No-Bake S-Containing Mold/DI Metal Interactions: Consequences and Potential Applications
The ductile iron liquid metal is very reactive with environmental gases and solid molds after a nodulizing treatment. Mold-metal reactions could alter the spheroidal graphite shape to vermicular or flake. In this research, the metal-mold reactions were enhanced by various sulfur additions to the no-bake mold inserts to study these phenomena and to artificially produce layered dual-graphite structure in the casting. Thermodynamic and solidification modeling together with sets of different experimental techniques were applied to a test casting with internal core passages representing the cylinder head of a diesel engine. The effects of insert surface shape and location in the mold; content and type of sulfur-containing agent; coating; pouring temperature and additional chilling were experimentally studied and discussed. These results could be used to better understand the metal-mold interaction, prevent surface defects and design dual-graphite structure processes.
Graphite degeneration in the superficial layer of high Si-ductile iron casting as influence of inoculation and protective coating against sulphur diffusion into the iron melt
Abstract The objective of the present paper is to evaluate the occurrence of degenerate graphite in a surface layer on high Si ductile iron (0.032%Mgres, 3.37%C, 3.44%Si, 0.44%Mn, 4.43%CE), solidified in standard thermal analysis ceramic cup. S-bearing coating is applied on the inner surface of ceramic cup, with and without iron powder protective coating against S diffusion into the iron melt. Based carbonic material coating is also used as reference. Eutectic undercooling is normally 23% decreased by inoculation, but also depending on the nature of the applied coatings: less effect of S-bearing coating, while carbon and especially iron powder-bearing coatings reduced the beneficial effect of inoculation (higher addition, higher undercooling). Measured surface layer thickness in only Mg treated iron casting is higher by matrix evaluation (912 μm) compared to 716 μm obtained by graphite evaluation. Inoculation applied after Mg-treatment leads to decreased surface layer thickness to 195 μm and 108 μm, respectively. S-bearing coating increases the skin size of inoculated iron casting to 253 μm (matrix evaluation) and 176 μm (graphite evaluation). A layer iron powder addition on the S-bearing coating reduces the skin size to 132 μm and 66 μm, respectively, while supplementary iron powder addition avoids the surface layer formation, similarly to based carbonic material coating application.
A unified analysis of filling and solidification in casting with natural convection
Abstract In this paper, a unified model for simultaneous filling and solidification is applied to the two-dimensional filling and solidification of a square cavity. The effects of wall temperature and gate position on solidification are examined. The mixed natural-convection flow and residual flow resulting from the completion of filling are included in this study to investigate the coupled effects of filling and natural convection on solidification. Two different filling configurations (assisting flow and opposite flow due to the gate position) are analyzed to study the effects of residual flow on solidification. The results clearly show the necessity to carry out a coupled filling and solidification analysis, including the effect of natural convection. A numerical algorithm that uses the implicit volume of fluid (VOF) method for filling and a general, implicit, source-based method for solidification are presented.