The tundish safety linings play an important role in the prevention of tundish breakouts and at the same time helps in the retention of heat in the system(reduces temperature loss) and protects the shell from cracking.
Safety lining design is a balance between three keys areas of heat flow (shell protection, thermal losses), insulation material strength (lining integrity) and chemical wear(higher corrosion). When the amount of insulation will increase then the temperature of the lining increases and therefore the wear increases exponentially but the shell temperature decreases.
Thermal
Peak Temperature: Due to the presence of thin working lining which ranges from 30-50mm in thickness the safety lining temperature can reach very high temperatures. Therefore a refractory material that can withstand high temperature is to be selected. Thus alumina-based material are a suitable choice.
Thermal Shock: Thermal cycling for the safety lining is not of high concern and becomes a serious issue when the tundish is water-cooled, but can be neglected in case of normally air cooled scenario.
Mechanical
Impact: The working lining takes care of the impact and the safety lining suffers from very less impact. Only in certain cases when the steel skull gets stuck on the lining there can be a considerable impact because of the use of backhoe machine.
Abrasion: Abrasion is also not a big concern unless and until the working lining is worn out and the steel can penetrate through it. Although the frequency of such an occurrence is rare.
Applied stress: The height of the sidewall is fairly low,but depending on the length of a tundish. For a monolithic safety wall depending on the length the amount of expansion can be huge, and expansion joints must be built into the lining to compensate for the expansion. The ends of the tundish between the shell and the lining are fixed with soft insulation board that provides compressibility and allows for the expansion of this large mass of safety lining.
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 the correct match needs to be made. Hence a castable of either high alumina or spinel based material is normally used. The range of slag chemistry are Al203-3-35%,Cao01-40%,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 is not a problem for the safety lining of a tundish.
Thermo- Mechanical
Strain of thermal expansion– The height of the sidewall is fairly low, but depending on the length of a tundish. For a monolithic safety wall depending on the length the amount of expansion can be huge, and expansion joints must be built into the lining to compensate for the expansion. The ends of the tundish between the shell and the lining are fixed with soft insulation board that provides compressibility and allows for the expansion of this large mass of safety lining.
Chemical Mechanical and thermo-mechanical chemical
Spalling of the penetrated zones- This does not necessarily apply for tundish safety lining as the combined effect of all factors acting simultaneously is rare.
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