Riser Design For Green Sand and Ductile Iron Castings

Shrinkage defects in ductile iron riser contacts has long been one of the most frustrating defects to eliminate for the foundry engineer. While process variation can definitively contribute to the occurrence of these defects most can be prevented if the risers are properly designed and/or applied to the castings to be fed. There are several proven methods for the designing risers some of which go back over 40 years ago. There are also new methods available today with the advancements of simulation software. Four of these riser design methods were evaluated for their ability to produce an internally sound casting and their yield efficiency. While all methods are still valid the Solidification Modeling Method also resulted in additional quality benefits by predicting other potential defects. Finally, many actual casting examples with riser contact shrinkage were reviewed and evaluated in order to prove that the root cause of most shrinkage defects in ductile iron riser contacts are the result of design or application mistakes. While the study involved large green sand ductile iron castings, the design and application recommendations are applicable to other casting sizes and molding methods