• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.96-101
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• 2001

This paper shows the temperature characteristics of a high speed angular contact ball gearing which is 7004C type with ISO P2 tolerance class. A built-in motor type high speed spindle which adopts an oil-air lubrication system was used to measure the temperature rise up to 60,000rpm. The gearing temperature was measured using thermocouples that were attached to the outside surfaces of the outer rings. The result showed that the continuous test method which was suggested in this paper is more effective than on and off method and the lubrication oil supply rate should be reduced in high speed rolling bearings as long as the seizure does not occur. And the result were confirmed that the bearings packed with ceramic balls are superior to those with steel balls in temperature characteristics.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.3
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• pp.241-247
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• 2014

The voltage source PWM inverter generally used to drive the air conditioning (A/C) fans has been posing a large issue that the bearings in air conditioning fan motors are highly possible to be corroded electrically. Potential difference called shaft voltage is generated between inner and outer rings of the bearings due to inverter switching. The shaft voltage causes bearing lubricant breakdown dielectrically. As a result, bearing current is caused. This current causes the bearing corrosion. In previous work, we demonstrated that the shaft voltage can be reduced by using an insulator inserted between the outer and inner cores of the rotor in an air conditioning fan motor without grounding. This paper proposes the other countermeasure for reducing the shaft voltage in fan motors. The countermeasure which adds a capacitor between the brackets and the stator core is effective even for fan motors with non-insulated rotor. The effectiveness is confirmed by both simulated and experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.745-750
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• 2011

In a hope to better understand the flow and convective heat transfer characteristics inside a ball bearing, air flow between the rolling elements and raceways at high speed bearing rotation is numerically investigated using a simplified inner geometry of bearing and a CFD technique. Flow simulation results reveal the pressure distribution of airflow and the shear stress distribution on the ball surface, of which nonuniformity becomes significant with the increasing rotational speed. Also, the local point of maximum shear stress coincides with the stagnation flow area on the surface of rolling elements. A complex pattern of three-dimensional vortex structures is found in the air flow due to the relative motion of bearing elements and three different types of vortex pairs exist around the rotating and orbiting rolling elements.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.303-310
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• 2005

The systems with probe and SIL(Solid Immersion Lens) mechanisms have been researched as the technology to perform NFR(Near Field Recording). Most of them use the flying head mechanism to accomplish high recording density and fast data transfer rate. In this paper, ABS shape of flying head was optimized with the object of securing the maximum compliance ability of OFH. We suggest low different optimization processes to predict the static flying characteristics for the OFH. Two different approximation methods, regression analysis and back propagation neural network were used. And we compared the result of directly connected(between CAE and optimizer) method and two approximated optimization results. Design Optimization Tool(DOT) and ${\mu}GA$ were used as the optimizers.

• Tribology and Lubricants
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• v.21 no.6
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• pp.283-288
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• 2005

This paper presents the theoretical model and analysis results to investigate the effect of Coulomb damping in the sub-structure of a foil bearing. Vertical and horizontal deflection of a bump is restricted by friction of the bump. Equivalent viscous damping of the bump foil is derived from the Coulomb friction. Dynamic equation of the bump is constituted by stiffness and damping terms. The air film is modeled by the compressible Reynolds equation. A perturbation approach and finite difference numerical method is used to determine the static and dynamic performance of the bearing from the coupled fluid-structural model. The analysis result shows that the static and dynamic performance is enhanced by the bump friction.

• Tribology and Lubricants
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• v.16 no.4
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• pp.247-252
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• 2000

As the demand for higher areal recording densities requires a lower flying height of the slider, the variation of the flying height of the slider during drive operation becomes of great concern. The variation of the flying height is closely related with the slider design parameters such as air bearing shape, cavity depth, shallow step depth, crown, camber, pitch offset, roll offset, gram load, and so on. The objective of this work is to optimize the cavity depth and the shallow step depth, which are the control factors in air bearing design, using Robust Design method. It was found that the shallow step depth was statistically significant in affecting the variation of flying height, therefore the level of the shallow step depth should be chosen to minimize the variation of flying height.

• KSTLE International Journal
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• v.7 no.2
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• pp.27-34
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• 2006

Knudsen number is the ratio of molecular mean free path versus mm thickness and the criterion to determine the flow form. When its value is lower than 0.01, the flow can be assumed to has no slip boundary condition. And in the case that the value is between 0.01 and 10, then the flow has slip boundary condition at both the adjacent walls. The condition of the air flow between the rotating journal and top foil in the air foil bearing is determined by the rotating speed and load, and the Knudsen number is also varied by those values. Because the molecular mean free path is variable to the pressure and temperature, more exact formulation is necessary to understand and analyze the flow regime. In this study, the analysis considering Knudsen number formulated with those variables (pressure, temperature and mm thickness) was executed. The approximate value was examined using the equation to confirm whether the flow has the slip or no-slip boundary condition. From the analytic investigation, it was decided to range approximately 0.01 to 1.0 and the flow can be supposed to have the slip boundary condition. Under the condition of the slip flow, the static characteristics of the air foil bearing were examined using modified Reynolds equations. The results were compared with those considering no slip condition. It shows that the slip condition makes the flow decelerates and the load carrying capacity decreases compared with no slip condition. And as the bearing number and eccentricity ratio increase, the load carrying capacity also increased at both the cases. From this result, it can be supposed that the bearing torque also increases. In the analysis of the dynamic characteristics, the perturbed Knudsen number was taken into consideration. Because the Knudsen number is expressed as the terms of each variable, the perturbed equation can be simply derived. The results of both cases considering and not considering Knudsen number were compared each other. In the case of the direct terms of the stiffness and damping coefficients, the difference between both cases was little and increased as the bearing number and eccentricity ratio increased. And the cross terms have less or more differences.

• Tribology and Lubricants
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• v.18 no.5
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• pp.364-370
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• 2002

In this paper, numerical analyses were undertaken to calculate the static and dynamic performances of step-pocket, inward pumping spiral grooved, outward pumping spiral grooved and herringbone grooved bearings. For each bearing, optimal values for various design parameters were obtained to maximize the load capacity and the stiffness and bearing performances were calculated. The optimized performances of these bearings were compared to conclude that the performance of step-pocket bearing is better than the other bearings.

• Tribology and Lubricants
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• v.7 no.2
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• pp.51-60
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• 1991

For the accurate run-out of a light rotor shaft the sliding bearings supplied with externally pressurized air are effectively applied, and it is important to predict the static and dynamic characteristics of rotor-bearing system. In this study direct numerical method is applied to solve the perturbed Reynolds' equation. To solve it the perturbed dimensionless mass flow rate is used as the boundary condition under the inherently-compensated restrictor. The dynamic characteristics of a rotor supported in the externally pressurized air bearings are analyzed, and as a result the orbit of the journal center is calculated. The theoretical results are investigated and discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.351-358
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• 1993

Recently a high speed spindle system for machine tools has attracted considerable attention to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices and so on. And a lubrication experiment for evaluating the performance of the spindle system is carried out. Especially, in order to establish the lubrication conditions related to the development of a high speed spindle system, the effects of oil supply rate, rotational spindle speed and so on are studied and discussed on the bearing temperature rise, bearing temperature distribution and frictional torque. And the effect of spindle system structure on the bearing temperature distribution is investigated.