor affecting the stability of mechanical face seals in many fields, especially under cryogenic conditions. Here, a numerical model based on the saturated vapor pressure is established to investigate the vaporization phase transition property of liquid oxygen sealing film. The novelty of this model is to take the influence of heat transfer and face distortions into consideration at the same time. The pressure and temperature distributions as well as face distortions are calculated, and then the property of vaporization phase transition and sealing performance are analyzed. It is found that spiral grooves may lead to the complex film temperature distributions and irregular vaporization distributions. With the increase in seal temperature and decrease in seal pressure, the vaporization area extends from the low-pressure side to the grooves area, and the vaporization rate increases rapidly. The more important thing is that the vaporization often brings a drastic fluctuation and non-monotonic change in opening force. Specifically, with the increase inin seal temperature from 55 K to 140 K, the opening force fluctuates violently, and the fluctuation range is more than 50%, showing an obvious instability. Finally, this study provides a design range of pressure and temperature values for liquid oxygen face seals. In these ranges, this kind of face seals can have a stable operation, which is beneficial to the practice engineering related to the complex properties of sealing fluid. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)

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20 pages, 12530 KiB  

Open AccessArticle

Research on Calculation and Optimization Methods for Tooth Flash Temperature and Meshing Power Loss of the Gear System in Drum Shearer

by Bo Bai, Run Mao, Wenchao Guo and Shimin Mao

Appl. Sci. 2024, 14(12), 5222; https://doi.org/10.3390/app14125222 - 16 Jun 2024

Cited by 2 | Viewed by 1024

Abstract

The operating conditions of the drum shearer are very complex, and its ranging arm gear system often suffers from gear scuffing and wear. Gear scuffing is caused by the adhesive wear, which is due to the instantaneous friction and flash temperature of the [...] Read more.

The operating conditions of the drum shearer are very complex, and its ranging arm gear system often suffers from gear scuffing and wear. Gear scuffing is caused by the adhesive wear, which is due to the instantaneous friction and flash temperature of the tooth surface, and the gear meshing power loss is also caused by tooth surface friction. In order to resist tooth scuffing and improve meshing efficiency of the transmission system, an improved semi-analytical tooth surface flash temperature calculation method was used. The tooth flash temperature status under various working conditions were analyzed in detail. Based on the mechanical model of the shearer drum picks, the load condition of the drum was analyzed. Under these load and boundary conditions, the misalignments of each gear pair in the ranging arm were calculated. The tooth surface load distribution was calculated under the gear misalignments, and then the theoretical tooth surface flash temperature and meshing power loss were determined. Next, the tooth micro-geometry was modified to reduce flash temperature and meshing power loss. The flash temperature distribution pattern of the optimized tooth surface was studied under various working conditions, and the meshing power loss was also obtained. Finally, experiments were conducted to verify the effects of the optimized tooth surface on the friction temperature rise and the effectiveness of the modification method. Tooth surface optimization aimed at reducing tooth surface flash temperature can also effectively reduce meshing power loss, which has a significant effect on gear anti-scuffing and energy saving. Full article

(This article belongs to the Topic Research on the Mechanical Wear of Gear-Shaped Parts)

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