Mechanisms and mechanics of porosity formation in ductile iron castings

• Autorzy: Perzyk M. , Witemberg-Perzyk D.
• Języki publikacji: EN

Abstrakty

EN

Shrinkage defects in ductile iron castings can be of two basic types: shrinkage cavities associated with the liquid contraction prior to the expansion period of the iron as well as the porosity, which may appear even if the liquid shrinkage is fully compensated. In the present paper two possible mechanisms of the porosity are presented and analyzed. The first one is the Karsay's mechanism based on the secondary shrinkage concept. The second one is the mechanism acting during the expansion period of the iron, first suggested by Ohnaka and co-authors and essentially modified by the present authors. The mechanical interactions between casting and mould are determined for the both mechanisms. Their analysis leads to the conclusion, that porosity forms during expansion period of the melt. The direct cause is the negative pressure which appears in the central part of the casting due to the differences in expansion coefficients of the fast cooling surface layer and slow cooling inner region. Observations concerning feeding behavior of ductile iron castings, based on this mechanism, agree well with industrial practice. The secondary shrinkage is not only needless to induce the porosity, but the corresponding mechanism of its occurrence, proposed by Karsay, does not seem to be valid.

Słowa kluczowe

EN

casting defects; ductile cast iron; porosity formation; feeding; mechanical analysis

PL

wady odlewów; żeliwo sferoidalne; porowatość odlewów

• Wydawca: Komisja Odlewnictwa Polskiej Akademii Nauk Oddział w Katowicach
• Czasopismo: Archives of Foundry Engineering
• Rocznik: 2007
• Tom: Vol. 7, iss. 4
• Strony: 147--150
• Opis fizyczny: Bibliogr. 5 poz., wykr.

Twórcy

autor

Perzyk M.

autor

Witemberg-Perzyk D.

• Warsaw University of Technology, Metal Casting Section, Narbutta St 85, 02-524 Warszawa, Poland,

Bibliografia

• [1] S. I. Karsay, Ductile Iron III. Gating and Risering. Qit - Fer et Titane Inc., 1981, Canada.
• [2] Ductile Iron I. Production. The state of the Art, 1992, Qit - Fer et Titane Inc., 1993, Canada.
• [3] The Sorelmetal Book of Ductile iron. Rio Tinto Iron & Titanium Inc., 2004, Canada.
• [4] R. Hummer, Feeding Requirements and Dilatation During Solidification of Spheroidal Cast Iron - Conclusions for Feeder Dimensioning, Giesserei-Praxis, Nos. 17-18 (1985), p. 241-254.
• [5] I. Ohnaka, J. Iwane, H. Yasuda, J. Zhu, Prediction of porosity defect in spheroidal graphite iron castings, Int. Jour. of Cast Metals Res. vol. 16 Nos.1-3 (2003), p.293-299.