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
  • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
  • B22D11/003—Aluminium alloys
• • 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
  • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
  • B22D11/049—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds for direct chill casting, e.g. electromagnetic casting
• • 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
  • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould

Definitions

• Molten aluminum can then come into contact with the water coolant in various locations in the casting pit (e.g. between the ingot butt or bottom and the starting block, on the metal (usually steel) bottom block base, the pit walls or at the bottom of the pit) as well as in the ingot cavity where the water can enter through a rupture in the ingot shell below the bottom of the mold.
• Water during a "bleed- out” or "run-out” can cause an explosion from (1) conversion of water to steam from the thermal mass of the aluminum heating the water to >212°F or (2) the chemical reaction of the molten metal with the water resulting in release of energy causing a chemical reaction generated explosion.
• U.S. Patent No. 4,651 ,804 describes a more modern aluminum casting pit design. According to this reference, it has become standard practice to mount the metal melting furnace slightly above ground level with the casting mould at, or near to, ground level and lower the cast ingot into a water containing pit as the casting operation proceeds. Cooling water from the direct chill flows into the pit and is continuously removed there-from while leaving a permanent deep pool of water within the pit. This process remains in current use and, throughout the world, probably in excess of 5 million tons of aluminum and its alloys are produced annually by this method.
• Al-Li alloy . . . underwent a violent reaction It has also been announced by the Aluminum Association Inc. (of America) that there are particular hazards when casting such alloys by the direct chill process. The Aluminum Company of America has subsequently published video recordings of tests that demonstrate that such alloys can explode with great violence when mixed with water. Other work has demonstrated that the explosive forces associated with adding lithium to aluminum alloys can increase the nature of the explosive energy several times that for aluminum alloys without lithium. When molten aluminum alloys containing lithium come into contact with water, there is the rapid evolution of hydrogen, as the water dissociates to Li-OH + H + .
• U.S. Patent No. 5,212,343 teaches the addition of aluminum, lithium (and other elements as well) to water to initiate an explosive reaction.
• 5,212,343 describes the method to perform this intense interaction for producing a water explosion via the exothermic reaction.
• This patent describes that with the addition of elements such as lithium a high energy of reaction per unit volume of materials is achieved.
• the addition of lithium or some other chemically active element promotes explosions.
• These patents teach a process where an explosive reaction is a desirable outcome.
• These patents reinforce the explosiveness of the addition of lithium to the "bleed-out” or "run-out", as compared to aluminum alloys without lithium.
• 4,651,804 is to minimize the potential of an explosion at the bottom of the casting pit when a "bleed-out” or "run-out” occurs during casting of Al-Li alloys. This technique continues to use the coolant water to cool the molds and cool the ingot shell, even after a bleed-out. If the coolant is turned off there is a potential for more serious problems with a melt-through of the molds or additional melt-throughs of the ingot shell causing additional potential for explosions when molten aluminum-lithium and water come into contact.
• 4,593,745 describes using a halogenated hydrocarbon or halogenated alcohol.
• U.S. Patent Nos. 4,610,295; 4,709,740 and 4,724,887 describe the use of ethylene glycol as the ingot coolant.
• the halogenated hydrocarbon typically ethylene glycol
• the halogenated hydrocarbon must be free of water and water vapor. This is a solution to the explosion hazard, but also introduces a strong fire hazard and is costly to implement and maintain.
• a fire suppression system is required within the casting pit to contain potential glycol fires.
• a typical cost to implement a glycol based ingot coolant system including a glycol handling system, a thermal oxidizer to de-hydrate the glycol, and a casting pit fire protection system is on the order of $5 to $8 million dollars (in today's dollars) .
• Casting with 100% glycol as a coolant also brings in another issue.
• the cooling capability of glycol or other halogenated hydrocarbons is different than that for water, and different casting practices as well as casting tooling are required to utilize this technology.
• glycol has a lower heat conductivity and surface heat transfer coefficient than water
• the microstructure of the metal cast with 100% glycol as a coolant tends to have coarser undesirable metallurgical constituents and exhibits higher amount of centerline shrinkage porosity in the cast product. Absence of finer microstructure and simultaneous presence of higher concentration of shrinkage porosity has a deleterious effect on the properties of the end products manufactured from such initial stock.
• Figure 1 is a cut-away view of one section of a direct chill casting system.
• Figure 2 is a top view schematic representation of a portion of the system of Figure 1 illustrating a configuration for injecting simultaneously with a coolant or serially therewith inert fluid to a direct chill casting mold or a coolant feed to cool the ingot during normal casting operations.
• Figure 3 is a top view schematic representation of a portion of the system of Figure 1 following the stopping of the flow of liquid coolant (water) and injecting only inert fluid as the coolant during or following a "bleed-out" or "run-out”.
• Figure 1 shows components of a direct chill (DC) casting system.
• System 10 includes casting pit 12 into which cast ingot 14 is lowered by a casting cylinder (not shown) during a casting operation.
• Mold 16 is seated on casting table 18.
• Molten metal e.g., Al-Li alloy
• the molten metal that is fed into mold 16 is supported by platen 8 on casting cylinder 9.
• Mold 16 is cooled by coolant contained in reservoir 20 within mold 16 and shapes ingot 14 as molten metal is fed from above at a predetermined, time varying rate.
• Casting cylinder 9 is displaced at a predetermined rate in a downward direction in this view to produce an ingot having a desired length dimension and a desired geometrical shape as defined by the perimeter of casting mold
• the molten metal added to mold 16 is cooled in mold 16 by the cooler temperature of the casting mold and through introduction of a coolant that impinges on ingot 14 after it emerges from the mold cavity through a plurality of conduit feeds 13 (two shown) around mold 16 at its base.
• a coolant e.g., water
• the coolant is water
• mixture 24 of water and air is produced in casting pit 10 about the periphery of ingot 14, and into which freshly produced water vapor gets continuously introduced as the casting operation continues.
• the embodiment of a casting system shown in Figure 1 also includes "bleed-out” detection device 17 such as an infrared thermometer.
• "Bleed-out” detection device 17 may be directly and/or logically connected to controller 15 associated with the system.
• controller 15 contains machine-readable program instructions as a form of non-transitory tangible media.
• a signal is sent from "bleed-out” detection device 17 to controller 15.
• the machine readable instructions stored in controller 15 cause movement of platen 8 and molten metal inlet supply (not shown) to stop, and coolant flow (not shown) into reservoir 20 associated with mold 16 to stop and/or be diverted.
• system 10 includes coolant feed system 21 that is placed in the coolant feed, either between reservoir 20 and conduit feed 22 or upstream of reservoir 20.
• coolant feed system 21 is upstream of reservoir 20.
• Mold 16 (illustrated in this embodiment as a round mold) surrounds metal 14.
• coolant feed system 21 includes valve system 28 connected to conduit feed 22 that feeds reservoir 20.
• Suitable material for conduit feed 22 and the other conduits and valves discussed herein includes, but is not limited to, stainless steel (e.g., a stainless steel tubular conduit).
• Valve system 28 includes first valve 30 associated with first conduit 33.
• First valve 30 allows for the introduction of a coolant (generally water) from coolant source 32 through valve 30 and conduit 33.
• Valve system 28 also includes second valve 36 associated with second conduit 37.
• second valve 36 allows for the introduction of an inert fluid from inert fluid source 35 through the valve and conduit 37.
• Conduit systems 33 and 37 connect coolant source 32 and inert fluid source 35, respectively, to conduit feed 22.
• An inert fluid is a liquid or gas that will not react with lithium or aluminum to produce a reactive (e.g., explosive) product and at the same time will not be combustible or support combustion.
• an inert fluid is an insert gas.
• a suitable inert gas is a gas that has a density that is less than a density of air and will not react with lithium or aluminum to produce a reactive product.
• Another required property of a suitable inert gas to be used in the subject embodiment is that the gas should have a higher thermal conductivity than ordinarily available in inert gases or in air and inert gas mixtures.
• An example of such suitable gas simultaneously meeting all of the aforesaid requirements is helium (He).
• He helium
• mixtures of helium and argon may be used. According to one embodiment, such a mixture includes at least about 20 percent helium. According to another embodiment, such a mixture includes at least about 60 percent helium.
• first valve 30 is open and second valve 36 is closed.
• second valve 36 is closed.
• inert fluid from inert fluid source 35 may be mixed with coolant from coolant source 32 during normal casting conditions.
• a position of valve 36 may be selected to achieve a desired flow rate, measured by a flow rate monitor associated with valve 36 or separately positioned adjacent valve 36 (illustrated downstream of valve 36 as second flow rate monitor 39) (e.g., a pressure monitor for an inert fluid source).
• a flow rate monitor associated with valve 36 or separately positioned adjacent valve 36 (illustrated downstream of valve 36 as second flow rate monitor 39) (e.g., a pressure monitor for an inert fluid source).
• each of first valve 30, second valve 36, first flow rate monitor 38 and second flow rate monitor 39 is electrically and/or logically connected to controller 15.
• Controller 15 includes non-transitory machine-readable instructions that, when executed, cause one or both of first valve 30 and second valve 36 to be actuated. For example, under normal casting operations such as shown in Figure 2, such machine-readable instructions cause first valve 30 to be open partially or fully and second valve 36 to be closed or partially open.
• first valve 30 is closed to stop the flow of coolant (e.g., water) from coolant source 32.
• first valve 30 is closed to reduce the flow of coolant to a rate that is greater than a flow rate of zero, but less than a predetermined flow rate selected to flow onto an emerging ingot providing a direct chill and solidification of the metal.
• the flow rate of coolant is reduced to a rate that is acceptably safe (e.g., a few liters per minute or less) given the additional measure(s) implemented to address "bleed-out” or "run-out".
• second valve 36 is opened to allow the admission of an inert fluid from inert fluid source 35, so that the only inert fluid is admitted into conduit feed 22.
• an inert fluid is an inert gas such as helium (He)
• inert gas such as helium (He)
• the area at the top of casting pit 10 and about mold 16 is immediately flooded with inert gas thereby displacing mixture 24 of water and air and inhibiting the formation of hydrogen gas or contact of molten Al/Li alloy with coolant (e.g., water) in this area, thereby
• coolant e.g., water
• Velocities of between 1.0 ft/sec and about 6.5 ft/sec, preferably between about 1.5 ft/sec and about 3 ft/sec and most preferably about 2.5 ft/sec are used.
• check valve 40 and check valve 42 associated with first valve 30 and second valve 36, respectively.
• Each check valve inhibits the flow of coolant and or gas backward into respective valves 30 and 36 upon the detection of a bleed- out and a change in material flow into mold.
• coolant supply line 32 is preferably also equipped with by-pass valve 43 to allow for immediate diversion of the flow of coolant to an external "dump" prior to its entry into first valve 30, so that upon closure of first valve 30, water hammering or damage to the feed system or leakage through valve 30 is minimized.
• the machine-readable instructions in controller 15 include instructions such that once a "bleed-out" is detected by, for example, a signal to controller 15 from an infrared thermometer, the instructions cause by-pass valve 43 to be actuated to open to divert coolant flow; first valve 30 to be actuated sequentially to closed; second valve 36 actuated to open to allow admission of an inert gas.
• one suitable inert gas is helium.
• Helium has a relatively high heat conductivity that allows for continuous extraction of heat from a casting mold and from solidification zone once coolant flow is halted. This continuous heat extraction serves to cool the ingot/billet being cast thereby reducing the possibility of any additional "bleed-outs” or "run-outs” occurring due to residual heat in the head of the ingot/billet. Simultaneously the mold is protected from excessive heating thereby reducing the potential for damage to the mold.
• thermal conductivities for helium, water and glycol are as follows: He; 0.1513 Wm _1 « K _1 ; H20; 0.609 W « m _1 « K _1 ; and Ethylene Glycol; 0.258 Wm _1 « K _1 .
• thermal conductivity of helium, and the gas mixtures described above are lower than those of water or glycol, when these gases impinge upon an ingot or billet at or near a solidification zone, no "steam curtain" is produced that might otherwise reduce the surface heat transfer coefficient and thereby the effective thermal conductivity of the coolant.
• a single inert gas or a gas mixture exhibits an effective thermal conductivity much closer to that of water or glycol than might first be anticipated considering only their directly relative thermal conductivities.
• Figures 2 and 3 depict a billet or round section of cast metal being formed, the apparatus and method of the present invention is equally applicable to the casting of rectangular ingot.

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