Thermal Distortion Testing at Ferrous Superheat Temperatures

As the ever-growing need to produce complex castings increases, so does the complexity of cores and molds. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand the thermal-mechanical effect suffered by the cores and molds when different binders, additives and coating are used for precision sands at the superheat temperature for an alloy. Thermal distortion is an American Foundry Society (AFS) standardized test for chemically bonded sands. The device can accommodate an AFS standard 50 mm disk-shaped specimen that is 8 mm thick. The specimen is automatically brought into direct symmetrical contact with a hot surface. The machine applies a ramping force to the specimen which represents a hydrostatic head pressure experienced by a core and mold wall during filling with a molten casting alloy. Further, the machine maintains a constant force signifying filled mold through casting solidification. During this time, the instrumentation is designed to capture temperature from the specimen both longitudinal (axial) and radial movement in the specimen. Until now, the maximum test temperature was 1000 °C (1832 °F) which underestimates a ferrous superheat temperature. In this study, results show interesting graphical representations of the amplified thermal-mechanical distortions in various polyurethane cold box sand systems at cast iron interfacial superheat temperatures. Most conspicuous was the augmented pyrolysis and sand loss occurring at the hot surface specimen interface.