Pattern for making a sand mold with a back draft

Claim 2

A pattern for forming a heat-cured sand mold having a back draft area, said pattern comprising, substantially annular metal portion tapering convergently from a base to form that portion of the mold which has no back draft area, said metal portion having an irregular surface on the end opposite said base, a flexible portion for forming a back draft area in said mold which is diametrically smaller than said metal portion and molded and bonded to said irregular surface on the end of said metal portion, said flexible portion being of a normal unflexed shape which complements the back draft area of said mold, said flexible portion being of a sufficient hardness so as not to deform during heat curing of the mold, and said flexible portion also being of sufficient resiliency to deform and pass out of said back draft are of said mold without damage to the latter as said mold and pattern are separated.

Claim 3

A pattern for forming a heat-cured sand mold having a back draft area, said pattern comprising, a substantially annular metal portion tapering convergently from a base to form that portion of the mold which has no back draft area, said metal portion having a generally cylindrical and axially extending central opening and also having an external surface inclined to the longitudinal axis of said metal portion and forming a large end and a small end of said metal portion, a flexible portion for forming a back draft area in said mold diametrically smaller than and secured along the small end of said metal portion opposite said base and of a normal shape which complements The back draft area of said mold, said flexible portion forming a generally radially extending flange extending from said small end of said metal portion, said flexible portion also having a rounded internal corner joining one end of said central opening and the rest of said flange, said flexible portion being of a sufficient hardness so as not to deform during heat curing of the mold, and said flexible portion also being of sufficient resiliency to deform and pass out of said back draft area of said mold without damage to the latter as said mold and pattern are separated.

Claim 4

A composite pattern for forming a cured sand mold having an internal back draft portion comprising: a rigid partial pattern portion convergently tapering from a base and not having any back draft portions which is capable of being withdrawn from a cured sand mold without disturbing said cured sand mold, said rigid partial pattern forming a substantial portion of said composite pattern; a flexible partial pattern portion for forming any back draft portions of said composite pattern, said flexible partial portion having sufficient rigidity to maintain dimension and configuration during formation of the mold cavity when covered with a sand mixture to be cured and sufficient resilience to egress from such back draft portions and when said composite pattern is removed as a unit after the sand mold is cured; and interconnecting means for holding said rigid partial pattern portion and said flexible partial pattern portion in tight registry on the end opposite said base to form a precision composite pattern that can be removed from a cured sand mold with an internal back draft without disrupting the same.

Claim 5

The composite pattern as defined in claim 5 wherein the interconnecting means includes a structure on the rigid partial pattern portion to which the flexible partial pattern portion is bonded.

Claim 6

The composite pattern as defined in claim 5 wherein the flexible partial pattern portion is tapered having a decreasing cross section from its connection to the rigid partial portion to its extremities to facilitate its removal from a cured sand mold.

Claim 7

The composite pattern as defined in claim 5 wherein the interconnecting means includes an undercut projection to which the flexible partial pattern portion is bonded thereby holding said flexible partial pattern portion in tight registered engagement with said rigid partial pattern portion.

Claim 8

The composite pattern as defined in claim 5 wherein the composite pattern has a circular configuration with a flaring back draft portion formed with the flexible partial pattern portion.

Claim 9

The composite pattern as defined in claim 5 wherein the flexible partial pattern portion is formed of an elastomer with dimensional stability at temperatures employed to cure a precision sand mold employing a thermally cured resin and sand mixture.

Claim 10

The composite pattern as defined in claim 10 wherein the elastomer is silicon rubber.

Claim 11

The composite pattern as defined in claim 10 wherein the rigid partial pattern portion is formed of metal.

Claim 12

The composite pattern as defined in claim 5 wherein both the rigid and partial pattern portion and the flexible partial pattern are cylindrical and joined in axial registry by the interconnecting means.

Claim 13

The composite pattern as defined in claim 13 wherein the flexible partial pattern portion includes an oblique diverging flange that is the back draft portion and is joined to the rigid partial pattern portion where it tapers continuously to a decreasing cross section.