shell molding[′shel ‚mōld·iŋ]
a method for the production of shaped castings from metal alloys in molds that consist of a mixture of granular sand (usually quartz sand) and a synthetic powder (usually phenol-formaldehyde resin and Bakelite powder). The use of clad grains of sand (covered with a layer of synthetic resin) is preferable.
Shell molds are made by one of two methods. The mixture is spread onto a metal pattern that has been heated to 300°C and held for a while, until a thin, hardened layer forms; the excess mixture is then removed. When using a clad mixture, it is blown into the space between the heated model and the exterior contour plate. Both methods require subsequent hardening of the coating on the model in a furnace at temperatures up to 400°C. The resulting shell half-molds are fastened together, and the liquid melt is poured into the mold. To prevent deformation of the molds when the melt is poured into them, they are placed in a metal jacket before casting, and the space between the mold and the jacket walls is filled with metal shot, whose presence also affects the temperature conditions during cooling of the casting.
Shell molding is used to produce castings weighing up to 25 kg. The advantages of this method are higher productivity than casting in sand molds, control of the mode of cooling of the casting, and the possibility of mechanizing the process.
P. P. BERG