• Tribology and Lubricants
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• v.35 no.4
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• pp.237-243
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• 2019

Through this study, we investigate the effects of ultrasonic nanocrystal surface modification (UNSM) technology on the fatigue life of needle roller bearings. The fatigue life of untreated and UNSM-treated needle roller bearings is evaluated using a roller fatigue tester at various contact stress levels under oil-lubricated conditions. We can ascertain that the fatigue life of an UNSM-treated needle roller bearing was extended by approximately 34.3% in comparison with an untreated one, where the effectiveness of UNSM technology diminishes with increasing contact stress. The surface roughness and surface hardness of needle roller bearings before and after being treated by UNSM technology are compared and discussed to understand the role of UNSM technology in improving the fatigue life of needle roller bearings. In addition, a fractograph of the damaged bearings is observed using a scanning electron microscopy to shed light on the fracture mechanisms of bearings under different contact stress levels. We can therefore conclude that the application of UNSM technology to the needle roller bearings improves the fatigue life by reducing the friction coefficient and increasing the wear resistance; this may be attributed to a reduction in surface roughness from 0.5 to $0.149{\mu}m$ and an increase in surface hardness from 58 to 62 HRc.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3269-3273
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• 2012

In this study, we report a new method for the high contrast imaging of biomolecular interactions at roller printed protein surfaces using thermotropic liquid crystals (LCs). Avidin was roller printed and covalently immobilized onto the obliquely deposited gold surface that was decorated with carboxylic acid-terminated self-assembled monolayers (SAMs). The optical response of LCs on the roller printed film of avidin contrasted sharply with that on the obliquely deposited gold surface. The binding of biotin-peroxidase to the roller printed avidin was then investigated on the obliquely deposited gold substrate. LCs exhibited a non-uniform and random orientation on the roller printed area decorated with the complex of avidin and biotin-peroxidase, while LCs displayed a uniform and planar orientation on the area without roller printed proteins. The orientational transition of LCs from uniform to non-uniform state was triggered by the erasion of nanometer-scale topographies on the roller printed surface after the binding of biotin-peroxidase to the surface-immobilized avidin. The specific binding events of protein-receptor interactions were also confirmed by atomic force microscopy and ellipsometry. These results demonstrate that the roller printing of proteins on obliquely deposited gold substrates could provide a high contrast signal for imaging biomolecular interactions using LC-based sensors.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.227-228
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• 2002

One of the serious challenges in developing rotary compressor with HFC refrigerant is the prediction of scuffing times and wear amounts between vane and roller surface. In this study, the tribological characteristics of sliding surfaces using roller-vane geometry of rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads and surface roughness. During the tests, friction force, wear scar width, time to failure, surface temperature, and surface roughness were monitored. Because severe wear was occurred on vane surface, TiN coating was applied on sliding surfaces to prolong the wear-life of vane-roller interfaces. From the sliding tests, it was found that there was the optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in the amount of friction and wear between roller and vane surfaces.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.538-543
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• 2008

A roller with a shaft and hot oil paths for pressing electrodes of polymer batteries were modeled and analyzed by FEM. There are many hot oil tubes in the roller and shaft, through which $72^{\circ}C$ hot oil flows for heating the surface of a roller and shaft. Thermal deformations and temperatures distributions of the roller and shaft were calculated and a convection boundary condition on surfaces was used. The influence of existence of a groove in the shaft on the flatness of a roller surface caused by thermal deformation was investigated. In addition, the amount of spring-back of electrodes under vacuum pressure and heating was calculated after the hot rolling process. It was shown from this study that the groove in one shaft had a favorable effect on the surface flatness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.238-241
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• 2007

A roller straightening process is a metal forming technique to improve the geometric quality of products such as straightness and flatness. The geometrical quality can be enhanced by eliminating unnecessary deformations produced during upstream manufacturing processes and minimizing any detrimental internal stress during the roller straightening process. The quality of steel cords can be achieved by the roller straightening depends the process parameters. Such process parameters are the roll intermesh, the roll pitch, the diameter of rolls, the number of rolls and the applied tension. This paper is concerned with the design optimization of the roller straightening process for steel cords with the aid of elasto-plastic finite element analysis. Effects of the process parameters on the straightness of the steel cord are investigated by the finite element analysis. Based on the analysis results, the optimization of the roller straightening process is performed by the response surface method. The roller straightening process using optimum design parameters is carried out in order to confirm the quality of the final products.

• Tribology and Lubricants
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• v.20 no.6
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• pp.337-342
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• 2004

One of the serious challenges in developing rotary compressor with HFC refrigerant is the prediction of scuffing times and wear amounts between vane and roller surfaces. In this study, the tribological characteristics of sliding surfaces using vane-roller geometry of rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads and surface roughness. During the test, friction force, wear depth, time to failure and surface temperature were monitored. Because severe wear occurred on vane surface, TiN coating was applied on sliding surfaces to prolong the wear life of vane-roller interfaces. From the sliding test it was found that there was the optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on the load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in the amounts of friction and wear between roller and vane surfaces.

• Korean Journal of Applied Biomechanics
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• v.20 no.4
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• pp.415-420
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• 2010

The purpose of this study was to compare the thickness of the abdominal muscles during single leg holding exercise (SLH) in a hooked lying position on stable surface and on a foam roller. Healthy twenty subjects who had no medical history of lower extremity or lower back pain were recruited for this study. Muscle thickness of transverse abdominis (TrA), internal oblique (IO), and external oblique (EO) was recorded using real-time ultrasonography during SLH. Paired t-test with Bonferroni adjustment was used to compare the muscles thickness during SLH on stable surface and on a foam roller. The result showed that TrA and IO muscle demonstrated greater thickness during SLH on foam roller than those on the stable surface. This finding suggests that SLH on an unstable foam roller is more effective to increase thicknesses of TrA and IO muscles than stable surface.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2279-2284
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• 2007

This study is intended to analyze the effect of thin ink-film thickness around rotating printing roll on the printing quality in the gravure printing process which is used for making electronics circuit like a RFID tag with a conductive ink. The present work numerically estimates the film thickness around rotating roller partially immersed in ink, for which the volume of fluid (VOF) method was adopted to figure out the film formation process around rotating roller. Parameter studies were performed to compare the effect of ink viscosity, surface tension, roller rotating speed, immersed angle on the film thickness. The result indicates that the film thickness has a strong dependency on the fluid viscosity, while the surface tension has negligible effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1328-1334
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• 2006

In the rolling mills for sheet metal rolling, paper rolling and etc., the impurities of roller surface have crucial effects on the surface quality of the products obtained by rolling. The Roll Cleaner is a device to remove impurities on roller surface during a rolling operation. Nip Pressure means the line pressure interacted between the roll cleaner blade and the roller surface. The nip pressure is the most important parameter which decides the performance of roll cleaner, and it depends upon several factors including the cleaner design and its blade stiffness. This study, first, analyzes the mechanism of the nip pressure generation for a roll cleaner designed commercially, which is an crucial process for effective design of roll cleaners. Second, the technique for the measurement of nip pressure is developed, which is useful to verify the performance of roll cleaners and to setup them properly at factory floor.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.221-226
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• 2002

One of the serious challenges in developing rotary compressor with HFC refrigerant is the prediction of scuffing times and wear amounts between vane and roller surfaces. In this study, the tribological characteristics of sliding surfaces using vane-roller geometry of rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads and surface roughness. During the test friction force, wear depth, time to failure and surface temperature were monitored. Because severe wear was occurred on vane surface, TiN coating was applied on sliding surfaces to prolong the wear-life of vane-roller interfaces. From the sliding test it was found that there was the optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on the load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in role amounts of friction and wear between miler and vane surfaces.