Aluminium Sand Casting

[Audio] Hi This is Darsh Nishad going to talk about Aluminium Sand Casting.

[Audio] The objective of this experiment is to understand green sand moulding process and melting of aluminium metal and its casting in the mould made by the above process.

[Audio] During the casting of Aluminium, two kinds of grains can be seen - equiaxed and columnar. Outer equiaxed grains are formed on the mould wall and are usually small, with random orientations Mould walls are at a much lower temperature (usually room temperature) than the liquid, thus rapidly cool the liquid layer in contact with it. This causes high undercooling, thus a high nucleation rate, thus small grain size. Region is called chill zone.

[Audio] Metal solidifying in chill zone releases latent heat of fusion - temperature becomes close to equilibrium melting temperature. Favourably oriented equiaxed crystals grow along heat flow direction (perpendicular to mould wall). High crystal growth, little nucleation. Growth stopped by grains / crystals nucleating ahead of columnar front.

[Audio] Inner equiaxed grains are called central zone which lies at the center of ingot. The Grains are equiaxed and randomly oriented, though larger than chill zone The Thermal gradient decreases with distance from the coldest surfaces They are Formed due to detachment of dendrite arm from columnar dendrites (through viscous force of the flow). Serve as nucleation sites The Low undercooling causes larger crystal sizes (than chill zone)..

[Audio] This is how Crystal Zones in Cast Aluminium looks like.

[Audio] The formula of casting yield = weight of the casting divided by total amount of metal poured.

[Audio] This is how a riser looks like thankyou. Riser (Diagram).