The upper end of a submerged nozzle is connected to the bottom of the tundish, and the lower end extends into the mold. This ensures that the molten steel exiting the tundish is not exposed to the air, preventing the steel from escaping, reducing the ingress of inclusions, and protecting the steel from oxidation. In addition to being subject to severe thermal shock, erosion, and corrosion from the molten steel, submerged nozzles are also subject to intense corrosion from the mold slag. Because the mold slag is a highly corrosive material with a low melting point and low viscosity, containing fluorite and potassium and sodium oxides, it corrodes submerged nozzles much more severely than long nozzles. Therefore, the requirements for submerged nozzles are much higher than those for long nozzles. With the advancement of metallurgical technology and intensified market competition, the demand for steel quality has become increasingly stringent, and the use of guarded pouring has increased. Consequently, the use of submerged nozzles has also increased. This is not only required for high-quality steel, but also for standard steel.
Submerged nozzles originated in the 1960s, initially using fused quartz. The performance and characteristics of fused quartz unmanned nozzles are essentially the same as those of fused quartz long nozzles, so they will not be elaborated here. Because submerged nozzles operate in much harsher conditions than long nozzles, they erode more quickly. Except for steel mills with very low continuous casting heats, they cannot meet the requirements of high-level continuous casting and special steel continuous casting. The authors have improved the fused quartz nozzle by using a more corrosion-resistant refractory composite material in the slag line to extend its service life, which has achieved significant progress.
With the advancement of continuous casting technology, especially with the casting of specialty steels, quartz-based submerged nozzles no longer meet the service life requirements and also negatively impact steel quality. This necessitated the development of new materials for unmanned nozzles. Research led to the development of aluminum-carbon-based submerged nozzles, which significantly improved service life. To meet thermal shock resistance requirements, a certain amount of mullite and fused quartz were added to aluminum-carbon-based submerged nozzles. However, the mullite and quartz components were still insufficiently resistant to corrosion by specialty steels such as high-manganese steel, particularly mold slag, significantly impairing their resistance to corrosion, hindering further improvements in continuous casting service life. To address this issue, composite unmanned nozzles were developed. These consisted of zirconium-carbon or borated zirconium-carbon materials along the slag line, aluminum-zirconium-carbon or aluminum-carbon materials as the main body, and carbon-free materials such as aluminum-magnesium and Sialon ceramics as the inner layer to accommodate the casting of low-carbon steels. When casting aluminum-killed steel, nozzles often experienced nodules and blockage.
For this situation, using a permeable ring for argon blowing in submerged nozzles and using non-carbon refractory materials and calcium zirconate materials for the inner layer have achieved good results. For urgent needs, steel mills require submerged nozzles that can be used without baking. Therefore, high-thermal-shock-resistant submerged nozzles should be developed to meet user requirements. By designing trapezoidal submerged nozzles and placing impellers within the nozzle bore to modify the flow field, inclusions in the molten steel can be floated and nodules can be prevented. Improving the submerged nozzle structure is also a key aspect of submerged nozzle development. Another significant issue with submerged nozzles is surface oxidation during the casting process, which can lead to loss of strength and damage. Therefore, applying an anti-oxidation coating to the surface has achieved good results. A good anti-oxidation coating often prevents oxidation and decarburization of the nozzle during firing. Another issue is the high thermal conductivity of carbon-containing refractory materials, which results in high nozzle surface temperatures. This creates a poor operating environment and lowers the molten steel temperature, exacerbating nodules. The solution is to add a layer of refractory fiber felt to the surface of the submerged nozzle, which has achieved good results. In short, submerged nozzles that meet user requirements, enable casting of different steel grades, and offer long life are being developed.
Currently, the service life of submerged nozzles in my country is still low, generally less than 10 hours. This is due to a variety of factors, including poor material quality, insufficient durability, unstable product quality, conservative use, and insufficient molten steel supply, which hinders continuous casting and causes disconnections. Japanese submerged nozzles, on the other hand, can sometimes have a service life of over 15 hours, leaving us with a significant gap. Therefore, innovation in materials and improvement in their use are necessary to enhance the quality and application of submerged nozzles in my country.
Submerged Entry Nozzles Advantages:
1.Improved Steel Quality: By preventing reoxidation and ensuring a clean steel stream, the SEN contributes to the production of high-quality steel with minimal defects.
2.Enhanced Process Control: The SEN facilitates precise flow rate control and distribution of molten steel, optimizing the casting process for specific product requirements.
3.Reduced Operational Costs: The SEN’s role in maintaining steel quality helps to minimize production of off-grade steel, reducing overall costs.
4.Improved Safety: By keeping the molten steel submerged during transfer, the SEN contributes to a safer working environment.
Submerged Entry Nozzles Application:
Submerged entry nozzles (SENs) play a crucial role in the steel casting process. They are instrumental in controlling the flow of molten metal, ensuring its quality and integrity during the casting operation. The integration of Argon injection in these systems introduces a significant advancement in minimizing defects throughout the production cycle.
The primary function of a submerged entry nozzle is to direct the flow of molten steel from the ladle into the mold, while also reducing turbulence which can lead to imperfections. By utilizing a porous ring design for the Argon Injection SEN, operators can achieve a controlled gas flow ranging from 0.1 to 0.3 MPa. This precision allows for the effective injection of Argon gas into the molten steel, altering its properties in a favorable manner.
More details about submerged entry nozzle
What is a submerged entry nozzle?
The submerged entry nozzle (SEN) has been used to transport the molten steel from tundish to the mould. The main purpose of the SEN usage is both to prevent oxygen and nitrogen pick-up by molten steel and to achieve the desired flow condition in the mould.
What is the use of tundish nozzle?
The tundish nozzle controls the flow rate of molten steel by adjusting the outlet diameter, ensuring the molten steel flows uniformly and controllably into the mold. The tundish nozzle helps reduce the entry of impurities and contaminants into the molten steel flow.
What are the three functions of the nozzle?
The nozzle has three functions, namely: a) to generate thrust; b) to conduct the exhaust gases back to the free-stream conditions; and c) to establish the mass flow rate through the engine by setting the exhaust area.
