1. Introduction

Nevertheless diversity and multiplicity of electromagnet-ic systems for stirring by continuous casting of steels thatappeared during 50-years of previous century thanks to S.Junghans and O. Shaaber, the conventional stirring systemsfor billet/bloom casting that are in operation by numeroususers, are uniform, extreme simple, reliable metallurgicalinstallation that should based on the next scientific-techni-cal principles:

1. In-mold stirrer does not make the obstacles forworkability of mold;

2. The copper mold has to be simple and cheap, likemono-block, easy changeable;

3. For decreasing of magnetic flux leakage the magnet-ic system of stirrer has to be submerged into cooling water,being located as close to copper mold as possible;

4. The main intention of in-mold stirrer is taking awayof melt superheat and the stirrer has to provide efficientheat transfer through interface solidus–liquidus;

5. The revolving magneto-hydrodynamic flow in themold is a preferable for reaching of high heat transfer onthe interface and uniform freezing of ingot on the mold sur-face.

The aim of this publication is to show the new manner ofelectromagnetic in-mold stirring that allows to satisfy theabove-mentioned requirements, following the principle ofminimum changes in conventional, very rational caster. Asexample of the in-mold electromagnetic asynchronous stir-rer in-mold stirrer for bloom caster 300�400 mm was taken

in consideration. The mathematical two- and three-dimen-sional models of turbulent magneto-hydrodynamic flows(ANSYS software) and experimental data were used foranalysis of methods of electromagnetic stirrer improve-ment. The schematic view of in-mold electromagnetic stir-rer model is shown in the Fig. 1.

2. Meniscus Disturbance

Analyzing the situation with meniscus disturbance,which causes the lowering of surface quality and nonmetal-lic inclusions entrapping, let’s take in consideration onlymethods and equipment, which have found a place in widecasting practice: rotational asynchronous low frequencystirrer that is fed from multi-phase inverter. We avoid a nu-merous suggestions of electromagnetic molds such as mag-

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Improvement of In-mold Electromagnetic Stirrer by Feeding ofMagnetic System with Polyharmonic Current

Anatoly F. KOLESNICHENKO, Anastasiya A. KOLESNICHENKO1) and Viktoriya V. BURYAK1)

Net Shape Cast, Inc., 17 Lockerbie Drive, Valparaiso, IN 46385 USA. 1) Net Shape Cast (Ukraine), 87, 18/1 RusanivskaNaberezhna, Kiev 02154 Ukraine.

(Received on June 18, 2003; accepted in final form on September 26, 2003 )

The elaboration relates to a method of electromagnetic stirring in continuous casting of carbon steels,when the surface quality and entrapping of nonmetallic inclusions still remain as the major problems con-cerning of ingot quality and success on the steel market.

The improvement of surface quality of ingot means a decreasing or elimination of oscillating mark, cornercracking, and pinholes. Intensity of nonmetallic particles entrapping depends on meniscus disturbance: in-clusions do not penetrate into liquid portion of ingot through quiet meniscus. Based on the phenomenon ofelectromagnetic edge effect, which exists in each of asynchronous stirrer, by condition of feeding of mag-netic system by polyharmonic currents the new method of in-mold electromagnetic stirring has been devel-oped. Thanks to that the depth of oscillating marks decreases, the flow on the meniscus is suppressed, andthe meniscus disturbance and inclusions entrapping is prevented.

KEY WORDS: electromagnetic stirring; edge effect of asynchronous motor; polyharmonic magnetic fields;stirring intensity; meniscus disturbance; inclusions entrapping; oscillating mark; corner cracking.

Fig. 1. Schematic view of in-mold electromagnetic stirrer forbloom.

neto-impulse mold for fast billet casting,9) meniscus freemolds, providing a high meniscus position and electromag-netic pushing of liquid steel from “triple” point,5) and oth-ers. Let’s assume also that the perfect control of moltensteel feeding and steady position of meniscus are provided.

It is well-known that the liquid steel, coming into moldfrom tundish, under the action of in-mold electromagneticstirrer creates a complete three-dimensional magneto-hy-drodynamics flow at the top of mold. The hydrodynamicperturbation leads to appearing of surface defects in theingot. The rotating flow on the meniscus creates the hills inmold corners that usually surpass above mold powder andtherefore, prevents the penetration of mold powder into gapbetween mold and ingot near mold corners. At the sametime the rotating flow on the meniscus on the walls of sub-merged nozzle has the depression that is caused of non-metallic inclusions entrapping through disturbed meniscusinto ingot. The dual electromagnetic stirrer2) that consists oftwo asynchronous stators—main and brake—with differentdirection of electromagnetic torques, involved for brakingof rotation on meniscus, could not solve this problem be-cause another mechanism of meniscus disturbance adds tothe above mentioned one. The currents, which induce in theingot by both stators, joined in the common loop. The oneof horizontal part of this current loop locates directly belowmeniscus. The magnetic flux of both stators tries to avoidthe copper mold and ingot above and concentrates directlyat the meniscus, where interacts with above-mentioned ra-dial component of common induced current, gives a strongvertical (upward) component of oscillating electromagneticforce. This electromagnetic force, having a frequency thatis close to intrinsic frequency of gravity oscillation of freesurface, on the contrary to suppress the disturbance, swingsit and creates the strong vertical irregular and progressivewaves that “shakes” the meniscus.4) The conditions for cre-ation soliton waves appear here.

On the other hand, the braking torque, applying at thesufficient portion of ingot below meniscus, reduces thecommon stirring intensity and partially deprived the stirrerof its main quality—taking away of the melt superheat.2)

Therefore, the dual EMS for billet/bloom casters—that wasfirst time very popular solution—has been canceled after-ward in many casters, having submerged nozzles and usingthe mold powder.

Another solution regarding suppression of meniscusspinning provides the lowering of regular asynchronous sta-tor on the 150 mm and more below meniscus.11) This solu-tion that was implemented in the row of in-mold stirrers didnot allow the full elimination of the vortex around sub-merged nozzle. This vortex showed the decreasing ofmeniscus motion intensity but the cooling function of stir-rer decreased sufficiently,12) because hot incoming metaldoes not remain in the upper part of the mold and pene-trates to the lager depth.

An imposition of direct vertical magnetic field into thetop part of ingot13)—like in case of electromagnetic brakefor slab caster—was not effective when the in-mold electro-magnetic stirring was provided. The combination of twokinds of magnetic field—alternate and direct—leads to in-teraction of imposed direct magnetic flux with induced al-ternating current from main coil near meniscus. It causes

the meniscus oscillation with frequency, which was close tointrinsic frequency of gravity waves. This phenomenon ex-isted with common suppression of stirring intensity.

The method, which is suggested here especially for pre-vention of turbulence at the meniscus, is similar to1) butbased on the two phenomenons. The first is the edge effectthat develops differently by different frequencies of im-posed magnetic flux. The second is the simultaneous impo-sition of two alternate magnetic fields that creates in thesame regular inductor but by feeding of it with poly-fre-quency current.1)

The design of in-mold electromagnetic stirrer is typicalfor conventional industrial continuous bloom 300�400 mmcasting machines, is shown on Fig. 1:– six or four poles asynchronous stator that provides the

rotate motion of molten steel around mold axis,– low frequency current feeding,– tubular or assembled copper mold with or without sup-

ported stainless steel plates on the external sides of cop-per mold, water submerged coils, forced convectionwater-cooling of mold, and coils.The two- or three-phase magnetic system feeds from low

frequency inverter that generates the multiphase polyhar-monic currents with controlled phase sequence, amplitudesand harmonic structure.

Low frequency (0.8–3.0 Hz) current-component has di-rect phase sequence, and amplitude 100%, high frequency(13–20 Hz) component has the reverse phases sequence,and current amplitude equals to 50–75% depending on castingot sizes, mold geometry, steel grade and casting speed.

The principal electric scheme of polyharmonic currentsource (power supply) for in-mold stirrer is shown on Fig.2. The logical programmable electronic block that formsthe managing signals for power thyristors transforms the di-rect current from rectifier in complete alternate polyhar-monic current, having above-mentioned or any harmonicconsistence, amplitudes, and phase sequence. The polyhar-monic current applies to coils of inductor as in ordinarytwo- or three-phase asynchronous stirrer.

Above-mentioned current structure is determined fromstandpoint of using of edge effect for:– applying the reverse electromagnetic torque on the

meniscus to suppress the vortex at the meniscus,– reducing the vertical components of steel velocity for

prevention of inclusions entrapping into ingot,– saving the stirring intensity inside mold, nevertheless, the

opposite torque applied to meniscus of molten steel,– oscillation with amplitude 2 mm of meniscus edges for

increasing of molten mold powder flow into gap betweenmold and ingot walls,

– Joule heating of solidified shell edges, and melting of itfor lowering of point of initial solidification on 2–3 mmand prevention of touching and bending of shell edges

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Fig. 2. Structure of polyharmonic power supply for in-mold stir-rer. 1 – rectifier, 2 – block of polyharmonic current adjust-ing, 3 – block of power thyristors, 4 – EM Stirrer.

when mold oscillates.The explanation what is the edge effect of asynchronous

stirrer is given in Fig. 3. A magnetic flux, generating in thecoils of stator, unfortunately, can flow only partiallythrough copper mold and steel ingot because it meets theelectromagnetic resistance in the high conductive mold andingot as result of inducing of eddy currents. These currentscreate the own magnetic flux that prevents the penetrationof primary flux into mold and ingot. Resulting, the primarymagnetic flux tries to avoid the high conductive mold aboveand below. At the mold top, above meniscus, the magneticflux does not meet the obstacles and try to penetrate down-ward, into steel ingot trough meniscus. The higher a mag-netic field frequency component the more magnetic fluxavoids the mold and ingot and the higher is the concentra-tion of magnetic flux at the meniscus and especially at themeniscus edges. If a mold design provides the installationof steel ferromagnetic insert above in-mold stirrer, this in-sert absorb part of magnetic flux and the concentration ofmagnetic flux on the meniscus decreases, and, as result, de-crease the edge effect intensify. The magnetic flux, whichconcentrates on the meniscus edges, interacts with eddycurrents inside ingot, and creates the electromagnetic forcesand Joule heat sources.

The edge effect develops differently by different frequen-cies. The higher magnetic field frequency, the stronger anedge effect develops on the ingot surface (Fig. 4(a)), thestronger torque is applied to meniscus and the further theforce frequency from intrinsic frequency of meniscus“shaking”. Contrary, the low frequency rotating magnetic

flux easy penetrates into ingot and creates sufficient electro-magnetic torque in the middle of stirrer. At the same timeby low frequency the rotating torque on meniscus is smalland by decreasing of frequency lower than 2 Hz the rotatingtorque on meniscus can even have an opposite direction(Fig. 4(b)).

Therefore, the main idea of suppression of meniscus ro-tation and saving of high common stirring intensity is basedon the combination of frequencies components of feedingcurrent, which provides the using of positive properties ofdifferent frequency edge effect: strong low frequency rota-tion torque inside stirrer, but suppression of this frequencycomponent torque only at the meniscus, at the same time,applying of the high frequency breaking reverse torque onthe meniscus. The example of distribution of helical com-ponent of Lorenz force on the meniscus and inside stirrerby polyharmonic magnetic field, which has created withthis principle, is shown in the Fig. 5.

Before determination of consistency of polyharmoniccurrent that has to feed the magnetic system of stirrer needto determine the influence of current frequency on the levelof liquid steel stirring velocities. As follows from Figs. 6and 7, the higher common stirring intensity presents by cur-rent frequency f �5 Hz. Notable, that practically all in-mold stirrers are working by current frequency that is veryclose to this value.

Installation of ferromagnetic insert above in-mold stirrermakes a correction of edge effect and allows to suppress ofall velocity components at the meniscus that can be seen on the Figs. 6(a) and 6(b). The same decreasing of velocity

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Fig. 3. Magnetic field of in-mold stirrer by frequency f�5 Hz: a – regular EM stirrer, b – EM stirrer with ferromagneticinsert (thickness 30 mm), which decreases the concentration of magnetic field above meniscus.

Fig. 4. The distribution of rotating component Lorenz force density on meniscus (between points A and B) and in themiddle of stirrer (between points C and D) for different frequencies: a) for higher frequency 9 Hz, b) for lowerfrequency 1 Hz.

in the middle section of magnetic core occurs too, but inlower measure that follows from comparison of Figs. 7(a)and 7(b).

The behavior of the meniscus is determined by level ofvelocity components, especially axial downward directedvelocity component that response for entrapment of non-metallic particles into ingot. These velocities distinguish byfeeding of inductor with currents of different frequencies.Axial component of velocity at the meniscus for frequency

f �1 Hz and f �5 Hz equals to 0.017 m/s, for f �9 Hz thisvelocity equals to 0.008 m/s and for f �13 Hz 0.004 m/s.Near submerged nozzle the axial component of meniscusvelocity directed downward (inside ingot), but along moldwalls and particularly in mold corners—upward. The radialcomponents of velocities at the meniscus equals to 0.05 m/sby frequencies f �1 Hz and f �5 Hz, 0.03 m/s for f �9 Hzand 0.02 m/s by f �13 Hz. The electromagnetic forces havea direction from submerged nozzle to the mold walls and

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Fig. 5. The distribution of rotating Lorenz force density on meniscus (between points A and B) and in the middle of stir-rer (between points C and D) by polyharmonic current.

Fig. 6. Azimuth velocities on the meniscus by different current frequencies: a – regular EM stirrer, b – EM stirrer withferromagnetic insert above copper mold.

Fig. 7. Azimuth velocities on middle horizon of stirrer by different current frequencies: a – regular EM stirrer, b – EMstirrer with ferromagnetic insert above copper mold.

contribute to creation of cavity and entrapping of nonmetal-lic inclusions into ingot through meniscus near submergingnozzle.

The intensity of edge effect can be changed sufficiently ifthe concentration of magnetic flux above meniscus will bechanged. If the top of in-mold stirrer is covered by ferro-magnetic insert the part of magnetic flux that try to avoidthe copper mold and ingot will be absorbed and put backinto magnetic core of inductor. The level of all componentsof electromagnetic forces decrease:– vertical component decreases 3.5 · · · 5 times for current

frequency 5, 9, and 13 Hz, and for frequency f �1 Hz de-creases 9 times,

– radial force component that pushes the molten steel fromsubmerged nozzle to mold walls and so helps to entrapthe non metallic inclusions into ingot—decreases 3–3.5times for all frequencies,

– radial force component on mold walls, which responsesfor good contact with mold walls and level of oscillatingmark, decreases 4 · · · 6 times.Velocities in meniscus decrease sufficiently when the fer-

romagnetic insert was installed above in-mold stirrer: axialvelocity decreases in average on 15%. So, installation offerromagnetic insert above in-mold stirrer allows decreas-ing of meniscus disturbance.

But cardinal suppression of the flow on the meniscus oc-curs when the polyharmonic two-frequency current used forfeeding of stirrer coils. As mentioned above, the main prin-ciple of adjusting of current frequency-consistence basedon the combination of high frequency breaking torque forsuppression of meniscus motion and applying of low fre-quency torque for main mass of molten steel confined inmold. The feeding current has two—one low, and secondhigh frequency components. Each of current componentshas own amplitude. The phase sequences of three- or twophases high and low frequency components are opposite.Current amplitudes changes in the range 1.3 �Ilow/Ihigh�2.Installation of ferromagnetic plate above mold decreasesthe right (main) torque at the meniscus. The twelve differ-ent combination of frequency and current amplitude of lowand high components, which had allowed finding the vari-ant, when the maximum suppression of meniscus motiontakes place, were considered (see Table 1). The analysis ofall simulated electromagnetic parameters and kinematicstructures of MHD flow in mold with variation of frequen-cy and amplitude components of polyharmonic currents al-

lowed to choose the combination of these parameters thatprovides the suppression of meniscus disturbance, decreas-ing of oscillation mark.

Two current combinations have shown the best situationon the meniscus.Combination 1: low frequency component f�3 Hz,

I�275 A,high frequency component f�13 Hz,I�200 A.

Combination 2: low frequency component f�2 Hz,I�275 A,high frequency component f�20 Hz,I�200 A.

These current combinations have allowed to get the suffi-cient decreasing of all velocity components on the menis-cus comparatively with base regime for current of mono-frequency 5 Hz and current level I�275 A:– the helical velocity component on the meniscus de-

creased from 0.22 to 0.16 m/s, as result of appearing ofreverse breaking torque thanks to the current of high(17 · · · 20 Hz) frequency component and reverse phasessequence comparatively with current of low (0.8 · · · 1.0Hz) frequency component. In spite of dual stirrer, wherethe horizontal induced current along meniscus is strongerand holds a large space below meniscus, the high fre-quency breaking torque concentrates much close to thefree surface and did not suppress the common stirring in-tensity;

– frequency of axial forces exceed sufficiently the intrinsicfrequency of meniscus vertical waves;

– the ascending velocity on the corners of meniscus de-creased from 0.09 to 0.06 m/s;

– the vertical downward component velocity on the sub-merged nozzle decreased from 0.16 to 0.08 m/s.Figures 8 and 9 demonstrates the comparison of velocity

components on the meniscus and in the middle horizon ofstirrer by mono- and poly-frequency current in the coils ofin-mold stirrer.

3. Meniscus Instability and Entrapping of Inclusion

The mechanism of entrapping of nonmetallic inclusionsinto billet is based on instability of interface (meniscus) be-tween moving mediums below and above of it.7) Usually thewhirlpool presents at the meniscus as result of interactionof axial flow of fresh steel, passing through submerged noz-

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Table 1. Combination of frequency and current amplitude of low and high components, which were considered in calculation.

zle, with electromagnetic rotation of steel. The molten slagand the mold powder, which exists on the meniscus can beinstable. The appearing of interface instability is deter-mined by critical Reynolds Number.3,8)

Re�Dv (d slagR /n slagn steel)0.5 .....................(1)

where Dv – velocity difference between molten steel andmolten slag, d slag – the thickness of liquid slag layer on themeniscus, n slag and n steel – respectively kinetic viscosity ofliquid slag and molten steel, R – the radial distance from lat-eral internal wall of mold. When Re�500 · · · 700, the wavesdevelop at the interface, and apexes of them are as centersof dispersion of both liquids and creation of slag or steeldroplets. The higher the velocity difference and the lowerthe viscosity of liquid slag and steel, the easier instability ofinterface and droplets of both liquids—steel and slag is ob-tained. Droplets of molten slag can be involved into liquidportion of billet; nevertheless the difference of steel andslag densities is sufficient. If the mold powder is used as lu-bricant, usually the solid crust or layer of baked togethergranules appears on the meniscus, and difference of veloci-ties Dv increases. Let’s estimate this velocity difference. Ifthe kinetic viscosities of molten slag and steel by typical

conditions of middle carbon steel are respectivelyn slag�68.75 ·10�6 m2/s and n steel �0.865 ·10�6 m2/s, the dis-tance from mold walls R�50 mm, and the thickness of liq-uid slag layer d slag�3 mm, then velocity difference will beDv�0.314 · · · 0.44 m/s.

Other kinematics parameters: vortex on the meniscus andaxial components of involving velocity of mold powderparticles of being initially hard on meniscus is stipulated byexistence of strong vertical velocity component that iscaused because the steel flow through submerged nozzlejoins with vortex on meniscus from stirring action. The vor-tex has a strong vertical velocity component directed down-ward, near submerged nozzle into ingot, and this velocity isenough for involving of particles having size 200 and lessmicrons. The dependence of particle size from velocity dif-ference can be described by Stockes formula:

....................(2)

where Dv – velocity difference between molten steel andmolten slag, d particle size, r slag and r steel – respectivelydensity of liquid slag and molten steel, n steel – kinetic vis-

Dv � �d g2

181

rr n

slag

steel steel

Ê

ËÁˆ

¯̃

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Fig. 8. Comparison of helical velocities on the bloom meniscus by monoharmonic: (a) and polyharmonic (b) currents ofin-mold EMS.

Fig. 9. Comparison of helical velocities on the middle of bloom EMS by monoharmonic (a) and polyharmonic (b) cur-rents of in-mold EMS.

cosity of molten steel, g – gravitational acceleration.As follow from graph in Fig. 10, which is built according

to the Stockes formula, the level of velocity differences isenough for involving of particles that are presented on themeniscus.

4. Surface Quality

Long time exploitation of in-mold electromagnetic stir-rers has showed that revolving of liquid metal on the menis-cus can decrease the surface quality of ingot. By intensivestirring together with filling of steel through submergednozzle the revolving liquid steel on the meniscus has thehillocks in the corners of mold and hollows between cor-ners. Both, hillocks and hollows, are not stable, however,average vertical sizes of hillocks and hollows are in propor-tional to second power of circular velocity. The mold pow-der slips down from hillocks and collects in the hollows.Mold oscillations together with action of hillocks on thecorners leads to non-uniform distribution of mold powder,coming into gap between mold and ingot. Resulting, theheat contact between ingot and cold copper mold is differ-ent on the mold corners and between them: on the cornersthe heat flux 2 · · · 2.5 times exceeds the one between cor-ners. On the ingot ribs the thermal cross cracks appear.When the polyharmonic current flows through the coils ofmagnetic system, and the breaking torque on the meniscusallows to decrease here the rotate velocity from 0.22 m/s to0.16 m/s, and the vertical size of hillocks in mold cornersdecreases (0.22/0.16)2�1.89 times.

Another phenomenon that determines the surface qualityis the oscillating mark. For understanding how to decreasethe oscillating mark by feeding of magnetic system of stir-rer with polyharmonic currents, let mention the nature ofthis phenomenon.6) When the liquid steel feeds the moldthrough submerged nozzle, and the mold powder is used aslubricant, by oscillation of mold the solid shell edge touch-es with solid slag ring that is frozen on mold walls a littlebit above meniscus. This touching leads to bending of shelledge into ingot when the mold moves down. When themold rises up, a fresh crust is frozen on the mold wallabove bent portion, where the hollow creates. If the positionof point of initial solidification could be lowered, it has al-lowed the prevention of this touching. For example, the ap-plication of electromagnetic impulses or high frequency

magnetic field9,10) provides the pushing of meniscus edge tothe ingot center and leads to simultaneous induction heatinghere, and to local suppression of solidification intensity.Resulting, the curvature of meniscus surface here decreas-es, the mold powder obtains the easier access into gap be-tween mold and ingot and increasing of heat resistance ofgap with simultaneous Joule heating replace down the ini-tial solidification point. Similar mechanism is present whenthe stirrer is fed with above-mentioned polyharmonic cur-rent: nevertheless the intensity of electromagnetic force isless and radial pushing of edges is much smaller than incase of electromagnetic mold.9,10) The short-wave vibrationof meniscus near edges can make as better the access ofmold powder into gap.

The amplitudes of meniscus edges oscillation can be esti-mated with equation:

..................................(3)

where r – liquid steel density, t – time, Fz – axial compo-nent of electromagnetic force, u – vertical component of ve-locity at the meniscus edge. After double integration of thisequation for half period of oscillation, the edge amplitude:

.............................(4)

Here f – frequency of magnetic field. The values of esti-mated edge replacement is shown in Table 2.

Nevertheless amplitudes of edge oscillation were small,the effect of improvement of powder access into gap wasobserved by test on the simple physical unit. Figure 11demonstrates the device that consists of immovable stain-less steel vessel 2 with low melting metal Sn–Bi that hadconvex meniscus on the level a little bit above vessel edges.The vessel was surrounded by oscillating ceramic cylinder1 that created the gape around vessel edges 1.6 mm. Bothstainless steel vessel with low melting Sn–Bi alloy and ce-ramic cylinder were installed into magnetic field of modelinductor of single-pole 3-phase stator that generated themagnetic field similar to bloom mold electromagnetic stir-rer (MEMS). The magnetomotive forces of 6 coils were 5times lower comparatively with real bloom MEMS, butfield of forces was similar to original. The inductor was fedby polyharmonic current. The base regime for comparisonhad the monogamous frequency 5 Hz. The weight of moldpowder that fell down through gap between ceramic cylin-der and stainless steel vessel was measured periodically byweighing machine 6. When the magnetic field appeared themold powder increased the falling and the flow rate of mov-ing down powder was different by different current flowedthrough inductor. So, see Table 3, by combination of regimes

D zF

fz�

16 2◊ ◊r

du

d

Fz

t r�

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Fig. 10. The difference of velocities liquid steel and slag that areenough for involving particles into ingot.

Table 2. The values of estimated meniscus edge replacementunder the action of MEMS.

(here f low and f high – frequencies of polyharmonic currentcomponents, Ia,low – amplitude value of magnetomotive forceof low frequency component, Ia,high – amplitude value ofmagnetomotive force of high frequency component) thefirst regime has shown increasing of powder fall down on1.67/1.1�1.52 times by oscillating frequency 0.8 Hz and on1.71/1.1�1.55 times when oscillation frequency was in-creased to 2.1 Hz. So, influence of “mold” oscillation on thepower flow rate was lower, then current composition.

5. Conclusions.

(1) Sufficient improvement of conventional in-mold

stirrer with the same low frequency inverter can be ob-tained when the inverter generates the polyharmonics cur-rents, having low frequency 2–3 Hz and high frequencycomponent 13–20 Hz depending on ingot and mold size andgrade of cast steel. The inverter has to be equipped with lo-gistic adjuster of such current contents.

(2) The feeding of magnetic system of EMS by poly-harmonic three- or two-phase current allows to get the re-verse electromagnetic torque on the meniscus and suppressthe disturbance that in turn decreases the entrapping of par-ticles into ingot through meniscus.

(3) At the same time the feeding of magnetic system ofEMS by polyharmonic three- or two-phase current allowsto suppress on the meniscus the hillocks in the mold cor-ners, and, resulting, increase the mold powder incomingaround billet (bloom) corners, and allows to avoid thecracking of this corners during solidification.

(4) The feeding of magnetic system of EMS by poly-harmonic three- or two-phase current leads to oscillation ofmeniscus edges, and to increasing of mold powder entering.Resulting, the suppressing of the heat flux at the point ofinitial solidification that allows decreasing the oscillatingmark.

REFERENCES

1) K.-H. Spitcer, G. Reiter and K. Schwerdtfeger: Proc. of Int. Symp.on Electromagnetic Processing of Materials, ISIJ, Tokyo, (1994),178.

2) P. H. Dauby and S. Kunstreich: Proc. of ISS Tech 2003 Conf., ISS,Warrendale, PA, (2003), 491.

3) A. I. Raichenko, A. F. Kolesnichenko, V. T. Chemeris and M.Pavlicevic: Proc. of Int. Symp. on Electromagnetic Processing ofMaterials, Centre Francais de l’Electricite, Paris, (1997), 461.

4) A. F. Kolesnichenko, A. A. Kolesnichenko, V. Buryak and S. Vasyuk.Proc. of Int. Symp. on Electromagnetic Processing of Materials, ISIJ,Tokyo, (2000), 415.

5) P. Courbe, P. Naveau, C. Bertoletti, J. M. Jolivet, E. Perrin, C.Salaris, E. Weisseldinger, A. Oper and A. L. Spierings: Proc. of 3rdEuropean Conf. on Continuous Casting, Book 1, Madrid, (1998), 65.

6) I. Saucedo: Proc. of 1991 Steel Making Conf., ISS, Warrrendale, PA,(1991), 79.

7) S. Yamashita and M. Iguchi: ISIJ Int., 41 (2001), 1529.8) A. F. Kolesnichenko: Technological MHD Devices and Processes,

Naukova Dumka, Kiev, (1980), 190, (in Russian).9) M. Pavlicevic, A. Kolesnichenko and A. Poloni: US Patent 5,988,261,

(Date of Patent: Nov. 23, 1999).10) H. Kim, J.-P. Park, H. Jeong and J. Kim: ISIJ Int., 42 (2002), 171.11) K. Mayrhofer: US Patent 5 025 852, (Date of Patent: Jun. 25, 1991).12) E. Favre, S. Kunstreich and M.C. Nove: Steel Times Int., 9 (1998), 9.13) J. Szekely, O.J. Ilegbusi, L. Beitelman and J.A. Mulcachy: Proc. of

Symp. Magnetohydrodynamics in Process Metallurgy, TMS, LightMetal Division and ISS, (1992), 231.

f

f

I

Ilow

high

a,low

a,high

Hz

Hz

A trans

A trans� �

2

20

3600

4950,

◊◊

f

f

I

Ilow

high

a,low

a,high

Hz

Hz

A trans

A transand� �

3

13

3600

4950,

◊◊

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Table 3. Experimental data of low melting metal test.

Fig. 11. Unit for estimation of influence of melt edges vibrationon the mold powder flow rate: 1 – ceramic cylinder, 2 –stainless steel vessel with low melting alloy, 3 – EMS in-ductor, 4 – mold powder, 5 – oscillating drive, 6 – weigh-ing machine.