Working environment of ladle bottom argon blowing air bricks

Argon blowing from the ladle bottom is a crucial step in the LF furnace refining process, agitating the molten steel. Heating, adjusting the composition, and removing inclusions are all accomplished while the molten steel circulates and circulates while continuous argon blowing and agitation are maintained. The permeability of the ladle bottom blowing significantly impacts refining outside the furnace. If the ladle bottom blowing permeable bricks are impermeable or have low permeability, refining cannot be completed.

What are permeable bricks? They essentially serve as a channel for argon gas to enter the molten steel. The basic working principle is: argon enters the molten steel through the narrow gap of the permeable brick core, disperses in the molten steel in the form of bubbles and floats up. The surrounding molten steel is driven by buoyancy to form an upward flow above the permeable brick, reaches the top of the molten steel, turns to the horizontal direction, and then flows back downward along the wall of the ladle, so that the molten steel circulates in the ladle, thereby quickly melting the alloys and fluxes added to the molten steel, promoting the uniformity of the composition and temperature of the molten steel and the floating of inclusions in the molten steel, removing non-metallic inclusions and harmful gases in the steel, and achieving the purpose of refining the molten steel.

Analysis of working environment of breathable bricks

1. Scouring by High-Speed, High-Pressure Airflow and High-Temperature Molten Steel

During the refining process, argon is blown throughout the molten steel, stirring it. High-speed, high-pressure airflow is introduced into the ladle through the permeable bricks, imparting a certain amount of stirring energy to the molten steel. The stirring intensity is controlled by controlling the gas flow rate. This is what is observed visually as the molten steel in the ladle boiling. At this point, the interaction between the gas and the molten steel at the bottom of the ladle creates turbulent flow. Simultaneously, the recoil of the airflow severely scours the permeable bricks and the surrounding refractory materials.

2. Slag Erosion After Steel Pouring

After pouring the molten steel, during the period of waiting for back-pouring, the working surfaces of the permeable bricks come into contact with the molten slag. The slag continuously infiltrates the bricks along their working surfaces. Oxides such as CaO, SiO₂, and Fe₂O₃ in the slag react with the bricks, forming a eutectic that erodes the bricks.

3. Using an oxygen hose to purge the working surface of the air bricks during hot ladle repairs can cause melt damage

When purging the working surface of the air bricks, a reverse blowback method is typically used. After quickly connecting the quick-connect metal hose to the air brick argon blow pipe, the valve is opened to allow high-pressure gas to flow through the air bricks. Simultaneously, a worker uses a coarse oxygen hose to blow away any residual slag around the air bricks in front of the ladle until the bricks turn slightly black.

4. Extreme heat and cold during the ladle cycle and mechanical vibration during lifting

The ladle receives steel in alternating cycles, resulting in extreme heat for heavy ladles and extreme cold for empty ladles. Furthermore, the ladle is inevitably subjected to external forces and mechanical stress during operation.

The materials and development of breather bricks have undergone a series of changes in their composition and types over the course of their development. The materials used in breather bricks must be resistant to erosion and erosion by molten steel, exhibit high thermal shock resistance, possess stable physical and chemical properties, and be economically efficient. The three most widely used types of ladle breather bricks today are dispersion type, straight-through hole type, and slit type.

The air bricks used in the early days were high-alumina and magnesia. These air bricks have good thermal stability, but due to structural defects, their service life is insufficient, affecting the overall efficiency of the ladle.

Currently, ladle air bricks are primarily made of chrome corundum (spinel) and corundum-spinel, typically produced through a casting and high-temperature sintering process. High-temperature sintering of a corundum-spinel castable bonded with pure calcium aluminate cement produces three high-melting-point mineral phases: calcium hexaaluminate (CA₆, melting point 1890°C), magnesium aluminate spinel (MA, melting point 2100°C), and corundum (melting point 2050°C).

The excellent combination of plate-like calcium hexaaluminate and corundum or spinel in the matrix gives this material excellent slag resistance and high-temperature strength, earning it the title of an optimal matrix system. However, its thermal shock resistance is relatively poor, making it susceptible to thermal and structural spalling during use, limiting its service life. Corundum-spinel breathable bricks are a predominant product on the market. Thermal spalling during use can easily cause transverse cracks, leading to molten steel infiltration and significantly reducing the brick's service life. Therefore, improving the thermal shock resistance of corundum-spinel breathable bricks is a key approach to extending their service life.

Ladle Air Bricks