Lubricants

Research

23 pages, 17020 KiB

Open AccessArticle

A Computational Fluid Dynamics-Based Study on the Effect of Bionic-Compound Recess Structures in Aerostatic Thrust Bearings

by Fangjian Yuan, Hang Xiu, Guohua Cao, Jingran Zhang, Bingshu Chen, Yutang Wang and Xu Zhou

Lubricants 2024, 12(11), 385; https://doi.org/10.3390/lubricants12110385 - 7 Nov 2024

Viewed by 402

Abstract

To investigate the effect of recess structures on the static and dynamic performance of aerostatic thrust bearings and to explore superior designs, this study analyzes the load-capacity theoretical model, identifying that the throttling effect and pressure-holding effect of the recess are the key [...] Read more.

To investigate the effect of recess structures on the static and dynamic performance of aerostatic thrust bearings and to explore superior designs, this study analyzes the load-capacity theoretical model, identifying that the throttling effect and pressure-holding effect of the recess are the key factors determining the bearings’ static performance. Computational fluid dynamics (CFD) was used to evaluate three types of recess structures: a simple-orifice recess (SOR), a rectangular-compound recess (RCR), and a bionic-compound recess (BCR). The results indicate that the BCR structure demonstrates efficient transmission performance by reducing flow resistance and diverting air, while ensuring a reasonable pressure drop as the radial ratio α_i changes. Additionally, the smaller air capacity of the BCR structure contributes to enhanced bearing stability, showing clear advantages in both static and dynamic performance. This research illustrates the practical application of bionics in mechanical design and provides new theoretical foundations and design strategies for improving aerostatic bearing performance. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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23 pages, 4143 KiB

Open AccessArticle

End-to-End Intelligent Fault Diagnosis of Transmission Bearings in Electric Vehicles Based on CNN

by Yong Chen, Guangxin Li, Anhe Li and Bolin He

Lubricants 2024, 12(11), 364; https://doi.org/10.3390/lubricants12110364 - 23 Oct 2024

Viewed by 505

Abstract

Environmental noise and transmission components can cause significant interference in vibration signals, rendering the extraction of bearing fault features challenging in service scenarios. Traditional fault diagnosis methods rely heavily on professional domain knowledge, prior models, and signal preprocessing methods. The accuracy of fault [...] Read more.

Environmental noise and transmission components can cause significant interference in vibration signals, rendering the extraction of bearing fault features challenging in service scenarios. Traditional fault diagnosis methods rely heavily on professional domain knowledge, prior models, and signal preprocessing methods. The accuracy of fault diagnosis depends on the quality of the fault-sensitive features extracted by vibration signal preprocessing methods. An improved convolutional neural network (CNN) end-to-end intelligent fault diagnosis model based on raw vibration data (RVDCNN) is proposed. The time-domain vibration signal of the transmission bearing is converted into a continuous two-dimensional numerical matrix, and a two-dimensional CNN model is constructed through network structure optimization. The original time-domain vibration signal numerical matrix of the bearing is trained and tested to extract and learn abstract fault features of different fault types, and then the fault classification of the bearing is achieved. To verify the generalizability of the RVDCNN intelligent fault diagnosis model, it is applied to the recognition of rolling bearings in the two-speed mechanical automatic transmission of electric vehicles, achieving recognition accuracy of 99.11% for seven types of bearings. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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15 pages, 8729 KiB

Open AccessArticle

Power Losses of Oil-Bath-Lubricated Ball Bearings—A Focus on Churning Losses

by Florian de Cadier de Veauce, Yann Marchesse, Thomas Touret, Christophe Changenet, Fabrice Ville, Luc Amar and Charlotte Fossier

Lubricants 2024, 12(11), 362; https://doi.org/10.3390/lubricants12110362 - 23 Oct 2024

Viewed by 524

Abstract

This study investigates the power losses of rolling element bearings (REBs) lubricated using an oil bath. Experimental tests conducted on two different deep-groove ball bearings (DGBBs) provide valuable insights into the behaviour of DGBBs under different oil levels, generating essential data for developing [...] Read more.

This study investigates the power losses of rolling element bearings (REBs) lubricated using an oil bath. Experimental tests conducted on two different deep-groove ball bearings (DGBBs) provide valuable insights into the behaviour of DGBBs under different oil levels, generating essential data for developing accurate models of power losses. Observations of the oil bath dynamics reveal the formation of an oil ring at high oil levels, as observed for planetary gear trains, leading to modifications in the oil flow behaviour. The experiments demonstrate that oil bath lubrication generates power losses comparable to injection lubrication when the oil level is low. However, as the oil level increases, so do the power losses due to increased drag within the bearing. This study presents a comprehensive model for calculating drag losses. The proposed drag power loss model accounts for variations in oil level and significantly improves loss predictions. A comparison of existing models with the experimental results shows good agreement for both bearings, demonstrating the effectiveness of the developed model in accounting for oil bath height in loss calculations. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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11 pages, 3173 KiB

Open AccessArticle

Carrying Capacity of Spherical Hydrostatic Bearings Including Dynamic Pressure

by Shengdong Zhang, Dongjiang Yang, Guangming Li, Yongchao Cheng, Jichao Li, Fangqiao Zhao and Wenlong Song

Lubricants 2024, 12(10), 346; https://doi.org/10.3390/lubricants12100346 - 10 Oct 2024

Viewed by 508

Abstract

To calculate the carrying capacity of spherical hydrostatic bearings, a numerical calculation model was presented. The influence law of dynamic pressure effect on the carrying characteristics of liquid hydrostatic spherical bearings is revealed. Under general working conditions, the dynamic pressure effect caused by [...] Read more.

To calculate the carrying capacity of spherical hydrostatic bearings, a numerical calculation model was presented. The influence law of dynamic pressure effect on the carrying characteristics of liquid hydrostatic spherical bearings is revealed. Under general working conditions, the dynamic pressure effect caused by the radial eccentricity of the bearing has little influence on the bearing load characteristics parameters; when the minimum width of the gap between the sealing edge is very small and the bearing rotational speed is high, the dynamic pressure effect is more obvious. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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23 pages, 10212 KiB

Open AccessArticle

Combining Artificial Neural Networks and Mathematical Models for Unbalance Estimation in a Rotating System under the Nonlinear Journal Bearing Approach

by Ioannis Tselios and Pantelis Nikolakopoulos

Lubricants 2024, 12(10), 344; https://doi.org/10.3390/lubricants12100344 - 6 Oct 2024

Viewed by 626

Abstract

Rotating systems are essential components and play a critical role in many industrial sectors. Unbalance is a very common and serious fault that can cause machine downtime, unplanned maintenance, and potential damage to vital rotating machines. Accurately estimating unbalance in rotor–bearing systems is [...] Read more.

Rotating systems are essential components and play a critical role in many industrial sectors. Unbalance is a very common and serious fault that can cause machine downtime, unplanned maintenance, and potential damage to vital rotating machines. Accurately estimating unbalance in rotor–bearing systems is crucial for ensuring the reliable and efficient operation of machinery. This research paper presents a novel approach utilizing artificial neural networks (ANNs) to estimate the unbalance masses in a multidisk system based on simulation data from a nonlinear rotor–bearing system. Additionally, this study explores the effect of various operating parameters on oil film stability and vibration response through a combination of bifurcation diagrams, spectrum cascades, Poincare maps, and orbit and FFT plots. This study demonstrates the effectiveness of ANNs for unbalance estimation in a fast and accurate way and discusses the potential of ANNs in smart online condition monitoring systems. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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19 pages, 9051 KiB

Open AccessArticle

Dynamic Modeling and Behavior of Cylindrical Roller Bearings Considering Roller Skew and the Influence of Eccentric Load

by Yang Yang, Jiayu Wang, Meiling Wang and Baogang Wen

Lubricants 2024, 12(9), 317; https://doi.org/10.3390/lubricants12090317 - 14 Sep 2024

Viewed by 537

Abstract

At high speeds, skew and skid may frequently occur for the rollers in cylindrical roller bearings, especially when under eccentric load, as the uneven load distribution along the generatrix of the roller further aggravates this phenomenon. In this paper, a dynamic model of [...] Read more.

At high speeds, skew and skid may frequently occur for the rollers in cylindrical roller bearings, especially when under eccentric load, as the uneven load distribution along the generatrix of the roller further aggravates this phenomenon. In this paper, a dynamic model of a cylindrical roller bearing was established, taking into account roller skewing and interactions with the cage. Firstly, the interaction between the roller and the raceway was calculated by slicing the roller along its generatrix. Furthermore, the computation of the interaction between the roller and the cage is based on elastic theory, taking into account pocket clearance. Subsequently, the dynamic equations for both rollers and cage were derived. Based on this foundation, an investigation was conducted to reveal how rotational speed, radial loads, and moment loads affect roller slipping, skewing characteristics, and interactions with the cage under uneven load conditions. The findings indicate a direct proportionality between roller slipping and bearing speed while exhibiting an inverse relationship with load magnitude. Additionally, it was observed that both bearing speed and load have a direct influence on roller skewing angle. Moreover, normal interaction force between the roller and cage demonstrates a direct proportionality to bearing speed while inversely correlating with load magnitude. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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16 pages, 15735 KiB

Open AccessArticle

Study on the Friction Characteristics and Fatigue Life of Carbonitriding-Treated Needle Bearings

by Yong Chen, Xiangrun Pu, Lijie Hao, Guangxin Li and Li Luo

Lubricants 2024, 12(7), 234; https://doi.org/10.3390/lubricants12070234 - 24 Jun 2024

Viewed by 952

Abstract

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding [...] Read more.

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding surface strengthening treatment on the bearing friction, wear, and fatigue life. The carbon and nitrogen co-infiltration surface-strengthening method was employed to prepare cylindrical and disc samples. The surface hardness, residual austenite content, microscopic morphology and organization composition, coefficient of friction, and wear scar were studied to analyze the effect on the wear performance of the material. The bearing fatigue wear comparison test was conducted on a test bench to compare the actual fatigue life and surface damage of the needle bearing through conventional martensitic quenching heat treatment and carbonitriding treatment. The results demonstrate that the carbonitriding strengthening method enhances the toughness of the material while improving its surface hardness. It also improves the wear resistance of the needle roller bearings, and the fatigue life of the bearings is significantly improved. In conclusion, carbon and nitrogen co-infiltration treatment is a strengthening method that effectively extends the service life of needle roller bearings, indicating its high practical value. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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20 pages, 6217 KiB

Open AccessArticle

Research on Design and Optimization of Micro-Hole Aerostatic Bearing in Vacuum Environment

by Guozhen Fan, Youhua Li, Yuehua Li, Libin Zang, Ming Zhao, Zhanxin Li, Hechun Yu, Jialiang Xu, Hongfei Liang, Guoqing Zhang and Weijie Hou

Lubricants 2024, 12(6), 224; https://doi.org/10.3390/lubricants12060224 - 17 Jun 2024

Viewed by 858

Abstract

Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve [...] Read more.

Micro-hole aerostatic bearings are important components in micro-low-gravity simulation of aerospace equipment, and the accuracy of micro-low-gravity simulation tests is affected by them. In order to eliminate the influence of air resistance on the attitude control accuracy of remote sensing satellites and achieve high fidelity of micro-low-gravity simulation tests, in this study, a design and parameter optimization method was proposed for micro-hole aerostatic bearings for a vacuum environment. Firstly, the theoretical analysis was conducted to investigate the impact of various bearing parameters and external conditions on the bearing load capacity and mass flow. Subsequently, a function model describing the variation in bearing load capacity and mass flow with bearing parameters was obtained utilizing a BP neural network. The parameters of aerostatic bearings in a vacuum environment were optimized using the non-dominated sorting genetic algorithm (NSGA-II) with the objectives of maximizing the load capacity and minimizing the mass flow. Subsequently, experimental tests were conducted on the optimized bearings in both atmospheric and vacuum conditions to evaluate their load capacity and mass flow. The results show that in a vacuum environment, the load capacity and mass flow of aerostatic bearings are increased compared to those in standard atmospheric conditions. Furthermore, it has been determined that the optimal solution for the bearing’s load capacity and mass flow occurs when the bearing has an orifice aperture of 0.1 mm, 36 holes, and an orifice distribution diameter of 38.83 mm. The corresponding load capacity and mass flow are 460.644 N and 11.816 L/min, respectively. The experimental and simulated errors are within 10%; thus, the accuracy of the simulation is verified. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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28 pages, 9099 KiB

Open AccessArticle

WLI, XPS and SEM/FIB/EDS Surface Characterization of an Electrically Fluted Bearing Raceway

by Omid Safdarzadeh, Alireza Farahi, Andreas Binder, Hikmet Sezen and Jan Philipp Hofmann

Lubricants 2024, 12(5), 148; https://doi.org/10.3390/lubricants12050148 - 27 Apr 2024

Viewed by 1481

Abstract

Electrical bearing currents may disturb the performance of the bearings via electro-corrosion if they surpass a limit of ca. 0.1 to 0.3 A/mm². A continuous current flow, or, after a longer time span, an alternating current or a repeating impulse-like current, [...] Read more.

Electrical bearing currents may disturb the performance of the bearings via electro-corrosion if they surpass a limit of ca. 0.1 to 0.3 A/mm². A continuous current flow, or, after a longer time span, an alternating current or a repeating impulse-like current, damages the raceway surface, leading in many cases to a fluting pattern on the raceway. Increased bearing vibration, audible noise, and decreased bearing lubrication as a result may demand a replacement of the bearings. Here, an electrically corroded axial ball bearing (type 51208) with fluting patterns is investigated. The bearing was lubricated with grease lubrication and was exposed to 4 A DC current flow. It is shown that the electric current flow causes higher concentrations of iron oxides and iron carbides on the bearing raceway surface together with increased surface roughness, leading to a mixed lubrication also at elevated bearing speeds up to 1500 rpm. The “electrically insulating” iron oxide layer and the “mechanically hard” iron carbide layer on the bearing steel are analysed by WLI, XPS, SEM, and EDS. White Light Interferometry (WLI) is used to provide an accurate measurement of the surface topography and roughness. X-ray Photoelectron Spectroscopy (XPS) measurements are conducted to analyze the chemical surface composition and oxidation states. Scanning Electron Microscopy (SEM) is applied for high-resolution imaging of the surface morphology, while the Focused Ion Beam (FIB) is used to cut a trench into the bearing surface to inspect the surface layers. With the Energy Dispersive X-ray spectrometry (EDS), the presence of composing elements is identified, determining their relative concentrations. The electrically-caused iron oxide and iron carbide may develop periodically along the raceway due to the perpendicular vibrations of the rolling ball on the raceway, leading gradually to the fluting pattern. Still, a simulation of this vibration-induced fluting-generation process from the start with the first surface craters—of the molten local contact spots—to the final fluting pattern is missing. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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17 pages, 7366 KiB

Open AccessArticle

Simulation Analysis and Experimental Study on the Fluid–Solid–Thermal Coupling of Traction Motor Bearings

by Hengdi Wang, Han Li, Zheming Jin, Jiang Lin, Yongcun Cui, Chang Li, Heng Tian and Zhiwei Wang

Lubricants 2024, 12(5), 144; https://doi.org/10.3390/lubricants12050144 - 25 Apr 2024

Viewed by 961

Abstract

The traction motor is a crucial component of high-speed electric multiple units, and its operational reliability is directly impacted by the temperature increase in the bearings. To accurately predict and simulate the temperature change process of traction motor bearings during operation, a fluid–solid–thermal [...] Read more.

The traction motor is a crucial component of high-speed electric multiple units, and its operational reliability is directly impacted by the temperature increase in the bearings. To accurately predict and simulate the temperature change process of traction motor bearings during operation, a fluid–solid–thermal simulation analysis model of grease-lubricated deep groove ball bearings was constructed. This model aimed to simulate the temperature rise of the bearing and the grease flow process, which was validated through experiments. The results from the simulation analysis and tests indicate that the temperature in the contact zone between the bearing rolling element and the raceway, as well as the ring temperature, initially increases to a peak and then gradually decreases, eventually stabilizing once the bearing’s heat generation power and heat transfer power reach equilibrium. Furthermore, the established fluid–solid–thermal coupling simulation analysis model can accurately predict the amount of grease required for effective lubrication in the bearing cavity, which stabilizes along with the bearing temperature. The findings of this research can serve as a theoretical foundation and technical support for monitoring the health status of high-speed EMU traction motor bearings. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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21 pages, 6146 KiB

Open AccessArticle

Calibration of Oil Film Thickness Acoustic Reflection Coefficient of Bearing under Multiple Temperature Conditions

by Fei Shang, Bo Sun, Shaofeng Wang, Yongquan Han, Wenjing Liu, Ning Kong, Yuwu Ba, Fengchun Miao and Zhendong Liu

Lubricants 2024, 12(4), 125; https://doi.org/10.3390/lubricants12040125 - 7 Apr 2024

Cited by 1 | Viewed by 1382

Abstract

Rolling mill bearings are prone to wear, erosion, and other damage characteristics due to prolonged exposure to rolling forces. Therefore, regular inspection of rolling mill bearings is necessary. Ultrasonic technology, due to its non-destructive nature, allows for measuring the oil film thickness distribution [...] Read more.

Rolling mill bearings are prone to wear, erosion, and other damage characteristics due to prolonged exposure to rolling forces. Therefore, regular inspection of rolling mill bearings is necessary. Ultrasonic technology, due to its non-destructive nature, allows for measuring the oil film thickness distribution within the bearing during disassembly. However, during the process of using ultrasonic reflection coefficients to determine the oil film thickness and distribution state of rolling mill bearings, changes in bearing temperature due to prolonged operation can occur. Ultrasonic waves are susceptible to temperature variations, and different temperatures of the measured structure can lead to changes in measurement results, ultimately distorting the results. This paper proposes using density and sound speed compensation methods to address this issue. It simulates and analyzes the oil film reflection coefficients at different temperatures, ultimately confirming the feasibility and effectiveness of this approach. The paper establishes a functional relationship between bearing pressure and reflection coefficients, oil film thickness, and reflection coefficients. This allows for the compensation of reflection coefficients under any pressure conditions, enhancing the accuracy of oil film thickness detection. The proposed method provides technical support for the maintenance of plate rolling processes in the steel industry. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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18 pages, 16375 KiB

Open AccessArticle

Study on Cage Stability of Solid-Lubricated Angular Contact Ball Bearings in an Ultra-Low Temperature Environment

by Bing Su, Han Li, Guangtao Zhang, Fengbo Liu and Yongcun Cui

Lubricants 2024, 12(4), 124; https://doi.org/10.3390/lubricants12040124 - 7 Apr 2024

Cited by 2 | Viewed by 1622

Abstract

In the ultra-low temperature environment, the material properties of the bearing change, which puts forward higher requirements for the dynamic performance of the bearing cage. The bearings operating in ultra-low temperature environments commonly use solid lubricants. This study first focused on measuring the [...] Read more.

In the ultra-low temperature environment, the material properties of the bearing change, which puts forward higher requirements for the dynamic performance of the bearing cage. The bearings operating in ultra-low temperature environments commonly use solid lubricants. This study first focused on measuring the traction coefficients of molybdenum disulfide (MoS₂) solid lubricant in a nitrogen atmosphere, and the Gupta fitting model is constructed to derive the traction equation. Subsequently, the dynamic differential equation of angular contact ball bearings was established, and the stability of the bearing cage in a nitrogen environment was simulated and analyzed based on the dynamic model. The accuracy of the simulation model was verified through comparison. The results show that less than 10% of errors exist between the experimental data and the traction curve fitted by the Gupta model, and the stability of the cage is closely related to operating parameters and bearing structure parameters. Cage stability increases with axial load but decreases with radial load. The cage stability is optimal when the radial internal clearance of the bearing is approximately 0.06 mm. When other conditions remain unchanged and the ratio of the cage pocket hole gap to the cage guide surface gap is 0.2, the cage stability is the best. The research results will provide a foundation for the design and application of solid-lubricated angular contact ball bearings in ultra-low temperature environments. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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14 pages, 8936 KiB

Open AccessArticle

Calculation and Analysis of Equilibrium Position of Aerostatic Bearings Based on Bivariate Interpolation Method

by Shuai Li, Yafu Huang, Hechun Yu, Wenbo Wang, Guoqing Zhang, Xinjun Kou, Suxiang Zhang and Youhua Li

Lubricants 2024, 12(3), 85; https://doi.org/10.3390/lubricants12030085 - 7 Mar 2024

Cited by 2 | Viewed by 1352

Abstract

The solution of equilibrium positions is a critical component in the calculation of the dynamic characteristic coefficients of aerostatic bearings. The movement of the rotor in one direction leads to bidirectional variations in the air film force, resulting in low efficiency when using [...] Read more.

The solution of equilibrium positions is a critical component in the calculation of the dynamic characteristic coefficients of aerostatic bearings. The movement of the rotor in one direction leads to bidirectional variations in the air film force, resulting in low efficiency when using conventional calculation methods. It can even lead to iterative divergence if the initial value is improperly selected. This study concentrates on the orifice throttling aerostatic bearings and proposes a novel method called the bivariate interpolation method (BIM) to calculate the equilibrium position. The equilibrium equation for the rotor under the combined influence of air film forces, gravity, and external loads is established. A calculation program based on the finite difference method is developed to determine the equilibrium position. The process of solving the equilibrium position and the convergence is compared with the secant method and the search method. Furthermore, the variation trend of the equilibrium position and stiffness when the external loads changes are studied based on the BIM. Finally, the correctness of the BIM to solve the equilibrium position is proved by comparing it with the experiment results. The calculation results indicate that the BIM successfully resolves the problem of initial value selection and exhibits superior computational efficiency and accuracy. The equilibrium position initially moves away from the direction of the external load as the load increases, and then this gradually approaches the load direction. The main stiffness increases with increases in the external load, while the variation in cross stiffness depends on the direction of the external load. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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16 pages, 11790 KiB

Open AccessFeature PaperArticle

Simulation Analysis and Experimental Research on Electric Thermal Coupling of Current Bearing

by Zhiwei Wang, Shuanglong Mao, Heng Tian, Bing Su and Yongcun Cui

Lubricants 2024, 12(3), 73; https://doi.org/10.3390/lubricants12030073 - 26 Feb 2024

Cited by 2 | Viewed by 1682

Abstract

With the advancement of industries such as high-speed railways, new energy vehicles, and wind power, bearings are frequently exposed to various electric field environments, leading to the need for lubricating oil films of bearings to withstand voltage. One of the major issues caused [...] Read more.

With the advancement of industries such as high-speed railways, new energy vehicles, and wind power, bearings are frequently exposed to various electric field environments, leading to the need for lubricating oil films of bearings to withstand voltage. One of the major issues caused by the breakdown discharge process of the lubricating oil film in bearings is the generation of local instantaneous high temperatures. This temperature rise is a key factor contributing to problems such as high operating temperature of bearings, surface damage in the contact area, and degradation of lubrication performance. This research article focuses on the comprehensive influence of bearing friction and electrical factors. It establishes a heat source calculation model and a temperature field simulation model specifically for current-carrying bearings. This study analyzes both the overall temperature rise of bearings and the local temperature rise resulting from breakdown discharge. Furthermore, the accuracy of the simulation analysis is verified through experiments. The temperature field simulation and experimental results consistently indicate that electrical environmental factors can cause an increase in the overall temperature rise of a bearing. Additionally, the breakdown and discharge of the lubricating oil film generate local instantaneous high temperatures in the contact area of the bearing. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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18 pages, 7265 KiB

Open AccessArticle

Influence of Bearing Wear on the Stability and Modal Characteristics of a Flexible Rotor Supported on Powder-Lubricated Journal Bearings

by Faisal Rahmani, Emad Makki and Jayant Giri

Lubricants 2023, 11(9), 355; https://doi.org/10.3390/lubricants11090355 - 22 Aug 2023

Cited by 1 | Viewed by 1247

Abstract

This study has investigated the influence of journal bearing wear on the dynamic behaviour of a flexible rotor with a central disc. Rotors supported on journal bearings are susceptible to self-excited whirling, leading to unstable conditions. Prior knowledge of the stability limit speed [...] Read more.

This study has investigated the influence of journal bearing wear on the dynamic behaviour of a flexible rotor with a central disc. Rotors supported on journal bearings are susceptible to self-excited whirling, leading to unstable conditions. Prior knowledge of the stability limit speed is important to avoid the excessive vibration of rotating machines. For the study in this paper, journal bearings were lubricated with powder owing to high-temperature applications where conventional oil lubricants would fail to perform. The governing equations for lubrication were derived using a simplified grain theory based on the theory of dense gases. The rotor shaft was discretized considering Timoshenko beam elements. Modal analysis was conducted to obtain the system’s natural frequencies, mode shapes, damping factors, stability limit speed, and unbalance response. This study has also evaluated the influence of wear depth on the dynamic behaviour of the rotor shaft system and found that bearing wear significantly affects the stiffness and damping characteristics of lubricating film. Consequently, free and forced vibration behaviour is also affected. It has been found that increased wear depth improves stability limit speed but has little influence on the unbalance response. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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