Metal Working: Designing and Making Pistons

Learn the details of pouring, feeding and the solidification of iron and aluminum piston castings so you can do it yourself.

Microshrinkage in castings
Aluminum castings freeze by three different methods. In pure aluminum, shrinkage occurs as a deep pipe or at the centerline of the casting. Solidification of alloy #295, 94% aluminum, 5% copper, 1% silicon begins at the wall but progresses quickly to the center of the casting.  Fine grains form randomly in the center of the casting and freezing continues in a mushy state.  
Illustration Courtesy Chastain Publishing