PRODUCT INNOVATIONS New Product
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New Simulation Model Predicts Core Gas Defects Flow Science,
Santa Fe, N.M., has included a core gas model in the new- est version of its FLOW-3D casting process modeling software. The core gas model describes the generation of gas in sand cores dur- ing the pouring and cooling of metal. The gas comes from the decomposition of the chemical sand binder due to the heat from the metal. At the outer boundaries of the core material, there may be a flow of gas either in or out of the core. If not vented properly, gas may flow into the metal, resulting in gas porosity defects. This is most likely with cores that form thin interior features of castings that heat up quickly and have long venting paths. The core gas model in FLOW-3D is designed to predict the possibility of such gas defects and aid in the design of core venting that safely evacuates all the binder product gas from the cores. Graham-White Manufacturing, Sa-
lem, Va., is using the core gas model to identify and resolve core-related gas defects in a production gray iron valve casting. The metalcaster uses shell sand
Fig. 1. An iron valve casting with a T-core and saddle core assembly was simulated using FLOW-3D.
for molds and cores. The valve has two internal cavities shaped by a “saddle” core and a “T-core” (Fig. 1). The metalcaster discovered through testing that a casting with only a T-core does not have gas defects. The computations showed the same behavior, with gas pressures in the saddle core predicted to be twice those in the T-core. The prediction of the ac- tual blow also identified the saddle core as the main source of gas defects (Figs. 2-3). The model provided further insight by identifying the time of blow right be- fore the casting fill time of 1.5 seconds. Subsequently, gas from the cores is ad- equately vented through core prints, as the metal pressure is sufficiently high to seal the cores after the fill is complete. Ad-
ditional information from the FLOW-3D simulations indicated that the shell sand mold was not a significant source of gas defects due to its relatively high surface to volume ratio. Graham-White Manufacturing is investigating possibilities of additional venting for the saddle core, which may include drills from prints and/or forming the saddle core as a two-part assembly with a ring venting channel in the horizontal plane formed during coremaking. With FLOW-3D’s core gas model, further iterations of the core design can be simulated to find one that produces adequate ventilation in the core before tooling is made. MC Visit
www.flow3d.com for more information.
Figs. 2 and 3. Shown are peak outgassing pressures in the two cores after casting fill and locations of core gas blow into the metal right before the end of filling.
50 MODERN CASTING / February 2010
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