Inoculation of the melt

Under inoculating a molten metal is understood to mean the addition of solid materials of the same or different composition, usually in fine-grained form, with the aim of nuclei to create or assist in the formation.

Cast iron with spheroidal graphite

In addition to the metallurgical quality of the melt , the chemical composition and the casting temperature, the germination state is one of the most important criteria in the production of spheroidal graphite cast iron . After the magnesium treatment, the germination state of the melt is insufficient. The state of germination is largely dependent on the vaccination.

The aim of the inoculation is the formation of nuclei for a graphitic precipitation of the carbon and an activation of the substrates present in the melt. In order to be able to achieve this goal, certain proportions of elements such as oxygen , sulfur , aluminum and silicon must be available in the melt. They need to be present in an active form; H. must be able to react. In chemically bound form or coagulated as slag parts they are worthless.

Subversive trace elements, also called interfering elements, which negatively influence spheroidal graphite formation (e.g. lead , arsenic , antimony and titanium ) are neutralized to a certain extent by vaccination. For this, alkaline earth metals such as barium , strontium or rare earth metals ( rare earth elements) such. B. cerium or yttrium are suitable. Such SE elements are contained in many inoculants.

There are many ferrosilicon based inoculants available in the market . They are provided either as alloys or as a mixture of fine-grain alloys.

Decay of the vaccination effect

The germs formed by vaccination only have a relatively short lifespan. They are mostly dissolved again in the melt or oxidized through contact with air. The decrease in the vaccination effect is called fading or fading. For this reason, it is imperative to do the inoculation process as soon as possible before potting. The inoculant is therefore usually added to the melt in the pouring ladle or in the pouring stream.