Metal Casting

For the purpose of fully explaining the above and further objects of the invention, reference is now made to the following detailed description of preferred embodiments thereof, together with the accompanying drawings, wherein:

FIGS. 1, 2 and 3 are schematic sectional side views of the apparatus of the invention, illustrating successive steps in the operation of the methods of the invention.

Referring to the drawings, there is provided a partible sealable loading compartment 12 mounted on vertically movable support 14. Loading compartment 12 has, in its upper wall, a connection to differential pressure apparatus 16 and, in its lower mold supporting wall, a central opening 18 for supporting a gas permeable mold, generally designated 20, which may be of the shell type disclosed in said patents, having a vertical passage 22 with a lower open end 24 for introducing molten metal into mold cavities 26 therein. A crucible 30 for holding molten metal, providing an exposed molten metal upper surface 32, is positioned beneath loading compartment 12. Differential pressure apparatus 16 can be selectively operated in the usual manner to apply a differential pressure to compartment 12 and mold 20 relatively to crucible 30 to cause molten metal to fill mold cavities 26 through vertical mold passage 22. A hydraulic power cylinder 34 connected to movable support 14 is provided for relatively moving crucible 30 and compartment 12 with mold 20 toward and away from one another by selectively raising or lowering compartment 12 with mold 20.

According to the present invention, there is provided a single use, removable, rigid, permanently crimpable, disposable, hollow metal fill pipe, generally designated 40, having an upper flared portion providing a radially outwardly extending upper flange 42 with a lower portion 44 extending vertically downwardly therefrom. Upper flange 42 is sealingly interposed between the lower mold supporting wall of container 12 and the lower end of mold 20 around its opening 24 and lower portion 44 extends through central opening 18 of container 12 and vertically downwardly therefrom toward the molten metal surface 32 in crucible 30. A fill pipe crimping device, which may consist of a horizontally movable crimping element 50 operated by a hydraulic cylinder 52 mounted on the lower end of vertically movable support 14 and an opposed abutment 54, also mounted on support 14, is positioned between compartment 12 and crucible 30, with element 50 and abutment 54 on opposite sides of the lower portion 44 of fill pipe 40 in lowered position, as shown in the drawings, for selectively permanently crimping the lower portion 44 of fill pipe 40 to permanently close it after the filling of mold cavities 26 has been completed, in order to prevent reverse flow of molten metal back into crucible 30 as container 12 with mold 20 and fill pipe 40 are moved upwardly relatively away from crucible 30. At least the lower portion 44 of fill pipe 40 is of crimpable metal so that it can be permanently deformed by the advance of crimping element 50 toward abutment 54 to provide a permanently crimped portion 56, as shown in FIGS. 2 and 3, to permanently close its hollow interior to prevent flow of molten metal therethrough, even after crimping element 50 has been retracted, as shown in FIG. 3. In practice, with most fill pipe metals, fill pipe crimped portion 56 is welded closed by the action of crimping element 50 and abutment 54, with the weld being maintained because of the rapid heat loss from the metal fill pipe 40.

In operation, according to the methods of the invention, first, the lower portion 44 of fill pipe 40 is inserted through the lower opening 18 of open container 12, so that its flared upper portion 42 is supported by the lower wall of container 12 and its lower end portion 44 extends vertically downwardly toward crucible 30, spaced above the surface 32 of the molten metal in crucible 30. Next, mold 20 is placed on the upper surface of flared fill pipe portion 44 with its lower open end 24 concentric with fill pipe 40 so that fill pipe 40 is removably sealingly connected between the lower open end 24 of vertical mold passage 22 and the lower wall of container 12 surrounding container lower opening 18. Container 12 is then closed and connected to differential pressure apparatus 16.

Thereafter, container 12 with mold 20 and fill pipe 40 is moved downwardly by operating hydraulic power cylinder 34 to move the lower end of fill pipe 40 beneath the surface 32 of molten metal in crucible 30 to introduce molten metal from crucible 30 into the lower end of fill pipe 40, as shown in FIG. 1. A reduced differential pressure is then applied to container 12 and so to mold 20 by operating differential pressure apparatus 16 to cause molten metal to fill mold cavities 26 through fill pipe 40 and central vertical mold passage 22.

After mold cavities 26 have been filled, horizontally movable crimping element 50 is operated by hydraulic cylinder 52 to advance it horizontally toward opposed abutment 54 on the opposite side of the lower portion 44 of fill pipe 40, as shown in FIG. 2, to crimp the lower portion 44 of fill pipe 40 to provide a permanently crimped portion 56, as shown in FIGS. 2 and 3, to permanently close its hollow interior, preferably even after crimping element 50 has been retracted, as shown in FIG. 3, to prevent reverse flow of molten metal back into crucible 30 as container 12 with mold 20 and fill pipe 40 are moved upwardly relatively away from crucible 30. In practice, as noted above, the interior walls of fill pipe crimped portion 56 are welded closed by the action of crimping element 50 and abutment 54, by the application of crimping force for only a second or two, after which crimping element 54 is retracted, with the weld thereafter being maintained because of the rapid heat loss from the metal fill pipe 40. This is a particular advantage, since it reduces the casting cycle time and so increases production.

Finally, container 12 is opened and the filled mold 20 and fill pipe 40, locked together by the solidified metal, are removed in preparation for another molding cycle, and pipe 40 is removed from mold 20.

It is important that the metal or alloy of fill pipe be compatible with that being cast, so that, at least in some instances, the identical alloy be used. Since this will result in the lower end of fill pipe 40 melting as it is introduced to the surface 32 of molten metal in crucible 30, it is contemplated that hydraulic power cylinder 34 be operated to continue to move container 12 downwardly during the filling cycle of mold 20, after which its downward movement can be terminated and crimping element 50 operated to crimp fill pipe 40, after which further melting of the lower end of fill pipe is of no importance.

Alternatively, fill pipe 40 may have a thin ceramic outer coating, which, because of the short time fill pipe 40 is submerged in molten metal, prevents it from melting, but does not interfere with its crimping or welding. As another alternative, the lower portion of fill pipe 40 to be submerged in molten metal, below the portion to be crimped, may be of ceramic, since, due to the short time the lower portion of fill pipe 40 is submerged, only that portion of fill pipe 40 which is actually submerged is subject to melting.

We have discovered that, since the metal of the fill pipe almost always has a melting point substantially below the temperature of the metal in the crucible and the bare fill pipe melts rapidly, if the pipe is too thin, the pipe will collapse and the process will not work. If the pipe is too thick, metal solidifies on the inner and outer surfaces also rendering the process impractical. We have determined that the practical wall thickness for such a single use fill pipe in the range of diameters of one to three inches and lengths of five to 30 inches is 0.060 to 0.180 inches. This range of wall thickness is also compatible with formation of and maintenance of a permanently welded crimp.

We have also discovered that the location of the crimp must be at a distance of at least 1.5 times the pipe diameter from the pipe upper end and flange so that the crimping action does not distort the pipe flange and allow molten metal to run out of the joint between it and the permeable mold.

Although the description of the preferred embodiment herein has referred to molds of shell type disclosed in U.S. Pat. Nos. 3,863,706, 3,900,064 and 4,112,997, it is contemplated that other types of gas permeable molds may also be used in the practice of the invention, including conventional bonded or unbonded sand molds, as well as those of the "lost foam" type. In the latter, molding sand is packed around a polystyrene foam pattern with gating and molten metal is introduced directly into the foam, which vaporizes and escapes through the molding sand, leaving a casting which is a replica of the foam pattern.

Still further modifications of the invention, within the spirit of the invention and the scope of the claims, will be apparent to those skilled in the metal casting art.