Several commercial nodulizers for grey iron have been produced using a mechanical mixture of magnesium and ferro silicon alloy (43-48% Si), in the weight ratio of about one part of the former to about 15 parts of the latter. These products have had some undesirable characteristics. These include a relatively slow dissolving nodulizer and a high degree of variation in the results obtained from any given foundry.
To overcome these undesirable characteristics, the present invention relates to the use of an improved mixture of treatment particles. These treatment particles can be injected into molten iron to alloy and desulfurize the molten iron. The present invention also reduces the amount of waste associated with the production of such a magnesium-ferro-silicon alloy.
The mixture of the treatment particles consists of a relatively high percentage of metallic magnesium and a relatively high percentage of high melting temperature metal particles. These metal particles have an average melting temperature of at least about 2200 deg F. This combination is selected so as to inhibit the melting of the metallic magnesium particles during injection into the molten ferro-silicon alloy. The metallic magnesium particles are sized to facilitate easy conveyance to the molten ferro-silicon metal and thereby minimize material handling safety hazards.
This high-melting metal particle mixture can be injected into the molten iron by means of an injection lance with a diameter that is compatible with the volume of the molten iron. The metallic magnesium particles are sized to allow for an appropriate quantity of the high melting metal particles in the lance and to ensure that the particles are ejected from the lance without clogging the nozzle or otherwise preventing the injection of the treated iron into the molten ferro-silicon bath.
Another aspect of the invention relates to the use of a co-injection lance wherein metallic magnesium particles and high-melting alloy particles are mixed together prior to being injected into the molten iron. This method prevents clogging of the lance and also provides an increased range of casting parameters that can be controlled for a given casting, such as time of pouring or temperature of the metal being cast.
The co-injection lance can be a single or dual lance where the injection of magnesium and high-melting alloy particles is preferably carried out in a parallel sequence with the injection of molten iron. This is particularly useful when the molten iron is being cast into vertically parted molds.
When used as a nodulizing agent, these patented alloys have the ability to significantly increase the number of nodules formed in the molten iron. This increased nodule count has been observed in both ductile and gray iron. Ductile iron users have reported an up to 50 to 75 percent increase in the nodule count and in the overall microstructure of the nodular iron, including a significant reduction of carbide levels. Gray iron users have also been able to improve the Type A graphite levels in the nodular iron by improving the calcium content of the alloy.
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