Cores are compact mass of core sand (special kind of molding sand ) prepared separately that when placed in mould cavity at required location with proper alignment does not allow the molten metal to occupy space for solidification in that portion and hence help to produce hollowness in the casting. The environment in which the core is placed is much different from that of the mold. In fact the core has to withstand the severe action of hot metal which completely surrounds it. They may be of the type of green sand core and dry sand core. Therefore the core must meet the following functions or objectives which are given as under.

1. Core produces hollowness in castings in form of internal cavities.

2.  It must be sufficiently permeable to allow the easy escape of gases during pouring and solidification.

3. It may form a part of green sand mold

4. It may be deployed to improve mold surface.

5. It may provide external under cut features in casting.

6. It may be inserted to achieve deep recesses in the casting.

7. It may be used to strengthen the mold.

8. It may be used to form gating system of large size mold.

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