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Improper shape and size of the copper mould tube – in order to increase the contact surface between the molten steel and the mold copper tube, adjust the taper of the mould to adapt to the solidification shrinkage of the steel, thereby increasing the heat transfer of the copper mould tube and increasing the thickness of the billet shell. For conventional molds with linear tapers on high-speed billet casters, heat transfer at the meniscus rapidly solidifies the strand into a solid shell, and as the shell shrinks, the corners break away from the copper mould tube, stopping heat transfer. Thus, at the bottom of the mold, the shell continues to grow, except for remelting at the corners. When the billet shell leaves the mold, the temperature of the billet shell changes greatly, and increasing the pulling speed at this time may lead to breakout. If the adjusted taper is unsatisfactory, an air gap will be created between the mold and the shell, when the resistance of the air to the heat transfer in the mold reaches the maximum, it will seriously hinder the formation of the shell of the required thickness, and eventually lead to breakout . copper mould tube taper loss due to wear and deformation can lead to a significant increase in corner longitudinal cracks as a result of corner reheating. As far as the mold deformation is concerned, the reason is that the thickness of the copper mould tube is too thin to support the thermal expansion of the copper tube. It is also possible that when the dummy rod is inserted into the mold, the lower part of the mold is damaged and the mold is deformed. If the copper mould tube taper is too large, the drawing resistance will be increased, resulting in increased mold wear. Inverse taper plus heat shrinking increases the thickness of the air gap, which in turn increases corner wear, thus reducing the heat transfer that increases the surface temperature. This phenomenon is always accompanied by the hydrostatic pressure of the steel, which induces tensile strains on the corner surfaces, which in turn initiate cracks. Such cracks can substantially reduce the shell thickness in a fixed manner and may eventually lead to breakouts. The larger the copper mould tube fillet radius, the larger the air gap. The air gap hinders heat transfer, resulting in the formation of a thin billet shell, which is prone to breakout. In the slab/bloom caster, 4 separate copper plates are held in place, forming cavities surrounding them. If there is an air gap at the junction between the 2 copper plates, the initial metal will penetrate into the air gap and start to solidify, causing hanging in the later stage, resulting in steel breakout. Therefore, improper adjustment of the copper mould tube will affect the heat transfer mechanism, resulting in breakout.