8 pág.

# venkatersan_foseco

DisciplinaLingotamento Contínuo de Aços30 materiais70 seguidores
Pré-visualização5 páginas
```steel of wide
chemistry variations were casted in the
same tundish (Paul Rasmussen5 for Dofasco
Inc., Canada). Studies done in steel plants
like AK Middletown, OHIO USA, Sollac,
France, Nucor Hickman, USA. US Steel
Gary, USA, Algoma, Canada has also
revealed similar trends.
Recent trends, as discussed above, do
make it imperative to study in details the
fluid flow pattern for every plant\u2019s tundish
in order to design a custom made flow
modifier system. This will enable the steel
makers to optimise steel flow pattern in
the tundish in order to derive maximum
benefit.
2.3 Physical (Water) and Mathematical
Modelling
Fluid flow in steelmaking system has been
the subject of extensive study in recent
years. The approaches used included both
physical and mathematical modeling.
Mathematical predictions of flow pattern6-9
has gained wider popularity in recent years
with the advent of improved numerical
procedures and refined turbulence models.
When augmented by experimental work,
mathematical modelling can be useful in
explaining or verifying the observed results,
and for providing guidelines for experi-
mental design.
The flow of liquid steel in a continuous
casting system cannot be observed directly.
The application of the technique of
mathematical modelling is complicated by
the occurrence of intense turbulence and
biphasic flow in certain regions of the
system. Thus, physical modeling using
water at room temperature (due to
kinematic viscocity similarity with liquid
steel at 1600°C) as a medium is finding
widespread application for the study of
fluid flow in the tundish, especially in
designing tundish flow modifiers.
To attain similarity between two flowing
systems the flowing four conditions must
be met10-13
1. Geometric Similarity \u2013 the ratio of length
in one with the corresponding one of
the another is constant. This ratio is
termed as scale factor
2. Kinematic Similarity \u2013 the streamlines in
one system are geometrically similar to
the streamlines in the other system.
3. Dynamic Similarity \u2013 the magnitude of
forces at corresponding locations in
each system are in a fixed ratio.
4. Thermal Similarity \u2013 the dimensionless
numbers involving heat transfers are
equal in both systems. Thermal
similarity is not important when
considering flow within a tundish since
forced convection in these regions is
likely to be predominant.
2
Fig 3. Schematic diagram of various flow modifier position for Plant - B
Steady State Liquid Metal Level
1200 mm
Dam - 2 Dam - 1
Steady State Liquid Metal Level
320 mm
Baffle Dam - 1
Steady State Liquid Metal Level
320 mm 1000 mm
Dam - 1 Baffle
1000
mm
Steady State Liquid Metal Level
TURBOSTOP at 40 mm from end wall
TURBOSTOP at 40 mm from end wall
TURBOSTOP at 40 mm from end wall
TURBOSTOP at 40 mm from end wall
TURBOSTOP at 40 mm from end wall
Steady State Liquid Metal Level
Short Dam with drain holes
Steady State Liquid Metal Level
320 mm
180 mm
High Dam (1&2)
Steady State Liquid Metal Level Steady State Liquid Metal Level
Configuration - A Configuration - B
Configuration - C Configuration - D
Configuration - E Configuration - F&G
Configuration - H Configuration - I
320 mm
Baffle Dam - 1 Baffle
320 mm
Flow modifiers set-up studied for both type
of tundish is given in Table 2 and
schematic drawing showing positioning of
the flow modifiers is given in Fig 3 & 4.
4.2 C-Curve - RTD Curve Study (Steady
State)
C-Curve Study helps assess the flow
characteristics of steel in the tundish at
steady state casting condition with
different sets of flow modifiers. During the
experiment water is filled up to the
working level and then held at that level
with inlet and outlet flow remaining same
for a duration of 3theta (1 theta=one
tundish emptying time at existing flow
rate) to allow the bath to stabilise.
Subsequently a pulse of dye is injected as
tracer. The dye concentration is monitored
at the outlet at every 5sec time intervals.
Computer directly acquires the data and
concentration curve (C-Curve) is generated
online.
3. Reduction of Slag Emulsification during
4. Reduction of turbulence near the pouring
area \u2013 Minimise Red-Eye formation
Two type of slab caster tundish was
studied with the above primarily objective
which are
.Flat Bottom Tundish \u2013 Plant A
.Well Shaped tundish \u2013 Plant B
Table 1. shows the values of different
parameters used for water modelling (all
conversions are done using Froude number
similarity & Liquid Steel: Water density ratio
of 7:1)
4. Water Modelling Experiments
Done
4.1 Set-up
A 1/3rd & 1\u20442 scale tundish model for Plant
A & Plant B respectively was taken up for
Water Modelling Studies. Red colour liquid
food dye having similar density as that of
water was used as a tracer for both C-
Curve and F-Curve studies. The outlet dye
concentration was measured with the help
of an optical probe at an interval of 5 secs.
The concentration data is acquired online
by a computer through an data acquisition
set up while the experiment is going on. A
special software simultaneously plots the
respective curves (C-Curve & F-Curve) using
the online concentration values. At the end
of each experiment the computer
computes the values of key parameters
(e.g. Plug Volume %, Dead Volume % etc)
from C-Curve.
Table 1. Values of different parameters used for Water
Modelling Study
Table 2. Flow Modifier Set-up details
3
Fig 4. Schematic diagram of various flow modifier position
for Plant - A
Steady State Liquid Metal Level
626 mm
Brick Dam 250 mm Dam
Configuration - A & B
Steady State Liquid Metal Level
Weir
1650 mm
Configuration - C & D
Steady State Liquid Metal Level
Configuration - E & F
Steady State Liquid Metal Level
TURBOSTOP - 40 mm from end wall
Configuration - G
Steady State Liquid Metal Level
TURBOSTOP - 40 mm from end wall
TURBOSTOP - 40 mm from end wall
Configuration - H & I
Steady State Liquid Metal Level
Configuration - J
626 mm
Brick Dam 250 mm Dam
626 mm
Brick Dam 250 mm Dam
300 mm
Brick Dam / Medium Dam
High Dam -
75% of Liquid Metal Ht
300 mm
Weir
1900 mm
Theta (time taken to empty 1
tundish volume at above
mentioned casting rate)
Casting Rate 2.64 tons/min 2 tons/min24.19 lt/min of
water
50.51 lt/min of
water
Scale Factor (f) 1 11/3rd 0.5
Tundish Weight at steady state 24 tons 29 tons126.98 lt of
water
517.86 lt of
water
9.09 min 14.5 min314 secs 615 secs
Water Model
Study Value
Plant ValueWater Model
Study Value
Plant Value
Plant - BPlant \u2013 A
Parameter
A
B
C
D
E
F
G
H
I
J
A
B
C
D
E
F
G
H
I
SymbolDescriptionConfigurations
Plant - A
Plant - B
Brick Dam (Existing System)
250 mm Dam
Weir (1650 mm from shroud end wall) & Brick Dam
Weir (1650 mm from shroud end wall) & 250 mm Dam
Weir (1900 mm from shroud end wall) & Brick Dam
Weir (1900 mm from shroud end wall) & 250 mm Dam
TURBOSTOP Only
TURBOSTOP & Brick Dam
TURBOSTOP & Short Dam with holes
TURBOSTOP & High Dam, Dam ht - 75% steady state metal level
BD
D1
W(1650)+BD
W(1650)+D1
W(1900)+BD
W(1900)+D1
TS
TS+BD
TS+SD1/holes
TS+HD1
Striker Pad & Dams (1&2) (Existing System)
Striker Pad, Dam (1) & Baffle
Striker Pad, Baffle & Dam (2)
TURBOSTOP Only
TURBOSTOP & Short Dam with drain holes
TURBOSTOP & High Dam (1), Dam ht - 75% of steady state metal level
TURBOSTOP & High Dam (2), Dam ht equal to steady state metal level
TURBOSTOP & Baffle at 320 mm from the slope
TURBOSTOP & Baffle & Dam (1)
SP+D1+D2
SP+D1+B1
SP+B1+D2
TS
TS+SD1/holes
TS+HD1
TS+HD2
TS+B1/320
TS+B1+D1
Each test was also visually observed using a
video recorded and event recorded. Table 3
gives the parameters for which a com-
parative analysis is done for different sets
of flow modifiers.
The characterization of the flow for the
experimental RTD curves is carried out
using the methods of Sahai and Emi1 as
well as the principles presented by```