Title of Invention

A DEVICE FOR MINIMIZING TURBULENCE IN LIQUID STEEL TO INCREASE THE LIFE OF WORKING LININGS IN A CURVED WALL TUNDISH,AND A METHOD FOR CONFIGURATING THE DEVICE

Abstract This invention relates to an improved shroud - impact block assembly for a multiple strand continuous billet caster curve walled tundish at the spout side to continuously cast billets by developing impact block and shroud of various combinations of geometrical configurations to operate with minimum impact of tundish lining, impact block and shroud from turbulence while liquid metal powering in the tundish through shroud comprising controlling of turbulence of liquid metal by maintaining minimum shear stress on various parts of turbo stop, shroud and tundish wall wherein the impact block of any geometrical shape is constructed with a height of 330 to 530 mm and shroud immersion depth of 400 to 450 mm.
Full Text -2-
FIELD OF THE INVENTION
The present invention relates to an improved construction of Flow Modifier (FM) or Impact Block and Shroud for use in typical curved side wall Tundishes deployed in steel industry for continuously casting liquid steel into billets. The present invention has originated through test and studies of fluid flow behaviours in the Tundish through Flow Modifier and Shroud and accordingly Impact Block and Shroud have been constructed to minimize liquid steel turbulence, during casting, for securing quality of steel billets and increasing Tundish working lining life.
BACKGROUND OF THE INVENTION
The existing Fiow Modifier like Turbo-stop, Ripple pad, shrouds etc are made of refractory material to withstand liquid steel impact and control flow. These Flow Modifiers are of general purpose and do not give expected long casting durations in tundish having typical curved side wall configurations and operated under varying operating conditions.

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Drawbacks of existing impact Pot shroud assembly practice in tundish
The impact pot, which receives the impact of steel stream either shrouded or unshrouded, is suitably positioned in the Tundish such that the turbulence of flowing steel has been under control. Turbulence can adversely impact casting process due to stream flaring and erosion of working lining. Therefore, positioning of Impact Block is a very critical criteria for particular specific tundish geometry and operation practice of molten metal impact on the tundish lining. As higher turbulence causes wear of working lining, due to shearing strain, the positioning of impact pad is maintained normally away from side walls of Tundish.
In Tundish having curved side walls on the out-spout side the Impact Block takes a position very close to the curved wall to minimize strand flickering. Further during casting operation when steel is transferred into Tundish from Ladle through Shroud the casting process goes through two situations: (i) the tip of Shroud is above the liquid steel pool (ii) the Shroud is completely submerged in liquid steel. In the former case there is significant turbulence causing erosion of

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working lining especially in the event of Ladle change over time exceeds 2 minutes. In the latter case though the shear stress is mild the working lining receives considerable shear stress and erodes when casting durations exceed 10-15 hours.
DESCRIPTION OF THE INVENTION
The main object of the invention is to reduce the wear rate of tundish working lining, especially at the curved walls, by controlling flow dynamics in continuously casting liquid steel.
Another object of the invention is to develop Impact Block and Shroud geometrical optimization through observation of flow dynamics according to the shape and dimensions of the backup and shroud to increase the casting duration length >25 hours.

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A further object of the invention is to eliminate break-outs and improve safety of men and equipments.
During continuous casting of liquid steel into billets, liquid steel is transferred from Steel Ladle into another refractory lined container called Tundish having specific geometry and capacity through a refractory tube known as Shroud, the Shroud performs the following functions:
1. Prevents the oxidation of steel for metallurgical advantages
2. Guides the stream into the Impact Block
3. As the liquid steel pool builds up the Shroud is submerged in the pool and
turbulence is reduced.
The location of stream that falls into the Tundish with curved wall is different from normal Tundish with straight walk In Tundish having curved walls at the spout the Impact Block location is positioned closer to the out-spout to minimize stream flickering at the Mould. When Impact Block is closer to the out-spout the curved walls are more prone to impact of turbulence of liquid steel compared to tundishes having straight walls.

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According to the invention there is provided I an improved shroud - impact block
assembly for a multiple strand continuous billet caster curve walled tundish at the spout side to continuously cast billets by developing impact block and shroud of various combinations of geometrical configurations to operate with minimum impact of tundish lining, impact block and shroud from turbulence while liquid metal powering in the tundish through shroud comprising controlling of turbulence of liquid metal by maintaining minimum shear stress on various parts of turbo stop, shroud and tundish wall wherein the impact block of any geometrical shape is constructed with a height of 330 to 530 mm and shroud immersion depth of 400 to 450 mm.
The present invention has used concepts of derivations of relationship to study the important turbulence related issues, as detailed below, during casting, in a curved tundish. The invention found out, based on quantifiable results obtained from studied mathematical relationship the; important variables that effect the turbulence during long hours of casting.

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1. The effect of immersion depth of shroud, which can be varied by
a. increasing the length of shroud
b. altering the height of impact pot.
2. The shape of impact pad
3. The diameter of impact pad
4. The geometry of shroud at the steel exit end
The said constructional features of the impact pad and shroud are carried through observations of the following aspects: -
(a) Position of maximum stress:
Under dynamic casting conditions it has been tried to quantify maximum stress prone area. Between the two side walls, i.e. straight back wall and curved spout side wall, which are constantly exposed to the stream flashing the predicted maximum stress has been on the two curved walls close to the out-spout.

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(b) Impact of shroud immersion depth:
With increase of the shroud immersion depth in liquid steel, the distance of liquid steel level measured from the tip of exit end of shroud to the highest level of steel in the tundish, there is initially reduction of wall shear stress and further increase of the depth resulted in increasing trend of stress, which indicates that there is an optimum shroud immersion depth. Since the required increase in the shroud immersion depth can be achieved by using increasing the length of shroud or and Impact Block height, which is expected to significantly minimise shearing stresses on the curved wall.
(c) Shape of Impact Block
Changing the shape impact pot from rectangular to cylindrical does not bring in any advantage.

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The trapezoidal shape is larger in volume (compared to rectangular impact pot of the same height (430 mm) by 50 %. The bottom stress is seen to be about 26 Pa and the wall shear stress is about 12-13 Pa. In case of rectangular impact pot the bottom stress was 25 Pa and the wall shear stress was also between 12-13 Pa. So by making the volume of the impact pot larger there is no net significant benefit in terms of lowering the stress.
It has been concluded from the above observations that the existing operating practice of operating with Impact Block measuring height of 230 mm and shroud
immersion depth of 130 mm seems to be generating high stress on the wall of
i
the tundish, which can lead to break outs in the tundish.
By increasing the Impact Block height to 530 mm and the shroud immersion depth to 400 or 450 mm the maximum stress on the curved wall is reduced significantly.

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It is found that the cylindrical Impact Block produces the same maximum stress on the curved wails like that of the rectangular Impact Block.
The funnel shaped Shroud reduces the stress on the Impact Block bottom wall very much, but does not reduce the stress on the curved wall of the Tundish. Hence funnel shaped Shrouds are preferred to reduce stress on the bottom wall of Impact Block.
Use of trapezoidal shaped Impact Block having volume increase by 50 % more compared to the rectangular Impact Block has been found to be no special benefit in terms of reducing the stress on the tundish wall. So the rectangular Impact Block with higher height and a longer Shroud are suggested to extend the life of the Tundish.
In summary to improve the Tundish working lining life and prevent break-outs during long casting hours the conducted mathematical studies resulted in an invention that gives scope to redefine the geometry of Tundish Impact Block or

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Flow Modifier and its assembly as dictated by depth of alignment of Shroud. The invention predicted, based on mathematical relationship of liquid steel flow studies, in a billet caster tundish having curved out-spout wall, that it is possible to bring down the shear stress on the curved wall by bringing about the following changes.
(a) Increase shroud immersion depth from the present level of 130 mm to 400 to
450 mm by deploying relatively longer shrouds.
(b) Increase the Impact Block height from 230 mm to 530 mm by using modified
taller Impact Blocks.
(c) Modification of present circular cross section at the exit end of Shroud to
funnel shape.
The aforesaid optimum results are generated by conductivity mathematical studies using sequential steps as stated below:

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the enure computational aomain is aiscretizea to about s iaKn ceiis wnicn contains the shroud, tubo stop and the exit funnels. The Navier-Stokes equation is discretized over the control volume and the discretized equation is integrated for the control volume to yield an algebraic equation having velocity and pressure as variables. The pressure velocity coupling is solved through the SIMPLE algorithm. Then by the help of the continuity equation the momentum equation can be written as algebraic equations only for velocity which can be solved by algebraic multi grid solver. Then the continuity equation will be used to compute the pressure in all the cells and the iteration will proceed to the next one until convergence of both velocity and pressure. Thus the solution of the velocity field will be utilized to compute the wail shear stress for different values of shroud immersion depth and turbo stop height. A clear optimum value for both the parameters can be obtained which will generate minimum wall shear stress on the curved wall of the tundish thus enhancing the life of the tundish.
The incorporation of changes in height of Impact Block and alignment depth of Shroud by changing length to Shroud is expected to reduce the maximum shear stress on curved wall by 20 % from the existing level.

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The invention is applicable:
(i) to cast all types of steel billets having a range of carbons levels and casting temperatures decided by respective Liquidous temperatures
(ii) casting speeds up to 5 metres/min
(iii) casting billet having area of cross sections varying between
(iv) to all types of shrouds made by different routes including iso-static pressing.
(v) Impact Blocks having different chemistries and made by different fabricating routes including casting by using high alumina castables
(vi) Impact Blocks having different inside and outside cross-sectional designs

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(vii) all Impact Block geometries including cylindrical and trapezoidal
(viii) to all Shroud geometries including bell shaped end and circular cross
sections
(ix) Tundishes having curved walls at the spout wall of different sizes and
capacity
The invention will be better understood from the following description with reference to the accompanying drawings in which
Figure 1 shows assembly sketch of half portion of symmetrical
i Tundish showing position of the of shroud and
i Impact Block in the existing method.
Figure 2 shows schematic geometry of funnel shaped Shroud.
Figure 3 shows modified configuration of Impact Block measuring 530 mm height and shroud immersion depth of 450 mm.

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Figure 4 shows shear stress variation graph for studied variables according to the present invention.
Figure 5 represents a now diagram or tne steel casting assemby according to the invention showing the positions of the tundish, shroud and impact block showing shroud immersion depth of 450 mm, impact block height 530 mm with molten steel level of 900 mm in the tundish.
Figure 4 depicts the test results obtained tnrougn ooservation or maximum snear
stress resulted on the curved wall of the tundish Vs the shroud immersion depth in mm for Impact Block maintained at four heights - 230, 330,430 and 530 mm for any shape of rectangular, cylindrical or tropezodial.

it can be seen rrom tne grapn mat the maximum stress on me curvea wan decreases as the height of the I.B increases from 230 mm to 530 mm. The
decrease in maximum stress is higher for the I.B height of 230 mm, 330 mm and
430 mm and then the rate of decrease falls as the height increases to 530 mm. It can be marked from the graph that there is always; an optimum shroud immersion depth for each I.B height where the maximum' stress on the curved wall is the minimum. But other combinations of Impact Block height of 330,430, 530, with Shroud immersion depth of 440, 350, 400 respectively will give similar -esults.
It is observed from the graph that in all the above cases with the increase of
shroud immersion depths the stress on the curved wall of the tundish is .38 to .8
a minimum and after a critical limit the stress increases. It is observed that for
a turbo height of 530 mm and shroud depth of 400 mm the stress is minimum.

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Maximum shear stress as observed in various parts of turbo stop and on tundish wall for impact block height 430 mm and shroud depth 330 mm for different shapes of impact blocks are shown in Table 1.
it is ODservea from the able mat maximum stress on tne tunaisn wan is witnin
the range of 0.5 to 0.81, higher is for cylindrical impact block with funnel shaped
shroud. Maximum stress at bottom of Impact Block is minimum for cylindrical
impact block. Shear stress on side wall of impact block is minimum for cylindrical
shape of impact block and maximum stress on opposite plane wall of tundish is

minimum for cylindrical impact block and funnel shaped shroud.


Table -1

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The present invention has been applied in the Billet Caster Tundish having six Strand casting facility and curved walls at the out-spout and maintained with liquid steel depth up to 900 mm minimizing shear stress on the tundish wall, impact block and shroud with enhanced casting duration through the following characteristic features.
(i) The shape of Flow Modifier or Impact Block has little impact on turbulence control.
(ii) Impact Blocks deployed can have any shape including circular, rectangular, trapezoidal etc.
(iii) Flow Modifier or Impact Block height and Shroud depth of immersion plays vital role in turbulence control.
(iv) Maintaining (a) the maximum Shroud immersion depth up to 450 mm and (b) Impact Block height up to 530 mm (c) or any combinations within the specified limits.

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(vi) Use of typical Shroud having bell shaped, diverging geometry, towards liquid steel exit cross-section is also included.
The invention as herein described and illustrated with an embodiment, should not be read in {a restrictive manner as various adaptations, alterations, modifications are possible within the scope and limit of the invention as defined in the appended claims.

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WE CLAIM
1. An improved1 shroud - impact block assembly for a multiple strand
continuous billet caster curve walled tundish at the spout side to
continuously cast billets by developing impact block and shroud of various
combinationsi of geometrical configurations to operate with minimum
impact of tundish lining, impact block and shroud from turbulence while
liquid metal powering in the tundish through shroud comprising controlling
of turbulence of liquid metal by maintaining minimum shear stress on
various parts of turbo stop, shroud and tundish wall wherein the impact
block of any igeometrical shape is constructed with a height of 330 to 530
mm and shroud immersion depth of 400 to 450 mm.
2. An improved shroud - impact block assembly as claimed in claim 1
wherein, with the said assembly all types of steels billets of varying cross
sections and with respective liquidus temperatures are continuously cast
at a casting speed of 5 meters / min.

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3. An assembly as claimed in claim 1, 'wherein the shrouds and impact block of various refractory compositions including alumina refractories are prepared by different fabricating routes.
4. An assembly as claimed in the preceding claims wherein the impact block
are of rectangular, cylindrical or trapezoidal geometrical configurations
and have different inside and outside cross sections.
5. An assembly as claimed in claim 1, wherein the shroud is of bell shaped
end and of circular cross section or is of funnel shaped geometrical
configuration.
6. An assembly as claimed in the preceding claims wherein the casting
duration length is maintained more than 25 hours.

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7. An assembly as claimed in the preceding claims wherein, the shear stress
on the curved wall of the tundish, impact block and shroud are observed
through measurements on using algorithm for preparing logic and
collecting datas on monitor via a sensor and gather optimized dimensions
of the constituents of the assembly.
8. An assembly as claimed in the preceding claims wherein by maintaining a
turbo height of 530 mm and shroud immersion depth of 400 - 450 mm
the stress on the curved wall of the tundish is kept at minimum of 0.38 to
0.8 Pa.
9. An improved shroud - impact block assembly for a multiple strand
continuous billet caster tundish, substantially as herein described and
illustrated in the accompanying drawings.

Documents:

01209-kol-2006 abstract.pdf

01209-kol-2006 assignment.pdf

01209-kol-2006 claims.pdf

01209-kol-2006 correspondence others.pdf

01209-kol-2006 description(complete).pdf

01209-kol-2006 drawings.pdf

01209-kol-2006 form1.pdf

01209-kol-2006 form2.pdf

01209-kol-2006 form3.pdf

01209-kol-2006-correspondence-1.1.pdf

01209-kol-2006-form-9.pdf

1209-KOL-2006-ABSTRACT 1.1.pdf

1209-KOL-2006-ABSTRACT.pdf

1209-KOL-2006-AMANDED CLAIMS.pdf

1209-KOL-2006-AMANDED PAGES OF SPECIFICATION.pdf

1209-KOL-2006-CANCELLED PAGES.pdf

1209-KOL-2006-CLAIMS.pdf

1209-KOL-2006-CORRESPONDENCE.1.3.pdf

1209-KOL-2006-DESCRIPTION (COMPLETE).pdf

1209-KOL-2006-DRAWINGS 1.1.pdf

1209-KOL-2006-DRAWINGS.pdf

1209-KOL-2006-EXAMINATION REPORT REPLY RECIEVED 1.1.pdf

1209-KOL-2006-EXAMINATION REPORT.1.3.pdf

1209-KOL-2006-FORM 1 1.1.pdf

1209-KOL-2006-FORM 1.pdf

1209-KOL-2006-FORM 13.1.3.pdf

1209-KOL-2006-FORM 13.pdf

1209-KOL-2006-FORM 18.1.3.pdf

1209-KOL-2006-FORM 2 1.1.pdf

1209-KOL-2006-FORM 2.pdf

1209-KOL-2006-FORM 3.1.3.pdf

1209-KOL-2006-FORM 9.1.3.pdf

1209-KOL-2006-GPA.1.3.pdf

1209-KOL-2006-GRANTED-ABSTRACT.pdf

1209-KOL-2006-GRANTED-CLAIMS.pdf

1209-KOL-2006-GRANTED-DESCRIPTION (COMPLETE).pdf

1209-KOL-2006-GRANTED-DRAWINGS.pdf

1209-KOL-2006-GRANTED-FORM 1.pdf

1209-KOL-2006-GRANTED-FORM 2.pdf

1209-KOL-2006-GRANTED-LETTER PATENT.pdf

1209-KOL-2006-GRANTED-SPECIFICATION.pdf

1209-KOL-2006-OTHERS.pdf

1209-KOL-2006-REPLY TO EXAMINATION REPORT.1.3.pdf

1209-KOL-2006-REPLY TO EXAMINATION REPORT.pdf

abstract-01209-kol-2006.jpg


Patent Number 248330
Indian Patent Application Number 1209/KOL/2006
PG Journal Number 27/2011
Publication Date 08-Jul-2011
Grant Date 05-Jul-2011
Date of Filing 13-Nov-2006
Name of Patentee TATA STEEL LIMITED
Applicant Address JAMSHEDPUR-831 001
Inventors:
# Inventor's Name Inventor's Address
1 Ranjan Pal, Atanu TATA STEEL LIMITED JAMSHEDPUR-831 001
2 Kumar Dash, Sukanta TATA STEEL LIMITED JAMSHEDPUR - 831 001
3 Krishna, N.V.S. TATA STEEL LIMITED JAMSHEDPUR - 831 001
PCT International Classification Number B22D11/20
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA