Single casting mould-

Single casting moulds are destroyed for taking out the casting and are generally classified as expendable moulds. Moulds used for repeated castings are made of metals or graphite and are obviously much more expensive. Such moulds are classified as permanent moulds and are suitable for large scale production.

About mould-

The performance of a mould is generally evaluated in terms of green strength dry strength and permeability. Green and dry strengths refer to the ability of the green mould and dry mould to retain its shape, and are evaluated in terms of the stress required to rupture a standard specimen under compression. Permeability is a measure of porosity and is evaluated as air flow rate through a standard specimen under a prescribes pressure.

The basic requirement that moulding materials must meet are-

• Refractoriness to withstand the pouring temperature
• Cohesiveness to retain the moulded shape.
• Permeability to permit gases to escape
• Collapsibility for easy removal of casting