Melting additives

Nodulisers are alloys with Silicon as main component and traces of Magnesium, Cerium or Calcium with specific relevance. The nodulisation process enables the transformation of lamellar graphite into spheroidal or vermicular one, thus improving mechanical strength, elongation and material resilience.

ILARDUYA supplies a wide range of tailored nodulisers with varied grain size and different Magnesium, Calcium and Rare Earths content. Nowadays it also offers the possibility of nodulisation by cored wire allowing more accurate dosage and higher process yields.

Most foundries often debate on which noduliser best fits their process requirements. To simplify the question, next some guidelines on how to choose the best noduliser are shown.

Noduliser type	Temperature [ºC]		Ladle size [H:D]		Metal amount [kg]		Tundish cover
	< 1480	> 1480	1:1	2:1	< 500	> 500	Yes	No
FeSiMg 5/6 Ca 1
FeSiMg 8/10 Ca 2
FeSiMg 9 Ce 3
FeSiMg 5/6 RE 0
FeSiMg 8/10 RE 0
FeSiMg 5/6 Ca 2 RE 2
FeSiMg 6/7 Ca 3

The use of inoculants enables grain size reduction and minimises chilling tendency, improving castings mechanical properties and tooling. Inoculants are products mainly composed of Silicon combined with other materials such as Calcium, Barium, Aluminium, Strontium or Zirconium. Inoculants dosage ranges from 3-10 kg/t of iron and they should be added over the iron vein in the melting ladle as late as possible. Inoculation controls cast iron structure and properties by increasing the number of nucleation sites available for graphite flakes or graphite nodules growth in grey and ductile irons, respectively.

ILARDUYA gives professional advice to smelters on the most appropriate inoculant for their particular process. The choice will depend on particular conditions such as iron starting sulphur content (grey iron), temperature, fading time or dosing method. The wide range of available inoculants is mainly based on ferrosilicon alloys containing further elements with specific effects such as:

Aluminium: Metal commonly present in ferrosilicon and with inoculation ratio limited to 1,5% to avoid pinhole defects in green moulding castings.

Barium: Barium-containing inoculants are especially appropriate for long fading or long solidification-requiring processes such as those in large section castings. Barium contents over 3% are excessive and can provoke slag generation.

Calcium: Element with average inoculation capacity and usually added together with Aluminium or Barium. It is specially appropiate for low sulphur (0,03–0,05%) grey iron castings and for nodular iron casting of parts with average-sized section.

Strontium: Inoculants with ca. 1% strontium are extremely effective in grey medium and high-sulphur containing iron casting and reduced thickness castings. In ductile iron casting less than 1% Rare Earth content in nodulisers is required.

Zirconium: Zirconium-based inoculants have extraordinary inoculation properties and fading resistance. Furthermore, they are particularly indicated as nitrogen neutralisers in core-abundant castings.