This project was conducted to evaluate the effect of breaker core opening size on elemental segregation for top risered castings. The castings included cube castings and actual castings, both made from 8000 series, arc-melted carbon steel. The base carbon level in the melt was 0.28 percent for the cubes, and 0.34 percent for the castings. Both alloys were considered segregation prone. The pouring temperature for the cubes was 2880 deg F (1582 C), AND 2840 deg F (1560 C) for the castings. The top risers in all cases were insulated with exothermic/insulating insert sleeves. The mold material was resin-bonded sand. Castings made using the standard 50 percent opening breaker core based on the Washburn formula experienced under riser carbon segregation. Castings made using a full contact riser sleeve did not experience this problem. Computer simulations were initially conducted to determine the optimal breaker core opening size for elimination of under riser carbon segregation. Opening size of 50 percent, 60 percent, 65 percent, 70 percent and full contact were simulated. The results showed a significant reduction in under riser segregation for the 65 percent and 70 percent cases. Foundry trials were then conducted for the same breaker core opening designs on a casting with known segregation problems. The trials showed that the 70 percent opening was optimum for elimination of under riser carbon segregation for all castings tested. For top-risered, segregation prone carbon steel alloys, breaker core opening size should be increased to between 65 percent and 70 percent of the riser diameter to minimize under riser segregation.
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