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The Influence of Natural Convection and Electromagnetically Driven Flows on Segregation Freckle Formation

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Journal of Iron and Steel Research International 2012年第S1期19卷 459-462页

作者： Shevchenko Natalia Boden Stephan Eckert Sven Gerbeth Gunter Helmholtz-Zentrum Dresden-Rossendorf P.O.Box 51011901314 DresdenGermany

Visualizations of the solidification process were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with a Ga-25wt%In ***-solutal convection in the solidifying melt gives rise to the development of vertical segregation channels( 'chimneys').The probability of chimney formation depends sensitively on variations of both the concentration and temperature distribution.A forced melt flow perpendicular to the growth direction accelerates the growth of the secondary dendrite arms on the upstream side and suppresses the development of secondary arms on the downstream *** primary dendrite arm spacing is increased,whereas the secondary arm spacing remains unaffected. Flow-induced modifications of the local composition were observed within the mushy zone which may contribute to the formation of spacious segregation pattern.

关键词： solidification melt flow forced convection segregation freckle formation X-ray radiography

The LIMMCAST Program at HZDR:Modelling of Fluid Flow and Transport Phenomena in the Continuous Casting Process

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Journal of Iron and Steel Research International 2012年第S1期19卷 1-8页

作者： Gerbeth Gunter Eckert Sven Stefani Frank Timmel Klaus Wondrak Thomas Helmholtz-Zentrum Dresden-Rossendorf P.O.Box 51011901314 DresdenGermany

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical *** present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400℃.The parameters of the facility and the dimensions of the test sections will be given,and the possibilities for flow investigations in tundish,submerged entry nozzle and mould will be *** addition,the smaller set-up Mini-LIMMCAST will be presented,which works with the room-temperature liquid alloy *** main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal *** ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400℃.First results from LIMMCAST and Mini-LIMMCAST will be presented covering the following phenomena:fully contacfless electromagnetic tomography of the flow in the mould,flow monitoring by a multitude of ultrasonic sensors,and analysis of the flow in the mould under the influence of an electromagnetic brake: intensification of the flow turbulence contrary to the expected flow damping,injection of argon bubbles through the stopper rod:occurrence of pressure oscillations.

关键词： continuous casting liquid metal model mould flow flow measurements two-phase flow magnetic flow tomography ultrasound Doppler method

An Experimental Study of a Bubble-Driven Liquid Metal Flow Under the Influence of a Rotating Magnetic Field

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Journal of Iron and Steel Research International 2012年第S1期19卷 505-508页

作者： VOGT Tobias ANDRUSZKIEWICZ Artur ECKERT Kerstin ODENBACH Stephan ECKERT Sven GERBETH Gunter Helmholtz-Zentrum Dresden-Rossendorf Dresden 01314Germany Technische Universitt Dresden Dresden 01069Germany

In this study we investigate the flow structure in a liquid metal cylinder while a bubble-driven flow is superposed with a rotating magnetic field(RMF).Argon gas is injected through a nozzle into a column of the eutectic alloy GalnSn. Without electromagnetic stirring the bubble plume in the centre region of the cylindrical vessel produces a recirculation with high velocities near the free surface while the fluid velocities in the bottom region remain rather *** measurements revealed the potential of the RMF to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid *** periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.

关键词： bubbly flow rotating magnetic field electromagnetic stirring mixing

The Impact of an Oxidised Surface on the Melt Flow Driven by a Rotating Magnetic Field in a Cylindrical Column

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Journal of Iron and Steel Research International 2012年第S1期19卷 536-539页

作者： ECKERT Sven SHATROV Victor ZHANG Chaojie GERBETH Gunter Helmholtz-Zentrum Dresden-Rossendorf Dresden 01314Germany

This paper considers the situation where the liquid metal flow with a free surface covered by an oxide layer is driven by a rotating magnetic *** cylindrical configuration was investigated in an experiment accompanied by numerical *** oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls.A complex interaction occurs if both forces are in the same order of *** measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk *** numerical model was shown to be able to reproduce essential features of the phenomenon in a qualitative way.

关键词： electromagnetic stirring rotating magnetic field free surface oxide layer

Flow Control During Solidification of AlSi-Alloys by Means of Tailored AC Magnetic Fields

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Journal of Iron and Steel Research International 2012年第S1期19卷 574-577页

作者： ZHANG Yun-hu RBIGER Dirk VOGT Tobias ECKERT Sven GERBETH Gunte Helmholtz-Zentrum Dresden-Rossendorf Dresden 01314Germany

This paper presents an experimental study which in a first stage is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field *** stirring has been realized by utilizing time-modulated AC magnetic fields in different *** consider time-modulated fields or combinations of traveling magnetic fields(TMF)and rotating magnetic fields(RMF).In a second step solidification experiments are carried out to verify the effect of a certain flow field on the solidification *** results demonstrate that the melt agitation using modulated magnetic fields offers a considerable potential for a well-aimed modification of casting properties by an effective control of the flow field.

关键词： rotating magnetic field travelling magnetic field modulated fields solidification AlSi alloys

Inertial Waves Occurring in a Liquid Metal Column due to Pulsed Excitation by a Rotating Magnetic Field

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Journal of Iron and Steel Research International 2012年第S1期19卷 82-85页

作者： R BIGER Dirk VOGT Tobias FRANKE Sven CZARSKE Jürgen ECKERT Sven GERBETH Gunter Helmholtz-Zentrum Dresden-Rossendorf Dresden 01314Germany Technische Universitt Dresden Dresden 01069Germany

We present an experimental study concerning the flow inside a liquid metal column exposed to a pulsed rotating magnetic *** paper is aimed at highly resolved,quantitative velocity measurements in the eutectic GalnSn alloy.A novel ultrasound Doppler system was used two measure two-dimensional velocity fields of the secondary flow in the radial-meridional *** employs an array of 25 transducer elements allowing a fast electronic traversing with concurrently high spatial and temporal *** measurements revealed transient flow regimes showing distinct inertial oscillations and coherent vortex *** results demonstrate that the arising flow structure depends sensitively on the frequency of the RMF pulses.A maximum intensity of a periodic meridional flow can be observed,if the corresponding pulse frequency fp relates to the eigenperiod of the respective inertial mode in a developed *** electromagnetic stirring method that uses a modulated RMF offers considerable potential to enhance the stirring efficiency and to optimize the properties of castings by a well-aimed flow control during solidification.

关键词： rotating magnetic field electromagnetic stirring inertial wave flow control

Grain Refinement by Electromagnetic Stirring and the Impact on the Mechanical Properties of AlSi-Alloys

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Journal of Iron and Steel Research International 2012年第S1期19卷 341-344页

作者： RBIGER Dirk KRβIG Christoph ECKERT Sven GERBETH Gunter Helmholtz-Zentrum Dresden-Rossendorf 01314 DresdenGermany

This present study examines the directional solidification of A1Si7 alloys from a water cooled copper chill.A rotating magnetic field was used for melt *** magnetic field configurations were considered to demonstrate the impact of diverse flow conditions on the resulting microstructure and the mechanical *** solidified structure was evaluated in comparison to an unaffected solidified *** of the phase distribution, the grain size,the hardness and the tensile strength were *** results reveal the potential of magnetic fields to control the grain size,the formation of segregation freckles and the mechanical *** particular,time-modulated rotating fields demonstrated their capability to homogenize both the grain size distribution and to improve the mechanical properties.

关键词： rotating magnetic field solidification grain refinement mechanical properties AlSi alloys

Experimental Modelling of the Impact of a DC Magnetic Field on the Melt Flow in a Continuous Casting Mould

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Journal of Iron and Steel Research International 2012年第S2期19卷 862-865页

作者： TIMMEL Klaus WONDRAK Thomas RDER Michael STEFANI Frank ECKERT Sven GERBETH Gunther Helmholtz-Zentrum Dresden-Rossendorf

This paper describes experimental investigations of flow structures and related transport processes in the continuous casting mould under the influence of an external DC magnetic field at laboratory *** results will be presented here which have been obtained using a physical model(mini-LIMMCAST)operating with the low melting point alloy *** to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the Submerged Entry Nozzle(SEN)has been studied up to Hartmann numbers of about *** Ultrasound-Doppler-Velocimetry(UDV)was applied for measurements of the flow pattern in the *** conductivity anemometers were used to measure the turbulent quantities of the *** effect of the magnetic field on the flow structure turned out to be manifold and rather *** magnetic field causes a deflection of the jet,at which the respective exit angle from the nozzle ports becomes more ***,both the penetration depth of the discharging flow into the lower part of the mould and the impinging velocity of the jet onto the side wall are reduced.A significant return flow occurs in the adjacent regions of the *** vortices are formed with axes being aligned with the magnetic field *** vortical structures are typical for quasi-two-dimensional magneto-hydrodynamic(MHD)*** flow measurements do not manifest a general braking effect which would be expected as an overall damping of the flow velocity and the related fluctuations all-over the mould *** of the wall conductivity showed a striking impact on the resulting flow structures.

关键词： continuous casting liquid metal model electromagnetic brake ultrasonic flow measurement potential probes