Q: We are pouring a ductile iron casting with hard-to-feed areas and want to improve our yields. What products would you recommend for this application?
A: Foundries continue their quest for greater efficiency within their specific production requirements and process capabilities. Highly engineered feeding systems, in particular, offer the possibility for enhanced yield levels — even with complicated product shapes.
Mini-risers, most notably, will strategically optimize yields in these very cases.
Most metals are less dense in their liquid state than as a solid, so castings may shrink during cooling, which can create a void at the last point to solidify. A riser (also called a “feeder”) attaches to the mold at the point of molten metal entry, to prevent cavities from forming due to shrinkage during solidification because the last point to solidify is outside the mold proper.
A combination of shape and formulation have an important effect on the efficiency of the riser’s performance. Traditional risers have a feeding volume efficiency of 15%, while a blind exothermic riser increases that efficiency to 30%.
Mini-risers have the ability to increase the feed efficiency up to 70%. This has a hugely beneficial effect on finishing costs and the overall bottom-line of the casting operation.
Mini-risers are thicker-walled risers that provide the higher strengths that are required with high-pressure molding machines, while resulting in improved feeder performance and riser efficiency. These products are formed from highly exothermic sand or highly insulating alumina-silicate hollow spheres. Each of these product types are produced with a dimensional accuracy that greatly surpasses traditional fiber-based risers.
Further reductions in contact surface area are achievable. ASK Chemicals offers a patented reduced contact mini-riser — coupled with a static pin — that reduces feeder contact by an additional 50%. This helps significantly in the important steps of feeder removal and finishing. Additionally, shell breakers and formed green-sand breakers are alternate options for mini-risers. Green-sand breakers used reduced-contact feeder technology with metal inserts for horizontal compaction.
The ability to form the breaker from the current molding sand improves casting finish and speed of assembly. These materials can be used with a spring pin or static pin design (as illustrated here.)
Furthermore, mini-risers are available in insulating and highly exothermic formulations to meet a specific application requirement. Even highly exothermic formulations are available to combat “fish-eye” defects in ductile iron castings – which may be the best direction for you to proceed in quest for greater pouring efficiency and productivity.
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