JP4281690B2 - Immersion nozzle for continuous casting and continuous casting method - Google Patents

Description

  The present invention provides a continuous casting immersion nozzle (hereinafter also referred to as a swirl flow nozzle) that imparts a swirl flow to molten steel flowing down in the nozzle by a twisted plate swirl blade disposed inside, and the swirl flow nozzle. The present invention relates to the continuous casting method used.

  In continuous casting of steel, molten steel is poured into a mold through an immersion nozzle, and steel that has solidified in the mold is sequentially drawn out from below the mold, thereby continuously casting. In such continuous casting, when using an immersion nozzle having a plurality of discharge ports on the side surface of the lower end portion, in the immersion nozzle having no swirl blade, the molten steel is directly or indirectly collided with the nozzle bottom. It flows out from the discharge port later.

  The molten steel usually contains fine particles (hereinafter referred to as inclusions) mainly composed of alumina. Therefore, due to the complicated disturbance of the flow, inclusions are remarkably generated in the vicinity of the discharge port from the nozzle bottom.

Inclusions adhering to the vicinity of the discharge port
1) Destabilization of mold flow due to unstable discharge flow,
2) Decrease in casting speed due to increased pressure loss at the discharge port,
3) Interruption of continuous casting due to blockage of discharge port,
Etc. Therefore, various studies have been made for the purpose of stabilizing the molten steel flow and preventing the discharge port from being blocked.

  One of them is to impart a swirl flow to the molten steel flowing down the immersion nozzle. In a two-hole nozzle having two discharge ports opposed to the side surface of the lower end, the molten steel is forcibly distributed to the two discharge ports by centrifugal force due to the application of the swirling flow. It has been found that the collision is relaxed, the flow is stabilized, and inclusion adhesion near the discharge port is reduced.

In this swirl flow nozzle, the applicant, for example, in Patent Document 1, the molten steel flow direction length (hereinafter simply referred to as the length) in the twisted portion of the swirl blade is L (mm), the radius is R (mm), and the twist When the angle (angle obtained by projecting the torsion amount of the torsion plate onto a plane parallel to the diameter of the torsion plate) is θ (rad), the torsion pitch Pc of the swirl blade (the torsion plate is twisted by 180 °) An index representing the torsional strength, which is how many times the diameter is required.The smaller the value, the stronger the torsion, and it can be obtained by L · π / (2 · R · θ)). To 3.0, a twist angle θ of 60 ° to 180 °, an outer diameter (= 2R) of 50 mm to 250 mm, and a thickness of 5% to 30% of the outer diameter are proposed.
JP 2002-239690 A

  If the swirl flow nozzle proposed in Patent Document 1 is used, the adhesion of inclusions in the vicinity of the discharge port is reduced. However, when the inventors proceeded with continuous casting using this swirl flow nozzle, it has been found that the amount of inclusions attached to the swirl blade arrangement portion increases as the number of uses increases.

  The problem to be solved by the present invention is that in the continuous casting using the conventional swirl flow nozzle, the amount of inclusions adhering to the swirl blade arrangement portion increases as the number of uses increases.

The swirl flow nozzle of the present invention is
In order to prevent inclusions from adhering to the swirl blade arrangement part even if the number of uses increases,
The shape of the twist plate swirl blade is
(1) Outer diameter: 50 mm to 250 mm
(2) Length of torsion part: 30% to 200% of outer diameter of swirl vane
(3) Thickness of horizontal section: 5% to 30% of swirl vane outer diameter
(4) Twist angle of swirl blade: 60 ° ~ 180 °
Meet the requirements of
And,
A) The torsional gradient of the torsion plate type swirl blade was formed so as to be small on the molten steel inflow side and increased toward the molten steel outflow side.
Or
B) The torsional gradient of the outer peripheral portion in the vicinity of the molten steel inflow side of the twisted plate type swirl blade is gentler than the torsional gradient of the inner peripheral portion thereof.
This is the main feature.
In the present invention, the torsional gradient refers to the torsion angle per unit length in the axial direction of the swirl vane.

  And when the molten steel is continuously cast using the swirl flow nozzle of the present invention, even if the number of times of use is increased, the inclusion adhesion to the swirl blade arrangement portion can be effectively suppressed. The discharge flow from becomes stable. This is the continuous casting method of the present invention.

  According to the present invention, by optimally defining the shape of the swirl blade and improving the fluidity in the swirl blade, even if the number of uses increases, the inclusions can be effectively attached to the swirl blade arrangement portion. Therefore, the number of times of use of the swirl flow nozzle can be further extended.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings along with the processes leading to the establishment of the invention.
The inventors considered the relationship between the flow of the inclusions on the swirl blade arrangement part and the flow state of the swirl blade part, and the inclusions were attached at a place where flow disturbance and stagnation could occur. From this, we investigated the shape of the swirl vane to improve the fluidity at the same location.

  The inventors have observed the more detailed generation form of the swirling flow nozzle to which inclusions are attached, and found the following phenomenon as a result of matching the result with the analysis result by numerical calculation.

  First, a position about 1 cm from the upper end of the swirl vane on the molten steel inflow side (a diagram), a center part of the swirl vane (b diagram), and a position about 1 cm from the lower end of the swirl vane on the molten steel outflow side (c diagram). ) Was investigated. The result is schematically shown in FIG. According to this investigation result, the inclusion 1 is noticeably attached in the vicinity of the upper end of the swirl vane 2, and the adhesion to the inner wall 3 a of the swirl flow nozzle 3 is more prominent than the adhering to the swirl vane 2 itself. It turned out to be. In FIG. 1 (a), the central part of the swirl vane 2 is not described because it is missing during cutting.

  On the other hand, when the molten steel flow in the vicinity of the swirl vane was evaluated by numerical analysis, a flow was formed near the center of the swirl vane directly downstream from the nozzle inlet, but the nozzle inner wall near the upper end of the swirl vane During the development, it was found that the flow may stagnate or part of the flow may reverse and turn upward.

  Since the vicinity of the upper end of the swirl vane where this flow stagnation and partial flow reversal occurs coincides with the maximum occurrence of inclusion adhesion, the inclusion adherence to the nozzle inner wall of the swirl vane placement part is swirling. This is thought to be due to a flow failure near the inner wall of the nozzle at the upper end of the blade.

Based on the above results, the inventors have completed the swirl flow nozzle according to the present invention that can suppress the flow failure near the nozzle inner wall at the upper end of the swirl vane.
That is, the swirl flow nozzle of the first invention is
The shape of the twist plate swirl blade is
(1) Outer diameter: 50 mm to 250 mm
(2) Length of torsion part: 30% to 200% of outer diameter of swirl vane
(3) Thickness of horizontal section: 5% to 30% of swirl vane outer diameter
(4) Twist angle θ of swirl blade: 60 ° to 180 °
Meet the requirements of
In addition, the torsional gradient of the torsion plate type swirl blade is formed so as to be small on the molten steel inflow side and increase toward the molten steel outflow side.

Moreover, the swirl flow nozzle of the second present invention,
The shape of the twist plate swirl blade is
(1) Outer diameter: 50 mm to 250 mm
(2) Length of torsion part: 30% to 200% of outer diameter of swirl vane
(3) Thickness of horizontal section: 5% to 30% of swirl vane outer diameter
(4) Twist angle of swirl blade: 60 ° ~ 180 °
Meet the requirements of
In addition, the torsional gradient of the outer peripheral portion in the vicinity of the molten steel inflow side of the twisted plate type swirl vane is made gentler than the torsional gradient of the inner peripheral portion.

  In the swirl flow nozzle of the present invention, the outer diameter of the twist plate swirl vane is set to 50 mm to 250 mm. When the swirl vane provides a predetermined swirl flow, the molten steel flow is less than 50 mm. This is because the path becomes too narrow and easily clogged due to adhesion of molten steel and non-metallic inclusions in the steel, resulting in poor operability. On the other hand, if it exceeds 250 mm, the nozzle body becomes enormous and handling becomes difficult.

In addition, the length of the twisted portion of the swirl vane is 30% to 200% of the outer diameter of the swirl vane.
This is because if it is less than 30%, a required swirl flow cannot be imparted to the molten steel flowing down the nozzle. On the other hand, if it exceeds 200%, the nozzle body becomes too long and a large installation space is required.

  Further, the reason why the thickness of the swirl vane is 5% to 30% of the outer diameter of the swirl vane is that if it is less than 5%, the strength as the structure is insufficient and may be damaged during casting. . On the other hand, a thickness exceeding 30% is not only unnecessary for strength, but also unnecessarily increases the flow resistance. However, since the structural strength is required at the upper part of the swirl vane exposed to the molten steel flow from the tundish, even if the upper part is made thicker and the lower part is made thinner within the above-mentioned thickness range as necessary. Good.

  Further, when the twist angle θ of the swirl blade is 60 ° to 180 °, if it is less than 60 °, the occupied area of the swirl blade in the cross section of the flow path in the nozzle is reduced, and an even swirl flow is obtained. Because it disappears. On the other hand, it is meaningless to give a twist angle θ exceeding 180 °, and it causes unnecessarily increased flow resistance and makes it difficult to produce swirl vanes by compression molding.

Hereinafter, the detailed principle of the swirl flow nozzle of the present invention will be described.
As shown in FIG. 2, when the horizontal cross-sectional shape of the torsion plate-type swirl vane 2 is a straight line, the center of the swirl vane 2 (axis center of the swirl flow nozzle 3) indicated by 2a in FIG. The angle formed by the tangential plane of the surface of the swirl vane 2 with respect to the vertical line (the axis of the swirl flow nozzle 3) (hereinafter referred to as a slant) toward the outer periphery of the swirl vane 2 indicated by 2b (the inner wall 3a side of the swirl flow nozzle 3). Called degrees).

  For this reason, in the vicinity of the upper end of the swirl vane 2 on the molten steel inflow side where the swirl flow is not yet developed, the angle formed by the direction of the molten steel flow flowing down the outer periphery 2b of the swirl vane 2 and the surface of the swirl vane 2 is large. It becomes a shape close to a collision, and the above situation is considered to occur.

In this case, in order to improve the collision situation immediately downstream in the outer peripheral portion of the upper end of the swirl blade 2,
A. B. Suppression of the overall twist gradient on the upper end side of the swirl vane It is considered effective to correct the blade shape by suppressing the torsional gradient of the outer peripheral portion on the upper end side of the swirling blade.

  Of these, the correction of A corresponds to the first aspect of the present invention, and as shown in FIG. 3, the horizontal cross-sectional shape of the swirl vane 2 remains linear, and the upper end of the swirl vane 2 on the molten steel inflow side. To reduce the torsional gradient.

  According to the inventors' investigation, in the first aspect of the present invention, the torsional gradient suppression region is downstream from the upper end 2c on the molten steel inflow side of the swirl vane 2 by a length of at least 1/5 of the nozzle body inner diameter D. It was confirmed that it is desirable to set the range to the range (D / 2 range in FIG. 4).

  The torsional gradient in this range is 50% or less of the swirling blade having a single twisting gradient that obtains the required swirling amount, so that the flow situation at the inlet portion of the swirling blade 2 can be further improved. It was confirmed that inclusion inclusions can be reduced.

  The torsional gradient suppression region is defined as a range extending from the upper end 2c of the swirl vane 2 to the downstream side by a length of at least 1/5 of the nozzle body inner diameter D, according to the results of the investigation by the inventors. This is because the inclusion 1 was noticeably adhered within the range of the length of 1/5 of the nozzle body inner diameter D.

  Also, according to the results of investigations by the inventors, the torsional gradient in the above range is set to 50% or less of a single torsional gradient that obtains the required amount of swirling. This is because the swirl vane comes into contact with a shape close to a collision and a flow failure occurs in the vicinity of the inner wall of the nozzle.

  If this correction is performed with the same swirling blade length as in the case of a single torsional gradient, the entire swirling amount may be insufficient and the swirling may be insufficient. May be extended, or the torsional gradient on the downstream side may be increased.

  Regarding the increase in the torsional gradient on the downstream side of the swirl vane, if it is simply increased, flow disturbance may occur at the joint between the introduction part and the downstream part. The phenomenon can be suppressed by increasing the torsional gradient in a stepwise manner from the torsional gradient of the introduction portion without making the constant.

  On the other hand, the correction of B corresponds to the second aspect of the present invention, and is in the vicinity of the molten steel inflow side of the swirl vane 2 (in the example of FIG. 6, the range reaching the downstream side by a length that is ½ of the nozzle body inner diameter D). The horizontal cross-sectional shape of the swirl vane 2 is deformed stepwise with respect to the axial direction of the swirl flow nozzle 3 so that the torsional gradient of the outer peripheral part 2b in FIG. The suppression of the torsional gradient at the outer periphery 2b of the swirl vane 2 is realized.

  In this case, for example, when the swirl blade 2 is in the clockwise direction when viewed from the inflow side of the swirl flow nozzle 3, as shown in FIG. If it is gradually linear along with the turning along the axial direction, or if it is further changed from a straight shape to an inverted S shape, the torsional gradient in the vicinity of the outer periphery 2b of the swirling blade 2 can be reduced. It can suppress more effectively than a turning blade.

Such a horizontal cross-sectional shape is obtained by, for example, turning a curve of a cubic equation Y = A × X ³ with respect to the axial direction, and by monotonically decreasing the coefficient A as a function of the axial coordinate. The above-described modification is realized.

  Note that the twist angle θ when the horizontal cross-sectional shape of the swirl vane 2 is S-shaped is the S-shaped tangential direction at the center 2 a of the swirl vane 2 in the curve at the center position of the blade thickness of the horizontal cross-section of the swirl vane 2. Obtained as the direction of the swirl vane 2 in the cross section. For example, in the case of FIG. 5A, the direction of the upper end 2c of the swirl vane 2 is the left-right direction on the paper surface.

  If the molten steel is continuously cast using the swirl flow nozzle 3 of the present invention, even if the number of times of use increases, adhesion of inclusions to the arrangement portion of the swirl blades 2 can be effectively suppressed. The discharge flow from 2 is stabilized.

Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described.
A continuous casting experiment (slab thickness 270 mm, width 1600 mm) with low-carbon steel having the chemical components shown in Table 1 below was performed at a casting speed of 1.8 m / min in the stationary part. In addition, the molten steel provided for use is 600 tons.

  In the experiment, a swirl flow nozzle having a shape shown in Example 1 and Example 2 in Table 2 below, a swirl flow nozzle having a single torsional gradient (Comparative Example 1), and a swirl blade are provided. No immersion nozzle (Comparative Example 2) was used.

After continuous casting, the state of inclusions adhering to the swirl flow nozzle was observed by observing a cross section of the nozzle.
As a result, as shown in the attached thickness column of Table 3 below, when Example 1 satisfying claims 1 and 2 and Example 2 satisfying claims 3 and 4 were used, a comparative example was used. It became clear that the amount of adhesion decreased compared with 1 and 2. From this, it can be seen that in continuous casting using the swirl flow nozzle of the present invention, long-term operation can be continuously performed in a state where the discharge flow from the swirl flow nozzle is stable.

  The present invention is not limited to the above example, and it goes without saying that the embodiment may be appropriately changed within the scope of the technical idea described in each claim.

  The present invention can be applied not only to low carbon steel slabs but also to continuous casting of medium carbon steel, high carbon steel, and the like.

It is a schematic diagram of the inclusion adhesion state at a position about 1 cm from the upper end of the swirl vane (a diagram), a central portion of the swirl vane (b diagram), and a position about 1 cm from the lower end of the swirl vane (c diagram). . It is a figure explaining the shape of the conventional turning blade | wing, (a) is the figure seen from upper direction, (b) is the figure seen from diagonally upward. It is a figure similar to FIG. 2 explaining the shape of the swirl | wing blade in Example 1. FIG. It is an image figure of the swirl flow nozzle which suppressed the twist gradient of the molten steel inflow side of a swirl blade. It is the same figure as FIG. 2 explaining the shape of the turning blade | wing in Example 2. FIG. It is an image figure of the swirl flow nozzle in the case of suppressing the outer periphery side twist gradient on the molten steel inflow side of the swirl blade and gradually increasing it. It is a figure similar to FIG. 2 explaining the shape of the swirl | wing blade in the comparative example 1. FIG.

Explanation of symbols

2 swirl vane 2a center 2b outer periphery 2c upper end 3 swirl flow nozzle 3a inner wall

Claims (5)

A submerged nozzle for continuous casting that is attached to the downstream side of the flow rate adjusting device at the bottom of the tundish and has a twisted-plate swirl blade disposed therein,
The shape of the twist plate swirl blade is
(1) Outer diameter: 50 mm to 250 mm
(2) The length of the twisted portion in the flowing direction of the molten steel: 30% to 200% of the outer diameter of the swirling blade
(3) Thickness of horizontal section: 5% to 30% of swirl vane outer diameter
(4) Twist angle of swirl blade: 60 ° ~ 180 °
Meet the requirements of
An immersion nozzle for continuous casting, characterized in that the twist gradient of the twisted plate-type swirl blade is small on the molten steel inflow side and increases on the molten steel outflow side.   In the range from the upper end on the molten steel inflow side of the torsion plate type swirl vane to the downstream side by a length of at least 1/5 of the inner diameter of the nozzle body, the torsional gradient provides a single swirling amount necessary for the flowing molten steel. The immersion nozzle for continuous casting according to claim 1, wherein the torsional gradient is 50% or less. A submerged nozzle for continuous casting that is attached to the downstream side of the flow rate adjusting device at the bottom of the tundish and has a twisted-plate swirl blade disposed therein,
The shape of the twist plate swirl blade is
(1) Outer diameter: 50 mm to 250 mm
(2) The length of the twisted portion in the flowing direction of the molten steel: 30% to 200% of the outer diameter of the swirling blade
(3) Thickness of horizontal section: 5% to 30% of swirl vane outer diameter
(4) Twist angle of swirl blade: 60 ° ~ 180 °
Meet the requirements of
The continuous casting immersion nozzle is characterized in that the torsional gradient of the outer peripheral portion in the vicinity of the molten steel inflow side of the twisted plate type swirl vane is gentler than that of the inner peripheral portion.   The horizontal cross-sectional shape of the swirl vane is a shape in which a rectangle in the vicinity of the molten steel inflow side is bent in an S shape, and a vicinity of the molten steel outflow side is a straight or inverted S-shaped rectangle. The immersion nozzle for continuous casting described in 1. A continuous casting method, wherein molten steel is continuously cast using the immersion nozzle for continuous casting according to any one of claims 1 to 4.

Images