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Levenspiel16.
4.3 F-Curve \u2013 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 \u2013 A study was 
carried out for drain levels of 18 Tons & 15 
Tons and for Plant \u2013 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\u2013
B\u2013
C\u2013
D\u2013
E\u2013
F\u2013
G\u2013
H\u2013
I\u2013
J\u2013
A\u2013
B\u2013
C\u2013
D\u2013
E\u2013
F\u2013
G\u2013
H\u2013
I\u2013
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 \u2013 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 \u2013 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\u2013BD
G\u2013TS
H\u2013TS+BD
I\u2013TS+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\u2013SP+D1+D2
D\u2013TS
E\u2013TS+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