The key points for this module are:
When heating metal for casting, the heat required = The heat to raise the temperature to the melting point + the heat of fusion to convert it from solid to liquid + the heat to raise the molten metal to the desired temperature for pouring.
A pure metal solidifies at a constant temperature equal to its freezing point (same as its melting point) while most alloys freeze over a temperature range rather than at a single temperature.
Total solidification time depends on the size and shape of casting and govern by a relationship known as Chvorinov's rule.
Shrinkage occurs in three steps:
Liquid contraction during cooling prior to solidification
Contraction during the phase change from liquid to solid
Thermal contraction of the solidified casting during cooling to room temperature
The following are the steps in sand casting:
Pour molten metal into the sand mold
Allow the metal to solidify
Break up the mold to remove casting
Clean and inspect casting
Heat treatment of casting.
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