Question

Why are Kaolinite and Bentonite used as clay in molding sand?

(a) High expansion ratio

(b) High thermo-chemical stability

(c) High coefficient of expansion

(d) Non-reactive with molding sand

The question was asked during an internship interview.

The doubt is from Mold Making topic in portion Testing of Materials, Foundry & Powder Metallurgy of Engineering Material & Metallurgy

Answer 1

Correct choice is (b) High thermo-chemical stability

For explanation I would say: Clay binders are the most common types of inorganic binder as they are natural earthy material. The most common types of clay used in molding sand are fireclay, kaolinite, and bentonite. Kaolinite and bentonite clays are useful as they have high thermo-chemical stability.