Change in ductility of a raw sand-clay mold under influence of geometric and thermophysical properties of the casting

摘要

© 2020 National University of Science and Technology MISIS. All rights reserved.One of the ways to increase economic efficiency of the foundry is to reduce the product cost by reducing scrap, a significant proportion of which is formed due to formation of hot and cold cracks during solidification and cooling in the casting-mold system. The formation of cracks occurs due to the force interaction of casting with mold. Currently, a number of approaches are used to determine the value of stress state in the casting material and, accordingly, to determine the value of force interaction. The paper considers the developed estimation of stress-strain state of the casting-mold system, which is determined by deformation resistance of the molding mixture. Change in deformation resistance of the molding mixture is complex due to the multi-factor nature of resulting stresses interaction with thermal and component composition of the sand-clay layer. We have studied the influence of geometric parameters and thermophysical properties of the casting on deformation resistance of the molding mixture. A mathematical model was developed that takes into account the heat transfer between casting and mold, increase in mold dry layer, and the migration of moisture in layer of the sand-clay mixture. On the basis of mathematical modeling, we have made a quantitative analysis of the influence of thermophysical properties of casting (thermal conductivity, volumetric heat capacity, heat of crystallization, geometric parameters) on ductility of raw sand-clay mold with humidity of 5 expressed in terms of the average resistance to deformation under an obstruction element 100 mm long. It was established that increase in the above-mentioned factors, at a fixed time, increases the average value of deformation resistance. The quantitative relationship of the released heat with growth of the dry layer of the molding mixture is described. It was noted that dynamics of changes in the average temperature does not always coincide with increase in deformation resistance of the molding mixture.