The Tundish: A Crucial Component in Modern Steelmaking

The Basic Knowledge of Tundish Lining Refractories

In the intricate process of steelmaking, the tundish plays an essential role, acting as a critical intermediary between the ladle and the mold. The quality and performance of the tundish, often overlooked, are vital for ensuring smooth and efficient steel casting. But what exactly is a tundish, and why is its construction and maintenance so important? This article delves into the functions of the tundish, the materials used in its lining, and the innovations that are shaping its future.

What is a Tundish

The tundish is a refractory-lined vessel used in continuous casting, a process that allows for the efficient production of steel. Positioned between the ladle, which holds molten steel, and the mold, where steel solidifies, the tundish's primary function is to evenly distribute molten steel into the mold. This distribution is critical for producing high-quality steel with uniform properties.

Key Functions of the Tundish

Reducing Static Pressure

One of the primary roles of the tundish is to reduce the static pressure of the molten steel as it flows from the ladle to the mold. By reducing this pressure, the tundish helps to maintain a consistent flow, which is crucial for the quality of the final steel product.

Maintaining Stability

The stability of the molten steel surface within the tundish is vital for the continuous casting process. A stable surface ensures that the molten steel is injected smoothly into the mold, preventing defects in the final product.

Promoting Inclusion Removal

Inclusions, which are non-metallic impurities in the molten steel, can significantly affect the quality of the final steel product. The tundish promotes the floatation of these inclusions, allowing them to be removed from the steel. This process, known as inclusion removal, is crucial for producing clean, high-quality steel.

Molten Steel Diversion

For multi-stream casters, the tundish plays a key role in diverting molten steel to multiple molds simultaneously. This capability is essential for large-scale steel production, where efficiency and speed are paramount.

Storage of Molten Steel

The tundish also acts as a temporary storage container for molten steel. This storage capability is particularly important during ladle changes, allowing the continuous casting process to proceed without interruption, thereby increasing overall production efficiency.

Tundish Lining Refractory Composition

The composition of the tundish lining is critical for its performance. The lining not only protects the tundish shell from the extreme temperatures of molten steel but also influences the quality of the steel being cast.

Insulation Layer

The insulation layer, typically 10 to 30mm thick, is the first line of defense in the tundish lining. It is in direct contact with the tundish steel shell and is designed to minimize heat loss. Common materials used for this layer include asbestos board, insulation refractory brick, or light castable. The aluminum silicate fiber mat is highly effective due to its low thermal conductivity and ease of installation.

Permanent Layer

The permanent layer, which is 100 to 200mm thick, lies beneath the insulation layer. This layer is usually made of clay bricks or high-alumina castable materials. Its main function is to provide structural stability and protect the tundish from thermal and mechanical stress.

Working Layer

The working layer is the most critical part of the tundish lining as it comes in direct contact with the molten steel. This layer is typically 20 to 50mm thick and is made from materials that can withstand high temperatures and corrosive elements. Common materials include siliceous, magnesia, and forsterite insulation boards or coatings like magnesia-chrome or magnesium-calcium.

Block Bricks

Block bricks are used in the middle of the tundish and are crucial for the installation of the tundish outlet. These bricks are usually made of high-alumina material and play a significant role in maintaining the structural integrity of the tundish during operation.

End of Package Material

The materials used at the end of the tundish package are typically the same as those used in the working layer. This area is subject to intense wear and erosion due to the impact of molten steel, so high-alumina bricks or dense high-alumina bricks are commonly used. For areas that experience the most wear, such as the impact zone, zircon bricks or prefabricated blocks with enhanced strength are employed.

Cover Material

The cover of the tundish serves to insulate the molten steel and prevent splashing. It is typically made from clay or high-alumina castable materials, which provide excellent thermal insulation and durability.

Slag Wall (Weir)

The slag wall, or weir, within the tundish is designed to block slag and other impurities from entering the mold. These walls can be made from high-alumina refractory bricks or prefabricated blocks. In some designs, a molten steel filter is integrated into the slag wall to further improve the cleanliness of the steel.

Tundish and its Role in Continuous Casting of Steel

1. Buffering and Flow Control

- Reservoir Function: The tundish acts as a reservoir, providing a stable supply of molten steel to the casting mold even if there are fluctuations in the flow from the ladle.

- Flow Regulation: It smooths out any turbulence or pulsations in the molten steel flow, ensuring a steady and controlled delivery into the mold. This is essential for maintaining a consistent casting rate and preventing defects in the final product.

2. Inclusion Removal and Metallurgical Benefits

- Impurity Trapping: As the molten steel passes through the relatively quiescent environment of the tundish, non-metallic inclusions have time to float up and separate from the bulk steel. This process improves the cleanliness and quality of the steel.

- Temperature Homogenization: The tundish helps even out temperature variations within the molten steel, which is crucial for avoiding uneven cooling and solidification in the mold.

3. Thermal Management

- Heat Retention: By retaining a portion of the molten steel, the tundish minimizes temperature drops that could occur during transfer. This ensures the steel remains at the optimal temperature for casting, reducing thermal shock and related defects.

- Insulation Role: Tundishes are typically lined with refractory materials that not only protect the steel from contamination but also help in maintaining the high temperature needed for a consistent casting process.

4. Operational and Process Efficiency

- Continuous Operation: In continuous casting, the process must be steady and uninterrupted. The tundish allows for a decoupling of the ladle pouring and mold filling operations, which can operate at slightly different rates.

- Safety and Flexibility: It provides an operational safety margin, allowing operators to adjust for variations in molten steel supply without stopping the casting process. This flexibility is crucial for high-volume production environments.

Conclusion

The tundish is the last metallurgical vessel through which molten metal flows before solidifying in the continuous casting mold. During the transfer of metal through the tundish, molten steel interacts with refractories, slag, and the atmosphere.

The tundish is an indispensable component in the steelmaking process, playing a crucial role in ensuring the quality and efficiency of continuous casting. From reducing static pressure to promoting inclusion removal, the tundish's functions are vital for producing high-quality steel. With ongoing innovations in tundish technology and materials, the future of steelmaking looks even brighter, promising greater efficiency and superior product quality.