Question

When do we need more number of risers during casting?

(a) Feeding distance is low

(b) Feeding distance is high

(c) Thermal conductivity of mold is high

(d) Fluidity of molten metal is high

I had been asked this question in an online interview.

My doubt stems from Riser Design in portion Pattern and Mould, Principles of Gating & Risering of Casting-Forming-Welding I

Answer 1

Right choice is (a) Feeding distance is low

For explanation I would say: If feeding distance is high, number of the isolated zone in casting will be less thus less number of risers required. For high thermal conductivity, the metal will solidify faster and high fluidity molten metal will flow over a long distance which will result in less number of risers. If feeding distance is low, we have to use more risers to overcome isolated liquid pools.