Question

Oxides of alumina are always treated as impurities in the molding sand.

(a) True

(b) False

I have been asked this question by my college director while I was bunking the class.

I'm obligated to ask this question of Moulding Sand Binders and Additives in division Pattern Materials & Moulding Sand Tests of Foundry and Forging

Answer 1

Right answer is (b) False

Easy explanation: The oxides of alumina, sodium and magnesium have excellent binding properties. They are added to the molding sand to enhance its mold ability and dimensional properties. However, their constituency should be limited to 2% or less as its excess quantity can cause defects in the castings and effect the fusion point of silica sand.