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Metal Casting Technologies : March 2010
44 www.metals.rala.com.au BacktoBASICS Of course, the criticality of this effect does depend somewhat on the affinity of the particular alloy for oxygen (the tendency of the alloy to form oxides), so this is somewhat more important in alloys such as those of aluminum which have a great tendency to oxidize as opposed to, say, carbon steel which has a relatively lower affinity for oxygen. Almost all alloys, however, do have some tendency to form oxides and using flow simulation to design gating systems which minimize velocity and turbulence of the metal can be quite helpful in reducing flow-related defects in castings. Example 1: Aluminum permanent mould A first example which illustrates the importance of accurate flow modeling is an aluminum stator casting, made using the gravity tilt pour method in a permanent mould process. In this case, the mould is steel and is in several moveable parts. The casting has a cast-in stainless steel tube, and the mould is water cooled in the center as shown in Figure 3. The production casting exhibited an internal shrinkage porosity cavity on one side, even though the casting is essentially symmetrical. It was suspected that the tilt pour Fig 3. Tilt Pour Mold Design and Aluminum Casting Fig 4. Tilt Pour and Solidification Simulation showing asymmetrical temperature distribution in casting
Media Kit 2010