Q. Explain Sand and moulding sands?
Sand according to the amount of clayey matter they contain, the moulding sands are classified as:
• Silica sand: Up to 20% clay.
• Lean or weak sand: 2 to 10% clay
• Moderately strong sand: 10 to 20% clay
• Strong sand: Up to 30% clay
• Extra strong sand: Up to 50% clay.
There are three types of sand used for making moulds: natural, synthetic and chemically coated.