Effect of Reclamation on the Skin Layer of Ductile Iron Cast in Furan Molds

R Dańko,M Holtzer,S Żymankowska-Kumon,M Górny

doi:10.1007/s11665-013-0656-2

Abstract

The paper presents the results of investigations of the influence of the quality of molding sand with furan resin hardened by paratoluenesulfonic acid, on the formation of microstructure and surface quality of ductile iron castings. Within the studies different molding sands were used: molding sand prepared with fresh sand and molding sands prepared with reclaimed sands of a different purification degree, determined by the ignition loss value. Various concentrations of sulfur and nitrogen in the sand molds as a function of the ignition loss were shown in the paper. A series of experimental melts of ductile iron in molds made of molding sand characterized by different levels of surface-active elements (e.g., sulfur) and different gas evolution rates were performed. It was shown that there exists a significant effect of the quality of the sand on the formation of the graphite degeneration layer.

Highlights

Production of castings of ductile iron, in loose self-hardening molding sands with furfuryl resin hardened by paratoluenesulfonic acid, brings a danger of forming defected casting microstructure, which the most often occurs in its surface layer (Ref 1-10)
The graphite degeneration is caused by decreasing the magnesium concentration in the ductile iron near-surface layer since magnesium reacts with sulfur or oxygen, which diffuses from molding sand to metal
The ignition loss of the molding sand after three cycles of the reclamation treatment is nearly three times larger than that of the molding sand prepared on the fresh highsilica sand

Summary

Introduction

Production of castings (especially thin-walled) of ductile iron, in loose self-hardening molding sands with furfuryl resin hardened by paratoluenesulfonic acid, brings a danger of forming defected casting microstructure, which the most often occurs in its surface layer (Ref 1-10). This unfavorable effect is caused by sulfur contained in a hardener of resin binders, which enters the surface layer causing degradation of a nodular graphite into flake graphite. The gas evolution and sulfur and nitrogen contents were determined for molding sands, of which molds were made

Experimental Tests

Determination of Sulfur and Nitrogen Content in Molding Sands

Gas Volumetric Emission from Molding Sands

Investigations of Casting Microstructures

Conclusions