JPH10128506A - Immersion nozzle for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable casting and a good characteristic of a cast slab, in high speed continuous casting of a thin slab. SOLUTION: Sideward spouting holes 3, 3 on the side walls 2 on the short wall sides of a nozzle and downward spouting holes 5, 5 on the bottom wall 4 of the nozzle, are arranged symmetrical to the nozzle axial line Y-Y of the immersion nozzle 1 for supplying molten metal into a mold and a protrusion 6 projecting upward is arranged between the downward spouting holes 5, 5. By this constitution, the balance of molten metal spouting flow speeds from the sideward spouting holes 3 and the downward spouting holes 5 can be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to continuous casting.
The present invention relates to an immersion nozzle for supplying a molten metal into a mold, and more particularly to an immersion nozzle suitable for casting a thin and wide cast piece at a high speed.

[0002]

2. Description of the Related Art In recent years, speeding up of continuous casting has been promoted for the purpose of improving productivity. With this, the amount of molten metal per unit time passing through an immersion nozzle (hereinafter, abbreviated as a nozzle) is increased. There is a need. In addition, there is a tendency to reduce the thickness of the slab slab in order to save labor in the post-process, and accordingly, it is necessary to flatten the nozzle shape.

[0003] The speed of the molten metal discharge flow from the nozzle (hereinafter abbreviated as discharge flow) increases due to the increase in the amount of molten metal passing through the inside of the nozzle.
An increase in the penetration depth of the discharge flow into the deep part of the melt pool occurs. They cause the problems described below. That is, the solidified shell may be redissolved due to an increase in the discharge flow rate, and a breakout may occur. In addition, undulation of the surface of the molten metal may cause entrapment of powder or air bubbles, or may cause uneven thickness of the solidified shell, resulting in cracks or dents on the surface of the slab. Further, when the penetration depth of the discharge flow into the deep part of the molten metal pool is increased, nonmetallic inclusions are difficult to float and separate on the surface of the molten metal and are trapped inside the slab, which may deteriorate the cleanliness of the slab.

On the other hand, flattening of the nozzle shape causes the following two problems. One is that the gap between the nozzle and the inner wall of the mold is reduced and the flow of the molten metal is slowed down, and the metal produced there is caught in the slab, resulting in defects. Nozzle clogging occurs due to accumulation of metal inclusions.

[0005] Such a problem originates in an attempt to supply a large amount of molten metal to a narrow mold, and in order to solve the problem, various shapes are devised in both the outer shape of the nozzle and the shape of the discharge hole. Nozzles have been proposed. For example, Japanese Patent Application Laid-Open No. Sho 60-130456 discloses a nozzle having a flat and downwardly directed discharge hole and having a cylindrical flow resistance portion in a flow path inside the nozzle. Japanese Patent Application Laid-Open No. Sho 62-197252 discloses an example in which the flow resistance portion of the nozzle is replaced with a weir orthogonal to the flow of the molten metal.

[0006] According to these nozzles, the downward discharge flow is rectified by the action of the flow resistance portion and the drift is eliminated. However, since the discharge holes are only in the downward direction, the amount of molten metal passing through the inside of the nozzle increases. Then, the penetration depth of the discharge flow increases, and the cleanliness of the slab may deteriorate. In addition, the flow of the molten metal surface around the nozzle may be delayed, and metal plating may occur around the nozzle.

[0007] Therefore, in order to prevent the above-mentioned deterioration of the cleanliness of the slab and the prevention of the metal ingot, it is necessary to provide a horizontal discharge hole and supply the molten metal to the short side. As an example,
Japanese Patent Application Laid-Open No. 08-39208 discloses a nozzle having a lateral discharge hole 3 on the short side wall and a downward discharge hole 5 on the bottom wall shown in FIG.

However, according to the nozzle having such a shape, most of the discharged molten metal is discharged from the downward discharge holes 5 and hardly discharged from the lateral discharge holes 3. Therefore, the flow to the short side of the mold becomes extremely weak, and the heat supply to the short side of the mold becomes insufficient. Further, when the inside of the nozzle becomes negative pressure due to the downward discharge flow, there may be a problem that powder or the like is sucked from the lateral discharge holes 3. Furthermore, if the diameter of the downward discharge holes 5 is reduced to solve such a problem, non-metallic inclusions may accumulate in the nozzles or in the downward discharge holes 5 to cause nozzle clogging.

In view of the above results, the flow velocity of the molten metal in the molten metal pool in the mold is sufficiently high as long as powder or the like is not entrained on the surface of the molten metal. It is important that the deceleration be sufficiently low so that the floating time of the nonmetallic inclusions does not occur and the floating time of the nonmetallic inclusions can be secured.

[0010]

SUMMARY OF THE INVENTION According to the present invention, when continuously casting thin and wide cast slabs at a high speed, the metal surface is prevented from waving while preventing the surface of the molten metal from waving, and the solidified shell is prevented from remelting. An object of the present invention is to provide a nozzle capable of stably producing a high-quality cast piece by promoting the floating separation of nonmetallic inclusions.

[0012]

As described above, the ideal flow pattern of the molten metal discharge flow is a state in which an appropriate flow velocity is secured on the surface of the molten metal and the inside of the molten metal pool is sufficiently decelerated. For that purpose, it is required to disperse the discharge flow as much as possible.

The inventors of the present invention have studied conventional nozzles. As a result, the ejection holes are provided on the short side wall and the bottom wall of the nozzle, and the projections are provided between the ejection holes on the bottom wall. The molten metal discharge flow velocity in the holes is balanced, and the above-mentioned ideal flow pattern can be obtained.

In the immersion nozzle for continuous casting according to the present invention, a lateral discharge hole is provided on a short side wall of the nozzle and a downward discharge hole is provided on a bottom wall of the nozzle so as to be symmetrical with respect to the axis of the nozzle. An upwardly protruding projection is provided between the holes, and the lateral discharge holes and the downward discharge holes are integrally formed.

[0015]

FIG. 1 is a perspective view (partially broken view) as an example of a nozzle according to the present invention, and FIG.
FIG. 3 shows a side view of FIG. 1.
FIG. 4 shows a state in which the nozzle according to the present invention is applied to continuous casting, and shows a flow state of the molten metal inside and outside the nozzle.

In FIG. 1 to FIG. 3, lateral discharge holes 3, 3 are provided in the short side wall 2 of the nozzle 1, and downward discharge holes 5, 5 are provided in the bottom wall 4. An upwardly projecting projection 6 is provided between the downward discharge holes 5. The opening dimensions of the lateral discharge holes 3, 3 and the downward discharge holes 5, 5 are determined by the target casting speed and the slab size, but their arrangement is symmetrical with respect to the axis Y-Y of the nozzle.
If the arrangement of the discharge holes is asymmetric, the turbulent flow described later is deviated, and a drift of the discharge flow occurs, which is not preferable.

The operation of the nozzle according to the present invention will be described with reference to FIG. As shown in FIG. 4, the downward flow M of the molten metal poured into the nozzle 1 forms a turbulent flow T near the bottom wall of the nozzle by the protrusion 6. This turbulent flow T causes downward flow M
And the downward flow M is hindered by the resistance of the turbulent flow T. As a result, the downward flow M is discharged from the horizontal discharge holes 3 and 3 and the downward discharge holes 5 and 5 in a well-balanced manner. Therefore, the discharge flow from the horizontal discharge holes 3 does not hinder the formation of the solidified shell 8 by the mold 7, and the discharge flow from the downward discharge holes 5 does not hinder the floating separation of the nonmetallic inclusions.

The projection 6 functions to divide the molten metal in the nozzle 1 symmetrically with respect to the nozzle axis YY as if it were a watershed. Therefore, the shape of the protrusion 6 is preferably a mountain shape having a ridge line in the direction along the short side wall 2 as shown in FIG. 1, but may be a triangular pyramid or a cone, and the vertex of the protrusion 6 is not necessarily It may not be sharp, and the slope may be formed to draw a gentle curve.

Referring to FIG. 2, desirable dimensions of the nozzle of the present invention will be described. In FIG. 2, the protrusion 6 itself needs to have a strength that can withstand the pressure caused by the downward flow M of the molten metal poured into the nozzle.
It is preferable that the width W of the bottom surface be 30 mm or more.

If the apex angle θ of the projection 6 exceeds 120 degrees, the above-mentioned turbulent flow forming effect becomes insufficient, and if it is less than 30 degrees, the downward flow M of the molten metal poured into the nozzle is reduced. 6, the turbulence does not easily form. Therefore, it is desirable that the apex angle θ of the projection be 30 degrees or more and 120 degrees or less.

Further, when the upper end of the projection 6 is higher than the upper end of the horizontal discharge hole 3, the influence of the turbulent flow T affects the horizontal discharge flow, so that the molten metal is smoothly discharged from the horizontal discharge holes 3, 3. It is hard to be done. Therefore, it is desirable that the distance G between the upper end of the protrusion 6 and the upper end of the lateral discharge hole 3 shown in FIG.

In consideration of the above, the height H of the projection 4 is 5
It is desirable that the thickness be equal to or more than 50 mm.

When the values of the width W, the apex angle θ, and the height H of the projection 6 are set, the nozzle 1 is determined by a water model experiment or the like.
The flow state of the molten metal in the inside can be monitored, and each value can be searched and obtained so as to generate an effective turbulent flow T.

FIG. 5 is a cross-sectional view parallel to the long side wall of another nozzle according to the present invention.
The horizontal and downward discharge holes 9 are formed by integrally forming the discharge holes 3 and the downward discharge holes 5 and 5. In this case, although the strength of the nozzle itself is slightly impaired, it is possible to simplify the process of forming the ejection holes.

As described above, according to the nozzle of the present invention, the provision of the projections 6 makes it possible to adjust the balance between the discharge velocities of the horizontal discharge flow and the downward discharge flow, so that good quality cast slabs can be obtained. It can be obtained stably.

[0026]

EXAMPLES The effects of the present invention will be described below based on examples. The cross-sectional shape of the mold was 100 mm thick x 1000 mm thin, and SUS304 steel was cast at a speed of 2.2 m / min. The nozzle used had the shape shown in FIG. 1, and the cross-sectional dimensions were 60 mm on the short side and 175 mm on the long side, and the thickness of the refractory was 15 mm. The lateral discharge holes on the short side wall had a hole size of 30 mm × 30 mm.

The downward discharge holes on the bottom wall are 30 mm in the short side direction × 50 mm in the long side direction, and are provided in a pair so as to be symmetrical with respect to the center line of the nozzle axis. The protrusion 6 has a width W of 45 mm,
The height H was set to 20 mm. On the other hand, as a comparative example, a nozzle having a shape obtained by removing the protrusion 6 from the nozzle of FIG. The immersion depth of each nozzle was 135 mm.

In each of the casting experiments, a total of 300 tons was cast with a molten metal amount of 60 tons × 5 consecutive times. However, when the nozzle of the present invention was used, the entire casting could be stably completed without occurrence of breakout. The obtained slab did not show cracks or dents and had good surface quality. When non-metallic inclusions in the slab were examined, inclusions with a diameter of 50 μm or more
There were no particular problems in the range of 10 to 20 per g. After the experiment, the nozzle was disassembled and clogging was examined, but no trace of clogging was observed.

On the other hand, when the nozzle of the comparative example was used, metal was generated on the peripheral surface of the nozzle immediately after the start of casting, and the metal and the mold were united to make casting impossible.

[0030]

As described above, according to the present invention, in continuous casting, in particular, in high-speed continuous casting of thin and wide cast slabs, it is possible to prevent the metal surface from waving while preventing the surface of the molten metal from waving, and to recycle the solidified shell. By facilitating the floating separation of nonmetallic inclusions while preventing melting, it is possible to stably obtain good quality cast slabs.

[Brief description of the drawings]

FIG. 1 is an external perspective view (partially broken view) of an immersion nozzle according to an example of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is a side view of FIG. 1;

FIG. 4 is a view for explaining a flow state of a molten metal by an immersion nozzle according to an example of the present invention.

FIG. 5 is a cross-sectional view parallel to the long side wall of another immersion nozzle according to the present invention.

FIG. 6 is a cross-sectional view parallel to a long side wall of a conventional immersion nozzle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Immersion nozzle of this invention 2 ... Short side wall of nozzle 3 ... Horizontal discharge hole of short side wall 4 ... Nozzle bottom wall 5 ... Downward discharge hole of bottom wall 6 ... Projection Part 7: Mold 8: Solidified shell 9: Horizontal and downward discharge holes M: Direction of downward flow of molten metal in nozzle T: Turbulent flow of molten metal in nozzle W: Protrusion Width θ: apex angle of projection G: distance between upper end of projection and upper end of lateral discharge hole H: height of projection YY: nozzle axis

Claims (2)

[Claims] 1. An immersion nozzle for supplying molten metal into a mold, wherein the immersion snorle is directed laterally on a short side wall of a nozzle and downwardly directed on a nozzle bottom wall so as to be symmetrical with respect to a nozzle axis. A discharge hole; and a projection part projecting upward is provided between the downward discharge holes. 2. The continuous casting immersion nozzle according to claim 1, wherein the horizontal discharge hole and the downward discharge hole are formed integrally.