Shell Molding casting
Casting process in which the mold is a thin shell of sand held together by thermosetting resin binder
Figure Steps in shell‑molding: (1) a match‑plate or cope‑and‑drag metal pattern is heated and placed over a box containing sand mixed with thermosetting resin.
Figure Steps in shell‑molding: (2) box is inverted so that sand and resin fall onto the hot pattern, causing a layer of the mixture to partially cure on the surface to form a hard shell; (3) box is repositioned so that loose uncured particles drop away;
Figure Steps in shell‑molding: (4) sand shell is heated in oven for several minutes to complete curing; (5) shell mold is stripped from the pattern;
Figure Steps in shell‑molding: (6) two halves of the shell mold are assembled, supported by sand or metal shot in a box, and pouring is accomplished; (7) the finished casting with sprue removed.
Advantages and Disadvantages
§Advantages of shell molding:
§Smoother cavity surface permits easier flow of molten metal and better surface finish
§Good dimensional accuracy - machining often not required
§Mold collapsibility minimizes cracks in casting
§Can be mechanized for mass production
§Disadvantages:
§More expensive metal pattern
§Difficult to justify for small quantities
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