• Title/Summary/Keyword: Bearing Friction

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Performance Analysis of High-Speed Ceramic Ball Bearings Under Thrust Loads in EHD Lubrication (축방향 하중을 받는 고속 세라믹 볼베어링에 대한 EHD 윤활영역에서의 성능 해석)

  • 반종억;김경웅
    • Tribology and Lubricants
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    • v.14 no.2
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    • pp.26-34
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    • 1998
  • This paper presents a high-speed performance analysis of ball bearings with ceramic balls under thrust loads. The sliding velocity profiles between a ball and raceways were obtained by the 3-D quasi-dynamic equations of motion including both centrifugal force and gyroscopic moment derived by vector matrix algebra. The friction at the contact areas was obtained by the Bair-Winer's non-Newtonian rheological model and the Hamrock-Dowson's central film thickness in EHL analysis. The nonlinear equations were solved by the Newton-Raphson method and the underrelaxation iterative method. The friction torques and ball behaviors with various loads, ball materials, and contact angles were predicted by this model. It was shown that the friction torque was sensitive to thrust load and contact angle, and that the friction torque and the pitch angle of the bearing with ceramic balls are smaller than those of the bearing with steel balls.

Friction Effects on the Performance of Air Foil Bearings (공기포일베어링의 성능에 미치는 범프마찰효과)

  • Kim Young-Cheol;Lee Dong-Hyun;Kim Kyung-Woong
    • 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.

Physical and numerical modeling of drag load development on a model end-bearing pile

  • Shen, R.F.;Leung, C.F.;Chow, Y.K.
    • Geomechanics and Engineering
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    • v.5 no.3
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    • pp.195-221
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    • 2013
  • A centrifuge model study is carried out to investigate the behavior of pile subject to negative skin friction induced by pile installation, ground water drawdown and surcharge loading. A single end-bearing pile is examined as the induced negative skin friction would induce the most severe stress on the pile structural material as compared to friction piles. In addition, the behavior of the pile under simultaneous negative skin friction and dead/live loads is examined. To facilitate detailed interpretations of the test results, the model setup is extensively instrumented and involves elaborate test control schemes. To further examine the phenomenon of negative skin friction on an end-bearing pile, finite element analyses were conducted. The numerical analysis is first validated against the centrifuge test data and subsequently extended to examine the effects of pile slenderness ratio, surcharge intensity and pile-soil stiffness ratio on the degree of mobilization of negative skin friction induced on the pile. Finally experimental and numerical studies are conducted to examine the effect of applied transient live load on pile subject to negative skin friction.

Effects of Angular Acceleration on the Friction and Wear Characteristics of Gas Foil Thrust Bearings (회전각가속도가 가스 포일 스러스트 베어링의 마찰 및 마모 특성에 미치는 영향)

  • Sung Ho Hwang;Dae Yeon Kim;Tae Ho Kim
    • Tribology and Lubricants
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    • v.39 no.5
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    • pp.203-211
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    • 2023
  • This study experimentally investigates the effects of angular acceleration on the friction and wear performances of a gas foil thrust bearing (GFTB) using a typical GFTB with six pads. The outer radius of the bearing is 31.5 mm, the total bearing area is 2,041 mm2 , and the bump foil and incline (ramp) height are both 500 ㎛. The newly developed GFTB test rig for measuring the friction torque and coefficient measures the axial load, drag torque, lift-off speed, and touch-down speed. The experiment is conducted for angular accelerations of 78.5, 314.2, and 328.3 rad/s2 at axial loads of 5, 10, and 15 N, respectively. The test shows that the start-up friction coefficient increases with increasing axial load at the same angular acceleration, and the friction coefficient decreases with increasing angular acceleration under the same axial load. As the angular acceleration increases, the lift-off speed at the motor start-up increases, and the touch-down speed at the motor stop decreases. The wear distance of the GFTB for a single on/off cycle increases with increasing axial load at the same angular acceleration and decreases nonlinearly with increasing angular acceleration under the same axial load. The test results suggest that adjusting the rotational angular acceleration helps reduce bearing friction and wear.

An Experimental Study of the Friction and Temperature Characteristics of Engine Crankshaft Bearings (엔진 크랭크새프트 베어링의 마찰 및 온도 특성에 대한 실험적 연구)

  • 조명래;문호지;장인배;한동철
    • Tribology and Lubricants
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    • v.11 no.1
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    • pp.44-49
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    • 1995
  • Friction characteristic of an engine crankshaft bearing is affected by revolution speed, applied loads, and viscosity of lubrication. So, experimental investigation is required to observe the friction characteristics using these factors. Hydraulic cylinder, servo controller system which can be modified the applied load, and test rig for the observation of the characteristics of engine crankshaft bearings were designed and fabricated, and some experiments were performed. Friction torque, journal locus and circumferential temperature variation of crankshaft bearing were measured according to applied load, revolution speed, and oil inlet temperature.

Thermohydrodynamic Lubrication Analysis of High Speed Journal Bearing Considering Variable Density and Specific Heat (변화하는 밀도와 비열을 고려한 고속 저어널 베어링의 열유체 윤활해석)

  • 전상명;장시열
    • Tribology and Lubricants
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    • v.17 no.4
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    • pp.297-306
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    • 2001
  • Under the condition of variable density and specific heat, maximum pressure, maximum temperature, bearing load, friction and side leakage in high-speed journal bearing operation are examined within some degree of Journal misalignment. The results are compared with the calculation results under the conditions of constant density and specific heat, and variable density and constant specific heat. It is found that the condition of variable density and specific heat play important roles in determining friction and load of Journal bearing at high speed operation.

Evaluation of Running Friction Torque of Tapered Roller Bearings Considering Geometric Uncertainty of Roller (롤러의 형상 불확실성을 고려한 테이퍼 롤러 베어링의 구동마찰토크 평가)

  • Jungsoo Park;Seungpyo Lee
    • Tribology and Lubricants
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    • v.39 no.5
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    • pp.183-189
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    • 2023
  • A bearing is a mechanical component that transmits rotation and supports loads. According to the type of rotating mechanism, bearings are categorized into ball bearings and tapered roller bearings. Tapered roller bearings have higher load-bearing capabilities than ball bearings. They are used in applications where high loads need to be supported, such as wheel bearings for commercial vehicles and trucks, aircraft and high-speed trains, and heavy-duty spindles for heavy machinery. In recent times, the demand for reducing the driving friction torque in automobiles has been increasing owing to the CO2 emission regulations and fuel efficiency requirements. Accordingly, the research on the driving friction torque of bearings has become more essential. Researchers have conducted various studies on the lubrication, friction, and contact in tapered roller bearings. Although researchers have conducted numerous studies on the friction in the lips and on roller misalignment and skew, studies considering the influence of roller shape, specifically roller shape errors including lips, are few. This study investigates the driving friction torque of tapered roller bearings considering roller geometric uncertainties. Initially, the study calculates the driving friction torque of tapered roller bearings when subjected to axial loads and compares it with experimental results. Additionally, it performs Monte Carlo simulations to evaluate the influence of roller geometric uncertainties (i.e., the effects of roller geometric deviations) on the driving friction torque of the bearings. It then analyzes the results of these simulations.

Review of effects of friction coefficient of moving bearing on Stability of CWR (가동단 마찰계수가 장대레일 축력 안정성에 미치는 영향 검토)

  • Ryu Jae-Nam;Choi Young-Joon;Yang Sin-Chu
    • Proceedings of the KSR Conference
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    • 2004.10a
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    • pp.812-817
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    • 2004
  • Recently drastic improvement of railway technology has been accompanied by the construction of very high-speed tracks. It should be noticed that Continuously Welded Rail(CWR) has played significant role in technical development of railway and that installation of CWR is now being scheduled on existing lines as well as newly-built lines. In general, interaction between CWR and bridge deck takes place on bridge section and additional axial force and displacement is to be developed owing to temperature and braking/acceleration forces. This interaction is known to be mainly governed by span organizations and arrangements of foot bearings. In common practice, movable bearing is stationed and designed on the assumption that it is not able to transfer the horizontal force of upper decks. However, it is well known that horizontal resistance is developed in movable bearings due to friction and that friction coefficient of movable bearing is ranged from 0.03 to 0.20 depending on the material of bearings and magnitude of reactions. Therefore, it is easily reasoned out that friction of movable bearing can influence the mutual behavior of CWR and bridge decks. Suggested in this study is to investigate the validity and efficiency of friction effect of movable bearings in controlling the axial force and displacement of CWR on continuous railway bridges.

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A Case Study on the Design of Drilled Shaft on Soft Ground in Vietnam (베트남 연약지반에서의 현장타설말뚝 설계 사례)

  • Seo, Won-Seok;Cho, Sung-Han;Choi, Ki-Byung
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.591-604
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    • 2008
  • In this study, two design examples of drilled shafts on soft ground in Ho-Chi-Minh City, Vietnam are introduced. One is for a 27-story apartment and the other is for a Arch bridge over Saigon river. Unlikely the normal cases in Korea, all of the bored pile foundations are supposed to be placed on soil layers. Therefore, skin friction between pile and ground is the most crucial design parameter. Three methods using SPT N value of sandy soil -Korean Road Bridge Code(1996), Reese and Wright (1977), and O'Neill and Reese (1988)- were adopted to obtain an ultimate axial bearing capacity. In order to verify the calculated bearing capacity, 3 sets of static load test and a Osterberg Cell test were performed at an apartment site and a bridge site respectively. LRFD (Load Resistance Factored Design) method was compared with ASD (Allowable Stress Design) method. On application of ASD method, safety factor for skin friction was adopted as 2 or 3 while safety factor for end bearing was 3. The design bearing capacities from ASD method matched well with those from LRFD method when safety factor for skin friction was adopted as 2.

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