The design of an experiment to investigate the fluidity of aluminum silicon alloys in carbon dioxide cured molds

Abstract

The last decade has seen many new developments in the foundry industry, among them the CO₂ process for curing molds and cores. The CO₂ process consists essentially of mixing dry, clay-free, silica sand with an organic liquid sodium silicate binder, then ramming this mix into molds or core boxes and injecting CO₂ gas. The CO₂ gas reacts with the sodium silicate binder forming a silica gel which hardens rapidly in atmospheric conditions. The CO₂ molds are more resistant to metallostatic pressure and erosion than either green or dry sand molds but more expensive also. The CO₂ cores are hardened rapidly without the benefit of a baking cycle characteristic of the production of conventional organically-bonded cores. The CO₂ cores are more economically compared with other core-making processes than the CO₂ molds are compared with other sand-molding processes.

The casting property, fluidity, is a qualitative measure of the ability of a metal to completely fill a mold cavity and is normally expressed as inches of flow in a small channel. Mold material variables, gating and flow-channel variables, and metallurgical variables, such as metal composition and the number of degrees superheat, all affect the fluidity values.

This paper presents a spiral fluidity pattern for determining the fluidity of aluminum-silicon alloys in CO₂ molds made by a standard procedure. A standardized molding, melting, and pouring procedure is suggested to control certain fluidity variables while investigating the influence of other fluidity variables. Finally, a statistical method is presented to ascertain the significance of the effect certain variables may have on fluidity. Preliminary investigations pertinent to the major objective of this paper indicate aluminum-silicon alloys are less fluid in CO₂ molds than in green sand. Investigations also indicate that certain variabilities in testing procedure which an operating foundry might encounter have no statistically significant effect on fluidity.