The Influence of Acid Hardener on the Strength and Hot-Distortion Properties of No-Bake Sand Cores

Abstract

AbstractIn this research work, the effects of different amounts of acid hardener (30%, 40%, 60%, 80% weighted to the resin) on the hardening characteristics and hot-distortion properties of no-bake furan and no-bake phenolic bonded sand cores were studied. Bending tests were conducted on test bars with storage times of 1, 2, 3, 5, 7, 24h. Hot-distortion tests were carried out on specimens with storage times of 4h and 24h. The bending tests revealed that in the case of the furan binder system, the acid hardener is best utilized in terms of higher bending strength, in an amount of 40–60%, while in the case of the phenolic binder system, the amount of 60–80% acid hardener resulted in higher bending strength of the sand specimens. Too low (30%) acid hardener (catalyst) level produced low bending strength. Too high (80%) amount of acid hardener decreased the strength of the no-bake furan sand samples, and as can be seen from the SEM analysis, it damaged the binder bridges between the sand grains. The hot-distortion tests showed that there is a correlation between the catalyst content and the max. Deformation of the samples both in the furan and in the phenolic no-bake sand cores, which can be described with a maximum curve. Increasing the acid hardener changes the thermoplastic behavior of the phenolic resin, thus the binder bridges become more rigid and brittle. The acid hardener above 40% decreased the thermal stability of the furan and phenolic bonded test pieces. The research work also revealed significant differences between the specimens made with furan and phenolic binder and the effect of the storage time in terms of the bending strength and hot-distortion properties.