STOPPER ROD AND METHOD FOR INDUCING A ROTATIONAL FLOW OF A MOLTEN METAL

Abstract

Stopper rod (100) for controlling the flow of molten metal and for inducing a rotational flow of molten metal, said stopper rod (100) comprising a rod-shaped stopper body (101), said rod-shaped stopper body (101) extending along a central longitudinal axis (L) from a first end (105) to a second end (107), said rod-shaped stopper body (101) comprising a nose (103) at said second end (107), wherein said nose (103) provides an exterior surface; a chamber (109), said chamber (109) extending along said central longitudinal axis (L) within said stopper body (101) from said first end (105) towards said second end (107) and ending at a distance from said second end (107); at least one channel (111), preferably a plurality of channels (111), being provided on an exterior surface of said rod-shaped stopper body (101) and at least partially on said exterior surface of said nose (103), and at least partially running around said central longitudinal axis (L), and progressing along the direction of said central longitudinal axis (L); gas supply connecting means (123), said gas supply connecting means (123) connecting said chamber (109) and each of said at least one channel (111).

Claims

1. Stopper rod (100) for controlling the flow of molten metal and for inducing a rotational flow of molten metal, said stopper rod (100) comprising: 1.1. a rod-shaped stopper body (101), 1.1.1. said rod-shaped stopper body (101) extending along a central longitudinal axis (L) from a first end (105) to a second end (107), 1.1.2. said rod-shaped stopper body (101) comprising a nose (103) at said second end (107), wherein 1.1.3. said nose (103) provides an exterior surface; 1.2. a chamber (109), said chamber (109) 1.2.1. extending along said central longitudinal axis (L) within said stopper body (101) from said first end (105) towards said second end (107) and ending at a distance from said second end (107); 1.3. at least one channel (111), 1.3.1. said at least one channel (111) being provided on an exterior surface of said rod-shaped stopper body (101), 1.3.2. said at least one channel (111) being provided at least partially on said exterior surface of said nose (103), 1.3.3. said at least one channel (111) is at least partially running around said central longitudinal axis (L), and 1.3.4. said at least one channel (111) is progressing along the direction of said central longitudinal axis (L); and 1.4. gas supply connecting means (123), said gas supply connecting means (123) 1.4.1. connecting said chamber (109) and each of said at least one channel (111).

2. Stopper rod (100) according to claim 1, wherein said at least one channel (111) comprises a first channel wall (113), limiting each of said at least one channel (111) in a direction towards said first end (105), wherein said first channel wall (113) and said exterior surface of said nose (103) form a first edge (119), and wherein said first edge (119) has the shape of a sharp edge, said first edge (119) having a radius not above 2 mm.

3. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) defines a channel direction (112), and wherein each of said channel direction (112) is aligned at an angle (.sub.i) to the said central longitudinal axis (L), and wherein each of said angle (.sub.i) is in the range between 30 to 60.

4. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) defines a channel direction (112), and wherein each of said channel direction (112) is aligned at an angle (.sub.i) to the said central longitudinal axis (L), and wherein all of said angles (.sub.i) are the same.

5. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) runs along a helical path on said exterior surface of said nose (103).

6. Stopper rod (100) according to claim 1, said stopper rod (100) comprising an auxiliary gas supply connecting means (133), said auxiliary gas supply connecting means (133) leading from said chamber (109) and through said rod-shaped stopper body (101) into an auxiliary channel (131), said auxiliary channel (131) being provided on said exterior surface of said nose (103).

7. Stopper rod (100) according to claim 1, wherein each of said gas supply connecting means (123) lead into each of said at least one channel (111) by means of indirect permeability, wherein indirect permeability is achieved by at least one porous insert.

8. Stopper rod (100) according to claim 1, wherein said at least one channel (111) is a plurality of channels (111), each channel (111) of the plurality of channels (111) is arranged in a rotationally symmetric arrangement with respect to the said central longitudinal axis (L), such that the distance between each nearest neighboring channels (111) is the same.

9. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) has a maximum depth of at least 3 mm.

10. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) extends from a first channel end (111u) to a second channel end (111d), wherein said second channel end (111d) is closer to said second end (107) than said first channel end (111u).

11. Stopper rod (100) according to claim 1, wherein each of said at least one channel (111) extends from a first channel end (111u) to a second channel end (111d), wherein said second channel end (111d) is closer to said second end (107) than said first channel end (111u), wherein the distance between said first channel end (111u) and said second channel end (111d) defines a channel length (111l), wherein each of said at least one channel (111) has a maximum depth of at least 3 mm along at least 30% of said channel length (111l).

12. Stopper rod (100) according to claim 1, wherein said gas supply connecting means (123) lead into each of said at least one channel (111) at a position between 50 mm to 100 mm distance from said second end (107) of the stopper body (101).

13. Stopper rod (100) according to claim 1, wherein said stopper body (101) is made of a refractory ceramic material.

14. Method for controlling the flow of molten metal and for inducing a rotational flow of molten metal, comprising the steps: 14.1. a stopper rod providing step (300) in which a stopper rod (100) is provided, said stopper rod (100) comprising: 14.1.1. a rod-shaped stopper body (101), 14.1.1.1. said rod-shaped stopper body (101) extending along a central longitudinal axis (L) from a first end (105) to a second end (107), 14.1.1.2. said rod-shaped stopper body (101) comprising a nose (103) at said second end (107), wherein 14.1.1.3. said nose (103) provides an exterior surface; 14.1.2. a chamber (109), said chamber (109) 14.1.2.1. extending along said central longitudinal axis (L) into said stopper body (101) from said first end (105) towards said second end (107) and ending at a distance from said second end (107); 14.1.3. at least one channel (111), said at least one channel (111): 14.1.3.1. being provided on an exterior surface of said rod-shaped stopper body (102) and at least partially on said exterior surface of said nose (103), 14.1.3.2. at least partially running around said central longitudinal axis (L), 14.1.3.3. and progressing along the direction of said central longitudinal axis (L); 14.1.4. gas supply connecting means (123), said gas supply connecting means (123) 14.1.4.1. connecting said chamber (109) and each of said at least one channel (111); 14.2. a gas supply system providing step (310) in which a gas supply system (200) provides a gas (210) to said chamber (109); and 14.3. a gas guiding step (325) in which said gas (210) is guided at a gas flow (Q(t)) by said gas supply system (200) via said chamber (109) through said gas supply connecting means (123) to said at least one channel (111) of said stopper rod (100).

15. Method according to claim 14, with the additional steps of: 15.1. a tundish nozzle providing step (320) in which a tundish nozzle (9, 10) is provided, said tundish nozzle (9, 10) comprising a rotational flow measurement unit (20), capable of measuring the rotational flow (Rot(t)) of the molten metal inside of said tundish nozzle (9, 10); 15.2. a rotational flow determination step (330) in which the rotational flow (Rot(t)) of the molten metal inside of the tundish nozzle (9, 10) is determined by said rotational flow measurement unit (20); 15.3. a target providing step (340) in which a target for the rotational flow (Rot.sub.0) inside of the tundish nozzle (9,.10) is provided; 15.4 a gas increasing step (350) in which said gas flow (Q(t)) is increased in case said target for the rotational flow (Rot.sub.0) is higher than said determined rotational flow (Rot(t)); and 15.5. a gas decreasing step (360) in which said gas flow (Q(t)) is decreased in case said target for the rotational flow (Rot.sub.0) is lower than said determined rotational flow (Rot(t)).

16. Stopper rod (100) according to claim 1, said stopper rod (100) comprising a plurality of channels (111).

17. Stopper rod (100) according to claim 2, said first edge (119) having a radius not above 1 mm.

18. Stopper rod (100) according to claim 6, said auxiliary channel (131) is ring shaped, wherein said auxiliary channel (131) is of direct permeability, and wherein direct permeability is achieved by at least one selected from the group of: a hole and a pipe.

19. Stopper rod (100) according to claim 11, wherein each of said at least one channel (111) has a maximum depth of at least 7 mm along at least 50% of said channel length (111l).

20. Stopper rod (100) according to claim 11, wherein each of said at least one channel (111) has a maximum depth of at least 12 mm along at least 70% of said channel length (111l).

Description

[0078] Exemplary embodiments of the invention are explained in more detail by means of illustrations:

[0079] FIG. 1a, a cross-sectional view of a tundish comprising a stopper rod according to the invention, wherein in the bottom of the tundish there is provided an outlet in the form of a submerged entry nozzle;

[0080] FIG. 1b, a cross-sectional view of an alternative embodiment of a tundish comprising a stopper rod according to the invention, wherein in the bottom of the tundish there is provided an outlet in the form of a submerged entry shroud;

[0081] FIG. 2 left, a front view of the stopper rod according to FIGS. 1a and 1b;

[0082] FIG. 2 right, a cross-sectional view of the stopper rod according to FIGS. 1a and 1b;

[0083] FIG. 3a, a view of the nose of the stopper rod according to FIGS. 1a and 1b; and FIG. 3b, a channel of FIG. 3a in more detail;

[0084] FIG. 4, a view of the nose of the stopper rod according to a second embodiment of the invention;

[0085] FIG. 5, a view of the nose of the stopper rod according to a third embodiment of the invention;

[0086] FIG. 6, a view of the nose of the stopper rod according to a fourth embodiment of the invention;

[0087] FIG. 7 shows the result of a CFD simulation of a stopper rod according to FIGS. 1a and 1b with gas flow at different time steps;

[0088] FIG. 8 shows the result of a CFD simulation of a stopper rod according to FIGS. 1a and 1b without gas flow at different time steps;

[0089] FIG. 9 shows a graph depicting the gas flow Q and the induced circulation C as a function of the pressure p of a gas;

[0090] FIG. 10 shows a diagram of method steps according to an embodiment of the invention.

[0091] In order to better illustrate the features of the embodiments shown in the figures, the figures do not reflect the proportions of the embodiments according to practice.

[0092] FIG. 1a shows a tundish identified in its entirety by the reference sign 1, which is part of a continuous casting plant for casting steel. Tundish 1 comprises, as is known from the state of the art, a metal vessel 3 lined on its inside with a refractory material 5. Molten metal can be provided in the space enclosed by the refractory material 5. In the bottom 7 of tundish 1, a tundish nozzle 9 in the form of a submerged entry nozzle (SEN) is provided through which molten metal in tundish 1 can be cast into a mould (not shown). A vertically aligned central longitudinal axis L of a stopper rod 100 runs through the tundish nozzle 9.

[0093] Along the central longitudinal axis L a stopper rod 100 is arranged in its functional position. The stopper rod 100 is connected to a state-of-the-art lifting device (not shown) by means of which the stopper rod 100 can be lifted and lowered along the central longitudinal axis L. The stopper rod 100 comprises a stopper body 101 which comprises a stopper nose 103 at its second end/lower end. By means of the lifting device, the stopper rod 100 can be lifted into the second position shown in FIG. 1a, in which the tundish nozzle 9 is open, so that a molten metal provided in the tundish 1 can be casted through the tundish nozzle 9 (here: submerged entry nozzle 9). Furthermore, the stopper rod 100 can be lowered by means of the lifting device into a first position (not shown in FIG. 1a) in which the stopper nose 103 rests against the tundish nozzle 9 in such a way that it is closed by the stopper rod 100. Accordingly, the tundish nozzle 9 can be closed and opened by means of the stopper rod 100, thereby controlling the amount of molten metal flowing through the tundish nozzle 9. Further shown is a gas supply system 210 for providing a gas 200 to the stopper rod 100.

[0094] The tundish 1 shown in FIG. 1b is broadly identical to the tundish shown in FIG. 1a and indicated with the same reference signs as far as the tundish 1 according to FIG. 1a is identical to the tundish 1 according to FIG. 1b, only the gas supply system 210 for providing a gas 200 is not shown. The difference between the tundish 1 according to FIGS. 1a and 1b lies in the fact that in the bottom 7 of tundish 1 according to FIG. 1b there is provided a tundish nozzle 10 in the form of a submerged entry shroud (SES). As known from the art, submerged entry shroud 10 is comprised of an upper part 10.1, located at the bottom 7 of tundish 1, and a lower part 10.2, attached below upper part 10.1 such that the upper part 10.1 and the lower part 10.2 form a continuous chamber along the central longitudinal axis of submerged entry shroud 10.

[0095] FIG. 2 shows a first embodiment of the stopper rod 100 as shown in FIG. 1 in a front view (left) and in a cross-sectional view (right). The stopper rod 100 comprises a rod-shaped stopper body 101, the outer circumferential surface of which is rotationally symmetrical to the central longitudinal axis L of the stopper rod 100. The stopper body 101 extends along the central longitudinal axis L from its first, upper end 105 in the functional position according to FIG. 1 to its second, lower end 107 in the functional position according to FIG. 1. At its second end 107, the stopper body 101 comprises a nose 103. The nose 103 has its second nose end 104b aligned with the second end 107 of the stopper body 100. The outer surface of the stopper body 101 in a region between the first end 107 of the stopper body 100 until the first nose end 104a, has a circular cylindrical outer contour rotationally symmetrical to the central longitudinal axis L. The external surface of the nose 103, between a first nose end 104a and a second nose end 104b, is rotationally symmetrical to the longitudinal axis L and is generally dome-shaped.

[0096] The stopper body 101 has a chamber 109 which, as shown in FIG. 2 (right), extends along the central longitudinal axis L from the first end 105 in a direction towards the second end 107 into the stopper body 101 and ends in the stopper body 101 at a distance from the second end 107. The chamber 109 is rotationally symmetrical in relation to the central longitudinal axis and has a circular-cylindrical shape along most of its height.

[0097] The stopper body 101 preferably is made of a refractory material in the form of an alumina-carbon material (Al.sub.2O.sub.3C material). The stopper body 101 can be produced as a monoblock stopper body by means of isostatic pressing.

[0098] A gas supply system 200 provides a gas 210 to the stopper rod 100 at the first end 105, through which the gas 210, such as an inert gas such as argon or nitrogen, is led into the chamber 109. From chamber 109 the gas is further guided via gas supply lines 123 to the channels 111. In the channels 111 the gas 210 is accelerated along the channel direction 112 and finally exits the channels 111 into the molten metal and imposes a rotational flow to the molten metal.

[0099] In this embodiment six channels 111 are arranged on the outer surface of nose 103. All channels 111 follow a helical path around the central longitudinal axis L, that is they are at least partially running around said central longitudinal axis (L) (see FIG. 3a), and progressing along the direction (z) of said central longitudinal axis (L); The channels 111 are completely open to the outside, i.e. on the side of the channel 111 facing away from the stopper body 101, and are, according to its V-shaped cross-sectional area, limited by a first channel wall 113 and a second channel wall 115, which start from a common linear area which forms the channel bottom 117 of the channel 111 (see FIG. 3b). Towards the outer surface of the nose 103, the first channel wall 113 and the second channel wall 115 diverge and finally merge into the outer surface of the nose 103. The first channel wall 113 is limiting the channel 111 in a direction towards the first end 105 and forms a first edge 119 with the outer surface of the nose 103. The second channel wall 115 is limiting the channel 111 in a direction towards the second end 107 and forms a second edge 121 with the outer surface of the nose 103. The first edge 119 and the second edge 121 each form a sharp edge with a radius well below 0.5 mm. The first and second edges 119 and 121 run equally spaced to each other around the longitudinal axis L, and progressing along the direction of the central longitudinal axis, resembling a helical path of the channel 111 on the exterior surface of the nose 103. The distance between the first and second edges 119, 121 defines the width of the channel mouth, i.e., the width of channel 111 in the area in which channel 111 merges into the outer surface of nose 103 and is 10 mm in the embodiment. The shortest distance between an imaginary plane that extends between the first and second edges 119, 121 and the channel bottom 117 defines the depth of channel 111, which in the embodiment is 8 mm. This results in a cross-sectional area of channel 111 of 40 mm.sup.2.

[0100] Each channel 111 defines a channel direction 112 and each of the six channel directions 112 are aligned at an angle (.sub.i) to said central longitudinal axis (L). The angle (.sub.i) is defined as the smaller angle between said channel direction and said central longitudinal axis (L), in case of skew lines, the smaller angle between any two lines parallel to said channel direction and said central longitudinal axis (L). Here all angles (.sub.i) are the same with .sub.i=45 for all i=1 . . . 6.

[0101] From chamber 109, gas supply connecting means 123 in the form of one gas supply line 123 per channel 111 lead through the refractory material of the stopper body 101 into the respective channel 111. The six gas supply lines 123 each have a straight course with a circular cross-sectional area and are arranged symmetrically with respect to the central longitudinal axis L and are evenly spaced from each other. Accordingly, the six gas supply lines 123 are spaced from each other by a rotational angle of 60 (i.e., at =0, 60, 120, 180, 240, 300) with respect to the central longitudinal axis L. In accordance with their symmetry with respect to the central longitudinal axis L, the gas supply lines 123 lead into six channels 111 at six evenly spaced areas, which are also spaced from each other at a rotational angle of 60 (i.e., at =0, 60, 120, 180, 240, 300) with respect to the central longitudinal axis L, as can be seen particularly clearly in FIG. 3a, which is a view onto the stopper nose 103/onto the second end of the stopper body 107 (that is in its use position from below the stopper rod 100). Thus, the distance between each nearest neighboring channels 111 is the same (each neighboring pair of said plurality of channels 111 is equally spaced).

[0102] The gas supply lines 123 each extend along a respective longitudinal axis, with the six longitudinal axes of the gas supply lines 123 intersecting at a common point on the central longitudinal axis L. The six longitudinal axes of the gas supply lines 123 are each arranged at an angle of approximately 60 to the central longitudinal axis L of the stopper body 101, this angle being the smaller angle included between the section of the longitudinal axes of the gas supply line 123 passing through the gas supply lines 123 and the section of the central longitudinal axis L of the stopper body 101 passing through the second end 107 of the stopper body 101.

[0103] The gas supply lines 123 lead into each of the respective six channels 111 by means of direct permeability as shown in FIGS. 3a and 3b. In other words, the gas supply lines 123 allow the gas to flow via a discrete conduit into each of the respective six channels 111.

[0104] Each of the channels 111 extends from a first channel end 111u to a second channel end 111d, each second channel end 111d is closer to the second end 107 than the respective first channel end 111u. The distance between a respective first channel end 111u and said second channel end 111d defines a channel length 111l. In this example, all channel lengths 111l are the same, namely 160 mm (alternatively, as shown in the figures, all channel lengths 111l are the same, namely 50 mm, and each second channel end 111d is arranged at a distance of 50 mm from the second end of the stopper body 107). Each gas supply line 123 leads into one of the six channels 111 at a position in said channel at a distance of 80 mm from the second end of the stopper body 107.

[0105] An alternative first embodiment (not shown in the Figures) differs from the first embodiment mentioned above in that no second channel wall 115 limits the channel 111 in a direction towards its second end 107, thus also no second edge 121 is present. Here the channel diverges continuously and smoothly into the surface of the nose 103 in the direction towards its second end 107.

[0106] A second embodiment of FIG. 4 shows a stopper rod 100 with an auxiliary gas supply connecting means 133, which here is an auxiliary gas supply line, that leads from chamber 109 through the rod-shaped stopper body 101 into an auxiliary channel 131 with a ring-shaped geometry, the auxiliary channel 131 aligned on the exterior surface of the nose 103. The auxiliary channel 131 is arranged on the exterior surface of the nose 103 at a distance from the channels 111 in a direction towards the second end 107 (that is below the channels 111 in a use position). The auxiliary gas supply connecting means 133, which here is an auxiliary gas supply line, leads into the ring-shaped auxiliary channel 131 by means of direct permeability as shown in FIG. 4. In other words, the auxiliary gas supply connecting means 133, which here is an auxiliary gas supply line allows the gas to flow via a discrete conduit into the auxiliary channel 131. The ring-shaped auxiliary channel 131 is symmetrical in relation to said central longitudinal axis (L), that is, the central longitudinal axis passes through the center of the ring-shaped auxiliary channel 131. The radius of the auxiliary channel in this example is 15 mm, the slit of the ring-shaped auxiliary channel has a width of 0,5 mm.

[0107] A third embodiment of FIG. 5 shows a stopper rod 100 like the first or second embodiment, with the difference that the six gas supply lines 123 are leading into six channels 111 by means of indirect permeability. In other words, the gas supply lines 123 allow the gas to flow via a permeable structure into each of the respective six channels 111. Here the indirect permeability/porous structure spans within the region between 50 mm to 100 mm distance from said second end of the stopper body 107, where the gas supply lines 123 lead into the channel 111 at the bottom 117 of the channels 111.

[0108] A fourth embodiment of FIG. 6 is similar to the third embodiment of FIG. 5, except that the indirect permeability/porous structure spans over the whole channel length 111l from the first channel end 111u to the second channel end 111d.

[0109] In another embodiment a stopper rod (100) according to one of the first, second, third, fourth or fifth embodiment is provided, a gas supply system 200 supplies a gas 210 to the chamber 101 at a gas flow rate of 5 l/min, the gas being argon, whereas the gas is guided at this predetermined gas flow via the chamber 109 through the gas supply lines 123 to the six channels 111. In the channels 111 the gas 210 is accelerated along the channel direction 112 and finally exits the channels 111 into the molten metal and imposes a rotational flow to the molten metal.

[0110] Computer-based numerical simulations based on the CFD (computational fluid dynamics) method were performed for the stopper rod 100 according to the first embodiment, both with and without injection of a gas 210.

[0111] The results are shown in FIGS. 7 and 8. The left image of FIG. 7 shows the flow characteristics shortly after start of the metal flow and the gas injection (here at t=0,1 s after start of the gas injection). The flow lines (shown as black lines) inside the tundish nozzle 9 show an onset of rotational flow. The circulation (determined at the height indicated by the ellipsis) is C=0,063 m.sup.2/s. The right image shows the situation at t=11 s, where a strong rotational flow of the molten metal is observed inside of the tundish nozzle 9 (see helical path of the flow lines shown as black lines in the tundish nozzle 9). The circulation at t=11 s (at the height of the ellipse) is C=0,298 m.sup.2/s.

[0112] In FIG. 8 the results for the case without injection of a gas 210 can be seen. Here, during the whole simulation a low rotational flow is experienced inside the tundish nozzle 9 (at t=10 s, as shown in the left of FIG. 8, the rotational flow is low with a circulation C=0,018 m.sup.2/s, at t=21 s, as shown in the right of FIG. 8, the rotational flow is still low with a circulation C=0,022 m.sup.2/s,). Furthermore, the simulation shows that the flow is more unstable in case no argon is injected.

[0113] The result shows, that the stopper rods 100 of the embodiments are suitable for inducing a rotational flow into a molten metal by means of gas injection into the channels 111.

[0114] FIG. 9 in the upper graph schematically shows the results achieved by a stopper rod according to the third embodiment: a graph is shown with the gas flow Q (in l/min) of a gas 210 as a function of the pressure (in bar). Below a certain threshold pressure p.sub.thres basically no gas flow Q is observed (Q0). Above the threshold pressure p.sub.thres gas flow Q gradually rises, whereas all gas 210 is transported through the auxiliary gas supply connecting means 133, which here is an auxiliary gas supply line into the ring-shaped auxiliary channel 131. This is because the flow resistance of the six channels 111 of indirect permeability is higher than that of the ring-shaped auxiliary channel 131 of direct permeability. In this flow regime basically no or low rotational flow is induced into the molten metal (Rot(t)=C is small). Only above a saturation pressure p.sub.sat the gas 210 is starting to flow into the six gas supply lines 123 and into the six channels 111. By further increasing the pressure, more and more gas 210 is injected into the molten metal via the six channels 111, thereby increasing the rotational flow (Rot(t)=C is increasing in this regime). This is shown schematically in the lower graph of FIG. 9, where the induced rotational flow Rot (in this example in the form of the circulation, Rot(t)=C in units of m.sup.2/s) is shown as a function of the pressure (in bar). Thus, it is possible to induce a certain rotational flow into the molten metal by guiding a gas 210 at a (e.g., predefined) gas flow by a gas supply system 200 via a chamber 109 through gas supply connecting means 123 to the six channels 111 of the stopper rod.

[0115] To set a certain rotational flow of the molten metal, an additional rotational flow measurement unit 20 can be used. This makes it possible to either increase the gas flow in case a higher rotational flow of the molten metal is desired or to decrease the gas flow in case a lower rotational flow of the molten metal is required. Thereby an active control (with a feedback) of the induced rotational flow can be achieved. This is shown in FIG. 10, where a stopper rod 100 according to the invention is provided in a stopper rod providing step 300, a gas supply system 200 is provided in a gas supply system providing step 310, and a tundish nozzle 9, 10 comprising a rotational flow measurement unit 20 is provided in a tundish nozzle providing step 320. A gas 210 is guided in a gas guiding step 325 at a (e.g. predefined) gas flow (Q(t), at a certain time t) by the said supply system 200 via the chamber 109 through the gas supply connecting means 123 to the channels 111 of the stopper rod 100. The rotational flow (Rot(t) at time t, in this example the rotational flow is characterized by the circulation Rot(t)=C) of the molten metal inside of the tundish nozzle 9, 10 is determined in a rotational flow determination step 330 by the rotational flow measurement unit 20. A certain target for the rotational flow (Rot.sub.0=C.sub.0) inside of the tundish nozzle 9, 10 is provided in a target providing step 340. In case the target for the rotational flow (Rot.sub.0=C.sub.0) is higher than the determined rotational flow (Rot(t)=C), i.e. Rot.sub.0>Rot(t), the gas flow (Q(t)) is increased in a gas increasing step 350, e.g. by a certain amount Q, thus Q(t+1)=Q(t)+Q, which leads to an increase of rotational flow (Rot(t)=C). In case the target for the rotational flow (Rot.sub.0=C.sub.0) is lower than the determined rotational flow (Rot(t)=C), i.e. Rot.sub.0<Rot(t), the gas flow (Q(t)) is decreased in a gas decreasing step 360, e.g. by a certain amount Q, thus Q(t+1)=Q(t)Q, which leads to a decrease of rotational flow (Rot(t)=C). This allows to achieve and maintain a rotational flow (Rot(t)=C) at or at least close to the target for the rotational flow (Rot.sub.0=C.sub.0), thus Rot(t)=C=Rot.sub.0=C.sub.0.

[0116] List of reference numerals and factors: [0117] L Central longitudinal axis through stopper body [0118] r Radial distance (normal distance) from L [0119] Z z-axis along the direction of L, in the direction from the first end of the stopper body to the second end of the stopper body [0120] Rotational angle around L

[0121] .sub.i Angle between i-th channel direction and z-axis [0122] Q(t) Gas flow at a time t [0123] Rot(t) Determined rotational flow at time t [0124] Rot.sub.0 Target for the rotational flow [0125] C Circulation in m.sup.2/s [0126] C.sub.0 Target for the circulation in m.sup.2/s [0127] 1 Tundish [0128] 3 Metal vessel [0129] 5 Refractory material [0130] 7 Bottom of tundish [0131] 9 Tundish nozzle in form a submerged entry nozzle (SEN) [0132] 10 Tundish nozzle in form a submerged entry shroud (SES) [0133] 10.1 Upper part of submerged entry shroud (SES) [0134] 10.2 Lower part of submerged entry shroud (SES) [0135] 20 Rotational flow measurement unit [0136] 100 Stopper rod [0137] 101 Stopper body [0138] 103 Nose of stopper body [0139] 104a First nose end [0140] 104b Second nose end [0141] 105 First end of stopper body [0142] 107 Second end of stopper body [0143] 109 Chamber [0144] 111 Channel [0145] 111u First channel end [0146] 111d Second channel end [0147] 111l Channel length [0148] 112 Channel direction [0149] 113 First channel wall [0150] 115 Second channel wall [0151] 117 Channel bottom [0152] 119 First edge [0153] 121 Second edge [0154] 123 Gas supply connecting means [0155] 131 Auxiliary channel [0156] 133 Auxiliary gas supply connecting means [0157] 200 Gas supply system [0158] 210 Gas [0159] 300 stopper rod providing step [0160] 310 gas supply system providing step [0161] 320 tundish nozzle providing step [0162] 325 gas guiding step [0163] 330 rotational flow determination step [0164] 340 target providing step [0165] 350 gas increasing step [0166] 360 gas decreasing step