US2852823A - Casting apparatus - Google Patents

Description

Sept- 23 19.58 c F. GRAY ETAL 2,852,823

CASTING APPARATUS Filed Nov. 1s, 1945 United States Patent `Ciitce Patented Sept. 23, 1958 CASTING APPARATUS C F. Gray, Ames, and Richard H. Thompson, Cedar Rapids, Iowa, assignors to the United States of America as represented by the United States Atomic Energy Commission Application November 13, 1945, Serial No. 628,318 3 Claims. (Cl. 22-73) weight limits indicated. Because of the small amount of metal involved, the melt may not settle in a clear pool but may remain as droplets in the `ux. Castings or billets moulded from molten metal in this condition may not properly conform to the mold and, as a result, may contain irregularities. Furthermore, the metal in the castings may not be homogeneous and, therefore, may be more vulnerable to galvanic deterioration.

Another difficulty that may be encountered in connection with the melting of small ingots of uranium and similar heavy metals arises from the film or skin formed by the outside layer of the ingot which continues to en- Acase and restrain the interior metal after it has been heated to a molten condition. In order to pour the metal, the skin must be broken. Furthermore, capillary attraction and pockets formed by the pierced skin may prevent some of the available molten metal from iiowing to the mold.

It is, therefore, an object of this invention to overcome these diiiiculties and to provide a novel improved apparatus and method for small scale casting of metal objects such as, for example, uranium billets.

Another object is to provide a furnace of this type having a centrally disposed aperture in the bottom of the crucible and a pouring rod adapted to openand close the aperture, and, in addition, to break any restraining skin or film about the molten metal.

The invention accordingly resides in the features of construction, combination of elements, and arrangement of parts which will be exemplied in the construction hereinafter set forth in conjunction with the drawings and the scope of which will be indicated in the appended claims.

`For'a more complete understanding of the nature and scopeof the invention, reference may be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical cross-sectional view of a small-scale casting apparatus embodying the present invention, `and illustrating the pour rod in the melting position;

Fig. 2 is a sectional view taken through line 2-2 of Fig. l;

Fig. 3 is a sectional view taken through line 3-3 of Fig. 1;

Fig. 4 is a view of a portion of Fig. 1 illustrating the pour rod in pouring position;

Fig. 5 is a fragmentary sectional view of a modified crucible, valve, and mould; and

Fig. 6 is a fragmentary sectional view similar to Fig. 5 showing a valve of modified cross-section.

Referring to Figs. 1-4 of the drawings, the casting apparatus illustrated generally includes a cylindrical, graphite crucible 10 having a melting well 11 formed by an upper, interior, cylindrical wall 9 terminating in a bottom surface including an inwardly sloping conical portion 8 and a recessed bottom 7 in which a uranium pig or biscuit B may be melted. -A centrally disposed aperture or spout 12, in the bottom of the crucible 10, is normally closed by a tapered graphite valve 13 having an 'annular under surface 13a which seats on the bottom surface 7 of the crucible 10. The valve 13 may have a flat top surface as shown or may have the tapered portion extend to a point. A graphite pour rod 14 extends upwardly through the aperture 12 into a recess in the valve 13 centrally of the undersurface 13a. When the desired pouring temperature for the uranium pig B is reached, the valve 13 is raised by upward movement of the rod 14 and the tapered upper portion of the valve breaks any skin or film, such as an oxide or uranium carbide skin, under or about the molten metal biscuit B. Thereafter, the valve 13 floats on the molten metal and provides a pressure weight forcing the molten uranium or other metal to run out of the crucible spout 12.

The molten uranium metal from the crucible 10 flows through the spout 12 into a gate or channel 17 and then into the forming hollow 18 of a graphite mold 19 that is located beneath and supports the crucible 10. The crucible 10 and mold 19 are provided with interlocking ends 20 so that the two members may be readily aligned relative to one another.

The crucible and mold assembly is supported on a firebrick cylinder 21 which rests on a water--cooled brass base 22. Suitable inlet and outlet connections 24 and 23, respectively, supply cooling water to the waterjacket base 22.

A thermocouple 25 for temperature measurements extends upwardly through the base 22, the cylinder 21, and the mold 19 to a point in the crucible 10 adjacent the crucible Well 11. An insulating member 26 formed of Sillimanite half-tile or similar insulating material is set up around and over the crucible and mold assembly lso as to limit the loss of heat therefrom. A cylindrical quartz tube 27 surrounds the insulating member 26 and is sealed at its lower or open end by gasket 28 to the water-cooled base 22.

The water-cooled base 22 is provided with an axially disposed, cylindrical passageway 32 through which a steel valve rod 34, slidably supported by brace 35, extends, said rod 34 being coupled at 33 to the pouring rod 14. Suitable cooperating adjustable stops 36 and 37 are provided on the lower end of the rod 34 and a fixed support 38respectively, for limiting the upward movement of the rod 34.

The assembly is made fluid-tight by a rubber-tube vacuum seal 42 about the rod 34. In order to provide for evacuating the assembly, the seal 4.2 is secured to a T-joint 43, the upper end of which is fitted in the passageway 32 of the base. The assembly may be readily evacuated to a desired sub-atmospheric pressure through opening 44 of the T-joint 43. In order to insure complete evacuation at all points in the assembly, radially extending vents 45 are formed in the insulator cylinder 21 so as to connect the passageway 32 with the interior of both the quartz cylinder 27 and the insulator 26. Likewise, a vent 46 is disposed in the base of the crucible 10 and a vent 41 is provided in the crucible cover 4t) s0 as to vent the mold form 18 and the interior of the crucible 10 to the evacuated interior of the insulator 26.

In assembling the parts for casting, graphite push rod 14 is inserted in the steel coupling 33 on the end of steel push rod 34 and pinned` The thermocouple 25 is insei-ted next, adjusted to the correct height, and sealed in the base 22 with thermoplastic sealing wax. Then the mold base 21 is placed on the base 22 and the graphite mold 19 is set on the mold base 21. The next step is to cut the graphite push rod 14 so that it extends to a point l/s inch below the valve 13 when assembled. The stops 36 and 37 are adjusted so that when push rod 34 is pushed up until stop 36 contacts stop 37, the valve 13 is lifted from its seat and all molten metal in the crucible 10 may run into mold 19. The Crucible 10, valve 13, and small uranium block B are assembled next in order. Then the crucible lid 40, the insulator 26, the rubber gasket 28, and the quartz tube 27 are placed in position in order.

In operation, the assembly just described is evacuated through opening 44 and, thereafter, the crucible 10 is heated, as by an induction coil (not shown) around the quartz cylinder 27. When the desired pouring temperature is reached, the pouring rod 14 is raised to the extent permitted by the stops 36 and 37 to break any skin under the metal biscuit.

This operation raises valve 13 from the valve seat 7 and permits molten uranium to run into mold 18. The valve 13 thereafter floats on the molten uranium until it has all run out of the crucible 1i).

Modiiied crucible and valve constructions are shown in Figs. 5 and 6, in which the same reference numerals employed in Figs. 1 4 are used to denote the same or equivalent parts. Specifically, the crucible includes a substantially hemispherical bottom 50 having a small shallow aperture 12, as distinguished from the large aperture 12 in Fig. 1. The valve rod 14 extends through the graphite mold 19 and terminates in a substantially hemispherical head 52 (Fig. 5) or a conical head 54 (Fig. 6). In other respects, the modifications of Figs. 5 and 6 are the same as that shown in Fig. l, except that a second stop (not shown) may be provided on the rod 38 below the stop 37 shown in Fig. l to limit the downward movement of the valve rod 14.

In Figs. 5 and 6, the valve rod 14 is illustrated in full lines to show its position when a biscuit B is being melted in the crucible 10. The base of the hemispherical head 52 or conical head 54 is even or flush with the bottom 50 of the crucible 10. If the head is lower than such relation, the skin and carbide formation in the aperture 12 will prevent the valve rod 14 from being pushed up and, hence, will prevent the molten metal from running into the mold well 18. If the head is higher than such relation, carbide formation on the side of the rod 14 will prevent withdrawal of rod 14. The upper broken lines of the heads 52 and 54 indicate the piercing positions thereof, while the lower broken lines indicate the pouring positions.

In the modications of Figs. 5 and 6, the yield is affected by the thickness of the crucible bottom at the aperture 12. The depth of the aperture 12 should be 1A; inch or less, preferably less, for maximum yield; otherwise, it tends to hold the last drop of metal. A drop of molten uranium will amount to from 2 to 5 percent of the total yield on the scale of casting contemplated by the invention. The aperture 12 may be 1A inch in diameter, the rod 14, slightly less than 1A inch, a Clearance of 0.002 to 0.003 inch being permissible.

The method and apparatus described above constitute an improvement on the subject matter which is disclosed in the co-pending application of Harley A. Wilhelm and C F. Gray, iled December 8, 1944, Serial No. 567,283, and granted as U. S. Patent No. 2,782,475 on February 26, 1957.

Since certain changes may be made in the above construction and diierent embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense, the invention being defined by the appended claims.

What is claimed is:

1. An apparatus for casting uranium and particularly small quantities thereof, comprising a crucible having an aperture in the center of the bottom, a mold below and contiguous to the crucible and positioned to receive liquid owing through said aperture, a vertical valve rod slidably disposed in the aperture and adapted to have the upper end slid into the crucible, the upper end of the rod having a piercing head, a cylinder enclosing the crucible and mold in an air-tight manner, means for establishing a vacuum in the cylinder, and heating means about the Cylinder adjustable along the vertical axis thereof, whereby a skin encasing a molten metal body in the crucible may be punctured by the head and the molten metal drained into the mold and the skin retained in the Crucible.

2. An apparatus for casting uranium comprising a crucible having an aperture in the center of the bottom, a mold below and contiguous to the crucible andVpositioned to receive liquid iiowing through said aperture, a vertical valve rod slidably disposed in the aperture and adapted to have the upper end slid into the crucible, the upper end of the rod having a tapered piercing head, the surfaces of the crucible, the mold and the rod consisting of graphite, a cylinder enclosing the crucible and mold in an air-tight manner, means for establishing a vacuum within the cylinder, and heating means about the cylinder adjustable along the vertical axis.

3. An apparatus for casting uranium comprising a graphite crucible having an aperture in the center of the bottom, a graphite mold below and contiguous to the crucible and positioned to receive liquid owing through said aperture, a vertical cylindrical graphite valve rod slidably disposed in the aperture and adapted to have the upper end slid into the crucible, the upper end of the rod having a conical head, and an induction coil about the crucible and mold adjustable along its vertical axis.

AReferences Cited in the file of this patent UNITED STATES PATENTS 1,022,910 Whitney Apr. 9, 1912 1,318,452 Keyes Oct. 14, 1919 1,521,526 Godai Dec. 30,1924 1,540,515 Cuenot June 2, 1925 1,542,598 Begtrup June 16, 1925 1,542,784 Deppeler June 16, .1925 1,568,685 Moore Jan. 5, 1926 1,684,800 Muximoir er a1. sept. 1s, 1928 2,127,239 stoody Aug. 16, 193s 2,257,713 De Bats Sept. 30, 1941

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