Ladle aeration bricks, as the name suggests, are bricks used to inject gas into the bottom of a ladle. The argon gas bubbles caused by this injection carry impurities in the molten steel to the surface, thereby purifying the molten steel.
Ladle operations involve a repetitive cycle—from an empty ladle, through heating, tapping, filling, argon blowing, hoisting, and pouring—to returning the empty ladle and ladle repairs. Some ladles also undergo RH (reheating) and LF (low-frequency) treatments, resulting in a lengthy process and extended turnaround times. It is difficult to ensure that the aeration bricks remain in a continuous blowing state throughout this process. Under the static pressure of the molten steel, the blowing channels in the aeration bricks are prone to clogging, and reopening them requires maintenance to meet operational demands.
With internally mounted permeable bricks, replacement can only be performed during cold repairs of the ladle bottom; this results in cumbersome maintenance, frequent interventions, and a low ladle turnover rate. With externally mounted permeable bricks, the base brick remains unchanged while the core can be replaced under hot conditions, offering convenient maintenance and a fast ladle turnover rate; however, safety requires meticulous planning.
The use of argon-blowing permeable bricks—including the diffuse-type, which features a structure with irregularly distributed pores—did not become widespread until the 1960s. These bricks have unpredictable gas flow directions, difficult-to-control flow rates, are prone to clogging, and have a short service life. Straight-through permeable bricks maintain a stable gas flow direction but are prone to channel blockages and have a low reactivation rate, which affects argon-blowing performance. Slotted breather bricks: These feature fine slits within a dense brick body, providing high gas flow rates, effective stirring, a high rate of repeated activation, resistance to scouring and erosion, and a relatively long service life. (Yu Puliang, Master’s Thesis, Wuhan University of Science and Technology, 2009) Maze-type breather bricks consist of air passages formed by a large number of interconnected and intersecting main capillaries, making them less prone to clogging.
The main types of aeration bricks include diffuse-type aeration bricks (similar to Figure 1), directional-pore aeration bricks (similar to Figures 3 and 4), slit-type aeration bricks (similar to Figures 3 and 4), and labyrinth-type aeration bricks (similar to Figure 1). Aeration bricks are made of materials such as corundum, magnesium-chromium, aluminum-magnesium, and aluminum-chromium.
The installation location of the air-permeable bricks is determined by the purpose of ladle treatment: either at the center of the ladle bottom or offset from the center (with the air injection point located at a radius of 1/2 to 1/3 from the center of the ladle bottom). A central position facilitates desulfurization through slag lifting, while an eccentric position promotes molten steel homogenization and the flotation of inclusions.
For a 300-metric-ton ladle, the blow-through time for oriented slit-type permeable bricks was approximately 20 minutes, with a blow-through rate of ≥99%; the service life of permeable bricks from different manufacturers ranged from 23 to 31 cycles, with varying levels of performance.
Every technology or product category undergoes a development process. Around the 1990s, domestic ladle permeable brick technology developed rapidly, with various types of permeable bricks being applied, each presenting both advantages and disadvantages in terms of performance and results.
Early sandwich-type slotted permeable bricks involved wrapping a single brick with metal wire, sandwiching two bricks together, and encasing them in a steel shell to form the permeable element. Under high temperatures and prolonged use, the metal wire softened, leading to reduced permeability, and the air channels were prone to blockage and air leaks.
Early straight-through, directional venting bricks created air channels by threading steel wire through them. The steel wire had to be pulled out just as the refractory castable began to harden; otherwise, the wire would break off inside the castable and block the air channels.
Imported slotted venting bricks with inserted steel plates suffer from steel plate softening and melting, leading to easy blockage of the air channels. Imported venting bricks, which are manufactured by combining bricks of different thicknesses and shapes to form air channels, also suffer from steel seepage and blockage issues.
In the early 1990s, based on an analysis of imported steel-plate-insert and machined-combination vent bricks, the author adopted thin nylon strips as consumable vent material. After casting the gas-supplying core and firing it at high temperatures in a clay-brick tunnel kiln, the core was paired with square base bricks for use on W-steel ladles, resulting in significantly improved performance. Since then, numerous manufacturers of similar directional slit-type air-permeable bricks have emerged, and most of their designs follow this structure.