US3393836A - Metal dispensing apparatus - Google Patents

Description

July 23. 1968 H. GREENEWALD, JR .7 3,393,836

METAL DI SPENS ING APPARATUS Filed Nov. 12, 1965 2 Sheets-Sheet 1 IN VEN TOR.

HERBERT GREENEWALD, JR. BY

ATTORNEY July 23. 1968 H. GREENEWALD, JR

METAL DISPENSING APPARATUS 2 Sheets-Sheet 2 Filed Nov. 12, 1965 INVENTOR HERBERT GREENEWALD, JR.

ATTORNEY United States Patent 3,393,836 METAL DISPENSING APPARATUS Herbert Greenewald, Jr., Columbus, Ohio, assignor to North American Rockwell Corporation, a corporation of Delaware Filed Nov. 12, 1965, Ser. No. 507,384 Claims. (Cl. 222-152) ABSTRACT OF THE DISCLOSURE tion that repeatably passes through the apparatus rotational axis.

This invention pertains generally to metal casting, and particularly concerns apparatus for heating and pouring molten metal in connection with the forming of comparatively-large, thin-walled metal castings in a vacuum environment.

Basically, the instant invention utilizes a crucible having a substantially spherical interior and having a top charging/discharging opening with a fixed, smaller diameter; the crucible is positioned and operated in a manner whereby cooperating drive apparatus rapidly rotates the crucible from an upright heating/melting position to a completely inverted pouring position to discharge contained molten metal into a cooperating mold assembly, The invention requires crucible rotational rates that are generally in excess of a minimum of approximately 180 per second. By means of the top opening arrangement and rapid inversion, the discharged molten metal stream may be readily controlled for volumetric integrity, for repeatability of pouring rate, and for repeated position and directionality.

Accordingly, an important object of this invention is to provide crucible assembly means that may be operated to readily obtain a poured molten metal stream having improved volumetric integrity.

Another object of this invention is to provide crucible assembly means that may be operated to readily obtain a poured molten metal stream having improved flow rate repeatability.

A still further object of this invention is to provide crucible assembly means that may be operated to readily obtain a poured molten metal stream having improved position and directionality repeatability.

Another object of this invention is to provide crucible assembly electrode heating means that may be operated to readily obtain energy requirement and physical spacing characteristics of improved stability.

Other objects and advantages of this invention will become apparent from a consideration of the specification and drawings.

In the drawings:

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

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

3,393,836 Patented July 23, 1968 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; and

FIG. 8 is a sectional view taken at line 88 of FIG. 7.

A composite unit for practicing the instant invention in connection with the vacuum casting of molten metal 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 i12. 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 providide 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, especially if utilized in connection with the processing of aluminum alloys, generally is maintained at absolute pressure levels less than 800 microns of mercury. v

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 when the crucible is inverted. For most known applications, the ratio of the cross-sectional 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 necessary for producing satisfactory 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 compo nents 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 longitudinal (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 period of time of approximately one hour to heat molten aluminum 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 37 secured 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 and return 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 the 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 vacuum-sealing 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 apparatus 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 58 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 70 and removable cover 71 and also a mold assembly positioned interiorly on block 72. Leg members 723 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 76 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. 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. 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 accom lishing ejection of the completed casting from within mold 77. However, component 90 is provided primarily for controlling the directionality of metal solidificaion 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 a vacuum-sealing relation. Also, the vacuum en vironment within the interior of molding unit 12 is generally maintained, by means of the hereinbefore-referenced vacuum-producing apparatus, at abolute pressure levels less than approximately 2,000 microns of mercury; during the casting of molten aluminum alloys 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 thedrawings. 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 cast through open valve assembly 13 into aligned mold 77. Molten charge 109 is cast from crucible 19 into tmold 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 thin-walled aluminum alloy castings, a height H of approximately 4 feet has been found satisfactory for developing acceptable completed castings.

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. Details 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 runners 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 desired to flow molten metal through a comparatively thin section to a comparatively thick section. Mold 77 has an inwardlyprojecting core support 113 that is intermittently severed by gate 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 gate 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 mold 77 (FIG. 4) so that solidified metal is developed in regions above the uppermost configuration limits of the desired casting.

Although not shown in.the drawings, it is preferred that vacuum molding equipment 12 be provided with conventional air 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 purpore of casting aluminum alloys, is preferably 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 graphites having specific gravities of approximately 1.45 are 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 to a temperature generally in the range of 0.8 to 0.9 the molten metal pouring temperature. In the case of aluminum alloys, mold temperatures in the range of 800 F. to 1000 F. are usually satisfactory.

After the molten metal charge 109 has been cast into the mold assembly, heater 86 is turned off and cooling of the mold 77 is immediately initiated by means of watercooled jacket 89. Also, it is normally preferred that completed casting 110 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 to prevent heat transfer by conduction are generally minimal and often approximately 0.005".

I claim:

1. In metal casting apparatus, in combination:

(a) crucible means having a substantially spherical interior cavity for containing a charge of molten metal, and also having a horizontal axis of rotation that coincides with a diameter of said interior spherical cavity,

(b) discharge opening means having an outlet axis extending outwardly from said interior spherical cavity and normal to said axis of rotation and having a cross-sectional area substantially less than the maximum cross-sectional area of said interior spherical cavity, and

(c) drive means operably connected to said crucible means,

said drive means when actuated rapidly rotating said crucible means about said axis of rotation from a position whereat molten metal is contained against gravitational flow by said interior spherical cavity to a position whereat said discharge opening means is located below said axis of rotation with said outlet axis oriented in a vertical direction to thereby discharge molten metal from within said interior spherical cavity by gravitational flow in a vertical direction that will repeatably pass through said crucible means horizontal axis of rotation.

2. The invention defined by claim 1, wherein the ratio of said discharge opening means cross-sectional area to said interior spherical cavity maximum cross-sectional area is in the range of 1:25 to 1:3.

3. The invention defined by claim 1, wherein said crucible means is provided with a pair of opposed openings elevationally positioned above a contained molten metal level to receive reciprocable metal heating electrode means in non-sealing relation, each of said opposed openings being extended radially outward from said interior spherical cavity and having a longitudinal axis that coincides with said crucible means axis of rotation.

4. The invention defined by claim 1, wherein said drive means is operable to rotate said crucible means at a rate in excess of per second when actuated.

5. The invention defined by claim 4, wherein said drive means is operable to rotate said crucible means at a rate of approximately 600 per second when actuated.

References Cited UNITED STATES PATENTS 3,280,434 10/1966 Cecere 164258 3,336,971 8/1967 Tinquist 164258 FOREIGN PATENTS 266,111 5/1961 Netherlands.

J. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner.

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