Synthetic Solution for Molds and Cores?
An investigation looks at how sintered bauxite holds up to the demanding thermal conditions of the casting process. SCOTT GIESE, UNIV. OF NORTHERN IOWA, CEDAR FALLS, IOWA, AND RAFAEL CURIMBABA FERREIRA, GROUPO CURIMBABA, POÇOS DE CALDAS, BRAZIL
A
s the demand of mold- ing aggregates to meet special casting require- ments increases, sands
such as chromite and zircon have been introduced to the industry with the goal of producing defect-free, high quality castings while minimizing metalcasters’ post-processing costs. Te challenge of synthetic sand producers is supplying molding aggregates that are comparable to naturally occurring sands at a substantially lower cost. Changes in resin demand levels, possi- ble thermo-chemical reactions during mixing and higher permeability issues have become concerns for metalcasters who adopt these aggregates. Casting trials were performed to
evaluate the physical properties of synthetic aggregate materials directly produced from bauxite and compared to properties and casting performance of silica and chromite sand. Tis case study investigated the abilities of syn- thetic sand (sintered alumina produced directly from the mining source) to meet the harsh thermal conditions of the casting process while developing molding properties to address metal penetration and veining defects associ- ated with ferrous casting applications. Te trials evaluated physical
properties for each sand sample for AFS-GFN, tensile profiles, specific surface area, pH, acid demand value (ADV), base permeability, bulk and tapped density, specific heat capac- ity and linear expansion. Step-cone castings and Gertzman castings were
poured for evaluating casting quality performance in low carbon, low alloy steel, class 35 gray iron and 60-40-18 ductile iron. Tensile cores and cores for casting analysis were prepared using the furan nobake, phenolic ester-cured nobake and phenolic urethane cold box binder systems. Physical properties were determined to be comparable to the base line sands investigated. At the onset of the research work,
three major molding requirements— resin demand properties development associated with the synthetic sand,
surface quality and refractoriness— were addressed to assess the feasibil- ity of advancing the technology of a synthetic sand. To properly assess the performance of the synthetic sand system compared to natural alterna- tives, researchers performed tests for physical properties with three binder systems and ferrous casting experi- ments using two standard tests. Te sintered bauxite product
has demonstrated satisfactory cast- ing performance in a laboratory and metalcasting environment. Subse-
Fig. 1. This graph shows the linear expansion curves for the four sand mixtures. July 2015 MODERN CASTING | 29
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