Greensand molds with gating system.
Gating iron (Latin: ferrous) is different than gating aluminum or bronze (non-ferrous). Dross is produced with non-ferrous alloys , but NOT with iron. Dross is similar to the foam on top of beer.
When gating non-ferrous castings, dross is carried beyond the gate by the deep runner, clean metal enters the casting.
When gating iron, the metal is so heavy, 2 large openings (sprue/riser) are used to equalize the pressure.
Parameters of Gating
Alum castings 3lbs. or less- Bronze castings 9lbs or less
1/2″ sprue, 1″x 1″ runner up to 10″ long.
Alum castings 3-8 lbs.- Bronze 9-24 lbs.
3/4″ sprue, 1.5″x 1.5″ runner up to 14″ long.
Alum castings over 8 lbs. Bronze over 24 lbs.
1″ sprue, 2″x 2″ runner up to 18″ long.