AFS Library


Journal: Transactions of the American Foundrymen's Society V 67 P 553-576, 1959 (24 p)
Author: Cowles, R J

The difficulty of poor collapsibility, predominate as a limitation in the sodium silicate-C02 method of sand bonding, is obviated by establishing simple laboratory test methods to determine an optimum quantity of sodium silicate binder. This is designated as the minimum critical percentage for each sand considered. Additives such as sugar, coarse grain silica flour and iron oxide, properly used, contribute to the flowability, ramming qualities and green strength and enhance collapsibility as well as provide hot strength and cushion ing during thermal changes. The binder requirements should be developed on the hypothesis of adhesive bonding rather than on the basis of a mortar composition, which fills voids between the grains. Adhesive binders are most effective in thin films and with the greatest number of sand grain to grain adhesive contacts uniformly distributed in the sand structure. The viscosity and penetrating qualities of the binder composition determine the degree of correlation that binder requirements have to B.E.T. specific area measurements. The B.E.T. data can be used to designate those sands which will need more or less binder than their AFS fineness number indicates. A straight line correlation between minimum critical percentage and a dimension al parameter calculated from AFS fineness data, shape factors, ratio multipliers and specific volume ratios raised to the fourth power is given. The limitations due to high relative humidity and the use of clay additives are discussed. Experimental data, as well as numerous references, are used to support these findings.

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