• Tribology and Lubricants
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• 제10권4호
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• pp.75-81
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• 1994

In load sharing model, the load is supported by the contacting asperities and the lubricants. The asperity contact area of two sliding surfaces are relatively very small as compared with the apparent contact area. The asperity contact pressure is relatively higher than the lubricant pressure. With the combined effect of asperity and lubricant pressure, the surface roughness and temperature rise must be considered to calculate the lubricant film thickness of the line-contact bearing.

• Tribology and Lubricants
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• 제13권4호
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• pp.47-52
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• 1997

Friction torques, electrical contact resistances and bearing temperatures were measured on high speed angular contact ball beatings for the spindle of machine tools. The test bearings ran with oil-air lubrication at the thrust loads from 320 N to 1920 N and at the rotational speed of up to 12000 rpm. Electrical contact resistances between balls and races were measured to evaluate the formation of the lubricant film in the contact area. The test results with sufficient lubrication showed that the variations of friction torques were sensitive to the thrust loads and the rotational speeds, and that the friction torques were higher than those with insufficient lubrication. With insufficient lubrication and high thrust loads, the collapse of the lubricant film was detected even at a high rotational speed. It was concluded that these high speed beatings to run in condition of fluid lubrication should require monitoring not only the temperature increase of the bearing but also the lubricant film formation in contact areas resulting from the change in the applied load and the lubricant amount.

• 한국정밀공학회지
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• 제30권8호
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• pp.785-789
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• 2013

Worm gear sets may be either single- or double-enveloping. In a single-enveloping set, the worm wheel is cut into a concave surface, thus partially enclosing the worm when meshed. The double-enveloping worm gear is similar to the single-enveloping gear; however, the worm envelopes the worm gear. Thus both are throated. The double-enveloping worm gear has more of the tooth surface in contact than the single-enveloping worm gear. The larger contact area increases the load-carrying capacity. For this reason, double-enveloping worm gearing is widely applied in heavy-duty machinery, for applications including construction and metallurgy. In this paper, we designed a compact reduction gear that is highly efficient using double-enveloping worm gears. We calculated the bearing load in the worm gearing to select the bearing and the housing surface area according to the recommended values from AGMA(American Gear Manufacturers Association). The finite element method was used to assess the structural integrity.

• 한국항행학회논문지
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• 제12권6호
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• pp.653-658
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• 2008

자동차에 적용되는 각종 전자 부품의 복잡도는 21세기를 맞이하면서 급속도로 변화하고 있다. 특히, 각종 전기, 전자 시스템의 급증은 자동차의 안전과 직결되는 문제로 인식되고 있다. 차량의 전장 및 전자부품을 연결해주는 커넥터는 인간의 신경망과 같아서 조그마한 접촉 불량도 차량의 운전에 심각한 영향을 미칠 수 있다. 차량의 진동과 커넥터 단자의 열 변형으로 인한 프레팅 부식은 산화막을 형성하여 접촉저항을 증가시키고 특히 산화층은 진접촉면적의 감소와 상승저항 등 터널 효과에서 급격한 상승을 보이는 결과로 제어신호를 왜곡하여 작동기의 동작오류를 초례한다. 본 논문에서는 이러한 프레팅 부식 현상을 검증하기 위한 주석으로 도금된 구리 커넥터에 스텝핑 모터를 사용하여 일정한 변위를 갖는 미세 진동을 유발하여 프레핑 부식의 진행과 접촉저항의 변화를 고찰하여 이에 대한 대비책을 강구하고자 한다.

• Tribology and Lubricants
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• 제31권2호
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.215-220
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• 2003

Trepan prevents the wear of the inside part of a bearing when the initial shaft rotates. It continuously contacts with the eccentric part of the shaft in rotation and is loaded repeatedly. Therefore, even if an early crack of a trepan part is small, the crack may progress by the repeated load. If the crack progresses, very small chips come out. This Is put in the rotor and prevents the rotation of the compressor, There can be leaks in a microgroove and extreme wear can occur due to lack of oil on the surface contact part. Therefore, this study was carried out to compare and investigate the trepan strength and deflection characteristics between trepan locations and dimension changes using the finite element method and search a motor bearing for a model with bigger stiffness of a trepan part and the same deflection.

• 대한기계학회논문집
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• 제11권6호
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• pp.935-944
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• 1987

본 연구에서는 금속 표면의 정밀가공법을 연구대상으로 하여 구상흑연주철시 편을 미량의 테이퍼로 연삭가공하고 NACHI 6000ZZ 볼 베어링을 로울러로 사용하여 로 울러 다듬질을 행함으로써 로울러 지름 변화에 따른 가압력이 표면조도에 미치는 영향 을 구명하는데 목적을 두었으며 아울러 로울링(rolling)회수에 따른 펴면조도, 경도 및 직경의 변화량을 실험적으로 구명하였다.

• 한국지반공학회논문집
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• 제38권7호
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• pp.49-62
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• 2022

중공블록 기초공법은 육각형의 벌집구조로 제작된 콘크리트 중공블록을 혼합쇄석과 함께 치환 설치하여 연약지반을 보강하고 인위적인 층상지반을 형성하여 얕은 기초의 지지력 증가와 침하량을 감소시키는 지반보강 기초공법이다. 벌집구조의 중공블록은 기하학적으로 경제적인 구조임과 동시에 힘을 균형 있게 배분하는 안정적인 구조로 기초와 쇄석치환 보강층 사이에서 보강재로써 보강효과를 유발하는 것을 단편적으로 확인하였으나, 거동특성 규명은 아직 미비한 상태이다. 본 연구에서는 실내모형실험을 통해 보강재로써 중공블록의 보강효과를 파악하기 위해 실내 평판재하시험을 수행하였다. 하중-침하 곡선에서 비채움 조건(A-1-N)에서는 관입전단파괴가 발생한 반면에 채움 조건(A-1-F)은 항복이 나타나지 않은 선형 곡선을 나타내며, 원지반 대비 3배의 보강효과를 확인하였다. 중공블록의 구속효과 모식도를 바탕으로 중공블록 콘크리트부의 접지응력과 중공부 구속효과에 의한 수직응력 그리고 수평응력이 작용한 내벽의 내주면마찰력에 대한 관계식을 제안하였다. 관계식 계산결과 중공블록의 콘크리트부의 접지력은 재하하중의 약 65%이고, 중공부 단면에 작용하는 구속 수직력은 약 16.5%이고, 내주면마찰력은 약 18.5%로 분담하는 것으로 나타났다. 본 연구를 통해 중공블록이 보강재로써 상재하중이 작용할 때, 중공블록의 중공부 하단에서는 구속효과로 수직응력이 발생하고, 수평방향이 구속상태인 내부 모래에서 수평응력이 내벽에 작용하여 내주면마찰력이 발생하여 중공블록 콘크리트의 관입을 억제하고 선단 응력이 감소하는 거동특성을 규명하였다.

• Tribology and Lubricants
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• 제30권2호
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• pp.116-123
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• 2014

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

• Tribology and Lubricants
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• 제28권6호
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• pp.278-282
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• 2012

Various bearings such as deep-groove ball bearings, angular-contact ball bearings, and roller bearings are used to support the load and to lubricate between the shaft and the housing. The bearings of potential rolling systems in a turbo pump are the deep-groove ball bearings as comparing with the bearings with rolling elements such as cylindrical rollers, tapered cylindrical rollers, and needle rollers. The deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway and a retainer that maintain separation and help to lubricate the rolling element that is rotating in the raceways. In the case of water-lubricated ball bearings, however, fluid friction between the ball and raceways is affected by the entry direction of flow, rotation speed, and flow rate. In addition, this friction is the key factor affecting the bearing life cycles and reliability. In this paper, the characteristics of flow conditions corresponding to a deep-groove ball bearing are investigated numerically, with particular focus on the friction distribution on the rolling element, in order to extend the analysis to the area that experiences solid friction. A simple analysis model of fluid flow inside the water-lubricated ball bearing is analyzed with CFD, and the flow characteristics at high rotation speeds are presented.