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venkatersan_foseco


DisciplinaLingotamento Contínuo de Aços30 materiais62 seguidores
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G H I J
A B C D E F G H I
20
116
67 88
145 141 136 116
82
113
44 35 35 30 35
74 70
9695
Abs Res T ime (sec)
Emulsified Slag
Minimum Slag
Emulsification
No Emulsified SlagEmulsified Slag
Table 7
Tundish
Insol Al
Levels
<=0.005
<=0.003
50.77
23.08
69.75
36.13
Norma
l T/D
(%)
Total
TURBOSTOP
(%)
0
10
20
30
20
18 Tons (20/80 Transition)
15 Tons (20/80 Transition)
18 Tons (10/90 Transition)
15 Tons (10/90 Transition)
24
16 16
22 33 23
14 13
20
14
21
13
19
21
33
18
28
13
27
13
23
17
29
15
26
16
20 Tons (20/80 Transition)
15 Tons (20/80 Transition)
20 Tons (10/90 Transition)
15 Tons (10/90 Transition)
T
o
n
n
a
g
e
T
o
n
n
a
g
e
Configurations Configurations
Plant - A Plant - B
A G H H H HI
0
5
10
15
20
25
30
35
6.2 Mixed Grade Casting
Fig 7 gives the mixed grade tonnage 
calculated using formula descriped earlier. 
The graph clearly shows
1. The substantial reduction transition zone 
with TURBOSTOP.
2. In case of Plant-A least transition zone is 
achieved in case of configuration I i.e. 
TURBOSTOP and short dam where as in 
case of Plant-B only TURBOSTOP when 
used gave the best results.
6.3 Slag Emulsification Study
Photographs in Fig 5 indicates
1. Severe slag/metal mixing with the 
existing systems in case of of the both 
the tundishes( because of oil getting 
broken up into fine droplets and then 
mixing with water) which continued 
even after the shroud was immersed. 
This will obviously lead to high oxygen 
pick-ups during changeover.
2. The above phenomenon was nearly 
suppressed with the use of TURBOSTOP 
which is likely to result in cleaner steel 
at change-over.
7. Actual TURBOSTOP usage in 
the plant \u2013 The Benefits
7.1 Plant - A 
Initially TURBOSTOP & Short Dam with 
holes giving the best results during physical 
modeling was tried. During trial few cases 
of nozzle choking at the start-up was 
observed which was primarily due to the 
position of preheating burners in the 
casting platform. The dam when placed at 
300mm from the nozzle center caused 
underheating of the side away from the 
dam towards the npzzle as the burner 
flame being obstructed by the dam. Due to 
the above problem the use of Short Dam 
with holes was discontinued and 
TURBOSTOP was used along with brick 
dam
.Steel Cleanliness with TURBOSTOP
The improvement in steel cleanliness due 
to usage of TURBOSTOP was analysed 
based on ther following parameters
Insoluble Alumina in the Tundish
This was again analysed under 3 para-
meters
1. Insoluble Alumina Levels in the Tundish 
where Ladle Insoluble Alumina was 
greater than 50ppm \u2013 More the 
conversions of Ladle Insoluble Alumina 
higher than 50ppm to less than 50 & 
30ppm indicates better floatation of 
Alumina (Graph 1)
2. Insoluble Alumina Levels in the Tundish 
where Total Aluminium Drop from Ladle 
to Tundish is less than or equal to 
20ppm. This study is done to see the 
effect of Alumina inclusion floatation 
independent of Aluminium addition 
time. If Aluminium in the Ladle is added 
at a proper time the it will have 
sufficient time to go into solution and its 
drop will minimize (Table 7)
Graph 1 indicates that Insoluble Alumina 
Levels in the Tundish are lower with 
TURBOSTOP compared to that of Normal 
Tundish of Brick Dam, where as Table 7 
shows a consistent increase in the 
percentages of heats cast with TURBOSTOP 
shows lower levels of Tundish Insoluble 
Aluminium in those cases where addition 
of Aluminium was done to give it sufficient 
time to go into solution.
Class 1 & 2 Distribution at specific 
sulphur ranges
Table 8 shows a comparative analysis of 
Class 1&2 at specified Sulphur ranges. It 
shows a consistent trend of increase of 
Class 1 in any specified Sulphur Range with 
TURBOSTOP Tundish and decrease of Class 2 
in specific Sulphur Range, which shows the 
improving capacity of TURBOSTOP 
tundishes to convert more of Class 2 into 
Class 1, which again can be attributed to 
better floatation of Oxide Inclusions 
(reasons explained above). 
.Reduction in Transition Tonnage during 
Mixed Grade Casting
1. 53 cases of Grade change casting was 
done out of which one was done 
between JVCM02 (C% - 0.38-0.40) & 
JVCM03 (C% 0.54-0.55) a combination 
which was done earlier using normal 
tundish with brick dam only. In case of 
Brick Dam a total slab of length 8.5mts 
was affected due to composition 
variation where as in case of TURBO-
STOP it is 6.3 mts inspite the change 
over taking place at higher tonnage (14 
tons instead of 10 tons for the normal 
brick dam tundish)
2. Out of 53 grade change done
a. 19 Cases (e.g.Low C to High Carbon). 
For most of these radical Grade changes 
the Transition was over in a single Slab 
of 8.5 Mts around 17 Tons.
b. 34 cases were like to like (i.e Low 
Carbon to Low Carbon etc)
c. In 10 cases out of above 53 2 times 
Grade Change has been done in the 
same tundish
Graph 1
6
Fig 7. Transition Zone tonnage during Mixed Grade Casting
<=0.005
P
e
rc
e
n
ta
g
e
T insol Al
<=0.003
Insoluble Alumina
Distribution in 
Tundish where 
Ladle Insol 
AL > 50 ppm
0.00
10.00
20.00
30.00
40.00
Normal Tundish %
Total Turbostop %
50.00
60.00
50.18
50.78
17.33
18.07
.When such condition of cancellation of 
incoming velocity vector is achieved it not 
only substantially increase the steel 
residence time but also enhance plug flow 
thereby resulting in reduction of trantion 
zone. It also helps in minimizing the slag 
emulsification phenomenon during ladle 
change overs thereby producing cleaner 
steel.
.Since every plant is different modelling 
study is absolute imperative before arriving 
7.2 Plant \u2013 B
In Plant B TURBOSTOP was used along with 
short dam with holes (Configuration E) 
although only TURBOSTOP was giving the 
best results in order to prevent metal 
freezing at start of cast.
.Reduction in Transition Zone During 
Mixed Grade Casting 
Verification of Mixed Zone Tonnage as 
predicted by F-Curve Study was done in 
plant duing the period of Dec\u201999 \u2013 Jan\u201900. 
To assess the transition length, drillings 
were taken from transition slabs at a 
distance of 1m. A total of 7 cases were 
tested with significant chemistry variations 
with different combinations of tundish 
weight, casting speed and slab width. The 
transition length obtained by drillings was 
then compared with the L-2 predicted 
legth for both Conventional and TURBO-
STOP Tundishes.Table 9 gives the transition 
slabs details which was assessed.
Based on chemistry analysis of the drilling 
samples it was seen while mixing two 
grades the starting although not shifting 
TURBOSTOP Tundish gave a saving in 
Transition Zone of upto 10% approx which 
is a definite indicator of improved plug 
flow in the tundish.
.Reduction of Slag Emulsification during 
Ladle Change Overs 
Physical Modelling indications of much 
reduced slag emulsification at Ladle 
Change Overs were verified in the plant by 
measuring Oxygen ppm, result of which is 
given in the graph 2 & 3 The findings of 
which are
1. The total oxygen ppm measurement 
indicates a marked improvement w.r.t. 
minimization of slag emulsification 
phenomenon during ladle change overs 
with TURBOSTOP system even with 
change over tonnage being lower.
2. During Steady state marked difference 
was not being observed in steel oxygen 
ppm levels in the tundish with either of 
the 2 systems.
8. Conclusion
Water Modelling study and subsequent 
trials in the 2 plants showed that
.The use of multible hole baffles and weir 
although improve the flow characteristics 
in comparison to no flow modifiers the 
extent of such improvements was far from 
desirable.
.Efforts of increasing the steel residence 
time in the tundish further and thereby 
enhancing the flow characteristics dose not 
always yield positive results.
.In order to increase the residence time 
beyond the limits of what being achieved 
with baffles and weirs suppression of 
incoming energy of the metal stream is 
necessary. This can