Analysis on the Causes of Steel Breakout of Continuous Casting Billets(2)



D. Mold vibration frequency, amplitude

1. Unreasonable selection of crystallizer vibration frequency and amplitude. The mold has no negative slippage or small negative slippage, which causes steel breakout.

2. The vibration imitation arc difference and the large deflection will produce shear force on the billet shell, affect the lubrication of the mold slag, and increase the billet drawing resistance. From the perspective of heat transfer, the vibration imitation arc difference and the large deflection will increase the non-uniformity of the air gap between the shell and the copper tube, resulting in an increase in the thickness of the shell. The general reasons are that the vibration is unstable due to steel slag stuck on the east side of the vibration frame or the damage of the leaf spring, serious deflection of the mold, serious wear of the billet shell on both sides of the inner cavity of the copper tube and the inner east corner, and uneven heat transfer at the corners, which leads to corners Cracked steel.

  five. Two cold spray water

The temperature of the billet shell just out of the mold is high and the support is lost. At this time, uniform and strong cooling is required to promote the rapid growth of the billet shell. If the local cooling of the upper part of the secondary cooling is too weak, remelting will occur, resulting in steel leakage.

E. crystallizer

1) When the mold is assembled, the unevenness between the water jacket and the copper tube will cause uneven cooling of the copper tube, and the heat conduction on the side with small flow rate is low, resulting in thin steel leakage of the cast billet skin.

2) The taper of the copper tube of the mold is unreasonable: the thermal resistance of heat transfer in the mold is mainly the air gap. If the air gap is small, the thermal resistance is small. In the early stage of the use of the mold, the inner cavity curve of the copper tube is relatively close to the shrinkage curve of the billet shell, the air gap is uniform, the heat transfer is uniform, and the thickness of the billet shell is also relatively uniform. During use, the copper tube is constantly worn and deformed by heat. In the middle and later stages of use, the total taper becomes smaller, and the heat transfer under the meniscus is large, and the copper tube is partially deformed, which also increases the non-uniformity of the billet shell. The billet shell is prone to bulging at the lower part of the mold. Sampling shows that if the bulging amount of the 150mm×150mm casting billet is greater than 2mm, the deviation angle and internal cracking are prone to occur. Influence on the inner surface of the copper tube: During the use of the copper tube, due to the excessive and skewed cold steel placed in the treatment of the breakout accident, the face and corners are scratched, and the depth is greater than 1mm. During the steel drawing process, the scratched part of the shell The thermal resistance between the copper tube wall and the copper tube wall is large, the billet shell is thin, and it is prone to dents, and there are obvious cracks at the bottom of the dents. The quality of copper tube production is poor, especially the peeling off of local coating on the face and corner of the copper tube. The thermal resistance is increased, resulting in unstable heat transfer and easy to cause steel leakage. In addition, there are trachoma in the copper tube blank. With the increase of the amount of steel passing through the mold, the inner surface of the copper tube is worn, the trachoma leaks out, and the phenomenon of hanging steel occurs, and in severe cases, cracks are caused.