Page 95 - QRedition5.0 062021

Quality Requirements Edition 5.0 European Enamel Association

In cast iron with spherical graphite the element Magnesium has the function to convert the basis of cast-steel or chilled cast iron has been proved. Both grades are having the essential
lamellar crystallizing carbon (graphite) into the spherical state of crystallization during hardness and edge-stability (Vickers - Hardness HV above 650). Fractionated corundum
casting and the following thermal treatment. is also very well suitable.

Due to the ferritic structure and the spherical form of graphite, steel-like elasticity
properties are attained.

Besides the nucleus formation and separation of spherical graphite, magnesium binds
Sulphur as Magnesium Sulfide. This Magnesium Sulfide is preferably absorbed by the slag
of which it reduces its surface tension considerably, so that magnesium slags cannot be
wetted by glasses.

Castings are contaminated and not s u i t a b l e f o r enamelling if an inadequate
slag separation takes place during the casting process. Notice has to be taken of a good
slag separation. Particularly good enamelling results are attainable if a spherical graphite
iron can be produced with a magnesium content less than 0.05 %.

Just as negative as on lamellar cast iron are the trace elements Chromium, Molybdenum,
Nickel, Titanium and Vanadium if the max. concentrations, as mentioned, are exceeded.
Consequently the perlite is that much stabilized, that only an incomplete decomposition to
ferrite takes place during enamelling. This is not only leading to a fluctuating expansion
behaviour depending on the wall thickness of the casting; there are also zones having a
structural transformation during enamelling by which a degassing occurs.

As for the enamelling of lamellar cast iron, the surface of the casting has to be clean and
free of burned-in sand.

The medium roughness should not exceed 300 microns.

For cleaning the cast iron prior to enamelling only angular shot blasting material on the

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