Small Cross Section Billet Casting with Eddy Current Level Control
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Solution Overview
Problem
Existing methods for continuous casting of steel billets with small cross sections face challenges in reliably reducing center porosity and ensuring inner quality, as they are prone to excessive cooling, uneven cooling, and narrow operational conditions, leading to defects in seamless steel pipes.
Innovation Solution
A method involving the use of a cylindrical immersion nozzle with a single port, eddy current sensor for molten steel level control, electromagnetic stirring, a 3-8 m long cooling zone, and specific cooling water parameters to adjust the billet surface temperature and casting speed, ensuring the solid phase ratio at the billet center is within a controlled range during the final solidification period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If forced cooling is carried out excessively upstream relative to the point of final solidification, then the cooling effect is enhanced, but no more temperature allowance for cooling remains when center porosity formation risk is high
Solution Approach 1:
The patent applies preliminary action by performing initial cooling in the upstream region (2-15m before liquid core crater end) to create thermal shrinkage and compress the billet, then performs additional cooling only when the solid phase ratio reaches 0.95 or higher. This staged approach ensures cooling is applied at the right moments: first to create compression, then to eliminate porosity without excessive cooling that would remove temperature allowance.
2Productivity
If cooling is stopped when the core of the billet is not yet in a solidified state, then the cooling process is shortened, but return of heat causes increased center porosity or internal cracking
Solution Approach 1:
The patent implements feedback control by continuously monitoring the solid phase ratio at the billet center and using this information to determine when to continue or stop cooling. Cooling is maintained until the solid phase ratio reaches 0.95 or higher, ensuring the core is sufficiently solidified before stopping, thereby preventing heat return and subsequent porosity or cracking while avoiding unnecessarily prolonged cooling.
3Manufacturing precision
If the ranges of proper conditions for reducing center porosity are made narrow, then the cooling effect is optimized, but extraneous disturbances readily cause actual production conditions to deviate from proper ranges
Solution Approach 1:
The patent applies dynamics by making the cooling conditions adaptive rather than fixed. The cooling parameters (water flow rate, cooling zone position) are dynamically adjusted based on real-time monitoring of the solid phase ratio and billet temperature. This allows the system to maintain optimal porosity reduction effects while automatically compensating for extraneous disturbances such as variations in casting speed, steel composition, or ambient conditions.
4Reliability
If the billet surface temperature is lowered excessively, then the solidified shell shrinks and reduces center porosity, but the billet may undergo excessive thermal stress or deformation
Solution Approach 1:
The patent applies parameter changes by precisely controlling the billet surface temperature within specific ranges (900-1200°C at the entrance to the final solidification cooling zone) rather than using excessive cooling. The cooling water density is controlled at 20-300 L/(min·m²) and the specific amount of cooling water is limited to 0.1-0.8 L/kg-steel. These controlled parameter changes achieve sufficient thermal shrinkage for porosity reduction while preventing excessive thermal stress or deformation that would compromise billet integrity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach stabilizes the reduction of center porosity and improves the inner quality of the billet, resulting in a significant decrease in defects and enhanced productivity in seamless steel pipe production.
Implementation Method 1
a surface level of molten steel is measured using an eddy current sensor for molten steel level control in a mold
Implementation Method 2
motion of molten steel in the mold is adjusted by providing electromagnetic stirring
Implementation Method 3
the billet is cooled in a secondary cooling zone with cooling water in a specific amount of 0.1-0.8 liter (L)/kg-steel
Implementation Method 4
a cooling zone during the final period of solidification... in which the solid phase ratio at the billet center is 0.3-0.99 may be included
Implementation Method 5
subjecting the billet surface to forced water cooling... in response to the progress of solidification of the billet liquid core to cause the billet solidified shell to shrink and thus reduce the billet cross section
Data Source
AI summary
Continuously casting a billet with a small cross section by pouring molten steel into a mold using a cylindrical immersion nozzle is characterized by measuring the molten steel level in the mold using an eddy current sensor. The level is controlled based on the thus-measured value, motion of steel in the mold is adjusted by electromagnetic stirring, a cooling zone during the final period of solidification is disposed within a certain region ranging from the meniscus to the specific site, and casting speed is adjusted so that the region in which the solid phase ratio at the billet center is 0.3-0.99 may be included in the cooling zone during the final period of solidification. The secondary cooling water amount and the billet surface temperature at the entrance to the cooling zone the density of cooling water in the cooling zone during the final period of solidification are optimized.