The submerged nozzle in continuous casting is located between the ladle and the mold, serving to prevent molten steel oxidation, facilitate the continuous casting process, and prevent protective slag from entering the molten steel. The development of its materials has gone through three stages: fused quartz, Al₂O₃-C, and composite submerged nozzles.
Due to severe oxidation during open-tundish continuous casting, fused silica nozzles were adopted in China starting in 1973. This method was suitable for mild carbon steel but was not suitable for casting high-manganese steel, as corrosion was severe. In 1988, Al₂O₃-C nozzles were introduced, which were suitable for almost all steel grades, but they suffered from the defect of excessive erosion of the nozzle slag line by slag and molten steel. Finally, Al₂O₃-ZrO₂-C composite submerged nozzles were developed, featuring an Al₂O₃-C body and a ZrO₂-C slag line. Because ZrO₂ has a stable chemical composition and its dissolution into the slag at high temperatures increases viscosity, erosion is mitigated, thereby extending the nozzle’s service life. Practical use has demonstrated that its service life is nearly twice that of Al₂O₃-C nozzles. Currently, Al₂O₃-ZrO₂-C composite immersion nozzles are widely used.
In practical use, Al₂O₃-ZrO₂-C composite submerged nozzles are prone to nodule formation, which hinders the casting process. Since the nozzle structure is typically cylindrical, The straight section above the slag line is exposed to the atmosphere; due to the temperature drop caused by heat conduction through the nozzle wall, molten steel precipitates to form nodules, primarily composed of iron and iron oxides, which pose a relatively minor hazard. In the straight section below the slag line, influenced by the casting process, nodules of alumina and some iron and iron oxides form. Over time, the alumina and iron oxides continue to react, producing highly refractory iron-aluminum spinel-type compounds, which pose a more serious hazard.
This issue is typically addressed through two anti-clogging techniques: material modification and structural improvement. Structural improvement has proven to be particularly effective. This method involves modifying the straight-tube structure to a single-ring or double-ring stepped nozzle, which straightens the steel flow, prevents flow deviation, and avoids aluminum oxide precipitation. Internationally, Japan tested a ring-stepped central hole structure in 1992, achieving significant results that led to its widespread adoption. Currently, efforts should be made to promote the widespread application of single-ring or double-ring stepped nozzle technology in domestic continuous casting.
Submerged Entry Nozzle Key Applications & Engineering
Submerged nozzles are primarily used in high-temperature industrial processes:
Continuous Casting (Steel): The SEN directs molten steel from a tundish into the mold cavity. Its submerged nature prevents the liquid steel from reacting with the surrounding air, while specific port designs control fluid flow and bubble distribution.
Aerospace (Solid Rocket Motors): In rocket engineering, a submerged nozzle extends partially inside the combustion chamber. This configuration saves total vehicle length and aids in thrust vectoring (steering) while presenting unique challenges in thermal and acoustic management.
Liquid Mixing & Radiochemicals: Top-submerged nozzles are widely used to introduce compressed air or gas into liquid pools, driving efficient and passive mixing.
What is a submerged entry nozzle?
A submerged entry nozzle (SEN) for use in a casting machine to conduct molten steel from a tundish to a mold may include a housing having an inlet capable of receiving an incoming flow of molten steel from the tundish, a distribution zone capable of delivering the molten steel to the mold; and a main body having a bore capable of conducting molten steel therethrough from the inlet to the distribution zone, the bore having sectional geometries capable of alternately compressing and decompressing the molten steel flow in flow path zones to alternately increase and decrease the steel flow velocity with at least two flow path zones capable of compressing the molten steel flow, and to deliver the molten steel from the distribution zone into the mold with flow turbulence inhibited.
Submerged Entry Nozzles (SEN) Application:
In submerged casting, submerged entry nozzles are located between the tundish and the mould. The optimum design for a given submerged entry nozzle is influenced by the flow conditions, steel throughout, mould design and sequence time. Submerged entry nozzles primary functions are:
- To prevent reoxidation of the molten steel stream
- To prevent air aspiration and steel splashing when the molten stream strikes the liquid bath surface
- To control the fluid dynamics in the mould through optimization of the port geometrie
The demands of consumers force steelmakers to improve quality and increase operational efficiency. Consequently, the field of application for submerged entry nozzles is constantly extended and improved.
