Ladle → Tundish Protective Pouring (Long Nozzle Operation)
Preparation Stage
Inspect the Long Nozzle: Confirm the lining is undamaged and the argon gas channel is unobstructed. Preheat to above 800℃ (avoid quenching the molten steel by a cold lining).
Ladle Alignment: Align the ladle nozzle with the tundish impact zone, with a deviation ≤50mm. Before fully opening the ladle sliding nozzle, connect the long nozzle argon gas hose (pressure 0.3-0.5MPa).
Long Nozzle Installation:
The robotic arm inserts the long nozzle into the ladle’s lower nozzle, tightening the sealing ring (graphite + metal fiber) to ensure no gaps. Adjust the argon gas flow rate to 15-20L/min and check for leaks at the connections.
The long nozzle should be inserted into the molten steel in the tundish to a depth ≥100mm (confirm after the liquid level stabilizes), avoiding exposed flow.
Monitoring the casting process:
Observe the argon flow rate at the long nozzle throughout the process: if the fluctuation is > ±5L/min, immediately check the sealing condition; if the liquid level in the tundish is ≤500mm, do not raise the long nozzle.
At the end of the ladle casting process (remaining steel <5t), slowly close the sliding nozzle to avoid slag entrapment; after removing the long nozzle, check the lining corrosion (if the corrosion depth is >30mm, the ladle should be scrapped).
Tundish → Crystallizer Protection Casting (Submerged Inlet Nozzle + Protective Slag)
Submerged Inlet Nozzle (SEN) Preparation
SEN Inspection: No nodules on the inner wall, no cracks in the slag line; preheat to above 1000℃; no aging of the interface gasket, deviation ≤2mm after installation.
SEN Insertion into the Crystallizer: Depth controlled at 150-200mm (adjusted according to cross-section: 150mm for billets, 200mm for slabs), deviation from the crystallizer center ≤5mm.
Protective Slag Addition and Maintenance
When the crystallizer liquid level rises to 50mm above the SEN outlet, begin adding protective slag: initial addition is 1.2-1.5kg/m² (to cover the liquid surface), subsequent additions every 2-3 minutes (maintaining a slag layer thickness of 10-15mm).
Monitoring the protective slag condition: The thickness of the liquid slag layer should be controlled at 8-12mm, and the sintered layer thickness ≤5mm; if “crust” appears, gently break it with a tool (avoid disturbing the molten steel).
Gas protection (special steel grades): An argon gas sealing hood is installed above the crystallizer, with the O₂ content in the protective atmosphere ≤1% (online monitoring); the amount of tundish covering agent (carbonized rice husk) added is 1.5-2.0kg/t steel, completely covering the liquid surface.
Abnormal Handling
Air Leakage at the Long Nozzle: Immediately adjust the argon flow rate. If this is ineffective, urgently raise the long nozzle and close the ladle nozzle. Replace the long nozzle and recast.
Molding Slag Clumping: Stop adding molding slag. Clean the clumps with a special tool, add new molding slag, and adjust the casting speed (temporarily reduce by 0.1-0.2 m/min).
Key Point: The quality of continuous casting molding depends on meticulous operation. From millimeter-level control of the argon flow rate at the long nozzle and precise alignment of the submersible nozzle insertion depth to real-time control of the molding slag spreading thickness, deviations in every minute parameter can lead to secondary oxidation of the molten steel or excessive inclusions. Only by adhering to these meticulous requirements throughout the entire casting process can high-purity billets be produced consistently.
