Surface Graphite Degeneration in Ductile Iron Castings for Resin Molds |
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Authors: | Iulian Riposan Mihai Chisamera Stelian Stan Torbjorn Skaland |
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Institution: | aDepartment of Materials Science and Engineering, Politehnica University, Bucharest 060042, Romania bWindcast Group, Kristiansand 4673, Norway |
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Abstract: | The objective of this paper is to review the factors influencing the formation of degenerated graph-ite layers on the surfaces of ductile iron castings for chemical rosins-acid molding and coro-making systems and how to reduce this defect. In the rosin mold technique the sulphur in the P-toluol sulphonic acid (PTSA),usually used as the hardener, has been identified as one factor causing graphite degeneration at the metal-mold interface. Less than 0.15% S in the mold (or even less than 0.07% S) can reduce the surface layer depth. Oxygen may also have an effect, especially for sulphur containing systems with turbulent flows in the mold, water-bearing no-bake binder systems, Mg-Silica reactions, or dross formation conditions. Despite the lower level of nitrogen in the iron melt after magnesium treatment (less than 90 ppm), nitrogen bearing res-ins have a profound effect on the frequency and severity of surface pinholes, but a limited influence on sur-face graphite degeneration. |
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Keywords: | ductile iron castings surface graphite degeneration resin mold sulphur oxygen nitrogen |
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