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insight as to which sand additive should be used for specific casting results in steel castings and what, if any, trade-offs can be expected on mold/core properties. However, the effects of the sand additives on mold/core properties outlined by the results of this design of experiments are limited to the PUNB systems, as other binder systems have different mechanisms of reaction. Te V400 ESA was notable in

that it had a significant effect on slowing the work time/strip time but it also reduced the smoke opacity to about 50% of that seen with the other additives. Additional work is underway to further evaluate and quantify these effects.


Use of Sintered Bauxite in Molding Applications (15-075) Author

Scott Giese, Univ. of Northern Iowa, Cedar Falls, Iowa

Background Since the 1990s, synthetic

sands have been introduced to the metalcasting industry to address the limited availability of specialty sands and cost associated with transport- ing these sands over long dis- tances to the foundry. Derived and processed from lower cost ceramic materials, synthetic sands have been developed to meet molding and casting requirements attained from natural occurring specialty sands. Te challenge of synthetic sand producers is producing a comparable molding aggregate at a substantially lower cost. Additionally, changes in resin demand levels, possible ther- mo-chemical reactions when molding aggregate stream are mixed, and higher permeability issues leading to casting surface changes have been a concern in adopting these types of molding aggregates. Tis case study presents the pre-

liminary investigation of engineering a synthetic sand to meet the harsh ther- mal conditions of the casting process while developing molding properties to address metal penetration and veining

32 | MODERN CASTING May 2015

was sintered alumina produced directly from the mining source. To achieve these three research goals, physical properties with three binder systems and ferrous casting experi- ments using two standard tests were performed. A casting trial at a steel al-

loy casting facility was performed to advance the product from the laboratory environment to ac- tual part production, measuring the performance of the sintered bauxite product to silica sand used by the foundry. To observe the performance of the bauxite product, a complex stainless steel valve body with two internal cores was selected as the test casting. After casting and shakeout, the internal features of the stainless steel valve were observed for surface finish, comparing the zircon-coated silica sand cores to the uncoated bauxite 40/100 cores. For both cast- ings, no metal penetration or veining defects were observed. Te bauxite 40/100 cored area showed a slightly rougher surface than the zircon coat- ed silica sand cored area. However, the foundry manager indicated the surface finish of the bauxite 40/100 product was accepted and would be included into the finish casting lot.

Conclusions Assessment of the bauxite aggre-

This SEM photomicrograph shows the morphology of the Al-Ni (a), Al-Fe (b) and Al-Fe-Ni (c) eutectic at a cooling rate of 27C/second. Notice the long fibers of the eutectic phase in all systems.

defects associated with ferrous casting applications. At the onset of the research work,

three major molding requirements were addressed to assess the feasibil- ity of advancing the technology of a

synthetic sand: • resin demand properties develop- ment associated for the synthetic sand.

• surface quality. • Refractoriness.

Te synthetic sand investigated

gate indicates performance is compa- rable to other aggregates available in the metalcasting industry. No signifi- cant physical properties issues were observed to affect the mold-making performance of the bauxite prod- uct for three different sand binder systems. Physical property evaluation showed the heat capacity property of bauxite is similar to silica sand,

expansion characteristics comparable to zircon and chromite sand, and chemical properties analogous to the aggregate materials investigated. Trough some modification with the screen distribu- tion, the bauxite product subjected to laboratory and actual casting conditions performed equally well as silica sand, chromite sand, and zircon sand. Te se- ries of evaluation tests clearly illustrated bauxite can be used as synthetic sand for the metalcasting industry.

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