Tundish Inclusion Arrest

8/11/2019 Tundish Inclusion Arrest

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REQUIREMENT OF TUNDISH IN CCM:

Quality Improvement through Inclusion assimilation, tundishis used as a refining vessel

Higher productivity rates driven by increased greater

machine availability and improved product yield

Slag-free transfer

Optimized metal delivery systems to the mold

Thermal control, Chemical homogenization


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BENEFITS OF MORE TUNDISH DEPTH

Increases Metal Residence Time

Reduces the potential for Vortexing of tundish slags,

especially during transient conditions such as ladle exchanges.


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CRITERION FOR TUNDISH AS A REFINING

VESSEL

Elimination of sources of molten steel contamination,e.g., refractory erosion, reoxidation, ladle slag carryoverand tundish slag emulsification

Promotion of inclusion flotation and separation from themelt by means of flow modifying devices (FMDs), filters andengineered slags;

Introduction of technologies such as thermal control, slag-free transfer and optimized metal delivery systems to themold.


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CONSIDERATIONS FOR SELECTING OVERALL

TUNDISH DESIGN

Consideration of the product(s) to be cast.

Matching the number of strands to the shop pacing.

Cleanliness improvements.

Lining thickness and configuration.

Necessity for costly tundish furniture.

Tundish fly capability to support extended continuous

casting.

Yield losses.


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TYPES OF TUNDISH

B-TYPE TUNDISH: The trough-shaped tundish, alternately referred to as a boat- or bathtub-

shape, Variations of the rectangular-base trough include coffin-shaped and flared-trough

designs. The trough shape is commonly encountered in single- and two-strand slab casters,

and is also found on many bloom and billet casters.


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This type of Tundish offers a larger ladle stream pour box and a

more circuitous path to the strand than a conventional troughtundish.

V-shaped tundish


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The C-tundish is a combination of the boat- and V-

tundishes.

C-shaped tundish


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1. Encountered principally on bloom/billet machines,

2. Essentially a modified trough with a separate and usually central pour box

region. This design, while minimizing turbulence impacts to the inner strands

and ensuring a full metal head for delivery to all strands.

3. This design prone to short circuit issue of liquid steel, hence this is a

disadvantage of this design.

T-shaped tundish

POUR BOX REGION


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1. Design essentially consists of linked troughs, allowing the bridging of a ladle

exchange period without the drop in tundish weight experienced in conventional

tundishes.

2. Separate hydraulics allow two ladles to be poured into the tundish simultaneously,

and the teeming rates of the old and new heat are matched to equal the output rate

of the caster strand(s), such that tundish level will remain constant.

3. The quality of the ladle exchange portion is comparable to that cast under steady-state conditions in the middle of a ladle.

4. The elimination of thermal events associated with heat losses through the tundish

walls, as can be induced by large tundish level fluctuations.

H-shaped tundish


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1. Wolf and Chakraborty that longer tundishes withlower operating heights yieldmore efficient inclusions removal.

2. Flotation of larger inclusions is generally adequate for all tundishes, although small

inclusions (15 m) do not tend to be floated effectively in any tundish configuration.

3. Shallower designs allow better separation, as the relative distance to be coveredby an inclusion during StokesLaw flotation from the melt to the receptive

slag interface is smaller on average.

4. A shallower tundish also will provide better chemical transition compared to

tundishes of equal volume but greater operating depth, owing to the mixing behavior

of the streams. Notunderstood????

ADVANTAGES OF SHALLOWER TUNDISH:


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DISADVANTAGES OF SHALLOWER TUNDISH:

1. Reduced ability to dissipate turbulent ladle stream energy.

2. Increased chances of top slag Vortexing from the tundish into the mold.

Tundish metallurgy- a solution or limitation to clean steel, J. van der Stel,M.C.M.Cornellison,

B.Deo and R.Boom, Tundish Metallurgy, Vol II, AIME, 1990


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TUNDISH SOLUTION SHOULD PROVIDE FOLLOWINGS:

1. Sufficient volume to bridge ladle exchanges;

2. An appropriate operating depth;

3. Uniform flow distribution to all strands;

4. Optimal residence time for inclusion flotation;

5. A quiescent surface;

6. Thermal and chemical insulation, including appropriate refractories; and

7. Low drainage weight capability to optimize yield.


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Physio-Chemical Phenomena

13IIT Bombay7/5/2014

Ladle changeover and grade intermixing

Temperature drop and heat loss

Re-oxidation, inclusion generation

Slag emulsification

Slag vortexing

Inclusion removal

Strand freezing


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Following solution may be provided to a Tundish for achieving required inclusion

floatation


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PHYSICAL SHROUDING SYSTEMS

1. Fused silica ladle shrouds: Prone to chemical and physical

attack by the teeming stream

2. Alumina-Graphite (ALG) Refractories Shrouds: offers good

thermal shock resistance and resistance to metal and slag

attack,

TO PREVENT ASPIRATION THROUGH THE SHROUD WALLS:

1. sufficient refractory thickness and density, as well as low

permeability, are required

2. Glazes: By applying of glazes on the interior and exterior

surfaces of shroud walls to control oxidation


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SHROUD NITROGEN ASPIRATION CURE

Argon gas is injected in the

shroud bayonet seal which

provides a positive pressure and

minimizes air aspirations.

Submerged opening practices in

the pour box by suppressing the

turbulence using the required

shapes of pour box.


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DISADVANTAGES OF UNSUBMERGED LADLE OPENING1. Forces vigorous slag/metal interactions, leading to increased inclusion

formation

2. Provides exposure of the steel in the falling stream as well as in thetundish pour box to the atmosphere.

NOTE:

A submerged opening practicedoes require a shroud with a larger

diameter at the bottom than at

the top to prevent so-called

blowbacks during ladle open,

induced by resistance fromconstrictions.


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TUNDISH LINING:

1. It should be Inert and not be contributed to exogenous

inclusions in the steel.

2. Applications are being developed where the tundish lining is

designed to actually react with solid inclusions in the melt to

form liquid compounds that do not clog.

3. The control of reducible components in the lining, such as

silica and alkali oxides is also very important. If uncontrolled,

these can be leached out during the casting process and

contribute to formation of alumina inclusions, as the

dissolved aluminum in the steel will react with the more

reducible oxide species at the tundish wall.


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TUNDISH TOP SURFACE COVER:

Top surface of the tundish is protected from the atmosphere bythe addition of a tundish flux layer.

A few casters around the world are equipped with fully sealed

lids that can sustain an inert gas atmosphere above the melt and

atmospheric control is maintained by means of oxygen sensors.

FUNCTION OF SLAG COVER:

1. Inclusion absorption2. Thermal insulation

3. Chemical insulation

4. buffering of ladle slag


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STOPPER RODS:

A stopper rod is a tubular device that controls

flow to the mold by adjusting the openingbetween the rod tip and the tundish well nozzle.

Stoppers are mostly constructed of alumina

graphite, occasionally with tips incorporating the

use of magnesia, SiAlONs (pronounced sy-a-

lons, an advanced class of ceramics withexcellent wear characteristics) and/or porous

elements.


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A NEGATIVE PRESSURE AT THE FLOW CONTROL POINT i.e. UNDER THE STOPPER ROD TIP

Problem: A pressure difference of around 2035 psi between the tip of the stopper and

the metal above the flow control point.

Solution: Inert gas purging is required to negate air aspiration through the stopper rod.

Advantage of stopper rods is that it Reduce the propensity for vortex formation but it

doesnt completely remove the chance of vortexing.

Tundish well nozzles alignment has also become a very important and critical issue

which has to be taken care because just the misalignment of 2 degree from the vertical

can make tundish nozzle clogging worse or exacerbate and if the misalignment reaches

10 degrees from vertical it starts blocking or plugging faster significantly.


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SOME TUNDISH DESIGNS

HAVE TO ACCOMMODATE

FOLLOWING:

Product being cast like in a

combi-caster which are

designed to produce different

sections. These produce a

slab and sometime theseproduce 3 bloom strands.

When Slab is produced from

the combi-caster V-shaped

dam is replaced by two larger

angle dams and middle hole iscapped. This provision should

be given in a tundish.


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Water Modeling : An Effective First Approach

Our Water modelsflow system should be similar to the real flow system for Steel.

CRITERIA OF SIMILARITY:

GEOMETRIC SIMILARITY:

Geometric similarity requires that the ratios of all lengths be maintained to a constant

value. full-scale model detractors include requirements for large water supplies, large

building spaces, and significant pumping capacity. Thus, construction and operation ofsuch models are rather capital- and cost-intensive. reduced-scale models can be

constructed at a comparatively lower capital cost without requirements for extensive

bracing of the transparent Plexiglas walls.

REDUCED SCALE MODELS INCUR:

Lower Operating cost based mainly on the lower quantities of consumables, specificallythe water required.


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KINEMATIC SIMILARITY & DYNAMIC SIMILARITY:

Property Water (293K) Steel (1873K)Viscosity (cP) 1 6.4

Density (g/cm3) 1 7.08

Kinematic Viscosity (cs) 1 0.904

Surface Tension (mN/m) 7.3 1900

ADVANTAGES OF CHOOSING WATER:

1. Since the kinematic viscosities of the two fluids are nearly identical, water can

effectively serve as a medium to model liquid steel flow accurately.

2. It provides safe handling and transparency of medium, thus enabling simple and

effective flow visualization by means of a variety of fluid volume tracers


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Kinematic and dynamic similarity signify that fluid streamlines and dynamic forces

in the model system and the actual system are equivalent in magnitude, geometry

and direction.

All the system dynamics are defined by well known dimensionless expressions as

follows:

Froude Number: relates inertial forces to gravity and represents the bulk flow

within the tundish.

Reynolds Number: relates inertial forces to viscosity and the boundary flow

conditions that account for only a small fraction of the total flow in a tundish.

Weber Number: relates inertial forces to surface tension effect


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GOVERNING ACTIONS FOR THE FLUID FLOW:

A. The high-momentum incident ladle stream jet

B. Gravity-driven flow at the tundish-to-mold exit orifices

THERMAL SIMILARITY:

Thermal similarity is ignored generally due to the bulk flow of steel where forced

convection dominates such as tundishes, thermal phenomena may be ignored.

However, more recent studies have shown that thermal phenomena can result in

significant shifts in fluid flow behavior, even so-called INVERSION.

In tundishes, for example, this phenomenon is particularly important during ladle

switches, as steel from a new heat will mix in the tundish with the prior heat

under potentially non-isothermal conditions.

Depending on whether the thermal difference between the heats is positive or

negative, the flow kinetics are modified, and short-circuit times to reach different

strands are altered. Thus, recent water modeling studies have incorporated the

ability to mix cold and warm streams to provide simulation of transient

phenomena.


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TRACERS IN WATER MODELING:

DENSITY NEUTRAL TRACERS: EX. Water-soluble dyes

NON NEUTRAL DENSITY TRACERS: EX. saline solutions

Provide a slightly altered RTD profile

Relatively accurate

Repeatable RTD results

Provide valid modeling of the actual events occurring in these steelmaking reactors

Yield a profile of the concentration as determined at the outlet of the model

RTDcurves are drawn to obtain important information


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CONCEPT OF RESIDANCE TIME DISTRIBUTION(RTD):

The RTD is frequently plotted as dimensionless concentration versus dimensionless time.

The standard time axis is expressed using the mathematical function of mean residencetime (MRT).

MRT= WorkingVolume of steel in the tundish/ flow rate of steel out of tundish

MRT = 40 tonnes /8 tonnes/min= 5 min

A period of one MRT is also defined as ,RTD or C curves are often plotted to 2.5or 3

In this case, 3would equate to 15 minutes for the given conditions of tundish volume

and throughput. As the flow rate changes, so does .

Characteristic information obtained through an RTD CURVE:

PLUG VOLUMEDISPERSED PLUG VOLUME

MIXED VOLUME

DEAD VOLUME

These characteristics are used to evaluate the tundish flow conditions at steady-state

casting conditions.


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DESCRIPTION OF DEAD VOLUME

1. The ratio of mixed to dead volume indicates the mixing capability of a tundish.

2. Lowest temperature zones (maximum cooling) indicate the Dead Volume regionsduring the Steel flow.

3. The value of the dead volume is found to be more sensitive than the other two

volumes to find mixing capability and hence important to reduce this stagnant portion

as far as possible.


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CALCULATION OF RTDOF MELT FLOWING IN THE TUNDISH:

It is done by solving a time-dependent mass transport equation in the tundish. The plug,

mixed and dead flow fractional components of a particular tundish configuration can be

gauged visually from an RTD curve.

FOR STEADY STATE CONDITION:

The calculation assumes that a tracer is injected at the inlet at a given time and it

flows/disperses with the melt with the specified velocity field and turbulence conditionsobtained from the steady-state calculations. The calculated concentration at the tundish

outlet(s) is recorded as a function of time.

BOUNDARY CONDITION FOR UNSTEADY STATE FLOW:

The boundary conditions required for the solution of the unsteady-state mass transportequation have to express the physical constraints that all the bounding surfaces are

impervious to the tracer. Mathematically, this corresponds to zero flux of the tracer at all

bounding surfaces.


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PLUG FLOW:The plug flow fraction is defined by the advent of the first injected tracer volume at the

tundish outlet nozzle. Also known as the minimum residence time, this characterizes

the portion of the fluid that moves through the tundish in a plug manner.

()


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MIXED FLOW

The mixed fractionalsocalled dispersedvolume

is indicated by the tailof

the C-curve, viz. from the

apex to the time defined as

2. Mixed flow is an

important considerationfrom the perspectives of

temperature and chemistry

transition, as it shows the

tendency of two

concentrations to mix prior

to reaching the outletstream.


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Dead flow

It serves no useful purpose in the tundish and needs to be minimized, as it leads to

detrimental phenomena such as skull formation. Dead flow in RTD curves is generally

defined as the portion of the injected tracer persisting beyond 2.


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CONDITION TO ACHIEVE MAXIMUM INCLUSION SEPARATION RATIO:

1. a minimum spread of residence time

2. large ratio of plug to dead volume

3. relatively large ratio of plug to mixed volume

4. surface directed flow, and contained region of mixing.

REF: Y. Sahai, R. Ahuja, Fluid flow and mixing of melt in steelmaking tundishes, Ironmaking

Steelmaking 13 (5) (1986) 241252.


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BASIC SOURCE OF INCLUSIONS IN TUNDISH:

1. In the carry over slag from the ladle (micro droplets form)

2. Tundish slag

3. Eroded particles of refractory wall

4. Various chemical/steel deoxidation reactions

EFFECTS ON INCLUSION REMOVAL

Height and position of dams affect the removal of inclusion.[1]

The size of inclusions is the critical factor in determining the effectiveness of a giventundish design to separate and float out inclusions.

Inclusions with a large terminal velocity or larger particle diameter will readily float-up to

the slag-metal interface provided appropriate flow modifiers are incorporated into the

tundish geometry. [2,3]


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[1] P.K. Jha, P.S. Rao, A. Dewan, Effect of height and position of dams on inclusion removal

in a six strand tundish, ISIJ Int. 48 (2008) 154160.

[2] S. Joo, R.I.L. Guthrie, Heat flow and inclusion behaviour in a tundish for slab casting,

Can. Metall. Q. 30 (1991) 261269.

[3] A. Ruckert, M. Warzecha, R. Koitzsch, M. Pawlik, H. Pfeifer, Particle distribution andseparation in continuous casting tundish, Steel Res. Int. 80 (2009) 568574


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SIMULATION OF TUNDISH SLAG

1. Oils like Silicone and mineral oils are used to observe surface turbulence and

tundish slag emulsification.

2. It is desirable to minimize surface turbulence, which can cause disruptions to the

complete slag coverage of the tundish surface, often termed openeyes.

3. Slag emulsification be minimized during a ladle change during sequence casting,

this is the demand of clean steel practices.

4. The oil technique is very useful to model the slag/metal interfaces, but, from an

environmental standpoint, does require the modeler to exercise caution so that no

pollution from entrainment of the oil into the model discharge stream(s) occurs


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A water modeling rule of thumb that should be enforced by the modeler is that the

steady-state flow pattern inside a tundish does not fully materialize until three

theoretical mean residence times (3)have elapsed.

Well-designed FMD systems improve the inclusion separation in tundishes.

In fact, a recent trend in water modeling has been the use of overhead mirrors to

allow simultaneous observations of front and plan views of the flow.

One recent study utilizing multiple views of the flow showed that streams do not

move as fronts, but rather tend to display split streams.[17]

Integrity of FMDs is important, as cracks and fractures in the shapes can significantly

impact the fluid flow.


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EXAMPLE OF EFFECT OF PLACING FMDs IMPROPERLY:

It was observed in one instance[18] that Vortexing from the tundish surface into mold

occurred under steady-state conditions with an improperly placed baffle at the full

tundish operating head of 1000 mm.

It should be noted that when the

baffle was repositioned in the

tundish, the Vortexing could not be

re-created, suggesting that theconcentric flow velocities required to

sustain vortex motion over the well

nozzle had been diminished

significantly.


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PICTURE OF A BAFFLE


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Vortexing phenomena do not occur until the tundish level is in the 200300 mm

height range,[4] depending on tundish well nozzle placement.


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Wedged weir/dam combination

and partially collapsed baffles

have been known to cause

rolling action at the surface of

even deep tundishes;


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OTHER REQUIREMENTS RELATED TO TUNDISH DESIGN

Our design should be accompanied with the physical designs of shop floor entities like

design of tundish Car etc as well as allowable floor loadings and space clearances.These physical limitations should always be inculcated in our design.

TRANSITION MODELING


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TRANSITION MODELINGIn continuous casting, any grade change between heats results in a defined quantity of mixed

grade volume.

In modeling transitions, a tracer or dopant is introduced into the tundish model andhomogenized with water.

This mixture is considered the old steel (grade A). Grade A is drained to a specific depth to

simulate ladle exchange operations. Water of a different concentration, typically without tracer

addition, is used to simulate the introduction of new steel (grade B) at a flow rate simulating

normal tundish refill practice.

Once the normal operating depth is re-attained, the flow rate of grade B is throttled back to

normal steady-state casting conditions.

This procedure is visually observed, and the tracer concentration can be collected at the

outlet

Again, the data are graphed as a time-versus-concentration plot that is more commonly

referred to as an F-curve.

F-curves can be used to determine the length and predictability of grade change transitions at

various mixture requirements.


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Due to Reoxidation, we can see in the picture, the freshly made slag.

To avoid the reoxidation, we use a submerged nozzle, however during ladle changeoperation for few seconds there is an open ladle stream of steel entering the tundish.

The reoxidation product during that open stream pouring can actually affect the molten

steel of the tundish for the next 10 minutes of the casting.

Reoxidation during the transfer of heat

INACCURACY IN TRANSITION MODELING


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INACCURACY IN TRANSITION MODELINGPoor Mechanical properties at customer end due to down grading of the material

Discrepancy between plant data and a rudimentary transition model outdated by FMD

setup changes.

The model underestimated the actualtransition at 80% of intermix by some 43

tons, while the discrepancy at 95%

intermix completion more than doubled

this figure.

As can be seen from the plant data, theactual chemical transition reached 95%

completion within 2530 minutes,

depending on strand throughput,

whereas the old model would continue to

downgrade the strand chemical quality

for an additional 2025 minutes.

The yield implications in this case

suggest a lost opportunity to sell about 90

tons of prime material per transition

event. BY U. S. STEEL IN 1992.[20]


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Poor Mechanical properties at customer end due to down grading of the material

What is the reverse transitioning


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Melt flow for any tundish design can be characterized by the followings:

Solving Standard fluid flow equations

Solving the Heat Transfer EquationsSolving associated turbulence equations

Steady State Equation of the above categories are solved for the

period of normal casting Operations.

Time dependent or unsteady state equations are solved for the

period of ladle change operation

flow in a tundish is not necessarily laminar, it becomes mandatory to incorporate equations

for a turbulence model, such as the commonly used K-

and two-equation models.

Turbulence flow equation for 3 dimension has to be studied because of introduction of

ladle change phenomenon. During ladle exchange flow does not remain laminar.


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At the free surfaceoften assumed to be flat

At the symmetry planes, the normal velocity components and the normal gradients of all

other variables (momentum and scalar transport properties) are defined as zero.

At the jet entry, the velocity perpendicular to the free surface may be calculated from

the volumetric flow rate and the area of nozzle.

Since the jet flow generally is in highly turbulent range, a flat velocity profile in the

incoming jet may be assumed. Similar boundary conditions may also be imposed at the

outlet nozzle(s). ..TO BE ASKED BY VICHU SIR..AND WHAT IS FLAT

VELOCITY PROFILE????

The incoming liquid jet may be considered at a constant temperature. For modeling heatfluxes through free surface and each wall, heat fluxes are assigned or estimated.

q. What is NO-SLIP BOUNDARY CONDITION???


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The key to the success of modeling is, of course, the numerical solution procedure.

The computational domain is divided in a non-uniform grid in the three orthogonal

directions. It is generally a good practice to test the dependence of the grid size on thesolution of the problem. A finer grid does require more computing time but generally

results in a more accurate solution. Thus, a balance between the accuracy of the

solution and computer time must be struck.


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The solutions of the steady-state equations are:

Velocity

Temperature field: The temperature field in the tundish indicates the areas where it

may be possible to freeze metal.

Turbulence field: The turbulent flow field plots show fast-moving and relatively slow-

moving or stagnant regions in the tundish. Careful examination of the flow field may

give qualitative indications of the plug, mixed and dead volumes in the tundish. For

quantitative evaluation of the plug, mixed and dead volumes in a tundish, RTD

Techniques are used.

NOTE: The percentages of plug, mixed and dead flow is not sufficient for determining

what setup should be used.


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ROLE OF DEAD ZONES IN TUNDISH FLOTATION EFFICIENCY

Dead zones are mathematically defined by the region beyond 2on an RTD curve,

and physically are zones of quasi-stagnant flow.

These zones most prominently occur in the shadow of FMDs, viz. the areaimmediately behind a dam, weir, or baffle that the bulk flow bypasses.

The occurrence of dead volumes represents a deviation from ideal plug flow

behavior, resulting in a decrease in effective working volume of the tundish.

Mathematical modeling has proven to be quite effective in showing that merely

increasing the working volume of the tundish to counteract the reduced working

volume imposed by the stagnant flow region is not a guarantee for improved

inclusion flotation.

Fi id l f h f h h i l l i f h d d i ll


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Figure provides an example of the factthat the spatial location of the dead zones is equally as

important as its magnitude.

normal weir/dam combination

The inclusion trajectory lines show that the first The inclusions are short-circuited toward the


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scenario provides opportunities for contact

between the inclusions and the tundish slag

layer.

well nozzle and thus into the cast strand in

the case where the high dam precedes the

short weir.


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Effect of draining and filling as well as thermal gradients can be modeled using tank in

series approach borrowed from chemical Engineering concepts, These effects can have a

significant effect on the fluid flow in tundishes.


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ADVANTAGES OF CHANGING OPERATING PARAMETER

OVER USING Flow Control Devices.

Better Mixing may be achieved by changing the geometrical

parameters(width, height, nozzle distance and their simultaneous

change), compare to using flow control devices like weir, Dam etc.

The use of dams and weirs has also led to the formation of dead

volume regions in the leeward sides, which leads to inhomogeneous

mixing in the tundish.

Fixing up dams and weirs in a tundish being much-involved job

poses another difficulty.

MIXED VOLUME


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The mixed volume of tundish is closely connected with its inflow part, in which the kinetic

energy of pouring flow from the ladle ensures intensive mixing of steel.

PLUG FLOW

The characteristic feature of plug flow is uniform flow of liquid steel during which no elementforeruns the other elements. In the area of plug flow the steel flow has already the laminar

character and so there are better conditions for the rise of inclusions here. The flow of a body of

ice or viscous fluid with no shearing between adjacent layers; idealized flow without any mixing

of particles of fluid.

DEAD VOLUME OF TUNDISHThere are also areas in the tundish with the very slow flow of steel. These areas represent so-

called dead volume of tundish. Dead volume is defined as the area where the liquid steel stays

in tundish longer than the double of the average residence time. Existence of dead volume can

substantially decrease the active volume of tundish and so reduce the residence times of steel

in the tundish.In the area of dead volumes, the greatest danger of local solidification of steel

also exists.This is the reason for minimizing the dead volume in tundish.

SHORT-CIRCUIT FLOW:

When the coming steel practically immediately gets into the outlet of tundish, which is

undesirable with regard to steel purity and thermal homogeneity of cast steel in individual

strands.

In case of open pouring of steel the plunging Jetentrains the significant volume of air(or Gas , in case

OPEN POURING


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Ref: Y. Sahai, R. Ahuja, Fluid flow and mixing of melt in

steelmaking tundishes, Ironmaking Steelmaking 13 (5) (1986)

241252.

g ( ,

of an inert gas shrouded stream). The entrained gas

causes a strong upward buoyancy force and the

liquid flow in this region is reversed. The liquid

stream loses its downward momentum on entering

the tundish and reverses to the free surface, where

it flows downstream towards the tundish-mould

nozzle. In this case dead volume was found 23%

when no FMDs were used.

Use of Weir helps to push the flow downward and

eliminates the red circled dead zone but again

generate the blue circled dead zone region behind

itself. 17% DV is found.

Again use of Dam increases the dead volume by

creating the dead region (green circle) behind thedam. DV increases to 27% again by this.

Free surface and tundish wall Dead Zone remain

unchanged. (orange circled)


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TURBULANCE INHIBITORS:

By using turbulence inhibitor solely causes shortcut flow and bigger dead volume in the

tundish, and the tundish loses its metallurgical character in temperature, composition

and inclusion separation, but the turbulence inhibitor with an inner helical groove can beused to control the flow field in the inpouring area.

Ref: LIU Jin-gang , YAN Hui-cheng , Liu Liu , WANG Xin-

hua, Water Modeling of

Optimizing Tundish Flow

Field, JOURNAL OF IRON

AND STEEL RESEARCH,

INTERNAITONAL. 2007,14(3): 13-19

Each of these physical control devices creates a slow, secondary recirculation in the


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downstream region behind the device

The use of gas injection in conjunction with the physical control devices decreases the

dead volume by activating the low recirculating liquid and considerably increaes the

dispersed plug/dead volume ratio.

During Submerged stream pouring, liquid


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During Submerged stream pouring, liquid

enters the pool with sufficient downward

momentum to carry it right to the bottom.

Red circled regions are shown as dead

volume when there is no flow control

devices, blue circled is the dead zone when

weir is used and green circle indicates the

dead regions when dam is used.

Free surface and tundish wall Dead Zoneremain unchanged. (orange circled)

Ref: Y. Sahai, R. Ahuja, Fluid flow and mixing of melt in

steelmaking tundishes, Ironmaking Steelmaking 13 (5) (1986)

241252.


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Melt Flow Characterization in Continuous Casting Tundishes, Yogeshwar SAHAI and

Toshihiko EMI, ISIJ International. Vol. 36 (1996), No. 6, pp. 667-672

SOME QUERIES:


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Explain longitudinal mixing and transverse mixing??

In the plug fiow region, the longitudinal mixing is non-existent, however, there maybe

transverse mixing to any extent.


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Tundish Inclusion Arrest

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