Nodularisation treatment of the melt

Nodular cast iron is obtained by the addition of Mg, either pure or as a FeSiMg or NiMg alloy, to the molten metal. Prior to this, a desulphurisation treatment may be necessary to guarantee successful nodularisation. The presence of Mg in the melt provokes a solidification of the graphite phase in the sh e of microscopic spheres. This gives rise to higher mechanical properties, such as strength and ductility. 

There are several techniques that can be applied to introduce Mg into the liquid metal  

The pour over technique This is the simplest method, whereby the liquid metal is poured over the Mg alloy in the bottom of the ladle 

The Tundish Cover This is an improved sandwich technique, whereby the ladle is covered by a lid after the Mg alloy has been placed at the bottom of the ladle. The metal is poured in the concave lid and flows through a hole in the ladle, where the reaction takes place The plunging method Using a plunger bell, the Mg alloy is submerged in the liquid metal until the reaction is finished. During the treatment the ladle lid is closed, to prevent MgO fume emissions 

The G Fischer converter This process uses a special ladle that is closed tightly with a lid after the metal is poured into the converter in the horizontal position. The converter is then tilted into a vertical position, allowing the Mg alloy to react with the metal. Once the reaction is finished the converter is turned back into the horizontal position and is tapped after opening the lid 

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