Exploration of the causes of abnormal mold level fluctuation in thin slab continuous casting mold

Abnormal fluctuations in the mold can easily lead to slag entrainment during the thin slab continuous casting process. It is difficult to guarantee the uniform growth of the shell solidification of the slab. The quality of the slab is seriously affected. In this study, the data on thin slab mold level fluctuation were collected from a complete casting sequence of low-carbon steel in a Chinese plant. The discrete wavelet transform (DWT) method is used to decompose the mold level fluctuation and different process parameters. The frequency composition of abnormal fluctuations was clarified, and the causes of the abnormal fluctuations were revealed. The results show that the frequency ranges of abnormal fluctuations are concentrated in 0.3125–0.625 Hz and 0.625–1.25 Hz, and the low set mold level is where the maximum amplitude occurs. Within the time-frequency range, changes in parameters such as electromagnetic braking, mold oscillation, casting speed, stopper rod, and tundish weight cannot be completely matched to abnormal fluctuations collected by the eddy current sensor (ECS). It was found that the abnormal fluctuations in the ECS were that its equipment was disturbed through the analysis of the fluctuations collected by the radioactive source detection (RSD). The degree of disturbance is related to the height of the set mold level. The maximum fluctuation difference exceeded 6 mm between different collection methods when the set mold level was low. In this plant, the position of the ECS is to avoid the area of violent fluctuations of the surface molten steel and be moved appropriately towards the submerged entry nozzle (SEN) to reduce disturbance. When the current ECS position is unchanged, the mold level is set at approximately 305–309 mm, and the casting speed is matched to 4.8 m/min, which minimizes the disturbance with the ECS measurement.