What Is a Tundish?

The tundish is a refractory container used in short-flow steelmaking. It first receives molten steel poured from the ladle, and then distributes it to each mold through the tundish water outlet. As an important basic raw material, steel plays a pivotal role in the economic development of countries around the world.

Since the 1850s,

Tundish refractory lining mainly includes thermal insulation layer, permanent layer and working layer.

(1)

Tundish insulation boards are generally available in silicon, magnesium and forsterite.

(1) The application characteristics of various insulation boards are as follows:

1) Silicon insulation board is generally used for casting ordinary carbon steel, carbon structural steel and ordinary low alloy steel. During its use, there is a phase change of quartz, which causes volume expansion to make the reaction layer in contact with the slag densify, thereby preventing the infiltration of slag, and forming a high-viscosity glass phase on the surface, which further prevents effect.

2) Magnesium insulation boards can be used to cast high-quality steels such as aluminum killed steel, low alloy steel, and carbon structural steel. During use, it has stable high temperature performance, good resistance to alkaline slag erosion, and can absorb FeO in the slag to form magnesium fusite to generate volume expansion, form a dense structure on the surface of the insulation board, and reduce further penetration of the slag. In addition, the phosphate in the magnesium-based insulation board of the inorganic binder forms a high-temperature stable phase with the impurities CaO therein at a high temperature, and has good resistance to molten steel erosion.

3) Forsterite insulation board is mainly used for high-quality alloy steel. The high temperature performance is good during use, and the temperature change during the pouring process is small, because the inorganic binder is used, which eliminates the phenomenon of "silicon and hydrogen increase" in molten steel.

(2) The advantages of using a tundish insulation board are as follows:

1) The tundish can be baked without preheating, which can realize the opening of the cold pack and save the baking fuel;

2) Good insulation performance, which can reduce the steelmaking temperature of the steelmaking furnace by 5 ~ 10 , and the tundish is not easy to form cold steel;

3) The life of the permanent layer of the tundish is extended, which greatly reduces the consumption of refractory materials;

4) The insulation lining is easy to disassemble and lay, which saves 70% of labor compared with refractory clay bricks, and improves working conditions;

5) Compared with refractory brick lining. The content of inclusions in the slab greater than 50 m was significantly reduced.

(3) The disadvantages of the tundish insulation board are as follows:

1) When the silicon insulation board is applied to aluminum killed steel and low aluminum killed steel, the alloying elements such as AI and Mn in the molten steel and the refractory materials

Reaction generation

,

, Leading to an increase in the content of oxide inclusions in the slab, affecting the quality of the steel;

2) In multi-furnace continuous casting, the strength of the magnesium insulation board is not ideal. When using a magnesium insulation board with an organic binder, the organic binder therein will decompose hydrogen during use and enter the molten steel to produce steel. "Hydrogen embrittlement";

3) Because the thermal conductivity of the magnesium insulation board is relatively large, the temperature of the molten steel in the tundish changes greatly, and other insulation materials must be added to the side wall of the tundish, which increases the complexity of construction;

4) Magnesium insulation board formed under high temperature

Easy to combine phase with slag

The reaction produces low-melting substances, which will accelerate the penetration of slag and reduce the service life;

5) The main crystalline phase in the forsterite insulation board is forsterite, which is easy to interact with the slag in the slag during use.

The reaction generates low-melting substances such as forsterite (CMS), resulting in damage to the insulation panel structure and reducing the service life. ^[1]

Weir, also called slag weir or upper retaining wall. Across the entire tundish width, from the upper part of the molten steel surface to a certain distance from the bottom of the tundish, molten steel can flow through it. Its role in the tundish is:

1) It is possible to control the size of the impact zone of ladle flow injection, control the stirring intensity of ladle flow to tundish molten steel, and promote the collision and adhesion of inclusions to remove large particles.

2) The slag that enters the tundish with the ladle injection can be blocked in the injection impingement zone to reduce the secondary pollution of the molten steel caused by the ladle coil slag.

3) The tundish molten steel surface fluctuation caused by the impact of the injection flow of the ladle can be restricted to the upstream of the weir, and the liquid level of the tundish molten steel downstream of the weir can be stabilized to reduce the inclusions caused by surface slag rolling, secondary oxidation and mechanical scour the amount.

Dam, also known as diversion dam or lower retaining wall. Across the entire width of the tundish, it extends upward from the bottom of the tundish to a certain distance below the molten steel surface, and the molten steel flows through it. It has the following functions:

1) It can prevent the formation of short circuit flow in the tundish, extend the flow distance of molten steel in the tundish, and increase the residence time of molten steel in the tundish.

2) The impact of ladle injection can be limited to the impact zone, reducing the horizontal flow speed of molten steel.

3) Make the molten steel flowing through the dam flow towards the surface of the molten steel, shorten the floating distance of the inclusions, and facilitate the removal of the inclusions and the trapping of the top slag.

In tundish, dam and weir are often used together to obtain the ideal tundish molten steel flow and metallurgical effect.