Mini-riser advancements reduce riser size, weight footprint.
The mini-riser products use ASK's Exactcast coldbox technology, which replaces the sand-based exothermic formulation with an insulating mix of low density refractory material, reducing riser weight by 75%. Since the mini-risers weigh less, less exothermic material is needed to bring the sleeve to the same temperature as sand-based exothermic sleeves. This helps reduce the potential for aluminum contamination and graphite modularity degradation in the metal. Fluoride-free sleeve formulations also have been developed for ductile iron applications to eliminate the potential for fish-eye defects and graphite flake formation.
Along with the Exactcast riser design, the new mini-riser features a metal neck breaker. In this design, the riser is positioned on a pin with a conical metal tube. When green sand falls into the mold, it builds up around the metal neck. During mold compaction, the riser moves down and slides over the metal tube while the sand between the sleeve and the pattern is compacted. The result is a small riser neck with a breaker edge designed to knock off easily for better casting cleaning.
In many metalcasting facilities, grinding after the riser knock-off is not necessary with the metal neck breaker technology. As a result of the downward-moving riser, the molding sand under the riser is well compacted, and the casting has a perfect contact surface.
The low contact area of the mini-riser allows for proper feeding of difficult casting geometries, including a contoured geometry where the riser meets the casting and where a reduction in the contact area is needed. In a recent test at a metalcasting facility, it was found that manganese steel castings using the mini-risers could be fed with three to five times less feed metal than a normal cylindrical riser sleeve due to the alloy's low shrinkage rate. The riser's surface contact area with the casting also was reduced, leading to the possibility of knocking off the risers instead of using the arc-air cutting method.