Method for manufacturing continuous casting stopper

Abstract

The present invention provides a method for manufacturing a continuous casting stopper capable of uniformly discharging gas from a fitting portion with a nozzle or from the vicinity of the fitting portion. The present invention is a method for manufacturing a continuous casting stopper 1 that has a gas pool in a center portion in the vertical direction and a plurality of through-holes for gas discharge penetrating from the gas pool to an outer surface of a fitting portion with a nozzle underneath or of the vicinity of the fitting portion, the through-holes being formed of a thread-like disappearing body 3 composed of a material that disappears through heat treatment, the method being characterized in that the thread-like disappearing body 3 includes a large cross section portion 31 positioned on the gas pool side, and a small cross section portion 32 positioned on the outer surface side and having a cross sectional area smaller than that of the large cross section portion 31, wherein the length of the large cross section portion 31 is longer than the length of the small cross section portion 32.

Description

Method for manufacturing a stopper for continuous casting

[0001] The present invention relates to a method for manufacturing a continuous casting stopper having a gas discharge function, which controls the flow rate of molten steel by fitting from above into a nozzle disposed at the bottom of a tundish, mainly when discharging molten steel from the tundish into a mold in continuous casting of molten steel. In this specification, the continuous casting stopper is also simply referred to as a stopper.

[0002] In continuous casting of molten steel, stoppers, which control the flow rate of molten steel when it is discharged from a tundish into a mold, sometimes have a gas discharge function to prevent inclusions from adhering to the nozzle and fitting area. When inclusions adhere to the nozzle and fitting area, the deposits accumulate, peel off, and can enter the mold as foreign matter. This also increases the likelihood of fluctuations in the stopper opening, which can lead to fluctuations in the mold surface and the entrapment of powder within the mold. When gas discharge is uneven, such deposits accumulate in areas with low gas discharge, and the detached foreign matter deteriorates the quality of the cast slab. Therefore, uniform gas discharge is an important characteristic of stoppers to prevent the accumulation and peeling of deposits.

[0003] For example, Patent Document 1 discloses a tundish stopper whose tip is made of a porous graphite-containing carbon-bonded refractory material, and Patent Document 2 discloses a tundish stopper characterized by having a plurality of through holes of 0.1 to 0.5 mm radially arranged from the inner hole surface to the outer surface in a direction horizontal to the axis of the tundish stopper.

[0004] When gas is discharged from a porous refractory material with low strength as in Patent Document 1, there is no problem if the porous refractory material is placed at the tip of the stopper, but if the porous refractory material is placed at the fitting portion, the stopper may crack, chip, etc. due to stress generated when the fitting portion is pressed against the nozzle. Therefore, when gas is discharged from the fitting portion of the stopper or its vicinity in order to prevent deposition and peeling at the fitting portion and its vicinity, it is generally discharged from a small-diameter through-hole as disclosed in Patent Document 2.

[0005] However, as Patent Document 3 states, "When the raw material is introduced into the mold, the fixed combustible body may shift in position, or if the combustible body is a thin fiber, it may bend and entangle, making it technically difficult to set it in a fixed position as a through-hole" (page 2, upper right column, lines 6 to 10), it is very difficult to form small diameter through-holes as shown in Patent Document 2 with high precision according to design, and if the through-holes are not formed according to design, the gas will be discharged non-uniformly due to variations in the bubble diameter and discharge amount of the gas discharged from each through-hole, and the adhesion prevention function may become insufficient in areas where the gas discharge amount is low.

[0006] In order to solve the problems of Patent Document 2, Patent Document 3 discloses "a method for manufacturing a gas-injection type stopper head, characterized in that in a rubber press device, a cylindrical through-hole forming body made of combustible yarn perforated (blind-like) fabric is fixed to the tip of a molding mandrel, the body having warp threads arranged in the axial direction of the through-hole forming and weft threads arranged in the circumferential direction maintaining the spacing of the through-holes, and then refractory clay is filled into a mold to form the body, and then the mold is fired to burn out the cylindrical through-hole forming body of the combustible yarn perforated (blind-like) fabric, thereby forming fine through-holes for injecting gas."

[0007] Japanese Patent Publication No. 63-43185 Publication No. 6-73724 Japanese Patent Publication No. 1-205857

[0008] In the manufacturing method of Patent Document 3, as described above, the warp threads made of a woven fabric with a flammable yarn mesh (blind-like) are arranged in the axial direction of the through-hole formation, i.e., in the vertical direction. Therefore, the through-holes are also formed in the vertical direction, and gas is discharged from near the center of the tip of the stopper. In other words, in the stopper obtained by the manufacturing method of Patent Document 3, gas is only discharged from near the center of the tip, and not from the fitting portion or its vicinity, where deposits are likely to accumulate and peel off. On the other hand, in order to discharge gas from the fitting portion or its vicinity in the manufacturing method of Patent Document 3, the "warp threads made of a woven fabric with a flammable yarn mesh (blind-like)" must be arranged in a radial pattern that diverges toward the end. However, this makes the "warp threads made of a woven fabric with a flammable yarn mesh (blind-like)" more susceptible to deformation such as bending, crushing due to bending, displacement, etc., due to stress, etc., received during molding.

[0009] An object of the present invention is to provide a method for manufacturing a continuous casting stopper that is capable of uniformly discharging gas from the fitting portion with the nozzle or the vicinity thereof.

[0010] According to one aspect of the present invention, there is provided the following method for manufacturing a continuous casting stopper: A continuous casting stopper has a gas pool in the vertical center and a plurality of through holes for discharging gas that extend from the gas pool to the fitting portion with the nozzle below or to the outer surface in the vicinity thereof, and the through holes are formed by a filamentary vanishing body made of a material that disappears by heat treatment, wherein the filamentary vanishing body includes a large cross-sectional portion located on the gas pool side and a small cross-sectional portion located on the outer surface side and having a cross-sectional area smaller than that of the large cross-sectional portion, and the length of the large cross-sectional portion is longer than the length of the small cross-sectional portion.

[0011] According to the present invention, the filamentary vanisher body for forming the through hole for discharging gas that penetrates from the gas pool to the outer surface includes a large cross-sectional portion located on the gas pool side and a small cross-sectional portion located on the outer surface side, and the length of the large cross-sectional portion is longer than the length of the small cross-sectional portion, so that the filamentary vanisher body can be prevented from deforming, crushing, or shifting in position during molding, and a drop in pressure during gas discharge can be suppressed. This makes it possible to manufacture a continuous casting stopper that can uniformly discharge gas from the fitting portion with the nozzle or the vicinity thereof, and ultimately suppresses the adhesion of inclusions such as alumina to the fitting portion or the vicinity thereof.

[0012] Fig. 1 is a cross-sectional conceptual diagram showing the state of use of a stopper obtained by the manufacturing method of the present invention. Fig. 2 is a cross-sectional conceptual diagram showing an example of a filamentary vanishing body used in the manufacturing method of the present invention. Fig. 3 is a cross-sectional conceptual diagram showing an example of the arrangement of filamentary vanishing bodies in the manufacturing method of the present invention. Fig. 4 is a cross-sectional conceptual diagram showing another example of a filamentary vanishing body used in the manufacturing method of the present invention. Fig. 5 is a conceptual diagram showing yet another example of a filamentary vanishing body used in the manufacturing method of the present invention. Fig. 6 is a conceptual diagram showing a test method for confirming the gas discharge state of a stopper.

[0013] FIG. 1 conceptually illustrates a vertical cross section of a stopper 1 obtained by the manufacturing method of the present invention in use. The stopper 1 has a gas pool 11 in its vertical center and a plurality of through-holes 14 for gas discharge extending from the gas pool 11 to an outer surface 13 near a fitting portion 12 with a nozzle 2 below. In the description of this embodiment, the fitting portion 12 with the nozzle 2 and its vicinity are collectively referred to as the vicinity of the fitting portion 12. In this embodiment, the nozzle 2 is specifically a nozzle (upper nozzle) installed at the bottom of a tundish. That is, in this embodiment, the stopper 1 controls the flow rate of molten steel when discharging molten steel from a tundish into a mold during continuous casting of molten steel by fitting from above to a nozzle 2 installed at the bottom of the tundish. At this time, gas is discharged from the gas pool 11 through the plurality of through-holes 14 from the outer surface 13 near the fitting portion 12.

[0014] In this embodiment, the through holes 14 are formed by causing the filamentary vanishing body 3 shown in FIG. 2 to disappear by heat treatment. That is, the filamentary vanishing body 3 is made of a material that disappears by heat treatment. Note that, although a synthetic fiber such as nylon can be used as the material that disappears by heat treatment, there is no limitation thereto. In short, there are no limitations on the composition of the material that disappears by heat treatment, as long as it disappears at a temperature equal to or lower than the heat treatment temperature.

[0015] As shown in FIG. 2 , the thread-shaped disappearance body 3 includes a large cross-sectional portion 31 and a small cross-sectional portion 32. The cross-sectional area of ​​the large cross-sectional portion 31 is larger than the cross-sectional area of ​​the small cross-sectional portion 32. The length of the large cross-sectional portion 31 is also longer than the length of the small cross-sectional portion 32. In this embodiment, such thread-shaped disappearance bodies 3 are placed during molding, and the thread-shaped disappearance bodies 3 are disappeared by heat treatment, thereby forming the through-holes 14. Specifically, as shown in FIG. 3 , during molding using the mold 4, the base end of the large cross-sectional portion 31 is fixed to a core rod 41 inside the mold 4, and the tip end of the small cross-sectional portion 32 is fixed to the inner circumferential surface of the mold 4. Then, the mold 4 is filled with a moldable material 5 for the stopper, and molding is performed. After molding, the molded body is removed from the mold 4 and heat treated. This results in the stopper 1 shown in FIG. 1 . That is, stopper 1 is formed with gas pool 11 corresponding to the shape of core rod 41, and through-holes 14 corresponding to the shape of filamentary vanishing body 3 are formed so as to penetrate from gas pool 11 to outer surface 13 near fitting portion 12. In this case, through-hole 14 includes large cross-sectional portion 141 corresponding to large cross-sectional portion 31 of filamentary vanishing body 3, and small cross-sectional portion 142 corresponding to small cross-sectional portion 31 of filamentary vanishing body 3. Note that filamentary vanishing body 3 including large cross-sectional portion 31 and small cross-sectional portion 32 as shown in Figure 2 can be obtained, for example, by bonding synthetic fiber corresponding to large cross-sectional portion 31 and synthetic fiber corresponding to small cross-sectional portion 31.

[0016] As described above, in this embodiment, the filamentary vanisher body 3, which forms the through hole 14 for discharging gas that penetrates from the gas pool 11 to the outer surface 13 near the fitting portion 12, includes a large cross-sectional portion 31 located on the gas pool 11 side and a small cross-sectional portion 32 located on the outer surface 13 side, and the length of the large cross-sectional portion 31 is longer than the length of the small cross-sectional portion 32, so that the filamentary vanisher body 3 is prevented from deforming, collapsing, or shifting during molding, and a drop in pressure during gas discharge is suppressed. As described above, according to this embodiment, a stopper 1 that can uniformly discharge gas from the vicinity of the fitting portion 12 can be manufactured, and therefore the adhesion of inclusions such as alumina near the fitting portion 12 can be suppressed.

[0017] Here, if the design requires a large number of through holes 14, the small cross-section sections 32 of the filamentary vanisher body 3 can be configured to branch into multiple parts from the large cross-section section 31 toward the outer surface 13. For example, as shown in FIG. 4 , the small cross-section sections 32 can branch into two from the tip of the large cross-section section 31, or as shown in FIG. 5 , the small cross-section sections 32 can branch into four parts in total, with two branches near the tip of the large cross-section section 31 and two branches from the tip. By using a filamentary vanisher body 3 with multiple branched small cross-section sections 32 in this way, it is possible to maintain a distance between adjacent filamentary vanisher bodies 3 (large cross-section sections 31) on the gas pool 11 side, which has a shorter circumferential length, and to prevent problems such as contact between the filamentary vanisher bodies 3 (large cross-section sections 31) during molding. There are no particular limitations on the branching points or number of branches of the small cross-section sections 32, and the small cross-section sections 32 may branch into five or more parts from one location.

[0018] When using a filamentary vanisher 3 in which the small cross-section portions 32 branch into multiple parts in this way, it is preferable that the cross-sectional area of ​​the large cross-section portion 31 be larger than the total cross-sectional area of ​​the multiple branched small cross-section portions 32. Here, the cross-sectional areas of the large cross-section portion 31 and the small cross-section portion 32 refer to the cross-sectional areas of the large cross-section portion 31 and the small cross-section portion 32 in a cross section perpendicular to the longitudinal direction of each of the large cross-section portion 31 and the small cross-section portion 32. There are no particular restrictions on the cross-sectional shape of the filamentary vanisher 3, but a circle is generally preferred, and an ellipse or polygonal shape close to a circle may also be used.

[0019] The cross-sectional area of ​​the small cross-section portion 32 is preferably 0.1 to 0.8 mm in terms of the diameter of a circle. If the cross-sectional area of ​​the small cross-section portion 32 is less than 0.1 mm, clogging is likely to occur, while if it exceeds 0.8 mm, molten steel may infiltrate. On the other hand, the cross-sectional area of ​​the large cross-section portion 31 is preferably at least twice, more preferably at least four times, the cross-sectional area of ​​the small cross-section portion 32. If the small cross-section portion 32 branches into multiple portions, the cross-sectional area of ​​the large cross-section portion 31 is preferably at least twice, more preferably at least four times, the cross-sectional area of ​​each small cross-section portion 32. While there is no particular upper limit to the multiple of the cross-sectional area of ​​the large cross-section portion 31 relative to the small cross-section portion 32, a practical upper limit is approximately 200 times, taking into account factors such as the size of the stopper 1. The specific cross-sectional area of ​​the large cross-section portion 31 is appropriately determined depending on molding conditions such as molding pressure and the particle size composition of the clay. The cross-sectional area of ​​the large cross-section portion 31 is preferably larger the higher the molding pressure and the larger the particle size of the clay. However, the larger the cross-sectional area, the more the strength of the stopper decreases due to voids. Therefore, taking these factors into consideration, the cross-sectional area of ​​the large cross-section portion 31 is preferably 5 mm or less in terms of the diameter of a circle. Here, there are no particular restrictions on the particle size or composition of the clay, and both can be adjusted to suit individual operating conditions, etc., from the perspectives of inclusion adhesion during continuous casting, corrosion resistance, wear resistance, etc. Similarly, there are no particular restrictions on the molding method of the clay.

[0020] The length of the small cross-section portion 32 is preferably 10 mm or more from the viewpoint of preventing molten steel from coming into contact with the large cross-section portion 31 when the outer surface 13 side is melted or worn. Because the outer surface 13 side may be cut by machining during manufacturing, the length is set to include this machining allowance. The upper limit of the length of the small cross-section portion 32 is not particularly limited, but considering the condition of the present invention that the small cross-section portion 32 be shorter than the length of the large cross-section portion 31 and the size of the stopper 1, the upper limit is approximately 40 mm. The length of the large cross-section portion 31 is preferably 1.5 times or more the length of the small cross-section portion 32. The upper limit of the multiple of the length of the large cross-section portion 31 relative to the small cross-section portion 32 is not particularly limited and may be appropriately set based on common technical knowledge regarding stoppers, such as the size of the stopper.

[0021] To verify the effects of the present invention, the following stoppers were manufactured and the gas discharge state was confirmed. In Example 1, 16 filamentous vanishing bodies (large cross-sectional diameter = 1.4 mm, small cross-sectional diameter = 0.4 mm) were placed in a mold 70 mm above the tip of the stopper, facing from the gas pool side toward the outer surface and oriented 30 degrees downward from the horizontal, and a moldable material was filled in. CIP molding was then performed, and after removal from the mold, a heat treatment was performed at 1000°C to produce a stopper. The completed stopper was processed for air pipe connection, the air pipe was connected, and a test to confirm the gas discharge state was conducted using the method described below.

[0022] In this test, as shown in Figure 6, the stopper 1 was connected to an air pipe 6 and placed in a water tank 7, and air was supplied at a pressure of 0.12 MPa and a flow rate of approximately 4 L / min, and the presence of bubbles was visually confirmed. At this time, the stopper 1 was set upside down, and the variation in the diameter of the bubbles ejected from each through-hole 14 was visually confirmed. Furthermore, the bubbles from each through-hole 14 were collected by water displacement, and the amount of air ejected for a certain period of time (10 seconds) was measured.

[0023] As a comparative example, a similar test was also conducted on a stopper manufactured using 16 single filamentary vanishing bodies with a diameter of 0.4 mm. Furthermore, as Example 2, a similar test was also conducted on a stopper manufactured using eight filamentary vanishing bodies in which two small cross-section portions branched from the tip of the large cross-section portion, as shown in Figure 4. In Example 2, the diameter of the large cross-section portion was 1.4 mm, and the diameters of the two small cross-section portions were each 0.4 mm, the diameters of these large cross-section portion and small cross-section portion being the same as in Example 1. Furthermore, the number of small cross-section portions that serve as gas discharge holes was also the same, at 16, in both Examples 1 and 2.

[0024] As a result of the test, in the stopper of Example 1, there was little variation in the size of the air bubbles when observed visually, and the variation in the amount of air injected from the 16 through-holes after water substitution was 15%. In addition, in the stopper of Example 2, there was no problem with the state of the air bubbles when observed visually, and the variation in the amount of air injected after water substitution was approximately uniform at 20%. In contrast, in the stopper of the comparative example, the diameter of the air bubbles from two of the 16 through-holes was clearly small, and the variation in the amount of air injected after water substitution was 60%, resulting in an uneven amount of air injected.

[0025] REFERENCE SIGNS LIST 1 stopper 11 gas pool 12 fitting portion 13 outer surface 14 through-hole 141 large cross-sectional portion 142 small cross-sectional portion 2 nozzle 3 filament-like vanishing body 31 large cross-sectional portion 32 small cross-sectional portion 4 mold 41 core rod 5 clay 6 air pipe 7 water tank

Claims

1. A method for manufacturing a continuous casting stopper, which has a gas pool in the vertical center and a plurality of through holes for gas discharge that extend from this gas pool to the fitting portion with the lower nozzle or to the outer surface in the vicinity thereof, and in which the through holes are formed by a filamentary vanishing body made of a material that disappears by heat treatment, wherein the filamentary vanishing body includes a large cross-sectional portion located on the gas pool side and a small cross-sectional portion located on the outer surface side and having a cross-sectional area smaller than that of the large cross-sectional portion, and the length of the large cross-sectional portion is longer than the length of the small cross-sectional portion.

2. A method for manufacturing a stopper for continuous casting according to claim 1, wherein the small cross-sectional portion branches into a plurality of portions from the large cross-sectional portion toward the outer surface side.

3. A method for manufacturing a stopper for continuous casting according to claim 2, wherein the cross-sectional area of ​​the large cross-sectional portion is greater than the total cross-sectional area of ​​the plurality of branched small cross-sectional portions.

4. A method for manufacturing a stopper for continuous casting according to any one of claims 1 to 3, wherein the cross-sectional area of ​​the small cross-sectional portion is 0.1 to 0.8 mm in terms of the diameter of a circle, and the cross-sectional area of ​​the large cross-sectional portion is at least twice the cross-sectional area of ​​the small cross-sectional portion.

5. A method for manufacturing a stopper for continuous casting according to any one of claims 1 to 3, wherein the length of the small cross-section portion is 10 mm or more, and the length of the large cross-section portion is 1.5 times or more the length of the small cross-section portion.

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