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Abstract
In continuous casting steel industries, mold flux is added to provide thermal and chemical insulation for molten steel. The mold flux absorbs detrimental inclusions from the steel and promotes uniform heat distribution to prevent sticking. To promote flux infiltration, mold oscillation is used, but this creates oscillation marks that reduce local shell growth and increase temperatures. Wide (2-3 mm) and deep (0.5-0.9 mm) oscillation marks with areas of 1.1-2.5 mm² are observed, affecting the steel quality, which results in a loss of 6% per billet to the industry. To address this challenge, we propose an extrinsic Fabry-Perot interferometer (EFPI) sensor for high-temperature gap measurements. The proposed EFPI sensor has a wide measurement range of 10 µm to 1000 µm with a measurement uncertainty of 5 to 8 nm, and for larger gaps in the range of 1000 µm to 3.5 mm, the measurement uncertainty is 0.1 to 0.3 µm.
The EFPI sensors measure the gap during shrinkage due to rapid cooling of the flux material in real-time, providing a reliable and accurate measurement method for high-temperature gap sensing in a harsh environment. A smaller air gap between mold and solidified mold flux is favorable for strand lubrication and the thickness of mold flux film are crucial for production of higher-quality steel. A lower melting temperature of mold flux leads to greater liquid slag thicknesses and smaller maximum air gap thicknesses. A shortage of flux feeding into the gap can lead to air gaps, non-uniform heat flow, thinning of the shell, and longitudinal surface cracks. Thus, measuring the air gap and thickness of the mold flux aids in optimizing the melting temperature, flux feeding and mold oscillation frequency which can improve overall casting process.
