Strength
The ability of the sand mold to hold its geometric shape under the conditions of mechanical stress.
Permeability
The ability of a sand mold to permit the escape of gases and steam during the casting process.
Moisture Content
Moisture content affects a mold’s strength and permeability: a mold with too little moisture may break apart, while a mold with too much moisture can cause steam bubbles to be entrapped in the casting.
Flowability
The capacity of the sand to fill small cavities in the pattern. High flowability creates a more precise mold, and is therefore useful for detailed castings.
Grain Size
The size of the individual particles of sand.
Grain Shape
This property evaluates the shape of the individual grains of sand based on how round they are. Generally, three grain categories are used in foundry sand:
- Rounded Grainsands provide relatively poor bonding strength, but good flowability and surface finish.
- Angular Grainshave greater bonding strength because of interlocking, but poorer flowability and permeability than rounded grain sands.
- Sub-angular Grainsare the middle road. They possess better strength and lower permeability relative to rounded grains, but lower strength and better permeability than angular grains.
Collapsibility
The ability of the sand mixture to collapse under force. Greater mold collapsibility allows the metal casting to shrink freely as it solidifies, without the risk of hot tearing or cracking.
Refractory Strength
The mold must not melt, burn, or crack as molten metal is poured into it. Refractory strength measures the ability of molding sand to withstand extreme heat.
Reusability
The ability of molding sand to be reused (after sand conditioning) to produce other sand castings in subsequent manufacturing operations.
