|Working Refractory Lining – Tundish board or Basic Spray Mass or Dry Vibro Mass||Silica board / MgO board / MgO based Spray Mass / Dry Vibro Mass|
|Well block Precast shape||High Alumina Precast|
|Fixing Castable||80% Alumina|
|Tundish Flow Modifier (TFM) instead of tundish furniture ||85% Alumina Precast|
|Tundish Nozzle||Alumina graphite / Zirconia |
|Monoblock Stopper||Alumina graphite with Magcarbon (MgO-C) tip |
|SEN fixing Mortar||Basic mortar (MgO based)|
|TCD Mechanism / Submerged Nozzle||Alumina graphite with 80% ZrO2 and anti-clogging layer in bore|
|Ladle Shroud||Alumina graphite|
|Backup Lining||70% Alumina Low Cement Castable (LCC)|
|Impact Pad||Precast refractory shape with 80-90% Alumina Low Cement Castable (LCC)|
|Insulation||High strength Ceramic Fibre Board|
Functions and Importance of Tundish in Continuous Casting
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.
Article continues after the Ad -
Working lining remains in contact with steel and erosion is initiated at the metal-air interface with fluctuation of metal level in tundish. Different metallic oxides present in the metal are the primary eroding agents of tundish refractory lining. Slag coming in contact with tundish refractory during casting and the tundish covering powder are also responsible for erosion. The starting point of erosion is the formation of ‘Hair Cracks’ at the metal-air interface due to thermal spalling. Penetration of liquid metal and slag takes place through these Hair Cracks and subsequently erosion occurs. Lower erosion of working lining also ensures less nonmetallic inclusion in steel.
To know more about the advantages and disadvantages of each type please refer to our article -
The table below lists wide range of refractories with their qualities respectively that are used in Tundish during Continuous Casting for different applications :
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 polymerization of resin which gives strength to it.