Two Common Installation Methods and Construction Requirements for Ladle Porous Plugs

The configuration of porous plugs is determined by the volume of molten steel in the ladle, the stirring requirements dictated by the steel grade and process route, and the specific objectives of the ladle treatment. The placement of the bottom-blowing gas assembly is selected based on the intended purpose of the ladle treatment. Installing the porous plug at the center of the ladle bottom versus at an off-center position (with the blowing point located at one-half to one-third of the radius from the center) results in different stirring effects: central bottom argon blowing promotes reactions between the slag and the steel, as well as desulfurization by the top slag, whereas off-center bottom argon blowing enhances internal mixing, temperature homogenization, and the flotation of inclusions.

For instance, in CAS/CAS-OB processes, the porous plug must be installed at the center of the ladle bottom because the process requires argon to displace the slag layer beneath the immersion bell, thereby facilitating alloying or oxygen injection. Conversely, the LF (Ladle Furnace) process requires the porous plug to be positioned near the furnace door to accommodate operations such as carburization, alloying, and deoxidation. A greater number of porous plugs results in the generation of more fine bubbles, leading to more effective inclusion removal and superior steel quality; however, increasing the number of plugs also raises the risk of steel breakouts. Typically, for the production of ordinary carbon steel, a single porous plug suffices for ladles with a capacity of 70 tonnes or less, whereas ladles exceeding 70 tonnes require two porous plugs.

Porous plugs can be installed using either an internal or an external mounting method.

The internal mounting method involves pre-assembling the porous plug with its seating block outside the ladle. During the ladle lining process, the designated area at the ladle bottom is cleaned, and the surrounding bricks are laid; the pre-assembled plug and seating block unit is then hoisted into position, followed by the sequential laying of the ladle bottom and sidewall linings.

The external mounting method utilizes a seating block, a sleeve brick, and a porous plug. During ladle lining, the seating block is installed at the bottom, allowing the ladle bottom and sidewall linings to be constructed. Finally, refractory mortar is evenly applied to the outer surfaces of the sleeve brick and porous plug; they are then firmly inserted into the seating block in sequence. A base brick is placed at the bottom of the assembly, a flange is secured over it, and the unit undergoes preheating.

The internal mounting method is typically used when the service life of the ladle lining matches that of the porous plug, whereas the external method is suitable for situations requiring frequent plug replacement. Due to the lower safety, poor reliability, and cumbersome replacement process associated with the internal mounting method, almost all ladles currently employ the external mounting method.