It was expected that the new system of chills will change the solidification pattern of the casting and will have positive effects on the formation and distribution of the defects. The results are captured in Figures 12-14. In Figures 12a, b a new solidification pattern was predicted by means of the fraction liquid function at 42% and 75% solidified.
The size of the riser together with the new arrangement of the chills obviously positively affected solidification, completely avoiding the isolation of the liquid pools seen in Figure 7. Moreover, the steel plate placed below the casting evoked rapid cooling and facilitated directional so- lidification toward the riser. The comparison of centerline porosity indicates that the increased temperature gradients
Velocity [cm/s] Empty
887.7 824.9 760.9 697.5 634.1 570.7 507.3 443.9 380.4 317.0 253.6 190.2 126.8 63.4 0.0
via enhanced chilling readily eliminated likelihood of its formation see Figure 13. The only two areas that might be of concern are the two bottom pins. In the original lay- out, no porosity was present in these areas however this is not true for the current layout. This is depicted in Figures 13 and 14. Considering that part is used for transportation purposes and the entire casting weighs around 58 tons, this porosity cannot be neglected as it corrupts the mechanical properties and weakens those areas. This issue can be elim- inated by adding a sufficient draft to the pins and changing their solidification pattern. The critical value for porosity in Figure 14 has been set to 1%. Areas containing less than 1% porosity are considered “healthy” and thus they are fil- tered out by the X-Ray function.
Velocity [cm/s] Empty
817.3 758.9 700.6 642.2 583.8 525.4 467.0 408.7 350.3 291.9 233.5 175.5 116.8 58.4 0.0
(a) Figure 11. New filling pattern due to the redesigned gating system.
(b)
Figure 12a. Improved solidification pattern due to the reworked system of the chills- 42% solid.
70
Figure 12b. Fraction liquid at 75% solidified International Journal of Metalcasting/Fall 10
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