Ordliste
Feeder (riser) — definition
An extra reservoir of metal that stays liquid longer than the part and feeds the section as it shrinks during solidification.
Metal contracts as it goes from liquid to solid. Without a supply from outside, voids form — shrinkage porosity — where the section is thickest and solidifies last.
A feeder is an extra volume of melt positioned so that it solidifies after the part. For as long as the feeder is liquid, it can top up the contracting section.
Feeders are central to gravity die casting and sand casting. In high pressure die casting the mechanism is different: pressure is held through the gate while the part solidifies, and overflows handle the first melt.