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Which of the following gases is responsible for the Pin hole porosity in the molten metal?(a) Hydrogen(b) Nitrogen(c) Oxygen(d) Carbon-dioxideI had been asked this question in quiz.My question is taken from Aspiration Effect in division Pouring – Gating Design, Melting Furnaces, Melting and Casting Quality of Casting-Forming-Welding I

Answer»

Right answer is (a) Hydrogen

The explanation: This is CAUSED by the dissociation of water inside the mould cavity. As the molten metal gets solidified, it loses TEMPERATURE which decreases the solubility of GASES by expelling the dissolved gases. The hydrogen while leaving the solidifying metal would cause LONG pin holes showing the path of escape.



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