Breakout in continuous casting is a serious production accident in continuous casting. From billet continuous casting, the breakout phenomenon can be divided into: corner crack breakout, middle breakout, pull breakout, and start breakout.
From the analysis of the reasons of continuous casting breakout, it can be divided into:
Caused by Improper Operation
1. The nozzle of the mold is not centered, which causes the temperature of the molten steel in the mold to cool unevenly, resulting in uneven thickness and thickness of the cast billet shell.
2. The liquid level of the steel is not checked, which causes the molten steel to be too low to break out or to cause the steel billet to break and break out after the steel overflows. Or due to various reasons of production, the rhythm is unstable, resulting in large fluctuations in the pulling speed, and the solidification curve deviates from the inner cavity curve of the copper tube, which is prone to uneven thickness of the billet shell. The submerged nozzle has a short service life and is replaced frequently. The tundish needs to be raised as a whole when replacing it. The insertion depth of other flow nozzles is too shallow, and the liquid level is unstable, which is easy to cause slag leakage. Cold steel is connected between the nozzles, and the oxidized slag formed by blowing and burning with a small oxygen tube enters the mold, which is easy to cause slag leakage.
3. The slag ring in the mold is not caught in time, resulting in slag leakage of the casting billet.
4. The nozzle is blocked or mechanically broken, resulting in steel leakage.
Unreasonable Superheat of Steel
The crack leakage is closely related to the temperature and drawing speed of the ladle, which can ensure that the molten steel has certain superheat and can guarantee the smooth pouring of molten steel. The theoretical research shows that the thickness of mold outlet billet shell decreases by 3% when the superheat increases by 10℃. If the temperature is too high, the mold outlet billet shell will be thin and the high temperature strength will be low. Once the billet shell is broken by the stress, it is easy to produce cracks and steel leakage.
Steel Breakout Caused by Mold Slag
1) The addition of mold flux is not timely, resulting in no lubrication between the casting billet and the copper tube of the mold.
2) The choice of mold residue is unreasonable, that is, the melting point and dissolution rate are unreasonable.
The role of mold powder: heat insulation, prevent secondary oxidation, absorb inclusions, lubricate the shell and mold copper tube, and reduce frictional resistance. The mold flux for continuous casting should follow a reasonable melting temperature, melting speed and melting layer structure in the mold; stable and suitable viscosity; sufficient ability to absorb inclusions in steel.
Mold Vibration Frequency, Amplitude
1. The choice of vibration frequency and amplitude of the crystallizer is unreasonable. 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. The steel slag on the inner east side of the vibration frame or the damage of the leaf spring causes the vibration to be unstable, the mold deflection is serious, the billet shell is seriously worn on both sides of the inner cavity of the copper tube and the inner east corner, and the uneven heat transfer at the deflection angle leads to corner cracking and leakage. .
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.
Crystallizer
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.
The mold copper tube taper is not reasonable: the heat resistance of the mold heat transfer is mainly the air gap. If the air gap is small, the thermal resistance is small; if the air gap is large, the thermal resistance is large. At the early stage of using the mold, the inner cavity curve of the copper tube is close to the shrinkage curve of the billet shell, the air gap is uniform, the heat transfer is uniform, and the billet shell thickness is also uniform. In the process of use, the copper tube constantly wear and heat deformation. In the middle and late use, the total taper becomes smaller, and the downward heat transfer to the curved liquid surface is large, and the copper tube is deformed locally, which also increases the inhomogeneity of the blank shell. The billet shell is prone to bulge in the lower part of the mold. Sampling shows that the bulge diameter of 150mm×150mm billet is more than 2mm, which is prone to deviate Angle internal cracking, and the billet shell loses support after coming out of the mold, and is prone to steel leakage. Influence of inner surface of copper tube: Copper pipe in use process, as a result of processing steel leakage accident place cold steel and excessive askew, cause facial and corner cut, depth is greater than 1 mm above, in the process of tensile steel, cut billet shell and copper wall thermal resistance is big, the question of thin shell, prone to depression, and the bottom of the depression has obvious cracks, suddenly such as superheating temperature increase or improve the drawing speed, easy leaking in the crack of steel. The copper tube production quality is poor, especially the copper tube face and corner local coating off. Increased thermal resistance, resulting in heat transfer instability, easy to cause steel leakage. In addition, there is trachoma in the copper tube blank. With the increase of the amount of steel passed through the mold, the inner surface of the copper tube is worn out, and the trachoma leaks out.
Post time: Dec-05-2022