The Influence of the Matrix Grain Size and Mineral Addition on Improving the Knock-Out Properties of Molding Sands with an Inorganic Binder

This article presents the results of tests of molding and core sands with inorganic binders incorporating a mineral in the form of raw perlite ore. This material serves to reduce the final strength, thereby improving the knock-out properties. The assumption was made that the selection of the optimal fraction of the loosening additive, tailored to the grain size of the matrix of the molding sand used in foundries, could significantly affect its mechanical and technological parameters. The tests were conducted on molding sands prepared using three quartz sands with the addition of perlite ore of different grain sizes. In addition to determining the final tensile strength, the permeability and grindability of the molding sands were assessed. The results indicated that the raw perlite ore significantly reduced the final strength of the molding sands in each considered system, with the best efficiency achieved when using finer fractions. Moreover, the mineral’s addition had a minor impact on the technological properties of the molding sands, such as permeability and grindability.