Comparison of defects of two repair methods for converter taphole

The application of top-bottom combined blowing technology and slag irrigation for converter protection has expanded converter smelting products and significantly improved quality and production efficiency. Tapping, the final step in the converter steelmaking process, has become a crucial factor influencing smelting quality, output, and product variety. The service life, replacement time, and repair life of the taphole directly impact steelmaking efficiency and the converter smelting cycle. The sintering time and service life of converter taphole repair material directly impact steelmaking production.

Converter taphole repair material is a maintenance material used during taphole replacement or repair. Since the adoption of the slide plate slag blocking process at Henan Jigang No. 1 Steel Plant, the replacement of the taphole pipe bricks has placed stricter requirements on the integrity of the taphole seat bricks and higher positioning accuracy. The traditional replacement method has been unable to meet the process requirements of high-quality steel, and the entry of a large amount of repair material has an impact on the quality of the molten steel that cannot be ignored. In response to the above-mentioned defects in the converter repair process, Jigang and Ma'anshan Refractory Materials Company jointly researched and developed a new type of taphole repair material, pioneered a new approach to repair, and achieved satisfactory results on Jigang's two 120-ton converters.

Two ways to repair the taphole

While the nominal capacity of converters owned by Chinese steel companies varies, the methods for repairing the taphole are generally the same. There are two common methods.

One is to use a small gunning machine. After installing a new taphole pipe brick, a sealing compound is sprayed around the pipe brick. This semi-dry gunning compound typically contains around 15% moisture. After entering the furnace, some of the water in the gunning compound rapidly boils and evaporates, while the remaining water combines with the gunning compound and sinters around the pipe brick, protecting the pipe brick.

The other method involves spraying water directly onto the repaired area in conjunction with a cast material. Under the high temperature of the furnace, some of the water combines with the cast material and sinters, forming a protective layer.

Disadvantages of the two gunning methods

Although the above two methods solve the problem of replacing the taphole pipe bricks and repairing the surrounding corroded parts, thus ensuring the normal progress of smelting, they also have the following obvious defects.

(1) The lining of the converter is made of magnesia carbon bricks. A large amount of water enters the high-temperature furnace, causing the working surface of some lining bricks to quickly hydrate and form Mg(OH)₂. The result is that the bricks become powdery, expanded, and loose, and lose their lining function. The specific reaction formula is:

MgO+H₂〇→Mg(OH)₂

(2) Water ingress into the furnace causes rapid cooling effects, leading to cracks at the interface between the transition layer and the unchanged layer of the refractory bricks. As water continues to be added, these cracks gradually expand into fissures, resulting in brick fractures. A significant portion of the bricks will spontaneously detach, ultimately forming pits.

(3) Moisture introduced by semi-dry spray repair materials and manual water spraying at the tapping hole, particularly the difficult-to-control manual water volume, severely compromises the quality of the lining and seat bricks around the tapping hole. This manifests primarily as brick damage, loosening, loss of strength, and accelerated erosion in these areas. Consequently, steel leakage from the tapping hole becomes inevitable. Once leakage occurs, repair becomes exceptionally difficult, significantly impacting the converter's normal operation.

(4) The presence of water inside the furnace not only disrupts the furnace atmosphere but also poses multiple hazards, including safety risks and steel leakage. Converter magnesia-carbon bricks should avoid hydration even at room temperature, let alone under high-temperature conditions. Consequently, each replacement of the tapping hole pipe bricks causes varying degrees of damage to the lining bricks, seat bricks, and pipe bricks, significantly shortening the service life of this area. In the later stages, deep nipple-shaped pits often form in this region, and the service life of the pipe bricks is also relatively low, typically lasting under 200 furnace cycles. Frequent replacement of tapping nozzle bricks occurs, not including damage to other furnace lining bricks caused by water vapor.

(5) The frequent replacement of tapping hole pipe bricks throughout the furnace life cycle progressively worsens the operating environment for surrounding components, particularly the tapping seat bricks. By the later stages, these bricks are barely recognizable in their original form. Not only does the volume of repair material increase substantially, but the repair process itself becomes increasingly difficult and time-consuming.

At present, the main task of a considerable number of domestic converters in the later stage of use is to repair the taphole. A 120-ton converter uses the above method to replace the taphole pipe bricks, plus replace the slag stop slide, and the overall time is about two and a half hours.

Tap Hole Brick