• Tribology and Lubricants
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• v.34 no.4
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• pp.138-145
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• 2018

Elliptical bearings are widely used for large steam turbines owing to their excellent load carrying capacity and good dynamic stability. Power loss in bearings is an extremely important parameter, especially for high turbine capacities. Optimization of operation conditions and design variables such as bearing clearance and bearing length can reduce the power loss in elliptical bearings. Although changes in the oil supply method have served to increase the efficiency of the tilting pad journal bearing, it has not explicitly improved elliptical bearings. In this study, we verify the static characteristics of an elliptical bearing by changing the direction of oil supply. We evaluate the bearing power loss and bearing metal temperature, and compare the bearing performance and reliability in different test cases. The direction of oil supply is $90^{\circ}$ (9 o'clock) and $270^{\circ}$ (3 o'clock) when the rotor rotates in a counterclockwise direction. We use an elliptical bearing with an inner diameter and active length of 220.30 and 110.00 mm, respectively. Bearing power loss and bearing metal temperatures are measured and evaluated by rotor rotational speed, oil flow rate, and bearing load. The results reveal a 20 reduction in the power loss when the direction of oil supply is 90. Furthermore, the oil film on the upper part of the bearing has a high temperature when the direction of oil supply is $90^{\circ}$. In contrast, when the direction of oil supply is $270^{\circ}$, the oil film on the upper part of the bearing is relatively cold.

• Tribology and Lubricants
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• v.13 no.1
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• pp.70-75
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• 1997

The lubrication characteristics of high-speed ball bearings at oil-starvation have been investigated empirically using the bearings employed in small industrial gas turbine engines. For the close structural simulation, experiments carried our with bearing mounting supports of real engines, such as bearing housings and oil nozzle assemblies with squeeze film dampers. Thus the results of tests can be applied to the design and the development of gas turbine engines. Testing was done by simulating the oil-starvation conditions in engines, such as stopping the oil-supply to the bearing during normal operating, starting without oil-supply at atmospheric temperature, and accelerating with oil-supply at atmospheric temperature. From this study, the relative comparison of the frictional resistance and the resistance due to the bearing cavity oil was demonstrated visually, and the resistance due to the bearing cavity oil was dominant in the resistance of bearing at high speed.

• Tribology and Lubricants
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• v.9 no.1
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• pp.55-61
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• 1993

Recently, due to the erosion damage that were generated increasingly at alloy metals of slide bearing by cavity of lubricating oil with tendency of high speed and high output of reciprocating engine, there is a need to study the process on the formation of cavitation erosion, and the characteristic of cavitation erosion at lubricating oil environments under various condition for marine ship. Therefore, the apparatus of cavitation erosion experiment used 20 KHz, $24 \mu m$ piezoelectric vibrator. The main results obtained through this test method are as follows: 1. The max. erosion rate at lubricating oil environments was related to the change of space, oil film thickness, and shown to tendency of gear oil>system oil>turbine oil>mixed oil environments with different viscosity. 2. The pitted hole by cavitation erosion at high viscosity oil environments became small and deep, and in addition to, they appeared to be wide and shallow at low viscosity.

• Tribology and Lubricants
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• v.19 no.3
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• pp.133-138
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• 2003

The characteristics for bimorph PZT cantilever of laboratory-fabricated have been evaluated experimentally. The deflections of cantilever with PZT are result from a capillary force between a water drop and a tip of cantilever. The output voltage due to deflect cantilever are depend on the tip shape and thickness of cantilever. We applied a bimorph PZT cantilever to oil thickness measurement. This reasonable concept is that the output voltage be caused by different defected characteristics between oil and surface. Experimental results demonstrated that the high measurement accuracy of the oil film thickness is obtained from the probe.

• The KSFM Journal of Fluid Machinery
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• v.11 no.5
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• pp.50-56
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• 2008

Metal cutting operations involve generation of heat due to friction between the tool and the pieces. This heat needs to be carried away otherwise it creates white spots. To reduce this abnormal heat cutting fluid is used. Cutting fluid also has an important role in the lubrication of the cutting edges of machine tools and the pieces they are shaping, and in sluicing away the resulting swarf. As a cutting fluid, water is a great conductor of heat but is not stable at high temperatures, so to improve stability an emulsion type mixed fluid with water and oil is often used. It is pumped over the cutting site of cutting machines as a state of atomized water droplet coated with oil by using jet. In this paper, to develop cutting fluid supplying nozzle to obtain ultra thin oil film for coating water droplet, a numerical analysis of three dimensional mixed fluid Jet through multi-stage nozzle was carried out by using a finite volume method. Jet flow characteristics such as nozzle exit velocity, development of mixing region, re-entrance and jet intensity were analyzed. Detailed mixing process of fluids such as air, water and oil in the nozzle were also investigated. It is easy to understand complex flow pattern in multi-stage nozzle. Important flow Information for advance design of cutting fluid supplying nozzle was drawn.

• Tribology and Lubricants
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• v.23 no.6
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• pp.306-311
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• 2007

This paper presents the friction characteristics of pb-fres pin bushing bearings for an automotive gasoline engine. The external load is 100 N to 600 N and the speed of the pin bushing bearing is 1000 rpm to 3000 rpm against the rubbing surfaces. And the contact modes of rubbing surfaces between a piston pin and a pb-free pin bushing specimen are a dry friction, an oil lubricated friction and a mixed friction that is starved by a lack of engine oil. Two influential factors of a contact rubbing modes and a material property are very important parameters on the tribological performance of a friction characteristic between a piston pin and a pb-free pin bushing. The experimental result shows that the pin bushing speed of 2000 rpm shows a typical oil film lubricated sliding contact mode in which means that as the applied load is increased, the friction loss is increasing. But other contact mode depending on the speed and the load may affect to the fiction coefficient without a regular and uniform trend. In summary, the oil lubricated rubbing surface definitely decreases a running-in period in short and increase oil film stiffness, and this may leads the reduction of a friction loss.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.8
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• pp.110-116
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• 2020

Aircraft hydraulic oil reservoirs made with aluminum 7075 have an anodized coating to enable airtightness and corrosion resistance. To maintain a stable oil pressure, the internal surface roughness of the reservoir should be less than approximately 0.2 ㎛. To this end, precision polishing must be performed. However, ensuring the processing quality is challenging, as most polishing operations are performed manually, owing to which, the inner surface roughness is not uniform, and the product quality is irregular. Therefore, we developed a special superfinishing machine to realize the efficient inner polishing of an aircraft hydraulic oil reservoir, by using an abrasive film to improve the process throughput and uniformity. In the experiment involving the superfinishing of an anodized aluminum 7075 cylinder specimen by using the proposed machine, a higher surface roughness than that achieved in the repetitive manual polishing process could be realized.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.4
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• pp.52-66
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• 2003

Generally we have difficulty in removing oil using mechanical devices because recovery rate and recovery efficiency decrease remarkably when operating in thin oil films or in oils of very high viscosity In the Present study a series of experiments were carried out to study the effect of operating conditions on the rate of recovery for the spilled oil using a drum type skimmer. For each set of experiments depth of immersion, oil film thickness and the circumferential speeds were varied systematically to find the effects on the recovery rate. The results shows that recovery rate is dependent on the contact angle for the depth of immersion and the highest rate of oil recovery shows in the case of a contact angle of 45°(h/d=0.15). For the removal of spilled oil the optimal circumferential speed can be found as the critical value to reach the saturated recovery rate for a given oil film thickness and depth of immersion. Even in thin oil thickness we have enough recovery rate and recovery efficiency within critical circumferential speed this way.

• KSTLE International Journal
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• v.2 no.2
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• pp.103-113
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• 2001

The influence of aerated oil on high-speed journal bearing is examined by classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of air-oil mixture in fluid-film bearing. Convection to the walls and mixing with supply oil and re-circulating oil are considered. The live oil surface tension is considered as functions of temperature, API gravity and air volume ratio. With changing eccentricity ratio, it is investigated the effects of air bubbles on the performance of a high-speed plain journal bearing. Just at the moderate eccentricity ratios, even if the involved aeration levels are not so severe and the entrained air bubble sizes are not so small, it is found that the bearing load and friction farce may be changed so visibly for the high speed bearing operation.

• Tribology and Lubricants
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• v.26 no.3
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• pp.167-174
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• 2010

An apparatus for measuring oil oxidation was developed, which is capable of being mounted to mechanical devices for detecting power of fluorescent light reflected from oil in real time as an indication of the oil oxidation. This device has an advantage over conventional fluorescence spectrometers where the thin film is required for the measurement. Clean and used oil samples (mineral and synthetic oils) were tested by the developed apparatus that calculates a fluorescence quantum yield and a light absorption coefficient of the oil based upon the signals from the two light-receiving members and evaluates the degree of oil oxidation of test oils based on the fluorescence quantum yield. Results generally show that the developed device is able to effectively evaluate oil oxidation characteristics on-site in the field.