JPH01113159A - Submerged nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To shallow submergence of discharging flow of molten steel, to reduce inclusion, to clean a steel and to improve the steel by forming the shape of inner hole of a submerging nozzle in the continuous casting device under the specific condition. CONSTITUTION:The nozzle 1 is constituted by giving the following relation among the reverse tapered angle theta at low part 4 of the inner hole of the submerged nozzle 1, length (l) of the reverse tapered part and the diameter (d) of the straight line part at upper part. l.tantheta>=0.08d, l>=2d, theta<60 deg. By such constitution, the submergence of discharging flow of the molten steel for the bottom discharging type submerged nozzle is shallow and the inclusion is reduced and the quality of the steel is improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a nozzle for pouring molten steel in a tundish into a mold in a continuous casting method, in particular, a nozzle that is attached to the bottom of the tundish and whose lower end is immersed in the molten steel like a mold. This invention relates to an improvement in a submerged nozzle used for casting in an aerated state.

(Prior Art) When manufacturing high-quality steel using a continuous casting method, it is essential to carry out air-insulated casting using a submerged nozzle in order to avoid secondary oxidation of the molten steel flow.

For continuous machines with large mold cross-sections, immersion nozzles (
As shown in Fig. 6, a horizontal discharge type is adopted in which the discharge hole (C1 is oriented in the horizontal direction) from the lower end of the inner cavity of the molten steel passage, as shown in Fig. 6. In a casting machine, a lateral discharge type submerged nozzle (a) is connected to a mold (d).
) is small, as shown in Figure 6, the molten steel discharge flow indicated by arrow (8) collides with the solidified shell (e) forcefully and re-melts the shell, resulting in the melting of the slab. This can lead to problems such as vertical cracking and breakouts. In addition, the molten steel flow (13) that moves upward from the discharge flow (A) that collides with the shell and reverses at the meniscus ([1] lead to defects.

Therefore, in small-section high-speed continuous casting, as shown in Figure 7,
A bottom discharge type immersion nozzle (a) with a discharge hole (cl) at the bottom end.
l) is adopted.

(Problems to be Solved by the Invention) Although the bottom discharge type immersion nozzle described above prevents the solidified shell from remelting and the mold powder from being entrained, the downward flow of molten steel (A1) from the nozzle bottom flows into the mold. The depth of penetration into the molten steel area is deep.

The penetration of the molten steel discharge flow is closely related to the ability to float and remove inclusions present in the molten steel in the mold, and the shallower the penetration depth, the better the float removal ability and the better the cleanliness of the rope. be done. In this respect, the bottom discharge type submerged nozzle (al) has a problem in that the discharge flow (A1) penetrates deeply, which adversely affects the cleaning of steel.

The present invention solves the above-mentioned problems of the prior art, and provides a bottom discharge type immersion nozzle that can shallowly penetrate the molten steel discharge flow, reduce inclusions trapped in the slab, and improve the cleanliness of steel. The purpose is to provide

(Means for Solving the Problems) The object of the present invention is to taper the lower part of the inner cavity of the immersion nozzle in an appropriate manner in order to improve shallow penetration of the molten steel discharge flow from the bottom discharge type immersion nozzle. This is achieved by forming the discharge hole with a larger area, increasing the area of the discharge hole, and slowing down the discharge flow rate without disturbing the flow condition.

That is, the continuous casting immersion nozzle of the present invention has the following configurations:
The immersion nozzle in continuous casting is characterized by having a linear part at the upper part of the inner cavity (the lower part is formed into a tapered shape that widens toward the lower end discharge hole).

(Function) In the immersion nozzle of the present invention, the flow velocity of the molten steel discharge flow downward from the lower end discharge hole is reduced by a portion of the taper on the front side.
The penetration of the discharge flow is shallower, fewer inclusions are trapped in the slab, and the cleanliness of the steel is improved.

(Example) FIG. 1 shows the relationship between the cross-sectional shape of a continuous casting nozzle according to an example of the present invention and its various characteristic values.

This immersion nozzle (1) has a straight part (3) with a diameter d at the upper part of the inner cavity (2) of the molten steel passage, and a lower part (4) with a length l following the straight part (3).
) expands toward the lower end discharge hole (5) at a taper angle θ
It is formed into a tapered shape. (gl indicates the mold powder on the molten steel in the mold.

The penetration depth of the discharged molten steel flow in this immersion nozzle is mainly the length of the lower part of the taper! , a function 1 consisting of the taper angle θ is governed by the relationship with tan θ. Second
The figure shows the penetration depth index on the vertical axis and 1 tanθ on the horizontal axis.
Indicates the relationship between

When l tan θ=0, there is no taper, and the penetration depth index in that case is 1.0. As l tan θ increases, the penetration depth becomes shallower.

The larger the taper angle θ, the more effective it is, but if the taper angle is too large than 6°, a drift (C) will occur in the bore (2) as shown in Figure 3 (A), which will reduce the molten steel flow velocity. does not decrease, and the improvement effect of reducing the penetration depth decreases. FIG. 3 shows the relationship between the taper angle θ on the horizontal axis and the presence or absence of drift on the vertical axis. The point (Xl) in Figure 2 indicates that an excessive taper angle is not as effective in reducing the depth of penetration.Also, due to drifting of the flow, a stagnation part (b) is generated in the nozzle, which may cause the adhesion of inclusions. It becomes a starting point and impairs the molten W4 cleaning effect.

Also, regarding the taper part length i! It is appropriate that ≧2d. If the length of the tapered part is too short, as shown in FIG. 4(a), the flow velocity will not be uniform within the lumen, and the fluid will be discharged with the flow velocity at the central portion remaining high. FIG. 4(b) shows the relationship between the tapered part length l on the horizontal axis and the center discharge flow velocity index on the vertical axis. As a result, when l is smaller than 2d, the effect of reducing the penetration depth is small. Point (y) in FIG. 2 shows such an example.

! , θ is large, the wall thickness at the bottom of the submerged nozzle becomes thinner. In this case, as shown in the embodiment in FIG. 5, the outer periphery is also formed in a tapered shape to prevent the wall thickness of the lower end discharge hole from becoming thinner and to maintain heat resistance.

(Effects of the Invention) According to the present invention, the penetration of the molten steel discharge flow from the bottom discharge type immersion nozzle can be made shallower, the number of inclusions trapped in the slab is reduced, and the cleanliness of the steel is improved.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional side view of a continuous casting nozzle according to an embodiment of the present invention with various characteristic values filled in, and Fig. 2 is a function β of the characteristic values.
A chart showing tanθ on the horizontal axis and sinking depth index on the vertical axis. Figure 3 (a) is a longitudinal cross-sectional side view showing the occurrence of drifting when the taper angle is excessive, and Figure 3 (b) is the graph showing the taper angle. Figure 4 (a) is a vertical cross-sectional side view showing the molten steel flow velocity distribution at the lower end of the immersion nozzle, and Figure 4 (b) is a graph showing the presence or absence of drifted flow on the horizontal axis and the vertical axis shows the presence or absence of drifted flow. Chart showing the partial discharge flow rate index on the vertical axis, No. 5
The figure is a longitudinal sectional side view of a submerged nozzle for continuous casting according to a modified embodiment of the present invention, FIG. 6 is a longitudinal sectional side view of a conventional horizontal discharge nozzle in a mold, and FIG. 7 is a conventional bottom discharge nozzle. FIG. (1)...Immersion nozzle, (2)...Inner cavity, (3)...
...straight line part, (4) ...lower part, (5) ...discharge hole,
(d)...Inner lumen upper diameter, (81...Taper part length, (θ)...Taper angle, CC)...Noncurrent flow, (D
)... Stagnation part, (xi (y)... Point, (a) (a
l)...Immersion nozzle, mountain)...lumen, (c) (cl
)...Discharge hole, (dl...mold, (e)...solidified shell, (f)...meniscus part, (a...mold powder, (h)...powder particle, ( A) (Al)
... Molten steel discharge flow, (B) ... Reverse molten steel flow. Name of patent applicant's agent, 7-1,

Claims (2)

[Claims] (1) An immersed nozzle for continuous casting, characterized in that the lower part of the inner cavity of the immersed nozzle that continues from the upper straight part is tapered to widen toward the lower end discharge hole. (2) Between the taper angle θ of the lower part of the taper of the lumen, the length l of the lower part of the taper of the lumen, and the diameter d of the upper straight part of the lumen, ltan θ≧0.08d l≧2d θ<6°. An immersed nozzle for continuous casting according to claim 1 to which the invention relates.