Porcupine shell molds and method of making same

Claim 2

A process for manufacture of unbacked porcupine shell molds with substantial wall thickness comprising dipping a destructible pattern of a predetermined shape in a ceramic slurry containing a liquid vehicle, finely divided refractory particles and a heatsetting binder, dusting the resulting ceramic layer with refractory particles to provide a stucco coat, and drying such ceramic layer; repeating the dipping, dusting and drying operations to build up at least 3 refractory layers on the pattern; thereafter adhering stiff destructible threads to the outer layer in closely spaced relation throughout the outer layer of the shell mold, said threads having a length of about 0.4 inch to about 1 inch and being held in outwardly projecting positions; thereafter forming additional refractory layers by dipping the shell mold in a ceramic slurry to cover said threads and to cause the outer ceramic layers to form projections conforming to the shape of said threads; and firing the resulting porcupine shell mold to burn out said threads and thereby form threadlike voids in said mOld.

Claim 3

A process as defined in claim 1 wherein said threads comprise organic fibers and substantially all of said threads are applied in a single operation prior to the next application of the ceramic slurry.

Claim 4

A process as defined in claim 2 wherein said threads comprise Tampico fibers and are sprinkled on the outer surface of the shell mold during said single operation.

Claim 5

A process of making an unbacked porcupine shell mold of the character described for casting metal without a backing comprising the steps of dipping a destructible pattern of a predetermined shape in a ceramic slurry containing a liquid vehicle, finely divided refractory particles and a heat-setting binder, dusting the resulting ceramic layer with refractory particles, and drying said ceramic layer; repeating the dripping, dusting and drying operations to build up a plurality of refractory layers on the pattern; thereafter adhering stiff destructible threads to the outer layers of the shell mold in closely spaced randomly disposed relation throughout said outer layer while the mold is free of other reinforcing members so that all of the refractory layers then formed conform to the shape of the mold cavity, said threads having a length of about 0.4 inch to about 1 inch and being held in outwardly projecting positions; thereafter forming a plurality of additional refractory layers which cover the threads and form projections conforming to the shape of said threads; and firing the resulting porcupine shell mold to burn out said threads and thereby form threadlike voids in the walls of said mold.

Claim 6

A process of making an unbacked porcupine shell mold of the character described for casting metal without a backing comprising the steps of dipping a destructible pattern of a predetermined shape in a ceramic slurry containing a liquid vehicle, finely divided refractory particles and a heat-setting binder, dusting the resulting ceramic layer with refractory particles, and drying said ceramic layer; repeating the dripping, dusting and drying operations to build up a plurality of refractory layers on the pattern; thereafter adhering stiff destructible threads to the outer layers of the shell mold in closely spaced randomly disposed relation throughout said outer layer while the mold is free of other reinforcing members so that all of the refractory layers then formed conform to the shape of the mold cavity, said threads having a length of about 0.4 inch to about 1 inch and being held in outwardly projecting positions; thereafter forming a plurality of additional refractory layers which cover the threads and form projections conforming to the shape of said threads; and firing the resulting porcupine shell mold to burn out said threads and thereby form threadlike voids in the walls of said mold.

Claim 7

An unbacked porcupine shell mold formed in accordance with claim 4 for casting molten metal comprising a thick refractory body with an inner refractory layer forming a smooth internal surface defining a mold cavity of a predetermined shape and an outer refractory layer having a porcupine-like configuration, said body having inner refractory layers which conform substantially to the shape of said mold cavity and a multiplicity of closely spaced thread-like voids randomly distributed throughout said body outwardly of said inner layers, said voids having a length of about 0.4 to about 1 inch, extending radially outwardly, and being covered by additional refractory layers which conform generally to the contour of said threadlike voids and project outwardly in the vicinity of said voids, said shell mold being free of rope reinforcement.