A STOPPER ROD AND A METHOD FOR PROVIDING A UNIFORM GAS CURTAIN AROUND A STOPPER ROD

Abstract

The invention concerns a stopper rod and a method to provide a uniform gas curtain around a stopper rod.

Claims

1. Stopper rod (100) for controlling the flow of molten metal and for supplying gas during casting of molten metal, said stopper rod (100) comprising: 1.1 a rod-shaped stopper body (101), said rod-shaped stopper body (101) 1.1.1 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) defining a nose (103) adjacent to 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) 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); 1.3 a channel (111), said channel (111) 1.3.1 being provided on said exterior surface of said nose (103), and 1.3.2 running around said longitudinal axis (L); 1.4 gas supply means (123), said gas supply means (123) 1.4.1 leading from said chamber (109) and through said rod-shaped stopper body (101) into said channel (111).

2. The stopper rod (100) according to claim 1, with said channel (111) forming a ring.

3. The stopper rod (100) according to claim 1, with said exterior surface of said nose (103) being rotationally symmetrical in relation to said longitudinal axis (L).

4. The stopper rod (100) according to claim 1, wherein said channel (111) comprises a first channel wall (113), limiting the 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.

5. The stopper rod (100) according to claim 4, wherein said first edge (119) has a radius not above 1 mm.

6. The stopper rod (100) according to claim 4, wherein said channel (111) comprises a second channel wall (115), limiting the channel (111) in a direction towards said second end (107), wherein said second channel wall (115) and said exterior surface of said nose (103) form a second edge (121), and wherein the distance between said first edge (119) and said second edge (121) is in the range from 2 to 30 mm.

7. The stopper rod (100) according to claim 1, wherein said channel (111) has a depth in the range from 4 to 15 mm.

8. The stopper rod (100) according to claim 1, wherein said channel (111) has a depth in the range from 6 to 12 mm.

9. The stopper rod (100) according to claim 1, wherein said channel (111) has a cross section area in the range from 2 to 225 mm.sup.2.

10. The stopper rod (100) according to claim 1, wherein said gas supply means (123) are a plurality of gas supply lines (123), with each of said gas supply lines (123) leading into said channel (111) at an area, wherein said areas are spaced from each other.

11. The stopper rod (100) according to claim 10, wherein said areas are symmetrically spaced from each other.

12. The stopper rod (100) according to claim 10 having a total number of gas supply lines (123) in the range from 2 to 10.

13. The stopper rod (100) according to claim 10, wherein said chamber (109) has a cross-sectional area, and wherein each of the gas supply lines (123) has a cross-sectional area, and wherein said cross-sectional area of said chamber (109) is larger than the total area of all of said cross-sectional areas of said gas supply lines (123).

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

15. A method for providing a uniform gas curtain around a stopper rod, said method comprising: A. providing the stopper rod (100) according to claim 1; and B. introducing a gas into said chamber (109).

Description

[0088] The figures, each strongly schematized, show exemplary embodiments of the invention. Thereby shows

[0089] 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;

[0090] 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;

[0091] FIG. 2 a perspective view of the stopper rod according to FIGS. 1a and 1b;

[0092] FIG. 3 a perspective view of a longitudinal section along the longitudinal axis of the stopper rod as shown in FIGS. 1a and 1b;

[0093] FIG. 4 a view of a longitudinal section along the longitudinal axis of the stopper rod as shown in FIGS. 1a and 1b in the nose area;

[0094] FIG. 5 a view of a cross-section perpendicular to the longitudinal axis of the stopper rod as shown in FIGS. 1a and 1b along the section plane A-A as shown in FIG. 4;

[0095] FIG. 6 a detail of the view according to FIG. 4 in the area of the channel;

[0096] FIG. 7 a view according to FIG. 4, but with an alternative design of the channel;

[0097] FIG. 8 a view according to FIG. 4, but with a further alternative design of the channel;

[0098] FIG. 9 shows the deflection of the stopper rod according to the design shown in FIGS. 1 to 6 and of a stopper rod according to the art when gas passes through the stopper rods.

[0099] 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.

[0100] 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 longitudinal axis L runs through the tundish nozzle 9.

[0101] Along the 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 longitudinal axis L. The stopper rod 100 comprises a stopper body 101 which defines a stopper nose 103 at its 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 into the submerged entry nozzle. 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.

[0102] 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. The only 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.

[0103] FIG. 2 shows the stopper rod 100 as shown in FIG. 1 in a perspective view from above. 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. In the example shown in FIG. 1, the longitudinal axis L and the central longitudinal axis L of the stopper rod 100 run coaxially to each other or are identical, respectively. 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. Starting from the second end 107, the stopper body 101 defines the nose 103 which, starting from the second end 107, has a dome-shaped shape. The external surface of the nose 103 is rotationally symmetrical to the longitudinal axis L.

[0104] The outer surface of the stopper body 101, which extends from the first end 105, has a circular cylindrical outer contour rotationally symmetrical to the central longitudinal axis L.

[0105] The stopper body 101 has a chamber 109 which, as shown in FIG. 3, 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.

[0106] The stopper body 101 is made of a refractory material in the form of an alumina carbon material (Al.sub.2O.sub.3—C material).

[0107] A gas supply (not shown) is provided in the area of the first end 105, through which an inert gas such as argon or nitrogen can be fed into chamber 109.

[0108] A channel 111 is arranged on the outer surface of nose 103. The channel 111 runs continuously around the longitudinal axis L and is rotationally symmetrical to it, so that the channel 111 as a whole has the shape of a circular ring. As FIGS. 4 and 6 in particular show, channel 111 has a V-shaped cross-sectional area which is uniform, i.e. does not change along the course of channel 111. The channel 111 is completely open to the outside, i.e. on the side of the channel 111 facing away from the stopper body 101, and is, according to its V-shaped cross-sectional area, limited by a first wall 113 and a second wall 115, which start from a common linear area 117, which forms the channel bottom of the channel 111. Towards the outer surface of nose 103, the first and second walls 113, 115 diverge and finally merge into the outer surface of 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.

[0109] The first and second edges 119 and 121 run equally spaced to each other and rotationally symmetrically around the longitudinal axis L, corresponding to the even course of channel 111. 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.

[0110] From chamber 109, gas supply means in the form of four gas supply lines 123 lead through the refractory material of the stopper body 101 into channel 111. The four gas supply lines 123 each have a straight course with a circular cross-sectional area and are arranged symmetrically with respect to the longitudinal axis L and are evenly spaced from each other. Accordingly, the four gas supply lines 123 are spaced from each other by a rotation angle of 90° with respect to the longitudinal axis L. In accordance with their symmetry with respect to the longitudinal axis L, the gas supply lines 123 lead into channel 111 at four evenly spaced areas, which are also spaced at a rotation angle of 90° with respect to the longitudinal axis L, as can be seen particularly clearly in FIG. 5.

[0111] The gas supply lines 123 each extend along a longitudinal axis, with the four longitudinal axes of the gas supply lines 123 intersecting at a common point on the longitudinal axis L. The four longitudinal axes of the gas supply lines 123 are each arranged at an angle of approximately 45° to the central longitudinal axis L of the stopper body 101, this angle being 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.

[0112] Chamber 109 has a cross-sectional area of 1,300 mm.sup.2 and each of the gas supply lines has a cross-sectional area of 3 mm.sup.2. Thus, the cross-sectional area of chamber 109 is larger by the factor 108 than the total area of the cross-sectional areas of the gas supply lines 123.

[0113] In the area of the first end 105, the stopper body 101 has state of the art fasteners for fastening the stopper body 109 to a lifting device for lifting and lowering the stopper rod 100.

[0114] To produce the stopper rod 100, the stopper body 101 was first formed by isostatic pressing of the refractory material, whereby the fastener for fastening the stopper body 101 to the lifting device was formed into the refractory material (not shown in the Figures). The four gas supply lines 123 were then drilled into the isostatically pressed refractory material.

[0115] The stopper rod 100 is designed to form a uniform gas curtain around the stopper rod 100. For this purpose, during the use of the stopper rod 100 in tundish 1 as shown in FIG. 1, an inert gas is introduced into chamber 109 via the gas supply and passed through the four gas supply lines 123 through the stopper body 101 into channel 111. In channel 111, the gas can collect, distribute and then be discharged from channel 111, forming a uniform gas curtain around the stopper rod 100. During casting of molten metal from the tundish 1, this can significantly reduce the deflection of the stopper rod 100, thus improving the quality of the cast metal.

[0116] In order to determine the deflection reduction depending on the design of the channel of a stopper rod according to the invention, the deflection of the stopper rod 100 according to FIGS. 1 to 6 and the deflection of two alternative stopper rods, being in accordance with the stopper rod according to FIGS. 1 to 6, but each with a slightly different cross-sectional shape of the channel, were measured by means of water modelling. The two alternative cross-sectional shapes of the channel are shown in FIGS. 7 and 8.

[0117] The cross-sectional shape of channel 211 as shown in FIG. 7 corresponds to the cross-sectional shape of channel 111 except that the first side wall of the channel facing the first end 107 does not merge into the surface of nose 103 in the form of a sharp edge but in the form of a round edge, having a radius of about 5 mm.

[0118] Channel 311 according to FIG. 8 essentially corresponds to the shape of channel 111, but with a smaller channel depth of only 3 mm.

[0119] To determine the degree of deflection, the deflection of stopper rods was determined by optical assessment of a recorded image sequence. The horizontal movement of the stopper rod changed the pixel colour, from which the number of pixels with changed colour as a function of time was determined. A deflection index was calculated as the standard deviation value of changed pixels normalized to 100% for the value obtained for a stopper rod according to the art. Based upon this deflection index, the degree of deflection for a stopper rod according to FIGS. 1-6 has been measured and calculated.

[0120] The stopper rod according to the art was broadly identical to the stopper rod according to FIGS. 1-6 but with the differences, that the stopper rod according to the art did not comprise the channel 111 and the gas supply lines 123 but instead comprised a gas outlet along the central longitudinal axis in the nose area as described in EP 2 067 549 A1, EP 2 189 231 A1 or EP 2 233 227 A1.

[0121] FIG. 9 shows the results of the corresponding measurements. In FIG. 9, reference number 1 indicates the results of the measurement for the stopper rod according to the art with the deflection index being calculated as the standard deviation value of changed pixels normalized to 100%. Further, reference number 2 indicates the results of the measurement for the stopper rod according to FIGS. 1-6.

[0122] As can be seen from FIG. 9, the deflection of the stopper rod according to FIGS. 1-6 is only about 45% of the deflection index, and accordingly the deflection of the stopper rod according to FIGS. 1-6 is significantly below the deflection of a stopper rod according to the art.