venkatersan_foseco
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venkatersan_foseco

Disciplina:Lingotamento Contínuo de Aços29 materiais60 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 – 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 – 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 – 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’99 – Jan’00.
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