22_Extending the Life of the Tundish and Lining of the Intermediate Ladle in a Six-Strand Continuous Bar-Casting Machine

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ISSN 0967-0912, Steel in Translation, 2009, Vol. 39, No. 11, pp. 995999. Allerton Press, Inc., 2009.Original Russian Text A.N. Smirnov, A.L. Podkorytov, V.G. Klimov, S.G. Solovykh, A.V. Kravchenko, A.G. Kovalenko, 2009, published in Stal, 2009, No. 11, pp. 2327.

995

In the last two decades, there has been considerableinterest in increasing the productivity of continuous-casting machines and minimizing the organizationalcosts of casting. Ensuring long casting series from thesame intermediate ladle is an important aspect of suchmeasures [13]. This maintains stable operation of themachine and reduces the costs for refractory and thewaste of metal associated with shutdown. Correspond-ingly, the functions of the intermediate ladle are con-

stantly changing and expanding. Generalizing theknown designs, we may classify intermediate ladlesinto two basic groups:

ladles in which the refining of liquid steel is com-bined with averaging and dosing of the metal;

ladles in which the most favorable conditions forthe casting of superlong series (at least tends of melts)are created, so as to minimize casting delays.

Ladle designs also ensure metallurgical processessuch as the separation and emersion of nonmetallicinclusions, the introduction of additives in the melt,modification of nonmetallic inclusions by calcium,

heating of steel, and averaging of the melt temperatureand chemical composition [47]. At present, the basicdesign approaches and recommendations are based onphysical and mathematical simulation.

At the same time, in continuous casting, a practicalgoal in improving intermediate ladles is minimizationof the costs of steel production and casting. In particu-lar, this applies to high-productivity continuous-castingmachines operating at metallurgical mini mills [813].We know that, in such conditions, regular steel is

smelted and cast in open jets (Fig. 1), to produce squarebar blanks (with a side of 100160 mm).

In such conditions, there is no provision for refiningof the steel in the intermediate ladle, as a rule. Continu-ous-casting machines are regarded as operationally effi-cient if superlong series may be cast without replacingthe intermediate ladle and without shutdown of themachine. For example, at OAO Chelyabinskii Metallur-

gicheskii Kombinat, the mean series length is 39 melts(with a maximum of 54 melts) [12]. At Badische Stahl-werke (Germany), the mean series length is 4550 meltsfor a single ladle with a five-strand bar machine [14].

The casting of steel bar from a single intermediateladle in a continuous machine is limited by two basic fac-tors: the wear of the dosing nozzles; and the rapid wear

Extending the Life of the Tundish and Lining of the IntermediateLadle in a Six-Strand Continuous Bar-Casting Machine

A. N. Smirnov

a

, A. L. Podkorytov

b

, V. G. Klimov

c

, S. G. Solovykh

c

,A. V. Kravchenko

a

, and A. G. Kovalenko

b

a

Donetsk National Technical University, Donetsk, Ukraine

b

OAO Enakievskii Metallurgicheskii Zavod, Yenakiyevo, Ukraine

c

OOO Kalderis Ukraina, Donetsk, Ukraine

Abstract

Continuous steel-bar casting on a multistrand machine in superlong series is limited by the work-ing-layer wear of the intermediate ladles lining within the slag band and the region of jet incidence. The lininglife may be significantly increased by using high-strength concrete tundishes of special geometric shape, takingaccount of the specific ladle and the casting conditions. A fundamentally new metal-intake design for the cast-ing of superlong series at multistrand continuous bar-casting machines is investigated. In the converter shop atOAO Enakievskii Metallurgicheskii Zavod, a casting series of maximum length 64 melts proves possible. Thiscorresponds to the casting of 9300 t of steel from a single intermediate ladle. For optimal organizational and

technological conditions, increase in this characteristic by a factor of 1.51.6 may be expected.

DOI: 10.3103/S0967091209110084

1 2

3

4

Fig. 1.

Continuous bar casting (open jet): (

1

) rotating stand(

2

) steel-casting ladle; (

3

) intermediate ladle; (

4

) mold.


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of the ladle lining in the zone of jet incidence. Recentexperience shows that internal wear of the dosing nozzlemay be addressed by optimizing the steel preparation forcasting and using a device for rapid replacement of thedosing nozzles [1214]. Such devices depend on theintroduction of a special cassette with at least two dosingnozzles under the roof of the intermediate ladle. Ahydraulic drive moves the nozzles rapidly to their work-ing positions. (The motion cycle of the dosing nozzlelasts ~0.20.3 s). The device for rapid replacement of the

dosing nozzle increases the casting stability on accountof the best organization of jet flow and quasi-constantinstantaneous steel consumption, as well as minimiza-tion of the secondary steel oxidation between the inter-mediate ladle and the mold.

The fast wear of the linings working layer in theintermediate ladle is generally localized within the slagband adjacent to the jet-incidence zone. This may beattributed to turbulent flow in this section of the ladleand intense mixing of the steel fluxes with a slag cover-ing on account of turbulence. In superlong castingseries, active contact of the ladles gunite layer with theslag coating lasts tens of hours (with periodic variation

in the metal level). This practically eliminates the effec-tive use of high-strength refractories without additionalprotective measures.

Prolonged casting from a single intermediate ladleentails rational organization of the steel fluxes, so as toprevent additional disintegration of the working layerin the ladle lining. Analysis of ladle operation in a mul-tistrand continuous bar-casting machine with long andsuperlong casting series reveals the following func-tional characteristics:

constant contact of a certain part of the intermedi-ate ladles base with the metal jet leads to erosion of therefractory layer at the point of jet incidence;

periodic change in metal level in the intermediateladle (during replacement of the steel-casting ladles)changes the dynamics of the steel fluxes;

turbulence and active mixing of the metal with theslag coating in the zone of jet incidence results in wear

of the linings working layer;the contamination of the intermediate ladle with

slag from the steel-casting ladle changes the thicknessand properties of the slag coating in the intermediateladle during casting;

the temperature difference of steel from the cen-tral and extreme strands of the intermediate ladle mustbe minimal, so as to ensure stable casting.

Ensuring the casting of superlong series by appro-priate adjustment of all the operational features entailsthe use of special devices (tundishes, barriers) thataffect the hydrodynamics in the ladles liquid bath dur-ing the whole casting cycle.

In the present work, we study the metalslag mixingin the intermediate ladles of multistrand continuousbar-casting machines on physical and mathematicalmodels, so as to extend the working life of the liningsworking layer in specific conditions.

In developing the internal-cavity configuration ofthe tundish, we take account of the following require-ments:

the tundish must insure retardation of the incidentjet and limit the turbulence of the flows due to jet inci-dence from the steel-casting ladle;

the tundish must limit the turbulent mixing of themetal with the slag coating within a specific zone and

prevent intense mixing at the walls of the intermediateladle in the zone of jet incidence;

the position and configuration of the windows inthe tundish must ensure motion of uniform circulatingfluxes toward the far walls of the intermediate ladle(i.e., the dosing apertures of the extreme strands) andprevent direct incidence of metal from the steel-castingladle in the dosing nozzles of the middle strands.

In our view, these requirements may be met bymeans of a bucket-shaped tundish with lateral windowsfor directed steel outflow (Fig. 2). The efficiency ofsuch tundishes largely depends on their dimensions andposition.

Since the convective fluxes forming in the tundishand intermediate ladle are mainly regulated by the iner-tial and gravitational forces, it is expedient to optimizethe shape of the tundish by physical and mathematicalsimulation.

Dynamic similarity between the model of the inter-mediate ladle in which the fluxes are turbulent and itsindustrial analog will be maintained if the Froude num-ber is the same [15]. That requires matching of the rateof water inflow to the model system and the rate of steel

1

2

3

4

5

Fig. 2.

Bucket-shaped tundish in intermediate ladle of six-strand continuous bar-casting machine: (

1

) dosing nozzle;

(

2

) tundish; (

3

) gunite layer; (

4

) working layer; (

5

) ladlehousing.


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input to the industrial ladle. With the development ofturbulent flow, the Reynolds number in different inter-mediate ladles will be practically the same, regardlessof their configuration and dimensions [1618].

The basic goals of physical simulation may be statedas follows:

study of the scope for control of the metal flowfrom the steel-casting ladle to the intermediate ladle;

determination of the action of the metal jet fromthe steel-casting ladle on the mixing of the liquid phasein the intermediate ladle;

estimation of the mixing of metal and the slagcoating in the intermediate ladle during casting.

To this end, we select the rational geometric param-eters of the physical models in relation to continuous-casting parameters such as the speed and flow rate ofthe liquid entering the intermediate ladle [19]. The steelis simulated by water at 1825

C. (The viscosity of thewater is relatively similar to that of steel at the ladle-treatment and casting temperatures.) The slag coatingat the metal surface in the ladle is simulated by meansof silicone or transformer oil, characterized by highsurface tension and variable viscosity with temperaturevariation.

The physical model of the intermediate ladle ismade from organic glass. The scale of the model (1 : 3)is sufficient for real-time visual observation of all thehydrodynamic processes in the ladle. The motion of theconvective fluxes is recorded by means of a digitalvideo camera and by coloring local volumes of thedeparting liquid with ink. The residence time of the liq-uid in the ladle is determined electrochemically, with

the introduction of a small quantity of concentrated saltsolution in the water and measurement of the electricalconductivity at several points of the model [20].

As a result, it is found that, with a tundish of partic-ular size and configuration, conditions that limit the tur-bulent mixing of the metal with the slag coating withinthe tundish may be formulated (Fig. 3). The directionand intensity of metal flow from the windows of thetundish into the intermediate ladle are of great impor-tance here. It is also found, that, with a specific position

of the jet and windows, eddy turbulization may beobserved outside the windows of the tundish. This isundesirable, since it accelerates the disintegration of

the refractories in the intermediate ladle and tundish.

The position of the windows in the tundish relativeto the ladle cross section, as well as the window shape,has a significant influence on the flow patterns in theliquid bath of the intermediate ladle. As is evident fromFig. 4, a rational configuration of the tundish mayensure liquid motion parallel to the long walls of theladle. Then the convective flows leaving the ladle firstmove along the metal meniscus and are incident in theperipheral zone, where the dosing nozzles of the cast-ing machines extreme strands are located. Then the liq-uid fluxes are gradually redirected, until they predomi-nantly move toward the bottom of the ladle; these

downward fluxes continue to move to both the extremeand middle dosing nozzles. In fact, such liquid motionis characterized by an absence of critical-turbulencezones (even at the slagmetal interface) and of deadzones, which are hardly involved in mixing. This isespecially important in superlong casting series, so asto ensure stable casting. That convective-flow configu-ration is basically retained when the liquid level in theintermediate ladle falls by 3540%.

The results of physical simulation are in good agree-ment overall with the results of mathematical simula-tion for the intermediate ladle of a six-strand continu-ous bar-casting machine. This is particularly true of thedirection of motion of the basic convective flows andtheir behavior near the ladle walls. At the same time, itis found that the position of the windows in the tundishrelative to the axis of the incident jet is very importantin ensuring a rational convective-flow pattern. Thus,when the windows (or the tundish) are shifted by nomore than 7080 mm (in the ladle cross section), zonesof increased turbulence may be observed adjacent to thewalls of the ladle and the tundish. This leads to acceler-ated lining wear in the intermediate ladle.

Fig. 3.

Liquid surface in a bucket-shaped tundish (view ofthe physical model from above).

5 s 10 s 15 s

20 s 25 s 30 s

45 s 50 s 55 s

Fig. 4.

Dynamics of liquid motion from the tundish alongthe intermediate ladle.


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The geometric parameters of the windows in thetundish are optimized by mathematical simulation of thesteel fluxes in the bath of the intermediate ladle. The opti-mal parameters correspond to an absence of increasedturbulence adjacent to the ladle lining; minimization of

the dead zones; and approximately equal time for thesteel to move from the tundish to any dosing nozzle ofthe ladle. The last condition poses the most problems. Inthe present work, we adopt a design in which the path ofthe metal particles from the tundish to the first, second,fifth, and sixth strands is about 1520% less than the pathfor the middle strands in the immediate vicinity of thetundish walls. This flow pattern is retained with increasein window size by 1015% (by erosion of the walls dur-ing casting).

The results regarding the influence of the tundish onrational motion of the convective flows may be used todevelop designs for the tundish in the intermediate ladle

of the six-strand continuous bar-casting machine.The working life of the intermediate ladles lining(in the proposed configuration) is significantly limitedby partial disintegration of the walls of the tundish,which are subjected to certain loads for a considerabletime. According to mathematical simulation in whichnot only the flow dynamics but also the loading of thewalls by the metal fluxes are taken into account, thepressure at certain wall sections of the tundish may varyquite widely (Fig. 5). The sections at the windowperimeter and the rear wall of the tundish are under thegreatest load. Hence, to ensure equal strength of allstructural elements of the tundish, reinforcement of themost vulnerable sections with struts is expedient.

OOO Kalderis Ukraina has undertaken responsibil-ity for manufacturing the tundish, refining the configu-ration of its internal and external surfaces (in view ofproduction constraints), and selecting the appropriaterefractory. The operational capabilities of the tundishare investigated at the high-productivity six-strand con-tinuous bar-casting machine in the converter shop atOAO Enakievskii Metallurgicheskii Zavod. The con-verter shop includes three 160-t converters, two ladlefurnace units (metal mass in ladle 145 t), and two con-

tinuous bar-casting machines. In 2007 and 2008, theoutput of each of these machines was 2.27 million t.

The intermediate ladle of the multistrand continuousbar-casting machine takes a characteristic deltoid form.The design specifies casting in series of 68 melts, inview of the capacity of the intermediate ladle. In opera-tion, however, it is found that the machines designed andmanufactured by OAO NKMZ are highly functional and

have a certain reserve of productivity. This suggests thatit is expedient to extend the casting series, with improve-ment in the lining and operating conditions of the inter-mediate ladle.

The ladle lining developed by OOO KalderisUkraina is intended to harmonize the operation of allthe refractory elements, including the tundish, and toensure superlong casting series. In patching, the combi-nation of Kermag 85EN gunite (

90% MgO) for thewalls and base of the ladle and magnesite-based con-centrate for the walls of the tundish proves best.

In industrial tests, attention focuses on the wear ofthe walls in the tundish and the influence of its shape on

the working life of the ladle lining. This permits correc-tion of the gunite-layer thickness in zones of increasedwear and thickening of the wall after wear. It is alsoconfirms that the throughput of the tundish depends onits position in the intermediate ladle relative to the zoneof jet incidence.

According to data for February and March 2009,when using the proposed tundish design, the meanlength of the casting series is slightly more than42 melts (with a maximum of 64 melts). With furtherrefinement of casting in superlong series, we mayexpect rapid improvement in its characteristics. Coordi-nation of the organizational and technological aspects inensuring stable operation of continuous bar-castingmachines may ensure series of mean length 7080 melts,with a record value of 100 melts.

CONCLUSIONS

(1) Steel casting on multistrand continuous bar-cast-ing machines in superlong series is limiting by wear ofthe linings working layer in the intermediate ladle,within the slag band and the zone of jet incidence. Thelife of the ladle lining may be significantly extended byusing tundishes of special shape made of high-strengthconcrete, taking account of the specific ladle configura-tion and the casting conditions.

(2) The design of the tundish must be selected forthe specific conditions on the basis of physical andmathematical simulation.

(3) Our research provides the basis for a fundamen-tally new design of the tundish, permitting superlongcasting series for multistrand continuous bar-castingmachines. In the converter shop at OAO EnakievskiiMetallurgicheskii Zavod, the longest casting series is64 melts, which corresponds to the casting of 9300 t ofsteel from a single intermediate ladle. We believe that, in

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9.2

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7.9

Fig. 5.

Pressure distribution of fluxes at the wall of thetundish.


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favorable organizational and technological conditions,this figure may be increased by a factor of 1.51.6.

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Documents

22_Extending the Life of the Tundish and Lining of the Intermediate Ladle in a Six-Strand Continuous Bar-Casting Machine