1. Short Brick Core
The purge brick is located at the bottom of the ladle and withstands the hydrostatic pressure of molten steel during use. When the remaining length of the brick core is too short, the contact area between the brick core and the seat brick decreases, and the structural strength of the brick core itself is also reduced. Cracks are prone to occur under the influence of rapid heating and cooling. If the pressure that the brick core can bear is less than the hydrostatic pressure of the molten steel, the molten steel will crush the brick core until it falls off, or seep through the cracks in the brick body, leading to steel leakage accidents.
2. Excessive Oxygen Content
The argon gas used in the steel refining process requires a purity of 99.99%, and oxygen contamination is not allowed. However, in some steel plants, the argon gas used for refining has low purity, leading to oxygen mixing. The entrained oxygen causes secondary oxidation of the molten steel, affecting the refining effect. During the gas-blowing process, oxygen reacts with the molten steel at temperatures as high as 2000°C, accelerating the surface erosion of the purge brick. Under the scouring of the gas flow, the purge brick is rapidly eroded, reducing its service life and potentially causing steel leakage in severe cases. Whether slit-type, ceramic rod-type, or 弥散式 (diffusion-type) purge bricks, none can resist the erosion caused by the reaction between oxygen and molten steel.
3. Steel Leakage from Refractory Mortar Joints Outside the Purge Brick Core's Steel Shell
When assembling the purge brick on-site, a uniform layer of refractory mortar must be applied to the outer surface of the brick core, with a thickness generally required to be 2–3 mm. The operation procedure requires the brick core to be horizontally aligned with the inner hole of the seat brick, and the refractory mortar at the bottom of the brick core must not be scraped off by the seat brick or other objects during installation. If the mortar is unevenly applied or falls off during installation, the refractory mortar between the brick core and the seat brick will be thicker on one side and thinner on the other. The thicker side of the mortar joint is easily eroded by the molten steel, reducing the purge brick's service life. In the later stages of use, molten steel may seep through the mortar joint, leading to steel leakage. If the mortar on one side is scraped off, the steel shell cannot fully bond with the inner hole of the seat brick, leaving gaps. High-temperature gases will gradually oxidize and erode the steel shell, also prone to causing steel leakage.
4. Steel Leakage from Refractory Mortar Joints Inside the Purge Brick Core's Steel Shell
Causes:
During installation, the bottom of the purge brick core is not tightly secured to the base plate. Slight downward movement of the brick core during use creates gaps between the brick core and the steel shell, providing a pathway for molten steel to seep downward.
During use, excessive blowing pressure causes the purge brick core to move slightly upward under gas pressure. If the originally tight installation becomes loose, and the brick core falls back due to external forces when gas blowing stops, gaps form between the brick core and the steel shell, leading to steel seepage during subsequent use.
When installing the steel shell for the purge brick, the refractory mortar used may not sinter at low temperatures and has low strength. During use, due to the disturbance of the blown gas flow, local mortar is gradually blown away from the bottom, creating voids between the purge brick core and the steel shell. Molten steel seeps along these gaps into the gas chamber, causing steel leakage through the mortar joints.
5. Slit Leakage
Unreasonable slit design: The slit design of slit-type purge bricks is critical. While ensuring gas permeability, it must also prevent significant infiltration of molten steel into the slits, which could cause blockages and render the purge brick ineffective. Currently, most purge brick slit widths are between 0.15–0.2 mm. Given the wettability of molten steel with refractory materials, complete prevention of steel seepage into slits is impossible, but minor seepage does not affect gas flow. If one or more slits in the purge brick are too wide, molten steel will seep into the slits, form solidified steel (冷钢), and block the slits, making them unable to blow through.
Common causes of purge brick damage include:
Peeling of the purge brick core
When the ladle is hot-repaired and then positioned for the converter, the temperature inside the ladle is approximately 900°C, while the converter's end-point temperature is typically 1630°C. The thermal shock from this temperature difference causes peeling of the purge brick core, usually with a peeling thickness of 10–20 mm. After peeling, the tapered peeled portion does not fall off due to the brick's taper, affecting the gas permeability for the molten steel in the ladle.
Fracture of the purge brick seat
Thermal shock from temperature differences can also cause fractures in the purge brick seat, with fracture heights ranging from 100–200 mm. Without the protection of the seat brick, the brick core becomes eroded by molten steel and may also fracture. Such fractures pose significant hazards, especially in the later stages of purge brick use when the remaining brick is short, increasing the risk of ladle bottom steel leakage accidents.
Low strength and poor erosion resistance
When cleaning purge bricks with an oxygen lance during hot repairs, the normal erosion rate is 9–12 mm per furnace. If the brick strength is insufficient, the height of the brick core decreases significantly with each cleaning, causing the purge brick to be taken out of service before its specified lifespan. This disrupts normal ladle turnover and leads to production instability.
Erosion damage from molten steel scouring
When inert gas is blown through the purge brick, the backflow of gas flow exerts impact force on the exposed perimeter of the purge brick. The interaction between high-velocity molten steel and gas flow creates turbulent eddies. When the purge brick protrudes above the seat brick, its exposed portion is scoured and sheared by the eddies, forming a circular groove.
Excessive oxy-fuel damage
If the ladle's residual molten steel is not back-poured in time after continuous casting ends, solidified steel forms at the ladle bottom. Cleaning this requires using an oxygen lance directly against the purge brick core, which rapidly erodes the brick core.
Off-center burning of the purge brick core
When cleaning the purge brick with an oxygen lance pressed against the core, the oxy-fuel heating concentrates on a single point, easily burning the core off-center. This results in a sloped rather than flat surface on the brick core, with a height difference of over 50 mm. Off-center burning impairs gas permeability, and each subsequent cleaning exacerbates the deviation, forcing early retirement of the brick.
Low back-blow gas pressure
The back-blow gas (nitrogen) has a pressure of 0.5 MPa, while the oxygen lance pressure is 0.8 MPa. During oxy-fuel cleaning, molten steel can be blown into the purge brick slits, where it solidifies and blocks the slits, reducing gas permeability. Subsequent hot repairs further accelerate erosion of the brick core.
Spalling of corundum material around the purge brick and ladle bottom bricks
During ladle bottom lining, a 50–100 mm wide layer of self-flowing corundum material is poured around the purge brick seat to protect it. If the corundum material has insufficient strength or is poorly installed, it may spall, allowing molten steel to infiltrate and fracture the seat brick. Alternatively, fracture of the ladle bottom bricks around the seat brick can allow molten steel to infiltrate, causing both the corundum material and seat brick to fracture.