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Article
Publication date: 1 May 2006

Y. Zhang

To develop a more realistic model for molecularly thin film hydrodynamic lubrication by incorporating the fluid inhomogeneity and discontinuity effects across the fluid…

Abstract

Purpose

To develop a more realistic model for molecularly thin film hydrodynamic lubrication by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness in this lubrication.

Design/methodology/approach

The total mass flow of the fluid through the contact in a basic one‐dimensional molecularly thin film hydrodynamic lubrication is studied by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness, based on a simplified momentum transfer model between neighboring fluid molecules across the fluid film thickness. This flow is calculated according to the present approach and the theory of viscous flow between two contact surfaces. The total mass flow of the fluid through the contact in this lubrication is also calculated from conventional hydrodynamic lubrication theory, which was based on continuum fluid assumption in the whole lubricated contact. The ratio of this flow calculated from the present approach to that calculated from conventional hydrodynamic lubrication theory is here defined as the flow factor for a one‐dimensional molecularly thin film hydrodynamic lubrication due to the fluid inhomogeneity and discontinuity effects. Results of this flow factor are presented for wide operational parameters.

Findings

In the molecularly thin film hydrodynamic lubrication, when the fluid inhomogeneity and discontinuity across the fluid film thickness both are incorporated, the total fluid mass flow through the contact and thus the global fluid film thickness are increased. The combined effect of the fluid inhomogeneity and discontinuity across the fluid film thickness on the total fluid mass flow through the contact in this lubrication is determined by the operational parameter K=((∂p/∂xh2)/[6ηbulk(1−ξ)(ua+ub)]); when the operational parameter K is high, this effect is significant; when the operational parameter K is low, this effect is negligible. On the other hand, in this lubrication, when the combined effect of the fluid inhomogeneity and discontinuity across the fluid film thickness is incorporated, the shear stresses at the contact‐fluid interfaces are reduced and this reduction can be significant. This reduction may strongly depend on the value of the dimensionless discontinuity parameter Δ/D of the fluid across the fluid film thickness but weakly depend on the number n of the fluid molecules across the fluid film thickness.

Practical implications

An important and very useful research for the academic researcher and the engineer who are, respectively, engaged in the study and design of hydrodynamic lubrication on mechanical components especially of very low hydrodynamic lubrication film thickness. It is also important to the subsequent research of molecularly thin film hydrodynamic lubrication.

Originality/value

A new model of molecularly thin film hydrodynamic lubrication in one‐dimensional contacts is originally proposed and described by incorporating the fluid inhomogeneity and discontinuity effects across the fluid film thickness in this lubrication. This new model of molecularly thin film hydrodynamic lubrication is of importance to the theoretical study of molecularly thin film hydrodynamic lubrication.

Details

Industrial Lubrication and Tribology, vol. 58 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 13 March 2007

Emel Ceyhun Sabir and Erdem Koç

The main purpose of the study is to develop a theoretical model being capable of analysing the sealing and hydrodynamic‐hydrostatic lubrication mechanisms occuring between…

Abstract

Purpose

The main purpose of the study is to develop a theoretical model being capable of analysing the sealing and hydrodynamic‐hydrostatic lubrication mechanisms occuring between the mating surfaces of mechanical face seals.

Design/methodology/approach

The theoretical model developed is based on solving the governing basic lubrication equation (Reynolds differential equation) by employing a finite difference method. The main lubrication machanism is assumed to be converging‐diverging wedge which is formed by the relative tilt of the sealing surfaces. The non‐dimensional Reynolds equation was solved to give the pressure distribution and consequently the load and moment acting on the movable seal ring. The aim of the model is to predict the non‐dimensional hydrodynamic and hydrostatic load carrying capacity of the system.

Findings

Theoretical model developed is capable of estimating the hydrodynamic and hydrostatic behaviour of mechanical radial face seals. It is shown that a converging‐diverging wedge mechanism produces hydrodynamic pressure which in turn maintains the seperation of the surfaces. The tilt appears to be caused mainly by bearing misalignment. It has been shown that hydrostatic load or pressure centre is an important parameter for load balance of moving seal ring. It is easy and useful to calculate the dimensional parameters defined taking into account the different geometrical and operating parameters.

Originality/value

This paper offers a quick and easy opportunity to examine the hydrodynamic behaviour of movable seal ring of a mechanical face seal and provides a considerable contribution to the lubrication and sealing research area. With the general theoretical model developed, the behaviour of the seal ring can be modelled and estimated.

Details

Industrial Lubrication and Tribology, vol. 59 no. 2
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 1 January 2006

Y. Zhang

To review, analyze and present the effects of the contact‐fluid interfacial shear strength and contact‐fluid interfacial slippage and the critical importance of these…

Abstract

Purpose

To review, analyze and present the effects of the contact‐fluid interfacial shear strength and contact‐fluid interfacial slippage and the critical importance of these effects in elastohydrodynamic lubrication (EHL).

Design/methodology/approach

The experimental and theoretical research results of the contact‐fluid interfacial shear strength and its caused contact‐fluid interfacial slippage in hydrodynamic lubrication and especially in EHL obtained in the past decades and progressed in recent years by the present author and by others are reviewed. Analysis and presentation are made on both the contact‐fluid interfacial shear strength versus fluid pressure curve for a given bulk fluid temperature in an isothermal EHL and the influence of the bulk fluid temperature on this curve.

Findings

It is very clearly and well understood from the present paper that the value of the contact‐fluid interfacial shear strength in the inlet zone in an EHL contact, i.e. at low EHL fluid film pressures is usually low and usually has rather a weak dependence on the EHL fluid film pressure. This proves the correctness of the EHL theories previously developed by the author based on the assumption of this low value and dependence on the EHL fluid film pressure of the contact‐fluid interfacial shear strength. It is also very clearly understood that the bulk fluid temperature usually has a strong influence on the value of the contact‐fluid interfacial shear strength in EHL and the increase of this temperature usually significantly reduces the value of the contact‐fluid interfacial shear strength in EHL.

Practical implications

A very useful material for the engineers who are engaged in the design of EHL on gears, cams and roller bearings, and for the tribology scientists who thrust efforts in studying EHL and mixed EHL both by theoretical modeling and by experiments.

Originality/value

A new and generalized mode of mixed EHL is originally proposed by incorporating the finding of a more realistic mode of the contact regimes in a practical mixed EHL based on the contact‐fluid interfacial shear strength and contact‐fluid interfacial slippage effects. This mode of mixed EHL should become the direction of the theoretical research of mixed EHL in the future.

Details

Industrial Lubrication and Tribology, vol. 58 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 4 March 2014

Jinghu Ji, Yonghong Fu and Qinsheng Bi

– The purpose of this paper is to investigate a partially textured slider of infinite width with orientation ellipse dimples in liquid application.

Abstract

Purpose

The purpose of this paper is to investigate a partially textured slider of infinite width with orientation ellipse dimples in liquid application.

Design/methodology/approach

In this paper, the pressure distribution of lubrication between a partially textured slider and a smooth sliding slider is calculated by the multi-grid method. For the same dimple area, the influence of the ellipse dimple with geometric parameters, and distribution and orientation on the hydrodynamic lubrication is evaluated in terms of the dimensionless average pressure for a given set of operating parameters.

Findings

In the present work, the magnitude of the dimensionless average pressure seems proportional to the slender ratio. Consequently, the slender ratio may be chosen as large as possible based on fabrication techniques. The longer axes of ellipse dimples placed parallel to the direction of sliding always show the better hydrodynamic effect. Furthermore, the results show that the ellipse dimples can greatly improve hydrodynamic effect of partially surface textured slider of infinite width by proper design of these texturing parameters.

Originality/value

This paper develops a partial surface texturing infinitely width slider with orientation ellipse dimples for improving hydrodynamic lubrication.

Details

Industrial Lubrication and Tribology, vol. 66 no. 2
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 1 June 1956

Verein Deutscher Ingenieurs

Prof Dr. Ing. W. Peppler, in opening the Conference, suggested that insufficient attention was being paid to research on Lubrication and Wear in Germany at the present…

Abstract

Prof Dr. Ing. W. Peppler, in opening the Conference, suggested that insufficient attention was being paid to research on Lubrication and Wear in Germany at the present time. Whilst the work of Sommerfeld as early as 1904 and the existence of the Max Planck Gesellschaft, Department of Hydrodynamic Lubrication, in Göttingen was indicative of the German effort in the region of hydrodynamic lubrication it appeared from comparison of literature published in different countries during the past decade that Germany was falling behind England and U.S.A. in the study of boundary and mixed lubrication.

Details

Industrial Lubrication and Tribology, vol. 8 no. 6
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 8 February 2016

Xingxin Liang, Zhenglin Liu, Huanjie Wang, Xuhui Zhou and Xincong Zhou

The purpose of this study is to investigate the effects of partial texture location and dimple depth on load carrying capacity (LCC), friction coefficient and…

Abstract

Purpose

The purpose of this study is to investigate the effects of partial texture location and dimple depth on load carrying capacity (LCC), friction coefficient and circumferential flow of journal bearing.

Design/methodology/approach

Based on the Navier-Stokes equation, the methodology used computational fluid dynamics (CFD). A phase change boundary condition was applied on fluid domain, and the negative pressure at divergent region of oil film was considered.

Findings

It has been found that texture located at lubricant inlet area can improve the performance of the bearing, and the effect of shallow dimples is superior to the deep ones. However, the bearing performance will be reduced due to the texture located at the maximum pressure area. When texture is located at the lubricant outlet area, there will be two different situations: the part of the texture located within the oil film divergent area can improve the LCC, while the part that is beyond the divergent region will make the LCC decrease.

Originality/value

The lower-half oil film model was established only in this study to analyze the hydrodynamic lubrication performance of partial textured journal bearing, and the lower-half oil film was divided into three parts. A new cavitation algorithm was introduced to deal with the negative pressure. The formula for calculating the friction of liquid film is refined, including the consideration of vapor phase. The simulation results show that the location of partial texture have a great influence on the bearing performance.

Details

Industrial Lubrication and Tribology, vol. 68 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 10 September 2018

Leonid Burstein

This paper aims to assess the behavior of hydrodynamic lubrication between surfaces with pores of different sizes. The profiles of the opposite surfaces are treated by…

Abstract

Purpose

This paper aims to assess the behavior of hydrodynamic lubrication between surfaces with pores of different sizes. The profiles of the opposite surfaces are treated by lines with different number of pores that allow clarification of each of the surfaces influence on the lubricating film behavior.

Design/methodology/approach

A transient, spatially one-dimensional model of surfaces with surface-unequal pore numbers and sizes has been applied in the context of liquid lubrication. Special program for parametric study has been developed.

Findings

The calculations show that lubricating film between two surfaces with unequal pores provides better load support in comparison to the surfaces with equal pores. It is also shown that interaction between the pores of the opposite surfaces should be taken into consideration for defining better qualitative behavior of lubricating film.

Practical implications

The results of parametric calculations together with surface model can be used to design optimum lubrication quality of the rubbing surfaces.

Originality/value

The hydrodynamic behavior of a lubricating film between surfaces with different number of pore and their dimensions has been theoretically studied for the first time.

Details

Industrial Lubrication and Tribology, vol. 70 no. 7
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 11 April 2016

Zhenpeng He and Wenqin Gong

This paper aims to give the guidance for the design of the bearing.

Abstract

Purpose

This paper aims to give the guidance for the design of the bearing.

Design/methodology/approach

The finite element method, the multi-body dynamics method, the finite difference method and the tribology are combined to analyze the lubrication.

Findings

The performance parameters of crankshaft-bearing system such as the misalignment, the oil filling ratio and the oil groove are also investigated. Misalignment causes the pressure to incline on one side and the pressure increases obviously. Filling ratio has great relationship with pressure distribution; the factors influencing the filling ratio are also analyzed. Different oil groove models are investigated, as it can provide the theory for oil groove design, and three factors above are always combined to influence the lubrication characteristics.

Originality/value

The optimization of bearing system is conducted by orthogonal test and neural network, unlike the linear optimization theory. Neural network uses the nonlinear theory to optimize crankshaft-bearing system.

Details

Industrial Lubrication and Tribology, vol. 68 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 9 April 2018

Ruilong Du, Yinglong Chen and Hua Zhou

The purpose of this paper is to propose a simulation model for studying the lubricating gap between the ring gear and the case in internal gear pumps.

Abstract

Purpose

The purpose of this paper is to propose a simulation model for studying the lubricating gap between the ring gear and the case in internal gear pumps.

Design/methodology/approach

The pressure distribution of the wedge-shaped oil film between the ring gear and the case is obtained based on the theory of film lubrication using the Reynolds equation implemented with MATLAB. After that, the balance of the ring gear is achieved by the radial micro motion of the ring gear. The power loss due to the leakage and the shear stress is then calculated for optimized design of the radial clearance.

Findings

The hydrodynamic effect and the squeezing effect of the wedge-shaped oil film play a role in the hydrodynamic balance of the ring gear, and they become more intense when the operating speed gets lower and the pressure gets higher. The optimal radial clearance should stay between 20 and 25 µm for the minimum power loss.

Originality/value

The present research provides the first simulation model that treats the oil film between the ring gear and the case as wedge-shaped oil film and explains why the ring gear stays balanced. Furthermore, the simulation model can be regarded as a tool for optimized design of the radial clearance.

Details

Industrial Lubrication and Tribology, vol. 70 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

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Article
Publication date: 9 February 2010

C. Iliev

Testing of silicon nitride (Si3N4) or silicon carbide (SiC), sliding on itself in water, revealed that hydrodynamic lubrication can be obtained at low‐sliding velocity…

Abstract

Purpose

Testing of silicon nitride (Si3N4) or silicon carbide (SiC), sliding on itself in water, revealed that hydrodynamic lubrication can be obtained at low‐sliding velocity. The purpose of this paper is to study the performance of Si3N4‐metals pairs, sliding in water.

Design/methodology/approach

Ball on disc unidirectional sliding tests are run with Si3N4 against tool steel, stainless steel and cast iron in water. The friction force is recorded continuously and the wear is evaluated at the end of the run by geometric technique. In addition, SiC sliding on itself in oxidant solution (3 per cent solution of CrO3 in water) is tested.

Findings

The measured friction and wear of water‐lubricated Si3N4 against metals are higher compared to Si3N4 sliding on itself. At the end of the run‐in SiC, lubricated by the oxidant solution, obtains hydrodynamic lubrication and friction and wear are lower than in water‐lubricated SiC.

Research limitations/implications

The experimental results obtained are valid within the range of load and sliding velocity applied – 1‐10 N, 0.04‐0.33 m/s, respectively. The Si3N4 sliding against metals in water over sliding distance of 3,000 m has not shown tendency towards hydrodynamic lubrication.

Originality/value

The paper presents test data on friction and wear properties of Si3N4 sliding against metals in water. The low friction and ball wear rate of the SiC, lubricated by the oxidant solution, shows the potential of the 3 per cent distilled water solution of CrO3 to surpass water as a lubricant for SiC sliding bearings.

Details

Industrial Lubrication and Tribology, vol. 62 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

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