A Solidification Front Monitor for Metal Casting

Abstract

A feasibility study was performed to assess computed tomography (CT) as a method of detecting the position of the solidification front during metal casting. Since the liquid and solid phases of metals differ in density by 4 to 12 percent, CT has the ability to differentiate the two phases. The motivation for this work is the development of a real-time solidification sensor for the continuous casting of metals. A first-generation CT system for reconstructing two-dimensional images of solidifying tin was developed. The performance of the CT system was evaluated by reconstructing images of objects of known geometries. For the solidification experiment, CT scans were conducted on an actively heated and cooled crucible filled with pure tin. The tin existed in both liquid and solid phases, with the solidification front position tracked by thermocouples. The image of the two-phase tin experiment had poor contrast resolution, but a quantitative analysis of the image does indicate an approximate 7 percent difference between the liquid and the solid portions of the melt. However, the size of the liquid phase was not as large as that determined by thermocouple measurements. This is a result of temperature fluctuations in the melt during data acquisition, as well as the relatively low spatial resolution. Future work to improve system performance will include using a linear accelerator (linac) as the radiation source.