• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.703-703
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• 2013

다이아몬드상 탄소 박막(Diamond-like carbon, DLC) 박막은 낮은 마찰 계수, 높은 내마모성, 화학적 안정성, 적외선 영역에서의 높은 투과율 등의 장점을 바탕으로 MEMS (Micro-Electro Mechanical System) 소자와 MMAs (Moving Mechanical Assemblies)의 고체윤활코팅, 마그네틱 미디어와 하드디스크의 슬라이딩 표면 등 다양한 분야에 코팅소재로써 응용되어왔다 [1,2]. 현재 전기철도용 집전판은 마찰이 적고 전도성을 지니는 카본 소재로 구성되어 있다. 그러나 그 마모 비율이 너무 심하여 이를 개선할 수 있는 방안으로 고경도 저마찰력을 지니는 DLC 박막을 코팅 소재로써 제안하고자 한다. 그러나 기존에 DLC 박막은 절연특성이 매우 우수하기 때문에 기존에 전도성을 지니는 카본 집전판에 적용하기에는 어려움이 따른다. 따라서 DLC 박막 내에 실리콘(Si) 또는 금속(Metal)을 첨가시키거나, 금속 중간층을 포함시켜 전기적으로 전도특성을 향상시키는 방안이 제시되고 있으며, 본 연구에서는 DLC 박막과 유사하게 우수한 경도특성을 지니고, 낮은 마찰계수등을 지니는 비정질 탄소박막을 연구하여 카본 집전판에 코팅하고자하며, 특히 비정질 탄소박막에 금속 Ti를 도핑하여 집전판과의 접착력과 전기적 전도 특성을 향상시키고자 한다. Ti가 도핑된 탄소박막(TiC) 박막은 비대칭 마그네트론 스퍼터링(unbalanced magnetron sputtering; UBMS) 시스템을 이용하여 제작하였으며, 스퍼터링 조건 중 기판에 인가되어지는 기판온도에 따라 변화되어지는 TiC 박막의 트라이볼로지(Tribology) 특성을 고찰하고자 하였다. 증착시 기판온도의 증가는 TiC 박막의 경도, 마찰계수 특성등 트라이볼로지 특성을 향상시켰으며, 전기적 전도 특성을 향상시켰다. 이러한 결과는 스퍼터링 방법에 의해 증착되어진 TiC 박막내에 존재하는 sp2 결합과 관계가 있음을 확인할 수 있으며, 트라이 볼로지 특성은 TiC 박막내에 sp2 탄소결합의 비율 증가와 관련되어졌다. 특히 sp2 탄소결합은 TiC 박막 증착시 증가된 기판온도와 밀접한 관계가 있으며 기판온도의 증가에 따라 나노결정 클러스터의 크기와 수의 변화와 밀접한 관계가 있음을 확인하였다. 결국 기판온도는 TiC 박막의 트라이볼로지 특성을 향상시켰으며, 전기적 특성 또한 향상시켜 전기철도 집전판에 응용을 위한 소재로 평가할 수 있다.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.4
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• pp.65-69
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• 2012

Composite coating can be manufactured during the electroplating with the bath containing a suspension of particles: ceramic, polymer, nanopowders. Improvement of hardness, wear resistance, corrosion resistance and lubrication properties are well-known advantage of composite coating. In this study, nano $TiO_2$ powder dispersed Ni composite plating was investigated. The improvement of surface hardness and photo decomposition effects can be expected in this coating. Zeta potential was measured with pH. The effect of ultrasonication time and types of ultrasonicator were studied to minimize the agglomeration of $TiO_2$ nanopowders in the electrolyte. Optimum conditions for nano $TiO_2$ dispersed Ni composite coating were $40mA/cm^2$ of current density, pH 3.5, and $50^{\circ}C$. At these conditions, $TiO_2$ nanoparticles contents in the Ni deposit was 15-20 at.%.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.40 no.4
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• pp.337-343
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• 2004

This paper presents an experimental study of friction and wear properties of a unidirectional oriented continuous crbon-fiber reinforced epoxy composite at the ambient temperature. Friction and wear experiments were conducted in the three principal sliding direction of the fiber orientation in the composite were selected against the stainless steel counterpart specularly processed were using a pin -on-disc apparatus. Friction coefficient and specific wear rate at various normal loads and sliding velocities wear determined. When sliding took place against smooth and hard counterpart, the hightest were resistance and the lowest friction coefficient were observed in the anti-parallel direction. The wear track of the worn specimens was examined with a scanning electron microscope(SEM) to observe the damaged fibers on the surface. In addition, SEM observations of the worn surfaces allowed to identify the involved different wear mechanisms.

• Computational Structural Engineering
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• v.7 no.3
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• pp.133-141
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• 1994

When a bolt is tightened up to the range of plastic deformation, yielding may be governed by the combined stresses due to the axial force developed in the bolt and the frictional torque induced on the thread by the contact with the nut. Consideration is taken account of the fact that the unengaged portion of the thread has least sectional area, being subject to initial yielding. Once yielding has taken place some strain hardening effect may result. Incremental stress-strain relations are used to treat the continued yielding, which is equivalent to treat continued yielding as if summing up the effects of thin walled cylinders subject to plastic deformation. M10 bolts of fine threads are used for both computational and experimental purposes. Variation of axial forces and frictional torques vs. the frictional coefficients are presented together with other plots showing some characterist of bolt under plastic deformation. Finally, a design and control aid for the tightening(i.e., kind of nomograph) is presented, showing the relationships among the torque factor and frictional coefficients for that particular bolt used in the experiment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.7-14
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• 2017

This study manufactured a minimum quantity lubrication (MQL) supply system and identified the optimal MQL machining cutting conditions for plastic mold steel (SCM440). A series of experiments were consisted of twice. Optimal cutting conditions were derived using the Taguchi method, and cutting force variance; surface roughness; tool wear; and cutting temperature in dry, wet, and MQL machining were measured experimentally for these optimal conditions. The measured results decreased from dry to wet and MQL machining, being particularly large for dry machining due to increased cutting time. Measured MQL machining metrics were similar to those for wet machining, particularly for surface roughness, which is an index of machining quality.

• Fire Science and Engineering
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• v.34 no.3
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• pp.8-17
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• 2020

In this study, the characteristics of HFIX insulated wire sheaths contaminated by pollutants were examined. KS C IEC 60811-1-3 standard was followed in performing the water-resistance wire tests. Pollutants were selected, and the specimens were exposed to the pollutants for a maximum duration of four weeks. The maximum tensile load and the elongation rate were measured each week. As the period of pollution exposure increased, the maximum tensile load of the specimens decreased by 6.22% and 6.52% at room temperature and high temperature, respectively, and 19.94% for specimens coated with a rust-proof lubricant. The elongation rate also decreased rapidly, such that the reductions in the properties of the sheath were significant. From the analysis of the surfaces using a scanning microscope, as the contamination period increased, structural changes such as perforation, split, and melting occurred, and the mechanical properties of the specimens decreased. Therefore, it is necessary to develop and follow an inspection cycle and periodically carry out repairs to prevent the deterioration of insulated wires.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.2993-2999
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• 2015

Steel companies are applying Ni-B or Ni-Co alloy plating to protect the surface of Continuous casting mold, and they are using saccharin polish which causes crack on plating layer due to sulfur in saccharin. It is considered that the Ni-S compound causes the cracking and additional tensile stresses. The Ni-Mn-B ternary alloy plating was developed for suppression of crack by forming Mn-S compound before Ni-S compound is formed, but there were no domestic or international standard on the Ni-Mn-B alloy plating. Therefore, reliability evaluation standard was established to evaluate the newly developed Ni-Mn-B plating. To develop accelerating life testing method, FMEA(Failure Mode & Effective analysis) was used to analyze the cause of the main failure in plating. The Ni-Mn-B reliability standard included accelerating life test method, and it was categorized by the fundamental performance test, environment test, and accelerated life test, and was designed to guarantee 1 000 hours of B10 life with 80 % reliable level.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.237-237
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• 2010

에너지소비와 엔진 부품의 마모문제를 해결하기 위해, soft-phase를 doping한 hard상의 coating에 대한 실험이 최근 중요한 연구 테마로서 진행 중이다. 특히 MoN-Cu coating은 미국 Argon 연구소의 Erdemer박사 등에 의해, 고온 및 상온 윤활성이 우수한 코팅층으로 보고된 이후 많은 연구가 진행되고 있다. 그러나 기존 연구는 Mo와 Cu의 원소타겟을 이용한 연구가 주력이 되었다. 높은 경도와 저온 고온에서의 낮은 나노 혼합물 코팅 종류는 일반적으로 Mo와 Cu와 같은 원소 합금을 이용한 다수 타겟을 이용한 공정에 의해 진행되어왔다. 이러한 복수의 타겟에 의해 증착 동안에는, 정확한 조성, 큰 크기의 시편들의 균일 증착을 조절하기가 쉽지 않다. 또한, 코팅층에 3번째 성분을 추가하기가 어렵다는 문제점이 있다. 본 연구에서는, 최상의 마찰계수와 표면경도를 보이는 MoN-Cu층을 형성시키기 위하여 합금으로 단일 타겟을 제조하였다. 이를 위한 최적 조성을 결정하기 위하여 Mo, Cu 단일 타겟을 이용한 Unbalanced Magnetron sputtering 법으로 다양한 Cu 함량의 MoN+Cu 합금을 제조하였으며, 이에 대한 경도 및 마찰계수 측정을 통해 최적의 Cu 함량을 결정하였다. 이러한 최적 조성의 Cu 타겟제조를 기계적 합금화와 Spark plasma sintering 기술을 이용하여 제작하였으며, 복수의 합금 타겟과 단일 합금 타겟으로 제조된 코팅층의 물성 비교를 통해 합금 타겟의 우수성 여부를 확인하고자 하였다. 증착된 두 조건의 물성을 비교 단일 타겟은 두가지 타겟으로 증착한 것보다 비슷한 조성에서 경도가 높았으며 경도가 비슷한 조성에서는 마찰계수가 낮았다. 또 입자는 10 at.% Cu 조성에 대해 단일타겟이 50nm 결정립을 갖는 반해 단일타겟은 측정이 불가능할 정도의 미세한 결정립을 가졌다. Erdemir의 연구 결과에 의하면, Cu 함량이 증가함에 따라 columnar 형태의 코팅층구조가 나노 구조로 변한다고 하였는데, 본 연구에서 복수의 원소 타겟에서는 확인이 안되었으며, 단일 합금 타겟에서 완벽한 featurless 형태의 코팅층 구조와 우수한 조도의 박막층을 얻을 수 있었다. 이렇게 제조된 다양한 코팅층에 대한 마찰계수 측정이 진행중이다.

• Tribology and Lubricants
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• v.40 no.3
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• pp.103-110
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• 2024

Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.9
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• pp.644-655
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• 2011

VOCs (Volatile Organic Compounds) have adverse effects on human health and have caused serious global air pollution problems such as ozone depletion and cimate changes. The total of 56 target VOCs were selected to be monitored in this study for 4 years (2006~2009). The VOCs were measured every hour. The concentration of BTEX was higher than the other target compounds. Generally, the levels of VOCs measured in this study were higher than those measured by the other studies because Gamjeon and Jangrim monitering sites are located in industrial areas. The seasonal variations showed that the VOCs were the highest in winter. The temporal variations showed that the VOCs were high during commuting time on weekday. PMF model was used to resolve source types and source contributions of VOCs in this study. Identified sources and quantified contributions resolved by PMF were vehicle exhaust (15.22%), thinning solvent (29.83%), surface coating (17.13%), industries (13.95%), LPG vehicle (15.22%), combustion boiler (7.11%) and biogenic source (6.61%). Thinning solvent and Surface coating were the most contributed sources possibly due to manufactures and automobile garages in Gamjeon and solvent and paint manufactures in Sasang-Gu.