Evaluation of Shrinkage Tendency of Spheroidal Graphite Cast Iron

Abstract

  Test procedure for evaluating internal shrinkage tendency, excluding liquid state and external shrinkage, is investigated. The gate thickness of plate castings has been changed in order to vary the order of solidification time among plate, gate and riser. The optimum gate thickness has been decided so as to keep the gate in molten state while the riser feeds only liquid shrinkage of the plate and also to minimize external shrinkage of the plate. Thus internal shrinkage of the plate is properly evaluated by X-ray photography. Using these test castings, effects of carbon content of the melt and green sand mold strength on the shrinkage tendency have been studied. Additionally, comparison of the shrinkage tendency between green sand mold and metal-back shell mold, and spheroidal and flake graphite cast iron have been made. It was revealed that spheroidal graphite cast iron shrinks in a later stage of its solidification while flake graphite cast iron expands in the whole duration of its solidification.