• Tribology and Lubricants
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• v.34 no.2
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• pp.43-48
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• 2018

This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical $CO_2$ cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around $55^{\circ}C$ which is approximately $15^{\circ}C$ higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.119-126
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.68-71
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• 2003

Heat treatment is one of the critical manufacturing processes that determine the quality of a product. This paper presents experimental and analytical results for the quench of a ring gear in stagnant oil. The goal of this study is to develop heat transfer predicting model in an overall analysis of the quenching process. Thermal conductivities which are dependant on temperatures and convection coefficients which are obtained by inverse method are used to develop the accurate heat transfer model. The results of heat transfer model have a good agreement with experimental results.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.177-182
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• 2002

In the paper, the development of high-speed industrial turbo blowers with foil air bearings is presented as a first successful commercialization in the world. Their target market is various from wastewater treatment to cement factory processes which require compressed air ranging between 0.6 and 0.8 bar gauge. Employing the state-of·the-art technology of the high-speed BLDC motors, the bump-type foil air bearings and the high- efficient turbo impellers/diffusers, so much compact, efficient and silent blower machines of a single stage are now available in the market, aiming to replace the existing inefficient, bulky and noisy ones, such as roots blowers. The first production lines are established fur 25,75 and 150 hp class blowers. Rotational speeds from about 20,000 to 80,000 rpm are realized directly from the high-speed BLDC motors without any gear boxes, and no lubrication oil is required. A brief introduction of design, manufacture and test results is presented fur mechanical, electrical and aerodynamic performance.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.10a
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• pp.207-212
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• 1996

The shotpeening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shotpeening treatment for inner race of ball bearing on the roiling contact fatigue. Shotpeening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shotpeening treatment. This effect was found to be more pronounced to the full hardened bearing.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.05a
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• pp.338-341
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• 2007

This paper surveyed the deterioration phenomena of elevator system being operated in Apartments. It was proved that oil leakage, gear abrasion and metal corrosion are the main deterioration phenomena and the number of breakdown was increasing rapidly with 8 years elapsed from installations

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.531-536
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• 1994

Wrapping machines in cigarette factories are equipped with indexing drive units with roller gear cam. At present there are no simple, visual, diagnostic techniques for predicting failure in these nits at an early stage. This paper proposes that failure could be predicted by using either a modified version of kurtosis, or the Wigner distribution method. The nonlinear vibration model proposed in this paper takes into consideration the play between the m and the cam follower, and precisely simulates the actual vibration. Statistics on the variance in play, obtained from the data on time history, call then be used to evaluate the effects of tile mage oil the cam and cam follower.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.5
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• pp.589-595
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• 2002

Fluid mixing is ubiquitous and essential in many natural and industrial systems. Understanding the mixing processes that occur in these diverse systems is essential for predicting many aspects of practical importance. The objective of this study was to develop a new mixing element and to perform the experimental investigation of flow and mixing in a static mixer that is equipped the new element and the others. Glycerin and gear oil were used as mixing fluids. Pressure drops across the static mixer elements of different designs and different numbers were measured using a hydraulic manometer The axial and cross-sectional views of tracer mixing were photographed using a digital camera. The pressure drops of SSM mixer were about 20% less than that of Sulzer mixer whereas the mixing performance of SSM mixer was not so good as that of Sulzer mixer

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.181-184
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• 2003

The Four-Ball Tester has been widely used as a tool to charaterize lubricity for long time. In order to understand more acurate properties of lubricants, more test methods have been developed. Among the test methods, SRV test method was compared to Four-Ball Tester in this paper.

• Tribology and Lubricants
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• v.15 no.2
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• pp.150-155
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.