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Procedure Researchers investi-


• Cross flow in a partially encapsulated mold.


• Cross flow in an unencapsulated mold.


gated three modes of sup- plying helium to the mold (Fig. 1-2):


• Parallel flow in an unencapsulated mold. Te mold design for cross flow in a


partially encapsulated mold and unen- capsulated mold was configured so that the helium was supplied at the base and forced to pass through the mold in an upward direction under the pressure of the incoming helium supply. In the cross-flow method for an unen-


capsulated mold, helium was supplied in the same way as the encapsulated mold, but more system losses were expected. For parallel flow in an unencapsu- lated mold, two supply plates—one for the cope and one for the drag—were designed for supplying helium to the mold. Te plates were attached opposite the pouring basin and affixed to the mold so the point of helium supply was positioned at the middle of a groove cut in the mold to ensure parallel flow. Te relatively shorter travel distance along the casting, the position of the groove (cut close to the casting surface), the pressure of the incoming gas, and peripheral sealing of the supply plate ensured the helium traveled along the surfaces rather than leaking or moving to the sides (Fig. 3). Te effect of the helium flow rate, flow


direction and mold design on average as- cast grain size, SDAS and room tempera- ture tensile properties were investigated and compared to castings produced in the typical sand casting process. Te cross-flow modes were investi- gated with a 4-L/minute helium flow rate, while the parallel-flow mode was investigated at 1-L/minute, 4-L/minute and 8-L/minute flow rates. Helium was introduced to the mold after it was completely filled with molten alumi- num alloy 319. For each casting, 40 lbs. of alloy were melted in an induction furnace. Te av- erage pouring temperature was 1,562F (850C). Five thermocouples were


Jan/Feb 2013 | METAL CASTING DESIGN & PURCHASING | 27 Fig. 1. This schematic represents the general apparatus for applying helium to the sand mold.


Fig. 2. Shown is the schematic for the cross-flow (left) and parallel-flow modes for helium-assisted sand casting.


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