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The Change in Rolling Resistance of Bearing Surgaces Coated by a Soft Metallic Film
Kong, Hosung,Yoon, Eui-Sung,Yoon, Eui-Sung ENGINEERING TRIBOLOGY RESEARCH INSTITUTE KYUNGPOOK 1998 INTERNATIONAL SYMPOSIUM ON HIGH PERFORMANCE OF TRI Vol.1998 No.-
An experimental study was performed to discover the effect of a soft metallic film on the behavior of rolling resistance. Pure silver was coated on AII 52100 bearing steel by a thermal evaporation method, where the coating thickness ranged from 100 nm to 20,000 nm. A thrust ball bearing-typed test rig was used and the rolling resistance was measured with the contact cycles under various environmental conditions such as ambient air, vacuum, dry air and controlled humidity conditions. In order to find out the changes occurred at the contact surfaces, analyses were performed by using SEM and EPMA. Results showed that minimum rolling resistance was rather obtained after the initial coating failure where the fluctuation of rolling resistance ceased to remain stable. The rease of rolling resistance was resulted mainly from shakedown phenomena occurred at the contact patches which were agglomerated by transferred coating films. It was also found that rolling resistance was strongly affected by environmental conditions. Results suggested that humidity is related closely to the agglomeration of particles which affects the rolling resistance.
공호성(Hosung Kong),한흥구(Hung-Gu Han),김진욱(Jin Uk Kim),김경석(Kyoung Seok Kim),박종식(Jong Sik Park) 한국트라이볼로지학회 2019 한국윤활학회지(윤활학회지) Vol.35 No.2
This work aims to develop a dry lubricant for oilless bush, especially a solid lubricant, thereby creating a coating method with improved properties of anti-friction and load-carrying capacity without oil lubrication. In this work, spherical-shaped powders of thermosetting resin such as polyimide (PI) are mixed with a binder matrix obtained by mixing a fluorocarbon compound resin such as Polytetrafluoroethylene (PTFE) or Ethylene tetra fluoro ethylene (ETFE) with itself or with a non-fluorocarbon thermoplastic resin such as Polyether ether ketone (PEEK). And these dry lubricant mixtures are thickly coated (200-300 mm in the thickness) on the inner surface of the bush by using a wet-typed air-spray deposition method. It was found that the load-carrying capacity of the solid lubricant for excavator bush (60 mm in diameter) that operates under a high load condition (at 40 MPa) is greatly improved owing to the spherical-shaped powders of thermosetting resin. In addition, the coefficient of friction at the sliding surface is also reduced less than 0.1. Thick coating also lowers the contact stress at the edge of a bush that results in better tribological performances. The result suggests that the lubrication performance and durability life of the bush can be remarkably improved even without lubrication (oil or grease).
UV-Vis 분광분석에 의한 전기변압기 내 절연지 열화도 측정
공호성(Hosung Kong),한흥구(Hung-Gu Han) 한국트라이볼로지학회 2019 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.35 No.3
Insulated oil degradation produces charged by-products, such as acids and hydro-peroxides, which tend to reduce the insulating properties of the oil. In this study, UV-vis spectroscopy measurement technology is developed and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate its ability to monitor the degradation of electrical insulating paper. The degradation characteristics of the insulating paper are appropriately represented through various types of measurement methods, such as the Tan (delta) method, CO₂ gas production measurement, the titration method, and IR spectroscopy. The results are demonstrated to be well comparable to a change in the fluorescence emission ratio (FER), which is defined as the shift in fluorescence intensity in the measured wavelength range, and also to the chromatic ratio, which is defined as a color shift to longer wavelength ranges. The results also show that, by using UV-vis spectroscopy, it is possible to detect the degradation of the insulating paper. This study suggests that UV-vis spectroscopy can be applied as an alternative to high-performance liquid chromatography, which is the internationally recognized measurement technology for cellulose paper degradation. The FER detector is also verified to be useful as an effective condition-monitoring device for power transformers.
이슬점 응축 현상을 이용한 오일 내 수분함량 측정에 관한 실험적 연구
공호성(Hosung Kong),윤의성(Eui-Sung Yoon),한흥구(Hung-Gu Han),김학열(Hak Yeul Kim) 한국트라이볼로지학회 2004 한국트라이볼로지학회 학술대회 Vol.39 No.-
Presence of water in the lubricating oils could be one of the first indicators of potentially expensive and possibly catastrophic failure of the machine as it may cause displace the oil films to prevent the lubrication function of the oil or chemically react with many oil additives resulting in the oil degradation. In order to detect water content quantitatively in lubricating oils many methods and sensors has been developed. Among these, capacitive sensors including sensitive layer, whose dielectric factor changes according to the water content absorbed in the layer, are proposed mainly in the market. But these sensors are not sensitive to a high water content. Besides, the absorbing layer soils in time. In this work. an evaporation of water moisture from oil into air volume above lubricant surface and condensation of water vapor at a cooling surface was used to measure water content quantitatively in an lubricating oil. Laboratory test results of a prototype sensor were presented. Test results showed that the proposed method could be avaliable to measure a low levels of oil moisture.
Measurement of Electrical Insulating Oil Oxidation by Evaluating the UV Fluorescence Emission Ratio
Britantyo Wicaksono,Hosung Kong,Hung-Gu Han 한국트라이볼로지학회 2013 한국윤활학회지(윤활학회지) Vol.29 No.1
In this work, a new fluorescence emission measurement technology was introduced and experimentally compared with other measurement methods, such as the titration method and IR spectroscopy, to validate it for the oil oxidation measurement of electrical insulating oil. The oxidation characteristics of insulating oil were found to be fairly represented by the titration method and IR spectroscopy, and the results are comparable to a change in the fluorescence emission ratio that is defined as the shift in fluorescence intensity in the measured wavelength range. The result also shows that by the measurement of fluorescence emission ratio, it is possible to detect the oxidation of oil relatively earlier than by other methods. This study suggests that the developed technology can provide sufficient information for evaluating the insulating oil quality, and that the developed FER sensor can be used as an effective condition monitoring device of electrical insulating oil oxidation.
Utilization of color change in the condition monitoring of synthetic hydraulic oils
Ossia, Chinwuba Victor,Hosung, Kong,Markova, Lyiubov V. Emerald Group Publishing Limited 2010 Industrial lubrication and tribology Vol.62 No.6
<B>Purpose</B> - The purpose of this paper is to present an optical technique for the condition monitoring of synthetic hydraulic oil; a deviation from the current techniques based on electrical principles which could be masked by wear particles and polar contaminants in oil. <B>Design/methodology/approach</B> - Color-change detecting device was developed using light-emitting diodes, optic fibers and photodiodes of three-color-sensing elements. Color ratio (CR) and total contamination parameters based on transmitted light intensity in red, green, and blue wavelengths were used for oil chemical and particulate contamination assessment. <B>Findings</B> - CR criterion was found independent of the particulate contamination of oil; but depended on chemical degradation. Total contamination index of the device depended on both the chemical degradation and particulate contamination of the oil, being most sensitive in blue wavelength, and least in the red. Test results for synthetic hydraulic oils monitored corroborated with results of viscosity, total acid number, RDE emission spectrometry, particulate counts and UV-Vis photospectrometry. CR showed a clearer indication of oil degradation, compared to key monitoring parameters such as total acid number, viscosity, RDE emission spectrometry and particle counts. <B>Originality/value</B> - This paper demonstrates how oil chemical degradation and total contamination could be detected through the device, before incipient wear occurs at tribological interfaces. The results showed that the color-change parameters are effective criteria for the condition monitoring of synthetic hydraulic oils.