it provides data on ultimate strength, stiffness and toughness. In Fig. 1, the slopes, as well as the areas under the curve, are different. Te steeper slope represents the stiffer green sand system, and the larger area under the curve indicates tougher green sand. On the molding technology side of
green sand mold control, a new aera- tion filling method has been intro- duced as a better way to achieve com- plete sand filling and uniformly dense sand molds. In aeration filling, green sand is first fluidized, which greatly increases the flowability of the sand. Ten, low air pressure drives the sand into the mold for smooth filling. In aeration filling, most of the green sand properties, such as green compressive strength, permeability and mold hard- ness, are the same. However, friability, which is the bulk surface abrasive property, is less. Friability relates to the erosion of green sand due to molten metal flow. Tis implies aeration can produce molds at lower compactability (lower moisture) levels.
Lab Comparisons In order to learn more about the
difference between aeration and conventionally filled green sand molds, a modified cone jolt test was used to study mold samples from each mold- ing technique. Te laboratory proce- dure conducted at the Metal Casting Laboratory at Western Michigan Univ. consisted of three major steps. First, green sand was tempered to the desired compactability level. Next, AFS standard test specimens were prepared using gravity and aeration sand filling techniques. Finally, a series of AFS tests for green sand properties were performed. Te key variable on the sand
Fig. 2. The modified cone jolt tester (left) and data acquisition system are pictured.
Fig. 3. A sand squeezer (left) and stripping post were used to produce compactability and cone jolt specimens.
Table 1. Properties of Gravity and Aeration Filled Specimens at 30, 33 and 35% Compactability Levels AFS Test
Compactability (%) Bulk Density (g/cm3 Moisture Content (%) Specimen Weight (g) Permeability (#)
) Splitting Strength (psi)
Compression Strength (psi) Mold Hardness (#)
Gravity-Filled Lake Sand 30 (1.0)
0.98 (0.02) 1.9 (0.14) 158 (1.0) 228 (2.0) 3.9 (0.05) 21 (0.2) 92 (1.0)
33 (1.5)
0.89 (0.01) 2.5 (0.05) 158 (1.5) 233 (1.0) 5.4 (0.10) 24 (0.5) 94 (1.2)
35 (1.0)
0.88 (0.04) 2.7 (0.10) 152 (0.5) 261 (1.0) 5.0 (0.09) 24 (0.1) 96 (1.1)
0.99 (0.01) 2.5 (0.02) 160 (1.0) 220 (1.0) 3.4 (0.12) 17 (1.2) 93 (1.5)
Aeration-Filled Lake Sand 30 (0.2)
33 (0.2)
0.99 (0.01) 2.5 (0.01) 158 (1.0) 223 (1.5) 5.4 (0.20) 24 (1.0) 94 (1.0)
35 (1.0)
0.89 (0.02) 2.5 (0.01) 158 (0.5) 228 (1.2) 5.1 (0.10) 25 (1.2) 97 (0.5)
September 2013 MODERN CASTING | 31
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