Resin Shell Molding

The key feature of resin shell molding is the use of fine-grained, high-purity sand to provide smooth surfaces and dimensional accuracy for cores and similar castings. Traditional sand molds cannot use such fine sand as it significantly reduces mold permeability, leading to short-run castings or castings with gas defects due to delayed air and mold gas escape. However, the significant feature of resin shell molding is that , a shell with a thickness of only about 10 millimeters (0.4 inches). The ability to produce such thin external shell molds has been a revolutionary development in metal casting. The concurrent development of plastics, such as thermosetting resins (e.g., phenolic resins), provided the foundation for shell formation. In shell molding, fine sand is coated with a thermosetting resin that provides the relatively high strength required for the production of thin-section or shell molds.

To produce precision castings, the mold should accurately replicate the pattern details and size requirements, which are achieved through shell formation. This is because the resin bonding is formed when the mold contacts the heated pattern. Additionally, the mold separates from the pattern without the need for mold expansion as in wet sand molding. These features also apply to the production of cores. By using zircon sand instead of silica sand, casting precision can be further enhanced. This occurs because the expansion of zircon sand due to the heat generated by casting metal is lower and more predictable than that of silica sand.