• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.179-183
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• 1999

Rubbing occurs when a rotating element comes in contact with a stationary element. In the steam turbines, the rotating element is the rotor while the stationary elements are usually the oil deflectors and packing seals. Rubbing phenomenon may be often obseued on a new or rebuilt machine rather than on a machine that has been operating for several months or years. Rubbing in the turbine has been classified into two modes by the operating conditions: 1) start up or shut down, 2) steady state. At start up or shut down operation, rubbing produces synchronous whirl vibration, which are caused by thermal bow of the shaft due to localized heating on the shaft surface. While subsynchronous whirl vibration is caused by partial rubbing during the steady state operation. In this paper, the two case studies of troubleshooting for excessive vibration caused by rubbing in the actual steam turbines are investigated.

• Tribology and Lubricants
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• 제10권4호
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• pp.82-88
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• 1994

This paper deals with a FEM computation as well as measurement of the contact force and distribution of the temperature in rubber lip seals when the sealing interference between the rotating shaft and the lip edge is present. The study of the contact forces and distributions of the temperature and the sealing contact stress has always been one of the basic steps in the process of designing a lip seal. The calculated FEM results indicate that as the sealing interference increases, the contact force moderately increases compared with decreased sealing interference at the seal lip edge and radically increases the contacting width. And the FEM computation of oontact forces including nonlinear problems has been compared with experimental measurements with good agreement. The frictional heat does not dissipate promptly in the rubber seal lip and tends to accumulate at the contacting lip edge especially.

• Design & Manufacturing
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• 제14권4호
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• pp.1-10
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• 2020

The seal plays a role in preventing oil leakage when the lip and the rotating shaft come into contact with the fluid and air pressure. Recently, micro dimples or micro pockets are processed and used on the lubrication surfaces of thrust bearings, mechanical bearings, and piston rings. Compared to a smooth surface, micro dimples reduce friction and increase the life of parts. This paper analyzed various kinds of micro dimple shapes on the sealing surface, i.e. circle, rectangle, triangle, and trapezoid. For this purpose, Introduced the design of experiments to work out a micro dimple configuration, unlikely to be damaged from cracks and low in contact stress. As a result, the triangular dimple showed the best results. Optimal factors were dimple size 0.15 mm, dimple depth 0.0383 mm, dimple density 40%, and the maximum equivalent stress was 9.1455 MPa, and the maximum contact pressure was 9.6612 MPa. This paper analyzed the optimal shape of dimples by finite element analysis. As a research project, experiments and comparative analysis of micro dimple shapes are needed.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.194-204
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• 2016

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor's whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.

• 대한기계학회논문집
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• 제16권4호
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• pp.795-802
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• 1992

본 연구에서는 일정한 각도의 분사를 갖는 평씨일(plain seal)에 대하여 각 인자들이 누수성능에 미치는 영향을 수치적으로 조사하였다. 인자들로는 축방향 레 이놀즈수, 축회전속도, 분사의 유입속도, 간극비, 분사의 위치 및 유입각 등이 고려되 었다.

• 한국기계가공학회지
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• 제18권1호
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• pp.85-93
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• 2019

Oil seals are most essential parts in mechanical lubrication system to maintain the close gaps between stationary and high rotating components, and to help prevent oil leakages. Oil seals also can prevent harmful contaminants entering from outside to machinery, especially in severe environments. Therefore, the oil seals have an important performance in the machinery components. The performance of the oil seals are influenced by the design variables such as amount of interference gap between the main lip and shaft, the angle of main lip at air and oil sides and the distance between the garter spring and main lip. In the present study, a finite element analysis was performed to evaluate the oil seal performance with the considerations of number of oil seal dust lips and angle of the lip at oil side with the different design variables. As a result from the FEM analysis, the stress and contact pressure distributions was derived, based on this, performance of the sealing and durability were determined.

• International Journal of Fluid Machinery and Systems
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• 제3권2호
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• pp.102-112
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• 2010

Artificial heart pumps have attracted the attention of researchers around the world as an alternative to the organ used in cardiac transplantation. Conventional centrifugal pumps are no longer considered suitable for long-term application because of the possibility of occurrence of blood leakage and thrombus formation around the shaft seal. To overcome this problem posed by the shaft seal in conventional centrifugal pumps, the magnetically suspended centrifugal pump has been developed; this is a sealless rotor pump, which can provide contact-free rotation of the impeller without leading to material wear. In Europe, clinical trials of this pump have been successfully performed, and these pumps are commercially available. One of the aims of our study is to numerically examine the internal flow and the effect of leakage flow through the gap between the impeller and the pump casing on the performance of the pump. The results show that the pressure head increases compared with the pump without a gap for all flow rates because of the leakage of the fluid through the gap. It was observed that the leakage flow rate in the pump is sufficiently large; further, no stagnant fluid or dead flow regions were observed in the pump. Therefore, the present pump can efficiently enhance the washout effect.

• Tribology and Lubricants
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• 제12권1호
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• pp.42-46
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• 1996

This paper deals with a numerical study of the dynamic response of rubber oil seals for rotating shaft when interference as well as static and dynamic eccentricities are present. In loss of contact conditions the dynamic curve of oil seals is numerically simulated using the FEM package MSC/NASTRAN. The direct integration method is selected to analyze the time domain response of the seal lip-shaft contact. The computed results based on the experimental data indicate that the increased rotating speed may produce the gap separation between lip edge of rubber seals and shaft. These results will be very useful in predicting the dynamic leakage due to contact behaviors of rubber oil seals under dynamic conditions.

• Journal of Magnetics
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• 제22권2호
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• pp.299-305
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• 2017

Magnetic fluid, a new type of magnetic material, is a colloidal liquid constituted of nano-scale ferromagnetic particles suspended in carrier fluid. Magnetic fluid sealing is one of the most successful applications of magnetic fluid. As a new type of seal offering the advantages of no leakage, long life and high reliability, the magnetic fluid seal has been widely utilized under vacuum- and low-pressure-differential conditions. In practical applications, for improved pressure capacity, a multistage sealing structure is always used. However, in engineering applications, a uniform distribution of magnetic fluid under each tooth often cannot be achieved, which problem weakens the overall pressure capacity of the seals. In order to improve the pressure capacity of magnetic fluid seals and broaden their applications, the present study theoretically and experimentally analyzed the degree of non-uniform distribution of multistage magnetic fluid seals. A mathematical model reflecting the relationship between the pressure capacity and the distribution of magnetic fluid under a single tooth was constructed, and a formula showing the relationship between the volume of magnetic fluid and its contact width with the shaft was derived. Furthermore, the relationship of magnetic fluid volume to capacity was analyzed. Thereby, the causes of non-uniform distribution could be verified: injection of magnetic fluid; the assembly of magnetic fluid seals; the change of magnetic fluid silhouette under pressure loading; the magnetic fluid sealing mechanism of pressure transmission, and seal failure. In consideration of these causes, methods to improve the pressure capacity of magnetic fluid seals was devised (and is herein proposed).

• Tribology and Lubricants
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• 제31권3호
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• pp.102-108
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• 2015

In this research, we experimentally investigated the sealing performance of elastomeric rotary lip seals for washing machines. In general, NBR is used as a material for elastomeric rotary lip seals in washing machines, but the mixing formula of the rubber material can affect the sealing performance. In this study, we manufactured rotary lip seals using three kinds of NBRs with a different mixing formula, and examined the sealing performance using an acceleration test mode. The results of an SEM investigation into the surfaces of three kinds of specimens showed a much smaller wear volume and better sealing performance for the specimens with smaller particle sizes of mixing composition than for the specimen with the larger. Repeated deformation and recovery by the shaft-to-seal eccentricity on rotation were shown to cause a phase difference in the rubber material, and we measured the recovery ratio to find the influence of this phase difference on the sealing performance. As another method for checking the phase difference, we also measured tan ä, and a lower tan ä was revealed as the recovery ratio increased for each specimen. Specimens with a higher recovery ratio (lower tan ä) were shown to have a better sealing performance. Consequently, specimens with a smaller particle size in the mixing composition had a better sealing performance because they show a higher recovery ratio.