• Tribology and Lubricants
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• 제24권3호
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• pp.147-153
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• 2008

The effect of oil supply pressure on the performance of vapor cavitated short squeeze film dampers is examined. Vapor cavitation is characterized by film rupture occurring as a result of evaporating oils. The pressure of vapor cavity in the film is almost zero in absolute pressure and nearly constant. Pan's model about the shape of vapor cavity is utilized for studying the effect of vapor cavitation on the damping capability of a short squeeze film damper. As the level of oil supply pressure is increasing, vapor cavitation is suppressed so that the direct damping coefficient increases and the cross coupled damping coefficient decreases. Futhermore, the analysis of the unbalance responses of a rigid rotor supported on cavitated squeeze film dampers shows that a significant reduction in rotor amplitude and force transmissibility is possible by controlling the oil supply pressure into short squeeze film dampers.

• 소음진동
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• 제2권3호
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• pp.213-222
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• 1992

The effect of cavitation on the synchronous steady state response of a single rotor supported on cavitated squeeze film dampers executing a circular orbit is investigated theoretically. The Swift-Stieber boundary conditions and a long bearing approximation are utillized to evaluate the direct and the cross coupled damping coefficients of a cavitated squeeze film damper. For typical design parameters, frequency response curves are presented here to exhibit the effect of cavitation on the imbalance response and transmissibilities for both a flexible rotor and a rigid rotor. Investigations show that cavitation occured in a squeeze film damper produces bistable jump phenomena and deteriorates the performance of a squeeze film damper. This arises from that the large cavity causes substantial increment of the cross coupled damping which has radial stiffening effect. Furthermore, the large cavity causes the decrement of the direct damping which has pure damping effect. It is also observed that in the absence of cavitation, both rotor excursion amplitude and imbalance transmissibilities are very well damped.

• 소성∙가공
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• 제8권5호
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• pp.491-497
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• 1999

The effect of partial squeeze on the quality of casting products in the vacuum die casting was investigated to make defect free casting products with excellent mechanical properties. The partial squeeze and vacuum die casting process was industrially implemented in making reaction shaft support which was made of a hypereutectic Al-15%Si alloy. To combine squeezing and vacuum effects, the plunger injection system was designed and attached on the chill vent type vacuum machinery system. The combination of vacuum effect before injection and partial squeezing effect after injection resulted in defect free die casting products. The uniform distribution of fine eutectic and proeutectic Si obtained from trial process also provided excellent mechanical properties.

• 동력기계공학회지
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• 제7권4호
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• pp.44-48
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• 2003

Alumium alloys casting are gaining increased acceptance in the automotive and electronic industeries and squeeze casting is the most efficient method of manufacturing such mass produced parts. This study has been investigated the microstructures and mechanical properties of Al-7.0Si-0.4Mg(AC4C)alloy fabricated by squeeze casting process for development of Engine Mountain Bracket. The microstructure of squeeze casted specimen were composed of eutectic structure Alumimim solid solution and $Mg_2Si$ precipitates. The tensile strength of as-solid solution treatment Al-7.0Si-0.4Mg alloy revealed 2985MPa. It was found that Al-7.0Si-0.4Mg alloy have good aging hardening effect results are presented to show the validity of the control method.

• 열처리공학회지
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• 제12권1호
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• pp.1-8
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• 1999

This study has investigated the effect of aging treatment on the microstructure and mechanical properties of Mg-6Al-xZn(x = 1.5, 2.5) alloys fabricated by the squeeze casting process. The microstructures of as-squeeze cast were composed of pro-eutectic ${\alpha}$, super saturated ${\alpha}$ and ${\beta}(Mg_{17}Al_{12})$ compound. Aged at both $200^{\circ}C$ and $240^{\circ}C$, Mg-6Al-xZn alloys showed the peak hardness due to the formation of ${\beta}(Mg_{17}Al_{12})$ precipitates. The discontinuous precipitates of the lamella type are predominant at $200^{\circ}C$ aging treatment, while the finely dispersed continuous precipitates were dominant at $240^{\circ}C$ aging treatment. Mg-6Al-xZn alloys fabricated by the squeeze casting process had the better combination of tensile strength and elongation compared to the conventionally cast alloys. As zinc contents increased, the tensile strength was increased by the solid solution strengthening effect of zinc.

• 한국주조공학회지
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• 제13권3호
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• pp.259-267
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• 1993

The effects of casting processes-direct and indirect squeeze casting, permanent mold casting and die casting on the microstructure and mechanical properties were studied for the hypereutectic B390 aluminium alloy. The effects of T5 and T6 heat treatment were also examined. The direct and indirect squeeze casting showed no casting defects such as porosity and shrinkage were observed in permanent mold castings and die castings. The primary silicon phase was refined and homogeneously distributed in the order of indirect squeeze casting, diecasting, direct squeeze casting and permanent mold casting. Depletion of primary silicon phase in die casting surface was disappeared in indirect squeeze casting. Tensile strength of cast and heat treated specimens were increased in the order of direct squeeze casting, permanent mold casting, indirect squeeze casting and die casting. Hardness of indirect squeeze castings was larger than that of other castings. As indirect squeeze casting of B390 aluminium alloy, the time of T6 heat treatment to achieve high strength can be reduced.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.739-744
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• 2001

In order to investigate the stability of magneto-rheological fluid based squeeze film damper (MR-SFD), its negative stiffness effect, which arises from magnetization of MR-SFD, is identified theoretically and experimentally. The analytical model of MR-SFD includes the magnetic circuit as well as the displacement stiffness associated with the squeeze mode of MRF. Extensive experiments are carried out to measure the magnetic attraction forces generated in the MR-SFD, with the excitation frequency and the eccentricity of the journal varied, which are controlled by an active magnetic bearing. The simulation and experimental results are found to be in good agreement. It is concluded that the negative stiffness effect dominates only in the low frequency region because its effect diminishes in the high frequency region due to the eddy-current loss.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.623-624
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• 2011

• 한국주조공학회지
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• 제21권2호
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• pp.127-134
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• 2001

Misch metal (rare earth element, Ce, La, Nd, Pr) which has large influence on high-temperature stability and toughness was added to the Al-5%Ni-5%Mg alloy, and squeeze casting was used for Al-5%Ni-5%Mg-(Mm) alloys. The effect of applied pressure and misch metal additions on mechanical properties in Al-5%Ni-5%Mg alloy by direct squeeze casting has been investigated. The applied pressure were 0 MPa(gravity casting), 25, 50 and 75 MPa. Squeeze-cast Al-5%Ni-5%Mg-(Mm) alloys had better mechanical properties than those of non-pressurized cast alloys because of the increased cooling rate by the application of pressure during solidification. By the addition of misch metal in Al-5%Ni-5%Mg alloy, better combination of strength and elongation was obtained. The addition of 0.3%Mm in Al-5%Ni-5%Mg alloy improved the heat resistant property due to the formation of fine eutectic phases.

• 대한기계학회논문집
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• 제19권2호
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• pp.443-450
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• 1995

An analysis of the dynamics of a mechanical monoleaflet heart valve prosthesis in the closing phase is presented. Employing the moment equilibrium principles on the occluder motion and the squeeze film dynamics of the fluid between the occluder and the guiding strut at the instant of impact, the velocity of the occluder tip and the impact force were computed. The dynamics of fluid being squeezed between the occluder and the guiding struts is accounted for by Reynold's equation. The effect of the fluid being squeezed between the occluder and the guiding strut was to reduce the velocity of the occluder tip at the instant of valve closure as well as dampen the fluttering of the occluder before coming to rest in the fully closed position. The squeeze film fluid pressure changed rapidly from a high positive value to a relatively large negative value in less than 1 msec. The results of this study may be extended for the analysis of cavitation inception, mechanical stresses on the formed elements and valve components as well as to estimate the endurance limits of the prosthetic valves.