One no-bake approach, called the shell core process, is similar in principle to the shell molding process. Like shell molding, shell coring produces a hard, smooth and accurate surface. Sand, containing a thermosetting resin, is blown into a heated corebox. After a brief curing period, any loose, uncured sand is dumped out. The resulting shell core is hollow. Thickness of the core depends on the curing time: the longer the cure, the thicker the shell. Because the core is cured in the corebox, driers used in the oven-baking process are unnecessary. For shell coremaking, the corebox must be heated to 400—500°F. Hence the corebox must be made of metal.