Production process of continuous casting flux
Release time:
2022-01-31
To ensure Continuous casting flux For the reasonable use of continuous casting flux, giving full play to the role of slag in continuous casting process, and obtaining high-quality billets, it must be coordinated with the continuous casting process, otherwise it is difficult to play its role. Usually, continuous casting flux is closely related to the following process factors: stabilizing the mold liquid level, centering the immersion nozzle, reasonable nozzle size and insertion depth, stable withdrawal speed, vibration parameters, etc., combined with the protective slag. Let's learn about the production process of continuous casting flux.
Stable mold liquid level
Stable molten steel level during casting is the key to preventing surface defects in billets. Due to the change of steel water pouring surface in the mold, many surface defects are formed on the curved liquid surface. For example, subsurface slag (blockage, surface depression, surface cracks), the fluctuation of liquid level in low-carbon steel is easy to lead to the increase of carbon in molten steel.
When the mold experiences a large change in the hot water surface, if the dissolution rate of the mold flux is slow and the amount of liquid residue formed is small, the molten steel is easy to directly contact the mold wall, causing adhesion, and in severe cases, adhesion leakage will occur.
Stable liquid level in the crystallizer is a prerequisite for uniform melting of the crystallizer flux and obtaining a uniform liquid slag layer thickness, so that the slag film between the crystallizer flux and the shell is uniform, ensuring uniform heat transfer. Excessive local heat transfer rate will produce a large number of inclusions and cracks on the surface of the billet. Usually, the fluctuation of the mold liquid level is required to be controlled within 5mm.
Immersion nozzle centering
In order to maintain the uniform and symmetrical flow of molten steel in the mold, the intermediate tundish immersion nozzle must be accurately located in the center of the mold cross section. In this way, the heat of the molten steel injected into the mold can be uniformly absorbed by the mold, achieving uniform cooling and uniform billet shell thickness; on the other hand, the mold flux can be uniformly dissolved. Misalignment of the nozzle will inevitably lead to the deviation of molten steel flow in the crystallizer, causing the crystallizer liquid level to "turn over", resulting in a large number of inclusions on the surface and subsurface of the billet and uneven billet shell, and in severe cases, steel leakage accidents may occur. The nozzle looks simple at first glance, but it is actually very important, otherwise it is difficult to obtain high-quality castings.
Appropriate nozzle insertion depth
Immersion nozzle casting is a key technology for the smooth development of continuous casting technology. Selecting the appropriate nozzle structure and insertion depth is one of the important conditions to give full play to the role of slag in the continuous casting process and improve the quality of billets, which must be given full attention in the production process. The type and parameters of the immersion nozzle are mainly determined by the size, shape, withdrawal speed and steel grade of the casting cross section. After determining the immersion nozzle, the important parameter of nozzle insertion depth is also determined. Changes in the central position and insertion depth of the immersion nozzle will cause changes in the flow state of molten steel in the crystallizer.
The insertion depth of the nozzle refers to the length from the slag interface to the upper edge of the nozzle steel outlet. In order to cope with the nozzle erosion on the slag line, the insertion depth needs to be changed accordingly during operation. The insertion depth of the nozzle has an important impact on the quality of castings and must be precisely controlled. If the insertion depth is insufficient, the liquid level of the mold will turn over, and the thickness of the liquid slag layer will become uneven, resulting in a large number of defects on the casting. When the insertion depth is too deep, the liquid slag layer becomes inactive, the dissolution of the protective slag deteriorates, the liquid slag penetration is uneven, and longitudinal cracks are prone to occur in the center of the wide surface of the billet. The depth should be adjusted according to the casting parameters. Shallow insertion depth is suitable for increasing the steel outlet angle of the nozzle, increasing the billet cross section, using electromagnetic stirring, reducing the superheat of molten steel, and increasing the slag viscosity, etc.
Continuous casting flux, due to its lubrication and uniform heat transfer, is an important process affecting the performance of slag, which can only be achieved under the condition of stable withdrawal speed. In actual production, frequent changes in withdrawal speed have a great impact on the melting of slag, so constant withdrawal speed casting is advocated.
Continuous casting flux must not only have good performance, but also must be used correctly, and must be combined with appropriate casting technology to obtain high-quality continuous casting billets.
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