Details of Patenting for the process invention on Technology for increasing bloom caster tundish
life by specially shaped impact pad'.
1. Field of Invention:
Continuous casting of steel through fluid flow modification in tundish.
2. Description of known art:
The three-strand bloom caster at 6 hilai Steel Plant is unique in itself since it has been converted
from a Slab Casting machine to a bloom casting machine. The distance between each of the
three strands (# 1, #2, #3) is about 575 mm and metal pours into the tundish from the ladle
between #1 and #2 strands. The liquid steel from the tundish is distributed into the three moulds
strands through openings in the tundish. To control the flow of liquid steel in the water-cooled
copper moulds, stopper rods made of refractory material are used above the three openings in
; the tundish. Two dams on either side of the pouring stream are installed to control the erosion of
\stopper rods.
3. Drawback of the known art:
Due to the close proximity of the two stopper rods (steel outlets) to the incoming ladle stream
erosion of the stopper rods take place in the tundish restricting the tundish life. The presence of
dams around the impact area results in development of restricted metal circulation in the tundish
and freezing of the furthermost strand.
4. Object of invention:
? It is an object of the invention to provide a specially shaped impact pad which result in
improved flow characteristics of molten steel poured into a tundish, increasing the useful life
of the tundish particularly for a tundish in which the steel input and outlet zones are close to
each other.
? It is another object of the invention to derive a number of other advantages associated with
the use of turbulence inhibition pad in tundish.
? It is a further object to use such a pad, which will endure the shroud jet. is directed back on
itself and upward.
? It is another object to ensure that the shroud jet is decelerated and damped. Large areas of
high flow velocities or vortex formation are reduced and a more homogeneous flow patterns
develops.
? Yet another object is to ensure that the slag cover is maintained over the liquid steel and thus
reoxidation of steel is minimized, SEN cleaning is also minimized during the casting
sequence.
? A still further object is to use such a pad, which will ensure that the upward flow improves the
inclusion removal because the effective distance for a particle to the slag cover is reduced.
? Yet another object is to ensure that more homogeneous temperature distribution in the
tundish is realized thus avoiding freezing tendency in the furthest from inlet strand.
5. Details of the invention ( A Background study)
A modification of the existing fluid flow in the tundish has been carried out such that short
circuiting of the ladle stream to the two strands closest to the incoming ladle stream is avoided by
introducing a specially shaped impact pad called the turbulence inhibition pad beneath the
incoming molten steel stream from the ladle.
The steel flow in the tundish is modified such that it takes an upward direction towards the
incoming ladle stream and dampens the flow.
6. BRIEF STATEMENT OF THE INVENTION
According to this invention there is provided an improved erosion resistant impact pad for use in a
tundish below the ladle stream and made of refractory material characterized by the following:
(a) the pad is made from a castable refractory composition capable of withstanding continuous
contact with molten metal, preferably from a standard medium-to-high alumina refractory with
an alumina content in the range of 55% - 85% by weight; ;
(b) the pad has a configuration made of three surfaces.
i) a horizontal first surface for direct contact by the molten metal,
ii) a second surface which is on the send of the of the horizontal surface and
iii) a third surface which is a straight surface on top end of the curved surface,
iv) the respective curved surface and straight surface being contiguous with one another
and
v) the curved surface being contiguous with the end of the horizontal surface.
The other features are as follows:
(a) the straight surface is a vertical surface.
b) the curved surface has a uniform curvature and the curvature is concave.
c) the diameter of the bottom horizontal surface is more than the diameter of the top straight surface.
Further according to this invention there is provided an improved method of tapping steel from a
tundish having impact resistance refractory pad described above which comprises allowing the
molten steel to first contact a horizontal surface, then allowing the rising charge (stream) follow
through a concave surface, followed by allowing the charge to rise upwardly along vertical surface,
the bottom horizontal surface being circular in shape.
In this method, the flow rate of steel from the tundish is controlled to maintain the level of charge in
the distributor constant.
7. Brief Description of the accompanying drawings.
In the enclosed drawings, Fig. 1 represent schematically a conventional casting apparatus in 3 strand
bloom caster.
Figure 2 shows schematically the casting apparatus with the modified turbulence inhibition pad in
tundish placed under the ladle shroud (incoming metal stream).
Figure 3 shows in detail the flow pattern of the ladle stream after impacting with the modified
turbulence inhibition pad.
Figure 4 shows the impact pad in perspective view.
Since all details of the casting apparatus are identical except for the turbulence inhibition pad, we
describe the improved pad only in details and other details are well known and hence these casting
apparatus itself is described in brief.
From the details of figures 1 , 2, 3 and 4 , it will be noticed that the novel impact pad is isometrically
shown in Figure 4. The molten metal strikes the bottom horizontal surface 1 and molten metal
continues to rise with increased feed along the curved surface 2, then rise1 vertically along the surface
3. It will be noticed that the diameter of the top surface is less than the diameter of the bottom
surface, which helps in achieving the features of the invention and helps die erosion resistance.
Description of the casting apparatus.
The continuous casting process is a process of continuously casting metal (steel in this case) into
solidified shapes of slabs, blooms or billets for further rolling into final shapes as desired.
At Bhilai Steel Plant, Blooms are continuously cast from molten steel and then rolled into smaller
sixes for commercial applications. The molten steel and then rolled into smaller sixes for commercial
applications. The process of making liquid steel is a batch process or discontinuous in nature and so
a liquid metal holding unit called tundish is employed in which the liquid steel is first poured before it
passes to the water cooled copper moulds. The tundish acts as a reserve for the liquid steel before
the next ladle with liquid steel is brought for casting. The liquid steel is
then distributed to different moulds where it is cooled to form the shell of the bloom and is further
cooled in the strands with water sprays. The brief description of the casting apparatus is given
below
1 Ladle. A receptor of liquid steel poured from the converter and used for transferring the
liquid steel to the casting platform.
2 Tundish: the shallow refractory- lined basin on top of the continuous caster. It receives the
liquid steel from the ladle, prior to the cast, allowing the operator to precisely regulate the flow
of metal into the mold.
3 Stopper Rod: a device for controlling the flow of liquid steel from the tundish to the copper
moulds made from refractory material.
4. Mould: A water cooled copper made unit for solidifying the liquid steel shell with a definite
shape through which the continuously cast blooms are formed
i) The material required for carrying out the modification of the flow in the molten steel tundish
comprises of a refractory material body capable of withstanding high impact of molten steel
The body comprises of an impact surface for molten steel with stde-walls extending upward.
The inner face of the side-wall has a continuous curved surface, which merges into the upper
impact surface of the base, providing a concave recess around the base This shape
extends continuously around and above the impact surface. The specially shaped turbulence
inhibition pad is four-sided in plan view
The pad is made from a castable refractory composition capable of withstanding continuous
contact with molten metal, preferably from a standard medium- to- high alumina refractory
with an alumina content in the range of 55% - 85% by weight
ii) The tundish is a intermediate vessel in the continuous casting process, which receives
molten metal from the ladle through a shroud and passes the molten metal to the water
cooled copper moulds through openings in its bottom. Refractory stopper rods placed in the
tundish over the openings in the tundish control the passage of the molten metal. The impact
area in the tundish is fitted with the shaped impact pad known as turbulence inhibition pad
such that the incoming stream falls into the opening of the pad The fluid flow in the tundish
is modified in a way as to direct the flow towards the incoming stream and increase the metal
residence time in the tundish.
iii) To achieve consistently higher tundish life using a Turbulence Inhibition Pad (TIP), it is
essential to consistently have the ladle shroud centred over the TIP so that the incoming
stream is uniformly redirected back on to itself A centred ladle to tundish flow through the
shroud has equally distributed and higher metal residence times in the two nearest nozzles
which otherwise have problems of erosion at the stopper tips leading to uncontrolled casting
conditions and eventual termination of casting. By centering the
shroud over the TIP short-circuit flows to the nozzles are eliminated and separating
conditions for non-metallic inclusions are also improved.
iv) Essential steps of the process
a) Manufacture of specially shaped impact pad to desired dimensions '
bi Proper fixing of these TIF' in tundish bottom at desired location »
c) Ladle to tundish shrouding
dj Centering ot ladle shroud over TIP during casting operation
vi Any optional step to improve process ot invention
None
6.0 Details for justification of invention
The bloom caster tundish of the three strand configuration is usually terminated by the
2M;: or third heat of any sequence This effectively means a higher cost of production
due to frequent tundish changes and loss of productivity in terms of tundish skull and
machine preparation time for the next sequence to commence. Plant scale trials were
conducted for the specially designed impact pads fixed in the tundish beneath the inlet
ladle stream. The material used for the pads is a castable body made from alumina
wherein the alumina content was in between 70-85% by weight. Results from these
trials are shown in Table 1 below. A total of 17 heats were cast in 4 sequences which
means four tundishes were utilized to cast the above number of heats with the
maximum casting length of 5 heats in a single tundish covering a duration of about 500
minutes. All other sequences were successfully cast for 4 heats without any instance of
stopper running

7.0 Details to justify process
Widespread use of water flow-model studies have been made to simulate liquid steel
fluid flow patterns within an actual tundish by different Steelmaking facilities. These
water flow-models have helped in determining critical areas of tundish design such as
Depth of liquid pool in tundish and placement of fluid flow control devices in the tundish As a
result of these studies, it is well-known that the fluid flow generated by the incoming ladle stream
is reflected from the flat tundish floor toward the surface of the liquid steel The fluid flow thus
generated causes a turbulent boiling action and extensive wave motion at the surface of the steel
bath. Additionally, where the fluid flow forces are obstructed by structural barriers such as
tundish side and end walls, the ladle stream fluid flow surges upward causing excessive
turbulence at the surface of the liquid steel bath.
Flow model studies were carried out in a 0.5 scale model of the three strand bloom caster tundish
with the ladle inlet positioned between the strands #1 and #2 The studies involved visual
examination of the fluid flow under different casting rates to determine the special shape of the
impact pad.
8.0 Novel feature of process:
In the prior practice of installation of dam walls on either side of the pouring metal stream, the
metal flow is directed from the tundish bottom in an upward direction which accelerates the flow
and causes it to rebound' off the surface of the liquid metal in the tundish, causing short-circuit
flow to the closest exit strands in the tundish. In the present invention, the tundish flow
modification is such that the impact pad chamber releases the flow in an upward and outward
manner which lessens this type of short-circuit flow and extends the useful life of the tundish
We Claim
1. An improved erosion resistant impact pad for use in a tundish below the ladle stream and
made of refractory material characterized by the following.
(a) the pad is made from a castable refractory composition capable of withstanding
continuous contact with molten metal, preferably from a standard medium-to-high
alumina refractory with an aluminum content in the range of 55% - 85% by
weight.
(b) The pad has configuration made of three surfaces.
i. a horizontal first surface for direct contract by the molten metal
ii. a second surface which is on the end of the horizontal surface and
iii. a third surface which is a straight surface on top end of the curved
surface.
iv. The respective curved surface and straight surface being
contiguous with one another and
v. The curved surface being contiguous with the end of the horizontal
surface.
2. A refractory pad as claimed in Claim 1 wherein the straight surface is a horizontal
surface.
3. A refractory paid as claimed in Claim 1 wherein the curved surface has a uniform
curvature.
4. A refractory paid as clamed in Claim 3 wherein the curvature is concave.
5. A refractory pad as claimed in claims 1 to 4 wherein the diameter of the bottom horizontal
surface is more than the diameter of the top surface.
6. An improved method of tapping steel from a tundish having impact resistance refractory
paid as claimed in Claim 1 which comprised allowing the molten steel to first contact a
horizontal surface, then allowing the rising charge (stream) flow along a concave surface
thereby inducing a localized churning operation, flowed by allowing the molten steet to
rise upwardly along vertical surface, the bottom horizontal surface being circular in shape
and allowing the tundish to fill up.
7. An improved impact resistant refractory pad substantially as herein descried.

1. An improved erosion resistant impact pad for use in a tundish below the ladle stream and
made of refractory material characterized by the following.
(a) the pad is made from a castable refractory composition capable of withstanding
continuous contact with molten metal, preferably from a standard medium-to-high
alumina refractory with an aluminum content in the range of 55% - 85% by
weight.
(b) The pad has configuration made of three surfaces.
i. a horizontal first surface for direct contract by the molten metal
ii. a second surface which is on the end of the horizontal surface and
iii. a third surface which is a straight surface on top end of the curved
surface.
iv. The respective curved surface and straight surface being
contiguous with one another and
v. The curved surface being contiguous with the end of the horizontal
surface.