Reason:
(1) The head of the tundish stopper rod and the bowl of the upper water inlet are poorly baked. Because the bowl is low, the baking flame of traditional baking method can't reach the bowl, so the temperature of the bowl is 100 ~ 200℃ lower than that of other parts. The low temperature of molten steel can easily cause cold steel to pad bars and steel flow to get out of control, which leads to insufficient solidification of billet head and breakout during casting.
(2) The paper rope is loose, and molten steel leaks from its gap; Paper rope is damp, and it explodes after meeting molten steel, resulting in cracks, and molten steel leaks from the cracks.
(3) The iron scrap layer is too thin, which causes the molten steel to burn the paper rope and seep out from the gap; If the iron chip layer is too thick, the strength of the blank head will be insufficient and the blank shell will be broken; Iron filings are affected with damp, greasy or sundries, and explode or burn after encountering molten steel. The molten steel burns paper ropes and seeps out from gaps or the strength of billet head is insufficient, and the billet shell is broken.
(4) The traditional way of blocking dummy ingot is to plug the gap between dummy ingot head and crystallizer with paper rope. When molten steel arrives at the station for temperature measurement, iron nail chips with a thickness of 20 ~ 30 mm are evenly spread on the dummy ingot head, and then steel strips are placed on the iron nail chips in a cross way according to regulations. If the steel strip is not placed well, the molten steel will directly wash away the iron filings and paper ropes; If the steel strip is not melted sufficiently, the primary shell will be too thin, which will cause the shell to tear when drawing.
(5) There are the following problems in the operation: the steel flow in the casting is too large, which flushes iron chips or splashes molten steel on the crystal wall and corner joints to form steel clips; The starting speed is too fast, each time it exceeds 0.1m/min, and the primary shell can not bear its tensile force; Foreign matter enters the crystallizer and bites into the primary shell.
(6) There are the following problems in equipment: the dummy bar slides over 20mm; The mold corner gap is too large, exceeding 0.30mm .

In order to prevent steel leakage before pouring, adequate preparation and inspection should be made before pouring, with the following points to be paid attention to:
(1) Check the compaction of dummy ingot head and stacking of cold materials;
(2) Check the alignment between nozzle and crystallizer;
(3) Check whether there is cold steel on the crystallizer copper plate and whether the taper is appropriate;
(4) Check whether the secondary cooling nozzle is unblocked and intact;
(5) ?Understand the fluidity of molten steel, the temperature state of molten steel, the baking state of tundish?nozzle, and the quality of mold powder. The upper water inlet and immersion water inlet shall be fully baked to ensure that the temperature of immersion water inlet is above 800℃ within 2.5 hours, and the temperature of upper water inlet stopper is above 1100℃.
(6) ?The size of injection flow and the residence time of molten steel in the mold should be determined according to the section of slab.
(7) Once the initial drawing speed is generally kept at 0.5m/min, and the growth rate is slower (0.15m/min), so as to prevent excessive fluctuation of crystallizer liquid level.

Article Source:Causes and avoiding methods of open pouring breakout
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