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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Society of Tribologists and Lubrication Engineers
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The Korean Society of Tribologists and Lubrication Engineers
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Volume & Issues
Volume 30, Issue 6 - Dec 2014
Volume 30, Issue 5 - Oct 2014
Volume 30, Issue 4 - Aug 2014
Volume 30, Issue 3 - Jun 2014
Volume 30, Issue 2 - Apr 2014
Volume 30, Issue 1 - Feb 2014
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Analysis of Three-Pad Gas Foil Journal Bearing for Increasing Mechanical Preloads
Lee, Jong Sung ; Kim, Tae Ho ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 1~8
DOI : 10.9725/kstle.2014.30.1.1
In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.
Design Analysis for Enhancing Rotordynamic Stability of Process High-Speed Light weight Centrifugal Compressor - Part II: Improvements to Rotordynamic Stability
Lee, An Sung ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 9~14
DOI : 10.9725/kstle.2014.30.1.9
In this Part II study, rotordynamic stability analyses were carried out to confirm improvements to the stability of a process high-speed lightweight centrifugal compressor, depending on the effects of tilting pad journal bearing designs. The bearing design variables considered were the clearances, LBPs, LOPs, and preloads. The results showed that the rotordynamic stability of the subject compressor rotor-bearing system improves exactly in accordance with the effects of the bearing design variables, which were determined in the preceding Part I study, owing to reduced bearing stiffnesses. Specifically, it was confirmed that the stability of the rotor system can be greatly improved by increasing both the machined and assembled bearing clearances, but there were no stability improvements by simply changing from an LBP to an LOP design. In addition, it was confirmed that for given fixed machined bearing clearances, the stability can be additionally improved by decreasing the preloads, i.e., by increasing the assembled clearances. In conclusion, it may be necessary to improve the designs of the original tilting pad bearings to obtain a sufficient margin of rotordynamic stability against a possible aerodynamic cross-coupled stiffness in a process high-speed centrifugal compressor. Thus, increasing the machined and assembled bearing clearances and decreasing the preload could be effective solutions.
Sensitivity Analysis of Effective Viscosity Coefficients for Computing Characteristics of Ultrathin Gas Film Bearings
Kim, Ui Han ; Rhim, Yoon Chul ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 15~20
DOI : 10.9725/kstle.2014.30.1.15
A more accurate expression for effective viscosity is obtained using a linear regression of the data from Fukui-Kaneko's model, which are obtained through numerical calculations based on the linearized Boltzmann equation. Veijola and Turowski's expression is adopted as a base function for effective viscosity. The four coefficients in that equation are optimized, and sensitivity analysis is conducted for these coefficients. The results show that the coefficient for the first-order Knudsen number is the most accurate, whereas the coefficient in the exponential of the Knudsen number is the least accurate compared with Fukui-Kaneko's results. The expression for effective viscosity is accurate within 0.02% rms of Fukui-Kaneko's results for the inverse Knudsen numbers from 0.01 to 100 and surface accommodation coefficients ranging from 0.7 to 1.
Vibration Analysis for Failure Diagnosis of Cylinder Liner of Large Ship Engine
Koo, Hyunho ; Cho, Yonsang ; Park, Junhong ; Park, Heungsik ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 21~28
DOI : 10.9725/kstle.2014.30.1.21
Damage to the cylinder liner of large ship engines, such as scuffing on the surface, can occur very easily because it is operated in a corrosive environment. This scuffing may be due to oil film destruction and corrosive wear caused by water and sulfur included in the fuel, abrasive impurities, and poor lubricants. Thus, a method for monitoring the condition and diagnosing the failure of the cylinder liner and piston ring is needed. In this study, a reciprocating friction and wear test was carried out with a cast iron specimen, which simulated an engine cylinder in a corrosive atmosphere. The lubricants used were base oil, stirred oil with distilled water, a NaCl solution, and dilute sulfuric acid. The friction coefficient and frequency spectrum were measured using a load cell and acceleration sense in each experimental condition. We then used these results to diagnose the failure of the cylinder liner.
Tribological Properties of Heat-resistant Cast Steel Discs: Effect of Thermal Conductivity
Kim, H.S. ; Lee, J.S. ; Cho, D.H. ; Kang, S.W. ; Na, T.Y. ; Jang, H. ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 29~35
DOI : 10.9725/kstle.2014.30.1.29
The temperature-dependent tribological properties of brake discs for a train were examined in this study. The discs were produced using heat-resistant alloy steel, which showed different thermal conductivity after the heat treatments. A commercial brake friction material was used to evaluate the friction effectiveness, and the friction tests were carried out using a 1/5 scale dynamometer under various initial braking temperature conditions. The results showed that the tribological property of the disc was strongly affected by the heat treatment schedule. At low temperatures (below
), the friction coefficient increased as a function of disc temperature, indicating that frictional heat increased the adhesion between the disc and pad. In addition, fade was observed at high temperatures (above
); it was pronounced in the case of the disc with low thermal conductivity. The different fade resistances observed in the discs with different heat treatment schedules appear to be influenced by microstructural changes such as carbide redistribution occurring during the heat treatments, which affected the thermal conductivity.
Adhesive, Friction, and Deformation Behaviors of Pig Skin under Various Exposure Times to Air
Shin, Hyunduk ; Ahn, Hyo-Sok ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 36~45
DOI : 10.9725/kstle.2014.30.1.36
Understanding steel/skin contact phenomena is important for the study of object manipulation in robotics and has been a topic of great interest. In this study, pig skin was taken as a surrogate model for human skin, and its adhesive, friction, and deformation behaviors were measured under various exposure times to air. Indentation, friction, and scratch tests were performed at
and 45% relative humidity. The influences of adhesion and deformation on the coefficient of friction were characterized; the pig skin was found to be sensitive to the sliding velocity and normal load under the controlled experimental conditions.
Analysis of Design Parameter Characteristics for Automobile Passive Dampers
Noh, DaeKyung ; Jang, JooSup ; Seo, WonJin ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 46~51
DOI : 10.9725/kstle.2014.30.1.46
In this study, we attempted to characterize the physical meaning of the design parameters used for automobile passive dampers by considering the slit, disc, and hole, which influence the pressure characteristics. We also analyzed the change in the pressure characteristics when mixing various slits and discs. Finally, we used a computer simulation to implement lag according to nitrogen gas and analyzed the dependence of frequency on the nitrogen gas pressure.
Synthesis of Biodiesel Components and Analysis of Their Fuel Characters
Lim, Young-Kwan ; Jeong, Choong-Sub ; Han, Kwan-Wook ; Do, Jin-Woo ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 52~58
DOI : 10.9725/kstle.2014.30.1.52
Because food crops serve as the raw materials for biodiesel, the increasing use of biodiesel as an alternative fuel can lead to adverse effects such as food price inflation and may contribute to global starvation. To solve these problems, efforts are being made to explore various nonedible raw materials for producing biodiesel. Different raw materials impart different fuel characteristics to biodiesel. In this study, we synthesized pure fatty acid methyl ester (FAME), which is a biodiesel component, and then analyzed its fuel properties. The fuel properties of pure FAME would be useful in producing biodiesel from various new raw materials.
Improvement of Tribological Characteristics of Multi-Scale Laser-Textured Surface in terms of Lubrication Regime
Kim, Jong-Hyoung ; Choi, Si Geun ; Segu, Dawit Zenebe ; Jung, Yong-Sub ; Kim, Seock-Sam ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 59~63
DOI : 10.9725/kstle.2014.30.1.59
Laser Surface Texturing(LST) is a surface engineering process used to improve tribological characteristics of materials by creating patterned microstructures on the mechanical contact surface. In LST technology, a pulsated laser beam is used to create arranged dimples on a surface by a material ablation process, which can improve such as load capacity, wear resistances, lubrication lifetime, and reduce friction coefficients. In the present study, the effect of multi-scale LST on lubricant regime was investigated. A pulsed Nd:YAG laser was applied on the bearing steel(AISI 52100) to create arranged dimples. To optimize the surface texturing effect on friction, multi-scale texture dimples with some specific formula arrays were fabricated by combining circles, ellipses and the laser ablation process. The tribological testing of multi-scale textured surface was performed by a flat-on-flat unidirectional tribometer under lubrication and the results compared with that of the non-textured surface. Through an increase in sliding speed, the beneficial effect of multi-scale LST performance was achieved. The multi-scale textured surface had lower friction coefficient performances than the non-textured surface due to the hydrodynamic lubrication effect.
Dynamic Model to Predict Effect of Race Waviness on Vibrations Associated with Deep-Groove Ball Bearing
Hwang, Pyung ; Nguyen, Van Trang ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 30, issue 1, 2014, Pages 64~70
DOI : 10.9725/kstle.2014.30.1.64
This paper presents a numerical model for investigating the structural dynamics response of a rigid rotor supported on deep-groove ball bearings. The numerical model was used to investigate the influence of race waviness on the dynamic characteristics of a rotor ball bearing system, which is very important from a design viewpoint. The forth-order Runge-Kutta numerical integration technique was applied to determine the time displacement response, Poincare map, and frequency spectra. The analysis demonstrated that the model can be used as a tool for predicting the nonlinear dynamic behavior of a rotor ball bearing system under different operating conditions. The results of this study may help further understanding of the nonlinear dynamics of a rotor bearing system.