What is the primary purpose of a riser during the manufacturing of a casting?

The primary purpose of a riser during the manufacturing of a casting is to provide additional molten metal for shrinkage. When a casting solidifies, it experiences volumetric contraction as the metal cools. This can lead to voids or defects in the final part if not adequately addressed. The riser acts as a reservoir of molten metal, allowing for a continuous supply to the casting as it shrinks during cooling. By ensuring that the casting has access to additional material, risers are critical in preventing defects such as shrinkage cavities.

While strengthening a cast, improving surface finish, and facilitating rapid cooling are important aspects of the casting process, they do not primarily address the issue of ensuring adequate material remains available to compensate for shrinkage. The design and placement of risers are meticulously planned in casting processes to control this aspect, thereby enhancing the overall integrity of the casting.