Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/16—Controlling or regulating processes or operations
  • B22D11/18—Controlling or regulating processes or operations for pouring
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like
  • B22D41/50—Pouring-nozzles
  • B22D41/58—Pouring-nozzles with gas injecting means

Definitions

• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 .
• 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.
• 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.
• the molten metal 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.
• control over the rate at which the process occurs is critical to achieving a satisfactory result.
• 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.
• 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.
• 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.
• 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.
• a metal casing member 36 is secured about the exterior surface of the lower extremity of nozzle 22 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.
• 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" ⁇ *f ⁇ "ld' 40 withi-nr-n ⁇ z-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.
• the nozzle 22 may be .
• 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 6 m.) and about 1.57 X 10 3 inches (4 X 10 5 m.).
• 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 6 m.) and about 1.57 X 10 3 inches (4 X 10 5 m.).
• 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.
• a member of the inert gases be selected as a flow control fluid, preferably argon or nitrogen.
• 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.
• 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.
• 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.
• 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.
• practice of the present invention obviates significant limitations which existed in previous methods of .controlling molten.metal flow, during continuous casting.
• 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.
• 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.
• 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.
• 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.
• 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 5 inches (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.
• 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.
• 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.
• a second embodiment of flow control system 26 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.
• 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.
• a third embodiment of flow control system 26 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
• 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.
• second refractory portion 62 may be formed of a zirconia graphite composition.
• nozzle 52 of-fch-is—embodiment may he conveniently encased in a metal casing member 64.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Casting Support Devices, Ladles, And Melt Control Thereby (AREA)

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Cited By (6)

Citations (5)

• 1983
  • 1983-06-13 EP EP19830902357 patent/EP0130988A4/de not_active Withdrawn
  • 1983-06-13 WO PCT/US1983/000921 patent/WO1984002670A1/en not_active Application Discontinuation

Patent Citations (5)

Non-Patent Citations (1)

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