US3381742A - Metal casting and solidification - Google Patents

Description

May 7, 1.8

H. GREENEWALD, JR

METAL CASTING AND SOLIDIFICATION 4 Sheets-Sheet 1 Filed June 23, 1967 INVENTOR.

HERBERT GREENEWALD, JR.

ATTORNEY y 1968 H. GREENEWALD. JR 3,381,742

METAL CASTING AND SOLIDIFICATION Filed June 23, 1967 4 Sheets-Sheet 2 HERBERT GREENEWALD, JR.

y 1968 H. GREENEWALD, JR 3,381,742

METAL CASTING AND SOLIDIFICATION Filed June 23, 1967 4 Sheets-Sheet 5 ZIO INVENTOR. HERBERT GREENEWALD, JR.

ATTORNEY y 7, 1963 H. GREENEWALD, JR 3,381,742

METAL CASTING AND SOLIDIFICATION Filed June 2s, 1967 4 Sheets-Sheet 4 INVENTOR.

HERBERT GREENEWALD, JR.

ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE This invention pertains generally to metal casting and solidification, and particularly concerns methods and apparatus having demonstrated utility in connection with the forming of comparatively-large, defect-free, thin-walled, precisely-dimensioned castings from molten alloys and the like in controlled environments.

Cross-references This application is a continuation-impart of pending application Ser. No. 508,318, filed Nov. 17, 1965, now abandoned, and assigned to the assignee of this application.

Summary of the invention Basically, the instant invention involves use of a refractory-like casting mold that is heated in a controlled environment prior to metal casting to an elevated temperature which is related to the alloy liquidus temperature and the alloy pouring or casting temperature and which is dependent on the super-cooling characteristics of the metal composition. After the pre-heated mold is filled with molten metal, controlled cooling in a novel manner is utilized to develop particularly desired .direction and rate of metal solidification front progress and also to enable molten metal to be maintained in a fluid condition from a gate region, through thin mold cavity sections, and to any metal solidification front located at relatively lower and comparatively thicker casting sections to obtain a defect-free casting without nee-d of a gate and riser arrangement. The instant invention has been utilized in connection with the casting, in a vacuum environment, of molten conventional aluminum casting alloys to form components having a missile nose section configuration with wall thicknesses of approximately 0.040" throughout substantial surface regions. The invention has also been utilized in connection with the casting, in a controlled inert and non-vacuum environment, of heat-treatable, high strength aluminum alloys to form thin-walled components of aircraft quality having typical airframe structural member size and configuration characteristics. As used in this application, the term thinwalled has reference to casting configurations having a Shape Factor, as established by the American Foundrymens Society, substantially greater than approximately 100. The Shape Factor is defined as the ratio between the projected area and the average thickness of the casting configuration.

Description" 0 the drawings FIG. 1 is a schematic front elevational view, partially in section, of a composite vacuum casting unit having one embodiment of apparatus for practicing this invention incorporated therein;

FIG. 2 is a similar view, but from a side elevation, of the vacuum pouring equipment and mold assembly included in the unit of FIG. 1;

FIG. 3 is a plan view of the mold assembly illustrated in FIGS. 1 and 2;

FIG. 4 is an elevational view of the mold assembly incorporated in the vacuum casting unit of FIG. 1 showing apparatus operation in connection with the ejection of a completed vacuum casting;

FIG. 5 is a sectioned perspective view of portions of the mold assembly of FIGS. 1 through 4 illustrated in exploded relation to portions of a casting produced therein;

FIG. 6 is a sectioned elevational view of the components shown in FIG. 5 in engaged relation;

FIG. 7 is a plan view of the interior of a portion of the completed casting of FIGS. 4 through 6;

FIG. 8 is a sectional view taken at line 8-8 of FIG. 7;

FIG. 9 is a schematic elevational view of an alternate molding unit embodiment that may be utilized in the practice of the instant invention in connection with the casting and solidification of molten heat-treatable, highstrength aluminum alloys;

FIG. 10 is a schematic illustration of a control arrangement for the heating/cooling means incorporated in the apparatus of FIG. 9;

FIG. 11 is a perspective view of a thin-walled casting for aircraft structural member applications and cast and solidified from a heat-treatable, high-strength aluminum alloy using the apparatus of FIGS. 9 and 10;

FIG. 12 is a sectional view of still another embodiment of apparatus for practicing the instant invention; and

FIG. 13 is a schematic illustration of a control arrangement for the heating/cooling means incorporated in the apparatus of FIG. 12.

Detailed description A composite unit for practicing the instant invention in connection with the vacuum casting of molten metal such as a conventional aluminum casting alloy is illustrated schematically in FIG. 1 of the drawings and is referenced generally by the numeral 10. Such unit is basically comprised of vacuum pouring equipment 11 and joined vacuum molding equipment 12. A valve assembly 13 is provided for selectively functionally isolating equipment assemblies 11 and 12 from each other.

Vacuum pouring equipment 11 is basically comprised of a housing and an interiorly-located melting/pouring crucible assembly. The equipment housing is comprised of 'body portion 14 and cover portion 15 secured to such body portion in vacuum-sealing relation. Cover 15 is provided with an inlet 16 and body portion 14 with an outlet 17 for use in charging and subsequently discharging metal into and from the interiorly-located crucible assembly. Although inlet 16 is illustrated in the drawings as having attached removable cover 18, such inlet 16 in normal practice preferably cooperates through a valved connection with a furnace that supplies metal in molten form to the crucible assembly in pouring equipment 11. If the metal to be cast by vacuum pouring equipment 11 can be conveniently charged into the crucible assembly in solid form, melting may be accomplished by use of the hereinafter-described indirect arc electrodes. The housing of equipment assembly 11 basically functions to maintain the interiorly-located crucible assembly in a vacuum environment. Such vacuum environment, if utilized in connection with the processing of conventional aluminum casting alloys or other metal alloys not subject to element depletion in the molten condition at reduced ambient pressures, generally is maintained at absolute pressure levels less than 800 microns of mercury.

The basic component of the melting/pouring crucible assembly of equipment 11 is a refractory crucible 19 having a substantially spherical interior cavity; such crucible is preferably contained by the housing comprised of body portion 20 and attached cover portion 21. A top opening 22 passes through cover portion 21 and crucible 19 to the spherical cavity and is for admitting metal to the crucible interior and more importantly for controlling, through an appropriate size limitation, the rate of discharge of contained molten metal whenthe crucible is inverted. For most known applications, the ratio of the crosssectional area of opening 22 to the maximum cross-sectional area of the spherical cavity of crucible 19 must be in the range of 1:25 to 1:3 to obtain with this invention those discharged molten metal stream characteristics considered desirable for repeatedly producing defect-free, comparatively-large, thin-Walled castings, at least of the type shown in the drawings.

Apparatus 11 also includes a water-cooled hollow arm 23 that is connected to housing body 20 and that serves for supporting crucible 19 and also for accomplishing rotation of crucible 19 to an inverted position for molten metal pouring. The longitudinal axis of arm 23 preferably passes through, or very close to, the centroid of the spherical interior of crucible 19. (Such centroid also preferably very nearly coincides with the center of gravity of the crucible 19 and housing 20, 21 combination.) Arm 23 cooperates with a conventional bearing bushing 24- and such bushing in turn is retained by bearing block 25. Bearing components 24 and 25 are carried by brackets 26 connected to housing body 14. A sprocket 27 is rotationally connected or keyed to arm 23 and is used to cause rotation of crucible 19 (and housing 20, 21) to an inverted position for metal pouring. Details with respect to a preferred form of actuating mechanism for rotating sprocket 27 (and arm 23) are shown in FIG. 2.

Equipment 11 is provided with metal heating/melting means having conventional graphite electrodes 28 and 29 that are reciprocable within crucible openings 30 and 31. The axes of openings 30 and 31 are aligned with the iongitudinal (rotational) axis of support arm 23. The molten metal within crucible 19 is referenced as 32. It is preferred that electrodes 28 and 29 not be immersed in metal 32 during maintained operation of the heating/melting means. Thus, charged metal is heated/melted in a vacuum environment by radiation primarily and not by conduction. Important operating advantages relating to stabilized metal heating/melting energy and power requirements and stabilized electrode spacing requirements are obtained in this manner. In one instance, electrode apparatus similar to that shown in the drawings has been operated in a vacuum environment for a periodof time of approximately one hour to heat molten conventional aluminum casting alloy without requiring electrode spacing adjustment. Water-cooled electrode holders 33 and 34 support electrode elements 28 and 29 in a conventional manner and are engaged with leads 35 and 36, respectively, of an electrical energy supply (not shown) Electrical supplies of 500 ampere and volt (alternating current) capacity have proved satisfactory in connection with the practice of this invention in several applications.

Each electrode holder (33, 34) is carried by a pair of posts 37secured to housing body 14 and in turn by a cooperating support plate 38. An actuator 39 is provided to advance/retract its related electrode holder to control the position of the tip of the associated electrode within the interior of crucible 19. In the FIG. 1 arrangement, a conventional pneumatic accumulator 40 having a rod portion connected to an electrode holder, flow control valve 41, and control valve 42 combination are provided for regulating electrode position. Such apparatus is normally connected to a compressed air supply line such as 43.

Several services of a utility nature are provided for unit 11. First, cooling water supply andreturn lines 44 and 45 are provided in flexible form and serve to conduct cooling water to and from the hollow interior of support arm 23. Similar flexible cooling water supply and return lines 46 and 47 are provided outside housing 14, 15 for cooling each of electrode holders 33 and 34. Flexible line 48 is provided within the housing for conducting an inert gas, chemically compatible with molten metal 32, from a supply outside of unit 11 to the interior of crucible 19 for agitation and metal degassing purposes. Flexible thermocouple leads 49 are connected to conventional sheathed thermocouple 50 immersed within molten metal 32. Each of the service lines illustrated in FIG. 1 passes through the wall of housing 14 in a vacuumsealing manner.

The interior of pouring unit 11 communicates with conventional vacuum-producing equipment (not shown) through the inlet designated 51 by means of vacuum line 52 and selectively operable valve member 53. A similar valve 54- serves to operably connect vacuum line 52 to the inlet opening 55 of molding unit 12.

As shown in FIG. 2, the preferred embodiment of apparatu 10 includes a chain 56 for operably driving sprocket 27 and arm 23. Rods 57 and 58 pass through vacuum seals 59 and 60 to the exterior of housing 14, 15 and are interiorly connected to opposite ends of chain 56. Rods 57 and 5'8 are essentially the rod elements of conventional actuators 61 and 62. Depending on desired direction of rotation, such actuators are alternately connected by valve 63 to the pressurized air supply line designated 64-. By use of the illustrated interconnection between actuator cylinders and valve, rods 56 and 57 may be moved in opposite directions to rapidly rotate sprocket 27 and support arm 23 and thereby invert crucible 19 to pour contained molten metal into vacuum molding unit 12 as hereinafter-described. It is generally necessary that the crucible assembly in unit 11 be rotated at angular rates above approximately 180 per second to obtain satisfactory pouring for comparatively-large, thin-walled aluminum castings. In one embodiment of this invention an average rotational rate of approximately 600 per second has been found both desirable and readily attainable.

Vacuum molding unit 12 includes a housing consisting of both body and removable cover 71 and also a mold assembly positioned interiorly on block 72. Leg members 73 support block 72 on the equipment interior bottom. A water-cooled chill plate 74 with serpentinelike cooling coil 75 attached thereto at the underside in heat transfer relation rests on spacers 73 positioned on block 72. Mold 77 in turn rests on the insulating medium 78 that overlays chill plate 74. Medium 78 may have the specific form of layers of asbestos material as shown in FIG. 6. Mold 77 is rigidly secured to block 72 by means of hold-down plate 79 and cooperating tie rods 80. A hollow mold core 81 is located within mold 77 and is clamped and maintained in position by rotatable arm 82. Details regarding suitable compositions and methods of manufacture for molds and for mold cores thatmay be advantageously utilized in the practice of this invention are provided in co-pending application 'Ser. No. 498,046, filed Oct. 19, 1965 and assigned to the assignee of this application. Arm 82 is supported at rotational axis 83 and is actuated by cylinder 84 and its projecting rod 85. An electrical resistance mold heater 86 engages the exterior of mold 77 and is connected to leads 87 and 88 of an electrical supply (not shown). The mold assembly in apparatus 12 is further provided with a water-cooled exterior jacket 89 that minimizes outward radiation of heat during mold heating by element 86. Also, a water-cooled chill block 90 is positioned in the mold assembly to close out the bottom of the mold interior metal-receiving cavity and is located in spaced-apart relation to both mold 77 and chill plate 74 to eliminate heat transfer therebetween by conduction. See FIG. 6. Chill block 90 is connected to and moved by actuator 91 through rod member 92 for accomplishing ejection of the completed casting from within mold 77. However, component 90 is provided primarily for controlling the directionality of metal solidification in the mold assembly.

Several utility services are provided to the components located within unit 12. Pressurized hydraulic fluid supply line 93 and return line 94 are provided for operating ejection actuator 91. Similar supply and return lines 95 and 96 cooperate with clamping actuator 84. Cooling water supply and discharge lines 97 and 98 cooperate with cooling coil 75 at the underside of chill plate 74. Cooling water supply and discharge lines 99 and 100 are preferably flexible, pass through appropriate passageways in block 72, and serve to furnish cooling water to the internal passageways of piston-driven chill block 90. Cooling water supply and discharge lines 101 and 102 function to furnish cooling water to mold jacket 89. The electrical supply lines to terminals 87 and 88 are designated 103 and 104, respectively. As in the case of unit 11, all utility services to unit 12 pass through the Wall of body 70 in vacuum-sealing relation. Also, the vacuum environment within the interior of molding unit 12 is generally maintained, by means of the hereinbefore-referenced vacuum-producing apparatus, at absolute pressure levels less than approximately 2,000 microns of mercury; during the casting of certain molten aluminum alloys such as conventional 356 aluminum casting alloy or other molten alloys not subject to element depletion by vaporiz ation into a mold assembly similar to that comprised of components 72 through 90, vacuum conditions of approximately 800 microns of mercury (absolute) have been found entirely satisfactory.

The valve assembly 13 which functionally connects vacuum pouring equipment 11 to vacuum molding equipment 12 includes a pneumatic actuator 105 connected by lines 106 and 107 to a directional control valve (not shown). As in the case of equipment assemblies 11 and 12, details with respect to control valve connections, construction, and operation are not shown in the drawings. Such details are considered to be entirely within the capability of persons reasonably skilled in the related arts.

The valve element of assembly 13 is actuated to an open condition for metal casting in unit 10. FIG. 2 illustrates, by a broken line notation, the outline configuration 109 of a molten metal charge 32 being east through open valve assembly 13 into aligned mold 77. Molten charge 109 is cast from crucible 19 into mold 77 without having any imparted motion components acting transverse to a vertical casting direction. Mold 77, accordingly, receives metal from a vertical direction that coincides the outlet axis of opening 22 when crucible 19 is in an inverted condition. The casting force imparted to mass 109, and the related casting time, is determined by the height H. In the case of the hereinafter described thinwalled aluminum alloy castings, a height H of approximately 4 feet has been found satisfactory for developing acceptable completed castings in a vacuum environment.

FIG. 4 of the drawings illustrates a complete casting 110 being ejected from mold 77 by means of cylinder 91 following metal solidification. A portion of casting 110 is cut away to show the interior location of core 81. De-

tails with respect to the configuration of the lowermost portion of casting 110 and cooperating mold assembly portions are shown in further detail in FIGS. 5 through 8.

Completed casting 110, in the embodiment of the drawings, has a chill base portion 111 that is connected to the casting principal wall section by nlnners 112.. Such chill base and runners, which may be subsequently removed from the completed casting if serving no functional purpose, are provided to develop metal solidification directionality. In the case of configurations similar to that of component 110, at least, such cooling directionality is provided because it is in part required that molten metal be flowed through a comparatively thin section to solidifi cation front locations in the comparatively thick lower casting section shown by the figures. Mold 77 has an inwardly-projecting core support 113 that is intermittently severed by Openings 114 and that cooperates with an underside mating surface of core 81. The lowermost surface of core 81 is spaced apart from chill block 90 and the vertical separation defines the upper and lower limits of chill base 111. The runners designated 112 are formed by metal solidification within the regions of openings 114. In the equipment arrangement of FIGS. 1 through 4, no provisions are made for a conventional casting riser or sprue. However, excess metal is cast into the annular gate of the upper region of mold 77 (FIG. 4) so that solidified metal will exist in regions above the uppermost actual configuration limits of the desired casting.

Although not shown in the drawings, it is preferred that vacuum molding equipment 12 be provided with conventional ambient air-to-vacuum interlock and material transfer devices in order to facilitate removal of completed castings 110 from the equipment interior without having to completely destroy the vacuum environment developed therein. Such devices are also utilized in practice for placing successive new cores in mold 77 for use in producing additional castings.

Several details with respect to particular characteristics of equipment 12 are worthy of separate notice. First, mold 77, for the purpose of casting aluminum alloys and particularly if a limited number of castings of a given configuration are required, may advantageously be constituted of dense, fine-grained graphite in a fully-graphitized condition. One particular material that has been found useful is available from Union Carbide Corporation under the designation ATJ. This material has a specific gravity of 1.85 with grain sizes not exceeding 6 mils. Although not all materials possibly suitable for constructing mold 77 have been investigated, it has been determined that gr-aphite s having specific gravities of approximately 1.45 or less are generally unsatisfactory because of excessive porosity.

Mold heater 86 is utilized to heat mold 77 (and core 81) in the vacuum environment of equipment 12 prior to metal casting. The exact mold temperature is determined with reference to the super-cooling characteristics of the alloy being cast. In the case of conventional aluminum casting alloys, for instance, it is generally preferred that mold 77 be heated to a temperature in the range of 800 F. to 1000 F. prior to met-a1 pouring; such preferred mold temperature is in the general range of 0.8 to 0.9 the molten metal pouring temperature. As disclosed by my copending applications for U.S. Patent Ser. Nos. 614,- 837 and 614,838, filed Feb. 9, 1967, the preferred mold temperature must be above the alloy liquidus temperature in some instances; in the case of casting heat-treatable, high-strength aluminum alloys, and because of a reduced range of super-cooling, the preferred mold temperature (1200 F., minimum) is greater than the general 0.9 upper limit value for the alloy pouring temperature for conventional aluminum casting alloys in relation to the minimum alloy pouring temperature (1250 F.). It is anticipated that the mold pre-heat temperature preferred for the super-cooling characteristic of alloys in the general family of nickel-cobalt alloys might be to as low as 0.6 to 0.7 the normal alloy casting or pouring temperature. The decimals used in this paragraph are used merely as a guide for roughly comparing Fahrenheit temperatures and do not refer to absolute temperatures.

After the molten metal charge 109 has been cast into the mold assembly, heater 86 is turned off and the alloy directional solidification initiated at chill block 90 is con tinuecl by the continued circulation of cooling water through service lines 99 and 100. Continued circulation of Water through jacket 89 in-part continues to minimize heat radiation and in-part supplements control of directional solidification for the illustrated casting configuration. Also, it is normally preferred that complete casting be ejected from mold 77 and removed from the interior of equipment 12 immediately after metal solidification. In this manner, the cycle time between successive castings may be kept to a minimum. The clearances between chill block 90 and adjacent portions of mold 77 and chill plate 74 are generally minimal and often approximately 0.005" to prevent unwanted direct heat transfer from mold 77 by conduction.

FIG. 9 illustrates molding equipment in an embodiment 200 that may be utilized with slightly-modified pouring equipment 11 for the purpose of casting heat-treatable, high-strength aluminum alloys into comparatively-large, defect-free, thin-Walled casting configurations. The modifications required for pouring element 11 are not shown in the drawings since they essentially involve obvious changes to permit providing a hydrocarbon-free and moisture-free, inert environment, such as high-purity argon, within the equipment housing in preference to a vacuum environment. As previously-suggested, heat-treatable, high-strength aluminum alloys are subject to element depletion when heated to and maintained at elevated temperatures under low pressure conditions. Accordingly, unit 11 is preferably provided with a cooperating source of inert atmosphere that normally is back-filled into the interior of the housing after evacuation by line 52 to a vacuum condition. Also, equipment 200 of FIG. 9 involves a mold assembly for casting aircraft-quality components having a typical airframe structural member configuration with substantial thin-walled web and flange portions.

As shown by FIG. 9, molding unit 200 includes a housing having body 201 and removable cover 202 and also includes a mold assembly 203 supported by the interior surf-ace of equipment bottom 204. A cooling-water chamber 205 closes the bottom of container portion 206 of mold assembly 203 and supports casting mold halves 207 and 208. Mold halves 207 and 203 in the FIG. 9 equipment embodiment are first wrapped or fixed in proper relation to each other as by glass-fibered fabric 209 and are then backed or supported in container 206 in the required joined relation by granular medium 210 such as zircon sand. The interior casting cavity of combined mold halves 207 and 208 in the FIG. 9 arrangement is provided with a thin-walled configuration corresponding to the exterior configuration of aircraft structural member 211 of FIG. 11, such mold interior configuration being oriented in an essentially vertical direction and being joined directly to an uppermost mold gate region 212 without necessarily including an intermediate or cooperating mold riser region. Mold assembly 203 is positioned interiorly of-electrical resistance heating elements 213 through 215 which in turn are positioned within the heat radiation shield formed by water jacket 216. Asbestos layers 217 and 218 are provided in equipment 200 for the purpose of insulatingcontainer 206 and water jacket 216, respectively, from resistance heating elements 213 through 215. Although not shown, container 206 may be provided with suitable attach fittings to facilitate lowering and lifting complete mold assembly 203 into and from body portion 201 after removal of cover 202.

As in the case of the vacuum molding equipment of FIG. 1, various utility services are connected to the functional elements located in the interior of equipment 200. More specifically, water supply line 219 and water return line 220 cooperate with mold cooling chamber 205 and in sealed relation to housing body 201. Electrical power leads 221 through 226 cooperate in pairs with resistance heating elements 213 through 215, respectively. Such electrical power leads also cooperate with housing body portion 201 in sealed engagement. Cooling water is generally continuously circulated to and from water jacket 216 by means of supply and return lines 227 and 228. In addition to the hereinafter-described control arrangement, equipment 200 differs from unit 12 in one further aspect. A gas supply line 229 controlled by valve 230 normally functions to provide an inert atmosphere such as high-purity argon at pressures of of Hg, for example, to the interior of equipment 200 by back-filling after a vacuum has been established for purging purposes by operation of cooperating vacuum line 52 and valve 54.

As shown by FIG. 9, equipment arrangement 200 also includes spaced-apart. thermocouple elements 231 through 233, such elements being a part of the cooperating equipment control arrangement illustrated schematically by FIG. 10. Such elements function to sense the actual moldmetal temperature existing at the mold regions or zones respectively adjacent resistance heating elements 213 through 215. Thermocouple element 231 measures the temperature controlled by heating element 213, thermocouple element 232 is associated with the mold Zone a jacent resistance heating element 214, and thermocouple element 233 in essence measures the temperature of the mold interior cavity portion and joined riser region 212 adjacent heating element 215. As shown by FIG. 10, thermocouple elements 231, 232, and 233 (which elements may be in the form of Chromel-Alumel junctions and leads in stainless steel sheaths) respectively cooperate with convention-al heater temperature controllers 234 through 236. Each of controllers 234 through 236 ccoperates with one of conventional switch assemblies 237 through 239 to regulate the flow of electrical energy (current) to respectively connected resistance heating elements 213 through 215. The arrangement of FIG. 10 in addition includes a programmer 240 that sequentially programs connected controllers 234 through 236 and also controller 241 for water valve switch 242 to achieve the desired directional solidification of molten metal in mold assembly 203. Switch 242 functions, when activated, to open normally closed water valve 243 located in water supply line 219-connected to chamber 205. Thermocouple element 244 (FIG. 10), although not shown in the FIG. 9 arrangement, may be incorporated in equipment 200 to detect the mold temperature at chamber 205; such is connected to controller 241 to achieve proper cycling of water valve 243 during molten metal directional solidification. 7

Details of the program output of programmer 240 for the controllers 234 through 236 and for controller 241 to obtain directional metal solidification in mold assembly 203 may be developed with respect to the specific process parameter values disclosed by my previouslyreferenced co-pending applications concerning the casting of heat-treatable, high-strength aluminum alloys, during the mold heating phase of equipment operation, programmer 240' causes controllers 234 through 236 to establish and maintain a preselected mold elevated temperature, as for instance a temperature in the range of 1200 F. to 1250 F., as sensed by thermocouple elements 231 through 233, prior to metal casting from unit 11. During such mold heating phase of operation, programmer 240 causes controller 241 to maintain switch 242 in an open condition and water valve 242 in a closed condition. When mold assembly 203 has been heated to the preselected minimum elevated mold temperature (and after the mold cavity, including gate region 212, has been filled with molten metal), programmer 240 functions to cause controller 241 to open water valve 243 to initiate directional solidification and to cause controllers 234 through 236 to function in cascade to obtain the desired control of directionality of metal solidification. Specifically, controllers 234 through 236 control directionality of metal solidification in response to temperatures sensed by thermocoupled elements 231 through 233 to obtain solidification front progression from metal-mold portions adjacent to chamber 205 to metal-mold portions adjacent gate region 212, such in-part being accomplished by maintaining a minimum temperature (for instance, in the range of 500 F. to 600 F.) in sequential mold positions during directional solidification. Initially, controller 234 opens switch 237 until such time as the mold temperature sensed by thermocouple element 231 reaches the pre-set minimum temperature through the cooling influence of chamber 205; thereafter, controller 234 cycles switch 237 to maintain the preselected minimum temperature in response to temperature changes sensed or detected by thermocouple element 231. When controller 234 commences its cycling of heater 213, controller 235 functions to open switch 238; when the mold region adjacent element 232 reaches the preselected minimum temperature, controller 235 then cycles heating element 214 in response to the temperature condition sensed by thermocouple element 232 to maintain the same preselected minimum temperature. When controller 235 commences cycling heater element 214 at the minimum temperature, programmer 240 causes controller 236 to open switch 239 thus permitting the mold region that includes gate portion 212 to cool last to the prescribed minimum temperature. When the minimum temperature of 500 F. to 600 F. is achieved and sensed by thermocouple element 233, directional solidification of the alloy in mold assembly 203 is normally completed. Programmer 240 then normally operates, through controller 241, to open switch 242 and thereby close valve 243. If annealing of the casting in the mold is to be accomplished following directional solidification, programmer 240 may be made to additionally control controllers 234 through 236 so that each maintains the required elevated annealing temperature (500 F.-600 F.) for the required additional period of time hours) prior to mold cool-down and casting removal. If the completed thin-walled casting formed by directional solidification is to be removed from mold assembly 203 at the preselected minimum temperature and prior to any annealing, programmer 240 normally functions to condition the apparatus of FIG. for a mold heating and directional solidification control repeat sequence.

FIG. 12 illustrates molding equipment in an embodiment 300 that may be utilized without separate pouring equipment such as unit 11 of FIG. 1 for the purpose of r casting molten metal into thin-walled casting configurations. Equipment 200 contains elements necessary for accomplishing metal melting within the environment in the interior of the housing comprised of body 301 and removable cover 302. A combined mold and melting crucible assembly 303 is included in equipment 300 and is supported on support 304 positioned on the equipment interior bottom. A cooling-water chamber 305 closes the bottom of container portion 306 of assembly 303 and supports casting mold halves 307 and 308 as well as crucible liner members 309. Mold halves 307 and 308 in the FIG. 12 equipment embodiment are preferably wrapped or fixed in proper relation to each other as by fibered glass fabric 310 and are then backed or supported in container 306 in the required joined relation by granular medium 311 such as the previously-referenced zircon sand. The interior casting cavity of combined mold halves 307 and 308 is provided with a thin-walled casting configuration such as that corresponding to the exterior configuration of aircraft structural member 211 of FIG. 11, for example. The mold interior cavity configuration also is oriented in an essentially vertical direction and is joined directly to an uppermost mold gate region 312 without the necessity of an intermediate or cooperating mold riser region. A comparatively finewoven graphite fabric 313 is positioned at the entrance to gate region 312 and serves to support the casting metal charge contained within the crucible liner made up of members 309. As in the case of mold halves 307 and 308, a granular refractory medium such as 311 may be used to back crucible elements 309 in proper assembled relation in container 306. Mold assembly 303 is positioned interiorly of electrical resistance heating elements 314 and 315 carried by support structure 316. Electrical resistance heating element 314 is associated with the region of mold halves 307 and 308; heating element 315 is positioned adjacent the region of melting crucible 309. Assembly 303 and the associated adjacent heating elements are in turn positioned within the heat radiation shield formed by water jacket 317. Attach fittings 318 are a part of container portion 306 and facilitate lowering and lifting assembly 303 into and from body portion 301 after removal of cover 302.

Equipment 300 also includes the manually-operated tap rod reference as 319 extending to the region of graphite fabric 313 and cooperating with cover 302 in sealed relation to the equipment interior environment. Briefly, tap rod 319 is moved downwardly to pierce fabric 313 and allow molten metal to flow into gate region 312 after alloy melting has been completed. At least in the case of certain aluminum alloys, the molten alloy wetting characteristic relative to graphite fabric 313 is suflicient to retain molten metal within crucible 309 until a proper pouring or casting temperature has been attained.

As in the case of previous equipment arrangements 12 and 200, various utility services are connected to the elements located in the interior of unit 300, More specifically, water supply line 320 and water return line 321 are supported in-part by the exterior of container 306 and cooperate with mold cooling chamber 305. Such lines are provided with suitable disconnect fittings 322 and cooperate with housing body 301 in sealed relation. Electrical power leads 323 and 325 are connected to resistance heating element 314 and cooperate with equipment body portion 301 in sealed relation; similar leads 325 and 326, shown partially in FIG. 12, are connected to resistance heating element 315. Cooling-water is generally continuously circulated to and from water jacket 317 by means of supply and return lines 327 and 328 during equipment operation. As in the case of the equipment of FIG. 9, an environmental gas supply line 329 controlled by valve 330 normally functions to provide an inert atmosphere to the interior of equipment 300 as by back-filling after a vacuum has been established for purging purposes by operation of vacuum line 331 and valve 332.

Equipment arrangement 300 also includes spaced-apart thermocouple elements 333 through 335, such elements being a part of the cooperating equipment control arrangement illustrated schematically by FIG. 13. Such elements function to sense actual mold-metal temperatures existing at the adjacent mold regions or zones. Thermocouple element 336 measures the temperature at the metal within melting crucible 309. As shown by FIG. 13, thermocouple elements 333-through 335 (Whichelements may be similar to the junction and lead elements of the FIG. 10 scheme) cooperate with conventional heater controller 337. Thermocouple element 336 cooperates with conventional heater temperature controller 338. Controllers 337 and 338 cooperate with conventional switch assemblies 339 and 340, respectively, for the purpose of controlling the delivery of electrical energy to the respectively connected resistance heating elements 314 and 315. A transformer (not shown) may be connected to a suitable power supply to serve as a source of electrical energy for apparatus 300.

The arrangement of FIG. 13 in addition includes a conventional programmer 341 that sequentially programs controllers 337 and 338 and also conventional controller 342 for water valve switch 343 to achieve the desired metal melting and subsequent directional solidification of metal in crucible 309 and mold halves 307 and 308. Switch 343 functions, when activated, to open normally closed Water valve 344 located in water supply line 320 exterior to body portion 301 and interior cooling chamber 305.

Details of the program output of programmer 341 for controllers 337, 338, and 342 to obtain the required metal melting and molten metal directional solidification in assembly 303 may be based on specific process parameter values as disclosed by my previously-referenced co-pending applications concerning the casting of heat-treatable, high-strength aluminum alloys. During the alloy melting and mold heating phase of equipment operation, programmer 341 causes controllers 337 and 338 to establish and maintain preselected temperatures relative to assembly 11 303. Controller 337, for instance, operates switch 339 to establish and maintain a mold temperature inthe range of 1200 F. to 1250 F. by regulating heating element 314 in response to the minimum temperature detected by any of thermocouple elements 333 through 335. Controller 338 cycles switch 340 to establish and maintain a required minimum molten metal temperature prior to casting, in the range of 1250 F. to 1350 F., for example, by means of resistance heating element 315 and in response to temperatures sensed by thermocouple element 336. When the required temperatures have been reached,

as evidenced by conventional associated temperature display instrumentation (not shown), tap rod 319 may be operated to pierce graphite fabric 313 and cause molten metal to flow into mold halves 307 and 308 to fill the interior thin-walled configuration cavity and also adjacent gate region 312. When mold halves 307 and 368, including gate region 312, are filled with molten metal, programmer 341 functions to cause controller 342 to open water valve 344 to initiate directional solidification and to cause controller 337 to open switch 339. Thereafter, controller 337 functions to cycle switch .339 in response to the minimum temperature detected by any of thermo couple elements 333 through 335 to maintain a preselected minimum temperature (for instance, a temperature in the range of 500 F. to 600 F.) during directional solidification. Controller 338 functions to cycle switch 340 at a control temperature approximatin the metal casting temperature (1250 F.) until such time as the preselected metal-mold minimum temperature is detected by each of thermocouple elements 333 through 335. When directional solidification is completed (as manifested by detecting the minimum metal-mold temperature at each of elements 333 through 335), programmer 341 then normally functions through controller 342 and switch 343 to close water valve 344. If annealing of the casting in mold halves 307 and 308 is to be accomplished following directional solidification, programmer 341 may be made to additionally control controllers 337 and 338 to maintain the required elevated annealing temperature (500 F.600 F., for example) for the required additional period of time hours, for example) prior to mold cool-down and casting removal. If the completed thinwalled casting formed by directional solidification is to be removed from mold halves 307 and 393 at the preselected minimum metal-mold temperature, programmer 341 should function tocondition apparatus 300 for a repeated control sequence of metal melting, mold heating, and directional solidification.

I claim:

1. Apparatustfor directionally solidifying molten metal into a thin-Walled configuration having a Shape Factor substantially in excess of 100, and comprising in combination:

(a) mold means having an interior cavity with a thinwallcd configuration portion of Shape Factor substantially in excess of 100 oriented in a substantially vertical direction and with a gate configuration portion positioned above and in joined relation to the uppermost part of said thin-walled configuration portion,

(b) COOling means positioned in proximity to the lowermost part of saidmold means interior cavity thinwalled configuration portion, separated from said gate configuration portion by said thin-walled configuration portion, and selectively activated to reduce the temperature of molten metal contained in said mold means on an accelerated basis by flowed coolant,

(c) heating means surrounding said mold means at said interior cavity in heat transfer relation and selectively activated to elevate the temperature of adjacent portions of said mold means,

(d) sealed chamber means containing said mold means, said cooling means, said heating means, and an environment controlled to a non-reactive pressure and composition condition in relation to molten metal contained in said mold means, and

(e) control means for selectively activating said cooling means and said heating means to obtain directional solidification of molten metal contained in said mold means interior cavity thin-walled configuration and gate configuration portions and in said sealed chamber means environment, said control means being arranged for activating said heating means and said cooling means to heat said mold means to an elevated temperature above approximately 0.8 the temperature of the molten metal to be cast into said mold means at the time of casting molten metal into said mold means interior cavity thin-walled configuration and gate configuration portions and to afterwards directionally solidify molten metal cast into said elevated temperature mold means first in said mold means interior cavity progressively from said thin-walled configuration portion lowermost part to said thin-walled configuration portion uppermost part and then in said mold means interior cavity gate configuration portion.

2. The apparatus defined by claim 1, wherein said heating means is comprised of a plurality of separate heating elements each selectively activated by said control means and each positioned at a different one of successive zones comprising the vertical extent of said mold means interior cavity, said control means being adapted to first simultaneously activate each of said heating elements while maintaining said cooling means in an inactivated condition to heat said mold means to said mold means elevated temperature at the time of casting molten metal into said mold means interior cavity, and said control means being adapted to afterwards simultaneously activate said cooling means while selectively inactivating said heating elements progressively from the heating element associated with the zone most adjacent said mold means interior cavity thin-walled configuration portion lowermost part to the heating element associated with the zone most adjacent said mold means interior cavity gate configuration portion for determinate sequential periods to directionally solidify molten metal cast into said mold means.

3. The apparatus defined by claim 2, wherein said control means includes thermocouple elements that each sense the mold means temperature at a different one of said successive zones, said thermocouple elements determining the duration of each of said determinate sequential periods of heating element selective inactivation as a result of sensing a preselected minimum temperature and causing said control means to cyclically activate each of said heating elements and maintain the associated zones of said mold means at said preselected minimum temperature during directional solidification of molten metal in said mold means and after individual heater element determinate period inactivation by said control means.

4. The invention defined by claim 3, wherein said con trol means is adapted to inactivate said cooling means after the molten metal cast in said mold means has been directionally solidified, said control means adapted to cyclically activate each of said heating elements to maintain said mold means at said preselected minimum temperature after said cooling means has been inactivated.

5. The apparatus defined by claim 1, wherein a radiation shield means is additionally included in said sealed chamber means, said radiation shield means surrounding said mold means and said heating means throughout the vertical extent of said mold means interior cavity.

6. The apparatus defined by claim 1, wherein said heating means is comprised of a first heating element selectively activated by said control means and positioned at a first zone extending substantially throughout the vertical extent of said mold means interior cavity and of a second heating element selectively activated by said control means and positioned at a second zone adjacent and above said first zone, said control means being adapted to first activate at least said first heating element while maintaining said cooling means in an inactivated condition to at least inpart heat said mold means to said mold means elevated temperature at the time of casting molten metal into said mold means interior cavity, and said control means being adapted to afterwards activate said cooling means While selectively activating said second heating element and inactivating said first heating element for a determinate period of time to directionally solidify molten metal cast into said mold means.

7. The apparatus defined by claim 6, wherein said control means includes a thermocouple element that senses the mold means temperatureestablished by said first heating element at said first zone, said thermocouple element being adapted to determine the duration of said determinate period of first heating element selective inactivation as a result of sensing a preselected minimum temperature and cause said control means to cyclically activate said first heating element to maintain said mold means at said preselected minimum temperature during directional solidification of molten metal in said mold means and after first heating element determinate period inactivation by said control means.

8. The apparatus defined by claim 1, wherein said heating means is comprised of a first heating element selectively activated by said control means and positioned at a first zone extending substantially throughout the vertical extent of said mold means interior cavity and of a second heating element selectively activated by said control means and positioned at a second zone adjacent and above said first zone, said control means being adapted to first activate said first and second heating elements while maintaining said cooling means in an inactivated condition to at least in-part heat said mold means to said mold means elevated temperature at the time of casting molten metal into said mold means interior cavity, and said control being adapted to afterwards inactivate said cooling means while selectively inactivating said first and second heating elements progressively from said first heating element to said second heating element for determinate sequential periods to directionally solidify molten metal .cast into said mold means.

9. The apparatus defined by claim 8, wherein said control means includes a thermocouple element that senses the mold means temperature established by said first heating element at said first zone, said thermocouple element being adapted to determine the duration of said determinate period of first heating element selective activation as a result of sensing a preselected minimum temperature and cause said control means to cyclically activate said first heating element to maintain said mold means at said preselected minimum temperature during directional solidification of molten metal in said mold means and after first heating element determinate period inactivation by said control means.

10. The apparatus defined by claim 9, wherein said control means is adapted to selectively activate said second heating element after a determinate period determined as a result of sensing said preselected minimum temperature, said preselected minimum temperature being sensed by said thermocouple element.

References Cited UNITED STATES PATENTS 1,876,073 9/1932 Player 164-121 2,782,476 2/1957 Brennan 164348 3,248,764 5/1966 Chandley 164-127 3,204,301 9/1965 Flemings et al. 164-426 X J. SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Assistant Examiner.

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