It is used for making cores and sometimes called oil sand.
This is silica sand mixed with core oil composed of linseed oil, resin, light mineral oil and other binding materials.

A pure silica sand employed on the faces of the pattern before moulding is known as parting sand.
When the pattern is withdrawn from the mould, the moulding sand sticks to it.
To avoid sticking, parting sand is sprinkled on the pattern before it is embedded in the moulding sand

The purpose of a gate is to Delivers molten metal into the mould cavity
A proper method of gating system is that it leads the pure molten metal to flow through a ladle to the casting cavity, which ensures proper and smooth filling of the cavity. This depends on the layout of the gating channels too, such as the direction and the position of the runner, sprue and ingates.

A riser, also known as a feeder, is a reservoir built into a metal casting mold to prevent cavities due to shrinkage.
Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.