EP4368311A1

EP4368311A1 - Immersion nozzle

Info

Publication number: EP4368311A1
Application number: EP21949359.0A
Authority: EP
Inventors: Kanae Nishio; Hiroyasu NIITSUMA; Riccardo CONTE
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2021-07-09
Filing date: 2021-07-09
Publication date: 2024-05-15
Also published as: KR20240034747A; JP7427138B2; CN117580657A; CA3223418A1; JPWO2023281726A1; WO2023281726A1

Abstract

A flow channel 21 in a first section 2 has a lateral cross-sectional shape that is a circular shape. A flow channel 41 in a second section 4 has a lateral cross-sectional shape that is a rectangular shape. A flow channel 31 in a connection section 3 has a shape with which the flow channel 21 in the first section 2 is continuously connected to the flow channel 41 in the second section 4. The rectangular shape of the second section 4 has long sides each having a length a and short sides each having a length b, with a ratio a/b between the length a and the length b being 3 or greater and 7 or less. The flow channel 41 in the second section 4 has a cross-sectional area S₂, the flow channel 21 in the first section 2 has a cross-sectional area S₁, and the cross-sectional area S₂ is larger than S₁. The openings 5 include two first openings 51 and two second openings 52. The first openings 51 are open, in one-to-one correspondence, in two side faces 44 of the second section 4. One second opening 52A of the two second openings 52 is open while extending from one side face 44A of the two side faces 44 to a bottom face 45 of the second section 4. Another one second opening 52B of the two second openings 52 is open while extending from another one side face 44B of the two side faces 44 to the bottom face 45 of the second section 4.

Description

Technical Field

The present invention relates to an immersion nozzle to be used to continuously cast thin slabs.

Background Art

Attention has been directed to omission of a slab heating process and energy-saving effects achieved by so-called direct coupling, i.e. directly coupling continuous casting and hot rolling of a resulting slab. To realize this, thinner slabs on the continuous casting side are being sought. When casting a thin slab (e.g. with a thickness of 200 mm or less), a mold needs to be flattened, and necessarily an immersion nozzle also needs to be flattened (e.g. Patent Document 1).

Prior Art Documents

Patent Documents

Patent Document 1: JP H08-039208A

Summary of Invention

Technical Problem

Especially, skinning is often problematic in thin-slab casting. This is because the surface temperature of thin slabs is more likely to drop than that of ordinary slabs due to the large slenderness ratio of the area of a molten steel surface, and the larger the nozzle cross-sectional area of an immersion section is, the more likely the temperature drops due to heat removal using the nozzle.
According to the immersion nozzle described in Patent Document 1, it is possible to prevent sticking of base metal that occurs between the immersion nozzle and a mold wall and skinning on a molten metal surface that occurs near the short sides of a wide mold, as well as the occurrence of a molten metal suction phenomenon, remelting of a solidifying shell, and the like. However, it cannot be said that the immersion nozzle described in Patent Document 1 sufficiently suppresses skinning in a meniscus part.
There is demand for realization of an immersion nozzle capable of suppressing skinning in a meniscus part in thin-slab continuous casting.

Solution to Problem

An immersion nozzle according to the present invention is an immersion nozzle having a flow channel and openings; the immersion nozzle comprising: a first section; a connection section; and a second section, the first section, the connection section, and the second section being provided in this order from a base end side, wherein the flow channel in the first section has a lateral cross-sectional shape that is a circular shape, the flow channel in the second section has a lateral cross-sectional shape that is a rectangular shape, the flow channel in the connection section has a shape with which the flow channel in the first section is continuously connected to the flow channel in the second section, the rectangular shape of the second section has long sides each having a length a and short sides each having a length b, with a ratio a/b between the length a and the length b being 3 or greater and 7 or less, the flow channel in the second section has a cross-sectional area S₂, the flow channel in the first section has a cross-sectional area S₁, and the cross-sectional area S₂ is larger than the cross-sectional area S₁, the openings include two first openings and two second openings, the first openings are open, in one-to-one correspondence, in two side faces of the second section that correspond to the two short sides, one of the two second openings is open while extending from one of the two side faces to a bottom face of the second section, the bottom face being a face at a leading end of the second section, and another one of the two second openings is open while extending from another one of the two side faces to the bottom face.
Using the immersion nozzle having the above configuration in thin-slab continuous casting can suppress skinning in the meniscus part.
Preferred examples of the present invention will be described in detail below. Note that the following preferred examples are not intended to limit the scope of the present invention.
In the immersion nozzle according to the present invention, it is preferable as one aspect that each of the first openings has an opening area S₃ in a corresponding one of the side faces, each of the second openings has an opening area S₄ in a corresponding one of the side faces and an opening area S₅ in the bottom face, and the opening areas S₃, S₄, and S₅ satisfy expressions (1) and (2) below: $S_{4} < S_{5}$
$(S_{4} + S_{5}) / S_{3} \geq 1.5$
A discharge flow discharged from the nozzle hits a short side of the mold and separates into an upward flow and a downward flow. Here, if the upward flow is excessively strong, powder entrainment or the like is likely to occur, while if the downward flow is excessively strong, inclusions, bubbles, or the like is unlikely to rise to the surface. According to the above configuration, the balance between the upward flow and the downward flow is optimized, and an excessive meniscus flow can be suppressed.
In the immersion nozzle according to the present invention, it is preferable as one aspect that each of the first openings has an opening area S₃ in a corresponding one of the side faces and an opening area S₆ on a flow channel side, and the opening area S₃ is smaller than the opening area S₆.
According to this configuration, the occurrence of a suction flow in the first opening can be suppressed.
In the immersion nozzle according to the present invention, it is preferable as one aspect that the immersion nozzle has a largest width of 300 mm or less.
According to this configuration, workability is improved when implementing work to replace the immersion nozzle using a quick changer. This enables the nozzle to be quickly changed during casting, which can meet the increasing need to cast high-grade steel types that involve strict casting conditions in thin-slab continuous casting.
Further features and advantages of the present invention will become clearer with the description of the following illustrative and non-limiting embodiments, which are described with reference to the drawings.

Brief Description of Drawings

FIG. 1 is a front cross-sectional view of a nozzle according to an embodiment.
FIG. 2 is a side cross-sectional view (cross-sectional view taken along a line II-II in FIG. 1) of the nozzle according to the embodiment.
FIG. 3 is a lateral cross-sectional view (cross-sectional view taken along a line III-III in FIG. 1) of a first section of the nozzle according to the embodiment.
FIG. 4 is a lateral cross-sectional view (cross-sectional view taken along a line IV-IV in FIG. 1) of a second section of the nozzle according to the embodiment.
FIG. 5 is a side view of the second section of the nozzle according to the embodiment.
FIG. 6 is a bottom view of the second section of the nozzle according to the embodiment.

Description of Embodiments

An embodiment of the immersion nozzle according to the present invention will be described with reference to the drawings. The following is a description of an example where the immersion nozzle according to the present invention is applied to an immersion nozzle 1 (hereinafter referred to simply as a "nozzle 1"), which is used to slab continuous casting with a mold thickness of 200 mm or less.

Overall configuration of immersion nozzle

The nozzle 1 is a tubular member made of a refractory material. A flow channel for allowing molten steel to flow is formed inside the nozzle 1, which has openings 5 at a leading end. The nozzle 1 has a first section 2, a connection section 3, and a second section 4 in this order from a base end side, and these sections have different shapes (FIGS. 1 and 2). The nozzle 1 is joined to upstream equipment (such as a stopper or a sliding nozzle; not shown) at the first section 2, and molten steel flowing from the upstream equipment flows through the flow channel. The second section 4 includes the openings 5 (first openings 51 and second openings 52), from which the molten steel flows out to a mold (not shown).
The type of refractory material that constitutes the nozzle 1 is not specifically limited, and may be any refractory material conventionally used in this field. Examples of such refractory materials include alumina-graphite, magnesia-graphite, spinel-graphite, zirconia-graphite, calcium zirconate-graphite, high-alumina, alumina-silica, silica, zircon, and spinel. Zone lining may also be applied as appropriate.
The following description mentions directions based on the orientation shown in FIG. 1. That is, when mentioning the up-down direction, "up" (including upper part, above, upper side, upstream etc.) refers to the base end side (first section 2 side), and "down" (including lower part, below, lower side, downstream etc.) refers to the leading end side (second section 4 side).
Also, when mentioning a cross section of the flow channel, it refers to a cross section in a direction orthogonal to the above-defined up-down direction (a direction orthogonal to the paper plane of FIG. 1), and this cross section is referred to as a lateral cross section, unless otherwise stated. Note that when the nozzle 1 is used, molten steel flows from the above-defined upper side toward the above-defined lower side. Thus, the above-defined lateral cross section is also a cross section relative to the flow direction of the molten steel.

Configuration of first section

The first section 2 is a main section on the base end side of the nozzle 1. The lateral cross section of a flow channel 21 in the first section 2 has a circular shape (FIGS. 1 to 3). Note that the circular shape as used herein is not limited to a circular shape in the mathematical sense, and may be a shape that can be dealt with as a substantially circular shape. Accordingly, a deviation (tolerance etc.) from a mathematically circular shape that may occur in an attempt to realize a circular shape as an industrial product is acceptable. A cross-sectional area S₁ of the flow channel 21 in this embodiment is 6000 mm².

Configuration of second section

The second section 4 is a main section on the leading end side of the nozzle 1. The lateral cross section of a flow channel 41 in the second section 4 has a rectangular shape (FIGS. 1, 2 and 4). Note that the rectangular shape as used herein is not limited to a rectangular shape in the mathematical sense, and may be a shape that can be dealt with as a substantially rectangular shape. Accordingly, deformation (chamfering etc.) that is ordinarily applied in an attempt of realizing a rectangular shape as an industrial product may be imparted, and a deviation (tolerance etc.) from a mathematically rectangular shape is acceptable.
A cross-sectional area S₂ of the flow channel 41 in this embodiment is 10000 mm². Accordingly, the cross-sectional area S₂ of the flow channel 41 is greater than the cross-sectional area S₁ of the flow channel 21. The flow velocity of molten steel discharged from the openings 5 is reduced by thus making the cross-sectional area in the downstream area (flow channel 41) larger than the cross-sectional area in the upstream area (flow channel 21). This causes an upward flow in the mold and suppresses an excessive meniscus flow.
In the lateral cross-sectional shape of the flow channel 41 in this embodiment, the rectangle has long sides 42 each having a length a of 200 mm, and short sides 43 each having a length b of 50 mm (FIG. 4). Thus, the ratio a/b between the lengths a and b is 4.0. Note that numerical values of the rectangular shape are not limited to the above values and may be changed in the range of the ratio a/b from 3 to 7. If the ratio a/b is changed, both the length a of the long sides 42 and the length of the short sides 43 of the rectangular shape may be changed. Meanwhile, the length b of the short sides 43 is restricted by the length of the short sides of the mold, and the length a of the long sides 42 is, therefore, more flexible in general.
The ratio a/b being in the range from 3 to 7 makes a molten steel flow unlikely to detach from the wall face of the flow channel 41 and allows for an appropriate flow. In contrast, the ratio a/b being less than 3 makes the length a of the long sides 42 excessively small and makes it difficult to secure an inner tube cross-sectional area necessary for casting. Further, the ratio a/b being greater than 7 makes the length a of the long sides 42 excessively large and makes the weight of the nozzle 1 more likely to increase, which may increase the load of a worker or a device that handles the nozzle 1. In addition, the ratio a/b being greater than 7 may cause the flow channel 31 to be steeply deformed in the longitudinal direction of the connection section 3 and may detach the molten steel flow from the wall face of the flow channel.
The lateral cross-sectional shape of the substantial part (refractory material part) of the second section 4 also has a rectangular shape in correspondence with the rectangular shape of the lateral cross section of the flow channel 41. Thus, the second section 4 has a bottomed rectangular column shape. A face of the rectangular shape that corresponds to each long side 42 has a width W of 270 mm, which is the largest width of the nozzle 1. The largest width W of the nozzle 1 thus being less than 300 mm improves workability when implementing work to replace the nozzle 1 using a quick changer, which is favorable. This is because the largest width W of the nozzle 1 being less than 300 mm makes it easier to secure room for the work to replace the nozzle 1 within the mold due to the dimensional relationship between the nozzle 1 and the mold.

Configuration of opening

The first openings 51 are open in side faces 44 of the second section 4 that correspond to the short sides 43 of the rectangular shape (FIGS. 1 and 5). Two first openings 51 are provided. The two first openings 51 (51A and 51B) are open in two side faces 44 (44A and 44B) corresponding to two short sides 43 (43A and 43B) in one-to-one correspondence. The first openings 51 being open in the side faces 44 allow the molten steel flow to be discharged toward the short sides of the mold. This can cause an upward flow in the mold and promote heat supply to a meniscus.
Also, two second openings 52 are open while extending between the side faces 44 and a bottom face 45, which is a face of the second section 4 at the leading end in the longitudinal direction (FIGS. 1, 5 and 6). Of the two second openings 52, one second opening 52A is open while extending between the side face 44A (one side face) and the bottom face 45, and the other second opening 52B is open while extending between the side face 44B (the other side face) and the bottom face 45. The second openings 52 being open in the above mode allow the molten steel flow to be discharged to the lower side of the mold and enable appropriate distribution of the molten steel flow in the mold.
In this embodiment, an opening area S₃ of each first opening 51 in the corresponding side face 44 (the area of the first opening 51 shown in FIG. 5) is 2700 mm². An opening area S₄ of each second opening 52 in the corresponding side face 44 (the area of the second opening 52 shown in FIG. 5) is 2000 mm², and an opening area S₅ thereof in the bottom face 45 (the area of the second opening 52 shown in FIG. 6) is 5000 mm². Based on the above opening areas, the following expressions (1) and (2) hold. $S_{4} < S_{5}$
$(S_{4} + S_{5}) / S_{3} \geq 1.5$
The first openings 51 and the second openings 52 having the opening areas that satisfy the expressions (1) and (2) can optimize the balance between the upward flow and the downward flow and suppress an excessive meniscus flow. Note that the opening area S₃ of the first openings 51 and the opening areas S₄ and S₅ of the second openings 52 are not limited to the above values and may be changed as long as the expressions (1) and (2) are satisfied.
In this embodiment, an opening area S₆ of each first opening 51 on the flow channel 41 side is 4000 mm². Accordingly, the opening area S₃ of each first opening 51 in the side face 44 is smaller than the opening area S₆ on the flow channel 41 side.
Adopting a configuration in which the opening area S₆ of each first opening 51 on the flow channel 41 side is greater than or equal to the opening area S₃ thereof in the side face 44 gradually decreases the cross-sectional area of the flow channel toward outlets of the molten steel flow in the flow direction, and thus rectifies the molten steel flow. This suppresses the occurrence of a suction flow in an upper part of the first opening 51 and makes it easier for the molten steel to be smoothly discharged from the entire first openings 51.

Configuration of connection section

The connection section 3 is a section that continuously connects the first section 2 to the second section 4 (FIGS. 1 and 2). The connection section 3 includes a flow channel 31 having a shape that continuously connects the flow channel 21 in the first section 2 having a circular cross-sectional shape to the flow channel 41 in the second section 4 having a rectangular cross-sectional shape. The cross-sectional shape of the flow channel 31 is, therefore, circular at an upper end 32 and rectangular at a lower end 33.

Other Embodiments

Lastly, other embodiments of the immersion nozzle according to the present invention are described. Note that the configuration disclosed in the following embodiments can also be applied in combination with configurations disclosed in other embodiments as long as no contradiction arises.
In the above embodiment, a description has been given of an example of a configuration in which the opening areas S₃, S₄, S₅, and S₆ of the openings 5 (first openings 51 and second openings 52) satisfy the expressions (1) and (2), and S₃ is smaller than Se. However, the immersion nozzle according to the present invention need not satisfy at least either the expressions (1) or (2), and S₃ may be greater than S₆.
In the above embodiment, a description has been given of an example of a configuration in which the largest width W of the nozzle 1 is 270 mm, which is less than 300 mm. However, the largest width of the immersion nozzle according to the present invention may be 300 mm or greater.
Regarding other configurations as well, it should be understood that the embodiments disclosed herein are in all respects illustrative and the scope of the present invention is not limited thereby. Those skilled in the art would readily understand that modifications can be made as appropriate without departing from the gist of the present invention. Therefore, other embodiments modified without departing from the gist of the present invention are naturally encompassed in the scope of the present invention.

Examples

The present invention will be further described below by describing examples. However, the present invention is not limited by the following example.

Test method

Nozzles with various dimensional conditions were designed, and numerical fluid dynamics calculations were performed for modes of discharged molten steel flow using fluid analysis software PHOENICS produced by CHAM-japan. The dimensional conditions for examples and comparative examples are as listed in Tables 1 below. Flow velocity contour plots were output based on the calculation results. Note that the following parameters were applied in the calculations.

Number of calculation cells: Approximately 500,000 (which may vary depending on the model)
Fluid: Molten steel (1560 °C, density: 7.08 g/cm³)
Casting speed: 4 tons per minute
Mold size: 1200 mm × 150 mm

Evaluation of meniscus flow velocity

Meniscus flow velocities were identified based on the output flow velocity contour plots for the examples and comparative examples. The results were evaluated on a three-point scale from A to C, according to the value of meniscus velocity.

A: Meniscus flow velocity is 10 cm/second or greater and 25 cm/second or less.
B: Meniscus flow velocity is greater than 25 cm/second and 35 cm/second or less.
C: Meniscus velocity is less than 10 cm/second or greater than 35 cm/second.

Detachment of molten steel flow

For the examples and comparative examples, the output flow velocity contour plots were visually checked to identify the occurrence of detachment of the molten steel flow in the second section 4, and the results were judged (A or C).

A: Molten steel flow along the wall surface is formed in the entire area of the second section 4.
C: Detachment of molten steel flow is observed in the second section 4.

Suction flow in first opening

For the examples and comparative examples, the output flow velocity contour plots were visually checked to identify the presence and extent of a suction flow in the first openings 51. The results were evaluated on a three-point scale from A to C, according to the observed states.

.A: Molten steel flow is discharged from the first openings 51 without stagnation.
B: Stagnation of the molten steel flow is recognized near the first openings 51.
C: A suction flow into the first opening 51 is recognized.

Results

Table 1 shows the dimensional conditions and evaluation results for the examples and comparative examples. In examples 1 to 6, where the ratio a/b was in the range from 3 to 7, the evaluation result regarding detachment of the molten steel flow was A. In contrast, in a comparative example 1, where the ratio a/b was 8.0, the evaluation result regarding detachment of the molten steel flow was C. In the examples 1 to 6, where S₂ was greater than S₁, the meniscus flow velocity was within an appropriate range (rated A or B). In contrast, in a comparative example 2, where S₂ was smaller than S₁, the meniscus flow velocity was not in a favorable range (rated C).

Note that in the examples 3 to 6, where S₃, S₄, and S₅ satisfied the expression (2), the meniscus flow velocity was within a more preferable range than in the examples 1 and 2, where S₃, S₄, and S₅ did not satisfy the expression (2). In the examples 5 and 6, where S₃ was smaller than S₆, more favorable results were obtained in terms of a suction flow in the first openings than in the example 1, where S₃ was equal to S₆, and the examples 2 to 4, where S₃ was greater than S₆.

[Table 1]

		Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6	Comp. Ex. 1	Comp. Ex 2
Long side length a	[mm]	300	300	250	350	200	300	400	300
Short side length b	[mm]	70	100	70	70	60	50	50	50
Ratio a/b	-	4.3	3.0	3.6	5.0	3.3	6.0	8.0	6.0
Flow channel cross-sectional area in first section S₁	[mm²]	5027	5027	5027	2827	2827	1963	2827	2827
Flow channel cross-sectional area in second section S₂	[mm²]	7800	15600	6300	9300	3200	2600	3600	2600
Size relationship betw. S₁ and S₂	-	S₂ > S₁	S₂ > S₁	S₂ > S₁	S₂ > S₁	S₂ > S₁	S₂ > S₁	S₂ > S₁	S₂ < S₁
Opening area of first opening (side) S₃	[mm²]	2400	4800	1500	2000	1500	1000	1000	1000
Opening area of second opening (side) S₄	[mm²]	600	1800	900	1200	900	600	1600	1600
Opening area of first opening (bottom) S₅	[mm²]	2700	3300	2550	4050	2250	3300	1500	1500
Opening area of first opening (flow channel side) S₆	[mm²]	2400	4200	1440	1920	1800	1200	800	800
Size relationship betw. S₄ and S₅	-	S₄ < S₅	S₄ < S₅	S₄ < S₅	S₄ < S₅	S₄ < S₅	S₄ < S₅	S₄ > S₅	S₄ > S₅
(S₄+S₅)/S₃	-	1.4	1.1	2.3	2.6	2.1	3.9	3.1	3.1
Size relationship betw. S₃ and S₆	-	S₃ = S₆	S₃ > S₆	S₃ > S₆	S₃ > S₆	S₃ < S₆	S₃ < S₆	S₃ > S₆	S₃ > S₆
Meniscus flow velocity		B	B	A	A	A	A	C	C
Detachment of molten steel flow		A	A	A	A	A	A	C	A
Suction flow in first opening		B	B	B	B	A	A	C	C

Industrial Applicability

The present invention can be used in an immersion nozzle for thin-slab continuous casting, for example.

Description of Reference Signs

1: Immersion nozzle
2: First section
21: Flow channel
3: Connection section
31: Flow channel
32: Upper end of connection section
33: Lower end of connection section
4: Second section
41: Flow channel
42: Long side
43: Short side
44: Side face
45: Bottom face
5: Opening section
51: First opening
52: Second opening

Claims

An immersion nozzle (1) having a flow channel and openings; the immersion nozzle (1) comprising:
a first section (2);

a connection section (3); and

a second section (4),

the first section (2), the connection section (3), and the second section (4) being provided in this order from a base end side,

wherein the flow channel (21) in the first section (2) has a lateral cross-sectional shape that is a circular shape,

the flow channel (41) in the second section (4) has a lateral cross-sectional shape that is a rectangular shape,

the flow channel (31) in the connection section (3) has a shape with which the flow channel (21) in the first section (2) is continuously connected to the flow channel (41) in the second section (4),

the rectangular shape of the second section (4) has long sides (42) each having a length a and short sides (43) each having a length b, with a ratio a/b between the length a and the length b being equal to, or greater than, 3 and equal to, or less than, 7,

the flow channel (41) in the second section (4) has a cross-sectional area S₂, the flow channel (21) in the first section (2) has a cross-sectional area S₁, and the cross-sectional area S₂ is larger than the cross-sectional area S₁,

the openings include two first openings (51) and two second openings (52),

the first openings (51) are open, in one-to-one correspondence, in two side faces (44) of the second section (4) that correspond to the two short sides (43),

one of the two second openings (52) is open while extending from one of the two side faces (44) to a bottom face (45) of the second section (4), the bottom face (45) being a face at a leading end of the second section (4), and

another one of the two second openings (52) is open while extending from another one of the two side faces (44) to the bottom face (45).
The immersion nozzle according to claim 1,
wherein each of the first openings (51) has an opening area S₃ in a corresponding one of the side faces (44), each of the second openings (52) has an opening area S₄ in a corresponding one of the side faces (44) and an opening area S₅ in the bottom face (45), and the opening areas S₃, S₄, and S₅ satisfy expressions (1) and (2) below: $S_{4} < S_{5}$
and $(S_{4} + S_{5}) / S_{3} \geq 1.5$
The immersion nozzle according to claim 1 or 2,
wherein each of the first openings (51) has an opening area S₃ in a corresponding one of the side faces (44) and an opening area S₆ on a flow channel side, and the opening area S₃ is smaller than the opening area S₆.
The immersion nozzle according to any one of claims 1 to 3, wherein the immersion nozzle has a maximum width of 300 mm or less.