The Current Situation of Continuous Casting Tundish Usage and the Reasons Influencing Its Service Life

1.2 Factors affecting the lifespan of intermediate packages:

(1) Quality of refractory materials:

① The working layer is in direct contact with the molten steel and is a critical component. The masonry materials for the working layer are semi silica, high alumina, zircon, or insulation panels made of silica, magnesium, and magnesium olivine; Alternatively, magnesium based, magnesium chromium based, and magnesium calcium based coatings or castables can be used.

② The brick for the water outlet of the intermediate package is embedded at the bottom, which belongs to the weak part of the intermediate package. High aluminum and high-temperature resistant materials are usually used.

③ The working layer at the bottom of the intermediate ladle is easily damaged by the impact of molten steel, and requires resistance to erosion and wear. High strength tar magnesia bricks, high alumina bricks, and aluminum chromium bricks are mainly used. Zirconia bricks are also used in the impact zone of molten steel.

④ The intermediate ladle cover is placed on the intermediate ladle to provide insulation and prevent splashing of molten steel. It is usually made of clay or high-alumina refractory casting materials as the ladle cover.

(2) Production organization and operational level:

① The molten steel level in the intermediate ladle should remain stable or have minimal fluctuation during the production process; The production organization requires that the production capacity of the converter normally matches the production capacity of the continuous casting, and should avoid damage to the inner lining of the intermediate ladle caused by large fluctuations in the steel level due to delayed continuous casting of the molten steel.

② The temperature of the molten steel to the continuous casting platform should be reasonable to avoid excessive overheating of the molten steel from flushing the inner lining of the intermediate ladle; It is necessary to avoid the harm to the inner lining of the intermediate ladle caused by the temperature of the molten steel being too low and the temperature rising due to oxygen permeation into the intermediate ladle.

③ Intermediate ladle structure: The continuous casting intermediate ladle adopts structures such as retaining walls, dams, and turbulence controllers, which not only make the flow of molten steel in the intermediate ladle reasonable, but also facilitate the upward floating of non-metallic inclusions in the molten steel, improve the quality of molten steel, and improve the service life of the intermediate ladle.

Measures to improve the lifespan of intermediate packages

2.1 The working layer of the intermediate package adopts dry materials

Under certain process conditions and the material and masonry form of refractory materials in the intermediate ladle, the service life of the intermediate ladle mainly depends on the chemical erosion, high-temperature melting loss, and mechanical erosion of the working layer steel. The use of dry materials has strong resistance to erosion and erosion, meeting the requirements of long-term continuous pouring.

2.2 The lining is made of magnesium refractory material

Magnesium refractory materials have a strong ability to adsorb inclusions in steel, and have good resistance to corrosion and erosion, which can meet the requirements of high continuous casting furnace numbers and improve the quality of molten steel. After use, observe that the lining slag line of the intermediate ladle is the thinnest, and other parts are between 30-40mm. After one pouring is completed, it is also easy to remove the intermediate ladle.

2.3 Using a current stabilizer

Due to the direct impact of the molten steel flow from the ladle into the tundish, the erosion of the tundish is severe, and in serious cases, it may even cause leakage. For this reason, it was decided to use a current stabilizer. The material of the current stabilizer is magnesia-carbon, and its structure is a container-like shape with a hollow interior. The bottom of the inner cavity of the current stabilizer is large, while the opening is small. The use of this structure in the continuous casting tundish stabilizer has a significant and stable effect on preventing slag entrapment in the area of the ladle nozzle. The quality of the molten steel in the tundish is high, and the consumption of refractory materials in the tundish is low.

2.4 Increase the liquid level of molten steel in the intermediate ladle

The original minimum liquid level requirement for pouring steel into the tundish was 600mm, but now it has been changed to be greater than 700mm. With the increase in the liquid level of the molten steel, the residence time of the molten steel in the tundish has been extended. In deeper molten pools, the resistance between the molten steel from the ladle and the stabilizer has increased, and the flow velocity at the contact surface of the stabilizer is smaller, resulting in less impact force on the stabilizer. This has increased the continuous casting time of the stabilizer and also improved the service life of the tundish.

2.5 Improving slag overflow operation

Originally, the overflow port was located close to the pouring point, making slag overflow difficult. As the number of continuous casting furnaces increases, the slag volume becomes large and cannot be discharged in time, leading to severe erosion of the ladle lining at the slag line and affecting the quality of molten steel. To address this, the position and shape of the slag overflow port have been modified, and an assessment system has been established. The slag thickness must not exceed 30mm, and proper operational rhythm requires timely slag discharge. The slag thickness should be controlled below 30mm to prevent severe erosion of the slag line on the ladle wall and the occurrence of steel penetration. At the same time, the large ladle contractor should strengthen their operations while controlling the excess steel in the ladle, to avoid a large amount of slag being transferred into the tundish, which could cause severe erosion of the slag line on the tundish wall.

2.6 Improving the service life of the tundish nozzle

Improve production scheduling level, reduce choking caused by waiting for steel and other reasons, stabilize the temperature of molten steel on the stage, reduce secondary pouring caused by operational problems, thereby improving the service life of the tundish nozzle and thus improving the service life of the tundish.

2.7 Improving the deoxidation process of molten steel

The deoxidizer used by Xigang is mainly silicon aluminum barium. In order to improve the deoxidation effect, the amount of deoxidizer added is increased, and a comprehensive deoxidation process is carried out by feeding silicon calcium wire into the ladle to modify the inclusions in the molten steel. This process not only improves the deoxidation effect of converter steel and reduces oxide inclusions in steel, but also enhances the castability of steel and eliminates the clogging at the tundish nozzle caused by poor fluidity of steel. At the same time, the free oxygen content in the molten steel decreases, thereby reducing erosion on the tundish nozzle and improving the lifespan of the tundish.

2.8 Reasonable temperature system

To ensure the normal pouring of molten steel, the superheat of the molten steel in the intermediate ladle is strictly controlled at 10-25 ℃. In order to improve the success rate of the first batch of pouring, the tapping temperature of the converter is 30-40 ℃ higher than the normal pouring temperature. Control the temperature of molten steel in the intermediate ladle according to the middle and lower limits, and increase the qualification rate from 80% to 95%.

2.9 Ensure baking effectiveness

When baking the intermediate package, the central burner of the baking device should be aligned with the center of the tundish to ensure the baking effect of the tundish. Specific requirements for baking the intermediate package: medium heat baking shall not be less than 30 minutes, and high heat baking shall not be less than 1 hour. Medium heat baking refers to the flame reaching the bottom of the package without escaping, while high heat baking refers to the gas valve being fully open or essentially fully open, with the flame hitting the bottom of the package and rebounding, the air volume being appropriately matched, and the flame temperature reaching its maximum. Once high heat baking begins, the dry working lining intermediate package must not be extinguished or have the flame reduced midway, ensuring that the temperature of the tundish wall reaches 1000°C or above before pouring.

2.10 Improving Production Organization Models

Reasonably utilize the production organization mode, arrange the use of intermediate packages in a planned manner, avoid waste of intermediate packages, and under normal circumstances, use intermediate packages reasonably in the order of masonry to fully maximize their service life.

2.11 Reasonable production system

The connection of molten steel between the converter and continuous casting is a necessary condition to ensure the normal production of continuous casting. It is required that the molten steel supplied to continuous casting is delivered on time, the information transmission of production scheduling is enhanced, and a reasonable production organization is carried out to ensure the stability of the molten steel level in the tundish. At the same time, it is ensured that the liquid level in the tundish remains within the required range to guarantee the service life of the tundish.