• Title/Summary/Keyword: Hydrodynamic Friction

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Fundamental study on the effect of friction reduction based micro-scale surface texturing (Micro-scale surface texturing을 기반으로 한 저마찰효과에 대한 기초연구)

  • Chae Younghun;Kim SeockSam
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2004.11a
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    • pp.17-24
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    • 2004
  • Surrface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

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Friction Characteristics for Density of Micro Dimples Using Photolithography (포토리소그라피를 이용한 마이크로 딤플의 밀도에 따른 마찰 특성)

  • Kim Seock-sam;Chae Young-hun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.3 s.234
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    • pp.411-417
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    • 2005
  • Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

Friction Characteristics of the Piston-Ring Assembly Varying Engine Operation Coditions (운전조건변화에 따른 피스톤-링 결합체 마찰특성)

  • 윤정의;김승수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.6
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    • pp.1510-1519
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    • 1994
  • It is important to understand the friction characteristics between piston-ring assembly and cylinder wall for the friction loss reduction as well as the solution of problem such as scuffing wear and oil consumption. A new system was developed for the piston-ring assembly friction force measurement. This system was applied to the friction force measurement to find its functional relationship with variables such as engine speed, oil viscosity, and engine load. The friction mean effective pressure(fmep) was found to have a linear relationship with$(\vpsilon{U})^{0.42}$ under motering and with$(\vpsilon{U})^{0.45}$ under firing operations, where $\vpsilon$ is the kinematic oil viscosity and U is mean piston speed.

Analysis of the Dynamic Behavior and Lubrication Characteristics of the Piston-Cylinder System in Reciprocating Compressors (왕복동형 압축기 피스톤-실린더계의 동적 거동 및 윤활특성 해석)

  • 김태종
    • Tribology and Lubricants
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    • v.18 no.4
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    • pp.291-298
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    • 2002
  • In this study, a numerical analysis f3r the piston secondary dynamics and lubrication characteristics of small refrigeration reciprocating compressors is presented. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic forces and moments as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, and pin location on the stability of the piston, the oil leakage, and friction losses.

Non-Newtonian thermal Effects in Elastohydrodynamic Lubrication between the Two Rolling Systems

  • Kim, Joon-Hyun;Kim, Joo-Hyun
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.10b
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    • pp.87-88
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    • 2002
  • To analyze complicated phenomena on the fluid hydrodynamic and the elastic deformation between sliding body surfaces, an analysis to the elastohydrodynamic lubrication of sliding contacts has been developed taking into account the thermal and non-Newtonian effects. The computational technique handled the simultaneous solution of the non-Newtonian hydrodynamic effects, elasticity, the load, the viscosity variation, and temperatures rise. The results included the lubricant pressure profile, film thickness, velocity, shear stress, and temperature distribution, and the sliding frictional force on the surface at various slip conditions. These factors showed a great influence on the behavior resulted in the film shape and pressure distribution. Especially, Non-Newtonian effects and temperature rise by the sliding friction force acted as important roles in the lubrication performance.

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Friction Characteristics between the Cylinder Block and the Spherical Valve Plate in Hydraulic Axial Piston Pump (유압 액셜 피스톤 펌프에서 실린더 블록과 구면 밸브 플레이트 사이의 마찰 특성)

  • 김종기;오석형;정재연
    • Tribology and Lubricants
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    • v.14 no.4
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    • pp.23-28
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    • 1998
  • To increase the efficiency of the hydraulic axial piston pumps, it is need to know the various characteristics in the sliding contact parts of them. Especially, friction characteristics between the cylinder block and the valve plate in the hydraulic axial piston pumps plays an important role to high power density. In this paper, we tried to clarify friction characteristics between the cylinder block and the spherical valve plate in bent-axis-type axial piston pump in experimentally. Results are arranged as follow; (1) friction torque between the cylinder block and the spherical valve plate has a proportional relation to weight or rotational speed, and is strongly affected by temperature. (2) Friction torque strongly depends on force balance ratio in valve plate. (3) In this experiment, lubrication condition between the cylinder block and the spherical valve plate is under hydrodynamic lubrication.

Friction characteristics between the cylinder block and the valve plate in axial piston pump (액셜 피스톤 펌프에서 실린더 블록과 밸브 플레이트 사이의 마찰 특성)

  • 김종기;정재연
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1998.04a
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    • pp.249-255
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    • 1998
  • To increase the efficiency of the hydraulic axial piston pumps, we have to know the various characteristics in the sliding parts of them. Especially, friction characteristics between the cylinder block and the valve plate in the hydraulic axial piston pumps plays an important role to high power density. In this paper, we tried to clarify friction characteristics between the cylinder block and the spherical valve plate in bent-axis-type axial piston pump by using of modeling experiment. The main results of this study are these; (1) Friction torque between the cylinder block and the spherical valve plate has a proportional relation to weight or rotational speed, and is strongly affected by temperature. (2) Friction torque strongly depends on force balance ratio. (3) In this experiment, lubrication condition between the cylinder block and the spherical valve plate is under hydrodynamic lubrication.

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A Study on the Numerical Friction Model for the Extrusion (압출성형을 위한 마찰수식 모델에 관한 연구)

  • Oh P. K.;Kim J. S.;Yu S. K.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2002.11a
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    • pp.15-22
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    • 2002
  • To carry out perfectly the forming analysis of the extruding products, it is necessary that the friction boundary condition between dies and blanks should be worked out the accuate numerical friction models. But the numerical friction models adapting in the conventional Extrusion forming software may be large different from the actual conditions. Expecially, the use of the existing extrusion forming software is possible only in the limitted range owing to the unaccuracy of the high speed forming work. Therefore, tile prepare of this study is to develop the numerical friction model which describes the friction boundary condition mathematically well, to improve the accuracy of the extrusion farming analysis, and finally to expand the applying areas of the results.

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Influence of Pad-Pivot Friction on the Performance of Tilting-Pad proceeding Bearing (패드와 피봇 사이의 마찰이 틸팅패드 저널베어링에 미치는 영향)

  • Kim, Sung-Gi;Kim, Kyung-Woong;Ha, Hyun-Cheon
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.1016-1021
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    • 2004
  • The need for developing a mathematical model for pad-pivot friction in tilting pad proceeding bearings has been well-recognized, since previous experimental work about the performances of the bearings hypothesized that the friction in the bearings is closely related to their performances. Especially, the sliding friction between pad and pivot in the ball and socket type of the bearings can influence the performance of the bearing. We propose a mathematical model for pad-pivot friction in the ball and socket type, which considers the geometrics of the pad and pivot of the bearings, by assuming the sliding friction in the ball and socket bearing as Coulomb friction. By utilizing the proposed model for pad-pivot friction, we show the analysis of Reynolds equation and energy equation, which explain the thermo-hydrodynamic characteristics of tilting pad proceeding bearings, by taking into account the turbulence and inlet pressure building as well. The results of the study show that the performance of titling-pad proceeding bearings can be greatly influenced by the pad-pivot friction. In particular, we have shown that the analysis of the pad-pivot friction is useful to explain the static proceeding loci and the dynamic characteristics of the ball and socket type of the bearings. Furthermore, for a given operating condition, we can obtain various equilibrium states which satisfy the static equilibrium conditions, by considering the pad-pivot friction.

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Dynamic Analysis of the Piston Slap Motion in Reciprocating Compressors

  • Kim, Tae-Jong
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.10b
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    • pp.411-412
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    • 2002
  • Piston-cylinder system are widely used in power engineering applications. In reciprocating refrigeration compressors, where extremely low friction losses are required, ringless pistons are being used to diminish the friction between piston rings and cylinder wall. Since the ringless piston has the freedom of lateral motion there is a potential danger that it will occasionally hit the cylinder wall while moving up and down along it's axis. A good design must therefore provide a smooth and stable reciprocating motion of the piston and ensure that the fluid film separating the piston from the cylinder wall is maintained all times. And the compromise between refrigerant gas leakage through the piston-cylinder clearance and the friction losses is required utilizing a dynamic analysis of the secondary motion for the high efficiency compressor. To this end, the computer program is developed for calculating the entire piston trajectory and the lubrication characteristics as functions of crank angle under compressor running conditions. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses.

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