Question

What is the advantage of having a low bulk density of a sand-mix?

(a) Higher strength

(b) Good refractoriness

(c) Higher flow ability

(d) Higher permeability

The question was asked by my school teacher while I was bunking the class.

My question is based upon Green Sand Mould in division Pattern and Mould, Principles of Gating & Risering of Casting-Forming-Welding I

Answer 1

Right option is (d) Higher permeability

To explain: Low bulk density of sand mix results in equal size of grains with smooth round shape, this further results in increase in volume of voids due to less bulk density and hence a higher permeability which permits an easy outflow of the gases from the molten metal.