Apparatus and Process for delivering molten steel to a continuous casting mold

Abstract

Apparatus and Process for delivering molten steel to a continuous casting mold with high inclusion removal capability and high mold pool flow optimization potential includes a tundish with a novel design and a metal distributor comprising a main chamber body connected to a vacuum device and tubes for metal exchange between the tundish, the distributor and the casting mold. At least one of the tubes has gas injection devices to perform gas lifting functions. The new design of the tundish enables it to receive all the steel in a ladle without leaving any heel and refining the steel to an extremely low inclusion level. The distributor is able to achieve an effective hydrostatic head relative to the mold metal level of the order of 10−2 m or below in the submerged entry nozzle and obtain fully filled and stable flow with low disturbance inside the SEN and therefore is able to deliver the molten steel at low velocities at SEN exits with minimum turbulent disturbance and high flow, thermal and chemical homogeneity over the entire metal bath in the mold. The invention also makes it possible to leave no heels in either the tundish or the distributor when they are replaced. The invention is particularly useful for thin slab and strip casting processes where mold flow control is critical to the casting process.

Description

BACKGROUND OF THE INVENTION[0001]In conventional continuous casting of steel, a tundish positioned above the mold is used to slow down steel poured from a ladle. From the tundish, steel flows through submerged immersion nozzles (SEN) to the casting mold and solidifies while being pulled out from the mold.[0002]The principal role of a tundish is flow modification and control. Some refining functionalities may be needed with inclusion removal as the main focus. Currently, due to its inherent deficiencies resulting from its relative position between the ladle and the mold, no tundish can perform ideally in either flow control or in inclusion removal.[0003]For the flow control or optimization, capability of the current tundish system is seriously impaired due to the fact that there exists a large hydrostatic head in the tundish relative to the steel pool in the mold. Stop rods and sliding gates must be used to regulate the steel flow rates. As a result, chaotic pressure field inside the...

AI Technical Summary

Benefits of technology

The invention is a new system for delivering molten steel from a ladle to a mold in the continuous caster process. The system is designed to improve the quality and efficiency of the casting process. It consists of a tundish and a distributor. The tundish has special refining structures to achieve low inclusion levels in the steel. The distributor has a main chamber and several conduits, including a submerged entry nozzle, a lifting tube, and a down tube. The system delivers consistent and cleaner steel to the mold with improved flow patterns and reduced turbulent disturbance. It also reduces the impact of slag on the casting process and allows for better removal of inclusions. Overall, the system improves the quality of the casted steel and reduces costs.

Problems solved by technology

Currently, due to its inherent deficiencies resulting from its relative position between the ladle and the mold, no tundish can perform ideally in either flow control or in inclusion removal.

For the flow control or optimization, capability of the current tundish system is seriously impaired due to the fact that there exists a large hydrostatic head in the tundish relative to the steel pool in the mold.

As a result, chaotic pressure field inside the SEN and disturbing flow streams at SEN exits are created.

Such flow distribution in the mold makes optimization of the flow and thermal fields in the mold for improved casting extremely difficult.

To fundamentally change this situation, improvements in shape change or internal structure modification of the current tundish system can hardly be sufficient since the root cause is the chaotic flow state inside the SEN resulting from the high hydrostatic pressure in the tundish.

Such situation also limits the use and the effectiveness of the more advanced SEN designs with variable exit opening shapes and dimensions needed for the optimized steel delivery to the mold.

Furthermore, the chaotic and multi-phase flow inside the SEN also promotes the aggregation and precipitation of the inclusions along the phase interfaces and makes the SEN clogging more severe.

However, since it needs frequent replacement and repair, the size and weight of a tundish can not be too large.

This limits the possibility of creating sufficient inclusion removal conditions in the tundish for inclusions to collide and aggregate and grow large enough to float out of the steel bath.

Such shortcomings cannot be fundamentally improved with any internal flow control devises or filters.

This inevitably reduces metal yield and profitability of the process.

The current tundish systems are particularly weak in removing inclusions with sizes smaller than 20 μm which in many cases, particularly for those steel grades with total oxygen content below 10-20 ppm, makes up the majority of the oxygen content.

Since the micro inclusions in the molten steel rise very slowly, it takes a long time for them to reach the top slag. e.g., for an oxide of 30 μm, it takes more than 10 minutes to rise a distance of 0.3 meters.

It is then not practical to remove inclusions smaller than 30 μm in a conventional tundish by floatation only.

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