The process of resin-shell molding, sometimes referred to as the Croning or C-process, involves the formation of molds and cores from thermosetting resin-bonded sand mixtures which are brought in contact with preheated metal patterns.

In carrying out the process, a suitable sand mixture including the resin binder is dumped onto the metal pattern which is normally heated in the range of from 300° to 600° F. The resin adjacent the hot pattern surface softens under the heat and flows around the sand grains to bond them together into a thin, soft layer usually three-sixteenths to one-fourth inch in thickness. The pattern is then inverted and the excess resin-sand mixture which has not been affected by the heat falls away leaving behind a bonded shell adhering to the pattern.

The bonded shell is further heated to cure the resin and harden the shell which is then removed from the pattern ready for use. Molds and cores made in this manner exhibit good strength, smooth surfaces, high permeability to mold gases, easy collapsibility after casting, and good dimensional accuracy. Consequently, the resin-shell molding process has an important place in the foundry industry in spite of the relatively high cost of resin binders.