MAIN CAUSES OF CRACK FORMATION AND SHELL BREAKOUT IN A SLAB CCM

Abstract

This article presents an analysis of the causes of crack formation and shell breakouts within the mold of a slab continuous casting machine (CCM) and examines approaches to their pre-failure diagnosis. The continuous casting process is characterized by high complexity due to the simultaneous occurrence of thermal, hydrodynamic, and phase-transformation processes, which imposes stringent requirements on the stability of technological parameters. It has been established that the key factors contributing to defect formation are non-uniform heat extraction, thermal stresses, steel chemical composition, liquid-phase hydrodynamics, and deviations in secondary cooling regimes. It is demonstrated that increasing the casting speed by 5–10% relative to the nominal value of 1.08 m/min results in a reduction in the thickness of the solidified shell, particularly along the narrow face of the mold. A similar effect was observed when the metal temperature in the tundish was raised by 5–15 °C above the baseline value of 1528 °C; this leads to a systemic thinning of the shell and an increased probability of a breakout. An analysis of CCM downtime patterns during the first half of 2025 revealed that unscheduled stoppages accounted for approximately 70% of total downtime events, while scheduled preventive maintenance accounted for 17 instances. The article reviews modern diagnostic methods based on monitoring temperature fields, cooling water flow rates and pressures, metal levels, oscillation parameters, and withdrawal speeds. The necessity of a comprehensive data analysis approach is substantiated to enhance equipment reliability and mitigate the likelihood of emergency situations.