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

In 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.

PREDICTION OF AZ91 CASTING MISRUNS AND ALLOY FLUIDITY USING NUMERICAL SIMULATION

Prediction of the misrun formation in thin-walled castings of magnesium alloys is a crucial task for foundry. The computer simulation of the casting processes can be used to solve this problem. A reasonable simulation results requires the correct thermal properties of the alloy and the mold over a wide range of temperatures and the value of interfacial heat transfer coefficient between the casting and the mold, and the critical solid fraction at which the alloy flow in the mold is choked off. In this paper we determine the interfacial heat transfer coefficient between the magnesium alloy ML5 (AZ91) and the sand mold with a furan binder. It was done by the comparing the simulated spiral test lengths with the experimental spiral test lengths obtained under the same conditions. Above the liquidus temperature the interfacial heat transfer coefficient IHTCL = 1500 W/(m2 ·K) at pouring temperatures 670 and 740 °С and IHTCL = 1800 W/(m2 ·K) at pouring temperature 810 °С. Below the solidus temperature the interfacial heat transfer coefficient IHTCS = 600 W/(m2 ·K). We also determined the critical solid fraction of ML5 (AZ91) magnesium alloy for the casting made in the furan bonded sand mold (at a cooling rate ~2 K/s) and it was 0.1–0.15. We compared the simulated misruns position and the experimental misrun position in the «Protective cup» casting produced from the ML5 (AZ91) alloy into the sand mold with furan binder. The value of the critical solid fraction was clarified. The castings were made at pouring temperatures 630 and 670 °C, and the critical solid fraction was 0.1 in both cases.

Identification and Quantification of Gases Releasing From Furan No Bake Binder

Sand samples with furan binder were prepared using Sand, Furfuryl Alcohol and Toluene Sulfonic Acid with ratio 100:0.85:0.30. To identify and quantify gases releasing from furan binder various studies like FTIR, TGA and GC-MS were carried out. After analyzing our materials using above mentioned characterizations the chemical formula of the Resin and Binder and amount of gases releasing from composition were confirmed. After studying various reports on pyrolysis process of furan binder calculation of the % of various gases emitting during pyrolysis process of furan was carried out. Sample of gas collected from mold was analyzed using GC-MS. Based on GCMS measurement various gases emitting from furan sand mold were identified and their amount were calculate and compared with the international standers of permissible gas emission limits in a foundry. The purpose of this paper is to assist foundries in pollution prevention by devising clean technologies which maintain or improve the quality of ambient surrounding. This paper aimed at minimization of pollution of air by using various techniques.