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Metal Casting Technologies : June 2008
Optimize Core Performance CDC PROCESS The CDC process is essentially a three step process that involves the simultaneous but separate melting of two alloys. In the first step, alloy A is poured into a mold and a solid layer builds up from heat extraction through the mold walls. When the solid shell is at the desired thickness, the remaining central liquid is decanted back into the crucible. Alloy B is then poured to fill the remaining cavity. If the appropriate level of superheat is chosen for alloy B then a thin section at the surface of the shell of alloy A will be re-melted, and the local alloying of the two metals prevents the formation of a discrete interface. Instead, a gradient in composition and microstructure forms between the two alloys, producing a functional gradient material. The CDC Process has been adapted to a number of conventional casting methods including several gravity and low pressure casting processes. The low pressure technique for the CDC Process is based on an extension of low pressure permanent mold casting, which allows FGM casting in a closed mold using counter-gravity filling to avoid melt turbulence. The process is described below. As shown in Figure 2, two crucibles are placed beneath the casting mold. A graphite block containing two barrel valves is situated between the crucibles and the mold. With barrel valve A (above alloy A) open and valve B closed (Figure 2a), chamber A is pressurized causing alloy A to rise through the tube and into the mold. After the layer of alloy A has solidified, the gas pressure is removed and the remaining liquid A drops back into the crucible (Figure 2b). Valve A is then closed and valve B opened. Gas pressure above the melt in chamber B forces the liquid alloy B up the graphite tube and into the mold where it solidifies to form the functional gradient material (Figure 2c). 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. ® CORE AND MOULDING SANDS Unimin Australia Limited Tel.: +613 9586 5400 Fax: +613 9586 5411 E-mail: email@example.com Figure 2: Low pressure apparatus and casting sequence for the CDC Process Worldwide: www.metalcaster.com ®INCAST is a registered trademark. All rights reserved. ©2003