RIDGED TUNDISH STOPPER

Abstract

A stopper (1) is provided that includes ridges (12) in contact with the slag in a tundish (60). Each ridge (12) has a radial extension (21) that is less than half a radius (20) of the stopper (1) measured at the ridge (12). The ridges (12) decrease the creation of vortices by the stopper (1) and increase thus its lifetime. The ridges (12) are disposed in quincunx along the lateral wall (10).

Claims

1. A stopper (1) for controlling the flow of liquid metal (65) out of a tundish (60), the stopper extending in an axial direction (101) between an upper end (91) and a lower end (92) and being radially limited by a lateral wall (10) comprising a plurality of ridges (12), wherein the ridges (12) extend at least partially along a circumferential direction (103) on the lateral wall (10), wherein each ridge (12) has a radial extension (21) being at least 0.01 times the radius (20) of the stopper (1) taken at said ridge (12), characterized in that each ridge (12) has a radial extension (21) that is less than half a radius (20) of the stopper (1) taken at said ridge (12), the ridges (12) have an angular extension (), in a plan perpendicular to the axial direction (101), lower than 180, the ridges (12) are disposed in quincunx along the lateral wall (10).

2. The stopper according to claim 1, wherein the angular extension () is lower than 90.

3. The stopper according to claim 1, wherein the ridges (12) have a top side (51), and a bottom side (53), and at least one of the top side (51) and the bottom side (53) is angled with respect to the axial direction (101) such that the top side (51) and the bottom side (53) are getting closer as they extend radially away from the axis (100) of the stopper (1).

4. The stopper according to claim 1, wherein the ridges (12) are disposed as a plurality of circumferential rows (25, 26) comprising a first row (25) and a second row (26), the ridges (12) in at least one of the rows (25, 26) having their top side (51) angled by an angle (1) between 20 and 60 with respect to the axial direction (101) and/or their bottom side (53) angled by an angle (3) between 20 and 60 with respect to the axial direction (101).

5. The stopper according to claim 3, wherein the ridges (12) have a tip (52) parallel to the axial direction (101).

6. The stopper according to claim 1, comprising a higher part (55), a ridged part (56) comprising the ridges (12), and a bottom part (57) comprising the lower end (92), the ridged part (56) being between the higher part (55) and the bottom part (57), the ridged part (56) being contiguous to the higher part (55) and to the bottom part (57), wherein the difference between the diameter (22) of the stopper (1) at the uppermost ridge (121) and twice the radial extension (21) of the uppermost ridge (121) is higher than any diameter (58) of the stopper (1) in the higher part (55) and higher than any diameter (59) of the stopper (1) in the bottom part (57).

7. The stopper according to claim 1, wherein some of the ridges (12) are, at least partially, located around a narrowing (96) of a through hole (94) of the stopper (1).

8. The stopper according to claim 1, wherein each ridge (12) has an axial extension (41) being at least 0.01 times the diameter (22) of the stopper (1) at the uppermost ridge (121), preferably between 0.01 and 0.4 times the diameter (22) of the stopper (1) at the uppermost ridge (121), more preferably between 0.03 and 0.24 times the diameter (22) of the stopper (1) at the uppermost ridge (121), even more preferably between 0.05 and 0.16 times the diameter (22) of the stopper (1) at the uppermost ridge (121).

9. The stopper according to claim 1, wherein at least two of the ridges (12) are separated along the axial direction (101) by a gap (19), the gap (19) preferably having an axial extension (42) between 0.02 and 0.3 times the diameter (22) of the stopper (1) at the uppermost ridge (121), preferably between 0.04 and 0.2 times the diameter (22) of the stopper (1) at the uppermost ridge (121), more preferably between 0.05 and 0.1 times the diameter (22) of the stopper (1) at the uppermost ridge (121).

10. The stopper according to claim 1, wherein each ridge (12) has a radial extension (21) between 0.01 and 0.4 times the radius (20) of the stopper (1) taken at said ridge (12), preferably between 0.05 and 0.3 times the radius (20) of the stopper (1) taken at said ridge (12), more preferably between 0.1 and 0.2 times the radius (20) of the stopper (1) taken at said ridge (12).

11. A system for continuous casting comprising: a tundish (60) comprising an exit hole (61); liquid metal (65) in the tundish (60), the liquid metal having a top surface (66); a stopper (1) according to claim 1, configured for closing the exit hole (61) and disposed in such a way that the top surface (66) of the liquid metal (65) is in contact with at least some of the ridges (12); and a support (69) holding the stopper (1).

12. The system according to the claim 11, further comprising: a mould (64) or casting tool below the tundish (60) configured to receive liquid metal flowing through the exit hole (61); a sensor (67) for sensing the liquid metal in the mould (64) or casting tool; and a data processing unit (68) connected to the sensor (67) and to the support (69) and configured for controlling the support (69) as function of information received from the sensor (67).

13. A method for controlling a stopper (1) in a system comprising: a mould (64) or casting tool below the tundish (60) configured to receive liquid metal flowing through the exit hole (61); a sensor (67) for sensing the liquid metal in the mould (64) or casting tool; and a data processing unit (68) connected to the sensor (67) and to the support (69) and configured for controlling the support (69) as function of information received from the sensor (67), wherein the support (69) moves the stopper (1) vertically.

14. The method according to claim 13, wherein the support (69) moves the stopper (1) vertically with a frequency between 0.1 Hz and 100 Hz.

15. The method according to claim 13, wherein the system according to claim 12, and wherein the sensor (67) sends information to the data processing unit (68), and the data processing unit (68) controls the support (69) based on said information in such a way that the support (69) moves the stopper (1) vertically.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] These and further aspects of the invention will be explained in greater detail by way of example and with reference to the accompanying drawings in which:

[0031] FIG. 1 is a vertical cross-section of a tundish,

[0032] FIG. 2 is a vertical cross-section of a part of a stopper,

[0033] FIG. 3 is a horizontal cross-section of a part of a stopper, along the plan shown III-III at FIG. 2,

[0034] FIG. 4 is a vertical cross-section of a part of a tundish with a stopper,

[0035] FIG. 5 is a zoom on the stopper of FIG. 4,

[0036] FIG. 6 is a 3D view of a part of the stopper of FIG. 4,

[0037] FIG. 7 is a 3D view of a part of a stopper,

[0038] FIG. 8a is a vertical cross-section of a part of a tundish with a stopper according to the prior art,

[0039] FIG. 8b is a vertical cross-section of a part of a tundish with a stopper,

[0040] FIG. 9a is a vertical cross-section of a part of a tundish with a stopper according to the prior art, and

[0041] FIG. 9b is a vertical cross-section of a part of a tundish with a stopper.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0042] The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The drawings described are only schematic and are non limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.

[0043] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

[0044] Furthermore, the various embodiments, although referred to as preferred are to be construed as exemplary manners in which the invention may be implemented rather than as limiting the scope of the invention.

[0045] The term comprising, used in the claims, should not be interpreted as being restricted to the elements or steps listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression a device comprising A and B should not be limited to devices consisting only of components A and B, rather with respect to the present invention, the only enumerated components of the device are A and B, and further the claim should be interpreted as including equivalents of those components.

[0046] FIG. 1 represents a tundish 60. In the tundish 60, liquid metal 65 flows from a ladle shroud 62 to an exit hole 61. The top surface 66 of the liquid metal is a layer of slag. A stopper 1 controls the flow of metal through the exit hole 61.

[0047] The stopper 1 comprises a refractory material. The stopper 1 has an upper end 91 (which may be called first end) connected to a support 69 that moves the stopper 1 vertically, and a lower end 92 (which may be called second end) able to close the exit hole 61. The stopper 1 may comprise a sleeve 93, preferably located closer to the upper end 91 than to the lower 92, and made of a material more resistant to erosion than the rest of the stopper 1. The stopper 1 comprises a through hole 94 for gas injection. The exit hole 61 is connected to a tundish upper nozzle 71 and a submerged nozzle 70 leading the liquid metal to a mould 64 or casting tool.

[0048] The mould 64 or casting tool below the tundish 60 receives the liquid metal flowing through the exit hole 61 when it is not totally obstructed by the stopper 1. A sensor 67 detects at least one characteristic of the liquid metal 72 in the mould 64 or casting tool, for example the metal level. The sensor 67 sends information to a data processing unit 68 that controls the support 69. The information is thus used to move the stopper 1 vertically. The vertical position of the stopper controls the flow into the exit hole 61. In addition to its vertical motion regulating the flow through the exit hole 61, the stopper 1 may oscillate vertically (which may be called dithering). The frequency of the oscillations is preferably in the range from 0.1 Hz to 100 Hz, more preferably from 0.2 Hz to 10 Hz, and its amplitude in the range from 0.2 to 10 mm.

[0049] FIGS. 2 and 3 illustrate a stopper 1 in an embodiment of the invention. The stopper 1 has an axis 100. The stopper 1 is hereby described referring to an axial direction 101 (which is vertical in use), a radial direction 102 (horizontal in use and extending away from the stopper axis 100), and a circumferential direction 103 (horizontal and perpendicular to the radial direction 102).

[0050] The stopper 1 has a lateral wall 10 shaped by ridges 12 that protrude radially. The lateral wall 10 circumferentially surrounds the stopper 1. The ridges 12 have a top side 51, a tip 52 and a bottom side 53.

[0051] Considering any of the ridges 12, its radial extension 21 can be determined and the radius 20 of the stopper 1 at the considered ridge 12 can also be determined. In the invention, the radius 20 of the stopper 1 at any considered ridge 12 is more than twice the radial extension 21 of said considered ridge 12, preferably more than three times the radial extension 21 of said considered ridge 12, more preferably more than four times the radial extension 21 of said considered ridge 12. As visible at FIG. 2, the radius 20 of the stopper 1 measured at a ridge 12 may be equal the sum of the radial extension 21 of said ridge 12 with the radius up to said ridge 12.

[0052] The stopper 1 comprises a group 16 of ridges 12 comprising at least two adjacent ridges 12 separated along the axial direction 101 by a gap 19. These two ridges 12 are not completely aligned axially. The radial extension 21 of a ridge 12 is preferably measured with respect to the deepest point of all the gaps 19 adjacent to said ridge 12. Preferably, the stopper 1 comprises up to 100 ridges. The ridges 12 are not totally along the axial direction 101: any of the ridges 12 is either only circumferential, or partially circumferential and partially axial. At least some of the ridges 12 may be in the sleeve 93.

[0053] For conciseness in the present document, the diameter 22 of the stopper 1 at the uppermost ridge 121 is identified hereby as DU. Preferably, the ridges 12 have an axial extension 41 between 0.01 DU and 0.4 DU, preferably between 0.03 DU and 0.24 DU, more preferably between 0.05 DU and 0.16 DU. The axial extension 41 is preferably measured as close as possible to the axis 100, i.e., at the beginning of the ridge 12. Preferably, the gaps 19 have an axial extension 42 between 0.02 DU and 0.3 DU, preferably between 0.04 DU and 0.3 DU, more preferably between 0.05 DU and 0.1 DU.

[0054] For conciseness in the present document, the radius 20 of the stopper 1 at a ridge 12 is identified hereby as RS. Preferably, each ridge 12 has a radial extension 21 between 0.01 RS and 0.4 RS, preferably between 0.05 RS and 0.3 RS, more preferably between 0.1 RS and 0.2 RS.

[0055] The stopper 1 may be cylindrical or have a conical vertical section. The conical vertical section may be such that an angle between 1 and 30 exists between the lateral wall 10 and the axial direction 101. The ridges 12 have an angular extension, in a plan perpendicular to the axis 100, lower than 180, preferably lower than 90, 60 or 45.

[0056] FIG. 4 illustrates a stopper 1 with its lower end 92 closing the exit hole 61 of the tundish 60. The exit hole 61 is connected to the tundish upper nozzle 71. The lower end 92 is covered by an anti-stick coating 95.

[0057] FIG. 5 is a zoom into the stopper 1 of FIG. 4, showing the radial extension 21 of the ridge 12, and the radius 20 of the stopper 1 at this ridge 12. The radial extension 21 of the ridge 12 is measured from the line 190 which is axial and passes at the deepest point of the gap 19 adjacent to said ridge 12.

[0058] The ridges 12 are disposed in a plurality of circumferential rows 25, 26 on the lateral wall 10. Each row horizontally surrounds the stopper 1. The plurality of circumferential rows 25, 26 comprises preferably only two rows 25, 26: a first row 25 and a second row 26, the first row 25 being closer to the upper end 91 than the second row 26. The ridges 12 of the lowest of all the rows 25, 26 may be configured to contact the tundish upper nozzle 71. The quincunx disposition of the ridges 12 implies a circumferential offset between ridges 12 of adjacent rows 25, 26. Each row 25, 26 may comprise between three and twelve ridges 12. The number of ridges 12 in the rows 25, 26 is preferably identical. Within each row 25, 26, the ridges 12 have preferably an identical shape. The ridges 12 of different rows 25, 26 may have identical or different shapes. For example, in the stopper 1 of FIGS. 4 and 5, the ridges 12 are identical within each row 25, 26 but are different between rows 25, 26. The ridges 12 of the second row 26 are preferably located, at least partially, around a narrowing 96 of the through hole 94 of the stopper 1.

[0059] The top side 51 of the ridges 12 make an angle 1 with the axis 100, 1 being measured downwards. The bottom side 53 of the ridges 12 make an angle 3 with the axis 100, 3 being measured upwards. The angles 1 and 3 are preferably such that the top side 51 and the bottom side 53 extend radially away towards each other. In other words, such top and bottom sides are getting closer as extending away from the axis 100. The angles 1 and 3 may be between 20 and 60. As shown on FIGS. 4 and 5, 1 may be lower than 3 for the first row 25 and higher than 3 for the second row 26. The tip 52 of the ridges 12 may be parallel to the axis 100.

[0060] The stopper 1 preferably comprises a higher part 55, a ridged part 56 comprising the ridges 12, and a bottom part 57 comprising the lower end 92. The higher part 55 may comprise the upper end 91. The ridged part 56 is directly between the higher part 55 and the bottom part 57. In a preferred embodiment of the invention, the ridged part 56 has a diameter, taken without the ridge 12 (which is the difference between the diameter 22 of the stopper 1 at the uppermost ridge 121 and twice the radial extension 21 of the uppermost ridge 121), that is higher than any of the diameter 58 of the higher part 55 or the diameter 59 of the bottom part 57, irrespective of where the diameter 58 of the higher part 55 is measured or where the diameter 59 of the bottom part 57 is measured. In other words, the ridges 12 are located in the thickest section of the stopper 1.

[0061] FIGS. 6 and 7 illustrate two stoppers 1 according to the invention, wherein the ridges 12 are closer to the lower end 92 than to the upper end 91. The angles 1 and 3 are below 90 in the embodiment of FIG. 6, and, in the embodiment of FIGS. 7, 1 is higher than 90 and 3 is lower than 90. The tip 52 of the ridges 12 may be planar, sharp, or rounded.

[0062] FIGS. 8a to 9b compare Computional Fluid Dynamics (CFD) simulations for a stopper 2 without any ridge (called below standard stopper) and a stopper 1 with ridges 12 as illustrated at FIG. 6 (called below ridged stopper). On these figures, reference 111 is the direction of the flow, reference 112 is the slag and reference 113 is the steel.

[0063] FIG. 8a (for the standard stopper 2) and 8b (for the ridged stopper 1) show the direction of the flow 111. It appears that, under the same conditions, the steel 113/slag 112 interface bent downwards for the standard stopper 2 while this interface is globally flat for the ridged stopper 1.

[0064] FIG. 9a (for the standard stopper 2) and 9b (for the ridged stopper 1) show the slag entrainment. It appears that, under the same conditions, the slag 112 is entrained into the tundish upper nozzle 71 for the standard stopper 2 while the slag 112 is not entrained into the tundish upper nozzle 71 for the ridged stopper 1.

[0065] Although the present invention has been described above with respect to particular embodiments, it will readily be appreciated that other embodiments are also possible. Moreover, the feature(s) of any described or illustrated stopper is (are) hereby considered as combinable with feature(s) of any other stopper(s).