Formation mechanism of gas cavity defects in lost foam iron castings |
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| Authors: | Wanliang Sun H. E. Littleton C. E. Bates |
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| Affiliation: | 1. Department of Materials Science and Engineering, School of Engineering, University of Alabama at Birmingham, Birmingham, AL 35294, USAswayne@uab.edu;3. Department of Materials Science and Engineering, School of Engineering, University of Alabama at Birmingham, Birmingham, AL 35294, USA |
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| Abstract: | The formation mechanism of gas cavity defects in lost foam iron castings was studied by laboratory and in-plant experiments. By scanning electronic microscopy and spectral analysis in the laboratory, carbon concentration and coating residues were observed on the bottom and/or the wall of the gas cavity defects. This indicates that the entrapped foam pyrolysis products are the cause of the gas cavity defects, which is quite different from the causes of the same defect in open cavity mould castings. In-plant measurements show that pyrolysis products were entrapped into the molten metal by erratic metal filling. Also, the metal temperature near the defect area, where metal filled last, is close to or even lower than the solidus temperature of the metal. The cold metal trapped the pyrolysis products inside the casting, resulting in the gas cavity defect. Based on the above observations, new process parameters were used, and the casting scrap rate dropped significantly from 25 to 5%. IJCMR/469 |
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| Keywords: | Gas cavities Lost foam casting Cast iron Investment casting Defects Mould filling Metal flow |
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