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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 28, Issue 6 - Dec 2012
Volume 28, Issue 5 - Oct 2012
Volume 28, Issue 4 - Aug 2012
Volume 28, Issue 3 - Jun 2012
Volume 28, Issue 2 - Apr 2012
Volume 28, Issue 1 - Feb 2012
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Journal Bearing Design Retrofit for Process Large Motor-Generator - Part I : Bearing Performance Analysis
Lee, An Sung ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 197~202
DOI : 10.9725/kstle-2012.28.5.197
In this study, with the purpose of fundamentally improving the unbalance response vibration of a large PRT motor-generator rotor by design, a performance improvement design analysis is carried-out by retrofitting tilting pad bearings, replacing the plain partial journal bearings that were originally applied for operation at a rated speed of 1,800 rpm. In this process, a goal of the design analysis is to obtain a design solution for maximizing the direct stiffness of the bearings while satisfying the key basic lubrication performance requirements such as the minimum lift-off speed and maximum oil-film temperature. The results show that with a careful design application of tilting pad journal bearings for operation at such a relatively low speed of 1,800 rpm, direct stiffness increment of the bearings by about two times can be effectively achieved. Prevention of pad unloading is also considered in the analysis. Moreover, the designs of elliptical and offset half journal bearings are also analyzed and reviewed.
Quantitative Lateral Force Calibration of V-shaped AFM Cantilever
Lee, Huijun ; Kim, Kwanghee ; Kim, Hyuntae ; Kang, Boram ; Chung, Koo-Hyun ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 203~211
DOI : 10.9725/kstle-2012.28.5.203
Atomic force microscopy (AFM) has been used as a tool, not only for imaging surfaces, but also for measuring surface forces and mechanical properties at the nano-scale. Force calibration is crucial for quantitatively measuring the forces that act between the AFM probe of a force sensing cantilever and a sample. In this work, the lateral force calibrations of a V-shaped cantilever were performed using the finite element method, multiple pivot loading, and thermal noise methods. As a result, it was shown that the multiple pivot loading method was appropriate for the lateral force calibration of a V-shaped cantilever. Further, through crosschecking of the abovementioned methods, it was concluded that the thermal noise method could be used for determining the lateral spring constants as long as the lateral deflection sensitivity was accurately determined. To obtain the lateral deflection sensitivity from the sticking portion of the friction loop, the contact stiffness should be taken into account.
Measurement of Normal Spring Constant of Colloidal Probes for Atomic Force Microscope
Kim, Dae-Hyun ; Kim, Min-Seok ; Hahn, Junhee ; Ahn, Hyo-Sok ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 212~217
DOI : 10.9725/kstle-2012.28.5.212
A modified thermal noise method was proposed to measure the normal spring constants of the colloidal probes for an atomic force microscope. We used commercial tipless cantilevers (length 150, width 30, nominal k 7.4 N/m) and borosilicate spheres with a diameter of 20 to fabricate colloidal probes. The inverse optical lever sensitivity of both the tipless cantilever and colloidal probes were used to measure the normal spring constant of the colloidal probes. We confirmed the accuracy and usefulness of our method by comparing the measurement results with those obtained using the nanoforce calibrator (NFC), which reportedly has an uncertainty of 1.00%. The modified thermal method showed a good agreement (~10% difference) with the NFC, allowing us to conclude that the modified thermal method could be employed for the effective measurement of the normal spring constants of colloidal probes.
A Comparative Study of the Navier-Stokes Equation & the Reynolds Equation in Spool Valve Analysis
Hong, Sung-Ho ; Son, Sang-Ik ; Kim, Kyung-Woong ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 218~232
DOI : 10.9725/kstle-2012.28.5.218
In a spool valve analysis, the Reynolds equation is commonly used to investigate the lubrication characteristics. However, the validity of the Reynolds equation is questionable in a spool valve analysis because cavitation often occurs in the groove and the depth of the groove is much higher than the clearance in most cases. Therefore, the validity of the Reynolds equation in a spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and the Navier-Stokes equation. Dimensionless parameters are determined from a nondimensional form of the governing equations. The differences between the lateral force, friction force, and volume flow rate (leakage) obtained by the Reynolds equation and those obtained by the Navier-Stokes equation are discussed. It is shown that there is little difference (less than 10%), except in the case of a spool valve with many grooves where no cavitation occurs in the grooves. In most cases, the Reynolds equation is effective for a spool valve analysis under a no cavitation condition.
Effect of Atmosphere on Corrosive Wear of Alloy Cast Iron for Cylinder Liner of Large Ship Engine
Koo, Hyunho ; Cho, Yonsang ; Cho, Hwayoung ; Park, Heungsik ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 233~239
DOI : 10.9725/kstle-2012.28.5.233
The engine of a large ship operates under wet conditions using a fuel such as bunker C oil, which includes sulfur and many impurities. A cylinder liner made of cast iron is very susceptible to damage such as scuffing on the surface. This scuffing can reliably be attributed to the destruction of the oil film and the corrosion wear caused by water and sulfur included in the fuel, along with abrasion impurities and poor lubricants. In this study, a reciprocating friction and wear test was carried out with a cast iron specimen, which was used to simulate an engine cylinder in a corrosive environment. Base-oil and stirred oil containing distilled water, NaCl solution, and dilute sulfuric acid were used as lubricants. The friction surface was analyzed using a microscope and EDAX, and the friction coefficient was measured using a load-cell under each experimental condition. We then attempted to investigate the damage to the cylinder liner using the results.
Design Improvement of Carrier Finger on Sheet Metal Forming Line for the Prevention of Scratch
Lee, Min ; Kim, Tae Wan ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 240~245
DOI : 10.9725/kstle-2012.28.5.240
In this study, we developed a new carrier finger to prevent scratches in a sheet metal forming line. The developed carrier finger was designed to have a streamlined shape with a larger radius of curvature at the edges, as well as a smaller contact area. To evaluate the scratch alleviation effect, a sliding contact analysis and scratch test using the pin on a plate wear tester were conducted for both the old and new carrier fingers. The results show that, for both transverse and longitudinal movements of the strip, the newly designed carrier finger reduces both the friction and scratch depth by its streamlined shape, which decreases the pressure spike at the edge.
A Study on Thermal Behavior and Stress Characteristics of Discs under Braking Conditions for Automobiles
Baek, Il-Hyun ;
Journal of the Korean Society of Tribologists and Lubrication Engineers, volume 28, issue 5, 2012, Pages 246~251
DOI : 10.9725/kstle-2012.28.5.246
Disc brakes and brake linings are part of the braking system in automobiles; this system works due to the braking power between the disc and pad. Vehicle braking systems have complex environments due to the geometry of the disk and pad, the material properties, the braking conditions, etc. Braking energy is converted into thermal energy during the braking process, due to the frictional heat between the disc brake and pad. This heat is changed to a heat flux, which affects the thermal stress of the disc. The purpose of this study was to use the fluid dynamics software ANSYS CFX to investigate the inner flow characteristics of the air and the heat transfer of the disc, and to analyze the effects on the thermal stress of the disc brake.