FIELD OF THE INVENTION
The present invention relates to a method to maintain optimum super heat during
steel casting based on an accurate prediction of turn down temperature. Further,
the method takes in to account all the operations happing in the route of ladle for
prediction of turn down temperature.
BACKGROUND OF THE INVENTION
The control of liquid steel temperature during steel making and casting process is an
important factor responsible for producing quality steel including enhancement in
productivity of the plant. Ladle is an important metallurgical vessel used to transfer
molten steel from one station to another. The phenomenon of heat transfer taking
place in ladles needs to be understood for prediction of liquid steel temperature. The
assessment of thermal profile of liquid steel from BOF converter to caster can be
done through consideration of heat losses at all points. The prior art practice of
application of high tapping temperature to avoid low superheat problem leads to
high super heat cases during casting. The high superheat compels the operators to
reduce the casting speed and hence, leads to production losses.
The researchers have recognized that super heat can be controlled by an accurate
prediction of the turn down temperature. The prediction of the turn down
temperature requires generation of a liquid steel thermal profile for the complete
process cycle of the ladle. The thermal profile of the liquid steel is highly dependent
upon particular plant and its practices. There are known turn down temperature
prediction systems which however, substantially lacks in accuracy of prediction
results. The prediction according to the prior art are based

on the effect of a few of the total operational parameters and unreliable heat
equations are used to solve the equations. The prior art methods of temperature
prediction also ignore various complexities involved in the ladle operations arising
during its complete process cycle.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method to maintain optimum
super heat during steel casting based on an accurate prediction of turn down
temperature.
Another object of the invention is to propose a method to maintain optimum super
heat during steel casting based on an accurate prediction of turn down temperature,
which considers all the operational parameters and uses linear heat equations.
Still another object of the invention is to avoid production losses during steel casting
due to high superheat.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method to maintain optimum super heat during
steel casting based on an accurate prediction of turn down temperature. According
to the method, turn down temperature is first predicted in a module, which is
applied as a controlling variable to maintain super heat temperature within an
optimum range during the process of steel casting. The turn down temperature
prediction model is a linear-expression of turn down temperature with parameters
identified as influencing contributors towards heat transfer

mechanism. A Computational Fluid Dynamics (CFD) based analysis is conducted for
a complete process cycle of the ladle to identify these influencing parameters. CFD
simulations are further performed by varying the identified parameters to impart
sensitivity to the data and obtain a trend of the identified parameters. A plant scale
experimentation of the developed module exhibits a small variation in the band of +
10°C with actual turn down temperature in 92% of the cases.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a Process route of a ladle cycle.
Figure 2 shows schematic representations of ladle operations in the process
route of ladle.
Figure 3 shows a sectional view of industrial scale ladle.
Figure 4 shows a liquid steel thermal profile predicted by CFD model according to
the invention.
Figure 5 shows a liquid steel thermal profile for different slag layer thicknesses.
Figure 6 shows liquid steel thermal profile for different Tapping temperature.
Figure 7 shows variation of liquid steel temperature with time for different ladle
life.
Figure 8 shows variation of hot face temperature green ladle and ladle in
circulation after at least 50 heats.
Figure 9 shows plant trial results of turn down temperature prediction model.
Table 1 shows chill Factor of Alloys.
Table 2 shows coefficients and constants of equation for turn down temperature.

DETAILED DESCRIPTION OF THE INVENTION
A ladle completes its process cycle through at least three different routes named as
Direct, LF and RH. Direct route of a ladle is more prone to the problem of high super
heat due to time limitation. Hence, the applicability of the disclosed invention is
more useful for the ladles passing through direct route. Computational fluid
dynamics (CFD) analysis is conducted for all the direct route processes to develop
comprehensive understanding of ladle operations in this route. Figure 1 shows a
process cycle of a ladle in direct route. The schematic description of the
phenomenon taking place in the ladle through this route can be seen from figure 2.
The brief description of these processes is given below:
Green Ladle pre-heating: Green ladle is a ladle, which is included in the ladle
process cycle for the first time. This ladle is pre-heated up to hot face temperature
of 1000°C, before being sent for tapping. The phenomenon of pre-heating takes
place for approximately 10 hrs and is one of the important steps in the ladle cycle.
Tapping: The next step in the ladle cycle is tapping. The ladle after attaining
required hot face temperature is sent for tapping. In this process, the molten steel
from the BOF vessel is poured to the heated ladle and ferroalloy additions are made
in the ladle.
OLP: The online purging is the next process in the cycle of a ladle. The molten steel
in the ladle is purged to attain uniform temperature and chemistry at this process.
Ferroalloy additions are also made during purging to attain required composition of
steel.
Holding Period: This is the time period between end of Online purging and start of
teeming. During this period the ladle is kept on hold. The ladle cover is placed

on the ladle during this period. However, the ladle can be without the cover for
some time especially during transportation.
Teeming : Teeming is defined as the phenomenon during which the molten steel is
poured from the ladle to the mould through a tundish in a continuous casting
process. In this process, the molten steel is flowed in the tundish through the ladle
nozzle.
TAT : The emptied ladle is cleaned and repaired to prepare for next tapping. The
time spent during these processes is defined as turn around time (TAT). The
continuous heat losses from refractory walls take place during this period.
An industrial scale ladle considered in the present invention for thermal analysis can
be seen from figure 3. Without de-limiting the scope of the invention, an exemplary
embodiment, a ladle is of conical shape with height of 4.56m, with an outside
diameter of 3.99 m at the top and 3.45 m at the bottom. The ladle is filled with
molten steel up to the height of 3.41m from inside bottom wall, equivalent to 160
tonne. The side wall of the ladle with a thickness of 0.3 m consists of at least five
layers of different materials. The material used and their thickness is described in
figure 3. The specifications of ladle are provided to better understand the process of
the current invention and should not be construed to limit the scope of the
invention.
A relationship was established by governing mathematical equations for all the
processes described above. The equations are then solved for a computational
domain of the ladle. The drop in temperature is calculated based on the chill factor
as mentioned in Table 1. CFD simulations is further performed by varying

different parameters to study their sensitivity in respect of liquid steel temperature
drop. The CFD analysis of the ladle operations in direct route is briefly described
below:
Prediction of Liquid steel thermal profile in ladle through direct route: The thermal
profile for molten steel during tapping to OLP and then to the end of the holding
period is generated through CFD simulation. The temperature drop of the molten
steel for addition of ferroalloy is also considered in the simulation. Figure 4 shows a
plot of steel temperature with time for various stages of the ladle. The linear
variation of the temperature with time can be observed from figure 4.
Effect of slag thickness on liquid steel temperature drop: The thickness of the slag
layer is considered to be one of the important parameters for reduction of the heat
loss at the top surface. Hence, simulations are performed for three different
thickness of the slag layer. Figure 5 shows a variation of steel temperature with time
for three different slag layer thicknesses. Though, the slag layer has an effective
role in control of heat losses.
Effect of tapping temperature on temperature drop of molten steel: The initial
temperature gradient between the molten steel and refractory walls depends upon
the tapping temperature. A variation in tapping temperature is assumed to have a
role on the heat losses taking place in the molten steel. The simulation for the whole
cycle of the ladle is, therefore performed by varying the tapping temperature. Figure
6 shows the variation of steel temperature with time for different tapping
temperature. No significant change is observed in the trend of the plot. The minor
variation in the net drop of temperature is noticed during this period.

Effect of ladle life: Ladle life is one of the important parameters to be considered for
estimating temperature drop of the molten steel. The refractory of the ladle gets
eroded with increase in the ladle life. The reducing thickness enhances the
heat transfer from hot faces to steel shell. The simulation is performed for five
different life of a ladle. These are 15, 30, 45, 60 & 75 Heats. Figure 7 shows the
variation of steel temperature with the time (from tapping start to end of holding
period) for different life of ladles. However, there is no relation between increase in
temperature drop with ladle life. The comparison of these cases with green ladle can
also be seen from figure 7. The trend of the curve in figure 7 is similar for all the
cases. However, the presence of comparatively high initial refractory temperature
leads to low temperature drop inside the green ladle. Thus, it can be derived from
these plots that the role of ladle life in relation to molten steel temperature is
insignificant.
Effect of turn around time: As the Ladle gets engaged for a considerable amount of
time in slag dumping and repairing before going for next tapping, the heat loss from
the refractory walls continues during this period and hence the temperature of the
ladle walls keeps falling. Figure 8 shows a plot of hot face temperature with TAT for
various zone of the ladle. The plot also presents a comparison between a green
ladle and a ladle in circulation. Though, the temperature drop after 90 minutes of
TAT becomes minor but still significant.
Empirical expression for prediction of turn down temperature: CFD analysis of the
ladle operations resulted in producing comprehensive data about the liquid steel
thermal profile. The data from CFD simulation are used to calculate the turn down
temperature for developing an effective super heat control mechanism. The linear
expression for the turn down temperature is developed through a

regression analysis of the .CFD data, and the chill factor given in Table 2, is
incorporated. Eqn. 1 presents this expression of the turn down temperature.
Predicted Turn down Temperature = Liquidus temperature +al* (Turn Around time)
+ a2* (Total time) + a3* (Purging duration) + a4* (casting duration) + a5*(femn)
+ a6*(Simn)- a7* (Aluminum) + a8* (line) + aO + S (1)
Here,
Predicted Turn down Temperature (in °C)
Liquidus temperature (in °C)
Total Time : Estimated time (in minutes) between tapping start to casting start.
Turn Around Time: Time (in minutes) spends in repairing and slag dumping in
previous heat of ladle.
Purging duration: Estimated Purging duration (in minutes) of current heat.
Casting Duration: Estimated Casting duration (in minutes) of current heat.
Aluminum: Amount of Aluminum addition (in Kg.)
Femn: Amount of ferromanganese addition (in Kg).
Simn: Amount of silicomanganese addition (in Kg).
Lime: Amount of lime addition (in Kg).
S: Desired super heat at the caster for a current heat (in °C).
The value of coefficient aO to a8 of eq. 1 depends upon variability of practices in a
given operational set-up. The range of these coefficients can be seen from Table 2.
Table 2 provides values of coefficients applicable for 160 tonne ladle.
Example:
The developed method and equation 1 were used to calculate the turn down
temperature. The results of plant trial can be seen from figure 9. The trial is done
for 50 heats of direct route and 92% of the predictions show a variation of ±10°C in
comparison with the actual turn down temperature.

The developed method is very useful in reducing the energy losses due to
overheating. Also, since turn down temperature can be calculated with good
accuracy, the process results in controlling the steel quality in turn.

WE CLAIM :
1. A method for controlling the super heat during casting, the method
comprising:
calculating turn down temperature, wherein the turn down
temperature is calculated based upon the equation 1;
Turn down Temperature (in °C) = Liquidus temperature (in °C)
+al*(Turn Around time) + a2* (Total time) + a3* (Purging duration)
+ a4* (casting duration) + a5*(femn) + a6*(Simn) - a7* (Aluminum)
+ a8* (line) + aO + S (1)
Total Time: Estimated time (in minutes) between tapping start to
casting start.
Turn Around Time: Time (in minutes) spent in repairing and slag
dumping in previous heat of ladle.
Purging duration: Estimated Purging duration (in minutes) of current
heat.
Casting Duration: Estimated Casting duration (in minutes) of current
heat.
Aluminum: Amount of Aluminum addition (in Kg.)
Femn: Amount of ferromanganese addition (in Kg).
Simn: Amount of silicomanganese addition (in Kg).
Lime: Amount of lime addition (in Kg).
S: Desired super heat at the caster for a current heat (in °C)
al-a8: are coefficients and depend upon variability of the practices
followed in a given operational set-up.

2. The method as claimed in claim 1, wherein the 92% of the turn down
temperature calculations show a variation of ±10°C in comparison with the
actual turn down temperature.

ABSTRACT

The invention relates to a method to maintain optimum super heat during steel
casting based on an accurate prediction of turn down temperature. The current
invention proposes a novel method of using turn down temperature as a controlling
variable to maintain desired super heat during casting. The invention can be used
for predicting turn down temperature by considering all the operations happing in
the route of ladle.