This situation is common in many copper tube production bases for small square billets, and if it persists, it is not normal. In short, the temperature in the meniscus region of the copper mold tube is too high. What causes this in a copper mold tube system? There are many influencing factors; otherwise, the crystallizer would not be considered the heart of continuous casting.
For example, in a copper mold tube, the operating water temperature, cooling flow rate and pressure, water quality, and uniformity of the water gap all directly affect thermal stability. High casting speed, excessive furnace running cycles using the same copper mold tube, insufficient protective slag addition leading to a thin slag layer, and the material and plating type of the copper mold tube also significantly influence heat transfer behavior.
Excluding relatively stable factors such as copper mold tube material, the most critical variables include water temperature control, cooling water quality, and protective slag performance. In particular, insufficient slag coverage in the crystallizer can cause uneven heat flux distribution on the copper mold tube surface. The blackening observed on the four sides of the copper mold tube is often a strong indicator of a thin slag layer.
Under high-temperature molten steel conditions, uneven heat transfer causes asymmetric solidification on the copper mold tube surface. This leads to inconsistent heat flux density, uneven shell growth, and an increasing air gap between the solidified shell and the copper mold tube wall. As a result, heat transfer becomes unstable and less efficient.
Once stress concentration occurs, the risk of cracks increases, and breakout may happen when the billet exits the crystallizer, directly affecting production safety and the service life of the copper mold tube.
