Despite the drawbacks, late in-
stream inoculants often were used in conjunction with a solid cast in-mold inoculant. Recent develop- ments with in-mold inserts, how- ever, have allowed metalcasters to avoid the problems with in-stream, granular inoculations by moving to an entirely in-mold process. These inserts, placed either in the pouring basing or in the drag portion of the mold (Fig. 2), are practical options for late inoculation that provide uniform dissolution, avoid inocu- lant fade and prevent atmospheric contact during dissolution. Using smaller starter inserts can
Fig. 3. This on-casting photomicrograph shows the preferred nodular formation of graphite.
the facility) can produce inoculant fade, which diminishes its effect. In-stream inoculation, as a granu- lar material placed in the mold or pouring basin, also has potential
drawbacks, including: • Undissolved silicon in the casting. • Inoculation that is not uniformly dispersed.
• Slag inclusions.
help ensure proper inoculation of the first iron into the mold or basin. Tis iron then becomes feed metal in a riser and is last to solidify, so it is likely to form chunky graphite. At Glidewell, the in-mold inocula-
tion for the torque arm consisted of two 11-lb. (5-kg) inserts rammed up in the pouring basin. One insert included
34 | MODERN CASTING August 2013
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