Controlling Solidification in the Casting

It is common casting practice to use a "riser" as a reservoir of molten metal . The risers act as "back fills" which feed molten metal into the casting as it shrinks during solidification.  

• A riser, being the last section to solidify, acts as a "trap" for the solidification shrinkage.

Risers are commonly positioned to feed into the sections of a casting which will be the last sections to solidify.  In that position the risers promote "directional solidification".

• Directional solidification is defined as the process in which the casting -- "cools and solidifies progressively from thin sections to heavy sections with constant metal feed into the heavy sections."  

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