In layman’s terms, the tundish (picture 2 above) is a refractory container, which is used to contain molten steel poured from the ladle (picture 1 above), and then diverted to each mold (picture 3, 6 above).
Reduce pressure to stabilize steel flow. The height of the liquid level in the ladle is at least 5-6 meters, the impact force is great, and the range of changes during the casting process is also great. The liquid level of the tundish is lower than the steel drum, and the change range is small, so it is used to stabilize the molten steel casting process and reduce the erosion of the primary shell in the mold by the steel flow.
The role of storage and protection of molten steel. The molten steel is stored and the temperature of the molten steel is uniform. At the same time, the tundish liquid surface covering agent, shroud and other protective devices are used to reduce the external pollution of the molten steel in the tundish.
Remove impurities. Separate and float non-metallic inclusions and molten steel.
Shunting effect. On the multi-stream continuous casting machine, the tundish distributes the molten steel to the various molds, playing a role of splitting.
Continuous pouring effect. When replacing the ladle, it can indirectly play a role in ensuring the normal progress of multi-furnace continuous casting.
Metallurgical function of tundish
- Purification function. At present, most units use clean steel production technology. In the tundish, measures such as wall weir, argon blowing, and ceramic filter can be used to reduce the content of non-metallic inclusions in the steel.
- Temperature adjustment function, in order to make the temperature difference of the molten steel in the tundish less than 5℃, close to the liquidus temperature during casting, and reduce the center segregation, the temperature of the molten steel is often adjusted by adding small pieces of scrap steel to the tundish, spraying iron powder, etc. .
- Refining function. Double-layer slag is added to the surface of the molten steel in the tundish to absorb the floating inclusions in the steel to prevent the nozzle from being blocked.
- Heating function. In the tundish, induction heating and plasma heating are used to accurately control the molten steel casting temperature.
Tundish process requirements
Good heat dissipation, small area, good heat preservation performance, simple appearance, convenient for casting and cleaning, and good structural stability under long-term high temperature conditions. Figure II
The structure of the tundish
The tundish is composed of a tundish body, a cover, a stopper, and a sliding nozzle. The tundish body shell is welded by steel plate, the inner lining of the tundish is made of refractory material, the bottom of the bag is provided with nozzles, and a pair of hooks and trunnions for hoisting are provided on both sides of the tundish for easy lifting and transportation. In addition, considering the tundish nozzles In the event of an accident, molten steel overflows, so there is an overflow groove, and slag weirs are installed on both sides of the ladle nozzle to reduce the degree of molten steel slag entrapment and control the flow of molten steel. The tundish cover is welded by steel plates, and there are castables for heat preservation and prevention of molten steel splashing. The package cover is provided with preheating holes, stopper rod holes and tundish pouring holes. A retaining wall structure is designed in the ladle to isolate the disturbance of the molten steel in the tundish from the molten steel from the ladle, and make the flow of the molten steel in the tundish more reasonable.
The structural parameters of the tundish mainly include length, width and capacity.
The length of the tundish mainly depends on the distance of the nozzle position of the tundish (the tundish length of the single-strand continuous casting machine depends on the distance between the position of the ladle nozzle and the position in the nozzle of the tundish; the flow of the multi-strand continuous casting machine and the continuous casting machine Number and nozzle spacing are related).
The capacity of the tundish is mainly determined according to factors such as the capacity of the ladle, the section size of the steel billet, the number of flow of the tundish, the pouring speed, and the time that the molten steel stays in the tundish, and it is generally 20% to 40% of the capacity of the ladle. With the development of steelmaking in recent years, the tundish capacity is gradually increasing.
The width of the tundish is determined according to the amount of molten steel stored in the tundish. Generally, under the premise of easy and length determination, the higher the tundish, the smaller the width.
The inner wall of the tundish has a certain slope, which is to facilitate the cleaning of residual steel and residue in the tundish. The general slope is 10~20%.
Refractory materials for tundish can be divided into three categories in terms of function:
The first category is lining materials, which are mainly composed of insulation layer, permanent layer and working layer;
The second category is steady flow components, including weirs, retaining walls, ceramic filters, flow stabilizers, etc.;
The third category is the flow control part, which is the three major parts that people often say, including stoppers, sliding nozzles, sizing nozzles and intrusive nozzles.
Among them, intrusive nozzles, shrouds, integral stoppers, sizing nozzles and sliding nozzles and other key functional refractories for continuous casting are the main factors that restrict the life of the continuous casting system.
The permanent layer of the tundish is generally made of aluminum and silicon refractories. From the early use of refractory products such as clay bricks and high alumina bricks to the current use of unshaped refractories for casting, the thickness of the permanent layer of the small and medium-sized tundish is about 160~180mm. , The wall of the package is about 120~140mm, and the thickness of the permanent layer of the large tundish is about 150~200mm. The working lining of the tundish is often constructed with magnesium dry materials.