FORM 2
THE PATENT ACT 197 0 (39 of 1970)
&
The Patents Rules, 2003 COMPLETE SPECIFICATION
(See Section 10, and rule 13)
1. TITLE OF INVENTION
AN EXTENSION BEING ATTACHED IN A CASTING APPARATUS FOR INCREASING METALLURGICAL LENGTH OF CASTING APPARATUS
2. APPLICANT(S)
a) Name : JSW ISPAT STEEL LIMITED
b) Nationality : INDIAN Company
c) Address : CASABLANCA, PLOT NO. 45,
SECTOR -11,
CBD BELAPUR,
NAVI MUMBAI-4 0 0 614
MAHARASHTRA, INDIA
3. PREAMBLE TO THE DESCRIPTION
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 the casting apparatus being used for casting of molten or liquid steel. More particularly it relates to addition of a new segment at the bottom of the casting apparatus to increase the metallurgical length of the casting apparatus which ultimately increases the speed of the casting apparatus.
BACKGROUND OF THE INVENTION
Continuous casting is the process whereby molten steel is solidified into a "semi finished" billet, bloom or slab for subsequent rolling in the finishing mills. Essentially, a continuous caster is composed of a tundish, a mold oscillator, a group of cast-strand supporting rolls, rolls for bending and straightening the cast strand, rolls to pinch and withdraw the cast strands, a group of spray nozzles, a shearing apparatus for cutting the cast strand, a dummy bar for extracting the cast strand at the start of casting, and other components. Such continuous caster is shown in figure 1.
To start the casting process, a dummy bar (which is connected to an external mechanical withdrawal system) (not shown in figure) is inserted in the mold and positioned so that the top of the dummy bar closes the bottom of the mold. Liquid steel is delivered in a ladle (2) to the casting floor where it is poured at a controlled rate into the tundish (3). Liquid metal flows through submerged entry nozzle (4) in the bottom of the tundish (3) and fills the mold (5). When the liquid metal level in the mold (5) reaches a predetermined position, withdrawal of the dummy bar is initiated. The withdrawal speed of the dummy bar is preset based on the casting speed required or the metal flow rate from the tundish (3). When the dummy bar head, which is now attached to the solidified shape being cast, reaches a certain position in the withdrawal system, it is mechanically disconnected and the dummy bar removed. The solidified cast shape continues through the withdrawal system to the shearing equipment.
Solidification of the liquid steel starts in the water cooled mold (5) and continues progressively as the strand (6) moves through to the casting apparatus. Freezing begins at the liquid steel meniscus level (M) in the mold forming a shell in contact

with the walls of the mold. The distance from the meniscus level (M) to the point of complete solidification within the apparatus is called the METALLURGICAL LENGTH (ML). Obviously, the point of complete solidification must occur ahead of the straightener (9). Casting conditions are established such that the strength of the solidified steel shell leaving the mold (5) is sufficient to withstand the ferrostatic pressure of the liquid steel in the mold. To prevent sticking of the solidified shell to the mold wall, the mold (5) is oscillated in a vertical direction. Friction between the shell and the mold is minimized by the introduction of mold powder {mold flux) which forms a fluid slag.
Below the mold, additional heat is removed from the strand in the secondary cooling zones (7) and solidification is completed. The secondary cooling zones (7) consist of a series of water sprays (8). Flow rates are closely controlled to obtain optimum cooling rates and strand surface temperatures. Support role units (Segments) are provided to contain the strand to avoid transverse movement and to prevent bulging of the hot solidifying shell from internal ferrostatic pressure. Secondary cooling region (7) is followed by a bending unit and straightener (9).
After straitening the cast section is cut to the desired length by the shearing apparatus and these are either discharged to a storage area or to the hot rolling mill. A wide range of strand dimensions can be cast depending on final application: 'slabs' for flat products such as plate and strip, 'blooms' for sections such as beams, and 'billets' for long products such as wire.
Therefore in the continuous casting process, molten metal is delivered from the bottom of a transfer vessel (the tundish) into a mold cavity. Here, the water-cooled walls of the mold extract heat to solidify a shell that contains the liquid pool. The shell is withdrawn from the bottom of mold at a "casting speed" that matches the inflow of metal, so that the process ideally operates at steady state and constant meniscus level in mould. Below the mold, water sprays extract heat from the surface, and the strand core eventually becomes fully solid when it reaches the "metallurgical length.
Currently available caster has limited metallurgical length which does not permit caster to increase its speed beyond particular speed. It ultimately reduces the

productivity. Therefore it is a need to provide caster with increased metallurgical length.
OBJECTS OF THE INVENTION:
The main object of the present invention is to provide a casting apparatus with increased metallurgical length which increase the productivity of the casting apparatus.
Another object of the present invention is to provide a casting apparatus with increased metallurgical length which increase the quality of the product.
Yet another object of the present invention is to provide a casting apparatus with increased metallurgical length which improves casting speed.
Yet another object of the present invention is to provide a casting apparatus with increased metallurgical length which improves slab thickness.
Yet another object of the present invention is to provide a casting apparatus with increased metallurgical length which improves the cost efficiency.
Yet another object of the present invention is to provide a casting apparatus with increased metallurgical length which improves the yield.
SUMMARY OF THE INVENTION:
Accordingly to achieve the aforesaid objects present invention provides an extension being attached between secondary cooling zone and straightening roller unit in a casting apparatus for increasing metallurgical length of casting apparatus, said extension comprising:
a roller bridge assembly comprising a pair of roll bridge unit, each of said roll bridge unit comprises:

• pair of rolls, the diameter of said rolls is more than the diameter of rolls being used in secondary cooling zone;
• locking arrangement for the purpose of attachment of said extension between secondary cooling zone and straightening roller unit;
• plurality of spray nozzles for spraying the water for cooling the strand;
• water supply unit to supply water to spray nozzles for spraying purpose; and
• a frame to hold a pair of rolls, locking arrangement, spray nozzles and water supply unit.
According an embodiment of the invention one of the roll bridge units is fixed and other is movable.
According to another embodiment of the invention roller bridge unit further comprises lubrication unit being provided on said frame for providing lubrication to rolls.
According to yet another embodiment of the invention size of rollers of each roll bridge unit is 737x160 mm and 677x160 mm and pitch of each roll is 195 mm.
Further there is provided Casting apparatus having increased metallurgical length and being provided with an extension in accordance to present invention.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 Shows the continuous casting apparatus in accordance to prior art.
Figure 2 Shows the segment in accordance to present invention being
attached at the bottom of the continuous casting apparatus as shown in figure 1 to increase the metallurgical length of the continuous casting apparatus.

DETAILED DESCRIPTION OF THE INVENTION:
The above, and the other objects, features & advantages of invention will become apparent from following description read in conjunction with the accompanying drawings.
The metallurgical length of a caster is an important factor for achieving desired casting speed without breakout of the sequence in the continuous casting process. Metallurgical length of a caster should be less than or equal to the machine length of the caster. If the metallurgical length is less then high casting speed can not achieved. If caster with short metallurgical length runs with high speed, the partially solidified portion of the strand could not able to withstand the Ferro-static pressure of the liquid metal without secondary roll support, so there is large possibility of breakout. So in our present innovation the metallurgical length of the caster increased with increase in the machine length of the caster.
Now referring to figure 2, the segment in accordance to present invention being attached at the bottom of the continuous casting apparatus as shown in figure 1 to increase the metallurgical length of the continuous casting apparatus is shown.
The segment (11) in accordance to present invention is attached between secondary cooling zone (7) and straightening roller unit (9) in a casting apparatus (1) for increasing metallurgical length of casting apparatus (1). The segment (11) comprises a roller bridge assembly (12) which comprises a pair of roll bridge units (13, 14). Both roll bridge units (13, 14) are connected to each other. One roll bridge unit (13) is fixed and other (14) is loose.
Each of roll bridge unit (13, 14) comprises a pair of rolls (15, 16, 17, 18). These rollers (15, 16, 17, 18) are arranged in two number of rows. The size of roll is 737x160 mm and 677x160 mm. The rolls (15, 16, 17, 18) are accommodated in the bearing blocks (19). The bearing blocks (19) not only accommodate the rolls (15, 16, 17, 18) but also ensures their free rotation. The pitch of roll is 195 mm. The diameter of these rolls (15, 16, 17, 18) is more than the diameter of rolls being used in secondary cooling zone. The diameter of roll (15, 16, 17, 18) is 160 mm which is 10

mm more than that of the rolls used in the secondary cooling zone (7). This increase in roll diameter is designed because with progress of solidification there is decrease in overall volume of the cast product due to solidification shrinkage. So to accommodate the decrease in volume of the cast product the gap between the fixed Roll Bridge (13) and loose Roll Bridge (14) is decreased by increasing roll diameter.
Further locking arrangement (20, 21) is provided for the purpose of attachment of the segment (11) between secondary cooling zone (7) and straightening roller unit (9). The plurality of spray nozzles (22) are provided with spray pipe (23) for spraying the water for cooling the strand. These spray nozzles (22) are connected to distributor (24). The distributors (24) supply the water to spray nozzles for spraying purpose. The grease line (31) is provided for lubricating the rolls (15, 16, 17, 18).
All the components (20, 21, 22, 23) of each roll bridge unit (13, 14) are mounted on the frames (25, 26). Each roll bridge unit (13, 14) consists of a frame (25, 26). Lifting legs (27, 28, 29, 30) are provided at the corners to ensure the lifting of the segment (11).
As the machine length increased, the length of the semi solidified strand in the segment section increased. So with this increase in the machine length, the support to the long semi solidified strand increased. So the metallurgical length of the caster is increased. With this increase in metallurgical length, the speed of the caster also increased.
Following examples will show that how the speed of casting apparatus increases with increase in metallurgical length (ML).

EXAMPLES:
i. Calculation of maximum casting speed of the existing (prior art) casting apparatus:
The metallurgical length can be calculated by following equation:
Metallurgical Length (L) = (X/K)2 x Vc (equation 1)
Casting speed (Vc) = L/(X/K)2 (equation 2)
Where:
L is Metallurgical length (Cast distance from mold steel meniscus,
where solidification begins).
X is half slab thickness.
K*27.
Vc is casting speed.
Now, L = 6.97 m X = 31 mm K = 27.2
After putting above values in equation 2, Vc = 5.37 m/min.

ii. Calculation of maximum casting speed of the casting apparatus in accordance to present invention:
Here L = 7.36 m X = 31 mm K = 27.2
After putting above values in equation 2,
Vc = 5.67 m/min.
From above examples, it is clear that metallurgical length of the casting apparatus can be increased by adding the segment of present invention and which ultimately increases the casting speed.

INDUSTRIAL APPLICABILITY:
Casting apparatus with increased metallurgical length in accordance to present invention is used for continuous casting of the steel or other molten metal. A wide range of strand dimensions can be cast depending on final application: 'slabs' for flat products such as plate and strip, 'blooms' for sections such as beams, and 'billets' for long products such as wire. Because of increased metallurgical length the casting apparatus improves the yield, quality, productivity and cost efficiency.
Although the present invention has been described with respect to specific, preferred embodiments, various changes and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.

WE CLAIM:
1. An extension being attached between secondary cooling zone and straightening roller unit in a casting apparatus for increasing metallurgical length of casting apparatus, said extension comprising:
a roller bridge assembly comprising a pair of roll bridge unit, each of said roll bridge unit comprises:
• a pair of rolls being arranged in a row, the diameter of said rolls is more than the diameter of rolls being used in the secondary cooling zone;
• locking arrangement for the purpose of attachment of said extension between the secondary cooling zone and the straightening roller unit;
• plurality of spray nozzles for spraying the water for cooling the strand;
• water supply unit to supply water to spray nozzles for spraying purpose; and
• a frame to hold a pair of rolls, locking arrangement, spray nozzles and water supply unit.

2. The extension as claimed in claim 1 wherein one of the roll bridge units is fixed and other is movable.
3. The extension as claimed in claim 1 wherein size of rollers of each roll bridge unit is 737x160 mm and 677x160 mm.
4. The extension as claimed in claim 1 wherein pitch of each roll is 195 mm.
5. The extension as claimed in claim 1 wherein roller bridge unit further comprises lubrication unit being provided on said frame for providing lubrication to rolls.

6. Casting apparatus having being provided with an extension as claimed in any of the claims 1 to 5, the extension is attached between secondary cooling zone and straightening roller unit in the casting apparatus.