RU2825349C2 - Immersion nozzle - Google Patents

Abstract

FIELD: foundry.

SUBSTANCE: invention relates to continuous casting. Immersion nozzle with flow channel and holes comprises first (2) and second (4) sections and connecting section (3) arranged between them. Cross-section of flow channel (21) in the first section has a round shape, in the second section it has a rectangular shape, and in the connection section a shape providing for continuous connection of the flow channel in the first and second sections. Cross-section area S₂ of flow channel (41) of the second section is larger than cross-section area S₁ of flow channel (21) of the first section. Second section of rectangular shape has long sides, each of which has length a, and short sides, each of which has length b, wherein ratio a/b is 3 or more and 7 or less. Holes (5) have two first holes (51) and two second holes (52). First holes are made one by one on two side surfaces of the second section corresponding to the two said short sides. Two second holes pass each through one of two side surfaces to the lower surface of the second section.

EFFECT: preventing formation of crust on convex-concave part of thin slabs during continuous casting.

4 cl, 6 dwg, 1 tbl, 1 ex

Description

Field of technology to which the invention relates

The present invention relates to a submersible nozzle intended for continuous casting of thin slabs.

State of the art

It is known that attention was paid to eliminating the slab heating process and achieving energy savings through the so-called direct combination, i.e. direct combination of continuous casting and hot rolling of the resulting slab. For this purpose, thinner slabs are identified on the continuous casting side. When casting a thin slab (e.g. 200 mm or less thick), it is necessary to align the mold and the immersion nozzle (e.g. known from Patent Document No. 1).

Documents known from the prior art: Patent document No. 1 - JP H08-039208A.

Disclosure of invention

In particular, when casting thin slabs, casting skin often causes problems. This is because the surface temperature of thin slabs is more likely to be lower than that of ordinary slabs due to the large flexibility coefficient of the molten steel surface area, and the larger the cross-sectional area of the immersion section nozzle, the greater the likelihood of the temperature being reduced due to heat dissipation when using the nozzle.

According to the structure of the immersion nozzle described in Patent Document 1, it is possible to prevent the adhesion of the base metal that occurs between the immersion nozzle and the mold wall and the formation of a crust on the surface of the molten metal that occurs near the short sides of the wide mold, as well as the suction of the molten metal, the remelting of the solidifying shell, and the like. However, it cannot be said that the immersion nozzle known from Patent Document 1 sufficiently suppresses the formation of the casting crust in the convex-concave portion.

There is a need to create a submersible nozzle capable of suppressing the formation of a crust on a convex-concave part during continuous casting of thin slabs.

Solution to the problem

The immersion nozzle according to the present invention is a immersion nozzle having a flow channel and openings; wherein the immersion nozzle comprises: a first section; a connecting section; and a second section, wherein the first section, the connecting section and the second section extend in the specified order from the end face of the base, and the flow channel in the first section has a longitudinal cross-sectional shape, that is, a circular shape, the flow channel in the second section has a longitudinal cross-sectional shape, that is, a rectangular shape, the flow channel in the connecting section has a shape in which the flow channel in the first section is in constant communication with the flow portion in the second section, the rectangular shape of the second section has long sides, each of which has a length a, and short sides, each of which has a length b, wherein the ratio a/b between the length a and the length b is 3 or more and 7 or less, the flow channel in the second section has a cross-sectional area S ₂ , the flow channel in the first section has a cross-sectional area S ₁ , wherein the cross-sectional area S ₂ is larger than the cross-sectional area S ₁ , the openings include two first openings and second openings, the first openings are open in accordance with one to one on two side surfaces of the second section, which correspond to the two short sides, one of the two second openings is open and extends from one of the two side surfaces from the bottom side of the second section, wherein the bottom surface is the surface at the front end of the second section, and the second of the two second openings is open and extends from the other of the two side surfaces to the bottom surface.

The use of a submersible nozzle having the above configuration in continuous casting of thin slabs makes it possible to suppress the formation of casting skin in the convex-concave part.

Preferred embodiments of the present invention will be described in detail below. The following preferred embodiments do not limit the scope of the present invention.

In the immersion nozzle according to the present invention, it is preferable as one embodiment that each of the first openings has an opening area S ₃ on the corresponding one of the side surfaces, each of the second openings has an opening area S ₄ on the corresponding one of the side surfaces and an opening area S ₅ on the lower face, and the opening areas S ₃ , S ₄ and S ₅ satisfy expressions (1) and (2) given below:

S ₄ < S ₅ , (1)

(S ₄ + S ₅ ) / S ₃ ≥ 1.5, (2)

The discharge flow coming out of the nozzle hits the short side of the mold and is divided into an ascending flow and a descending flow. If the ascending flow is too large, powder entrainment or the like may occur, and if the descending flow is too large, there is a low probability that inclusions, bubbles, etc. will rise to the surface. According to the above device configuration, the balance between the ascending flow and the descending flow is optimized, and the excessive flow in the convex-concave part can be suppressed.

In the immersion nozzle according to the present invention, it is preferable as one variant that each of the first openings has an opening area S ₃ on the corresponding one of the side surfaces and an opening area S ₆ on the side of the flow channel, wherein the opening area S ₃ is less than the opening area S ₆ .

According to this implementation, the occurrence of suction flow in the first hole can be suppressed.

In the immersion nozzle according to the present invention, it is preferable, as one embodiment, that the immersion nozzle has a greatest width of 300 mm or less.

According to this implementation, the workability of the immersion nozzle replacement work is improved using the quick-change device. This enables the nozzle to be quickly changed during casting to meet the growing demand for casting high-quality steels that require strict conditions in the continuous casting of thin slabs.

Other features and advantages of the present invention will become more apparent from the description of the following illustrative and non-limiting embodiments, which are described with reference to the drawings.

Brief description of the 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 along line II-II in Fig. 1) of a nozzle according to an embodiment.

Fig. 3 is a side cross-sectional view (cross-sectional view along line III-III in Fig. 1) of a first section of a nozzle according to an embodiment.

Fig. 4 is a side cross-sectional view (cross-sectional view along line IV-IV in Fig. 1) of a second section of a nozzle according to an embodiment.

Fig. 5 is a side view of the second section of the nozzle according to an embodiment.

Fig. 6 is a bottom view of a second section of a nozzle according to an embodiment.

Implementation of the invention

An embodiment of a immersion nozzle according to the present invention will be described with reference to the drawings. Below, an example is described in which the immersion nozzle according to the present invention denotes a immersion nozzle 1 (hereinafter referred to as "nozzle 1"), which is used for continuous casting of slabs with a mold thickness of 200 mm or less.

General configuration of the immersion nozzle

The nozzle 1 is a tubular element made of a refractory material. Inside the nozzle 1, having openings 5 at the front end, a flow channel is formed, allowing molten steel to flow. The nozzle 1 has a first section 2, a connecting section 3 and a second section 4 in this order from the end side of the base, and these sections have different shapes (Figs. 1 and 2). The nozzle 1 is connected to upstream equipment (for example, a plug or a sliding nozzle; not shown) in the first section 2, and molten steel flowing out of the upstream equipment flows through the flow channel. The second section 4 contains openings 5 (first openings 51 and second openings 52), from which molten steel flows into a mold (not shown).

The type of refractory material from which the nozzle 1 is made may be any refractory material traditionally used in this field. Examples of such refractory materials include alumina-graphite, magnesia graphite, spinel-graphite, zirconia-graphite, calcium zirconate-graphite, high alumina, alumina-silicon dioxide, silicon dioxide, zircon and spinel. If necessary, zonal lining can also be applied.

In the following description, directions are indicated based on the orientation shown in Fig. 1. When the up-down direction is mentioned, “up” (including the upper part, top, upper side, upstream, etc.) refers to the base end side (the first section 2 side), and “down” (including the lower part, bottom, lower side, downstream, etc.) refers to the front end side (the second section 4 side).

In addition, when the cross-section of the flow channel is mentioned, it refers to the cross-section in the direction orthogonal to the above-mentioned up-down direction (the direction orthogonal to the plane of the paper in Fig. 1), and this cross-section is called a longitudinal cross-section unless otherwise specified. When the nozzle 1 is used, the molten steel flows from the above-mentioned upper side to the above-mentioned lower side. Therefore, the above-mentioned longitudinal cross-section is also a cross-section with respect to the flow direction of the molten steel.

Configuration of the first section

The first section 2 is a main section on the end side of the base of the nozzle 1. The longitudinal cross-section of the flow channel 21 in the first section 2 has a circular shape (Figs. 1 to 3). The circular shape used here is not limited to a circular shape in a mathematical sense and may be a shape that can be regarded as a substantially circular shape. Accordingly, the deviation (tolerance, etc.) from the mathematically circular shape that may occur when attempting to realize the circular shape as an industrial product is acceptable. The cross-sectional area S ₁ of the flow channel 21 in this embodiment is 6000 mm ² .

Configuration of the second section

The second section 4 is a main section on the front end side of the nozzle 1. The longitudinal cross-section of the flow channel 41 in the second section 4 has a rectangular shape (Fig. 1, 2 and 4). The rectangular shape used here is not limited to a rectangular shape in the mathematical sense and may be a shape that can be regarded as a substantially rectangular shape. Accordingly, a deformation (chamfering, etc.) that is usually applied when trying to give a rectangular shape to an industrial product can be imparted, and a deviation (tolerance, etc.) from a mathematically rectangular shape is allowed.

The 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 larger than the cross-sectional area _S1 of the flow channel 21. The flow rate of the molten steel discharged from the openings 5 is reduced due to the fact that the cross-sectional area in the downstream region (flow channel 41) becomes larger than the cross-sectional area in the upstream region (flow channel 21). This causes an upward flow in the mold and suppresses excessive spreading in the convex-concave portion.

In the shape of the longitudinal cross-section of the flow channel 41 in this embodiment, the rectangle has long sides 42, each of which has a length a equal to 200 mm, and short sides 43, each of which has a length b equal to 50 mm (Fig. 4). Thus, the ratio a/b between the lengths a and b is 4.0. The numerical values of the rectangular shape are not limited to the above values and can be changed in the range of the ratio a/b from 3 to 7. If the ratio a/b is changed, then both the length a of the long sides 42 and the length of the short sides 43 of the rectangular shape can be changed. In this case, the length b of the short sides 43 is limited by the length of the short sides of the shape, and the length a of the long sides 42, therefore, generally allows for changes in a wider range.

The ratio a/b in the range from 3 to 7 makes it unlikely that the molten steel flow will separate from the wall surface of the flow channel 41 and ensures the appropriate flow. On the contrary, the ratio a/b of less than 3 makes the length a of the long sides 42 excessively small and makes it difficult to ensure the cross-sectional area of the inner tube required for casting. In addition, the ratio a/b exceeding 7 makes the length a of the long sides 42 excessively large and increases the likelihood of increasing the weight of the nozzle 1, which may increase the load on the workers or the device that moves the nozzle 1. In addition, the ratio a/b exceeding 7 may lead to a sharp deformation of the flow channel 31 in the longitudinal direction of the connecting section 3 and to a separation of the molten steel flow from the wall surface of the flow channel.

The longitudinal cross-sectional shape of the main part (the refractory part) of the second section 4 also has a rectangular shape in accordance with the rectangular shape of the longitudinal cross-section of the flow channel 41. Thus, the second section 4 has the shape of a rectangular column with a bottom. The rectangular-shaped face that corresponds to each long side 42 has a width W equal to 270 mm, which is the largest width of the nozzle 1. Thus, the largest width W of the nozzle 1, which is less than 300 mm, improves the convenience of processing when performing work on replacing the nozzle 1 using the quick-change device, which is a positive effect of the invention. This is explained by the fact that the largest width W of the nozzle 1, which is less than 300 mm, provides more space for the work on replacing the nozzle 1 inside the mold due to the size ratio between the nozzle 1 and the mold.

Making holes

The first openings 51 are opened in the side surfaces 44 of the second section 4, which correspond to the short sides 43 of the rectangular shape (Fig. 1 and 5). Two first openings 51 are provided. The two first openings 51 (51A and 51B) are opened on two side surfaces 44 (44A and 44B), corresponding to two short sides 43 (43A and 43B), in a one-to-one correspondence. The first openings 51, opened on the side surfaces 44, allow the flow of molten steel to be diverted to the short sides of the mold. This can cause an upward flow in the mold and promote the supply of heat to the convex-concave part.

In addition, two second openings 52 are open and extend between the side surfaces 44 and the lower surface 45, which is the surface of the second section 4 at the front end in the longitudinal direction (Fig. 1, 5 and 6). Of the two second openings 52, one second opening 52A is open and extends between the side surface 44A (one side surface) and the lower surface 45, and the other second opening 52B is open and goes between the side surface 44B (the other side surface) and the lower surface 45. The second openings 52, open as indicated above, allow the flow of molten steel to be diverted to the lower side of the mold and ensure the appropriate distribution of the flow of molten steel in the mold.

In this embodiment, the area _S3 of each first hole 51 on the corresponding side surface 44 (the area of the first hole 51 shown in Fig. 5) is 2700 ^mm2 . The area _{S4 of} each second hole 52 on the corresponding side surface 44 (the area of the second hole 52 shown in Fig. 5) is 2000 ^mm2 , and their area _S5 in the lower surface 45 (the area of the second hole 52 shown in Fig. 6) is 5000 ^mm2 . Based on the above hole areas, the following expressions (1) and (2) are valid.

S ₄ < S ₅ , (1)

(S ₄ + S ₅ ) / S ₃ ≥ 1.5, (2)

The first openings 51 and the second openings 52, having opening areas that satisfy expressions (1) and (2), make it possible to optimize the balance between the ascending flow and the descending flow and to suppress the excessive flow in the convex-concave part. The area S ₃ of the first openings 51 and the areas S ₄ and S ₅ of the second openings 52 are not limited to the above values and can change if expressions (1) and (2) are satisfied.

In this embodiment, the area S ₆ of each first opening 51 on the side of the flow channel 41 is 4000 mm ² . Accordingly, the area S ₃ of each first opening 51 on the side surface 44 is less than the area S ₆ of the opening on the side of the flow channel 41.

The embodiment in which the area S ₆ of each first opening 51 on the side of the flow channel 41 is greater than or equal to their area S ₃ on the side surface 44 gradually reduces the cross-sectional area of the flow channel toward the outlet openings of the molten steel flow in the direction of the flow, and thus straightens the flow of molten steel. As a result, the occurrence of a suction flow in the upper part of the first opening 51 is suppressed and the smooth discharge of molten steel from all first openings 51 is facilitated.

Execution of the connecting section

The connecting section 3 is a section which continuously connects the first section 2 with the second section 4 (Fig. 1 and 2). The connecting section 3 comprises a flow channel 31 having a shape which continuously connects the flow part 21 in the first section 2, which has a circular cross-sectional shape, with the flow part 41 in the second section 4, which has a rectangular cross-sectional shape. Thus, the cross-sectional shape of the flow channel 31 is circular at the upper end 32 and rectangular at the lower end 33.

Other implementation options

Finally, other embodiments of the immersion nozzle according to the present invention are described. The embodiment disclosed in the following embodiments can also be used in combination with the configurations disclosed in other embodiments, if there are no contradictions.

In the above embodiment, a description is given of an example of a configuration in which the areas _S3 , _S4 , _S5 and _S6 of the openings 5 (the first openings 51 and the second openings 52) satisfy the expressions (1) and (2) and _S3 is smaller than _S6 . However, the immersion nozzle according to the present invention does not necessarily have to satisfy at least neither the expressions (1) nor (2), and _S3 may be larger than _S6 .

In the above embodiment, a description is given of an example of a configuration in which the largest width W of the nozzle 1 is 270 mm, that is, less than 300 mm. However, the largest width of the immersion nozzle according to the present invention may be 300 mm or more.

As regards also other embodiments, it should be understood that the embodiments disclosed herein are illustrative in all respects, and the scope of the present invention is not limited to them. Those skilled in the art will readily understand that various changes can be easily made without departing from the spirit of the present invention. Therefore, other embodiments changed without departing from the spirit of the present invention are within the scope of the present invention.

Examples

The present invention will also be described below by way of examples. However, the present invention is not limited to these examples.

Test method

Nozzles with different sizes were designed and numerical hydrodynamic calculations were performed for the flow regimes of the discharged molten metal using the PHOENICS fluid analysis software from CHAM-Japan. The dimensional conditions for the examples and comparative examples are shown in Table 1 below. Based on the calculation results, flow velocity contour graphs were derived. The following parameters were used in the calculations.

- Number of calculation cells: approximately 500,000 (may vary depending on the model).

- Liquid: molten steel (1560°C, density: 7.08 g/ ^cm3 ).

- Pouring speed: 4 tons per minute.

- Mold size: 1200 mm × 150 mm.

Estimation of flow velocity in the convex-concave part

The flow velocities in the convex-concave part were determined based on the output flow velocity contour graphs for the examples and comparative examples. The results were evaluated on a three-point scale from A to C according to the value of the velocity in the convex-concave part.

A: The flow velocity in the convex-concave part is 10 cm/s or more and 25 cm/s or less.

B: The flow velocity in the convex-concave part is greater than 25 cm/s and 35 cm/s or less.

C: The speed of movement in the convex-concave part is less than 10 cm/s or more than 35 cm/s.

Separation of the molten steel flow

In the examples, the output flow velocity contour graphs were visually checked to detect the occurrence of molten steel flow separation in the second section 4, and the results were then evaluated (A or C).

A: A flow of molten steel along the wall surface is formed over the entire area of the second section 4.

C: In the second section 4, separation of the molten steel flow is observed.

Suction flow at the first hole

For the examples, the output flow velocity contour graphs were visually inspected to determine the presence and extent of the suction flow in the first holes 51. The results were assessed on a three-point scale from A to C according to the observed condition.

A: The molten steel stream is discharged from the first holes 51 without stagnation.

B: Near the first holes 51, a stagnation of the molten steel flow was detected.

C: Suction flow detected into first port 51.

Results

Table 1 shows the measurement conditions and the evaluation results for the examples and comparative examples. In examples 1 to 6 where the ratio a/b was in the range of 3 to 7, the evaluation result of the molten steel flow separation was A. On the contrary, in comparative example 1 where the ratio a/b was 8.0, the evaluation result of the molten steel flow separation was C. In examples 1 to 6 where S ₂ was larger than S ₁ , the flow velocity in the convex-concave portion was within the appropriate range (estimated A or B). On the contrary, in comparative example 2 where S ₂ was smaller than S ₁ , the flow velocity in the convex-concave portion was not in the favorable range (estimated C).

In examples 3 to 6, where S ₃ , S ₄ and S ₅ satisfied the expression (2), the flow velocity in the convex-concave portion was in a more favorable range than in examples 1 and 2, where S ₃ , S ₄ and S ₅ did not satisfy the expression (2). In examples 5 and 6, where S ₃ was smaller than S ₆ , more favorable results were obtained in terms of the suction flow in the first openings than in example 1, where S ₃ was equal to S ₆ , and examples 2 to 4, where _S3 was larger than S ₆ .

[Table 1]

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Wed.
Example 1 Cf. Example 2 Length of the long side a [mm] 300 300 250 350 200 300 400 300 Length of short side b [mm] 70 100 70 70 60 50 50 50 a/b ratio - 4.3 3.0 3.6 5.0 3.3 6.0 8.0 6.0 Cross-sectional area of the flow channel in the first section S ₁ [mm ² ] 5027 5027 5027 2827 2827 1963 2827 2827 The cross-sectional area of the flow channel in the second section S ₂ [mm ² ] 7800 15600 6300 9300 3200 2600 3600 2600 Size ratio between S ₁ and S ₂ - S₂> S₁ S₂> S_{1 S2} > _{S1 S2} > _S1 S₂> S₁ S₂> S_{1 S2} > _S1 S₂< S₁ Area of the first hole (side) S ₃ [mm ² ] 2400 4800 1500 2000 1500 1000 1000 1000 Area of the second hole (side) S ₄ [mm ² ] 600 1800 900 1200 900 600 1600 1600 Area of the first hole (bottom) S ₅ [mm ² ] 2700 3300 2550 4050 2250 3300 1500 1500 Area of the first hole (from the flow channel side) S ₆ [mm ² ] 2400 4200 1440 1920 1800 1200 800 800 Size ratio between S ₄ and S ₅ - S₄< S₅ S₄< S₅ S₄< S₅ S₄< S₅ S₄< S₅ S₄< S_{5 S4} > _{S5 S4} > _S5 (S ₄ +S ₅ )/S ₃ - 1.4 1,1 2,3 2.6 2.1 3.9 3.1 3.1 Size ratio between S ₃ and S ₆ - _S3 = _S6 S₃> S₆ S₃> S₆ S₃> S₆ S₃< S₆ S₃< S₆ S₃> S_{6 S3} > _S6 Flow velocity in the convex-concave part B B A A A A C C Separation of the molten steel flow A A A A A A C A Suction flow at the first hole B B B B A A C C

Industrial applicability

The present invention can be used, for example, in a submersible nozzle for continuous casting of thin slabs.

Description of symbols

1: Immersion nozzle

2: First section

21: Flow channel

3: Connecting section

31: Flow channel

32: Upper end of connecting section

33: Lower end of the connecting section

4: Second section

41: Flow channel

42: Long side

43: Short side

44: Lateral surface

45: Bottom Face/Surface

5: Hole section

51: First hole

52: Second hole.

Claims (19)

1. An immersion nozzle having a flow channel and openings, containing: first section; connecting section; and the second section, the first section, the connecting section and the second section are arranged in the specified order from the end side of the base, wherein the flow channel in the first section has a circular cross-section, the flow channel in the second section has a rectangular cross-section, the flow channel in the connecting section has a shape in which the flow channel in the first section is continuously connected to the flow channel in the second section, the second rectangular section has long sides each of length a and short sides each of length b, wherein the ratio a/b between length a and length b is 3 or greater and 7 or less, the flow channel in the second section has a cross-sectional area of S ₂ , the flow channel in the first section has a cross-sectional area of S ₁ , and the cross-sectional area of S ₂ is greater than the cross-sectional area of S ₁ , the holes contain two first holes and two second holes, the first holes are opened one at a time on the two side surfaces of the second section, which correspond to the two short sides, one of the two second openings is open through one of the two side surfaces to the bottom surface of the second section, the bottom surface being the surface at the front end of the second section, and another of the two second openings is open through the other of the two said side surfaces to the said lower surface. 2. The nozzle according to claim 1, wherein each of the first openings has an area S ₃ on the corresponding one of the side surfaces, each of the second openings has an area S ₄ on the corresponding one of the side surfaces and an open section S ₅ on the bottom surface, and the areas S ₃ , S ₄ and S ₅ satisfy expressions (1) and (2) given below: S ₄ <S ₅ (1); and (S ₄ +S ₅ )/S ₃ ≥1.5 (2). 3. A nozzle according to claim 1 or 2, wherein each of the first openings has an area S ₃ on the corresponding one of the side surfaces and an area S ₆ on the side of the flow channel, wherein the area S ₃ is less than the area S ₆ . 4. A nozzle according to any one of paragraphs. 1-3, which has a greatest width of 300 mm or less.