Method of making and using a ceramic shell mold
AssigneeCaterpillar Tractor Co.
InventorRichard C. Ostrowski
Life of this patent
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Abstract
A method of making a shell mold (6) includes alternately applying a ceramic coating composition (8) and a stucco composition (10) to an expendable pattern, the presence of graphite being substantially avoided therein, and applying a barrier coating (16) thereto including a ceramic powder, a binder, and a preselected amount of graphite. A preferred range of graphite of about 13 to 17 Wt. % in the barrier coating (16) minimizes decarburization of a ferrous article formed in the cavity of the shell mold (6).
Claims13
A method of making a ceramic shell mold (6) comprising:
- Step (a) alternately applying a coating composition (8) including a ceramic powder and a binder, and then a stucco composition (10) including granular refractory material to an expendable pattern a preselected number of times, drying the coating between applications, and forming a resultant multi-layered mold, said multi-layered mold having less than 0.5 Wt.% graphite:
- Step (b) heating the multi-layered mold, removing the pattern, and forming a resultant hardened mold (12);
- and
- Step (c) applying a barrier coating (16) to the exterior surface of the multi-layered mold (12) while the hardened mold (12) is at a preselected temperature above ambient, said barrier coating (16) including a mixture of a ceramic power, a binder, and a preselected amount of particulate graphite within a range of about 4 to 20 Wt.% of the solid portion of the barrier coating (16).
A method of investment casting of a ferrous article in a shell mold (6) comprising:
- Step (a) applying a coating composition (8) including a ceramic powder and binder to an expendable pattern, said ceramic powder being selected from the group consisting essentially of fused silica, vitreous silica, crystalline silica, alumina silicate, alumina, magnesium silicate, zircon, zirconium silicate, and clay, and binder being selected from the group consisting essentially of colloidal silica sol, ethyl silicate, aluminum phosphate, and aqueous alkali metal silicate;
- Step (b) applying a stucco composition (10) including a grangular refractory material:
- Step (c) alternately repeating Steps (a) and (b) a preselected number of times and forming a multi-layered mold, said multi-layered mold having less than 0.5 Wt.% graphite;
- Step (d) heating the multi-layered mold and forming a hardened mold (12) having an internal cavity (14);
- Step (e) applying a barrier coating (16) to the exterior surface (20) of the hardened mold (12) at a location spaced from the internal cavity (14) and while the hardened mold (12) is at a preselected temperature above ambient, said barrier coating (16) having a solid portion and being a mixture of a ceramic powder, a binder, and a preselected amount of finely divided graphite, said preselected amount of graphite being within a range of about 4 to 20 Wt.% of the solid portion of the barrier coating (16);
- Step (f) heating the hardened mold (12) and barrier coating (16) and forming a hot shell mold (6);
- and
- Step (g) pouring a ferrous molten metal into the internal cavity (14) of the hot shell mold (6).
Dependencies are inferred from the claim text.