A riser or a feeder head is a passage of sand made in the cope to permit the molten metal to rise above the highest point in the casting after the mould cavity is filled up. Risers serve a dual function. They compensate for solidification shrinkage which is a very common casting defect and are a heaf source so that they freeze last and promote directional solidification.

Types of Risers : There are two types risers :Top or open risers and side or blind risers.

Riser shape and Size : The metal in the riser should remain in the molten state for a longer time than in the mould cavity.

It means a heaf looses in riser should therefore be kept to a minimum. It means a riser most freeze more slowly than the casting. Those there shape should be such as to give volume-to-surface-area ratio a maximum value. This ratio is maximum for a sphere. Therefore this is the ideal shape of a riser.

As regards the height of the riser, it must be fall enough to ensure that any pipe formed in it does not penetrate the casting.