• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1975-1981
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• 1991

A new numerical solution of the elastohydrodynamic lubrication(EHL) problem of an axially profiled cylindrical roller is presented. A finite difference method and the Newton-Raphson method are used to solve the nonlinear system equations. A non-uniform grid system is adopted to reduce the number of grid points and to obtain accurate solution. For two different types of profiles which have similar elastostatic pressure distribution, the EHL results show large differences. Especially the difference in film shape is larger than in pressure distribution. Therefore, the magnitude of the minimum film thickness should be a major criteria to design the axial profile of the roller. Variations of the minimum film thickness with dimensionless parameters show considerably different behavior from those of infinite solution and show a good agreement with the experimental data in literatures. Present numerical scheme can be used generally in the analysis of three-dimensional EHL problem.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.101-110
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• 1997

An experimental study was performed to discover the tribological behaviors of pure silver coated 52100 bearing steel. Pure silver coatings ranging from 80 nm to several micrometers were produced by a thermal evaporation coating method. Experiments using a thrust ball bearing-typed rolling test-rig were performed for the investigations of the influence of coating thickness on the tribological rolling behavior. The existence of optimum film thickness which revealed minimum rolling resistance was discovered. A careful analysis on the contact surfaces for the optimum film thickness has been performed. The contact patches produced by the transferred silver films played an important role for the rolling resistance to keep low.

• Tribology and Lubricants
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• v.13 no.3
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• pp.85-92
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• 1997

An experimental study was performed to discover the tribological behaviors of pure silver coated 52100 bearing steel. Pure silver coatings ranging from 80 nm to several micrometers were produced by a thermal evaporation coating method. Experiments using a thrust ball bearing-typed rolling test-rig were performed for the investigations of the influence of coating thickness on the tribological rolling behavior. The existence of optimum film thickness which revealed minimum rolling resistance was discovered. A careful analysis on the contact surfaces for the optimum film thickness has been performed. The contact patches produced by the transferred silver films played an important role for the rolling resistance to keep low.

• Tribology and Lubricants
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• v.28 no.2
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• pp.70-80
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• 2012

Non-contact type mechanical face seals installed in mechanical systems prevent leakage of working fluid using thin working fluid film between stator and rotor. For that purpose, various kinds of surface profiles, grooves and conings have been applied on seal surfaces of stator and rotor to generate hydrodynamic and hydrostatic pressure. The thickness distribution of working fluid film is one of important factors which affect the working performances of mechanical face seal, and it is strongly affected by the surface height profiles of stator and rotor. Therefore, appropriate design of surface height profiles of stator and rotor is necessary to optimize the working performances and life of mechanical face seal. In this study, numerical analysis using finite volume method was conducted to estimate the working performances of wavy mechanical face seals which have 36 coning combinations. As results, minimum thickness of working fluid film, leakage volume of working fluid and friction torque in static equilibrium condition of mechanical face seal, and stiffness of working fluid film were obtained. The results show that the working performances of mechanical face seal were affected by the coning combinations which can change the thickness distribution of working fluid film and pressure distribution in sealing region of mechanical face seal.

• Tribology and Lubricants
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• v.14 no.3
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• pp.87-93
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• 1998

Crank pin bearing in two-stroke marine diesel engine is operated under quite severe conditions since the elements are big and heavy and the sliding speed is very slow. Therefore it is very difficult to form oil film. In this paper, two types of bearings with different groove shape are compared. One has circumferential oil groove at lower position and the other has lengthwise oil groove at upper position. Bearing clearance, oil inlet pressure and length to diameter ratio are selected as design parameters. Locus of journal center and minimum oil film thickness are investigated to compare two cases.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.578-583
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• 1997

Abstract-Crosshead bearing in two-stroke marine diesel engine is operated under quite severe condition since the load on the bearing is sybject to the loading in a unidirectional and the sliding speed is very slow and oscillatory. So it is very difficult to form oil film and maintain the load. In this paper, two types of bearing are compared. One has large sized oil pocket and the seleted as multi-small oil grooves. Bearing clearance, oil inlet oressure and bearing types are selected as analysis parameters. Loci of journal center are presented to compare several cases. It is found that bearing clearance and shape affect to minimum film thickness.

• Journal of Drive and Control
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• v.10 no.3
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• pp.7-13
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• 2013

Hydraulic vane pumps are widely used in various hydraulic systems because of its compactness and light weight. It is well known that the vanes and cam ring are separated by very thin liquid films which result in the EHL state. Contrary to the case of cylindrical roller bearings, the inlet and side boundary pressures are much higher than the atmospheric pressure. In this paper, a numerical solution of the EHL of finite line contacts between the cam ring and vane tip with profiled ends is presented. Using a finite difference method with non-uniform grids and the Newton-Raphson method, converged solutions are obtained for moderate load and material parameters. The EHL pressure distribution and film shape are considerably affected by pump delivery pressure and the side boundary condition applied. Both the maximum pressure and the minimum film thickness always occurred near the edge regions. The present results can be used in the design of optimum vane profile in hydraulic vane pump.

• Tribology and Lubricants
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• v.25 no.3
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• pp.157-162
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• 2009

In this paper, the hydrodynamic pressure and minimum oil film thickness of a pin bush bearing for a connecting rod have been analyzed as functions of the number of oil grooves and an arc length of oil grooves. The lubrication characteristic of a pin bush is governed by oil groove design factors, which are considered in this study. The most influential design parameter is a number of oil grooves, which is three oil grooves with an arc length of oil groove, 1/6($60^{\circ}$). This means that oil groove with a long arc length of a pin bush does not contribute to the hydrodynamic pressure development. Thus the optimal design of a pin bush is necessary with an increased number of oil grooves and a reduced arc length.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.437-442
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• 2018

This work reports the preparation of Al-Ti based oxide thin films and their optical properties. Although the transmittance of a $TiO_2/Al2O_3$ bilayer structure was as high as 90% at wavelengths of 600 nm or larger, the reflectance of the bilayer reached its minimum at wavelengths of around 360 nm. The transmittance of an 89-nm-thick $TiO_2$ thin film rapidly increased and then decreased at a critical wavelength because of destructive interference. The wavelength corresponding to the reflectance minimum increased after an increase in $TiO_2$ film thickness. The smooth surface morphology of the AlTiO thin film was retained up to a film thickness of 65 nm, and the transmittance of the film was inversely proportional to film thickness, in accordance with the general tendency for optical films. The reflectance of the AlTiO film at visible light wavelengths was lower than that of the $TiO_2$ film, which implies that the AlTiO film is suitable for applications as an optical thin film layer in semitransparent solar cells.

• Tribology and Lubricants
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• v.32 no.4
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• pp.132-139
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• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.