Stopper rod and system for continuous casting

Abstract

The utility model relates to a stopper rod (1) and a system for continuous casting, the system for continuous casting comprises the stopper rod (1), and the stopper rod comprises a ridge part (12) contacted with slag in a tundish (60). Each ridge (12) has a radial extension (21) that is less than half of the radius (20) of the stopper (1) measured at said ridge (12). The ridge (12) is raised and lowered around the stopper rod (1). The ridge (12) reduces the generation of vortices of the stopper (1) and thus prolongs the life of the stopper.

Description

Technical Field

[0001] The utility model relates to a stopper rod for controlling the flow of molten metal through an outlet hole of a tundish towards a mold or a casting tool. Background Art

[0002] Stopper rods are generally used to control the flow of liquid metal flowing out of a tundish and towards a mold or a casting tool. The stopper rod includes an elongated body having a lower end designed to close an outlet hole at the bottom of the tundish. The stopper rod moves up and down to close or open the outlet hole.

[0003] The lower end of the stopper rod is immersed in the liquid metal. The upper end of the stopper rod is in the air. The middle part of the stopper rod contacts a slag layer floating at the interface between the liquid metal and the air. The slag flowing downward along the stopper rod in a vortex form chemically and mechanically erodes the stopper rod, thereby locally reducing the diameter of the stopper rod and shortening its service life. In addition, when the liquid metal level is low, the slag may be driven downward by the vortex into the outlet hole.

[0004] In order to suppress the vortex, Document CN 110788314 A discloses a stopper rod having a large stop and a rib plate.

[0005] In order to extend the service life of the stopper rod, Document KR 20140140429 A discloses a stopper rod made of an elongated body and a removable protective member located at the height of the slag. It is expected that the slag will erode the removable protective member, so the removable protective member can be removed and replaced with a new one.

[0006] CN 106735153 A describes a stopper rod with a ring, aiming to promote the floating of inclusions to improve the cleanliness of molten steel.

[0007] The problem with these known stopper rods is that they include thick protrusions, thus greatly increasing the local diameter of the stopper rod and therefore increasing its movement resistance in the liquid metal. Therefore, the up and down movement of the stopper rod cannot be finely controlled. Summary of the Utility Model

[0008] The purpose of the utility model is to provide a stopper rod that reduces the vortex along its side wall.

[0009] The purpose of the utility model is to provide a stopper rod with a particularly long service life.

[0010] The present utility model relates to a stopper for controlling the outflow of liquid metal from a tundish. The stopper extends axially between an upper end and a lower end and is radially defined by a lateral wall including a plurality of ridges, wherein the ridges extend at least partially along the circumferential direction on the lateral wall, wherein at least two of the ridges are separated by a gap along the axial direction, wherein each ridge has a radial extension that is at least 0.01 times the radius obtained by the stopper at the ridge, wherein each ridge has an axial extension that is at least 0.01 times the diameter of the stopper at the uppermost ridge, and is characterized in that each ridge has a radial extension less than half of the radius obtained by the stopper at the ridge, at least a part of at least one of the ridges rises along the circumferential direction, and at least a part of at least another of the ridges descends along the circumferential direction, and each ridge extends between one or more upper points closest to the upper end and a corresponding number of one or more lower points closest to the lower end.

[0011] The inventors have shown by simulation that such a plurality of ridges extending up and down break up larger eddies, which cause slag entrainment along the lateral wall and thus cause strong erosion. In addition, they have shown that the average wall shear stress on the stopper is reduced compared to a stopper without such ridges. They have also shown that this oscillating shape of the plurality of ridges prevents the detachment of a stable large eddy in the wake of the stopper (the detachment of a stable large eddy increases the risk of slag entrainment).

[0012] The stopper according to the present utility model does not include any thick protrusions, since all the ridges are radially limited by half of the radius of the stopper at the height of the ridge in terms of size. This absence of thick protrusions provides low movement resistance and thus good control response. In the stopper of KR 20140140429 A, there is no such upper limit for the radial dimension of each ridge of the claimed stopper, where a removable protective member with reference numeral 200 is provided with extremely large ridges. In this prior art document, the "thread" with reference numeral 110 is not intended to be used without the removable protective member or to be in contact with slag, and forms a single ridge rather than a plurality of ridges.

[0013] In the present utility model, the ridges extend at least partially along the circumferential direction and thus are not only axial, but also form the upper and lower sides of the gap. The inner side of the gap is the lateral wall between the ridges, and the outer side of the gap is open. The gap accommodates a certain volume of liquid metal and / or slag, which tend to stay in the gap during the vertical movement of the stopper, thus reducing the erosion of the stopper. The radial extension of the ridge is measured with respect to the deepest point of all the gaps adjacent to the ridge.

[0014] At least two of the ridges separated along the axial direction are preferably axially aligned, but do not have to be completely axially aligned. The stopper rod is preferably a single piece. The stopper rod is preferably molded as a single piece. The ridges are preferably integral with the stopper rod, and in particular with the upper end and the lower end.

[0015] The stopper rod does not include any such protrusion having a radial extension greater than half of the radius obtained by the stopper rod at the protrusion. The stopper rod does not include any removable protective member around the side wall. The ridges are preferably not helical.

[0016] The side wall is the outer surface. The ridges are preferably designed to contact the slag at the top surface of the liquid metal. The ridges extend partially along the circumferential direction and partially along the axial direction on the side wall.

[0017] A plurality of ridges form a swinging shape along the side wall. The ridges extend in a shape that swings between one or more upper points and one or more lower points. The ridges extend as a wave (or at least a part of a wave) between one or more upper points and one or more lower points.

[0018] In an embodiment, the side wall has a first diameter at the uppermost ridge and a second diameter at the lowermost ridge, and the first diameter is greater than the second diameter. In other words, the side wall narrows when extending downward at the height of the ridges. This narrowing of the stopper rod reduces the diameter in the middle region and thus reduces the weight of the stopper rod.

[0019] In an embodiment, the side wall includes two elongated passages circumferentially defined by at least half of the ridges. The stopper rod may include more than two elongated passages. The elongated passages are positions along the circumference of the side wall where the liquid is less disturbed by the vertical movement of the ridges. In other words, the elongated passages are passages for keeping the liquid more stable around the stopper rod. Therefore, the elongated passages reduce the influence of the waves generated due to this vertical movement.

[0020] In an embodiment, the ridges are completely received in the recesses on the side wall.

[0021] The ridges do not extend radially farther than the recesses. This shape is particularly meaningful for avoiding waves.

[0022] The stopper rod includes at least two ridges that are closer to the upper end than to the lower end. The at least two ridges are vertically located at the steady-state casting level height of the slag in the tundish.

[0023] The present utility model also relates to a system for continuous casting, the system comprising:

[0024] · A tundish, the tundish including an outlet hole;

[0025] · Liquid metal in a tundish, the liquid metal having a top surface;

[0026] · A stopper rod as described herein, the stopper rod being configured to close the outlet hole and arranged such that the top surface of the liquid metal contacts at least some of the ridges; and

[0027] · A support member that holds the stopper rod.

[0028] In an embodiment, the system further includes:

[0029] · A mold or casting tool below the tundish, the mold or casting tool being configured to receive the liquid metal flowing through the outlet hole;

[0030] · A sensor for sensing the liquid metal in the mold or casting tool; and

[0031] · A data processing system connected to the sensor and the support member and configured to control the support member based on the information received from the sensor.

[0032] With such a system, the vertical movement of the stopper rod is controlled based on measurements in the mold or casting tool, and thus the metal flow into the outlet hole is controlled.

[0033] The present utility model also relates to a method for controlling a stopper rod as described herein in a system as described herein, wherein the support member vertically moves the stopper rod, preferably vertically moves the stopper rod at a frequency between 0.1 Hz and 100 Hz.

[0034] With the stopper rod according to the present utility model, the vertical movement of the stopper rod is not weakened by any thick protrusions, which is particularly advantageous for rapid oscillation.

[0035] In an embodiment,

[0036] · The sensor sends information to the data processing system,

[0037] · The data processing system controls the support member based on the information in such a way that the support member vertically moves the stopper rod. Description of the Drawings

[0038] These aspects and additional aspects of the present utility model will be explained in more detail by way of example and with reference to the drawings, in which:

[0039] Figure 1 is a vertical cross-sectional view of the tundish,

[0040] Figure 2 is a vertical cross-sectional view of a part of the stopper rod,

[0041] Figure 3A horizontal sectional view of a part of the stopper along the Figure 2 plane III-III shown in

[0042] Figure 4 A 3D view of a part of the stopper,

[0043] Figure 5 A 3D view of a part of the stopper,

[0044] Figure 6a A 3D view of a part of the stopper,

[0045] Figure 6b A 3D view of a part of the stopper,

[0046] Figure 6c A 3D view of a part of the stopper,

[0047] Figure 7a A top view of a part of a tundish with a stopper according to the prior art,

[0048] Figure 7b A top view of a part of a tundish with a stopper,

[0049] Figure 8a A vertical sectional view of a part of a tundish with a stopper according to the prior art,

[0050] Figure 8b A vertical sectional view of a part of a tundish with a stopper,

[0051] Figure 9a A vertical sectional view of a part of a tundish with a stopper according to the prior art,

[0052] Figure 9b A vertical sectional view of a part of a tundish with a stopper,

[0053] Figure 10 A graph showing the change in volume of simulated high-energy eddies over time,

[0054] Figure 11a A top view of a part of a tundish with a stopper according to the prior art,

[0055] Figure 11b A top view of a part of a tundish with a stopper,

[0056] Figure 12 A graph showing the change in area of high-energy eddies on the top surface of the simulated liquid over time,

[0057] Figure 13a Shows the side wall of a stopper of the prior art, on which the wall shear stress is depicted,

[0058] Figure 13b shows the side wall of the stopper rod on which the wall shear stress is depicted, and

[0059] Figure 14 is a graph showing the simulated wall shear stress varying with time. Detailed Description of the Invention

[0060] The present invention will be described with reference to specific embodiments and certain drawings, but the present invention is not limited thereto. The described drawings are only illustrative and not restrictive. In the drawings, for illustrative purposes, the dimensions of some elements may be exaggerated and not drawn to scale.

[0061] In addition, the first, second, third, and similar terms in the description and claims are used to distinguish similar elements and not necessarily to describe a sequential or chronological order. These terms are interchangeable where appropriate, and the embodiments of the present invention may be operated in an order different from that described or shown herein.

[0062] In addition, although various embodiments are referred to as "preferred", they should be construed as exemplary ways of implementing the present invention rather than as limiting the scope of the present invention.

[0063] The term "comprising" used in the claims should not be construed as limited to the elements or steps listed thereafter; this term does not exclude other elements or steps. This term needs to be construed as specifying the presence of the stated features, integers, steps, or components mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components or a combination thereof. Thus, the scope of the expression "a device comprising A and B" should not be limited to a device consisting only of components A and B, but for the purposes of the present invention, only the components A and B of the device are listed, and further claims should be construed as including equivalents of these components.

[0064] Figure 1 denotes the tundish 60. In the tundish 60, the liquid metal 65 flows from the ladle long nozzle 62 to the outlet hole 61. The top surface 66 of the liquid metal is the slag layer. The stopper rod 1 controls the flow of the metal through the outlet hole 61.

[0065] The stopper 1 includes refractory material. The stopper 1 has an upper end 91 (which may be referred to as the first end) and a lower end 92 (which may be referred to as the second end), the upper end being connected to a support 69 that vertically moves the stopper 1, and the lower end being capable of closing the outlet hole 61. The stopper 1 may include a slag line 93, which is preferably located closer to the upper end 91 than to the lower end 92 and is made of a material more corrosion-resistant than other parts of the stopper 1. The stopper 1 includes a through-hole 94 for injecting gas. The outlet hole 61 is connected to the tundish nozzle 71 and the submerged nozzle 70, so as to guide the liquid metal to the mold 64 or the casting tool.

[0066] When the outlet hole is not completely blocked by the stopper 1, the mold 64 or the casting tool below the tundish 60 receives the liquid metal flowing through the outlet hole 61. A sensor 67 detects at least one characteristic of the liquid metal 72 in the mold 64 or the casting tool, such as the metal level. The sensor 67 sends information to a data processing unit 68 that controls the support 69. Thus, the information is used to vertically move the stopper 1. The vertical position of the stopper controls the flow rate into the outlet hole 61. In addition to its vertical movement for regulating the flow rate through the outlet hole 61, the stopper 1 can also vertically oscillate (which may be referred to as "dithering"). The frequency of the oscillation is preferably in the range from 0.1 Hz to 100 Hz, more preferably in the range from 0.2 Hz to 10 Hz, and its amplitude is in the range from 0.2 to 10 mm.

[0067] Figure 2 and Figure 3 The stopper 1 in an embodiment of the present invention is shown. The stopper 1 has an axis 100. The stopper 1 is herein described with reference to an axial direction 101 (which is vertical in use), a radial direction 102 (which is horizontal in use and extends away from the stopper axis 100), and a circumferential direction 103 (which is horizontal and perpendicular to the radial direction 102).

[0068] The stopper 1 has a side wall 10 formed by radially protruding ridges 12. The side wall 10 circumferentially surrounds the stopper 1. Considering any one 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 present invention, the radius 20 of the stopper 1 at any considered ridge 12 is greater than twice the radial extension 21 of the considered ridge 12, preferably greater than three times the radial extension 21 of the considered ridge 12, more preferably greater than four times the radial extension 21 of the considered ridge 12. As Figure 2 can be seen, the radius 20 of the stopper 1 measured at the ridge 12 can be equal to the sum of the radial extension 21 of the ridge 12 and the radius up to the ridge 12.

[0069] The stopper 1 includes at least two ridges 12. The stopper may include two, three, four or five ridges 12. The stopper 1 includes a group 16 of ridges 12, the group including at least two adjacent ridges 12, the at least two adjacent ridges being separated by a gap 19 along the axial direction 101. Preferably, the stopper 1 includes fewer than 100 ridges. The ridges 12 do not extend completely along the axial direction 101: any one of the ridges 12 is partially circumferential and partially axial. At least some of the ridges 12 may be in the slag line 93.

[0070] Herein, for the sake of simplicity, the diameter 22 of the stopper 1 at the uppermost ridge 121 is herein identified as DU. Preferably, the ridges 12 have an axial extension 41 between 0.01DU and 0.4DU, preferably between 0.03DU and 0.24DU, more preferably between 0.05DU and 0.16DU. The axial extension 41 is preferably measured as close as possible to the axis 100, i.e., at the start of the ridge 12. Preferably, the gap 19 has an axial extension 42 between 0.02DU and 0.3DU, preferably between 0.04DU and 0.3DU, more preferably between 0.05DU and 0.1DU.

[0071] Herein, for the sake of simplicity, the radius 20 of the stopper 1 at the ridge 12 is herein identified as RS. Preferably, each ridge 12 has a radial extension 21 between 0.01RS and 0.4RS, preferably between 0.05RS and 0.3RS, more preferably between 0.1RS and 0.2RS.

[0072] The stopper 1 may be cylindrical or may have a conical vertical section at least at the height of the ridges 12 in such a way that the diameter 22 of the stopper at the uppermost ridge 121 is greater than the diameter 23 of the stopper at the lowermost ridge 122. The conical vertical section may be such that there is an angle α between 1° and 30° between the lateral wall 10 and the axial direction 101.

[0073] In some embodiments of the present utility model, the ridge 12 has an angular extension β in a plane perpendicular to the axis 100, β being less than 350°, possibly less than 180°. Thus, the ridge 12 terminates circumferentially at a circumferential end 15. Examples of such embodiments are visible in Figure 3 and Figure 4 In other embodiments of the present utility model, as shown in Figures 5 to 6c the ridge 12 has an angular extension β equal to 360° in a plane perpendicular to the axis 100.

[0074] Figure 4shows circumferentially partial and axially partial ridges 12. These ridges circumferentially define an elongate passageway 13. Preferably, the elongate passageway 13 has an angular extent greater than 2° and less than 30° in a plane perpendicular to axis 100. The elongate passageway 13 is circumferentially defined by some of the ridges 12 (e.g., by at least half of the ridges 12). In other words, these elongate passageways are located between the circumferential ends 15 of some of the ridges 12 (e.g., half of the ridges). These elongate passageways are preferably parallel to axis 100. In Figure 4 each ridge 12 extends between an upper point 31 and a lower point 32, and some of the ridges 12 rise with the circumferential direction 103, and some of the ridges 12 fall with the circumferential direction 103.

[0075] Figure 5 and Figures 6a to 6c shows ridges 12 whose shape sways between two upper points 31 (“upper” means closest to the upper end 91) and two lower points 32 (“lower” means closest to the lower end 92). These ridges 12 have two portions that rise with the circumferential direction 103 and two portions that fall with the circumferential direction 103. Within the scope of the present utility model, each ridge 12 can, for example, sway between an upper point and a lower point, sway between two upper points and two lower points; or generally, sway between N upper points and N lower points, where N is an integer from 1 to 10.

[0076] Figures 6a to 6c shows lines 200 that are tangent to the lateral walls 10 above and below the ridges 12. Considering all the tangents, a tangent cone or cylinder can be drawn. In Figure 6a and Figure 6b the lateral walls 10 include recesses 14. The recesses 14 are due to the concave surfaces of the lateral walls 10, i.e., the recesses 14 are recesses relative to the tangent cone or cylinder. In Figure 6a and Figure 6b the ridges 12 are completely received within the recesses 14. In other words, the ridges do not project beyond the tangent cone or cylinder. In Figure 6a the ridges 12 are radially inward relative to the tangent cone or cylinder; in Figure 6b the ridges are radially tangent to the tangent cone or cylinder. In Figure 6c the ridges 12 project beyond the tangent cone or cylinder.

[0077] Figure 6cShows the axial distance 18 between the upper point 31 and the lower point 32 of one of the ridges 12 in the ridge portion. Preferably, for each ridge 12, the axial distance 18 between any upper point 31 and any lower point 32 is between 0.01 and 0.4 times the diameter 22 of the stopper rod 1 at the uppermost ridge 121, preferably between 0.03 and 0.24 times the diameter 22 of the stopper rod 1 at the uppermost ridge 121, and more preferably between 0.05 and 0.16 times the diameter 22 of the stopper rod 1 at the uppermost ridge 121.

[0078] Within the scope of the present utility model, and as Figures 5 to 6c shown, each ridge 12 is preferably parallel to one or two axially adjacent ridges 12, and more preferably the same as one or two axially adjacent ridges.

[0079] Figures 7 to Figure 14 A computational fluid dynamics (CFD) simulation of a stopper rod 2 without any ridges (hereinafter referred to as a standard stopper rod) and a stopper rod 1 with ridges 12 as Figure 6c shown (hereinafter referred to as a ridged stopper rod) was compared. The ladle submerged entry nozzle is on the right side of these figures, so the fluid flows from right to left.

[0080] Figure 7a (For the standard stopper rod) and Figure 7b (For the ridged stopper rod) show the top surface 66; Figure 8a (For the standard stopper rod) and Figure 8b (For the ridged stopper rod) show the central section of the tundish. They show the velocity contours in m / s and the arrows indicating the flow direction. In both cases, vortices appear in the wake behind the stopper rod.

[0081] Figure 9a (For the standard stopper rod) and Figure 9b (For the ridged stopper rod) show the central section of the tundish, where the high-energy vortices are shown in black. It can be seen from the figure that the ridges 12 reduce the generation of large vortices, which pose a risk of slag entrainment. Figure 10 Shows the change in volume of the high-energy vortices over time. Table I provides the average volume and the maximum volume derived from the Figure 10 graph.

[0082] Table I

[0083] Standard stopper 2 Ridge stopper 1 Average volume of high-energy eddy current (liters) 1.96 1.66 Maximum volume of high-energy eddy current (liters) 3.81 2.98

[0084] Figure 11a (For the standard stopper rod) and Figure 11b(For the ridge-type stopper) A top view of the tundish is shown, where the high-energy eddies are black, and where the arrows indicate the flow direction. As can be seen from the figure, the ridge 12 reduces the generation of high-energy eddies on the top surface in the wake of the stopper 1. Table II provides the areas in these figures with vorticity enstrophy ξ > 2s -2 The area.

[0085] Table II

[0086] Standard stopper 2 Ridge stopper 1 <![CDATA[Area (cm -2 2 ) with vorticity enstrophy ξ > 2s> 459 225

[0087] Figure 12 Shows the variation of the area of high-energy eddies on the top surface 66 with time. Table III provides the average area and the maximum area derived from the Figure 12 Curve graph.

[0088] Table III

[0089] Standard stopper 2 Ridge stopper 1 <![CDATA[Average area (cm 2 ) of the high-energy eddy currents on the top surface 324 287 <![CDATA[Maximum area (cm 2 ) of the high-energy eddy current on the top surface 462 397

[0090] In summary, Figures 7 to Figure 12 Show that the rising and falling ridges 12 have a significant effect on the generation of eddies, especially on the generation of large eddies, which play an important role in the erosion of the stopper.

[0091] Figure 13a (For the standard stopper) and Figure 13b (For the ridge-type stopper) Show the side walls of the stopper, where the streamlines indicate the flow direction, the wall shear stress contours [Pa], and the black areas indicate the high wall shear stress regions. As can be seen from the figure, for the standard stopper 2, the shear stress is uniformly distributed on the surface, while for the ridge-type stopper 1, the shear stress is concentrated on the ridge (but not higher than the shear stress of the standard stopper 2). Table IV provides the average wall shear stress in these figures.

[0092] Table IV

[0093] Standard stopper 2 Ridge stopper 1 Average wall shear stress (Pa) 0.28 0.21

[0094] Figure 14 Shows the variation of the wall shear stress with time. Table V provides the average wall shear stress and the maximum wall shear stress derived from the Figure 14 Curve graph.

[0095] Table V

[0096] Standard stopper 2 Ridge stopper 1 Average wall shear stress (Pa) 0.36 0.28 Maximum wall shear stress (Pa) 0.46 0.39

[0097] Compared with the standard stopper 2, the wall shear stress in the ridge-type stopper 1 is lower, and the expected mechanical erosion is also lower.

[0098] Although the present utility model has been described above with respect to specific embodiments, it is readily understood that other embodiments are also possible. In addition, any feature of the stopper rod described or shown herein is considered to be combinable with any other feature of any other stopper rod.

Claims

1. A stopper rod (1) for controlling the outflow of liquid metal (65) from a tundish (60), the stopper rod extending in an axial direction (101) between an upper end (91) and a lower end (92) and being radially defined by a lateral wall (10) including a plurality of ridges (12), Among them, the ridges (12) extending at least partially along a circumferential direction (103) on the lateral wall (10), wherein at least two of the ridges (12) are spaced apart by a gap (19) along the axial direction (101), wherein each ridge (12) has a radial extension (21) that is at least 0.01 times the radius (20) of the stopper rod (1) at the ridge (12), wherein each ridge (12) has an axial extension (41) that is at least 0.01 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121), characterized in that each ridge (12) has a radial extension (21) less than half of the radius (20) of the stopper rod (1) at the ridge (12), at least a part of at least one of the ridges (12) rises with the circumferential direction (103), and at least a part of at least another of the ridges (12) falls with the circumferential direction (103), and each ridge (12) extends between one or more upper points (31) closest to the upper end (91) and a corresponding number of one or more lower points (32) closest to the lower end (92).

2. The stopper according to claim 1, wherein, The lateral wall (10) has a first diameter (22) at the uppermost ridge (121) and a second diameter (23) at the lowermost ridge (122), the first diameter (22) being greater than the second diameter (23).

3. The stopper according to any one of the preceding claims 1-2, wherein, The ridges (12) are fully received in recesses (14) on the lateral wall (10).

4. The stopper rod according to claim 1, wherein The axial distance (18) between each upper point (31) and each lower point (32) of the same ridge (12) is between 0.01 times and 0.4 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

5. The stopper according to claim 4, wherein, The axial distance (18) is between 0.03 times and 0.24 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

6. The stopper according to claim 5, wherein, The axial distance (18) is between 0.05 times and 0.16 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

7. The stopper according to claim 1, wherein, The ridges (12) have an angular extension (β) less than 180° in a plane perpendicular to the axial direction (101).

8. The stopper rod according to claim 1, wherein Each ridge (12) circumferentially terminates at two circumferential ends (15); and wherein the lateral wall (10) includes two elongated passages (13) between the circumferential ends (15) of some of the ridges (12).

9. The stopper according to claim 8, wherein, The elongated passages (13) are parallel to the axial direction (101).

10. The stopper according to claim 1, wherein, Each ridge (12) is parallel to one or two axially adjacent ridges (12).

11. The stopper according to claim 1, wherein, Each ridge (12) is identical to one or two axially adjacent ridges (12).

12. The stopper according to claim 1, wherein, Each ridge (12) has an axial extension (41) between 0.01 times and 0.4 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

13. The stopper according to claim 12, wherein, Each ridge (12) has an axial extension (41) between 0.03 times and 0.24 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

14. The stopper rod according to claim 13, wherein, Each ridge (12) has an axial extension (41) between 0.05 times and 0.16 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

15. The stopper rod according to claim 1, wherein, Each gap (19) has an axial extension (42) between 0.02 times and 0.3 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

16. The stopper according to claim 15, wherein, Each gap (19) has an axial extension (42) between 0.04 times and 0.2 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

17. The stopper according to claim 16, wherein, Each gap (19) has an axial extension (42) between 0.05 times and 0.1 times the diameter (22) of the stopper rod (1) at the uppermost ridge (121).

18. The stopper rod according to claim 1, wherein, Each ridge (12) has a radial extension (21) between 0.01 times and 0.4 times the radius (20) of the stopper rod (1) taken at the ridge (12).

19. The stopper according to claim 18, wherein, Each ridge (12) has a radial extension (21) between 0.05 times and 0.3 times the radius (20) of the stopper rod (1) taken at the ridge (12).

20. The stopper rod according to claim 19, wherein, Each ridge (12) has a radial extension (21) between 0.1 times and 0.2 times the radius (20) of the stopper rod (1) taken at the ridge (12).

21. A system for continuous casting, characterized in that, The system comprises: · A tundish (60) that includes an outlet hole (61); · Liquid metal (65) in the tundish (60), the liquid metal having a top surface (66); · A stopper rod (1) according to any one of the preceding claims 1-20, the stopper rod being configured to close the outlet hole (61) and arranged such that the top surface (66) of the liquid metal (65) contacts at least some of the ridges (12); and · A support (69) that holds the stopper rod (1).

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