Bonded breakout is the main breakout form in continuous casting production. According to statistics, bonded breakout accounts for more than 50% of many breakout. The so-called bonding is due to the fluctuation of mold liquid level, and there is no liquid slag between meniscus solidification shell and copper plate, which leads to bonding in serious cases. When the billet is drawn, the friction resistance increases, and the bonding point breaks, which extends downward and to both sides, forming a V-shaped fracture line, and breakout occurs when it reaches the exit of the crystallizer.

The occurrence of bond breakout is as follows: the occurrence rate of breakout in wide inner arc surface is higher than that in wide outer arc surface (about 3:1); Bond fracture is more likely to occur near the middle of the wide surface (about 300 mm around the nozzle); The large broken plate is easy to leak steel in the middle of the wide surface; However, small sections appear near narrow surfaces; The breakout probability of aluminum killed steel is higher than that of aluminum-silicon killed steel. When the crystallizer copper plate is used for more than 200 heats, the liquid slag can not flow in evenly because of the rough coating of the copper plate, and the tendency of breakout increases; When the dosage of mold flux is less than 0.25kg/t steel, the probability of breakout increases.

Reasons for breakout: 1) The mold flux has high Al2O3 content and high viscosity, and crusts on the liquid surface, which makes the slag poor in fluidity and difficult to flow between the blank shell and the copper plate to form a lubricating slag film. 2) High casting speed under abnormal conditions. Such as high casting speed when the liquid level fluctuates and high casting speed when the molten steel temperature is low. 3) The liquid level fluctuation of crystallizer is too large, such as excessive argon blowing, blockage of submerged nozzle, serious deviation of nozzle flow, dew condensation at nozzle during ladle changing, etc., which will cause liquid level fluctuation.