Question

Which of the following reasons is the incorrect reason for the blow holes inside the castings?

(a) Presence of moisture in the mould

(b) Lower venting

(c) Lower permeability of the mould

(d) High pressure of the molten metal

I have been asked this question in a job interview.

Enquiry is from Aspiration Effect topic in portion Pouring – Gating Design, Melting Furnaces, Melting and Casting Quality of Casting-Forming-Welding I

Answer 1

Correct choice is (d) High pressure of the molten metal

The best I can explain: Moisture left in the mould and core converted into steam because of the presence of heat in the molten metal. The parts of steam entrapped in the castings end up as blow holes, same as the aspiration effect. Lower venting and lower permeability of the mould is also responsible for the blow holes inside the castings.