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Levenspiel16.

4.3 F-Curve – Grade change study

F-Curve study gives an idea of the nature
of fluid flow with respect to casting of two
different grades in two consecutive heats
in the same tundish. Through this study it
is possible to get an estimation of the
transition zone. These tests are conducted
at different draining levels with fill up rate
upto the steady state being twice that of
the steady state. For Plant – A study was
carried out for drain levels of 18 Tons & 15
Tons and for Plant – B it was 20 Tons and
15 Tons.

In the F-Curve experiment water is filled to
tundish working level and both outlet and
inlet are closed. Subsequently 20cc of dye
is homogenously mixed with the entire
volume of water (to represent old steel).
Then the outlet is opened at steady state
flow rate and the coloured liquid is drained
upto a specific level and then fresh water
(new steel) from inlet is started at double
the steady state flow rate to fill up up to
the working level. After the working level is
reached the inlet flow is brought back to
original steady state flow rate and
experiment is continued for duration of 40.
The concentration is measured at the
outlet at every 5sec time interval and the
data is directly taken up by the computer
to give a concentration ratio vs. time curve
(F-Curve). This curve gives the time interval
for transition mixes of
.10%-90%
.20%-80%

The 1st case (10%-90%) indicates the time
elapsed between 10% & 90% of new steel
at the outlet. This results can be followed if
the acceptance level of chemistry com-
position in the final slab is 90% of the
ladle chemistry. It should be mentioned
that 10% of new steel implies 90% of old
steel and vice versa. Similarly the 2nd case
results can be followed if the acceptance
level is 80%.
The above studies were carried out for
configurations given in Table 4.
For both cases existing system was
compared with configurations of
TURBOSTOP giving best possible MRT.

4.4 Slag Emulsification Study at Ladle
Change Overs

This experiment was done to understand
the extent of emulsification of top layer of

Table 3. Parameters for comparative analysis

Table 4. Configuration details for F_Curve Study

Table 5. Experimental results of RTD Curve study

tundish slag and entrainment during ladle
change over period for drain levels of
15Tons.
In this experiment mineral oil (representing
slag) is put on the top of water (repre-

senting liquid steel) and the tundish is
drained upto 15 Tons level. Subsequently,
inlet flow is started at double the steady
state speed and continued till the working
level is reached. In this time the duration
slag metal mixing is observed and video

4

Minimum Residence Time This is the time when concentration of dye at the outlet is 1% of total dye injected
(This represents the time taken for a fluid element to reach the nozzle after it enters
the tundish at steady state)

Plug Flow The flow in which all fluid through the tundish travel at nearly the same velocity
(This corresponds to the volume fraction of steel which moves in a laminar fashion
with no back mixing)

Dead Flow The flow of steel in the tundish, which is nearly stagnant.

Mixed Flow Turbulent flow in which there is complete mixing.

Peak Concentration The maximum concentration point in the curve.

Peak Time The time at which the peak concentration is reached.

DescriptionParameter

A

G

H

I

SymbolDescriptionConfigurations

Plant - A

Brick Dam (Existing System)

TURBOSTOP Only

TURBOSTOP & Brick Dam

TURBOSTOP & Short Dam with holes

BD

TS

TS+BD

TS+SD1/holes

A

F

H

Plant - B

Striker Pad & Dams (1&2) (Existing System)

TURBOSTOP Only

TURBOSTOP & Short Dam with drain holes

SP+D1+D2

TS2

TS2+SD1/holes

A–

B–

C–

D–

E–

F–

G–

H–

I–

J–

A–

B–

C–

D–

E–

F–

G–

H–

I–

24.59

24.77

28.56

27.89

26.54

27.89

19.97

20.36

18.06

17.19

24.19

27.19

25.82

16.80

17.85

22.78

25.84

26.10

26.10

6.42

13.87

11.20

11.22

9.65

11.22

23.62

22.22

30.19

30.65

18.89

10.95

14.24

23.53

23.00

22.18

18.88

13.41

18.34

68.99

61.36

60.24

60.89

63.81

60.89

56.41

57.42

51.75

52.16

56.92

61.86

59.94

59.67

59.15

55.04

55.28

60.49

55.56

0.0642

0.1387

0.1120

0.1122

0.0965

0.1122

0.2362

0.2222

0.3019

0.3065

0.1889

0.1095

0.1424

0.2353

0.2300

0.2218

0.1888

0.1341

0.1834

20

44

35

35

30

35

74

70

95

96

116

67

88

145

141

136

116

82

113

0.4493

0.5068

0.4478

0.4380

0.4504

0.4540

0.5960

0.6342

0.6307

0.6339

0.5529

0.4845

0.5146

0.6869

0.6709

0.5340

0.5172

0.4817

0.4626

0.9887

0.9961

0.9185

0.9275

0.8785

0.9403

1.3359

1.2510

1.2893

1.3451

1.0478

0.9407

0.9402

1.1077

1.1660

1.2144

1.1281

0.9340

1.0613

Configurations

Plant - A

Plant - B

Dead
Vol(%)

Plug
Vol(%)

Mixed
Vol(%)

MRT-Min.
Residence

Time

Absolute
Value of
MRT(sec)

Peak
Time

Peak
Conc.

BD

D1

W(1650)+BD

W(1650)+D1

W(1900)+BD

W(1900)+D1

TS

TS+BD

TS+SD1/holes

TS+HD1

SP+D1+D2

SP+D1+B1

SP+B1+D2

TS

TS+SD1/holes

TS+HD1

TS+HD2

TS+B1/320

TS+B1+D1

ecorded. Static photo graphs are presented
in Fig 17. (each photograph was taken just
after the new ladle is opened). This
experiment was carried out for Existing
System and only TURBOSTOP for both the
plants.

5. Results

5.1 Steady State Casting – C-Curve
Study

Table 5 shows the results for C-Curve
Study carried out for the above mentioned
type of tundish

5.2 Grade Change Study – F-Curve

Table 6 gives the result of F-Curve Study
against flow modifier nomenclature for
both type of tundish.
In order to estimate the tonnage of
Transition Zone during mixed grade casting
the following equation was used for each
case

Model Time(Sec) = Time Difference x Theta

Actual Time in the plant(min) = (Model
Time/(Scale factor)1/2)/60

Transition Zone Tonnage (Tons) = Actual
Time in plant(min) x Casting Rate(tons/min)

5.3 Slag Emulsification Study

Fig 5 gives comparative photographs for
the existing system as well as only
TURBOSTOP for Ladle Change overs at 15
Tons . The photographs are taken just after
the ladle opening.

6. Discussion

6.1 Steady State Fluid Flow Characteristics

Fig 6 gives a graphical representation of
the Absolute Minimum Residence
Time(MRT). The graph shows

1. The effieciency of properly designed
turbulence suppressing pad
TURBOSTOP in substabtial improvement
of residence time of steel in the tundish.

2. Mere obstacles in the path of the steel
flow in the tundish by means of baffles,
weirs or dams dose not necessarily
mean result in improved residence time.

3. In terms of position of Weir/Baffle closer
to the shroud better is the results.

4. Incorpoarating Baffles along with
TURBOSTOP substantially reduce
residence time.

5. In case of Plant-A the best MRT is
obtained when TURBOSTOP is used
along with a high dam where as in case
of Plant-B only TURBOSTOP was the
best. Infact in case of Plant-B MRT
progressively decreased with the
increase of dam height.

Table 6. Experimental results of F-Curve Test

5

Fig 5. Photographs of Slag Emulsification at Ladle Change Overs

Fig 6. Minimum Redidence Time movement for different flow modifier configurations.

A–BD

G–TS

H–TS+BD

I–TS+SD1/holes

0.8410

0.6464

0.5656

0.5925

0.7185

0.4297

0.5788

1.1914

0.9211

0.9697

0.8833

1.1290

0.9196

0.9893

0.6685

0.6626

0.5554

0.5281

0.6199

0.4517

0.5174

0.9920

0.8996

0.8412

0.7760

0.9524

0.8006

0.9089

A–SP+D1+D2

D–TS

E–TS+SD1/holes

Plant - A

Plant - B

Plant - B

Configuration A Configuration E

Drain Level 18 Tons

10/90 Time Diff.20/80 Time Diff. 10/90 Time Diff.20/80 Time Diff.

10/90 Time Diff.20/80 Time Diff. 10/90 Time Diff.20/80 Time Diff.

Drain Level 15 TonsConfigurations

Drain Level 20 Tons Drain Level 15 TonsConfigurations

Plant - B

Configuration A Configuration G

Plant - B

200

150

100

50

0

Plant - A

Configurat ion

Configurat ion

T
im

e
 (

se
c)

T
im

e
 (

se
c)

150

100

50

0
A B C D E F