Title of Invention	A PROCESS FOR INCLUSION FLOATATION IN TUNDISH
Abstract	A process for improving the cleanliness of steel, by inclusion floatation in liquid steel in tundish. Increased level of inclusions lead to nozzle chocking and defects at the user end. The process of forced floatation of inclusions in liquid steel according to the invention by argon/bubbling/purging through tundish bottom, especially achieved desired floatation for sizes of inclusions smaller than 50m. Bubbling from the bottom of the tundish increases the collision rate, floatation and absorption. Advantageoulsy, used ladle bottom porous plugs are embedded into the dam at tundish bottom, to favor measured flow rate of argon gas through an embedded pipe and a rotameter. Selective argon flow rate was maintained depending on the slag thickness and metal depth in tundish. Reduction in inclusions up to 60% and 40 % were achieved for sizes greater than 50μm and 25μm, respectively.

Title of Invention

A PROCESS FOR INCLUSION FLOATATION IN TUNDISH

Abstract

A process for improving the cleanliness of steel, by inclusion floatation in liquid steel in tundish. Increased level of inclusions lead to nozzle chocking and defects at the user end. The process of forced floatation of inclusions in liquid steel according to the invention by argon/bubbling/purging through tundish bottom, especially achieved desired floatation for sizes of inclusions smaller than 50m. Bubbling from the bottom of the tundish increases the collision rate, floatation and absorption. Advantageoulsy, used ladle bottom porous plugs are embedded into the dam at tundish bottom, to favor measured flow rate of argon gas through an embedded pipe and a rotameter. Selective argon flow rate was maintained depending on the slag thickness and metal depth in tundish. Reduction in inclusions up to 60% and 40 % were achieved for sizes greater than 50μm and 25μm, respectively.

Full Text	FORM 2 THE PATENT ACT 1970 (39 OF 1970) & The Patent Rules, 2003COMPLETE SPECIFICATION (See Section 10 and Rule 13) 1 TITLE OF THE INVENTION : A PROCESS FOR INCLUSION FLOATATION IN TUNDISH. 2 APPLICANT (S) Name : JSW Steel Limited. Nationality : An Indian Company. Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg State of Maharastra, India. ,Mumbai - 400 026, 3 PREAMBLE TO THE DESCRIPTION COMPLETE The following specification particularly descibes the invention and the manner in be performed. which it is to FIELD OF THE INVENTION: The present invention is directed to a process for improving the cleanliness of steel in tundish by forced floatation of inclusions in liquid steel. Inclusions conventionally picked up by liquid steel, while in primary and secondary steel making process, are due to initial filling up or ladle change over when the metal is exposed to ambient air which leads to oxygen pick up and this excess oxygen in turn provide more inclusion formation in first slab and immediately after ladle change over, usually maximum large sized inclusions. The present invention is directed to achieving forced floatation of inclusions in liquid steel by argon/bubbling/purging through tundish bottom, especially to float sizes of inclusions smaller than 50mm. The invention would favour reduction in non-metallic inclusions especially Al203 and importantly also about 60% and 40% reduction in inclusion of size greater than 50 and 25 m respectively. The invention further directs to improving the quality and yield of first slab, efficiency of inclusion floatation at lower casting speeds and lengthening of refractory life. BACKGROUND AND PRIOR ART: It is well known that in continuous casting the molten steel passes from ladle to mould through a intermediate buffer called tundish. The tundish is a flow distributor and is designed to maximize the liquid steel residence time in order to promote inclusion flotation. The continuous caster is also associated with other supporting equipments like a mold, a mold oscillator, rolls for cast strands, pinch roll and withdrawing roll for the cast strand, a group of spray nozzle, a torch cutter for cutting cast strand, a dummy bar for extracting the cast strand at start of casting etc. The performance of these auxiliaries, apart from the fundamental process of primary and secondary steel making, influence the quantum of metallic as well as non-metallic inclusions of various sizes and adversely affect cleanliness of steel, unless controlled during metal residence at the tundish. Decreased cleanliness or higher amount of inclusion leads to nozzle choking and defects at the application end. In addition, during the initial filling up or ladle change over, metal is exposed to ambient air and leads to oxygen pickup. The extra oxygen also leads to more inclusion formation in first slab and immediately after ladle changeover. Results show that first slab has maximum large size inclusions. Shops operating at high productivity, end up at less processing time and leads to increased inclusions in the steel. It is well known in the art of continuous 2 casting steel slabs that flotation of inclusions in the tundish by the use of dams, weirs, baffles and other devices are effective for removing inclusions of size greater than 50mm. But inclusions smaller than 50mm do not come up easily. There is therefore a persistent need in the art to make some changes in tundish configuration to incorporate means for improved flotation of inclusion during the residence time of liquid metal at the tundish such that the amount of inclusions can be brought down in continuous cast slabs, by picking them up in larger proportion in floatation in tundish itself. OBJECTS OF THE INVENTION: It is thus the basic object of the present invention to improve cleanliness of the cast steel by a process of inclusion floatation in steel at tundish, whereby it would be possible to improve inclusion floatation in tundish, especially the inclusions including the sizes smaller than 50 mm. A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish by argon bottom purging to achieve reduction in inclusions up to 60 % for sizes greater than 50 mrn and up to 40% for sizes greater than 25 mm, respectively. A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish, to achieve improvement in quality and yield of first slab. A further object of the present invention is directed to reduce non-metallic inclusions and especially Al203 in cast steel, by improved floatation of inclusions by said bottom purging of argon in tundish, under all conditions of casting. A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish such as to achieve a significant reduction in oxide pick up thereby avoiding nozzle clogging and in the process lengthening the life of refractory lining in tundish. 3 A still further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish such that the efficiency of inclusion floation increases at lower casting speed. Another object of the present invention is directed to a tundish adapted for efficient inclusion floatation involving used ladle bottom porous plug to thus provide for the desired simple and cost-effective means for said inclusion floatation up to desired level. A still further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish favoring reduction of percentage of inclusions of larger size with increase in throughput. SUMMARY OF THE INVENTION: Thus according to the basic aspect of the present invention there is provided a process for inclusion floatation in tundish comprising: controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation. A further aspect of the present invention is directed to a process for inclusion floatation in tundish comprising bubbling of Argon from the bottom of the tundish. A still further aspect of the present invention is directed to a process for inclusion floatation in tundish comprising bubbling of argon from the bottom of the tundish through porous plugs embedded with respect to the bottom of the tundish. A still further aspect of the present invention is directed to a process for inclusion floatation in tundish wherein bubbling of argon from the bottom of the tundish through porous plugs comprises using used ladle bottom porous plugs. In the above process for inclusion floatation in tundish preferably the plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter. 4 In accordance with an aspect of the invention, the process for inclusion floatation in tundish comprises providing selective numbers of selectively spaced apart and preferably about 150mm apart disposed porous plugs embedded for optimized location of the purging arrangement. According to a further aspect of the present invention of a process for inclusion floatation in tundish comprises maintaining the argon flow rate between 20-50lpm w.r.t. slag thickness and metal depth. According to another important aspect of the present invention said process for inclusion floatation in tundish comprises bubbling Argon before ladle opening in empty tundish for improvement in quality and yield of first slab. A still further aspect of the present invention is directed to a tundish adapted for efficient inclusion floatation comprising: means for controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation. According to a still further aspect the tundish includes said means for controlled bottom purging comprising porous plugs preferably used ladle bottom porous plugs embedded with respect to the bottom of the tundish. A still further aspect of the present invention is directed to a tundish wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter. A further aspect of the present invention is directed to a process of forced floatation of the inclusions in liquid steel in tundish wherein said preferred locations for bubbling were obtained by shifting the dam by 140mm towards left compared to conventional position. 5 A still further aspect of the present invention directed to a process of forced floatation of the inclusions in liquid steel in tundish by adopting argon bubbling from bottom of tundish wherein said process achieved a reduction up to 60% and 40% in inclusions of size greater than 50mm and 25mm, respectively. In the above disclosed process of inclusion floatation in liquid steel in tundish a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life. Also, such process of forced floatation of the inclusions in liquid steel in tundish increased efficiency of floatation of inclutions at lower casting speed. According to yet further aspect of the present invention in the process of forced floatation of the inclusions in liquid steel in tundish, the percentage of inclusion of larger size reduced with increase throughput. The present invention and its objects and advantages are described in greater details with particular reference to the non-limiting exemplary illustrations as per the accompanying figures. BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES: Figure 1: is an illustration of arrangement of porous plugs embedded into the dam of tundish favoring desired bubbling/bottom purging at tundish, according to the present invention. DETAILED DESCRIPTION OF THE ACCOMPANYING FIGURES: Conventional means for inclusion flotation in the tundish by the use of dams, weirs, baffles and other devices are only effective for removing inclusions of sizes greater than 50mm. But inclusions smaller than 50mm were usually do not float easily. To achieve reduction of amount of inclusions in liquid steel, particularly of sizes smaller than 50 mm, controlled bubbling of inert gas was experimented in tundish for inclusion flotation. It was observed by adopting mathematical and physical modeling that bottom purging in tundish enhances flotation of even smaller size inclusions. Turbulence created by bubbling-in argon gas from bottom of the tundish increases the collision rate, flotation and absorption. An extensive 6 plant scale trial was taken up to achieve minimum level of inclusions in the cast slab employing forced inclusion flotation via argon bubbling through tundish bottom. Arrangement was made for forming a curtain perpendicular to the flow of steel for bubbling of argon from bottom of the tundish. Reference is now invited to figure 1 which illustrates the arrangement wherein used ladle bottom porous plugs, cut to 100 mm are embedded into the dam at the tundish bottom. Separate arrangement for argon flow at controlled/measured rate was made through an embedded pipe which is in turn connected through a Rotameter. Three plugs were fixed at distances of 150 mm apart. Locational arrangement of the purging used ladle porous plugs were optimized based on account of flow profile generated by water modeling experiments for the operational tundish. To facilitate favored bottom bubbling in tundish the dam location is shifted to 140 mm towards left from the previous location. Optimized bubbling locations, thus achieved, enabled the bulk of inclusions to travel minimum distance before getting into the slag. This maximized flotation of inclusions during bubbling. The flow rate of Argon was maintained in the range from 20 to 50 liters per minute, depending on slag thickness and metal depth. Several trials were carried out with different casting sections and throughputs. Optimum gas flow rate was calculated theoretically and further adjusted practically with a series of experiments. Sampling was done at different locations in the tundish and slab. Inclusion distribution study was made to compare the effect with the normal heats and improvements achieved were noted as discussed hereunder. The above process of bottom purging lead to reduction in non-metallic inclusions especially Al203 in cast steel, under all conditions of casting. This establishes the fact that inclusion flotation has improved with bottom purging.In particular, there was up to 60% and 40% reduction in inclusion of size greater than 50 mm and 25 mm respectively. Advantageously, according to an aspect of the invention, bubbling argon before the ladle opening in empty tundish showed improvement in quality and yield of first slab. Additionally, a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life. Efficiency of inclusion flotation increases at lower casting speed could be achieved and importantly, the percentage of inclusion of larger size reduces with increase in throughput. 7 WE CLAIM: 1. A process for inclusion floatation in tundish comprising: Controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation. 2. A process for inclusion floatation in tundish as claimed in claim 1 comprising bubbling of Argon from the bottom of the tundish. 3. A process for inclusion floatation in tundish as claimed in anyone of claims 1 or 2 comprising bubbling of argon from the bottom of the tundish through porous plugs embedded with respect to the bottom of the tundish. 4. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 3 wherein bubbling of argon from the bottom of the tundish through porous plugs comprises using used ladle bottom porous plugs. 5. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 4 wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter. 6. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 5 wherein selective nos. of selectively spaced apart preferably about 150mm apart porous plugs are embedded in the with optimized location of the purging arrangement. 7. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 6 wherein the argon flow rate was maintained between 20-50lpm w.r.t. slag thickness and metal depth. 8. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 7 comprising bubbling Argon before ladle opening in empty tundish for improvement in quality and yield of first slab. 8 9. A tundish adapted for efficient inclusion floatation comprising: means for controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation. 10. A tundish as claimed in claim 9 wherein said means for controlled bottom purging comprises porous plugs preferably used ladle bottom porous plugs embedded with respect to the bottom of the tundish. 11. A tundish as claimed in anyone of claim 9 or 10 wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter. 12. A process for inclusion floatation in tundish and a tundish for carrying out such process substantially as herein described and illustrated with reference to the accompanying figures. Dated this 7th day of February, 2007. Anjan Sen Of Anjan Sen & Associates (Applicants agent) 9 ABSTRACT A PROCESS FOR INCLUSION FLOATATION IN TUNDISH. A process for improving the cleanliness of steel, by inclusion floatation in liquid steel in tundish. Increased level of inclusions lead to nozzle chocking and defects at the user end. The process of forced floatation of inclusions in liquid steel according to the invention by argon/bubbling/purging through tundish bottom, especially achieved desired floatation for sizes of inclusions smaller than 50mm. Bubbling from the bottom of the tundish increases the collision rate, floatation and absorption. Advantageoulsy, used ladle bottom porous plugs are embedded into the dam at tundish bottom, to favor measured flow rate of argon gas through an embedded pipe and a rotameter. Selective argon flow rate was maintained depending on the slag thickness and metal depth in tundish. Reduction in inclusions up to 60% and 40 % were achieved for sizes greater than 50mm and 25mm, respectively. Figure 1. 10

Full Text

FORM 2 THE PATENT ACT 1970 (39 OF 1970) & The Patent Rules, 2003COMPLETE SPECIFICATION (See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A PROCESS FOR INCLUSION FLOATATION IN TUNDISH.
2 APPLICANT (S)
Name : JSW Steel Limited.
Nationality : An Indian Company.
Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg State of Maharastra, India. ,Mumbai - 400 026,
3 PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification particularly descibes the invention and the manner in be performed. which it is to

FIELD OF THE INVENTION:
The present invention is directed to a process for improving the cleanliness of steel in tundish by forced floatation of inclusions in liquid steel. Inclusions conventionally picked up by liquid steel, while in primary and secondary steel making process, are due to initial filling up or ladle change over when the metal is exposed to ambient air which leads to oxygen pick up and this excess oxygen in turn provide more inclusion formation in first slab and immediately after ladle change over, usually maximum large sized inclusions. The present invention is directed to achieving forced floatation of inclusions in liquid steel by argon/bubbling/purging through tundish bottom, especially to float sizes of inclusions smaller than 50mm. The invention would favour reduction in non-metallic inclusions especially Al203 and importantly also about 60% and 40% reduction in inclusion of size greater than 50 and 25 m respectively. The invention further directs to improving the quality and yield of first slab, efficiency of inclusion floatation at lower casting speeds and lengthening of refractory life.
BACKGROUND AND PRIOR ART:
It is well known that in continuous casting the molten steel passes from ladle to mould through a intermediate buffer called tundish. The tundish is a flow distributor and is designed to maximize the liquid steel residence time in order to promote inclusion flotation.
The continuous caster is also associated with other supporting equipments like a mold, a mold oscillator, rolls for cast strands, pinch roll and withdrawing roll for the cast strand, a group of spray nozzle, a torch cutter for cutting cast strand, a dummy bar for extracting the cast strand at start of casting etc. The performance of these auxiliaries, apart from the fundamental process of primary and secondary steel making, influence the quantum of metallic as well as non-metallic inclusions of various sizes and adversely affect cleanliness of steel, unless controlled during metal residence at the tundish. Decreased cleanliness or higher amount of inclusion leads to nozzle choking and defects at the application end. In addition, during the initial filling up or ladle change over, metal is exposed to ambient air and leads to oxygen pickup. The extra oxygen also leads to more inclusion formation in first slab and immediately after ladle changeover. Results show that first slab has maximum large size inclusions. Shops operating at high productivity, end up at less processing time and leads to increased inclusions in the steel. It is well known in the art of continuous
2

casting steel slabs that flotation of inclusions in the tundish by the use of dams, weirs, baffles and other devices are effective for removing inclusions of size greater than 50mm. But inclusions smaller than 50mm do not come up easily.
There is therefore a persistent need in the art to make some changes in tundish configuration to incorporate means for improved flotation of inclusion during the residence time of liquid metal at the tundish such that the amount of inclusions can be brought down in continuous cast slabs, by picking them up in larger proportion in floatation in tundish itself.
OBJECTS OF THE INVENTION:
It is thus the basic object of the present invention to improve cleanliness of the cast steel by a process of inclusion floatation in steel at tundish, whereby it would be possible to improve inclusion floatation in tundish, especially the inclusions including the sizes smaller than 50 mm.
A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish by argon bottom purging to achieve reduction in inclusions up to 60 % for sizes greater than 50 mrn and up to 40% for sizes greater than 25 mm, respectively.
A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish, to achieve improvement in quality and yield of first slab.
A further object of the present invention is directed to reduce non-metallic inclusions and especially Al203 in cast steel, by improved floatation of inclusions by said bottom purging of argon in tundish, under all conditions of casting.
A further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish such as to achieve a significant reduction in oxide pick up thereby avoiding nozzle clogging and in the process lengthening the life of refractory lining in tundish.
3

A still further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish such that the efficiency of inclusion floation increases at lower casting speed.
Another object of the present invention is directed to a tundish adapted for efficient inclusion floatation involving used ladle bottom porous plug to thus provide for the desired simple and cost-effective means for said inclusion floatation up to desired level.
A still further object of the present invention is directed to a process of forced floatation of inclusions of liquid steel in tundish favoring reduction of percentage of inclusions of larger size with increase in throughput.
SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention there is provided a process for inclusion floatation in tundish comprising:
controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation.
A further aspect of the present invention is directed to a process for inclusion floatation in tundish comprising bubbling of Argon from the bottom of the tundish.
A still further aspect of the present invention is directed to a process for inclusion floatation in tundish comprising bubbling of argon from the bottom of the tundish through porous plugs embedded with respect to the bottom of the tundish.
A still further aspect of the present invention is directed to a process for inclusion floatation in tundish wherein bubbling of argon from the bottom of the tundish through porous plugs comprises using used ladle bottom porous plugs.
In the above process for inclusion floatation in tundish preferably the plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter.
4

In accordance with an aspect of the invention, the process for inclusion floatation in tundish comprises providing selective numbers of selectively spaced apart and preferably about 150mm apart disposed porous plugs embedded for optimized location of the purging arrangement.
According to a further aspect of the present invention of a process for inclusion floatation in tundish comprises maintaining the argon flow rate between 20-50lpm w.r.t. slag thickness and metal depth.
According to another important aspect of the present invention said process for inclusion floatation in tundish comprises bubbling Argon before ladle opening in empty tundish for improvement in quality and yield of first slab.
A still further aspect of the present invention is directed to a tundish adapted for efficient inclusion floatation comprising:
means for controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation.
According to a still further aspect the tundish includes said means for controlled bottom purging comprising porous plugs preferably used ladle bottom porous plugs embedded with respect to the bottom of the tundish.
A still further aspect of the present invention is directed to a tundish wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter.
A further aspect of the present invention is directed to a process of forced floatation of the inclusions in liquid steel in tundish wherein said preferred locations for bubbling were obtained by shifting the dam by 140mm towards left compared to conventional position.
5

A still further aspect of the present invention directed to a process of forced floatation of the inclusions in liquid steel in tundish by adopting argon bubbling from bottom of tundish wherein said process achieved a reduction up to 60% and 40% in inclusions of size greater than 50mm and 25mm, respectively.
In the above disclosed process of inclusion floatation in liquid steel in tundish a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life.
Also, such process of forced floatation of the inclusions in liquid steel in tundish increased efficiency of floatation of inclutions at lower casting speed.
According to yet further aspect of the present invention in the process of forced floatation of the inclusions in liquid steel in tundish, the percentage of inclusion of larger size reduced with increase throughput.
The present invention and its objects and advantages are described in greater details with particular reference to the non-limiting exemplary illustrations as per the accompanying figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: is an illustration of arrangement of porous plugs embedded into the dam of tundish favoring desired bubbling/bottom purging at tundish, according to the present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING FIGURES:
Conventional means for inclusion flotation in the tundish by the use of dams, weirs, baffles and other devices are only effective for removing inclusions of sizes greater than 50mm. But inclusions smaller than 50mm were usually do not float easily. To achieve reduction of amount of inclusions in liquid steel, particularly of sizes smaller than 50 mm, controlled bubbling of inert gas was experimented in tundish for inclusion flotation. It was observed by adopting mathematical and physical modeling that bottom purging in tundish enhances flotation of even smaller size inclusions. Turbulence created by bubbling-in argon gas from bottom of the tundish increases the collision rate, flotation and absorption. An extensive
6

plant scale trial was taken up to achieve minimum level of inclusions in the cast slab employing forced inclusion flotation via argon bubbling through tundish bottom. Arrangement was made for forming a curtain perpendicular to the flow of steel for bubbling of argon from bottom of the tundish.
Reference is now invited to figure 1 which illustrates the arrangement wherein used ladle bottom porous plugs, cut to 100 mm are embedded into the dam at the tundish bottom. Separate arrangement for argon flow at controlled/measured rate was made through an embedded pipe which is in turn connected through a Rotameter. Three plugs were fixed at distances of 150 mm apart. Locational arrangement of the purging used ladle porous plugs were optimized based on account of flow profile generated by water modeling experiments for the operational tundish. To facilitate favored bottom bubbling in tundish the dam location is shifted to 140 mm towards left from the previous location.
Optimized bubbling locations, thus achieved, enabled the bulk of inclusions to travel minimum distance before getting into the slag. This maximized flotation of inclusions during bubbling. The flow rate of Argon was maintained in the range from 20 to 50 liters per minute, depending on slag thickness and metal depth. Several trials were carried out with different casting sections and throughputs. Optimum gas flow rate was calculated theoretically and further adjusted practically with a series of experiments. Sampling was done at different locations in the tundish and slab. Inclusion distribution study was made to compare the effect with the normal heats and improvements achieved were noted as discussed hereunder.
The above process of bottom purging lead to reduction in non-metallic inclusions especially Al203 in cast steel, under all conditions of casting. This establishes the fact that inclusion flotation has improved with bottom purging.In particular, there was up to 60% and 40% reduction in inclusion of size greater than 50 mm and 25 mm respectively.
Advantageously, according to an aspect of the invention, bubbling argon before the ladle opening in empty tundish showed improvement in quality and yield of first slab. Additionally, a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life. Efficiency of inclusion flotation increases at lower casting speed could be achieved and importantly, the percentage of inclusion of larger size reduces with increase in throughput.
7

WE CLAIM:
1. A process for inclusion floatation in tundish comprising:
Controlled bubbling of inert gas in tundish for inclusion floatation by bottom purging in tundish to thereby enhance floatation of even the smaller size inclusions and favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation.
2. A process for inclusion floatation in tundish as claimed in claim 1 comprising bubbling of Argon from the bottom of the tundish.
3. A process for inclusion floatation in tundish as claimed in anyone of claims 1 or 2 comprising bubbling of argon from the bottom of the tundish through porous plugs embedded with respect to the bottom of the tundish.
4. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 3 wherein bubbling of argon from the bottom of the tundish through porous plugs comprises using used ladle bottom porous plugs.
5. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 4 wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter.
6. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 5 wherein selective nos. of selectively spaced apart preferably about 150mm apart porous plugs are embedded in the with optimized location of the purging arrangement.
7. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 6 wherein the argon flow rate was maintained between 20-50lpm w.r.t. slag thickness and metal depth.
8. A process for inclusion floatation in tundish as claimed in anyone of claims 1 to 7 comprising bubbling Argon before ladle opening in empty tundish for improvement in quality and yield of first slab.
8

9. A tundish adapted for efficient inclusion floatation comprising:
means for controlled bubbling of inert gas in tundish for inclusion floatation by bottom
purging in tundish to thereby enhance floatation of even the smaller size inclusions and
favour minimum level of inclusion in the cast slab obtained of such forced inclusion floatation.
10. A tundish as claimed in claim 9 wherein said means for controlled bottom purging comprises porous plugs preferably used ladle bottom porous plugs embedded with respect to the bottom of the tundish.
11. A tundish as claimed in anyone of claim 9 or 10 wherein plurality of said porous plugs are operatively connected to an arrangement for supply of argon gas which is further operatively connected to a Rota meter.
12. A process for inclusion floatation in tundish and a tundish for carrying out such process substantially as herein described and illustrated with reference to the accompanying figures.
Dated this 7th day of February, 2007. Anjan Sen
Of Anjan Sen & Associates (Applicants agent)
9

ABSTRACT
A PROCESS FOR INCLUSION FLOATATION IN TUNDISH.

A process for improving the cleanliness of steel, by inclusion floatation in liquid steel in tundish. Increased level of inclusions lead to nozzle chocking and defects at the user end. The process of forced floatation of inclusions in liquid steel according to the invention by argon/bubbling/purging through tundish bottom, especially achieved desired floatation for sizes of inclusions smaller than 50mm. Bubbling from the bottom of the tundish increases the collision rate, floatation and absorption. Advantageoulsy, used ladle bottom porous plugs are embedded into the dam at tundish bottom, to favor measured flow rate of argon gas through an embedded pipe and a rotameter. Selective argon flow rate was maintained depending on the slag thickness and metal depth in tundish. Reduction in inclusions up to 60% and 40 % were achieved for sizes greater than 50mm and 25mm, respectively.
Figure 1.
10

Documents:

248-MUM-2007-ABSTRACT(GRANTED)-(17-2-2012).pdf

248-mum-2007-abstract.doc

248-mum-2007-abstract.pdf

248-MUM-2007-CANCELLED PAGES(25-1-2012).pdf

248-MUM-2007-CLAIMS(AMENDED)-(24-6-2011).pdf

248-MUM-2007-CLAIMS(AMENDED)-(25-1-2012).pdf

248-MUM-2007-CLAIMS(GRANTED)-(17-2-2012).pdf

248-MUM-2007-CLAIMS(MARKED COPY)-(25-1-2012).pdf

248-mum-2007-claims.doc

248-mum-2007-claims.pdf

248-mum-2007-correspondance-received.pdf

248-mum-2007-correspondence (12-3-2007).pdf

248-MUM-2007-CORRESPONDENCE(20-1-2012).pdf

248-MUM-2007-CORRESPONDENCE(26-12-2011).pdf

248-MUM-2007-CORRESPONDENCE(27-08-2008).pdf

248-MUM-2007-CORRESPONDENCE(28-11-2011).pdf

248-MUM-2007-CORRESPONDENCE(IPO)-(17-2-2012).pdf

248-mum-2007-description (complete).pdf

248-MUM-2007-DESCRIPTION(GRANTED)-(17-2-2012).pdf

248-MUM-2007-DRAWING(GRANTED)-(17-2-2012).pdf

248-mum-2007-drawings.pdf

248-mum-2007-form 1 (12-3-2007).pdf

248-MUM-2007-FORM 18(27-08-2008).pdf

248-MUM-2007-FORM 2(GRANTED)-(17-2-2012).pdf

248-MUM-2007-FORM 2(TITLE PAGE)-(GRANTED)-(17-2-2012).pdf

248-mum-2007-form 2(tittle page)-(9-2-2007).pdf

248-mum-2007-form-1.pdf

248-mum-2007-form-2.doc

248-mum-2007-form-2.pdf

248-mum-2007-form-26.pdf

248-mum-2007-form-3.pdf

248-MUM-2007-REPLY TO EXAMINATION REPORT(24-6-2011).pdf

248-MUM-2007-REPLY TO HEARING(25-1-2012).pdf

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Patent Number

251030

Indian Patent Application Number

248/MUM/2007

PG Journal Number

08/2012

Publication Date

24-Feb-2012

Grant Date

17-Feb-2012

Date of Filing

09-Feb-2007

Name of Patentee

JSW STEEL LIMITED

Applicant Address

JINDAL MANSION, 5-A, DR.G.DESHMUKH MARG, MUMBAI.

Inventors:

#	Inventor's Name	Inventor's Address
1	MAZUMDAR, DEBASISH	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
2	RANJAN, MADHU	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
3	DABBIRU, SATISH KUMAR	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
4	TATHICHERLA, RAJENDRA	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
5	BALANAGI, REDDI PRASAD	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
6	KUPPALA, HARINATH VENUGOPAL	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
7	RAO, RAVISHEKHAR VENKAT	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
8	TIWARI, ASHIWINI KUMAR	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
9	KOPPOLU, ANJANEYULU	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
10	SURYANARAYANA, VISHWANTH CHANDRASHIKARAIAH	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
11	RAJAGOPAIAN, MADHUSUDANA	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
12	SARKAR, ABHIJIT	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.
13	KARANDE, AJIT KUMAR, MAZUMDAR DEBASISH, RANJAN MADHU	JSW Steel Limited, R & D and SS, Vidyanagar Works, Vidyanagar, Toranagallu, Bellary-583 275.

PCT International Classification Number

B22D11/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA