An exchangeable nozzle for a nozzle changer system, a method for manufacturing such a nozzle, a nozzle changer system comprising such a nozzle and a tundish comprising such a nozzle changer system

Abstract

The invention concerns an exchangeable nozzle for a nozzle changer system for billet casting, a method for manufacturing such a nozzle, a nozzle changer system comprising such a nozzle and a tundish comprising such a nozzle changer system.

Claims

1. An exchangeable nozzle (200) for a nozzle changer system (11) for billet casting, said exchangeable nozzle (200) comprising: 1.1 a tubular member (201); 1.1.1 said tubular member (201) extending along a longitudinal axis (L) from a first end (209) of said tubular member (201) to a second end (211) of said tubular member (201); said tubular member (201) comprising: 1.1.2 an inner passageway (213) extending through said tubular member (201) along said longitudinal axis (L) from said first end (209) of said tubular member (201) to said second end (211) of said tubular member (201); 1.1.3 an inlet (215) opening into said inner passageway (213) at said first end (209) of said tubular member (201); and 1.1.4 an outlet (217) opening into said inner passageway (213) at said second end (211) of said tubular member (201); 1.2 said tubular member (201) comprising partially stabilized sintered zirconia; 1.2.1 said partially stabilized sintered zirconia being partially stabilized by MgO; and 1.2.2 said partially stabilized sintered zirconia having a degree of stabilization not above 26% by mass; and 1.3 said tubular member (201) comprising free carbon.

2. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a degree of stabilization in the range from 1 to 26% by mass.

3. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a degree of stabilization in the range from 2 to 20% by mass.

4. The exchangeable nozzle (200) according to claim 1, wherein the difference of linear thermal expansion of said tubular member (201) at 1,100° C. and 1,200° C. is below 0.1 percentage points.

5. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a MgO content in the range from 1 to 3% by mass.

6. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a SiO2 content not above 1.5% by mass.

7. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a ZrO2+HfO2 content of at least 92% by mass.

8. The exchangeable nozzle (200) according to claim 1, said partially stabilized sintered zirconia having a ZrO2+HfO2 content in the range from 94 to 97% by mass.

9. The exchangeable nozzle (200) according to claim 1, said tubular member (201) comprising free carbon in an amount in the range from 0.1 to 4.0% by mass in relation to the mass of the tubular member (201) without said free carbon.

10. The exchangeable nozzle (200) according to claim 1, wherein said tubular member (201) is embedded in a ceramic refractory material (203).

11. The exchangeable nozzle (200) according to claim 1, wherein said ceramic refractory material (203) is at least partially covered by a metal shell (219).

12. The exchangeable nozzle (200) according to claim 1, said exchangeable nozzle (200) being connectable to an upper nozzle (100) of a nozzle changer system (11) for billet casting, wherein said upper nozzle (100) comprises an inner passageway (113) for guiding molten metal through said upper nozzle (100) and wherein said exchangeable nozzle (200) is connectable to said upper nozzle (100) such that, when said exchangeable nozzle (200) is connected to said upper nozzle (100), said inner passageway (113) of said upper nozzle (100) and said inner passageway (213) of said exchangeable nozzle (200) form a continuous channel.

13. A method for manufacturing an exchangeable nozzle according, said method comprising the following steps: 13.1 providing a tubular member, 13.1.1 said tubular member extending along a longitudinal axis from a first end of said tubular member to a second end of said tubular member; said tubular member further comprising: 13.1.2 an inner passageway extending through said tubular member along said longitudinal axis from said first end of said tubular member to said second end of said tubular member; 13.1.3 an inlet opening into said inner passageway at said first end of said tubular member; and 13.1.4 an outlet opening into said inner passageway at said second end of said tubular member; 13.1.5 said tubular member comprising partly stabilized sintered zirconia; 13.1.6 said partly stabilized sintered zirconia being partly stabilized by MgO; and 13.1.7 said partly stabilized sintered zirconia having a degree of stabilization not above 26% by mass; and 13.2 impregnating said tubular member with a carbon containing impregnation.

14. A nozzle changer system (11) for billet casting, said nozzle changer system (11) comprising: 14.1 an upper nozzle (100), said upper nozzle (100) comprising an inner passageway (113) for guiding molten metal through said upper nozzle (100); 14.2 an exchangeable nozzle (200); 14.3 wherein said exchangeable nozzle (200) is exchangeable between a first position and a second position; 14.3.1 wherein in said first position, said exchangeable nozzle (200) is connected to said upper nozzle (100) such that said inner passageway (113) of said upper nozzle (100) and said inner passageway (213) of said exchangeable nozzle (200) form a continuous channel; 14.3.2 and wherein in said second position, said exchangeable nozzle (200) is released from said upper nozzle (100), wherein said exchangeable nozzle (200) comprises: a tubular member (201); said tubular member (201) extending along a longitudinal axis (L) from a first end (209) of said tubular member (201) to a second end (211) of said tubular member (201); said tubular member (201) comprising: an inner passageway (213) extending through said tubular member (201) along said longitudinal axis (L) from said first end (209) of said tubular member (201) to said second end (211) of said tubular member (201); an inlet (215) opening into said inner passageway (213) at said first end (209) of said tubular member (201); and an outlet (217) opening into said inner passageway (213) at said second end (211) of said tubular member (201): said tubular member (201) comprising partially stabilized sintered zirconia; said partially stabilized sintered zirconia being partially stabilized by MgO; and said partially stabilized sintered zirconia having a degree of stabilization not above 26% by mass; and said tubular member (201) comprising free carbon.

15. A tundish (1) comprising a nozzle changer system (11) according to claim 14.

Description

[0085] The attached FIGS. 1-3, strongly schematized, show an exemplary embodiment of the invention. FIGS. 4-8 also show measurement results for measuring the linear thermal expansion of tubular members for generic exchangeable nozzles.

[0086] In detail

[0087] FIG. 1 shows a sectional view of an exemplary embodiment of a tundish according to the invention comprising a nozzle changer system according to the invention comprising an exchangeable nozzle according to the invention;

[0088] FIG. 2 shows a section of the view according to FIG. 1 in the area of the nozzle changer system;

[0089] FIG. 3 shows the tundish according to FIG. 1, but with the exchangeable nozzle in a different position; and

[0090] FIGS. 4-8 shows measurement results for measuring the linear thermal expansion of tubular members for generic exchangeable nozzles.

[0091] The tundish shown in FIG. 1 is marked in its entirety with the reference sign 1. Tundish 1 comprises, as is known from the state of the art, a metal vessel 3 lined on the inside with a refractory material 5. In the space enclosed by the refractory material 5, molten metal (not shown) can be provided. The tundish 1 is part of a continuous casting plant for continuous billet casting.

[0092] A spout 9 is provided at the bottom 7 of tundish 1, through which the molten metal provided in tundish 1 can be discharged into a mould (not shown) arranged below tundish 1.

[0093] The spout 9 is formed by an exemplary embodiment of nozzle changer system 11 according to the invention. The nozzle changer system 11 comprises an upper nozzle 100 permanently installed in the bottom 7 of the tundish 1 and an exchangeable nozzle 200. The exchangeable nozzle 200 is movable relative to the upper nozzle 100, as explained in detail below.

[0094] FIG. 2 shows an enlarged view of the tundish 1 in the area of the nozzle changer system 11. The geometry of the nozzle changer system 11 and its arrangement at the bottom 7 of the tundish 1 correspond to the state of the art. In this respect, the upper nozzle 100 is essentially rotationally symmetrical in relation to a vertical longitudinal axis L. The upper nozzle 100 comprises a tubular member 101 made of a refractory material. The tubular member 101 is rotationally symmetrical to the longitudinal axis L, whereby the tubular member 101 has a constant wall thickness, so that the inner and outer contour of the tubular member 101 each has a circular cylindrical shape. The tubular member 101 is embedded in a refractory material 103 of the upper nozzle 100, wherein the refractory material 103 encompasses the tubular member 101 on the outside thereof. An upper section 105 of refractory material 103 is completely located in the bottom 7 of tundish 1. This upper section 105 has a circular-cylindrical outer contour rotationally symmetrical to the longitudinal axis L. A lower section 107 of the upper nozzle 100, adjacent to the upper section 105 below the upper section 105, protrudes above the bottom 7 of the tundish 1. This lower section 107 is also rotationally symmetrical to the longitudinal axis L and also has a circular-cylindrical outer contour. The lower section 107 has a smaller outer diameter than the upper section 105. At its upper end 109, the upper section 105 of the upper nozzle 100 expands conically outwards and merges into a section 12 in the bottom 7 of the tundish 1, which also expands conically upwards.

[0095] Below the upper nozzle 100, there is arranged an embodiment of an exchangeable nozzle 200 on the upper nozzle 100. The exchangeable nozzle 200 comprises a tubular member 201 which extends along the longitudinal axis L from a first (here upper) end 209 to a second (here lower) end 211. The tubular member 201 is rotationally symmetrical to the longitudinal axis L with a constant wall thickness, so that the inner and outer contour of the tubular element 201 each have a circular cylindrical shape. The tubular member 201 of the exchangeable nozzle 200 has the same inner diameter as the tubular member 101 of the upper nozzle 100. The tubular member 201 encloses an inner passageway 213 which extends from the first end 209 to the second end 211 along the longitudinal axis L through the tubular member 201. At first end 209, inlet 215 opens and at second end 211, outlet 217 opens into inner passageway 213.

[0096] The tubular member 101 of the upper nozzle 100 defines an inner passageway 113. At the position shown in FIG. 2, the longitudinal axes L of the tubular member 101 of the upper nozzle 100 and of the tubular member 201 of the exchangeable nozzle 200 are aligned. Since the tubular member 101 of the upper nozzle 100 and the tubular member 201 of the exchangeable nozzle 200 have the same inner diameter, the tubular member 101 and the tubular member 201 form a continuous channel with a constant inner diameter.

[0097] The tubular member 201 of the exchangeable nozzle 200 consists of sintered zirconium dioxide partially stabilized with MgO and has a degree of stabilization of 11.9%. Furthermore, the tubular member 201 comprises free carbon in an amount of 1.6 mass %. Therefore, the tubular member has been impregnated with a carbon comprising impregnation in the form of a coal tar pitch. For impregnation, the tubular member 201 was soaked with such pitch. Afterwards, the tubular member was tempered at 500° C. until the proportion of free carbon in the tubular element 201 amounts to 1.6 mass % (duration about 1 h), referred to the tubular element 201 without the free carbon.

[0098] The chemical composition of the tubular member 201, determined by X-ray fluorescence analysis (XRF) according to DIN EN ISO 12677:2013-02, is given in Table 1 below and designated E1T.

[0099] The tubular member 201 of the exchangeable nozzle 200 is completely surrounded on its outer circumference by a refractory material 203 and thus embedded in the refractory material 203. Refractory material 203 is a refractory ceramic casting compound based on alumina. The refractory material 203 is rotationally symmetrical to the longitudinal axis L and has an upper section 205 and an adjacent lower section 207. The upper section 205 has a circular cylindrical outer contour and the adjacent lower section 207 has a conically tapering outer contour. On its upper side, the upper section 205 is flat and runs perpendicular to the longitudinal axis L. The lower section 107 of the refractory material 103 of the upper nozzle 100 is also flat on its underside and runs perpendicular to the longitudinal axis L. In the example shown in FIGS. 1 and 2, the upper surface of the upper section 205 of the exchangeable nozzle 200 is in full contact with the lower surface of the lower section 107 of the upper nozzle 100, so that no gap is visible in the figures along this contact surface between the upper nozzle 100 and the exchangeable nozzle 200.

[0100] At its radial outer periphery, the refractory material 203 of the exchangeable nozzle 200 is enclosed by a metal shell 219.

[0101] The exchangeable nozzle 200 shown in the exemplary embodiment of the figures can be moved between a first and a second position. FIGS. 1 and 2 show the exchangeable nozzle 200 in the first position and FIG. 3 in the second position. In the first position shown in FIGS. 1 and 2, the inner passageway 113 of the upper nozzle 100 and the inner passageway 213 of the exchangeable nozzle 200 form a continuous channel as shown above. In the second position of the exchangeable nozzle 200 shown in FIG. 3, the exchangeable nozzle 200 is released from the upper nozzle 100.

[0102] In the first position of the exchangeable nozzle 200 shown in FIGS. 1 and 2, molten metal provided in tundish 1 can be discharged from tundish 1 through the continuous channel formed by inner passageway 113 and inner passage way 213 and poured into a mould located below tundish 1.

[0103] By means of a nozzle changer schematically shown in FIG. 3 and marked with the reference sign 300, the exchangeable nozzle 200 can be held in the first position shown in FIGS. 1 and 2 and can also be moved to the second position shown in FIG. 3, in which the exchangeable nozzle 200 is released from the upper nozzle 100. In this position, the exchangeable nozzle 200 can be removed from the nozzle changer 300 and exchanged by a new exchangeable nozzle. This new exchangeable nozzle can then be moved by the nozzle changer 300 to the first position shown in FIGS. 1 and 2.

[0104] Tests were carried out to determine the properties of tubular members for exchangeable nozzles. To produce the tubular members, powders of zirconium dioxide (grain size <40 μm), magnesia (<150 μm) and quartz flour as well as an organic binder were provided. The raw materials and the binder were then mixed together in different proportions, pressed into green bodies and then sintered by ceramic firing. Tubular members for an exchangeable nozzle were then obtained, which are designated E1, E2, E3 and E4 in Table 1 below and had the physical values and chemical compositions specified in Table 1. One of each of these tubular members E1, E2, E3 and E4 was then soaked with pitch and tempered, so that the tubular members designated in Table 1 as E1T, E2T, E3T and E4T were obtained, which each had a proportion of free carbon of about 1.6% by mass, based on the mass of the respective tubular member without the free carbon. The physical properties and chemical composition of the tubular members according to E1T, E2T, E3T and E4T are also given in Table 1.

[0105] The chemical composition of the free carbon comprising tubular members E1, E2, E3 and E4 and no free carbon comprising tubular members E1T, E2T, E3T and E4T was determined by X-ray fluorescence analysis (XRF) according to DIN EN ISO 12677:2013-02.

TABLE-US-00001 TABLE 1 E1 E2 E3 E4 E1T E2T E3T E4T Degree of 3.8 12.6 25.7 >33 4.6 11.9 26.5 33.5 stabilization [mass %] Bulk 5.07 5.07 4.53 4.42 5.13 5.08 4.66 4.53 density [g/cm.sup.3] Open 10.7 10.5 20.8 20.9 5.6 6.1 10.6 10.5 porosity [volume %] MgO 1.82 2.42 2.22 4.00 1.81 2.45 2.22 3.90 [mass %] SiO.sub.2 0.99 1.01 0.04 1.06 0.99 0.96 0.04 0.97 [mass %] ZrO.sub.2 + 96.0 95.2 96.7 93.9 96.1 95.5 96.6 94.0 HfO.sub.2 [masse %] LOI 0.21 0.13 0.24 0.17 1.29 1.27 2.88 3.25

[0106] In Table 1, only the tubular members E1T and E2T correspond to tubular members in an exchangeable nozzle according to the invention.

[0107] The linear thermal expansion of the tubular members according to Table 1 was determined according to the standard DIN 51045-4:2007-01. The results of these tests are shown in FIGS. 4 to 8.

[0108] The linear thermal expansion for the temperature interval between room temperature and 1,500° C. was determined.

[0109] FIG. 4 shows the linear thermal expansion of the exchangeable nozzle E1T (solid line) and E1 (dashed line). It can be clearly seen that the linear thermal expansion of the tubular members E1 and E1T up to a temperature of just below 1,200° C. is similar. However, just below the temperature of 1,200° C., the linear thermal expansion of the tubular member E1 decreases abruptly.

[0110] The linear thermal expansion of the tubular member E1 changes from about 0.80% at 1,100° C. to about −0.20% at 1,200° C. and thus by about 1.00 percentage points in this temperature interval. In contrast, the linear thermal expansion of the tubular member E1T at 1,100° C. is about 0.77% and at 1,200° C. about 0.75%. In this respect, the difference in linear thermal expansion in this temperature interval for the tubular member E1T is only about 0.02 percentage points.

[0111] A similarly small change in the linear thermal expansion of the tubular member E2T is shown in FIG. 5, where the linear thermal expansion of the tubular member E2T is represented by a solid line and the tubular member E2 by a dashed line.

[0112] While the linear thermal expansion was measured in the experiments according to FIGS. 4, 5, 7 and 8 in an argon atmosphere, the measurement according to FIG. 6 was performed in an air atmosphere. The impregnation of the tubular member E2T oxidized completely. FIG. 6 clearly shows that in this case the tubular members E2 and E2T have generally the same linear thermal expansion.

[0113] According to FIG. 7, the tubular member E3T (solid line) and E3 (dashed line) have generally the same linear thermal expansion.

[0114] FIG. 8 also shows that the tubular member E4T (solid line) and E4 (dashed line) have generally the same linear thermal expansion.

[0115] As FIGS. 4 and 5 show, with a degree of stabilization of not more than 26% in the tubular member, a reduced change in linear thermal expansion, especially in the temperature interval between 1,100° C. and 1,200° C., can only be observed if the tubular members comprise free carbon in accordance with the invention.

[0116] If this free carbon is burnt out again, this reduced change in linear thermal expansion cannot be determined, as shown in FIG. 6.

[0117] FIG. 7 also shows that a reduction in linear thermal expansion in the tubular member can no longer be observed if the degree of stabilization is above 26%.