Systems for controlling the superheat of the metal exiting the CIG apparatus in an electroslag refining process

Information

  • Patent Grant
  • 6196427
  • Patent Number
    6,196,427
  • Date Filed
    Thursday, December 21, 1995
    29 years ago
  • Date Issued
    Tuesday, March 6, 2001
    23 years ago
Abstract
Systems for controlling the superheat of the stream of molten metal from an electroslag refining apparatus is taught. The systems include the introduction of unrefined metal into an electroslag refining process apparatus in which the unrefined metal is first melted at the upper surface of the refining slag. The molten metal is refined as it passes through the molten slag. The refined metal is collected in a cold hearth apparatus having a skull of refined metal formed on the surface of the cold hearth for protecting the cold hearth from the leaching action of the refined molten metal. A cold finger bottom pour spout or exit orifice is formed at the bottom of the cold hearth to permit dispensing of molten refined metal from the cold hearth. The super heat of the molten metal flowing through the exit orifice of the cold finger apparatus is controlled, preferably utilizing a processor, such as a computer, by coordinating the rate of induction heat supplied to the metal within the cold finger apparatus and the rate of heat removal from the metal within the cold finger apparatus through the cold finger apparatus itself thereby providing metal having a specific superheat exiting the exit orifice.
Description




BACKGROUND OF THE INVENTION




The present invention relates generally to control of the flow of refined metal in an ESR-CIG apparatus. The ESR apparatus is an electroslag refining apparatus and the CIG apparatus is a cold wall induction guide tube apparatus, also referred to herein as a cold wall induction guide mechanism and a cold finger nozzle mechanism. More particularly, the invention relates to controlling the superheat (temperature) of liquid metal flowing to, through and from (as a metal stream) the CIG apparatus. Most particularly, the invention relates to controlling the superheat of the metal provided to an atomization zone during spray forming operations by varying the superheat dynamically in coordination with an atomization manifold oscillation angle.




Such control of the liquid metal superheat is important to numerous applications which can be made using the refining apparatus including atomization processing and relates generally to direct processing of metal passing through an electroslag refining operation. One example of molten metal refining is referred to as electroslag refining, and is illustrated and described in U.S. Pat. No. 5,160,532—Benz et al, assigned to the same assignee as the present invention, the disclosure of which is hereby incorporated by reference.




In an electroslag process, a large ingot of a preferred metal may be effectively refined in a molten state to remove important impurities such as oxides and sulfides which may have been present in the ingot. Simply described, electroslag refining comprises positioning a metal ingot over a pool of molten material in a suitable vessel or furnace where the molten material pool may include a surface layer of solid slag, an adjacent underlayer of molten slag and a lowermost body of refined molten ingot metal. The ingot is connected as an electrode in an electrical circuit including the molten metal pool, a source of electrical power and the ingot. The ingot is brought into contact with the molten slag layer and an electrical current is caused to flow across the ingot/molten slag interface.




This arrangement and process provides electrical resistance heating of the slag and melting of the ingot at the noted interface with the molten ingot metal passing through the molten slag layer as a refining medium to become a part of the body of refined ingot metal. It is the combination of controlled resistance melting and passage of the molten ingot metal through the molten slag layer which refines the ingot metal to remove impurities such as oxides, sulfides, and other undesirable inclusions.




Spray forming is a process using gas atomization to produce a spray of droplets of liquid metal followed by solidification of the spray on a solid body to directly form a billet or billet preform. In metal spray forming, a small stream of refined molten metal from the furnace is directed to pass through a molten metal spray forming atomizer generally comprising a closed peripheral manifold about a central aperture. The manifold may be equipped with gas inlet means and plural gas jet exit means. A gas under pressure is supplied to the manifold to exit through the gas jets in converging streams which impinge the passing metal stream to convert or break up the metal stream into a generally expanding spray of small molten metal droplets. This spray is caused to impinge and deposit on a suitable collector surface to generate a metal billet or other metal object.




An important variable in this process is the gas-to-metal ratio (GMR) which indicates the amount of atomization gas relative to the amount of molten metal which is required to effectively atomize the metal stream to form a spray and to cool the spray in-flight before striking the billet or preform. The spray is scanned across a revolving substrate to build a uniform layer. As it becomes necessary to enlarge the diameter of the preform, it becomes increasingly necessary to control the local temperature of the spray. A relatively hotter spray is desired near the outer diameter of the preform, a relatively cooler spray is desired at the centerline of the preform.




Best results are believed obtained when the molten metal spray pattern from the atomization zone is directed angularly against the collector or preform object rather than perpendicular. An angular impingement provides improved deposition efficiency as well as improved preform metal density and microstructure.




Most previous attempts at varying the gas to metal ratio (GMR) targeted the variation of the gas pressure, thus varying the quantity of gas applied to the atomization process while maintaining the metal stream flow rate as near constant as possible. While this approach has been successful, such an approach is difficult to implement because the gas pressures must be rapidly pulsed.




An alternate approach has recently been suggested in copending patent applications Ser. No. 08/537,966 and Ser. No. 08/537,963 assigned to the assignee of the present application, the disclosure of each is hereby incorporated by reference. In these patent applications, the approach disclosed included methods and systems for varying the molten metal flow rate to the atomization zone while maintaining the rate of delivery of the atomizing gas to the molten metal stream constant thereby minimizing the gas pulsation control problem if not eliminating it altogether.




While this approach has the potential for significant cost savings, an alternate method and system for controlling the temperature of the spray impacting the preform would be to vary the temperature of the molten metal melt entering the atomization zone and thus the temperature impacting the preform during spray forming operations.




Thus, it would be desirable to develop systems for varying the superheat of the molten metal provided to the atomization zone while maintaining the rate of delivery of the atomizing gas to the molten metal stream constant in order to control the temperature of the metal spray delivered to the preform. Such systems could include, among other means, providing varying power to the CIG unit, including the induction power, voltage or current so as to vary, for example, electromagnetically or thermally, the superheat of the metal proximate exit orifice from the CIG, which would in turn dynamically vary the temperature of the metal melt flow therefrom to the atomizer and to further coordinate the controlled, varying metal superheat flow with the scan angle of the atomizer relative to the preform in order to achieve the appropriate spray temperature at various oscillation angles on contact with the preform.




SUMMARY OF THE INVENTION




In one of its broader aspects, the present invention includes systems for controlling the superheat of melt flowing from a cold wall induction guide tube mechanism comprising: a cold wall induction guide tube mechanism including a neck having an exit orifice; a skull of melt operatively formed in the mechanism; a reservoir of melt above the mechanism; a stream of melt exiting the exit orifice of the mechanism; means, operatively positioned relative to the mechanism, for selectively controlling the superheat of the melt contained proximate the neck of the mechanism such that the superheat of the melt exiting the exit orifice is selectively increased or decreased thereby controlling the temperature of the flow melt flowing from the mechanism to an atomization zone and then onto the surface of the preform.




Another aspect of the present invention includes systems for controlling the spray from an atomization zone for impacting a preform during the spray forming of the preform comprising: a cold wall induction guide tube mechanism including an orifice having a diameter; a reservoir of melt operatively connected to the mechanism; a stream of melt exiting the orifice; a skull of melt operatively formed in the cold wall induction guide tube mechanism; means, operatively connected to the cold wall induction guide tube mechanism, for controlling the temperature of the melt proximate the orifice such that the temperature of the melt from the orifice is selectively varied; means, operatively positioned below the orifice, for forming a preform; and an atomizer, operatively positioned between the orifice and the preform forming means, for atomizing the melt into metal spray.




It is, accordingly, one object of the present invention to provide systems for selectively varying the superheat of the melt proximate the orifice in a cold wall induction guide tube during electroslag refining of metal used in spray forming operations.




Another object is to provide systems for coordinating the temperature of the liquid metal provided to an atomizer during atomization of metal from an electroslag refining apparatus during the spray forming of a preform.




Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a semischematic vertical sectional view of a representative electroslag refining apparatus suitable for use with the present invention.





FIG. 2

is a semischematic vertical sectional representative illustration of the apparatus of

FIG. 1

but showing structural details of the cold wall induction guide tube and the atomizer;





FIG. 3

is a semischematic vertical section in detail of the cold finger nozzle and atomizer of the structures of

FIG. 2

;





FIG. 4

is a semischematic illustration in part in section of the cold finger nozzle portion of an apparatus similar to that illustrated in

FIG. 3

but showing the apparatus free of molten metal;





FIG. 5

is a simplified schematic illustration of one form of a non-circular atomizer used in the spray forming process; and





FIG. 6

is a simplified schematic functional illustration of an atomizer impacting a stream of molten metal to produce spray from an atomization zone during the spray forming process.











DETAILED DESCRIPTION OF THE INVENTION




In carrying out the present invention, an electrode or ingot of metal to be refined is introduced directly into an electroslag refining apparatus for refining the metal and producing a melt of refined metal which is received and retained within a cold hearth apparatus mounted immediately below the electroslag refining apparatus. The molten metal is dispensed from the cold hearth through a cold finger orifice mounted directly below the cold hearth reservoir. The flow of melt from the cold finger apparatus is controlled by one or by a combination of mechanisms including thermal and electro-mechanical means.




If the rate of electroslag refining of metal and accordingly the rate of delivery of refined metal to a cold hearth approximates the rate at which molten metal is drained from the cold hearth through the cold finger orifice, an essentially steady state operation is accomplished in the overall apparatus and the process can operate continuously for an extended period of time and, accordingly, can process a large bulk of unrefined metal to refined metal.




The processing described herein is applicable to a wide range of alloys which can be processed beneficially through the electroslag refining processing. Such alloys include nickel- and cobalt-based superalloys, zirconium and titanium-based alloys, and ferrous-based alloys, among others. The slag used in connection with such metals will vary with the metal being processed and will usually be the slag conventionally used with a particular metal in the conventional electroslag refining thereof.




The several processing techniques may be combined to produce a large body of refined metal because the ingot which can be processed through the combined electroslag refining and cold hearth and cold finger mechanism can be a relatively large supply ingot and can, accordingly, produce a continuous stream of metal exiting from the cold finger orifice over a prolonged period to deliver a large volume of molten metal.





FIGS. 1 and 2

are semischematic elevational views in part in section of a number of the essential and auxiliary elements of apparatus for carrying out the electroslag refining and atomization aspects of the present invention. A vertical motion control apparatus


10


is shown schematically. It includes a structure


12


mounted to a vertical support


14


for containing a motor or other mechanism adapted to impart rotary motion to a member


16


for example, for illustrative purposes only, a screw or screw mechanism. An ingot support station


20


comprising means


22


, such as, for illustrative purposes only, a bar, threadedly engaged at one end to the member


16


and supporting the ingot


24


at the other end by conventional means


26


, for example, for illustrative purposes only, a bolt. It being understood that the present illustration is representative in nature only and that in an industrial setting pneumatic, electronic and other well-known methods and apparatus would actually be used, as is known in the art.




An electroslag refining station


30


comprises a cooled, such as, for example, by water, reservoir


32


containing a molten slag


34


, an excess of which is illustrated as solid slag granules


36


. A skull of slag


75


may form along the inside surfaces of the inner wall


82


of vessel


32


due to the cooling influence of the cooling water flowing against the outside of inner wall


82


.




A cold hearth station


40


is mounted immediately below the electroslag refining station


30


and includes a cooled, such as, for example, by water, hearth


42


containing a skull


44


of solidified refined metal and also a body


46


of liquid refined metal. Cooled reservoir


32


may be formed integrally with the cooled hearth


42


.




The bottom dispensing structure (shown as an empty dashed box)


80


of the apparatus is provided in the form of a cold finger orifice. The cold hearth dispensing station


80


and the cold finger orifice will be explained more fully below.




Electric refining current is supplied by station


70


. The station includes the electric power supply and control mechanism


74


. It also includes the conductor


76


carrying current to the bar


22


and, in turn, to ingot


24


. Conductor


78


carries current to the metal vessel wall


32


to complete the circuit of the electroslag refining mechanism.




As illustrated by

FIG. 2

, the station


30


is an electroslag refining station disposed in the upper portion


32


of the vessel and the cold hearth station


40


is disposed in the lower portion


42


of the vessel. The vessel is preferably a double walled vessel having an inner wall


82


and an outer wall


84


. Between these two walls, a cooling liquid


86


, such as, for example, water is provided, as is conventional practice with some cold hearth apparatus. The cooling liquid


86


may be flowed to and through the flow channel between the inner wall


82


and outer wall


84


from supply means and through conventional inlet and outlet means which are conventional and which are not illustrated in the figures. The use of cooling liquid


86


to provide cooling to the walls of the cold hearth station


40


is necessary in order to provide cooling at the inner wall


82


and thereby to cause the skull


44


to form on the inner surface of the cold hearth structure.




The cooling liquid


86


is not essential to the operation of the electroslag refining or to the upper portion of the electroslag refining station


30


but such cooling may be provided to ensure that the liquid metal


46


will not make contact with the inner wall


82


of the containment structure because the liquid metal


46


could attack the wall


82


and cause some dissolution therefrom to contaminate the liquid metal of body


46


within the cold hearth station


40


. Also, in

FIG. 2

, a structural outer wall


88


is illustrated. Such an outer wall may be made up of a number of flanged tubular sections


90


,


92


.




The cold finger structure is shown in detail in

FIG. 3

in its relation to the processing of the metal from the cold hearth structure and the delivery of liquid melt


46


from the cold hearth station


40


, as illustrated in

FIGS. 1 and 2

.

FIG. 3

shows the cold finger with the solid metal skull and with the liquid metal reservoir in place. By contrast,

FIG. 4

illustrates the cold finger structure without the liquid metal, or solid metal skull in order that more structural details may be provided and clarity of illustration may be achieved. Cold finger structures are not themselves novel structures and have been described in the literature (see, for example, the discussion in U.S. Pat. No. 5,348,566).




One structure useful in the present invention combines a cold hearth with a cold finger orifice so that the cold finger structure effectively forms part, and in the illustration of

FIG. 3

, the center lower part, of the cold hearth. This combination preserves the advantage of the cold hearth mechanism by permitting the purified alloy to form a skull, by its contact with the cold hearth, and thereby to serve as a container for the molten version of the same purified alloy. In addition, the cold finger orifice structure of station


180


of

FIG. 3

is employed to provide a more controllable generally funnel shaped skull


183


and particularly of a smaller thickness on the inside surface of the cold finger structure. As is evident from

FIG. 3

, the thicker skull


44


in contact with the cold hearth and the thinner skull


183


in contact with the generally funnel shaped cold finger structure are essentially continuous.




One reason why the skull


183


is thinner than


44


is that a controlled amount of heat may be put into the skull


183


and into the generally cone shaped portion of the liquid metal body


46


which is proximate the skull


183


by means of the induction heating coils


185


. The induction heating coil


185


is cooled by flow of a cooling liquid, such as, for example, water through the coolant and power supply


187


. Induction heating power supplied to the unit


187


from a power source


189


is shown schematically in FIG.


3


.




One significant advantage of the cold finger construction of the structure of station


180


is that the heating effect of the induction energy penetrates through the cold finger structure and acts on the body of liquid metal


46


as well as on the skull structure


183


to apply heat thereto. This is one of the features of the cold finger structure and it depends on each of the fingers of the structure being insulated from the adjoining fingers by an air or gas gap or by an insulating material. Hence the term CIG or cold wall induction guide tube mechanism.




This arrangement is clearly illustrated in

FIG. 4

where both the skull and the body of molten metal are omitted from the drawing for clarity of illustration. An individual cold finger


97


, as shown in

FIG. 4

, is separated from the adjoining finger


92


by a gap


94


, which may be provided with and filled with an insulating material such as a ceramic material or with an insulating gas. The details of the figure are fully disclosed in U.S. Pat. No. 5,348,566, assigned to the assignee of the present application, the disclosure of which is herein incorporated by reference.




Because it is possible to control the amount of heating and cooling passing from the induction coils


185


to and through the cold finger structure of station


180


, it is possible to adjust the amount of heating or cooling which is provided through the cold finger structure both to the skull


183


as well as to the generally cone shaped portion of the body


46


of molten metal in contact with the skull


183


.




As shown in

FIG. 4

, the individual fingers such as


90


and


92


of the cold finger structure are provided with a cooling fluid such as water by passing water into the receiving pipe


96


from a source not shown, and around through the manifold


98


to the individual cooling tubes such as


100


. Water leaving the end of tube


100


flows back between the outside surface of tube


100


and the inside surface of finger


90


to be collected in manifold


102


and to pass out of the cold finger structure through water outlet tube


104


. This arrangement of the individual cold finger water supply tubes such as


100


and the individual separated cold fingers such as


90


is essentially the same for all of the fingers of the structure so that the cooling of the structure as a whole is achieved by passing water in through inlet pipe


96


and out through outlet pipe


104


.




The net result of this action is best illustrated in

FIG. 3

where a stream


156


of molten metal is shown exiting from the cold finger orifice structure. This flow is maintained when a desirable balance is achieved between the input of cooling water and the input of heating electric power to and through the induction heating coils


185


and


135


.




The induction heating coils


85


of

FIG. 4

show a single set of coils operating from a single power supply


87


supplied with power from the power source


89


. In the structure of

FIG. 3

, two induction heating coils are employed, the first is placed adjacent the tapered portion of the funnel shaped cold finger device and supplies heat principally to the controllable skull


183


. A power source


189


supplies power to power supply


187


and this power supply furnishes the power to the set of coils


185


positioned immediately beneath the tapered portion of the funnel shaped cold finger structure. A second power source


139


furnishes power to power supply


137


and power is supplied from the source


137


to a set of coils


135


which are positioned along the vertical down spout portion of the cold finger apparatus to permit a control of the flow of molten metal from bath


46


through the vertical portion of the cold finger apparatus.




An increase in the amount of induction heating through coil


135


(see

FIG. 3

) can cause a remelting of the solidified plug of metal in the vertical portion of the cold finger apparatus and a renewal of stream


156


of molten metal through passageway


130


. When the stream


156


is stopped or slowed, there is a corresponding growth and thickness of the skull


128


in the vertical portion or neck of the funnel shaped cold finger apparatus.




The regulation of the amount of cooling water flowing to the cold finger apparatus itself as well as the flow of induction heating current through the coils


185


and


135


and particularly the coil


135


regulates the thickness of the thinner skull


128


and the thickness of skull


128


is one of several parameters which regulates the rate of flow of metal from the reservoir


46


.




Increases or decreases in the amount of induction heating power through the coils


135


,


185


can cause a desired effect, namely an increase or decrease in the superheat of the liquid metal stream


156


exiting the passageway


130


. The electromagnetic energy can be used to control the superheat or temperature of the liquid metal in the cold finger apparatus and the stream


156


such that the temperature of the spray


228


impacting the preform


229


is selectively increased or decreased. Thus, the power applied to the coils


135


,


185


has a direct influence on the superheat or temperature of metal from the reservoir


46


, thus having a direct effect on the temperature of the metal during atomization and subsequently on the spray


228


impacting the preform


229


.




In general, during operation of the ESR-CIG system, a steady state is desired in which the rate of metal melted and entering the refining station


30


as a liquid is equal to the rate at which liquid metal is removed as a stream


156


(see

FIG. 3

) through the cold finger structure and provided to the atomizer


231


for atomization into spray to be formed into a preform. Slight adjustments to increase or decrease the rate of melting of metal are made by adjusting the power delivered to the refining vessel from a power supply such as


74


. Also, in order to establish and maintain a steady state of operation of the apparatus, the ingot must be maintained in contact with the upper surface of the body of molten slag


34


and the rate of descent of the ingot into contact with the melt must be adjusted through control means within box


12


to ensure that touching contact of the lower surface of the ingot with the upper surface of the molten slag


34


is maintained.




The deep melt pool


46


within cold hearth station


40


is an advantage in the electroslag refining because a specific flow rate can be established from the reservoir of melt


46


through the flow path


130


(see

FIG. 3

) from the cold finger apparatus


180


.




Generally, control or stoppage of the flow through passageway


130


is accomplished by supplying or withdrawing heat from the melt and essentially increasing or decreasing the size of the skull


128


in the passage way


130


with stoppage occurring with the freezing the metal within the passageway


130


. In supplying or withdrawing heat from the melt, it will be appreciated that there are essentially two sources of heat for the metal within passageway


130


. One source is heat which is generated in the metal by operation of the coils


135


and


185


. The second source is the heat within the melt itself as it flows down from reservoir


46


. Although it is possible to stop heating the melt in passageway


130


by stopping the supply of power from power source


137


the metal will remain molten because molten metal is flowing down reservoir


46


to passageway


130


and brings with it the heat of fusion and a degree of superheat already present in the melt.




There are also a number of ways in which heat is removed from melt in passageway


130


. A primary source of heat removal and the one which causes the skull


128


to remain in place is the cooling accomplished by flow of water in the cold fingers, such as


100


. It is possible to increase or reduce the rate of cooling water flow through the cold fingers in order to increase or decrease the superheat of the melt. Such increase or decrease in the superheat of the melt will increase or decrease the temperature of molten metal delivered to the atomization zone. Thus, one method of controlling the heat of the spray


228


delivered to the surface of the preform


229


is to control the temperature of the melt in passageway


130


that is delivered to the atomization zone


237


.




It will be appreciated that the melt superheat regulating means, as discussed above, can be used in combinations, such as, for example, in conjunction with a processor or computer, for controlling the superheat of the melt in passageway


130


, subsequently, for controlling the temperature of the metal stream delivered to the atomization zone


237


and for controlling the temperature of the spray


228


delivered to the surface of the preform


229


.




When either an increase or a decrease in the superheat of the molten metal within the passageway


130


is desired, the cooling is appropriately increased or reduced, induction heating through coils


135


and/or


185


are appropriately increased or reduced in order to control the superheat or temperature of the melt in passageway


130


.




At the lowermost part of vessel


32


a controlled drain orifice


130


communicates with molten metal pool


46


. A stream of molten metal


156


is caused to flow from orifice


130


through a spray forming atomizer


231


. In one form, atomizer


231


comprises a hollow atomizer manifold with a central aperture


232


which is concentrically positioned to receive metal stream


156


therethrough. Atomizer


231


also includes a peripheral row of gas jets or orifices


225


in a peripherally continuous tapered or conical edge surface


226


. Atomizer


231


is connected to a source (not shown) of a gas under pressure, and the combination of the gas jet orifices


225


and conical surface


226


provides a plurality of gas streams


227


which converge at a downstream apex on the passing metal stream


156


. The controlled interaction of the gas jet streams


227


with metal stream


156


causes metal stream


156


to break down and be converted to an expanding spray plume or pattern


228


of small molten metal droplets.




Spray pattern


228


is directed against a collector or preform


229


to provide, for example, a billet of refined ingot metal or other ingot metal objects. Collector


229


may be a fixed or moving surface including a rotating surface such as the surface of a rotating cylinder or mandrel. The efficiency and effectiveness of deposition of molten metal spray


228


on a collector surface to provide a refined metal object is facilitated and improved when the spray pattern


228


may be angularly adjusted with respect to the collector. Angular adjustment also leads to improved density and microstructure of the refined metal product. Continuous and repetitive angular adjustment may also be utilized to provide an oscillating or scanning motion of the atomizer


231


.




In order to provide angular adjustment, atomizer


231


may be mounted for angular adjustment rotation about a transverse axis so that the plane of the atomizer is not perpendicular to the metal stream


156


. Also, by mounting atomizer


231


for angular adjustment rotation, the defined spray pattern


228


may be more advantageously matched to different surface configurations of collector or preform


229


as compared to a non-adjustable atomizer where the spray pattern is fixedly directed to a limited area of the collector, a condition which may require a complex adjustable mounting of a collector which, for example, may weigh from about 50 lbs. to about 15 tons.




One simple and convenient adjustable mounting for atomizer


231


may comprise a pair of diametrically opposed radially extending stub shafts


233


with atomizer


231


therebetween.




In the past, there have been definite limits to the degree of angular adjustment of atomizer


231


. For example, metal stream


156


is a smooth cohesive stream passing concentrically through atomizer


231


with a predetermined atomizer clearance with respect to overall structure of atomizer


231


and its operating characteristics including the use of gas jets from orifices


225


or projecting nozzles.




In a recently issued patent, U.S. Pat. No. 5,366,206, the disclosure of which is hereby incorporated by reference, the spray


228


forming atomizer


231


, disclosed therein, had a defined aperture elongated and non-circular such as an elliptical or oval configuration. An elongated, ovate, or elliptical aperture provides an extended range of angular adjustment of an atomizer


231


while maintaining a satisfactory central aperture exposure for the passing metal stream


156


during spray forming.




Such an elongated non-circular aperture spray forming atomizer is illustrated in FIG.


5


. The atomizer


31


comprises a hollow tubular manifold ovately formed to define a central and elongated aperture


232


, elliptical, for example and is fitted with and supported by diametrically opposite shafts


233


so that atomizer


231


may be rotated about the common axis of shafts


233


, i.e. about a transverse and minor axis of the elliptical aperture


232


. One or both shafts


233


may be hollow or tubular to also serve as gas supply conduits for atomizer


231


.




The ability to selectively adjust the direction of the molten metal spray pattern


228


provides a greater choice in the position and kind of collector or preform object which is employed. For example, in order to avoid the large bending moments in correspondingly large billets, e.g. approaching 20,000 lbs., it is desirable to orient the billet in a vertical position. Ordinarily, the usual metal melting structure, such as electroslag assembly,

FIG. 1

, also occupies a vertical position and supplies a vertical melt stream


156


. Accordingly, some means is required to provide extended angular adjustability for atomizer


231


,

FIG. 5

, in order to direct spray pattern


228


at selectively advantageous angles to a vertical billet preform. The elongated, oval, or elliptical aperture in the atomizer


231


serves as such means. Very large and cumbersome preforms may be placed in a vertical position where bending moments are minimal and subjected to an advantageously directed spray pattern


228


.




As shown in

FIG. 6

, the molten metal stream


156


passes through an atomizer


231


(

FIG. 5

) for conversion into a molten metal plume or spray pattern


228


(FIG.


2


). As illustrated, the atomizer


231


is angularly adjustable about a transverse axis so that it is tilted from its horizontal position, from the viewer's perspective. Maximum adjustment angle is achieved without interference between the atomizer and the passing molten metal stream because of the elongated aperture


213


in atomizer


231


which permits an increased angular adjustment over a circular atomizer. The oval or elliptical aperture


213


provides ample clearance for molten metal stream


156


to provide a gas jet impact or atomization zone


217


for a molten metal spray pattern


228


of increased angular adjustment or deflection.




As illustrated in

FIG. 6

, a major elongation is not required to obtain the benefits of increasing the angle of adjustment without ring/metal stream interference. Consequently the atomizer used, in the illustration of the present invention, provides maximum advantage where the space available may be at a minimum. The oval or elliptical atomizer


231


(

FIG. 2

) is supported for angular adjustment rotation about the minor axis of an elliptical aperture


232


, i.e. across the illustrated shaft supports


233


to take maximum advantage of the extended range of adjustment provided by the elliptical configuration of aperture


232


. Various rotational adjustment means may be attached to one or both shafts


233


for remote electrical or mechanical operation.




The above configuration provided an improved spray forming atomizer for converting a molten metal stream, passing through the atomizer, into a molten metal spray


228


. An elongated aperture in the atomizer provided increased angular adjustment of the spray pattern for increased spray


228


deposition effectiveness. Ovate and other elongated aperture configurations may be considered to have major and minor transverse axis dimensions, one of which is longer than the other resulting in what may be defined as providing more clearance, in one direction for the passing metal stream than in the same direction if the atomizer were axially rotated 90°.




Referring again to

FIG. 2

, it may be the case that the atomized molten metal spray


228


impacts an area on the large preform


229


that is substantially less than the cross-sectional area of the preform


229


. In such a case, it is necessary to manipulate either the spray forming atomizer


231


, the preform


229


, or both, beneath the spray


228


to achieve a uniform build up of atomized and reconsolidate material on the preform


229


.




For example, the atomizer


231


may be caused to rock, or “scan ” about an axis perpendicular to the axis of the preform


229


while, simultaneously, the preform


229


is caused to rotate beneath the spray


228


and withdraw from the spray


228


at a rate equal to the rate at which material is added to the top of the preform. A steady state operation is accomplished and the process can operate continuously for an extended period of time. In those cases where the preform


229


is substantially larger than the impinging atomized molten metal spray


228


, it has been found experimentally that undesirable thermal transients may occur in the resulting metal preform


229


. More particularly, the temperature of the preform


229


at the center line may remain at an elevated temperature for a period of time sufficient to allow undesired metallurgical processes to occur such as, for example, grain growth.




In the past, the gas-to-metal ratio (GMR) has been statically adjusted so as to eliminate the undesired thermal transients at the center line of the preform


229


. Unfortunately, the resulting cooler spray


228


causes a separate, but equally undesired, thermal transient at the outer diameter which gives rise to other metallurgical defects, typically porosity. Statically adjusting the GMR to satisfy the conflicting requirements of the center line and the outer diameter of the preform


229


has, in the past, limited the maximum diameter preform


229


that can be obtained with the process.




Since preform


229


diameter directly effects the process throughput and thus, process economics, it is desirable to achieve as large a diameter as possible. One method to achieve the higher diameter is to manipulate the GMR with scan angle such that the spray


228


enthalpy is optimized for the location on the preform


229


onto which it will be attached. Typically, this requires a cooler spray


228


at the centerline, and a hotter spray


228


at the outer diameter. As mentioned above, previous attempts at varying the GMR have targeted the variation in gas pressure, thus varying the quantity of gas applied to the atomization process.




An even more recent attempt, and also mentioned above, to vary the GMR was by accomplishing the controlled variation in the metal flow rate, thus, varying the flow rate of the metal supplied to the atomization process in order to vary the GMR. In order to be effective, the metal flow rate must be modulated in coordination with the scan angle of the atomizer


231


to ensure that the appropriate spray


228


conditions exist at the appropriate geometric locations on the preform


229


, including the correct GMR.




As mention above, in spray forming, the spray


228


is scanned across a revolving substrate to build a uniform layer. As it becomes necessary to enlarge the diameter of the preform


229


, it becomes increasingly necessary to control the local temperature of the spray


228


. A hot spray


228


is desired near the outer diameter, a cool spray


228


is desired at the centerline. Thus, controlling the GMR by varying the rate of flow of the molten stream


156


to the atomization zone in coordination with or as a function of scan angle is one method to optimize the subsequent heat transfer conditions of the spray


228


on the preform.




It is known that the temperature of the metal stream is a prime variable in determining the temperature of the substrate on the spray formed preform


229


. For example, an about 25° C. change in the superheat of the metal entering the atomization zone


237


can change temperature of the spray at the preform by about 5° C. or more.




In the past, it was not been practical or desirable to vary the temperature of the metal stream at the high frequencies (1-50 Hz) required in spray forming because a large mass of metal must be effected in conventional melting systems other than that described in the present application. However, the cold-walled induction guide does allow such high frequency variation because the energy is applied to a relatively small volume of metal. A ten kilowatt variation in power can result in a change in the superheat of approximately 10° C. which, in turn, can effect the temperature of the substrate on the spray formed preform


229


.




Such controlled power variation is useful during spray forming to control the temperature of the spray


228


emanating from the atomization zone and impacting on the preform


229


. Specifically, by controlling the superheat or temperature of the stream of metal exiting the cold-walled induction guide orifice


130


, along with other variable and controllable parameters, it is possible to ensure a relatively hotter spray


228


near the outer diameter and a relatively cooler spray


228


at and proximate the centerline of the preform


229


. By modulating the power output to the cold-walled induction guide in coordination with the oscillation angle of the scanning atomizer


231


such that the temperature/superheat of the flowing metal is appropriately controlled.




It should be understood that, since the operating parameters differ for various geometries, materials and the like, those skilled in the art should be able to design an induction coil and associated power supply or other functionally equivalent means to accomplish the above.




To obtain the desired effect of a varying spray temperature with the preform surface area impacted, it is necessary to coordinate the induction power with the spray scan angle using an appropriate control system, such as, for example, a computer. It may most likely be necessary to determine the temperature of the resulting surface on the preform using an appropriate temperature measuring means, such as, for example, an optical pyrometer adjusted such that a series of temperature readings are sent to the computer. Alternatively, a video imaging system, appropriately calibrated to send the spatial variation in temperature on the preform surface to the computer may be employed. The measured temperature is then used as a parameter for manipulating the induction power provided the coils or adjust the cooling liquid flow rate to selectively increase or decrease the superheat or temperature of the melt in the passageway


130


. The superheat of the melt in passageway


130


is then coordinated and controlled by the computer. Such control system provides for spray temperature control so important in the spray forming of preforms, as discussed above. An appropriate control system could include any number of well know systems which a person skilled in the art could modify and implement to effectuate the controlled spray forming of a preform by varying the temperature of the spray according to the appropriate scan angle.




Best spray forming results are believed obtained when the size of the spray pattern impacting the preform/collector is substantially smaller than the size of the overall preform/collector and the spray is scanned across the surface of the preform/collector and when the temperature of the melt is varied as it enters the atomization zone in order to apply spray having the desired conditions at the various locations on the preform/collector.




While the systems contained herein constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise systems, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.



Claims
  • 1. A system for controlling the temperature of the melt exiting a cold wall induction guide tube mechanism comprising:a cold wall induction guide tube mechanism including a neck having an exit orifice; a skull of melt operatively formed in the mechanism; a reservoir of melt above the mechanism; a stream of melt exiting the exit orifice of the mechanism; means for dynamically varying superheat of said melt stream at a plurality of cycles per second for correspondingly varying temperature of the stream of melt exiting the exit orifice wherein the temperature of melt flowing from the exit orifice of the mechanism is selectively increased or decreased thereby controlling the temperature of the melt provided to an atomization zone.
  • 2. The system of claim 1 wherein the superheat varying means comprises:an induction heater.
  • 3. The system of claim 1 wherein the superheat varying means comprises:a cooling liquid.
  • 4. A system for controlling the temperature of the spray from an atomization zone for impacting a preform during the spray forming of the preform comprising:a cold wall induction guide tube mechanism including an orifice having a diameter; a reservoir of melt operatively connected to the mechanism; a stream of melt exiting the orifice; a skull of melt operatively formed in the cold wall induction guide tube mechanism; means, operatively connected to the cold wall induction guide tube mechanism, for for dynamically varying superheat of said melt stream at a plurality of cycles per second for correspondingly varying temperature of the melt flowing from the orifice; means, operatively positioned below the orifice, for forming a preform; and an atomizer, operatively positioned between the orifice and the preform forming means, for atomizing the melt into metal spray.
  • 5. The system of claim 4 wherein the superheat varying means further comprises:induction heating means, operatively positioned proximate the mechanism orifice, for transferring heat to the melt in the mechanism.
  • 6. The system of claim 4 wherein the superheat varying means further comprises:electromagnetic means, operatively positioned proximate the mechanism orifice, for electromagnetically increasing the liquid melt superheat.
  • 7. An electroslag refining assembly including a reservoir of molten metal and an exit orifice in the reservoir through which a molten metal stream exits from the reservoir;induction coil means for induction heating of the mechanism; a reservoir of melt operatively positioned relative to the mechanism; a skull of melt in the mechanism; a stream of the melt exiting the bottom of the mechanism; and means, operatively connected to the induction coil means, for selectively increasing and reducing the induction heating power supplied to the mechanism for dynamically varying superheat of said melt stream at a plurality of cycles per second for correspondingly varying the temperature of the melt exiting the bottom of the mechanism.
  • 8. A molten metal assembly comprising:a reservoir of molten metal; an exit orifice operatively positioned in the reservoir; a skull of melt formed in the mechanism; a stream of molten metal exiting the bottom of the mechanism; means, operatively connected to the exit orifice, for selectively heating and cooling the melt for dynamically varying superheat of said melt stream at a plurality of cycles per second for correspondingly varying the temperature of the stream passing through the mechanism; a spray forming atomizer, operatively positioned relative the exit orifice, for generating a spray pattern of droplets; and mounting means, operatively connected to the spray forming atomizer and a gas supply means, for directing the atomizer such that the spray pattern of droplets impact a preform.
  • 9. A system for controlling the spray from an atomization zone for impacting a preform during the spray forming of the preform comprising:an electroslag refining station; a cold hearth station having molten metal therein operatively positioned relative to the electroslag refining station; a cold hearth dispensing station including a cold finger orifice, operatively positioned relative to the cold hearth station, for dispensing the molten metal therefrom; a skull operatively formed in the cold hearth and the cold finger orifice; induction coils, operatively positioned proximate the cold finger orifice, for providing heat to the molten metal in the vicinity of the cold finger orifice; a hydrostatic heard of molten metal above the cold finger orifice; means, operatively connected to the induction coils, for dynamically varying superheat of said melt stream at a plurality of cycles per second for correspondingly regulating the temperature of the molten metal in the cold finger orifice; means, operatively positioned below the orifice, for forming a preform; an atomizer, operatively positioned between the orifice and the preform forming means, for converting the melt into metal spray and means, operatively connected to the atomizer, for providing gas at a substantially constant gas pressure to the atomizer.
  • 10. A system for refining a metal ingot comprising:means for electroslag refining said ingot to produce a discharge stream of refined liquid metal; means for injecting an atomization gas to impinge said stream to produce a spray for forming a solidified deposit thereof on a billet; and means for dynamically varying superheat of said discharge stream at a plurality of cycles per second for correspondingly varying temperature of said spray at said billet.
  • 11. A system according to claim 10 further comprising:means for rotating said billet; means for scanning said injected atomization gas at an oscillating scan angle; and said superheat varying means being further effective to vary said spray temperature in coordination with said oscillating scan angle.
  • 12. A system according to claim 11 wherein said superheat varying means are effective for increasing temperature of said spray as said billet increases in diameter.
CROSS REFERENCE TO RELATED APPLICATION

The present invention is related to patent applications Ser. No. 08/537,966 and Ser. No. 08/537,963, both filed on Oct. 2, 1995.

US Referenced Citations (4)
Number Name Date Kind
5160532 Benz et al. Nov 1992
5310165 Benz et al. May 1994
5332197 Benz et al. Jul 1994
5348566 Sawyer et al. Sep 1994