Question

Hardness of green sand mould can be increase by _____

(a) increase in permeability

(b) decrease in permeability

(c) increase in moisture content beyond 6 percent

(d) increase in both moisture content and permeability

This question was addressed to me in an online quiz.

My doubt is from Green Sand Mould topic in chapter Pattern and Mould, Principles of Gating & Risering of Casting-Forming-Welding I

Answer 1

The correct choice is (b) decrease in permeability

The best I can explain: A decrease in permeability usually indicates a closed structure in the rammed sand, and if the decrease continues, it will lead to tighter packing and fewer voids hence increase in hardness of the green sand mould. This increase in hardness can be measured by mould hardness tester.