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11 – 20 of over 1000Kang Yan, Hulin Li, Ning Ding, Dan Jiang and Xianghui Meng
Friction and wear are very important factors in predicting the performance of journal bearings, particularly under heavy load in start-up processes. However, there are few…
Abstract
Purpose
Friction and wear are very important factors in predicting the performance of journal bearings, particularly under heavy load in start-up processes. However, there are few relevant studies on the numerical model. This study aims to establish a transient-mixed lubrication model to predict the performance of journal bearings, focusing on the friction and wear behavior under heavy load during start-up.
Design/methodology/approach
The average Reynold equation, three-dimensional energy equation, shear stress model for friction and Archard model for wear are coupled in the transient model by finite difference method. The linear wear simulation method is bought out to reduce the update times and the calculation time.
Findings
The different start-up accelerations and linear wear times set are compared and discussed, which indicates a reasonable start-up acceleration is necessary for journal bearings under heavy load during start-up, and setting linear wear times is an effective method to reduce the simulation time significantly. Furthermore, the wear profile in the start-up process spreads in both the clearance and circumferential directions, but mainly in the clearance direction, which increases the minimum film thickness and affects the friction performance.
Originality/value
This study is of great significance for the numerical prediction of the transient performance of journal bearings during start-up considering friction and wear.
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Wei Pu, Jiaxu Wang, Guangwu Zhou, Ke Xiao and Junyang Li
The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of…
Abstract
Purpose
The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts.
Design/methodology/approach
The most recently published mixed elastohydrodynamic (EHL) model by Pu and Zhu is used. Three different machined rough surfaces are discussed and the correlated inclined angle of surface velocity varies from 0° to 90° in the analyzed cases. These cases are carried out in a wide range of speeds (five orders of magnitude) while the simulated lubrication condition covers full-film and mixed EHL down to the boundary lubrication.
Findings
The results indicate that the variation of the average film thickness corresponding to different entrainment angles is distinct from those without considering surface roughness. In addition, the surface topography appears to have an immense effect on the lubrication film thickness in the exceptive situation.
Originality/value
This paper has not been published previously. Surface roughness has attracted much attention for many years owing to the significant influence on lubricating property. However, previous studies mainly focus on the counterformal contact with the same direction between surface velocity and principal axis of the contact zone. Little attention has been paid to the specific condition with the arbitrary direction of rolling and sliding velocities found in hypoid gears and worm, and some other components. The purpose of this study is to describe and observe the effect of surface topography associated with arbitrary directions of rolling and sliding velocities on the performance of lubricating films in elliptical contacts based on the most recently published mixed EHL model by Pu and Zhu.
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Hua Zhang, Guangwu Zhou, Ping Zhong, Kepeng Wu and Xingwu Ding
The purpose of this paper is to study the influence of friction coefficient of materials with different elastic modulus on the variation of velocity and load under water…
Abstract
Purpose
The purpose of this paper is to study the influence of friction coefficient of materials with different elastic modulus on the variation of velocity and load under water lubrication and oil lubrication conditions.
Design/methodology/approach
Low-viscosity lubricating oil and water were used as lubricants to test the friction performance of the ball-disc contact friction pair in the lubrication state on the universal micro-tribometer multi-functional friction and wear test system.
Findings
In the same speed range, the lubrication states from soft to rigid materials are not necessarily similar to each other. Generally, the material with low elastic modulus is suitable in low-viscosity lubricant environments, while the material with high elastic modulus has relatively smaller friction coefficients in oil-lubricated environments compared with water lubrication. However, the coefficients of polyethylene, polytetrafluoroethylen and polyoxymethylene are exceeded by rubber’s coefficients under water lubrication in the same experiment environments, and their lubrication states are not affected by lubricants. The friction coefficient of the friction pair decreases with the increase of loads; however, it does not apply to all materials. The friction coefficients of materials with smaller elastic modulus such as rubber under high loads are rather large. Therefore, the elastic modulus of the material under high loads is a factor to be considered.
Originality/value
The Stribeck curves study of the ball-disk contact friction pair comprising soft and rigid materials, whose elastic modulus is from hundreds of GPa to a few of MPa, was carried out. The influence of different speeds, loads and lubricants on the friction coefficient of the friction pair was revealed, which provided a research basis for the selection and matching of friction pair materials.
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Chunxing Gu, Li Dai, Di Zhang and Shuwen Wang
This paper aims to study the startup performance of thrust bearing. The effects of acceleration scenarios, roughness, the area ratio of texture and texture depth on the transient…
Abstract
Purpose
This paper aims to study the startup performance of thrust bearing. The effects of acceleration scenarios, roughness, the area ratio of texture and texture depth on the transient startup performance of the thrust bearing were analyzed.
Design/methodology/approach
The lubrication model is solved by the Reynolds equation with the mass-conservation boundary condition. The Greenwood and Tripp contact model is used to predict asperity contact load. The finite volume method is used to discretize the governing equations.
Findings
By studying the bearing performance with different acceleration functions, it was found that the higher the acceleration at the beginning of the startup, the faster the thrust bearing operates under the hydrodynamic lubrication regime in the start stage. It appears that the friction and contact time of asperity increase with the increasing roughness. The optimal area ratio of texture is within 30%–50%. The depth of texture ranging from 1 to 2 is the best.
Originality/value
This paper proposes a transient mixed lubrication analysis model of the thrust bearing. This model can be used to analyze the variations of tribological performance and lubrication regime of the thrust bearing under different acceleration scenarios.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2022-0268/
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Shi Chen, Zhiyong Han, Qiang Zeng, Bing Wang, Liming Wang, Liuyang Guo and Yimin Shao
Hydro-viscous drive (HVD) clutches are widely used in equipment requiring soft start, such as fans and pumps, to transmit torque and adjust speed by changing the gap distance…
Abstract
Purpose
Hydro-viscous drive (HVD) clutches are widely used in equipment requiring soft start, such as fans and pumps, to transmit torque and adjust speed by changing the gap distance between friction pairs. This paper aims to propose a novel two-parameter evaluation method for HVD during the mixed lubrication stage. The objective is to develop an effective model that establishes the relationship between these parameters and the actual surface topography.
Design/methodology/approach
In the presented methods, the fractal features of the real manufacturing surface are calculated based on the power spectrum function by the ultra-depth three-dimensional microscope. After that, the hybrid friction model of the friction plate is established based on mixed elasto-hydrodynamic lubrication theory, boundary friction model and fractal theory. Then the torque and load bearing characteristics of the clutch are obtained, and the influences of the surface fractal features are investigated and discussed. Finally, the Weierstrass–Mandelbrot function is adopted for the surface topography characterization and evaluation.
Findings
The results indicate that the proposed method exhibits good accuracy, while the speed difference between the friction pair exceeds 2,500 rpm. It is concluded that this paper proposed a way to evaluate the torque and loading capacity of HVD considering the real manufacturing surface topography and is helpful for surface optimization.
Originality/value
The originality and value of this study lie in its development of a novel torque and load bearing capacity evaluation method for HVD in mixed lubrication stage, considering manufacturing surface topography and describing the real manufacturing surface.
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Anastasios Zavos and Pantelis Nikolakopoulos
Compression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top…
Abstract
Purpose
Compression rings are the main sources of frictional losses in internal combustion engines. The present paper aims to present a thermo-mixed hydrodynamic analysis for coated top compression rings. To understand the coating effects, the main tribological parameters are investigated into a ring-cylinder conjunction in a motorbike engine. Furthermore, flow simulations have been carried out on how different worn profiles on the cylinder inner liner affects friction, lubricant film and localized contact deformation of the coated compression rings.
Design/methodology/approach
In this paper, the basic geometrical dimensions of the top compression ring-cylinder system are obtained from a real motorbike engine. A 2D axisymmetric CFD/FLOTRAN model is created for coated compression rings. Flow simulations are performed by solving the Navier-Stokes and the energy equations. The load capacity of the asperities is also taken into account by Greenwood and Tripp contact model. Realistic boundary conditions are imposed to simulate the in-plane ring motion. The simulation model is validated with analytical and experimental data from the literature. Under thermal considerations, the contribution of worn cylinder profiles in conjunction with different coated compression rings is presented.
Findings
This research shows that because of thermal effects, the boundary friction is higher at reversals and the viscous friction is lower because of reduced oil viscosity. As regards to the isothermal case, the viscous friction is greater because of a higher lubricant viscosity. In the case of chromium-plated ring, boundary friction was 16 per cent lower than a grey cast iron ring taking into account thermal effects. Regarding the localized contact deformation, the coated compression rings showed lower values under different worn cylinder shapes. In particular, hard wear-resistant (Ni-Cr-Mo) coating showed the slighter local deformation. Therefore, the worn cylinder profiles promote boundary/mixed lubrication regime, whereas the lobed profile of cylinder inner liner becomes more wavy.
Originality/value
The solution of the thermo-mixed lubrication model, concerning the piston ring and worn cylinder tribo pair by taking into account the coating of the top compression ring.
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Dong Guan, Harry H. Hilton, Zhengwei Yang, Li Jing and Kuan Lu
This paper aims to investigate the lubrication regime in spherical pump, especially under different structural parameters and operational conditions.
Abstract
Purpose
This paper aims to investigate the lubrication regime in spherical pump, especially under different structural parameters and operational conditions.
Design/methodology/approach
A ball-on-plane configuration is adopted to represent the contact model between spherical piston and cylinder cover. The governing equations, which include the Reynolds and elasticity equations, are solved and validated by Jin–Dowson model. Both minimum film thickness and lambda ratio (ratio of minimum fluid film thickness to combined surface roughness of the piston and cylinder cover) of the equivalent model are obtained using an established model.
Findings
The results indicate that piston diameter and radial clearance are the two main factors affecting the pump lubrication regime. Other related parameters such as rotation speed of the piston, load, viscosity of working medium, material matching and surface roughness of piston and cylinder cover also have different impacts on the lubrication regime of the spherical pump.
Originality/value
These results emphasize the importance of the design and manufacturing parameters on the tribological performance of spherical pumps and these are also helpful in improving the spherical pump lubrication regime and enlarging its life cycle. This is to certify that to the best of the authors’ knowledge, the content of this manuscript is their own work. This manuscript has only been submitted to this journal and never been published elsewhere. The authors certify that the intellectual content of this manuscript is the product of their own work and that all the assistance received in preparing this manuscript and sources has been acknowledged.
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Wei Cao, Jiaxu Wang, Wei Pu, Ying Zhang, Jiqiang Wu, Si Ren and Jianbing Long
Previous studies were mainly focused on profile designation of bearing rollers and lubrication performance without considering roller-races skidding. However, the width of round…
Abstract
Purpose
Previous studies were mainly focused on profile designation of bearing rollers and lubrication performance without considering roller-races skidding. However, the width of round corner, load, rotational speed and some other parameters have significant effects on the roller-races sliding speed. This paper aims to investigate the effect of round corner on lubricating characteristics between the heavily loaded roller and inner race considering skidding and roughness.
Design/methodology/approach
A mixed elastohydrodynamic lubrication (EHL) model which is capable of handling practical cases with 3D machined roughness is combined with the skidding model to investigate the effect of round corner on lubricating characteristics between the heavily loaded roller and inner race.
Findings
The width of round corner and round corner radius have a desirable range under certain operating condition, within which the maximum pressure, stress and maximum flash temperature remain low. The optimized range is sensitive to the operating condition. Roughness and skidding narrow the optimized range of round corner radius. Roughness increases the pressure peak, Mises stress and friction coefficient. At the same time, skidding and roughness have obvious effects on film thickness at the contact center area if the round radius is small.
Research limitations/implications
This paper uses the Harris skidding model that has a relatively bigger error, which is not accurate if the bearing load is less.
Practical implications
This paper unifies the skidding model and mixed EHL model which can be used as a tool for optimization design and lubricating performance analysis of cylindrical roller bearing.
Originality/value
Lubrication analyses for roller bearing are assumed to be pure rolling contact between roller and races in a previous study, which could not reflect the real contact characteristics. The skidding model is merged into a mixed EHL model which can be used as a dynamic tool to analyze the lubricating performance considering the round corner, skidding and roughness.
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Zhongliang Xie, Zhu-shi Rao, Na Ta and Ling Liu
As the companion paper of Part I, this paper aims to get more insight into the essence of lambda and to reveal its nature and role in the transition of lubrication states. Mixed…
Abstract
Purpose
As the companion paper of Part I, this paper aims to get more insight into the essence of lambda and to reveal its nature and role in the transition of lubrication states. Mixed lubrication (ML) model with micro-asperities contacts has been discussed in details in Part I.
Design/methodology/approach
Mimetic algorithm is used to get numerical solutions. Relationships between film thickness ratios and lubrication states transition with different external loads, rotating speeds, radial clearances, elastic modulus, surface hardness and roughness parameters are obtained.
Findings
The characteristic parameters of transitions from boundary lubrication (BL) to ML and ML to hydrodynamic lubrication (HL) are studied to determine how these parameters change with above factors. Finally, the essence and major influencing factors of lambda are summarized for such bearings.
Originality/value
In Part II, the authors believe that the paper presents for the first time: further insight into the essence of the lambda ratio, and its role in the lubrication states transition are given; the determinations of the characteristic parameters of transition from BL to ML and ML to HL are investigated for the first time; the characteristic parameters of transitions from BL to ML and ML to HL are also studied to determine how parameters (external load, rotating speed, radial clearance, elastic modulus, surface hardness and roughness parameter) change with above factors; a summary of the essence and major influencing factors of lambda for such bearings is given.
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Cavitation in piston-ring lubrication is studied as part of the performance of piston-ring assemblies. Cavitation degrades performance in engineering applications and its effect…
Abstract
Purpose
Cavitation in piston-ring lubrication is studied as part of the performance of piston-ring assemblies. Cavitation degrades performance in engineering applications and its effect is that it alters the oil film pressure, generated at the converging-diverging wedge of the interface. Studies tried to shed light to the phenomenon of cavitation and compare it with cavities that have been identified in bearings. The paper aims to discuss this issue.
Design/methodology/approach
Lubricant formulations were used for parametric study of oil film thickness (OFT) and friction providing the OFT throughout the stroke and LIF for OFT point measurements. Lubricant formulation affects cavitation appearance and behaviour when fully developed.
Findings
Cavitation affects the ring load carrying capacity. Different forms of cavitation were identified and their shape and size (length and width) is dictated from reciprocating speed and viscosity of the lubricant. A clear picture is given from both techniques and friction results give quantifiable data in terms of the effect in wear and cavitation, depending on the lubricant properties.
Research limitations/implications
Engine results are limited due to manufacturing difficulties of visualisation windows and oil starvation. Therefore, full stroke length sized windows were not an option and motoring tests were implemented due to materials limitations (adhesive and quartz windows). Lubricant manufacturer has to give data regarding the chemistry of the lubricants.
Originality/value
The contribution of cavitation in piston-ring lubrication OFT, friction measurements and lubricant parameters that try to shed light to the different forms of cavitation. A link between viscosity, cavitation, shear thinning properties, OFT and friction is given.
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