Exothermic risers are open or closed cavities in casting molds which are filled with liquid metal during casting at the same time as the casting.
The dimensions of a riser are designed so that its solidificationmodulus is larger than the junction in the casting in order to avoid cavities in the casting. Due to the larger solidificationmodulus (s.a. Modulus, Casting modulus), the riser keeps the metal inside it liquid for longer and can therefore balance out a lack of volume in the solidification phase of the casting. In this way, the final point of solidification occurs within the riser and the “sealing” of the cast piece is ensured.
These risers made of exothermic-insulating or exothermic or highly-exothermic material (s. Exothermic mixture) are available as cylindrical and oval cases or closed riser sleeves with or without breaker cores. They are inserted into the mold using different methods depending on the molding process (Fig. 1 and 2, ASK Chemicals, Foseco Foundry Division Vesuvius GmbH).
Through an exothermic reaction, the risers achieve a solidification time which is two to three times longer in comparison with large natural sand risers. Accordingly, the riser volumes and riser surface area on the casting are reduced and the yield is increased considerably.
Insulating riser sleeve