Nodularisation

The efficiency, the qualitative assessment of flue-gas production and the complexity of the various nodularisation methods are compared in Table 3.20. 

Comment Easy operation Optimised sandwich but more maintenance High mainte- nance High mainte- nance Expensive installation Different design of pouring system High mainte- nance 

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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. 

Table 3.20 Comparison of various nodularisation procedures [110, Vito, 2001], [225, TWG, 2003]...

The type of exhaust collection applied depends on the technique used for nodularisation (see 2.4.12.4). Depending on the technique, significant amounts of MgO can be released as a white smoke. Properties of the various nodularisation techniques are given in Table 3.20. In general techniques with a higher take-up efficiency result in lower emissions. This is the case for the in-mould process, where the nodularisation takes place during pouring. 

For in-crucible nodularisation, techniques using a lid or cover result in a significant reduction of the emission. 

If the nodularisation off-gas is not captured, this could result in the melting shop filling-up with a white smoke, and MgO dust drop out. Exhausting without filtration can result in a visible emission from the foundry. A large volume of visible particulate can be generated in a relatively short period of time, but usually only lasts for a short duration (5 to 10 minutes for each batch treated). 

In-crucible nodularisation may be performed at a specific stand or location in the melting shop. The crucible with the molten metal is brought to this point after pouring, but before taking it to the casting furnace or station. This allows the installation of a fixed hood for exhaust capture. 

The technique of exhaust capture and filtration applies for foundries using in-crucible nodularisation techniques. No information on applicability to the in-mould nor ductilator was provided. 

For the production of nodular iron, nodularisation is performed. BAT for nodularisation is to select a nodularisation technique with no ofT-gas production or to capture the produced MgO smoke, using a lid or cover equipped with extraction equipment or by using a fixed or movable hood, and to... 

Nodularisation magnesium treatment of cast iron to change the carbon particles into nodular/spheroidal shape... 

The actual metal treatment applied depends on the type of product made. BAT is to collect the exhaust gas from AOD converters using a roof canopy and to collect and treat the off-gas from nodularisation, using a bag filter. BAT is also to make the MgO-dust available for recycling. 

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