How to use zirconia tundish nozzle?

 

The use of zirconia tundish nozzles must strictly follow the "Installation - Preheating - Pouring - Maintenance - Replacement" process. The core of product usage is ensuring proper sealing during installation and thorough preheating to prevent molten steel leakage or nozzle rupture, thereby safeguarding continuous casting stability.

 

Installation is the critical prerequisite directly impacting subsequent operational safety. Key focus areas include sealing integrity and positioning accuracy.

• Ladle Cleaning: First clean the nozzle installation hole at the ladle bottom, removing residual refractory materials, steel slag, or debris. Ensure the mounting surface is flat and free of protrusions to prevent sealing failures caused by contaminants.
• Nozzle Positioning and Installation: Align the zirconia nozzle with the installation hole at the ladle bottom. Slowly insert and adjust it to a vertical position, ensuring the nozzle center aligns with the mold center to prevent molten steel flow deviation.
• Sealing Treatment: Fill the gap between the nozzle and mounting hole with specialized refractory mortar or install a refractory fiber sealing ring. Gently compact using a gland or bolts to ensure complete sealing, preventing molten steel leakage during pouring.

 

 

Zirconia material is sensitive to temperature differentials. Direct contact with high-temperature molten steel may cause thermal shock cracking, necessitating preheating.

Preheating Method:

Preheat the entire ladle or supplementally preheat the nozzle area to prevent localized underheating.

Preheating Requirements:

1. Preheat temperature must reach 800-1000°C, with uniform ladle temperature throughout. Temperature difference between inner and outer nozzle walls must not exceed 300°C.
2. Control heating rate to no more than 200°C per hour to prevent nozzle cracking from excessive heating speed.
3. Determine preheat duration based on ladle size and nozzle specifications, typically lasting 2-4 hours to ensure complete thermal penetration and elimination of internal moisture.

 

 

The core of pouring is to stabilize the molten steel flow rate while monitoring the nozzle condition to prevent abnormalities.

Start-up Procedure:

After molten steel enters the ladle, once the liquid level reaches the specified height, open the sliding nozzle or stopper at the bottom of the nozzle. Slowly adjust the opening to ensure molten steel flows into the mold at a stable velocity.

Flow Control Principles:

• Initial Stage: Avoid excessive flow velocity. Begin with a low flow rate to initiate flow. Once a stable crust forms inside the mold, gradually increase to normal flow velocity.
• Normal Pouring: Match the nozzle flow rate to the billet pulling speed to maintain a stable liquid level within the mold. This prevents overflow from excessive levels or leakage from insufficient levels.
• Real-Time Monitoring: During pouring, utilize mold liquid level detectors, cameras, or manual observation to closely monitor for molten steel leakage from the nozzle and ensure uniform flow patterns. Adjust promptly if abnormalities occur.

 

 

Although zirconia nozzles exhibit excellent erosion resistance, prolonged use may still lead to blockages or localized erosion, necessitating targeted maintenance.

• Anti-clogging measures: If inclusions in molten steel adhere to the nozzle's inner wall, reducing flow velocity, inert argon gas can be introduced from the bottom or side of the nozzle to clear the inclusions. Alternatively, moderately increasing the ladle temperature can lower the melting point of inclusions, reducing adhesion.
• Preventing Localized Erosion: Avoid prolonged erosion of a specific area of the nozzle by molten steel. If significant localized wear is detected, appropriately reduce the casting speed to extend the nozzle's service life.

 

 

When the nozzle's performance deteriorates to the point where it no longer meets continuous casting requirements, it must be replaced promptly to avoid compromising billet quality.

Criteria for scrapping:

• The nozzle's inner diameter has expanded beyond 15% of its initial size (e.g., from an initial diameter of 50mm to 57.5mm or greater), resulting in uncontrollable flow rates.
• The nozzle exhibits visible cracks, perforations, or leaks.
• The service life reaches its design limit.

Replacement Procedure

After the ladle cools to ambient temperature, remove the gland and sealing layer. Use specialized tools to extract the old nozzle from the mounting hole. Clean residual refractory mortar, then install the new nozzle following the installation steps.

 

 

• Avoid direct contact with molten steel when the nozzle is not preheated or insufficiently preheated, as this may cause thermal shock fracture of the zirconia material.
• Refrain from forcefully striking the nozzle during installation to prevent internal cracking due to mechanical impact.
• Different steel grades exhibit varying erosion rates on nozzles. Select nozzles with matching zirconia content-e.g., use high-purity zirconia nozzles for stainless steel casting.

 

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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