• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.297-300
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• 2001

Physical modeling technique is applied to investigate foam generation in molten aluminum. By using room temperature water with specially designed equipment, the effects of stirrer type, fluid viscosity(glycerine added to water) and stirring velocity on foam generation behaviors are intensively analysed The distribution and size of bubbles varied with each process parameters but the most important parameters are stirring velocity and fluid viscosity. The results obtained from physical simulation have been confirmed by actual aluminum foam generation experiment at various process variables.

• Transactions of Materials Processing
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• v.17 no.1
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• pp.9-12
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• 2008

Recently, industries and academic institutes have been interested in the rheology forming technology for light weight materials. However, this rheocasting process has advantages such as the high initial investment cost and the lower mechanical properties than thixocasting. In this study, the continuous fabrication of rheological material with a spiral stirring equipment(mechanical stirring system) was newly devised to overcome the disadvantages of rheocasting process. The experimental parameters were stirring time($0{\sim}1200sec$), stirring velocity ($0{\sim}100rpm$) and stirring temperature($650{\sim}680^{\circ}C$). The optimal conditions for fabricated rheological material of A6061 alloy were stirring time at 300sec, stirring velocity at 60rpm and stirring temperature at $650^{\circ}C$. At these results, the equivalent diameter was $45{\sim}65{\mu}m$, mean roundness was $1.4{\sim}1.6$ and Vickers hardness was 60Hv.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.463-466
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• 2005

The microstructure and mechanical properties of rheocast A356 aluminum alloy by electromagnetic stirring are studied. In the electromagnetic stirring, main parameters are stirring current and stirring time. Stirring current is ranged from 0 A to 60 A, and stirring time is 20, 40, and 60 sec. In the rheocasting, injection velocity and applied pressure are changed. In this paper, the effect of stirring current and stirring time on the morphology and mechanical properties are investigated and analyzed.

• Transactions of Materials Processing
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• v.10 no.7
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• pp.558-564
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• 2001

An experimental modeling is applied to investigate the formation of forms in molten aluminum By using a specially designed equipment, the effect of process variables, such as the shape of stirrer, stirring velocity and fluid viscosity, on the formation of foams were studied in the glycerine added water. Bubbles formed in water had various diameter from 1 to 10 mm and the number of bubbles was 0 to 20/$cm^2$. It turned out that among various variables the stirring velocity and fluid viscosity played important roles on the formation of bubbles. The results obtained from the model experiment were preyed to be convincible also in the real aluminum foam.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.136-144
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• 2002

Melting method has long been considered difficult to realize because of problems such as the low foamability of molten metal, the varying size of cellular structures and solidification shrinkage. The parameters to solve the problem in electric furnace were stirring temperature, stirring velocity, heating velocity and foaming temperature It is important to consider the effects of induction heating, because it brings about the inner flow by the temperature gradient. Aspect ratio also depends on the induction heating. Mechanical properties are dependent on cell sizes and aspect rations. Therefore, this paper presents the effects of these parameters on the cell sizes. For the sake of this, combined stirring process was used to fabricate aluminum foam materials by the above mentioned parameters. Image analysis was performed to calculate the cell sizes, distributions, and aspect ratioes at the cross section of feared aluminum in the direction of height.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.12
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• pp.1615-1623
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• 1997

Numerical study on the chaotic stirring of the screw extruder model proposed has been performed. The velocity field was used in obtaining the trajectories of passive particles for studying the stirring effect of the screw extruder. Two nonlinear dynamical tools, that are Poincare sections and Lyapunov exponents, were used in analysing the stirring effect. The Poincare sections and the Lyapunov exponents show that the stirring effect is most satisfactory, when n(the number of flights in a section) is 1, for the case a (aspect ratio ; flight height divided by the spacing between flights) being O.1. It is also required to set n=3, or 5 at a= 0.2, 0.3 for a uniform stirring.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.537-547
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• 1995

Numerical study on the chaotic stirring of viscous flow in an alternately driven cavity has been performed. Even under the Stokes-flow assumption, the inherent singularity at the corners made the problem not so easily accessible. With some special treatments to the region near the corners, the biharmonic equation was solved numerically by using the fully implicit method. The velocity field was then used in obtaining the trajectories of passive particles for studying the stirring effect. The three tools developed in the field of the nonlinear dynamics and chaos, that are the Poincare sections, the unstable manifolds, and the Lyapunov exponents, were used in analysing the stirring effect. It was shown that the unstable manifolds obtained in this study well fit the experimental results given by the previous investigators. It is predicted that the best stirring can be obtained when the aspect ratio a is near 0.8 and the dimensionless period T is in the range 4.3 - 4.7.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.121-122
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• 2003

In this study a microchannel with various arrangement of blocks is newly proposed. This design comprises periodically arranged simple blocks. In this configuration, the stirring is greatly enhanced at a certain geometric parameter set. To characterize the flow field and the stirring effect both the numerical and experimental methods were employed. To obtain the velocity field, three-dimensional numerical computation to the Navier Stokes equations are performed by using a commercial code, FLUENT 6.0. The fluid-flow solutions are then cast into studying the characteristics of stirring with the aid of Lyapunov exponent. The numerical results show that the particles' trajectories in the microchannel heavily depend on the block arrangement. It was shown that the stirring is significantly enhanced at larger block-height and it reaches maximum when the height is 0.8 times the channel width. We also studied the effect of the block stagger angle, and it turns out that the stirring performance is the best at the block angel ${45^\circ}$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.163-166
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• 1997

Aluminium foam material is a highly porous material having complicated cellular structure defined by randomly distributed air pores in metallic matrix. this structure gives the aluminium a set of properties which cannot be achieved by any of conventional treatments. The properties of aluminium foam material significantly depend on its porosity, so that a desired profile of properties can be tailored by changing the foam density. Melting method is the one of foaming processes, which the production has long been considered difficult to realize becaues of such problems as the low foamability of molten metal, the varying size of. cellular structures, solidification shrinkage and so on. These problems, however, have gradually been solved by researchers and some manufacturers are now producing foamed aluminum by their own methods. Most of all, the parameters of solving problem in electric furnace were stirring temperature, stirring velocity, foaming temper:iture, and so on. But it has not considered about those in induction heating, foaming velocity and foaming temperature in semi-solid state yet. Therefore, this paper presents the effects on these parameter to control cell size, quantity and distribution.

• Resources Recycling
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• v.32 no.2
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• pp.33-42
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• 2023

Metal emulsions have been studied for several decades as a method of increasing the efficiency of the steelmaking process. This study was performed using a water model, observable at room temperature, to compensate for the disadvantages of the high-temperature experiment, the results of which are difficult to observe visually. As a substitute for metal-in-slag emulsions, experiments were conducted by dropping distilled water into silicone oil and comparing the results with the results of a calculation by momentum balance equations. The descending velocity of the water droplet decreased as the diameter of the droplet and viscosity of the fluid (silicon oil) increased. To simulate the descending velocity of a water droplet in silicon oil under stirring conditions, the flow rate of the fluid (silicon oil) was measured by particle image velocimetry (PIV) methods. The calculation of the descending velocity of the water droplet was in good agreement with the measured values, with and without stirring a viscous silicone oil.