Examining Lost Foam beads. (Lost Foam).
In their presentation "Influence of Bead Chemistry on Metal Velocity and Defect Formation in Aluminum Lost Foam Casting" (03-105), D. Hess, D. Askeland and C. Ramsay, Univ. of Missouri-Rolla, examined the effect of three foam characterisitics (bead type, bead fusion and nominal pattern density on metal velocity and defect formation.
Two chemistries of expanded polystyrene beads were examined, including untreated beads and those treated with a bromide-based additive. Both beads had a molecular head weight of 280,000 and an average size of 350 microns.
The bromide additive was found to be effective in reducing the incidence of pyrolysis-related defects in aluminum lost foam castings, nearly eliminating folds and blisters. The fusion of the beads during blowing of the patterns also influenced the severity of the pyrolysis defects, with fewer defects observed when the beads were well fused.
Compared with the bead type and fusion level, the effect of nominal pattern density, liquid infiltration rate and permeability of the coating on the incidence of pyrolysis defects was almost negligible. High pattern density did slightly reduce metal velocity (as expected), while liquid infiltration rate and permeability had no effect.
In their presentation "Effect of Foam Pattern Fusion on the Quality of Lost Foam Aluminum Castings: Real Time and Digital X-ray Observations" (03-083), W. Sun, H. Littleton and C. Bates, Univ. of Alabama-Birmingham, examined the variability in lost foam patterns and how it affects casting quality.
The research found that castings poured with patterns having a low degree of fusion exhibited more surface defects. In addition, castings poured with patterns having a nominal degree of fusion were found to contain more internal anomalies. Last, when the lost foam pattern was modified with a pattern pre-coat, the number of fold defects decreased while a porosity line developed, indicating the presence of internal defects.
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|Date:||Jun 1, 2003|
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