• Tribology and Lubricants
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• v.38 no.5
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• pp.205-212
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• 2022

This paper presents experimental measurements of the structural characteristics of a two-pad beam-type gas foil journal bearing and its rotordynamic performance for a high-speed motor-driven turbocompressor. The test bearing had two top foils and two beam foils, each with an arc length of ~180°. Each beam foil was etched to obtain 40 beams with six geometries of different lengths and widths. The insertion of beam foils into the bearing housing produces equivalent beam heights. The structural tests of the bearing with a non-rotating journal revealed a smaller bearing clearance and larger structural stiffness for the load-on-pad configuration than for the load-between-pads configuration. Rotordynamic performance measurements during driving tests up to 100 krpm demonstrated synchronous vibrations and subsynchronous vibrations with large amplitudes. The test was repeated after inserting the shim between the top foil and beam foil to reduce the bearing radial clearance. The reduced bearing clearance resulted in a reduction in the peak amplitude of the synchronous vibrations and an increase in the speed at which the peak amplitude occurred. In addition, the onset speed and amplitude of the subsynchronous vibrations were dramatically increased and diminished, respectively. The rotor coast-down tests at 100 krpm show that the reduction in the bearing clearance extends the time to rotor stop, thus implying an improvement in hydrodynamic pressure generation and a reduction in bearing frictional torque.

• 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.

• KSTLE International Journal
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• v.2 no.2
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• pp.146-149
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• 2001

Recently, laser printers have been developed to have high-speed laser scanner with hydrodynamic bearings. Among the bearings, herringbone grooved bearing (HGB) produces hydrodynamic pressure by high-speed rotating and so make the surfaces between the shaft and sleeve separated. Accordingly, the bearings with non-contact rotation are suitable to high-speed rotating and have long bearing life and reliability. HGB is a kind of journal bearing and uses oil for a lubricant. HGB has excellent stiffness and load carrying capacity. Also, HGB is leakage-free due to groove pumping action. Consequently, HGB is valuable to be applied to high-performance devices such as hard disk drive, copier, and so on.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.8
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• pp.408-415
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• 2006

This paper deal with control and design of 50,000rpm class Active Magnetic Bearing(AMB) system for high speed precision motor. In the design of AMB system, the design parameters adopted high robust rotor shaft, Active Magnetic Bearing, sensor and control system. In the design of Magnetic Bearing, 2-D Finite Element Method(FEM) is used and transfer matrix method is using for rotor dynamics. The control accuracy of high speed AMB system is demonstrated by experimentations.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.1
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• pp.51-58
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• 2005

The development of the high-efficiency machine-tools equipment and new cutting tool materials with high hardness, heat- and wear-resistance has opened the way to application of high-speed cutting process. The basic argument of using of high-speed cutting processes is the reduction of time and the respective increase of machining productivity. In this sense, the spindle units may be regarded as one of the most important units, directly affecting many parameters of high-speed machining efficiency. One of the possible types of spindle units for high-speed cutting is the air-bearing type. In this paper, we propose the mathematical model of the dynamic behavior of the air-bearing spindle. To provide the high-level of speed capacity and spindle rotation accuracy we need the adequate model of "spindle-bearings" system. This model should consider characteristics of the interactions between system components and environment. To find the working characteristics of spindle unit we should derive the equations of spindle axis movement under the affecting factors, and solve these equations together with equations which describe the behavior of lubricant layer in bearing (bearing stiffness equations). In this paper, the three influence coefficients are introduced, which describe the center of spindle mass displacement, angle of shaft rotation around the axes under the unit force application and that under the unit torque application. These coefficients are operated in the system of differential equations, which describes the spindle axis spatial movement. This system is solved by Runge-Kutta method. Obtained trajectories and amplitude-frequency characteristics were then compared to experimental ones. The analysis shows good agreement between theoretical and experimental results, which confirms that the proposed model of air-bearing spindle is correctis correct

• Tribology and Lubricants
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• v.35 no.2
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• pp.114-122
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• 2019

High-speed rotating machinery requires low cost and reliable bearing elements with low friction, stable rotordynamic characteristics, and a simple design. This study experimentally evaluates the effects of bearing-support elements on the vibrational characteristics of a small-sized, high-speed permanent magnetic motor. A series of coast down tests from 100 krpm characterize the vibrational behaviors, rotor displacement, and housing acceleration of motors supported by ball bearings, ball bearings with a metal mesh damper, and gas foil bearings, respectively. Two eddy-current sensors installed in the horizontal and vertical directions measure the displacement of the rotor at its front nut, and a 3-axis accelerometer attached to the motor housing measures the housing acceleration. The test results reveal that synchronous (1X) vibration components most significantly affect the rotor displacement and housing acceleration, independent of the bearing-support elements. The motor supported by the deep-groove ball bearings results in the largest rotor vibrations increasing with speed; this is due to the absence of a damping mechanism. Additionally, the metal mesh damper effectively reduces the rotor displacement, housing acceleration, and sound-pressure level in the high-speed region (i.e., above 40 krpm), thus implying its substantial damping performance when installed on the outer race of the ball bearing. Lastly, the gas foil bearing supported motor yields the smallest rotor displacement, housing acceleration, and lowest sound-pressure level because of its hydrodynamic airborne operation, which does not require rolling elements that may cause mechanical friction and vibrations.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.475-481
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• 2001

Foil bearings have been successfully used for small high speed rotors, such as ACM(Air Cycle Machine), turbo charger, turbo compressor, high speed motor, etc. Recently advanced researches are concentrated on the high load capacity and the extreme temperature foil bearings to extend the application boundary. Some bearings are already adopted into cryogenic machines and micro gas turbines. In this paper, a foil journal bearing designed for high load capacity, which is under development, is introduced. The bearing is for the turbo refrigerator which has a rotor of 18${\~}$25 kgf rotating at 23,000${\~}$38,000 rpm. This application is well beyond conventional spectrum of foil bearings because the rotor is relatively heavy and the rotational speed is low. Therefore, the development is challenging. The foil bearing is a bump type, the size is 60mm in diameter and 50mm in length, the operating fluid is air and rotational speed is 26,000 rpm. In-house software was developed and used for bearing design. Tested maximum load capacity is 80kgf, 0.62 in terms of load capacity coefficient, and testing is being continued.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.567-568
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• 2011

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1227-1236
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• 2012

The low speed machinery faults are usually caused by the bearing failure of the rolling elements. As the life time of the bearing is limited, the condition monitoring of bearing is very important to maintain the continuous operation without failures. A few monitoring techniques using time domain, frequency domain and fuzzy neural network vibration analysis are introduced to detect and diagnose the faults of the low speed machinery. This paper presents a method of fault detection for the rolling element bearing in the low speed machinery using the Wiener filtering and shock pulse counting techniques. Wiener filter is used for noise cancellation and it clearly makes the shock pulse emerge from the time signal with the high level of noise. The shock pulse counting is used to determine the various faults obviously from the shock signal with transient pulses not related with the bearing fault. Machine fault simulator is used for the experimental measurement in order to verify this technique is the powerful tool for the low speed machine compared with the frequency analysis. The test results show that the method proposed is very effective parameter even for the signal with high contaminated noise, speed variation and very low energy. The presented method shows the optimal tool for the condition monitoring purpose to detect the various bearing fault with high accuracy.

• The KSFM Journal of Fluid Machinery
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• v.5 no.3 s.16
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• pp.7-14
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• 2002

A new foil bearing, ViscoElastic Foil Bearing(VEFB) is suggested with the need for a high damping foil bearing. Sufficient damping capacity is a key technical hurdle to super-bending-critical operation as well as widespread use of foil bearings into turbomachinery. The super-bending-critical operation of the conventional bump foil bearing and the VEFB is examined, as well as the structural dynamic characteristics. The structural dynamic test results show that the equivalent viscous damping of the VEFB is much larger than that of the bump bearing, and that the structural dynamic stiffness of the VEFB is comparable or larger than that of the bump bearing. The results of super-bending-critical operation of the VEFB indicate that the enhanced structural damping of the viscoelastic foil dramatically reduces the vibration near the bending critical speed. With the help of increased damping resulting from the viscoelasticity, the suppression of the asynchronous orbit is possible beyond the bending critical speed.