As-Cast Surface Characterization for Steel Using Disk-Shaped Chemically Bonded Sand Specimens
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00520-4
Abstract Chemically bonded sand systems are an important and growing part of foundry technology, and their interaction at the mold–steel interface is of great interest. With today’s emphasis on near-net-shape steel castings, and with ever more stringent casting quality requirements, there is a need to quickly and affordably characterize as-cast surface quality. In addition, characterizing shakeout performance is necessary to meet today’s steel casting efficiency requirements. New AFS standard tests using disk-shaped specimens (AFS 3344-18-S), such as the thermal distortion test (AFS 3350-18-S), have proved to be efficient and effective techniques for detecting anomalies and measuring distortions for chemically bonded sand binder systems. However, these laboratory tests are unable to address all the influences at the mold–steel interface. Furthermore, simulation software is not yet able to predict mold/steel interfacial conditions. Thus, performing actual casting
trials remains necessary. This paper aims to investigate, for steel castings, the effects different chemically bonded sand systems have towards shakeout performance and ascast surface quality. An improved steel casting trial, using disk-shaped specimens, that allows several core specimens to be wetted simultaneously was employed. As-cast surface quality was assessed using a state-of-the-art 3D macroscope. Results suggest that various chemically bonded sand systems provide different shakeout performances and ascast surfaces.
Introduction and Purpose
strengthening reactions from secondary curing, and core weakening from pyrolysis. When evaluating thermal distortion data, it is important to understand and distinguish between thermo-mechanical distortions that are caused by the binder and the sand base aggregate.2
Directional heating of chemically bonded molding sand generates anisotropic thermal gradients in materials. When the bonded sand system contacts molten metal, the heat transferred causes thermo-chemical reactions that result in dimensional changes. At any given temperature, these dimensional changes, or thermal distortions, are attributable to simultaneous changes in both the sand and the binder.1 Depending on the type of binder used and the temperature at any point in the sand, thermally induced reactions occur simultaneously along with sand expansion leading to significant distortions in shape.1 With organic chemically bonded systems, such reactions generally include the release of volatile materials, possible core
International Journal of Metalcasting
Keywords: burn-on (inclusive of terms such as burn-in, penetration, and adhering coating), disk-shaped specimens, casting trial, chemical sand binder, surface roughness, thermal distortion testing
The thermal distortion test (TDT) (AFS 3350-18-S), using a disk-shaped specimen (AFS 3344-18-S), can assess the thermo-mechanical behavior of chemically bonded sand systems.3 For the TDT, temperature can be set to re
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