US 3690367 A
The apparatus and method for effecting the restructuring of metals disclosed herein provides a container for holding molten metal in a controlled atmospheric or vacuum environment into which an open-ended shell mold is immersed so that the wall of the mold separates and confines molten metal intended to be formed from the surrounding molten mass. A chill means is placed in engagement with the confined molten metal at the top opening of the mold which begins solidification thereof at the molten metal interface. Means are provided for moving the chill means so that the solidified portion of the formed part is withdrawn from the mold as required. Planned withdrawal of the solidified portion creates a continuously new interface area which then progressively solidifies until the formed part is completed.
Description (OCR text may contain errors)
1 51 Sept. 12,1972
1541 APPARATUS FOR THE RESTRUCTURING 0F METALS  Inventor: Floyd La Mar Daniels, Los Angeles,
 Assignee: Anadite Incorporated,
 Filed: July 5, 1968  Appl. No.: 742,875
South  US. Cl. ..164/335, 164/260, 164/136, 164/353, 164/259, 164/338, 164/348,
 Int. Cl. ..B22d 41/00  Field of Search ..164/356, 133, 136, 335, 127, 164/348, 258, 256, 253, 254, 260, 261, 259,
61, 62, 63, 65, 77, 107, 4, 60, DIG. ll, DIG.
3,287,769 11/1966 l-Iess et al ..164/256 X 2,873,491 2/1959 Brennan ..164/258 X 1,972,945 9/ 1934 Nilson ..164/133 X 3,198,606 8/1965 Lyons ..148/1 .6 X 3,481,796 12/1969 ..148/l.6 2,747,971 5/1956 .5 2,248,868 7/1941 I-lanawalt ..164/256 FOREIGN PATENTS OR APPLICATIONS 553,551 6/1932 Germany ..164/136 Primary Examiner-J. Spencer Overholser Assistant Examiner-V. K. Rising Attorney-Roger A. Mar-rs  ABSTRACT The apparatus and method for effecting the restructuring of metals disclosed herein provides a container for holding molten metal in a controlled atmospheric or vacuum environment into which an open-ended shell mold is immersed so that the wall of the mold separates and confines molten metal intended to be formed from the surrounding molten mass. A chill means is placed in engagement with the confined molten metal at the top opening of the mold which begins solidification thereof at the molten metal interface. Means are provided for moving the chill means so that the solidified portion of the formed part is withdrawn from the mold as required. Plarmed withdrawal of the solidified portion creates a continuously new interface area which then progressively solidifies until the formed part is completed.
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APPARATUS FOR THE RESTRUCTURING OF METALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to apparatus and methods for restructuring materials and, more particularly, to improved forming techniques for restructuring molten metal into a shaped solid form with complete control of microstructure development, regardless of structure configuration so that the resulting parts are relatively free of discontinuities normally associated with conventionally cast parts and which inherently exhibit high strength-to-weight ratios.
2. Description of the Prior Art As the usefulness of castings having relatively high strength-to-weight ratios have expanded from simple configurations to more complex, lighter in weight, and larger in size components for structural applications, the demand for greater soundness and reliability has proportionately increased. Economy dictates the development of new processes which will provide metal components with uniform structural continuity and in alloys comparable to those now used in wrought form.
In the past, it has been the conventional practice in producing castings to pour or inject molten metal into mold cavities. Solidification of this metal has been relatively uncontrollable due to the fact that the entire casting must transform from liquid to solid in various zones throughout the casting mass. The manner in which metal freezes determines the castings mechanical-properties and soundness. Therefore, the properties of castings, solidified in the conventional manner, will vary in proportion to the solidification pattern achieved.
Since casting is performed in atmosphere, hydrogen is present in the cast part which weakens the part structurally in proportion to the amount of hydrogen embodied in the casting. It is the conventional practice to minimizethis problem by degassing the metal in the crucible before pouring by introducing chlorine and other commercial preparations into the melt immediately prior to pouring. Regardless of the thoroughness of degassing the melt, hydrogen is absorbed during the pouring operation so that there seldom a totally hydrogen free casting.
Another conventional casting constant that is deleterious to casting quality and strength is the entrapment of oxides formed on the surface of molten metal because of being melted in the presence of oxygen. Founding processes usually include protective measures, such as screens, to filter out the oxide formations, and runner extensions to entrap them, but oxide inclusions are almost always present to some degree in castings and are the cause of rejection and low yield.
There is always a delicate balance, in conventional founding methods, between the pouring temperature and casting quality. If the pouring temperature is high gas absorption is high; if the pouring temperature is low, thin areas of the casting cavity do not fill completely.
Inspection procedures are costly when conventional castings are used for critically structural applications. This is because the defects (gas porosity, shrinkage porosity, oxide inclusions, segregation, etc.) are normal in some percentage in almost every lot of production castings and must be discovered by nondestructive methods, such as X-Ray, die penetrant, sonic, magnetic and visual inspection aids or the like. The castings in which defects are found are then measured against specification standards, with the result that, rarely, total acceptance, generally partial rejection and occasionally total rejection occurs. Obviously, more stringent requirements produce greater losses.
It is a well known and standard procedure in all forms of casting, including the processes previously mentioned, that the molds require gating" and adequate venting of gasses as well as a reservoir in the form of a funnel-like riser which supplies a quantity of liquid metal to the cooling section of the casting.
These gates and risers tend to function as a reservoir source to feed new metal to sections that are cooling and crystallizing with consequent shrinkage. It has long been known that this is an essential step in effecting casting systems and without proper reservoir place ment, castings tend to fracture or exhibit highly undesirable variations in metal soundness. These gating procedures and techniques have been utilized mainlyfor the control of solidification and the prevention of poorly distributed cooling or chilling of a mold and its metal content due to variation in the casting cross-sectional configuration between one point and another. It is common, of course, for castings to have widely varied sections and there are limits related to every technique of casting with respect to the ratio between the thinnest and the thickest section of a given casting. The ability to achieve a wide variety of variation between thin and heavy sections is a function of feeding and chilling to induce directional solidification. Venting the molds to eliminate entrapment of air make possible the removal of gasses that can cause improper mold filling.
Gates or columns of metal designed around the desired casting first serve as a passage to deliver metal to the cavity. Secondly, extra areas of molten metal in larger masses that make up these columns remain at elevated temperatures, serving to sustain heat in the mold. These extra areas also function as reservoirs of molten metal to feed the casting sections, thus controlling direction of solidification. Gates employed in molding often consist of far more metal than the product being cast (aluminum 3 to 1 ratio average). When this fact is coupled with the requirement of a reservoir to supply the gates and the mold itself, there is a substantial amount of non-productive metal that is not usable in critical castings.
This is particularly true in investment casting techniques or lost wax systems where extremely thin sections are possible. In these types of castings, purity of metal is of primary importance because even very small foreign particles can cause rejection of a part. In addition to the expense of surplus metal that is wasted in connection with such casting, there is major engineering effort and planning associated with the placement of this gating and the determination of size, direction and relationship with adjoining gates along with metal and mold temperatures closely controlled at high expense.
Therefore, a need has long existed to provide an apparatus and process relatively free of gating and riser provisions which incorporate means for controlling the direction of solidification of metal free of detrimental defects. Improvement in restructuring metals which are permitted by modern technological approach and conceptual improvement can readily reduce thecost of such parts, when compared to the cost of producing castings by previous methods and apparatus.
Summary of the invention Accordingly, the above-mentioned problems and difficulties encountered with conventional casting and metal parts fabrication areobviated by the present invention which facilitates quality and quantity production of metal parts by simplification of mold preparation and processing techniques. The need for employing conventional pouring, gating methods and heat distribution within the mold are eliminated or greatly minimized so that controlled directional solidification results.
In one form of the invention, a container is employed for holding a quantity of molten metal in a vacuum environment into which a thin-walled, hollow mold or form is inserted through the upper surface of the molten mass. The mold is open-ended so that the molten metal will flow through the bottom opening of the mold into the hollow cavity thereof so as to be separated from the surrounding mass by the wall of the mold. A cold chill means is introduced through the top opening of the mold into contact with the captured molten metal within the cavity at which time solidification occurs at the contacting interface. Means are provided for moving the chill means upwardly so that the solidified-portion of the molded part is carried with it. The solidification progressively occurs at the interface characterized by the area of solidification since the cooling interface changes as the chill means and solid metal is moved upward. Preferably, but not necessarily, the process is performed in a vacuum and/or an inert atmosphere to avoid contamination such as embrittlement normally caused by hydrogen contact for example. Therefore, the container including the molten mass, mold and chill means are located within a suitable vacuum environment.
Furthermore, means may be provided for stirring or agitating the molten metal disposed at the solid liquid interface whereby a surface current is created in order to reduce the growth of dendrites as the metal solidifies. The molten metal solidifies in a continuous restructured manner to create a plane solidification front or a narrow solidification front on previously solidified metal. In at least one controlled experiment involving X-Ray examination, characteristics of the produced part greatly simulate the characteristics of a forging except for the greater weight reduction in favor of the part produced by the present invention.
Therefore, it is among the primary objects of the present invention to provide a novel apparatus and method for the controlled solidification of a casting in a continuous growth manner, utilizing a narrow liquidusto-solidus zone for the development of a shaped part within va shell mold.
Another object of the present invention is to provide a novel apparatus and method for the elimination of gating, risers and .pouring procedures normally employed in mold preparation.
Still another object of the present invention is to provide a novel restructuring apparatus for metal which provides for the reduction in the overall quantity of metal required for the casting process and which employs molten metal for heat control purposes.
Still a further object of the present invention is to simplify the production of mold techniques, particularly in areas of precision casting where exceedingly critical dimensions are a factor and the engineering of gating is time-consuming, costly, and also, involving costly removal and hand working gated areas to the desired close tolerance dimensions of the casting.
Yet another object of the present invention is to provide a novel apparatus and method for effecting therestructuring of metals from a molten form to a solid form wherein solidification is controlled at the interface to retard the formation of voids, flaws, occlusions, segregations, etc. so that a resultant molded part is produced having high density characteristics.
A further object of the present invention is to produce shaped forms with exceptionally thin walls, being consistently free of defects, that-require little'or no non-destructive inspection. The nearly zero incident of rejection in customer receiving records will greatly reduce inspection costs.
Still a further object of the present invention is to provide a production method for producing large and complex structured components in alloys which are reactive to atmospheric elements in the molten condition and in elevated temperature condition in the solid state. The inventive apparatus provides for vacuum environment and inert gas environment to accomplish this. It is unique in that the reactive metal is not transferred from a melting crucible to mold cavities by ladling, pouring, or through launders, all of which would have to be done mechanically in a vacuum chamber by conventional casting methods.
Another object of the present invention is to provide a mold that is completely submerged in a molten bath,
inside and outside. This may be accomplished either by submerging the mold or by other means such as lifting or lowering the metal. It isobvious that the structure of this divider type mold may be as frail. as handling problems would allow. Now would the frailty of the mold be a problem during the lifting and solidifying stage since the lifting device would be directly attached to the most upper section of the solidifying metal. The mold having completed its purpose of isolating liquid metal in a shape waiting for solidification (which would take place near the surface of the molten metal) could then crumble and fall away or hang to the surface of the cooling form (casting) and eventually be removed mechanically.
A further object of the present invention is to provide a control over solidification rates. This feature will make it possible to successfully restructure molten metal of alloys with short, medium and long freezing ranges into sound useful components.
Another object of the present invention is to provide a novel sonic and ultrasonic impingement directly on increases diffusion and convection in the solidification zone, which reduces the concentration of impurities in grain boundary zones. This unique feature reduces dendrite growth and increases the degree of their branching.
Another object of the present invention is to provide a method for achieving the transformation of liquid metal to solid metal on a single solidification plane. This solidification process progresses in equilibrium, resulting in a crystalline microstructure free of multiphase dendrites surrounded by embrittling eutectic compounds.
Another object of the present invention is to provide mechanically controlled, fully programmed rates of restructuring of metals in accordance with individual configuration characteristics. This feature provides for more accuracy than can be achieved by human skill and provides a method whereby several restructuring apparatus may be operated concurrently, with a minimum of required labor.
A still further object of the present invention is the production of critically structural parts such as airplane wings, flaps, landing gear struts for example, that are produced under process constants so that the product will be associated with wrought metal components with respect to reliability standards whereby the universal application of casting factors to downgrade the material because they are castings are eliminated.
Another object of the present invention is to provide electrical energy through the first solids formed which creates additional activity of the liquid-solid interface wherein the electrical charge breaks up the nonequilibrium formation of solids to a nearly equilibrium state so that benefits. are derived from the microstructure thus formed that exhibit higher mechanical properties than can be obtained in non-equilibrium solidification.
Yet another object of the present invention is to provide a novel method of introducing fiber reinforcement to the forming solids which encompasses a submerged tube entering at the bottom of the mold for introducing a gas that acts as an elevator to carry metallic or nonmetallic fiber or hollow non-reactive inorganic sphere particles to the point of solids being formed in a controlled program manner. When gas is used alone or with fiber an additional stirring action is produced, again aiding the agitation of the semi-solid (mush) zone.
It is a further object of the invention to include means for generating induction currents that stir the fluid metal inside and outside the submerged mold.
BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:
FIG. 1 is a diagrammatic view of one form of the novel apparatus for effecting the restructuring of metals to produce shaped forms in accordance with the present invention;
FIG. 2 is a diagrammatic view similar to that of FIG. 1 illustrating another embodiment of the present invention for effecting restructuring of metal from the molten state to a solid state;
FIG. 3 is a greatly enlarged view, shown diagrammatically, of the plane front or solidification front between the molten material and the solid material which is present in the embodiment shown in FIG. 2; and
FIGS. 4, 5a and 5b are block diagrams illustrating the steps employed in performing the methods set forth by the present invention such'as may be used by the apparatus shown in FIGS. 1 and 2 respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, one form of a novel apparatus for producing precision and high quality shaped forms is shown in which a mold 10 is illustrated in cross-section so as to expose an internal cavity 11 for receiving molten metal via an opening 12. The mold cavity 11 forms a tortuous path through which the molten metal will travel as it fills when such molten metal is poured from a crucible 13 via a pour spout 14. Preferably, the mold is characterized by being composed of a thinwalled structure having an extremely low coefficient of expansion when exposed to great variations in temperature and which providesv high thermal transfer properties permitting the passage of heat through the structure of the mold to an external heat sink or chill means as will be described in greater detail subsequently.
The mold 10 is placed in a vacuum area 15 which is defined by an annular ceramic lining 16 that is encased on the interior of a steel jacket 17. An insulated steel cover 18 is provided with a seal 20 at its connection with the main body of the jacket 17 so that the cover may be readily removed to place the mold within the chamber area 15. The seal 20 is insulated from the hot internal gasses of the chamber 15 by contact between ceramic faces 21 which provides a tortuous path therebetween.
The interior of chamber 15 is connected to a suitable vacuum source 22 via a conduit 23 incorporating a vacuum valve 24. By this means, the area of chamber 15 may be readily evacuated to a desired vacuum level.
The mold is heated in chamber 15 by any suitable means such as by ignited gasses or electrical heating coils. For example, gasses to be ignited may be in troduced to a mixing chamber 25 through a valve 26 while air may be admitted through a valve 27 via a manifold 28 surrounding the mixing chamber 25. Actuation of an electrical switch 30 effects the energization of a spark gap provided in a spark plug 31. When the spark occurs, the combined gas and air in the mixing chamber is ignited which then circulates the heated gas around mold 10. The heated gasses will rise through the chamber-l5 and will be exhausted via vents 32 and 33 when the cover 18 has been removed. Mold heating is performed prior to drawing a suitable vacuum.
Crucible 13 holds a quantity of molten metal which is poised over the mold opening 12. Heat passing around the mold rises and melts the metal in the crucible. When the metal has reached its proper molten temperature, and the mold has also been adequately heated molten metal may be ladled from a separate reservoir and placed in crucible 13 at temperatures ready to pour. As an alternative, valves 26 and 27 are turned off to stop the flow of gas and air. However, when electrical coils are used for heating, these will remain on. After the mold and crucible have been sufficiently heated, cover 18 is placed on seals 20 and vacuum source 22 may be applied to chamber 15 by opening valve 24 and pump-down of the chamber ensues to enclose the molten metal in an evacuated chamber with the heated mold. A vacuum probe 34 provides an indication of air pressure within the chamber and when the proper and desired vacuum has been achieved, a crank handle 35 is turned so as to pour the contents of crucible 13 into opening 12 and into the mold cavity 11.
The vacuum condition within chamber 15 is maintained briefly and then air valve 27 is opened to admit atmosphere to the chamber. Cover 20 remains on the chamber and the mold is slowly lowered from the heated area of chamber 15 into a chill section 36. The chill section is enclosed in a steel jacket 37 supporting the vacuum chamber and in sealed relationship therewith by means of an annular seal 38. However, if desired, the chill section may be an open area where air or gas cooling may be employed. A piston unit 40 reciprocally moves through the chill section 36 and includes a ceramic platform or cap 41 which supports the mold 16 in the chamber 15. The piston unit moves through the chill section 36 on a stabilizing bearing 42 secured on the bottom of the steel jacket 37. Suitable means are employed for moving the piston unit such as actuator 43 for operating a rack and pinion mechanism for example.
Cold air under pressure passes through a valve 44 from a suitable source into an annular manifold 45 via conduit 46 and is dispensed from a plurality of dispensing orifices 47 in a peripheral air jet pattern encircling the area through which the mold must pass as the piston unit moves down. This chilling air blast is directed to strike the mold in a defined line about its periphery. As the mold is continuously lowered to the maximum position as shown in broken lines by the numeral 48, it has passed at a controlled speed (depending on mass) through this air blast of cold air which chills the mold and causes progressive crystallization of the molten metal in the cavity 11 from the bottom upwardly. This crystallization effectively produces the normal metal shrinkage, but because of the defined line of solidification that is occurring, liquid from the upper portion of the mold feeds the shrink as crystallization occurs.
Temperatures within the heated chamber will be sufficient to melt or maintain the molten metal in a molten state. The temperature of the air applied to the mold in the cooling chamber 36 can be ambient air, refrigerated air, or air in which the moisture content is controlled to produce an evaporative cooling effect as it strikes the mold itself. The purpose of the cooling chamber is to function as a heat sink for the cooling of the mold and can perform in a variety of ways, other than the system illustrated. It is conceivable, for example, that a molten metal bath could exist in this chamber, utilizing a metal of lower temperatures than that employed in the mold itself. Gradual immersion of the heated mold in this bath of lower temperature metal will accomplish the solidification in a well defined line on a gradual basis in a similar manner as the air jets shown in the preferred form. Obviously, such a molten metal heat sink bath may require some form of temperature control as the lowering of the mold into the metal would raise the temperature substantially.
Other forms of heat sinks may be used such as powdered or shaped copper, powdered aluminum, or any powdered or crystalline form prepared expressly for this purpose and selected with respect to its heat transfer properties and melting temperature. Such powders employed in a fluidized bed may provide effective heat transfer properties to accomplish the identical purpose as that performed by a liquid heat sink or by the application of cold air. The intimacy of mold surface and the surrounding medium, whatever its nature, may effectively determine the time required to exchange temperature from the mold to the heat sink. The high temperature area of this chamber can function at any desired temperature suited to the material being employed for the production of the casting. The same applies to the cooling area and the material contained therein. For various effects and controlled conditions, it may be desirable to have this material at an elevated temperature, or at a temperature lower than ambient temperature.
Significantly, experimentation has shown improvement in the strength of materials formed using the techniques of the present invention in fine dendrite arm spacing, fine eutectic distribution and the intricate branching of dendritic formation. Mechanical properties are improved, the homogeneous uniformity is vastly improved, and there is an apparent crystalline tightness that is particularly valuable in thin cross-sectional configurations and complex designs where high strength is essential because of minimum metal content.
The inventive concept includes a modification of the embodiment shown in FIG. 1 wherein the introduction of hot air into chamber 37 is made for the purpose of maintaining a liquid metal condition inside the mold and creating controlled solidification by chilling and followed by lifting the shell into a cooler upper chamber. This is a faster method although less desirable because it creates a broader solidification zone. The fill metal will find its way into the cavity by conventional means or by a leveling bottom entry where a ceramic ball-cock arrangement is employed wherein a ball will float up during metal entry and reseat by metal pressure upon removal.
Referring now to FIG. 2, another embodiment of the present invention is shown in which a tub or container 60 is supported on a block 61 resting on the bottom of an open furnace 62 so that the container is substantially surrounded by the upright wall 63 defining the furnace. The container is filled with molten metal 64 by suitable means which substantially fills the cavity of the container so that a liquidous surface 65 is disposed a short distance from the entrance to the container. A shell divider, hereinafter referred to as mold 66, similar in characteristics to the mold 10 described with respect to the embodiment of FIG. 1, is immersed into the liquidous metal 64 and is supported therein by means of a reciprocating device 67 having a tapering termin ating end 68 adapted to be fixed to an upper portion 70 of the mold 66. Terminating end 68 may be fixed to the mold by any suitable means so that the mold will downwardly depend from the device 67 in complete submergence in the molten metal 64. In one form, securement is achieved by means of wires 69 integrally formed at one end with the top of the mold and by their opposite ends to a metal chill bar 86. Spacing between the .container and the furnace sidewall provides a combustion or heating chamber 69 exposed to atmosphere at its upper end by suitable venting.
It is to be noted that the bottom of the mold 66 includes an orifice opening or port 71 through which the molten metal may enter into a mold cavity 72 defined by the sidewalls of the mold 66. To illustrate the adaptability of the present invention, it is seen that mold 66 includes a core 73 so that it is to be understood that complex castings or formed parts can be fabricated The reciprocating device 67 is carried on a housing 82 having a hydraulic motor and pump drive means 83 for reciprocally moving the device in a vertical direction. The device includes a piston 84 carried on the upper end of shaft 84' which may be suitably attached to a vibrator 85.
The opposite end of the reciprocating device 67 from its end driven by hydraulic motor 83, is provided with a metal chill bar 86 fixedly located immediately behind tapered portion 68. To effect maximum controlled cooling, the major length of the device 67 is provided with a continuous passageway 90 through which cool by the present method and apparatus. Inasmuch as the mold 66 is submerged within the liquidous metal, the metal will flow into the cavity 72 up to the terminating end 68 of the device 67 so that the cavity is completely filled with molten metal. Passageways 87 provide suitable venting during mold cavity fill. In this manner, the sidewalls of the mold separate or divide the molten metal within the cavity 72 from the surrounding molten mass. Because of this feature, the mold 66 is not a mold such as commonly employed in conventional casting practices.
Heat radiating from the sidewall 63 and the bottom of the furnace sufficiently heats the container 60 so that the metal 64 is maintained in a molten state. Electrical resistance heating of the sidewall is effected by coil 63 energized by a power source 92. The molten metal, in turn, aids in heating the mold 66 so that a uniform temperature in the container, mold and the metal may be maintained. As a consequence, there is a minimum of metal disturbance due to extraneous conditions. By maintaining this temperature within the mold as a function of molten metal on the outside of the mold itself, there is a minimum mold requirement. The necessity for employing gating or risers is completely eliminated except for the opening 71 which is not considered gating in the conventional sense as defined herein.
The reciprocating device 67 constitutes a piston and cylinder assemblage and is slidably carried on a top plate 74 sealing one end of a chamber body 75 which is mounted on the peripheral edge of the furnace 63 by means of a flange mount 76. The body 75 completely encloses the entrance to the container so that the interior area of the body defined by the annular sidewall thereof, the upper surface 65 of the molten metal and the underside of plate 74 provides a vacuum chamber 77. The vacuum chamber is suitably connected to a vacuum source 78 by means of a conduit 80 and a shutoff valve 81. By this means, the chamber 77 may provide a controlled atmosphere. In one form, circulating cold nitrogen may be introduced to chamber 77 so that the chamber becomes a cold air chamber when it is desired to effect solidification of the captured molten metal within the cavity 72. If desired, heating coils 79 may be located within the vacuum chamber so that the temperature of the chamber may be precisely controlled in the event it is desired to maintain the chamber heated, but at lower temperature than the molten mass.
water, cool air or a selected coolant may be passed under pressure. Furthermore, a toroidal manifold 88 may be located in the vacuum chamber encircling the chill bar and having a plurality of dispensing jets 89 directed to impinge streams of coolant directly on the exterior surface of the mold as it is raised into the vacuum chamber.
A forming or solidification front, as shown in detail in FIG. 3, is present in a zone near the top surface 65 of the molten metal in which the molten metal within cavity 72 adjacent the chill means such the chill bar 86 and end 68 changes state from that of a liquid to that of a solid. Lying in the same plane as the solidification front, there is provided an induction coil 91 which is connected to a suitable electrical energy source 92. The purpose of the induction coil is to provide a magnetic field within the solidification front to create sufficient turbulence in the molten metal at this zone in order to control the solidification front. The turbulence of the metal will cause diffusion in the bulk liquid so that dendrites will either not form or will be restricted in uncontrolled growth.
Another means is provided for establishing turbulence at the solidification front which includes an ultrasonic vibrator 93 adapted to radiate ultrasonic energy to the molten metal 64 within the solidification front zone. Also, vibrator 85 may be employed for the same purpose.
The solidification front provides a sharply defined line of temperature change. This line is represented by the level 65 of the metal in the container and the gradual movement of the mold containing metal past this level into the cooler zone within the chamber 77. This operation is generally conducted at a very slow rate. A crystallizing effect and solidification occurs in the solidification front zone when the device 67 is slowly moved upwardly. By the means and methods shown in FIG. 2, the thermal equilibrium is maintained between the mold material and the metal filling the mold cavity. The complete absence of turbulence during the filling of the mold is experienced, which is a major departure from conventional casting procedures when pouring is employed. The absence of contact with air during the mold filling procedure and the ability to utilize thin shell molds not requiring strength to maintain configurational accuracy is also of great benefit.
The container of molten metal is vacuum degassed by the vacuum chamber which is sealed by the flanged connection 76 or, if desired, by means of submergence of the chamber base slightly into the molten metal such as may be represented by the joining of the body with the upper edge of container 60. Valve 81 connects the vacuum source including a vacuum pump to the chamber 77 and another valve 79' may be employed for connecting the chamber with a supply of gas such as Argon, for example. Harmful gases can be eliminated from the molten metal by the vacuum operation and the vacuum can be replaced with an inert or other beneficial gas without the degassed metal coming into contact with air during the solidification cycle of producing the parts.
The chill bar 86 may be composed of a copper base alloy and when the solidification commences next to the chill, the bar and the attached metal and mold is raised mechanically by the device 67. Preferably, the raising of the device is programmed electronically with respect to the mass and configuration of the formed part. The container, mold and vacuum arrangement are adjustable so that, as the mold is raised, intimate contact of the solidified portion of the form and the molten metal is maintained so that the atmospheric environment is not broken whether it is vacuum or controlled atmosphere.
A unique metallurgical feature of the present metal restructuring system is a very narrow solidification front. This can be described as a three phase condition, as shown in FIG. 3, during the solidification process consisting of molten metal at the bottom, controlled growing or forming of solids in intimate contact with liquid slightly lower than the molten metal surface, and the solid formed part above the second phase. This progression assures extremely short feeding distance with practically no labyrinth of growing dendrites through which liquid metal flows to supply the dendrites and to replace volumetric contraction due to normal shrinkage. This is in direct contrast to the mode of solidification normally practiced in conventional casting methods wherein solidification occurs in various zones over the entire mass, thus making it difficult to achieve 100 percent homogeneity.
It can be anticipated that titanium and other reactive metals can be successfully formed by the'inventive system because of the occlusion of reactive gases; therefore, casting of titanium or any reactive metals can be handled by the present invention.
The inventive concept also includes a modification wherein the metal, having filled the mold as in the apparatus'of-FIG. 2, may be lowered away from the filled mold and the metal within the mold held from draining out by ceramic ball-cock. This liquid metal inside the mold can then be kept liquid by using only the induction electrical field of induction coils 91. This can be accomplished by lowering the container 60 and metal 64 to a lower level and allowing the current created by the induction coils to maintain the fluid condition necessary for controlled solidification. The use of laser beams may be applied, at a controlled intensity, to accomplish control of maintaining a state of liquid metal inside the mold.
The steps for performing the inventive process employing the apparatus shown in FIG. 1 is illustrated in the block diagram of FIG. 4. Initially, a quantity of solid metal which may be an exotic metal type or alloy for example, is placed into the crucible 13 and is heated (90) to a sufficient temperature within an overall range between l-4,000 Fahrenheit by the combusted gas heat' generated in mixing chamber 25 to melt the source material. During this initial step, the cover 18 is removed so that chamber 15 is vented to atmosphere. During thisheating stage, the mold 10 is heated to a sufficient temperature within the 500 Fahrenheit of the molten source material temperature compatible with accepting the molten metal from the crucible. After heating, the cover 18 is secured in place to enclose 15 which is then evacuated (92) within the range of 100-5 microns of mercury by means of vacuum source 22 via valve 24 so that a sufficient vacuum surrounds the mold and crucible. If desired, an inert gas may be introduced into chamber 15. Next, handle 35 is rotated so that molten metal pours (93) from spout 14 of the crucible into the opening 12 of the mold so that the molten metal is transferred into the mold cavity 11. Next, actuator 43 is energized to move the piston unit 40 in a downward direction which causes the bottom of the mold to pass into the cooling chamber 36. As the bottom of the crucible enters chamber 36, it is directed past the cooling jets 47 which effects the solidification of the molten metal within the mold cavity by applied chilling (94) from ambient temperature to minus 60 Fahrenheit, for example. The solidified metal supports the molten metal on top thereof until additional molten metal is solidified as the mold moves downwardly past the cooling jets. By this means, the solidification of the molten metal is controlled in a gradual manner while permitting gravity to feed the crystal formation within the mold cavity itself through the continuous availability of molten metal above so as to eliminate (hot shorting) fracturing within the mold cavity. Finally, the mold is completely positioned in the cooling chamber 36 where the solidified metal within the mold cavity is allowed to cure by cooling (95) to ambient temperature for example. Upon removal of the mold from the apparatus, the mold surrounding the solidified material may be readily broken away so as to expose the completed and form ed part having the form and configuration of the mold interior.
Referring now to FIG. 5a, the steps for performing the process employing the apparatus shown in FIG. 2 is illustrated in connection with the use of reactive materials. Initially, a vacuum is created within the range of 100-5 microns of mercury within chamber 77 by vacuum source 78 via valve 81. Next, a quantity of source material metal is melted (101) by the furnace heat within the range of 100 to 4,000 Fahrenheit to its molten state within the confines of the container 60. When the metal has become completely liquidous, sur face 65 will be established as the bottom of the vacuum chamber 77. Next, the piston and cylinder assemblage 67 carrying the shaped mold 66 in a preheated condition (102) within 500 Fahrenheit of the molten source material temperature is immersed (103) by being lowered through the chamber 77 into the molten metal causing the metal to flow into the mold cavity via orifice opening 71. When the member 67 has been completely lowered, the metal will have completely filled the mold cavity and the shell mold functions as a means for separating the cavity from the surrounding molten mass. After the cavity has been filled, the mold is heated further by conduction from the molten metal so that thermal equilibrium is produced. If desired, the vacuum may be replaced by inert gases, such as argon or helium, so as to facilitate rapid transition to the solid at the liquid/solid interface. This modified step is represented by controlled environment block (104). Next, the molten metal near the top of the cavity is agitated (105) by means of the ultrasonic vibrators 85, 93 or the induction coil 91 so that the molten metal near the surface 65 is thoroughly stirred. While the metal is being agitated, chilling is commenced (106) such as by circulating coolant via passageway 90 and the member 67 is raised (107) so that the mold gradually breaks through the surface 65 into the vacuum chamber. The temperature gradient between the relatively cooled chamber 77 augmented by the coolness of the chill bar 86, which is cooled by means of coolant passing through passage 90 and secondary cooling jet ring 88 with respect to the heated molten metal in the crucible, commences solidification of the molten metal within the cavity near the surface level 65.. As the mold is drawn into chamber 77, the molten metal in the cavity becomes solidified progressively. The temperature of the chamber is controlled (108) from room temperature to minus 60 degrees Fahrenheit for example by the. electrical resistance heating or coolant conducting coils 79 as long as the temperature is maintained below the temperature of the molten metal. When sufficiently cooled, the vacuum of chamber 77 may be broken (109) and the walls of the mold broken away (1 Once solidification has started in the mold, the mold is raised, depending on the mass being molded, at a speed no greater than the ability of the solid metal to form new solids and the new solids, in turn, form more solids and so forth.
As may be readily observed, the heat sinking methods such as circulating cold fluids or cold air or gases through the solid chill bar, also applying cold air or gases directly on the exposed mold thus dictating the heat gradient between the liquid and solid state of the molten metal within the mold cavity. The undesirable heat radiating from the metal mass may be controlled, if needed, by floatinglight-weight or pre-formed refractory globules on the surface of the metal mass. This final phase permits the metal in the main cavity to supply itself with the replacement metal required during solidification from the lower portions of the cavity, not part of the main cavity section and it, in turn, will draw from the main mass of metal since the crystals of solidifying metal are emerging up through the surface of the molten mass in shapes dictated by the metal dividing action of the mold walls, not necessarily by the pressure containing vessels used conventionally by those skilled in the art of foundry practices. For this reason, the structure of the mold, functioning as a divider, may be as frail as handling will allow, nor will the frailty of the mold be a problem during the lifting and solidifying stage since the lifting device may be directly attached to the most upper portion of the solidifying metal. The mold, having completed its purpose of isolating liquid metal in a shape in preparation for solidification, which takes place near the surface of the molten metal, may then crumble and fall away or hang to the surface of the cooling form and eventually be removed mechanically.
Where a condition of vacuum or controlled atmosphere is required before, during and after removal of the mold from the metal mass, such as when titanium or other reactive metals are employed, a simple chamber-like device capable of containing the mold and withstanding the temperature of the metal can be positioned in such a fashion as to make direct contact with the metal mass. Thereby, a positive vacuum seal is maintained. An alternate method is possible by lowering a pressurized cylinder into the metal mass, displacing the internal metal until, at a desired time, it is allowed to rise in and around the mold previously positioned in the cylinder. By repressurizing the chamber with an inert gas, the metal is caused to recede at a predetermined rate which would satisfy the feeding requirements of the solidifying metal inside the mold. This method ensures that all metal going into the mold is the more preferred bottom metal and it also offers a second method for withdrawing the mold from the metal by pressurizing the metal to a lower level. Obviously vacuum can be used to draw the metal into the chamber containing the mold as the chamber is being lowered into the metal mass. The rate of descent of metal mass can be controlled by the lessening of vacuum by control of inert gas supplied.
Referring now to FIG. 5b, the steps are shown for restructuring non-reactive materials which commence by melting (111) the source metal within the temperature range of from l00-4,000 Fahrenheit, pre-heating (112) the mold to a temperature within 500 Fahrenheit of the molten source material temperature and immersing (113) the heated mold into the molten metal. The steps are similar to those previously described with respect to the processing of reactive metals. Next, a vacuum is drawn (114) of from -5 microns of mercury followed by stirring (115) of the molten metal within the mold cavity. Particularly, agitation is performed near the surface level of the molten mass. The molten metal adjacent the chill means is chilled (116) at the solidification zone and as the molten metal solidifies, the solids are raised (ll7 into the cooler environment of the chamber under controlled temperature (118) conditions. Once cured in the cooler environment of the chamber, the vacuum may be broken (119) and the wall of the mold broken away (120).
lt is to be understood that in another form of the invention, the mold may remain in the surrounding liquidous metal and that only the solid form restructured in the solidification zone will be raised into the cooler chamber. In this instance, the wall of the mold will not be present and therefore, break-away eliminated.
By the above methods and apparatus, it will be seen that a greatly improved system is provided for the forming of metals in a heat conductive mold of heterogenous structure, that this method can result in great economies in metal forming techniques in general, will result in an improved product with better structural characteristics than is presently the case where heat transfer is not uniformly accomplished, and is dependent on the employment of conventional gating procedures.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to coverall such changes and modifications as fall within the true spirit and scope of this invention.
What is claimed is:
1. Apparatus for restructuring metals for producing shaped forms by transforming metal in a fluid molten state to a solid state comprising:
a container for holding a body of molten metal having an exposed surface level;
means surrounding said container below said surface level for heating said container and said molten metal;
a divider type mold having an internal cavity open at its opposite ends and disposed in said body of molten metal so that its uppermost opening is substantially adjacent said surface level and said lower most opening conducts molten metal into said cavity whereby molten metal within said cavity is separated from the surrounding molten metal mass except for the presence of said molten metal in said lowermost opening;
a chill means including a chill bar disposed over said surface level in alignment with said uppermost mold opening and adapted to engage with said molten metal within said cavity at said surface level thereof;
means for moving said chill bar into engagement with said molten metal within said cavity and for drawing said chill bar with said molten metal after solidification from said body of molten metal;
said chill bar being of lower temperature than the temperature of said molten metal whereby solidification of said molten metal within said cavity occurs upon engagement therewith; and
divider type mold composed of temperature sensitive material effective to break away from said solidified metal as it separates from said surface level.
2. The invention as defined in claim 1 including a bond established between said chill bar and said solidified metal so that said solidified metal is attached to said chill bar and further a heat sink is provided in addition to said chill bar for effecting solidification of 5 said molten metal adjacent thereto.
3. The invention as defined in claim 1 including means releasably securing said mold to said chill bar.
4. Apparatus for restructuring material to produce a shaped form comprising:
a body of molten source material having a surface level;
a divider type mold having an open-ended internal cavity immersed in said molten source material body so as to separate a portion thereof which occupies said internal cavity and is divided from the mass of said molten source material body;
cooling means supported above said surface level operable to selectively engage said separated portion approximately at said surface level;
said cooling means being of lower temperature than said confined molten source material whereby said material at the interface of engagement with said cooling means will be characterized thereby having established therein a solidification front adapted to transform or convert the state of said molten separated portion to a solid form having the congruent shape of said internal cavity; means operably connected to said cooling means for moving said solid form away from said surface level at a pre-determined rate so that said solidification front progressively moves along the entire length of said separated portion of said molten source material; and said divider type mold is composed of temperature sensitive material effective to break away from said solidified metal as it separates from said surface level.