文档介绍：Risers
Risers are designed and placed so as to ensure filling the cavity during solidification.
They also act to relieve gas pressure in the mold and to reduce pressure on the lifting surfaces of the mold.
The volume of metal in the riser should be sufficient to retain heat long enough to feed the shrinkage cavity and to equalize the temperature in the mold, avoiding casting strains.
The riser requirements vary with the type of metal being poured.
Gray cast iron, for example, needs less feeding than some alloys because a period of graphitization occurs during the final stages of solidification, which causes an expansion that tends to counteract the metal shrinkage.
Many nonferrous metals require elaborate feeding that tends to counteract the casting.
Two riser designs for the same casting are shown in -4.
Risers are placed near the heavy sections of the casting.
The feed metal must be located above the highest point of the point of the casting.
Chill Blocks
Chill blocks are metal blocks placed in the mold for localized heat dissipation.
They may be placed at an intersection or joint where there is paratively large volume of metal to cool, thus relieving a hot spot or maintaining a more uniform cooling rate and better microstructure.
They may also be placed at far surface of a mold, away from a riser or sprue.
This will help the far end of the mold to freeze rapidly, pr