How can I determine if a zirconia tundish nozzle needs to be replaced?

 

Determining whether a zirconia tundish nozzle requires replacement hinges on the extent of performance degradation and associated safety risks, preventing quality defects in steel billets or safety incidents due to delayed replacement.

 

 

Long-term exposure to molten steel erosion causes gradual enlargement of zirconia nozzles. When the inner diameter exceeds permissible limits, stable flow control becomes impossible, necessitating replacement.

Inspection Method:

Measure the nozzle's inner diameter using specialized equipment, focusing on the inlet and outlet ends-the areas most severely eroded.

Replacement Criteria:

Replace if the inner diameter expansion exceeds 15% of the initial dimension.

Replace if irregular deformation occurs (e.g., localized bulging, ovalization), even if expansion is below 15%, to prevent disrupted molten steel flow patterns.

 

 

Inspect the nozzle for cracks, perforations, or other damage. Such defects directly cause molten steel leakage and require immediate replacement.

• Cracks: Examine both inner and outer walls for visible cracks. Even minor cracks (length >5mm) may expand due to thermal shock during preheating or pouring, leading to rupture.
• Leakage: If molten steel seeps from the nozzle's sides or bottom during pouring, perforation has occurred. Pouring must be halted immediately for replacement.
• Damage: If refractory material detaches from the nozzle tip or inner wall, it contaminates the molten steel with refractory impurities, compromising billet purity. Replacement is required.

 

 

Replace the nozzle immediately upon detecting any of the following functional failures, even if its appearance or dimensions show no obvious abnormalities, to prevent disrupting production continuity.

Uncontrolled Flow:

• Excessive molten steel flow persists even when the sliding nozzle or plug rod is adjusted to the smallest opening.
• Sudden or unstable flow reduction prevents maintaining billet pulling speed. This may result from internal blockage by Al₂O₃ inclusions, which cannot be cleared by argon purging.

Abnormal Flow Pattern:

• The molten steel stream deviates upon exiting the nozzle, causing excessive fluctuations in the liquid level within the mold.
• Splashing or diverging flow streams indicate an uneven inner surface or localized depressions within the nozzle. These imperfections can draw in air, forming bubbles that compromise billet quality.

 

 

Lifetime Threshold:

Based on the nozzle's design lifespan, intensified inspections are required when the number of furnace pours reaches 90% of the design value. If the nozzle reaches or exceeds its design lifespan, replacement is recommended even if no apparent issues exist in appearance or functionality.

Process Change Requirements:

If subsequent high-purity steel grades are to be poured, the nozzle must be replaced with a new one even if the current nozzle has not reached its lifespan. This prevents contamination of molten steel by residual inclusions in the old nozzle.

If the ladle undergoes major overhaul, the nozzle must be replaced simultaneously to avoid performance mismatches between new and old refractory materials.

 

 

After each pour concludes and the ladle has cooled, conduct further offline inspection of the nozzle to inform future usage.

Examine the nozzle's inner wall for severe erosion marks.

Gently tap the nozzle with a hammer. A clear, crisp sound indicates no internal cracks. A dull sound signifies internal cracking, rendering the nozzle unusable.

 

Changtai Silicon Industry reminds you that to ensure operational safety, you must regularly inspect the condition of the zirconia tundish nozzle.

Anyang Changtai Silicon Industry Co., Ltd. is a comprehensive manufacturer specializing in the design, processing, and sales of zirconia high-temperature products. If you require zirconia high-temperature products, please email us at: zhang@ayctgy.com. We will respond to your inquiry promptly upon receipt.

 

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