• Tribology and Lubricants
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• 제17권1호
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• pp.28-32
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• 2001

A new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under all bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number＞0.01, we can not ignore the effect of slip for Journal bearing.

• Tribology and Lubricants
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• 제10권1호
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• pp.46-55
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• 1994

The static and dynamic analysis of air lubricatied tilting pad journal bearing which considers tilting effect of each pad, preload but which neglects pad inertia effect and deflection are performed. A direct numerical method is used in evaluating the static characteristics such as load carrying capacity, friction force and small peturbation method is used for calculation of dynamic characteristics. Stiffness and damping coefficients are compared with the variation of the preload. And these coefficients are slightly decreased with increased compressibility number under the constant bearing load carrying capacity.

• Journal of Mechanical Science and Technology
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• 제16권8호
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• pp.1102-1108
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• 2002

In this study, a topological design sensitivity of the ai. bearing surface (ABS) is suggested by using an adjoint variable method. The discrete form of the generalized lubrication equation based on a control volume formulation is used as a compatible condition. A residual function of the slider is considered as an equality constraint function, which represents the slider in equilibrium. The slider thickness parameters at all grid cells are chosen as design variables since they are the topological parameters determining the ABS shape. Then, a complicated adjoint variable equation is formulated to directly handle the highly nonlinear and asymmetric coefficient matrix and vector in the discrete system equation of air-lubricated slider bearings. An alternating direction implicit (ADI) scheme is utilized for the numerical calculation. This is an efficient iterative solver to solve large-scale problem in special band storage. Then, a computer program is developed and applied to a slider model of a sophisticated shape. The simulation results of design sensitivity analysis (DSA) are directly compared with those of FDM at the randomly selected grid cells to show the effectiveness of the proposed approach. The overall distribution of DSA results are reported, clearly showing the region on the ABS where special attention should be given during the manufacturing process.

• 대한기계학회논문집
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• 제14권6호
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• pp.1487-1494
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• 1990

본 연구에서는 공기분자간 평균 자유비형거리(molecular mean free path)를 고려한 수정된 레이놀즈 방정식을 공기막 두께의 미소 교란항에 대하여 전개하여 비선 형 정적 평형방정식과 교란 미분방ㄹ정식을 구하였다. 비선형 정적 평형방정식을 슬 라이더의 정량적인 거동형태를 표시하므로 이를 이용하여 슬라이더의 정적특성을 구할 수 있다. 이에 반하여, 동적 교란미분 방정식은 슬라이더의 간극함수에 대한 각종 교란에 의하여 유발되는 반발압력을 정성적으로 나타내므로, 슬라이더의 외부교란에 대한 응답특성 및 자기복원특성 등을 구할 수 있다. 이러한 특성을 서스펜션에 부착 된 헤드 시스템의 운동방정식에 함께 고려하여 시스템의 동적 특성을 해석하고 슬라이 더의 설계변수가 이에 미치는 영향을 고찰하고저 한다.

• 한국세라믹학회지
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• 제34권1호
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• pp.7-12
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• 1997

건조 및 다습한 대기의 무윤활 또는 액체 윤활, 미끄럼 속도 그리고 온도 등 여러 조건 하에서 SiC-강 미끄럼 시 SiC가 나타내는 마모거동에 대하여 조사하였다. 또 SiC의 제조공정이 SiC 마모에 미치는 영향도 미끄럼 속도를 달리하면서 고찰하였다. 무윤활 미끄럼 시 대기 습도는 일종의 윤활제 역할을 하며, 특히 대기가 매우 건조한 조건 하에서 미끄럼 속도는 마모에 큰 영향을 미친다. 그리고 SiC의 제조공정 및 재료표면의 거칠기는 미끄럼 속도의 크기여하에 따라 상이한 마모거동을 초래한다. 특히 온도는 마모를 심화시키는 요인이어서 윤활 미끄럼 조건 하에서도 마모를 크게 가속한다.

• Tribology and Lubricants
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• 제6권1호
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• pp.74-81
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• 1990

The threshold of instability for a rigid rotor supported in externally pressurized airlubricated circular or non-circular journal bearings of finite length is theoretically analyzed. The analysis is performed for a bearing having one feeding plane, no recess volume, which is assumed to be a line source, and is based on a first order perturbation of journal center motion about steady state position. And then linearized system dynamic analysis is carried out. Numerical results are given, showing the threshold of instability as a function of supply pressure ratio, feeding parameter and load. It is shown that the region that 2-lobe bearing is more stable than circular bearing exists and whirl ratio of 2-lobe bearing is less than that of the other types of bearing.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 춘계학술대회 논문집
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• pp.121-126
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• 1993

Tiling pad journal bearing that has high stability is analyzed about air-lubricated bearing that is usually used to need high precision by using the Direct analysis. The pressure that supports the shaft is occured by the differences between the shaft and pads radii of curvatures. So the characteristics of load capacity for their variable values is important. In this paper the load capacity is compared with some the eccentricity ratio values of0.1, 0.2, 0.5, 0.8. The large load capacity comes from large eccentricity ratio, highbearing number and high preload. But if the preload become high too much, then the shaft makes contact with pads.

• Tribology and Lubricants
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• 제17권6호
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• pp.441-446
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• 2001

In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the lift time of the coating and design the rotating machinery supported by bump bearings.

• 대한기계학회논문집
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• 제13권4호
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• pp.764-770
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• 1989

This paper analyze the steady state performance of a self-acting air lubricated slider bearing in hard disk/head system. Modified Reynolds' equation is derived from the steady state compressible Navier-Stokes equation, under slip-flow conditions. Finite difference technique and numerical procedure are described by using Newton-Raphson iteration method to slove the non-linear equations. These techniques are applied to conventional slider bearings and the effects of molecular mean free path(MMFP) for a recording surface of hard disk are shown. The calculation procedure developed here, wide applicabilities in practical head design procedures, and converges rapidly.

• 한국표면공학회지
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• 제43권6호
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• pp.278-282
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• 2010

In this research, the friction and wear characteristic behaviors of coating materials of TiAlN and CrAlN were investigated. The wear test was conducted in air and un-lubricated state using the reciprocating friction wear tester. Temperature were 50 and $120^{\circ}C$, and load were 3, 7, and 11 kgf for tests. By comparing the coefficient of friction and observing the wear microstructure, the friction and wear characteristic behaviors of TiAlN and CrAlN coating layers on SKD61 were investigated. The coefficient of friction of CrAlN coating was lower than that of TiAlN at all conditions. Therefore, CrAlN was suggested to be more advantageous coating than TiAlN for the extrusion mold of aluminum.