as the core diameter decreases. If venting is necessary in this situation, defects should increase in cores with smaller diamteres, where nearly no venting was avail- able. Instead, the opposite was true. Apparently, venting did not play a significant role in this situation. Te results of these tests led to


two conclusions: 1. Cores with diameters of


0.375 in. or more are rigid enough to resist significant deforma- tion during casting of aluminum when positioned vertically. Cores oriented horizontally would be subject to gravity and buoyancy forces that could result in greater deflection. 2. Gaseous emissions from a


binder concentration of 1.7% is not a significant issue in casting aluminum. ■


Fig. 7. Liquid penetrant testing showed various defects.


32 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2015


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