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Based on the solidification results, a wedge casting was designed which enabled the evaluation of alpha-case layer defects with respect to different section thicknesses of the casting and different cooling rates. Tis is shown in Fig. 3. An equipment vendor produced the test mold using a 3-D printer. Silica sand with a 105 AFS-GFN was the aggregate and a furan binder system was used. Te mold was coated with the EAC. A Baumé of 80 was used. Te test mold is shown in Fig. 4. Te molds were poured at Rock Island Arsenal using a vacuum induction melting furnace and vacuum pour- ing chamber. Te resulting casting was sectioned according to predetermined thicknesses. Te cross sections were then evaluated for its microhardness using a Buehler microhardness tester. A mag- nification of 500X was used with a load of 500 g (1.1 lb.), and the microhardness was measured across all cross sections in steps of 50-150 micrometers. Charts were plotted using the depth in microm- eters for the X axis and the microhard- ness for the Y axis.


Baumé to determine a suitable Baumé for coating cores and molds. A target range of 10-15 seconds for zahn cup measure- ment and 75% solid fraction were set as optimal for coating applications. A Baumé of 78 or 80 resulted in


3


desired viscosity and percent solids results for the experimental alumina coating (EAC). It was decided to coat the test molds and cores at a Baumé of 80. Table 1 shows the detailed results obtained from the tests. Ceramic and silica sand Gertz-


mann cores bonded with furan binder


Table 1. Coating Characterization Results Baume


64 66 68 70 72 74 76 78 80


Zahn Cup (s) 4.41


4.57 4.76 5.26 5.75 6.26 6.90 8.12


10.32


Table 2. Preliminary Titanium Casting Results Sample


Fig. 3. This is the designed wedge casting.


Zirconia with sodium silicate Alumina with sodium silicate Ceramic with sodium silicate Ceramic with furan resin


Table 3. Silica Sand Titanium Casting Results Section Thickness


2 in. 1.5 in.


1.25 in. 1 in.


Fig. 4. This is the top view of the 3-D printed silica sand test mold for titanium casting.


34 | MODERN CASTING April 2015


0.75 in. 0.5 in.


0.25 in.


Results and Conclusions Zahn cup, viscosity and


percent solid results from the coating characterization were plotted against the respective


system were placed in the molds. Low alloy steel with a target chemistry of 0.3 % carbon, 0.6% silicon and 0.5% manganese was poured in these molds with a target pouring temperature of 2,912F (1,600C). Later, the castings were cleaned and photographed. Figures 5 and 6 show the castings from cores made of ceramic and silica sand. Both cores were coated with the experimental alumina coating (EAC). It can be seen that both the castings with the EAC have no visible defects except for a small area of sand burn on the bottom of the casting made of the ceramic sand. From the steel casting results, it can be seen that the EAC is effective in forming a protective layer around the core. As a result, it was decided to use the


Viscosity (cp) 22.22


28.5 34.4 38.8 51.8 76 95


131.4 169.4


% Solids (%) 58.70%


61.20% 64.10% 65.40% 67.40% 69.00% 73.00% 75.60% 76.50%


Maximum Vickers Hardness Number


465.69 479.61 587.8


510.89


Alpha Case Layer Depth (microns)


115 129 237 160


Maximum Vickers Hardness Number


520 470 684 640 544 535 544


Alpha Case Layer Depth (microns)


170 120 325 290 194 185 194


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