JPS61150759A - Casting nozzle for steel making - Google Patents

Abstract

PURPOSE:To prevent the nozzle clogging arising from the alumina in a molten metal and the change of a casting speed by using a material which forms a low melting compd. by reacting with alumina to form the upper half of a casting nozzle for steel making where the flow rate is relatively low and using a heat resistant material to form the lower part thereof. CONSTITUTION:The upper half of the casting nozzle for steel making where the flow rate is relatively low and the fine Al2O3 in the molten steel is liable to deposit is formed of the CaO-MgO-Al2O3 refractories which form the low melting compd. by reacting with Al2O3. The lower half where the flow rate is high and Al2O3 does not deposit is formed of the alumina or zirconia refractories which are highly resistant to heat and wear and are free from the change of the pore diameter. Such combined nozzle prevents the nozzle clogging and the change of the casting speed and has therefore the longer life.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to, for example, molten steel (including alloy steel, the same shall apply hereinafter).
This invention relates to the shape of a molten steel casting nozzle that is attached to the bottom of a tundish for casting molten steel supplied from a ladle into a tundish into a mold in continuous casting.

[Purpose of the invention]

Therefore, even if the nozzle is equipped with a small-diameter discharge hole, the nozzle hole will not be clogged due to A1203 in the molten steel, and the outflow velocity of the molten steel in continuous casting can be kept constant. The purpose of this invention is to provide a composite nozzle that can perform the following functions.

[Prior art and its problems]

During continuous casting of molten steel, molten steel is supplied from a ladle into a tundish and is poured into a mold through a nozzle attached to the bottom of the tundish.

When pouring molten steel into the mold from such a tundish, there is a problem in that the nozzle attached to the bottom of the tundish becomes clogged.

The phenomenon of nozzle blockage can be divided into the following types depending on the form of blockage.

l'D Blockage due to temperature drop of molten steel.

■ Blockage due to deposits such as AI 203 adhering to and growing on the inner surface of the nozzle.

■ Blockage due to foreign non-metallic inclusions such as bricks mixed in molten steel adhering to and accumulating on the inner surface of the nozzle.

■ Due to a combination of the above ■, ■, and ■.

Such nozzle blockage makes it difficult or impossible to feed molten steel into the mold. Therefore, although various measures to prevent nozzle clogging have been studied, there are still many unsolved problems.

In particular, squares with a side of 200 m or less or a cross-sectional area of 4
A billet with a small cross-sectional area of 00 crn” or less is
In continuous casting using a multi-strand method using a small diameter nozzle of ~20 IIm, aluminum killed steel with a Sal and AI content of 0.0030wt% or more is
Since the precipitation of 2O3 inevitably increases, the nozzle becomes severely clogged, making casting virtually impossible.

The reason why Al2O3 is generated in molten steel is as follows.

(Al2O3 contained in the refractory lining of tanditshu gets mixed into the molten steel.

4j) A1 added to molten steel for the aluminum kill treatment and O in the molten steel react to generate Al2O3.

■ A1 added to molten steel for aluminum guild treatment
and FeO in the slag react to generate Al2O3.

・;Φ Molten steel subjected to aluminum kill treatment is oxidized by air to generate Al2O3.

Generally speaking, Al2O3 generated in molten steel is largely affected by the above (1) and (2), but in the case of continuous casting, the above @
The impact is also large.

A portion of the Al2O3 generated as described above floats up and is separated from the molten steel, but most of it is present in the molten steel as fine particles of several microns in size. the result.

Places where temperature decrease occurs during continuous casting 1 For example, Al2O3 is precipitated at the nozzle of a ladle or tundish, and the precipitated Al2O3 becomes a base point and grows as a deposit, which is the main cause of clogging the nozzle.

In order to prevent the above-mentioned nozzle clogging, various methods have been studied in the past, and for example, a first-order method is known.

■ Suppress the production of Al2O3 by preventing slag entrainment and air oxidation of molten steel.

■ Heating or keeping the ladle, tundish, and nozzle warm to prevent the temperature of the molten steel from dropping.

■ Connect the nozzle to a material that is said to be difficult for U2CI3 to adhere to (for example, zirconia refractories, zirconia refractories with fused silica added, or fused silica). Prevents Al2O3 from adhering inside the nozzle.

However, the above-mentioned methods are insufficiently effective in continuous billet casting using small-diameter nozzles, and cannot completely prevent nozzle clogging.

Incidentally, the shape of a conventionally used tundish nozzle is generally as shown in FIG.

3 is a nozzle with a space for blowing Ar gas inside, 4 is a nozzle whose entire nozzle is made of porous refractory material,
No. 5 is the most commonly used type and is made of solid refractory material except for the nozzle hole. Each of them is a single unit and is used together with the immersion nozzle 6 inside the mold. There is a type shown in Figure 3 that combines a tundish nozzle and an immersion nozzle, and the inflow part to the nozzle is a mating type...7.
Cap type...8. There is a composite type of nozzle, but there has never been a composite nozzle that considers the nozzle inserted in both directions from a functional standpoint.

[Summary of the invention]

The gist of the present invention is that a single nozzle is usually divided into an upper half and a lower half from a functional standpoint.

That is, the areas where the relative moving speed of the molten metal is slow on the molten metal contact surface of the nozzle, in other words, the areas where AI, 03, etc. are likely to adhere (the upper half) react with Al2O3 in the molten metal to produce a low melting point compound. By using refractories that are easy to melt, the nozzle hole wall is oriented vertically downward, and the relative moving speed of the molten metal is maximum, and if H exchange is performed, the deposition of Al2O3 is extremely unlikely to occur, and the pouring speed in continuous casting is The lower half, which determines this, is characterized by being made of a material that is resistant to thermal erosion.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the steel manufacturing nozzle of the present invention.

As can be seen from the font, the total length of the nozzle is mostly divided by the central part of C, with the upper half serving as the chemical reaction part and the lower half serving as the molten metal flow velocity control part.

The upper half must include a point where the molten metal introduction forming an arcuate or inclined surface transitions into a vertical hole.

In addition, the flow rate control section in the lower half is entirely a vertical hole, but if it is made extremely short, it is likely to suffer melting and deformation due to high heat.
A certain length is required depending on the diameter of the hole.

In the drawing, 1 is a chemical reaction section and 2 is a flow rate control section.

The chemical composition of l is made of GaO-MgO-Al2O3-based refractory, and examples include Ca044.5%, Mg044.5%, Al203.
2 is an alumina-based or zirconia-based refractory, and the former has a composition of 20.0 to 24.0% Si8 and Al203.
72.0-76.0%, later as 5I0
233.0%.

A material containing 01.5% Al and 65.0% Zr was used.

In addition, compositions that can be used as chemical reaction parts include:
Regarding the example of CaO-MgO-At203 system, [
[Effects of the invention] Conventionally, when considering measures to prevent nozzle clogging caused by Al2O3, the nozzle has been considered as an integral part of the chemical reaction part, and the functions of the nozzle have not been considered separately, resulting in unnecessary costs. For example, if a nozzle that easily reacts with Al2O3 is molded as a single component using only a single component, clogging due to the accumulation of Al2O3 cannot be prevented. However, depending on the composition of the refractory, the pouring speed of the molten metal may have to be changed due to the enlargement of the outlet due to melting.

In the above embodiments, a molten metal inlet having an arcuate cross section was used as the nozzle inlet, but it goes without saying that a straight inclined surface as shown in Fig. 2 and 3 may also be used. Any fitting method can be used, and the composition of the chemical reaction part is not limited to the CaO-Mg0-AI, 03 system, but it also reacts with Al2O3 in the molten metal to generate and dissolve a low melting point compound. Anything is fine as long as it is the same, and this idea is exactly the same for the composition of the second set. The dimension of 1 is not particularly limited as long as it is a length that includes some vertical hole parts including the transition part to the vertical hole.

It goes without saying that this nozzle can also be used as a discharge nozzle from a ladle.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the casting nozzle for steel making of the present invention, Fig. 2 shows three types of single nozzles conventionally used for explanation, and Fig. 3 shows a tundish nozzle and a submerged nozzle in one unit. This is an example of two types. In the figure, 1 is a chemical reaction section, 2 is a flow rate control section, 3 is a nozzle equipped with a space for blowing, 4 is a nozzle made entirely of porous refractory material, and 5 is a solid nozzle that is usually used most often. , 6 is an immersion nozzle, 7 is an integrated discharge nozzle and immersion nozzle with a different refractory material fitted on top,
8 shows a discharge nozzle-immersion nozzle integrated type in which a different refractory material is fitted into a cap shape.

Claims (1)

[Claims] A casting nozzle for steelmaking consisting of an upper half consisting of a chemical reaction section that reacts with fine Al_2O_3 in the molten metal to generate and dissolve low-melting compounds, and a lower half consisting of a molten metal flow rate control section with excellent high temperature resistance.