The Importance of Riser Volume in Metal Casting

Why must the volume of the riser be greater than the volume of the casting in metal casting?

1) greater 2) smaller 3) equal 4) not related

Final answer:

The riser's volume must be greater than that of the casting to prevent shrinkage cavities and ensure a defect-free casting by supplying molten metal during solidification.

Explanation: In the context of foundry engineering and metal casting, the volume of the riser must always be greater than the volume of the casting. This is to ensure that the riser, which acts as a reservoir of molten metal, solidifies after the main casting. The riser supplies additional material to compensate for shrinkage that occurs as the metal cools and solidifies, hence preventing defects such as shrinkage cavities. The riser's effectiveness is related to its size because a larger volume of molten metal will retain heat for a longer period, allowing it to feed the casting until it fully solidifies.