Casting systems and methods with auxiliary cooling onto a liquidus portion of a casting

Information

  • Patent Grant
  • 6427752
  • Patent Number
    6,427,752
  • Date Filed
    Thursday, February 3, 2000
    24 years ago
  • Date Issued
    Tuesday, August 6, 2002
    22 years ago
Abstract
A casting system with auxiliary cooling onto a liquidus portion of the casting can produce a metal casting that comprises a fine-grain, homogeneous microstructure. The microstructure is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from a liquidus state to a solid state. The casting system with auxiliary cooling onto a liquidus portion of the casting can comprises an electroslag refining system as a source of liquid metal; a nucleated casting system; and at least one cooling system that supplies coolant onto a liquidus portion of the casting. The liquidus portion of the casting is cooled in a manner sufficient to provide a casting microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification from a liquidus state to a solid state.
Description




BACKGROUND OF THE INVENTION




The invention relates to casting systems and methods with auxiliary cooling onto a liquidus portion of the casting. In particular, the invention related to clean metal nucleated casting systems and methods with auxiliary and direct cooling onto a liquidus portion of the casting.




Metals, such as iron-(Fe), nickel-(Ni), titanium-(Ti), and cobalt-(Co) based alloys, are often used in turbine component applications, in which fine-grained microstructures, homogeneity, and essentially defect-free compositions are desired. Problems in superalloy castings and ingots are undesirable as the costs associated with superalloy formation are high, and results of these problems, especially in ingots formed into turbine components are undesirable. Conventional systems for producing castings have attempted to reduce the amount of impurities, contaminants, and other constituents, which may produce undesirable consequences in a component made from the casting. However, the processing and refining of relatively large bodies of metal, such as superalloys, is often accompanied by problems in achieving homogeneous, defect-free structure. These problems are believed to be due, at least in part, to the bulky volume of the metal body and the amount and depth of the liquidus metal during the casting and solidification of the ingot.




One such problem that may often arise with respect to superalloys comprises controlling the grain size and other microstructure of the refined metals. Typically, refining processing involves multiple steps, such as sequential heating and melting, forming, cooling, and reheating of the large bodies of metal because the volume of the metal being refined is generally of at least about 5,000 pounds and can be greater than about 35,000 pounds. Further, problems of alloy or ingredient segregation also occur as processing is performed on large bodies of metal. Often, a lengthy and expensive sequence of processing steps is selected to overcome the above-mentioned difficulties, which arise through the use of bulk processing and refining operations of metals.




A known such sequence used in industry, involves vacuum induction melting; followed by electroslag refining (such as disclosed in U.S. Pat. Nos. 5,160,532; 5,310,165; 5,325,906; 5,332,197; 5,348,566; 5,366,206; 5,472,177; 5,480,097; 5,769,151; 5,809,057; and 5,810,066, all of which are assigned to the Assignee of the instant invention); followed, in turn, by vacuum arc refining (VAR) and followed, again in turn, by mechanical working through forging and drawing to achieve a fine microstructure. While the metal produced by such a sequence is highly useful and the metal product itself is quite valuable, the processing is quite expensive and time-consuming. Further, the yield from such a sequence can be low, which results in increased costs. Furthermore, the processing sequence does not ensure defect-free metals, and ultrasonic inspection is generally employed to identify and reject any components that include such defects, which results in further increase in costs.




A conventional electroslag refining process typically uses a refining vessel that contains a slag-refining layer floating on a layer of molten refined metal. An ingot of unrefined metal is generally used as a consumable electrode and is lowered into the vessel to make contact with the molten electroslag layer. An electric current is passed through the slag layer to the ingot and causes surface melting at the interface between the ingot and the slag layer. As the ingot is melted, oxide inclusions or impurities are exposed to the slag and removed at the contact point between the ingot and the slag. Droplets of refined metal are formed, and these droplets pass through the slag and are collected in a pool of molten refined metal beneath the slag. The refined metal may then be formed into a casting or ingot (collectively referred to hereinafter as “castings”).




The above-discussed electroslag refining and the resultant casting may be dependent on a relationship between the individual process parameters, such as, but not limited to, an intensity of the refining current, specific heat input, and melting rate. This relationship involves undesirable interdependence between the rate of electroslag refining of the metal, metal ingot and casting temperatures, and rate at which a refined molten metal casting is cooled from its liquidus state to its solid state, all of which may result in poor metallurgical structure in the resultant casting.




Further, electroslag refining may not provide for the controlling of an amount and depth of the liquidus portion in a casting. A reduced solidification rate may result in the casting having properties and characteristics that are not desirable. For example, and in no way limiting, the undesirable characteristics may include inhomogeneous microstructure, defects including (but not limited to) impurities, voids and inclusions, segregations, and a porous (non-dense) material resulting from entrapped air due to slow solidification.




Another problem that may be associated with conventional electroslag refining processing comprises the formation of a relatively deep metal pool in an electroslag crucible. A deep melt pool causes a varied degree of ingredient macrosegregation in the metal that leads to a less desirable microstructure, such as a microstructure that is not a fine-grained microstructure, or segregation of the elemental species so as to form an inhomogeneous structure. A subsequent processing operation has been proposed in combination with the electroslag refining process to overcome this deep melt pool problem. This subsequent processing may be vacuum arc remelting (VAR). Vacuum arc remelting is initiated when an ingot is processed by vacuum arc steps to produce a relatively shallow melt pool, whereby an improved microstructure, which may also possess a lower hydrogen content, is produced. Following the vacuum arc refining process, the resulting ingot is then mechanically worked to yield a metal stock having a desirable fine-grained microstructure. Such mechanical working may involve a combination of steps of forging, drawing, and heat treatment. This thermo-mechanical processing requires large, expensive equipment, as well as costly amounts of energy input.




An attempt to provide a desirable casting microstructure has been proposed in U.S. Pat. No. 5,381,847, in which a vertical casting process attempts to control grain microstructure by controlling dendritic growth. The process may be able to provide a useable microstructure for some applications, however, the vertical casting process does not control the source metal contents, including but not limited to impurities, oxides, and other undesirable constituents. The process, as set forth in the patent, does not control the depth or the liquidus portion or provide anything to enhance the solidification rate of the casting, which may adversely impact the casting's microstructure and characteristics.




Therefore, a need exists to provide a metal casting process that produces a casting with a relatively homogeneous, fine-grained microstructure, in which the process does not rely upon multiple processing steps that controls the depth of the liquidus portion of the casting. Further, a need exists to provide a metal casting system that produces a casting with a relatively homogeneous, oxide-free, fine-grained microstructure. Also, a need exists to provide a metal casting process and system that produces a casting that is essentially free of oxides and/or entrapped air due to slow solidification rates.




SUMMARY OF THE INVENTION




An aspect of the invention sets forth a casting system for producing a metal casting. The casting system comprises auxiliary cooling onto a liquidus portion of the casting and can produce a metal casting that comprises a fine-grain, homogeneous microstructure. The microstructure is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from a liquidus state to a solid state. The casting system with auxiliary cooling onto a liquidus portion of the casting can comprise an electroslag refining system; source of liquid metal, such as a nucleated casting system; and at least one cooling system that supplies coolant onto a liquidus portion of the casting. The casting is cooled in a manner sufficient to provide a microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification from a liquidus state to a solid state.




A further aspect of the invention provides a method for forming a metal casting using auxiliary cooling onto a liquidus portion of the casting. The method produces a metal casting that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from a liquidus state to a solid state. The method comprises forming a source of clean refined metal that has oxides and sulfides refined out by electroslag refining; forming the casting by a nucleated casting process; and cooling a liquidus portion of the casting. The cooling comprises directing coolant onto the liquidus portion of the casting, wherein the step of cooling is sufficient to provide a microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification from a liquidus state to a solid state.











These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.




BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic illustration of a clean metal nucleated casting system with auxiliary cooling onto a liquidus portion of the casting having cooling system, an electroslag refining system, and nucleated casting system;





FIG. 2

is a partial schematic, vertical sectional illustration of the clean metal nucleated casting system, as illustrated in

FIG. 1

, that illustrates details of the electroslag refining system;





FIG. 3

is a partial schematic, vertical section illustration in detail of the electroslag refining system of the clean metal nucleated casting system for producing a casting;





FIG. 4

is a partial schematic, part sectional illustration of the electroslag refining system of the clean metal nucleated casting system for producing a casting; and





FIG. 5

is a schematic illustration of a further casting system with a nucleated casting system and auxiliary cooling onto a liquidus portion of the casting.











DESCRIPTION OF THE INVENTION




Casting systems and methods with auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention, can be provided on casting systems, such as, but not limited to, vertical casting systems and casting systems that include vertical casting with electroslag refining and cold-induction guides. The systems and methods with auxiliary cooling onto a liquidus portion of the casting will be described hereinafter with respect to vertical casting with electroslag refining and cold-induction guides, as illustrated in

FIGS. 1-4

. However, this description is not intended to limit the invention in any way, and the scope of the invention comprises casting systems and methods with auxiliary cooling onto a liquidus portion of the casting with other metal formation processes and systems.




The casting systems and methods with auxiliary cooling onto a liquidus upper portion (liquidus portion) of the casting, and alternatively, auxiliary and direct cooling onto a liquidus portion of the casting (hereinafter referred to as “auxiliary cooling onto the liquidus portion”) can produce a casting with essentially oxide free and impurity free characteristics. The casting that is formed can also be dense and essentially non-porous. The term “casting” includes any casting, such as a preform, ingot, and the like. The term “essentially free” means that any constituents in the material do not adversely influence the material, for example its strength and related characteristics, and the term “essentially non-porous” means that the material is dense, amounts of entrapped air are minimal, and does not adversely influence the material.




The clean-liquid metal source for the casting systems and methods with auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention, can comprise any appropriate liquid metal source, such as, but not limited to, an electroslag refining apparatus, which can provide a clean liquid metal due to the electroslag refining steps. For example, and in no way limiting the invention, the electroslag refining apparatus can comprise an electroslag refining (ESR) system in cooperation with a cold-induction guide (CIG), as set forth in the above-mentioned patents to the Assignee of the instant invention.




Alternatively, the source for the casting systems and methods with auxiliary cooling onto a liquidus portion of the casting can comprise a vertical casting arrangement, as disclosed in U.S. Pat. No. 5,381,847. Therefore, a nucleated casting system may permit a plurality of molten metal droplets to be formed and pass through a cooling zone, which is formed with a length sufficient to allow up to about 30 volume percent of each of the droplets to solidify on average. The droplets are then received by a mold and solidification of the metal droplets is completed in the mold, such as, but not limited to, auxiliary cooling, as embodied by the invention. The droplets retain liquid characteristics and readily flow within the mold, when less than about 30 volume percent of the droplets is solid.




In order to enhance the solidification rate of the liquidus portion of the metal, the casting systems and methods, as embodied by the invention, provide coolant directly onto the liquidus (upper) portion of the casting to enhance cooling of the liquidus portion of the casting. The coolant will reduce the temperature of the liquidus portion of the casting, and provide expedited cooling and enhanced solidification of the liquidus portion of the casting. The expedited cooling and enhanced solidification of the liquidus portion will reduce the amount of entrapped gas that can be generated during operation or retained therein, thus forming a dense casting that contains few entrapped gas voids. Further, the expedited cooling and enhanced solidification rates of the liquidus portion will enhance the microstructural characteristics of the casting by reducing the grain size, providing an essentially segregation free microstructure, and a homogeneous microstructure. The auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention, can produce a casting possessing a homogeneous, fine-grained microstructure for many metals and alloys, including, but not limited to, nickel-(Ni) and cobalt-(Co) based superalloys, iron-(Fe), titanium-(Ti), alloys, which are often used in turbine component applications. The castings formed by the auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention, can be converted into a final casting, a billet, or directly forged with reduced processing and heat treatment steps, due to their homogeneous, fine-grained microstructure.




Accordingly, a casting method including auxiliary cooling onto a liquidus portion of the casting can be used to produce high quality forgings that can be used in many applications, such as but not limited to rotating equipment applications, such as, but not limited to, disks, rotors, blades, vanes, wheel, buckets, rings, shafts, wheels, and other such elements, and other turbine component applications. The description of the invention will refer to turbine components formed from castings, however, this is merely exemplary of the applications within the scope of the invention.




Referring to the accompanying drawings,

FIG. 1

illustrates a semischematic, part-sectional, elevational view of an exemplary casting system


3


with auxiliary cooling onto a liquidus portion of the casting by a cooling system


500


, as embodied by the invention.

FIGS. 2-4

illustrate details of features illustrated in FIG.


1


. The casting system


3


will be initially discussed with a description of the electroslag refining system


1


and the nucleated casting system


2


to facilitate the understanding of the invention.





FIG. 1

is a schematic illustration of a casting system


3


with an auxiliary cooling system


500


for cooling of a liquidus portion of the casting, as embodied by the invention, for producing a casting


145


. In

FIG. 1

, the metal for the clean metal nucleated casting system


3


and its associated clean metal nucleated casting processes is provided by an electroslag refining system


1


. The clean metal is fed to a nucleated casting system


2


. The electroslag refining system


1


and nucleated casting system


2


cooperate to form a clean metal nucleated casting system


3


, which in turn forms the auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention.




The electroslag refining system


1


introduces a consumable electrode


24


of metal to be refined directly into an electroslag refining system


1


, and refines the consumable electrode


24


to produce a clean, refined metal melt


46


(hereafter “clean metal”). The source of metal for the electroslag refining system


1


as a consumable electrode


24


is merely exemplary, and the scope of the invention comprises, but is not limited to, the source metal comprising an ingot, melt of metal, powder metal, and combinations thereof. The description of the invention will refer to a consumable electrode, however this is merely exemplary and is not intended to limit the invention in any manner. The clean metal


46


is received and retained within a cold hearth structure


40


that is mounted below the electroslag refining apparatus


1


. The clean metal


46


is dispensed from the cold hearth structure


40


through a cold finger orifice structure


80


that is mounted and disposed below the cold hearth structure


40


.




The electroslag refining system


1


can provide essentially steady state operation in supplying clean metal


46


if the rate of electroslag refining of metal and rate of delivery of refined metal to a cold hearth structure


40


approximates the rate at which molten metal


46


is drained from the cold hearth structure


40


through an orifice


81


of the cold finger orifice structure


80


. Thus, the clean metal nucleated casting process can operate continuously for an extended period of time and, accordingly, can process a large bulk of metal. Alternatively, the clean metal nucleated casting process can be operated intermittently by intermittent operation of one or more of the features of the clean metal nucleated casting system


3


.




Once the clean metal


46


exits the electroslag refining system


1


through the cold finger orifice structure


80


, it enters into the nucleated casting system


2


. Then, the clean metal


46


can be further processed to produce a relatively large ingot of refined metal. Alternatively, the clean metal


46


may be processed through to produce smaller castings, ingots, castings, or formed into continuous cast castings. The clean metal nucleated casting process effectively eliminates many of the processing operations, such as those described above that, until now, have been necessary in order to produce a metal casting having a desired set of material characteristics and properties.




In

FIG. 1

, a vertical motion control apparatus


10


is schematically illustrated. The vertical motion control apparatus


10


comprises a box


12


mounted to a vertical support


14


that includes a motive device (not illustrated), such as but not limited to a motor or other mechanism. The motive device is adapted to impart rotary motion to a screw member


16


. An ingot support structure


20


comprises a member, such as but not limited to a member


22


, that is threadedly engaged at one end to the screw member


16


. The member


22


supports the consumable electrode


24


at its other end by an appropriate connection, such as, but not limited to, a bolt


26


.




An electroslag refining structure


30


comprises a reservoir


32


that is cooled by an appropriate coolant, such as, but not limited to, water. The reservoir


32


comprises a molten slag


34


, in which an excess of the slag


34


is illustrated as the solid slag granules


36


. The slag composition used in the clean metal nucleated casting process will vary with the metal being processed. A slag skull


75


may be formed along inside surfaces of an inner wall


82


of reservoir


32


, due to the cooling influence of the coolant flowing against the outside of inner wall


82


, as described hereinafter.




A cold hearth structure


40


(

FIGS. 1-3

) is mounted below the electroslag refining structure


30


. The cold hearth structure


40


comprises a hearth


42


, which is cooled by an appropriate coolant, such as water. The hearth


42


contains a skull


44


of solidified refined metal and a body


46


of refined liquid metal. The reservoir


32


may be formed integrally with the hearth


42


. Alternatively, the reservoir


32


and hearth


42


may be formed as separate units, which are connected to form the electroslag refining system


1


.




A bottom orifice


81


of the electroslag refining system


1


is provided in the cold finger orifice structure


80


, which is described with reference to

FIGS. 3 and 4

. A clean metal


46


, which is refined by the electroslag refining system


1


so as to be essentially free of oxides, sulfides, and other impurities, can traverse the electroslag refining system


1


and flow out of the orifice


81


of the cold finger orifice structure


80


.




A power supply structure


70


can supply electric refining current to the electroslag refining system


1


. The power supply structure


70


can comprise an electric power supply and control mechanism


74


. An electrical conductor


76


that is able to carry current to the member


22


and, in turn, carry current to the consumable electrode


24


connects the power supply structure


70


to the member


22


. A conductor


78


is connected to the reservoir


32


to complete a circuit for the power supply structure


70


of the electroslag refining system


1


.





FIG. 2

is a detailed part-sectional illustration of the electroslag refining structure


30


and the cold hearth structure


40


in which the electroslag refining structure


30


defines an upper portion of the reservoir


32


and the cold hearth structure


40


defines a lower portion


42


of the reservoir


32


. The reservoir


32


generally comprises a double-walled reservoir, which includes an inner wall


82


and outer wall


84


. A coolant


86


, such as but not limited to water, is provided between the inner wall


82


and outer wall


84


. The coolant


86


can flow to and through a flow channel, which is defined between the inner wall


82


and outer wall


84


from a supply


98


(

FIG. 3

) and through conventional inlets and outlets (not illustrated in the figures). The cooling water


86


that cools the wall


82


of the cold hearth structure


40


provides cooling to the electroslag refining structure


30


and the cold hearth structure


40


to cause the skull


44


to form on the inner surface of the cold hearth structure


40


. The coolant


86


is not essential for operation of the electroslag refining system


1


, clean metal nucleated casting system


3


, or electroslag refining structure


30


. Cooling may insure that the liquid metal


46


does not contact and attack the inner wall


82


, which may cause some dissolution from the wall


82


and contaminate the liquid metal


46


.




In

FIG. 2

, the cold hearth structure


40


also comprises an outer wall


88


, which may include flanged tubular sections,


90


and


92


. Two flanged tubular sections


90


and


92


are illustrated in the bottom portion of FIG.


2


. The outer wall


88


cooperates with the nucleated casting system


2


to form a controlled atmosphere environment


140


, which is described hereinafter.




The cold hearth structure


40


comprises a cold finger orifice structure


80


that is shown detail

FIGS. 3 and 4

. The cold finger orifice structure


80


is illustrated in

FIG. 3

in relation to the cold hearth structure


40


and a stream


56


of liquid melt


46


that exits the cold hearth structure


40


through the cold finger orifice structure


80


. The cold finger orifice structure


80


is illustrated (

FIGS. 2 and 3

) in structural cooperation with the solid metal skull


44


and liquid metal


46


.

FIG. 4

illustrates the cold finger orifice structure


80


without the liquid metal or solid metal skull, so details of the cold finger orifice structure


80


are illustrated.




The cold finger orifice structure


80


comprises the orifice


81


from which processed molten metal


46


is able to flow in the form of a stream


56


. The cold finger orifice structure


80


is connected to the cold hearth structure


40


and the cold hearth structure


30


. Therefore, the cold hearth structure


40


allows processed and generally impurity-free alloy to form the skulls


44


and


83


by contacting walls of the cold hearth structure


40


. The skulls


44


and


83


thus act as a container for the molten metal


46


. Additionally, the skull


83


(FIG.


3


), which is formed at the cold finger orifice structure


80


, is controllable in terms of its thickness, and is typically formed with a smaller thickness than the skull


44


. The thicker skull


44


contacts the cold hearth structure


40


and the thinner skull


83


contacts the cold finger orifice structure


80


, and the skulls


44


and


83


are in contact with each other to form an essentially continuous skull.




A controlled amount of heat may be provided to the skull


83


and thermally transmitted to the liquid metal body


46


. The heat is provided from induction heating coils


85


that are disposed around the cold hearth structure. An induction-heating coil


85


can comprise a cooled induction-heating coil, by flow of an appropriate coolant, such as water, into it from a supply


87


. Induction heating power is supplied from a power source


89


, which is schematically illustrated in FIG.


3


. The construction of the cold finger orifice structure


80


permits heating by induction energy to penetrate the cold finger orifice structure


80


and heat the liquid metal


46


and skull


83


, and maintain the orifice


81


open so that the stream


56


may flow out of the orifice


81


. The orifice may be closed by solidification of the stream


56


of liquid metal


46


if heating power is not applied to the cold finger orifice structure


80


. The heating is dependent on each of the fingers of the cold finger orifice structure


80


being insulated from the adjoining fingers, for example being insulated by an air or gas gap or by a suitable insulating material.




The cold finger orifice structure


80


is illustrated in

FIG. 4

, with both skulls


44


and


83


and the molten metal


46


are omitted for clarity. An individual cold finger


97


is separated from each adjoining finger, such as finger


92


, by a gap


94


. The gap


94


may be provided and filled with an insulating material, such as, but not limited to, a ceramic material or insulating gas. Thus, the molten metal


46


(not illustrated) that is disposed within the cold finger orifice structure


80


does not leak out through the gaps, because the skull


83


creates a bridge over the cold fingers and prevents passage of liquid metal


46


therethrough. Each gap extends to the bottom of the cold finger orifice structure


80


, as illustrated in

FIG. 4

, which illustrates a gap


99


aligned with a viewer's line-of-sight. The gaps can be provided with a width in a range from about of 20 mils to about 50 mils, which is sufficient to provide an insulated separation of respective adjacent fingers.




The individual fingers may be provided with a coolant, such as water, by passing coolant into a conduit


96


from a suitable coolant source (not shown). The coolant is then passed around and through a manifold


98


to the individual cooling tubes, such as cooling tube


100


. Coolant that exits the cooling tube


100


flows between an outside surface of the cooling tube


100


and an inside surface of a finger. The coolant is then collected in a manifold


102


, and passed out of the cold finger orifice structure


80


through a water outlet tube


104


. This individual cold finger water supply tube arrangement allows for cooling of the cold finger orifice structure


80


as a whole.




The amount of heating or cooling that is provided through the cold finger orifice structure


80


to the skulls


44


and


83


, as well as to the liquid metal


46


, can be controlled to control the passage of liquid metal


46


through the orifice


81


as a stream


56


. The controlled heating or cooling is done by controlling the amount of current and coolant that pass in the induction coils


85


to and through the cold finger orifice structure


80


. The controlled heating or cooling can increase or decrease the thickness of the skulls


44


and


83


, and to open or close the orifice


81


, or to reduce or increase the passage of the stream


56


through the orifice


81


. More or less liquid metal


46


can pass through the cold finger orifice structure


80


into the orifice


81


to define the stream


56


by increasing or decreasing the thickness of the skulls


44


and


83


. The flow of the stream


56


can be maintained at a desirable balance, by controlling coolant water and heating current and power to and through the induction heating coil


85


to maintain the orifice


81


at a set passage size along with controlling the thickness of the skulls


44


and


83


.




The operation of the electroslag refining system


1


of the clean metal nucleated casting system


3


will now be generally described with reference to the figures. The electroslag refining system


1


of the clean metal nucleated casting system


3


can refine ingots that can include defects and impurities. A consumable electrode


24


is melted by the electroslag refining system


1


. The consumable electrode


24


is mounted in the electroslag refining system


1


in contact with molten slag in the electroslag refining system. Electrical power is provided to the electroslag refining system and ingot. The power causes melting of the ingot at a surface where it contacts the molten slag and the formation of molten drops of metal. The drops are collected after they pass through the molten slag as a body of refined liquid metal in the cold hearth structure


40


below the electroslag refining structure


30


. Oxides, sulfides, contaminants, and other impurities that originate in the consumable electrode


24


are removed through dissolution in to the slag as the droplets form on the surface of the ingot and pass through the molten slag. The molten drops are drained from the electroslag refining system


1


at the orifice


81


in the cold finger orifice structure


80


as a stream


56


. The stream


56


that exits the electroslag refining system


1


of the clean metal nucleated casting system


3


that forms castings comprises a refined melt that is essentially free of oxides, sulfides, contaminants, and other impurities.




The rate at which the metal stream


56


exits the cold finger orifice structure


80


can further be controlled by controlling a hydrostatic head of liquid metal


46


above the orifice


81


. The liquid metal


46


and slag


44


and


83


that extend above the orifice


81


of the cold finger orifice structure


80


define the hydrostatic head. If a clean metal nucleated casting system


3


with an electroslag refining system


1


is operated with a given constant hydrostatic head and a constant sized orifice


81


, an essentially constant flow rate of liquid metal can be established.




Typically, a steady state of power is desired so the melt rate is generally equal to the removal rate from the clean metal nucleated casting system


3


, as a stream


56


. However, the current applied to the clean metal nucleated casting system


3


can be adjusted to provide more or less liquid metal


46


and slag


44


and


83


a above the orifice


81


. The amount of liquid metal


46


and slag


44


and


83


above the orifice


81


is determined by the power that melts the ingot, and the cooling of the electroslag refining system


1


, which create the skulls. By adjusting the applied current, flow through the orifice


81


can be controlled.




Also, the contact of the consumable electrode


24


with an upper surface of the molten slag


34


can be maintained in order to establish a steady state of operation


1


. A rate of consumable electrode


24


descent into the melt


46


can be adjusted to ensure that contact of the consumable electrode


24


with the upper surface of the molten slag


34


is maintained for the steady state operation. Thus, a steady-state discharge from the stream


56


can be maintained in the clean metal nucleated casting system


3


. The stream


56


of metal that is formed in the electroslag refining system


1


of the clean metal nucleated casting system


3


exits electroslag refining system


1


and is fed to a nucleated casting system


2


. The nucleated casting system


2


is schematically illustrated in

FIG. 1

in cooperation with the electroslag refining system


1


.




The nucleated casting system


2


comprises a disruption site


134


that is positioned to receive the stream


56


from the electroslag refining system


1


of the clean metal nucleated casting system


3


. The disruption site


134


converts the stream


56


into a plurality of molten metal droplets


138


. The stream


56


can be fed to disruption site


134


in a controlled atmosphere environment


140


that is sufficient to prevent substantial and undesired oxidation of the droplets


138


. The controlled atmosphere environment


140


may include any gas or combination of gases, which do not react with the metal of the stream


56


. For example, if the stream


56


comprises aluminum or magnesium, the controlled atmosphere environment


140


presents an environment that prevents the droplets


138


from becoming a fire hazard. Typically, any noble gas or nitrogen is suitable for use in the controlled atmosphere environment


140


because these gases are generally non-reactive with most metals and alloys within the scope of the invention. For example, nitrogen, which is a low-cost gas, can be in the controlled atmosphere environment


140


, except for metals and alloys that are prone to excessive nitriding. Also, if the metal comprises copper, the controlled atmosphere environment


140


may comprise nitrogen, argon, and mixtures thereof. If the metal comprises nickel or steel, the controlled atmosphere environment


140


can comprises nitrogen or argon, or mixtures thereof.




The disruption site


134


can comprise any suitable device for converting the stream


56


into droplets


138


. For example, the disruption site


134


can comprise a gas atomizer, which circumscribes the stream


56


with one or more jets


142


. The flow of gas from the jets


142


that impinge on the stream can be controlled, so the size and velocity of the droplets


138


can be controlled. Another atomizing device, within the scope of the invention, includes a high pressure atomizing gas in the form of a stream of the gas, which is used to form the controlled atmosphere environment


140


. The stream of controlled atmosphere environment


140


gas can impinge the metal stream


56


to convert the metal stream


56


into droplets


138


. Other exemplary types of stream disruption include magneto-hydrodynamic atomization, in which the stream


56


flows through a narrow gap between two electrodes that are connected to a DC power supply with a magnet perpendicular to the electric field, and mechanical-type stream disruption devices.




The droplets


138


are broadcast downward (

FIG. 1

) from the disruption site


134


to form a generally diverging cone shape. The droplets


138


traverse a cooling zone


144


, which is defined by the distance between the disruption site


134


and the upper surface


150


of the metal casting that is supported by the mold


146


. The cooling zone


144


length is sufficient to solidify a volume fraction portion of a droplet by the time the droplet traverses the cooling zone


144


and impacts the upper surface


150


of the metal casting. The portion of the droplet


138


that solidifies (hereinafter referred to as the “solid volume fraction portion”) is sufficient to inhibit coarse dendritic growth in the mold


146


up to a viscosity inflection point at which liquid flow characteristics in the mold are essentially lost.




The partially molten/partially solidified metal droplets (referred to hereinafter as “semisolid droplets”) collect in mold


146


. The mold may comprise a unitary and one-piece mold, as illustrated in the broken lines of FIG.


1


. Alternatively, the mold may comprises a withdrawal mold, which includes a retractable base


246


that can be withdrawn from sidewalls of the mold


146


. The following description of the invention will discuss a withdrawal mold as an exemplary, non-limiting mold, and is not intended to limit the invention in any manner. The retractable base


246


can be connected to a shaft


241


to move base away from the sidewalls in the direction of arrow


242


. Further, the shaft


241


may rotate the retractable base


246


in the direction of arrow


243


to provide most portions of the mold to a cooling system, which is described hereinafter. The semisolid droplets behave like a liquid if the solid volume fraction portion is less than a viscosity inflection point, and the semisolid droplets exhibit sufficient fluidity to conform to the shape of the mold. Generally, an upper solid volume fraction portion limit that defines a viscosity inflection point is less than about 40% by volume. An exemplary solid volume fraction portion is in a range from about 5% to about 40%, and a solid volume fraction portion in a range from about 15% to about 30% by volume does not adversely influence the viscosity inflection point.




The spray of droplets


138


creates a liquidus, upper portion


148


disposed proximate the surface of the casting


145


in the mold


146


. The depth of the liquidus, upper portion


148


is dependent on cooling of the liquidus portion, the solidification rate thereof, and various clean metal nucleated casting system


3


factors, such as, but not limited to, the atomization gas velocity, droplet velocity, the cooling zone


144


length, the stream temperature, and droplet size. The liquidus, upper portion


148


can be created with a depth in the mold


146


in a range from about 0.005 inches to about 1.0 inches. An exemplary liquidus, upper portion


148


within the scope of invention comprises a depth in a range from about 0.25 to about 0.50 inches in the mold. In general, the liquidus, upper portion


148


in the mold


146


should not be greater that a region of the casting, where the metal exhibits predominantly liquid characteristics. Typically, expedited solidification of the liquidus portion minimizes gas entrapment and resultant pores in the casting.




A cooling system


500


(FIG.


1


), as embodied by the invention, can extract heat from the liquidus portion


148


of the casting


145


to expedite its cooling and enhance its solidification. The cooling system


500


comprises a coolant supply


501


. The coolant can comprise any appropriate coolant, such as, but not limited to, an inert cooling gas that will not react with the material of the casting. Exemplary cooling gases within the scope of the invention comprise, but are not limited to, argon, nitrogen, and helium. In the cooling system


500


, the coolant is directed onto the liquidus portion of the casting


145


, while the casting


145


can be withdrawn from the mold


146


, if the mold comprises a withdrawal mold. The coolant exits the cooling system


500


in the form of a spray


503


after passing through a coolant conduit


502


from the coolant supply


501


. The coolant conduit


502


can comprise any appropriate conduit that allows passage of the coolant from the coolant source


501


to a position proximate the liquidus portion


148


of a casting


145


. The shape and configuration of the coolant conduit


502


may take any shape and configuration as long as the coolant can be directed to the liquidus portion


148


of the casting


145


, such as inside the zone


144


. While the illustrations set forth the coolant conduit


502


being curved and angled, this shape and configuration is merely exemplary, and is not intended to limit the invention in any manner. Other shapes and configurations of the coolant conduit


502


, for example, but not limited to, straight and coiled, are within the scope of the invention.




The cooling system


500


, as embodied by the invention, can comprise a configuration as illustrated. Further, the cooling system


500


can comprise a plurality of one or all of the elements of the cooling system


500


. For example, and in no way limiting of the invention, the cooling system


500


can comprise one source that is in fluidic communication with a plurality of coolant conduits


502


to form a plurality of sprays


503


. Further, the cooling system


500


can comprise a plurality of supplies


501


, each communicating with a coolant conduit


502


and coolant spray


503


. Also, a coolant conduit


502


may form a plurality of sprays


503


from a single coolant conduit


502


. The above descriptions are merely exemplary and are not intended to limit the invention in any manner.




The mold


146


can be formed of any suitable material for casting applications, such as but not limited to, graphite, cast iron, and copper. Graphite is a suitable mold


146


material since it is relatively easy to machine and exhibits satisfactory thermal conductivity for heat removal via the cooling systems, as embodied by the invention. As the mold


146


is filled with semisolid droplets


138


, its upper surface


150


moves closer to the disruption site


134


, and the cooling zone


144


is reduced. At least one of the disruption site


134


or the mold


146


may be mounted on a moveable support and separated at a fixed rate to maintain a constant cooling zone


144


dimension. Thus, a generally consistent solid volume fraction portion in the droplets


138


is formed. Baffles


152


may be provided in the nucleated casting system


2


to extend the controlled atmosphere environment


140


from the electroslag refining system


1


to the mold


146


. The cooling system


500


can extend through the baffles


152


, as illustrated in the figures. The baffles


152


can prevent oxidation of the partially molten metal droplets


138


and conserve the controlled atmosphere environment gas


140


. Heat that is extracted from the casting


145


completes the solidification process of the liquidus upper portion


148


of the casting


145


to form solidified castings for further use. Sufficient nuclei are formed in casting


145


produced so that upon solidification, a fine equiaxed microstructure


149


can be formed in the casting


145


.




The casting system


3


inhibits undesirable dendritic growth, reduces solidification shrinkage porosity of the formed casting and casting, and reduces hot tearing both during casting and during subsequent hot working of the casting and casting. Further, the clean metal nucleated casting system


3


produces a uniform, equiaxed structure in the casting which is a result of the minimal distortion of the mold during casting, the controlled transfer of heat during solidification of the casting in the mold, and controlled nucleation. The clean metal nucleated casting system


3


enhances ductility and fracture toughness of the casting compared to conventionally castings.




The above-described cooling system


500


has been discussed in regard to a casting system


3


, which comprises an electroslag refining system


1


as a source of liquid metal, a nucleated casting system


2


, and a cooling system


500


. However, the scope of the invention further comprises use of cooling systems, as embodied by the invention, with a casting system that comprises a nucleated casting system with any appropriate source of liquid metal. For example, the supply of liquid metal may comprise a nucleated casting system alone, as illustrated in FIG.


5


. The casting system


510


in

FIG. 5

comprises a nucleated casting system


2


, which is similar to the nucleated casting system in

FIGS. 1-4

. The nucleated casting system


2


of

FIG. 5

is illustrated with a withdrawal mold


146


, however, any appropriate mold is within the scope of the invention.




The nucleated casting system


2


comprises a disruption site


134


that is positioned to receive a liquid metal stream


512


from any appropriate source


511


. For example, and in no way limiting of the invention, the source


511


of the liquid metal stream may comprise a vacuum arc remelting (VAR) system, a vacuum induction melting (VIM) system, an electroslag refining (ESR) system (as discussed above) with or without a cold induction guide (CIG) system, and other systems that pertain to the purification of crude or impure metals. The above systems are merely exemplary, and are not intended to limit the invention in any manner.




The disruption site


134


converts the liquid metal stream


512


from the source


511


into a plurality of molten metal droplets


138


. The stream


512


can be fed to disruption site


134


in a controlled atmosphere environment


140


that is sufficient to prevent substantial and undesired oxidation of the droplets


138


. The controlled atmosphere environment


140


may include any gas or combination of gases, which do not react with the metal of the stream


512


. For example, if the stream


512


comprises aluminum or magnesium, the controlled atmosphere environment


140


presents an environment that prevents the droplets


138


from becoming a fire hazard.




The disruption site


134


can comprise any suitable device for converting the stream


512


into droplets


138


. For example, the disruption site


134


can comprise a gas atomizer, which circumscribes the stream


512


with one or more jets


142


. The flow of gas from the jets


142


that impinge on the stream can be controlled, so the size and velocity of the droplets


138


can be controlled. Another atomizing device, within the scope of the invention, includes a high pressure atomizing gas in the form of a stream of the gas, which is used to form the controlled atmosphere environment


140


. The stream of controlled atmosphere environment


140


gas can impinge the metal stream


512


to convert the metal stream


512


into droplets


138


. Other exemplary types of stream disruption are described above.




The droplets


138


are broadcast downward (

FIG. 1

) from the disruption site


134


to form a generally diverging cone shape. The droplets


138


traverse a cooling zone


144


, which is defined by the distance between the disruption site


134


and the upper surface


150


of the metal casting that is supported by the mold


146


. The cooling zone


144


length is sufficient to solidify a volume fraction portion of a droplet by the time the droplet traverses the cooling zone


144


and impacts the upper surface


150


of the metal casting. The partially molten/partially solidified metal droplets (referred to hereinafter as “semisolid droplets”) collect in mold


146


. The mold may comprise a retractable base


246


, which can be withdrawn from sidewalls of the mold


146


so as to define a withdraw mold. The retractable base can be connected to a shaft


241


to move base away from the sidewalls in the direction of arrow


242


. Further, the shaft


241


may rotate the retractable base


246


in the direction of arrow


243


to provide most portions of the mold to a cooling system, which is described hereinafter. Details of the remainder of the nucleated casting system


2


are as set forth in the above description.




The casting system


500


provides auxiliary cooling to the directly cooling to the liquidus portion


148


of the casting


145


. The auxiliary cooling is in addition to the cooling that occurs during the solidification of the casting


145


itself, for example cooling that occurs by thermal conduction from walls of the mold


146


. Thus, a casting system that is provided with a cooling system


500


, as embodied by the invention, can form a casting that is essentially oxide free and impurity free, and can also be densely formed and essentially non-porous because few air voids are allowed to cool in the casting due to the enhanced solidification rate resulting from the auxiliary cooling onto a liquidus portion of the casting, as embodied by the invention. Further, the expedited cooling and enhanced solidification rates of the liquidus portion of the casting will enhance the microstructural characteristics of the casting by reducing the grain size, providing an essentially segregation free microstructure, and a homogeneous microstructure.




While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within the scope of the invention.



Claims
  • 1. A casting system with auxiliary cooling onto a semi-solid portion of the casting for producing a metal casting, the metal casting comprising a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state, the casting system comprising:an electroslag refining system; a nucleated casting system; and at least one auxiliary cooling system, comprising a coolant source and a coolant conduit, wherein the conduit is shaped to direct the coolant directly onto the semi-solid portion of the metal casting, so that the semi-solid portion of the casting is cooled in a manner sufficient to provide a casting microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification from a semi-solid state to a solid state.
  • 2. A casting system according to claim 1, wherein the electroslag refining system comprises:an electroslag refining structure adapted to receive and to hold a refining molten slag, a source of metal to be refined in the electroslag refining structure; a body of molten slag in the electroslag refining structure, the source of metal being disposed in contact with the molten slag, an electric supply adapted to supply electric current to the source of metal as an electrode and through the molten slag to a body of refined metal beneath the slag to keep the refining slag molten and to melt the end of the source of metal in contact with the slag, an advancing device for advancing the s source of metal into contact with the molten slag at a rate corresponding to the rate at which the contacted surface of the electrode is melted as the refining thereof proceeds, a cold hearth structure beneath tie electroslag refining structure, the cold hearth structure being adapted to receive and to hold electroslag refined molten metal in contact with a solid skull of the refined metal formed on the walls of the cold hearth vessel, a body of refined molten metal in the cold hearth structure beneath the molten slag, a cold finger orifice structure below the cold hearth adapted to receive and to dispense a stream of refined molten metal that is processed by the electroslag refining system and through the cold hearth structure, the cold finger orifice structure having a orifice, a skull of solidified refined metal i n contact with the cold hearth structure and the cold finger orifice structure including the orifice.
  • 3. A casting system according to claim 1, wherein the nucleated casting system comprises:a disruption site through which a stream of liquid metal is formed into molten metal droplets; and a cooling zone that that receives the molten metal droplets, the molten metal droplets being solidified in the cooling zone into semisolid droplets such that, on average, about 5% to about 40% by volume of each semisolid droplet is solid and the remainder of the semisolid droplet is molten; and a mold that collects the droplets in a semi-solid and solidifies the droplets thereby forsing a casting having a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free and segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state.
  • 4. A casting system according to claim 2, wherein the nucleated casting system comprises:a disruption site through which a stream of liquid metal is formed into molten metal droplets; and a cooling zone that that receives the molten metal droplets, the molten metal droplets being solidified in the cooling zone into semisolid droplets such that, on average, about 5% to about 40% by volume of each semisolid droplet is solid and the remainder of the semisolid droplet is molten; and a mold that collects the droplets in a semi-solid portion and solidifies the droplets thereby forming a casting having a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free and segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from semi-solid state to a solid state, and the cooling system comprises a coolant that is applied onto a semi-solid portion of the casting.
  • 5. A casting system according to claim 1, wherein the semi-solid portion of the casting is generated by metal droplets in an upper area of the casting and, within the semi-solid portion, on average, less than about 50% by volume of an average droplet is solid.
  • 6. A casting system according to claim 1, wherein the coolant conduit applies coolant as a spray.
  • 7. A casting system according to claim 1, wherein the casting comprises at least one of nickel-, cobalt-, titanium-, or iron-based metals.
  • 8. A casting system according to claim 1, wherein the casting comprises a turbine component.
  • 9. A casting system with auxiliary cooling onto a semi-solid portion of the casting for producing a metal casting, the metal casting comprising a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state, the casting system comprising:a source of liquid metal; a metal disruption site through which a stream of the liquid metal is formed into molten metal droplets; and a cooling zone that receives the molten metal droplets, the molten metal droplets being solidified in the cooling zone into semisolid droplets such that, on average, about 5% to about 40% by volume of each semisolid droplet is solid and the remainder of the semisolid droplet is molten; and a mold that collects the droplets in a semi-solid portion and solidifies the droplets, thereby forming a casting having a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free and segregation defect-free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state, and an auxiliary cooling system that supplies coolant onto a semi-solid portion of the casting in a manner sufficient to cool the semi-solid portion of the metal casting, wherein the semi-solid portion of the metal casting is cooled in a manner sufficient to provide a casting microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification from a semi-solid state to a solid state.
  • 10. A system according to claim 9, wherein the system according to claim 1, wherein the auxiliary cooling system comprises:a coolant supply and a coolant conduit to apply coolant directly onto a semi-solid portion of the casting.
  • 11. A system according to claim 9, wherein the coolant conduit applies the coolant to at least one of a casting mold and casting in the form of a spray.
  • 12. A system according to claim 9, wherein the casting comprises at least one of nickel-, cobalt-, titanium-, or iron-based metals.
  • 13. A system according to claim 9, wherein the casting comprises a turbine component.
  • 14. A casting method with auxiliary cooling onto a semi-solid portion of the casting for forming a metal casting, the metal casting comprising a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state, the method with auxiliary cooling onto a semi-solid portion of the casting comprising:forming a source of clean refined metal that has oxides and sulfides refined out by electroslag refining; forming a casting by a nucleated casting process; and cooling a semi-solid portion of the casting, the step of cooling comprises directing coolant onto the semi-solid portion of the casting, wherein the step of cooling is sufficient to provide a casting microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect free, and essentially free of voids caused by air entrapped during solidification from a semi-solid state to a solid state.
  • 15. A method according to claim 14, wherein the step of forming a source comprises electroslag refining that comprises:providing a source of metal to be refined; providing an electroslag refining structure adapted for the electroslag refining of the source of metal and providing molten slag in the vessel; providing a cold hearth structure for holding a refined molten metal beneath the molten slag and providing refined molten metal in the cold hearth structure; mounting the source of metal for insertion into the electroslag refining structure and into contact with the molten slag in the electroslag refining structure; providing an electrical power supply adapted to supply electric power; supplying electric power to electroslag refine the source of metal through a circuit, the circuit comprising the power supply, the source of metal, the molten slag and the electroslag refining structure; resistance melting of the source of metal where the source of metal contacts the molten slag and forming molten droplets of metal; allowing the molten droplets to fall through the molten slag; collecting the molten droplets after they pass through the molten slag as a body of refined liquid metal in the cold hearth structure directly below the electroslag refining structure; providing a cold finger orifice structure having a orifice at the lower portion of the cold hearth structure; and draining the electroslag refined metal that collects in the cold hearth orifice structure through the orifice of the cold finger orifice structure.
  • 16. A method according to claim 15, wherein the source of metal comprises an alloy selected from at least one of nickel-, cobalt-, titanium-, or iron-based metals, and the casting formed by the clean metal nucleated casting process comprises at least one of nickel-, cobalt-, titanium-, or iron-based metals.
  • 17. A method according to claim 15, wherein a rate of advance of the source of metal into the refining structure corresponds to the rate of resistance melting.
  • 18. A method according to claim 15, wherein the step of draining comprises forming a stream of molten metal.
  • 19. A method according to claim 15, wherein the electroslag refining structure and the cold hearth structure comprise upper and lower portions of the same structure.
  • 20. A method according to claim 15, wherein the step of supplying electric power comprises forming a circuit in the refined liquid metal.
  • 21. A method according to claim 15, wherein the step of draining comprises establishing a drainage rate that is approximately equivalent to a rate of resistance melting.
  • 22. A method according to claim 15, wherein the step of forming a casting comprises:disrupting a stream of clean metal from the source of clean metal into molten metal droplets; partially solidifying the molten metal droplets such that, on average, from about 5% to about 40% by volume of each droplet is solid and the remainder of each droplet is molten; and collecting and solidifying the partially solidified droplets in a mold forming the casting, in which a turbulent zone is generated by the droplets at an upper surface and, the step of collecting and solidifying the partially solidified droplets collects the droplets in the turbulent zone, and, on average solidifies less than about 50% by volume of the droplet.
  • 23. A method according to claim 22, wherein the step of partially solidifying the molten metal droplets solidifies, on the average, from about 15% to about 30% by volume of the droplet.
  • 24. A method according to claim 22, wherein the step of collecting and solidifying the partially solidified droplets comprises collecting and solidifying about 5% to about 40% by volume of the droplet.
  • 25. A method according to claim 22, wherein the step of disrupting comprises impinging at least one atomizing gas jet on the stream.
  • 26. A method according to claim 15, wherein the step of electroslag refining comprises:providing a source of metal to be refined, providing an electroslag refining structure adapted for the electroslag refining of the source of metal and providing molten slag in the vessel, providing a cold hearth structure for holding a refined molten metal beneath the molten slag and providing refined molten metal in the cold hearth structure, mounting the source of metal for insertion into the electroslag refining structure and into contact with the molten slag in the electroslag refining structure, providing an electrical power supply adapted to supply electric power, supplying electric power to electroslag refine the source of metal through a circuit, the circuit comprising the power supply, the source of metal, the molten slag and the electroslag refining structure; resistance melting of the source of metal where the source of metal contacts the molten slag and forming molten droplets of metal, allowing the molten droplets to fall through the molten slag, collecting the molten droplets after they pass through the molten slag as a body of refined liquid metal in the cold hearth structure directly below the electroslag refining structure, providing a cold finger orifice structure having a orifice at the lower portion of the cold hearth structure, and draining the electroslag refined metal that collects in the cold hearth orifice structure through the orifice of the cold finger orifice structure, and the step of forming a casting comprises: disrupting a stream of clean metal from the source of clean metal into molten metal droplets; partially solidifying the molten metal droplets such that, on average, from about 5% to about 40% by volume of each droplet is solid and the remainder of each droplet is molten; and collecting and solidifying the partially solidified droplets in a mold forming the casting, in which a turbulent zone is generated by the droplets at an upper surface and, the step of collecting and solidifying the partially solidified droplets collects the droplets in the turbulent zone, and, on average solidifies less than about 50% by volume of the droplet.
  • 27. A method according to claim 15, wherein the step of cooling comprises providing an auxiliary cooling system that comprises a coolant supply and a coolant conduit, the step of cooling further comprises applying coolant onto a semi-solid portion of the casting.
  • 28. A method according to claim 15, wherein the step of cooling comprises applying coolant in the form of a spray.
  • 29. A casting method with auxiliary cooling onto a semi-solid portion of the casting for forming a metal casting, the metal casting comprising a fine-grain, homogeneous microstructure that is essentially oxide and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification of the metal from a semi-solid state to a solid state, the method comprising:forming a source of clean refined metal that has oxides and sulfides refined out by electroslag refining; forming a casting by nucleated casting; and cooling a semi-solid portion of the metal casting by applying a coolant directly onto a semi-solid portion of the casting, wherein the step of cooling is sufficient to cool the semi-solid portion of the metal casting to provide a microstructure that comprises a fine-grain, homogeneous microstructure that is essentially oxide- and sulfide-free, segregation defect-free, and essentially free of voids caused by air entrapped during solidification from a semi-solid state to a solid state.
  • 30. A casting system according to claim 1, wherein the conduit is shaped to direct the coolant directly onto the upper surface of the semi-solid portion of the metal casting.
Parent Case Info

This application claims priority of a Provisional Application entitled “Clean Metal Nucleated Casting Systems and Methods” by Carter et al., U.S. Ser. No. 60/121,187, which was filed on Feb. 23, 1999.

US Referenced Citations (13)
Number Name Date Kind
3833047 Tovini Sep 1974 A
4612649 Griebel, III et al. Sep 1986 A
5160532 Benz et al. Nov 1992 A
5310165 Benz et al. May 1994 A
5325906 Benz et al. Jul 1994 A
5348566 Sawyer et al. Sep 1994 A
5381847 Ashok et al. Jan 1995 A
5472177 Benz et al. Dec 1995 A
5480097 Carter, Jr. et al. Jan 1996 A
5649993 Carter, Jr. et al. Jul 1997 A
5769151 Carter, Jr. et al. Jun 1998 A
581066 Knudsen et al. Sep 1998 A
5809057 Benz et al. Sep 1998 A
Foreign Referenced Citations (2)
Number Date Country
01313181 Dec 1989 EP
2 174411 Nov 1986 GB
Provisional Applications (1)
Number Date Country
60/121187 Feb 1999 US