The secondary cooling section of continuous casting process may influence the output of the casting machine and the quality of the cast billet. The high quality and high yield of continuous casting depends to a large extent on the intensity of the secondary cooling, cooling process, cooling water distribution and control. If the casting billet in the second cooling zone undergoes improper cooling intensity or uneven cooling, it will induce and produce various defects.
Uneven cooling intensity will lead to the casting also surface temperature shows a periodic rebound, causing billet shell expansion, when the stress applied to the solidification front more than the strength of steel can withstand, will produce intermediate cracks; at the same time, the periodic changes in temperature will lead to repeated phase changes in the solidified billet shell, inducing the formation of subcutaneous cracks in the cast billet; if the surface temperature of the cast billet at the straightening point is in the third brittle temperature zone, a surface transverse crack will appear at the trough of the billet vibration marks.
If the secondary cooling degree is too weak, it will lead to high surface temperature of the cast billet, under the action of the static pressure of the steel, the solidified billet shell will creep and produce the phenomenon of drum belly. When the cooling intensity is too large, will promote the columnar crystal developed easily to form a "bridge" structure, so that the central segregation and sparse intensification.
To uniform cool the billet, so that the billet in the secondary cooling section when all solidified, and the temperature is not less than 900 ℃ is appropriate; if the liquid core needs straightening, the secondary cooling to solidify the billet to a sufficient thickness.
Support and guide the billet and dummy bar to prevent the billet from deformation.
For curved continuous casters with straight mould or multiple radius of curvature, the secondary cooling unit also acts as a bending or straightening device for the cast billet.
If the multi-roller pulling and straightening machine is used, part of the second cooling zone of the pinch roll itself is also the driving roll, which plays the role of pulling the billet.
For elliptical continuous casting machine, the second cooling zone itself is also the segment straightening zone. The importance of the secondary cooling device of the arc continuous casting machine is no less than the mould, which directly affects the quality of the cast billet, the operation of the equipment and the operation rate of the casting machine.
