• Tribology and Lubricants
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• 제2권2호
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• pp.12-19
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• 1986

냉각성, 난연성, 그리고 경제성의 면에서 우수한 윤활특성을 갖고 있는 이멀션윤활제를 사용하여 로울러와 프레이트간의 선접촉 및 광간섭계의 실험장치를 통하여 탄성유체윤활 영역에서의 윤활기구 및 분산립자의 거동기구를 명확히 하여 다음과 같은 결론을 얻었다. 1. 스퀴즈 유막내의 유동은 윤활간극이 비교적 넓은 경우와 좁은 경우로 대별하여 전자의 경우에는, 입자분포 및 속도분포의 영향이 크게 나타나며, 후자의 경우는 이멀션입자가 간극내에 정지하여 유막두께의 감소와 더불어 변형되어 간다. 2. 스퀴즈 유막내의 O/W, W/O 각 이멀션의 유동은 간극이 클 경우, 입경에 의한 속도차가 역으로 나타나고, 작은 경우에는 잔류액적의 분포가 서로 다르며 그밖에 O/W 형은 W/O 형에 비하여 분산입자가 쉽게 변형하는 것을 알 수 있다. 3. EHL영역입구부에서는 입자의 유동속도가 극히 적은 정체영역이 존재하며, 그 부근에서의 입자의 거동은 입경에 따라서 다르다. 4. 2색광에 의한 광간섭선의 관찰에 의하여 탄성유체윤활 영역내를 통과하는 이멀션유를 확인함과 동시에 EHL영역입구부에서의 분열거동이 관찰되었다.

• Tribology and Lubricants
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• 제31권6호
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• pp.245-250
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• 2015

This study investigates the lubrication characteristics of fuel injection pumps with reference to different fuel oils. Medium-speed diesel engines use fuel oils with various viscosities, such as heavy fuel oil (HFO, which is a high-viscosity fuel oil) and light diesel oil (LDO, which is a low-viscosity fuel oil). When fuel oil with a low viscosity is used, both fuel oil and lubricating oil lubricate the system. Thus, the lubrication of the fuel injection pump is in a multi-viscosity condition when the fuel oil in use changes. We suggest three cases of multi-viscosity models, and divide the fuel injection pump into three lubrication sections: a, the new oil section; b, the mixed oil section; and c, the used oil section. This study compares the lubrication characteristics with variation of the multi-viscosity model, clearance. The volume of Section b does not affect the lubrication characteristics. The lubrication characteristics of the fuel injection pump are poor when high-viscosity fuel oil transfers to low-viscosity fuel oil. This occurs because the viscosity in the new oil section (i.e., Section a) dominates the lubrication characteristics of the fuel injection pump. However, the lubricant oil supply in the used oil section (i.e., Section c) can improve the lubrication characteristics in this condition. Moreover, the clearances of the stem and head significantly influence the lubrication characteristics when the fuel oil changes.

• Tribology and Lubricants
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• 제27권6호
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• pp.326-331
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• 2011

The purpose of this paper is to analyze and discuss the effects of surface roughness by comparing the elastohydrodynamic lubrication(EHL) analysis of smooth surface and rough surface as the ball bearing. In order to do this, The average flow model is adapted for the interaction of the flow rheology of lubricant and surface roughness. The average Reynolds equation and the related flow factor which describes the coupled effects of surface roughness and flow rheology, the viscosity-pressure and density-pressure relations equations, the elastic deformation equation, and the force balance equation are solved simultaneously. The results show that effects of surface roughness on the film thickness and pressre distribution should be considered especially in EHL contact problems.

• Corrosion Science and Technology
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• 제20권1호
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• pp.7-14
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• 2021

PosMAC^® is a brand of Zn-Mg-Al hot-dip coated steel sheet developed by POSCO. PosMAC^® can form dense surface oxides in corrosive environments, providing advanced corrosion resistance compared to traditional Zn coatings such as GI and GA. PosMAC^® 3.0 is available for construction and solar energy systems in severe outdoor environments. PosMAC^®1.5 has better surface quality. It is suitable for automotive and home appliances. Compared to GI and GA, PosMAC^® shows significantly less weight reduction due to corrosion, even with a lower coating thickness. Thin coating of PosMAC^® provides advanced quality and productivity in arc welding applications due to its less generation of Zn fume and spatters. In repeated friction tests, PosMAC^® showed lower surface friction coefficient than conventional coatings such as GA, GI, and lubricant film coated GA. Industrial demand for PosMAC^® steel is expected to increase in the near future due to benefits of anti-corrosion and robust application performance of PosMAC^® steel.

• 대한치과보철학회지
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• 제44권6호
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• pp.740-750
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• 2006

Statement of problems. In an attempt to reduce screw loosening, dry lubricant coatings such as pure gold or tefron have been applied to the abutment screw. However, under repeated tightening and loosening procedures, low wear resistance and adhesion strength of coating material produced free particles on the surface of abutment screw and increased frictional resistance resulting in screw tightening problems. Purpose. The aim of this study was to compare friction coefficient, adhesion strength, vickers hardness and evaluate coating surface of titanium alloy specimens coated with TiN(titanium nitride), ZrN(zirconium nitride) and WC(tungsten carbide). Material and method. Titanium alloy(Ti-6Al-4V) discs of 12mm in diameter and 1mm in thickness divided into 4 groups. TiN, ZrN and WC was coated for the specimens of 3 groups respectively, and those of 1 group were not coated. Each group was made up of 4 specimens. In this study, sputtering method was used among the PVD(Physical Vapor Deposition) techniques available for TiN, ZrN and WC coatings. Friction coefficient, adhesion strength, vickers hardness and coating surface of 4 groups were measured. Results. 1. For all three coating conditions, friction coefficient was significantly decreased. Especially, ZrN coated surface showed the lowest value. $TiN(0.39{\pm}0.02)$, $ZrN(0.24{\pm}0.01)$, $WC(0.31{\pm}0.03)$. 2. TiN coating showed the highest adhesion strength, however ZrN coating had the lowest value. $TiN(25.3N{\pm}1.6)$, $ZrN(14.8N{\pm}0.6)$, $ WC(18.4N{\pm}0.7)$. 3. Vickers hardness of all three coatings was remarkably increased as compared with that of none coated specimen. TiN coating had the highest Vickers hardness, however WC coating showed the lowest value. $TiN(1865.2{\pm}33.8)$, $ZrN(1814.4{\pm}18.6)$, $WC(1008.5{\pm}35.9)$. 4. The ZrN or WC coated specimen showed a homogeneous and smooth surface, however the rough surface with defects was observed for TiN coating. Conclusions. When TiN, ZrN and WC coating applied to the abutment screw, frictional resistance would be reduced, as a result, the greater preload and prevention of the screw loosening could be expected.