Thin-walled ring-shaped core, also known as a knock-off or constriction core, which is inserted between the casting and the feeder. These breaker cores can be produced from resin-coated sand using the Croning process or using the cold box process. Depending on the application, all common molding materials like quartz sand, chromite sand, special sand, etc. are used as materials for these cores (Fig. 1, Foseco Foundry Division Vesuvius GmbH). Ceramic breaker cores are also used, metallic breaker cores are increasingly used.
Since the breaker core is quickly heated up by the liquid metal during casting and creates a heat center at the constriction formed in the feeder neck, it cannot freeze prematurely. In addition, the constriction makes it easier to clean and separate the feeder from the casting. The casting yield is increased.
Metallic breaker cores are mainly used on automatic molding lines today, directly under the exothermic feeder.
FEEDEX K (Fig. 2, Foseco Foundry Division Vesuvius GmbH) highly exothermic feeder sleeves combine the best in class feeding performance that foundries with unsurpassed knock-off cleanliness and consistency.
The unique design of the stepped steelbreaker core and optimized neck configuration allow spot feeding application to even the smallest casting contact areas, create a defined knock-off edge at the casting surface and ensure excellent sandcompaction underneath the feeder sleeve.
Since the compaction mechanism is confined to the core and not the feeder, FEEDEX K sleeves offer consistent, predictable feed metal volumes for improved process security reduce the risk of loose exothermic material falling into the feeding cavity (Fig. 3, Foseco Foundry Division Vesuvius GmbH)
An additional benefit of using a steelbreaker core is the avoidance of graphite degeneration problems due to exothermic material coming into contact with the surface of the casting.