• Elastomers and Composites
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• 제53권4호
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• pp.213-219
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• 2018

The degradation mechanism and physical properties of an FKM O-ring were observed with thermal aging in this experiment. From X-ray photoelectron spectroscopy (XPS) analysis, we could observe carbon (285 eV), fluoro (688 eV), and oxygen (531 eV) peaks. Before thermal aging, the concentration of fluoro atoms was 51.23%, which decreased to 8.29% after thermal aging. The concentration of oxygen atoms increased from 3.16% to 20.39%. Under thermal aging, the FKM O-ring exhibited debonding of the fluoro-bond by oxidation. Analysis of the C1s, O1s, and F1s peaks revealed that the degradation reaction usually occurred at the C-F, C-F2, and C-F3 bonds, and generated a carboxyl group (-COOH) by oxidation. Due to the debonding reaction and decreasing mobility, the glass transition temperature of the FKM O-ring increased from $-15.91^{\circ}C$ to $-13.79^{\circ}C$. From the intermittent CSR test, the initial sealing force was 2,149.6 N, which decreased to 1,156.2 N after thermal aging. Thus, under thermal aging, the sealing force decreased to 46.2%, compared with its initial state. This phenomenon was caused by the debonding reaction and decreasing mobility of the FKM O-ring. The S-S curve exhibited a 50% increase in modulus, with break at a low strain and stress state. This was also attributed to the decreasing mobility due to thermal aging degradation.

• 제어로봇시스템학회논문지
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• 제11권4호
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• pp.337-343
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• 2005

In this paper, experimental studies of force control of the crack tracking robot are presented. The crack tracking robot should maintain constant contact with the road to perform cleaning process of the crack effectively. Regulating desired force on the road requires a sophisticated force control algorithm. Here, two main force control algorithms such as the impedance force control and the explicit force control are used. Performances of two force control algorithms are compared.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.545-548
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• 2002

Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.123-124
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• 2006

Usually, hydraulic cylinder is widely used as the actuator in the equipment of construction machines, airplane and military machines. In case of these devices, due to use under severe environment such as water, $SiO^2$ and dust, etc. seal which has high packing ability and long service life has been required. These characteristics are largely influenced by material and geometries of seal such as approach angle, withdrawal angle and interference. Recently, many a study about seal material has been performed so that many materials have been developed. But the concrete studies including the relationships between geometry of seal and sealing performance have hardly been performed yet. Therefore, in this study, we predicted the deformation behavior and contact normal distribution of dust seal with the variation of geometries of seal lip using finite element analysis. And based on the results of analyses, we discussed the effects of the design variables fur sealing performance of the dust seal.

• 한국가스학회지
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• 제11권1호
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• pp.34-39
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• 2007

본 본문에서는 LPG 용기용 밸브의 개폐과정에서 발생하는 밸브패킹과 밸브시트의 상대접촉 마찰작용에 따른 밀봉성에 대한 FEM 해석결과를 제시하고 있다. 개폐용 밸브의 밀봉작용은 나일론-66으로 제조한 디스크 형상의 밸브패킹이 원형 파이프의 밸브시트 단면을 막아 LP 가스의 외부 송출을 차단하면서 완료된다. 밸브패킹은 밸브시트에 대하여 평면으로 접촉밀봉을 하는 경우와 원형홈의 둥근접촉 형상에 대한 밀봉 압착력을 확보하는 두 가지가 있다. FEM 해석 및 실험적 연구결과에 의하면, 밸브패킹을 사용하기 이전의 평면접촉 밀봉 작용력은 4.9 MPa로 높지만, 밸브를 사용한 이후의 원형홈 접촉 밀봉력은 4.4 MPa로 약간 낮게 나타났다. 그러나 이들 최대응력은 나일론 소재의 항복응력 83 MPa에 비하여 대단히 낮은 값이기 때문에 현재의 개폐밸브용 패킹은 과도하게 설계되었다 할 수 있다.

• 한국기계가공학회지
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• 제17권6호
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• pp.24-30
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• 2018

Dental implants are currently widely used as artificial teeth due to their good chewing performance and long life cycle. A dental implant consists of an abutment as the upper part and a fixture as the lower part. When chewing forces are repeatedly applied to a dental implant, gap at the interface surface between the abutment and the fixture is often occurred, and results in some deteriorations such as loosening of fastening screw, dental retraction and fixture fracture. To cope with such problems, a sealing-type abutment having a number of grooves along the conical-surface circumference was previously developed, and shows better sealing performance than the conventional one. This study carries out optimization of the groove shape by genetic algorithm(GA) as well as structural analysis in consideration of external chewing force and pretension between the abutment and the fixture. The overall optimization system consists of two subsystems; the one is the genetic algorithm with MATLAB, and the other is the structural analysis with ANSYS. Two subsystems transmit and receive the relevant data with each other throughout the optimization processes. The optimization result is then compared with that of the conventional one with respect to the contact pressure and the maximum stress. The result shows that the optimized model gives better sealing performance than the conventional sealing abutment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.65-69
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• 2001

In this study, the deformation of the free surface motion of a magnetic fluid for the change in electromagnetic force is discussed. In case, magnetic fluid in characteristics of fluid adjusted to the opposite direction of the gravity direction. Thus, the device of a magnetic fluid proposed the complete zero-leakage Sealing and the surface actuator. The device of surface deformation as well comparison between numerical simulation and experiments as will be presented.

• 대한의용생체공학회:의공학회지
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• 제41권5호
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• pp.210-218
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• 2020

Vessel sealing is a medical device that converts electrical or ultrasonic energy into thermal energy and leads to seal, coagulate, and cut the vessel by protein modification within the walls or surrounding connective tissues. As most of surgeries have recently been conducted with minimally invasive surgery, the demand and market for vessel sealing are expected to get bigger. However, there is a problem that electrosurgical or ultrasonic surgical is applied and we have a high risk to evaluate the strength of seal, because the collateral and particular standards currently in force follows have not been establish. Therefore, in this study, we investigated some papers studied on the efficacy and safety of the device, the guidance of FDA and test papers previously conducted from 3 individual subject device made in Korea. We found there is a relationship between burst pressure and the performance of the device, therefore, we propose the vascular bursting pressure test for evaluating the safety and performance of the vessel sealing.

• 한국초전도ㆍ저온공학회논문지
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• 제26권1호
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• pp.25-30
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• 2024

High-temperature superconducting rotors offer advantages in terms of output-to-weight ratio and efficiency compared to conventional phase conduction motors or generators. The rotor can be cooled by conduction cooling, which attaches a cryocooler, and by refrigerant circulation, which uses circulating liquid or gas neon, helium and hydrogen. Recent work has focused on environmental issues and on high-temperature superconducting motors cooled with liquid hydrogen that can be combined with fuel cells. However, to ensure smooth supply and return of the cryogenic cooling fluid, a cryogenic rotational coupling between the rotating and stationary parts is necessary. Additionally, the development of a sealing structure to minimize fluid leakage applicable to the coupling is essential. This study describes the design and performance evaluation of a non-contact sealing method, specifically a labyrinth seal, which avoids power loss and heat load caused by friction in contact sealing structures. The seal design incorporates a spiral flow path to reduce leakage using centrifugal force, and computational fluid dynamics (CFD) simulations were conducted to analyze the flow path and rotational speed. A performance evaluation device was configured and employed to evaluate the designed seal. The results of this study will be used to develop a cryogenic rotational coupling with supply and return flow paths for cryogenic applications.

• 한국정밀공학회지
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• 제22권3호
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• pp.29-37
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• 2005

In this study, the control of the free surface deformation of a magnetic fluid for the change in electromagnetic force is discussed. The free surface of magnetic fluid is formed by the balance of surface force, gravity, pressure difference, magnetic normal pressure and magnetic body force. Magnetic fluid in characteristics of fluid adjusted to the opposite direction of the gravity direction. Thus, the device of a magnetic fluid proposed the complete zero-leakage sealing, oscillator for surface control, boundary layer control, MHD, flow control, flow using magnetic levitation system and surface actuator. This study show the deformation of surface rise due to the intensity of the magnetic field and possibility of two-dimensional control of magnetic fluid through the feedback data of hall sensor.