Tundish nozzle structure and continuous casting machine

Abstract

In the nozzle structure of the tundish, poor stopping of molten metal is suppressed. [Solution] The nozzle structure of the tundish is provided at the bottom of the tundish that holds molten metal and includes an outlet nozzle that causes the molten metal stored in the tundish to flow downward, and a stopper that is movable vertically within the tundish and closes the entrance of the outlet nozzle by coming into contact with it, wherein at least one of the portion of the outlet nozzle that comes into contact with the stopper and the portion of the stopper that comes into contact with the outlet nozzle is mainly made of zirconia.

Description

Technical Field

[0001] The present disclosure relates to a nozzle structure of a tundish and a continuous casting machine.

Background Art

[0002] In Patent Document 1, in an immersion nozzle provided in a tundish, a ceramic spraying film with a thickness of 100 to 1000 microns is formed at a portion for adjusting the molten steel flow at the fitting portion with a stopper. The ceramic spraying film is made of ZrO2-based material with CaO of 10% by weight or less, or spinel-based material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the nozzle structure of the tundish, the outflow of molten metal from the outflow nozzle is prevented by pressing a stopper against the inlet of the outflow nozzle. However, when problems such as damage or deformation occur in the outflow nozzle or the stopper, or when molten metal adheres to the contact portion between the outflow nozzle and the stopper, a gap may occur between the outflow nozzle and the stopper when the stopper is pressed against the inlet of the outflow nozzle. That is, even when the stopper is in the closing mode of closing the outflow nozzle, a gap may occur between the outflow nozzle and the stopper. When the size of this gap exceeds a predetermined value, poor stoppage of the molten metal leaking from the gap between the outflow nozzle and the stopper occurs due to the molten metal in the tundish leaking.

[0005] An object of the present disclosure is to suppress poor stoppage of molten metal in the nozzle structure of a tundish.

Means for Solving the Problems

[0006] The nozzle structure of a tundish according to a first aspect of the present disclosure comprises a discharge nozzle provided at the bottom of a tundish for holding molten metal, which discharges the molten metal stored in the tundish downward, and a stopper that is movable vertically within the tundish and closes the entrance of the discharge nozzle by coming into contact with it, wherein at least one of the portion of the discharge nozzle that comes into contact with the stopper and the portion of the stopper that comes into contact with the discharge nozzle is mainly made of zirconia.

[0007] A tundish nozzle structure according to a second aspect of the present disclosure is, in the tundish nozzle structure according to the first aspect, wherein the outflow nozzle is a cylindrical body that penetrates the bottom and is formed mainly of zirconia.

[0008] A third aspect of the present disclosure is a tundish nozzle structure in the first or second aspect of the tundish nozzle structure, wherein the stopper comprises a cylindrical rod portion and a head portion detachably attached to the lower end of the rod portion, and the entire head portion is mainly formed of zirconia.

[0009] In the nozzle structure of the tundish according to the fourth aspect of this disclosure, the rod portion constitutes a refrigerant flow path.

[0010] A continuous casting machine according to a fifth aspect of the present disclosure comprises a ladle, a tundish having a nozzle structure of any one of the first to fourth aspects for collecting molten metal discharged from the ladle, and a mold for shaping the molten metal discharged from the tundish through an outlet nozzle into a predetermined shape. [Effects of the Invention]

[0011] According to this disclosure, it is possible to suppress poor stopping of molten metal in the nozzle structure of a tundish. [Brief explanation of the drawing]

[0012] [Figure 1]A side view of a continuous casting machine according to one embodiment of the present disclosure. [Figure 2] This is a side cross-sectional view of the tundish (a cross-sectional view along the line 2X-2X in Figure 1) showing the state in which the first molten steel is being stored in the tundish. [Figure 3] This is a side cross-sectional view of the tundish (a cross-sectional view along the line 2X-2X in Figure 1) showing the state in which the first molten steel is flowing from the tundish into the mold. [Figure 4] This is a side cross-sectional view of the tundish (a cross-sectional view along the line 2X-2X in Figure 1) showing the state in which the second batch of molten steel is being stored in the tundish. [Figure 5] This is a side cross-sectional view of the tundish (a cross-sectional view along the line 2X-2X in Figure 1) showing the state in which the second molten steel is flowing from the tundish into the mold. [Figure 6] This is a side cross-sectional view of the tundish showing the outlet nozzle blocked by the stopper. [Figure 7] This is a side cross-sectional view of the tundish showing the outlet nozzle inlet in an open position. [Figure 8] This is a diagram showing the configuration of the control device. [Figure 9] This is an illustrative diagram showing the behavior of molten steel in gaps. [Figure 10] This graph shows the incidence rate of stopping failures in the examples and comparative examples. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments for carrying out the technology of this disclosure will be described with reference to the drawings. Components indicated by the same reference numerals in each drawing are the same or similar components. In the embodiments described below, descriptions and reference numerals that are repeated may be omitted. Furthermore, the drawings used in the following description are all schematic, and the dimensional relationships and ratios of each element shown in the drawings do not necessarily correspond to reality. Also, the dimensional relationships and ratios of each element do not necessarily correspond between multiple drawings.

[0014] Hereinafter, the configuration of the continuous casting machine 10 according to an embodiment of the present disclosure will be described.

[0015] As shown in FIG. 1, the continuous casting machine 10 has a tundish 12, a mold 16, support rolls 18, a cooling device 20, a cutting machine 22, and conveying rolls 24.

[0016] The tundish 12 is a container from which molten steel W refined in a converter (not shown) is discharged through an injection nozzle 52 from a ladle 50 that stores the molten steel W. This tundish 12 has a nozzle structure ST. The tundish 12 can primarily store the molten steel W discharged by the nozzle structure ST. At the bottom 12A of the tundish 12, a nozzle 15 for discharging the molten steel W into the mold 了 16 is provided. The nozzle 15 extends downward from the bottom 12A. The nozzle 15 is composed of an outflow nozzle 30, a sliding nozzle 32, a lower nozzle お 34, and a submerged nozzle 36 in order from the top. Note that the outflow nozzle 30 is also referred to as an upper nozzle. Note that the molten steel W in the present embodiment is an example of the molten metal in the present disclosure.

[0017] The mold 16 is a mold that receives the molten steel W flowing out from the tundish 12 through the nozzle 15, cools it, and solidifies the surface layer of the molten steel W. A slab S of a predetermined shape is formed by this mold 16. As this mold 16, for example, a water-cooled copper mold may be used.

[0018] A plurality of support rolls 18 are arranged below the mold 16, support the slab S formed by the mold 16, and feed it downstream.

[0019] The cooling device 20 is a device that is arranged below the mold 16, has a function of cooling the slab S supported by the support rolls 18 and fed downstream.

[0020] The cutting machine 22 is a device that has a function of cutting the slab S into a predetermined length.

[0021] The conveyor roll 24 transports the cast slab S, which has been cut to a predetermined length, to the next process.

[0022] Next, the nozzle structure ST of the tundish according to this embodiment will be described.

[0023] As shown in Figure 2, the nozzle structure ST of the tundish 12 comprises an outflow nozzle 30 and a stopper 40.

[0024] The outflow nozzle 30 is located at the bottom 12A of the tundish 12 that holds the molten steel W. This outflow nozzle 30 is cylindrical and penetrates the bottom 12A. As shown in Figure 3, the outflow nozzle 30 causes the molten steel W stored in the tundish 12 to flow downward. Specifically, as shown in Figures 3 and 7, the molten steel W stored in the tundish 12 flows downward through the inside of the outflow nozzle 30 from the inlet 30A that opens at the bottom 12A of the outflow nozzle 30. Then, as shown in Figure 3, the molten steel W that has passed through the outflow nozzle 30 flows into the mold 16 through the sliding nozzle 32, the lower nozzle 34, and the immersion nozzle 36.

[0025] As shown in Figure 7, the upper inner edge 30B of the outflow nozzle 30 gradually increases in diameter towards the inlet 30A. In this embodiment, as an example, the upper inner edge 30B of the outflow nozzle 30 is curved in an arc shape when viewed in cross-section.

[0026] As shown in Figures 2 and 3, the stopper 40 is configured to move vertically within the tundish 12. Specifically, the stopper 40 is configured to move vertically by a lifting device 70 (see Figure 8). The configuration of this lifting device 70 is not particularly limited, but for example, a lifting device equipped with a rack and pinion mechanism or a mechanism using a lead screw may be used.

[0027] As shown in Figures 2 and 6, the stopper 40 has the function of closing the inlet 30A of the outflow nozzle 30 by coming into contact with the outflow nozzle 30. Specifically, by moving the stopper 40 downward, the outer circumference of the tip side of the stopper 40 is pressed against the upper inner edge 30B of the outflow nozzle 30, thereby closing the inlet 30A. In this embodiment, when the control device 60 (see Figure 8) selects the closing mode for the stopper 40, the lifting device 70 moves the stopper 40 downward and stops at a predetermined position. This predetermined position is a pre-set position where the outer circumference of the tip side of the stopper 40 is pressed against the upper inner edge 30B of the outflow nozzle 30. The predetermined position is set, for example, when the continuous casting machine 10 is installed, when parts of the stopper 40 are replaced, or during maintenance.

[0028] Furthermore, as shown in Figure 2, the stopper 40 comprises a cylindrical rod portion 42 and a head portion 44 detachably attached to the lower end of the rod portion 42. As shown in Figure 6, a male threaded portion 42A is formed at the lower end of the rod portion 42. The head portion 44 has a female threaded portion 44A into which the male threaded portion 42A is screwed. The head portion 44 is attached to the rod portion 42 by screwing the male threaded portion 42A into the female threaded portion 44A. Note that the attachment and detachment structure between the rod portion 42 and the head portion 44 is not limited to a screw structure; other attachment structures may also be used.

[0029] Furthermore, the outer circumference 44B on the tip side of the head portion 44 (the lower end edge in Figures 2 and 3) gradually decreases in diameter towards the tip. In this embodiment, as an example, as shown in Figures 6 and 7, the outer circumference 44B on the tip side of the head portion 44 is curved in an arc shape when viewed in cross-section.

[0030] In this embodiment, in the occlusion mode of the stopper 40, as shown in Figure 6, the outer peripheral portion 44B on the tip side of the head portion 44 comes into contact with the upper inner edge portion 30B of the outflow nozzle 30.

[0031] As shown in Figure 6, at least one of the portion of the outflow nozzle 30 that contacts the stopper 40 and the portion of the stopper 40 that contacts the outflow nozzle 30 is formed mainly of zirconia. In this embodiment, the portion of the outflow nozzle 30 that contacts the stopper 40 and the portion of the stopper 40 that contacts the outflow nozzle 30 are each formed mainly of zirconia. However, this disclosure is not limited to this configuration, and only the portion of the outflow nozzle 30 that contacts the stopper 40 may be formed mainly of zirconia, or only the portion of the stopper 40 that contacts the outflow nozzle 30 may be formed mainly of zirconia. Here, "formed mainly of zirconia" means that the proportion of zirconia exceeds 50%. For example, in the case of the outflow nozzle 30, 80% or more is more preferable, and 90% or more is even more preferable. In the case of the stopper 40, 60% or more is more preferable, and 70% or more is even more preferable. Furthermore, the zirconia components contained in the material can be measured, for example, using an X-ray fluorescence analyzer in accordance with JIS R 2012 Chemical Analysis Method for Zircon-Zirconiated Refractories.

[0032] In this embodiment, as an example, the entire outlet nozzle 30 is formed mainly of zirconia.

[0033] In this embodiment, as an example, the entire head portion 44 is formed mainly of zirconia.

[0034] Furthermore, as shown in Figures 2 and 3, the rod portion 42 of the stopper 40 may constitute a refrigerant flow path, and refrigerant C may be supplied from the cooling device 72. In this case, the rod portion 42 is cooled by the refrigerant C supplied to the refrigerant flow path within the rod portion 42. The head portion 44 in contact with the rod portion 42 is also cooled by heat conduction. In this embodiment, as an example, the continuous casting machine 10 is equipped with a cooling device 72, but the disclosure is not limited to this configuration, and a separate device from the continuous casting machine 10 may be equipped with a cooling device 72, and the refrigerant C may be supplied to the refrigerant flow path within the rod portion 42 when the continuous casting machine 10 is in operation. In this embodiment, air is used as the refrigerant C, but the disclosure is not limited to this configuration.

[0035] The tundish 12 of this embodiment is composed of an inner layer 13 and an outer layer 14, as shown in Figure 2. The inner layer 13 is made of refractory material. The outer layer 14 is made of steel material. The outer layer 14 is also called the steel shell. The discharge nozzle 30 is composed of a bottom inner layer 13A that constitutes the bottom 12A of the inner layer 13 and a bottom outer layer 14A that constitutes the bottom 12A of the outer layer 14. The discharge nozzle 30 penetrates the bottom inner layer 13A and the bottom outer layer 14A.

[0036] Furthermore, the continuous casting machine 10 is equipped with a control device 60. This control device 60 controls the operation of each part that constitutes the continuous casting machine 10. As shown in Figure 8, the control device 60 includes a CPU (Central Processing Unit) 63, a main memory 64 that provides temporary storage, an auxiliary storage device 65 that provides non-volatile storage, and an input / output interface (I / F) 66. The CPU 63, main memory 64, auxiliary storage device 65, and input / output I / F 66 are connected to each other via a bus 67.

[0037] The auxiliary storage device 65 can be implemented using a Hard Disk Drive (HDD), Solid State Drive (SSD), flash memory, etc. The auxiliary storage device 65 stores various programs for operating the continuous casting machine 10, controlled by the control device 60. The CPU 63 reads the various programs for continuous casting from the auxiliary storage device 65, loads them into the main memory 64, and executes the processes described in the various programs sequentially, thereby performing continuous casting using the continuous casting machine 10.

[0038] The input / output interface 66 is connected via wired or wireless connection to each component of the continuous casting machine 10. In Figure 8, the lifting device 70, sliding nozzle 32, and cooling device 72 of the continuous casting machine 10 are shown connected to the input / output interface 66, while other components are not shown.

[0039] Next, a continuous casting method using the continuous casting machine 10 of this embodiment will be described.

[0040] First, the molten steel W1 is cast using the continuous casting machine 10 (see Figure 1). Specifically, as shown in Figures 2 and 6, the control device 60 selects a closure mode for the stopper 40 and controls the lifting device 70 so that the vertical position of the stopper 40 is at a predetermined position. As a result, the nozzle 15 is closed by the stopper 40. The molten steel W1 discharged from the ladle 50 is then temporarily stored in the tundish 12 (see Figure 2). Subsequently, the control device 60 controls the lifting device 70 to move the stopper 40 upward, as shown in Figures 3 and 7, and open the inlet 30A of the outflow nozzle 30. When the inlet 30A of the outflow nozzle 30 opens, the molten steel W1 flows out into the mold 16 through the nozzle 15. The molten steel W1 that flows into the mold 16 is formed into a slab S of a predetermined shape. The slab S formed in the mold 16 is sent downstream by the support roll 18. The cast slab S is then cooled by the cooling device 20 and cut to a predetermined length by the cutting machine 22. The cut cast slab S is then transported to the next process by the conveyor roll 24.

[0041] Next, when switching from molten steel W1 to molten steel W2 of a different steel type, i.e., when performing continuous casting of different steel types, after most of the molten steel W1 has been discharged from the tundish 12, the outlet nozzle 30 is blocked by the stopper 40, as shown in Figure 4. Then, the molten steel W2 discharged from the ladle 50 is temporarily stored in the tundish 12, and then, as shown in Figure 5, the stopper 40 is moved to open the inlet 30A of the outlet nozzle 30, and the molten steel W2 is discharged into the mold 16 through the nozzle 15. The molten steel W2 that has flowed into the mold 16 is formed into a slab S of a predetermined shape. The slab S formed in the mold 16 is sent downstream by the support roll 18. The slab S is then cooled by the cooling device 20 and cut to a predetermined length by the cutting machine 22. The cut slab S is conveyed to the next process by the conveying roll 24.

[0042] The flow rates of molten steel W1 and W2 flowing through nozzle 15 are controlled by the opening and closing amount of sliding nozzle 32. Sliding nozzle 32 is controlled by control device 60.

[0043] Next, the effects and advantages of this embodiment will be described. In this embodiment, at least one of the parts of the outlet nozzle 30 that contact the stopper 40 and the part of the stopper 40 that contacts the outlet nozzle 30 is mainly formed using zirconia. By using zirconia in the contact area between the outlet nozzle 30 and the stopper 40, molten metal is less likely to adhere to it, and the formation of a gap between the outlet nozzle 30 and the stopper 40 can be suppressed. Furthermore, because zirconia is a material with excellent resistance to erosion, using zirconia in the contact area between the outlet nozzle 30 and the stopper 40 can suppress the formation of a gap between the outlet nozzle 30 and the stopper 40 due to erosion. In addition, because zirconia is a material with excellent wettability to molten steel, using zirconia in the contact area between the outlet nozzle 30 and the stopper 40 can suppress leakage of molten steel W from the gap even if a slight gap occurs between the outlet nozzle 30 and the stopper 40. Therefore, in this embodiment, poor stopping of molten steel W in the tundish 12 can be suppressed.

[0044] In this embodiment, the entire outlet nozzle 30 is formed mainly of zirconia. Therefore, compared to a configuration in which, for example, only the surface layer of the outlet nozzle is formed mainly of zirconia, the resistance to erosion of the outlet nozzle 30 can be further improved.

[0045] In this embodiment, the entire head portion 44 of the stopper 40 is formed mainly of zirconia. Therefore, compared to a configuration in which, for example, only the surface layer of the head portion 44 is formed mainly of zirconia, the resistance to erosion of the head portion 44 can be improved. Furthermore, the occurrence of cracks (sparing) due to thermal undulation of the head portion 44 can be suppressed. In addition, since the head portion 44 of the stopper 40 can be detached from the rod portion 42, the head portion 44 can be replaced or maintained. This makes it possible to suppress malfunctions in the stopper 40 over a long period of time. Furthermore, since the rod portion 42 of the stopper 40 is cylindrical, the tensile strength of the rod portion 42 is improved, and warping of the rod portion 42 can be suppressed. This makes it possible to suppress axial misalignment between the stopper 40 and the outflow nozzle 30.

[0046] In this embodiment, refrigerant C is supplied from the cooling device 72 to the refrigerant flow path in the rod portion 42, so that the head portion 44 is cooled via the rod portion 42. Cooling the head portion 44 helps to suppress melting damage to the head portion 44.

[0047] According to this embodiment, the load-bearing capacity, erosion resistance, spalling resistance, and non-adhesion of inclusions and molten steel to the stopper 40 are improved. In addition, the erosion resistance, spalling resistance, and non-adhesion of inclusions and molten steel to the outflow nozzle 30 are improved.

[0048] (Example test) In this disclosure, the wettability of zirconia used in the outlet nozzle and stopper with respect to molten steel was verified. The wettability of zirconia was determined by forming through holes in a plate-shaped refractory material and observing the leakage of molten steel from these through holes, as shown in Figure 9. Figure 9 is a two-dimensional diagram simulating the contact situation between molten steel and refractory material. The force of the molten steel falling under its own weight and the interfacial tension between the molten steel and refractory material are expressed by equation (1). It was considered that even if there was a gap between the outlet nozzle and the stopper, if the interfacial tension between the molten steel and refractory material exceeded the force of the falling molten steel, failure to stop the flow could be avoided. By modifying equation (1) to equation (2), the limit gap between the outlet nozzle and the stopper that allows for the complete closure of the molten steel flow was determined. The calculation results of the limit gap are shown in Table 1. The larger the limit gap, the more effectively the molten steel can be stopped even if there is a gap between the outlet nozzle and the stopper. This indicates that to suppress stopping failures, it is preferable to select a material such as zirconia that not only prevents leakage up to a certain gap but also has low adhesion and erosion resistance.

[0049]

number

[0050]

number

[0051] [Table 1]

[0052] Furthermore, by applying the technology disclosed herein to a continuous casting machine, the rate of stop failures can be reduced to 2%, and deformation problems of the stopper head can be completely suppressed (see Figure 10). Details of the example shown in Figure 10 are shown in Table 2 below.

[0053] [Table 2]

[0054] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above, and it is of course possible to implement it in various other forms without departing from its spirit. [Explanation of Symbols]

[0055] 10 Continuous casting machines 12 Tan Dish 12A bottom 13 Inner Layer 13A Bottom inner layer 14 Outer layer 14A bottom outer layer 15 nozzles 16 molds 18 Support Rolls 20 Cooling device 22 Cutting machine 24 Conveyor Rolls 30 Outlet nozzles 30A entrance 30B Upper inner edge 32 Sliding Nozzles 34 Lower nozzle 36 Immersion nozzle 40 Stopper 42 Rod section 42A Male threaded section 44 Head section 44A Female thread section 44B Outer circumference of the tip side 50 ladle 52 Injection nozzle 60 Control device 70 Lifting device 72 Cooling device C Refrigerant ST Nozzle Structure S slab W Molten steel W1 Molten steel W2 Molten Steel

Claims

1. A discharge nozzle is provided at the bottom of a tundish for holding molten metal, and discharges the molten metal stored in the tundish downwards. A stopper that is movable vertically within the tundish and closes the entrance to the outlet nozzle by coming into contact with the outlet nozzle, Equipped with, At least one of the portion of the discharge nozzle that contacts the stopper and the portion of the stopper that contacts the discharge nozzle is formed mainly of zirconia. The nozzle structure of the tundish.

2. The discharge nozzle is a cylindrical body that penetrates the bottom and is entirely made of zirconia. The nozzle structure of the tundish according to claim 1.

3. The stopper comprises a cylindrical rod portion and a head portion detachably attached to the lower end of the rod portion. The entire head portion is mainly formed using zirconia. The nozzle structure of a tundish according to claim 1 or claim 2.

4. The inside of the rod portion constitutes a refrigerant flow path. The nozzle structure of the tundish according to claim 3.

5. A tundish having the nozzle structure of a tundish as described in claim 1, for collecting molten metal discharged from a ladle, A mold for shaping the molten metal that flows out of the tundish through the outlet nozzle into a predetermined shape, A continuous casting machine equipped with the following features.

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