AU2007249057B2

AU2007249057B2 - Regulation method for throughflow and bottom nozzle of a metallurgical vessel

Info

Publication number: AU2007249057B2
Application number: AU2007249057A
Authority: AU
Inventors: Martin Kendall
Original assignee: Heraeus Electro Nite International NV
Current assignee: RHI AG
Priority date: 2004-11-26
Filing date: 2007-12-17
Publication date: 2010-08-12
Anticipated expiration: 2025-11-17
Also published as: AU2007249057A1

Description

S&F Ref: 742292D1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Heraeus Electro-Nite International N.V., of Centrum Zuid of Applicant : 1105, 3530, Houthalen, Belgium Actual Inventor(s): Martin Kendall Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Regulation method for throughflow and bottom nozzle of a metallurgical vessel The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(1065236_1) Regulation Method for Throughflow and Bottom Nozzle of a Metallurgical Vessel The invention relates to a method for regulating the throughflow through a bottom nozzle of a metallurgical vessel. Furthermore the invention relates to a bottom nozzle of a metallurgical s vessel. In particular, in steel melting the liquid metal is cast from a distributor, for example in a continuous casting plant. It flows through a bottom nozzle arranged in the floor of the distributor housing. Adherence of material to the wall of the bottom nozzle during throughflow is disadvan tageous. The cross section of the aperture is thereby decreased, so that the flow properties are to disadvantageously affected. To prevent the adherence of material to the wall, an inert gas such as argon is often introduced into the throughflow aperture. However, excessive amounts of gas negatively affect the steel quality, for example by the formation of cavities in the steel which lead to surface defects when the steel is rolled. A material for a bottom nozzle is described, for example, in WO 2004/035249 Al. A bot 15 tom nozzle within a metallurgical vessel is disclosed in KR 2003-0017154 A or in US 2003/0116893 Al. In the latter publication, the use of inert gas is shown, with the aim of reduc ing the adherence of material to the inner wall of the bottom nozzle (so-called clogging); this is similarly described in JP 2187239. A mechanism with a gas supply regulation is known in detail from WO 01/56725 Al. Nitrogen is supplied according to the Japanese publication JP 8290250. 20 JP 3193250 discloses a method for observing the adherence or clogging of material with the aid of numerous temperature sensors arranged one behind the other along the bottom nozzle. The introduction of inert gas into the interior of the bottom nozzle is further known from, among oth ers, JP2002210545, JP61206559, JP 58061954, and JP 7290422. It is furthermore known from a few of these publications, in addition to introduction of inert gas, to prevent the access of oxy 25 gen as far as possible by the use of housings around a portion of the bottom nozzle. An excess pressure of inert gas is partially produced within such a housing, for example in JP 8290250. A housing around a valve of the bottom nozzle, to prevent the entry of oxygen, is disclosed in JP 11170033. The throughflow of the metal melt through the bottom nozzle is controlled by sliding gates, according to the above-mentioned publications. These sliding gates slide perpendicularly 30 of the throughflow direction of the metal and can thus close the bottom nozzle. Another possibil ity for throughflow regulation is a so-called plug bar (also termed stopper rod), as known e.g. from JP 2002143994.

2 In the Korean publication KR 1020030054769 A, the arrangement of a housing around the valve of a bottom nozzle is described. The gas present in the housing is sucked out by means of a vacuum pump. JP 4270042 describes a similar housing. Here, as in others of the above-mentioned publications, a non-oxidizing atmosphere is produced 5 within the housing. The housing has an aperture through which the inert gas can be supplied. A further arrangement, in which the gas is sucked out of the housing partially surrounding the bottom nozzle, in order to produce a vacuum within the housing, is known from JP 61003653. 10 Object of the Invention It is the object of the present invention to substantially overcome or ameliorate one or more of the disadvantages of the prior art. Summary of the Invention is The present invention provides a bottom nozzle for a metallurgical vessel, the bottom nozzle having a flow passage for discharging molten metal from the vessel, the bottom nozzle comprising: an upper nozzle arranged in a floor of the metallurgical vessel, a lower nozzle arranged below the upper nozzle, 20 the flow passage being in the form of an aperture formed in the nozzles, the aperture having a wall sealed against flow of the molten metal therethrough, a gas-tight housing having an upper end, a lower end, and an interior surface, the housing at least partially surrounding the nozzles to thereby prevent penetration of gas into the aperture between the upper and lower ends of the housing, the housing being 25 adapted to enclose the lower nozzle with a portion of the interior surface of the housing abutting an exterior surface of the lower nozzle, and a thermally insulating solid arranged between the wall of the aperture and the housing. Preferably, the housing comprises plural housing portions, the housing portions 30 being interconnected in a gas-tight manner, and at least one of the housing portions is connected to the upper nozzle and/or the floor of the metallurgical vessel. Preferably, the housing portions are arranged one above another. Preferably, a side surface of the at least one of the housing portions abuts an outside portion of the upper nozzle and/or the floor the metallurgical vessel.

3 Preferably, the bottom nozzle for a metallurgical vessel further comprises a valve for regulating molten metal flow, the valve being arranged above the upper nozzle or between the upper and lower nozzles. Preferably, a getter material is arranged within the housing or in the thermally 5 insulating solid. Preferably, the getter material is selected from the group consisting of titanium, aluminium, magnesium, and zirconium. Preferably, at least a portion of the housing has a tubular or conical form. Preferably, the tubular or conical form has an oval or circular cross-section. 1o Preferably, the housing comprises steel, and the thermally insulating solid comprises aluminium oxide. Preferably, the thermally insulating solid comprises predominantly aluminium oxide. Preferably, at least one of the upper and lower nozzles has heater means. IS A bottom nozzle according to the invention for a metallurgical vessel, with an upper nozzle arranged in the floor of a metallurgical vessel and a lower nozzle arranged below the upper nozzle, has a wall, at least sealed to flow of metal melt, of the throughflow aperture through the nozzles, the nozzles being at least partially surrounded by a gastight housing such that the housing gastightly encloses the lower end of the lower 20 nozzle at its periphery, wherein it abuts on the outside of the nozzle with a portion of its inner side, and a thermally insulating solid is arranged between the wall of the throughflow aperture and the housing. The term "at least partially" means that of course the nozzles can not be surrounded by the housing for example at their openings. The housing prevents the penetration of gas. It has an upper end and a lower end and is 25 gastight between these ends. With this arrangement, the bottom nozzle has two basic seals, namely a melt flow seal in the region of the wall of the throughflow aperture and a gas seal in the colder region of the bottom nozzle remote from the throughflow aperture. Thereby fewer temperature-resistant materials can be used for achieving gastightness. By "gastight", absolute gastightness is of course not to be understood, but a smaller gas flow 30 is possible, for example less than 10 ml/s, preferably less than I ml/s, in particular preferably about of the order of 10-4 ml/s, depending on the kind and location of the seals/materials. Such a value is smaller by at least an order of magnitude than in the known prior art. The minimisation of clogging is the result of the gastightness (especially oxygentightness).

3a The housing preferably has plural housing portions, gastightly connected together and preferably arranged one above the other, at least one housing portion being gastightly connected to the upper nozzle and/or the floor of the metallurgical vessel, preferably abutting with a portion of its side surface on the outside of the upper nozzle 5 and/or of the floor. It is furthermore appropriate that a valve for regulating the metal melt flow is arranged above the upper nozzle, or between the upper and lower nozzles. In the former case, the valve is a stopper rod; in the 4 latter case, a sliding gate. Preferably a permanent getter material, particularly from the group titanium, aluminum, magnesium or zirconium, is arranged within the housing or in the thermally insulating material. The housing is appropriately formed as at least partially tubular (hollow cylinder) or coni 5 cal, preferably with oval or circular cross section. The housing can appropriately be constructed of steel, and the thermally insulating material can preferably contain aluminum oxide. It can be reasonable that at least one of the nozzles has a heating means. The invention is explained hereinafter by way of example using a drawing. 10 Figure 1 shows a bottom nozzle for performing the method according to the invention, Figure 2 shows a time diagram of temperature/pressure, Figure 3 shows a bottom nozzle sealed according to the invention. The bottom nozzle shown in Figure 1 in the floor of a distributor for steel melt 2 has an upper nozzle 3 within the floor 1. Electrodes 4 for producing an electrochemical effect or as is heaters are arranged in this nozzle 3. The floor 1 itself has different layers of a refractory mate rial and a steel housing 5 on its outside. A sliding gate 6 for regulating the flow of steel melt is arranged below the upper nozzle 3, and below it a lower nozzle 7 which projects into the metal melt container 8, which for example belongs to a continuous casting plant for the steel. The steel melt 2 flows through apertures 9 into the metal melt container 8. A temperature sensor 10 20 measures the temperature at the outside of the lower nozzle. When this temperature falls, this indicates an increase of clogging within the lower nozzle 7, since the insulation between the outside of the lower nozzje 7 and the steel melt 2 flowing through increases. The temperature sensor 10, together with the pressure sensor 11, effects the regulation of the argon supply through the inert gas aperture 13 to the metal melt 2 via a pressure regulation 12. 25 A pressure/temperature course with time is shown in Figure 2. With falling temperature (thick line), the argon pressure is increased stepwise, so that the argon flow into the throughflow aperture causes a release of the clogging on the wall. Thereafter the temperature measured on the outer wall rises again as far as a value which remains constant. The argon pressure/argon flow can in this way be set to a minimum at which the formation of clogging is just prevented or 30 kept slight.

5 The bottom nozzle shown in Figure 3 has a basically two-part seal, namely a seal which seals to melt flow along the inside of the throughflow aperture and a housing 14 which effects a gastight sealing to the outside (between the atmosphere of the environment and the throughflow aperture), the individual seals being arranged in a clearly lower temperature region. The hous 5 ing 14 consists of plural portions 14a and 14b and in principle is extended into the metal sleeve 15, which encloses the upper nozzle 3 on its outside and opens into a flange 16, on which a portion of the outer surface of the upper housing portion 14b is sealingly arranged. The various seals are shown in the Figure. So-called type 1 seals 17 exist between opposed movable por tions on the sliding gate 6. They are at least partially exposed to the metal melt. Type 2 seals 18 1o are arranged between refractory portions of the bottom nozzle 1, i.e. for example between por tions of the sliding gate 6 and the upper nozzle 3 or the lower nozzle 7. These type 2 seals 18 are also at least partially directly exposed to the metal melt or to the temperature of the liquid steel. Furthermore, the wall of the throughflow aperture of the bottom nozzle 1 itself represents a seal (type 3 seal), which is influenced by the choice of material. The seals described above 15 are in principle present in all known arrangements. They can, for example, be formed of alumi num oxide. The sealing effect of the type 3 seals can be improved by high temperature glass layers, among other things. The portions of the outer housing 14 form a type 4 seal, which are not exposed to steel melt or to comparable temperatures. These seals can be formed of metal, for example steel, or from dense sintered ceramic material. Type 5 seals 19 are between por 20 tions of the housing 14 and movable portions of the throughflow regulation means, such as the push rods 20 of the sliding gate 6. They are not exposed to liquid steel and, according to the specific temperature conditions, can consist of Inconel (up to 800 0 C), of aluminum, copper, or graphite (up to about 450 0 C), or of an elastomeric material (at temperatures up to about 200 0 C), and also the type 6 seals 20 between the individual housing portions. Furthermore, type 7 seals 25 21 exist as a transition between the refractory material of the upper nozzle 3 or the lower nozzle 7 and the housing 14 or metal sleeve 15 surrounding these on the outside, and prevent gas, particularly oxygen, from penetrating along at the connection place between these components into the cavity 22 between the housing portion 14b and the sliding gate 6. A reduced pressure is thereby ensured within the cavity 22 with respect to its surroundings during the throughflow of 30 metal melt 2 through the bottom nozzle 1. This type 7 seal can be produced and set by the manufacturer of the nozzles. The upper nozzle 3 can be formed of zirconium dioxide, and the lower nozzle of alumi num oxide. Foam-type aluminum oxide with low density and closed pores can also be used, likewise aluminum oxide-graphite, other refractory foamed materials or fiber materials. An oxy 35 gen getter material, for example titanium, aluminum, magnesium, yttrium or zirconium, can be 6 arranged in the thermally insulating material of the lower nozzle 7 or between the lower nozzle 7 and the housing portion 14a, as a mixture with the refractory insulating material or as a separate portion. The bottom nozzle according to the invention has a substantially smaller leakage rate 5 than known systems. Type 1 or type 2 seals have a leakage rate of about 10 3 -10 4 , or 102-103, ml/s, and standard materials for type 3 seals lead to leakage rates of 10-100 ml/s. Type 4 seals lead to a leakage rate of negligibly less than 108 ml/s when metal (for example steel) is used as the material. Type 5 and type 6 seals, when polymer material is used, have a leakage rate of about 10-4 ml/s and, with the use of the corresponding graphite seals, reach a leakage rate of io about 1 ml/s. Type 7 seals are similar to a combination of type 3 and type 4 seals, and can reach a leakage rate of 1-10 ml/s. The leakage rates are related to the operating state of the bottom nozzle. The standardized leakage rate (Nml/s) = leakage rate (ml/s) x pav 0 / 1 atm x 273KTavg 15 Pavg = (pin + pout)/2 <atm> Tavg = (Tin + Tout)/2 <K> avg = average value. Thereby the standardized leakage rate according to the invention is of the order of mag nitude of 1-10 Nml/s, while the combination of type 1, type 2 and type 3 seals leads in the best 20 case to 150 Nml/s.

Claims

1. A bottom nozzle for a metallurgical vessel, the bottom nozzle having a flow passage for discharging molten metal from the vessel, the bottom nozzle comprising: 5 an upper nozzle arranged in a floor of the metallurgical vessel, a lower nozzle arranged below the upper nozzle, the flow passage being in the form of an aperture formed in the nozzles, the aperture having a wall sealed against flow of the molten metal therethrough, a gas-tight housing having an upper end, a lower end, and an interior surface, the io housing at least partially surrounding the nozzles to thereby prevent penetration of gas into the aperture between the upper and lower ends of the housing, the housing being adapted to enclose the lower nozzle with a portion of the interior surface of the housing abutting an exterior surface of the lower nozzle, and a thermally insulating solid arranged between the wall of the aperture and the is housing.

2. A bottom nozzle as claimed in claim 1, wherein the housing comprises plural housing portions, the housing portions being interconnected in a gas-tight manner, and wherein at least one of the housing portions is connected to the upper nozzle and/or the floor of the metallurgical vessel. 20

3. A bottom nozzle as claimed in claim 2, wherein the housing portions are arranged one above another.

4. A bottom nozzle as claimed in claim 2 or 3, wherein a side surface of the at least one of the housing portions abuts an outside portion of the upper nozzle and/or the floor the metallurgical vessel. 25

5. A bottom nozzle as claimed in any one of the preceding claims, the bottom nozzle further comprising a valve for regulating molten metal flow, the valve being arranged above the upper nozzle or between the upper and lower nozzles.

6. A bottom nozzle as claimed in any one of the preceding claims, wherein a getter material is arranged within the housing or in the thermally insulating solid. 30

7. A bottom nozzle as claimed in claim 6, wherein the getter material is selected from the group consisting of titanium, aluminium, magnesium, and zirconium.

8. A bottom nozzle as claimed in any one of the preceding claims, wherein at least a portion of the housing has a tubular or conical form.

9. A bottom nozzle as claimed in claim 8, wherein the tubular or conical 35 form has an oval or circular cross-section. 8

10. A bottom nozzle as claimed in any one of the preceding claims, wherein the housing comprises steel, and wherein the thermally insulating solid comprises aluminium oxide.

11. A bottom nozzle as claimed in claim 10, wherein the thermally s insulating solid comprises predominantly aluminium oxide.

12. A bottom nozzle as claimed in any one of the preceding claims, wherein at least one of the upper and lower nozzles has heater means.

13. A bottom nozzle for a metallurgical vessel substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings. 10 Dated 22 January 2010 Heraeus Electro-Nite International N.V. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON