The role of tundish in the continuous casting process evolved from that of a buffer between the ladle and mould to being a grade separator and also a device for removing unwanted inclusions through metallurgical processes / chemical reactions. The tundish is intended to deliver the molten metal to the moulds evenly and at a designed throughput rate and temperature without causing contamination by inclusions. It distributes molten steel in continuous casting moulds and is typically operated at a constant bath depth to ensure a constant feed rate into the mould required to achieve a constant throughput. In the sequence of continuous casting, tundish directly control the molten steel in the last stage of liquid steel processing and the refractories used here are therefore, required to have high stability and special properties. Tundish is one of the most important areas of Refractory Application and so, is also one of the biggest ‘cost control center’ in the continuous casting process.
Tundish Refractory Lining
After Bricked Lining and then Gunnable Lining, Tundish Boards (or Board Lining) came into existence as working lining. Silica boards are used for MS grade and MgO boards for SS grade and for high Ca ppm steel. The reason being silica is attacked by lime, alumina and iron oxide present in the steel.
However, for longer duration casting Sprayable Lining such as MgO spray mass (Magnesite spray mass) are widely used with MgO content varying from 70 - 90% and minimum silica content. For example, for 10-12 hrs casting, 70-75% MgO with silica content below 15% are working well. But to achieve 20-25 hrs life, 90% MgO with silica content less than 10% with 35-40 mm thickness at wall and 50-60 mm thickness at the bottom are required. Separate preheating arrangement is required to form the chemical bonding in spray mass after application at around 1000°C.
Of late, tundish spray mass has gradually been replaced by Dry Vibro mass to further elongate the casting sequence. MgO content varies from 70-90% with low silica content to achieve a sequence length of 12-15 hrs to 35-40 hrs. One advantage of Dry Vibro mass is that it ensures low hydrogen pick up in steel as it does not require water for application. Approximately 0.7-0.9 ppm hydrogen pick up is reported as compared to 1.8-2.4 ppm in spray mass. Special drying arrangement is required for drying this mass at around 300°C for 24 hrs to develop polymerisation of resin which gives strength to it.
Tundish Refractory Lining
After Bricked Lining and then Gunnable Lining, Tundish Boards (or Board Lining) came into existence as working lining. Silica boards are used for MS grade and MgO boards for SS grade and for high Ca ppm steel. The reason being silica is attacked by lime, alumina and iron oxide present in the steel.
However, for longer duration casting Sprayable Lining such as MgO spray mass (Magnesite spray mass) are widely used with MgO content varying from 70 - 90% and minimum silica content. For example, for 10-12 hrs casting, 70-75% MgO with silica content below 15% are working well. But to achieve 20-25 hrs life, 90% MgO with silica content less than 10% with 35-40 mm thickness at wall and 50-60 mm thickness at the bottom are required. Separate preheating arrangement is required to form the chemical bonding in spray mass after application at around 1000°C.
Of late, tundish spray mass has gradually been replaced by Dry Vibro mass to further elongate the casting sequence. MgO content varies from 70-90% with low silica content to achieve a sequence length of 12-15 hrs to 35-40 hrs. One advantage of Dry Vibro mass is that it ensures low hydrogen pick up in steel as it does not require water for application. Approximately 0.7-0.9 ppm hydrogen pick up is reported as compared to 1.8-2.4 ppm in spray mass. Special drying arrangement is required for drying this mass at around 300°C for 24 hrs to develop polymerisation of resin which gives strength to it.
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