Essence of Continuous Casting Flux Knowledge
Release time:
2021-12-02
Continuous casting flux What is its function? During casting, powdery or granular slag material should be continuously added to the surface of the mold steel, which is called protective slag. Continuous casting flux has the following functions:
(1) Heat insulation and heat preservation to prevent heat dissipation;
(2) Isolating the air to prevent oxygen in the air from entering the molten steel for secondary oxidation, affecting the quality of the steel;
(3) Absorbing and dissolving inclusions floating from the molten steel to the interface between the molten steel and the slag, purifying the molten steel;
(4) There is a layer of slag film lubrication between the crystallizer wall and the solidified shell, which can reduce the pulling resistance and prevent the solidified shell from sticking to the copper plate;
(5) Filling the air gap between the billet shell and the crystallizer to improve the heat transfer of the crystallizer.
A good protective slag should fully exert the above five functions, thereby improving the surface quality of the slab and ensuring the smooth progress of continuous casting.
What are the requirements for the melting mode of continuous casting flux?
In order to complete the above five functions, the protective slag added to the crystallizer during continuous casting must have a prescribed melting method, that is, a three-layer structure of a powder slag layer, a sintered layer, and a liquid slag layer is formed on the surface of the steel.
Low-melting-point (1100 ~ 1200℃) slag powder is added to the surface of the high-temperature molten steel (approximately 1500℃) in the crystallizer, forming a slag layer with a certain thickness (approximately 10 ~ 15 mm) on the surface of the molten steel. The heat transfer from the molten steel to the slag layer slows down, and the slag on the slag layer is heated, and the slag powder is sintered together to form a so-called sintered layer (temperature approximately 10 ~ 15 mm).
During the casting process, due to the up and down vibration of the crystallizer and the downward movement of the solidified shell, the liquid slag layer on the surface of the molten steel is continuously squeezed between the shell and the copper wall through the interface between the molten steel and the copper wall, forming a solid slag film on the surface of the copper wall and a liquid slag film on the surface of the solidified shell, which plays a lubricating role on the mold wall and the shell surface, just like adding lubricating oil when the motor shaft rotates. At the same time, the slag film fills the air gap between the billet shell and the copper wall, reduces the thermal resistance, and improves the crystal heat transfer.
As the casting proceeds, the liquid slag on the surface of the molten steel is continuously consumed, while the sintered layer falls to the surface of the steel and melts into a liquid slag layer, and the powder slag layer becomes a sintered layer. Then, new mineral slag powder is added to the mold to maintain the three-layer structure, and the mold powder is continuously consumed by this cycle.
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