Process Encyclopaedia

Overview

• 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.

Process details

Materials and shapes

• 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.

Economics

• The basic equipment cost is low - from £500 to £3,000; 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+.

Typical products

• Engine blocks
• cylinder heads
• pump housings
• machine tool bases
• ship propellers

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