US2966709A - Casting furnaces - Google Patents

Description

Jam 3 1961 R. H. RUPPEI. ET AL 2,966,709

CASTING FURNACES Filed July l0, -1945 3 Sheets-Sheet 2 eZ Zers Jan. 3, 1961 R. H. RUPPEL. ET AL 2,966,709

CASTING FURNACES Filed July 10, 1945 3 Sheets-Sheet 5 United States Patenti() CASTING FURNACES rRobert H. Ruppel, Granite City, `Ill., -and Charles E.

Winters, Oak Ridge, Tenn., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed July 10, 1945,Ser. No.604',278

3 Claims. (Cl. 22-73) 'Ihis invention relates generally to electric furnaces,

and more particularly to a-vacuum billet-casting furnace of the induction type for recasting uranium rand/ or other heavy metals, said furnace being constructed to eliminate Y Ain a form suitable for rolling and fabrication into slugs for neutronic reactors. The biscuits `as formed in the above process have traces ofslag, magnesium and lime. In addition, pipes are formed in the billets during cooling which pipes preclude the*Y rolling of the billets into slugs suitable for neutronic reactors.

The present invention kis concerned with yovercoming rthe above diiiiculties and has for a principalobject the `provision of an induction furnace for remelting and recasting in vacuum uranium and/or other heavy metals in large quantities into billets yof pure metal whichare free from shrinkage holesfformed during-cooling.

Another object of this invention'is to provide an ap- 'p-aratus for casting metallic ingots relatively free from .blow-holes, slag particles Iandnon-metallic inclusions.

As will hereinafter appear, the objectsare accomplished by providing a yvacuum casting furnace comprising a melting furnace-and a casting apparatus in combination. The furnace of this invention operates' within the com- `mercial range of frequencies from 60 cycles and upwards and may, therefore,be termed a highlfrequency -vacuum induction furnace.

In furnaces of the vacuuminduction type, theA electromagnetic fields producedin the vicinity ofthe furnace have a detrimental heating effect on the enclosing casing and, also, 'on the magnetic-materials such as iron or steel inthe vicinity of the furnace. To overcome these casting furnace constructed l in accordance lwith the teachings of the'present invention;

Fig. 2 is a top plan viewofithe vacuum casting furnace yshown in Fig. l;

Fig. 3 is a vertical cross-sectional view, 'partlyincelevvation, on the line 3-3 of Fig. 2;

Fig. 4 is an enlarged plan view of the rotatable mold itable;

FigpS is a plan .view ofthegraphitev meltingcrucible, part of the top being broken away for clarity; and

,r 2,966,709 `Patented Jan. 3, 19.61

Ffice 2 Fig. 6 is'a' vertical cross-sectional view, partly! in-elevation, on the line 6--6 of Fig.5,V showing the protective jguide for'the graphite plugfor controlling the ilow-of one sideoilthe main cylindrical shell 1-3 and atthe bottom thereof is anoutwardly flanged `manhole opening y17lfor the insertion and removal of billet molds18,.which will `rbe described laterv in detail in. the. description of the operation ofthe vacuum casting-furnace. The flange of 4the manhole opening 17 is provided with agrooved supporting ring 19A to which lis secured a removable cover20. The cover 20 is connected yto a bracket .'23 which is pivotally connected to a support armi 21, pivotally mounted ,at its other end onbracketsZZ Weldedto the cylindrical ,gasket"26, it is evident, a vacuum-tight seal -is .provided between the cover'itl and the shell 13, and .a closure-is `formed `which maybe readily opened for the Yinsertion and removal of the billet moldslS,

In the bottom shel1`12 is another flangedmanhole,

-which is provided withfa waterjacket-ZS and .with couplings as shown for thenattachrnent Yoftpipingfrom a cooling system. Suitably attached .to-the manhole opening 27 in a-vacuum tightrelation'ship is a Bakelite .cover '29. vThe Bakelite cover 29 Vsupports water cooled bushings 30, to which is connected a Watercooled'conductor F31 yfor the helical induction coil32-forheatingthe metal to'be melted within la Crucible construction, whichywith the heating coil, is described in detailbelow.

Also supported by the bottom shell 12 .ofthe-furnace is a rotating `rnoldtable construction 33. lThe mold-table construction 33 is mounted for rotary=movement-in a ilanged bracket 534- forming avacuum tight jointy Wit-han annular flanged member 35 suitablyaiXed-to the runder side of shell 12. 'The mold'vtable 33 is-supported ona vertical shaft 36 suitably journaled Yinthebracket 34-and provided with vertical adjustment by acollar 37. -The collar 37 is pr0vided-with a set.screwQfor.securing-thc shaft 36 in its verticallyadjustedposition; -A vacuum tight seal is provided for the support bracket 341and the shaft 36 in the form of a suitable packing-gland-{not shown) aflixed'to the bracket 3-4 aboutthe circumference of the shaft 36 andintheannular space formedfbetween the shaft and the bracketfi. Ahand wheel 38 is-aflxed to the shaft 36 to rotate the-mold table -33-assuccessive molds 18 are poured. .The mold table 33-is.provided with a chamber 39 so that it may Abe water cooled. `Waterris admitted throughtheinlet piping 40passe through-holes 41 into the chamber 39, and discharged fronrthechamber 39 through the annularrspace -42providedvbetween the inletpipe 40 Yand the-shaft 36 and :through outlet 43.

Steel supporting brackets 44varevaiiixed-to=the interior Vof the shell 13 on a rlevel with thef-topfof-the manhole opening 17 to provideasupport for azcircular- Transite compressed asbestossupportingmember V4S whichfsupports a crucible construction to be described-later. The diameter ofthe-supporting member-45 is lessthan thelinside diameter-of theUshell 13 totprovidean `annulares-pace .for .a cooling coilconstruction-46and alsoto;provide a passage to the'bottom portion of the furnace so that the 'furnace may be thoroughly evacuated. The cooling coil construction 46 extends from the bottom of the supporting member 45 to the top of the shell 13 where it is aixed to the supporting ring 15. The cooling coil construction 46 is formed from copper pipe flattened to the shape-illustrated in Fig. l and helically coiled to t the interior of the shell 13 with a spacing between the coils of substantially 1A inch. The coil construction 46 is soldered to the shell 13 in heat conducting relationship. Referring to Fig. 2, the cooling coil connections for the inlet and outlet extend through the shell as at 47 and 48 connecting to a suitable supply of coolant. A copper band 49 may be soldered to the tubes to provide suitable support.

A sighting glass construction 50 is provided, as illustrated in Figs. 1 and 2, for viewing the pouring of the molten metal into the ingot molds 18. A hole 51 is provided through the Transite support 45 in the line of sight 52 (dotted line) between the sighting device 50 and the top of the mold 18.

A vacuum exhaust connection 53 of suitable size is provided for connecting the vacuum furnace in a suitable system for continuously evacuating the furnace to the vacuum desired. A manometer may be connected at `54 for determining the amount of vacuum in the furnace.

The Water jacketed cover 16 is provided with a water chamber 55 formed by outer and inner dished shells 56 4 Figs. l and 2. A lifting connection 62 in the form of an inverted U-bolt bolted to the cover 16, as illustrated,

is provided for the removal and replacement of the cover of the vacuum casting furnace when it is desired to load an enclosed melting crucible 63 after each heating.

A sighting glass 64 is provided for viewing the melting operation from time to time. The cover 16 is provided with suitable centering lugs 66 which work in conjunction with a centering pin 67 and the outlet connection 61 for aligning the cover. A vacuum tight joint between the cover 16 and the shell 13 is provided by a suitable gasket therebetween.

The cover 16 is provided with a bracket construction 68 pivotally supporting a lever 69 pivotally connected for vertically reciprocating a stopper rod 7l) for actuating a graphite rod 71 which serves to open and close a hold 72 inthe bottom of the crucible 63, Figs. and 6. The rod 70 is mounted for reciprocation within a vacuum tight construction provided by the member 73 and the packing gland 74 forming a vacuum tight seal. The rod 70 is pivotally connected at its upper end to the lever 69 by an intermediate toggle member 75 and at its lower end to the graphite rod 71 through a member 76 which provides for the replacement of the graphite rod 71. A Weight 77 is hung at the outer end of the lever 69 for l biasing the graphite rod 71 to a position to effectively stopping the pouring of the molten metal.

Referring in detail to the crucible construction 63 and the induction heating coil construction 32, a circular insulating re brick 80 is axially mounted on the Transite supporting member 45 and is provided with a conical off-center hole 81 in alignment with an off-center hole 82 in the member 45. The pouring hole 72 of the crucible 63-is mounted so that the axes of the hole 72 and the holes 81 and 82 are in alignment. Referring to Figs. 5 and 6,

the crucible 63 which is mounted on the insulating brick 80, is formed of graphite to withstand the high temperatures of thev molten metal and is provided with a conically shaped bottom as shown in Fig. 6, which is provided with an inclined pouring groove 83, with the direction of inclination from the center of the crucible outward to the pouring hole 72. A counter bore 84 is provided for the reception of the end of the graphite rod 71. Graphite rod guards 85 are provided for shielding the rod 71 from the metal and also to provide a slot for the vertical movement of the rod. These rod guards 85 are dowelled to the side of the crucible, as illustrated at 86. Vent holes 87 are provided at the top of the crucible to permit evacuation of the crucible 63. A cover S8 is provided for the crucible 63 and has a sight hole 89 in alignment with the line of sight of the sighting device 64 in the cover' of the furnace and is further provided with an opening for the vertical movement of the graphite rod 71. An insulating brick 91 is positioned on top of the cover 88 and is provided with a sighting hole 92 in alignment with the hole 89 but olfset with respect thereto to provide better vision of the molten metal Within the crucible 63. The brick 91 is also provided with a tapered hole 93 in alignment with the hole 90 for the passage of the graphite rod 71.

Mounted on the support 45 and surrounding the crucible 63 and the bottom and top insulating bricks therefor is an annularly formed member 94 formed of insulating brick providing a chamber for the crucible 63. From this construction, it is evident that the metal which is being melted Within the crucible 63 is thoroughly insulated to provide for elicient melting of the metal and to prevent dissipation of large amounts of heat to the water cooled shell of the furnace, thus providing for longer life of the furnace. Furthermore, upon deterioration and breakage of the insulating brick and crucible, these may be readily replaced. Insulating members 95 support the coil 32. These members 9S are provided with grooves 96 in which the water cooled helical induction coil 32 is positioned, insulating each coil of the construction from each other and providing an eifective support. The water cooled induction coil construction 32 is connected to the conductors 31 which, in turn, are suitably connected to a source of high frequency power suitable to melt the metal Within the crucible 63 and raise it to the temperature desired for pouring. An annular Transite plate member 97 of suitable thickness is mounted on the top of the member 95 and the insulating member 94 and is provided with a hole of suicient diameter to permit the passage of the crucible 63 and the insulating bricks 80 and 91 for replacement. The diameter of this plate member 97 is less than the inside diameter of the shell 13 to permit evacuation of the furnace and to provide room for the cooling coils 46.

In order to pour the metal, molds 18, preferably 4 in number, are mounted on the rotary mold table 33 for successive rotation in and out of position underneath the pouring hole 72 of the crucible 63. Although it is preferred to pour 4 molds at a pouring, any number may be poured, depending upon the size of the molds mounted on the plate 33. Upright brackets 98 'have atlixed thereto adjustable horizontal U-shaped members 99 for surrounding and retaining the crucibles 18 in position.

The billet mold 18 is preferably formed of graphite with an enlarged portion 101 at the top in which is mounted a graphite ring member 102 provided with a hole through which the molten metal is poured and which serves to form a test egg which may be sawed off after the metal has been cooled and removed from the mold 18.

In order to provide illumination Within the vacuum furnace when the metal is not up to temperature and is not being poured, an electric light 103 may be provided and is preferably supported from the shell 13 by a suitable bracket construction 104.

In the operation of the vacuum casting furnace, biscuits of uranium, for example, are removed from the bomb where originally cast and are roughly trimmed of adherent slag and blow holes by an air hammer. These biscuits must be remelted and cast into the desired shape in order to remove the slag and other impurities. This is done by removing the cover 16 from the furnace and placing into the furnace the crucible 63 in which has been placed 3 or 4 biscuits, the number and size depending upon the size of the final billet desired. The graphite crucible 63 in a preferred size is approximately 18 inches high and 12 inches in diameter with the pouring hole 72 in the bottom near one edge as described. This hole 72 is then plugged by the long graphite stopper rod 72 extending out from the -top of the crucible 63 and connected as described to the rod 70. The graphite rod 71 is protected by the graphite guards 85 from breakage by the biscuits falling against it, these guards being quartercircular strips as described, one on each side of the graphite rod 71. The crucible containing the biscuits of uranium and the furnace are then evacuated since uranium is inherently pyrophoric, and heated to about 2550 F. As the material melts most gaseous materials boil oif and are evacuated, and the solid impurities rise to the top of the crucible 63 and are not poured into the molds 18. After the material is thoroughly boiled out, it is allowed to cool to 2400 F. and run into the billet molds 18 except the top slag or scum portion. The temperature may be suitably observed with optical pyrometers placed in alignment with the sighting device 64 at the top of the furnace.

The four billet molds 18 are preheated to drive off volatile material and cooled and are then placed in the furnace prior to the evacuation and heating thereof. The billet molds 18 are placed under the crucible of the induction furnace on the rotatable mold plate 33 so that they can be brought successively under the run-out hole 72 of the crucible 63. 'Ihe metal is run out of the crucible 63 by lifting the graphite stopper rod 71 and allowing the metal to run into each mold 18 in turn, until each of them is lled. The size of a preferred cast billet as removed from the mold is approximately 4%6 inches in diameter and 16 inches in over-al1 length with an egg portion approximately half the diameter of the original mold and 21/2 inches long, leaving the resultant billet approximately 131/2 inches long after removal of the egg for testing. Molds for casting in which the egg is formed at the bottom may be used.

In casting the billets, particularly when uranium is cast, the formation of pipes resulting from shrinkage while cooling may be prevented by pouring the metal into the mold 18 up to labout 2 inches from the top. The graphite rod 71 is then lowered, closing the pouring hole of the crucible 63 and a period of approximately two minutes is allowed to elapse depending upon the size of the mold, temperature of molten metal and cooling rate, the vacuum being maintained on the furnace during the entire casting period; and then the graphite stopper rod 71 is again raised and the mold lled while the pouring is watched through the sighting device 50. The cast billets are then allowed to remain in the furnace until they are relatively cool, remaining in the furnace approximately three hours after which the molds 18 with the billets therein may be removed by opening the closure 20 and rotating the mold table 33 with the hand wheel 38, bringing t-he molds 18 into position in front of the opening from which the molds 18 and the cast billets therein may be readily removed.

After a batch has been cast, the crucible 63 is refilled with a batch of metal and new billet molds 18 are placed on the billet table 33, the casting furnace sealed up, the vacuum again applied to the furnace and heat applied through the induction heating coil 32 until another batch is ready for pouring.

It is evident that a simple vacuum casting furnace has been provided for the vacuum casting of large amounts of metal so that the resultant billets are relatively free from impurities such as slag inclusions, light metals, occluded gases, and shrinkage holes in the form of pipes." Obviously, the resultant billets as cast have small loss in weight in view of the fredom from the above defects, and high yield from the billets when they are rolled or otherwise fabricated may be obtained.

There has also been described a novel form of vacuum casting device in which successive molds may be cast from the metal from the meltingy crucible, the pouring hole of the crucible suitably opened and closed with a plug actuated from the exterior of the furnace and the vacuum being maintained during the melting and casting operations.

Although this invention has been particularly described with reference to the melting and casting in vacuum of a heavy metal such as uranium, it is equally adaptable for the melting of thorium and other heavy metals where a high degree of purity is required in the resultant cast billet.

Obviously, many modifications may be made in the specific embodiment disclosed herein without departing from the intended scope of the invention. The features of the invention which are believed to be new are expressly set forth in the accompanying claims.

What is claimed is:

l. In a casting furnace, a shell, a mold table eccen- Y trically arranged within said shell, said mold table including means for supporting a plurality of molds, means for rotatably supporting the mold supporting means, said mold supporting means being adapted to be rotated from the exterior of said shell in which the table is located, means for cooling the mold supporting means, means for vertically adjusting the mold supporting means, a crucible above said mold-supporting means, said crucible having a pouring hole eccentrically arranged in the bottom thereof, and closing means for said hole, means for opening said closing means for said hole from the outside of said shell, and means for maintaining said furnace under a vacuum during melting and casting.

2. A furnace for casting uranium billets comprising a shell, evacuating means, a melting crucible for the uranium, said crucible having a pouring hole in the bottom near one side, means for opening and closing the pouring hole from the outside of said shell, a rotatable table inside said shell below the melting crucible, means for adjusting said table vertically to carry molds of various heights and means for cooling said table.

3. A melting and casting furnace comprising a watercooled shell, a removable Water-cooled cover therefor forming a vacuum-tight tit with the shell, a melting crucible supported in the upper portion of the shell having a pouring hole eccentrically arranged in the bottom, means for heating metal within the crucible to a molten state, rotatable means for supporting a plurality of casting molds in said shell beneath the melting crucible, means for closing the pouring hole in the crucible comprising a vertically mounted stopper rod, means for actuating the stopper rod from the exterior of said shell, a closure in said shell adjacent to the means for supporting the molds whereby the molds may be mounted on the supporting means prior to casting and removed therefrom after casting, means for viewing the molten metal within the crucible, means for viewing the pouring of the metal, and means for maintaining said furnace under a vacuum during the period of melting and casting.

References Cited in the ile of this patent UNITED STATES PATENTS 204,307 Duif May 28, 1878 1,839,106 Loth Dec. 29, 1931 2,085,450 Rohn June 29, 1937 2,140,607 Thompson Dec. 20. 1938` 2,156,998 McCullough May 2, 1939 2,285,523 Lindemuth June 9, 1942

Images