Simple Solutions That Work! Issue 8

In the last decade, to improve the performance of high potency rare earth based-inoculants, a thin coating of ferrous sulphide and ferrous oxide was applied as a surface treatment to the ferrosilicon-based inoculant. However, this approach provided only a limited amount of oxy- sulfide particles that would adhere to the surface of individual inoculant particles. In addition, this “coating” easily was removed during shipping prior to being used. The only method by which suitable additions of oxygen and sulfur can be incorporated into any inoculating agent is by using suitable blending techniques and selecting proper particle sizing. An example of adding controlled amounts sulfur with of rare earths (as cerium) on improving inoculation and reducing carbides was first demonstrated by R.L. Naro and J.F. Wallace in 1970 and the results are shown in Figure 2. This research showed the importance of controlling both gray iron sulphur and rare earth levels in the molten iron. Balanced ratios of rare earths (cerium) and sulphur, without the presence of ferrosilicon drastically reduced undercooling, completely eliminated chill and promoted favorable graphite shapes in grey irons. Using this concept, patented technology (U.S. Patent 6,293,988B) has been developed and is based on a ferrosilicon-free inoculant, mechanically blended alloy that contains high levels of calcium and stoichimetric amounts of sulfur and oxygen, similar to the Naro and Wallace research findings. Using proprietary blending techniques, this new alloy has demonstrated remarkable abilities to reduce shrinkage, improve inoculation (reduced chill, elimination of carbides) improve nodule count and nodule shape. Alternate methods to introduce sulphur and oxides onto the surface of a cerium/calcium containing ferrosilicon based inoculant is the limited amount of these materials than can be coated onto the surface of the ferrosilicon particle substrate, thereby limiting the critical amounts of sulphur and oxygen needed to boost inoculant potency. Adding late additions of sulphur and oxygen provides a clean, fresh source of sulfur and oxygen. The combination of fresh sulfur and oxygen allows the other proprietary inoculating elements (calcium, aluminum, barium, etc) to react in-situ and provide multiple times the nucleation sites of other, less potent inoculants. Sphere-o-Dox (SOD) has shown remarkable abilities to solve many troublesome inoculation situations. SOD is a proprietary blend of oxy-sulphide forming elements that provide a high volume of graphite forming nuclei when added to molten gray or ductile irons. Not only has it replaced high-potency rare earth containing inoculants at numerous foundries, but it can be used as an inoculant enhancer to improve the performance of all ferrosilicon- based inoculants, such as standard calcium-bearing, barium-bearing or rare earth containing alloys. As a result, greater efficiencies during inoculation treatment have been obtained at significantly lower addition rates, in both grey iron and ductile irons, resulting in significant metal treatment cost savings. An example of how SOD can be used as an inoculant enhancer is illustrated by the experience of Foundry A. Foundry A is a medium sized foundry making thin (0.25 inches or less) section, shell molded castings. For years, carbides have been a serious problem. Continued on page 34 33 0.01%C e 0.05% Ce 0.05%Ce + 0.02%S Base 0.01% Ce 0.03% Ce 0.03% Ce + 0.01% S 0.03% Ce + 0.03% S 0.06% Ce 0.06% Ce + 0.06% S Base 0.01%C e 0.05% Ce 0.05%Ce + 0.02%S Base 0.01% Ce 0.03% Ce 0.03% Ce + 0.01% S 0.03% Ce + 0.03% S 0.0 C BASE 0.01%Ce 0.03%Ce 0.03%Ce+ 0.03%Ce+ 0.06%Ce 0.06%Ce+ BASE 0.01%Ce 0.05%Ce 0.05%Ce+ Figure 2. Effect of oxy-sulphide forming elements (Ce and S) on the chilling tendency of a 4.3 carbon equivalent grey iron