FIELD OF THE INVENTION
This invention relates to a single strand tundish that is used in steelmaking
operation. More particularly, the invention relates to a method of operating a
tundish at a maximum operating level of molten steel therein.
BACKGROUND OF THE INVENTION
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In a process of continuous casting of steel, molten steel is poured from a ladle
into an intermediate vessel, known as a tundish, and from the tundish into a
continuous casting mould. Other than buffering the batch operation into a
continuous one, the tundish also plays an important role in reducing unwanted
non-metallic inclusions as; the steel passes through the furnitures of the tundish,
for example, a variety ofibaffles, dams, weirs and impact pads positioned in the
tundish. In this context, a baffle acts as an obstruction to steel flow extending
from the floor of the tundish to above the uppermost level of the molten steel,
wherein a dam acts as an obstruction protruding upwardly from the floor of the
tundish and over which the steel must flow. A weir is an obstruction protruding
downwardly into the molten steel and under which the steel must flow. An
impact pad, made of anerosion-resistant material, is placed on the flow of the
tundish. It has a base to receive an incoming stream from the ladle, and a
sidewall extending upwardly along the periphery of the base. The base of the
impact pads has a surface shaped to receive and reverse the direction of fluid
flow generated by the incoming ladle stream. Baffles, dams, weirs and impact
pads are individually andicollectively known as tundish furniture.
Depending on the shape and size of a tundish, and desired metallurgical
performance, several furniture sets can be configured. However, adaptability of
different furnitures have their own pros and cons, for example, increased cost
and maintenance, low metallurgical performance, more turndown time.
Therefore, selection of the peak metallurgical performance of a tundish including
the most suitable type of furniture are the pre-requisities to achieve the best
production at lower cost and maintenance. The efforts were made to have a set
of furniture to match the best in class performance. The ideas were drawn from
various existing tundish furniture and a systematic study was undertaken for the
tundish furniture to achieve a simple design.
Indian Patent IN teaches, an improved device for continuous casting of steel
which comprises of a container/ladle having an outlet (downstream entry). The
outlet is provided at one side of a tundish at a distance in the range of 1/12 to
1/4 from one side of the end wall of the said tundish. The tundish having baffle
comprising multiple holesrof diameter ranging from 5 to 15 mm., placed at a
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distance of 1/12 to 1/2 of the length of the tundish from said outlet. The tundish
is provided with multiple outlets.
EP0636439 describes a baffle for directing the flow of molten metal in a
metallurgical vessel comprises a plate with many holes or openings which pass
through the plate, some of which have fluted edges to their side walls. The flutes
are defined by alternate obstructive peaks and valleys whilst the axis of the holes
may be normal to the plate or slanted at an angle.
US5246209 teaches a tundish having first and second flow control walls which
define a flow receiving space. A plurality of outlets are located in the bottom of
the tundish and toward the front thereof. Each flow control wall includes a
plurality of openings located closer to the back of the tundish than toward the
front and located closer to the bottom of the flow control wall than the top
thereof.
US5064175 discloses a method and devices for removing alumina and other
inclusions from steel contained in tundishes. According to this invention, molten
steei in tundishes can be contacted with high surface area ceramic shapes which
remove the alumina and other impurities contained in steel. Certain ceramic
shapes, in particular tundish baffles, having a large surface area which acts as
alumina traps for molten steel contained in tundishes are also disclosed.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved single
strand tundish in a continuous casting process.
Another object of the invention is to propose an improved single strand tundish
in a continuous casting process, which is enabled to restrict pour zone
turbulence, flow pattern and residence time distribution parameters for steady
state casting.
A further object of the invention is to propose an improved single strand tundish
in a continuous casting process, which eliminates heat loss and inclusion
removal.
SUMMARY OF THE INVENTION
Accordingly, there is provided a single strand tundish having an outlet in its base,
the outlet being longitudinally spaced along the tundish from a pour zone. A
designed baffle placed at a longitudinal distance from the pour zone. The baffle
comprises plurality of horizontal holes configured at specified distance from each
other to have a controlled flow that provides a plug volume allowing the inclusion
to float up. A baffle brick may readily be chosen by the average skilled man
of the art from variety of available ones made of erosion resistant material well
known to its fabricators. A baffle restricts the pour zone turbulence near inlet by
virtually dividing the tundish into two zones. At the same time, the baffle cuts-off
meniscus ensuring that no overlying slag moves from the inlet to outlet region of
the tundish.
According to a particular characteristics of the invention, the baffle has twelve
holes placed in three rows each row having four holes to allow passage of the
molten steel from the inlet to outlet. The diameter of the holes is around 15.5%
of the tundish base width to maximize the total pass area and holes were
distributed uniformly as per this dimension. The passage through the baffle is
straight and horizontal. The pitch between any two holes is equal to the diameter
of a hole, wherein the first hole starting from base is configured at a location
being half of the pitch diameter.
According to a particular characteristic of the invention, the distance between the
inlet and baffle may vary from 15 to 30% of the longitudinal distance between
the inlet (pouring point) and tundish outlet.
According to another characteristic of the invention, the baffle height extends
beyond the liquid steel height at steady state in the tundish. The baffle extents
full width of the tundish.
According to yet another characteristic of the invention, a furniture in the form of
a baffle is provided for the tundish.
Preferably, the tundish has one outlet longitudinally spaced on one side of the
pour zone.
Preferably, the shape of the baffle outer walls are smoothly inclined towards
inward to have sufficient strength at its base.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Embodiments of the invention are now described by way of example only with
reference to the accompanying drawings in which:
Fig. 1 is a diagrammatic illustration in longitudinal cross-section of a tundish
showing the effect on steel flow with the furniture used in the present invention;
Fig. 2 is a similar view to Fig. 1 showing the effect on steel flow of the best in
class furniture of prior art;
Fig. 3 is a baffle for use in the invention;
Fig. 4 is a residence time distribution graph of the prior art tundish furniture;
Fig. 5 is a residence time distribution graph of the tundish as per present
invention;
Fig. 6 is a velocity magnitude profile of the tundish meniscus as per the present
invention;
Fig. 7 is a comparison data for Fig. 6 and 8 velocity magnitude profile;
Fig. 8 is a velocity magnitude profile of the tundish meniscus of the prior art
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tundish furniture;
TABLE 1 Comparative parameters for both tundish of prior art and the invention.
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DETAIL DESCRIPTION OF THE INVENTION
A best known prior art case is described here: The molten steel is poured into

the tundish through the shroud submerged in the molten steel in the tundish.
The flow of molten steel into the tundish creates enormous turbulence around
the pouring point. To minimize turbulence around pouring point a set of dam-
weir has been put as depicted in Fig. 2. This dam-weir combination virtually
splits the tundish into two parts retaining most of the turbulence confined within
the first part itself whereas a dam has been provided near the outlet to avoid
short-circuiting to the outlet along bottom.
As per the invention, a designated baffle is provided between inlet and outlet. It
would be shown with example that the furniture set-up as per invention was
found to be at par than that of the best prior art case.
The desired fluid flow characteristics like bulk circulation through top surface,
surface directed flow etc were retained in this case (Fig. 1 and 2). This is
reflected in Residence Time Distribution (RTD) analysis (Fig. 4 and 5) as well.
The switch over from double peak for the prior art to single peak for the present;
invention indicates elimination of short circuiting flow within the tundish. As.
detailed in Table 1, Plug Volume fraction (PV) was similar for the two cases while
Dead Volume fraction (DV) is increased to 15% from 9% due to recirculation:
patterns forming at the top near the baffle. Minimum Residence Time (MRT) and
Average Residence Time (ART) are at par with best-in-class case. Though max
surface velocity is higher than that of the best known prior art, but gets reduced
to safe limit near the outlet (Fig. 6 and 8).
The furniture set-up as per the present invention is a simple alternative to the
best in class furniture used in prior art.
In Fig. 1, a tundish 1 as per the invention has a floor 2 and end walls 3. A baffle
4 is located on floor 2 at certain distance from the inlet shroud 5.
In Fig. 2, a tundish 9 as per the best in class has a floor 10 and walls 11. A dam-
weir combination 12 is located after shroud 13.
A shroud 5 from a ladle (not shown) is positioned so that steel poured into the
tundish at one side of the tundish. The tundish has an outlet region 6 spaced
towards longitudinal end of the tundish, the actual outlet in the base of the
tundish not being shown.
The arrows show the directions of steel flow, as derived by modeling of actual
tundish. The surface directed flow zones 8, 16 have been revealed.
Again in Fig. 2, the steel flow patterns are indicated by arrows as derived by
modeling of actual tundish.
Overall, the steel flow pattern is at par / similar to the best in class tundish
furniture.
The baffle 4 shown in Fig. 3 has a base 22 with an inner surface 18 to face
vigorous incoming stream of molten steel. The shape is same as inner
dimension of the tundish i.e. trapezoidal and fits well within the tundish with
sidewalls 17. The upstanding sidewalls 17 join inner walls of the tundish tightly.
The baffle has numerous straight horizontal openings 19 running through the
material from inner surface to outer surface 20. The openings 19 are uniformly
placed, being cylindrical, and these openings 19 are aligned to extend in the
longitudinal direction of the tundish. The outer surface 20 is provided to give the
baffle a suitable thickness for strength and joining with inner tundish walls. The
inner, outer surface and sidewalls end in a top surface 21, it is raised beyond
steady state operating level of the tundish. In the Figure, a symmetrical part of
the baffle is shown up to a symmetry 7.
Velocity magnitude at the meniscus 23 of tundish provided with the furniture as
per the invention is shown in Fig. 6. Shroud position 25 is as depicted in the Fig.
Velocity magnitude at the meniscus 24 of tundish of the best in class furniture is
shown in Fig. 8. Weir position 26 is a depicted in the Fig.
ADVANTAGES OF THE INVENTION
It will be understood that the type of tundish furniture set arrangement in
accordance with present invention has many advantages, for example:
1. The designated baffle in accordance with present invention ensures
required residence time distribution. Clearly, a good residence time
increases inclusion removal from the steel. A low level of dead volume
fraction reduces the number of static flow regions of the tundish and, in
turn achieves temperature homogenization and inclusion removal.
2 The fluid flow in the tundish equipped with the designated baffle
ensures that the surface directed flow is at steady state operation hence
maximum contact with overlying slag / flux layer is made possible to
maximize inclusion capture. The fluid flow also avoids short circulating of
incoming liquid steel to outlet of the tundish.
3. The metallurgical performance of the furniture set surpasses the
prior furniture namely, a dam-weir combination.
4. Another advantage of the invention is lower cost. The comparable
cost of such furniture is much lower than that of the prior art.
5. A still another advantage of the invention is the reduction in steel
re-oxidation due to reduced turbulence in the flow after the designed
baffle. The baffle cuts down any meniscus disturbances that may be
coming from inlet turbulent stream to maintain the downward top surface
calm and stable.
6. Yet another advantage of the invention is low level of ladle slag
exiting from the tundish outlet.
Moreover, the invention allows to maintain best performance of the tundish with
a designated baffle furniture, even after eliminating multiple sets of tundish
furniture.
To enable the invention to be fully understood, the furniture set and its
characteristic will be described hereinafter by way of non-limiting examples.
WE CLAIM:
1. A method of operating a tundish at a maximum operating level of molten
steel therein, the tundish comprising a floor having an outlet, a pour zone, and
side walls extending upwardly from the floor, the side walls extending above the
maximum operating level of molten steel in the tundish; a designated baffle
positioned on the tundish floor adjacent the pour zone, the baffle comprising a
plurality of horizontal holes uniformly configured with cylindrical in shape and
aligned in a longitudinal direction of the tundish; the method comprising the
steps of:
(a) positioning the designated baffle in the tundish on the floor adjacent an inlet
at distance of 15-30% of the longitudinal distance between an inlet shroud and
the outlet, and baffle extending upwardly from the floor beyond the maximum
operating level of molten steel in the tundish;
(b) pouring molten steel in a stream into the tundish pour zone so that the steel
impacts the tundish bottom and rigorous streams touches upon an inner surface
of the baffle with partial quantity exiting through openings in the baffle; and
(c) configurating the openings in baffle to have maximum passage area to
ensure an optimum pitch in between to have sufficient strength of the baffle, the
hole diameter of the baffle being maintained at 15.5% of the tundish base width.

The invention discloses a single strand tundish with furniture for efficient
molten metal flow characteristics which has an outlet in its base. The outlet is
spaced longitudinally of the tundish from a pour zone. The pour zone is
positioned to receive a stream of molten steel from a ladle. A baffle (furniture)
is provided on the floor of the tundish near the pour zone, the baffle has
numerous holes to allow passage of molten steel from the pour zone towards
outlet smoothly. The holes are cylindrical in shape, placed uniformly and
aligned to longitudinal direction of the tundish. The baffle is positioned at a
distance from inlet of 15-30% of the longitudinal distance between an inlet
shroud and the outlet. The holes are configured to have maximum possible
passage area with an optimum level of overall baffle strength. The diameter of
the hole is kept at about 15.5% of the tundish base width. The baffle extends
upwardly from the tundish floor beyond the maximum operating level of steel
in the tundish.