Simple Solutions That Work! Issue 10

I t is well known that metals change volume during solidification. This volume change must be compensated during solidification otherwise shrinkage defects can occur in a casting, making it unusable for its stated purpose. This has been solved through the use of adding a metal reservoir commonly known as a “feeder” the purpose of which is to supply liquid metal to the casting as it cools and solidifies. As this technology has developed and been improved, newer types of feeder materials have become available, including combinations of exothermic-insulating and highly exothermic compositions. The choice of material depends upon the application. For more demanding casting designs, highly exothermic sleeves have become more wide-spread. The exothermic reaction is started when molten metal meets the feeder. This initiates a highly energetic reaction generating heat. This keeps the metal, contained within the feeder, liquid and SVETLANA DODIK-PELJA Business/Product Manager HA INTERNATIONAL ARTICLE TAKEAWAYS: • Exothermic sleeves for demanding casting designs • Compact feeders for liquid metal savings • High strength cold box feeder systems for automatic sand molding, eliminates sand around contact and feeder breakage OPTIMIZED FEEDING SYSTEMS 22 extends the feeder solidification time to a greater degree than insulating feeders. The benefit has been to minimize feeder volumes and improve casting yields. To take advantage of these new opportunities, compact feeder designs using sodium silicate binder systems with glued-on breaker cores (typically made using resin coated sand) were used and still are today. Due to their much lower volume, this yielded savings in liquid metal and gave better productivity to the molding line. Even with this system, reduced breaker core diameters of the compact feeder systems and the use of pins mounted directly on the pattern, resulted in increased possibilities for locating the feeders on the casting. Subsequent development of faster green sand molding equipment with increasingly higher compressive pressure to produce castings with tighter tolerances, has created requirements for more feeder sizes and different geometries to feed complex and thin-walled castings. However, the higher compressive pressures of modern molding machines, which result in higher hardness of the green sand needed to produce near net shape castings, result in frequent damage to the breaker cores and feeders The introduction of cold-box (c-b) bonded feeding systems solved this problem by providing a feeder with high strength to resist the compressive force of today’s molding machines, yet allow complete collapsibility and burn-out during the casting process. In addition, c-b bonded feeders exhibit repeatable, precise tolerances, and can be shipped long distances without damage and stored for long periods of time without degrading. Newer designs, with compressible lower parts, such as the tele- feeder, offer unique advantages during use. During compaction of the green sand, the upper section of the tele-feeder slides telescopically over the lower section. This means that the lower section is not exposed to the molding pressure and, therefore, damage. When the upper section slides over the lower section, additional compaction of the green sand under the lower section takes place. This is the transition area