Effect of additives on hot strength retained strength and breakdown properties of sodium silicate bonded sands

The National Metallurgical Laboratory has developed a self setting agent for use with sodium silicate bonded sand. An attempt has been made to study systematically the effect of some of the common additives on the sodium silicate bonded sand hardened by NML self setting agent with particular reference to their effect on hot strength, retained strength, collapsibility and casting characteristics. The results indicate that high temperature testing, especially retained strength values, are reliable for evaluating breakdown properties of sodium silicate bonded sands. None of the additives could yield a mix with breakdown property comparable to that of conventional moulding or core sands. Addition, especially of saw dust, molasses and sulphite lye were found to be the most effective in considerably improving the breakdown property of sodium silicate bonded sands. However, they adversely affect other foundry properties, such as, friability of the mould due to sawdust, rate of hardening due to molasses and sulphite lye. Taking into consideration the overall performance of different additives, dextrine alone or in combination with coal dust was found to yield better results. (Shri T.A. Beck, Scientist, Shri G.N. Rao, Scientist and Prof. V.A. Altekar, Director; National Metallurgical laboratory)