PRODUCT INNOVATIONS
Mini-Riser Advancements Reduce Riser Size, Weight, Footprint Recent improvements
in Exactcast risers from ASK Chemicals, Dublin, Ohio, have been applied to new mini-riser products that allow metalcasters to reduce the size and weight of their risers and the riser’s footprint left on the casting. Te mini-risers also improve casting yield through better feeding performance, which can make room in the mold for more castings. The mini-riser prod- ucts 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 exo- thermic 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 graph- ite nodularity degradation in the metal. Fluoride-free sleeve formula- tions 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 Exactcast mini-riser feeding a manganese steel casting (left) reduced the amount of feed metal and riser con- tact area of the same casting fed with a standard cylindrical sleeve (right).
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 bet- ter 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, includ- ing 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 met- alcasting 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. Visit
www.ask-chemicals.com for more information.
A difficult-to-feed manganese steel casting (left) exhibits reduced contact areas from the Exactcast mini-risers. As a result of the downward moving riser (above) the molding sand under it is well compacted, producing an optimal contact surface.
February 2012 MODERN CASTING | 53
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