Vacuum Assisted Filling of Lost Foam Castings

20100198
Journal: Transactions of the American Foundry Society, Vol. 118, Paper No. 10-062, P 493-501, 2010
Author: Littleton, H.E.; Druschitz, A.P.

Research in the UAB/AFS/DOE Lost Foam consortium has shown that the pressure differential between the sand and molding cavity plays a dominant role in the removal of pattern pyrolysis products. This phenomenon was first discovered during pouring of high silicon aluminum alloys that historically produce large amounts of surface defects commonly named “alligator skin”. Studies at various pressure differentials, using vacuum during pouring, revealed that the alligator skin could be eliminated. Hence, the vacuum was removing the pyrolysis products in a timelier manner. A subsequent study, pouring an engine block with A319 alloy at various temperatures, has revealed that improved mechanical properties can be achieved with moderate vacuum levels and pouring temperatures as low as 1250F (677C). This lower pouring temperature presumably reduces the hydrogen content of the melt, resulting in lower metal porosity, a major factor controlling mechanical properties, especially elongation.