Table 1. DOE Array


Figure 10. Graph of DOE core shrinkage. Effects of Process Variables


While the testing showed that shrinkage is consistent for PUCB cores produced with the same materials under the same conditions, the effects of different materials and pro- cessing conditions had yet to be quantified. A DOE was de- veloped based on variations that could occur in the casting plant’s coreroom. Variables to be evaluated included: binder %, level of a fused silica addition, blow pressure, mixed sand benchlife, gassing time to vary amine exposure, the PUCB binder formulation, and a water addition to simulate possible moisture in the blow air at the core machine. Levels for each variable were selected based on the possible extremes of op- erating conditions. The DOE was constructed in a Taguchi L8 orthogonal array as shown in Table 1.


68


Eight sand mixes were produced with the conditions speci- fied in the DOE. Eight cores then were produced from each mix. All eight cores were weighed, then four cores were tested for transverse strength, and four cores were placed in the dial indicator fixture for shrinkage testing over 24 hours. The shrinkage was measured at 1, 2, 3, 4, 5, 6 and 24 hours, and the averages of the four bars were recorded, as shown in Table 2 and Figure 10.


DOE Data Analysis


Level averages were calculated for each data set, and ANOVA tables were constructed. The results for both core weight and transverse strength were as expected. Core weight was most strongly affected by the water ad-


International Journal of Metalcasting/Summer 10


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