Shrinkage cavity is inevitable in casting. When the metal cools and solidifies, its volume will shrink, resulting in shrinkage.
What we need to solve is to make the shrinkage cavity occur in the part that has no impact on the casting quality.
When making the mold, set the riser at the position where the metal volume is large and it is estimated that shrinkage cavity will occur, so that shrinkage cavity can be generated on the riser. This is a basic principle, which depends on the shape of the casting.
Casting shrinkage cavity is because the casting solidifies in the way of layer by layer solidification, and the liquid and solidification shrinkage are greater than the solid shrinkage, forming large and concentrated holes at the last solidification part of the casting. Sequential solidification, addition of riser and cold iron, and reasonable design of casting structure to prevent casting shrinkage.