Four main causes of damage to ladle purging plugs

During the use of ladle gas-permeable bricks in steel plants, the primary causes of damage are thermal stress, mechanical stress, mechanical wear, and chemical erosion.

The gas-permeable brick assembly consists of two parts: the gas-permeable core and the seating block. When bottom gas blowing is activated, the working face of the core comes into direct contact with the high-temperature molten steel. As the injected gas is relatively cool, a significant temperature gradient develops between the gas and the molten steel; with repeated use, the core undergoes cycles of rapid heating and cooling, leading to increasingly severe erosion and a high susceptibility to cracking.

The working face of the ladle bottom purging plug is in direct contact with molten steel at high temperatures, while the temperature at the non-working face remains relatively low. During the cyclic operations of receiving steel, casting, and hot repair, the purging plug and surrounding refractory materials undergo volumetric changes due to temperature fluctuations. Because of the temperature gradient and the differing thermal expansion coefficients between the altered layer and the original material layer, the degree of volumetric change varies gradually from the working face to the non-working face; this generates shear forces that induce transverse cracking in the purging plug, potentially leading to a complete transverse fracture in severe cases.

During the steel tapping process, the molten steel exerts intense scouring action on the bottom of the ladle, thereby accelerating the erosion of the porous plug. If the upper surface of the porous plug protrudes above the ladle bottom, it is subjected to shear forces and scouring caused by the flow of molten steel; the protruding section is typically eroded away after just one use. Additionally, rapidly closing the valve after the refining process concludes can cause a back-surge of molten steel, further accelerating the plug's erosion.

The working face of the porous plug core remains in prolonged contact with steel slag and molten steel. These substances contain oxides such as Fe₂O₃, FeO, MnO, MgO, and SiO₂. Chemical reactions between these components and the constituents of the porous plug (such as Al₂O₃ and SiO₂) produce low-melting-point compounds (e.g., FeO·Al₂O₃, 2(MnO)·SiO₂·Al₂O₃), which are subsequently washed away.