The tundish spray lining which was first developed in the 1980s is extensively used in recent times. The thickness varies from 25-75 mm. The lining generally comprises of MgO-SiO2 mix with MgO ranging from 60-90% and is sprayed with the help of a robotic machine that can cut off almost 10% of the material consumption, or by manual application. The lining thickness and the magnesia percentage are varied depending on the need for higher sequence. The working lining protects against slag wear(different metallic oxides and ladle carry over slag and tundish covering compound contributes to erosion) and prevents corrosion of the safety lining, provides resistance to thermal shock, provide good insulation, remain inert to steel and not contribute to oxygen and nitrogen pickup, and promote steel cleanliness. The proper application imparts shrinkage properties which help in deskulling after rendering its service.
Thermal
Peak Temperature: Being in direct contact with steel, the temperature of the lining rises to that of the steel. High-temperature resistant materials (high m.p) are to employed.
Thermal Shock: Although the thermal cycling is not of huge concern but comes into picture when there is a variation in the bath level in the tundish. During normal operation practice the top part which is not with steel cools off and when the level rises, the top lining comes in contact with steel but certain fall in level exposes it to the ambient air temperature making it more susceptible to thermal shock. The preheating of the lining is important as far as thermal cycling is concerned.
Mechanical
Impact: The impact from the steel is less but in certain cases when the shroud is inclined or the turbulence inhibitor box is misplaced considerable impact can take place.
Abrasion: The abrasion is less during the steady-state casting operations.
Applied stress: The height of the lining is quite less. Thickness is quite less as well and thus the expansion compensation to be given will not be huge and can expand without much restriction.
Chemical
Dissolution: Wear by dissolution depends on the chemical compatibility of the slags with bricks. Slags in the tundish are wide-ranging in chemistry and therefore proper selection is to be made. Therefore a castable of either high alumina or spinel or magnesia based is normally preferred. The slag chemistry are Al203-3-35%,Cao-01-40%,SiO2 -3-90% ,MgO-1-20% and FeO-1-3%.
Penetration: Penetration is caused by low viscosity metal/ slag or highly wetting metal/slag penetrating into porous refractories which can be a problem for the safety lining of a tundish owing to the fair porosity. The porosity factor is to be investigated at the time of material selection and application, especially for higher casting sequence.
Thermo- Mechanical
Strain of thermal expansion– The strain is considerably low because of its low height and thickness.
Chemical Mechanical and thermo-mechanical chemical
Spalling of the penetrated zones- This does not apply because the combined action of all the factors is rare.
