• The KSFM Journal of Fluid Machinery
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• v.6 no.2 s.19
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• pp.7-14
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• 2003

This paper describes reliability characteristics of an air foil journal bearing for high-speed turbomachinery at a room temperature. To verify the reliability of air foil journal bearing, lift-off characteristics, load carrying capacity, and 10,000 cycle start-stop test were performed with a motor-driven test rig. A lift-off test shows the relationship between the rotating speed of the shaft and the frictional torque with bearing surface. About a load-carrying capacity, the tested air foil journal bearing produced a load capacity of 500N at an operating speed of 15,000rpm, which is compared with results of numerical analysis and empirical coefficients. Finally, the trends in change of start torque, stop torque, and bearing temperature were shown during a 10,000-cycle start-stop test of an air foil journal bearing. We found that an air foil bearing performs well, as a supported bearing for the high-speed turbocompressor.

• The KSFM Journal of Fluid Machinery
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• v.16 no.3
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• pp.18-25
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• 2013

Recently the requirement of long-term mobile energy source for mobile robot or small-sized unmanned vehicle is highly increased, and the micro turbine generator(MTG) which is known to have high energy and power density is under development. MTG is designed to have air foil bearing and high speed rotor of which operating speed is 400,000rpm. In the development stage of high speed rotor and bearing, stability analysis for the full operational speed range is essential and the dynamic coefficients such as stiffness and damping coefficients of bearing depending on the rotational speed are required for that. Although perturbation method is usually used to identify the dynamic coefficients, it's not easy to give the perturbation to the high speed rotating rotor. In this study, we present the dynamic coefficients measurement system for air foil bearing which consists of electromagnets, gap sensors, high speed motor and controller. This measurement system can exert the sine sweep force to the rotor-bearing, measure the displacement of rotor and get FRF(Frequency response function) of rotor-bearing. The least square estimation method is applied to identify the dynamic coefficients of bearing from the measured frequency response at the different rpm and the identified dynamic coefficients for the wide rotational speed range are presented.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.239-244
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• 1997

Recently, the high speed rotation and accuracy is needed in the field of electro-optic devices. But it is difficult for ball bearing to satisfy such conditions. So, we have developed the hemispherical type aerodynamic bearing for LSU(Laser Scanning Unit) motor. The hemispherical type aerodynamic bearing is able to support radial and axial load simultaneously. In this research, We have developed mass production method and tested the perromance of aerodynamic bearing in comparision with ball bearing at the speed of 23,000rpm. In the result, we proved that the properties of aerodynamic bearing is better than ball bearing's.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.398-403
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• 2004

The demand of high speed machining is increasing because the high speed cutting providers high efficiency of process, short process time, improved metal removal capacity and better surface finish. Active magnetic bearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting. The automatic control concept of magnetic bearing system provides ability of intelligent control of spindle system to increase accuracy and flexibility by means of adaptive vibration control. This paper describes a design and development of a milling spindle system which includes built-in motor with power 5.5㎾ and maximum speed 70,000rpm, HSK-32C tool holer and active magnetic bearing system. Magnetic actuators are designed for satisfying static load condition. The Performances of manufactured spindle system was examined for its static and dynamic stiffness, load capacity, and rotational accuracy. This spindle was run up to 70,000 rpm stably, which is 3.5 million DmN.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.96-100
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• 2011

The hydrostatic bearings have a relatively small run-out comparing to its shape error by fluid film effect in hydrostatic state as like pneumatic bearing and have a high stiffness, load capacity and damping characteristics. As there is no maintenance and semipermanent in these bearing type, it has been usually adopted as main spindle bearing for grinding machine. In this thesis, to develop hydrostatic bearing for high speed spindle, the cooler setting temperature, bearing clearance and nozzle pressure of belt-driven hydrostatic bearing are investigated. The bearing temperature is decreased, as the cooler setting temperature is lower, nozzle pressure is higher and bearing clearance is wider. The front temperature of bearing is nearly $8^{\circ}C$ higher than the rear one up to 13,000 rpm of spindle revolution. The thermal deflection of X-axis is ${\pm}16\;{\mu}m$ in range of 12,000 rpm-13,000 rpm. Therefore, it is conformed that the built-in motor hydrostatic bearing can be used to high speed spindle.

• Tribology and Lubricants
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• v.12 no.4
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• pp.28-34
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• 1996

The lubrication characteristics of high-speed ball bearings have been investigated empirically using 45mm bore split inner ring ball bearings employed in small industrial gas turbine engines with oil-jet lubrication method. For the close structural simulation, experiments carried out 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 directly applied to the design and the development of gas turbine engines. Testing was done by varying operating speeds, axial load on bearings, and lubricant flow rates. During testing, the temperature of bearing at outer-ring face, the power consumption of the driving motor, and the rotating resistance of the bearing were measured. From this study, the representative factors for lubrication characteristics at high speed was found, and the most important one was not operating speed but axial load up to 1.95 million dmN speed and 2969 N axial load. Furthermore, the detailed variation of the rotational resistance of the bearing could be visualized by measuring the change of the radial load under the bearing supports. The rotational resistance consists of the frictional resistance and the bearing-cavity oil resistance.

• Tribology and Lubricants
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• v.16 no.2
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• pp.91-98
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• 2000

A slot restrictor air journal bearing has high load capacity and high stiffness. The stability characteristics of the slot restrictor air journal bearing are studied theoretically and experimentally to forecast and to prevent the whirl instability. As for the high speed rotating machinery, the instability called'whirl'occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. Therefore, the forecasting and prevention of the occurrence of whirl instability is a very important subject especially to develop highly efficient high speed rotating machinery. The bearing with the slot restrictor that varies about circumferential direction is used for the purpose of the prevention of whirl instability.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.350-357
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• 1998

Slot restrictor air journal bearing has high load capacitance and high stiffness. Stability characteristics of slot restrictor air journal bearing are studied theoretically to forecast and to prevent the whirl instability. As for the high speed rotating machinery, the instability called 'whirl' occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. Therefore, the forecasting and prevention of the occurence of whirl instability is a very important subject especially to develop highly efficient high speed machinery. The bearing with the slot restrictor that varies about circumferencial direction is used for the purpose of the prevention of whirl instability.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.9
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• pp.94-102
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• 2010

The spindle is the main component in machine tools. To develop high speed machine tools, a lot of studies have been carried out for high speed spindle. Bearing is very important part in spindle. The bearing clearance is influenced by shrink fit and thermal expansion during operation. The designer must take into account the reduction of shrink fits. The aims of this study are to grasp the shrink fits and behavior of a bearing which is a deeply connected with fatigue life of bearing and performance of spindle through FEM(Finite Element Method). This paper proposed optimum value of shrink fit considering deformation of spindle and stress of fitting area using design of experiments. Thus, the proposed formula can be used to obtain bearing internal clearance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.06a
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• pp.109-115
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• 2000

The spindle unit is core parts in high precision machine tools. Diverse static, dynamic and thermal charateristics of spindle unit are needed for special purpose of machine tools. Compromise between those charateristics will be done in concept design phase. High static stiffness at spindle nose may be very important performance for heavy cutting work. High dynamic stiffness is also useful to high precision and high speed machine tools. Improvement of thermal charateristics in spindle lead to high reliability of positioning accuracy. For high speed spindle structure, the design parameter such as, bearing span, diameter, bearing type and arrangement, preload, cooling and lubrication method should be in harmony.