The mechanisms of metal expansion penetration during solidification of grey cast iron

Sammanfattning: The production of high quality castings requires the casting surface to be clean and free from defects. One type of defect often found is caused by metal penetration into the sand mould. Metal penetration is a casting surface condition resulting from either physical, mechanical and/or thermochemical reactions or a combination of these at the mould–metal interface. The metal penetrates into the voids between the sand grains to various depths without displacing the grains, thus yielding a phase of sand grains surrounded by metal and frequently by mould-metal reaction products. The present work is devoted to investigating the mechanisms of metal expansion penetration during solidification of grey cast iron.The phenomenon of metal expansion penetration has been examined experimentally. A series of test castings were produced at two foundries, to study the influence of chemical composition, the casting temperature and the addition of inoculants with respect to both primary and eutectic phases.The experiments show that the type and amount of inoculant, the casting temperature and the chemical composition influence the metal expansion penetration.Two major types of metal expansion penetration mechanisms are suggested with respect to the nucleation and growth of the primary and eutectic phases. The expansion penetration mechanisms found in the experimental work were also identified on complex shaped industrial castings such as clutch components and cylinder heads.The entire casting process was simulated using commercial software, and in which nucleation and growth of all relevant phases was considered in order to investigate the solidification characteristics and porosity formation in the casting. A good correlation between the simulation and experiments on real castings was found.Density and volume change in grey cast iron seem to play a decisive roll in the occurrence of metal expansion penetration. Laboratory measurements of density variations are difficult. A novel method of modeling the density variation in cast iron has been introduced.