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Metal Casting Technologies : September 2007
Trust your most complex cores to INCAST ®. The ideal combination of geometry, density and particle size distribution, INCAST improves critical core making and casting properties including binder utilization, permeability and dimensional stability. Higher strength cores, better surface finish and increased efficiency and yield are the INCAST advantages. These sands are engineered for the metalcaster. Optimize Core Performance Unimin Australia Limited Tel.: +613 9586 5400 Fax: +613 9586 5411 E-mail: email@example.com Worldwide: www.metalcaster.com CORE AND MOULDING SANDS ® ® INCAST is a registered trademark. All rights reserved. ©2003 an atomically rough, non-faceted interface with the liquid iron. Despite the heat selected for evaluation, heat 1: CGI, heat 2: CGI of high nodularity, or heat 3: DI, microstructure transition at the casting surface was frequently observed. This graphite transition either involved a single phase step, such as the transition from compacted into flake graphite, or a multiple phase step, where spheroidal graphite transitioned into vermicular graphite that transitioned into flake graphite. Figure 5 shows selected photomicrographs where those transitions are quite evident. It was observed that the degree of skin formation at the surface depended upon the original metal chemistry. Skin severity decreased as the total residual magnesium in the melt increased. The depth of the skin also increased for coated cores. Although the pictures may indicate a consistent skin, in reality skin depth varied according to the location along the edge. Considering the test piece used, a pattern of wedge formation is the best way to describe skin development at the casting surface. At the corner of the sample, i.e., the location marked as zero as seen in Figure 3, skin formation was the least, and it continuously increased with distance. Figure 6 illustrates skin depth for samples from each heat. The trend of skin formation is the same but severity of the skin developed is greatly affected by the residual magnesium content in the samples. As observed, samples from heat 1 with the least amount of residual magnesium developed more flake skin formation. This confirms that magnesium and other spheroidizing elements play a major role in maintaining the desired graphite morphology. Figure 6. Skin depth for heats 1, 2 and 3.