til more iron could be added. The introduction of the thermal efficient tundish treatment ladle allowed the treatment to be conducted at considerably lower temperatures, with a sub- stantial reduction in MgFeSi usage.8
principle ladle treatments types can be seen in Fig. 3.
A complicating factor when trying to minimize Mg con- tent of the iron is that the spheroidizing effect of Mg dete- riorates over time as seen in Fig. 4. This effect is referred to as Mg fade. To compensate for Mg fade it is necessary to add extra Mg to cover the losses that will occur until pouring is completed. This is a larger issue for processes where the treated iron is maintained in an autopour for extended times.10
In-the-mould nodularizing treatment as seen in Fig. 5 repre- sents a solution to this problem. This method was invented by C.M. Dunks in 1977.11
dedicated reaction chamber in the mould thus making each mould a separate treatment.
Here the treatment is made in a
An overview of these
This way of treatment offered the advantage of eliminating the fading effect allowing a minimum of Mg to be added and eliminating the need for subsequent inoculation. The process demanded that pouring times be highly consistent, which led to ongoing developments with automatic pouring.
In-the-mould nodularizing treatment represents the ultimate optimization when it comes to minimum alloy usage due to maximum recovery and avoidance of any subsequent inocu- lation. In-the-mould nodularizing treatment also produced ductile iron with very low shrinkage and carbide tendency.
This method is suitable for cast iron foundries making large series of the same casting as it requires some set up work to design the gating system which includes alloy pockets.
When ductile iron was invented, numerous ways of intro- ducing the Mg to the melt were tested. Some methods have been more successful than others and have been steadily im- proved and remain in use.
Figure 3. Overview of the most common ladle treatments; pour over, Sandwich Cover and Tundish Cover.9
Figure 4. Typical decrease in residual Mg-level as a function of time according to Loper Jr. et al.10
International Journal of Metalcasting/Volume 8, Issue 2, 2014
Figure 5. Overview of in-the-mould treatment set up.12 9
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