• Journal of Technologic Dentistry
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• v.32 no.4
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• pp.307-315
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• 2010

Purpose: The purpose of this study was to investigate the change of microstructures and mechanical properties of pure titanium casting specimens as a function of mold temperatures. Methods: The pure titanium castings were fabricated using the centrifugal vacuum casting method with different mold temperatures of $200{\sim}500^{\circ}C$. The resulting castings were characterized by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and vicker,s hardness tester. Results: In case of the mold temperatures over $400^{\circ}C$, the porosity, surface crack and large grain size were observed in resulting castings. Conclusion: In this work, The most suitable mold temperature in casting of pure titanium was $300^{\circ}C$.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.43-44
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• 2005

The effect of break down of centrifugal pump due to entrained air has not been clarified yet. Thus, air-water two-phase flow experimental apparatus was installed to clarify the effect of break down. The performance results of a single-phase flow satisfied reappearance. Also, the heads coincided well impeller types.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.410-415
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• 2000

Slip factor is defined as an empirical factor being multiplied to theoretical energy transfer for the estimation of real work input of a centrifugal compressor. Researchers have tried to develop a simple empirical model, for a century, to predict a slip factor. However most these models were developed on the condition of design point assuming inviscid flow. So these models often fail to predict a correct slip factor at off-design condition. In this study, we summarized various slip factor models and compared these models with experimental and numerical data at off-design condition. As a result of this study, Wiesner's and Paeng and Chung's models are applicable for radial impeller, but all the models are not suitable for backswept impeller. Finally, the essential avenues for future study is discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.574-578
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• 2003

The objective of this paper is to decide optimal location of pin-hole to minimize stress concenstation around hole in rotating disc. The focus of this investigation is to evaluate the effect of pin-hole for stress distribution around hole using optimum design technic and finite element analysis. Design variables are radial and angular location of pin-hole from center of hole, objective function is maximum stress around hole in rotating disc. We use first order method of optimization technic.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.4
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• pp.29-35
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• 2003

The rotating machineries always generate harmonic frequencies of their own rotating speed, and increment of vibration amplitude affects to the equipments which connected to the vibrational source and causes industrial calamities. The life cycle of equipments can be extended and damages to the human beings could be prevented by identifying the cause of malfunctions through prediction of the increment of vibration and records of vibrational history. In this study, therefore, diagnostic expert algorithm for the centrifugal pump is developed by integrating fuzzy inference method and signal processing techniques. And the validity of the developed diagnostic system is examined via various computer simulations.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.16-22
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• 2012

Acoustic pressure field around the centrifugal fan is predicted by a aero-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using commercial code, while the acoustic waves generated inside the centrifugal fan and shroud are predicted by solving the far field acoustics analysis. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades with the shroud. Acoustic results is validated by experimental results This paper describes the influence of geometric parameters on the noise generation from the section of blades and shroud. One of the effective ways to reduce BPF noise is optimization method using Genetic Algorithm, which effectively minimize eccentricity, is suggested. New improving design was developed by optimization method.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.118-125
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• 2003

In this study, we carried out the finite element analysis for the screw of centrifuge that is the weakest part of the centrifuge for sewage management. Centrifugal force caused by rotation with velocity of 4000rpm was applied at the screw. Structural analysis was done with respect to the change of the ratio of blade pitch($R_P$), shaft diameter($R_D$) and extended hole($R_E$). When the area of circular hole is equal to that of extended holes, maximum equivalent stresses in the screw with circular and extended circular hole were compared. And then natural frequency analysis was executed for the same model. Three mode shapes were used to explain the vibration characteristics of each screw. Convergence study was accomplished fur more accurate results.

• Journal of the Korean Society for Precision Engineering
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• v.8 no.4
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• pp.126-136
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• 1991

In order to reduce the possibilities of personnel injuries and damages to machines and to obtaim higher efficiency and machining accuracy in the manufacturing system, the chucking technology has recentry become important. The chucking technology of work greatly affects both the grometrical accuracy and fonctional performance of the workpiece. In this study, the dynamic gripping force of a 3-jaw power chuck is investigated on the factors of the shape of jaw and the shape of workpiece. From this investigation, the following observations are obtained. 1) The higher stiffness of workpiece is, the higher decrease of dynamic gripping force is. 2) The nearer to the root of jaw is, the higher decrease of dynamic gripping force is. 3) The centrifugal force of affectting the decrease of dynamic gripping force has to be considered in the centrifugal force of affecting jaw.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.56-61
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• 1986

Rotor dynamic response of pumps is greatly influenced by the nature of the hydraulic forces arising from wearing seal, balance drum and impeller, etc.. Therefore, rotor dynamic analysis should be conducted during the design stage in order to aleviate some of the vibrational problems which might occur during the operational life of pumps. Previsousely, the authors have proposed the method to obtain the dynamic seal coefficients of the annular plain seal, convergent and divergent tapered seals, parallel grooved seal, spiral grooved seal and annular stepped seal. On the basis of these results, this paper presents the investigated effect of seals on the stability behavior of a centrifugal pump. The results show the effects of seal geometry, pressure difference, clearance, length/diameter ratio, on stability behavior.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.611-614
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• 2002

Rotating stall in vaneless diffusers of centrifugal compressor occurs in the diffuser wall due to flow separation at large inlet flow angle. For this reason, the critical inlet flow angles are suggested by several researchers. Beyond this critical angle, flow separates in the diffuser, and develops into rotating stall. This paper studied this critical flow angle. Rotating stall is measured through eight fast-response pressure transducers which are equally spaced around the circumference at the inlet and exit of a vaneless diffuser. Experiments are done from 20000rpm to 60000rpm for the diffuser stall. Two-cell structure which rotates at $6{\~}l0{\%}$ of impeller speed is fully developed at $20000{\~}40000rpm$, and three-cell structure which rotates at $7{\~}9{\%}$ of impeller speed is fully developed at $50000{\~}60000rpm$. This paper shows that the critical inlet flow angle is not constant but related with tip speed of impeller. As tip speed increases, so does the critical inlet flow angle.