Ladle safety lining is very important as far as the prevention of ladle breakouts is concerned and at the same time, it helps in the retention of heat and protects the shell from cracking.
Thermal
Peak Temperature: The temperature can be considerably high if the working lining gets worn out. But the chances of steel penetrating into the safety lining is rare and thus it will experience ambient temperature in the 600-900degree centigrade range. Thus refractory with a high melting point is not required if and only this factor is taken into consideration.
Thermal Shock: Although thermal cycling is not of huge concern. The preheating of the lining is somewhat important as far as thermal cycling is concerned.
Mechanical
Impact: The impact from the steel is minimal but in certain cases like dig out.
Abrasion: The abrasion is less and comes into only at the time when the working lining is lost.
Applied stress: The height of the lining is quite high but the temperature is low so there is less applied stress when bricks are used. But when monolithic materials are used huge expansion takes place and expansion joints are to be built to compensate for the expansion. Ramming materials are used for the ladle safety wall to allow for the expansion.
Chemical
Dissolution: Wear by dissolution depends on the chemical compatibility of the slags with bricks. Slags are wide-ranging in chemistry but are basic in nature and therefore a basic refractory is preferred. Magnesia or dolomite is, therefore, a suitable option.
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 the ladle.
Thermo- Mechanical
Strain of thermal expansion– Expansion allowance is required when monolithic refractory and if such provisions are not available the expansion of such huge mass will create an immense strain on the refractory.
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.
Material Chosen
Safety wall: Although brick can be used but the most common practice being the use of monolithic refractory either cast in place or shotcrete into place. Alumina-based refractory is used to add refractoriness in case the working lining is lost. Stainless steel needles are also used to impart long-term toughness. In the case of brick, the two-layer lining is used, one being the one with magnesia, magnesia spinel, or alumina spinel, and the other layer being the insulation board. Sometimes dry vibratable material is also used as the safety lining.
Safety bottom: The best practice employed is 25mm of levelling layer of dry vibratable on the shell and then a precast medium alumina safety bottom is used (50-60% alumina) is used in one or two pieces with lap joints to ensure minimum penetration.
