Process Encyclopaedia

Other names / variants: green sand casting

Sand casting is the oldest form of casting and has been used for millennia.
It is still widely used today and in the US alone about 15,000,000 tonnes of metal are cast every year.
Although almost any sand can be used, a mixture of synthetic sand, clay and water, called green sand, is preferred by most foundries.

Most metals can be cast, the limit is the melting temperature - the higher it is, the greater the cost.
There is almost no limit to the size of a sand casting - casings over 5m wide are routinely made (e.g. ship propellers).
Most shapes can be made, but the surface often has a characteristic rough finish which may need machining.
Removing the extra material left from risers/gates etc. can also greatly add to the cost of the finished product.
Porosity can be a problem leaving parts that are prone to cracking.

The basic equipment cost is low - from Ł500 to Ł3,000; automation and higher temperature furnaces can increase this a lot. Dies can be cheap, but take some time to make.
The limit on the production rate is usually the cooling. Small parts can be produced at several an hour - large parts can take hours or even days to cool fully.
The labour intensive nature of the process mean it is usually only economic for small batches, although dedicated automation can increase this to 10,000+.