The old rule for new/core sand additions is 300 lbs. per ton of metal poured, but that approach needs to be re-evaluated (and made more exact) for current molding methods and materials.
Article from the Foundry Management & Technology August 2005 issue by Mark Ziegler.
In order to understand the effect of core sand and the various binder systems on green sand properties and castings, the new sand's contribution to the dilution must be established. The objective of this research is to create a model where different amounts of new sand and core sand are added to system sand so that the green sand's properties and casting results can be evaluated. Initial work by the Green Sand Committee of CISA has shown that certain levels of new sand can be added, along with new clay/additives, to maintain consistent green sand properties. The study also found that there are critical levels where major changes in the green sand properties occur.Read More