Studies on mould wall movement of nodular iron castings in green sand mould

Abstract

The investigation was undertaken to determine the effect of addition of sodium base, calcium base and chemically treated bentonites on mould wall movement. Sodium base bentonites from Kutch were represented by MI and Mangal mineral bentonites, the calcium base by Assam bentonite, and for the chemically treated bentonite, the latter was treated with sodium carbonate. The casting was made in nodular iron of a definite composition in the shape of unfed 3" diameter sphere. The effect of various parameters such as moisture content, bentonite concentration and type of solidification shrinkage, as well as on mould wall movement, was investigated. It was observed that the diameter of the sphere and the volume of the shrinkage pipe increased with increase in the moisture content for a bentonite addition of 5 to 20%. With MI bentonite, it was found that mould wall movement decreased for lower bentonite centent, under bentonite, it was found that mould wall movement decreased for lower bentonite content, under constant water content. On the other hand, when bentonite and water contents were unchanged mould wall movement was found to be maximum in case of Assam bentonite and minimum for the chemically treated bentonite. The extent of mould wall movement in moulds prepared by MI and Mangal mineral bentonites was in between that of Assam bentonite in the 'received' condition and the same treated chemically. From these observations it is concluded that moulds prepared with chemically treated bentonites are the most stable, while among the naturally occurring bentonites stability in mould is imparted more by the sodium base bentonites than the calcium base bentonites. (Shri R.R. Dash, Senior Laboratory Assistant, Dr. R.K. Dubey, Scientist and Shri P.K. Gupte, Scientist and Head of General Metallurgy Division, National Metallurgical Laboratory)