Abstract: An apparatus for molding experimental, prototype and replacement parts from rubber materials. The apparatus consists of a mold having walls made from layers of fiberglass cloth and laminating resin reinforced with a mixture of quartz sand and laminating resin; a frangible cellular core made of a two component system polyurethane foam core and a hard outer coating of a quick set resin; a wax; and a release agent. The frangible core is formed by coating the surfaces of a core forming cavity of a core box with the wax to fill in irregularities; buffing the wax coating to provide a smooth finish; applying the release agent over the wax; coating the release agent with the hard quick set resin; and filling the core forming cavity with the two component system polyurethane foam. The frangible core is inserted in the mold, a rubber polymer is injected into the mold and the frangible core is removed from the part by breaking the core into small pieces after the part is removed from the mold.

Abstract: A method for molding experimental, prototype and replacement parts from rubber-like materials using a frangible core wherein a core is made by coating a cavity with a mold release agent, coating the release agent with a quick set resin, pouring a two-part polyurethane resin into the cavity, sealing the cavity and allowing the polyurethane to foam, expand and adhere to the quick set resin.