JPS5852455B2 - How to prevent blockage of submerged nozzle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing blockage of a submerged nozzle in continuous casting of molten metal, particularly steel.

More specifically, the present invention relates to a method of continuously supplying flux to the inner wall surface of a submerged nozzle (hereinafter referred to as a nozzle) to prevent nozzle clogging.

It is well known that when aluminum-killed steel is conventionally cast in a continuous casting process, deoxidation products in the steel often adhere and grow on the inner wall surface of the nozzle, causing clogging problems.

In order to prevent nozzle clogging during casting, (1) use a nozzle that is somewhat soft and has low thermal conductivity;

(2) A method of forcibly heating the outer periphery of the nozzle or insulating the nozzle surface to prevent the inside from cooling; (3) A method of blowing inert gas from the nozzle wall or upper part through a hollow chamber or porous brick; ( 4) Casting conditions (
(5) improving the temperature of molten steel, deoxidizing agent), and (5) creating a two-layer nozzle structure or applying a coating material.

These methods tend to produce less alumina-based deposits than when molten steel is fed through known nozzles.

However, all of these methods do not sufficiently prevent blockages and presently cause many troubles.

For another purpose, Japanese Unexamined Patent Publication No. 48-8620 discloses a specially shaped extent nozzle for a ladle that can add additives at the same time as pouring molten steel.

However, the purpose of the nozzle described above is to improve the yield of additives used and to uniformize the state of mixing and dissolution, and is not a method for preventing blockage of the nozzle.

The present inventors analyzed nozzle blockages in continuous casting of aluminum-killed steel and investigated the blockage mechanism, and found that the flow rate of molten steel on the nozzle inner wall surface was slow and that the unevenness of the nozzle inner wall surface was caused by deoxidation products. It was found that this has a large effect on adhesion.

It was also found that the lack of lubricity on the inner wall surface made it easier to adhere.

Once deposits are formed, the surface becomes even more uneven, promoting the growth of deposits.

These blockages consist of fine alpha-alumina or calcium aluminate-based deoxidation products and are produced in large quantities at temperatures near the freezing point of the steel.

The apparent viscosity of molten steel with alumina-based deoxidation products dispersed in the steel increases, which increases the adhesion of deoxidation products to the inner wall surface of the nozzle.

The reason why there is little solidified metal of molten steel in the blockage that adheres to the inner wall surface of the nozzle after use is presumed to be that the molten steel drains during use.

Therefore, in order to eliminate this alumina-based deposit, it is necessary to bring the molten steel flow into a highly turbulent state during use, or to make the inside surface of the nozzle lubricant.

Moreover, even if it adheres, it is necessary to forcefully remove it physically or dissolve it chemically.

That is, the present invention proposes a method for preventing clogging of submerged nozzles by supplying a flux that has both the functions of lubricant and dissolving deposits.

The gist of the present invention is that on the side surface of the unimmersed part of the molten steel of the immersion nozzle,
A method for preventing blockage of a submerged nozzle, characterized by providing one or more flux supply ports at an appropriate angle below the horizontal line and supplying flux from the supply ports.

According to the method of the present invention, alumina-based blockages do not adhere to the inner wall surface of the nozzle, and alumina-based inclusions are dissolved and absorbed by the flux, and due to the difference in specific gravity within the mold (black specific gravity at the time of melting is about 2 to 2.5, molten steel Since the cast iron is removed by flotation at a specific gravity of about 7 to 8), a clean slab with fewer nonmetallic inclusions can be produced.

The drawing is a schematic longitudinal sectional view showing an embodiment of the present invention,
2 is a tundish nozzle, 4 is a sliding nozzle, 5 is an immersion nozzle, 6 is a flux supply port, 9 is a hopper, and 10 is a conduit.

A flux supply port 6 is provided on the side of the unimmersed portion of the molten steel of the immersion nozzle 5, a conduit 10 is inserted, the atmosphere is sealed, and an inert gas is supplied under pressure to the conduit 10, and the flux in the hopper 9 is transferred to the immersion nozzle 5. The flux is supplied through the flux supply port 6.

Incidentally, the amount of flux supplied can be appropriately selected by opening and closing the valves 11 and 12 and the inert gas pressure.

A film of molten flux and small bubbles of inert gas appears between the molten steel and the nozzle inner surface.

This flux and inert gas film provides lubricity and prevents deoxidation products present on the surface of molten steel passing through the nozzle from adhering to the nozzle inner wall, and also prevents deoxidation products from adhering to the nozzle inner wall. is dissolved and absorbed by flux,
It is possible to prevent the phenomenon of narrowing and clogging of the nozzle inner wall hole due to removal of insects that adhere to the deoxidized product.

In order to carry out the method of the present invention, as a result of various experiments, the input angle of the flux supply rotor 60 was determined to be 0 to 80 degrees downward from the horizontal line.
, preferably 0 to 45 degrees, and the shape can be modified to circular, square, etc., but the strength of the immersion nozzle 50 and the seal with the conduit 10 are 3 to 30 mφ, preferably 3 to 20 mmφ
A circular shape is preferred, and in order to create a uniform film of flux and inert gas on the inner wall of the immersion nozzle, the number of installations is preferably 1 to 5 on the circumference of 50 immersion nozzles.

Note that the installation position is preferably above the meniscus line, that is, generally above the molten steel immersion part, from the viewpoint of operational safety and the flow of molten steel in the nozzle.

The flux used in the method of the present invention is preferably a flux that easily absorbs alumina-based deoxidation products, such as a composition shown in Table 1 that does not contain carbon, and may be in the form of powder, granules, or short rods. It is possible.

It is preferable to supply the flux in an amount of 0.1 to 0.2 kg/molten steel, and if it is less than 0.1 kg/molten steel, the effect of dissolving and absorbing the deoxidation products adhering to the inner wall of the nozzle will be reduced. This causes the inner wall of the nozzle to become clogged.

Moreover, when it exceeds 0.2 kg/t of molten steel, the amount of flux in the mold increases, causing an entrainment phenomenon.

The inert gas is preferably Ar HN2,
Used at a blowing pressure of 1-2 kg/cwt.

If it is less than 0.1 kg/cn1, it will be difficult for the flux to enter the nozzle pipe, and if it exceeds 2 kg/crl, the flux will be mixed into the molten steel, causing flux to be entrained within the mold.

According to the method of the present invention, the synergistic effect of the inert gas and the flux that absorbs the deoxidized products eliminates the nozzle clogging phenomenon, and also promotes the metallurgical reaction, resulting in clean steel free of inclusions.

Next, examples of the present invention will be described.

In continuous casting of aluminum killed steel, using an alumina graphite immersion nozzle, the granule flux shown in Table 1 was adjusted to 0.1 to 0.2 at an Ar gas blowing pressure of 0.5 kg/cf7f.
Molten steel t was supplied.

At this time, four consecutive castings were completed without any problems using one immersion nozzle.

Compared to the conventional method, which caused casting difficulties in the middle of two consecutive castings, the nozzle life can be greatly extended.
In addition, clean steel without inclusions was obtained.

[Brief explanation of drawings]

The drawing is a schematic vertical sectional view showing an example of a continuous casting apparatus in which a flux supply port is provided in a submerged nozzle for carrying out the method of the present invention. In the figure, 1. Bottom of Nitan dish, 2: Tan dish nozzle, 3: Iron shell, 4 Ni sliding nozzle, 5: Immersion nozzle, 6: Flux supply port, 7 Ni mold, 8: Mold additive, 9: Flux hopper, 10: Conduit. .

Claims (1)

[Claims] 1. One or more flux supply ports are provided at an appropriate angle below the horizontal line on the side surface of the unimmersed portion of the molten steel of the immersion nozzle, and flux is supplied from the supply ports. Method for preventing blockage of submerged nozzles. 2 The angle of the flux supply port below the horizontal line is O~
80', the method for preventing blockage of a submerged nozzle according to claim 1. 3. The method for preventing blockage of a submerged nozzle according to claim 1, wherein the inner diameter of the flux supply port is between 3 and 30 mm.