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

FIELD OF THE INVENTION
The present invention relates to a method of controlled ramping of liquid steel level in tundish during ladle change over for reduced emulsification and a system to implement said method. More particularly, the present invention is directed to automatic tundish filling at controlled slow rate to control/avoid emulsification between the liquid steel poured in the tundish from ladle and the tundish covering slag during ladle change over. Importantly, the filling rate is maintained as low as possible favoring minimizing/eliminating on one hand emulsification of liquid steel by silica based covering slag, and on the other hand ensure improved cleanliness/quality of steel and thus avoiding defects/rejection of slabs cast during ladle change over. The method of auto ramping of tundish also avoids manual operation and thus ensuring improved working condition and safety of operators. The system and method of auto ramping of tundish weight according to the present invention is thus having prospect for wide scale application in tundish filling in continuous caster of steel plants with significant advantage in terms of improved cast steel quality, less rejection and improved productivity/yield in a simple, safe and cost effective manner.
BACKGROUND ART
The conventional continuous casting plant for slabs/billets involves a continuous caster comprising a tundish, a mold, a mold oscillator, a group of cast-strand supporting rolls. The function of the rolls includes operations like bending and/or straightening the cast strand, rolls to pinch and withdraw the cast strands. The continuous casting strands also include a group of spray nozzles for cooling, a torch cutter for cutting the cast strand, a dummy bar for extracting the cast strand at the start of casting, and other related components. In continuous casting the molten steel passes from ladle to mould through an intermediate buffer called tundish. The tundish is essentially a flow distributor adapted to maximize the liquid steel residence time in order to promote inclusion flotation. Importantly, the performance of a tundish is evaluated in the light of process control parameters like inclusion floatability, slag entrainment, solid skull etc., that are essential variables to be taken care of in tundish design along with the fluid flow conditions therein during operation.

It is well known in the art of iron and steel production and processing, that steei making shops operate at high productivity wherein each tundish is used to cast 8-10 heats for a sequence of a similar grade. The time between the closure of empty ladle and opening of other filled ladle is the ladle changeover time, when the casting process still continues in continuous caster. During this ladle change over time, the steel level in the tundish goes down. When the new steel is poured in tundish at this low level, creates high emulsification between the steel and tundish covering slag. In conventional practice, the high velocity stream exiting through the ladle shroud proceeds directly vertically downward to the tundish bottom and strikes the flat impact pad placed at the bottom with negligible lateral dispersion. Upon striking a flat impact pad, the stream is deflected in numerous horizontal directions with little change in velocity. In effect, the fast flowing liquid steel proceeds up the adjacent walls of the tundish, causing turbulence at the surface, opening up the slag cover, exposing the steel to oxygen and nitrogen pickup, and allowing entrapment of slag and inclusions. The flow pattern then carries the entrained nonmetallic material toward the ladle shroud where this is carried downward and mixed within the bulk of the liquid steel volume and subsequently solidified in the mould. These entrapped slag particles act as source of defects during processing. It has been also established that most of the defects are found in ladle change over slabs.
There has thus been in a continuing need in the related art to developing a method for controlled filling of liquid steel in the tundish so as to avoid emulsification between the steel and tundish covering slag, reduce silica based inclusions or slag entrapments in liquid steel due to pouring pattern and turbulence creation in tundish, particularly during ladle change over when steel level goes down, leading to poor quality of slabs cast during the time of change over , making these slabs unfit for further processing. It has also been a requirement in the art to implement such controlled steel entry in tundish at a desired slow rate in an automated manner involving a system therefore, reducing human intervention favoring safe and operator friendly operation while ensuring improved quality and productivity.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide a method for controlled auto ramping of liquid steel in tundish adapted to reduce emulsification by controlled

slow steel filling rate of tundish during the ladle change over and a system to implement such method.
Another object of the present invention is directed to a method for weight based controlled ramping of liquid steel in tundish adapted to reduce emulsification by controlled rate of steel filling in tundish wherein silica inclusion or slag entrapment is reduced to improve steel cleanliness/quality of cast steel during the ladle change over.
A further object of the present invention is directed to a method for weight based controlled auto ramping of liquid steel in tundish adapted to reduce emulsification by controlled rate of steel filling in tundish wherein the control system for tundish filing is linked with tundish weight governing the slide gate opening.
A still further object of the present invention is directed to a method for weight based controlled auto ramping of liquid steel in tundish adapted to reduce emulsification by controlled rate of steel filling in tundish wherein the system and method for tundish filling is developed based on simulating the actual casting conditions by water modeling.
A still further object of the present invention is directed to a method for weight based auto ramping of liquid steel in tundish adapted to reduce emulsification wherein steel filing rate of tundish is maintained as low as possible as function of tundish throughput.
A still further object of the present invention is directed to a method for weight based controlled auto ramping of liquid steel in tundish adapted to reduce emulsification wherein defects in ladle change over slabs are minimized/eliminated, resultantly increasing productivity and yield in continuous casting.
A still further object of the present invention is directed to a method for weight based controlled auto ramping of liquid steel in tundish adapted to reduce emulsification wherein an automated system for slide gate opening commensurate with desired steel filing rate is implemented, controlled by increase in tundish weight in small steps. A still further object of the present invention is directed to a method for weight based controlled auto ramping of liquid steel in tundish adapted to reduce emulsification wherein said auto ramping of tundish steel level favour avoiding manual operation and also improving the work condition.

SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention the same is directed to a method of controlled ramping of tundish weight for reduced emulsification comprising,
carrying out controlled slow rate of steel filing in tundish as a function of throughput ensuring maximum steel cleanliness free of any inclusions/entrapment.
Another aspect of the present invention is directed to a method of controlled ramping of tundish weight for reduced emulsification wherein said controlled slow rate of steel filling comprises said filling in auto control mode up to a desired safe level with slide gate opening operated pneumatically governed by tundish weight through a programmable logic controller.
A further aspect of the present invention is directed to said method of controlled ramping of tundish weight for reduced emulsification, wherein rate of steel filling is as low as possible, preferably 1.15 times the throughput.
A still further aspect of the present invention is directed to a method of controlled ramping of tundish weight for reduced emulsification, wherein rate of filling is selected so that tundish filing is completed in 10-15 minutes during ladle change over.
According to yet another important aspect of the present invention directed to said method of controlled ramping of tundish weight for reduced emulsification wherein percentage of the slide gate opening through a programmable logic controller is based on the tundish weight .
A still further aspect of the present invention is directed to said method of controlled ramping of tundish weight for reduced emulsification wherein slide gate opening rate is optimized such as to obtain an increment of 0.6t/min in tundish weight in small steps, preferably about 3 steps per minute.
A still further aspect of the present invention is directed to said method of controlled ramping of tundish weight for reduced emulsification wherein, auto filling of tundish

runs to steady state level, preferably 2 tonnes less than full level of tundish as a factor of safety, in 10-12 minutes.
Yet another aspect of the present invention is directed to a system adapted for controlled ramping of tundish weight for reduced emulsification and carry out the method, comprising
steel filling control means linked to tundish weight adapted for controlled slow rate of steel filling in tundish as a function of throughput ensuring maximum steel cleanliness free of any inclusions/entrapment.
Further said system according to the present invention comprising
said steel filling control means comprising the slide gate opening is pneumatically controlled by tundish weight, and
a programmable logic controller (PLC) operatively controlling the percentage slide gate opening, governed by desired increase in tundish weight in small incremental steps.
The various objects and advantages of the present invention are described in greater details with reference to the following accompanying non limiting illustrative figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
Figure 1: is the graphical illustration of the tundish weight vs time plot for the tundish filling pattern followed during ladle changeover in conventional practice.
Figure 2: is the graphical illustration of the tundish weight vs time plot for the slow tundish filling pattern followed during ladle changeover according to the auto ramping method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
Reference is first invited to the accompanying Figure 1 that graphically illustrates the tundish weight vs time plot for the tundish filing pattern followed during ladle changeover in conventional practice. It is clearly apparent from the accompanying Figure 1 that the liquid steel level at tundish is diminished from 32T level to 22t usually within 3 minutes when steel level in tundish goes down substantially and a fresh ladle is placed over tundish for filling. In the conventional practice, filling is completed at relatively faster speed taking about only 1 minute to replenish the steel level to 32T. This steel filling practice leads to turbulence of steel flow past the tundish wall, particularly when steel level in the tundish goes down. When the new steel is poured in tundish at this low level, it creates high emulsification between the steel and tundish covering slag, due to the high velocity of stream exiting through the ladle shroud proceeding directly vertically downward to the tundish bottom, strikes the flat impact pad and then is deflected in numerous horizontal directions with little change in velocity. In effect, the fast flowing liquid steel proceeds up the adjacent walls of the tundish, causing turbulence at the surface, opening up the slag cover, exposing the steel to oxygen and nitrogen pickup, and allowing entrainment of slag and inclusions. The flow pattern then carries the entrained nonmetallic material toward the ladle shroud where this is carried downward and mixed within the bulk of the liquid steel volume and subsequently solidified in the mould. These entrapped slag particles acts as source of defects during processing. It has been also established that most of the defects are found in ladle change over slabs.
In order to overcome the disadvantages and limitations of the prior art tundish filling practice, the steel filling regime of the present invention is directed to developing a method for tundish weight based auto ramping of liquid steel in tundish during the ladle change over adapted to reduce emulsification by controlled slow rate of steel filling in tundish and a system to implement such ramping method.
Reference is now invited to the accompanying Figure 2 that graphically illustrates the plot of tundish weight vs time for the slow tundish filling pattern followed during ladle changeover according to the auto ramping method of the present invention. It is clearly apparent from the accompanying Figure 2 that the tundish filling is carried out at a much

slower rate taking more time to replenish the spent quantity of liquid steel from fresh feed from a new ladle after change over.
As the tundish size and dimensions (width, breadth and depth of liquid) are normally fixed and cannot be varied, the present invention conducted detailed study of emulsification behavior using a 0.4 scale Perspex sheet water model, simulating the casting conditions during ladle changeover. It has been concluded from observed results that to ensure maximum steel cleanliness, emphasis is needed on rate of tundish filling. It has been further established experimentally that the rate of filling is as low as possible, preferably 1.15 times the throughput. This practice results in complete tundish filling in a time duration of 12 -IS minutes as compared to conventional fast filling taking 1-2 minutes. Also to have precise control on rate of filling, the same has to be carried out in auto mode avoiding human intervention.
Automatic slow filling technique has been adopted in a caster in real life operation and found to be very effective. Due to unavailability of exact measurement of slide gate opening in relation to the steel flow, filling control system developed is linked to tundish weight. Tundish weight thus governs percentage of the slide gate opening through a programmable logic controller (PLC). An optimized opening rate is maintained to get an increment of 0.6t/min in tundish weight in small steps (3 steps per min). The filling continues in auto control mode till two tonnes less than the full level of tundish is complete, as a safety measure for the continuous operation. This ramping of tundish steel level runs automatically as the slide gates open. Under the new regime tundish is filled to steady state level in 10-12 minutes as compared to conventional method of 1-2 minutes. Resulting steel samples with slow tundish filling shows minimum of silica based inclusions resulting from emulsification of silica based covering slag, therefore improving steel quality.
It is thus possible by way of the present invention to developing a method for weight based auto ramping of liquid steel in tundish during ladle change over adapted to reduce emulsification by controlled slow rate of steel filling in tundish and a system to implement such ramping method. The method involves low filling rate of steel as a function of the ladle through put and result in complete ladle filling in 12-15 minutes time so that turbulence in liquid steel is avoided and silica inclusion or slag entrapment is minimized/eliminated ensuring improved cleanliness and quality of cast steel. The system

of the invention is having PLC based control of pneumatically operating/opening slide gate for steel filling in tundish favoring automatic weight based filling of tundish up to a safe level. The auto ramping method and system for tundish according to the present invention is thus capable of wide industrial application in steel industry with less defects and rejections of change over slabs in continuous casting, with improved productivity at less cost in a safe and reliable manner.

We Claim:
1. A method of controlled ramping of turtdish weight for reduced emulsification
comprising
carrying out controlled slow rate of steel filling in tundish as a function of throughput ensuring maximum steel cleanliness free of any inclusions/entrapment.
2. A method of controlled ramping of tundish weight for reduced emulsification as claimed in claim 1 wherein said controlled slow rate of steel filling comprises said filling in auto control mode up to a desired safe level with slide gate opening operated pneumatically governed by tundish weight through a programmable logic controller.
3. A method of controlled ramping of tundish weight for reduced emulsification as claimed in anyone of claims 1 or 2 , wherein rate of steel filling is as low as possible, preferably 1.15 times the throughput.
4. A method of controlled ramping of tundish weight for reduced emulsification as claimed in anyone of claims 1 to 3 , wherein rate of filling is selected so that tundish filing is completed in 10-15 minutes during ladle change over.
5. A method of controlled ramping of tundish weight for reduced emulsification as claimed in anyone of claims 1 to 4 , wherein percentage of the slide gate opening through a programmable logic controller is based on the tundish weight .
6. A method of controlled ramping of tundish weight for reduced emulsification as claimed in anyone of claims 1 to 5, wherein slide gate opening rate is optimized such as to obtain an increment of 0.6t/min in tundish weight in small steps, preferably about 3 steps per minute.
7. A method of controlled ramping of tundish weight for reduced emulsification as claimed in anyone of claims 1 to 6 wherein auto filing of tundish runs to steady state

level, preferably 2 tonnes less than full level of tundish as a factor of safety, in 10-12 minutes.
8. A system adapted for controlled ramping of tundish weight for reduced
emulsification and carry out the method as claimed in anyone of claims 1 to 7,
comprising
steel filling control means linked to tundish weight adapted for controlled slow rate of steel filling in tundish as a function of throughput ensuring maximum steel cleanliness free of any inclusions/entrapment.
9. A system as claimed in claim 8 comprising,
said steel filling control means comprising the slide gate opening is pneumatically controlled by tundish weight, and
a programmable logic controtter (PLC) operatively controlling the percentage slide gate opening, governed by desired increase in tundish weight in small incremental steps.
10. A method of weight based auto ramping of tundish steel level during ladle change
over and a system for implementation thereof substantially as here in described with
reference to the accompanying illustrative drawings.