Patent Application
20240238869
The present invention relates to an immersion nozzle to be used to continuously cast thin slabs.
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).
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.
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:
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.
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.
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 (
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
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
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 (
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 (
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 (
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.
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 (
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 (
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
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.
The connection section 3 is a section that continuously connects the first section 2 to the second section 4 (
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 S6. 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.
The present invention will be further described below by describing examples. However, the present invention is not limited by the following example.
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.
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.
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).
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.
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.
The present invention can be used in an immersion nozzle for thin-slab continuous casting, for example.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/025890 | 7/9/2021 | WO |
