A Computed Tomography Sensor for Solidification Monitoring in Metal Casting

A novel method for delineating the solidification front in metal casting has been developed using the attenuation phenomenon of electromagnetic radiation (γ-rays or x-rays) and computed tomography (CT). The densities of the liquid and solid phases that exist during metal casting may differ anywhere from 4 to 12% depending on the metal. As in the medical imaging field, CT provides an excellent means of mapping this density variation in a solidifying casting into two- or three-dimensional images. In an effort to develop an industrial-scale sensor, laboratory-scale experiments have been conducted using a cobalt-60 (Co^60) radioisotope and a sodium-iodide (NaI) scintillation detector. The CT image reconstruction was performed on a crucible containing pure tin in a two-phase state. Although the spatial resolution and data acquisition speed were not optimum, the CT images clearly differentiate the liquid and solid phases of the tin in the crucible. To maximize resolution and minimize data acquisition time, a linear accelerator (linac)-based CT sensor is being developed and tested for application in the continuous casting of steel and aluminum alloys.