JPH0133258Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to improvement of a long nozzle for continuous casting.

(Prior art) Among thin sheet materials, high-grade thin sheet materials such as tinplate and steel sheets for automobiles have a high level of internal quality requirements and are often prone to problems due to internal quality deterioration. 400μ
It is well known that this is caused by the inclusion of microscopic inclusions in molten steel.

In order to prevent these 50 to 400μ microscopic inclusions from entering molten steel, it is effective to generate microbubbles by blowing inert gas such as argon gas or nitrogen, and remove them using the buoyancy of these microbubbles. It is also known that

Furthermore, various nozzles such as porous refractories or simply long nozzles provided with pores are used as an inert gas blowing device in continuous casting. Among these, as a long nozzle that is particularly effective in floating and removing minute inclusions in molten steel, for example, as in Japanese Patent Application Laid-Open No. 58-9750, a submerged nozzle with a slit within the molten steel level is used. An immersion nozzle has been proposed that is provided with a cylindrical gas blowing part to generate microbubbles and also to suppress the precipitation of alumina-based inclusions adhering to the inner wall surface of the immersion nozzle.

However, the above-mentioned immersion nozzle can always stably blow microbubbles into the molten steel by providing a gas injection part within the portion of the inner surface of the immersion nozzle that is always in direct contact with the molten steel. but,
Since the molten steel contact level within the immersion nozzle varies widely from 50 to 300 mm, precipitation of alumina-based inclusions within this range cannot be suppressed. In addition, if a gas injection part is provided that covers this range in order to suppress the precipitation of alumina-based inclusions, the inner cylindrical gas injection part will differ greatly between the molten steel immersed part and the non-immersed part, and the alumina inclusions mentioned above will The effect of suppressing system inclusions is greatly deteriorated, and the molten steel in the mold may boil due to non-uniform gas flow and an increased amount of blown gas.
Situations such as quality deterioration may occur due to an increase in inclusions in molten steel.

(Problems to be Solved by the Invention) The present invention solves the drawbacks of the conventional immersion nozzle as described above by stably supplying microbubbles into the immersion nozzle, and moreover, by supplying microbubbles to the molten steel immersion area and the non-immersion area. By sufficiently suppressing the precipitation of alumina-based inclusions on the wide inner surface of the immersion nozzle, and also suppressing boiling in the mold due to non-uniform gas injection or large amount injection, The objective is to obtain high quality slabs by preventing inclusions from being drawn in.

(Means for solving the problem) The present invention provides a long nozzle for continuous casting in which a slit portion communicating with a gas supply pipe is provided between the outer wall of a cylindrical body and the inner wall made of a breathable refractory. The layer thickness of the breathable refractory having a slit portion communicating with the pipe is Lu>
L, the gas flow within the long nozzle is made uniform over a wide range.

The long nozzle according to the present invention will be described below.
The inventors discovered that in casting using the conventional long nozzle as described above, the molten metal level in the long nozzle fluctuates widely during casting due to changes in the amount of molten metal cast, the state of blockage of the discharge hole, etc. I was able to find out. In addition, this wide fluctuation in the molten metal is caused by Ar,
When injecting an inert gas such as _N2 , the amount of gas discharged varies greatly between the immersed part and the non-immersed part of the molten steel.
The present invention was developed as a result of discovering that this variation causes a deterioration in the quality of steel due to boiling in the mold, entrainment of inclusions, etc. Hereinafter, the elongated nozzle according to the present invention will be described in further detail based on an embodiment shown in the drawings.

FIG. 1 shows a cross-sectional view of a submerged nozzle as a long nozzle according to the present invention, FIG. 2 shows an enlarged cross-sectional view of part A in FIG. 1, and FIG. 4 shows a long nozzle according to the present invention. A cross-sectional view of an embodiment of a ladle long nozzle as a nozzle is shown.

In the figure, a cylindrical body 1 made of a refractory material such as alumina graphite, zircon, or silica tube has a taper that engages with a pouring nozzle (not shown) provided in a ladle or tundish. The portion 2 and the tip portion 3 are provided with discharge holes 4a and 4b for molten steel. The vicinity 5 of the molten steel immersed part inside this cylindrical body 1 is located between the outer wall 6 and the molten steel immersed part 5.
A breathable refractory 7 is provided in contact with the inner cylinder surface, which is a molten steel inflow passage, and between the outer wall 6 and the breathable refractory 7, argon in the factory or
A slit portion 9 is provided which is integrally fixed by means such as screwing with a piping 8 made of a flexible hose, steel pipe, etc., which communicates with an inert gas pressure source (not shown) such as nitrogen.

Next, the level of the molten steel in the cylindrical body 1 has a normal level F and a maximum level G due to fluctuations in work. It becomes the immersion part 11. The layer thickness L of the breathable refractory 7 of this constantly immersed part 10,
Layer thickness Lu of the breathable refractory 7 of the emergency immersion part 11
are set so that Lu>L.

Therefore, when determining the layer thicknesses L and Lu of the breathable refractory 7, the air permeability of a normal refractory is determined by the airflow amount being Q, the thickness of the refractory (here, the width from the slit part to the molten metal interface) L Refractory thickness at the top of
When expressed as Lu, Q becomes ∝Lu ^- 〓, and on the other hand, when the thickness of the refractory at the bottom is L, it is expressed as Q∝Ll ^- 〓. Therefore, the constantly immersed part (hereinafter simply referred to as immersed part) 1
The parameter β, which is the ratio of the discharge flow rate Q _dip from 0 and the discharge flow rate Q _{Npo dip} from the non-immersed part 11, is β=
As shown in FIG. 5, it has been experimentally determined that if Q _{Npo dip} /Q _dip ≦0.2, boiling will occur in the mold.

Based on this result, when Lu and L are calculated, Q _dip = a・L ^- 〓 (1)
(However, a: apparent discharge flow rate) Q _{Npo dip} = a・Lu ^- 〓 (2) β=Q _{Npo dip} /Q _dip ≦0.2 (3) a・Lu ^- 〓/a・L ^- 〓0.2 (4) , it is still a good value.

In addition, α, which is the parameter of the gas discharge amount mentioned above, is determined by the refractory material.
For example, the porosity of alumina graphite is 18 to 22.
%, α=0.6 to 1.0, and furthermore, normal breathable refractories (porous plugs) with relatively low porosity have α=5.0, and normal ones have α=10.0 to 20.0. Using the α value, the values of Lu and L determined by the above formula are the values shown in FIG. 6, and the α value of the constituent refractory is preferably 1.0 to 10.0.

As shown in FIG.
It is possible to set the layer thickness Lu to Lu>L and to suppress boiling in the mold due to the blown gas. Further, FIG. 4 shows a case in which a long nozzle is provided, but it is completely the same as above except that the discharge hole 4a is open at the tip. In addition, when the layer thickness of the breathable refractory 7 in the emergency non-immersion part 11 and the normally immersed part 10 is Lu>L, the layer thickness Lu may be determined in stages as shown in FIG. Furthermore, Lu may be formed to become thicker from the constantly immersed portion 10 in a sequentially curved or linear manner (not shown).

Cylindrical body 1 (immersion nozzle) configured as described above
Molten steel is poured into the cylindrical body 1 from a pouring nozzle (not shown) through discharge holes 4a and 4b provided at the tip.
The material is then cast into a mold (not shown). During this casting, at the contact part with the molten steel in the cylindrical body 1,
An inert gas such as argon gas or nitrogen gas is injected into the molten steel through the slit 9 provided in the cylindrical body 1 and the breathable refractory 7 to prevent the precipitation of inclusions and promote the floating of inclusions. Plan. At this time, as the level of the molten steel in the cylindrical body 1 fluctuates considerably from F to G, the flow rate of the immersed section 10 and the non-immersed section 11 fluctuates widely, and especially the discharge from the non-immersed section 11. In order to increase the flow rate, the layer thickness L of the breathable refractory 7
, Lu and Lu>L, the amount of inert gas blown in the longitudinal direction of the cylindrical body 1 is made uniform, and precipitation of inclusions is suppressed in a wide area of the cylindrical body 1, and boiling in the mold is prevented. can effectively prevent the occurrence of

(Effects of the invention) As described above, by using the long nozzle of the invention, it is possible to suppress the precipitation of inclusions in the non-immersed part of molten steel, and also to suppress the precipitation of inclusions in the non-immersed part of molten steel. This is an extremely excellent long nozzle for continuous casting that can clean molten steel by preventing boiling within the mold.

[Brief explanation of the drawing]

FIG. 1 shows a sectional view of a submerged nozzle as a long nozzle according to the present invention, FIG. 2 shows an enlarged sectional view of section A in FIG. 1, and FIG. FIG. 4 shows a cross-sectional view of an embodiment of a ladle long nozzle as a long nozzle according to the present invention, and FIG. Quantity Q _{Npo dip} / Indicates the Q _dip of the immersion part and the occurrence index of boiling in the mold, and the 6th
The figure shows Lu and L without boiling for α values.
Indicates the layer thickness. DESCRIPTION OF SYMBOLS 1... Cylindrical body, 2... Taper part, 3... Tip part, 4a, 4b... Discharge hole, 6... Outer wall, 7...
Breathable refractory, 9...Slit portion.

Claims (1)

[Scope of utility model registration request] In a long nozzle for continuous casting, in which a slit portion communicating with a gas supply pipe is provided between the outer wall of the cylindrical body and the inner wall made of breathable refractory, the layer thickness of the breathable refractory is A long nozzle for continuous casting, characterized in that the layer thickness Lu and the layer thickness L of the constantly immersed part are Lu>L.