• Journal of Power System Engineering
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• v.12 no.3
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• pp.66-71
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• 2008

Diamond-like-carbon (DLC) coatings could be good candidates as solid lubricants for cutting tools in dry machining of aluminum alloy. In this work, DLC thin films were produced as a friction reduction coating for WC-Co insert tip using the plasma immersion ion beam deposition (PIIED) technique. DLC coatings were also coated on $Al_2O_3$ specimens and high temperature wear tested up to $400^{\circ}C$ in dry air to observe the survivability of the DLC coating in simulated severe cutting conditions using a pin-on-disc tribotester with Hertzian contact stress of 1.3GPa. It showed reduced friction coefficients of minimum 0.02 up to $400^{\circ}C$. And cutting performance of DLC coated WC-Co insert tips to Al 6061 alloy were conducted in a high speed machining center. The main problems of built-up edge formation in aluminum machining are drastically reduced with improved surface roughness. The improvements were mainly related to the low friction coefficient of DLC to Al alloy and the anti-adhesion of Al alloy to WE due to the inertness of DLC.

• Tribology and Lubricants
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• v.32 no.1
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• pp.9-17
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• 2016

Contact between solid surfaces is one of the most important factors that influence dynamic behavior in micro/nanoscale. Although numerous theories and experimental results on contact behavior have been proposed, a thorough investigation for nanomaterials is still not available owing to technical difficulties. Therefore, molecular dynamics simulation was performed to investigate the contact behavior of nanomaterials, and the application of conventional contact theories to nanoscale was assessed in this work. Particularly, the contact characteristics of cylindrical nanowires were examined via simulation and contact theories. For theoretical analysis, various contact models were utilized and work of adhesion, Hamaker constant and elastic modulus those are required for calculation of the models were obtained from both indentation simulation and tensile simulation. The contact area of the cylindrical nanowire was assessed directly through molecular dynamics simulation and compared with the results obtained from the theories. Determination of the contact area of the nanowires was carried out via simulation by counting each atom, which is within the equilibrium length. The results of the simulation and theoretical calculations were compared, and it was estimated that the discrepancy in the results calculated between the simulation and the theories was less than 10 except in the case of the smallest nanowires. As the result, it was revealed that contact models can be effectively utilized to assess the contact area of nanomaterials.

• Tribology and Lubricants
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• v.34 no.5
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• pp.191-196
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• 2018

Bunker C is used in heavy-lift ships, furnaces, and boilers for generating heat, and power. Bunker C has only four regulations for quality standards and is rarely inspected in Korea. For these reasons, other oils such as used lubricant oil are commonly blended with Bunker C. This illegal mixture of fuel can damage the boilers, engines and affect the environment adversely. In this study, we investigate the fuel properties and perform atomic analysis of illegal Bunker C blended with used lube oil. The test results show that higher quantities of used lube oil in Bunker C have higher flash points, total acid numbers, copper corruption, solid contamination, and metal components. Further, increasing quantities of used lube oil in Bunker C cause lower viscosity, sulfur, and V content. However, adequate sample (approximately 1 L) is needed to evaluate presence of adulterants in Bunker C, we attempted the SIMDIST analysis. In the SIMDIST chromatogram, the used engine oils are detected for longer retention times than Bunker C owing to the high boiling point. We also quantitatively analyzed the lube oil content using SIMDIST.

• Tribology and Lubricants
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• v.12 no.3
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• pp.107-114
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• 1996

MoS$_{2}$ bonded film was applied to reduction gears, and its lubricating properties were experimentally evaluated in terms of the power transmission efficiency and the frictional noise with a dynamo-typed gear test rig. Tests were performed in both oil lubrication and dry condition where the rotating velocity and loading torque were varied. In dry condition, MoS$_{2}$ bonded films effected the power transmission efficiency to increase about 5%, and the frictional noise level to decrease about 6 dB under the test operating conditions. It well proved that MoS$_{2}$ bonded films were a very effective solid lubricant for reduction gears. In oil lubricating conditions, the frictional properties of the coated gears were mainly governed by the lubricating oil, and lubricating effects of MoS2 bonded films were not evident. The result suggested that lubricating effect of MoS$_{2}$ bonded films would be limited to prevent a damage of reduction gears in the initial run when they were used in oil lubrication conditions.

• Tribology and Lubricants
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• v.21 no.1
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• pp.33-38
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• 2005

Fretting is the oscillatory motion with very small amplitudes, which usually occurs between two solid surfaces in contact. Fretting wear is the removal of material from contacting surfaces through fretting action. Fretting wear of steam generator tubes in nuclear power plant becomes a serious problem in recent years. The materials for the tubes usually are Inconel 690 (I-690) and Inconel 600 (I-600). In this paper, fretting wear tests for I-690 and I-600 were performed under various applied loads in water at room temperature. Results showed that the fretting wear loss of I-690 and I-600 tubes was largely influenced by stick-slip. The fretting wear mechanisms were the abrasive wear in slip regime and the delamination wear in stick regime. Also, I-690 had somewhat better wear resistance than I-600.

• Tribology and Lubricants
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• v.23 no.1
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• pp.14-18
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• 2007

SCM415 alloy was implanted with nitrogen ions using plasma source ion implantation (PSII), at a dose range of $1{\times}10^{17}\;to\;6{\times}10^{17}N^{+}cm^{-2}$. Auger electron spectrometry (AES) was used to investigate the depth profile of the implanted layer. Friction and wear tests were carried out on a block-on-ring wear tester. Scanning electron microscopy (SEM) was used to observe the micro-morphology of the worn surface. The results revealed that after being implanted with nitrogen ions, the frictional coefficient of the surface layer decreased, and the wear resistance increased with the nitrogen dose. The tribological mechanism was mainly adhesive, and the adhesive wear tended to become weaker oxidative wear with the increase in the nitrogen dose. The effects were mainly attributed to the formation of a hard nitride precipitate and a supersaturated solid solution of nitrogen in the surface layer.

• Tribology and Lubricants
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• v.27 no.2
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• pp.109-114
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• 2011

The low temperature characteristics of automotive diesel have been legally regulated due to the fact that solid particle in diesel at low temperature can cause severe problems in the vehicle. The biodiesel is well known for eco-friendly fuel, which is one of the most popular alternative petrodiesel, but it is easy to solidified at low temperature than petrodiesel at low temperature. For that reason, in this study, we investigated the low temperature fuel characteristics of diesel-biodiesel blends which were prepared to mix 6 different kinds of biodiesel to winter diesel fuel, respectively. Also, we confirmed to improve low temperature fuel characteristics by pour point depressant.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.3
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• pp.5-10
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• 2004

The effect of bronze sintered friction materials on frictional and mechanical properties is studied with the content(8~18 wt,%) and shapes (flake and irregular) of graphite that is used as solid lubricants to meet diverse characteristics such as low coefficient of friction, low wear rate and high bending strength. The content and shapes of graphite are optimized by statistical experiments. Friction test was carried out measure friction coefficient, temperature dependence and wear rate. As a result of experiments, the density, hardness and bending strength with a shape of flake graphite are lower and decrease rapidly than that of Irregular, as the content of graphite increases up to 18 wt% Aftei friction test, coefficient of friction is 0.3~0 4 and wear rate is $0.32{\sim}2.98{\times}10^{-7}cm^3/kg{\cdot}m$. When the content of graphite increases, coefficient of friction increases In a shape of flake graphite and decreases in a shape of irregular graphite.

• Tribology and Lubricants
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• v.28 no.6
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• pp.278-282
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• 2012

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.

• Tribology and Lubricants
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• v.33 no.5
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• pp.202-206
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• 2017

In this study, the hydrophobicity properties for riblet surfaces that replicate shark skin are simulated. Riblet surfaces with surface roughness on riblets are generated numerically based on the measured data of real shark skin. We assumed that a rib on a scale is hemi-elliptical surface. The surface used in the simulation for the calculation of contact angle is composed of 9 scales like checkerboard type with a roughness. The contact angle of a water droplet can be calculated using the Wenzel equation and Cassie-Baxter equation for the generated riblet surfaces. The variation of contact angles with a fractional depth of penetration for the generated shark skin surfaces without and with coatings is demonstrated in the condition of solid-air-water. The results show that the contact angle for the surface without coating decreases with an increase of the fractional depth of penetration more drastically than that for the surface with coating. We compared the experimental and simulated results. It is shown that the measured contact angles of the shark skin template and the shark skin replica are within the simulated results. Therefore the contact angle of water droplet for rough surfaces can be estimated by the developed numerical method in this study.