Question

1)Describe what a “riser” is in the context of sand casting.

What are its functions?

In light of Chvorinov’s rule, what should be taken into account when determining the geometry, dimension, and location of a riser in a sand casting mold?

Answer 1

a riser is a vertical passage which helps in the continous suupply of liquid molten metal to the casting to allow for liquid shrinkage and solid shrinkage. It also hepls t identify if the cavity inside the casting is filled, while pouring the molten metal. Riser acts as a reservoir for molten metal supply.

According to Chvorinovs rule, the time for solidification of a riser is

When surface area of the cavity of the riser is more, the molten metal gets solidifies quickly, hence the geometry of the riser should be such that the ratio of V/A shpuld be as high as possible. And for that purpose, Cylindrical risers are used, and also the 'height to diameter' ratio is calculated to obtain the highest V/A ratio. The locaton of the riser is selected such that the time required for the molten metal to flow into the cavity of the casting is as less as possible. Hence the riser is placed above the cavity of the casting either to its side or at its center. For large castings, more than one riser are used.