Abstract
To study the effect of risering on the microporosity in grey iron castings, two kinds of test pieces having 600×160×70 and 200×70×25mm were made by casting in CO2 sand mold in which the riser was provided at the top of each casting. Melting was made in a crucible furnace and a cupola. The chemical composition of cast irons, the size of risers, and the conditions of pouring are shown in Table 1. To reduce the effect of phosphorous on the internal porosity, its content was kept to be below 0.1%. The micoroporosity of iron castings was measured by microscopical inspecting the section of the castings along their center line which was carefully polished. As shown in Fig. 1, percentage of microporosity was increased with increasing the carbon equivalent, while it was decreased with increasing the size ratio of riser to casting. The decreasing effect of risers upon the microporosity was more remarkable in case of higher C.E. than in case of lower C.E.. In larger castings, solidification time had effect upon microporosity. In case of test castings without riser, there took place no directional solidification. The directional solidification was favored by increasing the size of riser, which resulted in decreasing the microporosity. The microporosity increased with increasing the soldification time when castings were not provided with any riser. However, if risers of proper size were provided for castings, the mircoporosity was not influenced by the length of solidification time.
