The role of continuous casting slag protection
Release time:
2023-02-15
Continuous casting flux What is its function? During casting, powder or granular slag is continuously added to the surface of the mold steel. This slag is called protective slag. Continuous casting flux has the following functions:
(1) Heat insulation, preventing heat loss;
(2) Isolating air, preventing 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 steel-slag interface, purifying the molten steel;
(4) There is a slag film between the crystallizer wall and the solidified shell, which plays a lubricating role, reducing the pulling resistance and preventing the solidified shell from sticking to the copper plate;
(5) Filling the gap between the shell and the crystallizer to improve the heat transfer of the crystallizer.
A good protective slag should fully exert the above five functions to improve the surface quality of the casting and ensure 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 specified melting method, that is, a three-layer structure of powder slag layer, sintered layer, and liquid slag layer is formed on the surface of the steel.
Low-melting-point (1100 ~ 1200℃) slag powder is added to the surface of high-temperature molten steel (about 1500℃) in the crystallizer, forming a slag package layer (about 10 ~ 15 mm) with a certain thickness 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 the so-called sintered layer (temperature about 10 ~ 15 mm).
During casting, 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, playing a lubricating role on the crystallizer wall and the shell surface, just like adding lubricating oil when the motor shaft rotates. At the same time, the slag film fills the gap between the 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 steel surface and melts into a liquid slag layer, and the powder slag layer becomes a sintered layer. Then, new slag powder is added to the crystallizer to maintain the three-layer structure, and this cycle continuously consumes the crystallizer protective slag.
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