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Bronze casting showing sprue and risers
In foundry work, a Sprue is the passage through which metal is poured into a mold. The term can also refer to the excess metal on a rough casting, which solidified in the sprue hole. The term has the identical usage in the plastic injection-molding industry.
Sprues can serve as filters, heat sinks and as feeders. Bronze in particular has a high shrinkage rate as it is cooling, a sprue can continue to provide molten metal to the casting, providing it is large enough to retain its heat and stay liquid, as metal in the main casting cools and shrinks. The design of the sprue and runner system can be also utilized to trap unwanted dross and sand from continuing into the main cavity, this may include adding porous material to the runners, or designing the sprue to eject the dross to the side of the sprue (cyclone effect).
"The amount of the sprue and the velocity of fluid flow depends on the head." Meaning that sprue is the extra liquid in a tube when your pouring metal into a molding. So sprue is a liquid in a tube that will flow depending on head.
Metalworking:
