• Tribology and Lubricants
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• 제14권2호
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• pp.35-41
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• 1998

The $WS_2$ solid lubricant synthesized through the vapour phase transport method was coated on the commercial bearing steel (SUJ 2) substrate, and the tribological behaviour of the lubricant was investigated using a ball-on-disk type tester. The $WS_2$ powder was spray-coated at room temperature using compressed air, and the change of friction coefficient was examined in various conditions, i.e., specimen configuration, atmosphere (air and nitrogen), applied load and rotating speed. $WS_2$ coated ball and disk showed the optimum friction coefficient of 0.07 and wear life of 45,000 cycles in the nitrogen atmosphere under 0.3 kgf and 100 rpm, whereas relatively high coefficient of 0.13 and reduced wear life of 4,000 cycles were observed in air atmosphere. The effect of rotating speed on the friction coefficient was not observed both in nitrogen and in air atmospheres. This confirmed that the spray-coated $WS_2$ solid lubricant was effective in reducing the friction coefficient and improving wear life in nitrogen atmosphere, and the oxygen and moisture existing in air could seriously deteriorate the lubrication effect of $WS_2$ coating layer.

• 복합신소재구조학회 논문집
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• 제6권4호
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• pp.51-57
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• 2015

Various hybrid dampers have been developed in Korea to control the vibration due to a wind and earthquake. In order to minimize the installment space, cost and construction process, the new hybrid friction damper is developed. This hybrid damper is composed of several rotary friction components having two frictional joint. Because of these components, the building vibration due to wind and earthquake can be mitigated by hybrid friction damper. In this paper, various dependency tests were carried out to evaluate on the structural performance of two joint rotational friction component of the hybrid damper. Test results show that two joint rotational components do not depend on a displacement and a frequency of forcing but friction coefficients is reducing as a clamping force is increasing.

• 한국해양공학회지
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• 제11권1호
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• pp.10-15
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• 1997

Copper and its alloy had been used widely because of its pronouncing characteristics on their high thermal and electrical conductivity. Various fusion welding methods, such as SMAW, SAW, GTAW, GMAW, Electroslag welding amd so on are applied to weld copper and its alloy. But fusion welding of copper has so many welding problems. THe most serious problems were poor penetration amd high thermal contration stress due to its high thermal conductivity and porosity could be formed by rapid cooling rate of fusion welding. In order to avoid such fusion welding problems, preheating, peering and heat treatment must be applied to obtain sound weld joint of copper. But preheating induce another welding problem such as grain coarsening of weld heat affected zone. This grain coarsening reduces ductility and strength of weld joint. In this view of point, friction welding of copper is triedm to obtain sound weld joint of copper by reducing metallurgical problems. This study introduced new concept of heat input for evaluating the friction weldability of copper. As a result, weldability of copper could be evaluated by this new concept of heat input.

• 한국산학기술학회논문지
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• 제16권10호
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• pp.7166-7175
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• 2015

본 논문은 대형 텔레비전 스탠드의 높이 조절에 있어 마찰력 감소를 위한 가스 스프링 사용에 대한 연구이다. 대상은 가스 스프링을 사용하는 50인치 이상의 대형 텔레비전의 높이 조절 동작에 적용되었다. 높이 조절 동작에 마찰력 감소를 얻기 위해서는 피스톤 로드에 작용하는 가스 씰 조임 기술을 개발해야 한다. 가스 씰 조임 기술이 작용하기 위해서는 가스 씰 조임 부의 내경, 커팅 각도 설계 및 소재 변경을 통해서 마찰력 향상을 얻을 수 있다.

• Corrosion Science and Technology
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• 제7권5호
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• pp.283-287
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• 2008

The drag reduction agency (DRA) for gas pipeline, a novel method used for reducing friction or drag on a gas flowing to increase the transmission efficiency of gas pipeline, is a more flexible and economical technology than internal flow efficient coatings. In this paper, an effective DRA has been developed in Authors' Institute by analyzing the hydrodynamic friction resistance on internal gas pipeline and then studying the work mechanism and molecular structure of DRA. In the meantime, a group of property test for selecting DRA material has been determined, including viscosity, contact angle, volatility, corrosion, slab extending, and flow behavior in horizontal tube. The inhibition efficiency and drag reduction efficiency of the developed DRA have been investigated finally based on the relevant test methods. Results of corrosion test show that the developed DRA has very good inhibition effect on mild steel by brushing a thin layer of DRA on steel specimens, giving inhibition efficiency of 91.2% and 73.1% in 3%NaCl solution and standard salt fog environment respectively. Results of drag-reducing test also show that the Colebrook formula could be used to calculate friction factors on internal pipes with DRA as the Reynolds number is in the range of $0.75\times10^5\sim2.0\times10^5$. By comparing with normal industrial pipes, the friction resistance coefficient of the steel pipe with DRA on internal wall decreases by 13% and the gas flux increases by 7.3% in testing condition with Reynolds number of $2.0\times10^5$.

• Journal of Advanced Marine Engineering and Technology
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• 제39권4호
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• pp.399-404
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• 2015

최근 국제 원유가의 폭등으로 선박의 연료비 부담이 상대적으로 가중되고 있으며, 또한 연료의 연소과정에서 발생하는 온실가스에 대한 국제적 규제 움직임도 가속되고 있다. 이에 따라 에너지 효율 개선을 위해서 선체의 설계변경, 마찰저항을 줄이기 위한 도료개발, 엔진의 열효율을 개선하기 위한 첨가제 개발, 연료를 절감하기 위하여 저속운전 등 다양한 방법들이 적용되고 있다. 따라서 최근 고유가 시대에 선박의 고속화와 대형화 및 에너지 절감형 선형의 개발이 필수요건이 되고 있다. 또한 선체 표면의 국부 영역에서 저항 값들의 정성 및 정량적인 변화와 보다 세밀한 분석은 불가피하다고 판단되어진다. 따라서 본 연구는 에너지 효율 개선을 위한 기초연구로서 현재 운항중인 선박의 선체에서 자생하는 해양생물로 인한 마찰저항을 확인하기 위하여 도크 전 후의 엔진성능을 분석하고 그 결과를 도크와 도크사이 2.5년의 데이터와 비교함으로서 주기관의 성능, 마찰저항과 부하변화 및 연료소비량과 선속에 미치는 연구 결과 등을 보고한다.

• Tribology and Lubricants
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• 제36권1호
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• pp.11-17
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• 2020

In manufacturing operations, oil plays a crucial role in reducing friction and wear among interacting surfaces at varying velocities, loads, and temperature. Hydrocarbon oil is considered the origin of lubrication oils. However, this base oil has been limited in its use as it is a principal cause of pollution. This research focuses on identifying a biodegradable base oil lubricant that possesses a stable coefficient of friction and viscosity with temperature. Friction analysis is conducted by employing a pin on a disk tribotester with a fixed load of 10 N at varying sliding speeds ranging from 0.06 m/s to 0.34 m/s. Oil viscosity analysis is perfomed at room temperature by using a rotary viscometer. Tests are performed using canola oil and paraffin oil as lubricants. The results indicate that the viscosity of canola oil is more efficient than paraffin oil. The non-dimensional characteristic number according to the Stribeck curve reveals an elastohydrodynamic lubrication regime with canola oil lubrication. A comparison of both lubricants reveals that, the friction efficiency of canola oil and paraffin oil does not differ considerably. However, the friction in canola oil is observed to decrease more than that in paraffin oil at an elevated sliding speed. The tests confirm that canola oil is potent in minimizing the friction coefficient of SCM440 bodies interacting with one another as well as acted upon by load.

• 한국정보전자통신기술학회논문지
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• 제12권2호
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• pp.113-119
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• 2019

우리는 선행연구로 다기능 마찰력 측정기를 개발해 왔고 본 논문에서는 적응화 평활화 방법을 적용하여 마찰력 측정기의 성능을 개선하고자 하였으며, 스크래치 테스트를 통해 시편에 대한 마찰력과 마찰면의 모니터링 기능을 심도 있게 분석하였다. 일반적으로 강판을 가공하여 사용하고자 할 때 마찰을 줄이기 위해서 윤활유를 사용하지만, 윤활유는 환경오염의 큰 원인이기 때문에 본 연구에서는 윤활강판을 사용하였다. 특히, 윤활강판의 마찰계수는 유기, 무기 등의 시편의 종류 및 코팅층의 상태에 따라 변화하기 때문에 합금화 용융아연도금강판과 같은 다양한 시편에 대한 정밀한 실험을 통해 분석하였다. 이를 토대로 적응화 평활화법을 이용하여 잡음이 제거된 정확한 마찰계수를 측정할 수 있는 측정기의 성능을 향상시킬 수 있음을 검증하였다. 그 결과로서 마찰계수 0.16에 대하여 적응화 평활화법을 이용한 경우 저감률이 0.0417%임을 보였다.

• Tribology and Lubricants
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• 제6권1호
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• pp.36-51
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• 1990

A parametric study of the thermal effects of a half-circumferential grooved journal bearings under aligned and misaligned conditions has been carried out by solving numerically the coupled Reynolds and energy equation system. Five different sets of boundary conditions for the energy equation have been used which include mixing between recirculating oil and inlet oil and a contraction ratio for the cavitation region. The effects of changes of the inlet oil temperature and pressure, the wall temperature and the L/D ratio have also been examined. For the range of parameters found in internal combustion engines, the mixing effectiveness at the groove and the resulting final mixture temperature have been found to be as important as the wall temperature and the heat transfer rate. The variability of the temperature, though, has been shown to smooth out the peaks of both pressure and friction during misaligned condition Distributions of friction and pressure in the oil are also examined which may be useful in attempts to reduce friction without reducing load. Results for an axial grooved bearing are also presentsed for comparision purpose.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 가을 학술발표회 논문집
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• pp.457-464
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• 1999

The active earth pressure on the retaining wall is reduced by 3-Dimensional effects of the ground. Therefore, the test was focused on reducing the earth pressure on the retaining wall by inserting the vertical reinforcement in the backfill ground to develope the 3-Dimensional effects. Model tests in sand were peformed to measure the 3-Dimensional effects of the vertical reinforcement on the active earth pressure and its distribution and results were compared with the theories. The size of the vertical reinforcement, the geometry of the backfill space, and the wall friction of vertical reinforcement were varied. It was observed that the active earth pressure and its distribution on the underground structure were affected by the size of the vertical reforcements and wall friction.