FIELD OF INVENTION

The present invention relates to optimizing the availability of billet caster in particular smaller size billet caster in slab casting process. More particularly, the invention relates to an improved process of slab casting in a smaller-size billet caster with tundish capacity of 20 to 30 tonnes.

BACKGROUND OF INVENTION

The flying tundish practice of prior art adapted at slab caster enables to achieve drastic reduction of the set up time. However, this process is not suitable for smaller section billet casters. According to the prior art, in a continuous casting process, a new tundish is taken-up while retaining the slab in the mould from the previous tundish. Thus, the process of casting can only be re-started upon replacement of the previous tundish by a new tundish resulting in a complete halt of the machine preparation steps leading to a higher set-up time including loss of production. The flying tundish practice has been tried on several times at smaller billet caster but failed mainly due to non joining of fresh liquid with the billets still held in the mould from the previous tundish.
Conventional method of starting the casting process requires many activities to be carried out. These steps take several minutes before the casting operation starts, thereby reducing the caster availability. The primary reasons for failure of the prior art flying a tudish are as follows:
• Non joining of fresh liquid because of very small section size of billet, the liquid available for joining in the billet being very small as compared to a slab.
• safety norms prescribed prohibits reducing the cooling of the billet in a mould.

• Number of operators to start casting depends on number of strand machine. For example, the number of operators shall be six for a six-strand machine as compared to one operator in slab casting. Also all six strands of the machine are to be opened simultaneously thus requiring all six operators to operate from a single compact platform.
• Very high speed of the billet causes a breakage from the joint and thus failure of the strands.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved process of slab casting in a smaller size billet caster with tundish capacity of 20 to 30 tonnes, which eliminates the disadvantages of prior art.
Another object of the invention is to propose an improved process of slab casting in a smaller size billet caster with tundish capacity of 20 to 30 tonnes, which increases the availability of the caster for achieving enhanced production.
A still another object of the invention is to propose an improved process of slab casting in a smaller size billet caster with tundish capacity of 20 to 30 tonnes, which eliminates frequent breakage of the castings from the joints during the production.
A further object of the invention is to propose an improved process of slab casting in a smaller size billet caster with tundish capacity of 20 to 30 tonnes, which increases the process set-up time and reduces strand-failure.

DETAIL DESCRIPTION OF THE INVENTION
Accordingly, the invention provides a process in which all the strands are closed one by one instead of all at a time and that the strands are prepared simultaneously. The sequential process steps according to the invention is illustrated in Table 1.

TABLE 1
Process Steps Time in Min Remarks
1. Close 2 std immediately after the last ladle is closed 0
1. cast steel in the tundish 15
3. Prepare these two closed strands 5 Parallel activity
4. When tundish level is 10 tons close another two strands and prepare the strand 5 Parallel activity
5. When the tundish level is 7 tons, open the protection plate and prepare the new tundish for casting 5 Parallel activity
6. When the tundish level is 5 tons close the balance two strands and take out the tundish and place the new tundish over mould simultaneously 2
7. Prepare the two strands closed at process step 6 5 Parallel activity
8. Place the ladle in casting position and centre the new tundish 2
9. Change the oscillation parameter and select the casting mode. 2 Parallel actiVity
10. Open the ladle

Thus while the tundish liquid is being cast (1S-minutes), all the strands are closed one by one and prepared simultaneously. This takes additional S minutes in starting a new casting phase and thereby eliminating the excess set up completely.
Thus, according to the present invention, when the last ladle of sequence is emptied out, the casting of liquid steel in the tundish (capacity 30 tonnes) continues for 10 min. During this time, the strands are closed one by one and prepared simultaneously. The tundish is taken out while a new tundish is taken parallely. New ladle is opened into the new tundish. Casting starts. This eliminates most of the activities while some are made parallel.
Unlike flying tundish, all strands are new thus reducing the risk of strand-failure due to fresh liqUid not joining properly with the solidifying strands. Also in flying tundish of prior art, any delay in opening the ladle may cause casting to fail. ThE good ladle condition and free ladle opening of ladle are prerequisites for operating the innovative flying tundish process in small-size casters.

WE CLAIM

1. An improved process of slab casting in a billet caster with tundish capacity of approximately 20 to 30 tonnes, comprising the steps of:
- closing a first pair of strands of the caster immediately after the last ladle is closed;
- casting liqUid steel in a first tundish of the caster with a first oscillation parameter, and simultaneously cleaning and preparing said first pair of closed strands for fresh operation;
- closing a second pair of strands when liquid steel at said first tundish reduces to a level of around 33%, and preparing and cleaning said second pair of strands;
- opening the protection plate of the caster when the level of steel is reduced to around 24% in the first tundish, and preparing a second tundish for operation;
- closing a third pair of strand when the level of steel is reduced to around 15% in the first tundish, simultaneously replacing the first tundish with the second tundish, and cleaning including preparing said third pair of strands;
- placing the ladle in casting mode and centering the second tundish including implementing a second oscillating parameter and activating the casting mode; and
- opening the ladle after completion of the slab casting.

2. An improved process of slab casting in a billet caster with tundish capacity of approximately 20 to 30 tonnes, as sUbstantially described and illustrated herein with reference to the accompanying drawings.