The installation of the porous plug on the ladle bottom is useful in homogenizing temperature and chemistry, better slag/metal interaction for impurity removal, faster processing through ladle metallurgy stations, higher yields. However, stirring is associated with increased bottom wear and shorter campaign life due to the abrasion of the bottom. Vigorous purging leads to bath turbulence which causes wear of the side walls. Thus ladle stirring is detrimental from the refractory point of view. The position and the number of plugs are also essential in determining the effectiveness of the purging. Although, ladle stirring can also be brought about by the use of electromagnetic stirring.
Ladle porous plug system essentially consists of a plug, sleeve, block, shell, C clamp,tie-down system. Sleeves provide stability to the plug and the air setting plastic provides good strength and minimal shrinkage in service to prevent any joints or looseness in the material. Mortar is added to compensate for the horizontal expansion of the plug.
Thermal
Peak Temperature: The plug being in contact with the steel reaches the temperature of the steel. The temperature is very high from the refractory point of view and calls for high-temperature-resistant materials.
Thermal Shock: Thermal cycling is very high for plugs and depends on the number of heats in the day and the number of times the plug is turned on and off. The tip of the plug being in contact with steel is at high temperature and when cold argon flows through it stress is generated on the plug.
Mechanical
Impact: The impact on the plug is moderate but depends on the position and the height of the impact stream.
Abrasion: Abrasion can be a huge factor and the placement of bottom plugs causes abrasion of the bottom. Abrasion is dependent on the stir profile and a higher flow rate of argon is responsible for higher bath movement and more abrasion of the bottom and the plug.
Applied stress: The height of the plug is fairly low to cause applied stress on the plug.
Chemical
Dissolution: Wear by dissolution depends on the chemical compatibility of the slags with bricks. Slag is basic in nature and therefore a basic refractory is compatible. High alumina or alumina spinel or alumina zirconia are some of the preferred choices.
Penetration: Penetration is caused by low viscosity metal/ slag or highly wetting metal/slag penetrating into porous refractories. The slag sits on the bottom of the ladle. Oxygen lancing of the plug creates a high-temperature low viscosity slag which can be drawn deep into the plug.
Thermo- Mechanical
Strain of thermal expansion-The The height of the sidewall is fairly low and there is less vertical stress. But some horizontal stress is generated as the plug is constrained inside the block. Mortar joints allow for some expansion but are susceptible to steel penetration.
Chemical Mechanical and thermo mechanical chemical
Spalling of the penetrated zones-This is the key wear mechanism. Thermal cycling due to cold argon flow along with low viscosity slag generated due to oxygen lancing causes spalling.
Choice of material:
Alumina-magnesia spinel or alumina-zirconia mix is the preferred choice.
