US2419716A - Mold assembly for centrifugal casting - Google Patents

Description

April 29, 1947. GREENWELL 2,419,716

' MOLD ASSEMBLY FOR CENTRIFUGAL CASTING Filed Sept. 13, 1945 525T EZTZVI Fr EE'ZZ WE fatentecl Apr. 29, i947 li EOLD ASSEMBLY FOR CENTRIFUGAL CASTING Everett N. Greenwell,

The Indiana Steel Valparaiso, Ind., assignor to Products Company, Chicago,

111., a corporation of Indiana Application September 13, 1945, Serial No. 615,988

14 Claims.

This invention relates to a mold assembly and I more particularly to a mold assembly including ceramic mold inserts of a refractory composition for the centrifugal casting of metals and alloys of relatively high melting points.

In accordance with the principles of my invention, preformed mold inserts are employed to provide accurately dimensioned mold cavities. The mold cavities found most satisfactory are those made of a refractory composition by a molding, die pressing or other forming operation. The mold inserts so formed may then be baked or fired to develop a high temperature bonding property. These-mold inserts are arranged in associated relationship so as to form the mold cavities with separate gates leading thereinto.

In order to facilitate the assembling and dismantling of a mold assembly, I employ sectorshaped members for receiving and positioning the mold inserts in superimposed relationship circumferentially of the pouring cavity of the mold assembly. These sector-shaped members, which may also be formed of a refractory ceramic composition, are arranged Within a tapered cylindrical shell to provide an annulus about the pouring cavity, and the individual mold inserts are stacked in the cylindrical cavity provided for the purpose by the assembled sector-shaped members. By the use of such an arrangement, the cast metal does not touch any metal surfaces and, therefore, does not become unduly chilled during the casting operation. The individual mold inserts, when stacked one upon the other, provide individual gates into the ultimate mold cavities of the inserts.

After the articles have solidified, they can be removed without destruction of the sectorshaped members and without damage to the castings themselves. Heretofore, when an integral carrier or holder for the mold inserts wasemployed, it took as much as twenty minutes or more to knock out the castings from the mold and a considerable portion of the castings were damaged. With the segmented carrier of the present invention, however, the mold assembly can be dismantled after casting in five minutes or less and at the same time the possibility of damaged castings is practically eliminated.

Furthermore, the elimination of any metal surface for contact with the cast metal reduces the chilling of the castings and reduces, therefore, the likelihood of cold shuts or cracked castings being produced, as was the case, when using metal parts in the mold assembly that came into contact with the cast metal. Oftentimes'it is necessary to mold inserts are held produce castings of fine grain for physical strength, and with such a design, the present form of mold assembly may not be entirely suited. On the other hand, the present type of mold assembly gives better surface characteristics and greatly facilitates the casting operation.

It is therefore an important object of this invention to provide a mold assembly in which a plurality of preformed, accurately dimensioned tightly in superimposed relationship within sector-shaped members that are maintained in the form of a ring, or annulus, within an outer cylindrical shell, thereby facilitating the setting up and dismantling of the mold assembly.

It is a further important object of this invention to provide a mold assembly for use with highly refractory ceramic mold inserts, and in which the insert carrier is segmented for ease of assembling and dismantling. It is a further important object of this invention to provide a mold assembly for use in the precision casting of high melting point metals and alloys by the use of centrifugal force, which mold assembly presents no metal surfaces for contact with the cast metal or alloy and therefore insures better surface characteristics of the castmgs.

It is a further important object of this invention to provide a mold assembly for use in centrifugal precision casting, in which the mold may be easily assembled and dismantled because of the use of a segmented carrier for .the individual molds inserts, the arrangement being such as to substantially eliminate any possibility of damaged castings.

Other and further important objects of this invention will be apparent from the disclosures in thespecification and the accompanying drawing,

On'the drawings:

Figure 1 is a top plan view, partly broken away, of the mold assembly embodying the principles of my invention. 7

Figure 2 is an enlarged sectional view taken substantially along the line II-lI of Figure 1, with parts in elevation and parts broken away.

Figure 3 is a perspective view of a sector-shaped member of the carrier, or holder, for the individual mold inserts. Y

As shown on the drawings:

The reference numeral 10 indicates generally a mold assembly embodying the'principles of my invention. Said mold assembly comprises a mounted, cylindrical receptacle l I having an open; flanged, upper end l2 and aclosed bottom wall l3. The receptacle H is adapted to be mounted upon a centrifugal table l4 driven through a shaft l5.

For mounting purposes, the table Id is provided with clamping members it secured to the centrifugal table M by means of bolts H. The receptacle H has bolted to its underside a flanged ring [8, the fianges ill of which are adapted to be engaged by the clamping members 16. Bolts 20 secure the ring M3 to the undersurface of the bottom wall I3. An annular insulating gasket 2| may be inserted between the ring l8 and the bottom wall l3 to reduce the amount of heat conducted from the mold assembly to the centrifugal table l4.

A graphite disk 22, or a disk of any other relatively refractory and non-heat-conductive material, is positioned within the casing H against the bottom wall l3. An annular mold insert fixture, or carrier, indicated generally by the reference numeral 23 is then inserted into the casing H for positioning on top of the graphite disk 22.

Said annular mold insert fixture, or carrier 23 includes a ring 24 having an outer cylindrical surface for fitting within the casing II and an inner tapered surface 25. The ring 24 may be of metal or other suitable material and may be cast or formed integrally. Individual, sector-shaped, refractory members 26 are arranged within said shell 24 to form together a ring R within the ring 2 3. Each of the individual, sector-shaped members 28 (Figure 3) is formed of baked ceramic material of highly refractory composition, although for some purposes the members may be formed of metal or a metal alloy. As shown, each sector-shaped member 26 has an outer frustoconical surface 21 that conforms to the taper of the inner surface 25 of the ring 24. The purpose of this tapered surface arrangement is to insure that the sector-shaped members 26 are locked into place upon insertion of a ring R within the ring 24. Each of the members 26 is further provided with a segmental, right-cylindrical surface 28 on either of its radial faces for cooperation with similar segmental-cylindrical surfaces to form cylindrical cavities-C for the reception of a plurality of superimposed mold-inserts 29. The inner surfaces 30 of the members 26 may be plane or rounded, but as shown are plane and are provided with beveled edges 3-! leading toward the cavities C.

Each'of the mold inserts 29 is preferably in the form of a relatively short cylinder having a diameter that enables it to besnugly received within one of the cavities C. As illustrated in Figure 2, each mold insert 29 is provided with a plane-upper annular edge 32 upon which rests a filler insert 33. Said filler insert 33 is also formed of a refractory ceramic composition and is provided-with a cut away portion forming a gate 34 for entrance of the cast metal into the individual mold cavity MC of the adjacent mold insert 29 therebelow. As shown, each of the mold inserts 23 and the filler insert 33 is provided with an axially extending bore and a cylindrical rod 35 of graphite or the like is inserted through the aligned bores when the inserts are in superimposed position within the cavities C. It will be understood, however, that the showing is merely illustrative of one type of mold insert and that'other forms may be used with or without the graphite rod 35 to form holes in the final casting.

In making the mold inserts used in my assembly, a composition comprising a substantially dry mixture of a finelydivided refractory material,

such as alumina, or the like, and suitable low and high temperature bonding agents, is placed in a master mold and pressed to the desired size, shape and dimensions, including those with the recesses therein to form the mold cavities MC. After being molded to shape and dimensions, the green" mold inserts are then dried, baked and fired to form refractory or ceramic mold inserts of the type illustrated in Figures 1 and 2. The recesses, such as the recesses forming the individual mold cavities MC, are in this way very accurately dimensioned, allowance being made for the forming of the mold inserts for change of size during the firing step forcontraction of the cast metal article upon cooling, so that the final cast article can be kept within very close tolerances indeed.

After the ring 24, inner ring R and mold and filler inserts 29 and 33 have been assembled within the casing H above the graphite disk 22, an asbestos or other heat insulating and highly refractory gasket 36 is laid over the top of the assembled ring R, and the spacing ring 31 inserted into the top of the casing H to rest upon the gasket 36. A clamping ring 38 is laid on top of the spacing ring 31 and clamped down by means of J-shaped clamping bolts 39 that pass through the flanged upper portion l2of the casing H and are held in place by means of nuts 40.

The assembled mold provides a central pouring cavity P-C, into which the molten metal is poured during the casting operation. The mold assembly P is set to rotating upon the centrifugal table [4 at a suitable speed, usually between 400 to 1700 R. P. and molten metal is poured into the mold assembly through the pouring cavity P-C. Due to the high speed of revolution of the mold assembly, the molten'metal is thrown outwardly and upwardly, so that the cross-section of the surface of the' molten'metal, after the individual mold cavities MC have been filled, takes substantially the shape of the pouring cavity P-C except that the surface becomes slightly tapered downwardly and inwardly. Due to the centrifugal force withiwhichthe molten metal is thrown outwardly, metal enters each of the individual cavities MC through the gate 34,to fill said individual cavities -and-the gate itself. Since the mold inserts are clamped tightly together by means of the clamping ring 38 and spacing ring 31, together with the J-shaped bolts 39 and nuts 40, no metaloan force its way in between :the upper surfaces 32'andthe under surfaces of the insert filler '33, except, of course, at the'gates34. The upper and lower surfaces of the castingssare thus smooth except for the portions of metal that fill the gates 34. i

After the casting operation is'completed' and thecast metal -alloy"hashad an opportunity to solidify, the mold assembly is taken apart and the segmentalv annular ring R dismantled. Iflthe amount or molten. metal poured hasfbeen Iclosely gauged, there "will: be only a thin; shell of metal over the inner periphery of the segmental annular mold=insert carrying ring R, and this canbe readily broken away attherestricted portions of the metal in gates; "Eachstack of mold inserts and filler inserts i's'then'freed by removing the sector-shaped memb'ers 26 from between' said stacks,"andeachz stack is then broken up to free the individual cast: articles. The portions of the graphite rod 35: ar e" either forced: or drilled out to leave J the centralrop'enings formed thereby in the. individual castings,

The moldiassemblmof' my invention thus makes it possible-to casti various metals and alloys, inl eluding highly refractory metals and alloys, in relatively small shapes to close tolerances. While it is not necessary to resort to centrifugal casting to carry out the method of my invention, it is advantageous to make use of centrifugal casting in the case of high meltin point metals and alloys that are sluggish in their flow even at tem peratures above their melting points. This is particularly true of certain permanent magnet a1- loys, such as alloys of the alnico type containing aluminum, cobalt, nickel and sometimes small proportions of other metals. Where a metal or alloy has a relatively low'melting point or is relatively fluid at easily obtainable temperatures, the casting may be carried out in a stationary mold, or with the use of suction or pressure, as desired.

The form and arrangement of my mold assembly greatly facilitate the casting operation since it makes it easier to assemble and dismantle the mold before and after casting, respectively, Furthermore, as already pointed out, there are certain advantages in so arranging the mold assembly that no metal come into contact with the cast metal or metal alloy. This is a continuationin-part of my copending application Serial No. 538,61e, filed June 3, 1944, entitled Mold Assembly for Precision Casting.

It will, of course, be understood that various details of construction may be varied through a wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims,

I claim as my invention:

1. A mold assembly comprising an open-ended shell of generally cylindrical shape, a plurality of sector-shaped members within said shell and forming together a ring having a central pouring cavity and a plurality of circumferentially spaced smaller cavities, and a plurality of mold inserts arranged in superimposed relationship within said smaller cavities and forming together individual mold cavities having gates leadin thereinto from said pouring cavity.

2. In a. mold assembly, an annular segmental member providing circumierentially spaced recesses, a plurality of mold inserts stacked one upon another in each of said recesses, said mold inserts forming together mold cavities and gates leading into said cavities, and a ring of generally cylindrical shape holding said segmental member and mold inserts in assembled relationship.

3. In a mold assembly, an annular member composed of a plurality of sector-shaped parts providing circtunferentially spaced mold insert receiving recesses, a plurality of mold inserts stacked one upon another in each of said re cesses, said molds forming together mold cavities and gates aligned for leading into said mold cavities, and means for holding said mold inserts in close contact with each other and for retaining said segmental annular member in association with said mold inserts for the centrifugal casting of molten material into said mold cavities,

l. In a casting assembly, a casing, a ring therein having a tapered inner wall, a plurality of individual sector-shaped members forming together an annular ring having a tapered wall conforming with the tapered wall of said first ring and having individual recesses spaced circumferentially thereof, and a plurality of mold inserts mounted in superimposed relationship within said recesses and providing mold cavities and gates leading thereinto.

i, an annular ring havin a tapered wall conforming with the tapered wall of said first ring and having individual recesses spaced circumferentially thereof, a plurality of mold inserts mounted in superimposed relationship within said recesses and providing mold cavities and gates leading thereinto, and means for holding said mold inserts and sector-shaped members in tight association.

6. In a mold assembly an annular member having recesses spaced about the inner peripherythereof and openings intosaid recesses, a plurality of mold inserts stacked one upon another in each of said recesses, said molds forming together mold cavities and gates alined with said.

openings and leading into said cavities and means: for holding said mold inserts in close contact with each other.

'7. In a mold assembly an annular member having recesses spaced about the inner periphery thereof and openings into said recesses, a plu-- rality of mold inserts stacked one upon another in each of said recesses, said mold forming together mold cavities and gates alined with said openings and leading into said cavities, means for holding said mold inserts in close contact with each other and a casing for retaining said annular member during centrifugal casting of molten material into said mold cavities.

8. In a casting assembly, a casing, a fixture mounted therein having a relatively deep recess with a restricted opening thereinto the full depth thereof, a plurality of mold inserts fitted into said recess one adjacent another, said mold inserts forming together a plurality of mold cavities and gates alined with said restricted opening and leading into said cavities, and means for holding said mold inserts tightly together,

9. In a casting assembly, a cylindrical casing open at the top and having a closed bottom wall, a liner in the bottom thereof, an annular fixture resting on said liner and provided with a plurality of recesses spaced about the inner periphry thereof and having restricted radially extending full length openings, a plurality of mold inserts fitted into said recesses, said mold inserts forming together a, plurality of mold cavities and gates alined with said restricted openings and leading into said cavities, an annular member overlying said fixture to close the upper ends of said recesses and means for clamping said fixture between said annular member and said bottom liner.

10. In a casting assembly, a cylindrical casing open at the top and having a closed bottom wall, a non-heat conductive liner in the bottom thereof, an annular fixture resting on said liner and provided with a plurality of recesses spaced about the inner periphery thereof and having restricted radially extending full length openings, a plurality of mold insert-s fitted into said recesses, said mold inserts forming together a plurality of mold cavities and gates alined with said restricted openings and leading into said cavities, an annular member overlying said fixture to close the upper ends of said recesses, means for clamping said fixture between said annular member and said bottom liner and means for rotating said casing about its axis to cause molten material poured onto said bottom liner to be thrown centrifugally through said restricted opening and gates into said mold cavities.

11. In a casting assembly, a cylindrical casing open at the top, a non-heat conductive refractory liner for the bottom of said casing, an annular fixture resting on said liner, saidffixtu're having a plurality ofrbor'es spaced about the inner periphgates alined with said restricted entrances and means closing the upper ends of said bores but providing an opening through which molten material can be poured onto said bottom liner to 'be centrifugally thrown through said restricted entrances and said gates into said mold cavities;

12. In a, casting assembly, a cylindrical casing open at the top, a non-heat conductive refractory liner for the bottom of said casing, an annular fixture resting on said-liner, said fixture havin a plurality of bores spaced about the inner periphery thereof and opening therethrough to provide restricted full length entrances to said bores, a plurality of ceramic mold inserts fitted into'said bores one upon another, said moldinserts forming together a plurality of 'mold cavities with gates alined with said restricted entrances and means clamping said fixture against said liner andiclos ing the upper ends of 'said'bores but providing an opening through which molten material can be poured onto said bottom liner to be centrifu-' gally thrown through said restricted entrances and said gates into said mold cavities.

13. In a mold assembly, an annular member having, recesse's spaced about the inner periphery thereof parallel to the axis of saidmember andihaving openings in the inner periphery into saidgrecesses, a plurality of preformed mold inseas. arranged in contacfiwith one another in said i-ecess'es, said"rnold inserts forming'tog tlier a' plurality of '"mold cavities and gates. leading thereinto for receiving fluid material introduced through 'said openings, and means for holding said'iiiserts in tight contact with each other.

'14. Inacentrifugal mold assembly an annularmember having a closed outer periphery and 'de'-' finingbores having lateral openings through the innenperipheryvinto theinterior of said member, a plurality .of preformed mold insertspacked in said bores, said mold-inserts forming togethr a EVERETT N. GREENWELI Q REFERENCES CITED The following references are of record in the file :ofthis patent:

UNITED STATES PATENTS Number Name a Date 2,299 860 Stoo dy Oct. 27; 1942' 359,484 Whitley Mar, 15, 1887 2,027,963 De Bats Jan. 14,1936

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