A vast amount of literature and advice is written on the best ways to nodularise ductile iron with magnesium ferrosilicon ladle design, pockets, alloy compositions and so on. However, little is said about the Mg alloy reactivity management to get the best magnesium recovery.
Elkem has developed a family of specialised materials designed to optimise the magnesium recovery and reduce reactivity, provide a better nucleation level in the iron and improve the cleansing of iron and change the slag condition to one that is easy to remove.
Many foundries use steel coins often covered with oil, cast plates or even machining swarf as a cover for the MgFeSi in the ladle to try to delay the start of the Mg reaction and increase the ferrostatic head in the ladle to increase the Mg bubbles/iron contact and improve recovery of the magnesium. Many foundries use no cover at all.
The Topseed conditioner range is based on a high density FeSi containing a balanced amount of active elements like calcium, barium and aluminium. The active elements act as a deoxidant when added as support for the MgFeSi and also add nuclei to counter the negative effect on nucleation of adding magnesium. Even a small addition of Topseed will delay the onset of the reaction and provide measureable consistent improvements in the Mg recovery and metallurgical quality of the iron.
The improved performance of MgFeSi has, in many foundries, led to either a reduction in the amount of Mg- FeSi added or a reduction in the magnesium content of the MgFeSi alloy, in itself a mechanism for improving the metallurgical quality of the iron, the Mg reactivity and recovery.
Often, the reaction slag is liquid and difficult to remove, almost invariably involving the use of unexpanded perlite as a coagulant. The additions of a proper amount of balanced active elements through Topseed improve the cleaning of iron and transform the slag into a dry, “popcorn” type, which is very easy to skim. Some foundries have eliminated the use of the environmentally unfriendly coagulants through the use of Topseed.
Three grades of Topseed conditioner are available, each with different levels of active elements and this provides the opportunity to use Topseed in most operating conditions.
For further details contact Ceramic and Alloy Specialists on TEL: 011 894 3039 or visit www.ceramic-alloy.co.za