• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.768-772
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• 1994

공작기계의 주축은 최근 고속화,고정밀화 및 고강성화되어가는 경향이 커지고 있다. 이러한 경향에 따라서 주축의] 설계는 매우 중요하며, 주축용 베어링은 앵귤러 콘택트 볼베어링이 많이 사용되고 있다. 공작기계의 주축은 고속 회전에 따른 고강성의 필요성이 증대하게 되고, 고상성을 얻기 위하여 축 방향의 일정한 예압을 주게된다. 이 예압량은 결국 축 방향의 하중이므로 주축용 베어링의 수명을 변화 시키게 된다. 따라서 축 방향 하중의 변화에 따른 베어링의 수명 특성을 파악하여야 하며, 적절한 베어링 수명의 판단을 통해 기계의 보수 및 관리에 관한 재경비를 절감할 수 있다. 그러므로 본 연구에서는 실험을 통해 베어링의 특성 주파수를 이끌어 내고 주파수 스펙트럼 분석을 이용하여 베어링의 상태를 진단하 는 기본겆인 데이터를 얻는다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.62-68
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• 1997

현재 널리 보급되어 있는 볼베어링은 몇개의 볼에 의해 작동하기에 회전이 불균일하며 진동과 소음이 크다. 이는 고속에서 한계를 갖는 주된 원인이 되고 있다. 또한 그리스의 손실로 인한 수명의 단축이나, 유출된 그리스로 인한 손상은 제품의 내구성에 치명적인 결과를 초래한다. 더욱이 기존에 사용하는 소형 정밀 베어링은 전량 수입에 의존하고 있으며, 기술 선진국의 기술이전 회피로 개발이 어려우며, 수입물량도 확보하기 어려운 상황이다. 이를 극복하기 위한 하나의 방법이 볼과 그리스를 대신해서 유체의 압력을 이용한 유체동압베어링의 개발이다. 유체동압을 이용한 베어링의 장점은 그리스의 누유가 없고, 이로 인한 설계상의 제약이 없으며, 볼베어링으로는 불가능한 고속회전에 적합하고, 안전성이 뛰어나며 회전이 균일하여 제품의 신뢰성을 향상시킬 수 있다. 유체동압 함유소결함유베어링은 진동과 소음이 적고, 저렴하며 구조가 간단하고, 급유기를 필요로 하지 않는 자기윤활(self-lubrication)특성과 생산성 등 많은 장점을 가지고 그 사용범위가 점차 광범위하게 넓어지고 있지만, 저속상태에서의 유막형성, 고속상태에서 기름의 누유, 고하중상태에서 강도와 기공의 눌어붙음과 출발과 정지 시에 발생하는 두 금속간의 직접 접촉을 피할 수 없는 것과 같은 해결해야 하는 문제를 가지고 있다. 본 연구에서는 이러한 단점을 해결하기 위하여 유체동압 함유소결베어링이 마찰특성을 알아보고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1654-1663
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• 1994

Even if the ball bearing was conservatively designed considering the dynamic capacity and the rating life, sometimes the bearing was early failed on account of the misalignment and the lubricant contaminations etc. Misalignment was generated when bearing-shaft system transmitted large power and when the bearing was inadequately mounted. It was possible to predict the fatigue life of ball bearing under the misalignment considering the motions of ball, cage and raceway, and the factors of the effect on fatigue life. Misalignment affected on ball bearing as radial and moment load and the relationships between misalignment and moment were obtained. In this paper, the analysis of the load distributions between ball and raceway, and the prediction of fatigue life of deep groove ball bearing under radial and moment loads were carried out. And, the new formulation of equivalent dynamic load considering the effects of moment load was proposed.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.53-61
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• 2016

Angular misalignment has a significant effect on the characteristics of angular contact ball bearings (ACBBs). This paper presents an analysis of fatigue life for ACBBs subjected to angular misalignment. A simulation model is developed with de Mul's bearing model and the ISO basic reference rating life model. Simulation is performed to calculate the life of the ACBBs subjected to angular misalignment. The numerical results show that angular misalignment influences the load distribution significantly, thus reducing the bearing rating life. The fatigue life of ACBBs is decreased by angular misalignment regardless of axial preload, external radial load and rotational speed. The results show that angular misalignment should be maintained at less than 1mrad for ACBBs.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3149-3158
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• 1994

In this paper, using the formulation of dynamic equivalent load considering the effects of moment load and the equation to estimate the cage rotational speed, the new life equation of deep groove ball bearing under radial and moment loads was proposed. Fatigue life test apparatus with the measuring equipment of shaft and cage speed was designed and developed to be capable of subjecting combined radial and moment load. Fatigue life tests were executed by sudden death test method and the reliability of fatigue lives was evaluated by Weibull distribution analysis. From the results of fatigue tests and analysis, the relationships between film parameters and life adjustment factors were acquired. And it was turned out that so as to estimate the effect of moment load on fatigue life, the life adjustment factor as well as the dynamic equivalent load must be taken into account.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.101-105
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• 2001

고속절삭을 통해서 생산성과 가공정밀도의 향상을 도모할 수 있기 때문에, 최근 머시닝센터를 중심으로 한 공작기계 주축계의 고속화는 눈부시게 발전하고 있다. 그러나 주축계가 고속화될 수록 증가하는 베어링에서의 발열은 베어링의 수명단축, 주축계의 열변형 증대 등을 초래하고, 궁극적으로 공작기계의 성능을 저하시키게 된다. 따라서 고속으로 회전하는 베어링에서의 발열을 효과적으로 억제할 수 있는 윤활방법에 대한 연구들이 활발히 진행되고 있다. 따라서 본 연구에서는 공작기계용 고속주축계의 냉각특성을 규명하기 위한 노력의 하나로 압축공기를 이용한 고속주축 계의 냉각실험을 수행하였다. 고속주축계의 실험모델은 오일에어윤활방법, 앵귤러콘택트 볼베어링, 이중분사노즐, 냉각 자켓등을 사용해서 제작하였으며, 특히 고속주축계의 공기냉각방법에 대한 유용성은 실험결과로 부터 입증하였다.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.35-44
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• 2022

This study aims to evaluate the stress and life of cylindrical roller bearings used in aircraft gearboxes, and to select a roller profile that minimises the contact stress between bearing rollers and raceways. The mounting clearance of four points contact ball bearing was determined, so that cylindrical roller bearings support all radial loads, and the bearing mounting position was determined to maximise the bearing lives. In addition, the static safety factor and dynamic life of bearing were predicted according to ISO 76 & ISO/TS 16281 using the load spectrum determined based on the operating load cases of aircraft gearboxes. Furthermore, the optimal roller profile was selected by analysing the contact stress according to the roller profile shape, and the safety of each roller was evaluated. The results stated that the required safety factor and lifetime were satisfied, and Johns Gohar roller profile was optimal.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.5
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• pp.44-55
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• 2007

The method for fatigue life prediction of ball bearing is proposed applying the algorithm of contact fatigue prediction based on stress analysis. In order to do this, a series of simulation such as initial surface stress analysis, EHL analysis, subsurface stress analysis and fatigue analysis are conducted from the loading at each ball location calculated for a bearing subjected to external bearing load and contact shape function. And uniaxial fatigue tests are performed to obtain fatigue parameter of AISI 52100 steel. It was found that since stress is usually higher at the inner raceway contact than at the outer raceway contact, fatigue failure occurs on the inner raceway first. When the fatigue life calculated in the stress-based method are compared with L50 life of L-P model, Crossland criterion for the radial load increment is similar to L50 life and Dang Van criterion for the axial load increment is similar. In the case of EHL contact, there is no difference of fatigue life between dry contact and EHL contact, when maximum Hertz pressure exceeds 2.5GPa.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.261-266
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• 2003

Foil air bearing, which is a noncontact bearing utilizing viscosity of operating fluid and elastic deformation of foil structure, has several advantages over rolling element bearings in terms of oilless environment, long life, high speed operation, and high temperature application over $500^{\circ}C$ . Recently advanced researches are actively being performed for the application to the extreme temperature such as gas turbines, as well as conventional small turbo machinery. In this paper, the principle of foil air bearing is introduced and a feasibility study to adopt a foil bearing as the turbine bearing of 65 HP turbo shaft engine, which is under development for UAV, is presented.

• Tribology and Lubricants
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• v.27 no.3
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• pp.162-166
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• 2011

This study is aimed to predict the fatigue life for bearings under combined radial, thrust and moment load. In order to do this, a series of simulation such as bearing load distribution, initial surface stress, subsurface stress and fatigue analysis is needed. And using the bearing's material fatigue property we can predict fatigue life for ball bearing.