Sand Effect

The sand used in cores had a significant effect on porosity formation. Severe subsurface porosity was prevalent with silica sand, while castings made with washed-and-dried lake sand were entirely sound. The behavior of lake sand may be attributed to either its larger quantity of surface impurities, bulk impurities or greater permeability.

To determine the effect of surface purity on influencing gas porosity, an acid treatment was administered to the lake sand to remove trace impurities. The sand was soaked in a 10% solution of sulfuric acid for 24 hr, followed by a 24-hr water wash and dry. Still, no porosity was observed with the treated sand.

Because of the known effect of permeability on porosity and the potential chemical effect of sand type, several other sands having a range of compositions, permeabilities and AFS grain fineness distributions were tested for relative porosity susceptibility.

There isn’t a correlation between AFS grain fineness and permeability and porosity sensitivity. The lower the impurity level and, particularly, the iron oxide content of the sand, the greater the sensitivity of the system to porosity. Although pure, round-grained sands offer outstanding core and moldmaking properties, they may not produce the best castings, as lower purity sands do.

Table of contents
[Paper Header]
[Porosity Study]
[Binder Ratio] [Binder Level] [Casting Temperature] [Section Size]
[Sand Effect] [Iron Oxide Additions] [ Binder Dispersion/Mixing]
[Metal Composition] [Core Age]
[Eliminating Porosity]
[Ti and Zr Additions] [In-the-Mold Additions] [ Core Washes]
[Core Post-Baking]
[Discussion]