NUMERICAL SIMULATIONS AND EXPERIMENTAL STUDY OF HOT CORE DISTORTION PHENOMENON IN MAGNESIUM CASTING

摘要

This paper presents the results of experimental and numerical studies of the hot distortion phenomenon in the phenolic urethane cold box systems during magnesium casting. Dual Pushrod Dilatometry has been used to measure a thermal expansion/contraction of phenolic urethane cold box sand core specimens at temperatures range from 20℃ to 600℃. High temperature tensile tests showed that the tensile strength of the phenolic urethane cold box sand cores is significantly affected by the bench life, temperature and binders level. High temperature hot distortion furnace tests on cylindrical cores showed that some coatings increase the temperature limit when distortion starts, but can't prevent it. The hot distortion test during magnesium casting showed that regardless of the application of coating, the type of coating, and anti-veining additives, all cores with density greater than the density of the molten metal (magnesium alloy) were significantly distorted. Numerical simulations of the liquid metal flow around the cylindrical sand core and analysis of dynamic forces acting on the core during fill process showed that a buoyancy force is the major contributor to the hot distortion. It is concluded that the one of the solutions in preventing the hot distortion of sand cores is optimizing their weight, which will balance the buoyancy force and will bring the resultant force to the minimum. The hot distortion test castings using optimized sand cores with density almost equal to the density of the molten magnesium proved our predictions, and hot distortion has been prevented.