Manufacturing castings with high density is only successful if the solidification progress in the casting is directional towards the riser; i.e. if the casting areas that are the most remote from the riser solidify earlier than those casting sections that are close to the riser
This gradient in the solidification progress (solidification time gradient) must not be reversed in any point or area of the casting throughout the entire solidification period. Solidification progress in the above-defined sense is referred to as directional solidification. However, numerous castings do not comply with the requirements for directional solidification due to location of their risers. In case that special technological or constructional measures must be taken to achieve solidification progress that promotes feeding, this condition is referred to as controlled or directed solidification.
However, it is not always possible to fulfill the requirement for directional solidification through strategic positioning of risers. For this reason, it has long been state of the art in casting to implement chills and even cast in internal chills for direction of solidification. The following benefits are achieved through strategic extraction of heat: