EP0130988A1

EP0130988A1 - Flow control nozzle for continuous casting

Info

Publication number: EP0130988A1
Application number: EP83902357A
Authority: EP
Inventors: Mark K. Fishler
Original assignee: Vesuvius Crucible Co
Current assignee: Vesuvius Crucible Co
Priority date: 1983-01-03
Filing date: 1983-06-13
Publication date: 1985-01-16
Also published as: WO1984002670A1; EP0130988A4

Abstract

Un ajutage (22) utile dans la coulée en continu de métaux en fusion est pourvu d'éléments permettant de réguler et/ou interrompre l'écoulement du métal en fusion au travers de l'ajutage. Le système de régulation d'écoulement (26) comprend l'utilisation de parties réfractaires de l'ajutage perméables aux fluides.A nozzle (22) useful in the continuous casting of molten metals is provided with elements for regulating and / or interrupting the flow of molten metal through the nozzle. The flow control system (26) includes the use of refractory parts of the fluid-permeable nozzle.

Description

Flow Control Nozzle For Continuous Casting

Field of the Invention

The present invention relates to continuous casting for progressively forming an - elongated casting from molten material, and more particularly to facilities and methods for controlling the flow of such molten material during continuous casting.

Discussion of, the Technical Problem

In the art of continuous casting of molten metals, it is known to deliver a metered flow of the molten metal from a tundish through an elongated conduit in a refractory nozzle toward a continuous casting mold positioned therebelow. There are a number of facilities known in the art for controlling and/or terminating the flow of molten metal during such a procedure.

For example, U.S. Patent Number 2,005,311 to Belding teaches the use of a stopper rod positioned within a ladle for controlling the flow of molten metal from an outlet orifice in the lower surface of the ladle. However, such apparatus is limited by the expense and complexity of its substantial number of moving parts and is further limited because such a stopper rod may erode in the hostile environment of the ladle and both introduce undesirable contaminants into the molten metal and limit the duration of the casting procedure.

A second known facility for controlling molten metal flow during continuous casting utilizes a sliding gate valve ^"at the exterior surface of an outlet orifice of the ladle, which valve may be mechanically repositioned to restrict and/or terminate the flow of molten metal therethrough. However, such sliding gate valves may be limited because of the erosion of their refractory plates during use, which erosion may introduce undesirable contaminants into the molten metal and ultimately require the casting process to be terminated for replacement procedures.

A third known method for controlling molten metal flow includes utilizing a refractory nozzle having a very precisely defined inner bore diameter and maintaining a constant static pressure of molten metal thereabove, such that a preselected molten metal flow results. However, such a control method may be limited because of erosion of the inner bore of the ceramic nozzle and because of difficulties in maintaining a constant static pressure of molten metal. Moreover, such a method does not provide a convenient mechanism for quickly terminating molten metal flow in the event of a casting emergency. It would be desirable to have a molten metal flow control facility and method which avoids such limitations of the prior art.

Summary of the Invention

The present invention provides a method _<-,£ _an<3 apparatus for controlling molten metal "flow during continuous casting which is mechanically simple, minimizes erosion problems to increase the length of casting runs, makes possible a more constant casting speed for improved metallurgical properties in the casting, and facilitates the termination of a casting run if an emergency should arise. The flow control system of the present invention includes means for controllably exerting fluid pressure upon the flowing molten metal with a magnitude sufficient to control and/or terminate the delivery thereof from an upper container, e.g., a ladle or tundish, to a lower container, e.g., a tundish or casting mold. The flow control facility may include a refractory nozzle member having at least portions which are permeable to the passage of the selected flow control fluid. A fluid source provides the selected fluid under pressure to the refractory nozzle member, through which it percolates into the bore thereof in a controllable degree to form a flow control fluid barrier in the bore. Molten metal flow is thereby conveniently controllable by adjusting the pressure and volume of selected fluid supplied to the refractory nozzle member. In preferred embodiments of the invention, a fluid manifold is formed around or with in the refractory nozzle member , and an inert gas is selected as the flow control flu id . Practice of the present invention eliminates the need for and the limitations associated with the stopper rods , sliding gate valves, or precise-bore nozzles prev iously: utilized, iθ- con trol_ Jnolten_meJtal flow... ..

Description of the Drawing

Figure 1 is a partially schematic , cross-sect ional elevated s ide v iew of a continuous casting system incorporating features of the present invention.

Figure 2 is an elevated s ide view of a refractory nozzle having facilities for controlling the flow of molten metal therethrough.

Figure 3 is an elevated s ide view similar to Figure 2 showing a second embodiment of a refractory nozzle having facilit ies for controlling the flow of molten metal therethrough.

Figure 4 is an elevated s ide view similar to Figure 2 showing a third embod iment of a refractory nozzle having facilities for controlling the flow of molten metal therethrough.

OMPI Description of Preferred Embodiments

With reference to Fig. 1, a continuous casting steel making operation includes a supply 10 of molten steel contained within a refractory- lined ladle 12. Molten steel is teemed from the ladle 12 through a nozzle 14 and a shroud 16 into a tundish 18. The molten steel in the tundish IB^~ is then delivered into a continuous casting mold 20, preferably to a level below the upper surface of the molten metal therein, through a nozzle 22 and a shroud 24.

On introduction into the continuous casting mold 20, the molten metal begins to solidify as it flows through the casting~-mold 20, with the outer portions of the molten metal solidifying first to form a shell. The molten metal adjacent the interior of the casting mold .20 is retained within this outer shell even after the metal exits from the casting mold 20 until such time as it cools to a completely solid form.

Thus, control over the rate at which the process occurs is critical to achieving a satisfactory result.

With continued reference to Fig. 1, the rate at which molten metal is delivered from ladle 12 to tundish 18 may be conveniently controlled through the operation of a flow control system 26 incorporating features of the present invention. Likewise, the rate at which molten metal is delivered from tundish 18 to casting mold 20 may be conveniently controlled through the use of a second flow control system 26 positioned therebetween.

With reference also to Fig. 2, a flow control system 26 is shown in greater detail in -sse-in tire "tundish T8.^"The operation and construction of the flow control system 26 will be discussed herein in reference to such use, although it should be appreciated that a like discussion would be applicable to use of the flow control system 26 to control flow from the ladle 12.

In accordance with a first embodiment of the present invention,, flow control system 26 includes a fluid supply 28, a fluid pressure control facility 30, and a fluid supply line 32 which is secured to the exterior surface of nozzle 22 in any convenient manner. Nozzle 22 is formed of a refractory material and is secured within and extends below tundish 18 to provide an outlet passageway 34 therefrom. About the exterior surface of the lower extremity of nozzle 22 is secured a metal casing member 36 to which fluid supply line 32 is preferably secured. An inlet port 38 is provided into the body of nozzle 22 to provide communication between fluid supply line 32 and a fluid manifold 40 which is formed within the body walls of nozzle 22. In operation, the flow control system 26 controls the flow rate of molten metal through outlet passageway 34 by providing therein to a controllable degree a fluid barrier which limits the flow of molten metal. This result is achieved by providing a selected fluid at a selected pressure from fluid supply 28 to the fluid ^" ma"π*fθ"ld' 40 withi-nr-nαz-z-le 22_* -At least-those portions of nozzle 22 between fluid manifold 40 and outlet passageway 34 are preferably formed of a porous or fluid-permeable refractory material through which the selected fluid may be controllably forced under pressure. Although not limiting to the invention, the nozzle 22 may be . formed of aluminum oxide, zirconium oxide, magnesium oxide, alumina graphite, zirconia graphite or combinations thereof. Porous portions of nozzle 22 preferably are provided with an open porosity between about 12 percent and about 30 percent with an average pore size between about 1.18 X 10 ⁵ inches (3 X 10 ⁶m.) and about 1.57 X 10 ³ inches (4 X 10 ⁵m.). Of course, the particular composition, open porosity and average pore size selected for a given application of nozzle 22 will depend in part upon the fluid selected, the magnitude of pressure utilized therewith and the dimensions of outlet passageway 34. In this regard, it is preferred that a member of the inert gases be selected as a flow control fluid, preferably argon or nitrogen. Although not limiting to the invention, it is preferred that the fluid barrier generated within the outlet passageway 34 by the practice of the present invention be maintained uniformly with respect to the outlet passageway 34 so that the direction of flow of the molten metal remains unaffected thereby. For example in Fig. 2, the outlet passageway 3 ..AS substantially cylindrical in shape, and it is preferred that the path of flow of molten metal therethrough remain centrally aligned with the axis of outlet passageway 34 without being diverted, e.g. flared, side to side therefrom by the affect of the fluid barrier. Accordingly, in the embodiment of Fig. 2 it is preferred that the fluid permeability of the portions of nozzle 22 between the fluid manifold 38 and the outlet passageway 34 be uniform, so that a substantially annular fluid barrier may be formed about the peripheral surface of outlet passageway 34 which limits the path of flow of molten metal to the area therewithin without altering the direction of such flow. In practice it has been determined that the fluid barrier of the present invention actually may have the beneficial affect of stabilizing the flow of molten metal after its departure from outlet passageway 34 by minimizing "snaking", the curved descent path commonly observed in a falling metal stream. If flow rate is to be decreased, additional fluid pressure may be utilized to form an annular fluid barrier of greater dimensions, and molten metal flow may be conveniently terminated by the application of sufficient pressure to form a fluid barrier which closes outlet passageway 34.

As can now be appreciated, practice of the present invention obviates significant limitations which existed in previous methods of .controlling molten.metal flow, during continuous casting. For example, the mechanical simplicity associated with the present invention is to be preferred to the complexity associated with stopper rod and sliding gate valve technology. Precise flow rate control may be achieved in the practice of the present invention by the simple expedient of adjusting a fluid pressure valve. Additionally, the present invention removes the erosion problems associated with stopper rods and sliding gate valves, and thereby significantly increases the length of a continuous casting run.

Moreover, the life expectancy of nozzle 22 itself would likely be extended because molten metal flows therethrough for a portion of its passage within the confines of the fluid barrier formed within outlet passageway 34, thereby minimizing the erosion which results from direct contact between the molten metal and a refractory material. Finally, selection of argon or nitrogen as the fluid for use in the practice of the invention provides the incidental benefit of minimizing undesirable oxidation of the molten metal as it passes through the outlet passageway 34 of nozzle 22.

EXAMPLE I

A nozzle 22 substantially as shown in ^Figure 2 was. formed of a jzirconia graphite. _ composition having an outlet passageway 34 extending therethrough with a vertical dimension of 4 inches (100 mm.) and a diameter in its lower cylindrical portion of .54 inches (13.5 mm.). The wall members of nozzle 22 were of a thickness ranging from between about 1 inch (25 mm.) to about .28 inches (7.0 mm.), and substantially uniformly therethrough had an open porosity of about 15-17 percent and an average pore size of about 1.38-1.58 X 10 ⁵inches (3.5-4 X 10 ⁶ m.). An elongated annular open area was formed within the wall members of nozzle 22 to provide gas manifold 40, the gas manifold 40 uniformly spaced about the outlet passageway 34 at a distance of about .33 inches (8.25 mm.) and having a thickness of about .04 inches (1.0 mm.).

A tundish 18 similar to the one shown in Figure 1 was provided with three outlet openings for continuous casting with three streams of molten metal simultaneously. Nozzle 22 incorporating features of the invention was secured to tundish 18 to control molten metal flow through one of the outlet openings, and conventional precise-bore nozzles were secured to tundish 18 to control flow through each of the other two outlet openings. No shrouds 24 were utilized, the streams free-falling into the casting molds 20.

TRIAL 1

After conventional preheating of the nozzles and other elements of the system, casting was initiated with a heat of steel with temperatures reaching 2935° F (1613°C) in the ladle 12 and 2830° F (1554°C) in the tundish 18. Initially, nozzle 22 was operated in a conventional, non-fluid-pressurized mode, but a number of minutes into the cast, argon was supplied under pressure to the nozzle 22. Shortly thereafter the molten metal flow through nozzle 22 reduced substantially and ultimately ceased completely. Argon pressure was thereafter diminished and molten metal flow resumed through nozzle 22. Continued adjustment of the argon supply yielded a stable and consistent molten metal flow. Particularly, a casting speed of 42 inches per minute was found to be maintainable with very little variation therefrom, while the casting speeds achievable with the other two nozzles fluctuated between 40 and 50 inches per minute continuously. Such a uniform casting speed is a much desired condition, because variations in casting speed inevitably result in undesirable

OMPI variations in the metallurgical structure of the casting due to differences in cooling rate between portions thereof. Practice of the present invention yielded a substantially constant casting speed and a correspondingly more homogenous casting. Four heats of steel were cast before the trial was terminated, and it was observed during the trial that the_molten metaJL from-nozzle 22__ flowed more true, i.e., less snaky, into the casting mold, and the stream from nozzle 22 had a brighter color, indicating less undesirable oxidation thereof. Upon removal, nozzle 22 failed to reveal any signs of erosion from use during the trial.

TRIAL 2

A nozzle 22 substantially identical to that used in Trial 1 was employed in this trial, and a shroud 24 was secured to the lower portion thereof to pass the molten metal stream into the casting mold 20. Again, three streams of molten metal were initiated with ladle temperatures" reaching 2935°F (1613°C) and tundish temperatures reaching 2850°F (1566°C) . After casting was initiated the argon supply was opened to nozzle 22 and casting speeds stabilized for each of the nozzles at about 50 inches per minute. ^{^}Thereafter, molten metal flow through nozzle 22 was controllably reduced to yield a casting speed of 40 inches per minute by a gradual increase in the argon pressure. Thereafter casting speed was increased to 50 inches per minute again by decreasing argon pressure to nozzle 22.

Facilities were not available to measure accurately the argon pressures and volumes utilized during the trials, particularly because of the substantial temperature increase to which___ the argon was subjected as it was supplied from a room temperature source to a casting temperature environment within the nozzle 22.

SECOND EMBODIMENT

With reference now to Figure 3, a second embodiment of flow control system 26 is shown, including a nozzle 42 of refractory material having an outlet passageway 44 therethrough.

Nozzle 42 is substantially encased by but spaced from a metal casing member 46, thereby leaving an open annular space about nozzle 14 to provide a fluid manifold 48. Fluid supply line 32 is secured to metal casing member 46 in a manner to provide communication between the fluid supply 28 and fluid manifold 48. Nozzle 42 is formed of one of the aforementioned refractory compositions, having a substantially uniform open porosity and average pore size within the aforementioned ranges.

OMP In operation, a selected fluid is provided at a selected pressure to fluid manifold 46, from whence it percolates through the wall members of nozzle 42 to form an annular fluid barrier within outlet passageway 44 to control molten metal flow therethrough. The metal casing member 46 must be formed of an appropriate material ,to. withstand the hg.stULe conditions to .. which it is subjected adjacent its upper edge.

THIRD EMBODIMENT

With reference now to Figure 4, a third embodiment of flow control system 26 is shown, including a -nozzle 52 formed of a plurality of refractory materials and having an outlet passageway 54 therethrough. Nozzle 52 includes an internal fluid manifold 56 to which pressurized fluid is passed through an inlet port 58 which communicates with fluid supply line 32 in any convenient manner. The wall members of nozzle 52 are formed of a first refractory portion 60 positioned adjacent the exterior surfaces of nozzle 52, and a second refractory portion 62 positioned between the fluid manifold 56 and the outlet passageway 54. First refractory portion 60 is provided with a relatively low fluid- permeability and second refractory portion 62 is provided with a relatively high fluid permeability, whereby pressurized fluid present in fluid manifold 56 is induced to percolate into

^OM^P outlet passageway 54 to form a flow-controlling fluid barrier therein in accordance with the teachings of the present invention. Although not limiting to the invention, first refractory portion 60 may be formed of an alumina graphite composition while second refractory portion 62 may be formed of a zirconia graphite composition. - Additionally,- nozzle 52 of-fch-is—embodiment may he conveniently encased in a metal casing member 64.

Of course, it will be appreciated that the embodiments described herein are intended to define the presently best known manner of practicing the instant invention, but in no way are they intended to limit the scope of .the invention. Rather, the scope of the invention is defined in the claims which immediately follow.

Claims

I CLAIM:

1. In a facility for the casting of molten metals wherein said molten metal is delivered from an upper, container into a lower container through an intermediate nozzle member, the improvement comprising:

molten metal flow control means, said flow control means including means for controllably exerting fluid pressure upon said molten metal with a magnitude sufficient to control the rate of delivery of said molten metal.

2. The facility as set forth in Claim 1, wherein said pressure exerting means comprises:

a fluid source;

a fluid release mechanism positioned adjacent the molten metal delivery path between said upper and lower containers;

means providing fluid communication between said fluid source and said fluid release mechanism; and

means for controlling the pressure at which said fluid is supplied to said fluid release mechanism, whereby the

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rate of delivery of said molten metal is controlled.

3. The facility as set forth in Claim 2, wherein said nozzle member is formed of a refractory composition and includes an inner molten metal passageway extending between said upper and._..lower containers,.,wherein said fluid release mechanism comprises:

a fluid permeable portion of said nozzle member oriented to surround said molten metal passageway such that fluid which is controllably pressured through said fluid permeable portion of said nozzle member provides a fluid barrier to the passage of molten metal through said molten metal passageway to control the flow thereof.

4. The facility as set forth in Claim

3, wherein said fluid is an inert gas.

5. The facility as set forth in Claim

4, wherein said fluid is argon or nitrogen.

6. The facility as set forth in Claim 5, wherein said refractory composition of said nozzle member is selected from the group consisting of aluminum oxide, zirconium oxide, magnesium oxide, alumina graphite and zirconia graphite and combinations thereof.

7. The facility as set forth in Claim 6, wherein said fluid permeable portion of said nozzle member includes an open porosity between about 12 percent and about 30 percent and an average pore size between about 1.18 X 10 inches (3 microns) and 1.57 X 10 inches (40 microns) .

8. The facility as set forth in: Claim

7, wherein said molten metal passageway adjacent said fluid permeable portion is cylindrical in shape, and wherein the fluid permeability of said fluid permeable portion is substantially uniform about said molten metal passageway to provide a substantially uniform annular fluid barrier about the circumference of said molten metal passageway.

9. The facility as set forth in Claim

8, wherein said fluid release mechanism further comprises a fluid release manifold surrounding said fluid permeable portions of said nozzle member.

10. The facility as set forth in Claim

9, wherein said fluid release manifold is formed within the body portion of said nozzle member.

11. The facility as set forth in Claim

10, wherein said fluid permeable portion of said nozzle member is formed of a first refractory composition having a relatively high fluid permeability and other portions of said nozzle member are formed of a second refractory

OMPI composition having a relatively low fluid permeability.

12. The facility as set forth in Claim 11, wherein said upper container comprises a tundish, said lower container comprises a casting chamber, and said molten metal comprises a ferrous or nonferrous metal.

13. A method of controlling the flow of a molten metal as it is delivered during a continuous casting procedure from an upper container to a lower container through the bore of an intermediate nozzle member, comprising:

forming at least portions of said intermediate nozzle member adjacent said bore of a selected fluid permeable refractory material; and

forcing a selected fluid through said fluid-permeable portions of said intermediate nozzle member into said bore with sufficient pressure and volume to limit the rate at which molten metal would otherwise pass through said bore.

14. The method as set forth in Claim 13, wherein said fluid permeable portions of said intermediate nozzle member are formed to surround a selected portion of said bore, wherein said selected fluid is forced therethrough at a substantially uniform pressure and volume to maintain said molten metal spaced from the periphery of said bore..

15. The method as set forth in Claim 14 further comprising:

_ increasing_the volume _ard_ pressure at which said selected fluid is forced into said bore to decrease the rate of flow of molten metal therethrough.

16. The method as set forth in Claim

14, further comprising:

decreasing the volume and pressure at which said selected fluid is forced into said bore to increase the rate of flow of molten metal therethrough.

17. The method as set forth in Claim 14, wherein said fluid permeable refractory material is selected from the group consisting of aluminum oxide, zirconium oxide, magnesium oxide, alumina graphite, and zirconia graphite, and combinations thereof.

18. The method as set forth in Claim 17, wherein said selected fluid is an inert gas.

19. The method as set forth in Claim 18, wherein said selected fluid is argon or nitrogen.

20. The method as set forth in Claim 19, wherein said forming step is practiced to provide fluid-permeable portions having an open porosity between about 12.percent and about 30 percent and an average open pore size between about 1.18 X 10 inches (3 microns) and about 1.57 x 10 ^J inches (40 microns) .

21. The method as set forth in Claim 20 wherein said upper container comprises a tundish and wherein said lower container comprises a continuous casting mold.