To emphasize the importance of fluid flow in casting, let’s briefly describe a basic
gravity-casting system, as shown in Fig. 10.8. The molten metal is poured through a
pouring basin or cup; it then flows through the gating system (consisting of sprue,
runners, and gates) into the mold cavity. As also illustrated in Fig. 11.3, the sprue is
a tapered vertical channel through which the molten metal flows downward in the
mold. Runners are the channels that carry the molten metal from the sprue into the
mold cavity or connect the sprue to the gate (that portion of the runner through
which the molten metal enters the mold cavity). Risers (also called feeders) serve as
reservoirs of molten metal to supply any molten metal necessary to prevent porosity
due to shrinkage during solidification