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Effective Factors on the Shrinkage Porosity Defect of Ductile Iron in Centrifugal Casting

Maghsoudi, Mohammad Mahdi | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46681 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Varahram, Naser; Davami, Parviz
  7. Abstract:
  8. The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
    In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces simultaneously, and the last metal to feed inside the casting exhibits this shrinkage. To comprehensively study the role of different factors, single-parameter as well as multi-parameter tests were defined. In this regard, the melt composition, inoculation consist of inoculants and inoculation method, pouring temperature, mould rotational speed, thickness of coat and directional solidification establishment by enhancement of mould cooling effect and also reduction of inner air fluid cooling effect, were considered as the most important ones. All the designed tests resulted in a reduction of random samples shrinkage percent. The best results achieved through changing the melt composition in a way that the Carbon weight percent may be increased to 3.5-3.7 and Silicon weight percent may be decreased to 1.5-1.7 holding a constant carbon equivalent value. Combination of the latter change with stream inoculation in the end of trough was also been found to be beneficial. Additionally, combination of parameter tests consisting directional solidification establishment by use of outer mould water spray and socket-spigot mould close to prevent the inner air fluid convection and reduction of coat thickness to 1-1.1 mm from 1.3 mm was another effective approach. Eventually, several production parameters such as mould and stream inoculation difference and the effect of coat on the microstructure of ductile iron were investigated
  9. Keywords:
  10. Ductile Cast Iron ; Directional Solidification ; Coating Thickness ; Centrifugal Casting ; Shrinkage Porosity ; Hot Mould Method

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