JP7196746B2 - Pouring equipment for continuous casting - Google Patents

Description

The present invention relates to a pouring apparatus for continuous casting.

In the continuous casting of molten metal, such as molten steel, molten steel contained in a ladle is poured into a tundish and poured from the tundish into a mold. A flow control mechanism such as a sliding gate is provided at the bottom of the tundish, an immersion nozzle is provided downstream of the sliding gate, and a discharge hole for discharging molten steel into the mold is provided on the side near the lower end of the immersion nozzle. there is

In large-section bloom continuous casting and slab continuous casting, there are two discharge holes on the side of the submerged nozzle, and the discharge holes are usually provided on both sides in the width direction of the mold (the width direction of the slab). On the other hand, in small-section bloom continuous casting and billet continuous casting, a single discharge hole directed downward is provided at the lower end of the submerged nozzle. Hereinafter, it is also referred to as a “single-hole submerged nozzle”. The present invention is directed to a pouring apparatus for continuous casting using a single-hole submerged nozzle as the shape of the discharge hole of the submerged nozzle.

In continuous casting using a single-hole submerged nozzle, as the discharge flow penetrates deeply into the strand, the surface temperature of the molten steel in the mold tends to drop, and the surface of the molten steel begins to skin, trapping bubbles and inclusions that rise to the surface. easier. As a result, it is known that problems such as deterioration in the quality of the cast slab center and surface layers and poor slag formation of mold powder occur (see Non-Patent Document 1). In addition, it leads to operational problems such as breakouts and broken submerged nozzles.

In Patent Document 1, a continuous casting submerged nozzle, which is used in a continuous steel casting method and has a twisted plate-type swirl vane installed therein to impart a swirl flow to molten steel flowing down the nozzle, is called a "swirl flow nozzle." A continuous casting method using this swirling flow nozzle is disclosed.
According to Patent Document 1, when a swirling flow nozzle is applied to a single-hole submerged nozzle having one discharge hole at the bottom of a cylindrical nozzle, the discharge flow spreads due to centrifugal force and is discharged, resulting in a decrease in the discharge flow velocity. An electromagnetic braking effect is obtained in that the depth of penetration of the discharged flow into the slab is reduced. This effect promotes the floating of inclusions in the mold (for example, Non-Patent Document 2), increases the temperature of the metal surface (meniscus) in the mold, promotes the formation of molten slag of mold powder, and improves the slab surface. It is expected that the temperature inside the slab will decrease, equiaxed grains will increase, and porosity (shrinkage cavities) defects in the center of the slab will decrease.
Furthermore, according to Patent Document 1, as a result of using a single-hole submerged nozzle having an expanded cross section from the inner wall of the nozzle hole toward the discharge hole and using a swirling flow nozzle, molten steel flowing down while swirling is caused by centrifugal force. Since the discharge spreads horizontally, non-metallic inclusions are brought deep into the slab by the discharge flow, and the molten steel supply to the molten steel surface (meniscus) in the mold is insufficient, resulting in a drop in temperature and the formation of air bubbles and non-metallic inclusions. This solves the problem of hindrance to floating separation. Also, since the stagnation area of the molten steel flow in the vicinity of the discharge hole becomes smaller, adhesion of inclusions to the discharge hole is also reduced. The swirling molten steel is discharged while spreading laterally due to centrifugal force, creating an upward flow to the surface of the mold (meniscus), raising the temperature of the surface of the mold and promoting the separation of air bubbles and non-metallic inclusions. You can get the effect of being

Patent Document 2 discloses a method of imparting a swirl flow in the submerged nozzle by devising the shape of the intermediate nozzle in the process of pouring from the tundish into the mold. are complex and difficult to manufacture. Furthermore, Patent Document 3 discloses a method of swirling the molten steel by providing a notch in the flow path of the sliding gate. The swirling effect is not maintained due to weak swirl and erosion of the grooves and notches.

In Patent Document 1, in a swirl flow nozzle in which a torsion plate type swirl vane is installed inside the nozzle, the swirl vane torsion pitch Pc, the swirl vane torsion angle θ, the outer diameter of the swirl vane, and the thickness of the swirl vane are defined within a predetermined range. In addition, a method of continuous casting using a swirl flow nozzle is disclosed in which the inner diameter is narrowed between the lower end of the swirl vane and the discharge hole, and the required head estimated value H between the tundish and the mold is kept within a predetermined range. It is

JP-A-2002-239690 JP-A-07-303949 Japanese Patent Application Laid-Open No. 2001-129646

Yuichi Tsukaguchi et al., "Swirling Flow Immersion Nozzle for Continuous Casting of Round Billets" Tetsu to Hagane Vol. 93 (2007) No. 9, pp575-582 A. Vaterlaus et al, 3rd Conf. on CC(1998), 715

As described in Patent Document 1, continuous casting using a single-hole submerged nozzle is performed after forming a swirl flow in the molten metal flow flowing down the submerged nozzle by installing a torsion plate-type swirl vane in the submerged nozzle. By doing so, the swirling molten steel is discharged while spreading laterally due to centrifugal force, creating an upward flow to the surface of the mold (meniscus) and raising the temperature of the surface of the mold, creating bubbles and non-metallic inclusions. flotation separation is promoted.
In addition, the rise in the surface temperature of the molten steel can also be expected to suppress skinning of the molten surface.
On the other hand, the torsion plate-type swirl vane provided in the submerged nozzle is easily eroded, and there is a problem that the effect does not last. If the submerged nozzle is replaced when the swirl vane is eroded, the life of the submerged nozzle is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pouring apparatus for continuous casting that can impart a swirling flow to the flow of molten metal that flows down through the submerged nozzle without shortening the service life of the submerged nozzle and the sliding gate.

That is, the gist of the present invention is as follows.
[1] A pouring device for continuous casting for pouring molten metal into a mold,
Having a sliding gate for adjusting the flow rate of the molten metal and an immersion nozzle provided below the sliding gate,
The sliding gate has a plurality of plates formed with passage holes through which the molten metal passes, at least one of the plates being a slidable slide plate,
The channel holes in each plate form upstream surface openings on the upstream surface of the plate surface located upstream of the molten metal passing therethrough, and form upstream surface openings on the downstream surface located downstream of the surface of the plate. Forming the apertures, the direction from the center of gravity of the upstream side surface aperture pattern to the center of gravity of the downstream side surface aperture pattern is defined as the channel axis direction,
The channel axis line inclination angle α formed by the channel axis direction and the downstream direction perpendicular to the sliding surface of the plate (hereinafter referred to as the “sliding surface perpendicular downstream direction”) is 5° or more and 75° or less,
The direction in which the channel axis direction is projected onto the sliding surface is called the sliding surface channel axis direction, and the direction in which the slide plate slides when the sliding gate is closed is called the sliding closing direction. The angle formed by the sliding surface flow path axis direction clockwise with respect to the closing direction when viewed in the sliding surface perpendicular downstream direction is called a flow path axis rotation angle θ (within a range of ±180 degrees). The axis line rotation angle θ differs between the adjacent plates, and the θ of the plate on the most upstream side is θ ₁ , the θ of the plate one downstream thereof is θ ₂ , and the θ of the plate one further downstream is θ Numbered in order from ₃ , and Δθ _N = θ _N - θ _N+1 (N is an integer of 1 or more and up to the number of plates - 1),
All the angles Δθ _N are 10° or more and less than 170° to form a counterclockwise swirling flow in the submerged nozzle, or all the angles Δθ _N are more than -170° and -10° or less and the submerged nozzle Form a clockwise swirl flow in
A pouring apparatus for continuous casting, wherein the submerged nozzle has a single discharge hole opened at the bottom of the submerged nozzle.
[2] The pouring apparatus for continuous casting according to [1], wherein the shape of the discharge hole of the submerged nozzle is formed so as to have an expanded tubular shape from the inner wall of the submerged nozzle toward the outlet of the discharge hole. .
[3] The pouring apparatus for continuous casting according to [1] or [2], wherein the number of plates forming the sliding gate is two or three and the number of slide plates is one.

By using the present invention as a continuous casting pouring device for pouring molten metal into a mold, continuous casting using a single-hole immersion nozzle can be performed without shortening the life of the immersion nozzle or sliding gate. Forming a swirling flow in the molten metal flow flowing down the submerged nozzle, forming an upward flow to the metal surface (meniscus) in the mold, raising the temperature of the metal surface, and promoting the floating and separation of bubbles and non-metallic inclusions. can be done.

1 is a conceptual cross-sectional view showing a pouring apparatus for continuous casting according to the present invention; FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a sliding gate of a pouring device for continuous casting of the present invention, (A) is an upper fixed plate, (B) is a slide plate, (C) is a plan view of a lower fixed plate, and (D) is a sliding gate. A front view of a combination of a gate and an immersion nozzle, (E) is a view taken along line EE, and (F) is a sectional view taken along line FF. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a sliding gate of a pouring apparatus for continuous casting of the present invention, (A) is a view from the AA arrow, (B) is a view from the BB arrow, and (C) is a view from the CC arrow. , (D) is a front view of a combination of the sliding gate and the immersion nozzle, and (E) is a view taken along line EE. It is a diagram showing the flow in the sliding gate of the present invention, (A) is an AA arrow view, (B) is a BB arrow view, (C) is a CC arrow view, (D) is a front view of a combination of a sliding gate and an immersion nozzle, and (E) is a view taken along line EE. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the sliding gate of the pouring apparatus for continuous casting of this invention, (A) is an upper fixed plate, (B) is a slide plate, (C) is a front view which combined a sliding gate and a submerged nozzle, (D ) is a view taken along the line DD, and (E) is a cross-sectional view taken along the line EE. FIG. 1 is a view showing a sliding gate of a continuous casting pouring apparatus of the present invention, (A) is a view from the AA arrow, (B) is a view from the BB arrow, and (C) is a sliding gate and an immersion nozzle. Combined front view, (D) is a DD arrow view. 1 is a diagram showing an example of an upper fixing plate of the present invention, where (A) is a plan view, (B) is a front view, (C) is a side view, and (D) is a cross-sectional view taken along line DD. FIG. 10 is a view showing a sliding gate of a comparative example, (A) is an upper fixing plate, (B) is a slide plate, (C) is a front view of a combination of a sliding gate and an immersion nozzle, and (D) is a DD arrow view. FIG. (E) is a cross-sectional view taken along line EE. FIG. 10 is a view showing a sliding gate of a comparative example, (A) is a view along the AA arrow, (B) is a view along the BB arrow, (C) is a front view of a combination of a sliding gate and an immersion nozzle, (D ) is a DD arrow view. FIG. 3 shows a conventional sliding gate, where (A) is an upper fixed plate, (B) is a slide plate, (C) is a plan view of a lower fixed plate, and (D) is a front view of a combination of a sliding gate and an immersion nozzle. (E) is a view taken along line EE, and (F) is a sectional view taken along line FF. FIG. 2 is a diagram showing a conventional sliding gate, (A) is an AA arrow view, (B) is a BB arrow view, (C) is a CC arrow view, and (D) is a sliding gate. A front view of a combination of submerged nozzles, and (E) is a view taken along line EE. FIG. 3 is a cross-sectional view showing the shape of a discharge hole in the submerged nozzle of the pouring apparatus for continuous casting of the present invention; It is sectional drawing which shows the streamline of the discharge flow from the discharge hole front-end|tip, (A) is the example of this invention which formed the swirl flow, (B) is the comparative example which does not form a swirl flow.

The present invention, as shown in FIG. 1, is a continuous casting pouring device 20 for pouring molten metal into a mold 22, comprising a sliding gate 1 for adjusting the flow rate of the molten metal, and a sliding gate 1. and a submerged nozzle 11 provided below. A swirling flow is formed at the sliding gate 1, and the molten metal flows downward while swirling through the inner hole 12 of the submerged nozzle. The immersion nozzle 11 has a discharge hole 13 formed downward at its bottom, and the molten metal flowing down the submerged nozzle inner hole 12 is discharged from the discharge hole 13 while forming a swirling flow. ), the discharge flow 19 spreads concentrically from the center axis end of the submerged nozzle in the casting direction and the horizontal direction in the mold, enabling discharge.

《Sliding Gate》
First, the sliding gate of the present invention will be described with reference to FIGS. 1 to 11. FIG.
The sliding gate 1 is used for the purpose of adjusting the flow rate of the molten metal 23 in the process of pouring the molten metal 23 from the tundish 21 into the mold 22 in continuous casting of molten metal such as steel. In the sliding gate 1 constructed by stacking two or three plates 2 , each plate 2 is provided with a channel hole 6 . Slide the slide plate 4 of the plates constituting the sliding gate 1, and when the sliding gate 1 is "open" due to the overlapping of the flow passage holes 6 of each plate, the flow from the upstream side to the downstream side of the flow passage hole 6 Molten metal flows toward the side. A direction perpendicular to the sliding surface 30 of the plate 2 and directed to the downstream direction (sliding surface vertical downstream direction 32) is directed vertically downward from top to bottom.

10 and 11, in a conventionally used sliding gate, the channel hole 6 of the plate 2 normally has a cylindrical inner peripheral shape, and the axial direction of the cylinder is perpendicular to the sliding surface. It is configured parallel to the direction 32 . On the other hand, in the present invention, as shown in Figs. By appropriately combining two or three plates with oblique holes in different directions, the molten metal flow inside the sliding gate 1 and the submerged nozzle 11 on the downstream side thereof can be controlled only toward the downstream side. Instead, the circumferential flow velocity is added to form a swirling flow.

As the cross-sectional shape of the channel hole 6, a cylindrical shape having a perfectly circular cross section perpendicular to the axial direction is normally used. In the sliding gate 1 of the present invention, the channel hole 6 formed in the plate 2 is not limited to a cylindrical shape, and the axial direction of the channel hole may also change within the plate. No. Therefore, first, the axis of the channel hole 6 formed in the plate 2 is defined.

The passage hole 6 of the conventional sliding gate 1 will be described with reference to FIG. A sliding gate 1 of FIG. 10 has three plates 2, and consists of an upper fixed plate 3, a slide plate 4, and a lower fixed plate 5 from the upstream side. Each plate 2 has a cylindrical shape with a perfectly circular cross section, and is formed with a channel hole 6 whose axial direction is oriented in the direction perpendicular to the sliding surface 30 (vertical downstream direction 32 of the sliding surface). there is The upstream surface of each plate is called an upstream surface 7u, and the downstream surface thereof is called a downstream surface 7d. A figure (upstream side surface aperture) formed by the inner peripheral surface of the channel hole 6 on the upstream surface 7u is called an upstream aperture 8u. A figure (downstream side surface aperture) formed by the inner peripheral surface of the channel hole 6 on the downstream surface 7d is referred to as a downstream aperture 8d. In the example shown in FIG. 10, the axis of the cylindrical shape of the channel hole 6 is perpendicular to the sliding surface, so in FIGS. 10(A) to (C), the upstream opening 8u and the downstream opening 8d overlap. . If the shapes of the upstream opening 8u and the downstream opening 8d are regarded as figures, respectively, the center of gravity of the figures can be defined. The center of gravity of the upstream surface aperture figure is called the upstream center of aperture 9u, and the center of gravity of the downstream surface aperture figure is called the lower center of gravity 9d. In the example shown in FIG. 10, both the upstream apertures 8u and the downstream apertures 8d are circular in shape, so the centroids 9u and 9d of the upstream apertures coincide with the centers of the perfect circles. Next, a flow path axial direction 10 is defined as a direction that passes through the upstream hole center of gravity 9u and the downstream hole center of gravity 9d and faces the downstream side. In the example shown in FIG. 10 , the channel axis direction 10 is the same as the sliding surface perpendicular downstream direction 32 . In FIG. 10(F), the line depicted by the dashed dotted line is the channel axial direction 10 .

Next, referring to FIG. 2, the passage hole 6 of the sliding gate 1 of the present invention will be explained. The sliding gate 1 of FIG. 2 has three plates, and consists of an upper fixed plate 3, a slide plate 4, and a lower fixed plate 5 from the upstream side. Each plate is formed with a channel hole 6 whose axial cross section is a perfect circle and whose axial direction is tilted from the downstream direction 32 perpendicular to the slide surface. The upper fixing plate 3 will be described as an example with reference to FIGS. 2(A) and 2(F). FIG. 2(F) is a cross-sectional view taken along line FF of FIG. 2(A). Since the axial direction of the cylinder and the sliding surface perpendicular downstream direction 32 are inclined, the upstream opening 8u and the downstream opening 8d are drawn at different positions in FIG. 2(A). Since the cross section in the axial direction is a perfect circle and the axial direction is a cylinder inclined from the downstream direction 32 perpendicular to the sliding surface, the upstream opening 8u and the downstream opening 8d each form an ellipse slightly deviating from a perfect circle. ing. However, it is drawn as a perfect circle on the drawing for convenience. The centroids of the respective figures of the upstream apertures 8u and the downstream apertures 8d can be defined as the upstream aperture centroid 9u and the downstream aperture centroid 9d. Furthermore, the channel axis direction 10 can be determined so as to pass through the upstream hole center of gravity 9u and the downstream hole center of gravity 9d and face the downstream side. In FIG. 2(F), the line depicted by the dashed dotted line is the channel axial direction 10 . In the example shown in FIG. 2 , the channel axial direction 10 coincides with the axial direction of the cylindrical shape that forms the channel hole 6 and has a perfectly circular cross section in the axial direction. Here, the angle between the downstream direction perpendicular to the sliding surface of the plate (sliding surface perpendicular downstream direction 32) and the channel axis direction 10 is defined as channel axis inclination angle α. Here, the reason why the center of gravity of the opening is used instead of the center of the circle to determine the direction of the channel axis is to universally define the direction of the channel axis even when the shape of the aperture is not a perfect circle.

In the example shown in FIG. 10, the downstream opening 8d of the upper fixed plate 3 and the upstream opening 8u of the slide plate 4, and the downstream opening 8d of the slide plate 4 and the upstream opening 8u of the lower fixed plate 5 are aligned with each other. At the same time, the sliding position of the slide plate 4 is fixed, that is, the sliding gate 1 is fully open (see FIG. 10(D)). In the sliding gate 1 shown in FIG. 10, the opening degree of the sliding gate 1 can be reduced by moving the slide plate 4 leftward in the figure. FIG. 11 shows the same sliding gate 1 as in FIG. 10 with the degree of opening reduced to 1/2. By further moving the position of the slide plate 4 to the left in the figure, the sliding gate 1 can be fully closed. The same applies to the examples shown in FIGS. In FIG. 2, the sliding gate 1 is fully open, the downstream opening 8d of the upper fixed plate 3 and the upstream opening 8u of the slide plate 4, the downstream opening 8d of the slide plate 4 and the upstream opening 8u of the lower fixed plate 5 are The sliding position of the slide plate 4 is determined so as to match each other. FIG. 3 shows the same sliding gate 1 as in FIG. 2, with the opening degree of the sliding gate 1 being 1/2. Therefore, the direction in which the slide plate 4 slides when the sliding gate 1 is closed is hereinafter referred to as "sliding closing direction 33".

In the example of the present invention shown in FIG. 2, the channel axis direction 10 is inclined at the channel axis inclination angle α with respect to the sliding surface perpendicular downstream direction 32, so the channel axis direction 10 is projected onto the sliding surface. When the direction is defined as the sliding surface flow path axis direction 31, the sliding surface flow path axis direction 31 can be defined. In FIGS. 2A to 2C and 2F, the sliding surface flow path axial direction 31 is indicated by thin arrows. In addition, in FIGS. 2A to 2C, the sliding surface channel axial direction 31 overlaps the channel axial direction 10. As shown in FIG. In addition, in the example shown in FIG. 10, since the channel axis direction 10 faces the sliding surface perpendicular downstream direction 32, the sliding surface channel axis direction 31 does not appear in FIGS. .

Next, the angular relationship between the sliding surface channel axis direction 31 and the sliding closing direction 33 will be defined. The angle formed by the sliding surface channel axis direction 31 with respect to the sliding closing direction 33 clockwise when viewed in the sliding surface vertical downstream direction 32 is called a channel axis rotation angle θ. The channel axis rotation angle θ is defined as an angle in the range of ±180°. That is, when the sliding surface flow path axis direction 31 becomes an angle (θ') exceeding +180° clockwise when viewed in the sliding surface perpendicular downstream direction 32, "θ = θ' - 360°" Define the angle θ as a negative value. As a subscript of the angle θ, the θ of the most upstream plate is numbered as θ ₁ , the θ of the plate one downstream thereof is θ ₂ , and the θ of the plate one further downstream is θ ₃ . When θ _N is representatively expressed, N is an integer of 1 or more and means a numerical value up to the number of plates of the sliding gate 1 . In the example shown in FIG. 2, the upper fixed plate 3 has an angle θ ₁ =−45°, the slide plate 4 has an angle θ ₂ =+90°, and the lower fixed plate 5 has an angle θ ₃ =−135°.

Furthermore, in the sliding gate 1, the relationship of the channel axis line rotation angle between two plates that are in contact with each other is defined as follows. That is, Δθ _N is determined as Δθ _N =θ _N -θ _N+1 . Δθ _N is defined as an angle in the range of ±180 degrees, like θ _N above. That is, when Δθ _N becomes an angle (Δθ _N ') exceeding +180°, Δθ _N is defined as a negative value by setting "Δθ _N =Δθ _N '-360°". Also, when Δθ _N becomes an angle (Δθ _N ') less than -180°, Δθ _N is defined as a positive value by setting "Δθ _N =Δθ _N '+360°". As a result, Δθ _N becomes a number within the range of ±180°. Here, when Δθ _N is more than 0° and less than +180°, it indicates that the channel axis line rotation angle θ _N changes counterclockwise from upstream to downstream. Conversely, when Δθ _N is more than −180° and less than 0°, it indicates that the channel axis rotation angle θ _N changes clockwise from upstream to downstream. In the example shown in FIG. 2, since Δθ ₁ =θ ₁ -θ ₂ =-135° and Δθ ₂ '=θ ₂ -θ ₃ =225°, Δθ ₂ =Δθ ₂ '-360°=-135° . Both Δθ ₁ and Δθ ₂ are within the range of -180° to 0°, indicating that the channel axis rotation angle changes clockwise.

Based on the above preparations, the conditions that the sliding gate 1 of the present invention should have and the reasons thereof will be described.

In the conventional sliding gate 1, as shown in FIGS. 10 and 11, the flow channel axis direction 10 is perpendicular to the sliding surface, that is, the flow channel axis inclination angle α is 0°, and there is an inclination. I didn't. In contrast, the first feature of the present invention is that the channel axis direction 10 is inclined with respect to the sliding surface perpendicular downstream direction 32, and the channel axis line inclination angle α is not 0°. Since the flow path axis is tilted with respect to the downstream direction 32 perpendicular to the sliding surface, the molten metal flowing in the plate not only has a velocity component in the downstream direction 32 perpendicular to the sliding surface, but also has a velocity component in the downstream direction 32 perpendicular to the sliding surface. It has a perpendicular velocity component (horizontal velocity component). In the present invention, the channel axis line inclination angle α is 5° or more and 75° or less. By setting the angle α to 5° or more, the molten metal has a sufficient horizontal velocity component, which makes it possible to form a swirling flow in the submerged nozzle as described below. The angle α is preferably 15° or more, more preferably 25° or more. On the other hand, if the angle α is too large, it is not preferable from the viewpoint of ensuring the strength of the refractory and suppressing wear, so the angle α is set to 75° or less. The angle α is preferably 65° or less, more preferably 55° or less.

Regarding the opening of the sliding gate 1 during continuous casting, in a steady state in which the molten metal level in the tundish is constant and casting is performed at a constant casting speed, the opening of the sliding gate is fully opened (see FIG. 10). The cross-sectional area of the sliding gate passage hole is selected so that casting can be performed with the opening degree narrowed (see FIG. 11). In FIG. 11, the opening degree of the sliding gate 1 is 1/2. In this case, the opening area of the sliding gate 1 is calculated to be 0.31 times the cross-sectional area of the perfectly circular channel hole. During steady-state continuous casting, as a result of the narrowed small cross-section becoming the opening area, a high-speed flow with a small cross-section flows in the flow path on the downstream side of the slide plate 4 of the sliding gate 1. situation.

FIG. 3 shows a sliding gate in which the opening degree of the sliding gate 1 (fully opened) of the present invention having the shape shown in FIG. 2 is changed to 1/2. 3(A) is a view taken along the line AA in FIG. 3(D), in which the downstream opening 8d of the upper fixing plate 3 is partly drawn in solid lines and partly in dashed lines, and the slide plate 4 is drawn in the upstream direction. Only the aperture 8u (4) is similarly drawn with a partly solid line and a partly broken line. FIG. 3(B) is a view taken along line BB of FIG. 3(D), in which all the upstream openings 8u of the slide plate 4 are drawn with solid lines, and the downstream openings 8d are drawn with some solid lines and some broken lines. , the upstream opening 8u of the lower fixing plate 5 is also drawn with a solid line and a broken line, and the downstream opening 8d is drawn with a broken line. FIG. 3(C) is a CC arrow view of FIG. 3(D), in which all the upstream openings 8u of the lower fixing plate 5 are drawn with solid lines, and the downstream openings 8d are drawn with some solid lines and some broken lines. there is

The flow of molten metal in the passage hole of the sliding gate and in the submerged nozzle when the opening is set to 1/2 as shown in FIG. 3 will be described based on FIG. In FIG. 4, FIG. 4A is a view taken along line AA in FIG. 4, only the upstream aperture 8u is similarly drawn with a partly solid line and a partly broken line. 4(B) is a view taken along line BB in FIG. 4(D), in which the position of the downstream opening 8d (3) of the upper fixing plate 3 is indicated by a chain double-dashed line, and the upstream opening of the slide plate 4 is shown. 8u is drawn in full line, the downstream opening 8d is drawn in part in solid line and part in broken line, the upstream opening 8u of the lower fixing plate 5 is likewise drawn in part in solid line and part in broken line, and the downstream opening 8d is drawn in whole in broken line. is depicted in FIG. 4(C) is a CC arrow view of FIG. 4(D), in which the position of the downstream opening 8d (4) of the slide plate 4 is indicated by a two-dot chain line, and the upstream opening of the lower fixing plate 5 is shown. 8u is drawn entirely in solid lines, and the downstream opening 8d is drawn in partly in solid lines and partly in broken lines. Further, stream lines 18 of the molten metal are indicated by thick line arrows in FIGS. 4A to 4C, and by thick broken line arrows in FIGS.

Regarding the sliding gate 1 of FIGS. 2 and 3, as described above, the difference Δθ _N between the adjacent channel axis rotation angles θ _N is Δθ ₁ =Δθ ₂ =−135 _° . Since it is more than -180° and less than 0°, it indicates that the channel axis rotation angle θ _N changes clockwise from upstream to downstream. The molten metal flowing through the channel holes 6 of the upper fixed plate 3 flows along the channel axis direction 10 of the upper fixed plate 3 as shown in FIG. 4(A). At the contact surface between the upper fixed plate 3 and the slide plate 4, the downstream opening 8d of the upper fixed plate 3 (two-dot chain line in FIG. 4B) and the upstream opening 8u of the slide plate 4 (solid line in FIG. 4B) ) flow downstream in the small cross-section of the overlapping portion (opening). In the passage hole 6 of the slide plate 4, the downstream opening 8d of the upper fixed plate 3 (two-dot chain line in FIG. 4B) and the upstream opening 8u of the slide plate 4 (solid line in FIG. 4B) The molten metal flow flowing out from the small cross-section of the overlapping portion (opening) of the slide plate 4 along the inner wall surface (cylindrical surface) of the flow channel hole 6 as shown by the streamline 18 in FIG. The downstream opening 8d of the slide plate 4 (two-dot chain line in FIG. 4(C)) and the upstream opening 8u of the lower fixed plate 5 (solid line in FIG. 4(C)) form a swirling flow. flow out into the channel hole 6 of the lower fixing plate 5 from a small cross-section of the overlapping portion (opening portion). Inside the channel hole 6 of the lower fixed plate 5, a swirling flow is formed along the inner wall surface (cylindrical surface) of the channel hole 6 of the lower fixed plate 5, as shown by the streamline 18 in FIG. 4(C). , flows directly into the submerged nozzle 11 on the downstream side, and as shown in FIGS. move on.

When the conventional sliding gate 1 shown in FIG. 11 is used, all the kinetic energy of the molten metal flow when it flows out from the opening of the sliding gate 1 is spent on the flow velocity in the downstream direction. there is On the other hand, when the sliding gate 1 of the present invention as shown in FIG. As compared with the conventional sliding gate 1 shown in FIG. 11, it is possible to suppress the flow velocity in the downstream direction.

The difference between the channel axis rotation angles θ _N of adjacent plates to form a swirl flow in the flow channel hole 6 of the sliding gate 1 and also in the submerged nozzle downstream of the sliding gate 1 A condition for a certain angle Δθ _N will be described. As mentioned above, Δθ _N is defined as an angle within ±180°. Here, if Δθ _N is more than −10° and less than +10°, the difference between the channel axis rotation angles θ _N and θ _N+1 is too small to form a swirling flow. On the other hand, when Δθ _N is +170° or more or −170° or less, the absolute value of Δθ _N is too large, which rather hinders the formation of swirling flow. If the sliding gate 1 has two plates, only Δθ ₁ is defined and it is sufficient that the Δθ ₁ satisfies the above conditions. In addition to Δθ ₁ , Δθ ₂ and even more Δθ _N are defined when the sliding gate 1 has three or more plates. All of the Δθ _N must be 10° or more and less than 170°, or all of the angles Δθ _N must be more than -170° and -10° or less. As a result, when the channel axis direction 10 of the first and second plates changes clockwise, the third and subsequent plates also change clockwise in the same way. When the channel axis direction 10 changes counterclockwise, the third and subsequent sheets also change counterclockwise, so that a swirling flow can be effectively formed within the sliding gate. A more preferable range of Δθ _N is 30° or more and less than 165°, or more than -165° and -30° or less.

The number of plates forming the sliding gate 1 is preferably two or three. The examples shown in FIGS. 2 to 4 are for the case where the number of plates is three, as described above. In FIGS. 5 and 6, the number of plates is two, and the first plate from the upstream side constitutes the upper fixed plate 3 and the second plate constitutes the slide plate 4 . 5 shows the case when the opening is fully open, and FIG. 6 shows the case when the opening is 1/2. α=51.95°, θ ₁ =−26.57°, θ ₂ =+26.57°, Δθ ₁ =−53.14°, and a clockwise swirling flow can be formed. The reason why it is preferable that the number of plates forming the sliding gate 1 is 2 or 3 is that at least 2 plates are required to develop the throttle mechanism of the sliding gate, and 4 or more plates are unnecessary for flow rate adjustment. This is because the cost increases as the number of plates increases.

The channel hole 6 formed in the plate can also be a channel hole 6 having a shape as shown in FIG. FIG. 7 shows an example of the upper fixing plate 3. As shown in FIG. From the upstream surface 7u of the plate to the middle of the thickness, the shape of the flow passage hole 6 is a cylindrical shape with a perfectly circular cross section, and the axis of the cylinder is oriented in the downstream direction 32 perpendicular to the sliding surface. From the downstream surface 7d of the plate to the middle of the thickness, the channel hole 6 has a cylindrical shape with a perfectly circular cross section, and the axis of the cylinder is inclined from the downstream direction 32 perpendicular to the sliding surface. In the middle of the thickness of the plate, the channel hole 6 from the upstream surface 7u and the channel hole 6 from the downstream surface 7d are connected without a step. Even in a plate having channel holes 6 of such a shape, as shown in FIG. The direction facing the downstream aperture centroid 9d) can be defined as the channel axis direction 10. FIG.

The thickness of the plates constituting the sliding gate 1 may be the same, but the thickness of each plate may be different such that the slide plate 4 is the thinnest. In addition, the shape of the channel holes at the inlet and outlet of each plate of the sliding gate may be circles of the same size, but even if they are oval or elliptical, swirling flow can be obtained as long as the provisions of the present invention are met. is possible. Alternatively, the opening area may be different at the inlet and outlet of each plate.

The angle α may be the same or different for all plates.

《Water model experiment》
In order to quantitatively evaluate the horizontal component of the discharge flow during continuous casting, the velocity distribution near the discharge hole was measured by the particle image velocimetry method using a 1/1 scale water model experimental apparatus. In particular, attention was focused on the velocity distribution at a position 1.0D from the tip of the discharge hole when the gate inner diameter was D, and the average of the horizontal velocity components at that position was taken as the "horizontal direction velocity intensity". Here, the continuous casting 1/1 scale water model experiment sufficiently reproduces the molten steel flow from the viewpoint that the Froude number Fr and the Reynolds number Re match.

As the sliding gate, the sliding gate of the present invention that forms a swirling flow in the submerged nozzle (hereinafter referred to as the "present invention gate") and the conventionally used normal sliding gate (hereinafter referred to as the "normal gate"). prepared. Both the gate of the present invention and the normal gate have a plate thickness of 35 mm and a channel hole diameter of φ50 mm. Here, the channel holes match the diameter of the drill used to drill the holes in the plate.

Regarding the channel axis line inclination angle α between the channel axis direction 10 and the downstream direction perpendicular to the sliding surface 30 of the plate 2 (sliding surface perpendicular downstream direction 32), the α of the upper fixed plate 3 is changed to α ₁ , α of the plate 4 is numbered α ₂ , α of the lower fixing plate 5 is numbered α ₃ , and so on. Similarly, the upper fixed plate 3, the slide plate 4, and the lower fixed plate 5 are also used for the flow channel axis rotation angle θ, which is the angle formed by the sliding surface flow channel axis direction 31 in the clockwise direction when viewed in the vertical downstream direction 32 of the sliding surface. Each θ is numbered sequentially as θ ₁ , θ ₂ , θ ₃ .

_The gate of the present _invention has the _{shapes shown} in _FIGS . θ ₃ =−143.899° (36.101−180), forming a clockwise swirling flow in the molten steel flowing down the inner hole of the submerged nozzle. A normal gate has the shape shown in FIGS. 10 and 11, where α ₁ =α ₂ =α ₃ =0° and θ ₁ , θ ₂ , θ ₃ have no values.

The submerged nozzle 11 used was a single-hole submerged nozzle in which a discharge hole 13 was opened downward at the bottom of the submerged nozzle. As the shape of the discharge hole 13, three types shown in FIG. 12 were used. In FIG. 12A, the discharge hole 13 is a straight pipe. FIGS. 12B and 12C show an expanded tubular shape from the inner wall of the submerged nozzle toward the outlet of the discharge hole. FIG. 12(B) shows a cone type in which the discharge hole 13 expands linearly, and FIG. 12(C) shows a trumpet type in which the discharge hole 13 is smoothly curved from the inner wall. Furthermore, with regard to the straight tube single hole submerged nozzle, there is a normal straight tube single hole submerged nozzle in which the inner wall shape above the submerged nozzle is a simple cylinder, and a submerged nozzle with blades above which the blades shown in Patent Document 1 are formed. Two types of straight tube single-hole submerged nozzles were prepared.

The combinations shown in Table 1 were prepared for the sliding gate and the immersion nozzle, and a water model experiment was conducted for each of them.

For each of test condition C (invention example) and test condition E (comparative example) in Table 1, the flow velocity and flow direction of the discharge flow 19 on the downstream side of the discharge hole 13 were measured. Assuming that the inner diameter of the discharge hole is D (= 50 mm), the flow velocity and flow direction were measured at the outlet of the discharge hole, 1.0D below the discharge hole, and 2.0D below the discharge hole. The schematic diagram of the results is shown in FIG. Indicated. FIG. 13A shows test condition C (example of the present invention), and FIG. 13B shows test condition E (comparative example). As shown in FIG. 13, when a normal gate is used and a swirling flow is not imparted, the discharge flow 19 below the discharge hole 13 does not have a horizontal flow velocity component, and the flow path changes downward. The spread is also slight. On the other hand, in the case of the present invention in which a swirl flow is imparted, the discharge flow 19 below the discharge hole 13 has a horizontal flow velocity component, and the width of the flow passage increases as it goes downward. It became clear.

Table 1 also shows the measurement results of the horizontal direction velocity component strength and the casting direction velocity component strength for all test conditions A to E in Table 1.
First, when the exit shape of the discharge hole of the single-hole submerged nozzle is a straight pipe, the influence of the combination of the sliding gate (hereinafter simply referred to as "gate") and the upper internal structure of the submerged nozzle on the swirling flow was evaluated. As is clear from Table 1, when the submerged nozzle upper internal structure is a normal cylindrical structure and the combination with a normal gate (test condition E) shows a large discharge flow velocity in the casting direction, the submerged nozzle upper internal structure has vanes. It can be seen that the speed of the fluid flowing in the casting direction is small in the combination of the structure of (test condition D) with the normal gate and the combination of the gate of the present invention and the upper internal structure of the submerged nozzle with a normal cylindrical structure (test condition C). . This is because the immersion nozzle upper internal structure is a normal cylindrical structure, and the horizontal velocity that did not occur in the combination with the normal gate (test condition E) generates a swirling flow in the immersion nozzle. It is believed that this is because the structure was added with a combination of ordinary cylindrical structures (test condition C).
Next, using the gate of the present invention as a sliding gate, the effect of the exit shape of the discharge hole of the single-hole submerged nozzle was evaluated. Focusing on the outlet shape of the discharge hole of the single-hole submerged nozzle, even if the outlet shape is a straight pipe shape (test condition C), the effect of swirling suppresses the casting direction speed and adds the horizontal direction speed. On the other hand, when the outlet shape of the discharge hole is a trumpet shape (test condition A) or a chevron shape (test condition B), the effect of suppressing the speed in the casting direction and the horizontal flow are greater than those of the straight pipe shape (test condition C). The enhancement effect of directional velocity is revealed. This is believed to be due to the Coanda effect, in which the fluid flowing in the casting direction moves horizontally so that it is attracted to the trumpet-shaped or chevron-shaped wall due to the viscosity near the wall.

The present invention was applied to a bloom continuous casting apparatus (2 strands) with a ladle molten steel amount of 200 tons. The slab shape to be cast has a width of 250 mm and a thickness of 250 mm. The tundish capacity is 35 tons, and a pouring device for continuous casting is provided at the bottom of the tundish. A pouring device for continuous casting has a sliding gate for adjusting the flow rate of molten metal, and an immersion nozzle provided below the sliding gate. The sliding gate has three plates with passage holes through which the molten metal passes, and the central plate is a slide plate that can slide. The submerged nozzle is a single hole submerged nozzle.

As the sliding gate, the gate of the present invention similar to the water model experiment, a normal gate was used. Also, as the immersion nozzle, the same nozzle as in the water model experiment was used.

As a method for evaluating surface skinning due to a decrease in surface temperature, the rate of occurrence of powder entrapment defects in cast slabs after casting is taken up. The rate of occurrence of powder entrapment defects in the cast slab was evaluated as the rate of occurrence of defects caused by powder found at the product stage. Using a normal gate as a sliding gate of a pouring device for continuous casting and using a normal nozzle as an immersion nozzle (test condition E), the occurrence rate of powder entrainment defects was used as the standard (1.0), and the powder of each condition The occurrence rate of entrapment defects was indexed and defined as "slab quality".

The durability of the pouring apparatus for continuous casting was evaluated based on the longest casting time during which the refractory of the pouring apparatus for continuous casting can be used without replacement (hereinafter, "pouring time without replacement"). Using a normal gate as the sliding gate of the pouring device for continuous casting and using a normal nozzle as the immersion nozzle (test condition E), the casting time without replacement was used as the reference (1.0), and the casting time without replacement under each condition was indexed and defined as a "durability index".

Table 2 shows the conditions of the sliding gate and submerged nozzle used as the pouring device for continuous casting, and the casting results.

From Table 2, it is assumed that the bladed nozzle (test condition D) and the gate of the present invention (test conditions A to C), which generate a swirl in the hot water supply flow to the mold, improved the slab quality and reduced the hot water surface skinning in the mold. can. Furthermore, it can be seen that the cast slab quality is further improved by making the exit shape of the submerged nozzle into a chevron shape (test condition B) or a trumpet shape (test condition A). As shown in Table 1, this is in agreement with the tendency that the horizontal velocity component intensity shows a larger value when the exit shape of the discharge hole of the single-hole submerged nozzle is mountain-shaped or trumpet-shaped. In other words, it suggests that if the exit shape of the discharge hole is chevron-shaped or trumpet-shaped, the amount of heat supplied to the molten metal surface in the mold increases, and skinning of the molten metal surface in the mold is prevented. As for the durability of the refractory, the gates of the present invention (test conditions A to C) showed higher values than the bladed nozzle (test condition D), which showed the lowest value. Furthermore, it was found that the gates of the present invention (test conditions A to C) had a refractory durability index of 1.3, which was higher than that of the normal gate under test conditions E.

1 sliding gate 2 plate 3 upper fixed plate 4 slide plate 5 lower fixed plate 6 channel hole 7u upstream surface (upstream side surface)
7d downstream surface (downstream surface)
8u upstream aperture (upstream surface aperture)
8d downstream aperture (downstream surface aperture)
9u: Center of gravity of upstream aperture (center of gravity of upstream surface aperture pattern)
9d Downstream aperture center of gravity (downstream surface trench drawing center of gravity)
10 Flow path axis direction 11 Submerged nozzle 12 Submerged nozzle inner hole 13 Discharge hole 18 Stream line 19 Discharge flow 20 Continuous casting pouring device 21 Tundish 22 Mold 23 Molten metal 30 Sliding surface 31 Sliding surface flow path axis direction 32 Sliding surface vertical downstream direction 33 Sliding closing direction α Channel axis inclination angle θ Channel axis rotation angle

Claims (3)

A pouring device for continuous casting for pouring molten metal into a mold,
Having a sliding gate for adjusting the flow rate of the molten metal and an immersion nozzle provided below the sliding gate,
The sliding gate has a plurality of plates formed with passage holes through which the molten metal passes, at least one of the plates being a slidable slide plate,
The channel holes in each plate form upstream surface openings on the upstream surface of the plate surface located upstream of the molten metal passing therethrough, and form upstream surface openings on the downstream surface located downstream of the surface of the plate. Forming the apertures, the direction from the center of gravity of the upstream surface aperture pattern to the center of gravity of the downstream surface aperture pattern is defined as the channel axis direction,
The channel axis line inclination angle α formed by the channel axis direction and the downstream direction perpendicular to the sliding surface of the plate (hereinafter referred to as the “sliding surface perpendicular downstream direction”) is 5° or more and 75° or less,
The direction in which the channel axis direction is projected onto the sliding surface is called the sliding surface channel axis direction, and the direction in which the slide plate slides when the sliding gate is closed is called the sliding closing direction. The angle formed by the sliding surface flow path axis direction clockwise with respect to the closing direction when viewed in the sliding surface perpendicular downstream direction is called a flow path axis rotation angle θ (within a range of ±180 degrees). The axis line rotation angle θ differs between adjacent plates, and the θ of the plate on the most upstream side is θ ₁ , the θ of the plate one downstream of that is θ ₂ , and the θ of the plate one further downstream is θ Numbered in order from ₃ , and Δθ _N = θ _N - θ _N+1 (N is an integer of 1 or more and up to the number of plates - 1),
All the angles Δθ _N are 10° or more and less than 170° to form a counterclockwise swirling flow in the submerged nozzle, or all the angles Δθ _N are more than -170° and -10° or less and the submerged nozzle Form a clockwise swirl flow in
A pouring apparatus for continuous casting, wherein the submerged nozzle has a single discharge hole opened at the bottom of the submerged nozzle. 2. The pouring apparatus for continuous casting according to claim 1, wherein the shape of the discharge hole of the submerged nozzle is formed so as to have an expanded tubular shape from the inner wall of the submerged nozzle toward the outlet of the discharge hole. 3. The pouring apparatus for continuous casting according to claim 1, wherein the number of plates forming the sliding gate is two or three and the number of slide plates is one.

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