3.1 Change in density samples reduced pressure.
The change in density and cross section of samples regardless reduced time pressure the degassed melt. Density increases gradually after degassing, and reaches a relatively stable level with time. It can be seen that small pores are scattered and not the upper surface of the specimen with some pores swollen from the cross section of the sample. Provides visual observation through the vacuum chamber on the gas content measurement in melting aluminum to some extent. The shape of the upper surface and bubbles coming to the surface of the sample indicate the presence of gas during solidification sample cup. Convex surface is indicative of a high content of gas, and concave indicative of low gas content. The higher the specific gravity of the sample, the porosity is less present. Melt the density more than 2.58 × 103 kg / m3 was poured.
3.2 density distributions in solutions.
The relationship between the density and pore measurement area measured by image analyzer for different samples by lost foam casting and traditional sand casting. Spread can the data be seen, but it is clear that as the density of solutions increases, reduces the pore area and decreases the amount of porosity. Content and porosity can be considered gas at the density of the solutions. The density distributions for the height of the bar castings shown in Figs.4 and 5. Figure 4 shows the distribution by variation in density EPS foam from 12.5 kg / m3 to 25.0 kg / m3 for the silica sand packing. A density distribution at the model packing material shown in Fig.5. The highest speed at the top of the bar, while the lowest density is found at the middle part or middle-low parts. It may be closely related to the cooling rate. Solidification time is the upper part where the cooling quickly by the edge effect produced short large temperature gradient. Figure 6 shows the distribution of the measurement time for the height solidify the casting for three mold packing material. It can be seen that the upper part of the fastest and center very slowly, because the gas advanced by the pyrolysis of the pattern is polystyrene foam and flow turbulence during pouring pressure from the region solidify quickly to the region slowly . Density difference is 1.7% to 5% in the same solutions presented. Porosity manifests itself in different forms, ie massive shrinkage cavities, macroporosity, scattered pores, or microporosity. Scattered small pores observed by the high density region, while shrinking pores cavities are concentrated including the low density region. Brinell hardness is the inner region of the middle section containing concentrated pores including shrinking almost half of the neighbor.
